Patent Application
20240425368
The present disclosure relates to a process for performing an ammonia cracking reaction in a fluidized bed reactor wherein the reaction is performed without the need of an external heating device in the said fluidized bed reactor. The present disclosure aims to contribute to the replacement of the use of fossil carbon-based fuels heating devices. The present disclosure relates to the electrification of the chemical industry.
Climate change and ongoing energy transition make it mandatory to replace fossil carbon-based fuels in chemical production and recycled processes with a more environmentally friendly decarbonized source of energy.
Ammonia decomposition (cracking) is the reverse of ammonia production (see equation 1) and is an endothermic reaction.
NH3(g)→½N2(g)+3/2H2(g)ΔH=+46 kJ/mol
The temperature required for efficient cracking depends on the catalyst. There are a wide variety of effective materials, but some (e.g., supported Ni catalysts) require temperatures above 700° C. to obtain attractive levels of conversion. Others have high conversion efficiency at temperatures in the range of 450-550° C. (e.g., supported Ru catalysts).
The resulting gas mixture is composed of hydrogen and nitrogen (i.e., forming gas) in the proportion 3:1 (75 vol. % of H2 and 25 vol. % of N2) with a little amount (20-100 ppm) of residual undissociated ammonia. The latter being the results of the thermodynamic limitations of the reaction. Depending on the desired subsequent application, these remaining traces can act as a poison and should be removed. Therefore, the forming gas can be further purified, for example, with molecular sieves in a pressure swing adsorption device or a scrubber resulting in further reducing the uncracked ammonia to 1-3 ppm.
The present disclosure aims to provide a large-scale solution to one or more of the problems encountered in the prior art that is suitable for application in the industry, such as the chemical industry. The present disclosure aims to contribute to the replacement of the use of fossil carbon-based fuels heating devices in fluidized bed reactors. The present disclosure provides a solution to conduct a thermal splitting of ammonia into forming gas by use of exclusively electric power.
According to a first aspect, the disclosure provides for a process to perform an ammonia cracking reaction with production of hydrogen, said process comprising the steps of:
With preference, the catalytic composition comprises one or more metallic compounds selected from:
Surprisingly, it has been found that the use of electrically conductive particles in one or more fluidized bed reactors which are electrified, allows maintaining a temperature sufficient to carry out an ammonia cracking reaction requesting high-temperature conditions such as temperature reaction ranging from 250° C. to 1000° C. without the need of any external heating device. The use of at least 10 wt. % of electrically conductive particles within the particles of the bed allows minimizing the loss of heat when a voltage is applied. Thanks to the Joule effect, most, if not all, the electrical energy is transformed into heat that is used for the heating of the reactor medium. Since at least a part of the electrically conductive particles is used as support for the catalyst, the electrically conductive particles may have a double function.
The electrically conductive particles
For example, the electrically conductive particles are or comprise one or more selected from one or more metallic alloys, one or more non-metallic resistors, one or more metallic carbides, one or more metallic nitrides, one or more metallic phosphides, one or more carbon-containing particles, one or more superionic conductors, one or more phosphate electrolytes, one or more mixed oxides being doped with one or more lower-valent cations, one or more mixed sulphides being doped with one or more lower-valent cations, and any mixture thereof; with preference in a content of from 50 wt. % to 100 wt. % based on the total weight of the electrically conductive particles of the bed; preferably, from 60 wt. % to 100 wt. %; more preferably from 70 wt. % to 100 wt. %; even more preferably from 80 wt. % to 100 wt. % and most preferably from 90 wt. % to 100 wt. %.
In a preferred embodiment, the electrically conductive particles are or comprise one or more selected from one or more metallic alloys, one or more non-metallic resistors, one or more metallic carbides, one or more metallic nitrides, one or more metallic phosphides, graphite, carbon black, one or more superionic conductors, one or more phosphate electrolytes, one or more mixed oxides being doped with one or more lower-valent cations, one or more mixed sulphides being doped with one or more lower-valent cations, and any mixture thereof; with preference in a content of from 50 wt. % to 100 wt. % based on the total weight of the electrically conductive particles of the bed; preferably, from 60 wt. % to 100 wt. %; more preferably from 70 wt. % to 100 wt. %; even more preferably from 80 wt. % to 100 wt. % and most preferably from 90 wt. % to 100 wt. %.
With preference, the electrically conductive particles of the bed are or comprise one or more selected from one or more non-metallic resistors, one or more metallic carbides, one or more metallic nitrides, one or more metallic phosphides, one or more superionic conductors, one or more phosphate electrolytes, one or more mixed oxides being doped with one or more lower-valent cations, one or more mixed sulphides being doped with one or more lower-valent cations, and any mixture thereof; with preference in a content of from 50 wt. % to 100 wt. % based on the total weight of the electrically conductive particles of the bed; preferably, from 60 wt. % to 100 wt. %; more preferably from 70 wt. % to 100 wt. %; even more preferably from 80 wt. % to 100 wt. % and most preferably from 90 wt. % to 100 wt. %.
In an embodiment, the electrically conductive particles of the bed comprise one or more carbon-containing particles being graphite; with preference in a content from 10 wt. % to 100 wt. % based on the total weight of the electrically conductive particles of the bed; or from 10 wt. % to 90 wt. %, or from 10 wt. % to 80 wt. %, preferably from 15 wt. % to 70 wt. %, more preferably from 20 wt. % to 60 wt. %, even more preferably from 30 wt. % to 50 wt. %. For example, the electrically conductive particles of the bed are a mixture of graphite and particles of the catalytic composition.
For example, the electrically conductive particles of the bed are devoid of one or more carbon-containing particles selected from petroleum coke, carbon black, coke or a mixture thereof.
In an embodiment, the electrically conductive particles of the bed are devoid of one or more carbon-containing particles selected from graphite, petroleum coke, carbon black, coke or a mixture thereof. For example, the electrically conductive particles of the bed are devoid of graphite and/or carbon black. For example, the electrically conductive particles of the bed are devoid of petroleum coke and/or coke.
Alternatively, the electrically conductive particles of the bed are or comprise graphite and one or more selected from one or more metallic alloys, one or more non-metallic resistors, one or more metallic carbides, one or more metallic nitrides, one or more metallic phosphides, one or more superionic conductors, one or more phosphate electrolytes, one or more mixed oxides being doped with one or more lower-valent cations, one or more mixed sulphides being doped with one or more lower-valent cations, and any mixture thereof; with preference in a content of from 50 wt. % to 100 wt. % based on the total weight of the electrically conductive particles of the bed; preferably, from 60 wt. % to 100 wt. %; more preferably from 70 wt. % to 100 wt. %; even more preferably from 80 wt. % to 100 wt. % and most preferably from 90 wt. % to 100 wt. %.
As an alternative, the electrically conductive particles of the bed are one or more particles selected from one or more metallic alloys, one or more non-metallic resistors provided that the non-metallic resistor is not silicon carbide, one or more metallic carbides, one or more metallic nitrides, one or more metallic phosphides, graphite, carbon black, one or more superionic conductors, one or more phosphate electrolytes, one or more mixed oxides being doped with one or more lower-valent cations and/or one or more and/or mixed sulphides being doped with one or more lower-valent cations and any mixture thereof; with preference in a content of from 50 wt. % to 100 wt. % based on the total weight of the electrically conductive particles of the bed; preferably, from 60 wt. % to 100 wt. %; more preferably from 70 wt. % to 100 wt. %; even more preferably from 80 wt. % to 100 wt. % and most preferably from 90 wt. % to 100 wt. %.
For example, the electrically conductive particles of the bed are or comprise one or more selected from one or more metallic alloys, one or more non-metallic resistors, graphite, carbon black, one or more mixed oxides being doped with one or more lower-valent cations, one or more mixed sulphides being doped with one or more lower-valent cations, and any mixture thereof with preference in a content of from 50 wt. % to 100 wt. % based on the total weight of the electrically conductive particles of the bed; preferably, from 60 wt. % to 100 wt. %; more preferably from 70 wt. % to 100 wt. %; even more preferably from 80 wt. % to 100 wt. % and most preferably from 90 wt. % to 100 wt. %.
For example, the electrically conductive particles of the bed are or comprise graphite and one or more selected from one or more metallic alloys, one or more non-metallic resistors, one or more mixed oxides being doped with one or more lower-valent cations, one or more mixed sulphides being doped with one or more lower-valent cations, and any mixture thereof; with preference in a content of from 50 wt. % to 100 wt. % based on the total weight of the electrically conductive particles of the bed; preferably, from 60 wt. % to 100 wt. %; more preferably from 70 wt. % to 100 wt. %; even more preferably from 80 wt. % to 100 wt. % and most preferably from 90 wt. % to 100 wt. %.
For example, the electrically conductive particles of the bed are or comprise one or more selected from one or more metallic alloys, one or more non-metallic resistors, one or more mixed oxides being doped with one or more lower-valent cations, one or more mixed sulphides being doped with one or more lower-valent cations, and any mixture thereof; with preference in a content of from 50 wt. % to 100 wt. % based on the total weight of the electrically conductive particles of the bed; preferably, from 60 wt. % to 100 wt. %; more preferably from 70 wt. % to 100 wt. %; even more preferably from 80 wt. % to 100 wt. % and most preferably from 90 wt. % to 100 wt. %.
For example, the electrically conductive particles of the bed are or comprise one or more selected from one or more non-metallic resistors, one or more mixed oxides being doped with one or more lower-valent cations, one or more mixed sulphides being doped with one or more lower-valent cations, and any mixture thereof; with preference in a content of from 50 wt. % to 100 wt. % based on the total weight of the electrically conductive particles of the bed; preferably, from 60 wt. % to 100 wt. %; more preferably from 70 wt. % to 100 wt. %; even more preferably from 80 wt. % to 100 wt. % and most preferably from 90 wt. % to 100 wt. %.
Advantageously, step d) of recovering the products of the reaction is performed, wherein said products comprise gaseous products being a mixture of H2 and N2. Step d) is performed after step c).
In a preferred embodiment, the volumetric heat generation rate is greater than 0.1 MW/m3 of fluidized bed, more preferably greater than 1 MW/m3, in particular, greater than 3 MW/m3.
In a preferred embodiment, the at least one fluidized bed reactor is devoid of heating means. For example, the at least one fluidized bed reactor comprises a vessel and is devoid of heating means located around or inside the vessel. For example, at least one fluidized bed reactor is devoid of heating means selected from ovens, gas burners, hot plates, or any combination thereof. For example, all the fluidized bed reactors are devoid of heating means selected from ovens, gas burners, hot plates, or any combination thereof.
The solid particulate material (i.e., the particles) used in the fluidized bed reactor comprises solid particulates having electrical conductivity allowing generating heat and catalytic particulate material to catalyze the NH3 cracking reaction. The catalytic particulate material can also be electrically conductive and hence contribute to the generation of heat for the endothermic ammonia cracking reaction.
For example, the content of electrically conductive particles is ranging from 10 wt. % to 100 wt. % based on the total weight of the particles of the bed; preferably, from 15 wt. % to 95 wt. %, more preferably from 20 wt. % to 90 wt. %, even more preferably from 25 wt. % to 80 wt. % and most preferably from 30 wt. % to 75 wt. %. In the case where the content of electrically conductive particles based on the total weight of the particles of the bed is 100 wt. %, said electrically conductive particles are also catalytic particles
For example, the content of electrically conductive particles based on the total weight of the bed is at least 12 wt. % based on the total weight of the particles of the bed; preferably, at least 15 wt. %, more preferably, at least 20 wt. %; even more preferably at least 25 wt. %, and most preferably at least 30 wt. % or at least 40 wt. % or at least 50 wt. % or at least 60 wt. %.
For example, the electrically conductive particles have a resistivity ranging from 0.005 to 400 Ohm.cm at 800° C., preferably ranging from 0.01 to 300 Ohm.cm at 800° C.; more preferably ranging from 0.05 to 150 Ohm.cm at 800° C. and most preferably ranging from 0.1 to 100 Ohm.cm at 800° C.
For example, the electrically conductive particles have a resistivity of at least 0.005 Ohm.cm at 800° C.; preferably of at least 0.01 Ohm.cm at 800° C., more preferably of at least 0.05 Ohm.cm at 800° C.; even more preferably of at least 0.1 Ohm.cm at 800° C., and most preferably of at least 0.5 Ohm.cm at 800° C.
For example, the electrically conductive particles have a resistivity of at most 400 Ohm.cm at 800° C.; preferably of at most 300 Ohm.cm at 800° C., more preferably of at most 200 Ohm.cm at 800° C.; even more preferably of at most 150 Ohm.cm at 800° C., and most preferably of at most 100 Ohm.cm at 800° C. The selection of the content of electrically conductive particles based on the total weight of the particles of the bed and of the electrically conductive particles of a given resistivity influence the temperature reached by the fluidized bed. Thus, in case the targeted temperature is not attained, the person skilled in the art may increase the density of the bed of particles, the content of electrically conductive particles based on the total weight of the particles of the bed and/or select electrically conductive particles with a lower resistivity to increase the temperature reached by the fluidized bed.
For example, the density of the bed of particles is expressed as the void fraction. Void fraction or bed porosity is the volume of voids between the particles divided by the total volume of the bed. At the incipient fluidisation velocity, the void fraction is typically between 0.4 and 0.5. The void fraction can increase up to 0.98 in fast fluidised beds with lower values at the bottom of about 0.5 and higher than 0.9 at the top of the bed. The void fraction can be controlled by the linear velocity of the fluidising gas and can be decreased by recycling solid particles that are recovered at the top and sent back to the bottom of the fluidized bed, which compensates for the entrainment of solid particles out of the bed.
The void fraction VF is defined as the volume fraction of voids in a bed of particles and is determined according to the following equation:
wherein Vt is the total volume of the bed and is determined by
wherein A is the cross-sectional area of the fluidized bed and H is the height of the fluidized bed; and
wherein Vp is the total volume of particles within the fluidized bed.
For example, the void fraction of the bed is ranging from 0.5 to 0.8; preferably ranging from 0.5 to 0.7, more preferably from 0.5 to 0.6. To increase the density of the bed of particles, the void fraction is to be reduced.
For example, the particles of the bed have an average particle size ranging from 5 to 300 μm as determined by sieving according to ASTM D4513-11, preferably ranging from 10 to 200 μm and more preferably ranging from 20 to 200 μm or from 30 to 150 μm.
Determination by sieving according to ASTM D4513-11 is preferred. In case the particles have an average size of below 20 μm the determination of the average size can also be done by Laser Light Scattering according to ASTM D4464-15.
For example, the electrically conductive particles of the bed have an average particle size ranging from 5 to 300 μm as determined by sieving according to ASTM D4513-11, preferably ranging from 10 to 200 μm and more preferably ranging from 30 to 150 μm.
For example, said one or more metallic alloys are selected from Ni—Cr, Fe—Ni—Cr, Fe—Ni—Al or a mixture thereof. With preference, when said metallic alloy comprises at least chromium, the chromium content is at least 15 mol. % of the total molar content of said metallic alloy comprising at least chromium, more preferably at least 20 mol. %, even more preferably at least 25 mol. %, most preferably at least 30 mol. %. Advantageously yet, the iron content in the metallic alloys is at most 2.0 mol. % based on the total molar content of the said metallic alloy, preferably at most 1.5 mol. %, more preferably at most 1.0 mol. %, even more preferably at most 0.5 mol. %.
For example, a non-metallic resistor is silicon carbide (SiC), molybdenum disilicide (MoSi2), nickel silicide (NiSi), sodium silicide (Na2Si), magnesium silicide (Mg2Si), platinum silicide (PtSi), titanium silicide (TiSi2), tungsten silicide (WSi2) or a mixture thereof, preferably silicon carbide.
For example, said one or more metallic carbides are selected from iron carbide (Fe3C) and/or molybdenum carbide (such as a mixture of MoC and Mo2C).
For example, said one or more metallic nitrides are selected from zirconium nitride (ZrN), tungsten nitride (such as a mixture of W2N, WN, and WN2), vanadium nitride (VN), tantalum nitride (TaN), and/or niobium nitride (NbN).
For example, said one or more metallic phosphides are selected from copper phosphide (Cu3P), indium phosphide (InP), gallium phosphide (GaP), sodium phosphide Na3P), aluminium phosphide (AIP), zinc phosphide (Zn3P2) and/or calcium phosphide (Ca3P2).
For example, said one or more superionic conductors are selected from LiAlSiO4, Li10GeP2S12, Li3.6Si0.6P0.4O4, sodium superionic conductors (NaSICON), such as Na3Zr2PSi2O12, or sodium beta alumina, such as NaAl11O17, Na1.6Al11O17.3, and/or Na1.76Li0.38Al10.62O17.
For example, said one or more phosphate electrolytes are selected from LiPO4 or LaPO4.
For example, said one or more mixed oxides are ionic or mixed conductors being doped with one or more lower-valent cations. Advantageously, said mixed oxides are doped with one or more lower-valent cations, and are selected from oxides having a cubic fluorite structure, perovskite, pyrochlore.
For example, said one or more mixed sulphides are ionic or mixed conductors being doped with one or more lower-valent cations.
For example, the electrically conductive particles of the bed are or comprise a non-metallic resistor being silicon carbide.
For example, the electrically conductive particles of the bed are or comprise a mixture of a non-metallic resistor being silicon carbide and electrically conductive particles different from silicon carbide. The presence of electrically conductive particles different from silicon carbide in the bed is optional. It can be present as a starting material for heating the bed since it was found that the resistivity of silicon carbide at room temperature is too high to start heating the bed. Alternatively, to the presence of electrically conductive particles different from silicon carbide, it is possible to provide heat to the reactor for a defined time to start the reaction.
For example, the silicon carbide is selected from sintered silicon carbide, nitride-bounded silicon carbide, recrystallised silicon carbide, reaction bonded silicon carbide and any mixture thereof.
For example, the electrically conductive particles of the bed are or comprise a mixture of a non-metallic resistor being silicon carbide and electrically conductive particles different from silicon carbide and the electrically conductive particles of the bed comprises from 10 wt. % to 99 wt. % of silicon carbide based on the total weight of the electrically conductive of the bed; preferably, from 15 wt. % to 95 wt. %, more preferably from 20 wt. % to 90 wt. %, even more preferably from 25 wt. % to 80 wt. % and most preferably from 30 wt. % to 75 wt. %.
For example, the electrically conductive particles of the bed are or comprise a mixture of a non-metallic resistor being silicon carbide and electrically conductive particles different from silicon carbide and the said electrically conductive particles different from silicon carbide are graphite and/or one or more mixed oxides being doped with one or more lower-valent cations and/or one or more mixed sulphides being doped with one or more lower-valent cations.
For example, the electrically conductive particles of the bed are or comprise silicon carbide and molybdenum disilicide with from 10 wt. % to 90 wt. % of silicon carbide and from 90 wt. % to 10 wt. % of molybdenum disilicide, both based on the total weight of the electrically conductive particles of the bed.
For example, the electrically conductive particles of the bed are or comprise one or more mixed oxides being ionic conductor, namely being doped with one or more lower-valent cations; with preference, the mixed oxides are selected from:
For example, the electrically conductive particles of the bed are or comprise one or more mixed sulphides being ionic conductor, namely being doped with one or more lower-valent cations; with preference, the mixed sulphides are selected from:
With preference, the degree of substitution in the one or more mixed oxides doped with one or more lower-valent cations and having a cubic fluorite structure is between 1 and 15 atom % based on the total number of atoms present in the one or more oxides having a cubic fluorite structure, preferably between 3 and 12 atom %, more preferably between 5 and 10 atom %.
With preference, the degree of substitution in the one or more mixed oxides doped with one or more lower-valent cations is between 1 and 50 atom % based on the total number of atoms present in the one or more ABO3-perovskites with A and B tri-valent cations, in the one or more ABO3-perovskites with A bivalent cation and B tetra-valent cation or in the one or more A2B2O7-pyrochlores with A trivalent cation and B tetra-valent cation respectively, preferably between 3 and 20 atom %, more preferably between 5 and 15 atom %.
With preference, the degree of substitution in the one or more mixed sulphides doped with one or more lower-valent cations and having a cubic fluorite structure is between 1 and 15 atom % based on the total number of atoms present in the one or more oxides having a cubic fluorite structure, preferably between 3 and 12 atom %, more preferably between 5 and 10 atom %.
With preference, the degree of substitution in the one or more mixed sulphides doped with one or more lower-valent cations is between 1 and 50 atom % based on the total number of atoms present in the one or more ABS3 structures with A and B tri-valent cations, in the one or more ABS3 structures with A bivalent cation and B tetra-valent cation or in the one or more A2B2S7 structures with A trivalent cation and B tetra-valent cation respectively, preferably between 3 and 20 atom %, more preferably between 5 and 15 atom %.
For example, the electrically conductive particles of the bed are or comprise one or more metallic alloys; with preference, one or more metallic alloys are selected from Ni—Cr, Fe—Ni—Cr, Fe—Ni—Al or a mixture thereof.
With preference, when said metallic alloy comprises at least chromium, the chromium content is at least 15 mol. % of the total molar content of said metallic alloy comprising at least chromium, more preferably at least 20 mol. %, even more preferably at least 25 mol. %, most preferably at least 30 mol. %. Advantageously yet, the iron content in the metallic alloys is at most 2.0 mol. % based on the total molar content of said metallic alloy, preferably at most 1.5 mol. %, more preferably at most 1.0 mol. %, even more preferably at most 0.5 mol. %.
For example, the electrically conductive particles of the bed are or comprise a mixture of a non-metallic resistor being silicon carbide and particles different from silicon carbide wherein the particles different from silicon carbide are or comprise graphite; with preference, said graphite is graphite particles having an average particle size ranging from 5 to 300 μm as determined by sieving according to ASTM D4513-11, more preferably ranging from 10 to 200 μm and most preferably ranging from 30 to 150 μm.
For example, the content of the particles of a catalytic composition based on the total weight of the particles of the bed is ranging from 30 wt. % to 100 wt. %; preferably from 32 wt. % to 95 wt. %, more preferably from 35 wt. % to 90 wt. %, even more preferably from 37 wt. % to 85 wt. %, most preferably from 40 wt. % to 80 wt. %, even most preferably from 45 wt. % to 75 wt. % or from 50 wt. % to 70 wt. %. In the case where the content of the particles of a catalytic composition based on the total weight of the particles of the bed is 100 wt. %, said particles of a catalytic composition are also electrically conductive particles.
For example, the particles of a catalytic composition have an average particle size ranging from 5 to 300 μm as determined by sieving according to ASTM D4513-11, preferably ranging from 10 to 200 μm and more preferably ranging from 20 to 200 μm or from 30 to 150 μm.
Determination by sieving according to ASTM D4513-11 is preferred. In case the particles have an average size of below 20 μm the determination of the average size can also be done by Laser Light Scattering according to ASTM D4464-15.
The catalytic composition comprises one or more metallic compounds. With preference, the catalytic composition comprises one or more metallic compounds selected from:
For example, the one or more non-noble metals selected from Ni, Fe, Co, Mo, Cu and any mixture thereof are present in an amount ranging between 0.05 wt. % and 20.00 wt. % based on the total weight of the catalytic composition, preferably between 0.10 wt. % and 15.00 wt. %, more preferably between 0.50 wt. % and 10.00 wt. %, even more preferably between 1.00 wt. % and 5.00 wt. %.
For example, the one or more non-noble metals are or comprise Ni.
For example, the one or more noble metals selected from Ru, Rh, Pd, Ir, Pt and any mixture thereof are present in an amount ranging between 0.05 wt. % and 10.00 wt. % based on the total weight of the catalytic composition, preferably between 0.10 wt. % and 5.00 wt. %, more preferably between 1.00 wt. % and 3.00 wt. %, even more preferably between 1.50 wt. % and 2.50 wt. %.
For example, the one or more noble metals are or comprise Ru.
For example, the noble metal in the one or more bimetallic compounds is in an amount ranging between 10 ppm and 500 ppm, preferably between 50 ppm and 400 ppm, more preferably between 100 ppm and 250 ppm.
Advantageously, said catalytic composition further comprises one or more elements selected from one or more selected from alkali metals, alkaline earth metals and rare earth elements. For example, one or more alkali metals are one or more selected from Li, Na, K, Cs, and any mixture thereof. For example, one or more alkaline earth metals are one or more selected from Mg and/or Ca. For example, one or more rare earth elements are one or more selected from Ce, La, Sc, Y and any mixture thereof.
According to the disclosure, said catalytic composition further comprises a catalytic support being electrically conductive particles; with preference, electrically conductive particles being silicon carbide and/or graphite and/or carbon nanotubes, or alternatively, electrically conductive particles different from said silicon carbide. This allows intimate contact between the catalytic active material and the electrically conductive material.
With preference, said catalytic composition further comprises a specific surface area ranging between 10 m2/g and 1000 m2/g as determined by N2 adsorption measurement, more preferably between 50 m2/g and 900 m2/g, even more preferably between 100 m2/g and 800 m2/g, most preferably between 200 m2/g and 700 m2/g.
For example, the ammonia cracking reaction is conducted at a temperature ranging from 300° C. to 950° C., preferably from 350° C. to 900° C., more preferably from 400° C. to 850° C. and most preferably from 450° C. to 800° C. or from 480 to 950° C.
Advantageously, the disclosure also provides for partial cracking of ammonia, namely when the conversion of ammonia into forming gas is inferior to 50%, preferably ranging between 20% to 50% or between 20% to 30%, which can be interesting for performing smooth combustion of the generated hydrogen, occurs either
The conversion was determined by calculating the ratio of the difference between the amount of NH3 into the ammonia-containing feedstock and the amount of NH3 into the products recovered at step (d) over the amount of NH3 into ammonia-containing feedstock, said ratio is multiplied by 100 to be expressed in percentage.
For example, the ammonia cracking reaction is performed at a pressure ranging between 0.01 MPa and 10.0 MPa, preferably between 0.1 MPa and 5.0 MPa.
In an embodiment, said process comprises a step of pre-heating with a gaseous stream said fluidized bed reactor before conducting the ammonia cracking reaction in the fluidized bed reactor; with preference, said gaseous stream is a stream of inert gas and/or has a temperature comprised between 250° C. and 800° C. The said embodiment is of interest when the particles of the bed such as graphite and/or the electro-resistive material have too high resistivity at room temperature to start the electro-heating of the bed.
For example, the ammonia cracking reaction is conducted in presence of a dilution stream and is performed at a weight hourly space velocity of said reaction stream comprised between 0.1 h−1 and 100 h−1, preferably comprised between 1.0 h−1 and 50 h−1. The weight hourly space velocity is defined as the ratio of mass flow of the reaction stream to the mass of solid particulate material in the fluidized bed.
The ammonia-containing feedstock for the present process is selected from a feedstock comprising ammonia provided by Haber-Bosch process, by any biological process producing ammonia, by any electrochemical process producing ammonia or any combination thereof.
Optionally, the ammonia-containing feedstock is diluted with one or more diluent gases. The one or more diluent gases, when present, are one or more selected from steam, hydrogen, carbon dioxide, argon, helium, nitrogen and one or more hydrocarbons, such as methane. The one or more diluent gases are for example used as one or more fluidizing gases. With preference, the one or more diluent gases are one or more selected from steam, hydrogen, carbon dioxide, nitrogen and one or more hydrocarbons, such as methane. In an embodiment, when the diluent gases are at least a mixture of steam and one or more hydrocarbons, such as methane, then an endothermic steam reforming of hydrocarbons to produce synthesis gas is conducted concomitantly with said ammonia cracking reaction with production of hydrogen. In an alternative embodiment, when the diluent gases are at least a mixture of carbon dioxide and one or more hydrocarbons, such as methane, then an endothermic dry reforming of hydrocarbons to produce synthesis gas is conducted concomitantly with said ammonia cracking reaction with the production of hydrogen.
For example, in step (b), the particles of the bed are put in a fluidized state by passing upwardly through the said bed a gaseous stream; with preference, the gaseous stream is or comprises the ammonia-containing feedstock.
In particular, the products obtained in the present process may include hydrogen and/or nitrogen.
In a preferred embodiment, the outlet temperature of the reactor may range from 300 to 1100° C., preferably from 350 to 1050° C., more preferably from 400 to 1000° C., more preferably from 450° C. to 950° C.
In a preferred embodiment, the residence time of the ammonia-containing feedstock in the fluidised bed section of the reactor where the temperature is between 45° and 900° C., may range from 0.005 to 5.00 seconds, preferably from 0.10 to 1.20 seconds.
For example, the step of heating the fluidized bed is performed by passing an electric current at a voltage of at most 300 V through the fluidized bed, preferably at most 200 V, more preferably at most 150 V, even more preferably at most 120 V, most preferably at most 100 V, even most preferably at most 90 V.
For example, wherein the at least one fluidized bed reactor provided in step a) comprises a heating zone and a reaction zone, and wherein the step c) of heating the fluidized bed comprises the following sub-steps:
For example, wherein the at least one fluidized bed reactor provided in step a) comprises a heating zone and a reaction zone, and the step c) of heating the fluidized bed comprises the following sub-steps:
Thus, preferably, the particles are pre-heated and/or heated before step c) in a pre-heating zone and/or in a heating zone, so that:
The fluidizing stream may be a gaseous stream comprising one or more diluents, for example, one or more inert gas.
For example, in step b) the particles of the bed are put in a fluidized state by passing upwardly through the said bed a gaseous stream and when the heating zone and the reaction zone are mixed (i.e., the same zone); said gaseous stream (i.e., the fluidizing stream) may be or comprise an ammonia-containing feedstock.
For example, in step b) the particles of the bed are put in a fluidized state by passing upwardly through the said bed a gaseous stream and when the heating zone and the reaction zone are separated zones, the gaseous stream (i.e. the fluidizing stream) provided to the heating zone can be devoid of an ammonia-containing feedstock. For example, in step b) the particles of the bed are put in a fluidized state by passing upwardly through the said bed a gaseous stream and the process comprises providing at least one fluidized bed reactor being a heating zone and at least one fluidized bed reactor being a reaction zone, the gaseous stream provided in step b) to the heating zone is devoid of an ammonia-containing feedstock and the gaseous stream provided to the reaction zone is or comprises the ammonia-containing feedstock.
It is understood that the ammonia-containing feedstock is provided to the reaction zone and that when the heating zone is separated from the reaction zone, no ammonia-containing feedstock is provided to the heating zone.
Co-processing between ammonia cracking reaction with production of hydrogen and steam methane reforming reaction to produce synthesis gas Advantageously, one or more of the following is selected so that step (c) is conducted to perform concomitantly with said ammonia cracking reaction with production of hydrogen an endothermic steam reforming of hydrocarbons to produce synthesis gas:
Alternatively, one or more of the following is selected so that step (c) is conducted to perform concomitantly with said ammonia cracking reaction with production of hydrogen an endothermic dry reforming of hydrocarbons to produce synthesis gas:
For example, the one or more hydrocarbons are part of a hydrocarbon-containing feedstock and/or the one or more hydrocarbons have one or more carbon atoms, such as methane or a mixture of light hydrocarbons containing 1 to 5 carbon atoms. Advantageously, the hydrocarbon-containing feedstock also contains carbon dioxide. Preferably, the hydrocarbon-containing feedstock is natural gas, biogas or refinery gas, each can contain various amounts of carbon dioxide.
With preference, the molar ratio between the steam and the carbon in the hydrocarbon-containing feedstock is ranging between 2.0 and 5.0 moles of steam per mole of carbon in the hydrocarbon feedstock, preferably from 2.2 to 4.0, more preferably from 2.5 to 3.0. Advantageously, when step (d) is carried out, the products comprise at least forming gas (i.e., a mixture of H2 and N2) and unreacted ammonia. In the case where step (c) is conducted to perform concomitantly with the ammonia cracking reaction a steam reforming of hydrocarbons, then, when step (d) is carried out, the products further comprise carbon monoxide, carbon dioxide, unreacted hydrocarbons, and unreacted steam.
In an embodiment, when step (c) is conducted to perform only an ammonia cracking reaction with production of hydrogen, the process further comprises a step (j) of performing a combustion reaction on the products recovered at step (d), namely on the products that comprise at least forming gas and unreacted ammonia. With preference, said step (j) is carried out directly after step (d). With preference, the combustion reaction is performed at a temperature ranging between 1000° C. and 3000° C. This embodiment is preferably carried out when the conversion of the ammonia cracking reaction is partial.
In another embodiment, the process further comprises a step (e) of removal of the unreacted ammonia from the products recovered at step (d). This embodiment is preferably carried out when the conversion of the ammonia cracking reaction is complete because this leads to unreacted ammonia in an amount of about 20 ppm to 100 ppm in the forming gas that is formed upon cracking. With preference, said step (e) is one or more steps selected from
In the case where step (c) is conducted to perform concomitantly with said ammonia cracking reaction with production of hydrogen an endothermic steam reforming of hydrocarbons to produce synthesis gas or an endothermic dry reforming of hydrocarbons to produce synthesis gas, the process further advantageously comprises the following steps that are performed after the step (e) of removal of the unreacted ammonia from the products recovered at step (d):
For example, said step (f) is carried out in presence of a water-gas shift catalyst; with preference, said water-gas shift catalyst is selected from copper or iron-based catalyst.
According to a second aspect, the disclosure provides an installation to perform at least an ammonia-cracking reaction with production of hydrogen according to the first aspect, said installation comprises:
With preference, the at least two electrodes comprise or are made of tantalum.
Advantageously, at least one fluidized bed reactor is devoid of heating means. For example, at least one fluidized bed reactor is devoid of heating means located around or inside the reactor vessel. For example, all the fluidized bed reactors are devoid of heating means. When stating that at least one of the fluidized bed reactors is devoid of “heating means”, it refers to “classical” heating means, such as ovens, gas burners, hot plates and the like. There are no other heating means than the at least two electrodes of the fluidized bed reactor itself. For example, at least one fluidized bed reactor is devoid of heating means selected from ovens, gas burners, hot plates, or any combination thereof. For example, all the fluidized bed reactors are devoid of heating means selected from ovens, gas burners, hot plates, or any combination thereof.
In a preferred embodiment, the at least one fluidized bed reactor comprising at least two electrodes and a bed comprising particles is devoid of a structured packing such as honeycomb monoliths or crossed plate.
For example, the one or more diluent gases are used as one or more fluidizing gases. With preference, said one or more diluent gases are one or more selected from steam, hydrogen, carbon dioxide, argon, helium, nitrogen and one or more hydrocarbons, such as methane. More preferably, the one or more diluent gases are one or more selected from steam, hydrogen, carbon dioxide, nitrogen and one or more hydrocarbons, such as methane. In an embodiment, when the diluent gases are at least a mixture of steam and one or more hydrocarbons, such as methane, then an endothermic steam reforming of hydrocarbons to produce synthesis gas is conducted concomitantly with said ammonia cracking reaction with production of hydrogen. In an alternative embodiment, when the diluent gases are at least a mixture of carbon dioxide and one or more hydrocarbons, such as methane, then an endothermic dry reforming of hydrocarbons to produce synthesis gas is conducted concomitantly with said ammonia cracking reaction with production of hydrogen.
For example, the at least one reactor vessel has an inner diameter of at least 100 cm, preferably at least 200 cm, more preferably at least 300 cm.
With preference, the reactor vessel comprises a reactor wall made of materials that are corrosion-resistant materials and advantageously said reactor wall materials comprise nickel (Ni), SiAION ceramics, yttria-stabilized zirconia (YSZ), tetragonal polycrystalline zirconia (TZP) and/or tetragonal zirconia polycrystal (TPZ).
With preference, one of the electrodes is the reactor vessel or the gas distributor and/or said at least two electrodes are made in stainless steel material or nickel-chromium alloys or nickel-chromium-iron alloys.
For example, the at least one fluidized bed reactor comprises a heating zone and a reaction zone, one or more fluid nozzles to provide an ammonia-containing feedstock to the reaction zone, and optional means to transport the particles of the bed from the reaction zone back to the heating zone.
For example, the installation comprises at least two fluidized bed reactors connected one to each other wherein at least one reactor of said at least two fluidized bed reactors is the heating zone and at least another reactor of said at least two fluidized bed reactors is the reaction zone. With preference, the installation comprises one or more fluid nozzles arranged to inject an ammonia-containing feedstock to the at least one fluidized bed reactor being the reaction zone, means to transport the particles of the bed from the heating zone to the reaction zone when necessary and optional means to transport the particles from the reaction zone back to the heating zone. This configuration is remarkable in that a given particle bed is common to at least two fluidized bed reactors.
For example, the at least one fluidized bed reactor is a single fluidized bed reactor wherein the heating zone is the bottom part of the fluidized bed reactor while the reaction zone is the top part of the fluidised bed reactor. With preference, the installation comprises one or more fluid nozzles to inject an ammonia-containing feedstock between the two zones. The diameter of the heating zone and reaction zone can be different to accomplish optimum conditions for heating in the bottom zone and optimum conditions for methane conversion in the top zone. Particles can move from the heating zone to the reaction zone by entrainment and the other way around from the reaction zone back to the heating zone by gravity. Optionally, particles can be collected from the upper heating zone and transferred by a separate transfer line back to the bottom heating zone.
For example, the at least one fluidized bed comprises at least two lateral zones being an outer zone and an inner zone wherein the outer zone is surrounding the inner zone, with the outer zone being the heating zone and the inner zone being the reaction zone. In a less preferred configuration, the outer zone is the reaction zone and the inner zone is the heating zone. With preference, the installation comprises one or more fluid nozzles to inject an ammonia-containing feedstock in the reaction zone.
Advantageously, the installation further comprises a line fluidly connecting the electrified fluidized bed unit to the separation unit and/or to the combustion unit, and the installation further comprises a heat exchanger on said line.
With preference, the separation unit is or comprises a pressure swing adsorption (PSA) device and/or a scrubber and/or a condenser.
With preference, the combustion unit is or comprises an oven and/or a furnace and/or a burner.
When the water-gas shift (WGS) unit downstream of said electrified fluidized bed unit or of said separation unit is present, the WGS unit comprises at least one water-gas shift reactor to perform a water-gas shift reaction onto the carbon monoxide that is part of the syngas when endothermic steam reforming or dry reforming of hydrocarbons reaction is conducted concomitantly with said ammonia cracking reaction with production of hydrogen. Additional separation units can be present downstream said WGS unit, such as a first additional separation unit to separate a CO2-enriched stream from an effluent exiting the WGS unit, and/or a second additional separation unit, preferably downstream of said first additional separation unit, to separate a purified hydrogen stream, said second additional separation unit comprising preferably a pressure swing adsorption (PSA) device. Said second additional separation unit preferably also allows to remove a purge stream comprising unrecovered hydrogen, unreacted carbon monoxide and un reacted hydrocarbons, and the installation advantageously comprises a line to provide such purge stream at step (a).
According to a third aspect, the disclosure provides the use of a bed comprising particles in at least one fluidized bed reactor to perform at least an ammonia cracking reaction with production of hydrogen according to the first aspect, the use is remarkable in that the particles of the bed comprise electrically conductive particles and particles of a catalytic composition, wherein at least 10 wt. % of the particles of the bed based on the total weight of the particles of the bed are electrically conductive and have a resistivity ranging from 0.001 Ohm.cm to 500 Ohm.cm at a temperature of 800° C., and wherein the catalytic composition comprises one or more metallic compounds.
For example, the use comprises heating the bed comprising particles to a temperature ranging from 250° C. to 1000° C. in a first reactor, transporting the heated particle bed from the first reactor to a second reactor and providing an ammonia-containing feedstock to the second reactor; with preference, at least the second reactor is a fluidized bed reactor and/or at least the second reactor is devoid of heating means; more preferably, the first reactor and the second reactor are fluidized bed reactors and/or the first and the second reactor are devoid of heating means. For example, the second reactor is devoid of electrodes.
According to a fourth aspect, the disclosure provides the use of an installation comprising at least one fluidized bed reactor to perform at least an ammonia cracking reaction with the production of hydrogen, remarkable in that the installation is according to the second aspect. With preference, the disclosure provides the use of an installation comprising at least one fluidized bed reactor to perform at least an ammonia cracking reaction with the production of hydrogen in a process according to the first aspect.
The particular features, structures, characteristics or embodiments may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments.
For the disclosure, the following definitions are given:
The terms “comprising”, “comprises” and “comprised of” as used herein are synonymous with “including”, “includes” or “containing”, “contains”, and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. The terms “comprising”, “comprises” and “comprised of” also include the term “consisting of”.
The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g., 1 to 5 can include 1, 2, 3, 4, 5 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of endpoints also includes the recited endpoint values themselves (e.g., from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.
The term “transition metal” refers to an element whose atom has a partially filled d sub-shell, or which can give rise to cations with an incomplete d sub-shell (IUPAC definition). According to this definition, the transition metals are Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Ac, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, and Cn.
The metals Ga, In, Sn, TI, Pb and Bi are considered as “post-transition” metals.
The metals Au, Ag, Ru, Rh, Pd, Os, Ir and Pt show outstanding oxidation resistance and are considered “noble” metals. Other metals can be considered as “non-noble” metals.
The term “alkali metal” refers to an element classified as an element from group 1 of the periodic table of elements (or group IA), excluding hydrogen. According to this definition, the alkali metals are Li, Na, K, Rb, Cs and Fr.
The term “alkaline earth metal” refers to an element classified as an element from group 2 of the periodic table of elements (or group IIA). According to this definition, the alkaline earth metals are Be, Mg, Ca, Sr, Ba and Ra.
The term “rare earth elements” refer to the fifteen lanthanides, as well as scandium and yttrium. The 17 rare-earth elements are cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), and yttrium (Y).
The present disclosure provides a process to perform an ammonia-cracking reaction with production of hydrogen, said process comprising the steps of:
With preference, the catalytic composition comprises one or more metallic compounds selected from:
For example, the ammonia-containing feedstock for the present process is selected from a feedstock comprising ammonia provided by Haber-Bosch process, by any biological process producing ammonia, by any electrochemical process producing ammonia or any combination thereof.
For example, the electrically conductive particles of the bed are or comprise one or more selected from one or more carbon-containing particles, one or more metallic alloys, one or more non-metallic resistors, one or more metallic carbides, one or more metallic nitrides, one or more metallic phosphides, one or more superionic conductors, one or more phosphate electrolytes, one or more mixed oxides being doped with one or more lower-valent cations, one or more mixed sulphides being doped with one or more lower-valent cations, and any mixture thereof; with preference in a content of from 50 wt. % to 100 wt. % based on the total weight of the electrically conductive particles of the bed; preferably, from 60 wt. % to 100 wt. %; more preferably from 70 wt. % to 100 wt. %; even more preferably from 80 wt. % to 100 wt. % and most preferably from 90 wt. % to 100 wt. %.
For example, the electrically conductive particles of the bed are or comprise one or more selected from graphite, carbon black, one or more metallic alloys, one or more non-metallic resistors, one or more metallic carbides, one or more metallic nitrides, one or more metallic phosphides, one or more superionic conductors, one or more phosphate electrolytes, one or more mixed oxides being doped with one or more lower-valent cations, one or more mixed sulphides being doped with one or more lower-valent cations, and any mixture thereof; with preference in a content of from 50 wt. % to 100 wt. % based on the total weight of the electrically conductive particles of the bed; preferably, from 60 wt. % to 100 wt. %; more preferably from 70 wt. % to 100 wt. %; even more preferably from 80 wt. % to 100 wt. % and most preferably from 90 wt. % to 100 wt. %.
For example, the step of heating the fluidized bed is performed by passing an electric current at a voltage of at most 300 V through the fluidized bed, preferably at most 200 V, more preferably at most 150 V, even more preferably at most 120 V, most preferably at most 100 V, even most preferably at most 90 V.
The solid particulate material in the fluidized bed reactor is typically supported by a porous plate, a perforated plate, a plate with nozzles or chimneys, known as a distributor. The fluid is then forced through the distributor up and travelling through the voids between the solid particulate material. At lower fluid velocities, the solids remain settled as the fluid passes through the voids in the material, known as a packed bed reactor. As the fluid velocity is increased, the particulate solids will reach a stage where the force of the fluid on the solids is enough to counterbalance the weight of the solid particulate material. This stage is known as incipient fluidization and occurs at this minimum fluidization velocity. Once this minimum velocity is surpassed, the contents of the reactor bed begin to expand and become fluidized. Depending on the operating conditions and properties of the solid phase various flow regimes can be observed in such reactors. The minimum fluidization velocity needed to achieve bed expansion depends upon the size, shape, porosity and density of the particles and the density and viscosity of the upflowing fluid.
P.R. Gunjal, V.V. Ranade, in Industrial Catalytic Processes for Fine and Specialty Chemicals, (2016) reads that four different categories of fluidization based on the mean particle have been differentiated by Geldart that determine the fluidization regimes:
Fluidization may be broadly classified into two regimes (Fluid Bed Technology in Materials Processing, 1999 by CRC Press): homogeneous fluidization and heterogeneous fluidization. In homogeneous or particulate fluidization, particles are fluidized uniformly without any distinct voids. In heterogeneous or bubbling fluidization, gas bubbles devoid of solids are distinctly observable. These voids behave like bubbles in gas-liquid flows and exchange gas with the surrounding homogeneous medium with a change in size and shape while rising in the medium. In particulate fluidization, the bed expands smoothly with substantial particle movement and the bed surface is well defined. Particulate fluidization is observed only for Geldart-A type particles. A bubbling fluidization regime is observed at much higher velocities than homogeneous fluidization, in which distinguishable gas bubbles grow from the distributor, may coalesce with other bubbles and eventually burst at the surface of the bed. These bubbles intensify the mixing of solids and gases and bubble sizes tend to increase further with a rise in fluidization velocity. A slugging regime is observed when the bubble diameter increases up to the reactor diameter. In a turbulent regime, bubbles grow and start breaking up with the expansion of the bed. Under these conditions, the top surface of the bed is no longer distinguishable. In fast fluidization or pneumatic fluidization, particles are transported out of the bed and need to be recycled back into the reactor. No distinct bed surface is observed.
Fluidized bed reactors have the following advantages:
Uniform Particle Mixing: Due to the intrinsic fluid-like behaviour of the solid particulate material, fluidized beds do not experience poor mixing as in packed beds. The elimination of radial and axial concentration gradients also allows for better fluid-solid contact, which is essential for reaction efficiency and quality.
Uniform Temperature Gradients: Many chemical reactions require the addition or removal of heat. Local hot or cold spots within the reaction bed are avoided in a fluidized situation.
Ability to Operate the Reactor Continuously: The fluidized bed nature of these reactors allows for the ability to continuously withdraw products and introduce new reactants into the reaction vessel. On top of continuous operation of the chemical reactions, the fluidized bed allows also to continuously or at a given frequency withdraw solid material or add continuously or at a given frequency new fresh solid material thanks to the flowable solid particulate material.
Heat can be produced by passing an electrical current through a conducting material that has sufficiently high resistivity (the resistor) to transform electricity into heat. Electrical resistivity (also called specific electrical resistance or volume resistivity, is an intrinsic property independent of shape and size) and its inverse, electrical conductivity, is a fundamental property of a material that quantifies how strongly it resists or conducts electric current (SI unit of electrical resistivity is the ohm-meter (Q.m) and for conductivity Siemens per meter (S/m)).
When electricity is passed through a fixed bed of electrically conducting particulate solids, having a sufficient resistivity, the bed offers resistance to the flow of current; this resistance depends on many parameters, including the nature of the solid, the nature of the linkages among the particles within the bed, the bed voidage, the bed height, the electrode geometry, etc. If the same fixed bed is fluidized by passing gas, the resistance of the bed increases; the resistance offered by the conducting particles generates heat within the bed and can maintain the bed in isothermal conditions (termed an electrothermal fluidized bed or electrofluid reactor). In many high-temperature reactions, electrofluid reactors offer in situ heating during the reaction and are particularly useful for operating endothermic reactions and hence save energy because no external heating or transfer of heat is required. It is a prerequisite that at least part of the solid particulate material is electrically conducting but non-conducting solid particulates can be mixed and still result in enough heat generation. Such non-conducting or very high resistivity solids can play a catalytic role in the chemical conversion. The characteristics of the bed material determine the resistance of an electrothermal fluidized bed furnace; as this is a charge resistor type of heat generation, the specific resistivity of the particles affects the bed resistance. The size, shape, composition, and size distribution of the particles also influence the magnitude of the bed resistance. Also, when the bed is fluidized, the voids generated between the particles increases the bed resistance. The total resistance of the bed is the sum of two components, e.g., the electrode contact-resistance (i.e., the resistance between the electrode and the bed) and the bed resistance. A large contact-resistance will cause extensive local heating in the vicinity of the electrode while the rest of the bed stays rather cool. The following factors determine the contact-resistance: current density, fluidization velocity, type of bed material, electrode size and the type of material used for the electrodes. The electrode compositions can be advantageously metallic like iron, cast iron or other steel alloys, copper or a copper-based alloy, nickel or a nickel-based alloy or refractory like metal, intermetallics or an alloy of Zr, Hf, V, Nb, Ta, Cr, Mo, W or ceramic-like carbides, nitrides or carbon-based like graphite. The area of contact between the bed material and the electrodes can be adjusted, depending on the electrode submergence and the amount of particulate material in the fluidized bed. Hence, the electrical resistance and the power level can be manipulated by adjusting these variables. Advantageously, to prevent overheating of the electrodes compared to the fluidised bed, the resistivity of the electrode should be lower (and hence the joule heating) than of the particulate material of the fluidized bed. In a preferred embodiment, the electrodes can be cooled by passing a colder fluid inside or outside the electrodes. Such fluids can be any liquid that vaporises upon a heating, gas stream or can be a part of the colder feedstock that first cools the electrode before entering the fluidised bed.
Bed resistance can be predicted by the ohmic law. The mechanism of current transfer in fluidized beds is believed to occur through current flow along continuous chains of conducting particles at low operating voltages. At high voltages, a current transfer occurs through a combination of chains of conducting particles and arcing between the electrode and the bed as well as particle-to-particle arcing that might ionize the gas, thereby bringing down the bed resistance. Arcing inside the bed, in principle, is not desirable as it would lower the electrical and thermal efficiency. The gas velocity impacts strongly the bed resistance, a sharp increase in resistance from the settled bed onward when the gas flow rate is increased; a maximum occurred close to the incipient fluidization velocity, followed by a decrease at higher velocities. At gas flow rates sufficient to initiate slugging, the resistance again increased. Average particle size and shape impact resistance as they influence the contacts points between particles. In general, the bed resistivity increases 2 to 5 times from a settled bed (e.g. 20 Ohm.cm for graphite) to the incipient fluidisation (60 Ohm.cm for graphite) and 10 to 40 times from a settled bed to twice (300 Ohm.cm for graphite) the incipient fluidisation velocity. Non or less-conducting particles can be added to conducting particles. If the conducting solid fraction is small, the resistivity of the bed would increase due to the breaking of the linkages in the chain of conducting solids between the electrodes. If the non-conducting solid fraction is finer in size, it would fill up the interstitial gaps or voidage of the larger conducting solids and hence increase the resistance of the bed.
In general, for a desired high heating power, a high current at a low voltage is preferred. The power source can be either AC or DC. Voltages applied in an electrothermal fluidized bed are typically below 100 V to reach enough heating power. The electrothermal fluidized bed can be controlled in the following three ways:
1. Adjusting the gas flow: Because the conductivity of the bed depends on the extent of voidage or gas bubbles inside the bed, any variation in the gas flow rate would change the power level; hence the temperature can be controlled by adjusting the fluidizing gas flow rate. The flow rate required for optimum performance corresponds to a velocity which equals or slightly exceeds the minimum fluidization velocity.
2. Adjusting the electrode submergence: The power level can also be controlled by varying the electrode immersion level inside the bed because the conductivity of the bed is dependent on the area of contact between the conducting particles and the electrode: the surface area of the electrode available for current flow increases with electrode submergence, leading to a reduction in overall resistance.
3. Adjusting the applied voltage: although changing the power level by using the first two methods is often more affordable or economical than increasing the applied voltage, however in electrothermal fluidized beds three variables are available to control the produced heating power.
The wall of the reactor is generally made of graphite, ceramics (like SiC), high-melting metals or alloys as it is versatile and compatible with many high-temperature reactions of industrial interest. The atmosphere for the reaction is often restricted to the neutral or the reducing type as an oxidising atmosphere can combust carbon materials or create a non-conducting metal oxide layer on top of metals or alloys. The wall and/or the distribution plate itself can act as an electrode for the reactor. The fluidized solids can be graphite or any other high-melting-point, electrically conducting particles. The other electrodes, which is usually immersed in the bed, can also be graphite or a high-melting-point metal, intermetallics or alloys.
It may be advantaged to generate the required reaction heat by heating the conductive particles and/or catalyst particles in a separate zone of the reactor where little or substantially no ammonia-containing feedstock is present, but only diluent gases (i.e., fluidizing gas). The benefit is that the appropriate conditions of fluidization to generate heat by passing an electrical current through a bed of conductive particles can be optimized whereas the optimal reaction conditions during hydrocarbon transformation can be selected for the other zone of the reactor. Such conditions of optimal void fraction and linear velocity might be different for heating purposes and chemical transformation purposes.
In an embodiment of the present disclosure, the installation comprises two zones arranged in series, namely a first zone being a heating zone and a second zone being a reaction zone, where the conductive particles and catalyst particles are continuously moved or transported from the first zone to the second zone and vice versa. The first and second zones can be different parts of a fluidized bed or can be located in separate fluidized beds reactors connected one to each other.
In the said embodiment, the process to perform an ammonia cracking reaction with production of hydrogen said process comprising the steps of:
For example, the one or more diluent gases can be one or more selected from steam, hydrogen, carbon dioxide, argon, helium, nitrogen and one or more hydrocarbons, such as methane. The one or more diluent gases are for example used as one or more fluidizing gases. With preference, the one or more diluent gases are one or more selected from steam, hydrogen, carbon dioxide, nitrogen and one or more hydrocarbons, such as methane. In an embodiment, when the diluent gases are at least a mixture of steam and one or more hydrocarbons, such as methane, then an endothermic steam reforming of hydrocarbons to produce synthesis gas is conducted concomitantly with said ammonia cracking reaction with production of hydrogen. In an alternative embodiment, when the diluent gases are at least a mixture of carbon dioxide and one or more hydrocarbons, such as methane, then an endothermic dry reforming of hydrocarbons to produce synthesis gas is conducted concomitantly with said ammonia cracking reaction with the production of hydrogen.
For example, the at least one fluidized bed reactor is at least two fluidized bed reactors connected wherein at least one fluidized bed reactor is the heating zone and at least another fluidized bed reactor is the reaction zone. With preference, the at least one fluidized bed reactor being the heating zone comprises gravitational or pneumatic transport means to transport the particles from the heating zone to the reaction zone and/or the installation comprises means arranged to inject an ammonia-containing feedstock to the at least one fluidized bed reactor being the reaction zone. The installation is devoid of means to inject an ammonia-containing feedstock to the at least one fluidized bed reactor being the heating zone.
For example, the at least one fluidized bed reactor is a single fluidized bed reactor wherein the heating zone is the bottom part of the fluidized bed reactor while the reaction zone is the top part of the fluidised bed reactor. With preference, the installation comprises means to inject an ammonia-containing feedstock and optional one or more diluent gas between the two zones. The diameter of the heating zone and reaction zone can be different to accomplish optimum conditions for heating in the bottom zone and optimum conditions for hydrocarbon conversion in the top zone. Particles can move from the heating zone to the reaction zone by entrainment and the other way around from the reaction zone back to the heating zone by gravity. Optionally, particles can be collected from the upper heating zone and transferred by a separate transfer line back to the bottom heating zone.
Step c) provides that the ammonia-cracking reaction is performed on an ammonia-containing feedstock which implies that an ammonia-containing feedstock is provided. It is understood that the ammonia-containing feedstock is provided to the reaction zone and that when the heating zone is separated from the reaction zone then, with preference, no ammonia-containing feedstock with at least two carbons is provided to the heating zone.
When the heating zone and the reaction zone are mixed (i.e., the same zone); the fluid stream provided in step b) comprises an ammonia-containing feedstock.
To achieve the required temperature necessary to carry out the ammonia-cracking reaction, at least 10 wt. % of the particles based on the total weight of the particles of the bed are electrically conductive, have a resistivity ranging from 0.001 Ohm.cm to 500 Ohm.cm at 800° C.
For example, the electrically particles of the bed are or comprise one or more selected from one or more metallic alloys, one or more non-metallic resistors, one or more metallic carbides, one or more metallic nitrides, one or more metallic phosphides, one or more carbon-containing particles, one or more superionic conductors, one or more phosphate electrolytes, one or more mixed oxides being doped with one or more lower-valent cations, one or more mixed sulphides being doped with one or more lower-valent cations, and any mixture thereof; with preference in a content of from 50 wt. % to 100 wt. % based on the total weight of the electrically conductive particles of the bed; preferably, from 60 wt. % to 100 wt. %; more preferably from 70 wt. % to 100 wt. %; even more preferably from 80 wt. % to 100 wt. % and most preferably from 90 wt. % to 100 wt. %.
For example, the electrically particles of the bed are or comprise one or more selected from one or more metallic alloys, one or more non-metallic resistors, one or more metallic carbides, one or more metallic nitrides, one or more metallic phosphides, graphite, carbon black, one or more superionic conductors, one or more phosphate electrolytes, one or more mixed oxides being doped with one or more lower-valent cations, one or more mixed sulphides being doped with one or more lower-valent cations, and any mixture thereof; with preference in a content of from 50 wt. % to 100 wt. % based on the total weight of the electrically conductive particles of the bed; preferably, from 60 wt. % to 100 wt. %; more preferably from 70 wt. % to 100 wt. %; even more preferably from 80 wt. % to 100 wt. % and most preferably from 90 wt. % to 100 wt. %.
In an embodiment, the electrically conductive particles of the bed comprise one or more carbon-containing particles being graphite; with preference in a content from 10 wt. % to 100 wt. % based on the total weight of the electrically conductive particles of the bed; or from 10 wt. % to 90 wt. %, or from 10 wt. % to 80 wt. %, preferably from 15 wt. % to 70 wt. %, more preferably from 20 wt. % to 60 wt. %, even more preferably from 30 wt. % to 50 wt. %. For example, the electrically conductive particles of the bed are a mixture of graphite and particles of the catalytic composition.
In an embodiment, from 50 wt. % to 100 wt. % of the electrically conductive particles of the bed based on the total weight of the electrically conductive particles of the bed are devoid of graphite and/or carbon black; preferably, from 60 wt. % to 95 wt. %; more preferably from 70 wt. % to 90 wt. %; and even more preferably from 75 wt. % to 85 wt. %.
For example, the content of electrically conductive particles is ranging from 10 wt. % to 100 wt. % based on the total weight of the particles of the bed; preferably, from 15 wt. % to 95 wt. %, more preferably from 20 wt. % to 90 wt. %, even more preferably from 25 wt. % to 80 wt. % and most preferably from 30 wt. % to 75 wt. %.
For example, the content of electrically conductive particles based on the total weight of the bed is at least 12 wt. % based on the total weight of the particles of the bed; preferably, at least 15 wt. %, more preferably, at least 20 wt. %; even more preferably at least 25 wt. %, and most preferably at least 30 wt. % or at least 40 wt. % or at least 50 wt. % or at least 60 wt. %.
For example, the electrically conductive particles have a resistivity ranging from 0.005 to 400 Ohm.cm at 800° C., preferably ranging from 0.01 to 300 Ohm.cm at 800° C.; more preferably ranging from 0.05 to 150 Ohm.cm at 800° C. and most preferably ranging from 0.1 to 100 Ohm.cm at 800° C.
For example, the electrically conductive particles have a resistivity of at least 0.005 Ohm.cm at 800° C.; preferably of at least 0.01 Ohm.cm at 800° C., more preferably of at least 0.05 Ohm.cm at 800° C.; even more preferably of at least 0.1 Ohm.cm at 800° C., and most preferably of at least 0.5 Ohm.cm at 800° C.
For example, the electrically conductive particles have a resistivity of at most 400 Ohm.cm at 800° C.; preferably of at most 300 Ohm.cm at 800° C., more preferably of at most 200 Ohm.cm at 800° C.; even more preferably of at most 150 Ohm.cm at 800° C., and most preferably of at most 100 Ohm.cm at 800° C.
For example, the particles of the bed have an average particle size ranging from 5 to 300 μm as determined by sieving according to ASTM D4513-11, preferably ranging from 10 to 200 μm and more preferably ranging from 30 to 150 μm.
For example, the electrically conductive particles of the bed have an average particle size ranging from 5 to 300 μm as determined by sieving according to ASTM D4513-11, preferably ranging from 10 to 200 μm and more preferably ranging from 30 to 150 μm.
The electrical resistance is measured by a four-probe DC method using an ohmmeter. A densified power sample is shaped in a cylindrical pellet that is placed between the probe electrodes. Resistivity is determined from the measured resistance value, R, by applying the known expression ρ=R×A/L, where L is the distance between the probe electrodes typically a few millimetres and A the electrode area.
The electrically conductive particles of the bed can exhibit electronic, ionic or mixed electronic-ionic conductivity. The ionic bonding of many refractory compounds allows for ionic diffusion and correspondingly, under the influence of an electric field and appropriate temperature conditions, ionic conduction.
The electrical conductivity, σ, the proportionality constant between the current density j and the electric field E, is given by
where ci is the carrier density (number/cm3), μi the mobility (cm2/Vs), and Ziq the charge (q=1.6×10−19 C) of the ith charge carrier. The many orders of magnitude differences in σ between metals, semiconductors and insulators generally result from differences in c rather than μ. On the other hand, the higher conductivities of electronic versus ionic conductors are generally due to the much higher mobilities of electronic versus ionic species.
The most common materials that can be used for resistive heating is subdivided into nine groups:
A first group of metallic alloys, for temperatures up to 1150-1250° C., can be constituted by Ni—Cr alloys with low Fe content (0.5-2.0%), preferably alloy Ni—Cr (80% Ni, 20% Cr) and (70% Ni, 30% Cr). Increasing the content of Cr increases the material resistance to oxidation at high temperatures. A second group of metallic alloys having three components are Fe—Ni—Cr alloys, with maximum operating temperature in an oxidizing atmosphere to 1050-1150° C. but which can be conveniently used in reducing atmospheres or Fe—Cr—Al (chemical composition 15-30% Cr, 2-6% Al and Fe balance) protecting against corrosion by a surface layer of oxides of Cr and Al, in oxidizing atmospheres can be used up to 1300-1400° C. Silicon carbide as non-metallic resistor can exhibit wide ranges of resistivity that can be controlled by the way they are synthesized and the presence of impurities like aluminium, iron, oxide, nitrogen or extra carbon or silicon resulting in non-stoichiometric silicon carbide. In general silicon carbide has a high resistivity at low temperature but has good resistivity in the range of 500 to 1200° C. In an alternative embodiment, the non-metallic resistor can be devoid of silicon carbide, and/or can comprise molybdenum disilicide (MoSi2), nickel silicide (NiSi), sodium silicide (Na2Si), magnesium silicide (Mg2Si), platinum silicide (PtSi), titanium silicide (TiSi2), tungsten silicide (WSi2) or a mixture thereof.
Graphite has rather low resistivity values, with a negative temperature coefficient up to about 600° C. after which the resistivity starts to increase.
Many mixed oxides and/or mixed sulphides being doped with one or more lower-valent cations, having in general too high resistivity at low temperature, become ionic or mixed conductors at high temperature. The following circumstances can make oxides or sulphides sufficient conductors for heating purposes: ionic conduction in solids is described in terms of the creation and motion of atomic defects, notably vacancies and interstitials of which its creation and mobility is very positively dependent on temperature. Such mixed oxides or sulphides are ionic or mixed conductors, namely being doped with one or more lower-valent cations. Three mechanisms for ionic defect formation in oxides are known: (1) Thermally induced intrinsic ionic disorder (such as Schottky and Frenkel defect pairs resulting in non-stoichiometry), (2). Redox-induced defects and (3) Impurity-induced defects. The first two categories of defects are predicted from statistical thermodynamics and the latter form to satisfy electroneutrality. In the latter case, high charge carrier densities can be induced by substituting lower valent cations for the host cations. Mixed oxides and/or mixed sulphides with fluorite, pyrochlore or perovskite structure are very suitable for substitution by one or more lower-valent cations.
Several sublattice disordered oxides or sulphides have high ion transport ability at increasing temperature. These are superionic conductors, such as LiAlSiO4, Li10GeP2S12, Li3.6Si0.6P0.4O4, NaSICON (sodium (Na) Super Ionic CONductor) with the general formula Na1+xZr2P3−xSixO12 with 0<x<3, for example Na3Zr2PSi2O12 (x=2), or sodium beta alumina, such as NaAl11O17, Na1.6Al11O17.3, and/or Na1.76Li0.38Al10.62O17.
High concentrations of ionic carriers can be induced in intrinsically insulating solids and creating high defective solids. Thus, the electrically conductive particles of the bed are or comprise one or more mixed oxides being ionic or mixed conductor, namely being doped with one or more lower-valent cations, and/or one or more mixed sulphides being ionic or mixed conductor, namely being doped with one or more lower-valent cations. With preference, the mixed oxides are selected from one or more oxides having a cubic fluorite structure being at least partially substituted with one or more lower-valent cations, preferentially selected from Sm, Gd, Y, Sc, Yb, Mg, Ca, La, Dy, Er, Eu; and/or from one or more ABO3-perovskites with A and B tri-valent cations, being at least partially substituted in A position with one or more lower-valent cations, preferentially selected from Ca, Sr, or Mg, and comprising at least one of Ni, Ga, Co, Cr, Mn, Sc, Fe and/or a mixture thereof in B position; and/or from one or more ABO3-perovskites with A bivalent cation and B tetra-valent cation, being at least partially substituted with one or more lower-valent cations, preferentially selected from Mg, Sc, Y, Nd or Yb in the B position or with a mixture of different B elements in the B position; and/or from one or more A2B2O7-pyrochlores with A trivalent cation and B tetra-valent cation being at least partially substituted in A position with one or more lower-valent cations, preferentially selected from Ca or Mg, and comprising at least one of Sn, Zr and Ti in B position.
With preference, the one or more mixed sulphides are selected from one or more sulphides having a cubic fluorite structure being at least partially substituted with one or more lower-valent cations, preferentially selected from Sm, Gd, Y, Sc, Yb, Mg, Ca, La, Dy, Er, Eu; and/or from one or more ABS3 structures with A and B tri-valent cations, being at least partially substituted in A position with one or more lower-valent cations, preferentially selected from Ca, Sr, or Mg, and comprising at least one of Ni, Ga, Co, Cr, Mn, Sc, Fe and/or a mixture thereof in B position; and/or from one or more ABS3 structures with A bivalent cation and B tetra-valent cation, being at least partially substituted with one or more lower-valent cations, preferentially selected from Mg, Sc, Y, Nd or Yb in the B position or with a mixture of different B elements in the B position; and/or from one or more A2B2S7 structures with A trivalent cation and B tetra-valent cation being at least partially substituted in A position with one or more lower-valent cations, preferentially selected from Ca or Mg, and comprising at least one of Sn, Zr and Ti in B position.
With preference, the degree of substitution in the one or more mixed oxides doped with one or more lower-valent cations and having a cubic fluorite structure is between 1 and 15 atom % based on the total number of atoms present in the one or more oxides or sulphides having a cubic fluorite structure, in the one or more ABO3-perovskites with A and B tri-valent cations, in the one or more ABO3-perovskites with A bivalent cation and B tetra-valent cation or in the one or more A2B2O7-pyrochlores with A trivalent cation and B tetra-valent cation respectively, preferably between 3 and 12 atom %, more preferably between 5 and 10 atom %.
With preference, the degree of substitution in the one or more mixed oxides doped with one or more lower-valent cations is between 1 and 50 atom % based on the total number of atoms present in the one or more ABO3-perovskites with A and B tri-valent cations, in the one or more ABO3-perovskites with A bivalent cation and B tetra-valent cation or in the one or more A2B2O7-pyrochlores with A trivalent cation and B tetra-valent cation respectively, preferably between 3 and 20 atom %, more preferably between 5 and 15 atom %.
With preference, the degree of substitution in the one or more mixed sulphides doped with one or more lower-valent cations and having a cubic fluorite structure is between 1 and 15 atom % based on the total number of atoms present in the one or more ABS3 structures with A and B tri-valent cations, in the one or more ABS3 structures with A bivalent cation and B tetra-valent cation or in the one or more A2B2S7 structures with A trivalent cation and B tetra-valent cation respectively, preferably between 3 and 12 atom %, more preferably between 5 and 10 atom %.
With preference, the degree of substitution in the one or more mixed sulphides doped with one or more lower-valent cations is between 1 and 50 atom % based on the total number of atoms present in the one or more ABS3 structures with A and B tri-valent cations, in the one or more ABS3 structures with A bivalent cation and B tetra-valent cation or in the one or more A2B2S7 structures with A trivalent cation and B tetra-valent cation respectively, preferably between 3 and 20 atom %, more preferably between 5 and 15 atom %.
Said one or more oxides having a cubic fluorite structure, said one or more ABO3-perovskites with A and B tri-valent cations, said one or more ABO3-perovskites with A bivalent cation and B tetra-valent cation or said one or more A2B2O7-pyrochlores with A trivalent cation and B tetra-valent cation being at least partially substituted with lower valent cations, said one or more sulphides having a cubic fluorite structure, said one or more ABS3 structures with A and B tri-valent cations, said one or more ABS3 structures with A bivalent cation and B tetra-valent cation, said one or more A2B2S7 structures with A trivalent cation and B tetra-valent cation being at least partially substituted with lower valent cations also means that the same element, being a high-valent cation, can be reduced in the lower-valent equivalent, for example, Ti(IV) can be reduced in Ti(III) and/or Co(III) can be reduced in Co(II) and/or Fe(III) can be reduced in Fe(II) and/or Cu(II) can be reduced in Cu(I).
Phosphate electrolytes such as LiPO4 or LaPO4 can also be used as electrically conductive particles.
Metallic carbides, metallic nitrides and metallic phosphides can also be selected as electrically conductive particles. For example, metallic carbides are selected from iron carbide (Fe3C), molybdenum carbide (such as a mixture of MoC and Mo2C). For example, said one or more metallic nitrides are selected from zirconium nitride (ZrN), tungsten nitride (such as a mixture of W2N, WN, and WN2), vanadium nitride (VN), tantalum nitride (TaN), and/or niobium nitride (NbN). For example, said one or more metallic phosphides are selected from copper phosphide (Cu3P), indium phosphide (InP), gallium phosphide (GaP), sodium phosphide Na3P), aluminium phosphide (AIP), zinc phosphide (Zn3P2) and/or calcium phosphide (Ca3P2).
It is a preferred embodiment of the present disclosure, the electrically conductive particles that exhibit only sufficiently low resistivity at a high temperature can be heated by external means before reaching the high enough temperature where resistive heating with electricity overtakes or can be mixed with a sufficiently low resistivity solid at a low temperature so that the resulting resistivity of the mixture allows to heat the fluidized bed to the desired reaction temperature.
For example, the electrically conductive particles of the bed are or comprise silicon carbide. For example, at least 10 wt. % of the electrically conductive particles based on the total weight of the electrically conductive particles of the bed are silicon carbide particles and have a resistivity ranging from 0.001 Ohm.cm to 500 Ohm.cm at of 800° C.
In the embodiment wherein the electrically conductive particles of the bed are or comprise silicon carbide, the person skilled in the art will have the advantage to conduct a step of pre-heating with a gaseous stream said fluidized bed reactor before conducting said endothermic reaction in the fluidized bed reactor. Advantageously, the gaseous stream is a stream of inert gas, i.e., nitrogen, argon, helium, methane, carbon dioxide, hydrogen or steam. The temperature of the gaseous stream can be at least 250° C., or at least 300° C., or at least 350° C., or at least 400° C., or at least 450° C., or at least 500° C., or at least 550° C., or at least 600° C., or at least 650° C., or at least 700° C., or at least 750° C., or at least 800° C. Advantageously, the temperature of the gaseous stream can be comprised between 250° C. and 800° C., for example between 300° C. and 750° C. or between 350° C. and 700° C. Said gaseous stream of inert gas can also be used as the fluidification gas. The pre-heating of the said gaseous stream of inert gas is performed thanks to conventional means, including using electrical energy. The temperature of the gaseous stream used for the preheating of the bed does not need to reach the temperature reaction.
Indeed, the resistivity of silicon carbide at ambient temperature is high, to ease the starting of the reaction, it may be useful to heat the fluidized bed by external means, as with preference the fluidized bed reactor is devoid of heating means. Once the bed is heated at the desired temperature, the use of a hot gaseous stream may not be necessary.
However, in an embodiment, the electrically conductive particles of the bed are or comprise a mixture of silicon carbide particles and electrically conductive particles different from silicon carbide particles.
The pre-heating step may be also used in the case wherein electrically conductive particles different from silicon carbide particles are present in the bed. For example, it may be used when the content of silicon carbide in the electrically conductive particles of the bed is more than 80 wt. % based on the total weight of the particles of the bed, for example, more than 85 wt. %, for example, more than 90 wt. %, for example, more than 95 wt. %, for example, more than 98 wt. %, for example, more than 99 wt. %. However, a pre-heating step may be used whatever is the content of silicon carbide particles in the bed.
In the embodiment wherein the electrically conductive particles of the bed are or comprise a mixture of silicon carbide particles and electrically conductive particles different from silicon carbide particles, the electrically conductive particles of the bed may comprise from 10 wt. % to 99 wt. % of silicon carbide particles based on the total weight of the electrically conductive particles of the bed; preferably, from 15 wt. % to 95 wt. %, more preferably from 20 wt. % to 90 wt. %, even more preferably from 25 wt. % to 80 wt. % and most preferably from 30 wt. % to 75 wt. %.
For example, the electrically conductive particles of the bed are or comprise a mixture of silicon carbide particles and electrically conductive particles different from silicon carbide particles and the electrically conductive particles of the bed comprises at least 40 wt. % of silicon carbide particles based on the total weight of the electrically conductive particles of the bed; preferably at least 50 wt. %, more preferably at least 60 wt. %, even more preferably at least 70 wt. % and most preferably at least 80 wt. %.
In an embodiment, the electrically conductive particles of the bed may comprise from 10 wt. % to 90 wt. % of electrically conductive particles different from silicon carbide particles based on the total weight of the electrically conductive particles of the bed; preferably, from 15 wt. % to 95 wt. %, more preferably from 20 wt. % to 90 wt. %, even more preferably from 25 wt. % to 80 wt. % and most preferably from 30 wt. % to 75 wt. %.
However, it may be interesting to keep the content of electrically conductive particles different from silicon carbide particles quite low in the mixture. Thus, in an embodiment, the electrically conductive particles of the bed are or comprise a mixture of silicon carbide particles and electrically conductive particles different from silicon carbide particles and electrically conductive particles of the bed comprises from 1 wt. % to 20 wt. % of electrically conductive particles different from silicon carbide based on the total weight of the electrically conductive particles of the bed; preferably, from 2 wt. % to 15 wt. %, more preferably, from 3 wt. % to 10 wt. %, and even more preferably, from 4 wt. % to 8 wt. %.
For example, the electrically conductive particles of the bed are or comprise a mixture of silicon carbide particles and particles different from silicon carbide particles and the said particles different from silicon carbide particles are or comprise graphite particles.
Thus, in an embodiment, the electrically conductive particles are a combination of silicon carbide particles and graphite particles. Such electrically conductive particles, upon the electrification of the fluidized bed reactor, will heat up and because of their fluidification, will contribute to the raise and/or to the maintaining of the temperature within the reactor.
The Joule heating of graphite allows accelerating the heating of the reactant and/or of the other particles that are present within the fluidized bed reactor.
For example, graphite can be flake graphite. It is also preferable that the graphite has an average particle size ranging from 1 to 400 μm as determined by sieving according to ASTM D4513-11, preferably from 5 to 300 μm, more preferably ranging from 10 to 200 μm and most preferably ranging from 30 to 150 μm.
The presence of graphite particles in the bed allows applying the process according to the disclosure with or without the pre-heating step, preferably without the pre-heating step. Indeed, the graphite particles, upon the electrification of the fluidized bed reactor, will heat up and because of their fluidification, will contribute to raising and/or maintaining the desired temperature within the reactor.
For example, the silicon carbide is selected from sintered silicon carbide, nitride-bounded silicon carbide, recrystallised silicon carbide, reaction bonded silicon carbide and any mixture thereof.
Sintered SiC (SSiC) is a self-bonded material containing a sintering aid (typically boron) of less than 1% by weight.
Recrystallized silicon carbide (RSiC), a high purity SiC material sintered by the process of evaporation—condensation without any additives.
Nitride-bonded silicon carbide (NBSC) is made by adding fine silicon powder with silicon carbide particles or eventually in the presence of a mineral additive and sintering in a nitrogen furnace. The silicon carbide is bonded by the silicon nitride phase (Si3N4) formed during nitriding.
Reaction bonded silicon carbide (RBSC), also known as siliconized silicon carbide or SiSiC, is a type of silicon carbide that is manufactured by a chemical reaction between porous carbon or graphite with molten silicon. The silicon reacts with the carbon forming silicon carbide and bonds the silicon carbide particles. Any excess silicon fills the remaining pores in the body and produces a dense SiC—Si composite. Due to the left-over traces of silicon, reaction bonded silicon carbide is often referred to as siliconized silicon carbide. The process is known variously as reaction bonding, reaction sintering, self-bonding, or melt infiltration.
In general, high purity SiC particles have resistivity above 1000 Ohm.cm, whereas sintered, reaction bonded and nitride-bonded can exhibit resistivities of about 100 to 1000 depending on the impurities in the SiC phase. Electrical resistivity of bulk polycrystalline SiC ceramics shows a wide range of resistivity depending on the sintering additive and heat-treatment conditions (Journal of the European Ceramic Society, Volume 35, Issue 15, December 2015, Pages 4137; Ceramics International, Volume 46, Issue 4, March 2020, Pages 5454). SiC polytypes with high purity possess high electrical resistivity (>106Ω.cm) because of their large bandgap energies. However, the electrical resistivity of SiC is affected by doping impurities. N and P act as n-type dopants and decrease the resistivity of SiC, whereas Al, B, Ga, and Sc act as p-type dopants. SiC doped with Be, O, and V are highly insulating. N is considered the most efficient dopant for improving the electrical conductivity of SiC. For N doping of SiC (to decrease resistivity) Y2O3 and Y203-REM2O3(REM, rare earth metal=Sm, Gd, Lu) have been used as sintering additives for efficient growth of conductive SiC grains containing N donors. N-doping in SiC grains was promoted by the addition of nitrides (AlN, BN, Si3N4, TiN, and ZrN) or combinations of nitrides and Re2O3 (AlN-REM2O3(REM=Sc, Nd, Eu, Gd, Ho, and Er) or TiN—Y2O3).
For example, the content of the particles of a catalytic composition based on the total weight of the particles of the bed is ranging from 30 wt. % to 100 wt. %; preferably from 32 wt. % to 95 wt. %, more preferably from 35 wt. % to 90 wt. %, even more preferably from 37 wt. % to 85 wt. %, most preferably from 40 wt. % to 80 wt. %, even most preferably from 45 wt. % to 75 wt. % or from 50 wt. % to 70 wt. %. In the case where the content of the particles of a catalytic composition based on the total weight of the particles of the bed is 100 wt. %, said particles of a catalytic composition are also electrically conductive particles.
For example, the particles of a catalytic composition have an average particle size ranging from 5 to 300 μm as determined by sieving according to ASTM D4513-11, preferably ranging from 10 to 200 μm and more preferably ranging from 20 to 200 μm or from 30 to 150 μm.
Determination by sieving according to ASTM D4513-11 is preferred. In case the particles have an average size of below 20 μm the determination of the average size can also be done by Laser Light Scattering according to ASTM D4464-15.
The catalytic composition comprises one or more metallic compounds. With preference, the catalytic composition comprises one or more metallic compounds selected from:
For example, the one or more non-noble metals selected from Ni, Fe, Co, Mo, Cu and any mixture thereof are present in an amount ranging between 0.05 wt. % and 20.00 wt. % based on the total weight of the catalytic composition, preferably between 0.10 wt. % and 15.00 wt. %, more preferably between 0.50 wt. % and 10.00 wt. %, even more preferably between 1.00 wt. % and 5.00 wt. %.
For example, the one or more non-noble metals are or comprise Ni.
For example, the one or more noble metals selected from Ru, Rh, Pd, Ir, Pt and any mixture thereof are present in an amount ranging between 0.05 wt. % and 10.00 wt. % based on the total weight of the catalytic composition, preferably between 0.10 wt. % and 5.00 wt. %, more preferably between 1.00 wt. % and 3.00 wt. %, even more preferably between 1.50 wt. % and 2.50 wt. %.
For example, the one or more noble metals are or comprise Ru, preferably in an amount ranging between 0.05 wt. % and 10.00 wt. % based on the total weight of the catalytic composition
Commercially available catalysts that can be used to perform the ammonia cracking reaction can be ACTA Hypermec 10010 Ru catalyst, KATALCO™ 27-2 series for high temperature cracking (from Johnson Matthey), KATALCO™ 27-612 series for high temperature cracking (from Johnson Matthey), R-87 HEAT X™ (from Haldor Topsoe).
Advantageously, said catalytic composition further comprises one or more elements selected from one or more selected from alkali metals, alkaline earth metals and rare earth elements. For example, one or more alkali metals are one or more selected from Li, Na, K, Cs, and any mixture thereof. For example, one or more alkaline earth metals are one or more selected from Mg and/or Ca. For example, one or more rare earth elements are one or more selected from Ce, La, Sc, Y and any mixture thereof.
With preference, said catalytic composition further comprises a catalytic support. Advantageously, said catalytic support is electrically conductive particles; with preference, electrically conductive particles being silicon carbide and/or graphite and/or carbon nanotubes, or alternatively, electrically conductive particles different from said silicon carbide. This allows intimate contact between the catalytic active material and the electrically conductive material.
With preference, said catalytic composition further comprises a specific surface area ranging between 10 m2/g and 1000 m2/g as determined by N2 adsorption measurement, more preferably between 50 m2/g and 900 m2/g, even more preferably between 100 m2/g and 800 m2/g, most preferably between 200 m2/g and 700 m2/g.
The terms “bottom” and “top” are to be understood with the general orientation of the installation or the fluidized bed reactor. Thus, “bottom” will mean greater ground proximity than “top” along the vertical axis. In the different figures, the same references designate identical or similar elements.
The installation of the present disclosure is now described with reference to
The present disclosure provides for an installation to be used in a process to perform an ammonia cracking reaction with the production of hydrogen, said installation comprises
With preference, the at least two electrodes comprise or are made of tantalum.
When heating is required for whatever chemical and/or physical processes, burning of hydrogen might bring the required heat. However, the flame speed of hydrogen, which is the measured rate of the flame front in a combustion reaction, is generally fast. It is important to consider flame speed for determining the rate that a fire can move through the flammable mixture and subsequently distribute the fire throughout the system. If it is desired to reduce the flame speed, then it is interesting to dilute the hydrogen to be burned within one or more inflammable components to form a mixture that would benefit from a lower flame speed.
Upon partial cracking of ammonia, namely when the conversion of ammonia into forming gas is inferior to 50%, preferably ranging between 20% to 50% or between 20% to 30%, the combustion unit, preferably comprising an oven, a furnace, a burner or a combination thereof, downstream of the electrified fluidized bed unit allows to burn the mixture composed of forming gas (i.e., N2+H2) and ammonia. Said mixture has a flame speed that is lower than the flame speed of hydrogen but higher than the flame speed of ammonia. Partial cracking allows generating an ammonia/hydrogen mixture that possesses a higher flame speed than pure ammonia and is lower than pure hydrogen. This latter results in more stable and controllable combustion.
Upon complete cracking of ammonia, it is interesting to have a separation unit, preferably comprising a pressure swing adsorption (PSA) device and/or a scrubber and/or a condenser, placed downstream of the electrified fluidized bed unit to recover a purified hydrogen stream.
Indeed, the separation unit allows removing the unreacted ammonia which is present at about 20 ppm to 100 ppm in the forming gas that is formed upon cracking. The separation unit also allows removing a purge stream comprising nitrogen, so that a purified hydrogen stream can be recovered.
When performing cracking of ammonia to recover the hydrogen for further use, it is necessary to remove as much as possible the unreacted ammonia, since it can hamper further chemical processes if still present when using the hydrogen. For example, the PSA device comprises one or more adsorbers being one or more zeolites selected from zeolite 4A, zeolite 5A or zeolite 13X. For example, the scrubber uses acidic and/or alkaline solutions to remove the unreacted ammonia. After the passage within the separation unit, the amount of unconverted ammonia into the product stream has been lowered to a range varying from 1 ppm to 3 ppm. Depending on the desired application, further clean-up of the mixture is required with a membrane or a temperature swing adsportion (TSA) device to remove the nitrogen. This stream can then be conveyed into one or more storage tanks for further use.
For example, one electrode is a submerged central electrode or two electrodes 13 are submerged within the reactor vessel 3 of at least one reactor (18, 19, 37).
For example, the one or more diluent gases are one or more fluidizing gases, such as one or more selected from steam, hydrogen, carbon dioxide, argon, helium, nitrogen and one or more hydrocarbons, such as methane. With preference, the one or more diluent gases are one or more selected from steam, hydrogen, carbon dioxide, nitrogen and one or more hydrocarbons, such as methane. In an embodiment, when the diluent gases are at least a mixture of steam and one or more hydrocarbons, such as methane, then an endothermic steam reforming of hydrocarbons to produce synthesis gas is conducted concomitantly with said ammonia cracking reaction with production of hydrogen. In an alternative embodiment, when the diluent gases are at least a mixture of carbon dioxide and one or more hydrocarbons, such as methane, then an endothermic dry reforming of hydrocarbons to produce synthesis gas is conducted concomitantly with said ammonia cracking reaction with production of hydrogen.
In a preferred embodiment, the at least one fluidized bed reactor (18, 19, 37, 39) is devoid of heating means. For example, at least one fluidized bed reactor is devoid of heating means selected from ovens, gas burners, hot plates, or any combination thereof. For example, all the fluidized bed reactors are devoid of heating means selected from ovens, gas burners, hot plates, or any combination thereof. In a preferred embodiment, the at least one fluidized bed reactor comprising at least two electrodes and a bed comprising particles is devoid of a structured packing such as honeycomb monoliths or crossed plate.
For example, the reactor vessel 3 has an inner diameter of at least 100 cm, or at least 200 cm; or at least 400 cm. Such a large diameter allows to carry out the chemical reaction at an industrial scale, for example at a weight hourly space velocity of said reaction stream comprised between 0.1 h−1 and 100 h−1, preferably comprised between 1.0 h−1 and 50 h−1. The weight hourly space velocity is defined as the ratio of mass flow of the reaction stream to the mass of solid particulate material in the fluidized bed.
The at least one fluidized bed reactor (18, 19, 37) comprises at least two electrodes 13. For example, one electrode is in electrical connection with the outer wall of the fluidized bed reactor, while one additional electrode is submerged into the fluidized bed 25, or both electrodes 13 are submerged into the fluidized bed 25. Said at least two electrodes 13 are electrically connected and can be connected to a power supply (not shown). It is advantageous that said at least two electrodes 13 are made of graphite. The person skilled in the art will have an advantage that the electrodes 13 are more conductive than the particle bed 25.
For example, at least one electrode 13 is made of or comprises graphite; preferably, all or the two electrodes 13 are made of graphite. For example, one of the electrodes is the reactor vessel, so that the reactor comprises two electrodes, one being the submerged central electrode and one being the reactor vessel 3.
For example, the at least one fluidized bed reactor comprises at least one cooling device arranged to cool at least one electrode.
During use of the fluidized bed reactor, an electric potential of at most 300 V is applied, preferably at most 250 V, more preferably at most 200 V, even more preferably at most 150 V, most preferably at most 100 V, even most preferably at most 90 V, or at most 80 V.
Thanks to the fact that the power of the electric current can be tuned, it is easy to adjust the temperature within the reactor bed.
The reactor vessel 3 can be made of graphite. In an embodiment, it can be made of electro-resistive material that is silicon carbide or a mixture of silicon carbide and graphite.
With preference, the reactor vessel 3 comprises a reactor wall made of materials that are corrosion-resistant materials and advantageously said reactor wall materials comprise nickel (Ni), SiAION ceramics, yttria-stabilized zirconia (YSZ), tetragonal polycrystalline zirconia (TZP) and/or tetragonal zirconia polycrystal (TPZ). SiAION ceramics are ceramics based on the elements silicon (Si), aluminium (Al), oxygen (O) and nitrogen (N).
They are solid solutions of silicon nitride (Si3N4), where Si—N bonds are partly replaced with Al—N and Al—O bonds.
For example, the reactor vessel 3 is made of an electro-resistive material that is a mixture of silicon carbide and graphite; and the electro-resistive material of the reactor vessel 3 comprises from 10 wt. % to 99 wt. % of silicon carbide based on the total weight of the electro-resistive material; preferably, from 15 wt. % to 95 wt. %, more preferably from 20 wt. % to 90 wt. %, even more preferably from 25 wt. % to 80 wt. % and most preferably from 30 wt. % to 75 wt. %.
For example, the reactor vessel 3 is made of an electro-resistive material that is a mixture of silicon carbide and graphite.
For example, the reactor vessel 3 is not conductive. For example, the reactor vessel 3 is made of ceramic.
For example, the at least one fluidized bed reactor (18, 19, 37, 39) comprises a heating zone 27 and a reaction zone 29, one or more fluid nozzles 21 to provide a fluidizing gas to at least the heating zone from a distributor 31, one or more fluid nozzles 23 to provide an ammonia-containing feedstock and optional one or more diluent gases to the reaction zone from a distributor 33, and means 41 to transport the particles from the heating zone 27 to the reaction zone 29 when necessary, and optional means 35 to transport the particles from the reaction zone 29 back to the heating zone 27.
For example, as illustrated in
For example, as illustrated in
For example, as illustrated in
For example, the at least one fluidized bed reactor 37 being the heating zone 27 comprises at least two electrodes 13 whereas the at least one fluidized bed reactor 39 being the reaction zone 29 is devoid of electrodes.
For example, the at least two fluidized bed reactors (37, 39) are connected one to each other by means 41 suitable to transport the particles from the heating zone 27 to the reaction zone 29, such as one or more lines.
For example, the at least two fluidized bed reactors (37, 39) are connected one to each other by means 35 suitable to transport the particles from the reaction zone 29 back to the heating zone 27, such as one or more lines.
Advantageously, the installation further comprises a line fluidly connecting the electrified fluidized bed unit to the separation unit and/or the combustion unit, and the installation further comprises a heat exchanger on said line. For example, the heat exchanger allows to cool the forming gas before it goes into the separation unit or to adjust the temperature of the forming as before it goes into the combustion unit.
For example, said ammonia cracking reaction is conducted at a temperature ranging between 300° C. and 950° C., preferably between 350° C. and 900° C., more preferably from 400° C. to 850° C. and most preferably from 450° C. to 800° C. or from 480 to 950° C.
Advantageously, partial cracking of ammonia, namely when the conversion of ammonia into forming gas is inferior to 50%, preferably ranging between 20% to 50% or between 20% to 30%, which can be interesting for performing smooth combustion of the generated hydrogen, occurs either
For example, the ammonia cracking reaction is performed at a pressure ranging between 0.01 MPa and 10.0 MPa, preferably between 0.1 MPa and 5.0 MPa.
For example, the ammonia cracking reaction is conducted in presence of a reaction stream and is performed at a weight hourly space velocity of said reaction stream comprised between 0.1 h−1 and 100 h−1, preferably comprised between 1.0 h−1 and 50 h−1.
The residence time of the ammonia-containing feedstock in the fluidised bed section of the reactor where the temperature is between 45° and 900° C., may advantageously range from 0.005 to 5.0 seconds, preferably from 0.001 to 1.2 seconds, more preferably from 0.01 to 1.0 seconds, even more preferably from 0.1 to 0.6 seconds, or from 0.1 to 0.3 seconds.
Co-processing between ammonia cracking reaction with production of hydrogen and steam methane reforming reaction to produce synthesis gas
Advantageously, one or more of the following is selected so that step (c) is conducted to perform concomitantly with said ammonia cracking reaction with production of hydrogen an endothermic steam reforming of hydrocarbons to produce synthesis gas:
Alternatively, one or more of the following is selected so that step (c) is conducted to perform concomitantly with said ammonia cracking reaction with production of hydrogen an endothermic dry reforming of hydrocarbons to produce synthesis gas:
For example, the one or more hydrocarbons are part of a hydrocarbon-containing feedstock and/or the one or more hydrocarbons have one or more carbon atoms, such as methane or a mixture of light hydrocarbons containing 1 to 5 carbon atoms. Advantageously, the hydrocarbon-containing feedstock also contains carbon dioxide. Preferably, the hydrocarbon-containing feedstock is natural gas, biogas or refinery gas, each can contain various amounts of carbon dioxide.
With preference, the molar ratio between the steam and the carbon in the hydrocarbon-containing feedstock is ranging between 2.0 and 5.0 moles of steam per mole of carbon in the hydrocarbon feedstock, preferably from 2.2 to 4.0, more preferably from 2.5 to 3.0.
Advantageously, when step (d) is carried out, the products comprise at least forming gas (i.e., a mixture of H2 and N2) and unreacted ammonia. In the case where step (c) is conducted to perform concomitantly with said ammonia cracking reaction with production of hydrogen an endothermic steam reforming of hydrocarbons to produce synthesis gas, when step (d) is carried out, the products further comprise carbon monoxide, carbon dioxide, unreacted hydrocarbons, and unreacted steam.
In an embodiment, when step (c) is conducted to perform an ammonia cracking reaction with production of hydrogen, the process further comprises a step (j) of performing a combustion reaction on the products recovered at step (d), namely on the products that comprise at least forming gas and unreacted ammonia. With preference, said step (j) is carried out directly after step (d). This embodiment is preferably carried out when the conversion of the ammonia cracking reaction is partial.
In another embodiment, the process further comprises a step (e) of removal of the unreacted ammonia from the products recovered at step (d). This embodiment is preferably carried out when the conversion of the ammonia cracking reaction is partial.
With preference, said step (e) is one or more steps selected from
In case where step (c) is conducted to perform concomitantly with said ammonia cracking reaction with production of hydrogen an endothermic steam reforming of hydrocarbons to produce synthesis gas or an endothermic dry reforming of hydrocarbons to produce synthesis gas, the process further advantageously comprises the following steps that are performed after the step (e) of removal of the unreacted ammonia from the products recovered at step (d):
The water-gas shift reaction is advantageously detailed in “The water-gas shift reaction: from conventional catalytic systems to Pd-based membrane reactors—a review” from Mendes D. et al. (Asia-Pacific J. Chem. Engineering, 2010, 5, 111-137) and in “Performance of water-gas shift reaction catalysts: A review” from Pal D.B. et al. (Renewable and Sustainable Energy Reviews, 2018, 93, 549-565).
For example, said step (f) is carried out in presence of a water-gas shift catalyst; with preference, said water-gas shift catalyst is selected from copper or iron-based catalyst. This reaction is moderately exothermic and its equilibrium constant decreases with increasing temperature. The reaction is favoured thermodynamically at lower temperatures and kinetically at elevated temperatures but is unaffected by changes in pressure. WGS processes can be operated at high temperature (HTS) or low temperature (LTS) or combinations of both depending on the remaining desired CO in the product.
The HTS catalysts generally operate in the temperature range of from 310° C. to 450° C. and are called ferrochrome catalysts, containing both iron and chromium. The inlet temperature is kept as low as possible at about 350° C. to prevent excessive temperature rise in the reactor, a maximum outlet temperature of about 550° C. is pursued. The typical composition of HTS catalyst is reportedly about 70 to 75% Fe2O3, about 5 to 15% Cr2O3 and some alkali or alkaline earth oxides. Cr2O3 acts as a stabilizer and prevents the sintering of Fe2O3. The outlet concentration of a conventional Fe/Cr HTS WGS reactor can be as low as 3% CO, being the equilibrium concentration at 450° C.
The low temperature shift (LTS) reaction occurs at 200-250° C. using catalysts comprising a mixture of CuO, ZnO, Cr2O3 and Al2O3. The typical compositions of such catalysts are 20-75% ZnO, 15 to 35% CuO, 5 to 15% Cr203, 1-5% Mn, Al and magnesium oxides as balance. Copper metal crystallites are the active species in the catalyst. ZnO and Cr2O3 provide the structural support for the catalyst and Al2O3 is the carrier providing the surface area for dispersion and mechanical strength of the catalyst particles. The WGS reaction is traditionally conducted in two-or three-stage catalytic converters to allow smaller adiabatic temperature rise and better steam management. The first stage is characterized by working at higher temperatures, favouring fast CO consumption and minimizing catalyst bed volume. In the following stages, the reaction takes place at progressively lower temperatures for obtaining higher conversions, which are limited by the reaction equilibrium. Interstage cooling systems are used to conduct the next WGS reaction at a lower temperature, favouring the approach to equilibrium conversions.
The pressure for WGS can vary between 1 and 6 MPa for HTS and between 1 and 4 MPa for LTS.
Said step (g) of separating a CO2-enriched stream from said stream comprising carbon dioxide, hydrogen, unreacted carbon monoxide and unreacted hydrocarbons is advantageously performed by treating the stream comprising carbon dioxide, hydrogen, unreacted carbon monoxide and unreacted hydrocarbons obtained at step (f) in separation processes for hydrogen production with CO2 capture, such as adsorption, absorption, membranes and cryogenic/low-temperature processes. See study entitled “Hydrogen production with CO2 capture” from Voldsund M. et al. (International Journal of Hydrogen Energy, 2016, 4969-4992).
Pressure swing adsorption (PSA) is the currently most used technology for hydrogen purification with the possibility to obtain very pure hydrogen (Pressure swing adsorption technology for hydrogen production, K. Liu, C. Song, V. Subramani (Eds.), Hydrogen and syngas production and purification technologies (2010), p. 414).
In a PSA unit, the syngas is sent through an adsorbent column at high pressure, where impurities are adsorbed while hydrogen passes through with very limited adsorption. When the adsorbent is saturated, it is regenerated by lowering the pressure and purging. Typical adsorbents include silica gel, alumina, activated carbon, and zeolite, and they have different relative strengths of adsorption to different components. PSA units are typically operated at ambient temperature (adsorption is promoted at low temperature) and feed pressure of 2 to 6 MPa. The hydrogen product is produced at a slightly lower pressure than the feed due to pressure drop and the PSA off-gas is delivered at low pressure, typically 0.1 to 0.3 MPa. In standard plants without CO2 capture, the CO2-rich off-gas is often used as fuel due to the content of combustible components. Such CO2-rich off-gas is not suitable for the transport and storage of CO2.
Adsorption can be used to capture and purify CO2 from other gases with a CO2 selective adsorbent (U.S. Pat. No. 4,171,206; Purification of hydrogen by pressure swing adsorption, Sep Sci Technol, 35 (5) (2000), pp. 667; CO2 capture from SMRs: a demonstration project Hydrocarbon Process (September) (2012), pp. 63). This process comprises two purification steps: first adsorbent beds with activated carbon selectively remove wet CO2, before adsorbent beds with zeolites remove CH4, CO, N2, and the remaining CO2 from the hydrogen. Optionally the first pressure swing adsorption is a vacuum swing adsorption unit (VSA) that captures wet CO2, between the already existing SMR and PSA units. Most (>90%) of the CO2 is captured with purity greater than 97% (after compression and drying) from syngas.
Gas separation by absorption is carried out by bringing the gas in contact with a liquid solvent in a scrubber column, where the acid gases are dissolved. The rich solvent is sent to a regeneration/stripping column where it is heated and/or depressurised and which produces an overhead stream with the desorbed components, and one with a lean solvent that is sent back to the scrubber column. Liquid solvents can be divided into chemical and physical solvents. Chemical solvents react with CO2 (CO2 being a weak acid reacts with a base) and require a considerable amount of heat for regeneration. They offer fast reaction rates and hence small plant sizes. Typical chemical solvents are aqueous solutions of amines such as MEA, TEA and MDEA, or an aqueous solution of hot potassium carbonate (eg. the Benfield process). Physical solvents dissolve CO2 and are regenerated with reduced pressure and/or increased temperature, requiring less heat than chemical solvents. Typical technologies utilising physical solvents are the Rectisol®, Selexol™, and Purisol® technologies.
The absorption capacity of chemical solvents is relatively high at low CO2 partial pressures. The absorption capacity of physical solvents is lower than for chemical solvents at low CO2 partial pressures but increases linearly with CO2 partial pressure according to Henry's law. Chemical solvents are therefore preferred at low CO2 partial pressures while physical solvents are preferred at high CO2 partial pressures.
Membranes are selective barriers that let certain components pass through more easily than others (The part of the feed that passes through the membrane is the permeate while the part that does not pass through is denoted retentate). The transport of molecules through the membrane is driven by a difference in partial pressures over the membrane.
For hydrogen production with CO2 capture, both hydrogen and CO2 selective membranes can be used. Hydrogen selective membranes produce a permeate consisting of high-purity hydrogen at low pressure, and a retentate with impure CO2 at higher pressure. CO2 selective membranes typically produce a CO2 enriched permeate at low pressure, and a CO2 depleted retentate at high pressure. The hydrogen-selective membranes operating at low temperatures below 100° C. are polymeric membranes and are been used for hydrogen recovery from low-temperature process streams. High-temperature hydrogen-selective membranes can be divided into metallic membranes (300-700° C.), microporous ceramic membranes (200-600° C.), porous carbon membranes (500-900° C.) and dense ceramic membranes (600-900° C.). Their high-temperature operation makes them more applicable for steam reformer/water-gas shift processes. Several CO2 membrane types exist: polymeric CO2 selective membranes based on either solution-diffusion mechanism (the solution effect must dominate over diffusion), or facilitated transport mechanism; mixed matrix membranes, which consist of inorganic particles dispersed uniformly in a polymer matrix; and porous inorganic membranes that are CO2 selective either by surface diffusion or capillary condensation.
In cryogenic or low-temperature separation gas is cooled, and differences in boiling point are used to separate different chemical components. For separation of hydrogen, the gas mixture is cooled to cryogenic temperatures (s 150° C.). Contaminant gases are condensed at different temperature levels, while hydrogen remains in the gas phase. For separation of CO2, the gas mixture is cooled below the boiling point of CO2 at the given pressure (above the CO2 triple point at 5.2 bar and −56.6° C.), and the CO2 is condensed from lighter gaseous. An advantage of low-temperature separation is that the captured CO2 is in the liquid state and can be pressurized for transport by pumping at a low energy cost.
Said step (h) of is the step of separating a purified hydrogen stream and a purge stream comprising unrecovered hydrogen, unreacted carbon monoxide and unreacted hydrocarbons from said CO2-lean stream in a pressure swing adsorption (PSA) process. In such a PSA unit, the gas is sent through an adsorbent column at high pressure, where impurities are adsorbed while hydrogen passes through with very limited adsorption. When the adsorbent is saturated, it is regenerated by lowering the pressure and purging. Typical adsorbents include silica gel, alumina, activated carbon, and zeolite, and they have different relative strengths of adsorption to different components. PSA units are typically operated at ambient temperature (adsorption is promoted at low temperature) and feed pressure of 2 to 6 MPa. The hydrogen product is produced at a slightly lower pressure than the feed due to pressure drop and the PSA off-gas is delivered at low pressure, typically 0.1 to 0.3 MPa.
The process may further comprise the step of feeding the product stream comprising hydrogen to an upgrading unit and separating it into an upgraded hydrogen stream and an off-gas stream. The upgrading unit may be arranged so that the off-gas stream is recycled and mixed with the supply of feed gas before being passed over the structured catalyst. The upgrading unit may comprise a pressure swing adsorption unit (PSA), temperature swing adsorption unit (TSA), or a membrane, or even a combination. The PSA or TSA configurations are favourable solutions as they separate the hydrogen as the high-pressure stream leaving the upgrading unit, while the off-gas will be at low pressure. In a preferred embodiment, the upgrading unit is configured to produce an upgraded stream of substantially pure H2 and an off-gas of substantially pure N2. In one aspect, the process further comprises the step of feeding the upgraded hydrogen stream from said upgrading unit to a downstream plant for electricity production. The electricity production plant could, in an embodiment, be a solid oxide fuel cell or a gas engine. This allows for using the technology for energy storage when using ammonia as an energy vector.
N2 sorption analysis was used to determine the nitrogen adsorption/desorption isotherms using Micrometrics ASAP 2020 volumetric adsorption analyser. The dried samples were degassed at 523 K (249.85° C.) under vacuum overnight before the measurement. From these measurements, the specific surface area of the catalytic composition has been determined.
| Number | Date | Country | Kind |
|---|---|---|---|
| 22315015.2 | Jan 2022 | EP | regional |
The present application is a national stage application filed under 35 U.S.C. § 371 of International patent application PCT/EP2023/050458, filed on Jan. 10, 2023, which claims priority to European patent application EP 22315015.2, filed on Jan. 20, 2022, the entire contents of all of which are incorporated by reference herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2023/050458 | 1/10/2023 | WO |
