Patent Application
20240132343
The invention relates to the field of hydrogen production, storage and transport.
More specifically, it relates to a synthesis process of a liquid organic hydrogen carrier (LOHC) charged with hydrogen wherein a methanisation digestate is used as a hydrogen source.
It also relates to a process for recycling organic waste as well as a process for producing hydrogen implementing this synthesis process.
On account of its high mass energy density (33 kWh/kg) and its ability to be oxidised in the presence of oxygen in the form of pure water without releasing CO2, hydrogen is considered as an important energy carrier for completing the energy transition, in particular by substituting fossil fuels.
While hydrogen is capable of being used as a reagent in fuel cells to produce electricity, its primary use currently remains industry. Indeed, 75 million tonnes are consumed annually by the chemical industry, of which almost 45% for petroleum refining.
To date, steam reforming of hydrocarbons, essentially methane, is the most commonly used hydrogen production process for supplying industry with hydrogen as it is by far the most economical. Steam reforming consists of reacting, at temperature and in the presence of catalysts, methane with water to produce a mixture of H2, CO2, CO and water. At the steam reactor outlet, hydrogen is separated from CO2 and an excess mixture of CO, methane and water vapour (known as syngas) which is used as a fuel to supply the heat required for steam reforming.
However, for each tonne of hydrogen produced by steam reforming, approximately 10 tonnes of CO2 are emitted and generally released into the atmosphere.
Hydrogen production processes limiting, or suppressing, emissions of greenhouse gases, and, in particular, CO2 are therefore under study to supplement its production by steam reforming or to progressively substitute it.
Among these processes, water electrolysis, which consists of breaking water down into oxygen and hydrogen with an electric current (which, ideally, must itself be obtained from a low greenhouse gas emission electricity production sectors such as the nuclear, wind or solar sector), represents a technology of choice.
Two main types of electrolysis are considered with, on one hand, so-called “low-temperature” processes which are based on the use of proton conductive polymer membranes (known as PEM for Proton Exchange Membrane) and, on the other, so-called “high-temperature” processes which are based on the use of anionic or proton conductive ceramic membranes in SOEC (Solid Oxide Electrolysis Cell) systems.
However, with a view to generalising the use of hydrogen in industrial sectors other than those of petrochemicals and in the transport and housing sector, there are, beside its low carbon-footprint production, two technological barriers to be removed, namely its storage and its transport.
Indeed, given its very low mass density, hydrogen storage and transport currently involve either its liquefaction at atmospheric pressure but at an extremely low temperature (−253° C.) or by its compression at very high pressure (70 MPa) with, in both cases, the need for a control of the risks associated with its tendency to leak on account of its small size, its flammability, its ability to detonate and its harmful action on the metals and alloys included in the composition of the equipment wherein it is confined.
For this reason, research is now oriented towards the development of LOHCs.
LOHCs are organic compounds that are liquid or semi-solid at ambient temperature which can be alternately charged with and discharged of hydrogen via catalytic hydrogenation and dehydrogenation reactions. LOHCs have a high hydrogen storage density and make it possible to transport hydrogen safely.
Typical examples of LOHCs are aromatic hydrocarbons such as toluene and naphthalene which, by hydrogenation, produce methylcyclohexane and decalin. The latter can then be packaged to be stored and/or transported to the location where they will be used to produce hydrogen by catalytic dehydrogenation. Hydrogenation and dehydrogenation processes on several cycles can thus be produced with these compounds—as illustrated hereinafter for the toluene/methylcyclohexane pair—without a significant loss of yield.
For a focus on the recent developments achieved in terms of LOHCs, the reader is invited to refer to the article in the name of Purna Chandra Rao and Minyoung Yoon published in Energies 2020, 13(22), 1-23).
While LOHCs clearly represent a very interesting hydrogen storage and transport option, their integration in an energy and environmental transition strategy involves the possibility of hydrogenating them with hydrogen obtained from a production stream which is not only decarbonised but also inexpensive.
The aim of the invention is precisely that of providing a solution to these problems by proposing a process which makes it possible to synthesise an LOHC charged with hydrogen, annotated Hn-LOHC, using hydrogen produced from a methanisation digestate.
This process comprises at least the steps of:
Thus, according to the invention:
It is obvious that steps c) and d) can be carried out simultaneously or successively, in which case they can be carried out in any order, i.e. step c) can equally well be carried out after step d) as before step d).
According to the invention, the methanisation digestate is, preferably, a liquid digestate, i.e. corresponding to the liquid phase obtained when a methanisation digestate is subjected to a solid/liquid phase methanisation digestate, for example by means of a screw press, a belt press, a filter press or a centrifuge.
In step a), the gaseous ammonia is advantageously produced by desorption—also known as stripping—of the ammoniacal nitrogen (i.e. the assembly formed by ammonia in molecular form NH3 and that in ionised form NH4+) present in the liquid methanisation digestate.
This desorption is, preferably, carried out by circulating the liquid digestate in a column equipped with a packing such as Raschig rings, Pall rings, Berl saddles or similar, against the flow of a gas called transfer gas which is either nitrogen or a gas essentially consisting of nitrogen such as air. The transfer gas can be pre-heated, for example to a temperature of 50° C.-70° C., so as to promote ammoniacal nitrogen desorption.
Alternatively, the desorption can also be carried out by evacuation (referred to as vacuum stripping).
In any case, the process advantageously further comprises a purification of the gaseous ammonia produced carried out, for example, by means of a membrane filter.
According to the invention, the H0-LOHC is typically an aromatic or heteroaromatic, monocyclic or polycyclic, compound, optionally substituted by one or more alkyl, aryl, heteroaryl, arylalkyl or heteroarylalkyl groups, which meets, preferably, the following criteria:
Thus, it can in particularly consist of:
In step c), the catalytic amination of the H0-LOHC results in the formation of an aminated H0-LOHC and hydrogen according to the reaction:
H0-LOHC+NH3⇄H0-LOHC-NH2+H2
which in the case, for example, of toluene becomes:
It should be noted that this amination reaction can result in the presence of several NH2 groups on the same H0-LOHC molecule.
This amination is advantageously carried out in a reactor heated to the temperature which is, preferably, chosen according to the catalyst used but which is typically between 200° C. and 800° C. and, more specifically, between 350° C. and 500° C. and at a pressure which is typically between 0.1 MPa and 90 MPa and, more specifically, between 1.5 MPa and 11 MPa. The catalyst is, for example, a ceramic-metal composite, based on a metallic oxide such as an oxide of zirconium, nickel, cobalt, aluminium, a rare earth (yttrium or cerium oxide for example), and one or more active metals chosen from nickel, copper, zinc, platinum group metals (ruthenium, rhodium, palladium, iridium and platinum), vanadium, titanium, aluminium, silicon and actinides (uranium and thorium in particular).
In order to increase the yield from the animation of the H0-LOHC, it is possible to shift the chemical equilibrium of this reaction to the formation of hydrogen by consuming a portion of the hydrogen generated by this amination, in which case the amination is carried out in the presence of a oxidising gas such as oxygen, carbon monoxide, carbon dioxide, nitrogen monoxide, nitrogen dioxide, hydrogen peroxide or air.
Advantageously, the process further comprises a purification of the hydrogen produced by the catalytic amination of the H0-LOHC, which is carried out, for example, by means of a membrane filter.
In step d), the catalytic dissociation of the gaseous ammonia results in the formation of nitrogen and hydrogen according to the reaction:
2NH3→N2+3H2
This dissociation is advantageously carried out in a reactor heated to a temperature which is, preferably, chosen according to the catalyst used but which is typically between 450° C. and 800° C. and, more specifically, between 550° C. and 700° C. The catalyst is, for example a ceramic-metal composite comprising an active metal such as ruthenium, nickel or copper, and an oxide such as alumina, magnesia or a rare earth oxide such as cerine.
Here also, the process advantageously further comprises a purification of the hydrogen produced by the catalytic dissociation of gaseous ammonia, carried out, for example, by means of a membrane filter.
Regardless of the aminated H0-LOHC to be hydrogenated, its hydrogenation is typically carried out with a high hydrogen pressure, preferably between 5 MPa and 10 MPa. As the reaction is exothermic and therefore releases heat, the reactor wherein the hydrogenation is carried out typically reaches a temperature between 100° C. and 200° C. These conditions can, obviously, vary according to the aminated H0-LOHC and the catalyst used. The catalyst is, for example, a ceramic-metal composite comprising an active metal such as ruthenium, nickel or cobalt, and an oxide such as alumina, zirconia or a rare earth oxide such as cerine.
The hydrogen pressure is advantageously controlled in order to be limited to the hydrogenation reaction without reaching a hydrogenolysis which would initially result from the NH2 group(s).
According to the invention, the reactor wherein the catalytic dissociation of the gaseous ammonia is carried out and, where applicable, that wherein the catalytic amination of the H0-LOHC is carried out are advantageously heated by heat and/or electricity produced using a methanisation biogas. The same also advantageously applies for the transfer gas used for the desorption of the ammoniacal nitrogen if this transfer gas is pre-heated.
Thus, the synthesis process of an Hn-LOHC as defined above can advantageously be part of a process for recycling organic waste, which comprises at least the steps of:
The invention therefore also relates to such a process for recycling organic waste.
The invention further relates to a process for producing hydrogen, which comprises at least the steps of:
As known per se:
Other features and advantages of the invention will become apparent upon reading the following description which makes reference to the appended figures.
Of course, this further description is given only to illustrate the subject matter of the invention and is in no way intended to limit this subject matter.
Reference is made to
In this mode of implementation, the process comprises:
1. production of gaseous ammonia, NH3, by desorption (or stripping) of ammoniacal nitrogen from a liquid digestate;
2. purification of the gaseous ammonia thus produced and splitting thereof into a first and a second flow;
3. catalytic amination of an H0-LOHC by means of the gaseous ammonia from the first flow to convert this H0-LOHC into an aminated H0-LOHC and produce hydrogen;
4. catalytic dissociation of gaseous ammonia from the second flow to produce hydrogen;
5. purification of the hydrogen produced by the catalytic amination of the H0-LOHC and by the catalytic dissociation of ammonia; and
6. catalytic hydrogenation of the aminated H0-LOHC by means of the hydrogen thus purified to convert this aminated H0-LOHC into an aminated Hn-LOHC.
For this purpose and as seen in
The liquid digestate, which is subjected to this desorption, is obtained from the separation into a solid phase and a liquid phase of a methanisation digestate.
This liquid digestate essentially comprises nitrogen of which ammoniacal nitrogen, phosphorus in oxide form (P2O5), potassium in oxide form (K2O), calcium in oxide form (CaO) and magnesium, also in oxide form (MgO), in variable concentrations according to the organic waste from which the methanisation digestate was obtained.
The column 11 is supplied:
The liquid digestate and the nitrogen therefore circulate countercurrently in the column 11.
The nitrogen can be heated prior to its entry into the column 11, for example at a temperature of 50° C. to 70° C., to promote the desorption of the ammoniacal nitrogen.
At the top of the column 11, a gas phase is recovered essentially formed of ammonia and nitrogen and, at the base of the column 11, an ammoniacal nitrogen-depleted liquid digestate.
The gas phase thus recovered is directed towards a purification device 14, for example of the membrane filter type, making it possible to purify the ammonia by separating it from nitrogen and any other gases generated by the desorption, whereas the ammoniacal nitrogen-depleted digestate is removed from the process while being, for example, directed towards a storage unit (not shown in
As seen in
As regards the ammonia coming out of the purification device 14, it is split into two flows: a first flow which is directed towards a reactor 15 intended for the catalytic amination of the H0-LOHC and which is, therefore, supplied with this H0-LOHC, and a second flow which is directed towards a reactor 16 intended for the catalytic dissociation of ammonia.
In the reactor 15, the catalytic amination of the H0-LOHC is, for example, carried out at a temperature between 350° C. and 500° C. and at a pressure between 1.5 MPa and 11 MPa, using an Ni/CeO2 type catalyst.
As mentioned above, the yield from the animation of the H0-LOHC can be increased by consuming a portion of the hydrogen generated by this amination, by supplying the reactor 15 with a oxidising gas such as oxygen, carbon monoxide, carbon dioxide, nitrogen monoxide, nitrogen dioxide, hydrogen peroxide or air. In which case, the portion of the hydrogen generated by the catalytic amination of the H0-LOHC which is not consumed in the reactor 15 is evacuated from this reactor through, for example, a membrane filter to separate it from the oxidising gas.
Whether an oxidising gas is used or not for the catalytic amination of the H0-LOHC, the hydrogen coming out of the reactor 15 is then directed towards a purification device 18, for example of the membrane filter type, whereas the aminated H0-LOHC is directed towards a reactor 17 intended for its hydrogenation.
In parallel, in the reactor 16, the catalytic dissociation of the gaseous ammonia from the second flow from the purification device 14 is carried out. This dissociation is, for example, performed at a temperature between 550° C. and 700° C. and using an Ni/MgO catalyst.
The hydrogen produced in the reactor 16 is then directed towards the purification device 18 where it joins the hydrogen evacuated from the reactor 15.
Once purified by the purification device 18, the hydrogen is directed towards the reactor 17 to be used for the catalytic hydrogenation of the aminated H0-LOHC.
This hydrogenation is, for example, carried out with a hydrogen pressure between 5 MPa and 10 MPa and using a Ru/Al2O3 type catalyst.
The aminated Hn-LOHC produced in the reactor 17 is then sent to a zone intended for its packaging (not shown in
Reference is made to
In this mode of implementation, the process for recycling organic waste comprises:
1. methanisation of the organic waste to produce a methanisation digestate, on one hand, and a biogas, on the other;
2. separation of the methanisation digestate into a solid phase, referred to as solid digestate, and a liquid phase, referred to as liquid digestate;
3. synthesis of an Hn-LOHC from the liquid digestate by the synthesis process of an Hn-LOHC according to the invention; and
4. cogeneration, i.e. simultaneous production of electricity and heat, from the biogas.
For this purpose and as seen in
The methanisation digestate, once evacuated from the methaniser 21, is directed towards a solid/liquid separation unit 22 wherein it is separated into a solid digestate and a liquid digestate, for example by means of one or more screw press, belt press, filter press or centrifuge type devices.
The solid digestate thus obtained can be sent to a storage unit (not shown in
As regards the liquid digestate, it is directed towards an installation 23 intended for the synthesis of the Hn-LOHC, which can in particular be an installation of the type of that shown in
In parallel, the biogas produced in the methaniser 21 is directed towards a cogeneration unit 24 comprising, for example, a gas turbine coupled with an alternator and a heat recovery unit.
As illustrated in
Optimal recycling of organic waste is thus carried out.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2106270 | Jun 2021 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2022/051090 | 6/7/2022 | WO |
