Patent Application
20100294994
The present invention relates to a process for producing synthesis gas and hydrogen starting from liquid and possibly gaseous hydrocarbons.
In particular, the present invention relates to a catalytic partial oxidation process for producing synthesis gas and hydrogen starting from various kinds of liquid and gaseous hydrocarbon feedstocks, also containing relevant quantities of sulphurated, nitrogenous and aromatic compounds.
The present invention considers the fact that the technological evolution of the refining field is currently conditioned by two main factors:
1) the necessity of also refining low-quality crude oils
2) the necessity of satisfying increasingly strict legislations which reduce the limits on the polluting emissions of combustion processes.
The evolution of the demand and offer of crude oil can create a situation in which light oils will tend to become limited and it will therefore be necessary to increasingly utilize heavy or extra heavy oils as starting materials to produce combustible products. Heavy or extra heavy oils have a high content of sulphurated, nitrogenous products and aromatic compounds and their use will require an increase in investments on hydroprocessing processes with the consequence that the availability of hydrogen will be an element of crucial importance in this sector.
During 2006, about 48 million of tons (corresponding to 67×106 Nm3/h) of H2 were produced worldwide, mainly used in the production of ammonia (about 60%), in oil refining processes (about 26%), for the synthesis of methanol (about 10%) and the remaining 4% for other uses. Only the demand for H2 coming from refining and upgrading processes, however, is destined to grow very rapidly and consequently at a higher rate with respect to the overall demand.
Various sources estimate that, if the present development model does not change, hydrogen consumption will increase by more than 15% within 2015 (see, for example, SFA Pacific Inc. “Hydrogen—Synthesis Gas—Gas to Liquids: a Technical Business Analysis”; July 2005).
At present about 96% of the H2, industrially produced for refinery and up-grading uses is obtained through the Steam Reforming process (SR) of Natural Gas (NG) and of light naphtha, whereas the remaining 4% is produced through the non-catalytic Partial Oxidation (PO) process of the processing residues of petroleum (L. Basini, Issues in H2 and Synthesis Gas Technologies for Refinery, GTL and Small and Distributed Industrial Needs”, Catalysis today, 2005, 106, 34-40).
Both SR and non-catalytic PO produce synthesis gas, which is a mixture of H2 and CO, with smaller amounts of CH4 and CO2. Pure H2 is subsequently obtained from synthesis gas with a passage of Water Gas Shift (WGS—equation [2] in Table 1) and separation/purification of H2.
Another widely-used technology for the production of synthesis gas is Auto Thermal Reforming (ATR). ATR can only use highly desulphurized NG and is widely used for producing synthesis gas for methanol synthesis, oxosynthesis and Fischer-Tropsch processes, whereas it is not used for producing H2.
The characteristics of SR, non-catalytic PO and ATR are described in numerous documents in literature, among which: i) J. R. Rostrup-Nielsen, J. Sehested, J. K. Noskov. Adv. Catal. 2002, 47, 65-139; ii) R. Pitt, World Refining, 2001, 11(1), 6; iii) I. Dybkjaer, Petroleum Economist: Fundamental of Gas to Liquids, 1993, 47-49; iv) T. Rostrup-Nielsen, Catalysis Today, 2002, 71(3-4), 243-247, can be mentioned.
The main chemical reactions of the above processes are included in Table 1.
The SR technology is extremely efficient from an energy point of view and produces H2 from a light gaseous hydrocarbon feedstock and desulphurized through highly endothermal reactions (eq. [1], [3]).
The heat necessary for the reactions is generated inside an oven which includes “reformer tubes”; these tubular reactors are fed with a catalyst based on Ni deposited on a carrier typically consisting of mixed Mg and Al oxides. SR ovens having the greatest dimensions can house about 600 reformer tubes (with a diameter of 100 to 150 mm, and a length ranging from 10 to 13 m) and can produce synthesis gas in a single line from which more than 250,000 Nm3/hr of H2 can be obtained.
Non-catalytic PO is much less used in the production of H2, due to its lower energy efficiency and high investment costs. It can be advantageously applied only in the case of feedings with low-quality hydrocarbon feedstocks, such as heavy hydrocarbon residues from oil processing (petroleum coke, deasphalter pitch, residual oils, etc.) which cannot be transformed into synthesis gas with catalytic-type techniques. The high costs of this technology are due to: (i) the high temperatures of the synthesis gas produced at the outlet of the reactors (about 1,400° C.) which make the thermal recovery operations complex and non-efficient and (ii) the high oxygen consumptions. PO however has a great operative flexibility as it is a process to which liquid and gaseous hydrocarbon feedstocks can be fed. It is probable that in the future the competitiveness and diffusion of non-catalytic PO will increase as a result of the high costs of NG, the necessity of treating heavy crude oils and the possibility of integrating the production of H2 and energy with combined cycles (IGCC) (G. Collodi, Hydroc. Eng. 2001, 6(8), 27).
Even if SR and non-catalytic PO technologies are reliable and fully consolidated, they have a poor flexibility with respect to the necessity of varying the production capacity. These technologies, furthermore, have technical difficulties and high implementation costs when intermediate hydrocarbon feedstocks between desulfurized NG and heavy residues from oil processing are to be used as starting feedstocks.
The objective of the present invention is consequently to find a process for producing synthesis gas and therefore H2, having investment costs and energy consumptions lower than those of the processes of the known art and which has a wider flexibility both with respect to the productive capacity and to the possibility of being fed with various kinds of liquid, and possibly gaseous, hydrocarbon feedstocks, even containing relevant amounts of sulfurated and nitrogenous compounds.
An object of the present invention therefore relates to a process for the production of synthesis gas and hydrogen starting from liquid, possibly also mixed with gaseous hydrocarbon streams, hydrocarbon feedstocks, comprising at least the following operative phases:
1) nebulizing/vaporizing a stream of a liquid hydrocarbon feedstock consisting of one or more of the following hydrocarbons:
2) mixing the liquid nebulized/vaporized hydrocarbon stream coming from phase 1) with:
a) an oxidizing stream, possibly mixed with vapour,
b) possibly a gaseous hydrocarbon stream,
at a temperature varying from 50 to 500° C. and a pressure ranging from 2 to 50 atm, with the formation of a possibly biphasic liquid-gas reaction mixture;
3) passing the reaction mixture coming from phase 2) through at least one first structured catalytic bed, with the formation of a mixture of reaction products comprising H2 and CO, said structured catalytic bed comprising a catalytic partial oxidation catalyst, arranged on one or more layers, the reaction mixture flowing through each layer with a contact time varying from 0.01 to 100 ms, preferably from 0.1 to 10 ms;
4) cooling the mixture of reaction products coming from phase 3).
A further object of the present invention relates to equipment for effecting the process according to the present invention, comprising at least the following sections:
I) an inlet section into which liquid and gaseous reagent streams are fed, said section comprising a device for nebulizing/vaporizing the liquid streams, said device possibly being capable of utilizing vapour and/or a gaseous hydrocarbon stream as propellant;
II) a mixing section comprising a chamber having a cylindrical or truncated-conical geometry, for mixing the reagent streams at the exit from section I and forming a possibly biphasic homogeneous reaction mixture;
III) a reaction section comprising:
IV) a cooling section of the mixture of reaction products leaving section III).
The process according to the present invention allows the production of synthesis gas, and therefore of hydrogen, utilizing liquid or possibly gaseous hydrocarbon streams, whose use is currently of little convenience or technically complex.
These streams include naphthas, various kinds of gas oil, other products of refining and up-grading cycles of oil, other heavy residues and/or mixtures thereof. Examples of liquid hydrocarbon streams coming from refining and up-grading processes containing large quantities of sulfurated and nitrogenous compounds, which can be used for the purposes of the present invention, are the following: “Light Cycle Oils” (LCO), “Heavy Cycle Oils”, Vacuum Gas Oils (VGO) and “Deasphalted Oils” (DAO).
The stream of the liquid hydrocarbon feedstock is subjected to a first “nebulization/vaporization” phase wherein the low-boiling components are vaporized and the high-boiling components nebulized by means of a suitable device.
In order to facilitate the nebulization/vaporization of the liquid hydrocarbon feedstock, the device can also utilize a stream of a gaseous propellant, comprising gaseous hydrocarbons and/or vapour.
The process according to the present invention can also include a further phase 3a) wherein the mixture of reaction products comprising H2 and CO coming from phase 3) is passed through a further catalytic bed, comprising a catalyst capable of completing the partial oxidation reactions and promoting the steam reforming and/or CO2 reforming reactions, with a contact time ranging from 1 to 1,500 ms, preferably from 10 to 1,000 ms, possibly followed by another catalyst capable of promoting and completing the water gas shift reaction.
The gaseous hydrocarbon streams which can be used in the process described in the present invention comprise one or more streams selected from methane, NG, refinery gas or purge gas of oil up-grading processes, liquefied petroleum gas, (LPG) and/or mixtures thereof, possibly with the addition of CO2; even more preferably, the gaseous hydrocarbon feedstock consists of NG and refinery gas or purge gas of oil up-grading processes.
In addition to the possibility of treating various kinds of hydrocarbon feedstocks, the process according to the present invention also offers the possibility of varying the productivity of H2 to follow the requirements of refining operations. Not only the demand for H2 is increasing, in fact, but also the capacity and quality of the hydrocarbons produced by refining and up-grading operations can undergo a sequential evolution; in some cases, this evolution has cyclic characteristics during various periods of the year.
The process of the present invention can not only be used in refining environments in a strict sense, but more generally in oil up-grading environments and, in particular, in the up-grading of heavy and extra-heavy crude oils. In these production contexts, the production of H2 can be obtained with the process described by the present invention, utilizing various intermediate products of the processing cycles.
The process of the present invention, for example, can be usefully adopted for producing H2 for the EST process (PEP Review 99-2: ENI Slurry Hydroprocessing Technology For Diesel Fuel, WO2004/056947A1). The EST process, in fact, comprises a catalytic hydroprocessing treatment in slurry phase (
Other hydrocarbon cuts of the EST process, however, can also be used in the process for the production of H2 described in the present invention. Among these VGO can be mentioned in particular.
Finally, it can be noted that this type of hydrocarbon feedstock cannot be used in SR processes for technical reasons, whereas if these feedstocks were used in non-catalytic PO processes, there would be very high hydrogen production costs.
As mentioned above, in order to effect the process according to the present invention, a reaction equipment can be conveniently used, comprising at least the following sections (
I) inlet section of the liquid and gaseous reagent streams,
II) mixing section of the liquid and gaseous reagent streams,
III) reaction section,
IV) cooling section.
The following reagent streams can be fed to section I:
The propellant can also be added with CO2.
The reagent streams are fed to section I at a temperature ranging from 50 to 500° C., preferably from 100 to 400° C., and at a pressure ranging from 2 to 50 atm.
In the process according to the present invention the vapour can therefore be used both as a propellant stream and also for diluting the oxidizing stream. The dilution of the oxidizing stream allows the reduction of the partial pressure gradients of oxygen in the nebulization and mixing area (section II) and, consequently, the risk of triggering homogeneous gaseous combustion reactions.
The liquid hydrocarbon feedstock is fed to section I after pre-treatment which consists in heating the stream to a temperature sufficient for i) the feedstock to have a viscosity which is such as to allow its pumping and nebulization/vaporization in section II and ii) producing a mixture in section II with a temperature ranging from 50 to 500° C., preferably from 100 to 400° C.
The ratio which defines the quantity of liquid and gaseous hydrocarbon feedstocks fed to the reaction equipment, will be hereinafter be indicated as Cgas/Cliq. This ratio corresponds to the ratio between the number of carbon atoms fed as gaseous hydrocarbon feedstock and the number of carbon atoms fed as liquid hydrocarbon feedstock. The Cgas/Cliq ratio can have any value “n”, wherein n is higher than or equal to 0. The condition n=0 corresponds to the case in which vapour alone is used as propellant. The possibility of varying the composition of the hydrocarbon feedstock to be converted into synthesis gas, within such a wide range, makes the process according to the present invention particularly flexible, as it is possible to feed feedstocks of different nature and according to their availability in the refinery and, more generally, in up-grading contexts.
Section II is the mixing section in which the reagent streams are mixed. The mixing of the reagent streams is necessary for obtaining a homogeneous mixture to be subjected to the catalytic reaction in section III of the reaction equipment. This phase is carried out at a temperature varying from 50 to 500° C. and at a pressure ranging from 2 to 50 atm. The nebulization/vapourization and mixing processes must be effected so as to avoid reactions of triggering and back-propagation of flames and, in general, the triggering of radical reactions in gaseous phase. These reactions must be avoided as:
i) their exothermicity can lead to temperature rises which, if they were to extend to the reaction zone, could damage the catalyst and/or partially deactivate it,
ii) they cause the formation of carbonaceous residues or precursors of carbonaceous residues which could clog the catalytic beds and damage the thermal exchange systems in section IV,
iii) they reduce the selectivity of the reaction towards the desired products (H2 and CO) and the conversion of the hydrocarbon reagents.
The stream of liquid hydrocarbon feedstock must be nebulized/vaporized, before being mixed with the other reagent streams, possibly with the help of a gaseous propellant which can be added to the feedstock itself. For the nebulization/vaporization, section II envisages the use of a specific device called “atomization/nebulization” device.
The device for nebulizing the liquid hydrocarbon feedstock is preferably a device analogous to that described in WO2006/034868A1. This device envisages separate inlet areas for the liquid hydrocarbon stream and the possible propellant stream.
The nebulized liquid hydrocarbon stream is then mixed with the oxidizing stream in the mixing chamber of section II, located immediately upstream of the reaction section, forming a possibly biphasic liquid-gas mixture.
The gaseous propellant is preferably vapour and/or a hydrocarbon stream, such as for example natural gas, LPG, refinery gas or purge gas of up-grading processes and/or mixtures thereof, possibly with the addition of CO2.
The nebulization of the liquid hydrocarbon can take place with a single- or multi-step process. The addition can be envisaged, for example, in the atomization/nebulization device (total or partialized in a number of steps) of a quantity of gaseous propellant which allows a first dispersion of the liquid hydrocarbon feedstock. The expansion and nebulization of the liquid feedstock can be subsequently effected through suitably-sized orifices present in the mixing chamber, where the hydrocarbon stream is reached by the oxidizing stream.
The mixing chamber is installed immediately downstream of the atomization/nebulization device of the liquid hydrocarbon. Said chamber, whose purpose is to homogenize the reaction mixture before sending it onto the catalytic bed, can, for example, have a cylindrical or truncated-conical geometry. The volume of the mixing chamber must be such that the flows of nebulized/vaporized liquid hydrocarbon and oxidizing stream coming from the distribution area of the atomization/nebulization device, are closely mixed, preferably by diffusion, under such conditions as to reduce the volumes necessary for the mixing phenomena. The design of the mixing chamber must also avoid the formation of permanent deposits of the liquid reagents on the walls, as, at a high temperature, these residues can in fact create carbonaceous residues. In order to avoid the formation of carbonaceous residues, an expedient is to cover the walls of the mixing chamber with active catalytic species with respect to the partial oxidation reactions of the hydrocarbons. For this purpose, catalysts can be adopted, having a composition analogous to that of the catalysts used in the reaction section (section III) for catalyzing the transformation of the reagent streams into synthesis gas.
Finally, the reagent flows must be such that the residence times of the reagent streams in the mixing area are lower than the flame delay times, whereas the linear rates of the reagents must be higher than the flame rates. Both the flame delay times and flame propagation times vary in relation to the compositions of the reaction mixture and flow, pressure and temperature conditions.
In the reaction section (section III) the biphasic liquid-gas stream of reagents, coming from section II, reaches and passes through one or more structured catalytic beds comprising a suitable catalyst arranged on one or more layers. The structured catalytic beds can consist of catalytic gauzes and/or different kinds of metallic or ceramic monoliths. Structured catalytic systems of this type are described for example in: i) Cybulski and J. A. Mulijn, “Structured Catalysts and Reactors”; Series Chemical Industries, 2006, Vol. 110; Taylor and Francis CRC Press, ii) G. Groppi, E. Tronconi; “Honeycomb supports with high thermal conductivity for gas/solid chemical processes, “Catalysis Today, Volume 105, Issues 3-4, 15 Aug. 2005, Pages 297-304.
The mixture of reagents must pass through the layers of catalyst with very reduced contact times, ranging from 0.01 to 100 ms and preferably from 0.1 to 10 ms, so as to progressively promote the catalytic partial oxidation reactions (eq. [6]) and prevent the strong exothermicity of the total oxidation chemical processes (eq. [7]), competitive with the partial oxidation processes, from causing the back-propagation of the reactions in the mixture of reagents. This back-propagation would trigger flame processes which would cause losses in the overall selectivity of the reaction and the formation of carbonaceous residues.
CnHm+n/2 O2=n CO+m/2H2 [6]
CnHm+(n+m/4)O2=n CO2+m/2 H2O [7]
The short contact times also allow a gradual oxygen consumption during the passage of the reagent mixture from one catalytic layer to the subsequent one. This configuration of the reaction section and, in particular, the presence of structured catalysts allows the oxidizing stream to be partialized on various layers of catalyst, thus modulating the temperature rise in the reaction mixture and favouring the evaporation of the high-boiling hydrocarbon compounds rather than their thermal decomposition. The biphasic reaction mixture is transformed on the catalytic bed, under the above conditions, into a mixture of reaction products whose main components are H2 and CO and the minor components are CO2, vapour and CH4. These expedients allow the process according to the present invention to convert liquid hydrocarbon feedstocks also containing high quanti-ties of sulfurated and nitrogenous compounds into synthesis gas with reduced oxygen and energy consumptions.
Among the structured catalytic beds which can be used for the purposes of the present invention, it is preferable to use structured catalytic beds comprising a support of the metallic type, such as metallic gauzes, metallic foams, metallic honeycomb monoliths or other monoliths obtained by assembling corrugated metallic sheets.
Some of the catalysts of this kind are already used in industrial processes, such as ammonia production processes, catalytic combustion processes of hydrocarbons and, in particular, abatement processes of the particulate in the emissions of internal combustion engines, the abatement of volatile organic compounds (VOC) produced in numerous industrial processing cycles, water gas shift reactions.
Metallic alloys widely used in structured catalytic beds as a support of the active catalytic species are ferritic alloys commercially known as “FeCralloys”, which contain, for example, aluminum (0.5-12%), chromium (20%), yttrium (0.1-3%) and iron or those containing aluminum (5.5%), chromium (22%), cobalt (0.5%) and iron (see J. W. Geus, J. C. van Giezen, Catalysis Today, 1999, 47, 169-180). These alloys, passivated (surface oxidized) with a surface layer of aluminum oxide and/or other oxide systems (Ce—Zr oxide systems are often used), can undergo further washcoating treatment of various kinds to improve the anchorage of the active catalytic species. The catalytic sites are also generated on the oxide systems surfaces with various methods known to experts in the field (for example by impregnation with solutions of chemical compounds). In particular, the catalytic species which have proved to be active in the process according to the present invention contain the following types of transition metals: Rh, Ru, Ir, Pt, Pd, Au, Ni, Fe, Co also mixed with each other. The catalytic activity is preferably obtained with the use of systems of the bimetallic type containing Rh—Ru, Rh—Ni, Rh—Fe, Rh—Co, Ru—Ni, Ru—Fe, Ru—Co, Ru—Au, Ru—Pt, Rh—Ir, Pt—Ir, Au—Ir, and trimetallic systems containing Rh—Ru—Ni, Ru—Au—Ni, Rh—Ru—Co, Rh—Ir—Ni, Rh—Au—Ir.
An important advantage offered by supports of the metallic type is the possibility of varying their temperature by heating them electrically. The electric heating of the metallic supports not only allows fast start-up procedure but also the reactivity of the single catalytic layers to be varied with the same flow and composition of the reagent mixture. The use of electrically heated metallic supports also allows the mixtures of reagents to be fed at relatively low temperatures, reducing or avoiding the risk of substoichiometric combustion reactions in the mixing and nebulization section II.
A further advantage of metallic supports which can be heated electrically is the possibility of regenerating the catalytic activity of the surface species without interrupting the conversion process. The regeneration of the catalyst can be obtained by electrically heating the metallic support to a temperature which is sufficient for eliminating the substances which poison the catalyst, promoting their desorption and chemical transformation. These poisoning substances can consist of: i) sulfurated compounds which are unstable on surfaces heated to a high temperature and/or ii) carbonaceous deposits which can be formed by decomposition of the hydrocarbon compounds in particular unsaturated and/or high-boiling hydrocarbon compounds.
Section III can also comprise a final catalytic bed, located downstream of the previous beds, and with larger dimensions with respect to these. The mixture of reaction products comprising H2 and CO passes through the final catalytic bed, with contact times ranging from 1 to 1,000 ms, preferably from 10 to 100 ms. This latter bed can consist of a structured catalytic bed or catalyst pellets, such as for example the pellets described in US 2005/0211604 A1. The function of the latter catalytic bed is to complete the partial oxidation processes and improve the selectivity towards the production of synthesis gas by means of SR, CO2 Reforming and WGS processes (eq. [1-3] of Table 1).
In a preferred embodiment of the process according to the present invention, the last catalytic bed can also consist of a system capable of directly promoting WGS reactions.
At the end of the catalytic partial oxidation reaction, at the outlet of section III, the mixture of reaction products containing the synthesis gas has a maximum temperature of 1,200° C., preferably a maximum temperature of 1,150° C.
In section IV, the synthesis gas coming from section III is then rapidly sent to a thermal exchange area in which it undergoes a cooling process. The cooling must be rapid to avoid the triggering of undesired chemical processes, such as the formation of carbonaceous substances or precursors of carbonaceous substances such as unsaturated hydrocarbon molecules, in the unconverted hydrocarbon fraction. The cooling of the synthesis gas must also be completed rapidly to avoid methanation reactions [8] and disproportioning reactions of the carbon monoxide [9]:
CO+H2═CH4+H2O [8]
2 CO═CO2+C [9]
With respect to the non-catalytic PO process, the process for producing synthesis gas and hydrogen through the catalytic partial oxidation of liquid hydrocarbon feedstocks described herein has the following advantages:
1) the possibility of controlling the temperature peaks inside the reactors (Tmax 1,200° C., preferably 1,150° C., for the process according to the present invention against the approximately 2,000° C. of non-catalytic PO processes).
2) the possibility of catalytically controlling the selectivity of the reactions towards partial oxidation products (CO and H2), reducing the formation of by-products (carbonaceous residues and unsaturated precursors of carbonaceous residues), inevitable in substoichiometric processes in homogeneous gaseous phase;
3) the possibility of obtaining outlet temperatures of synthesis gas lower than 1,200° C. and preferably lower than 1,150° C.;
4) the possibility of varying both the composition and flow of hydrocarbon feedstock, in addition to the flows of the oxidizing stream and vapour.
The possibilities included in points 1) to 3) allow the exchange surfaces to be greatly reduced, in some cases avoiding the use of preheating ovens for the reagents with significant and favourable effects on the investment costs and energy consumption. These exchange surfaces and in particular preheating ovens are one of the main costs associated with the non-catalytic PO technology.
The possibilities included in the above points 2) and 3), on the other hand, allow a reduction in the oxygen consumption and simplify the treatment processes of the synthesis gas produced (cooling operations, washing, etc.) which represent the other two main cost items of non-catalytic PO processes.
Finally, the possibility included in point 4) above allows the conversion system of the hydrocarbon feedstocks into synthesis gas and therefore into hydrogen, to vary the production capacity of H2 (±60-80%) and also to use different hydrocarbon feedstocks available in the refinery without requiring significant modifications to the existing plants.
The process according to the present invention also allows synthesis gas and therefore H2 to be produced by alternating the use of natural gas and other gaseous hydrocarbons with various refinery feedstocks, whose exploitation is currently not economically convenient or is extremely complex from a technical point of view (for example LCO, HCO and DAO).
The process according to the present invention can be advantageously used for producing synthesis gas and therefore H2 starting from intermediate hydrocarbon feedstocks resulting from processings of the EST process, which cannot normally be used in traditional SR, non-catalytic PO and ATR processes.
It also allows the productivity of H2 to be varied for satisfying the requirements of refinery operations, as it is able to use the various refinery feedstock streams available, which undergo a sequential evolution, in some cases with cyclic characteristic during the year.
| Number | Date | Country | Kind |
|---|---|---|---|
| MI2007A002228 | Nov 2007 | IT | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP08/09752 | 11/17/2008 | WO | 00 | 8/2/2010 |
