Method for forming synthesis gas for liquid hydrocarbon production - Patents.com

Abstract

1. A method for forming a synthesis gas for liquid hydrocarbon production, the method comprising: providing a feed gas comprising carbon dioxide, hydrogen and sulfur compounds; passing the feed gas through a reverse water gas shift reaction chamber to convert a portion of the carbon dioxide and a portion of the hydrogen to carbon monoxide and water and at least a portion of the sulfur compounds to hydrogen sulfide to provide a carbon monoxide-rich feed gas; passing the carbon monoxide-rich feed gas through a carbon dioxide removal unit to provide a synthesis gas and a carbon dioxide-rich stream, the carbon dioxide-rich stream comprising carbon dioxide and hydrogen sulfide; passing the carbon dioxide-rich stream through a hydrogen sulfide removal unit to remove hydrogen sulfide from the carbon dioxide-rich stream to provide a purified carbon dioxide stream; and recycling the purified carbon dioxide stream into the feed gas.

Description

[Technical field]

[0001] The present invention relates to a method for forming synthesis gas for the production of liquid hydrocarbons, and to a method for producing liquid hydrocarbons from synthesis gas. [Background technology]

[0002] The Fischer-Tropsch process is a series of chemical reactions that convert a mixture of carbon monoxide and hydrogen into liquid hydrocarbons. These reactions are carried out in the presence of a metal catalyst, typically at temperatures between 150 and 300 °C, and at pressures ranging from one to several tens of atmospheres. The Fischer-Tropsch process ideally involves the reaction of the following reaction product: n H 2n+2 ), a series of chemical reactions that produce various hydrocarbons with different structures. The more useful reactions produce alkanes as follows: (2n+1)H2+n CO→C n H 2n+2 +n H2O where n is typically 1-100 or more. Formation of methane (n=1) is undesirable. Most of the alkanes produced tend to be linear and are suitable for upgrading to produce middle distillate fuels such as diesel and jet fuel. In addition to alkane formation, competing reactions produce small amounts of alkenes, as well as alcohols and other oxygenated hydrocarbons. By-product water is a by-product that is separated from the product of the Fischer-Tropsch reaction. The Fischer-Tropsch reaction is highly exothermic, with a standard enthalpy of reaction (ΔH) of -165 kJ / mol CO combination.

[0003] The synthesis gas (syngas) feed to a Fischer-Tropsch unit can come from a variety of feedstocks. For example, from steam and / or autothermal reforming of natural gas, high-temperature gasification of municipal solid waste and biomass, or reverse water-gas shift of carbon dioxide and hydrogen. The latter source is beneficial because it utilizes carbon dioxide that could otherwise be released to the atmosphere. Since carbon dioxide is usually a product of combustion, the carbon dioxide source tends to contain high concentrations of impurities such as carbonyl sulfide, hydrogen cyanide, ammonia, hydrogen sulfide and carbonyls, which deactivate the Fischer-Tropsch catalyst and therefore must be removed to single-digit ppb concentrations. To maximize the carbon dioxide efficiency of such processes, the carbon dioxide not converted in the reverse water-gas shift reactor is recirculated. However, such recirculation can result in impurities such as hydrogen sulfide building up in the recycle loop.

[0004] US Patent No. 6,107,353 describes a process for removing hydrogen cyanide and ammonia from synthesis gas prior to the hydrocarbon synthesis reaction. The process involves passing the synthesis gas over a catalyst to hydrolyze the hydrogen cyanide to ammonia. The hydrolyzed gas removed from the hydrolysis zone is then contacted with water in a scrubbing zone to dissolve the ammonia. However, this process requires the use of a hydrogen cyanide absorption zone before the synthesis gas enters the Fischer-Tropsch reactor to reduce the hydrogen cyanide and ammonia to ppb levels. The use of such a hydrogen cyanide absorption zone complicates the process.

[0005] U.S. Pat. No. 8,551,218 describes a process for reducing carbonyl sulfide, carbon disulfide, metal carbonyl compounds, hydrogen sulfide and hydrogen cyanide, ammonia and arsenic and chlorine compounds in a feed gas, comprising sequentially contacting the gas with a first purifying agent comprising activated carbon, a second purifying agent comprising alumina, a third purifying agent comprising zinc oxide, a fourth purifying agent comprising a zeolite material, and a fifth purifying agent comprising zinc oxide and copper oxide.

[0006] The present invention aims to address at least some of the problems associated with the prior art, or at least to provide a commercially acceptable alternative solution. Summary of the Invention

[0007] One aspect of the present disclosure is a method of forming a synthesis gas for liquid hydrocarbon production, the method comprising: Providing a feed gas comprising carbon dioxide, hydrogen, and sulfur compounds; providing a carbon monoxide-enriched feed gas by passing the feed gas through a reverse water gas shift reaction chamber to convert a portion of the carbon dioxide and a portion of the hydrogen to carbon monoxide and water and to convert at least a portion of the sulfur compounds to hydrogen sulfide; passing a carbon monoxide-enriched feed gas through a carbon dioxide removal unit to provide a synthesis gas and a carbon dioxide-enriched stream, the carbon dioxide-enriched stream comprising carbon dioxide and hydrogen sulfide; passing the carbon dioxide rich stream through a hydrogen sulfide removal unit to remove hydrogen sulfide from the carbon dioxide rich stream to provide a purified carbon dioxide stream; and recycling the purified carbon dioxide stream into the feed gas.

[0008] Another aspect of the present disclosure is a method for producing liquid hydrocarbons from a synthesis gas, the method comprising: forming a synthesis gas according to the methods described herein; and passing the synthesis gas through a Fischer-Tropsch reaction chamber to produce liquid hydrocarbon products. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a flow diagram of an example of a method according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In a first aspect, the present disclosure provides a method of forming a synthesis gas for liquid hydrocarbon production, the method comprising: Providing a feed gas comprising carbon dioxide, hydrogen, and sulfur compounds; providing a carbon monoxide-enriched feed gas by passing the feed gas through a reverse water gas shift reaction chamber to convert a portion of the carbon dioxide and a portion of the hydrogen to carbon monoxide and water and to convert at least a portion of the sulfur compounds to hydrogen sulfide; passing a carbon monoxide-enriched feed gas through a carbon dioxide removal unit to provide a synthesis gas and a carbon dioxide-enriched stream, the carbon dioxide-enriched stream comprising carbon dioxide and hydrogen sulfide; passing the carbon dioxide rich stream through a hydrogen sulfide removal unit to remove hydrogen sulfide from the carbon dioxide rich stream to provide a purified carbon dioxide stream; and recycling the purified carbon dioxide stream into the feed gas.

[0011] Each aspect or embodiment defined in this specification may be combined with any other aspect(s) or embodiment(s) unless expressly indicated otherwise. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature(s) indicated as being preferred or advantageous.

[0012] Advantageously, the resulting synthesis gas has a particularly low content of sulfur compounds, which, when used in a Fischer-Tropsch process, reduces poisoning of the Fischer-Tropsch catalyst, resulting in less frequent catalyst regeneration or replacement and a more efficient process.

[0013] The method includes recycling carbon dioxide into the feed gas, thereby increasing the carbon efficiency of the method. The inventors have surprisingly found that such recycling can be performed without hydrogen sulfide accumulating in the recycle loop. In conventional methods where the sulfur removal step is performed before the reverse water gas shift reaction chamber, not all of the sulfur species are typically removed from the feed gas. For example, certain sulfur compounds, such as carbonyl sulfide and sulfur dioxide, are difficult to adsorb using conventional sulfur removal units. Such species are converted to hydrogen sulfide in the reverse water gas shift reaction chamber, and a large portion of it is removed along with the carbon dioxide in the carbon dioxide removal / separation unit. Thus, hydrogen sulfide accumulates over time in the carbon dioxide recycle loop. As a result, over time, the amount of hydrogen sulfide may increase to a concentration where the carbon dioxide removal unit is unable to remove all of the hydrogen sulfide, increasing the amount of hydrogen sulfide entrained in the synthesis gas. In the present invention, the sulfur removal is performed in the carbon dioxide recycle loop, not before the reverse water gas shift reaction chamber, so hydrogen sulfide does not accumulate in the recycle loop. As a result, hydrogen sulfide contamination of the synthesis gas is kept to a minimum, if at all.

[0014] As used herein, the term "syngas" or "synthesis gas" can include a gas mixture containing hydrogen and one or both of carbon dioxide and carbon monoxide. In the method of the present invention, the first synthesis gas comprises carbon monoxide (i.e., CO) and hydrogen (i.e., molecular hydrogen, H2).

[0015] As used herein, the term "liquid hydrocarbon" may include chemical species formed from carbon and hydrogen and that are liquid at room temperature and pressure. Hydrocarbons typically include alkanes and typically contain from 5 to 100 or more carbon atoms per molecule.

[0016] The feed gas includes carbon dioxide (i.e., CO2), hydrogen, and sulfur compounds. The synthesis gas may include other gases, such as carbon monoxide, water, methane, and ammonia, as well as solid species, such as dust and coke. The composition of the feed gas may vary depending on its production method and the starting materials used.

[0017] The carbon dioxide may be a by-product of combustion. The carbon dioxide may come from flue gas. The carbon dioxide may come from a partial oxidation and / or gasification system.

[0018] The feed gas is passed through a reverse water gas shift reactor. Reverse water gas shift reactors are known in the art. The reverse water gas shift reactor is preferably an autothermal shift vessel and preferably contains a reverse water gas shift catalyst. Under the reverse water gas shift reaction, carbon dioxide and hydrogen are converted as follows:

[0019] [ka]

[0020] In this process, part of the carbon dioxide and part of the hydrogen are converted to carbon monoxide and water. As will be understood, not all of the hydrogen is converted. This is because the synthesis gas must contain hydrogen to undergo, for example, the Fischer-Tropsch reaction later.

[0021] In the reverse water gas shift reactor, sulfur compounds are converted to hydrogen sulfide. For example, sulfur dioxide and carbonyl sulfide can be converted as follows:

[0022] [ka]

[0023] Preferably, the majority of the compounds of sulfur are converted to hydrogen sulfide, and more preferably, substantially all of the compounds of sulfur are converted to hydrogen sulfide.

[0024] The carbon monoxide-rich feed gas is passed to a carbon dioxide removal unit, which are known in the art. As noted above, hydrogen sulfide is preferentially absorbed over carbon dioxide in the carbon dioxide removal unit.

[0025] The carbon dioxide rich stream is passed to a hydrogen sulfide removal unit, which are known in the art.

[0026] The process is typically carried out at elevated pressure, preferably between 1 and 5 MPa absolute.

[0027] Hydrogen is preferably generated by electrolysis of water. Such hydrolysis is preferably carried out using renewable energy. The use of such hydrogen, known as "green hydrogen", can make the process more environmentally friendly.

[0028] The sulfur compounds preferably include one or more of sulfur dioxide, mercaptans, disulfides, thiophenes and carbonyl sulfides. Such species may particularly cause poisoning of Fischer-Tropsch catalysts. In addition, such species are difficult to remove using conventional sulfur removal units, but are easily converted to hydrogen sulfide in the reverse water gas shift reaction chamber. The feed gas preferably further includes nitrogen compounds, more preferably selected from one or more of amines, hydrogen cyanide, nitric oxide and nitrogen dioxide, and by passing the feed gas through the reverse water gas shift reaction chamber, some of these nitrogen compounds are converted to hydrogen cyanide and / or ammonia. Such species may particularly cause poisoning of Fischer-Tropsch catalysts, especially cobalt catalysts. In addition, hydrogen cyanide and ammonia are easily removed from the synthesis gas, for example, by hydrolyzing hydrogen cyanide to ammonia and removing the ammonia using a scrubber.

[0029] The reverse water gas shift reaction chamber preferably contains a catalyst comprising nickel, which is particularly suitable for carrying out the reverse water gas shift reaction at advantageous temperatures and pressures and at high conversion rates.

[0030] The reverse water gas shift reaction chamber is preferably at a temperature of at least 700° C. Such temperatures may result in particularly high conversion rates of carbon dioxide and hydrogen to carbon monoxide and water. In addition, such temperatures may be particularly suitable for converting sulfur compounds to hydrogen sulfide at high conversion rates.

[0031] The carbon dioxide removal unit preferably uses a liquid chemical absorbent, more preferably selected from one or more of amines (e.g., alkylamines selected from MEA, DEA, and MDEA), or alkali metal carbonates, and / or a liquid physical absorbent, more preferably selected from one or more of methanol, glycol, or glycol ether. Such absorbents may be particularly suitable for removing carbon dioxide. In addition, such absorbents can absorb hydrogen sulfide in preference to carbon dioxide, so that only trace amounts of hydrogen sulfide, if any, are present in the synthesis gas. The liquid chemical absorbent may be part of a scrubber.

[0032] Preferably, the hydrogen sulfide removal unit comprises a particulate bed of copper sorbent, preferably a particulate bed of copper hydroxycarbonate sorbent, which is particularly suitable for absorbing hydrogen sulfide, such that recycle of hydrogen sulfide back into the feed gas is minimised.

[0033] The copper sorbent bed is preferably at a temperature between 0 and 150° C., more preferably between 10 and 100° C. Higher temperatures may favor reduction of copper in the sorbent to elemental copper due to the presence of reducing species such as hydrogen and carbon monoxide. Lower temperatures may favor "wetting" of the catalyst bed.

[0034] In a further aspect, the present disclosure provides a method for producing liquid hydrocarbons from a synthesis gas, the method comprising: forming a synthesis gas according to the method of the first aspect; and passing the synthesis gas through a Fischer-Tropsch reaction chamber to produce liquid hydrocarbon products.

[0035] The advantages and preferred features of the first aspect apply to this aspect as well.

[0036] Fischer-Tropsch reaction chambers are known in the art. Due to the particularly trace amounts of sulfur compounds in the synthesis gas, poisoning of the Fischer-Tropsch catalyst is suppressed compared to conventional processes. This eliminates the need for frequent catalyst regeneration or replacement, improving the efficiency of the process.

[0037] The temperature of the Fischer-Tropsch reaction chamber is preferably between 150° C. and 300° C. Lower temperatures may result in an undesirable reduction in the amount of liquid hydrocarbons generated. Higher temperatures may result in an increase in the energy costs of the process while not significantly increasing the amount of liquid hydrocarbons produced.

[0038] Preferably, passing the synthesis gas through a Fischer-Tropsch reaction chamber to produce the liquid hydrocarbon products comprises contacting the synthesis gas with a catalyst comprising cobalt, iron and / or ruthenium. Such catalysts may be particularly effective in catalyzing the Fischer-Tropsch reaction and / or may allow the reaction to proceed preferably at low temperatures and / or in high yields.

[0039] The hydrogen to carbon monoxide molar ratio in the synthesis gas is preferably between 1.8 and 2.2, as this is close to the stoichiometric ratio of about 2 for the Fischer-Tropsch reaction.

[0040] The hydrocarbon products from the Fischer-Tropsch reaction chamber may be separated from by-product water and unreacted gases and then converted to liquid hydrocarbon fuels, for example, by hydrocracking.

[0041] The synthesis gas preferably comprises hydrogen cyanide and the method further comprises, prior to passing the synthesis gas through the Fischer-Tropsch reaction chamber, converting at least a portion of the hydrogen cyanide to ammonia to provide a first synthesis gas that is enriched in ammonia and depleted in hydrogen cyanide; and passing the first syngas through a scrubber and contacting the first syngas with a scrubbing liquor to retain at least a portion of the ammonia contained in the first syngas in the scrubbing liquor and form a second syngas depleted in ammonia and hydrogen cyanide, wherein the syngas passed to the Fischer-Tropsch reaction chamber is the second syngas.

[0042] Fischer-Tropsch catalysts can be poisoned by hydrogen cyanide and ammonia. Scrubbers and scrubbing liquors are known in the art. A suitable scrubbing liquor may consist essentially of water. The efficiency of ammonia removal can be improved by increasing the residence time in the scrubber or by increasing the surface area of ​​the scrubbing liquor, for example, by using trays, structured packing, or random packing.

[0043] Preferably, converting at least a portion of the hydrogen cyanide to ammonia to provide a first synthesis gas comprises catalytic hydrolysis of hydrogen cyanide with water or steam. Catalytic hydrolysis is a simple method of converting hydrogen cyanide to ammonia since it can be carried out at relatively low temperatures by adding water. Thus, the simplicity and efficiency of the process can be improved. Water for hydrolysis may be sprayed into the synthesis gas stream before being fed to the hydrolysis bed or may be added to the synthesis gas as steam. The equilibrium reaction for this is as follows:

[0044] [ka]

[0045] Following hydrolysis, the synthesis gas is preferably cooled, more preferably to a temperature below 40° C., even more preferably to ambient temperature, before contacting the scrubber.

[0046] Preferably, the catalytic hydrolysis is carried out at a temperature above 100° C., preferably between 150° C. and 300° C. Lower temperatures may result in the hydrolysis proceeding undesirably. Higher temperatures may result in a smaller increase in hydrogen cyanide conversion, while increasing the energy costs of the process.

[0047] The hydrolysis is preferably carried out using an alumina catalyst, more preferably an activated alumina catalyst, as such catalysts may provide particularly high conversions and / or may advantageously allow operation at low temperatures.

[0048] The first synthesis gas preferably contains less than 10 ppbv hydrogen cyanide, which is particularly effective in preventing poisoning of the Fischer-Tropsch catalyst.

[0049] The second synthesis gas preferably contains less than 10 ppbv ammonia, which is particularly effective in preventing poisoning of the Fischer-Tropsch catalyst due to the trace amounts of hydrogen cyanide.

[0050] The scrubbing liquor preferably includes by-product water. The by-product water can be separated from the product recovered from the Fischer-Tropsch reaction chamber using conventional separation equipment. In a preferred embodiment, passing the second synthesis gas through the Fischer-Tropsch reaction chamber produces a liquid hydrocarbon product and by-product water, and the aqueous scrubbing liquor includes by-product water recovered from the Fischer-Tropsch reaction chamber. In addition, the by-product water will include dissolved carbon dioxide from the synthesis gas and from carbon dioxide generated as a by-product in the Fischer-Tropsch reaction chamber. The presence of carbon dioxide can improve the ammonia removal capacity of the scrubbing liquor. Thus, it is easier to reduce the ammonia and hydrogen cyanide content of the synthesis gas to single digit ppb levels. As a result, the poisoning of the Fischer-Tropsch catalyst is further suppressed and the Fischer-Tropsch catalyst needs to be regenerated or replaced less frequently, making the process more efficient. Furthermore, the use of hydrogen cyanide and ammonia absorption beds immediately prior to the Fischer-Tropsch reaction chamber may be avoided, which may be a simpler approach than conventional methods. The use of by-product water instead of using another water source such as boiler feed water or demineralized water simplifies the process and reduces operating costs. Furthermore, since the by-product water is recovered from the Fischer-Tropsch reaction chamber, the water does not contain catalyst poisons. Therefore, there is less introduction of poisons that may deactivate the catalyst compared to comparable processes using other scrubbing liquor sources. Although Fischer-Tropsch poisons may be present in other water streams such as boiler feed water with chemicals, the use of by-product water recovered from the Fischer-Tropsch reaction chamber in the aqueous scrubbing liquor ensures that these Fischer-Tropsch poisons are not added to the system.

[0051] The scrubbing liquid preferably contains at least 0.01 mol / L of carbon dioxide, more preferably at least 0.02 mol / L of carbon dioxide, which can particularly enhance the ammonia removal capacity of the scrubbing liquid.

[0052] In a preferred embodiment, the scrubbing liquor is preferably saturated with carbon dioxide under the temperature and pressure conditions of the scrubber.

[0053] The first syngas preferably contains hydrogen sulfide, and the method further comprises passing the first syngas through a sulfur guard bed upstream of the scrubber to remove hydrogen sulfide from the first syngas prior to passing the first syngas through the scrubber. The presence of hydrogen sulfide in the syngas can cause poisoning of the Fischer-Tropsch catalyst.

[0054] The sulfur guard bed preferably comprises zinc oxide, which is particularly effective at removing hydrogen sulfide, for example, by the following reaction: H2S+ZnO → ZnS+H2O

[0055] Sulfur guard beds are placed downstream of hydrogen cyanide hydrolysis to suppress the formation of toxic zinc cyanide (Zn(CN)2), which, when exposed to moisture during sorbent discharge and disposal, can release toxic HCN, posing a risk to personnel.

[0056] The sulfur guard bed is preferably operated at a temperature of from 15 to 230° C. Such temperatures can be particularly effective in removing hydrogen sulfide from the synthesis gas.

[0057] The method preferably further comprises adding an oxygen-containing gas to the second syngas prior to passing the second syngas through the Fischer-Tropsch reaction chamber, and passing the second syngas through a carbonyl guard bed to remove metal carbonyls from the second syngas. The presence of metal carbonyls in the syngas can cause poisoning of the Fischer-Tropsch catalyst. Removal of sulfur species, hydrogen cyanide and ammonia occurs prior to the addition of the oxygen-containing gas to avoid the generation of SOx and NOx.

[0058] The carbonyl guard bed preferably comprises activated carbon, which may be particularly suitable for removing carbonyls, for example, via catalytic oxidation on the carbon surface.

[0059] [ka]

[0060] The carbonyl guard bed is preferably operated at a temperature between 15 and 250° C., more preferably between 50 and 150° C. Higher temperatures may result in side reactions of the syngas with the deposited metals, such as methanation over nickel. Lower temperatures may result in a reduced degree of oxidation of the carbonyls.

[0061] The method preferably further comprises passing the second syngas through an oxygen guard bed to remove oxygen from the second syngas prior to passing the second syngas through the Fischer-Tropsch reaction chamber and after passing the second syngas through the carbonyl guard bed. The presence of oxygen in the syngas can cause poisoning of the Fischer-Tropsch catalyst.

[0062] The oxygen guard bed preferably contains a catalyst comprising platinum and / or palladium supported on alumina, such catalysts being particularly effective in removing oxygen from the synthesis gas.

[0063] The oxygen guard bed is preferably operated at a temperature of 100-250° C. Higher temperatures may result in undesirable side reactions, while lower temperatures may result in insufficient oxygen removal.

[0064] The invention will now be described with reference to the following non-limiting examples. EXAMPLES

[0065] An example of a process according to the invention is described with reference to Figure 1. Carbon dioxide feed 1 and hydrogen feed 2 are reacted in a Reverse-Water-Gas-Shift (RWGS) reactor 3 over a nickel catalyst to form carbon monoxide. The reaction is as follows: CO2+H2⇔CO+H2O

[0066] Unreacted carbon dioxide 4 is separated from the synthesis gas product stream 5 in CO2 capture unit 6 and recycled back to the RWGS reactor feed via line 7. H2S is absorbed along with the carbon dioxide by the amine in CO2 capture unit 6 and most of it is released in carbon dioxide stream 4. H2S can accumulate in the carbon dioxide recycle loop 7 if sulfur species such as H2S and SO2 are present in the carbon dioxide feed.

[0067] By passing through the RWGS reactor 3, SO2 is converted to H2S via the following reaction: SO2+3H2→H2S+2H2O COS present in the feed to the RWGS reactor 3 is hydrolyzed to H2S, which can also be subsequently removed.

[0068] [ka] Since the H2S formed in the carbon dioxide can be easily absorbed, a removal step using a copper adsorbent bed, such as copper hydroxycarbonate adsorbent, is placed in the CO2 sulfur guard bed vessel 8 in the carbon dioxide recycle loop 7 rather than in the fresh carbon dioxide feed 1.

[0069] Carbon dioxide 4 is pressurized with a compressor (not shown) and recycled back to the inlet of the RWGS reactor 3. A CO2 sulfur guard bed 8 is placed after the pressurization of carbon dioxide stream 4, as higher pressures allow for a reduced bed size. To prevent wetting of the bed, the gas stream is heated to about 50°C. This may be achieved by the addition of an electric or steam heater, or by heat exchange with a hot process fluid. In the CO2 sulfur guard bed vessel 8, H2S is captured and removed from the carbon dioxide recycle stream, thus reducing the amount of H2S fed to the CO2 capture unit 6.

[0070] To avoid poisoning of the downstream Fischer-Tropsch synthesis catalyst, the synthesis gas 5 from the CO2 capture unit 6 is compressed to an absolute pressure of about 5 MPa using a synthesis gas compressor (not shown) and then subjected to gas cleaning to reduce impurities to an appropriate level. The hot gas leaving the synthesis gas compressor is heated to 250°C via an interchanger and, optionally, by using a steam heater or an electric heater. HCN is subsequently hydrolyzed to NH3 in the HCN hydrolysis bed 9 on activated high surface area alumina. A water supply line 10, such as boiler feed water or demineralized water, is provided upstream of the HCN hydrolysis bed 9 to provide sufficient water for the hydrolysis of HCN. The water addition is preferably performed upstream of the final heater so that the risk of bed wetting due to steam generation is minimized. The HCN hydrolysis bed 9 is placed upstream of the synthesis gas sulfur guard bed 11, which contains a zinc oxide sorbent, to reduce the risk of toxic zinc cyanide formation. During discharge and disposal of zinc oxide sorbents, if zinc cyanide is exposed to moisture, toxic HCN can be released, posing a danger to personnel.

[0071] The hydrolysis reaction is as follows: HCN+H2O⇔NH3+CO

[0072] The synthesis gas recovered from the synthesis gas sulfur guard bed 11 is then cooled in a process interchanger (not shown) and then cooled to about 40° C. using cooling water. Water not consumed in the hydrolysis reaction is condensed and separated in the synthesis gas scrubbing drum 12 and sent to wastewater treatment.

[0073] In the syngas washing drum 12, FT by-product water 13 from the FT unit (not shown) is used to wash the syngas and remove amines and ammonia present in the syngas or formed by HCN hydrolysis. The syngas washing drum 12 contains trays or packing. The syngas wash water from the syngas washing drum 12 is sent to wastewater treatment.

[0074] To remove metal carbonyls from the syngas, a carbonyl guard bed 15 is provided downstream of the syngas scrubbing drum 12. An oxygen source 14 is provided upstream of the addition of oxygen 14 to avoid the generation of SOx and NOx.

[0075] After the syngas wash drum 12, the syngas stream is heated to 90° C. through a process interchanger (not shown) and then oxygen 14 is added.

[0076] The carbonyl guard bed 15 comprises an activated carbon bed. Carbonyls are catalytically oxidized on the carbon surface, for example, by the following reaction:

[0077] [ka]

[0078] The low temperature avoids side reactions between the synthesis gas and the deposited metal.

[0079] Excess oxygen in the synthesis gas recovered from the carbonyl guard bed 15 is removed by reacting with components of the synthesis gas in the oxygen guard bed 16 downstream of the carbonyl guard bed 15 .

[0080] The synthesis gas is heated in a process interchanger (not shown) followed by steam or electric heaters (not shown) to about 150° C. The oxygen guard bed 16 contains platinum or palladium on alumina which catalyzes the conversion of oxygen to water in the presence of hydrogen. O2+2H2→2H2O

[0081] The resulting clean synthesis gas stream 17 may then be fed to a FT unit (not shown).

[0082] The foregoing detailed description has been provided for purposes of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments described herein will be apparent to those of ordinary skill in the art and remain within the scope of the appended claims and their equivalents.

Claims

1. 1. A method for forming a synthesis gas for liquid hydrocarbon production, the method comprising: Providing a feed gas comprising carbon dioxide, hydrogen, and sulfur compounds; passing said feed gas through a reverse water gas shift reaction chamber to convert a portion of said carbon dioxide and a portion of said hydrogen into carbon monoxide and water, and to convert at least a portion of said sulfur compounds into hydrogen sulfide, thereby providing a carbon monoxide-enriched feed gas; passing the carbon monoxide-enriched feed gas through a carbon dioxide removal unit to provide the synthesis gas and a carbon dioxide-enriched stream, the carbon dioxide-enriched stream comprising carbon dioxide and hydrogen sulfide; passing the carbon dioxide-rich stream through a hydrogen sulfide removal unit to remove hydrogen sulfide from the carbon dioxide-rich stream to provide a purified carbon dioxide stream; and recycling said purified carbon dioxide stream into said feed gas.

2. The method of claim 1 , wherein the liquid hydrocarbon comprises an alkane.

3. 3. The method of claim 1 or 2, wherein the hydrogen is generated by electrolysis of water.

4. The method of any one of claims 1 to 3, wherein the compounds of sulfur include one or more of sulfur dioxide, mercaptans, disulfides, thiophenes, and carbonyl sulfides.

5. 5. The method of any one of claims 1 to 4, wherein the feed gas further comprises compounds of nitrogen, preferably selected from one or more of amines, hydrogen cyanide, nitric oxide and nitrogen dioxide, and passing the feed gas through the reverse water gas shift reaction chamber converts a portion of the compounds of nitrogen into hydrogen cyanide and / or ammonia.

6. The method of any one of claims 1 to 5, wherein the reverse water gas shift reaction chamber comprises a catalyst comprising nickel.

7. The method of any one of claims 1 to 6, wherein the reverse water gas shift reaction chamber is at a temperature of at least 700°C.

8. The carbon dioxide removal unit comprises: a liquid chemical absorbent, preferably selected from one or more of an amine or an alkali metal carbonate, and / or A method according to any one of claims 1 to 7, wherein a liquid physical absorbent is used, preferably selected from one or more of methanol, glycol or glycol ether.

9. A method according to any one of claims 1 to 8, wherein the hydrogen sulphide removal unit comprises a particulate bed of copper sorbent, preferably a particulate bed comprising copper hydroxycarbonate sorbent.

10. The method according to claim 9, wherein the bed is at a temperature of from 0 to 150°C, preferably from 10 to 100°C.

11. 1. A method for producing liquid hydrocarbons from synthesis gas, the method comprising: forming a synthesis gas according to the method of any one of claims 1 to 10; and passing the synthesis gas through a Fischer-Tropsch reaction chamber to produce liquid hydrocarbon products.

12. The method of claim 11, wherein the temperature of the Fischer-Tropsch reaction chamber is between 150°C and 300°C.

13. 13. The method of claim 11 or 12, wherein passing the synthesis gas through a Fischer-Tropsch reaction chamber to produce liquid hydrocarbon products comprises contacting the synthesis gas with a catalyst comprising cobalt, iron or ruthenium.

14. 14. The process according to any one of claims 11 to 13, wherein the molar ratio of hydrogen to carbon monoxide in the synthesis gas is from 1.8 to 2.

2.

15. The synthesis gas comprises hydrogen cyanide, and the method includes, prior to passing the synthesis gas through a Fischer-Tropsch reaction chamber, converting at least a portion of the hydrogen cyanide to ammonia to provide a first synthesis gas that is enriched in ammonia and depleted in hydrogen cyanide; 15. The method of any one of claims 11 to 14, further comprising passing the first syngas through a scrubber and contacting the first syngas with a scrubbing liquor to retain at least a portion of the ammonia contained in the first syngas in the scrubbing liquor and form a second syngas depleted in ammonia and hydrogen cyanide, wherein the syngas passed to the Fischer-Tropsch reaction chamber is the second syngas.

16. 16. The method of claim 15, wherein converting at least a portion of the hydrogen cyanide to ammonia to provide the first synthesis gas comprises catalytic hydrolysis of the hydrogen cyanide with water or steam.

17. The process according to claim 16, wherein the catalytic hydrolysis is carried out at a temperature above 100°C, preferably between 150°C and 300°C.

18. 18. The method according to claim 16 or 17, wherein the hydrolysis is carried out using an alumina catalyst, preferably an activated alumina catalyst.

19. 19. The method of any one of claims 15 to 18, wherein the first synthesis gas contains less than 10 ppbv hydrogen cyanide.

20. 20. The method of any one of claims 15 to 19, wherein the second synthesis gas contains less than 10 ppbv ammonia.

21. passing the synthesis gas through the Fischer-Tropsch reaction chamber produces liquid hydrocarbon products and by-product water; The method of any one of claims 15 to 20, wherein the scrubbing liquor comprises by-product water recovered from the Fischer-Tropsch reaction chamber.

22. 22. The method of any one of claims 15 to 21, wherein the first syngas comprises hydrogen sulfide, and the method further comprises passing the first syngas through a sulfur guard bed upstream of the scrubber to remove hydrogen sulfide from the first syngas prior to passing the first syngas through the scrubber.

23. 23. The method of claim 22, wherein the sulfur guard bed comprises zinc oxide.

24. The method of claim 22 or 23, wherein the sulfur guard bed is operated at a temperature of from 15 to 230°C.

25. 25. The method of any one of claims 22 to 24, wherein the second syngas comprises metal carbonyls, the method further comprising adding an oxygen-containing gas to the second syngas prior to passing the second syngas to the Fischer-Tropsch reaction chamber, and passing the second syngas through a carbonyl guard bed to remove the metal carbonyls from the second syngas.

26. 26. The method of claim 25, wherein the carbonyl guard bed comprises activated carbon.

27. 27. The method of claim 25 or 26, wherein the carbonyl guard bed is operated at a temperature of from 15 to 250°C, preferably from 50 to 150°C.

28. 28. The method of any one of claims 25 to 27, wherein the method further comprises passing the second syngas through an oxygen guard bed after passing the second syngas through the carbonyl guard bed and prior to passing the second syngas through the Fischer-Tropsch reaction chamber to remove oxygen from the second syngas.

29. 30. The method of claim 28, wherein the oxygen guard bed comprises a catalyst comprising platinum and / or palladium supported on alumina.

30. The method of claim 28 or 29, wherein the oxygen guard bed is operated at a temperature of from 100 to 250°C.

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