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 pressures ranging from one to several tens of atmospheres. Ideally, the Fischer-Tropsch process involves the reaction of the following formula: n H 2n+2 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 to 100 or greater. The formation of methane (n = 1) is undesirable. The majority of 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 Fischer-Tropsch reaction product. The Fischer-Tropsch reaction is highly exothermic, with a standard enthalpy of reaction (ΔH) of -165 kJ / mol CO₂ combination.

[0003] The synthesis gas (syngas) feed to a Fischer-Tropsch unit can originate from a variety of feedstocks, such as 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 advantageous because it utilizes carbon dioxide that would otherwise be released into the atmosphere. Because carbon dioxide is typically a combustion product, 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 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 recycled. However, such recycling can result in the accumulation of impurities, such as hydrogen sulfide, in the recycle loop.

[0004] U.S. Patent No. 6,107,353 describes a method for removing hydrogen cyanide and ammonia from synthesis gas prior to a hydrocarbon synthesis reaction. The method involves passing the synthesis gas through 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 method 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, which process comprises 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 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 into carbon monoxide and water and to convert at least a portion of the sulfur compounds into 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 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 a liquid hydrocarbon product. [Brief explanation 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 INVENTION

[0010] In a first aspect, the present disclosure provides a method of forming 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 into carbon monoxide and water and to convert at least a portion of the sulfur compounds into 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 stated otherwise. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature 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 present method includes recycling carbon dioxide into the feed gas, thereby increasing the carbon efficiency of the method. The inventors have surprisingly discovered that such recycling can be carried out without accumulating hydrogen sulfide in the recycle loop. Conventional methods that perform a sulfur removal step before the reverse water gas shift reaction chamber typically do not remove all sulfur species 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 most of them are removed along with 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 can increase to a concentration where the carbon dioxide removal unit is unable to remove all of the hydrogen sulfide, potentially increasing the amount of hydrogen sulfide entering the syngas. In the present invention, sulfur removal is performed in the carbon dioxide recycle loop rather than before the reverse water gas shift reaction chamber, preventing hydrogen sulfide from accumulating 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" (synthesis gas) can encompass 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, H).

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

[0016] The feed gas contains carbon dioxide (i.e., CO), hydrogen, and sulfur compounds. The synthesis gas may contain 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 can be a by-product of combustion. The carbon dioxide can come from flue gas. The carbon dioxide can 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, some of the carbon dioxide and some of the hydrogen are converted to carbon monoxide and water. As will be appreciated, not all of the hydrogen is converted, as the synthesis gas must contain hydrogen to undergo subsequent Fischer-Tropsch reactions, for example.

[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] The 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 sulfide. These species can particularly poison Fischer-Tropsch catalysts. Additionally, these species are difficult to remove using conventional sulfur removal units, but are readily converted to hydrogen sulfide in the reverse water-gas shift reaction chamber. The feed gas preferably further contains nitrogen compounds, more preferably nitrogen compounds selected from one or more of amines, hydrogen cyanide, nitric oxide, and nitrogen dioxide. 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. These species can particularly poison Fischer-Tropsch catalysts, particularly cobalt catalysts. Additionally, 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. Additionally, 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 an amine (e.g., an alkylamine selected from MEA, DEA, and MDEA) or an alkali metal carbonate, 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 preferentially over carbon dioxide, thereby minimizing the amount of hydrogen sulfide that may be 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, thereby minimizing the recycle of hydrogen sulfide into the feed gas.

[0033] The copper sorbent bed is preferably at a temperature of 0-150°C, more preferably 10-100°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 synthesis gas, the method comprising: forming synthesis gas according to the method of the first aspect; and passing the synthesis gas through a Fischer-Tropsch reaction chamber to produce a liquid hydrocarbon product.

[0035] The advantages and preferred features of the first aspect are the same for this aspect.

[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 undesirably reduced 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 product 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 molar ratio of hydrogen to carbon monoxide in the synthesis gas is preferably between 1.8 and 2.2, as this is close to the stoichiometric ratio of approximately 2 in 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 includes, 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 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. Ammonia removal efficiency 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 the first synthesis gas comprises catalytic hydrolysis of hydrogen cyanide with water or steam. Catalytic hydrolysis is a simple method for converting hydrogen cyanide to ammonia because it can be carried out at relatively low temperatures by adding water. This can improve the simplicity and efficiency of the process. 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 synthesis gas with 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 undesirably poor hydrolysis, while higher temperatures may result in a small 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, which may provide particularly high conversion rates and / or may advantageously allow operation at low temperatures.

[0048] The first synthesis gas preferably contains less than 10 ppbv of 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 amount of hydrogen cyanide.

[0050] The scrubbing liquor preferably contains 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 contains the by-product water recovered from the Fischer-Tropsch reaction chamber. Furthermore, the by-product water contains 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. Therefore, 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, reducing the frequency of Fischer-Tropsch catalyst regeneration or replacement, making the process more efficient. Furthermore, this method may be simpler than conventional methods because it may be possible to avoid the use of hydrogen cyanide and ammonia absorption beds immediately prior to the Fischer-Tropsch reaction chamber. Using by-product water instead of using another water source, such as boiler feedwater or demineralized water, simplifies the process and reduces operating costs. Furthermore, because the by-product water is recovered from the Fischer-Tropsch reaction chamber, the water does not contain catalyst poisons. Therefore, it is less likely to introduce catalyst poisons that could deactivate the catalyst than comparable processes using other scrubbing liquor sources. While Fischer-Tropsch poisons may be present in other water streams, such as chemically contaminated boiler feedwater, using by-product water recovered from the Fischer-Tropsch reaction chamber as an aqueous scrubbing liquor ensures that these poisons are not further introduced into the system.

[0051] The scrubbing liquor 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 liquor.

[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 synthesis gas preferably contains hydrogen sulfide, and the method further comprises passing the first synthesis gas through a sulfur guard bed upstream of the scrubber to remove hydrogen sulfide from the first synthesis gas prior to passing the first synthesis gas through the scrubber. The presence of hydrogen sulfide in the synthesis gas 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). When Zn(CN)2 is exposed to moisture during sorbent discharge and disposal, toxic HCN can be released, 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 includes adding an oxygen-containing gas to the second syngas before 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 before 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 metal, such as methanation over nickel. Lower temperatures may result in a reduced degree of carbonyl oxidation.

[0061] The method preferably further comprises passing the second syngas through an oxygen guard bed to remove oxygen from the second syngas before passing the second syngas through the Fischer-Tropsch reaction chamber and after passing the second syngas through the carbonyl guard bed, since 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, which is particularly effective in removing oxygen from 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. [Example]

[0065] An example of a process according to the present 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 recovery unit 6 and recycled back to the RWGS reactor feed via line 7. H2S is absorbed along with the carbon dioxide by an amine in CO2 recovery unit 6, releasing most of it in carbon dioxide stream 4. If sulfur species such as H2S and SO2 are present in the carbon dioxide feed, H2S can accumulate in the carbon dioxide recycle loop 7.

[0067] By passing through the RWGS reactor 3, SO2 is converted to H2S via the following reaction: SO2+3H2→H2S+2H2O Any COS present in the feed to 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] The carbon dioxide 4 is pressurized in a compressor (not shown) and recycled back to the inlet of the RWGS reactor 3. A CO sulfur guard bed 8 is placed after the pressurization of the 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 approximately 50°C. This may be achieved by adding an electric or steam heater, or by heat exchange with a hot process fluid. In the CO 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 the downstream Fischer-Tropsch synthesis catalyst, the syngas 5 from the CO2 capture unit 6 is compressed to approximately 5 MPa absolute pressure using a syngas compressor (not shown) and then subjected to gas cleaning to reduce impurities to an appropriate level. The hot gas exiting the syngas compressor is heated to 250 °C via an interchanger and, optionally, by using a steam or electric heater. HCN is then hydrolyzed to NH3 over activated high-surface-area alumina in the HCN hydrolysis bed 9. A water supply line 10, such as boiler feed water or demineralized water, is installed upstream of the HCN hydrolysis bed 9 to provide sufficient water for HCN hydrolysis. Water addition is preferably performed upstream of the final heater to minimize the risk of bed wetting due to steam generation. The HCN hydrolysis bed 9 is located upstream of the syngas sulfur guard bed 11, which contains a zinc oxide adsorbent, 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 may be released, posing a risk to personnel.

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

[0072] Next, the synthesis gas recovered from the synthesis gas sulfur guard bed 11 is 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, 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 that are present in the syngas or that are 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 synthesis gas, a carbonyl guard bed 15 is provided downstream of the synthesis gas 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) and subsequently by steam or electric heaters (not shown) to about 150° C. The oxygen guard bed 16 contains platinum- or palladium-loaded 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 can then be fed to a FT unit (not shown).

[0082] The foregoing detailed description has been provided for purposes of illustration and example, and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments set forth herein will be apparent to those skilled in the art and remain within the scope of the appended claims and their equivalents. The disclosure of the present invention may include the following aspects. (Aspect 1) 1. A method for forming 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 to convert at least a portion of the sulfur compounds to 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. (Aspect 2) 2. The method of embodiment 1, wherein the liquid hydrocarbon comprises an alkane. (Aspect 3) 3. The method of any one of aspects 1 to 2, wherein the hydrogen is generated by electrolysis of water. (Aspect 4) Aspect 4. The method of any one of aspects 1-3, wherein the sulfur compounds comprise one or more of sulfur dioxide, mercaptans, disulfides, thiophenes, and carbonyl sulfides. (Aspect 5) Aspect 5. The method of any one of aspects 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 wherein 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. (Aspect 6) Aspect 6. The method of any one of aspects 1 to 5, wherein the reverse water gas shift reaction chamber comprises a catalyst comprising nickel. (Aspect 7) Aspect 7. The method of any one of aspects 1-6, wherein the reverse water gas shift reaction chamber is at a temperature of at least 700°C. (Aspect 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 Aspect 8. The method of any one of aspects 1 to 7, wherein a liquid physical absorbent is used, preferably selected from one or more of methanol, glycol, or glycol ether. (Aspect 9) Aspect 9. The method of any one of aspects 1 to 8, wherein the hydrogen sulfide removal unit comprises a particulate bed of copper adsorbent, preferably a particulate bed comprising copper hydroxycarbonate adsorbent. (Aspect 10) 10. The method of claim 9, wherein the bed is at a temperature of from 0 to 150°C, preferably from 10 to 100°C. (Aspect 11) 1. A method for producing liquid hydrocarbons from synthesis gas, the method comprising: forming a synthesis gas according to a method according to any one of claims 1 to 10; and passing the synthesis gas through a Fischer-Tropsch reaction chamber to produce a liquid hydrocarbon product. (Aspect 12) 12. The method of claim 11, wherein the temperature of the Fischer-Tropsch reaction chamber is between 150 °C and 300 °C. (Aspect 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. (Aspect 14) Aspect 14. The method of any one of aspects 11 to 13, wherein the molar ratio of hydrogen to carbon monoxide in the synthesis gas is 1.8 to 2.2. (Aspect 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 enriched in ammonia and depleted in hydrogen cyanide; 15. The method of any one of aspects 11-14, 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. (Aspect 16) 16. The method of aspect 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. (Aspect 17) 17. The method of embodiment 16, wherein the catalytic hydrolysis is carried out at a temperature above 100°C, preferably from 150°C to 300°C. (Aspect 18) 18. The method of any one of claims 16 to 17, wherein the hydrolysis is carried out using an alumina catalyst, preferably an activated alumina catalyst. (Aspect 19) Aspect 19. The method of any one of aspects 15-18, wherein the first synthesis gas comprises less than 10 ppbv hydrogen cyanide. (Aspect 20) Aspect 20. The method of any one of aspects 15-19, wherein the second synthesis gas comprises less than 10 ppbv ammonia. (Aspect 21) passing the synthesis gas through the Fischer-Tropsch reaction chamber to produce liquid hydrocarbon products and by-product water; 21. The method of any one of aspects 15-20, wherein the scrubbing liquor comprises by-product water recovered from the Fischer-Tropsch reaction chamber. (Aspect 22) 22. The method of any one of aspects 15-21, 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 before passing the first syngas through the scrubber. (Aspect 23) 23. The method of claim 22, wherein the sulfur guard bed comprises zinc oxide. (Aspect 24) 24. The method of any one of claims 22 to 23, wherein the sulfur guard bed is operated at a temperature from 15 to 230°C. (Aspect 25) 25. The method of any one of aspects 22-24, wherein the second syngas comprises a metal carbonyl, and the method further comprises 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 carbonyl from the second syngas. (Aspect 26) 26. The method of claim 25, wherein the carbonyl guard bed comprises activated carbon. (Aspect 27) 27. The method of any one of claims 25 to 26, wherein the carbonyl guard bed is operated at a temperature of from 15 to 250°C, preferably from 50 to 150°C. (Aspect 28) 28. The method of any one of aspects 25-27, 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 before passing the second syngas through the Fischer-Tropsch reaction chamber to remove oxygen from the second syngas. (Aspect 29) 29. The method of embodiment 28, wherein the oxygen guard bed comprises a catalyst comprising platinum and / or palladium supported on alumina. (Aspect 30) 30. The method of any one of claims 28 to 29, wherein the oxygen guard bed is operated at a temperature of 100 to 250°C.

Claims

1. 1. A method for forming 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 to convert at least a portion of the sulfur compounds to 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 carbon dioxide removal unit comprises: Liquid chemical absorbents, and / or 10. The method of claim 1, wherein a liquid physical absorbent is used.

3. 10. The method of claim 1, wherein the hydrogen sulfide removal unit comprises a particulate bed of copper sorbent.

4. The method of claim 3, wherein the bed is at a temperature of from 0 to 150°C.

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

6. 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 enriched in ammonia and depleted in hydrogen cyanide; 6. The method of claim 5, 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.

7. 7. The method of claim 6, 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.

8. 8. The method of claim 7, wherein the catalytic hydrolysis is carried out at a temperature above 100°C.

9. 8. The method of claim 7, wherein the hydrolysis is carried out using an alumina catalyst.

10. passing the synthesis gas through the Fischer-Tropsch reaction chamber produces liquid hydrocarbon products and by-product water; The method of claim 6 , wherein the scrubbing liquor comprises by-product water recovered from the Fischer-Tropsch reaction chamber.

11. 7. The method of claim 6, 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 before passing the first syngas through the scrubber.

12. 12. The method of claim 11, wherein the sulfur guard bed comprises zinc oxide.

13. 12. The method of claim 11, wherein the sulfur guard bed is operated at a temperature of from 15 to 230°C.

14. 12. The method of claim 11 , wherein the second syngas comprises a metal carbonyl, the method further comprising adding an oxygen-containing gas to the second syngas before passing the second syngas to the Fischer-Tropsch reaction chamber, and passing the second syngas through a carbonyl guard bed to remove the metal carbonyl from the second syngas.

15. 15. The method of claim 14, wherein the carbonyl guard bed comprises activated carbon.

16. 15. The method of claim 14, wherein the carbonyl guard bed is operated at a temperature of from 15 to 250°C.

17. 15. The method of claim 14, wherein the method further comprises passing the second syngas through an oxygen guard bed after passing the second syngas through the carbonyl guard bed to remove oxygen from the second syngas before passing the second syngas through the Fischer-Tropsch reaction chamber.

18. 18. The method of claim 17, wherein the oxygen guard bed comprises a catalyst comprising platinum and / or palladium supported on alumina.

19. 18. The method of claim 17, wherein the oxygen guard bed is operated at a temperature of from 100 to 250°C.

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