Method for producing liquid hydrocarbons

Abstract

The Fischer-Tropsch (FT) process with a hybrid membrane / PSA configuration provides high component recovery rates from FT off-gas with minimal power consumption. Syngas from the syngas generation zone is reacted within the FT reaction zone to form a liquid stream and an off-gas stream. The off-gas from the FT reaction zone containing hydrogen, carbon monoxide, and methane reactants is recycled to the syngas generation zone. The purge stream from the recycle loop is sent to a membrane separation unit where it is separated into a permeate stream and a residue stream. The residue stream is separated within a pressure swing adsorption (PSA) unit into a fuel gas stream and a second stream. The second stream can be compressed and recycled to the syngas generation zone.

Description

Technical Field

[0001] (Priority Claim) This application claims the benefit of U.S. Provisional Patent Application No. 63 / 370,387, filed Aug. 4, 2022, which is hereby incorporated by reference in its entirety.

Background Art

[0002] The Fischer-Tropsch (FT) process can be used to produce sustainable aviation fuel (SAF) and other liquid hydrocarbon fuels. The FT process converts syngas into liquid hydrocarbons, which can be upgraded to fuels such as jet fuel in a fuel refining zone. The offgas from the FT reaction zone contains valuable hydrogen, carbon monoxide, and methane reactants and is recycled within the process to the syngas production zone. However, the FT offgas also contains inert gases such as nitrogen and argon. Since the inert gases accumulate within the process, they must be purged from the system. The purge stream also contains hydrogen and carbon-containing reactants (carbon monoxide and methane), resulting in loss of valuable reactants to the fuel and carbon emissions to the atmosphere.

[0003] Accordingly, there is a need for a process to efficiently and selectively purge the inert components from the FT process without excessive loss of hydrogen and carbon-containing reactants to the fuel gas and without increasing carbon emissions from the process.

Brief Description of the Drawings

[0004]

Figure 1

Mode for Carrying Out the Invention

[0005] The present invention relates to a Fischer-Tropsch (FT) process for producing sustainable aviation fuel (SAF) or other hydrocarbon liquid fuels from synthesis gas. The process includes a synthesis gas generation zone where synthesis gas is generated. The synthesis gas reacts in an FT reaction zone that includes an FT reactor. The liquid stream from the FT reaction zone can be sent to a fuel purification zone for further processing into various fuel products such as jet fuel. The offgas from the FT reaction zone contains beneficial hydrogen (molecular hydrogen), carbon monoxide, and methane reactants and is recycled within the process to the synthesis gas generation zone. A purge stream is withdrawn from the recycle loop to prevent the accumulation of inert gases such as nitrogen and / or argon. An efficient recovery system for the purge stream has been developed to recover hydrogen, methane, and carbon monoxide while selectively removing nitrogen from the fuel gas stream.

[0006] A hybrid membrane / pressure swing adsorption (PSA) configuration provides high component recovery rates with minimal power consumption. A unique PSA design has been developed to selectively recover both methane and carbon monoxide from the membrane residue gas with respect to nitrogen. Adsorbents include, but are not limited to, activated carbon and sodium Y zeolite. Other adsorbents that may be mentioned include activated alumina, silica gel, 5A zeolite, and 13X zeolite. For example, an activated carbon layer (20 - 80 volume %) at the feed end of the bed, followed by sodium Y zeolite (20 - 80 volume %) at the product end of the bed, has been found to provide high methane and carbon monoxide recovery rates compared to nitrogen. This scheme provides high methane and carbon monoxide recovery rates within the PSA unit while retaining the advantage of high H2 recovery rates of membrane separation. The adsorbent split and PSA cycle parameters can be optimized for selective methane and carbon monoxide recovery with respect to nitrogen.

[0007] Synthesis gas is generated from a feed stream containing a hydrocarbon or carbonaceous feedstock within a synthesis gas production zone. Suitable feed streams include, but are not limited to, natural gas, liquefied petroleum gas, naphtha, coal, biomass, etc., or combinations thereof.

[0008] The synthesis gas production zone includes a synthesis gas reactor. Suitable synthesis gas reactors include, but are not limited to, a steam reforming unit with an optional gas heating reformer, an autothermal reforming unit with an optional gas heating reformer, or a gasification unit, or a partial oxidation (POX) unit, a dry reforming unit, or combinations thereof.

[0009] The composition of the synthesis gas can vary depending on the process used to produce it. For example, a typical synthesis gas composition (dry basis) from a biomass gasification unit can be 20 - 50 mol% carbon monoxide, 20 - 40 mol% molecular hydrogen, 0 - 10 mol% methane, 10 - 30 mol% carbon dioxide, 0 - 2 mol% nitrogen, and 0 - 0.5 mol% argon.

[0010] The synthesis gas production zone can also include at least one treatment zone. A synthesis gas treatment unit can be used to adjust the H2:CO molar ratio and / or remove contaminants upstream of the FT reactor. Suitable treatment zones include, but are not limited to, an aqueous gas shift reactor, a carbon dioxide recovery unit, a contaminant removal zone, or combinations thereof.

[0011] Carbon dioxide is recovered from the synthesis gas (for sequestration) within a carbon dioxide recovery unit. Suitable carbon dioxide recovery units include, but are not limited to, an amine separation unit, a cryogenic separation unit, or a carbon dioxide PSA unit, or combinations thereof.

[0012] Suitable pollutant removal zones include, but are not limited to, sulfur removal zones. Suitable sulfur removal zones include, but are not limited to, hydrodesulfurization reactors, sulfur guard beds (e.g., guard beds containing zinc oxide), or combinations thereof.

[0013] The molar ratio of H2:CO in the syngas from the syngas reactor is adjusted in one or more of the processing zones within the syngas production zone such that the syngas is suitable in the FT reaction zone. The molar ratio of H2:CO ranges from 0.5 to 3.0, or 1.0 to 3.0, or 1.5 to 3.0, or 0.5 to 2.5, or 1.0 to 2.5, or 1.5 to 2.5, or 1.7 to 2.2.

[0014] The syngas is converted to liquid hydrocarbons in the FT reactor. The hydrocarbon products derived from the Fischer-Tropsch reaction range from methane to high molecular weight paraffin waxes containing more than 50 carbon atoms. A number of catalysts incorporating active metals such as iron, cobalt, ruthenium, rhenium, etc. are used to carry out the reaction, and both saturated and unsaturated hydrocarbons can be produced. The synthesis reaction is highly exothermic and temperature sensitive, so temperature control is required to maintain the desired hydrocarbon product selectivity. Suitable catalysts and reaction conditions can be selected by those skilled in the art.

[0015] The FT reaction zone produces a liquid hydrocarbon stream and an offgas stream. The liquid hydrocarbon stream can be sent to a fuel refining zone for purification to produce various types of fuels such as jet fuel. The fuel refining zone can include a hydrotreating zone.

[0016] The FT off-gas stream contains hydrogen, carbon monoxide, methane, and an inert gas such as nitrogen and / or argon. For example, the off-gas stream may contain 36 mol% hydrogen, 35 mol% carbon monoxide, 28 mol% methane, 0.4 mol% carbon dioxide, and 0.6 mol% nitrogen (dry basis). The temperature of the FT off-gas stream can be 40 - 70 °C, and the pressure can be 3 - 5 MPa(g). Most of the FT off-gas stream is recycled to the syngas production zone and / or the FT reaction zone (or both) for the conversion of residual methane, carbon monoxide, and hydrogen.

[0017] To prevent the accumulation of inert gas in the recycle loop, a purge stream is removed from the recycled off-gas stream. It is sent to a membrane separation unit where it is separated into a permeate stream and a retentate stream. The permeate stream contains hydrogen. For example, the permeate stream may contain 82 mol% hydrogen, 12 mol% carbon monoxide, 5 mol% methane, 0.8 mol% carbon dioxide, and 0.15 mol% nitrogen. The temperature of the permeate stream can be 40 - 70 °C, and the pressure can be 0.1 - 1.0 MPa(g). All or part of the permeate stream can be recycled to the FT reactor and / or the fuel purification zone. Alternatively, all or part of the permeate stream can be used elsewhere in the plant.

[0018] The retentate stream contains carbon monoxide, methane, and inert gas. For example, the retentate stream may contain 2 mol% hydrogen, 52 mol% carbon monoxide, 45 mol% methane, 0.2 mol% carbon dioxide, and 0.8 mol% nitrogen. The temperature of the retentate stream can be 40 - 80 °C, and after cooling, it can be 30 - 50 °C, and the pressure can be 3 - 5 MPa(g). The retentate stream is separated in a pressure swing adsorption (PSA) unit into a fuel gas stream and a second stream.

[0019] The fuel gas stream includes an inert gas and a first portion of methane and carbon monoxide. For example, the fuel gas stream may include 6 mol% hydrogen, 90 mol% carbon monoxide, 2 mol% methane, 0.0 mol% carbon dioxide, and 2 mol% nitrogen. The temperature of the fuel gas stream can be 30 - 50 °C and the pressure can be 3 - 5 MPa(g). The fuel gas stream can be recovered and used as fuel gas in various processes within the plant.

[0020] The second stream includes a second portion of methane and carbon monoxide. There is more carbon monoxide in the second stream than in the fuel gas stream. For example, the second stream can contain more than 50%, or more than 60%, or more than 70%, or more than 80% carbon monoxide in the residual stream. For example, the second stream may include 0.4 mol% hydrogen, 41 mol% carbon monoxide, 58 mol% methane, 0.2 mol% carbon dioxide, and 0.4 mol% nitrogen. The temperature of the second stream can be 0 - 30 °C and the pressure can be 0.03 - 0.1 MPa(g). The second stream can be compressed and recycled to the syngas production zone.

[0021] In some embodiments where oxygen is required in the syngas production zone, such as autothermal reforming, gasification, or partial oxidation, an electrolyzer can be used to produce oxygen and hydrogen, preferably using renewable electricity. The oxygen can be used in the syngas production zone and the hydrogen can be used in the FT reaction zone and / or the fuel purification zone.

[0022] Process 100 is shown in the figure. Feed stream 105 is introduced into the syngas production zone 110. The syngas production zone 110 can include one or more reactors and, as discussed above, can optionally include one or more treatment zones.

[0023] The effluent 115 from the syngas production zone 110 is sent to the FT reaction zone 120. The FT process produces a liquid hydrocarbon stream 125 and an FT offgas stream 130. The liquid hydrocarbon stream 125 can be quality - improved by purification in the fuel purification zone 132.

[0024] The FT offgas stream 130 containing hydrogen, carbon monoxide, methane, and an inert gas can be recycled to the syngas production zone 110.

[0025] The purge stream 135 is removed from the FT offgas stream 130 and sent to the membrane separation unit 140 where it is separated into a permeate stream 145 and a residue stream 150. The permeate stream 145 containing hydrogen can be compressed and recycled to the FT reaction zone 120 or the fuel purification zone 132, or used elsewhere in the plant.

[0026] The residue stream 150 containing carbon monoxide, methane, and an inert gas is sent to the PSA unit 155 where it is separated into a fuel gas stream 160 and a second stream 165. The fuel gas stream 160 containing the inert gas and some carbon monoxide is used as fuel gas. The second stream 165 containing carbon monoxide and methane is sent back to the syngas production zone 110 and / or the FT reaction zone 120.

Example

[0027] A computer simulation was performed for the process shown in the figure. The syngas production zone included a gasification zone with a biomass feedstock. An electrolyzer was used to produce oxygen for the gasification reactor, hydrogen for the fuel purification zone, and additional hydrogen for the FT reaction zone. The purge stream from the offgas recycle loop was first sent to a membrane unit for the selective permeation of hydrogen. This hydrogen in the membrane permeate was combined with the electrolyzer product hydrogen and sent to the FT reaction zone and the fuel purification zone. The membrane residue gas was sent to a PSA unit for the selective recovery of methane and carbon monoxide in the PSA tail gas. This tail gas stream was sent to the syngas production zone after compression. The first portion of the inert gas (nitrogen) and carbon monoxide was removed in the high-pressure product stream from the PSA unit and sent to fuel.

[0028] The results of the process simulation are shown in Table 1 below. By adding a PSA unit to the residual stream, the recovery of valuable methane and carbon monoxide reactants becomes possible, avoiding the carbon emissions associated with the combustion of these components in the fuel gas stream. Rather, they are recycled within the system and ultimately converted into sustainable aviation fuel.

[0029] [Table 1]

[0030] Specific embodiments The following is described in conjunction with specific embodiments, but it should be understood that this description is illustrative of the scope of the preceding description and the appended claims and is not intended to limit them.

[0031] In a first embodiment of the present invention, a feed stream containing a hydrocarbon or carbonaceous feedstock is introduced into a syngas production zone including a syngas reactor to produce a syngas stream containing syngas having a molar ratio of hydrogen to carbon monoxide in the range of 0.5 to 3.0; the syngas stream is reacted in an FT reaction zone including a Fischer-Tropsch (FT) reactor to form a liquid hydrocarbon stream containing liquid hydrocarbons and an FT offgas stream containing hydrogen, carbon monoxide, methane, and an inert gas; a portion of the FT offgas stream is recycled to the syngas production zone or the FT reaction zone, or both the syngas production zone and the FT reaction zone; a purge stream is removed from the FT offgas stream; the purge stream is separated in a membrane separation unit to form a permeate stream containing hydrogen and a residue stream containing carbon monoxide, methane, and an inert gas; the residue stream is separated in a pressure swing adsorption (PSA) unit into a fuel gas stream containing an inert gas and a first portion of carbon monoxide and methane, and a second stream containing a second portion of carbon monoxide and methane; and the second stream is introduced into the syngas production zone or the FT reaction zone, or both the syngas production zone and the FT reaction zone. This is a process for producing liquid hydrocarbons. One embodiment of the present invention further includes introducing the permeate stream into the FT reaction zone or a fuel purification zone, or both the FT reaction zone and the fuel purification zone, and is any one, any combination, or all of the previous embodiments up to the first embodiment of this paragraph. One embodiment of the present invention is that the syngas reactor includes a steam reforming unit having an optional gas heating reformer, or an autothermal reforming unit having an optional gas heating reformer, or a gasification unit, or a partial oxidation (POX) unit, or a dry reforming unit, or a combination thereof, and is any one, any combination, or all of the previous embodiments up to the first embodiment of this paragraph. One embodiment of the present invention is that the syngas production zone further includes at least one treatment zone including an aqueous gas shift reactor, a carbon dioxide recovery unit, a contaminant removal zone, or a combination thereof, and is any one, any combination, or all of the previous embodiments up to the first embodiment of this paragraph.One embodiment of the present invention is that the carbon dioxide recovery unit includes an amine separation unit, or a cryogenic separation unit, or a carbon dioxide PSA unit, or a combination thereof, one, any, or all of the previous embodiments of this paragraph up to the first embodiment of this paragraph. One embodiment of the present invention is that the pollutant removal zone includes a sulfur substance removal zone, one, any, or all of the previous embodiments of this paragraph up to the first embodiment of this paragraph. One embodiment of the present invention further includes introducing an oxygen stream into the syngas production zone, one, any, or all of the previous embodiments of this paragraph up to the first embodiment of this paragraph. One embodiment of the present invention further includes electrolyzing water to form an oxygen stream and a hydrogen stream, one, any, or all of the previous embodiments of this paragraph up to the first embodiment of this paragraph. One embodiment of the present invention is that the inert gas includes nitrogen or argon, or both, one, any, or all of the previous embodiments of this paragraph up to the first embodiment of this paragraph. One embodiment of the present invention is that the second portion of carbon monoxide is larger than the first portion of carbon monoxide, one, any, or all of the previous embodiments of this paragraph up to the first embodiment of this paragraph. One embodiment of the present invention further includes compressing the second stream before introducing the second stream into the syngas production zone or the FT reaction zone, or both the syngas production zone and the FT reaction zone, one, any, or all of the previous embodiments of this paragraph up to the first embodiment of this paragraph. One embodiment of the present invention further includes purifying the liquid hydrocarbon stream in a fuel purification zone to produce jet fuel, one, any, or all of the previous embodiments of this paragraph up to the first embodiment of this paragraph. One embodiment of the present invention is that the fuel purification zone is a hydrotreating zone, one, any, or all of the previous embodiments of this paragraph up to the first embodiment of this paragraph. One embodiment of the present invention further includes recovering a fuel gas stream, one, any, or all of the previous embodiments of this paragraph up to the first embodiment of this paragraph.

[0032] In a second embodiment of the present invention, a feed stream containing a hydrocarbon or carbonaceous feedstock is introduced into a syngas production zone including a syngas reactor to produce a syngas stream containing syngas having a molar ratio of hydrogen to carbon monoxide in the range of 0.5 to 3.0; reacting the syngas stream in an FT reaction zone including a Fischer-Tropsch (FT) reactor to form a liquid hydrocarbon stream containing liquid hydrocarbons and an FT offgas stream containing hydrogen, carbon monoxide, methane, and an inert gas; recycling a portion of the FT offgas stream to the syngas production zone or the FT reaction zone, or both the syngas production zone and the FT reaction zone; removing a purge stream from the FT offgas stream; separating the purge stream in a membrane separation unit to form a permeate stream containing hydrogen and a residue stream containing carbon monoxide, methane, and an inert gas; separating the residue stream in a pressure swing adsorption (PSA) unit into a fuel gas stream containing an inert gas and a first portion of carbon monoxide and methane, and a second stream containing a second portion of carbon monoxide and methane, wherein the second portion of carbon monoxide is greater than the first portion of carbon monoxide; introducing the second stream into the syngas production zone or the FT reaction zone, or both the syngas production zone and the FT reaction zone; introducing the permeate stream into the FT reaction zone or a fuel purification zone, or both the FT reaction zone and the fuel purification zone; and recovering the fuel gas stream. A process for producing liquid hydrocarbons, which includes: One embodiment of the present invention is that the syngas reactor includes a steam reforming unit having an optional gas heating reformer, or an autothermal reforming unit having an optional gas heating reformer, or a gasification unit, or a partial oxidation (POX) unit, or a dry reforming unit, or a combination thereof, any one, or all of the previous embodiments of this paragraph up to the second embodiment of this paragraph. One embodiment of the present invention is that the syngas production zone further includes at least one processing zone including an aqueous gas shift reactor, a carbon dioxide recovery unit, a contaminant removal zone, or a combination thereof, any one, or all of the previous embodiments of this paragraph up to the second embodiment of this paragraph.One embodiment of the present invention is one, any, or all of the previous embodiments of this paragraph up to the second embodiment of this paragraph, wherein the inert gas contains nitrogen or argon, or both. One embodiment of the present invention is one, any, or all of the previous embodiments of this paragraph up to the second embodiment of this paragraph, wherein the second portion of carbon monoxide is greater than the first portion of carbon monoxide. One embodiment of the present invention is one, any, or all of the previous embodiments of this paragraph up to the second embodiment of this paragraph, further comprising compressing the second stream before introducing the second stream into the syngas production zone.

[0033] Without further elaboration, using the foregoing description, those skilled in the art can utilize the present invention to the greatest extent without departing from the spirit and scope of the present invention, and can easily identify the essential characteristics of the present invention, make various changes and modifications to the present invention, and adapt it to various uses and conditions. Therefore, the foregoing preferred specific embodiments should be construed as illustrative only and not as limiting in any way the remainder of the disclosure, which is intended to cover various modifications and equivalent configurations within the scope of the appended claims.

[0034] In the above, all temperatures are described in degrees Celsius, and all parts and percentages are by weight unless otherwise indicated.

Claims

Claim 1 A process for producing liquid hydrocarbons, comprising: introducing a feed stream (105) comprising a hydrocarbon or carbonaceous feedstock into a syngas production zone (110) comprising a syngas reactor to produce a syngas stream (115) comprising syngas having a molar ratio of hydrogen to carbon monoxide in the range of 0.5 to 3.0; reacting the syngas stream (115) in an FT reaction zone (120) comprising a Fischer-Tropsch (FT) reactor to form a liquid hydrocarbon stream (125) comprising the liquid hydrocarbons and an FT offgas stream (130) comprising hydrogen, carbon monoxide, methane, and an inert gas; recirculating a portion of the FT offgas stream (130) to the syngas production zone (110) or the FT reaction zone (120), or both the syngas production zone (110) and the FT reaction zone (120); removing a purge stream (135) from the FT offgas stream (130); separating the purge stream (135) in a membrane separation unit (140) to form a permeate stream (145) comprising hydrogen and a residue stream (150) comprising the carbon monoxide, the methane, and the inert gas; separating the residue stream (150) in a pressure swing adsorption (PSA) unit (155) into a fuel gas stream (160) comprising the inert gas and a first portion of the carbon monoxide and the methane, and a second stream (165) comprising a second portion of the carbon monoxide and the methane; introducing the second stream (165) into the syngas production zone (110) or the FT reaction zone (120), or both the syngas production zone (110) and the FT reaction zone (120). A process for producing liquid hydrocarbons. Claim 2 The process according to claim 1, further comprising introducing the permeate stream (145) into the FT reaction zone (120) or a fuel purification zone (132), or both the FT reaction zone (120) and the fuel purification zone (132). Claim 3 The process according to claim 1 or 2, wherein the syngas reactor comprises a steam reforming unit having an optional gas heating reformer, or an autothermal reforming unit having an optional gas heating reformer, or a gasification unit, or a partial oxidation (POX) unit, or a dry reforming unit, or a combination thereof.

4. The process according to claim 1 or 2, wherein the syngas generation zone (110) further comprises at least one treatment zone including a water gas shift reactor, a carbon dioxide recovery unit, a pollutant removal zone, or a combination thereof.

5. The process according to claim 4, wherein the carbon dioxide recovery unit includes an amine separation unit, or a cryogenic separation unit, or a carbon dioxide PSA unit, or a combination thereof.

6. The process according to claim 4, wherein the pollutant removal zone includes a sulfur removal zone.

7. The process according to claim 1 or 2, wherein the inert gas includes nitrogen or argon, or both.

8. The process according to claim 1 or 2, wherein the second portion of the carbon monoxide is greater than the first portion of the carbon monoxide.

9. The process according to claim 1 or 2, further comprising compressing the second stream (165) before introducing the second stream (165) into the syngas generation zone (110) or the FT reaction zone (120), or both the syngas generation zone (110) and the FT reaction zone (120).

10. The process according to claim 1 or 2, further comprising purifying the liquid hydrocarbon stream in a fuel purification zone (132) to produce jet fuel.

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