Search

US-12618011-B2 - Process for synthesising hydrocarbons

US12618011B2US 12618011 B2US12618011 B2US 12618011B2US-12618011-B2

Abstract

A process for synthesising hydrocarbons is described comprising the steps of (a) making a synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide from a feedstock in a synthesis gas generation unit, (b) removing carbon dioxide to produce a carbon dioxide stream and purified synthesis gas comprising hydrogen and carbon monoxide for synthesis in a Fischer-Tropsch hydrocarbon synthesis unit wherein (i) at least a portion of the FT water stream is fed to an electrolysis unit to provide an oxygen stream, which is fed to the synthesis gas generation unit. Carbon dioxide stream recovered from the carbon dioxide removal unit and a portion of the hydrogen stream produced by the electrolysis unit are fed to a reverse water-gas shift unit to produce a carbon monoxide stream, with carbon monoxide stream from the reverse water-gas shift unit is fed to the Fischer-Tropsch hydrocarbon synthesis unit.

Inventors

  • Henry Arthur CLAXTON
  • Andrew James COE
  • Mark Joseph MCKENNA
  • Paul Robert TICEHURST

Assignees

  • JOHNSON MATTHEY DAVY TECHNOLOGIES LIMITED

Dates

Publication Date
20260505
Application Date
20210917
Priority Date
20201016

Claims (18)

  1. 1 . A process for synthesising hydrocarbons comprising the steps of (a) making a synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide from a feedstock in a synthesis gas generation unit, (b) removing carbon dioxide from the synthesis gas in a carbon dioxide removal unit to produce a carbon dioxide stream and purified synthesis gas comprising hydrogen and carbon monoxide, and (c) synthesising a mixture of hydrocarbons from the purified synthesis gas in a Fischer-Tropsch (FT) hydrocarbon synthesis unit, with co-production of a FT water stream, wherein (i) at least a portion of the FT water stream is fed to an electrolysis unit to provide an oxygen stream, which is fed to the synthesis gas generation unit, and a hydrogen stream, (ii) at least a portion of the carbon dioxide stream recovered from the carbon dioxide removal unit and a portion of the hydrogen stream produced by the electrolysis unit are fed to a reverse water-gas shift unit to produce a carbon monoxide stream, and (iii) at least a portion of the carbon monoxide stream from the reverse water-gas shift unit is fed to the Fischer-Tropsch hydrocarbon synthesis unit; wherein the FT water stream is treated upstream of the electrolysis unit to remove contaminants.
  2. 2 . The process according to claim 1 , wherein the feedstock comprises natural gas, associated gas, coal, biomass or municipal solid waste or equivalent containing non-biogenic carbon.
  3. 3 . The process according to claim 2 , wherein the feedstock is natural gas and the synthesis gas generation unit comprises a catalytic partial oxidation unit, a non-catalytic partial oxidation unit or an autothermal reformer.
  4. 4 . The process according to claim 2 , wherein the feedstock is coal, biomass or municipal solid waste or equivalent containing non-biogenic carbon and the synthesis gas generation unit comprises a gasifier, optionally with one or more downstream processing units selected from a partial oxidation unit, a tar reforming unit and purification reactors containing a purification material.
  5. 5 . The process according to claim 1 , wherein the carbon dioxide removal unit comprises a physical wash system or a reactive wash system.
  6. 6 . The process according to claim 1 , wherein the Fischer-Tropsch hydrocarbon synthesis unit comprises a tubular reactor in which catalyst carriers containing a Fischer-Tropsch catalyst are disposed within one or more tubes cooled by a cooling medium.
  7. 7 . The process according to claim 1 , further comprising a step (d) of upgrading the mixture of hydrocarbons synthesised in the Fischer-Tropsch hydrocarbon synthesis unit in a hydrotreating unit to produce hydrocarbon products.
  8. 8 . The process according to claim 7 , wherein the hydrotreating unit comprises one or more vessels containing a catalyst selected from a hydroisomerization catalyst, a hydrogenation catalyst, a hydrodeoxygenation catalyst, and/or a hydrocracking catalyst.
  9. 9 . The process according to claim 7 , wherein a portion of the hydrogen stream from the electrolysis unit is fed to the hydrotreating unit.
  10. 10 . The process according to claim 1 , wherein a water stream produced by the reverse water gas shift unit is fed to the electrolysis unit.
  11. 11 . The process according to claim 1 , wherein a portion of the hydrogen stream from the electrolysis unit is fed to the Fischer-Tropsch hydrocarbon synthesis unit.
  12. 12 . The process according to claim 1 , wherein an oxygen stream provided by the electrolysis unit is used to combust a portion of a feed gas comprising carbon dioxide and hydrogen fed to the reverse water-gas shift unit to raise the temperature of the feed gas.
  13. 13 . The process according to claim 1 , wherein water formed in the reverse water-gas shift unit is fed to the electrolysis unit.
  14. 14 . The process according to claim 1 , wherein a tail gas comprising one or more of methane, ethane, propane, butane and C5-C10 hydrocarbons, is recovered from the Fischer-Tropsch hydrocarbon synthesis unit, and is fed to the synthesis gas generation unit.
  15. 15 . The process according to claim 1 , wherein a tail gas comprising one or more of methane, ethane, propane, butane and C5-C10 hydrocarbons, is recovered from the Fischer-Tropsch hydrocarbon synthesis unit, and is subjected to a separate reforming step to form a reformed tail gas containing hydrogen, which is fed to the Fischer-Tropsch hydrocarbon synthesis unit and/or the reverse water-gas shift unit.
  16. 16 . The process according to claim 1 , wherein the hydrocarbon products recovered from the hydrotreating unit are fed to a separation unit to recover C1-C4 gases, a naphtha fraction, at least one kerosene and/or gas oil fraction and a heavy fraction.
  17. 17 . A system for performing the process according to claim 1 comprising (I) the synthesis gas generation unit, (II) the carbon dioxide removal unit coupled to the synthesis gas generation unit, and (III) the Fischer-Tropsch hydrocarbon synthesis unit coupled to the carbon dioxide removal unit, wherein: the electrolysis unit is coupled to the Fischer-Tropsch hydrocarbon synthesis unit, the reverse water-gas shift unit is coupled to the carbon dioxide removal unit and the electrolysis unit, and the Fischer-Tropsch hydrocarbon synthesis unit is coupled to the reverse water-gas shift unit.
  18. 18 . The system according to claim 17 , further comprising (IV) a hydrotreating unit coupled to the Fischer-Tropsch hydrocarbon synthesis unit for upgrading the mixture of hydrocarbons to produce hydrocarbon products.

Description

This invention relates to a process for synthesising hydrocarbons from synthesis gas comprising hydrogen and carbon monoxide. Processes for synthesis hydrocarbons from synthesis gases are known. For example, U.S. Pat. No. 9,163,180 discloses process for the conversion of carbon-based material to fuel bases by a hybrid route combining direct ebullient bed liquefaction and indirect liquefaction by gasification followed by a Fischer-Tropsch synthesis, including a stage of production of hydrogen resulting from non-fossil resources and a reverse water gas reaction stage. Electrolysis is used as a source of hydrogen for the liquefaction, reverse water reaction and Fischer-Tropsch synthesis. US2014288195 discloses a process for the thermochemical conversion of a carbon-based feedstock, such as biomass, to synthesis gas containing predominantly hydrogen and carbon monoxide comprising the following steps: (a) oxycombustion of the carbon-based feedstock to create a cogeneration of electricity and of heat; (b) high-temperature electrolysis of water using heat produced in step (a); (c) reverse water-gas shift reaction starting from the carbon dioxide produced in step (a) and from the hydrogen produced in step (b). We have realised that the process efficiency increased by using the water by-product of the Fischer-Tropsch synthesis in an electrolysis unit coupled to the reverse water-gas shift unit and Fischer-Tropsch synthesis unit. Accordingly the invention provides a process for synthesising hydrocarbons comprising the steps of (a) making a synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide from a feedstock in a synthesis gas generation unit, (b) removing carbon dioxide from the synthesis gas in a carbon dioxide removal unit to produce a carbon dioxide stream and purified synthesis gas comprising hydrogen and carbon monoxide, and (c) synthesising a mixture of hydrocarbons from the purified synthesis gas in a Fischer-Tropsch hydrocarbon synthesis unit, with co-production of a FT water stream, wherein (i) at least a portion of the FT water stream is fed to an electrolysis unit to provide an oxygen stream, which is fed to the synthesis gas generation unit, and a hydrogen stream, (ii) at least a portion of the carbon dioxide stream recovered from the carbon dioxide removal unit and a portion of the hydrogen stream produced by the electrolysis unit are fed to a reverse water-gas shift unit to produce a carbon monoxide stream, and (iii) at least a portion of the carbon monoxide stream from the reverse water-gas shift unit is fed to the Fischer-Tropsch hydrocarbon synthesis unit. The invention further provides a system for performing the process comprising (a) a synthesis gas generation unit for making a synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide from a feedstock, (b) a carbon dioxide removal unit coupled to the synthesis gas generation unit for removing carbon dioxide from the synthesis gas to produce a carbon dioxide stream and purified synthesis gas comprising hydrogen and carbon monoxide, and (c) a Fischer-Tropsch hydrocarbon synthesis unit coupled to the carbon dioxide removal unit for synthesising a mixture of hydrocarbons from the purified synthesis gas, with co-production of a FT water stream, wherein (i) an electrolysis unit is coupled to the Fischer-Tropsch hydrocarbon synthesis unit, configured to be fed with at least a portion of the FT water to provide an oxygen stream, which is configured to be fed to the synthesis gas generation unit, and a hydrogen stream, (ii) a reverse water-gas shift unit is coupled to the carbon dioxide removal unit and the electrolysis unit and configured to be fed with at least a portion of the carbon dioxide stream from the carbon dioxide removal unit and a portion of the hydrogen stream produced by the electrolysis unit, to produce a carbon monoxide stream, and (iii) the Fischer-Tropsch hydrocarbon synthesis unit is coupled to the reverse water-gas shift unit to receive at least a portion of the carbon monoxide stream. In the present invention, the carbon dioxide recovered from the synthesis gas by the carbon dioxide removal unit is combined with hydrogen from the FT water electrolysis unit and used in the reverse water-gas shift unit to produce additional carbon monoxide which is sent to the Fischer-Tropsch synthesis to increase the hydrocarbon product yield. FT water electrolysis may conveniently use electricity from renewable sources such as solar, wind or tidal power. By using renewable electricity, the overall carbon intensity of the process can be negative, resulting in overall negative carbon dioxide emissions. It also avoids the need to carbon capture and storage. Overall, the process of the present invention maximises the production of liquid fuels from the feed stock and helps to reduce carbon dioxide emissions. In the process of the invention the feedstock fed to the process may suitably comprise a gaseous feedstock such as natu