IPC분류정보
국가/구분 |
United States(US) Patent
등록
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국제특허분류(IPC7판) |
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출원번호 |
US-0625106
(2009-11-24)
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등록번호 |
US-8241400
(2012-08-14)
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발명자
/ 주소 |
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출원인 / 주소 |
- L'Air Liquide Societe Anonyme pour l'Etude et l'Exploitation des Procedes Georges Claude
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대리인 / 주소 |
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인용정보 |
피인용 횟수 :
0 인용 특허 :
18 |
초록
▼
The present invention provides a process for recovering gaseous hydrogen and gaseous carbon dioxide from a mixture of hydrocarbons by utilizing a system that includes a reformer unit, an optional water gas shift reactor, and a pressure swing adsorption unit in conjunction with a carbon dioxide purif
The present invention provides a process for recovering gaseous hydrogen and gaseous carbon dioxide from a mixture of hydrocarbons by utilizing a system that includes a reformer unit, an optional water gas shift reactor, and a pressure swing adsorption unit in conjunction with a carbon dioxide purification unit such as a cryogenic purification unit or a catalytic oxidizer. In this process, purified CO2 from the CO2 purification unit is used as a co-feed/co-purge in the pressure swing adsorption unit in order to produce a CO2 tail gas that includes a higher concentration of CO2.
대표청구항
▼
1. A process for recovering gaseous hydrogen and gaseous carbon dioxide from a mixture of hydrocarbons utilizing a reformer unit in conjunction with a pressure swing adsorption unit and a cryogenic purification unit, the process comprising the steps of: a) generating a hydrogen rich effluent that al
1. A process for recovering gaseous hydrogen and gaseous carbon dioxide from a mixture of hydrocarbons utilizing a reformer unit in conjunction with a pressure swing adsorption unit and a cryogenic purification unit, the process comprising the steps of: a) generating a hydrogen rich effluent that also contains at least carbon monoxide, carbon dioxide, methane and water vapor from one or more hydrocarbon feed streams in a reformer unit;b) optionally treating the hydrogen rich effluent in a water gas shift reactor in order to further enrich the hydrogen content of the hydrogen rich effluent and to also increase the carbon dioxide content in the hydrogen rich effluent by oxidizing a portion of the carbon monoxide present in the effluent to carbon dioxide thereby obtaining a water shift effluent;c) providing a pressure swing adsorption unit having at least two adsorption vessels that each contain two or more adsorbent beds, the at least two adsorption vessels being parallel to one another and being independently operated on a cycle that includes an adsorption step, a co-feed step, a depressurization step, a regeneration step and a re-pressurization step, with the proviso that the cycles in the at least two adsorption vessels run consecutively with at least one of the adsorption vessels being in a different step of the cycle compared to at least one of the remaining adsorption vessels and the two or more adsorbent beds having an intermediate draw area positioned between at least two of the adsorbent beds thereby allowing for the withdrawal of a methane rich gas stream from the intermediate draw area during the co-feed step of the hydrogen pressure swing adsorption cycle;d) introducing the hydrogen rich effluent or water gas shift effluent into at least one of the adsorption vessels of the pressure swing adsorption unit during the adsorption step of the hydrogen pressure swing adsorption cycle in order to allow for the recovery of a high purity gaseous hydrogen stream from the hydrogen rich effluent or the water gas shift effluent and the adsorption of the carbon monoxide, carbon dioxide, methane, water vapor and remaining hydrogen onto the adsorbents in the adsorbent beds of the pressure swing adsorption unit, the adsorption step being carried out at a pressure from about 250 psig to about 700 psig;e) withdrawing the high purity gaseous hydrogen stream from the pressure swing adsorption unit during the adsorption step and passing this high purity gaseous hydrogen stream on for further use;f) allowing the at least one adsorption vessel to enter into the co-feed step while introducing a purified carbon dioxide stream obtained from the downstream cryogenic purification unit in order to allow the carbon dioxide to displace methane and carbon monoxide adsorbed onto the adsorbents in the adsorbent beds thereby producing a methane rich stream;g) withdrawing the methane rich stream from the intermediate draw area positioned between at least two of the adsorbent beds and recycling this methane rich stream to the reformer unit;h) allowing the at least one adsorption vessel to enter the depressurization step by depressurizing the adsorbent beds of the at least one adsorption vessel in order to release the carbon dioxide, carbon monoxide, methane, water vapor and hydrogen adsorbed to the adsorbents in the adsorbent beds thereby producing a carbon dioxide rich pressure swing adsorption tail gas having an increased concentration of carbon dioxide;i) withdrawing the carbon dioxide rich pressure swing adsorption tail gas from the pressure swing adsorption unit;j) regenerating and re-pressurizing the adsorbent beds for further use;k) compressing the carbon dioxide rich pressure swing adsorption tail gas in a compressor unit to a pressure that ranges from about 250 psig to about 1000 psig in order to obtain a compressed carbon dioxide rich pressure swing adsorption tail gas;l) introducing the compressed carbon dioxide rich pressure swing adsorption tail gas into a cryogenic purification unit in order to produce a carbon dioxide purified stream and an incondensibles stream that contains methane, carbon monoxide and hydrogen; andm) withdrawing the carbon dioxide purified stream from the cryogenic purification unit and recycling at least a portion of the carbon dioxide purified stream to the pressure swing adsorption unit where the carbon dioxide purified stream is introduced into the adsorption vessels during the co-feed step of the cycle in order to increase the concentration of carbon dioxide in the hydrogen pressure swing adsorption tail gas. 2. The process of claim 1, wherein the reformer unit is selected from a steam hydrocarbon reformer unit and an oxygen fed autothermal reformer unit. 3. The process of claim 2, wherein the adsorption vessel contains four adsorbent beds with two of the adsorbent beds being adjacent to one another on one side of the intermediate draw area and the remaining two adsorbent beds being positioned on the other side of the intermediate draw area. 4. The process of claim 2, wherein the adsorption vessel comprises a first adsorbent bed that is separated from a second adsorbent bed by the intermediate draw area. 5. The process of claim 4, wherein the first adsorbent bed and the second adsorbent bed each independently comprise one or more adsorbents selected from activated alumina, silica gel, activated carbon, zeolites, and combinations thereof. 6. The process of claim 5, wherein the one or more adsorbents are in layers within the individual adsorbent beds. 7. The process of claim 4, wherein the first adsorbent bed contains one or more adsorbents that are selective for methane and carbon monoxide and the second adsorbent bed contains one or more adsorbents that are selective for carbon dioxide and water vapor. 8. The process of claim 7, wherein the one or more adsorbents are in layers within the individual beds. 9. The process of claim 7, wherein when the hydrogen rich effluent or the water gas shift effluent is introduced into the adsorption vessel during the adsorption step of the hydrogen pressure swing adsorption cycle, the hydrogen rich effluent or the water gas shift effluent comes into contact with the first adsorbent bed before it comes into contact with the second adsorbent bed. 10. The process of claim 2, wherein the carbon dioxide purified stream is introduced into the co-feed step of the pressure swing adsorption cycle at a pressure that is higher than the pressure during the adsorption step of the pressure swing adsorption cycle. 11. The process of claim 10, wherein the pressure during the co-feed step of the pressure swing adsorption cycle is from about 300 psig to about 750 psig. 12. The process of claim 2, wherein the CO2 recovered during the depressurization step of the pressure swing adsorption cycle is collected at two or more different pressure levels utilizing a compressor. 13. The process of claim 12, wherein the pressure levels of the various stages of the carbon dioxide compressor are the same as the pressure levels in the depressurization step of the pressure swing adsorption cycle. 14. The process of claim 1, wherein the portion of the carbon dioxide purified stream obtained from the cryogenic purification unit that is not utilized as a co-feed in the co-feed step of the pressure swing adsorption cycle is further compressed for additional use. 15. A process for recovering gaseous hydrogen and gaseous carbon dioxide from a mixture of hydrocarbons utilizing a reformer unit in conjunction with a pressure swing adsorption unit and a cryogenic purification unit, the process comprising the steps of: a) generating a hydrogen rich effluent that also contains at least carbon monoxide, carbon dioxide, methane and water vapor from one or more hydrocarbon feed streams in a reformer unit;b) optionally treating the hydrogen rich effluent in a water gas shift reactor in order to further enrich the hydrogen content of the hydrogen rich effluent and to also increase the carbon dioxide content in the hydrogen rich effluent by oxidizing a portion of the carbon monoxide present in the effluent to carbon dioxide thereby obtaining a water shift effluent;c) providing a pressure swing adsorption unit having at least two adsorption vessels, each adsorption vessel comprising two sections that are separate from one another and connected by a pipe that allows for the withdrawal of a methane rich gas stream from the pipe during the co-feed step of the hydrogen pressure swing adsorption cycle, each section of the adsorption vessels independently containing two or more adsorbent beds, the at least two adsorption vessels being parallel to one another and being independently operated on a cycle that includes an adsorption step, a co-feed step, a depressurization step, a regeneration step and a re-pressurization step, with the proviso that the cycles in the at least two adsorption vessels run consecutively with at least one of the adsorption vessels being in a different step of the cycle compared to at least one of the remaining adsorption vessels;d) introducing the hydrogen rich effluent or water gas shift effluent into at least one of the adsorption vessels of the pressure swing adsorption unit during the adsorption step of the hydrogen pressure swing adsorption cycle in order to allow for the recovery of a high purity gaseous hydrogen stream from the hydrogen rich effluent or the water gas shift effluent and the adsorption of the carbon monoxide, carbon dioxide, methane, water vapor and remaining hydrogen onto the adsorbents in the adsorbent beds of the pressure swing adsorption unit, the adsorption step being carried out at a pressure from about 250 psig to about 700 psig;e) withdrawing the high purity gaseous hydrogen stream from the pressure swing adsorption unit during the adsorption step and passing this high purity gaseous hydrogen stream on for further use;f) allowing the at least one adsorption vessel to enter into the co-feed step while introducing a purified carbon dioxide stream obtained from the downstream cryogenic purification unit into the lower (second) section, in order to allow the carbon dioxide to displace methane and carbon monoxide adsorbed onto the adsorbents in the adsorbent beds thereby producing a methane rich stream; The upper (first) section is isolated from the lower section.g) withdrawing the methane rich stream from the pipe positioned between the two sections of the adsorption vessel and recycling this methane rich stream to the reformer unit;h) allowing the at least one adsorption vessel to enter the depressurization step by depressurizing the adsorbent beds of the at least one adsorption vessel in order to release the carbon dioxide, carbon monoxide, methane, water vapor and hydrogen adsorbed to the adsorbents in the adsorbent beds thereby producing a carbon dioxide rich pressure swing adsorption tail gas having an increased concentration of carbon dioxide;i) withdrawing the carbon dioxide rich pressure swing adsorption tail gas from the pressure swing adsorption unit;j) regenerating and re-pressurizing the adsorbent beds for further use;k) compressing the carbon dioxide rich pressure swing adsorption tail gas in a compressor unit to a pressure that ranges from about 250 psig to about 1000 psig in order to obtain a compressed carbon dioxide rich pressure swing adsorption tail gas;l) introducing the compressed carbon dioxide rich pressure swing adsorption tail gas into a cryogenic purification unit in order to produce a carbon dioxide purified stream and an incondensibles stream that contains methane, carbon monoxide and hydrogen; andm) withdrawing the carbon dioxide purified stream from the cryogenic purification unit and recycling at least a portion of the carbon dioxide purified stream to the pressure swing adsorption unit where the carbon dioxide purified stream is introduced into the adsorption vessels during the co-feed step of the cycle in order to increase the concentration of carbon dioxide in the pressure swing adsorption tail gas. 16. The process of claim 15, wherein the reformer unit is selected from a steam hydrocarbon reformer unit and an oxygen fed autothermal reformer unit. 17. The process of claim 16, wherein each section of the adsorption vessel comprises two or more adsorbent beds that are adjacent to one another within each section of the adsorption vessel. 18. The process of claim 16, wherein the pipe further contains a first valve which allows for the withdrawing of the methane rich stream between the two sections of the adsorption vessel during the co-feed step of the pressure swing adsorption cycle. 19. The process of claim 18, wherein the pipe further contains a means of isolating the first section of the adsorption vessel from the second section of the adsorption vessel during the withdrawal of the methane rich stream from the pipe through the first valve. 20. The process of claim 19, wherein the means of isolating the first section of the adsorption vessel from the second section of the adsorption vessel comprises a second valve which remains closed during the withdrawal of the methane rich stream from the pipe. 21. The process of claim 15, wherein the first section of the adsorption vessel contains adsorbent beds that include an adsorbent that is selective for methane, carbon monoxide, and nitrogen and the second section of the adsorption vessel contains adsorbent beds that include an adsorbent that allows for the removal of carbon dioxide. 22. The process of claim 21, wherein the pipe that connects the two sections of the adsorption vessel includes a means for isolating the two adsorption vessel sections from one another during the depressurization step of the pressure swing adsorption cycle, thus preventing the methane, carbon monoxide and nitrogen adsorbed to the adsorbent in the first section of the adsorption vessel from mixing with the carbon dioxide adsorbed to the adsorbent of the second section of the adsorption vessel or the carbon dioxide from flowing back into the first section of the adsorption vessel. 23. The process of claim 15, wherein the carbon dioxide purified stream is introduced into the co-feed step of the pressure swing adsorption cycle at a pressure that is higher than the pressure during the adsorption step of the pressure swing adsorption cycle. 24. The process of claim 23, wherein the pressure during the co-feed step of the pressure swing adsorption cycle is from about 300 psig to about 750 psig. 25. The process of claim 15, wherein the carbon dioxide recovered during the depressurization step of the pressure swing adsorption cycle is collected at two or more different pressure levels utilizing a compressor. 26. The process of claim 25, wherein the pressure levels of the various stages of the carbon dioxide compressor are the same as the pressure levels in the depressurization step of the pressure swing adsorption cycle. 27. A process for recovering gaseous hydrogen and gaseous carbon dioxide from a mixture of hydrocarbons utilizing a reformer unit in conjunction with a pressure swing adsorption unit and a catalytic oxidizer unit, the process comprising the steps of: a) generating a hydrogen rich effluent that also contains at least carbon monoxide, carbon dioxide, methane and water vapor from one or more hydrocarbon feed streams in a reformer unit;b) optionally treating the hydrogen rich effluent in a water gas shift reactor in order to further enrich the hydrogen content of the hydrogen rich effluent and to also increase the carbon dioxide content in the hydrogen rich effluent by oxidizing a portion of the carbon monoxide present in the effluent to carbon dioxide thereby obtaining a water shift effluent;c) providing a pressure swing adsorption unit having at least two adsorption vessels that each contain two or more adsorbent beds, the at least two adsorption vessels being parallel to one another and being independently operated on a cycle that includes an adsorption step, a co-feed step, a depressurization step, a regeneration step and a re-pressurization step, with the proviso that the cycles in the at least two adsorption vessels run consecutively with at least one of the adsorption vessels being in a different step of the cycle compared to at least one of the remaining adsorption vessels and the two or more adsorbent beds having an intermediate draw area positioned between at least two of the adsorbent beds thereby allowing for the withdrawal of a methane rich gas stream from the intermediate draw area during the co-feed step of the hydrogen pressure swing adsorption cycle;d) introducing the hydrogen rich effluent or water gas shift effluent into at least one of the adsorption vessels of the pressure swing adsorption unit during the adsorption step of the hydrogen pressure swing adsorption cycle in order to allow for the recovery of a high purity gaseous hydrogen stream from the hydrogen rich effluent or the water gas shift effluent and the adsorption of the carbon monoxide, carbon dioxide, methane, water vapor and remaining hydrogen onto the adsorbents in the adsorbent beds of the pressure swing adsorption unit, the adsorption step being carried out at a pressure from about 250 psig to about 700 psig;e) withdrawing the high purity gaseous hydrogen stream from the pressure swing adsorption unit during the adsorption step and passing this high purity gaseous hydrogen stream on for further use;f) allowing the at least one adsorption vessel to enter into the co-feed step while introducing a purified carbon dioxide stream obtained from the downstream catalytic oxidizer unit in order to allow the carbon dioxide to displace methane and carbon monoxide adsorbed onto the adsorbents in the adsorbent beds thereby producing a methane rich stream;g) withdrawing the methane rich stream from the intermediate draw area positioned between at least two of the adsorbent beds and recycling this methane rich stream to the reformer unit;h) allowing the at least one adsorption vessel to enter the depressurization step by depressurizing the adsorbent beds of the at least one adsorption vessel in order to release the carbon dioxide, carbon monoxide, methane, water vapor and hydrogen adsorbed to the adsorbents in the adsorbent beds thereby producing a carbon dioxide rich pressure swing adsorption tail gas having an increased concentration of carbon dioxide;i) withdrawing the carbon dioxide rich pressure swing adsorption tail gas from the pressure swing adsorption unit;j) regenerating and re-pressurizing the adsorbent beds for further use;k) compressing the carbon dioxide rich pressure swing adsorption tail gas in a compressor unit to a pressure that ranges from about 250 psig to about 1000 psig in order to obtain a compressed carbon dioxide rich pressure swing adsorption tail gas;l) introducing the compressed carbon dioxide rich pressure swing adsorption tail gas into the catalytic oxidizer unit followed by introducing gaseous oxygen thereby allowing for the carbon monoxide, methane, and hydrogen to be combusted to produce an oxidized stream that contains carbon dioxide and water, the amount of oxygen being introduced being slightly below the stoichiometric requirement;m) condensing the oxidized stream to allow for the removal of water by cooling the oxidized stream to ambient temperature to produce a carbon dioxide purified stream; andn) withdrawing the carbon dioxide purified stream from the catalytic oxidizer unit and recycling at least a portion of the carbon dioxide purified stream to the pressure swing adsorption unit where the carbon dioxide purified stream is introduced into the adsorption vessels during the co-feed step of the cycle in order to increase the concentration of carbon dioxide in the hydrogen pressure swing adsorption tail gas. 28. The process of claim 27, wherein the reformer unit is selected from a steam hydrocarbon reformer unit and an oxygen fed autothermal reformer unit. 29. The process of claim 28, wherein the adsorption vessel contains four adsorbent beds with two of the adsorbent beds being adjacent to one another on one side of the intermediate draw area and the remaining two adsorbent beds being positioned on the other side of the intermediate draw area. 30. The process of claim 28, wherein the adsorption vessel comprises a first adsorbent bed that is separated from a second adsorbent bed by the intermediate draw area. 31. The process of claim 30, wherein the first adsorbent bed and the second adsorbent bed each independently comprises one or more adsorbents selected from activated alumina, silica gel, activated carbon, zeolites, and combinations thereof. 32. The process of claim 31, wherein the one or more adsorbents are in layers within the individual adsorbent beds. 33. The process of claim 30, wherein the first adsorbent bed contains one or more adsorbents that are selective for methane and carbon monoxide and the second adsorbent bed contains one or more adsorbents that are selective for carbon dioxide and water vapor. 34. The process of claim 33, wherein the one or more adsorbents are in layers within the individual beds. 35. The process of claim 33, wherein when the hydrogen rich effluent or the water gas shift effluent is introduced into the adsorption vessel during the adsorption step of the hydrogen pressure swing adsorption cycle, the hydrogen rich effluent or the water gas shift effluent comes into contact with the first adsorbent bed before it comes into contact with the second adsorbent bed. 36. The process of claim 28, wherein the carbon dioxide purified stream is introduced into the co-feed step of the pressure swing adsorption cycle at a pressure that is higher than the pressure during the adsorption step of the pressure swing adsorption cycle. 37. The process of claim 36, wherein the pressure during the co-feed step of the pressure swing adsorption cycle is from about 300 psig to about 750 psig. 38. The process of claim 28, wherein the CO2 recovered during the depressurization step of the pressure swing adsorption cycle is collected at two or more different pressure levels utilizing a compressor. 39. The process of claim 38, wherein the pressure levels of the various stages of the carbon dioxide compressor are the same as the pressure levels in the depressurization step of the pressure swing adsorption cycle. 40. The process of claim 27, wherein the portion of the carbon dioxide purified stream obtained from the cryogenic purification unit that is not utilized as a co-feed in the co-feed step of the pressure swing adsorption cycle is further compressed for additional use. 41. A process for recovering gaseous hydrogen and gaseous carbon dioxide from a mixture of hydrocarbons utilizing a reformer unit in conjunction with a pressure swing adsorption unit and a catalytic oxidizer unit, the process comprising the steps of: a) generating a hydrogen rich effluent that also contains at least carbon monoxide, carbon dioxide, methane and water vapor from one or more hydrocarbon feed streams in a reformer unit;b) optionally treating the hydrogen rich effluent in a water gas shift reactor in order to further enrich the hydrogen content of the hydrogen rich effluent and to also increase the carbon dioxide content in the hydrogen rich effluent by oxidizing a portion of the carbon monoxide present in the effluent to carbon dioxide thereby obtaining a water shift effluent;c) providing a pressure swing adsorption unit having at least two adsorption vessels, each adsorption vessel comprising two sections that are separate from one another and connected by a pipe that allows for the withdrawal of a methane rich gas stream from the pipe during the co-feed step of the hydrogen pressure swing adsorption cycle, each section of the adsorption vessels independently containing two or more adsorbent beds, the at least two adsorption vessels being parallel to one another and being independently operated on a cycle that includes an adsorption step, a co-feed step, a depressurization step, a regeneration step and a re-pressurization step, with the proviso that the cycles in the at least two adsorption vessels run consecutively with at least one of the adsorption vessels being in a different step of the cycle compared to at least one of the remaining adsorption vessels;d) introducing the hydrogen rich effluent or water gas shift effluent into at least one of the adsorption vessels of the pressure swing adsorption unit during the adsorption step of the hydrogen pressure swing adsorption cycle in order to allow for the recovery of a high purity gaseous hydrogen stream from the hydrogen rich effluent or the water gas shift effluent and the adsorption of the carbon monoxide, carbon dioxide, methane, water vapor and remaining hydrogen onto the adsorbents in the adsorbent beds of the pressure swing adsorption unit, the adsorption step being carried out at a pressure from about 250 psig to about 700 psig;e) withdrawing the high purity gaseous hydrogen stream from the pressure swing adsorption unit during the adsorption step and passing this high purity gaseous hydrogen stream on for further use;f) allowing the at least one adsorption vessel to enter into the co-feed step while introducing a purified carbon dioxide stream obtained from the downstream catalytic oxidizer unit into the lower (second) section, in order to allow the carbon dioxide to displace methane and carbon monoxide adsorbed onto the adsorbents in the adsorbent beds thereby producing a methane rich stream;g) withdrawing the methane rich stream from the pipe positioned between the two sections of the adsorption vessel and recycling this methane rich stream to the reformer unit;h) allowing the at least one adsorption vessel to enter the depressurization step by depressurizing the adsorbent beds of the at least one adsorption vessel in order to release the carbon dioxide, carbon monoxide, methane, water vapor and hydrogen adsorbed to the adsorbents in the adsorbent beds thereby producing a carbon dioxide rich pressure swing adsorption tail gas having an increased concentration of carbon dioxide;i) withdrawing the carbon dioxide rich pressure swing adsorption tail gas from the pressure swing adsorption unit;j) regenerating and re-pressurizing the adsorbent beds for further use;k) compressing the carbon dioxide rich pressure swing adsorption tail gas in a compressor unit to a pressure that ranges from about 250 psig to about 1000 psig in order to obtain a compressed carbon dioxide rich pressure swing adsorption tail gas;l) introducing the compressed carbon dioxide rich pressure swing adsorption tail gas into a catalytic oxidizer unit followed by introducing gaseous oxygen thereby allowing for the carbon monoxide, methane, and hydrogen to be combusted to produce an oxidized stream that contains carbon dioxide and water, the amount of oxygen being introduced being slightly below the stoichiometric requirement;m) condensing the oxidized stream to allow for the removal of water by cooling the oxidized stream to ambient temperature to produce a carbon dioxide purified stream; andn) withdrawing the carbon dioxide purified stream from the catalytic oxidizer unit and recycling at least a portion of the carbon dioxide purified stream to the pressure swing adsorption unit where the carbon dioxide purified stream is introduced into the adsorption vessels during the co-feed step of the cycle in order to increase the concentration of carbon dioxide in the pressure swing adsorption tail gas. 42. The process of claim 41, wherein the reformer unit is selected from a steam hydrocarbon reformer unit and an oxygen fed autothermal reformer unit. 43. The process of claim 42, wherein each section of the adsorption vessel comprises two or more adsorbent beds that are adjacent to one another within each section of the adsorption vessel. 44. The process of claim 42, wherein the pipe further contains a first valve which allows for the withdrawing of the methane rich stream between the two sections of the adsorption vessel during the co-feed step of the pressure swing adsorption cycle. 45. The process of claim 44, wherein the pipe further contains a means of isolating the first section of the adsorption vessel from the second section of the adsorption vessel during the withdrawal of the methane rich stream from the pipe through the first valve. 46. The process of claim 45, wherein the means of isolating the first section of the adsorption vessel from the second section of the adsorption vessel comprises a second valve which remains closed during the withdrawal of the methane rich stream from the pipe. 47. The process of claim 41, wherein the first section of the adsorption vessel contains adsorbent beds that include an adsorbent that is selective for methane, carbon monoxide, and nitrogen and the second section of the adsorption vessel contains adsorbent beds that include an adsorbent that allows for the removal of carbon dioxide. 48. The process of claim 47, wherein the pipe that connects the two sections of the adsorption vessel includes a means for isolating the two adsorption vessel sections from one another during the depressurization step of the pressure swing adsorption cycle, thus preventing the methane, carbon monoxide and nitrogen adsorbed to the adsorbent in the first section of the adsorption vessel from mixing with the carbon dioxide adsorbed to the adsorbent of the second section of the adsorption vessel or the carbon dioxide from flowing back into the first section of the adsorption vessel. 49. The process of claim 41, wherein the carbon dioxide purified stream is introduced into the co-feed step of the pressure swing adsorption cycle at a pressure that is higher than the pressure during the adsorption step of the pressure swing adsorption cycle. 50. The process of claim 49, wherein the pressure during the co-feed step of the pressure swing adsorption cycle is from about 300 psig to about 750 psig. 51. The process of claim 41, wherein the carbon dioxide recovered during the depressurization step of the pressure swing adsorption cycle is collected at two or more different pressure levels utilizing a compressor. 52. The process of claim 51, wherein the pressure levels of the various stages of the carbon dioxide compressor are the same as the pressure levels in the depressurization step of the pressure swing adsorption cycle.
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