Method for processing fischer-tropsch off-gas

Patent metadata

Field	Value
Publication number	US-9682342-B2
Application number	US-201314758449-A
Country	US
Kind code	B2
Filing date	Dec 31, 2013
Priority date	Dec 31, 2012
Publication date	Jun 20, 2017
Grant date	Jun 20, 2017

Abstract

This invention concerns a method for recovering carbon monoxide and carbon dioxide from Fischer-Tropsch off-gas by feeding Fischer-Tropsch off-gas through a column comprising an adsorbent bed, and discharging effluent, optionally rinsing the column and the adsorbent bed by feeding carbon dioxide and discharging effluent until at least 60% of the carbon monoxide that was present in the bed is discharged, pressurizing the column and adsorbent bed with carbon dioxide, rinsing the column and the adsorbent bed by feeding carbon dioxide, until at least 60% of the methane and optionally an amount equal to at least 50% of the carbon dioxide present at the commencement of this rinsing step is discharged, rinsing the column and adsorbent bed by feeding a mixture of hydrogen and nitrogen, pressurizing the column and adsorbent bed by feeding a mixture of hydrogen and nitrogen. With this method a feed comprising at least 50 vol % carbon monoxide can be produced. Furthermore, methane and carbon dioxide at a high pressure can be recovered from the Fischer-Tropsch gas. This can be fed to a gasifier or a reformer. In a preferred embodiment a gas comprising at least 80 vol % hydrogen is produced as well.

First claim

The invention claimed is:

1. A method for recovering carbon monoxide and carbon dioxide from a gas mixture comprising 5-50 vol % methane, 10-50 vol % carbon dioxide, 20-65 vol % carbon monoxide, 10-40 vol % hydrogen and 10-55 vol % nitrogen, calculated on the total volume of the gas mixture, said method comprising, in sequence, the following steps:
(1) feeding a gas mixture through a column comprising an adsorbent bed, said gas mixture comprising 5-50 vol % methane, 10-50 vol % carbon dioxide, 20-65 vol % carbon monoxide, 10-40 vol % hydrogen and 10-55 vol % nitrogen, calculated on the total volume of the gas mixture, the adsorbent bed comprising alumina, a carbon molecular sieve, silicalite, activated carbon, a zeolite, or mixtures thereof,
with upon commencement of said feeding, the bed and column being pre-saturated and pre-pressurized to a pressure in the range of 10 to 80 bar absolute (bar a), with pure hydrogen, or with a mixture of hydrogen and nitrogen, and
discharging effluent from the other end of said bed, and
continuing said feeding and said discharging until a carbon monoxide comprising gas has reached at least 45% of the length of the bed and has reached at most 80% of the length of the bed, calculated from the end of the bed at which the gas mixture is being fed; and

(2) ceasing the feeding of the gas mixture comprising 5-50 vol % methane, 10-50 vol % carbon dioxide, 20-65 vol % carbon monoxide, 10-40 vol % hydrogen and 10-55 vol % nitrogen, and reducing the pressure in the column and the bed by about 5 to 25 bar a, and
(3) optionally rinsing the column and the adsorbent bed by feeding a gas comprising at least 95 vol % carbon dioxide through the column and adsorbent bed,
the column and bed being at a pressure in the range of 5 to 75 bar a, and
discharging effluent from the other end of said bed, and
continuing said feeding and said discharging until at least 60% of the carbon monoxide that was present in the bed at the commencement of this rinsing step is discharged from the other end of said bed;

(4) pressurizing the column and adsorbent bed by about 5 to 25 bar a by feeding a gas comprising at least 95 vol % carbon dioxide,
(5) rinsing the column and the adsorbent bed by feeding a gas comprising at least 95 vol % carbon dioxide, through the column and adsorbent bed,
the column and bed being at a pressure in the range of 30 to 80 bar a, and
discharging effluent from the other end of said bed, and
continuing said feeding and said discharging until
at least 60% of the methane that was present in the bed at the commencement of this rinsing step is discharged from the other end of said bed, and

(6) ceasing the feeding of a gas comprising at least 95 vol % carbon dioxide, and reducing the pressure of the column and adsorbent bed to a pressure in the range of 1 to 5 bar a; and
(7) rinsing the column and adsorbent bed by feeding a mixture of hydrogen and nitrogen through the column and adsorbent bed
the column and bed being at a pressure in the range of 1 to 5 bar a, and

(8) pressurizing the column and adsorbent bed to a pressure in the range of 15 to 75 bar a by feeding a mixture of hydrogen and nitrogen.

2. A method according to claim 1 , wherein the feeding and discharging of step (5) are continued until
at least 60% of the methane that was present in the bed at the commencement of this rinsing step is discharged from the other end of said bed, and
an amount of carbon dioxide equal to at least 50% of the amount of carbon dioxide that was present at the commencement of this rinsing step is discharged from the other end of said bed.

3. A method according to claim 1 , wherein step (3) is performed.

4. A method according to claim 1 , wherein repeated cycles of steps (1) to (8) are performed.

5. A method according to claim 1 , wherein at least two columns that comprise an adsorbent bed are used for steps (1) to (8).

6. A method according to claim 5 , wherein the columns for steps (1) to (8) are connected in parallel.

7. A method according to claim 1 , wherein at least a part of the discharged effluent of step (3) is sent as feed to a Fischer-Tropsch reaction.

8. A method according to claim 1 , wherein the column and adsorbent bed are rinsed in step (7)
by feeding a gas comprising at least 95 vol % nitrogen through the column and adsorbent bed,
followed by feeding a mixture of hydrogen and nitrogen through the column and adsorbent bed,
the column and bed being at a pressure in the range of 1 to 5 bar a.

9. A method according to claim 1 , wherein a part of the effluent of step (2) is used as feeding gas in step (7).

10. A method according to claim 9 , wherein additionally a part of the effluent of step (1) is used as feeding gas in step (7).

11. A method according to claim 1 , wherein a part of the effluent of step (1) is used as feeding gas in step (8).

12. A method according to claim 11 , wherein additionally a part of the effluent of step (2) is used as feeding gas in step (8).

13. A method according to claim 1 , wherein a scrubbed Fischer-Tropsch off-gas from a Fischer-Tropsch reactor is fed to the column and adsorbent bed in step (1), and a part of the effluent of step (3) is sent as a recycle stream to the Fischer-Tropsch reactor that produced the off-gas.

14. A method according to claim 1 , wherein a scrubbed Fischer-Tropsch off-gas from a first Fischer-Tropsch reactor is used in step (1), and a part of the effluent of step (3) is sent as a feed stream to a second Fischer-Tropsch reactor.

15. A method according to claim 1 further comprising, in sequence, the following steps:
(A) feeding the effluent of step (1) through a column comprising an adsorbent bed, the adsorbent bed comprising alumina, a carbon molecular sieve, silicalite, activated carbon, a zeolite, or mixtures thereof,
with upon commencement of said feeding, the bed and column being pre-saturated and pre-pressurized to a pressure in the range of 20 to 80 bar absolute (bar a) with a gas comprising more than 95 volume % hydrogen, and
discharging effluent from the other end of said bed, and
continuing said feeding and said discharging until a nitrogen comprising gas has reached at least 45% of the length of the bed and has reached at most 80% of the length of the bed, calculated from the end of the bed at which the gas mixture is being fed; and

(B) ceasing the feeding of the effluent of step (1), and reducing the pressure in the column and the bed by about 2 to 5 bar a; and
(C) further reducing the pressure in the column and the bed by about 2 to 5 bar a; and
(D) reducing the pressure of the column and adsorbent bed to a pressure in the range of 1 to 5 bar a; and
(E) rinsing the column and adsorbent bed by feeding a gas comprising more than 95 volume % hydrogen through the column and adsorbent bed
the column and bed being at a pressure in the range of 1 to 5 bar a, and

(F) pressurizing the column and adsorbent bed to a pressure in the range of 5 to 50 bar a by feeding a gas comprising more than 95 volume % hydrogen and
(G) further pressurizing the column and adsorbent bed to a pressure in the range of 15 to 75 bar a by feeding a gas comprising more than 95 volume % hydrogen.

16. A method according to claim 15 , wherein repeated cycles of steps (A) to (G) are performed.

17. A method according to claim 15 , wherein at least two columns that comprise an adsorbent bed are used for steps (A) to (G).

18. A method according to claim 17 , wherein the columns for steps (A) to (G) are connected in parallel.

19. A method acco

Assignees

• Shell Oil Co

Inventors

• Sadasivan Vijayakumari Sivakumar

Classifications

• C10K1/32

  with selectively adsorptive solids, e.g. active carbon · CPC title

• B01D2253/106

  Silica or silicates · CPC title

• B01D53/047 Primary

  Pressure swing adsorption · CPC title

• B01D2253/116

  Molecular sieves other than zeolites · CPC title

• C10G2300/1022

  Fischer-Tropsch products · CPC title