A PROCESS FOR SEPARATING H2 FROM A GAS MIXTURE

Abstract

The present invention relates a process for separating H.sub.2, preferably both H.sub.2 and CH.sub.4, from a gas mixture comprising H.sub.2 and CH.sub.4 by means of a series of selective membrane units that avoids compressors and vacuums as well as an apparatus for carrying out said separation.

Claims

1.-21. (canceled)

22. A process for separating H.sub.2 from a gas mixture comprising H.sub.2 and CH.sub.4, the process comprising (i) a separation stage comprising (i.1) passing a feed gas stream F1 comprising H.sub.2 and CH.sub.4 at a molar ratio n(H.sub.2):n(CH.sub.4)=x(F1), 0<x(F1)0.5, through a membrane unit A comprising at least one membrane, the at least one membrane having a H.sub.2/CH.sub.4 selectivity of at least 10, at a pressure ratio across said at least one membrane, calculated as (pressure of feed gas stream F1/pressure of permeate gas stream P1) at constant temperature, of greater than 1, obtaining a permeate gas stream P1 comprising H.sub.2 and CH.sub.4 at a molar ratio n(H.sub.2):n(CH.sub.4)=x(P1); x(P1)>x(F1); and a retentate gas stream R1 comprising H.sub.2 and CH.sub.4 at a molar ratio n(H.sub.2):n(CH.sub.4)=x(R1); x(R1)<x(F1); (i.2) passing retentate gas stream R1 as a further feed gas stream F2 through a further separation stage, F2 having the same composition as R1; (ii) a further separation stage comprising (ii.1) passing F2 through a membrane unit B comprising at least one membrane, the at least one membrane having a H.sub.2/CH.sub.4 selectivity of at least 10, at a pressure ratio across said at least one membrane, calculated as (pressure of feed gas stream F2/pressure of permeate gas stream P2) at constant temperature, of greater than 1, obtaining a permeate gas stream P2 comprising H.sub.2 and CH.sub.4 at a molar ratio n(H.sub.2):n(CH.sub.4)=x(P2) of at least 1.4; x(P2)>x(F2); and a retentate gas stream R2 comprising H.sub.2 and CH.sub.4 at a molar ratio n(H.sub.2):n(CH.sub.4)=x(R2) of <0.17; x(R2)<x(F2); (ii.2) optionally passing retentate gas stream R2 as a further feed gas stream F3 through a further separation stage (iii), F3 having the same composition as R2; (iii) an optional further separation stage comprising (iii.1) passing F3 through a further membrane unit C comprising at least one membrane, the at least one membrane having a H.sub.2/CH.sub.4 selectivity of at least 10, at a pressure ratio across said at least one membrane (calculated as the (pressure of feed gas stream F3/pressure of permeate gas stream P3) at constant temperature), of greater than 1, obtaining a permeate gas stream P3 comprising H.sub.2 and CH.sub.4 at a molar ratio n(H.sub.2):n(CH.sub.4)=x(P3) of at least 0.39; x(P3)>x(F3); and a retentate gas stream R3 comprising H.sub.2 and CH.sub.4 at a molar ratio n(H.sub.2):n(CH.sub.4)=x(R3) of 0.01.

23. The process of claim 22, wherein no vacuum apparatus or compressor is operated downstream of the membrane unit A in the obtainment of the permeate gas streams and/or retentate gas streams.

24. The process of claim 22, wherein the at least one membrane comprised in the respective membrane unit A, B and/or C has a H.sub.2/CH.sub.4 selectivity of at least 10.

25. The process of claim 22, wherein according to (i.1) the pressure ratio across the at least one membrane comprised in membrane unit A, calculated as (pressure of feed gas stream F1/pressure of permeate gas stream P1) at constant temperature, is of at least 4.

26. The process of claim 22, wherein the mole ratio x(F1) is in the range of from 0.05 to 0.5.

27. The process of claim 22, wherein feed gas stream F1 has pressure in the range of from 5 to 100 bar (abs); and wherein the feed gas stream F1 has a temperature in the range of from 30 C. to 60 C.

28. The process of claim 22, wherein the mole ratio x(P1) is of at least 2.

29. The process of claim 22, wherein the permeate gas stream P1 has a pressure in the range of from >1 to 50 bar(abs).

30. The process of claim 22, wherein the mole ratio x(R1) is of at most 0.49, and wherein the retentate gas stream R1 has a pressure in the range of from 29.5 to 75.5 bar (abs).

31. The process of claim 22, wherein according to (i.1) the flow rate ratio of feed gas F1 to the retentate gas stream R1 calculated as (flow rate F1/flow rate R1) is in the range of from >1 to 2.

32. The process of claim 22, wherein according to (ii.1) the pressure ratio across the at least one membrane comprised in membrane unit B, calculated as (pressure of feed gas stream F2/pressure of permeate gas stream P2) at constant temperature, is of at least 4.

33. The process of claim 22, wherein the mole ratio x(P2) is of at least 1.5; and wherein the permeate gas stream P2 has a pressure in the range of from >1 to 15 bar(abs).

34. The process of claim 22, wherein the mole ratio x(R2) is of at most 0.15, and wherein the retentate gas stream R2 has a pressure in the range of from 29 to 75 bar (abs).

35. The process of claim 22, wherein according to (ii.1) the flow rate ratio of feed gas F2 to the retentate gas stream R2 calculated as (flow rate F2/flow rate R2) is in the range of from 1.05 to 2.

36. The process of claim 22, wherein according to (iii.1) the pressure ratio across the at least one membrane comprised in membrane unit C, calculated as (pressure of feed gas stream F3/pressure of permeate gas stream P3) at constant temperature is of at least 20.

37. The process of claim 22, wherein the mole ratio x(R3) is of at most 0.009, and wherein the retentate gas stream R3 has a pressure in the range of from 28.5 to 74.5 bar (abs).

38. The process of claim 22, wherein according to (iii.1) the flow rate ratio of feed gas F3 to the retentate gas stream R3 calculated as (flow rate F3/flow rate R3) is in the range of from 1.01 to 1.6.

39. An apparatus for separating H.sub.2, from a gas mixture comprising H.sub.2 and CH.sub.4, the apparatus comprising (I) a unit comprising (I.a) a feeding means for passing a feed gas stream F1 comprising H.sub.2 and CH.sub.4 to a membrane unit A; (I.b) the membrane unit A connected to the feeding means for passing a feed gas stream F1 according to (I.a), said membrane unit comprising at least one membrane, the at least one membrane having a H.sub.2/CH.sub.4 selectivity of at least 10; (I.c) an exiting means connected to the membrane unit A, for removing a permeate gas stream P1 from the membrane unit A; (Id) an exiting means connected to the membrane unit A for removing a retentate gas stream R1 from the membrane unit A; (II) a unit comprising (II.a) a feeding means, connected to the exiting means according to (Id), for passing the gas stream R1 as a feed gas F2 to a membrane unit B; (II.b) the membrane unit B connected to the feeding means for passing a feed gas stream F2 according to (II.a), said membrane unit comprising at least one membrane, the at least one membrane having a H.sub.2/CH.sub.4 selectivity of at least 10; (II.c) an exiting means connected to the membrane unit B for removing a permeate stream P2 from the membrane unit B; (II.d) an exiting means connected to the membrane unit B for removing a retentate stream R2 from the membrane unit B; (III) optionally a unit comprising (III.a) a feeding means, connected to the exiting means according to (II.d), said feeding means for passing the gas stream F3 to a membrane unit C; (III.b) the membrane unit C connected to the feeding means according to (III.a), said membrane unit comprising at least one membrane, the at least one membrane having a H.sub.2/CH.sub.4 selectivity of at least 10; (III.c) an exiting means connected to the membrane unit C for removing a permeate stream P3 from the membrane unit C; (III.d) an exiting means connected to the membrane unit C for removing a retentate stream R3 from the membrane unit C.

40. The apparatus of claim 39, wherein, in unit (I), there is no compressor upstream of the membrane unit A; wherein no vacuum apparatus is disposed downstream of the membrane unit A; and wherein in the unit (II), there is no compressor for compressing the gas exiting the unit (I), upstream of the membrane unit B.

41. A process for the production of ammonia, comprising using a permeate gas stream P1 and/or P2, obtained according to a process according to claim 22, as a reductant.

42. A process selected from the group consisting of acetylene production, methanol production, olefin production, power generation and combinations of two or more thereof, the process comprising using a retentate gas R2 and/or R3, obtained according to a process according to claim 22, as a hydrocarbon source.

Description

DESCRIPTION OF THE FIGURE

[0383] FIG. 1 Shown is a schematic of an apparatus according to preferred embodiments of the present invention. A feed stream F1 of a gas mixture comprising, preferably consisting of, H.sub.2 and CH.sub.4, is introduced into unit (I) comprising a membrane unit A. The feed stream F1 passes through the membrane unit A and is separated into permeate gas stream P1 and retentate gas stream R1. The hydrogen concentration present in P1 is greater than R1 and F1. R1 can be optionally divided into feed gas stream F2 and gas stream S1. The composition of feed gas F2 and optionally gas stream S1 is the same as retentate gas stream R1. Retentate gas stream R1 is passed as feed gas F2 into unit (II) comprising membrane unit B. The feed stream F2 passes through the membrane unit B and is separated into permeate gas stream P2 and retentate gas stream R2. The hydrogen concentration present in P2 is greater than R2 and F2. R1 can be optionally divided into feed gas stream F3 and gas stream S2. The composition of feed gas F3 and optionally gas stream S2 is the same as retentate gas stream R2. P2 can be further purified optionally for use as a reductant. Retentate gas stream R2 is passed as feed gas F3 into unit (III) comprising membrane unit C. The feed stream F3 passes through the membrane unit C and is separated into permeate gas stream P3 and retentate gas stream R3. The hydrogen concentration present in P3 is greater than R3 and F3. R3 has a hydrogen to methane mole ratio of 0.01 or less. P3 can optionally be further purified for use as a reductant or used as an energy source preferably for heating.

[0384] For instance when all streams are active in a three unit system as described above where membrane units A to C have a selectivity of 200; a simulation calculated with [0385] F1 having a pressure of 51 bar (abs) and a H.sub.2/CH.sub.4 molar ratio of 0.25 was separated by membrane unit A of unit (I) into [0386] P1 having a pressure ratio (pressure F1/P1 at constant T) of 10.2, a flow ratio of (flow F1/P1) of 15.43, and a H.sub.2/CH.sub.4 molar ratio of 19 and; [0387] R1 having a pressure of 50.5 bar (abs), a flow ratio of (flow F1/R1) of 1.069, and a H.sub.2/CH.sub.4 molar ratio of 0.174, R1 was further divided into F2 and S1 having the same composition and pressure of R1 with a flow ratio of (flow R1/F2) of 1.38 and a flow ratio of (flow R1/S1) of 3.58; [0388] F2 was further separated by membrane unit B of unit (II) into [0389] P2 having a pressure ratio (pressure F2/P2 at constant T) of 10.1, a flow ratio of (flow F2/P2) of 7.14, and a H.sub.2/CH.sub.4 molar ratio of 2.98 and; [0390] R2 having a pressure of 50 bar (abs), a flow ratio of (flow F2/R2) of 1.16, and a H.sub.2/CH.sub.4 molar ratio of 0.053, R2 was further divided into F3 and S2 having the same composition and pressure of R2 with a flow ratio of (flow R2/F3) of 3.04 and a flow ratio of (flow R2/S2) of 1.49; [0391] F3 was further separated by membrane unit C of unit (III) into [0392] P3 having a pressure ratio (pressure F3/P3 at constant T) of 38.5, a flow ratio of (flow F3/P3) of 15.28, and a H.sub.2/CH.sub.4 molar ratio of 1.6 and [0393] R3 having a pressure of 49.5 bar (abs), a flow ratio of (flow F3/R3) of 1.07, and a H.sub.2/CH.sub.4 molar ratio of 0.01.

CITED LITERATURE

[0394] Saltonstall, C. W., Calculation of the membrane area required for gas separations, Journal of Membrane Science, 1987, Volume 32, Issues 2-3, pages 185 to 193. [0395] Deutscher Verein des Gas- und Wasserfaches e.V. (2019), Anforderungen, Mglichkeiten und Grenzen der Abtrennung von Wasserstoff aus Wasser-stoff/Erdgasgemischen [0396] EP 2979743 A1