Membrane process for LPG recovery

Abstract

Liquefied Petroleum Gas (LPG) can be recovered from various streams using a multiple membrane recovery process producing hydrogen stream at high yield and high purity and a C3+ LPG stream at high yield with low energy expenditure.

Description

DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic of a typical LPG recovery process utilizing a single membrane separation unit producing a single valuable stream.

FIG. 2 is a schematic of preferred embodiments of an improved LPG recovery process of the present invention using an integration of two membrane separation units producing three streams: a high purity LPG stream, a high purity hydrogen stream, and a H₂ lean/enriched C₂⁻ stream.

Claims

1. A process for the recovery of a C3+ rich LPG stream and a high purity hydrogen stream from a hydrocarbon-containing feedstream comprised of hydrogen and C1, C2 and C3+ hydrocarbons, comprising: (a) feeding the hydrocarbon feedstream into a first membrane separation unit wherein the hydrocarbon-containing feedstream is contacted with a first side of at least one first rubbery polymer membrane,(b) retrieving a first retentate product stream which has a higher hydrogen mol % than the hydrocarbon-containing feedstream from the first side of the first rubbery polymer membrane and retrieving a first permeate product stream which has a higher C3+ mol % than the hydrocarbon-containing feedstream from a second side of the first rubbery polymer membrane,(c) feeding the first permeate product stream to a compressor wherein the first permeate product stream is raised in pressure,(d) feeding the higher pressure first permeate product stream to a knockout drum,(e) retrieving a liquid C3+ rich LPG product stream from the knockout drum, wherein the C3+ rich LPG product stream has a higher C3+ mol % than the first permeate product stream,(f) retrieving a vapor C2− rich stream from the knockout drum, wherein the C2− rich stream has a higher C2− mol % than the first permeate product stream,(g) feeding C2− rich stream into a second membrane separation unit wherein the C2− rich is contacted with a first side of at least one second rubbery polymer membrane,(h) retrieving a second retentate product stream which has a higher C2− mol % than the C2− rich stream from the first side of the second rubbery polymer membrane and retrieving a second permeate product stream which has a higher C3+ mol % than the C2− rich stream from a second side of the second rubbery polymer membrane, and(i) mixing at least a portion of the second permeate product stream with the first permeate product stream at a point upstream of the compressor.

2. The process of claim 1, wherein the first permeate product stream has a hydrogen purity of at least 70 mol %.

3. The process of claim 2, wherein the wt % of the hydrogen component of the first permeate product stream is at least 40 wt % of the hydrogen component in the hydrocarbon-containing feedstream.

4. The process of claim 3, wherein the C3+ rich LPG product stream has a C3+ purity of at least 70 mol %.

5. The process of claim 4, wherein the wt % of the C3+ component in the C3+ rich product stream is at least 80 wt % of the C3+ component in the hydrocarbon-containing feedstream.

6. The process of claim 5, wherein the rubbery polymer membranes have a glass transition temperature below 20° C.

7. The process of claim 6, wherein at least one of the rubbery polymer membranes is comprised of a material selected from polysiloxane and polybutadiene.

8. A process for the recovery of a C3+ rich LPG stream and a high purity hydrogen stream from a hydrocarbon-containing feedstream comprised of hydrogen and C1, C2 and C3+ hydrocarbons, comprising: (a) feeding the hydrocarbon-containing feedstream into a first membrane separation unit wherein the hydrocarbon-containing feedstream is contacted with a first side of at least one first rubbery polymer membrane,(b) retrieving a first retentate product stream which has a higher hydrogen mol % than the hydrocarbon-containing feedstream from the first side of the first rubbery polymer membrane and retrieving a first permeate product stream which has a higher C3+ mol % than the hydrocarbon-containing n feedstream from a second side of the first rubbery polymer membrane,(c) feeding the first permeate product stream to a knockout drum,(d) retrieving a liquid C3+ rich LPG product stream from the knockout drum, wherein the C3+ rich LPG product stream has a higher C3+ mol % than the first permeate product stream,(e) retrieving a vapor C2− rich stream from the knockout drum, wherein the C2− rich stream has a higher C2− mol % than the first permeate product stream,(f) feeding C2− rich stream into a second membrane separation unit wherein the C2− rich is contacted with a first side of at least one second rubbery polymer membrane,(g) retrieving a second retentate product stream which has a higher C2− mol % than the C2− rich stream from the first side of the second rubbery polymer membrane and retrieving a second permeate product stream which has a higher C3+ mol % than the C2− rich stream from a second side of the second rubbery polymer membrane,(h) feeding at least a portion of the second permeate product stream to a compressor wherein the second permeate product stream is raised in pressure,(i) mixing the higher pressure second permeate product stream with the first permeate product stream at a point upstream of the knockout drum.

9. The process of claim 8, wherein the first permeate product stream has a hydrogen purity of at least 70 mol %.

10. The process of claim 9, wherein the wt % of the hydrogen component of the first permeate product stream is at least 40 wt % of the hydrogen component in the hydrocarbon-containing feedstream.

11. The process of claim 10, wherein the C3+ rich LPG product stream has a C3+ purity of at least 70 mol %.

12. The process of claim 11, wherein the wt % of the C3+ component in the C3+ rich product stream is at least 80 wt % of the C3+ component in the hydrocarbon-containing feedstream.

13. The process of claim 12, wherein the rubbery polymer membranes have a glass transition temperature below 20° C.

14. The process of claim 13, wherein at least one of the rubbery polymer membranes is comprised of a material selected from polysiloxane and polybutadiene.