Liquid-phase separation of low molecular weight organic compounds
View Patent ↗A process for separating a component from a low molecular weight organic mixture by pervaporation. The process uses fluorinated membranes and is particularly useful for treating mixtures containing light organic components, such as methane, propylene or n-butane.
1. A pervaporation process for separating a first component from a liquid organic mixture, comprising the steps of:
a) passing the liquid organic mixture across the feed side of a separation membrane having a feed side and a permeate side, the separation membrane having a selective layer comprising a polymer comprising repeat units of a cyclic structure of an at least 5-member fluorinated ring, the polymer having a fractional free volume less than 0.3, a glass transition temperature of at least about 100° C., and an oxygen permeability below 800 Barrer;
(b) providing a driving force for transmembrane permeation;
(c) withdrawing from the permeate side a permeate vapor stream enriched in the first component compared to the liquid organic mixture;
(d) withdrawing from the feed side a residue liquid stream depleted in the first component compared to the liquid organic mixture.
2. The process of claim 1 , wherein the first component is propylene and the liquid organic mixture further comprises propane.
3. The process of claim 1 , wherein the first component is n-butane and the liquid organic mixture further comprises isobutane.
4. The process of claim 1 , wherein the first component is an aromatic compound.
5. The process of claim 1 , wherein the first component is a C 1-2 hydrocarbon and the liquid organic mixture further comprises C 3+ hydrocarbons.
6. The process of claim 1 , wherein the polymer is formed from a monomer chosen from the group consisting of fluorinated dioxoles, fluorinated dioxolanes and fluorinated cyclically polymerizable alkyl ethers.
7. The process of claim 1 , wherein the polymer comprises a perfluorinated polymer.
8. The process of claim 1 , wherein the polymer is a polyperfluoro (alkenyl vinyl ether).
9. The process of claim 1 , wherein the polymer comprises a copolymer.
10. The process of claim 1 , wherein the polymer has the formula:
where x and y represent the relative proportions of the dioxole and the tetrafluoroethylene blocks, such that x+y=1.
11. The process of claim 1 , wherein the polymer has the formula:
where n is a positive integer.
12. The process of claim 1 , wherein the separation membrane comprises a composite membrane.
13. The process of claim 1 , wherein the polymer is unfilled.
14. The process of claim 1 , wherein the oxygen permeability is below 300 Barrers.
15. The process of claim 1 , wherein the permeate side is at a pressure of at least about atmospheric pressure.
16. The process of claim 1 , further comprising passing at least a portion of a stream chosen from the permeate vapor stream and the residue liquid stream to additional separation treatment.
17. The process of claim 1 , further comprising condensing at least a portion of the permeate vapor stream.
18. The process of claim 1 , further comprising condensing at least a portion of the permeate vapor stream by dephlegmation.
19. The process of claim 1 , further comprising passing at least a portion of a stream chosen from the permeate vapor stream and the residue liquid stream to a distillation step.
20. The process of claim 1 , wherein the liquid organic mixture comprises a fraction from a distillation step.
21. A pervaporation process for separating a first component from a liquid organic mixture, comprising the steps of:
(a) passing the liquid organic mixture across the feed side of a separation membrane having a feed side and a permeate side, the separation membrane having a selective layer comprising a fluorinated polymer having a fractional free volume less than 0.3, a glass transition temperature of at least about 100° C., a fluorine:carbon atom ratio in the polymer of at least 1:1, and an oxygen permeability below 800 Barrer;
the separation membrane being further characterized in that it provides a membrane selectivity in favor of propylene over propane of at least about 3 and a propylene pressure-normalized flux of at least about 10 GPU when challenged at 20° C. with a liquid mixture of 50 wt % propylene/50 wt % propane at a feed pressure of 150 psig and a permeate pressure of 0 psig;
(b) providing a driving force for transmembrane permeation;
(c) withdrawing from the permeate side a permeate vapor stream enriched in the first component compared to the liquid organic mixture;
(d) withdrawing from the feed side a residue liquid stream depleted in the first component compared to the liquid organic mixture.
22. The process of claim 21 , wherein the first component is propylene and the liquid organic mixture further comprises propane.
23. The process of claim 21 , wherein the first component is n-butane and the liquid organic mixture further comprises isobutane.
24. The process of claim 21 , wherein the first component is an aromatic compound.
25. The process of claim 21 , wherein the first component is a C 1-2 hydrocarbon and the liquid organic mixture further comprises C 3+ hydrocarbons.
26. The process of claim 21 , wherein the polymer has a ratio of fluorine to carbon atoms of at least about 1:1.
27. The process of claim 21 , wherein the polymer comprises a perfluorinated polymer.
28. The process of claim 21 , wherein the polymer is a polyperfluoro (alkenyl vinyl ether).
29. The process of claim 21 , wherein the polymer comprises a copolymer.
30. The process of claim 21 , wherein the polymer has the formula:
where x and y represent the relative proportions of the dioxole and the tetrafluoroethylene blocks, such that x+y=1.
31. The process of claim 21 , wherein the polymer has the formula:
where n is a positive integer.
32. The process of claim 21 wherein the polymer is unfilled.
33. The process of claim 21 , wherein the oxygen permeability is below 300 Barrer.
34. The process of claim 21 , wherein the separation membrane comprises a composite membrane.
35. The process of claim 21 , wherein the permeate side is at a pressure of at least about atmospheric pressure.
36. The process of claim 21 , further comprising passing at least a portion of a stream chosen from the permeate vapor stream and the residue liquid stream to additional separation treatment.
37. The process of claim 21 , further comprising condensing at least a portion of the permeate vapor stream.
38. The process of claim 21 , further comprising condensing at least a portion of the permeate vapor stream by dephlegmation.
39. The process of claim 21 , further comprising passing at least a portion of a stream chosen from the permeate vapor stream and the residue liquid stream to a distillation step.
40. The process of claim 21 , wherein the liquid organic mixture comprises a fraction from a distillation step.
41. A pervaporation process for separating a liquid organic mixture comprising propylene and propane, comprising the steps of:
(a) passing the liquid organic mixture across the feed side of a separation membrane having a feed side and a permeate side, the separation membrane having a selective layer comprising a fluorinated polymer having a fractional free volume less than 0.3, a glass transition temperature of at least about 100° C., a fluorine:carbon atom ratio in the polymer of at least 1:1, and an oxygen permeability below 800 Barrer;
and either:
(i) wherein the selective layer comprises repeat units of a cyclic structure of an at least 5-member fluorinated ring, or
(ii) wherein the separation membrane is further characterized in that it provides a membrane selectivity in favor of propylene over propane of at least about 3 and a propylene pressure-normalized flux of at least about 10 GPU when challenged at 20° C. with a liquid mixture of 50 wt % propylene/50 wt % propane at a feed pressure of 150 psig and a permeate pressure of 0 psig;
(b) providing a driving force for transmembrane permeation;
(c) withdrawing from the permeate side a permeate vapor stream enriched in propylene compared to the liquid organic mixture;
(d) withdrawing from the feed side a residue liquid stream depleted in propylene compared to the liquid organic mixture.
42. The process of claim 41 , wherein the oxygen permeability is below 300 Barrer.