Method and system for light olefin separation

Abstract

A process is provided for separation of light olefins and paraffins and particular for the separation of propylene and propane comprising sending at least one olefin/paraffin stream to a distillation column and a membrane unit to produce an olefin stream comprising at least 92 mol % olefin. In an embodiment of the invention where the membrane unit is placed downstream from the column which can produce propylene streams at polymer grade of over 99.5 mol % propylene.

Claims

1. A process for separation of olefin and paraffin mixtures comprising sending at least one hydrocarbon stream to a distillation column to produce an upper stream more concentrated in olefin than said at least one hydrocarbon stream and a bottom stream more concentrated in paraffin than the at least one hydrocarbon stream and sending a portion of said upper stream in vapor phase comprising 72-90% olefin to a membrane unit to separate said upper stream into a permeate stream in vapor phase comprising at least 99 mol % olefin and a retentate stream in vapor phase comprising paraffin, wherein the portion of the upper stream is recycled to the distillation column after condensation, wherein said membrane unit comprises a plurality of membranes which are facilitated transport membranes comprising a solid nonporous polymer matrix layer on top of a nanoporous support membrane.

2. The process of claim 1 wherein said facilitated transport membranes comprise metal ions incorporated into said nonporous polymer matrix layer and nanopores on a skin layer surface of said nanoporous support membrane.

3. The process of claim 1 wherein said at least one hydrocarbon stream comprise at least two streams comprising different concentrations of olefin.

4. The process of claim 1 wherein said permeate stream comprises about 99.8 mol % olefin.

5. The process of claim 1 wherein at least a portion of said retentate stream is recycled to said distillation column to separate said retentate stream into a paraffin stream and an olefin stream.

6. The process of claim 1 wherein said hydrocarbon stream comprises C3 or C4 olefin and paraffin hydrocarbons.

7. The process of claim 1 wherein said olefin is propylene, wherein said paraffin is propane, and wherein said hydrocarbon stream comprises propylene and propane hydrocarbons.

8. The process of claim 1 wherein said olefin is ethylene, wherein said paraffin is ethane, and wherein said hydrocarbon stream comprises ethylene and ethane hydrocarbons.

9. The process of claim 1 wherein said olefin is C4 olefin, wherein said paraffin is C4 paraffin, and wherein said hydrocarbon stream comprises C4 olefin and C4 paraffin hydrocarbons.

10. The process of claim 1 wherein the upper stream contains <0.05% C4 olefins in the total olefins.

11. The process of claim 1 wherein the permeate stream is compressed and then condensed with cooling water.

12. The process of claim 5 wherein at least a portion of the retentate stream is condensed to liquid before recycling to the distillation column.

13. The process of claim 11 wherein the condensation of the upper stream not sent to the membrane is done via heat exchange with the distillation column bottom material supplying heat duty for the reboiler.

14. The process of claim 11 wherein at least a portion of the retentate stream is returned to the distillation column below the point of return of the upper stream that is not sent to the membrane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an embodiment of the invention with an olefin flow stream passing first through a membrane unit and then through a distillation column to separate olefins and paraffins.

(2) FIG. 2 shows an embodiment of the invention with one or more olefin flow streams first entering a distillation column and then passing through a membrane unit to separate olefins and paraffins.

DETAILED DESCRIPTION OF THE INVENTION

(3) The membrane technology of the present invention offers the capability of upgrading propylene from 75% purity or less to polymer grade 99.5% with the membranes and element design (1500-3000 elements depending on product capacity). For a distillation column, the overhead stream needs only be rectified to 75% or up to 90% and then further purified by the membranes to get to polymer grade product. By reducing the overhead purity, the reflux ratio decreases substantially, the reboiler duty also decreases, and the column diameter and height can also be reduced for a new design. For revamp cases, the same shell diameter can accommodate more feed to increase throughput or product capacity. Also, the overhead compression ratio decreases, requiring only single stage compressor (final pressure is 200-240 psig).

(4) Although the main object of the present invention is to separate propane and propylene, additional capacity may be added to separate C2, C4, as well as C5 mixtures.

(5) The present invention is made possible by the use of recently developed membranes including those described in US 2017/0354918 A1; U.S. application Ser. No. 15/615,134 filed Jun. 6, 2017; US 2018/0001277 A1; US 2018/0001268 A1; and U.S. application Ser. No. 15/599,258 filed May 18, 2017 incorporated herein in their entireties.

(6) US 2017/0354918 A1 disclosed a facilitated transport membrane comprising a relatively hydrophilic, very small pore, nanoporous support membrane, a hydrophilic polymer inside the very small nanopores on the skin layer surface of the support membrane, a thin, nonporous, hydrophilic polymer layer coated on the surface of the support membrane, and metal salts incorporated in the hydrophilic polymer layer coated on the surface of the support membrane and the hydrophilic polymer inside the very small nanopores, a method of making this membrane, and the use of this membrane for olefin/paraffin separations, particularly for C3=/C3 and C2=/C2 separations. The relatively hydrophilic, very small pore, nanoporous support membrane used for the preparation of the new facilitated transport membrane comprising a relatively hydrophilic, very small pore, nanoporous support membrane, a hydrophilic polymer inside the very small nanopores on the surface of the support membrane, a thin, nonporous, hydrophilic polymer layer coated on the surface of said support membrane, and metal salts incorporated in the hydrophilic polymer layer coated on the surface of the support membrane and said hydrophilic polymer inside the very small nanopores disclosed in the present invention comprises a relatively hydrophilic polymer selected from a group consisting of, but is not limited to, polyethersulfone (PES), a blend of PES and polyimide, cellulose acetate, cellulose triacetate, and a blend of cellulose acetate and cellulose triacetate. The relatively hydrophilic, very small pore, nanoporous support membrane described in the current invention has an average pore diameter of less than 10 nm on the membrane skin layer surface. The relatively hydrophilic, very small pore, nanoporous support membrane described in the current invention can be either asymmetric integrally skinned membrane or thin film composite (TFC) membrane with either flat sheet (spiral wound) or hollow fiber geometry.

(7) The hydrophilic polymer inside the very small nanopores on the surface of the relatively hydrophilic, very small pore, nanoporous support membrane of the facilitated transport membrane described in US 2017/0354918 A1 can be selected from, but is not limited to, a group of hydrophilic polymers containing chitosan, sodium carboxylmethyl-chitosan, carboxylmethyl-chitosan, hyaluronic acid, sodium hyaluronate, carbopol, polycarbophil calcium, poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA), sodium alginate, alginic acid, poly(vinyl alcohol) (PVA), poly(ethylene oxide) (PEO), poly(ethylene glycol) (PEG), poly(vinylpyrrolidone) (PVP), gelatin, carrageenan, sodium lignosulfonate, and mixtures thereof.

(8) The metal salts incorporated in the hydrophilic polymer layer coated on the surface of said support membrane and the hydrophilic polymer inside the very small nanopores of the facilitated transport membrane described in US 2017/0354918 A1 are preferred to be selected from silver salts or copper salts, such as silver(I) nitrate or copper(I) chloride.

(9) The dried, relatively hydrophilic, very small pore, nanoporous support membrane comprising hydrophilic polymers inside the very small nanopores on the membrane surface described in US 2017/0354918 A1 has carbon dioxide permeance of 800-10,000 GPU and no carbon dioxide/methane selectivity at 50 C. under 30-100 psig 10% CO.sub.2/90% CH.sub.4 mixed gas feed pressure.

(10) Some of the facilitated transport membranes described in US 2018/0001277 A1 are useful in the present invention. One high performance facilitated transport membrane 1.5MAg+/PI-50 that may be used has an asymmetric integrally skinned flat sheet membrane structure was fabricated from carboxylic acid containing poly(2,2-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride-3,5-diaminobenzoic acid-3,3-dihydroxy-4,4-diamino-biphenyl) polyimide (abbreviated as PI-50) that was synthesized from 2,2-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6 FDA) and a mixture of 3,5-diaminobenzoic acid (3,5-DBA) and 3,3-dihydroxy-4,4-diamino-biphenyl (HAB) (molar ratio of 3,5-DBA/HAB=1:4), wherein the carboxylic acid functional groups on PI-50 were ion-exchanged or chelated with silver (I) cation. Permeation testing experiments using humidified (relative humidity 80-100%) propylene and propane mixed vapor phase feed (30% propylene and 70% propane at 791 kPa (100 psig) and 35 C.) showed that this 1.5MAg+/PI-50 membrane had both high propylene (C3=) permeance (P.sub.C3=/L=259 GPU) and high propylene/propane (C3=/C3) selectivity (.sub.C3=/C3=466). Permeation testing experiments using humidified (relative humidity 80-100%) propylene and propane mixed vapor phase feed (70% propylene and 30% propane at 791 kPa (100 psig) and 35 C.) also showed that this 1.5MAg+/PI-50 membrane had both high propylene (C3=) permeance (P.sub.C3=/L=192 GPU) and high propylene/propane (C3=/C3) selectivity (.sub.C3=/C3=1000).

(11) Another new high performance facilitated transport membrane 3MAg+/PI-150 that may be used is an asymmetric integrally skinned membrane flat sheet structure that was fabricated from carboxylic acid containing poly(2,2-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride-3,5-diaminobenzoic acid-3,3,5,5-tetramethyl-4,4-methylene dianiline) polyimide (abbreviated as PI-150) derived from the polycondensation reaction of 6 FDA and a mixture of 3,5-DBA and 3,3,5,5-tetramethyl-4,4-methylene dianiline (TMMDA) (molar ratio of 3,5-DBA/TMMDA=2:1), wherein the carboxylic acid functional groups on PI-150 were ion-exchanged or chelated with silver cation. Permeation testing experiments using humidified (relative humidity 80-100%) propylene and propane mixed vapor phase feed (30% propylene and 70% propane at 791 kPa (100 psig) and 35 C.) showed that this 3MAg+/PI-150 membrane has both high propylene (C3=) permeance (P.sub.C3=/L=147 GPU) and high propylene/propane (C3=/C3) selectivity (.sub.C3=/C3=239).

(12) The facilitated transport membrane that is used may comprise a carboxylic acid functional group containing polyimide wherein the carboxylic acid functional groups are ion-exchanged or chelated with metal cations such as silver (I) or copper (I) cations. The metal cation ion-exchanged or chelated carboxylic acid functional group containing polyimide described in U.S. application Ser. No. 15/610,305 comprising a plurality of repeating units of formula (I)

(13) ##STR00001##
wherein X.sub.1 and X.sub.2 are selected from the group consisting of

(14) ##STR00002##
and mixtures thereof, and wherein X1 and X2 may be the same or different from each other; wherein Y.sub.1COOM is selected from the group consisting of

(15) ##STR00003##
and mixtures thereof and wherein M is selected from silver (I) cation or copper (I) cation; wherein Y2 is selected from the group consisting of

(16) ##STR00004##
and mixtures thereof, and R is selected from the group consisting of

(17) ##STR00005##
and mixtures thereof, and R is selected from the group consisting of H, COCH.sub.3, and mixtures thereof, and M is selected from silver (I) cation or copper (I) cation; wherein n and m are independent integers from 2 to 500; and wherein n/m is in a range of 1:0 to 1:10, and preferably n/m is in a range of 1:0 to 1:5.

(18) Preferably, X.sub.1 and X.sub.2 are selected from the group consisting of

(19) ##STR00006##
and mixtures thereof, and wherein X1 and X2 may be the same or different from each other; preferably Y.sub.1COOM is selected from the group consisting of

(20) ##STR00007##
and mixtures thereof; preferably Y2 is selected from the group consisting of

(21) ##STR00008##
and mixtures thereof.

(22) FIG. 1 shows a membrane/column system in which a hydrocarbon stream comprising about 65 mol % propylene enters a membrane unit 12. A permeate 22 exits membrane unit 12 and may be compressed by compressor 24 to produce a compressed propylene product stream 26 that then is combined with propylene product stream 30 with combined propylene product stream 32 which has about a 92-95 mol % level of propylene. A retentate stream that is primarily propane passes through line 14 to compressor 16. A compressed retentate stream 18 is shown entering distillation column 20. A propane-rich stream 28 exits the bottom of distillation column 20 and a propylene stream 30 exits the top of distillation column 20 to be combined with propylene product stream 26 with combined propylene product stream 32 having a purity of about 92-95 mol % propylene with up to 95-97 mol % propylene possible.

(23) FIG. 2 shows an alternative embodiment of a system that includes a distillation column and a membrane unit for separating propane and propylene. There are two feed streams 50 and 52 shown that contain different concentrations of propylene. For example, feed stream 50 may contain about 60-70 mol % propylene and feed stream 52 may contain about 25-45 mol % propylene. These two feed streams enter distillation column 54 that is a C3 splitter with a propane stream 86 exiting the bottom while a portion of propane stream 86 may be split off to be reboiled through heat exchanger 82. A partially purified propylene stream 56 that is about 72-90 mol % propylene is sent to compressor 58 and then compressed partially purified propylene stream 60 and then 62 is sent to membrane unit 64 with a purified permeate stream 66 being compressed in compressor 68 to produce a compressed permeate stream 70 which passes through heat exchanger 72 and on as product stream 74 that may be as high as polymer grade 99.3-99.8 mol % propylene. A portion of compressed partially purified propylene stream 60 may be recycled and cooled in heat exchanger 82 and returned to distillation column 54 through line 84. A retentate stream that is mostly propane is shown exiting membrane unit 64 through line 76, cooled in heat exchanger or chiller 78 and returning to distillation column 54 through line 80.

Specific Embodiments

(24) While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims.

(25) A first embodiment of the invention is a process for separation of olefin and paraffin mixtures comprising sending at least one hydrocarbon stream to a distillation column and a membrane unit to produce an olefin stream comprising at least 92 mol % olefin. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the at least one hydrocarbon stream comprises between 25-90 mol % olefin. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the at least one hydrocarbon stream first passes to the distillation column to produce an upper stream more concentrated in olefin than the at least one hydrocarbon stream and a bottom stream more concentrated in paraffin than the hydrocarbon stream and then sending a portion of the upper stream to a membrane unit to separate the upper stream into a permeate stream comprising at least 90-98 mol % olefin and a retentate stream comprising paraffin. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the membrane unit comprises a plurality of membranes wherein the membranes are facilitated transport membranes. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the facilitated transport membranes comprise a solid nonporous polymer matrix layer on top of a nanoporous support membrane. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the facilitated transport membranes comprise metal ions incorporated into the nonporous polymer matrix layer and the nanopores on the skin layer surface of the nanoporous support membrane. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the at least one hydrocarbon stream comprise at least two streams comprising different concentrations of olefin. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein one of the streams comprises about 25-45 mol % olefin and one of the streams comprises about 50-70 mol % olefin. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the permeate stream comprises about 99.3-99.8 mol % olefin. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein at least a portion of the retentate stream is recycled to the distillation column to separate the retentate stream into a paraffin stream and an olefin stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the hydrocarbon stream comprises C3 or C4 olefin and paraffin hydrocarbons. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the olefin is propylene, wherein the paraffin is propane, and wherein the hydrocarbon stream comprises propylene and propane hydrocarbons. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the olefin is ethylene, wherein the paraffin is ethane, and wherein the hydrocarbon stream comprises ethylene and ethane hydrocarbons. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the olefin is C4 olefin, wherein the paraffin is C4 paraffin, and wherein the hydrocarbon stream comprises C4 olefin and C4 paraffin hydrocarbons. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the upper stream contains <0.05% C4 olefins in the total olefins. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the permeate stream is compressed and then condensed with cooling water. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein at least a portion of the retentate stream is condensed to liquid before recycling to the distillation column. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the portion of the upper stream that is not sent to the membrane is recycled to the distillation column after condensation. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the condensation of the upper stream not sent to the membrane is done via heat exchange with the distillation column bottom material supplying heat duty for the reboiler. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein at least a portion of the retentate stream is returned to the distillation column below the point of return of the upper stream that is not sent to the membrane. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the distillation column has a lower reboiler duty than in a system comprising a distillation column without a membrane unit.

(26) Without further elaboration, it is believed that using the preceding description that one skilled in the art can utilize the present invention to its fullest extent and easily ascertain the essential characteristics of this invention, without departing from the spirit and scope thereof, to make various changes and modifications of the invention and to adapt it to various usages and conditions. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limiting the remainder of the disclosure in any way whatsoever, and that it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

(27) In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.