GB2192581A - Process for fabricating a separation medium - Google Patents
Process for fabricating a separation medium Download PDFInfo
- Publication number
- GB2192581A GB2192581A GB08716674A GB8716674A GB2192581A GB 2192581 A GB2192581 A GB 2192581A GB 08716674 A GB08716674 A GB 08716674A GB 8716674 A GB8716674 A GB 8716674A GB 2192581 A GB2192581 A GB 2192581A
- Authority
- GB
- United Kingdom
- Prior art keywords
- membrane
- solvent
- process according
- separation
- polyetherimide
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 238000000926 separation method Methods 0.000 title claims abstract description 35
- 238000000034 method Methods 0.000 title claims abstract description 24
- 239000012528 membrane Substances 0.000 claims abstract description 44
- 239000002904 solvent Substances 0.000 claims abstract description 25
- 229920001601 polyetherimide Polymers 0.000 claims abstract description 19
- 239000004697 Polyetherimide Substances 0.000 claims abstract description 16
- 238000001704 evaporation Methods 0.000 claims abstract description 15
- 230000008020 evaporation Effects 0.000 claims abstract description 15
- 239000000203 mixture Substances 0.000 claims abstract description 9
- 238000005345 coagulation Methods 0.000 claims abstract description 6
- 230000015271 coagulation Effects 0.000 claims abstract description 6
- 239000000835 fiber Substances 0.000 claims abstract description 5
- 230000001112 coagulating effect Effects 0.000 claims abstract description 4
- YMWUJEATGCHHMB-UHFFFAOYSA-N Dichloromethane Chemical group ClCCl YMWUJEATGCHHMB-UHFFFAOYSA-N 0.000 claims description 15
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 claims description 8
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 claims description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 5
- WYURNTSHIVDZCO-UHFFFAOYSA-N Tetrahydrofuran Chemical compound C1CCOC1 WYURNTSHIVDZCO-UHFFFAOYSA-N 0.000 claims description 4
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 3
- 150000002894 organic compounds Chemical class 0.000 claims description 3
- 238000005266 casting Methods 0.000 claims description 2
- 239000000460 chlorine Substances 0.000 claims description 2
- 229910052801 chlorine Inorganic materials 0.000 claims description 2
- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 claims description 2
- 125000001309 chloro group Chemical group Cl* 0.000 claims 1
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 claims 1
- 239000003960 organic solvent Substances 0.000 claims 1
- 239000007789 gas Substances 0.000 description 15
- 229920000642 polymer Polymers 0.000 description 9
- 239000010408 film Substances 0.000 description 8
- 229920000435 poly(dimethylsiloxane) Polymers 0.000 description 6
- 239000000758 substrate Substances 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- -1 poly(dimethylsiloxane) Polymers 0.000 description 4
- 229920004738 ULTEM® Polymers 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 230000035699 permeability Effects 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
- 238000009987 spinning Methods 0.000 description 3
- RYHBNJHYFVUHQT-UHFFFAOYSA-N 1,4-Dioxane Chemical compound C1COCCO1 RYHBNJHYFVUHQT-UHFFFAOYSA-N 0.000 description 2
- HEDRZPFGACZZDS-UHFFFAOYSA-N Chloroform Chemical compound ClC(Cl)Cl HEDRZPFGACZZDS-UHFFFAOYSA-N 0.000 description 2
- OFBQJSOFQDEBGM-UHFFFAOYSA-N Pentane Chemical compound CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 239000000701 coagulant Substances 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 229920001971 elastomer Polymers 0.000 description 2
- 230000008030 elimination Effects 0.000 description 2
- 238000003379 elimination reaction Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000012466 permeate Substances 0.000 description 2
- 239000005060 rubber Substances 0.000 description 2
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 1
- 229920004747 ULTEM® 1000 Polymers 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000001471 micro-filtration Methods 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 238000005381 potential energy Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- HNJBEVLQSNELDL-UHFFFAOYSA-N pyrrolidin-2-one Chemical compound O=C1CCCN1 HNJBEVLQSNELDL-UHFFFAOYSA-N 0.000 description 1
- 238000004626 scanning electron microscopy Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 238000000108 ultra-filtration Methods 0.000 description 1
- 229920002554 vinyl polymer Polymers 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/58—Other polymers having nitrogen in the main chain, with or without oxygen or carbon only
- B01D71/62—Polycondensates having nitrogen-containing heterocyclic rings in the main chain
- B01D71/64—Polyimides; Polyamide-imides; Polyester-imides; Polyamide acids or similar polyimide precursors
- B01D71/643—Polyether-imides
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/58—Other polymers having nitrogen in the main chain, with or without oxygen or carbon only
- B01D71/62—Polycondensates having nitrogen-containing heterocyclic rings in the main chain
- B01D71/64—Polyimides; Polyamide-imides; Polyester-imides; Polyamide acids or similar polyimide precursors
Abstract
A process for fabricating a separation medium in which a polyetherimide is dissolved in a solvent or mixture of solvents and a membrane cast. The polyetherimide membrane is then contacted with a coagulating medium to form the separation medium and prior to the coagulation step, the cast film is subjected to an evaporation stage in which solvent is allowed to evaporate from the film for a predetermined period of time. The membrane may take the form of a sheet, film or hollow fibre or other suitable form.
Description
SPECIFICATION
Process for fabricating a separation medium
The present invention relates to gas separation and liquid separation and more particularly relates to a process for the fabrication of separation media.
The separation of gas mixtures into their individual components has numerous applications and the development of membranes processes for these separations has become of increasing importance. The use of membrane processes for gas separation has certain advantages over alternative techniques for example those based on adsorption, absorption and liquefaction. These advantages include potential energy efficiency, compactness, relative simplicity and ease of operation. The modular nature of membrane technology also enables scaling up or reduction of capacity when necessary.
The membranes for the gas separation process are desirably (a) highly permeable to components of the mixture to be separated (b) highly selective for specific components ie the specific components have a high permeability relative to other constituents in the gas mixture (c) chemically inert and physically stable and (d) continuous ie free from defects such as pinholes.
The desired product may be the permeate or non-permeate or both.
Certain polymers appear to have characteristics making them suitable for use in the form of gas separation membranes. However conventionally prepared polymeric membranes generally have low gas permeation rates and poor selectivity often resulting in uneconomic separation.
The present invention relates to the fabrication of gas separation membranes comprising polyetherimide (PEI). PEI membranes are known for gas separation processes e.g. EP 113574 and the present invention is directed to a process for fabricating membranes having improved characteristics and properties over the known processes.
Thus, according to the present invention there is provided~a process for fabricating a separation medium comprising (a) dissolving a polyetherimide in a solvent or mixture of solvents (b) casting a polyetherimide membrane and (c) contacting the polyetherimide membrane with a coagulating medium to form the separation medium and (d) prior to the coagulation step, the cast film is subjected to an evaporation stage in which solvent is allowed to evaporate from the film for a pre-determined period of time. The membrane may take the form of a sheet, film or hollow fibre or other suitable form.
The invention also includes separation media whenever prepared by a process as hereinbefore described. The separation media may be of use in microfiltration and ultrafiltration as well as for gas separation purposes.
The length of the evaporation stage may vary from zero to thousands of seconds depending upon the solvent/polymer combination and the desired membrane properties. It is believed that the separation media form by the present process comprise a dense top layer and a porous substructure. By variation of the length of the evaporation stage, it is possible to tailor the separation media by controlling the dense layer thickness.
The coagulation step may be carried out in water but the use of organic or water/organic coagulants may be advantageous. Suitable organic compounds include acetone, tetrahydrofuran and isopropyl alcohol. It is believed that the use of certain organic coagulants may reduce the number of pores and defects in the dense top layer thereby yielding improved separation properties for the separation media.
The solvents systems used for forming the polyetherimide solution may comprise a single solvent or a mixture of solvents. Examples of suitable solvents include chlorine containing solvents such as dichloromethane and chloroform, and nitrogen containing cyclic solvents such as N-methylpyrrolidone. Preferred solvents include dichloromethane, N-methyl pyrrolidone, and dichloromethane/dioxane. The latter solvent systems appear to give separation media having a reduced macrovoid content.
The membranes may be in the form of hollow fibres. The hollow fibres may also be spun, under similar conditions to those described above, by use of conventional spinnerette technology.
When the membranes are to be fabricated for use as gas separation media, it is desirable that the separation medium or membrane formed by the process is coated with a thin layer of high permeability material so as to block defects in the membrane. One suitable group of materials are poly(dimethylsiloxane) rubbers (PDMS).
The invention will now be described by way of example only.
A poly(etherimide) was dissolved in dichloromethane to give a ca 25% solution by wt. A suitable polyetherimide is Ultem 1000 (manufactured by General Electric) . Sufficient dioxane was added to give a solution of ca 19% by wt. A film of polymer solution was cast onto a clean glass. plate using a 150 um doctor blade. The film was then left for an evaporation time of 10 seconds (ambient temperature). The film and substrate were then immersed into a bath of water/acetone (1:1 by volume) to induce coagulation. After 5 minutes residence time in the non solvent bath, the so-formed membrane and substrate were removed and allowed to dry.
A coating solution was prepared by dissolving poly(dimethylsiloxane) (PDMS) (Dow Corning
Sylgard 184) in pentane to make a 10% solution (by weight). 1% by weight of a proprietary curing agent was also added. This solution was poured onto the membrane and substrate and excess solution subsequently drained off. The membrane and substrate were then placed in an oven at 400C for 48 hours to cure the PDMS sealing layer. The membrane was then detached from the substrate by removing it carefully.
The prepared membrane was placed in an apparatus suitable for measuring the gas permeabil- ity of thin films. The results are shown in Table 1.
Table 1
Gas Permeation rate/(cm3(stp)/cm2.s.cmHg) CO2 5.71 x 10-7 CH4 1.30 x 10-8 The ideal separation factor,, for CO2/CH4 (defined as the ratio of the permeation rates) is thus 44.
The cross-section of the membrane was examined by scanning electron microscopy. The membrane consisted of three layers viz. (a) ca 10 um of PDMS rubber, (b) ca 5 um of dense poly(etherimide), and (c) ca 30 um of porous poly(etherimide) sub-structure. The membrane is thus asymmetric in structure.
In other experiments, the membrane was shown to exhibit a separation factor for H2/CO of 65. The membrane was stable at 1500C and withstood a pressure differential of 48 bar.
Effect of evaporation time is relevant also to other methods of membrane formation such as hollow fibre fabrication by use of wet or dry jet spinning.
The thickness of the dense layer formed during the preparation of the membrane is dependent on the evaporation time. The evaporation time is defined as the time period between freeing the nascent membrane from the polymer solution and immersion in the coagulation bath. Table 2 and the figure shows the variation of dense layer thickness and evaporation time for a particular
PEI membrane. For separation purposes it is desirable that the dense layer thickness is as small as possible and the figure illustrates the relevance of the evaporation time to obtaining this minimum thickness. In this particular case, the evaporation time for minimum dense layer thickness occurs at about 10 seconds. Table 2 also shows how the gas permeation rates are influenced by the dense layer thickness.
Table 2
Ultem poly(imide) films: Preparation conditions and permeation data
Sample No Evaporation Dense layer Permeation rate x 108/cm3(stp)cm-2s-1(cmHg)-1 Ideal Selectivity time/s thickness/um CO2 CO2 CH4 CH4 OcmHg 400 cmHg OcmHg 400cmHg OcmHg 400 cmHg 1 10 - 90.1 80.1 2.11 1.90 43 42 2 10 3 77.5 69.2 1.81 1.69 43 41 3 5 5 57.0 51.0 1.34 1.23 43 42 4 20 8 35.9 30.7 0.84 0.818 44 38 5 - 10 20.2 - 0.49 - 45 6 20 6 51.8 45.4 1.20 1.06 43 43 The above experimental work has been carried out using flat films but it is believed that the effect of evaporation time is relevant also to other method of membrane formation such as hollow fibre fabrication by use of wet or dry jet spinning.
In the preparation of membranes for gas separation asymmetric membranes, it is particularly desirable to avoid the formation of "finger" voids or macropores which may reduce the strength of the membrane. This may be achieved by the use of a finite evaporation stage and the use of relatively higher concentrations of polymer in the solvent.
Also the addition of a viscosifying agent to the polymer/solvent prior to formation of the membrane leads to the reduction or elimination of macropores. Thus, for example, a solution containing 28. 1% polyetherimide (Ultem) was prepared by dissolving the polymer with poly(vinyl) pyrrolidone (PVP) in UP such that the overall polymer content of the spinning solution was 37.5 wt %. The resultant membrane had for fewer macropores than far a membrane prepared from a 34.3 wt % polyetherimide (Ultem).
Furthermore, it has been found that the addition of a non-solvent for the polymer dope also assists in the reduction or elimination of macropores.
Claims (9)
1. A process for fabricating a separation medium comprising (a) dissolving a polyetherimide in a solvent or mixture of solvents (b) casting a polyetherimide membrane and (c) contacting the polyetherimide membrane with a coagulating medium to form the separation medium and (d) prior to the coagulation step, the cast film is subjected to an evaporation stage in which solvent is allowed to evaporate from the film for a pre-determined period of time.
2. A process according to claim 1 in which the membrane is in the form of a sheet, film or hollow fibre.
3. A process according to claim 1 or claim 2 in which the coagulating medium is water or a water/organic compound mixture.
4. A process according to claim 3 in which the organic compound is acetone, tetrahydrofuran or isopropyl alcohol.
5. A process according to any of the preceding claims in which the solvent is a chlorine containing or a nitrogen containing organic solvent.
6. A process according to claim 5 in which the solvent is dichloromethane, or n-methyl pyrrolidone.
7. A process according to claim 5 in which a mixture of solvents is used.
8. A process for fabricating a separation media as hereinbefore described.
9. Separation media wherever fabricated by a process according to any of the preceding claims.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB868617263A GB8617263D0 (en) | 1986-07-15 | 1986-07-15 | Separation media |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8716674D0 GB8716674D0 (en) | 1987-08-19 |
| GB2192581A true GB2192581A (en) | 1988-01-20 |
Family
ID=10601102
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB868617263A Pending GB8617263D0 (en) | 1986-07-15 | 1986-07-15 | Separation media |
| GB08716674A Withdrawn GB2192581A (en) | 1986-07-15 | 1987-07-15 | Process for fabricating a separation medium |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB868617263A Pending GB8617263D0 (en) | 1986-07-15 | 1986-07-15 | Separation media |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB8617263D0 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0418082A1 (en) * | 1989-09-15 | 1991-03-20 | The British Petroleum Company p.l.c. | Membrane fabrication |
| EP0422886A1 (en) * | 1989-10-10 | 1991-04-17 | E.I. Du Pont De Nemours And Company | Production of aromatic polyimide membranes |
| US7166148B2 (en) * | 2003-01-17 | 2007-01-23 | Smart Membrane Corp. | Gas separation membranes |
| US7179322B2 (en) | 2003-01-30 | 2007-02-20 | Smartmembrane Corp. | Oxygen and nitrogen enriched atmospheres in aircraft |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2051664A (en) * | 1979-05-17 | 1981-01-21 | Nitto Electric Ind Co | Preparing selective permeable membranes |
| EP0023406A1 (en) * | 1979-07-26 | 1981-02-04 | Ube Industries, Ltd. | Process for preparing aromatic polyimide semipermeable membranes |
| GB2073654A (en) * | 1980-03-31 | 1981-10-21 | Nitto Electric Ind Co | Preparing selective permeable membranes |
| EP0113574A2 (en) * | 1982-12-21 | 1984-07-18 | Sumitomo Electric Industries Limited | Gas-selectively permeable membrane and method of forming said membrane |
| EP0125908A2 (en) * | 1983-05-13 | 1984-11-21 | Exxon Research And Engineering Company | Asymmetric polyimide reverse osmosis membrane, method for preparation of same and use thereof for organic liquid separations |
-
1986
- 1986-07-15 GB GB868617263A patent/GB8617263D0/en active Pending
-
1987
- 1987-07-15 GB GB08716674A patent/GB2192581A/en not_active Withdrawn
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2051664A (en) * | 1979-05-17 | 1981-01-21 | Nitto Electric Ind Co | Preparing selective permeable membranes |
| EP0023406A1 (en) * | 1979-07-26 | 1981-02-04 | Ube Industries, Ltd. | Process for preparing aromatic polyimide semipermeable membranes |
| GB2073654A (en) * | 1980-03-31 | 1981-10-21 | Nitto Electric Ind Co | Preparing selective permeable membranes |
| EP0113574A2 (en) * | 1982-12-21 | 1984-07-18 | Sumitomo Electric Industries Limited | Gas-selectively permeable membrane and method of forming said membrane |
| EP0125908A2 (en) * | 1983-05-13 | 1984-11-21 | Exxon Research And Engineering Company | Asymmetric polyimide reverse osmosis membrane, method for preparation of same and use thereof for organic liquid separations |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0418082A1 (en) * | 1989-09-15 | 1991-03-20 | The British Petroleum Company p.l.c. | Membrane fabrication |
| WO1991004092A1 (en) * | 1989-09-15 | 1991-04-04 | The British Petroleum Company Plc | Membrane fabrication |
| EP0422886A1 (en) * | 1989-10-10 | 1991-04-17 | E.I. Du Pont De Nemours And Company | Production of aromatic polyimide membranes |
| US7166148B2 (en) * | 2003-01-17 | 2007-01-23 | Smart Membrane Corp. | Gas separation membranes |
| US7179322B2 (en) | 2003-01-30 | 2007-02-20 | Smartmembrane Corp. | Oxygen and nitrogen enriched atmospheres in aircraft |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8716674D0 (en) | 1987-08-19 |
| GB8617263D0 (en) | 1986-08-20 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |