CA2023691A1

CA2023691A1 - Composite membrane, its use and processes for pervaporation and gas separation using this composite membrane

Info

Publication number: CA2023691A1
Application number: CA002023691A
Authority: CA
Inventors: Holger Ohst; Karlheinz Hildenbrand; Rolf Dhein; Herbert Hugl
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1989-08-23
Filing date: 1990-08-21
Publication date: 1991-02-24
Also published as: DE3927787A1; JPH0386220A

Abstract

Composite membrane, it use and processes for per-vaporation and gas separation using this composite membrane A b s t r a c t A composite membrane consisting of i) a microporous membrane, containing inorganic fillers, of a film-forming thermoplastic polymer, the fillers having a specific surface area of 5-200 m2/g and representing 60-90% by weight of the total weight of the membrane, and ii) a permselective elastomeric separating layer applied to the membrane, is excellently suitable for processes for pervaporation and gas separation.

Le A 26 866 - Foreign countries

Description

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The invention relates to new composite m~mbranes, a process ~or their preparation and processes or per-vaporation and gas separation using ~hese composite membranes.
In pervaporation, a mixture of different liquid substances in liguid or vaporized form (feed) i6 brought up ~o a membrane which has different permeabili~ies to the individual substances of the feed. On the other ~ide of the membrane, a ~aseous permeate which is highly enriched or depleted in individual substances or groups of substances of the feed is collected. This pe~meate can be condensed again, for example for further processing.
If the feed i5 composed of a mixtuxe of gaseous substan-ces and if the driving force of the membrane process is essentially produced by application of an increased pressure on the feed side, this pxocess is to be equated technologically to gas separation.
Pervaporation processes are useful additions to other processes of substance separation, such as distil-lation or absorption. They provide a useful service, for ex~mple, in the separation of substance mixtures which boil azeotropically and in the removal of low concentra-tions of undesirable substances in ecologically releva~t separation tasks.
Various materials have been employed to date for the production of permselective membranes, that is to ~ay non-porous plastic membranes of polyethylene (US 2,953,520) and polyurethane membranes (US 3,776,970 Le A 2S 866 - 1 -3 ~g ~ i .J

and DE-AS 2,S27,629).
The following requirements, inter alia, are to be met for e~onomic use of pervaporation membranes:
(a) the highest possible selectivity in respect of the S substances to be separated, ~b) the highest possible permeation stream . density and ~c~ the longest possible life tmechanical and ~hemical 6tability).
The properties required are often excluded Erom the property pro~ile of conceivable materials, so that many film-forming polymers are excluded from use in membrane technology. A particular problem is the realiza-tion of a high permeation stream density. In principle, the thinnest possible membrane having a 6elective action is required ~or this, but this in turn qeneral~y does not have the required mechanical stability. Composite mem-branes which consist of a porous support stxucture and a thin layer having a selective action have therefore ~lready been proposed (Chem.-Ing.-Tech. 60 (1988~, 590).
Ultrafiltration membranes are proposed in this context for the porous support structure, but their surface porosity, because of their intended use, is very low so that a certain permeation stream density cannot be exceeded.
It has now been found that the ultrafiltration membranes known from EP 77,509, together with a perm-~elective elastomeric ~eparating layer, give composite membranes which combine a high selectivity with high permeation st~m - densities and excellent chemical and mechani~al resistance.

Le A 26 866 - 2 -~he invention accordingly relates to composite membranes consisting of i) a microporou~ membrane, containing inorganic fillers, of a film-forming thermoplastic polymer, the fil~er~ having a ~pecific surface area of 5-~00 m2/g and representin~ 60-gO~ by weight o~ the total weight of the membrane, and ii) a permselective elastomeric ~eparating layer applied to the membrane.
Suitable fillers are inorganic materials, which preferably have an average particle diameter of 0.05-0.5 ~, particularly preferably 0.2-0.4 ~ (determination with ~he aid of elec~ron microscopy counting methods).
Suitable material~ for this are titanium dioxide, zixcon-ium dioxide, c~rbon black, iron oxide, aluminium oxide.
SiO2, gypsum, barium sulphate, zinc oxide, zinc sulp]hide, talc (magnesium silicate), aluminosilicates, such as kaolin.ite, aChina clay~' or mica, calcium carbona~e, 6uch as calcite, dolomite, chalk or diatomaceous earthl and zeoli~es of natural or synthe~ic origin. Many of the ~ubstance~ mentioned are commercial products from variou~
manufacturers and are equally suitable if they lie within the suitable range of particle diameters and the specific surface area. ~he pigments can be treated with a dispers-ing agent in a manner fami.liar to the expert before their use according to the invention.
Titanium dioxide or a mixture of fillers in which titanium dioxide makes up at least 50~ by weight of the mixture i8 preferably employed. It may be advantageous to employ organically modified titanium dioxide for reasons Le A 26 866 - 3 -:

:
::

of better cvmpatibility wi~h the polymer matri~.
The preferred content of th~ filler in the total weight of the membrane i9 70-90~ by weight; the preferred specific surface area is 5-15 m2/~.
Film-forming thermoplastic polymers which, with the sta~ed amounts of the fillers mentione~, give a microporous membrane which can be used according to the invention are polyconden6akes, such as poly~mides, polyimides, polyamide imides, polyhydantoins, polymers ~ith aromatic heterocyclic compounds, polyparabanic acids or cyclic polyureas, polysulphones, polyether ketones and polyacrylonitriles and acrylonitrile copolymers, which can optionally carry cationic or anionic groups. Such polymers are known (intex alia DE-OS tGexman Published 1$ Specification) 2,642,979, DE-OS (German Published Specification) 2,554,922, DE-05 (German Published Specification) 1,494,433, DE-OS (Cerman Publi~hed Specification) 1,570,552, DE-OS (~enman Published Specif ic ation) 1,720,744, DE-OS ~German Published Specification) 1,770,146, DE-OS ~German Publi6hed Specification) 2,003,398, EP 4,287 and EP 8,895); from these polymers, all of which, together with the fillers, form microporous membranes having pore diameters in the range from 0.001 to 10.0 ~m, the expert can ~elect the one which i6 chemically the most suitable for use on certain substance mixtures to be treated by pervapora-tion.
These polymer~ fihould have a softening point above 120C, preferably above 150C, in order to have an adequate margin for the process temperature of the Le A 26 866 - 4 -pervaporation and gas æeparation. These requirements are preferably met by a polymer from the group comprisin~
polyhydantoins, polysulphones, polyether ketones, poly-amides, polyimides, polyamide imides and polyparabanic acids. Such polymers particularly preferably contain aroma~ic groups in the polymer chain, for example poly-amides of phenylenediamine and isophthalic acid, poly-amide~ of hexamethylenediamine and an aroma~ic dicar-boxylic acid, such as terephthalic acid or isophthalic acid, polyimides of trimellitic acid or pyromell.itic acid and an aromatic diamine or diisocyanate, or polysulphones of bi~phenol A and bis(p-chlorophenyl) sulphone.
Polymers which have proved to be especially ~uitable are polyhydantoins of the following formula ¦ R1 C - C0 of - ~-Rl ~ tl, t N~co~N-R~-N~co~-R~ ~ -n wherein R1 and R2 independently of one another denote Cl-Ca-alkyl and R3 and R4 independently of one another denote C2-C8-alkylene, C6-Cl2-arylene, C6H4-CH2-C6Hh-~
-C6H4-C ~ ~3 )z-C6H4-, -C6H4-0-C6H4- or -C6H4-S02-C6H4.
C~-Ca-alkyl is, for example, methyl, ethyl, propyl, butyl, hexyl or octyl, and branched isomers thereof; Cz-CB-alkylene i~, for example, ethylene, propylene, butylene, hexylene or octylene, and branched Le A ~6 866 - 5 -rJ ~, i~omers thereof. C~-C~2-arylene is, for example, phenyl~-ene, biphenylene or naphthylene, preferably phenylsne. At least one of the radicals R3 and R~ is furthermore prefer-ably arylene.
The values for the index n can vary within wide limits and are 2-200, preferably 2-150.
The diphenylmethane-polyhydan~oin of the follow-ing formula may be referred to a~ ~n e~ample:

H3 CH~
~3C-C e CO OC C-CH3 --------*`Co ~ H2 ~ N`CO'N ~ H2 ~ n (II).
~herea~ 6emipermeable membranes of the the~rmo-plastics mentio~ed already ~hrink irreversibly, .in a manner known to the expert, when they dry ~lightly, the membranes to be employed according to the invention which are enriched with inorganic fillers exhibit no deteriora-tion in their properties here and thus retain their pronounced surface porosity.
The composite me~brane according to the invention furthermore consists of a permselective elastomeric separating layer applied to the membrane according to i).
For this, these elastomeric polymers are applied to the microporous membrane by means of a conventional casting technique. Examples of elastomeric polymers are polybuta-diene, polyisoprene, polychloroprene, poly(butadiene-co-styrene),poly(dimethyl~iloxane),butadiene-acrylonitrile Le A 26 8.66 - 6 -.

copolymers, polyether urethane and/or polyester urethane and polyurethane-polyureas. Some of these pol~mers, such as polybutadiene and poly(butadiene-co-styrene), only achieve their elastomeric properties after crosslinking S (vulcanization) by heat or ¢aused by activating radia-tion. Examples of solvents for the application of these polymers ares ~ oluene, cyclohexane, tetrahydrofuran, acetone, methanol, methyl ethyl ketone~ ethyl acetate~ dLmethyl-formamide, alkanes and water, if the elastomers areemployed in the form of their aqueous dispersions.
~ixtures of these ~olvents can also often advantageously be used.
The casting solu~ions contain the elastomeric polymers in a concentration of 5 to 50~ by weight, preferably 10 to 25~ by weight, based on the t:otal casting solution.
The mechanical stability of the composite mem branes according ~o the invention can furthermore advan-tageously be increa~ed by a procedure in which themicroporous membrane according to i) is first applied to a support layer of coarse porosity made of a ~on-woven fabric or a woYen fabric, before the separating layer according to ii) is applied to i). Materials for this support layer of coarse porosity are, inter alia, poly-ethylene, polypropylene, polyamide, polyester, poly-phenylene ~ulphide or ~lass fibres in the form of non-wo~en fabrics or woven fabrics.
The invention furthermore relates to a process for the preparation of the abovementioned composite Le A 26 866 - 7 -membranes, which is characteri~ed in that a) a filler having a 6pecific surface area of 5-200 m2/g is dispersed in an amount of 60-~0~ by weight, based on the weight of the polymer and of the filler, into ~he solution of a film-forming polymer, a homogeneous casting ~olution ha~ing a visco~ity of 50~-15,000 cp being for~ed, b~ this solution i~ processed to give a membrane in the form of a film, a tube, a hose or a hollow fibre, ~he solvent being removed by precipitation coagula-tion, and c) a permselective elastomeric separating laye:r is applied to the membrane in the form of a &olution of the elastomer, with subsequent removal of the solvent by evaporation, and if appropriate the final 6tate of the elastomer is produced by crosslillking (radiation or heat).
The pxecipitation coa~ulation can be co~ined with the additional evaporation of the solvent.
~0 Suitable solvents here are: dimethylformamide ~DMF), N~-methyl-pyrrolidone (NMP)/ dLmethyl sulphoxide (DMS0), dLmethy~acetamide, dioxolane, dioxane, acetone, methyl ethyl ketone or cellosolve, preferably DMF and NMP, particularly preferably D~F. To achieve t~e viscos-ity mentioned, the polymer is in general contained in the solution in a concentration of ~ - 10~ by weight, based on the total casting solution. Filler is dispersed into 6uch ~olutions with the aid of a rapid-rotating ~tirrer (di~solver). Such di~p~rsions can additionally al~o contain about 1-10% by weight of CaCl2 or LiCl, bas~d on Le ~ 26 866 - 3 -~ 'ii 'J ~;.ai~cll.

the total weight of the dispersion, as pore-forming components. Such dispersions as ~he casting solution are degassed by being left to stand or applying a weak vacuum and are then applied in layer thicknesse~ of 50-400 ~, preferably 80-150 ~, to a carrier ~ubstrate with the aid of a doctor blade. ~he solvent is then removed by eva-poration or, preferably, by dipping into a coagulation bathl for example into pure water. ~fter a ~esidence time of, for example, 2 minute6, the microporo~ ~embrane containing fillers can be removed from th~ coagulation bath and dried with hot air.
The carrier substrate employed for the applica-tion of the casting solution can be one whicn merely serves to prepare ~he microporous membrane according to i) containing fillers, and i6 therefore peeled off again from i) after the coagulation operation. For this, the carrier substrate must be smooth and is, for example, glass, polyethylene terephthalate film or a siliconized carrier material. However, if the composite membrane according to the invention of i) and ii) i8 to be pro-: vided with a support material for improving the mechanical stability, materials which are permeable to liquid are used as the carrier subs~rate, such as non-woven fabric or woven fabric, to which the microporous membrane i) containing fillex exhibits good adhesion.
Examples of suitable materials for such a support :Layer of coarse porosity are, as already described above, polyethylene, polypropylene, polyester, polyamide, polyphenylene ~ulphide or glass fibres in the fox~ of non-woven fabrics or woven fabrics. The simultaneous use ~e A 26 866 - 9 -~J 3~ i~ff lf r~ J _~

of such a support layer is preferred fQr the preparation of the composi~e membranes according to the invention.
Before the membrane i8 ~ipped into a coagulation bath, 1-30% by weight of the solvent used can be evapora-S ted at a temperature of 40-100C.
It is urthermore known that, to increase ~he surface area of membranes, as well as being u~ed in the form of films, the preparation of which has ~ust been described, these can also be used in the ~orm of ~ubes, hoses or hollow fibres. To achieve maximum membrane surface areas with the minimum possible apparatus vol-umes, these can ~e arranged and used in 6pecific separat-ing units (modules). Such tubes, hoses or hollow fibres can be prepared, for example, using a concentric two-component nozzla and forcing the above-described castin~
solution containing filler throu~h the outer annular gap, whereas a coagulating agent, such as water, and in addition air or an inert gas are forced through the central nozzle opening, the casting solution issuing from the no~zle also entering into a coagulation bath, such as water' coa~ulation is in this way performed from the inside and from the outside.
After removal of the solvent by evaporation or by coagulation and drying, a pexmselective elastomeric separating layer is applied to the microporous membrane i) containing filler by the casting technique. In this procedure, for practical reasons it is very advantageous that the microporous membranes i) containing filler can be stored, handled and further processed in the dry state without changing their pore ~tructure.

Le A 26 866 - 10 -~ he thickness of ~his separating layer is 0.5-S00 ~, preferably 5-50 ~.
The composite membranes according to the inven-tion are outstandingly ~uitable for use in processes for pervaporation and gas separation.
The inven~ion thus furthermore relates to such processes for pervaporation and gas separation, which are characterized in that a composite memhrane of the type described above is employed.
An apparatus such as is described in DE~AS
(German Published Specification) 2~627/629 has been used for carrying out the pervaporation. In this, the com-posi~e membranes prepared were used in a measurement apparatus which can be screwed together, the upper half of which consisted of a cylindrical chamber having a capacity of 300 ml, into which the mixture to be separa-ted (feed) was introduced. The lower part of the appara-tus was an approximately hemispherical cover of low volume with a discharge connector. ~he composit~ membrane to be tested was ~upported on the permeate side by a ~intered matal plate; the app~rat-~s was sealed by Teflon ~ealing rings between the upper part and the membrane and between the sintered plate and lower part o~ the appara-tus which can be ~crewed together. The chargin~ side of the composite membrane was under the hydrostatic pressure of the feed under atmospheric pressure, and the permeate was continuou61y ~ucked off on the permeate side of the membrane. For this, the discharge connector of the apparatus was connected to a vacuum pump by a line via three cold traps connected in 6eries, which were cooled Le A 26 866 - 11 .
. . .

;i~ ,,i with a dry ice-acetone mixture. The permeate was con-densed virtually completely in the cold traps. The active membr~ne area was 39.6 cm~.
Other experiments were carried out with the aid of a pervaporator module as described in DE-OS (German Publi~hed Specification) ~,441,190. Such a module con-~ists of a plurality of flat components combined in the ~ame way ~s filter presses or plate heat exchangere, each pervaporator unit consisting of a feed chamber and a permeate chamber separated from this by means of the composite membrane according to the invention, a large number of perYaporator units being connected in parallel to form a module, a condenser constructed in the same way heing applied to the module and the module and the condenser being combined to form one component by means of cover plates and tension rods, suitable seals being inserted as intermediate layers and connecting, feed and removal channels being formed at the edge.
The composite membranes according to the inven-tion, in particular in their preferred embodiment with asupport layer of a non-woven fabric or a woven fabric, are suitable for a large number of ~uch pervaporation tasks. Thus, ~or example, it i8 possible to remove organic substances from water with a high separation effect. As organic substances there may be understood here: alcohols, such as methanol, ethanol, propanol, butanol and the like; esters, ~uch as ethyl acetate, methyl acetate, methyl propionate and the like; aldehydes and ketones, such as acetaldehyde, acetone, butanone and the like; aromatic compounds, such as phenol, aniline, Le A 26 866 - 12 -;~.3 .4~

chlorobenzene, toluene, cresoll the isomeric chloro-toluenes and the like; chlorinated aliphatic hydro-carbons, ~uch as methylene chloride, chloroform and the like; and ethers, such as diethyl ether, tetrahydrofuran, dioxane and the like. These organic ~ubstances mentioned as example~ are characterized by a water ~olubility which is at least low and a vapour pressure which is adeguate for the pervaporation process. Those composite me~branes according to the invention in which the microporous membrane i) containing fillers has been finished with poly(dLmethylsiloxan~) as ~he elastomeric separating layer ii) have pro~ed to be particularly suitable, for example, for these separation tasks. The removal of organic substances in a concentration range of 10~ down to 1 ppm i8 appropriate according to the pervaporation process. To form the elastomeric separating layer, for example, polytdimethylsiloxanes) which contain on the one hand vinylsilane groups and on the other hand hy~rido-~ilane groups and which undergo a hydrosilylation xeac-tion, as a crosslinking reaction, by means of heat andunder catalysis of a platinum compound sre emp~oyed.
Crosslinking reactions of poly(~iloxane) are also pos-- sible by peroxidic crosslinking of poly(fiiloxane) con-taining vinyl groups, by photochemical crosslinking of poly(siloxane) containinq acrylate or methacrylate groups or by condensation of hydroxyl-containing poly(siloxane) with tri- or ~etrafunctional ~ilicon compound , for example ~ilicon tetraacetate.
Compo~ite membranes according to the invention w~ich carry on the microporous membrane i~ containing Le A 26 866 - 13 -fillers an elastomeric separa~ing layer ii) of cross-linked poly(butadiene) and butadiene-styrene copolymers (random copolymers or block copolym~rs) or poly(norborn-ene) or poly(octenamer) or poly(butadiene-co-acrylo-nitrile) or ethene-propene copolymers, ~uch as, for example, EPDM rubber with ethylidene-norbornene units, are furthermore ~uitable for this separation task of 6eparation of organic substanceR, such a~ ha~e been described above, from water.
~he poly(butadiene~ can b,e crosslinked by addition of ~mall amounts tO.1 to 4% by weigh~) of a free radical crosslinking agent, for example dii~opropyl peroxydicarbonate or dibenzoyl peroxide as a free radical crosslinking agent, at elevated temperature (typically 40-80C), or by ~ulphur-containing crosslinking reagents.
A suitabl~ molecular weight range for 6uch poly(buta-dienes) is about M~ = 500,000 - 2,000,000 g/mol The build-up o the poly(butadiene-co-~tyrenes~ can be a random distri~ution of the styrene monomer unit in the poly(butadiene), or in the form of a tri-block copolymer with styrene end blocks and a poly(butadiene) central part. The cro~slinking reaction and molecular weights of these butadiene-~tyrene copolymers are analogous to those of the pure poly(butadienes).
Another task to be achieved with the composite membranes according to the invention by pervaporation is the removal of benzene, toluene, xylene, ethylbenzene, propylbenzene, chlorobenzene, dichlorobenzene, bromoben-zene, phenol, ~niline and other aromatic substance6 ~rom aliphatic or cycloaliphatic hydrocarbons. ~ut~tanding Le A 26 866 14 -_ _ results have been achieved in this separation task if, in the context of the composite membranes according to the inventionr the microporous membrane i) containing fillers has been coated with an elastomeric separating layer ii) of elastomeric polyurethanes. ~uch a microporous membrane coated by elastomeric polyurethanes, ~3uch as polyester-urethanes or polyether-urethanes, is 6imilarly outstand-ingly suitable for carrying out the r~moval of benzene, toluene, xylene, ethylbenzene, propylbenzene, chloroben-zene, dichlorobengene, bromobenzene, phenol, aniline orother aromatic substances from water.
The separation factor ~, which represents a measure of th~ selective permeabili~y of the me~brane, is in general quoted as a measure of the separating action;
15 it is defined by the following equation:
CAp C~m ~ = -- x CBp CAm in which CAP and CBP denote the concentrations of substances A
and B in the permeate (p) and C~ and C~ denote the corresponding concentrations in the mixture (m) to be separated (feed), wherein A in each case denotes the componen~ to be remo~ed and B denotes the other or the remaining ~ompon-ents of the mixture.
Because of the fundamental sLmilarity, as Le A 26 B66 - 15 -described above, of pervaporation with gas separation in the case where the feed is brought in gaseous form to the membrane, the composite membranes according to the invention are likewise outs~andingly suitable for gas 6eparation. To inve6tigate gas s~paration, in the case of ideally miscible gases it is not necessary to investigate a gas mixture, but it i6 adequa~e to test ~he individual gases in pure form on ~he membranes.
The ~eparation capacity of 6uch membranes for ~uch gases can then be described by the ratio of the îndividual gas permeabilities to one another. A membrane is selective for a gas A over a gas B if -- ~ 1 PB
wherein PA and P~ denote the permeabilities of gas A and B.
Example 1: Preparation of a porous support structure, polyhydantoin containing TiO2 A casting solution con~isting of 800.0 g of an 18% strength solution of diphenylmethane-polyhydantoin in N-methylpyrrolidone ~NMP);
816.0 g of titanium dioxide (commercial product R-RB~from Bayer A~ uspended in the solution with the aid of a dissolver; and 480.0 g of NMP, was prepared, the desired visco~ity of 3,~50 cP being reached.
The weight ratio of thermoplastic polymer/filler was 15:85.

Le A 26 866 - 16 -~he casting ~olution was filtared through a 25 ~m metal sieve with ~he aid of a pressure filter, degassed in vacuo and applied to a polypropylene non-wov~n fabric with a wet application of 150 ~m u6ing a doctor blade.
The polymer was coagulated in pure water and the finished membrane was dried with hot air, The following can likewise be used a~ the carrier non-woven f~brics: polyethylene non-woven fabric, poly-ester non-woven fabric, polyester wo~en fabric, poly-phenylene sulphide non-woven fabric or ylass fibre woven ~abxic .
Example 2 Preparation of a porous e~port structure polyacrylonitrile containing TiO2 Analogously to Example 1, a polymer/filler dispersion ~15:85) having a viscosity of 4,680 cP was prepared from 400.0 g of Dralon T ~olution, 14% strength in DMF, : 317.3 ~ of ti~anium dioxide R-RB 2 and : 100.O g o DMF, and was processed to give a porous carrier ~tructure in the ~ame manner as in Example 1. The carrier non-woven fabrics used were: polypropylene non-woven fabric and polyester non-woven fabric.
Exam~le 3: Preparation of a porous support structure, polyamide containing TiO2 Analogously to Example 1, a polymer/filler di~persion (15:85) having a viscosity of 2~260 cP was prepared from 400.0 g of Durethan T 40 ~olution, 15% ~trength in DMF, 18.0 g of CaCl2, powdered, Le A 26 866 - 17 -C~ "~ 1 340.0 g of titanium dioxide R-RB 2 and 50.0 g of DMF
and processed on a polypropylene non-woven f~bric to give a porous carrier ~tructure in the s~me manner as in Example 1.
Example 4: Preparation of a porous support structure polysulphone containing TiO2 Analogously to ~xample 1, a polymer~filler dispersion ~15:85) having ~ viscosity of 3,520 cP was prepar~d from 800.0 g of an 18~ strength solution of polysulphone (Udel 3500) in N-methylpyrrolidone;
816.0 g of titanium dioxide (commercial product R-~from Bayer AG), suspended in the solution with the aid of a dissolver; and 4B0.0 g of NMP , filtered, degassed and processed on a polyester non-woven fabric to give a porous carrier structure in the ~sme manner as in Example 1. 0 Example 5: Preparation of a composite membrane, poly-(dimethylsiloxane) as the active separating layer The porous support structures described in Example 1-3 were coated with a 50~ strength solution of a poly(dLmethylsiloxane) which can be crosslinked by heat (commercial product Silopren 2530 from Bayer AG) in toluene in a wet layer thicknes of 100 ~m. After the solvent had been evaporated, crosslinking by means of heat was carried out at 80C for one hour.

Le A 26 866 - 18 -c`i ~s ~

~x- support Coating Dry layer ~mpl~structure material thickness from Example 5a 1 Silopren 2530 50 ~m 5b 2 Silopren 2530 50 ~m 5c 3 ~ilopren 2530 50 ~m 5d 4 Silopren 2530 50 ~m Y~oe~_5~ Preparation of compoæi~e me~branes, poly-(butadiene) as the acti~e ~ep~rating layer The porous support structure described in ExamPle 1 was coated with poly~butadiene) and poly(bu~adiene-co-styrene) in toluene solution. The d~y layer thickness of the active separating layer was calculated from the solids content of the particular casting solution used and the thickness of the wet application. Some oi the elastomers, as the active ~eparating layer, mention~_d in the ~ollowing table were crosslinked by heat trea~ment of the cast membrane at 80C for 16 hours, dibenzoyl perox-ide in the stated amounts in % by weight having first~een added to the particular casting solution as a crosslinking agent.

Le A 26 866 - 19 -Ex- Support Coating Cross- Dry layer ample ~tructure material linking thickness from ~xample agent [~]
content ~
6a 1 Buna 22 CB 35 6b 1 Buna 22 CB 0.3 % 35 6c 1 Buna 22 CB 0.6 % 35 : 6d 1 Buna 22 CB 0.9 % 35 ~e 1 Buna EM 1500 30 6f 1 Solpren 1205 30 6g 1 Solpren BL 6533 30 6h 4 Buna 22 CB 0.9 ~ 35 Buna 22 Q i8 a poly(butadiene) having a cis-content of 98~ and a number-average molecular weight o~
M~ = 600,000 - 700,000. Buna EM 1500 is a randam copoly-mer of 77~ by weight of butadiene and 23~ of sty:rene.
Solpren 1205, in con~rast, is an SBS tri-block copolymer containing a total o 25% by weight of styrene and 75% of butadiene, and Solpren BL 6533 is a block copol~mer containing 40~ by weight of styrene.
Exam~le 7: U~e of the composite me~branes for removing ethanol from water by pervaporation The pervaporation experiments were carried out in an apparatus ~uch as is described in DE-AS (Gbrman Pub-lished Specification~ 2,627,S29, using a mixture of 10%
of ethanol and 90% of wa~er; the experiments in each case lasted 4 hour~ at room temperature and the composition of the penmeate was determined by refractometry.

Le A 26 866 - 20 -Composite Permeate Permea~e Concentration Separation membrane pressure flow rate of Et~H in factor according g/m2 . h the permeate ~E~
to _ _ Example 5a 3.4 mbar 250 25 ~ 3.0 Example 5b 3.5 ~bar 184 28 ~ 3.5 Example 5c 3.0 ~bar 315 26 % 3.1 Example 5d 0.2 mbar 414 16 ~ 1.8 Example 6a 6.6 mbar 569 19 % 2.2 _ _ Example 8:
The membrane described in Example 5a was tested with the aid of a pervaporator modulel such as is des-cribed, for example, in DE-OS (~erman Published Specifi-cation) 3,441,190, by feed ~olutions of various oomposi tions flowing over it. The experimental conditions and results are shown in Figures 1 and 2.

Le A 26 866 - 21 -~ - - o ~ . .; 3 ~/ ~.g -~ ~! ? J ~, ~ ~ C ~

.: 1 ~ \ ~ ~0 o,~o ~ __.~ ~ ~ ~ ~ ~o ~ o~ ~ ~
U h ~ r1 rt J~
t~
% ~ dM UO~B~ U~I~UO~ 3a ~i ~ 3 ~
. . _ ~ ~r.~ ~
-- ~r~~ 0~ u ~,C

~ O " ~ c ~ ~ oO , a ~ ~o~ c ~ _ \ ~o o T \ ~ o ~ ~--~ ~ ~_ ' ~,o ~
~ o o o o no~ Z~/~ a~eS M0l2 a~a~le~a _ Le A 26 866 - ~2 -~3~mE~_2~ Use of the composite membranes for the removal of phenol from water by pervaporation ~ he pervaporation experiments wer~ carried out analogously to Example 7 using different content~ of phenol in the feed ~olution.

Composite Feed Permeate Permeate Concen- Separation membran2 concen- pre~sure flow rate tration factor according tration g/m2 . h of phenol ~nol to of phenol in the permeate Example 5a 0.1 % O.2 ~bar 58 0.7 ~ 6.7 Example 5a 1.0 % O.3 mbar 37 ~10 ~ -Example 5a 500 % 6.0 mbar 58 >10 ~ -15Example 6a 0.5 ~ 6.8 mbar 179 1.75 ~ 3.5 . . _ ~ _.
* Phase separation occurred in the permeate, 80 that af~er the satura~ion concentration o~ 10% had been exceeded, the phenol content could no longer be determined by refractometry.
Example 10 ~
The properties of the membrane according to Example 5a were tested in the same way as in Example 7 with a pervaporator modulP, by feed solutions (phenol-water) of various compositions flowing over it. Theexperimental conditions and results are ~hown in ~igures 3 and 4.

Le A 26 866 - 23 -_ i~ 3 ~ ' 3 I I I ~3 .o I I I I ~
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o ~' ~ o o o o ~o O O O O c~ O a~
[ (1~ z w) / 6~] t ~ MO~ e~ ad Le A 26 866 - 24 -r ~ J ~3~ ~

Example 11: ~e of composite membranes for the removal of acetone from water by pervapora~ion (20~ by weight of acetone in the feed) The pervaporation Pxperiments were carried out 5 analogously to Example 7.

Composite Permea~e Permeate Concentration Separation membrane pressure flow rate of acetone factor according gJm2 ~ hin the noceton~
to permeate Example Sd 16 mbar 378 32 ~ 1.9 Example 5a 16 mbar 110 85 ~ 23 Example 6a 16 mbar 318 45 % 3.3 Example 6b 15 mbar 181 86 % 24 15Example 6c 16 mbar 156 86 4 24 Example 6d lS mbar lS2 85 ~ 22 Example 6e 16 mbar 30 48 ~ 3.7 Example 6f 18 mbar 73 80 % 16 Example 6g 16 mbar 47 62 % 6.5 ~
Example 12: Preparation of polyurethane pervaporation membranes for the removal of aromatic~ from aliphatics The porous membrane matrix obtained accorcling to : 25 Ex~mple 1 was coated with a polyurethane. For this, 100.0 g of polybutanediol adipate/ average molecular weight about 2,250 g.mol~l, 51.7 g of methylene di(phenyl i~ocyanate) ~MDI) and 15 g of butane-1,4-diol Le A 26 866 - 25 -J ~ , t were allowed to react with one another in a known manner.
A 30% strength Isolution (weight/volume) of this poly-urethane in a mixture of dLmethylform~mide and butanone (3:2) was filtered through a pres~ure filter and left to S stand until it was free from bubbles. This polyurethane solution was applied ~o ~he porou~; sup~ort mem~rane.
described in Example 1 with a wet application of 300 ~m.
The solven~ was removed with the aid of hot air.
Example 13: Use of the composite membrane from Bxample 12 10for the ~eparation of toluene and cyclohexane by pervaporation The membrane described in ~xample 12 was tested with the aid of a pervaporator module, such as i's des-cribed, for example, in DE-OS (German Published Specifica-15tion) 3,441,190, by feed solutions (toluene-cyclohexane) of various compositions flowing over it. The experimental conditions and results are shown in Figuxes 5 and 6 Le A 26 866 - 26 -. ~ _ ~ S

O ~D

% (~ uo~eT~ua~uo~ ~e~3~aa _ O

o 3~ C
. ., ~ ~

h~ Y ~ I ., " ~
. _~ ~. O U 0~
nt~ L~ a~
U~
t~ O ~D
O O O O O O C
( (~ 3~W*W) /6~) dr 3~eT ~1~ e~eamlaa _ Le A 26 866 - 27 -- : :

Example 14: Gas permeabilities of a polyurethane composite membrane A COmpOBite membrane as descri~ed in Ex~mple 12 was prepared with the sole difference that the thickness of the we~ application was vnly 100 ~m.
A circular membrane of 8 cm diameter was inves-tigated at 23~C for the gas per~eabilities of the following gases:
lo-6 m3 GasPermeability P in ~
m2 , h . b a r Helium 499 Nitrogen 30 Oxygen 106 Carbon dio~ide S75 Argon 67 ~ethane 71 Butane 133 ~ . _ A surprisingly good separation capacity for oxygen compared with nitrogen can be seen from the values. The ~electivity calculated i~
Po 2 10~
= - = 3,5 5uch a E~eparation capacity enables oxygen from the air to be enriched on the permeate s ide or oxygen to be depleted on the feed ~ide, which allows, if appropriate, i~olation of 02-depleted nitrogen as an inert gas.

Le A 26 866 - 28 -

Claims

1. Composite membrane consisting of i) a microporous membrane, containing inorganic fillers, of a film-forming thermoplastic polymer, the fillers having a specific surface area of 5-200 m2/g and representing 60-90% by weight of the total weight of the membrane, and ii) a permselective elastomeric separating layer applied to the membrane.

2. Composite membrane according to Claim 1, charac-terized in that the film-forming thermoplastic polymer is chosen from the group comprising polyhydantoins, poly-amides, polysulphones, polyether ketones, polyimides, polyamide imides, polyparabanic acids and polyacrylo-nitriles.

3. Composite membrane according to Claim 2, charac-terized in that the film-forming thermoplastic polymer contains aromatic monomers and has a softening point of at least 150°C.

4. Composite membrane according to Claim 1, charac-terized in that the filler is titanium dioxide or a mixture of fillers in which titanium dioxide makes up 50% by weight of the mixture.

5. Composite membrane according to Claim 1, charac-terized in that polybutadiene, polyisoprene, polychloro-prene, poly(butadiene-co-acrylonitrile), an EPDM rubber, poly(butadiene-co-styrene), poly(dimethylsiloxane), poly-ether urethane or polyester urethane is used as the elas-tomer for the separating layer.

6. Composite membrane according to Claim 1, Le A 26 866 - 29 -characterized in that the microporous membrane according to i) is first applied to a support layer of coarse porosity made of a non-woven fabric or a woven fabric, before the separating layer according to ii) is applied to i).

7. Composite membrane according to Claim 6, charac-terized in that polyethylene, polypropylene, polyester, polyamide, polyphenylene sulphide or glass fibre in the form of non-woven fabrics or woven farics is employed as the material for the support layer of coaxse porosity.

8. Process for the prepaxation of a composite membrane according to Claim 1, characterized in that a) a filler having a specific surface area of 5-200 m2/g is dispersed in an amount of 60-90% by weight, based on the weight of the polymer and of the filler, into the solution of a film-forming polymer, a homogeneous casting solution having a viscosity of 500-15,000 cp being formed, b) this solution is processed to give a membrane in the form of a film, a tube, a hose or a hollow fibre, the solvent being removed by evaporation or precipitation coagulation, and c) a permselective elastomeric separating layer is applied to the membrane in the form of a solution of the elastomer, with subsequent removal of the solvent by evaporation.

9. Process for pervaporation and gas separation, characterized in that a composite membrane consisting of i) a microporous membrane, containing inorganic fillers, of a film-forming thermoplastic polymer, the fillers having a specific surface area of 5-200 m2/g and Le A 26 866 - 30 -amounting to 60-90% by weight of the total weight of the membrane, and ii) a permselective elastomeric separating layer applied to the membrane is employed.

Le A 26 866 - 31 -