FR2710550A1 - Asymmetric membranes of high selectivity for separation of gases and process for the manufacture - Google Patents

Abstract

Asymmetric membranes for gas separation, made of rigid aromatic polyimides or copolyimides of high selectivity which have as monomers the dianhydride of diphenyldi(trifluoromethyl)methane-3,4,3',4'-tetracarboxylic acid and a monoaromatic meta-diamine or a mixture of monoaromatic meta-diamines. These membranes are manufactured according to a process which includes: - dissolving the polymer in a specific volatile solvent for the polymer, - the application of a film of polymer solution to a support or the extrusion of a polymer solution, - the partial evaporation of the solvent from the film or the tube, placing the film or the tube in contact with a specific coagulant liquid for the polymer solution and drying the coagulated film or tube.

Description

The present invention relates to highly selective membranes for the

  gas separation by the technique of gas permeation. More specifically, the invention relates to asymmetric fluorinated polyimide membranes for gas separation as well as to a method of manufacturing said membranes. The membranes of the invention are

  particularly effective for the decarbonation of natural gas.

  It is known that certain fluorinated aromatic polyimides, more specifically polyimides having half dianhydride dianhydride

  3,4,3 ', 4'-diphenyldi (trifluoromethyl) methane

  Tetracarboxylic acid, hereinafter called "6F dianhydride", and half diamine diamine with one or more aromatic rings have, in the glassy state, high permeabilities to certain gases and much lower to other gases. Such polymers are said to be both highly permeable (implied by certain gases) and highly selective. For example, pure gas permeability measurements have shown that some fluorinated aromatic polyimides are much more permeable to hydrogen, carbon dioxide, or water vapor than to methane and much more permeable to oxygen. than nitrogen. It should be noted that if the potentialities of separation offered by a polymer can be anticipated in the first approach according to the ratios of permeabilities measured on pure gases, called ratios of theoretical separation factors, it is desirable to refine these first results by measures (more laborious) on mixed gases. Indeed, the selectivities observed on mixed gases may be lower than the theoretical separation factors, especially when a constituent of the mixture plasticizes the polymer and thus facilitates the transport of another gas. Carbon dioxide and water vapor, for example, have plasticizing tendencies towards various aromatic polyimides. The gas permeabilities of the polymers are temperature sensitive. Permeabilities increase and selectivities decrease with increasing temperature. In some applications, the gas permeation is carried out at temperatures well above ambient, for example from 50 to 60 ° C for the purification of raw natural gas. Of the aromatic polyimides derived from 6F dianhydride, some have above-average selectivities and retain much of this selectivity at relatively high temperatures such as those just mentioned. These highly selective polyimides are characterized by very high glass transition temperatures, of the order of 300 C or more, in relation to very reduced chain flexibilities. Such polyimides are highly desirable for the manufacture of gas permeation membranes, but they do not lend themselves to this fabrication because of poor solubilities in organic solvents, particularly volatile solvents to be used for the construction of asymmetric high flux membranes. These membranes have a structure consisting of a thin dense skin supported by a much thicker porous substructure. The skin

  dense brings selectivity and substructure mechanical strength.

  The permeability of a membrane being practically determined by that of its dense skin, the thickness thereof must be as small as possible, for example of the order of a fraction of a micron, whereas the thickness

  substructure can reach for example a fraction of a millimeter.

  The membranes may be in the form of flat sheets or in the form of hollow fibers. Conventionally, the asymmetrical structure is formed by contacting, on one side, a film or a capillary extrudate of polymer solution with a coagulating liquid, namely a liquid that is miscible with the solvent of the polymer but not solvent itself. even of the polymer. The face exposed to the coagulant is previously superconcentrated polymer, preferably by limited evaporation of solvent. In contact with the coagulant, the solution gels on the surface and then, in the rest of the volume, is divided into two dispersed phases, one rich in polymer, the other poor in polymer and rich in coagulant. Removal of the solvent and coagulant leads to the asymmetric membrane. The permeability, the selectivity and the mechanical strength of the membrane depend on the quality of the starting polymer solution. The filterability of the solution is an indication of its degree of homogeneity and stability. A non-filterable solution on a filter having a retention threshold of 0.5 micrometer, or at the most 1 micrometer, is to be considered as rich in aggregates

  coarse or as in the process of gelling.

  Given the poor solubility of the more selective, that is to say the more rigid polyimides derived from 6F dianhydride, it has been proposed to use slightly more flexible species thanks to a diamine half allowing local movements of chain. But the solubility is improved to the detriment of the selectivity of the polymer. Thus, the relatively soft polyimides obtained with methylenedianiline and oxydianiline generally have selectivities to CO2 / CH4 mixtures at 55 ° C of about 25 and 30 respectively while the more rigid polyimide obtained with metaphenylenediamine may have a selectivity of 44 for example. It has even been discovered that with this latter polyimide

  can, under certain conditions, reach selectivities greater than 50.

  The importance of the selectivity gains to be expected from the development of

  membranes from stiffer polyimides.

  It is an object of the present invention to provide asymmetric polyimide membranes rigid enough to provide high selectivities to gases even at temperatures well above ambient. Another object of the present invention is a process for producing said membranes

  Asymmetric rigid polyimides for gas separation.

  The membranes of the invention consist of polyimides or copolyimides of which the dianhydride half is the 6F dianhydride of formula I

0 F3C CF3 0

He c / 1 o C oC He He

O O

  l. and half diamine 1,3-diaminobenzene or metaphenylenediamine, abbreviated mPDA, of formula II

H2N NH2

  II. Alternatively, the 1,3-diaminobenzene may be replaced in part or in whole by one or more of its mono- or di-methylated derivatives on the aromatic ring. The membranes may optionally be coated, on the skin side, with a sealing layer of micro-perforations and silicone elastomer protection in accordance with

a well-known practice.

  The membranes of the invention constituted as indicated above have theoretical separation factors (permeate ratios measured on pure gases) for the CO2 / CH4 couple of about 70 at room temperature and effective selectivities (ratio of permeances measured on mixed gas) for the same CO2 / CH4 pair

  from about 50 to 90 at room temperature.

  The fluorinated polyimides used for the elaboration of the membranes have glass transition temperatures of at least 250 C and viscosities

  of at least 0.3 (measured on solutions in N-

  methylpyrrolidone containing 1.0 gram of polymer per milliliter of solvent). They can be prepared by conventional methods of polyimide synthesis. However, polyimides having both relatively high molecular weights and acceptable solubilities are more easily obtained by the so-called chemical method in which the cyclization of the polyamic acid is carried out by adding a desiccant (acetic anhydride plus triethylamine by

example).

  The invention relates to planar membranes as well as hollow fibers.

  In a preferred version, the flat membranes are mechanically reinforced by a commercial glass fabric or a nonwoven fabric.

polyester also commercial.

  The method for manufacturing the membranes of the invention is characterized mainly by the combination of a particular type of solvent and a particular type of coagulant, especially adapted to the polyimides used. The method of implementation of the method obviously have differences depending on whether to develop flat membranes or hollow fibers. The process comprises: a) dissolving one or more of the specific polyimides of the invention at a total polymer concentration of between 10 and 35% by weight relative to the

  solution, in a solvent comprising at least 85% by mass of 1,4-

  dioxane and from 0 to 15% by weight of N-methyl-2-pyrrolidone, N, N-

  dimethylacetamide and / or gammabutyrolactone; b) applying the solution thus obtained to a film support or extruding it with an annular die in the form of hollow fiber filled with liquid; c) evaporating a portion of the solvent; d) contacting the film or the hollow fiber with a coagulating liquid consisting of a mixture of acetic acid and water comprising from 1 to 85% by weight of water, which mixture can be added in small amounts, other organic acids; e)

  to dry briefly the film or the hollow fiber, preferably washed with

  preliminary with water, methanol or ethanol; optionally f) subjecting the film or hollow fiber to heat treatment; and optionally g) coating the skin of the membrane with a thin layer of silicone elastomer intended to provide protection against abrasion and, where appropriate, to seal microcracks or microperforations. The process is generally carried out at room temperature at

  the exception, of course, of step (f), heat treatment.

  The different steps of the process are described in more detail below. Unless otherwise specified, transactions are carried out at

ambient temperature.

  The dissolution of the polyimide (s) is carried out in a solvent mixture prepared in advance. The main solvent, 1,4-dioxane, and the

  the complementary solvents, N-methyl 2 pyrrolidone, N, N-

  dimethylacetamide and / or gammabutyrolactone, are preferably dehydrated on molecular sieve 3A before use. The solution can have a polymer concentration of 12 to 35% by weight, preferably 12 to 30% in the case of flat membrane and 15 to 35% in the case of hollow fiber. Concentration sufficient for the solution to have a viscosity of at least 100 poises reduces the risk of rupture of the nascent fiber. On the other hand, solutions with a concentration greater than 35% by weight tend to give low permeability membranes. The polymer solution is filtered

  up to 0.5 and, if possible, about 0.2 micrometer.

  For the manufacture of flat membrane, the solution is applied using a bar or a knife on a support consisting preferably of a fabric or non-woven whose uncoated side is protected by a detachable polyolefin film against subsequent contact with the coagulant. The fabric, or the nonwoven, will remain embedded in the membrane and strengthen its mechanical strength. If the temperature chosen for the heat treatment does not exceed about 200 ° C., a commercial polyester nonwoven may be used. Beyond this, commercial glass fabric sized with a silane adhesion promoter, such as phenyltriethoxysilane, is used. The thickness of polymer solution

  deposited is preferably between 50 and 300 micrometers.

  The hollow fiber is obtained by extrusion of the polymer solution through the annular orifice of a die also comprising a circular central orifice through which a liquid for filling the core of the central fiber or liquid is ejected. The two orifices are separated by a tubular wall of negligible thickness at its end. The diameter of the central orifice and the width of the annular space are preferably substantially equal and between 0.05 and 0.5 millimeters. The central liquid is preferably a mixture of solvent and antisolvent in

  proportions conferring on the mixture slightly coagulating properties.

  The preferred liquid flow rate is around one-eighth the solution flow rate.

  From a distance of the order of 5 to 10 millimeters of the knife or orifice of the die, it is advantageously possible to expose the film or the extrudate to a flow of nitrogen which produces a superficial concentration of polymer. by solvent evaporation. The gaseous stream is guided towards the surface of the bath and released about 5 millimeters above it. Although the rate and rate of flow of nitrogen can not be set independently of the duration of exposure of the film or hollow fiber to this circulation, and vice versa, there is some latitude in the choice of operating conditions. In a preferred implementation of the process, the evaporation time is between 0.3 and 1 second and the gaseous vein has a thickness of 0.5 to 1.5 cm.

  and an average speed of 2 to 10 centimeters per second.

  The film or hollow fiber is then immersed in a coagulant bath where they stay for at least 4 seconds and preferably between 5 and 20 seconds. The coagulant consists of a mixture of acetic acid and water of acetic acid content included

  between 15 and 99% by weight and preferably between 15 and 80% by weight.

  More particularly in the case where the diamine half of the polyimide is 1,3-diaminobenzene, the preferred water content in the coagulant is between 40 and 85% by weight when the solvent mixture comprises N-methyl-2-pyrrolidone between 50 and 85% by weight when the solvent mixture comprises N, N-dimethylacetamide and between 55 and 85%

  in bulk when the solvent mixture comprises gammabutyrolactone.

  Optionally, this coagulant may be added with 1 to 5% by weight of formic acid and / or propanoic acid. It may also contain small amounts of methanol and / or ethanol, preferably less than one fifth of the body of water. It is filtered for example at about 0.2

micrometer before use.

  The coagulated membrane may advantageously be washed in a bath of water or light alcohol such as methanol or ethanol after removing, if necessary, the polyolefin protection. The residence time of the membrane in the washing bath is preferably greater than

  seconds and can be up to 5 minutes, for example.

  The membrane is dried in a stream of air at a temperature between ambient temperature and about 50 ° C. Then, the membrane is subjected to a heat treatment, preferably under primary vacuum, at increasing temperature, up to a value of between 90.degree.

  and 350 C and preferably between 110 and 200 C.

  Finally, the membrane may be covered, on the skin side, with a thin layer of silicone elastomer. For this, the skin of the membrane is brought into contact for a few seconds to a few minutes with a commercial formulation (such as, for example, the product Sylgard 184 from Dow Corning) diluted in a light saturated hydrocarbon such as

  pentane, which is allowed to evaporate at the end of the operation.

  The asymmetric membranes according to the invention are remarkable not only for their high separation factors and selectivities with respect to gases at ambient temperature but also by their higher temperature physical stability which renders them effective for the separation of hot gases. In this respect, the preferred membranes are those which consist of

  polyimide synthesized from 6 F dianhydride and 1,3 diaminobenzene.

  These membranes may have, in particular, theoretical CO2 / CH4 separation factors of approximately 100 to 110 at room temperature and from approximately 75 to 85 to 55 ° C. and selectivities of approximately 80 to 90 at ambient temperature and from approximately 40 to 70 to 55 C. The CO2 permeances of these

  Preferred membranes may be in the range of 2.10-10 to 4.5.10-10 Nm3.

  m-2.sl.Pa-1 (ie, about 2.7 × 10 -5 to 6.0 × 10 -5 Ncm 3 cm -2-1.cmHg -1) at room temperature and from about 2.5 × 10 -10 to 6.10- 10 Nm3.m'2.s'l.Pa 1

  (ie, about 3.3 x 10-5 to 8 x 10 x 10 Ncm 3 cm -2-s-1.cm Hg-1) at 55 ° C.

  The examples which follow are given by way of illustration of the invention and in no way limit the scope of the invention. The gas permeability measurements in a mixture are carried out under the following conditions. The skin side of the membranes is swept by a circulation of gaseous mixture under pressure at a rate sufficient to consider that the composition of this mixture is affected negligibly by the permeate flow. This flow rate, determined by successive approaches, is such that the partial flow rate of gas circulation that permeates the most rapidly (CO2, H2

  or 02) 50 times the partial flow of the same gas in the permeate stream.

  The permeate composition is determined by gas chromatography.

  For the calculation of mixed gas permeances, the partial pressure differentials of each gas are used. The (theoretical) separation factors and the (actual) selectivities are the two-gas permeation ratios measured respectively on pure gases and on gases in

mixed.

Examples 1 - 3

  Examples 1 to 3 illustrate the production of flat asymmetric membranes of polyimide 6F / mPDA under different conditions of a solvent medium for the synthesis of the polymer and the preparation of the solution.

  coagulate. The composition of the coagulant is adjusted to each case.

  In Example 1, a fluorinated aromatic polyimide whose repeating unit has formula III

0 F3C CF3 0

  It is prepared by a method of chemical imidization. To a solution of 43.26 g of 1,3-diaminobenzene in 700 ml of N-methyl-2-pyrrolidone under nitrogen is added gradually and with stirring 177.70 g of dianhydride "6F" (formula I). After the addition is complete, stirring is continued for 1 hour. Then, without stopping the stirring, 700 g of an equiponderal mixture of acetic anhydride and triethylamine are introduced. Stirring is continued for 3 hours. The polyimide is precipitated by pouring the solution into several times its volume of ethanol with vigorous stirring. Filtered, the precipitate is washed and dried under vacuum for 12 hours at room temperature and then 4 hours at 60 ° C. and finally 2 hours at 150 ° C. Analysis of the solid obtained

  indicates that it still contains 0.5% by weight of N-methyl-2-pyrrolidone.

  The polyimide has an inherent viscosity of 0.80 dl / g.

  This polyimide is dissolved at room temperature, under helium and with slow stirring, in a mixture previously dried over molecular sieve 3A of 1,4-dioxane and N-methyl-2-pyrrolidone so as to obtain a mass composition solution. following: 6F / mPDA polyimide: 22%, 1,4-dioxane: 74%, N-methyl-2-pyrrolidone: 4% including the residual amount in the polymer. The solution is filtered to 0.2 IIm under helium pressure and then allowed to degass under helium at atmospheric pressure for 12 hours in a container.

  wide enough so that the liquid height does not exceed 5 cm.

  A solution film approximately 150 μm in thickness is deposited using a blade applicator on a strip of commercial polyester nonwoven 1 m thick and 1 m wide advancing to the speed of 3 m per minute. The film is exposed for 6 seconds to a tangential stream of dry nitrogen of 300 l per minute flowing between the film and a wall placed at 1 cm thereof, in the opposite direction to the direction of advance of the film. The wall is folded over the edges so as to prevent the flow of nitrogen from reaching the

  face of the film located on the non-woven side.

  The film is then immersed for 15 seconds in a coagulant bath consisting of a mixture, filtered at 0.2 μm, acetic acid and water at 52% by weight of acid, a mixture which is continuously renewed at the rate of 51 by

  minute. The film, which has become an asymmetrical membrane, is washed against

  running for 20 seconds in a bath of ethanol hydrated to 10% by weight of water, renewed at a rate of 5 I per minute. The extrusion, coagulation and washing operations are carried out at about 20 ° C. The membrane then passes through a drying tunnel with dry air at 40 C before being wound on a metal coil. The coil is placed in a vacuum oven where the membrane is exposed to a temperature of C for 12 hours. Finally, the membrane is subjected to a conventional treatment for coating the skin with a silicone elastomer layer. The membrane is unwound from its coil horizontally, the skin side facing down. The skin is sprayed with a solution of 7% by weight in pentane of the commercial product Sylgard 184 (from Dow Corning company) On the edges, a margin of 3 centimeters is obscured by a Teflon mask.This margin is reserved for sealing of the membrane during the preparation of conventional spiral-type modules The membrane is dried at 40 C under light weight

  nitrogen stream before being rewound onto another coil.

  Permeances. separation factors and selectivities of the membrane are evaluated using measurements carried out on pure carbon dioxide (CO2), on pure methane (CH4), on a CO2-CH4 mixture saturated with water vapor, a mixture H2- CH4 and, finally, a 02-N2 mixture. The measurements on the mixture C O 2 and CH 4 are carried out under two different conditions of pressure and temperature, including conditions combining relatively high temperature.

  high and significant partial pressure of CO2.

  The results are in the attached Table I.

  Example 2 differs from Example 1 in the use of N, N-

  dimethylacetamide as a solvent for both the synthesis of the polyimide and for the preparation of the solution to be coagulated, which leads to change also the composition of the coagulant. The inherent viscosity of the polyimide is 0.75 dl / g. The polymer obtained has a residual solvent content of 0.7% by weight. The mass composition of the solution to be coagulated is as follows: polyimide 6F / mPDA: 22%, 1,4-dioxane 74%, N, N-dimethylacetamide: 4%. The mass composition of the coagulant is

% acetic acid and 45% water.

  The permeances, separating factors and selectivities of the visceral membrane

  with respect to the gases are given in the attached Table 2.

  Example 3 differs from Example 1 only in the use of gammabutyrolactone for the preparation of the polyimide solution to be coagulated. The synthesis solvent and the coagulant are unchanged. The solution to be coagulated, which contains a little synthetic solvent provided by the polymer, has the following mass composition: polyimide 6F / mPDA: 22%. 1,4-dioxane 74%, gammabutyrolactone

  3.9%. N-methyl-2-pyrrolidone: 0.1%.

  The permeances and selectivities of the membrane vis-à-vis the gases are in

annexed table 3.

  Examples 4 and 5 These examples illustrate the production of plane asymmetric membranes in

  monomethylated 6F / mPDA polyimides on the aromatic ring of the diamine.

  These polyimides have much higher permeabilities than the

  polyimide 6F / mPDA but, in return, lower selectivities.

  Example 4 relates to an asymmetric flat membrane consisting of a

  polyimide obtained by polycondensation of 6F and 2,6-dianhydride

  diaminotoluene or 2,6-toluenediamine, abbreviated to 2,6-TDA, and whose repeating unit has formula IV

0 F3C CF3 O

He I 1 C

II I

0 O CH3

  IV Synthesis of this polyimide is carried out as in Example I except that 48.87 g of 2,6-diaminotoluene are reacted with 177.70 g of 6F dianhydride. The polyimide has an inherent viscosity of 0.83 dl / g. The development of the membrane is as in Example I except that the coagulant is composed of 55% by weight of acetic acid and 45% by weight of water. The gas permeances and selectivities of the membrane are

in the attached Table 4.

  Example 5 relates to an asymmetric flat membrane consisting of a

  polyimide obtained by polycondensation of 6F and 2,4-dianhydride

  diaminotoluene or 2,4-toluenediamine, abbreviated as 2,4-TDA, and whose repeating unit has formula V

O F3C CF3 0

He / I

C C

-N JJ F N Q CH3

\ C m C / v H v v There he

0 0

  The synthesis of this polyimide is carried out as in Example I except that 54.48 g of 2,4-diaminotoluene is reacted with 177.70 g of

6F dianhydride.

  The polyimide has an inherent viscosity of 0.91 dl / g. The membrane is prepared as in Example I except that the coagulant is composed of 57% by weight of acetic acid and 43% by weight of water. The permences

  The gases and selectivities of the membrane are in the attached Table 5.

  Comparative Examples 1-22 These Examples Illustrate the Poor Performance in Gas Separation by Lack of Selectivity and / or Permeability of Flat Asymmetric Membranes Developed by Procedures Different from the Process of the Invention (Example 1) by the Nature of the Solvent polyimide and, optionally, that of the coagulant. The results are in the attached Table 6. Comparative Examples 23-26 These examples illustrate the effect, on the gas separation performance of the asymmetric membranes obtained, of the use of production procedures differing from the process of the invention (example 1) only by the nature chemical coagulant. The results, presented in the attached Table 7, reflect a very important

decrease in permeances.

  Comparative Examples 27-30 These Examples Illustrate the Effect on the Gas Separation Performance of the Asymmetric Flat Membranes Obtained from the Use of Production Procedures Which differ From the Process of the Invention (Example 1) Only by the Proportions components of the coagulant. The results are in Table 8 (Appendix). They indicate a rapid decrease in selectivities when the acetic acid content of the aqueous acetic acid solution increases beyond its maximum value in the process of the invention. The results indicate, on the other hand, a rapid decrease in permeances when the acetic acid content of the aqueous acetic acid solution decreases from its minimum value.

in the process of the invention.

  Comparative Examples 31 and 32 These examples illustrate the effect, on the gas separation performance of the planar asymmetric membranes obtained, of the use of production procedures differing from the process of the invention only in the proportions of the solvent components of the polyimide. The results are in the attached Table 9. They indicate a rapid decrease in selectivity as the 1,4-dioxane content of the solvent decreases from

  its minimum value in the process of the invention.

  Examples 5 and 6 Examples 5 and 6 illustrate the production of asymmetric membranes in

  fluorinated aromatic polyimides in the form of hollow fibers.

  Example 5 relates to asymmetric hollow fiber polyimide

6F / MPDA.

  The synthesis of the polyimide and the preparation of the solution to be coagulated are carried out as in Example 1, including the amounts of polymer and solution. This one is composed, in mass, of

  22% polyimide, 74% 1,4-dioxane and 4% N-methyl-2-

  pyrrolidone. In addition, a stock of central liquid is formed by mixing 50 g of acetic acid, 50 g of water and 25 g of 1,4-dioxane and filtering the mixture to 0.2 g. A die with the following characteristics is used: outer diameter of the annular orifice: 0.6 mm, internal diameter of the annular orifice: 0.2 mm, central orifice diameter: 0.19 mm. The end of the separation tube of the two orifices is located

  I mm in front of the end of the outer wall of the annular orifice.

  The coagulation tank is filled with 20 I of coagulant prepared as in Example 1 and consisting of an aqueous solution of acetic acid at 52% by weight of acid. The height of liquid in the tank is 1.2 m. The coagulant is continuously renewed at a rate of 0.5 l per minute. The end of the die is positioned 5 cm above the level of the coagulant. It is engaged in a vertical glass tube of 2 cm inside diameter which opens at 5 mm above the surface of the coagulant. The development of the hollow fiber is done under the following conditions. The polyimide solution is extruded at a rate of 200 ml per hour while the central liquid is emitted at a rate of 30 ml per hour and dry nitrogen circulates around the extrudate in the downflow direction at a rate of 92 liters per hour. hour. The extrudate stays for 15 seconds in the coagulant before emerging vertically in the form of a flexible solid hollow fiber which is pulled at a speed just sufficient to prevent its accumulation in the tray. The hollow fiber is then washed against the current for 20 seconds in a bath of ethanol at 10% by weight of water, renewed at a rate of 0.5 l per minute. The extrusion, coagulation and washing operations are carried out at about 20 ° C. Once washed, the fiber passes through a drying tunnel in dry air at 40 ° C. before being deposited in a cylindrical metal container. The container is placed in a vacuum oven where the

  membrane is exposed to a temperature of 150 C for 12 hours.

  Finally, the membrane is conventionally coated with a silicone elastomer layer. For this, the hollow fiber, taken up by a winding device, passes through a 20 C bath of 7% by weight solution in pentane of the commercial product Sylgard 184 from the company Dow Corning and

  is dried under a slight stream of nitrogen at 40 C.

  The permeances and selectivities of the membrane, measured on gas

  mixed are given in the attached Table 10.

  Example 6 relates to asymmetric hollow fiber made of polyimide 6F / 2,6-

  TDA. The synthesis of the polyimide is carried out as in Example 4 and

  the development of the membrane as in Example 5.

  The permeances and selectivities of the membrane, measured on gas

  mixed, are in the annexed table II.

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  T oo op u M uio.J o o u u r u d o u r w o o o u r w o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o g g Olu

9W Z 9IIAJPIS

[% C

06 * J

  09 am oeoufwe 0Q LS. "<9., mus IdM t:,. U Jd I * 1 pIP: .. I s10.d udl1: .. U..4! Jd dlN ç ': .. s1' dfl 9 : Jd DW: * P4dL w: e * ie.J w *: qJ 0: .eJw4d.j3.O: 'Se0mluIlej (', u% ce) ,, ('w% or) eC) (Pwo) o ( 0oUCo ('wOw%' OO ('woC) o ("H) 4" O :)) s6e6HP e <inlN (reo nse ") s> Jejyg sJnd ze ne.e

Table 6

  (Comparative Examples not in Accordance with the Invention) Solvan Polymide Solvent Co4gu Oualte CWaracuti: uLeaPv ,, .- lo -rt, & pàm * j Pmmeinatnoià20C s4wmangdegaz O raluraen physics PeMs;, e ...: * o, IMPa Unme : 7 MP of the Solubunda the soiu # 011 Paaonaw: O.II UPa re, t.; .. lo,; eó.ç ". P4U!: Otl'dPl rdi, é. COMélange ke F.m2Q * CH4 Cm44

3. 70% m n. S0% mo.

  (saturated with water) Pe.4 ,, * 4e "ee, '' '' '' '', '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '', '' '' '' '' '' '' '' '' '' '' '' ',' '' '' '' '' '' '' '' '' '' '' '' ',' '' '' '' '' '' '' '' '' '' '' '' '' ',' '' '' '' ',' '' '' '', '' '' '', '' '' ',' '' '', '' '' '', '' '' '' ',' '' '' ',' '' '' ',' '' '', '', '' '' '', '', '' '', '', '', '', '', '', '', '', '' '' ',' ',' '' '', '' '' ',' ',' '' '', '', '', '', '', '' '' MSOCK CO, COX = <m * OOQ CO Q ú 4 1 6FImPDA N-methyl-2-water 0.5 1m limpid 12 0 2u, 47 12 38 47 136 ungelled pyrrolidone 2 6F / mPDA N- methyl-2-methanol 0.5 μm limpid / 1 / O0.1 4 s 14 37 55 125 ungelled pyrrolidone 3 6 IFmPDA N-methyl-2-ethanol 0.5 clear pm 45 o 46 13 37 49 130 ungelled pyrrolidone 4 6F / mPDA N 5-methyl-2-acetyldehydrate 0.5 gm clear 4f7 Oi40 4. 16 35 69 108 ungelled acetic pyrrolidone water 50-50% mass 6F / mPDA N, N-dimethyl-water 0, clear limpid I / t 14 36 56 118 acetamide ungelled 6 6F / mPDA N, N-dimethylmethanol 0. 05pm limpid 48 0.44 41 17 35 68 112 ungelled acetamide 7 6F / mPDA NN-dimethyl-acid 0.Spm clear D0 o sO 4O 19 34 71 103 acetamideacetic no gelled water 50-50% mass c1 ul 8 6F / mPDA Tbutyro-water 0.5 Mm limpid 10 10 39 41 142 ungelled lactone 9 6F / mPDA.-hItyro-methanol 0 Clear Im lactose ungelled lactone Table 6 (cont. at IOSm ages of physiological lilabonysis Pr.t., a..t, MP Pro ame: 7 MPa of the lolunOl of Lia SOluton Prs.; * sio ntMWo, .P: a 0.1! Filtered MPa Mixture cOe H2 Merging. C, 4

M C * 4

CH4

- 70% mo ml. 20-80 mol%

  (Of course.),.,,,,,,,,,,,,, - 'CO, _; c, 0, 0 I CCO1; sr

  ## STR2 ## a lactose acetic acid + ungelled water 50-50% mass 11 6F / mPDA tetrahydro-water 0, 5 Amine O1 (a 4 7 37 27 120 furan for gelation 12 6F / mPDA tetrahydro-methanol 0, clear Spm, 1 l 77 36 29 115 turan in the course of gelling 13 6F / mPOA tetrahydroacid 0.5 Pm limpid 80 2, 53 79 33 34 101 acetic furan + in the waterway 50-50% gelling mass 14 6F / mPDA acetone water 1 clear Pm 7 '4,7 75 36 20 125 gelling 6F / mPDA acetone methanol 1 pm crystal clear 16 4F / mPDA acetone acid 1 wm limpid B to 8 34 28 105 acetic + in the waterway 50-50% gelation mass Table 6 (su;) (comparative examples no in accordance with the invention) Example Polytype Solvent Co40ln OuaHi4 Cncdstiqum v., .. l '.,. O', Z s .. f .. po .., .. PM20eC ur mdlngs gas uiOtI PlU -,. ## EQU1 ## .Ii..oe, 1g L Pa Pra.M anlaw. 1 MPa e Cm MCeO2angep H * CH 4.DTD: - 70% m.M 20.O0% mO.

  (satuié of water) Pa; B ..;, .. P ....,. i * r. te .... k PeAV S4wan P SRb.ndm 'COl ;. EXAMPLE 3: O / <, & 3 * ox> # am Mo "17 6F / 2.6-TOAN-methyl-2-water 0.5μm limpid & 0l / 70 40 27 34 85 54 ungelled pyrrolidone 18 6F / 2,6-TDAN-methyl-2-methanol 0.5 clear limon 3 g unpyretic pyrrolidone 19 6F / 2,6-TDAN-methyl-2-acid 0, Spim limpidin 38, -, 2 36 30 121 44 acetelic pyrrolidone + ungelled water 50-50% mass 6F / 2.4- TDAN-methyl-2-water 0.5 pm clear 41 4, 3 <40 33 97 52 ungelled pyrrolidone 21 6F / 2.4-TDAN 2-methyl-2-methanol 0.5 clear pine 4 6, 39 45 31 115 47 ungelled pyrrolidone 22 6F / 2,4-TDAN-methyl-2-acid 0.5 sec limpid 5 36 48 30 137 42 unreacted pyrrolidone acetic acid water 50- 50% mass t0, Mg _a 7 .. _. ' _N_.m4.a.a (. _

Table 7

  (comparative examples not in accordance with the invention) Eemope Poly'm SolviM Coagula Or "i4 Cacértiqu Pv-, a; Z." s .. SaI "Poemmkl. to 20 ° C, on a physical plane of the world, ",,,,,,,,,,,,,,,,,,,,,,,,. S RP Pru4nMv: 0.11 MPU 6lr44CO Manp l * Meteorecoe MeIMP b'c2 CH4 q Cm

- 70% ml 20 - 0% md.

  <she is crom) Peam;; *, i. P. '' '' '' '', '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' =: G, m, o 23 6FImPDA 1,4-dioxane + water 0,5 m limpid iz 0o1 3 12 33 45 110 N-methyl-2non-gelled pyrrolidone -5% mass 24 6F / mPDA 1,4-dioxane + methanol 0.5milimide AS 0, - '. N-methyl-2-non-gelled pyrrolidone -5% mass 6F / mPDA 1.4-dioxane ethanol 0.5 m limpid 2, N-methyl-2- non-gelled pyrrolidone 5% mass 26 6F / mPDA 1,4-dioxane. n-heplane 0, clear sim 40 O 205 10 42 38 155 N-methyl-2. ungelled pyrrolidone -5% mass

Table 8

  (comparative examples not in accordance with the invention) Eemp4 Polymidm SolvanlCo4gu4la Ouaté Cvaa4dntiicuPv, .. ':.;. O'C P .. a.n iJiP u Cà W u r mix of ga de HfllMtPvyslquel v <, 1. Prasom UIN: 7MP of the Soil of the Silk, Pelim: O.1 MP Mixture CKMange, CK, ClM

- 70% nol.20 -% m d.

(sIlatur ea)

  Per. .. (t ".. f M d4 aPemi 'If l P n deSil.

  COA to C, at a pH of 0.5 mPDA1,4-dioxane + 0.5 micron clear acid 54 A IS 3 (52 30 130 12 N-methyl-2-acetic acid + ungelled pyrrolidone water -5% mass 98-2% mass 28 6F / mPDA 1.4-dioxane + acid 0.5 pm limpid 46 o 7 s 5 43 49 163 128 N-methyl-2-acetic + ungelled pyrrolidone water -5% mass 90-10 % mass 29 6 IFmPDA1,4-dioxane + acid 0.5u m limpid 30 o Si'6 29 47 109 163 N-mne * / - 2-acetic + ungelled pyrrolidone water -5% mass15- 85% mass 6F / mPDA1,4 -dioxanic acid 0.5 & m limpid 2 O 50 23 41 84 149 N-methyl-2-acetic acid + ungelled pyrrolidone water -5% mass5-95% mase

  an.ioa tien.e $ a year M 1 1 _ 7.5. ir'3 Nm.m 4._ P_. _ _.

Table 9

  (Comparative Examples not in Accordance with the Invention) Eaxample Polyside SolventConguai Quaik Cvracanliqum Pvm, ... ',: *. ## EQU1 ## ## EQU1 ## ## where ### is greater than 1 milliliters per gram of fertilization per minute. als e.Md:O.IP ilr 'Mix this MahOp M2 *, CH - 70% mel 20 -10% mo t (satmw dsemi Pgv.eaaa t -s frustàP-eec S & 14g * P Wnua-M shbouge a CO 1 CH 4; Cs 4 c 1: C + *: Coo at 31 6F / mPDA 1,4-dioxane + 0.5 acid in clear 15 45 '5 38 56 137 Ungelled N-methyl-2-acetic acid I pyrrolidone u 30% mass 50-50% mass 32 6FImPDA 1,4-dioxane + acid 0,5 mm clear 25 4, s 1 22 43 79 168 N-methyl-2-acetic acid + ungelled pyrrolidone water -20% mass 50-50 % mass -ae e (nh "

  ## EQU1 ## ## EQU2 ##

  (dt1'0 P s uo d u ud o udd o ..... n o ... n o ... # Q 0? T.4ou1U4jd 6 g69 6'140. Ods / of ZO Oi4 tO. "Uu * dd {m C: .. Uo'Jd cl *: .. u J l :. - uor: ..OU. $ SS .. il% d d ...- Jd 3, o :, 3do: oinieJu ", j: .fi: dM4 & u, oje: oSim,. N: ',, wsJ 4 * 1of *

(i we) 4 ('u% o e)' m.

  (Po% o) O (1OW% 0 4 ('w% o) o. (' W% oc) o (* 'H). EO)

  oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo

  neelqelJ (1d1 g t 'O op jAuoussA o) Wom our4g1od -teú vpmor * 91 .. wlPPS. SO 'Adw OTZ * M. *' Jd 1 .., SO, 9U5 d Àv ú, C :: .. uo I 'd rp' ': orS..uesaUddf li1: .. dVJd O: .emdu: Esniwè tog: * Mq'adwej 3 ,: e sO1k, OEe :: I.j'edui low% Oe)% * (low% CO) 4 (, Puoz) (how% O (, Uwo / c) O ('pH ), P'C) o nuelquel "., 'To eIml Jil (11USD 9ns) aOuvfqe. Z L / neelqel

Claims (15)

  1. An asymmetric gas separation membrane made of polyimide or rigid aromatic copolyimide having as monomers the dianhydride of 3,4,3 ', 4'-tetracarboxylic acid diphenyldi (trifluoromethyl) methane and a monoaromatic metadiamine or a mixture of monoaromatic meta-diamines, said membrane comprising a dense skin and a porous sub-structure and having, for the CO2 / CH4 pair at room temperature, a theoretical separation factor of about 70 to 110 and an effective selectivity of about 50 to 90. 2. A membrane according to claim 1 wherein the   Monoaromatic meta-diamine is 1,3-diaminobenzene.   3. A membrane according to claim 1 wherein the monoaromatic meta-diamines are mono-methyl derivatives of 1,3-diaminobenzene. 4. A membrane according to claim 1 wherein the one or more   Monoaromatic meta-diamines are dimethyl derivatives of 1,3-   diaminobenzene. 5. A membrane according to claim 2, exhibiting a separation factor for the CO 2 / CH 4 pair at room temperature.   theoretical about 100 to 110 and a selectivity of about 80 to 90.   6. A membrane according to claim 5 having, for the CO2 / CH4 pair at 55 C, a theoretical separation factor of about   75 to 85 and a selectivity of about 40 to 70.   7. A membrane according to one of claims 1 to 6 coated with   side of the skin with a thin layer of silicone elastomer.   8. A method of manufacturing a membrane conforming to one of   Claims 1 to 6, process comprising:   (a) dissolving the polymer in a volatile solvent comprising dioxane, (b) applying a film of polymer solution to a support or extruding a tube of polymer solution, (c) Upon partial evaporation of the solvent from the film or tube, (d) * contacting the film or tube with a coagulating liquid comprising acetic acid and water,   (e) * and drying the film or coagulated tube.   A method according to claim 8, further comprising a step (f) heat treatment.   10. A method according to one of claims 8 and 9, comprising a   step (g) of depositing on the skin of said membrane a silicone elastomer layer from a preelastomer solution in a light hydrocarbon.   11. A method according to one of claims 8 to 10 wherein a   on the one hand, the polymer is a polyimide or copolyimide having as monomers the dianhydride of 3,4,3 ', 4'-tetracarboxylic acid diphenyldi (trifluoromethyl) methane and a monoaromatic metadiamine or a mixture of monoaromatic meta-diamines, wherein on the other hand, the solvent of the polymer is a liquid comprising at least 85% by weight of 1,4-dioxane and from 0 to 15% by weight of N-methyl-2-pyrrolidone, N, N-dimethylacetamide and / or gammabutyrolactone and wherein, finally, the coagulating liquid is a mixture of 15 to 99% by weight of acetic acid and 1 to 85% by weight of water.   12. A process according to claim 11 wherein on the one hand the monoaromatic meta-diamine is 1,3-diaminobenzene, wherein, on the other hand, the polyimide solvent is a liquid comprising at least one   less than 85% by weight of 1,4-dioxane and from 0 to 15% by weight of N-   methyl 2-pyrrolidone and wherein, finally, the coagulating liquid is a mixture of 15 to 60% by weight of acetic acid and 40 to 85% by weight of mass of water.   13. A process according to claim 11 wherein on the one hand the monoaromatic meta-diamine is 1,3-diaminobenzene, in which, on the other hand, the solvent of the polyimide is a liquid comprising at least one   less than 85% by weight of 1,4-dioxane and from 0 to 15% by weight of N, N-   dimethylacetamide and in which, finally, the coagulating liquid is a mixture of 15 to 50% by weight of acetic acid and 50 to 85% by weight of mass of water.   14. A process according to claim 11 wherein on the one hand the monoaromatic meta-diamine is 1,3-diaminobenzene, in which, on the other hand, the solvent of the polyimide is a liquid comprising at least 85% by weight of 1, 4-dioxane and from 0 to 15% by weight of gammabutyrolactone and in which, finally, the coagulating liquid is a mixture of 15 to 45% by weight of acetic acid and 55 to 85% by weight of mass of water.   15. A method according to one of claims 11 to 14 wherein the   solvent of the polyimide is a liquid comprising 94 to 98% by weight of 1,4-dioxane and 2 to 6% by weight of N-methyl-2-pyrrolidone,   N, N-dimethylacetamide and / or gamma butyrolactone.