FR2847175A1 - PROCESS FOR THE PREPARATION OF MICROPOROUS MEMBRANES - Google Patents

Abstract

The present invention relates to a process for preparing a microporous polymer membrane, based on at least one polymer P, said process comprising the steps of: (A) providing a medium comprising a solution of said polymer P in a mixture (S1 + S2) of two solvents, denoted S1 and S2 respectively, where said polymer P and said mixture (S1 + S2) are such that: (iv) the mixture (S1 + S2) forms a solvent system, in which the polymer P is soluble; (v) solvent S1 is more volatile than solvent S2, at least under certain conditions of temperature and pressure (ctp); and (vi) the polymer P is insoluble in the solvent S2; (B) making a liquid film from the medium produced in step (A); (C) placing the film of step (B) under the conditions temperature and pressure (ctp) above, for a sufficient time so that, following a selective evaporation of S1, the precipitation of all or part of the polymer P is observed in the form of a microporous polymer membrane; and (D) separating the residual solvents from the microporous polymer membrane obtained in step (C), and recovering said microporous polymer membrane. The invention also relates to the membranes obtained according to this process, as well as their uses.

Description

The present invention relates to a process for the preparation of membranes.

  microporous, preferably isotropic in nature.

  Conventionally, microporous polymer membranes are produced by stretching fibers, yarns or polymer membranes. The stretching process leads to micro-cracking phenomena, which gives the

  polymer obtained infines a microporous structure.

  In addition to this conventional method, there are also more specific methods implementing a particular mechanism called "phase inversion". The principle of the phase inversion mechanism consists in producing a homogeneous solution of polymer and in placing this solution under conditions such that a heterogeneous biphasic system is obtained comprising a continuous phase rich in polymers within which are dispersed droplets of 'a dispersed phase containing little or no polymers. Most often, the system is then spread out in the form of a film. Following the departure of the liquids present in this two-phase system, a microporous polymer film is obtained by gelation and solidification of the continuous phase rich in polymers and by replacement of the phase dispersed with air. Depending on the kinetics and thermodynamics of phase separation, and the affinity between the constituents, the structure produced is more or less porous with pores of more or less size.

less important.

  Several types of phase inversion process have been described in the literature. In most cases, the microporous membranes obtained according to these methods are produced by coagulation of a polymer solution, by addition of a large volume of a coagulating liquid (generally constituted wholly or partly by water) in a solution of the polymer, generally spread in the form of a film. For more details concerning this coagulation process, reference may in particular be made to US Patents 4,233,081, 6,013

  688, US 4,806,291, US 6,146,747, US 4,203,848, or 5,565,153.

  Another method implementing the phase inversion process consists in dissolving a polymer at high temperature in a latent solvent which is solid at room temperature (paraffin for example). By rapid cooling of the solution obtained, the phase inversion process is caused and the latent solvent solidified is trapped in the membrane matrix; the latent solvent solidified in the polymer matrix is then removed by a solvent bath (for example based on dichloromethane or methyl ethyl ketone). At this

  subject, we can in particular refer to the application DE 28 33 493.

  It can therefore be seen that the methods currently disclosed which use the phase inversion process are generally quite difficult to implement, insofar as they require precise control of the conditions to which the polymer composition and the implementation of the process are subjected. complex apparatuses such as coagulation baths or extraction baths. In addition, these processes generate large volumes of contaminated effluents (water containing organic solvents in the case of the use of coagulation baths, solvents to be reprocessed in the case of the use of extraction baths), this which involves further processing which translates

especially in terms of increased costs.

  However, the inventors have now discovered a new method implementing the phase inversion process, but which has the advantage of being

  simple, fast and low consumption of chemicals.

  More specifically, according to a first aspect, the present invention relates to a process for preparing a microporous polymer membrane, based on at least one polymer P, said process comprising the steps consisting in: (A) producing a medium comprising a solution of said polymer P in a mixture (S1 + S2) of two solvents, denoted respectively Si and S2, o said polymer P and said mixture (Sl + S2) are such that: (i) the mixture (S1 + S2) forms a solvent system, in which the polymer P is soluble; (ii) the solvent Si is more volatile than the solvent S2, at least under certain temperature and pressure conditions (ctp); and (iii) the polymer P is insoluble in the solvent S2; (B) producing a liquid film from the medium produced in step (A), generally on a flat surface; (C) place the film of step (B) under the aforementioned temperature and pressure conditions (ctp), for a sufficient time so that, following a selective evaporation of Si, the precipitation of all or part of the material is observed polymer P in the form of a microporous polymer membrane; and (D) separating the residual solvents from the microporous polymer membrane

  obtained in step (C), and recovering said microporous polymer membrane.

  The polymer P used according to the invention is, as a general rule, a

polymer of hydrophobic nature.

  Furthermore, a polymer P according to the invention preferably has an average molecular mass at least equal to 20,000 g / mole, this mass possibly being in particular between 30,000 and 1,000,000 g / mole, this molecular mass advantageously being at less than 50,000 g / mole and this

  molecular weight generally remaining less than 1,000,000 g / mole.

  Preferably, the polymer P is a polymer that is not soluble in water.

  Advantageously, the polymer P is poorly wettable with water, or even not

wettable by water.

  Thus, as polymers P which can be used according to the process of the invention, mention may be made in particular, without limitation, of poly (vinyl difluoride); poly (alkyl acrylate) and poly (alkyl methacrylate), where the alkyl group preferably denotes a methyl, ethyl, propyl or butyl group; polystyrenes (in particular shock polystyrenes); polysulfones; polyethersulfones; poly (vinyl chloride); polyesters, such as poly (ethylene terephthalate) or poly (ethylene naphthalate); poly (vinyl dichloride); poly (vinyl formai); poly (vinyl acetal); poly (vinyl acetate) or alternatively cellulose esters, in particular of the acetate, acetatepropionate, acetatebutyrate or nitrate type. In general, most commercial polymers for which a solvent Si is known can be used according to the invention. The solvents Si and S2 used in step (A) of the process of the invention each denote an organic solvent or, in certain cases, a mixture of two or even more organic solvents. In the case where Si and / or S2 denotes a mixture of solvents, it is generally preferable for one of the solvents of said mixture to be in the majority. Thus, when the solvent Si is a mixture of two or more solvents, it is generally preferable for this mixture to comprise a solvent if present in a content at least equal to 50% by mass, the other solvent (s) present ( s) in the mixture then advantageously representing between 5 and 50% by mass (and advantageously less than 40% by mass) relative to the total mass of the mixture. Similarly, when the solvent S2 denotes a mixture of two or more solvents, it is most often advantageous that this mixture comprises a solvent S2 present in a content at least equal to 50% by mass, the content of the other solvents generally being

  between 5 and 50%, and advantageously less than 40% by mass.

  Typically, the mixture (SI + S2) used in step (A) is a solvent system for the polymer P. Within the meaning of the present

  description, by "solvent system of polymer P" is meant a mixture of

  solvents, preferably monophasic and homogeneous, within which the solubility of the polymer P is at least equal to 50 g per liter, this solubility being advantageously at least equal to 60 g per liter and, more preferably, at

  less than 100 g per liter of polymer P in the mixture (Si + S2).

  In general, in order to achieve such solubility values, it is most often desirable for the polymer P to be soluble in the solvent SI, advantageously at a rate of at least 80 g per liter and, preferably, at a rate

at least 150 g per liter.

  In this regard, it should be emphasized that the solubility of most polymers in the various usual solvents is currently well known. For more details on this subject, we can in particular refer to the tables defined in the Polymer Handbook (J. Brandrup, EH Immergut and EA Grulke, J. Wiley & Sons, New York, 4th Edition (1999)) (see also 3rd edition, from 1975). To determine the solvent Si suitable for the use of a polymer P in the process of the invention, those skilled in the art may in particular refer to these

tables.

  On the other hand, it is necessary for the polymer P to be insoluble in the solvent S2 used according to the invention. In this context, it is generally preferred that the polymer P has a maximum solubility in the solvent S2 of less than or equal to 3 g / L, this maximum solubility preferably being at most equal to 1 g / L, and even more advantageously at most equal to 0.5 g / L (typically at

  more than 0.2 g / L, or even less than 0.1 g / L).

  Furthermore, the solvent Si used in the process of the invention is typically more volatile than the solvent S2, at least under the conditions (ctp) mentioned above. In this context, the solvent Si is advantageously a solvent having a vaporization temperature lower by at least 100 C, preferably lower by at least 20 C and more advantageously by at least

  250 C at the vaporization temperature of the solvent S2.

  In general, the solvent S1 used according to the process of the invention can, for example, be chosen from acetone, acetaldehyde, methyl acetate, dichloromethane, chloroform or tetrahydrofuran, it being understood that the exact nature of the solvent Si is to be adapted, on a case-by-case basis, as a function of the nature of the polymer P. Most often, the solvent S2 used in the process of the invention is chosen from alcohols, such as propanols (preferably isopropanol), butanols (preferably n-butanol), pentanols, or alternatively water, carboxylic acids such as acetic acid, or benzylic acid, ethers, in particular dimethyl ether or ethylene glycol dimethyl ether, esters such as propyl acetate, butyl acetate, or alkanes such as heptane, octane, or alternatively xylenes. Again, it goes without saying that nature

  of the solvent S2 is to be adapted as a function of the polymer P used.

  In general, the exact nature of the mixture of solvents (Si + S2) used in step (A) can vary to a fairly large extent subject to satisfying the various aforementioned conditions. We understand that the nature of

  suitable mixtures vary depending on the polymer P used.

  However, whatever the nature of the mixture (Si + S2), it is preferred, in the most general case, that the concentration of polymer P within the mixture (Si + S2) in the solution of step (A) , ie between 5 and 15% by mass, this concentration preferably being at least equal to 6% by mass (advantageously at least equal to 8% by mass) and remaining generally lower

or equal to 12% by mass.

  Furthermore, in the medium formed in step (A), it is preferable that, in the most general case, the mass ratio P / S2 is less than 5, this ratio being advantageously between 0.1 and 4. Advantageously, the mass ratio P / S2 within the medium formed in step (A) is greater than or equal to 0.15 (and more advantageously greater than or equal to 0.5), this ratio being

  preferably less than or equal to 3, and more advantageously less than or equal to 2.

  In the mixture (Si + S2) of step (A), it is moreover preferable that the mass ratio S2 / S1 is between 0.1 and 0.8 (and advantageously at least equal to 0.12, more preferably at least equal to 0.2), this mass ratio S2 / S1 generally being at least equal to 0.1 and most often remaining

  less than or equal to 0.5 (advantageously less than or equal to 0.4).

  Most often, it is preferred that the solution of the polymer P of step (A) is carried out by implementing a dissolution of the polymer P hot, if necessary, generally in a closed container, and at a temperature preferably higher or equal to 350 C, advantageously at least equal to 600 C, this temperature being able in certain cases to be higher than the boiling point of

solvent Si.

  Step (B) of the process of the invention consists in producing a liquid film from the medium produced in step (A). Generally, this film is produced on a flat surface, for example on a glass plate, or even a metal plate, in particular of the endless metal strip type. In general, step (B) consists of spreading the middle of step (A) using a knife, which makes it possible to obtain a layer of homogeneous and regular thickness. Preferably, the thickness of the film produced during step (B) is between 80 microns and 800 microns, whereby the thickness of the membrane obtained after drying in step (C) is generally between 15 microns and 100 microns. In certain particular cases, it may be advantageous for the thickness of the film produced in step (B) to be greater than or equal to 150 microns, or even 300 microns. Furthermore, it is generally preferred that the thickness of the film produced in step (B) remains less

  or equal to 600 microns and, preferably, less than or equal to 500 microns.

  In the most general case, step (B) of the process of the invention is carried out at a temperature ranging from 5 to 35 ° C. and, preferably between 15 and 250 ° C.,

  generally at atmospheric pressure.

  In the process of the invention, step (C) of selective evaporation of the solvent Si is generally carried out at a temperature between 15 and 50 C, generally under atmospheric pressure. In general, this step is carried out by leaving the film of step (B) to dry in the open air, or alternatively under a flow of gas (in particular a flow of air, nitrogen or argon). In general, the temperature for carrying out step (C) is advantageously at least equal to 20 C and, more preferably, at least equal to 25 C. In the most general case, step (D) of method of the invention consists of a step of evaporation of residual solvents (in the open air or under a gas flow for example, or even under vacuum, in particular if the nature of the solvents so requires). According to a particular embodiment of the present invention, the

  Polymer P used can be a poly (vinyl difluoride) (PVdF).

  In the case of the use of PVdF as polymer P, it is generally preferable for the solvent SI to be chosen from acetone and tetrahydrofuran, the solvent S1 preferably being acetone. Furthermore, it is preferred that the solvent S2 is chosen from butanols and propanols, the solvent S2 advantageously being n-butanol or isopropanol, n-butanol being preferred. In a particularly preferred manner, when the polymer P is a PVdF, the mixture (S1 + S2) of step (A) can be chosen from: - mixtures of acetone and nbutanol characterized by a mass ratio (n-butanol / acetone) ranging from 0.05 to 0.5 (preferably between 0.08 and 0.4), this ratio being advantageously between 0.15 and 0.25; mixtures of acetone and isopropanol characterized by a mass ratio (isopropanol / acetone) ranging from 0.1 to 0.6 (preferably between 0.12 and 0.5) this ratio preferably being between 0, 15 and 0.35; -mixtures of tetrahydrofuran and n-butanol characterized by a mass ratio (nbutanol / tetrahydrofuran) ranging from 0.1 to 0.6 (preferably

  between 0.12 and 0.5), this ratio preferably being between 0.15 and 0.35.

  When the polymer P designates PVdF, it is preferred, in the most general case, that the concentration of polymer P within the mixture (Si + S2) in the solution of step (A) is between 6 and 15% by mass, this concentration preferably being at least equal to 7% by mass and advantageously remaining less than or equal to 13% by mass. Furthermore, it is preferable that, in the medium formed in step (A), the PVdF / S2 mass ratio is between

  0.5 and 1.5, this mass ratio being advantageously between 0.7 and 1.3.

  According to another particular embodiment of the present invention, the

  polymer P can also denote a polystyrene.

  When the polymer P denotes a polystyrene, it is generally preferable for the solvent Si to be chosen from tetrahydrofuran, chloroform, dichloromethane and toluene, the solvent S1 preferably being tetrahydrofuran. It is also advantageous for the solvent S2 to be chosen from butanols, propanols and mixtures of these alcohols, the solvent S2 being of

  preferably isopropanol or an isopropanol / n-butanol mixture.

  In a particularly advantageous manner, when the polymer P is a polystyrene, the mixture (Si + S2) of step 2 can be chosen from: mixtures of tetrahydrofuran and isopropanol characterized by a mass ratio (isopropanol / tetrahydrofuran) ranging from 0.1 to 0.6, this ratio preferably being between 0.15 and 0.4; and - mixtures of tetrahydrofuran and a combination (isopropanol + n-butanol), characterized by a mass ratio ((isopropanol + n20 butanol) / tetrahydrofuran) ranging from 0.1 to 0.5, this ratio preferably being understood between 0.15 and 0.35, and by a mass ratio (isopropanol / nbutanol) ranging from 0.5 to 3, this ratio being

  preferably between 0.8 and 1.8.

  When the polymer P designates a polystyrene, the concentration of polymer P in the mixture (SI + S2) of the solution of step (A) is advantageously between 6 and 15% by mass and preferably between 7 and 12% en masse. It is often preferable that, in the medium formed in step (A), the polystyrene / S2 mass ratio is between 0.2 and 1, and preferably

between 0.3 and 0.5.

  According to yet another possible embodiment for the process of the invention, the polymer P used can be a polyethersulfone and in particular a cardo polyethersulfone. Where appropriate, this polyethersulfone can in particular have an average molecular mass of between 20,000 and 90,000, this

  average molecular weight can however be higher.

  When the polymer P denotes a polyethersulfone and in particular a cardo polyethersulfone, it is generally preferable for the solvent Si to be chosen from dichloromethane, chloroform and tetrahydrofuran, the solvent SI preferably being dichloromethane. Advantageously, and in that the solvent S2 is chosen from butanols, propanols and mixtures of these alcohols

  optionally in combination with water, the solvent S2 preferably being nbutanol or isopropanol, and preferably n-butanol.

  In a particularly advantageous manner, when the polymer P denotes a polyethersulfone is, the mixture (Sl + S2) of step A can be chosen from: - mixtures of dichloromethane and n-butanol characterized by a mass ratio (n-butanol / dichloromethane) ranging from 0.1 to 0.5, this ratio preferably being between 0.15 and 0.35; and - mixtures of dichloromethane and isopropanol characterized by a mass ratio (isopropanol / dichloromethane) ranging from 0.1 to 0.5,

  this ratio preferably being between 0.15 and 0.35.

  Furthermore, when the polymer P is a polyethersulfone, it is generally preferable for the concentration of polyethersulfone in the mixture (S1 + S2) of the solution from step A to be between 6 and 15% by mass, this concentration preferably being between 7 and 12% by mass. Furthermore, in the medium formed in step A, it is preferable that the mass ratio

  polyethersulfone / S2 is between 0.5 and 2.

  According to yet another possible embodiment for the process of the invention, the polymer P used can be a poly (vinyl chloride), in particular chosen from the so-called "normal" poly (vinyl chloride) and the

  poly (vinyl chloride) called "superchlorinated" type.

  When the polymer P denotes a poly (vinyl chloride), it is generally preferable for the solvent Si to be chosen from tetrahydrofuran, chloroform, dichloromethane and acetone, the solvent Si preferably being tetrahydrofuran. It is also advantageous for this solvent S2 to be chosen from butanols, propanols and mixtures of these alcohols, solvent S2

  preferably being n-propanol.

  In a particularly advantageous manner, when the polymer P is a poly (vinyl chloride), the mixture (S1 + S2) of step A can be chosen from mixtures of tetrahydrofuran and n-butanol, characterized by a mass ratio ( n-butanol / tetrahydrofuran) ranging from 0.1 to 0.6, this ratio being

  preferably between 0.15 and 0.4.

  When the polymer P denotes a poly (vinyl chloride), the concentration of the said polymer P in the mixture (Si + S2) of the solution of step (A) is advantageously between 6 and 15% by mass, and preferably between 7 and 12% by mass. It is then generally preferable that in the medium formed in step (A), the mass ratio P / S2 is between 0.15 and

  2, this ratio preferably being less than or equal to 1.

  Depending on the uses envisaged for the microporous membrane produced according to the method of the invention, different variants can be used

  specific to the process described above.

  Thus, according to a first variant, the microporous membrane obtained at the end of step (D) can be subjected to a subsequent step of surface hydrophilization. If necessary, this hydrophilization treatment can for example be carried out according to a method consisting in bringing the microporous membrane resulting from step (D) into contact with a solution of a hydrophilic polymer, such as a hydroxypropylcellulose, a poly (vinyl alcohol) or alternatively a surfactant, the concentration of polymer or surfactant then preferably being between 0.1 and 2 g / L, and advantageously between 0.2 and 0.9 g / L. Any other usual hydrophilization step, adapted to the nature of the polymer P, can be used in this context. According to another variant, which may prove to be particularly advantageous, the medium of step (A) can comprise, on an additional basis, solid particles (p). Where appropriate, said particles (p) most often have mean dimensions less than or equal to 4 microns, these mean dimensions advantageously being less than or equal to 2 microns, and generally remaining greater than or equal to 0.01 microns, this by what the microporous membrane obtained at the end of step (D) comprises at least a portion of said solid particles (p) integrated within its structure (and at least in

  part in the polymer walls of the porous structure).

  In the case of this particular variant, the particles (p) can in particular be particles based on metal oxide, carbon black, porous particles (in particular microparticles or nanoparticles) or

  much more crosslinked polymer particles.

  Advantageously, the particles (p) used in this context can be particles with catalytic properties, preferably chosen, if necessary, from particles based on metal oxide (preferably based on titanium oxide, advantageously in anatase form, where appropriate), particles based on carbon black, zeolitic particles and particles of crosslinked polymer, in particular particles of polymers comprising, on the surface, groups of acid or amine type, or alternatively complexed metal cations, whereby the microporous membrane obtained at the end of step (D) is a membrane usable as a membrane with catalytic property. The particular membranes obtained in this context, and their

  uses, constitute other particular aspects of the present invention.

  The aforementioned particles (p) can also be particles with sorbent properties. In this case, these particles are preferably chosen from particles based on activated carbon, silica (nanoporous or microporous), zeolitic particles and particles of crosslinked polymer. In this case, the membrane obtained at the end of step (D) is useful as a membrane with sorbent properties. The specific membranes obtained by using such particles, as well as their use as membranes with properties

  sorbents, constitutes other aspects of the present invention.

  In general, whether or not particles (p) are integrated, the 1o microporous polymer membranes obtained according to the process of the invention have a porosity at least equal to 0.5 and, typically, between 0.6

and 0.8.

  These membranes also have, as a general rule, pores with a diameter usually between 0.1 and 5 microns, the size of these

  pores generally remaining at least 0.2 microns and less than 1 micron.

  The thickness of the membranes obtained according to the process of the invention is as to

  it generally between 15 and 100 microns.

  The membranes obtained according to the process of the invention, which are not subjected to a surface hydrophilization step, can be used in particular as membranes permeable to gas and impermeable to liquids, in particular to water and aqueous solutions. . In this context, the membranes of the invention can, for example, be used as membranes for coating absorbent compositions, for example for carrying out the absorption of water vapor or of gas molecules such as oxygen or ethylene. , for example for applications in the food or pharmaceutical industry (packaging films for oxygen, water or ethylene absorbers, osmotic release devices, gas microfiltration (air, for example), etc. ..). These different uses constitute another particular object.

of the present invention.

  The membranes subjected to a step of grafting by hydrophilic groups can, for their part, be used as microfiltration membranes for liquids of an aqueous nature, in particular water or aqueous solutions. Thus, these hydrophilized membranes can in particular be used to carry out microfiltration of body fluids (such as blood), and, more generally, in all the traditional fields of microfiltration, such as those described for example in the Handbook of Industrial Membranes , K. Scott, Ed. Elsevier Advanced Sci., 1998), in particular the elimination of microorganisms (biotechnology, treatment of drinking or waste water ...), sterilizing filtration, or even the preparation of ultrapure water for l electronics industry. These particular uses constitute another aspect of the

present invention.

  The characteristics and the various advantages of the present invention will appear even more clearly in the light of the various examples.

illustrations set out below.

  EXAMPLE 1 Preparation of a microporous PVdF membrane (initial solvent system: acetone / n-butanol) A 13% by mass solution of poly (vinyl difluoride) s PVdF ("Kynar 741"), sold by the company Atochem) in an acetone / n-butanol mixture characterized by a mass ratio (n-butanol: acetone) of 0.19. This solution was produced by heating for 2 hours at 650C, in a closed enclosure, 1 g of PVdF, 7 ml of acetone and 1.3 ml of n-butanol, then allowing the homogeneous solution obtained to cool to temperature. ambient

(25 C).

  The solution obtained was spread on a glass plate, in the form of a

  film with a thickness of 200 μm, using a knife adjusted to this thickness.

  The plate and the film produced were then left under an extractor hood at room temperature (25 ° C.), whereby the acetone was evaporated. Following

  from this evaporation, a white membrane 40 gm thick was obtained.

  The residual solvent was then evaporated (essentially n-butanol), leaving the membrane obtained to dry in air, under a hood, at 250 ° C.

during 2 hours.

  At the end of the evaporation of all the solvents, a microporous membrane 40 gm thick was obtained, having pores with an average diameter equal to 0.5 μm (observable for example by electron microscopy) and a porosity by volume (estimated by electron microscopy) of 70%. The air permeance of the membrane obtained (volumetric air flow rate measured through the membrane subjected to an air flow with an upstream pressure of 1.01 bar and a downstream pressure of 1.00 bar, related to the overpressure (10 millibars)) is, by

cm2 of membrane, 30 cm3 / s / bar.

  EXAMPLE 2 Preparation of a microporous polystyrene membrane (initial solvent system THF / (isopropanol + n-butanol)) A 9.5% by mass solution of crystal (atactic) polystyrene was produced in a tetrahydrofuran (THF) mixture. / isopropanol / n-butanol, characterized by a mass ratio (THF: isopropanol: n-butanol) of (5.9: 0.36). This solution was produced by heating for two hours, at 70 ° C., in a closed chamber, 1.05 g of polystyrene, 8 ml of THF, 2 ml of isopropanol and 1.5 ml of n-butanol, then leaving cool the homogeneous solution obtained until

room temperature (250 C).

  The solution obtained was then spread out in the form of a film with a thickness of 400 gm on a glass plate, using a knife adjusted to this thickness. The plate and the film were then left under an extractor hood at room temperature (250C), whereby the THF was evaporated. To the

  following this evaporation, a 25 gm thick membrane was obtained.

  The residual solvent was then evaporated (isopropanol and n-butanol essentially by allowing the membrane to air dry, under a hood, at 25

C for 2 hours.

  At the end of the evaporation of all the solvents, a microporous membrane of thickness equal to 25 gm was obtained, having, per cm 2 of

  membrane, an air permeance of 15 cm3 / s / bar.

  EXAMPLE 3 Preparation of a microporous PVdF membrane incorporating catalytic anatase particles (initial acetone / nbutanol solvent system) 1 g of PVdF (Kynar 741) was introduced into a closed pyrex glass container, 0.5 g anatase powder (TiO2 sold by Degussa), 7 ml of acetone and 1 ml of n-butanol. The enclosure was brought to a temperature of 650C for 2 hours, then allowed to cool to room temperature (250C). The dispersion obtained was spread out in the form of a film with a thickness of 200 gim on a glass plate, using a knife adjusted to this thickness. The plate and the film were then left under an extractor hood at room temperature, so as to evaporate the acetone. Following this evaporation, we have

  obtained a white membrane 40 gm thick.

  The residual solvent was then evaporated (essentially n-butanol) by subjecting the membrane obtained to air drying in a hood, for 2 hours, at 25 ° C. At the end of the evaporation of all the solvents, a microporous membrane with a thickness equal to 40 microns was obtained having pores with an average diameter equal to 0.4 grm and having a volume porosity of 45%. The air permeance of the membrane obtained is, per cm2 of membrane, 8

cm3 / s / bar.

  In order to establish the accessibility of the anatase particles within the membrane produced, the following test was carried out: From the membrane produced, a tube of length equal to cm and an internal diameter equal to 3 cm was produced. . An aqueous salicylic acid solution was circulated in a loop in a tubular reactor comprising this tube.

  having an initial salicylic acid content of 40 ppm.

  Under the action of a rare gas discharge lamp with a power of 15 W (near UV light), complete degradation of the salicylic acid was obtained at a specific speed Vo (brought to the surface S of the membrane) Vo / S of 8.95.10-4 mmol / min / m2. The same experiment was carried out under the action of the sun, outside, at a temperature of 10 C. The rate of degradation then

  was measured equal to 1.43.10-3 mmol / min / m2.

  EXAMPLE 4 Preparation of a microporous polystyrene membrane (initial solvent system: isopropanol / FHF) A 9.7% by mass solution of the polystyrene as used in Example 2 was produced in a characterized isopropanol / THF mixture. by a mass ratio of 0.31. This solution was produced by heating for 2 hours at 600 ° C., in a closed enclosure, 1 g of polysytrene, 2.8 ml of isopropanol and 8 ml of THF, then allowing the homogeneous solution obtained to cool to

room temperature (250 C).

  The solution obtained was spread on a glass plate, in the form of a film with a thickness of 200 grm using a knife adjusted to this thickness. The plate and the film were then left under an extractor hood at room temperature, whereby the THF was evaporated. Following this evaporation, we have

  obtained a white membrane 40gm thick.

  An evaporation of the residual solvent (isopropanol for the most part) was then carried out by subjecting the white membrane obtained to air drying,

  in a hood, at 250 C, for 2 hours.

  At the end of the evaporation of all the solvents, a microporous membrane was obtained having pores with an average diameter equal to 0.5 A and having a volume porosity of the order of 70%. The air permeance of the

  membrane obtained was measured, per cm2 of membrane, equal to 30 cm3 / s / bar.

  EXAMPLE 5 Preparation of a microporous poly (chloride) membrane

  vinyl) (initial solvent system: n-butanoVMHF).

  A 7.7% by mass solution of poly (vinyl chloride) was produced in an n-butanol / THF mixture characterized by a mass ratio of 0.69. This solution was produced by heating for 2 hours at 60 ' C, in a closed chamber, 1 g of polyvinyl chloride, 6 ml of n-butanol and 8 ml of THF, then in

  allowing the solution obtained to cool to room temperature (250 C).

  The solution obtained was then spread on a glass plate in the form of a film with a thickness of 200 microns using a knife adjusted to this thickness. The plate and the film were left under an extractor hood at temperature

  ambient, whereby THF was evaporated.

  The residual solvents (essentially n-butanol) were then evaporated off by subjecting the white membrane obtained to air drying,

  in a hood, at 25 C, for 2 hours.

  At the end of the evaporation of all the solvents, a microporous membrane was obtained having pores with an average diameter equal to 0.5 microns, and having a volume porosity of the order of 60%. The air permeance of the membrane obtained was measured, per cm2 of membrane, equal to 4 cm3 / s / bar. EXAMPLE 6 Preparation of a microporous polyethersulfone membrane (initial solvent system: CH2Cl2 / nbutanol) A 9.5% by weight solution of a cardo polyethersulfone (PESC, sold by the company Jiangsu Engineering Plastics) was produced, of formula general: [t? 0S020] in a CH2Cl2 / n-butanol mixture characterized by a mass ratio (n25 butanol / CH2Cl2) of 0.205. This solution was made by heating for 2

  hours, at 600 C, in a closed enclosure, 1 g of PESC, 6 ml of CH2Cl2 and 2 ml of n-

  butanol, then allowing the homogeneous solution obtained to cool to the

room temperature (25 C).

  The solution obtained was spread in the form of a film with a thickness of 400 gm on a glass plate, using a knife adjusted to this thickness. The plate and the film were then left under an extractor hood at room temperature, so as to evaporate the acetone. Following this evaporation, we have

  obtained a white membrane 40gm thick.

  The residual solvent (n-butanol) was then evaporated off, subjecting the membrane obtained to drying in air, under a hood, at 250 ° C.

during 2 hours.

  At the end of the evaporation of all the solvents, a microporous membrane was obtained having, per cm2 of membrane, an air permeance

13 cm3 / s / bar.

Claims (30)

  1. Method for preparing a microporous polymer membrane, based on at least one polymer P, said method comprising the steps consisting in: (A) producing a medium comprising a solution of said polymer P in a mixture (Sl + S2) of two solvents, denoted Si and S2 respectively, o said polymer P and said mixture (Si + S2) are such that: (i) the mixture (S1 + S2) forms a solvent system, in which the polymer P is soluble; (ii) the solvent Si is more volatile than the solvent S2, at least under certain temperature and pressure conditions (ctp); and (iii) the polymer P is insoluble in the solvent S2; (B) producing a liquid film from the medium produced in step (A); (C) place the film of step (B) under the aforementioned temperature and pressure conditions (ctp), for a sufficient time so that, following a selective evaporation of Si, the precipitation of all or part of the material is observed polymer P in the form of a microporous polymer membrane; and (D) separating the residual solvents from the microporous polymer membrane   obtained in step (C), and recovering said microporous polymer membrane.   2. Method according to claim 1, characterized in that the concentration of polymer P within the mixture (Si + S2) in the solution of step (A) is between 5 and 15% by mass.   3. Method according to claim 1 or according to claim 2, characterized in that, in the medium formed in step (A), the mass ratio P / S2 is between 0.1 and 4.   4. Method according to any one of claims 1 to 5, characterized in that   that in the mixture (S1 + S2) of step (A), the mass ratio S2 / S1 is between 0.1 and 0.8.   5. Method according to any one of claims 1 to 5, characterized in that   that the thickness of the film produced in step (B) is between 80 microns and 800 microns.   6. Method according to any one of claims 1 to 5, characterized in that   that the polymer P is a poly (vinyl difluoride) (PVdF).   7. Method according to claim 6, characterized in that the solvent Si is chosen from acetone and tetrahydrofuran, and in that the solvent S2 is chosen   among butanols and propanols.   8. Method according to claim 6 or according to claim 7, characterized in that the concentration of PVdF within the mixture (Si + S2) in the solution   of step (A) is between 6 and 15% by mass.   9. Method according to any one of claims 6 to 8, characterized in that   that, in the medium formed in step (A), the mass ratio PVdF / S2 is between 0.5 and 1.5.   10. Method according to any one of claims 1 to 5, characterized in   that the polymer P is a polystyrene.   11. Method according to claim 10, characterized in that the solvent SI is chosen from tetrahydrofuran, chloroform, dichloromethane and toluene and in that the solvent S2 is chosen from butanols, propanols and mixtures of these alcohols.   12. Method according to claim 10 or according to claim 11, characterized in that the polystyrene concentration within the mixture (Si + S2)   in the solution of step (A) is between 6 and 15% by mass.   13. Method according to any one of claims 10 to 12, characterized in   what, in the medium formed in step (A), the mass ratio polystyrene / S2 is between 0.2 and 1.   14. Method according to any one of claims 1 to 5, characterized in   that the polymer P is a polyethersulfone. 15. The method of claim 14, characterized in that the solvent S1 is chosen from dichloromethane, chloroform, and tetrahydrofuran and that the solvent S2 is chosen from butanols, propanols and mixtures of   these alcohols possibly in association with water.   o0 16. Method according to claim 14 or according to claim 15, characterized in that the concentration of polyethersulfone within the mixture   (Sl + S2) in the solution of step (A) is between 6 and 15% by mass.   17. Method according to any one of claims 14 to 16, characterized in   what, in the medium formed in step (A), the mass ratio   polyethersulfone / S2 is between 0.5 and 2.   18. Method according to any one of claims 1 to 5, characterized in   that the polymer P is a poly (vinyl chloride).   19. The method of claim 19, characterized in that the solvent S1 is chosen from tetrahydrofuran, chloroform, dichloromethane and acetone, and that the solvent S2 is chosen from butanols, propanols and mixtures of these alcohols.   20. Method according to claim 18 or according to claim 19, characterized in that the concentration of polymer P within the mixture (Sl + S2)   of the solution of step (A) is between 6 and 15% by mass.   21. Method according to any one of claims 18 to 20, characterized in   what, in the medium formed in step (A), the mass ratio poly (chloride   vinyl) / S2 is between 0.15 and 2.   22. Method according to any one of the preceding claims,   characterized in that the microporous membrane obtained at the end of step (D)   is further subjected to a subsequent surface hydrophilization step.   23. Method according to any one of the preceding claims,   characterized in that the medium of step (A) further comprises particles   solids (p) with average dimensions less than or equal to 4 microns.   24. Method according to claim 23, characterized in that the particles (p)   are particles with catalytic properties.   25. The method of claim 23, characterized in that the particles (p)   are particles with sorbent properties.   26. Microporous membrane capable of being obtained by the process of   any one of claims 1 to 25.   27. Use of a membrane capable of being obtained by the process   of any one of claims 1 to 21, not subject to a step   surface hydrophilization, as a gas permeable membrane and impermeable to aqueous liquids.   28. Use of a membrane capable of being obtained according to the method of claim 22, as microfiltration membrane for liquids of aqueous in nature.   29. Use of a membrane capable of being obtained according to the process   of claim 24, as a membrane with catalytic properties.   30. Use of a membrane capable of being obtained according to the process   of claim 25, as a membrane with sorbent properties.