WO2002032557A1 - Method for producing a surface modified membrane - Google Patents

Abstract

The invention relates to a method for producing a surface modified membrane, comprising the following steps a) production of a solution containing a synthetic polymer M in the form of a membrane, a solution system and an agent A comprising at least one functional group, b) shaping the solution into a moulded body comprising a first and second side, c) allowing a reaction on at least one of the sides of the moulded bodies of a coagulation medium which contains in a dissolved form an agent B reacting with agent A, and at least one functional group. A separation phase follows and a membrane structure is formed which comprises an inner porous surface and outer surfaces, whereby agent B, during said reaction, reacts with agent A on at least one of the outer surfaces and d) optionally, the solvent system is extracted and optionally dried. Said method allows a surface modified membrane to be obtained as a result of the reaction product of A and B.

Description

 Process for the production of a surface-modified membrane

Membrana GmbH, Wuppertal

Description:

The present invention relates to a method for producing a surface-modified membrane.

A large number of methods are known for the surface modification of membranes, which can essentially be divided into chemical and physical modification methods.

The group of chemical modification processes includes those in which the surface of a membrane (carrier membrane) which has already been fully formed is changed chemically. For this purpose, other polymers or monomers are often covalently bonded to functional groups or to the end groups of the polymer forming the membrane, some of which are on the surface. In another example of a chemical modification process, a reactive monomer is applied to a carrier membrane and subsequently brought into contact with another monomer, the two monomers reacting to form a layer formed from a polymer network. Such a method is described in US Pat. No. 5,693,227. According to this document, a microporous polysulfone membrane is immersed in a solution of 1,3-phenylenediamine (PD) for two minutes and then removed from the PD solution. Excess PD solution is removed. The resulting substrate is immersed in a solution of trimesoyl chloride (TMC) for 20 seconds, forming a polymer network of PD and TMC forms. In addition to the process steps necessary for the production of the carrier membrane, this process therefore requires several further process steps and is therefore complex.

A method belonging to the group of physical methods for surface modification of membranes is known as bicomponent spinning. With a triple nozzle, which in the case of capillary or tubular membranes has three concentrically arranged outlet openings, another polymer solution is extruded around the outside of the spinning solution at the same time as the spinning solution and the inner filling, so that a thin film is formed on the spinning solution during phase inversion of the spinning solution-forming membrane and a layer is formed on the membrane. However, bicomponent spinning is already a technologically complex process because of the triple spinneret required.

Therefore, the object of the present invention is to provide a simpler method for the surface modification of membranes.

This object is achieved by a method for producing a surface-modified membrane comprising the steps a) preparing a solution comprising a membrane-forming synthetic polymer M, a solvent system and an agent A with at least one functional group, b) shaping the solution into a shaped body with a first and second side, c) allowing to act on at least one of the sides of the shaped body of a coagulation medium which contains an agent B reactive with agent A with at least one functional group, whereby phase separation takes place and a membrane structure is formed which has an inner pore surface and has outer surfaces, and wherein agent B reacts with agent A at least on one of the outer surfaces during exposure and d) optionally extracting the solvent system and optionally

Drying, resulting in a membrane modified by the reaction product of A and B.

The process according to the invention only requires the process steps which are anyway necessary for the production of the unmodified membrane. It is only necessary to add agent A in the preparation of the solution according to step a) and agent B in the preparation of the coagulation medium which is used in step c).

The membrane production itself is based on the processes known per se, in which the membrane structure is formed via a non-solvent-induced phase separation. The customary embodiments are also used in the method according to the invention.

In a preferred embodiment, the method according to the invention can be used to produce hollow fiber membranes by extruding the polymer solution through the annular gap of a suitable hollow fiber nozzle, feeding a lumen filling into the core bore of the nozzle. The extruded hollow thread is then brought into contact with a coagulation medium which does not dissolve the polymer. The membrane structure forms here. The extruded hollow thread can only be brought into contact with its outside with a coagulation medium, for example by passing it through a precipitation bath, with precipitation then taking place from the outside in. In another embodiment, the inner filling is a coagulation medium and the membrane structure precipitates from the inside out. Of course, it is also possible for the extruded hollow thread to be brought into contact with a coagulation medium both with its outside and with its inside. The precipitated hollow fiber is then drawn off from the precipitation bath, then the precipitation medium is extracted from the hollow fiber and, if necessary, the extractant is removed by drying, whereby the finished hollow fiber membrane is obtained which has an outer surface on the lumen side, has an outer surface on the outside and an inner pore surface.

According to the process variants described above for producing a hollow fiber membrane, step c) of the method according to the invention can be carried out in such a way that the hollow fiber is led into a precipitation bath as a coagulation medium which contains the agent B in solution, which means that agent at least on the outer surface of the outside of the resulting hollow fiber membrane B reacts with agent A. If, in the process according to the invention for forming the lumen, an inner filling, which contains the agent B and acts as a coagulation medium, is reacted, agent B reacts with agent A at least on the outer surface of the lumen side, that is to say on the lumen-side surface of the resulting membrane In the process according to the invention, if coagulation takes place both via the inner filling and via a precipitation bath, agent B can be dissolved in both coagulation media and thus a reaction of agent A with agent B can take place both at least on the outer surface of the outside and at least on the lumen-side surface , It is also possible that a different agent B is contained in the inner filling than in the precipitation bath, whereby a hollow fiber membrane is obtained which is modified at least on the outer surface of its outside by a different reaction product from A and B than at least on its lumen side outer surface. Thus, with the method according to the invention, after extracting the solvent system and optionally drying in step d), hollow fiber membranes can be produced which are surface-modified at least on the outer surface of their outside and / or lumen side by the reaction product of A and B.

In a further preferred embodiment, flat membranes can be produced with the method according to the invention. Here, for example, the polymer solution is molded on a roller using a casting box and then guided into the coagulation medium on the roller, which is partially immersed in a coagulation medium that does not dissolve the polymer, ie in a coagulation bath. It forms starting from the side facing away from the roller, the membrane structure. In another embodiment, the roller is first coated with a coagulation medium which does not dissolve the polymer, and then the polymer solution is formed into a film, for example with a casting box, on the roller coated with the coagulation medium, a membrane structure starting from the side of the film facing the roller formed. The film is then guided into the coagulation medium on the roller, which in turn is partially immersed in a coagulation medium, with coagulation to the membrane structure starting from the side facing away from the roller. The precipitated flat membrane is drawn off from the precipitation bath, then optionally the precipitation medium is extracted from the hollow thread and, if necessary, the extractant is removed by drying, whereby the finished flat membrane is obtained which has an outer roll-side surface, an outer surface on the precipitation bath side and an inner pore surface.

In accordance with the process variants described above for producing a flat membrane, step c) of the process according to the invention can be carried out in such a way that the film is formed on a roller, the roller being partially immersed in a precipitation bath containing agent B and the film on the roller through this precipitation bath to be led. In this case, agent B reacts with agent A at least on the outer surface of the side of the resulting flat membrane structure facing away from the roller. If a coagulation medium containing agent B dissolved in the agent is applied to the roller in the process according to the invention, the agent reacts at least on the outer surface the side of the resulting flat membrane agent B with agent A facing the roller. If in the process according to the invention coagulation takes place both via the precipitation bath and via the coagulation medium applied to the roller before the film is formed, agent A can be dissolved in both coagulation media and thus a reaction of agent A with agent B takes place both at least on the side facing away from the roller and at least on the side of the resulting flat membrane facing the roller. It is also possible that in the precipitation bath in which the The roller dips, a different agent B is contained in solution than in the coagulation medium, which is applied to the roller before the film is formed, whereby a flat membrane is formed which is modified on its outer roller-side surface by a different reaction product from A and B than on their outer surface on the precipitation bath side. Thus, with the method according to the invention, after optionally extracting the solvent system and optionally drying in step d), flat membranes can be produced which are surface-modified at least on the outer roller-side surface and / or on their outer precipitation-bath-side surface by the reaction product of A and B.

Depending on the precipitation conditions in step c) of the method according to the invention, a large number of different membrane structures can be formed.

For example, an asymmetrical membrane structure with a fine-pored or non-porous surface is formed by selecting a solvent system in step a) of the process according to the invention which leads to a rapid phase inversion with the coagulation medium acting in step c). In this case, agent B cannot penetrate into the interior of the membrane structure that is formed, or can only do so to a small extent, and a reaction of agent B with agent A takes place mainly on the outer surface. In some cases, dense layers can be produced from the reaction product of agent A with agent B on the outer surface.

Furthermore, the membrane formed in step c) of the method according to the invention by phase separation can be microporous on the outer surface. Such a membrane structure is known to arise, for example, by selecting a solvent system in step a) of the process according to the invention which leads to a slow phase inversion with the coagulation medium acting in step c). In this case, agent B can not only act on the outer surface but on the inner pole during the exposure of the coagulation medium. React surface with Agent A, creating a membrane with a very large modified surface.

With regard to the membrane-forming polymer used in the process according to the invention, use can be made of the known synthetic polymers suitable for the production of membranes. The membrane-forming synthetic polymer M used in step a) to prepare the solution is preferably a polyethersulfone, polysulfone or polyarylethersulfone. Other polymers such as polyethylene oxide, polyhydroxyether, polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol or polycaprolactone, or inorganic substances such as SiO _{2 can also} be added to the solution as additives, with which, for example, the pore formation or the hydrophilicity of the membrane can be influenced. In a particularly preferred embodiment of the process according to the invention, polyethersulfone is used as the membrane-forming synthetic polymer M.

A particularly preferred solvent system consists of caprolactam and butyrolactone. The membrane structure can be influenced by the ratio of caprolactam to butyrolactone. The more caprolactam is used in relation to butyrolactone, the more the membrane structure formed tends towards an asymmetrical membrane with a fine-pored or non-porous outer surface. The more butyrolactone is used in relation to caprolactam, the more the membrane structure tends towards a membrane that is microporous on the outer surface. Such methods are described, for example, in EP-A-0361085 or in EP-A-0357021, the disclosure of which is expressly referred to here.

The fact that according to step c) of the method according to the invention agent B is reactive with agent A means in the context of the present invention that A and B are reactive under the conditions of the phase inversion, the reaction having to take place while the coagulation medium is left to act, i.e. in a time which is between about 0.1 second and about 1 minute, depending on the membrane production process.

In the process according to the invention, agent A and agent B each have at least one functional group.

In a preferred embodiment of the process according to the invention, agent A and agent B each have two functional groups and react in step c) to form a linear polymer. Surface-modified membranes can be produced with a high stability of the surface modification when the membrane is used in various application media, especially when the reaction product from agent A and agent B is a high-molecular product.

In a further preferred embodiment of the process according to the invention, agents A and / or B each have more than two functional groups and react in step c) to form a crosslinked polymer. The surface-modified membrane in this way can be used in almost any application medium without any signs of detachment from the surface modification because the crosslinked polymer from A and B is not soluble in any application medium due to its network property.

Agents with high reactivity are required to carry out the method according to the invention. In a preferred embodiment of the process according to the invention, a dicarboxylic acid chloride or a diisocyanate is used as agent A.

Terephthaloyl chloride or hexamethylene diisocyanate is particularly preferably used as agent A in the process according to the invention because these agents have a particularly high reactivity. In a preferred embodiment of the method according to the invention, agent B contains at least one imino group and two amino groups because these agents have a high reactivity.

Agent B diethylenetriamine or polyethyleneimine is particularly preferred in the process according to the invention because their amino and imino groups have a particularly high reactivity.

In a further preferred embodiment of the process according to the invention, agent A is terephthaloyl chloride and agent B is polyethyleneimine. With this combination of agents A and B, a membrane modified with a crosslinked polymer of terephthaloyl chloride and polyethyleneimine can be produced, which has a large number of imino groups derived from the polyethyleneimine, which due to their high reactivity can be used for a wide range of adsorption purposes. If you choose e.g. Manufacturing conditions which lead to a microporous membrane on the outer surface result in a membrane which is modified not only on its outer surface but also on its pore surface by the crosslinked polymer of terephthaloyl chloride and polyethyleneimine and which provides a very large surface area for adsorption reactions , Such membranes can e.g. with polyether sulfone as the membrane-forming synthetic polymer M and a solvent system of butyrolactone and caprolactam with an excess of butyrolactone.

In a further preferred embodiment of the invention, agent A is hexamethylene diisocyanate and agent B is diethylene triamine. A membrane modified with a crosslinked polymer of hexamethylene diisocyanate and diethylene triamine can thus be produced. For example, if one selects manufacturing conditions that lead to a membrane that is pore-free on the outer surface or has only a few pores, a membrane is obtained that is modified practically only on its outer surface by the crosslinked polymer of hexamethylene diisocyanate and diethylene triamine. Such a membrane can be used, for example, with polyethersulfone as the membrane-forming membrane synthetic polymer M and a solvent system made from equal parts of butyrolactone and caprolactam. The crosslinked polymer forms a layer on the outer surface of the membrane, the thickness of which can be adjusted, for example, by the amount of hexamethylene diisocyanate. This embodiment of the method according to the invention is therefore particularly suitable for the production of nanofiltration membranes. Of course, the aforementioned combination of hexamethylene diisocyanate and diethylene triamine can also be used in processes in which a microporous membrane is produced on its surface.

In the process according to the invention, a solution is preferably prepared in step a) which contains 0.1 to 10% by weight of agent A.

Furthermore, in step c) of the process according to the invention, the coagulation medium contains agent B in a concentration of 0.1 to 10% by weight.

The surface modification achieved is not sufficiently pronounced below the minimum concentrations mentioned. Above the maximum concentrations mentioned, there may be an undesirable disturbance in the formation of the membrane structure.

The invention is explained in more detail using the following example.

example

A casting solution at 20 ° C., consisting of 18% by weight of polyether sulfone, 8% by weight of polyvinylpyrrolidone, 37% by weight of caprolactam and 37% by weight of butyrolactone, is worked onto a glass plate and immediately immersed in a 20 ° C. precipitation bath, which consists of glycerin and caprolactam in a ratio of 1: 1 with the addition of 2% by weight of diethylene triamine (DETA). Furthermore, three further flat membranes are produced, each using casting solutions of the abovementioned composition and adding 1, 2 or 8% by weight hexamethylene diisocyanate (HMDI), based on the casting solution. Otherwise, the procedure is as in the previous paragraph.

FIG. 1 shows SEM images of the flat membranes produced with 0, 1, 2 or 8% by weight of HMDI. The picture line a) shows the glass plate and the picture line b) the surfaces facing the precipitation bath side as well as the picture line c) the total cross sections and the picture line d) the cross sections of the flat membranes facing the precipitation bath side.

FIG. 1 shows that the flat membrane produced without HMDI (0% by weight HMDI) has an asymmetrical pore structure, the pore size decreasing in the direction of the side facing the precipitation bath. FIG. 1 also shows that when HMDI is added, a layer is formed on the membrane surface facing the precipitation bath side (picture lines c) and d) with 1, 2 and 8% by weight of HMDI). The layer consists of a polymer network, which was formed by polymerizing HMDI with DETA to a polyurea. Finally, FIG. 1 shows that by selecting a certain amount of HMDI, the desired values of surface porosity (picture line b) and thickness (picture lines c) and d)) of the layer can be set in a targeted manner.

Claims

Process for the production of a surface-modified Membrane Membrana GmbH, Wuppertal 1. A process for producing a surface-modified membrane comprising the steps a) producing a solution comprising a membrane-forming synthetic polymer M, a solvent system and an agent A with at least one functional group, b) shaping the solution into a shaped body with a first and second side c) allowing to act on at least one of the sides of the shaped body of a coagulation medium which contains an agent B which is reactive with agent A and has at least one functional group dissolved, as a result of which phase separation takes place and a membrane structure is formed which has an inner pore surface and outer surfaces, and wherein agent B reacts with agent A on at least one of the outer surfaces during the exposure to it and d) optionally extracting the solvent system and optionally drying, whereby a membrane modified by the reaction product of A and B is formed. 2. The method according to claim 1, characterized in that in step a) the membrane-forming synthetic polymer M is a polyether sulfone, polysulfone or polyaryl ether sulfone. 3. The method according to claim 1 or 2, characterized in that in step a) the solvent system consists of caprolactam and butyrolactone. 4. The method according to one or more of claims 1 to 3, characterized in that agent A and agent B each have two functional groups and react in step c) to form a linear polymer. 5. The method according to one or more of claims 1 to 3, characterized in that agent A and / or agent B each have more than two functional groups and react in step c) to form a crosslinked polymer. 6. The method according to one or more of claims 1 to 5, characterized in that agent A is a dicarboxylic acid chloride or a diisocyanate. 7. The method according to claim 6, characterized in that agent A is terephthaloyl chloride or hexamethylene diisocyanate. 8. The method according to one or more of claims 1 to 3 and 5 to 7, characterized in that agent B contains at least one imino group and two amino groups. 9. The method according to claim 8, characterized in that agent B is diethylenetriamine or polyethyleneimine. 10. The method according to one or more of claims 1 to 3 and 5 to 9, characterized in that agent A is terephthaloyl chloride and agent B is polyethyleneimine. 11. The method according to one or more of claims 1 to 3 and 5 to 9, characterized in that agent A hexamethylene diisocyanate and agent B Is diethylenetriamine. 12. The method according to one or more of claims 1 to 11, characterized in that in step a) a solution is prepared which contains 0.1 to 10 wt .-% of agent A. 13. The method according to one or more of claims 1 to 12, characterized in that in step c) the coagulation medium contains the agent B in a concentration of 0.1 to 10 wt .-% dissolved.