DE19643566C2 - Method and device for membrane modification - Google Patents

Description

The invention relates to a membrane manufacturing process ren, in which membranes known per se by graft-co- Polymerization can be chemically modified, and one after modified membrane obtainable by this process.

Membranes are dependent on the separation process faced with very different substances, with gases, Liquids and solids. Accordingly diverse are therefore also the interactions within the border layers of adjacent phases.

To improve membranes, they are already on different ways by physical or chemi processes have been modified. The ver various processes have been used, for example photo-induced graft co-polymerization (surface photo grafting), grafting with ionizing radiation (grafting with ionization radiation), plasma treatment ment), plasma polymerization, Ko Corona discharge and flame treatment (Flame treatment). All of these methods can be fictional according to what is used below is discussed in more detail.

It is therefore known to chemically modify membranes ren, thereby their properties and thus their on to change and / or expand the range of terms or with the modified membranes solve new separation tasks can. In the simplest case, only the middle one is used Pore diameter while constricting the through Knife distribution reduced, so that finer particles in ver bond can be separated with improved selectivity can, see A. Oechel, Photochemisch indu adorned gas phase graft co-polymerization of Acrylmo nomers on ultrafiltration membranes made of polyacrylic tril; Dissertation Humboldt University Berlin, 1995. This procedure can lead to the sealing of the pores be, whereby a gas flow is excluded.

It is also known to modify membranes by transferring the properties of the graft to them while at the same time largely maintaining the pore structure of the membrane; in this regard, reference is made to M. Ulbricht, A. Oechel, C. Lehmann, G. Thomasch ewski, HG Hicke, in J. Appln. Polymer sci. 55: 1707-1723 ( 1995 ).

It is also known to adjust the hydrophilicity / hydrophobicity of the membrane in a targeted manner via the photo-induced graft polymerization depending on the agents used (monomers, initiators) which are brought to the membrane by a liquid, cf. M. Ulbricht, H. Matuschewski, A. Oechel, HG Hicke, in Proc. Euromembrane 1995 (Ed. W R. Bowen, RA Fields, JA Howell), Bath 1995 , pp. 398-401.

In this way it is also possible to use the pore size aims to decrease.

In all of these known methods, a membrane side with the agents and the high-energy radiation faced so the property of this membrane side specifically change and the process-specific penetration depth to limit.

In the simplest case, the membrane to be modified is flooded with the chemical agents in the presence of high-energy radiation; compare the Oechel 1995 cited above. It is also known (C. Liu, CR Martin, Composite membranes from photochemi cally synthesis of ultrathin polymer films, Natur 352 ( 1991 ), 50-52) to use a carrier liquid which is at rest within the membrane pores and which passes through the underside Capillary ascension was introduced. The radical polymerization can be carried out by excitation with an Xe lamp brought up from above.

The known methods and techniques now have the Disadvantages that they become a non-uniform polymer layer, to different sized pores and / or to one lead to uncontrolled layer growth.

The object of the present invention is to improve membrane modification process and an improved one and in particular to provide more selective membrane which for nanofiltration processes, gas separation and pervapora tion can be used.

This task is solved by teaching independent claims.

In the inventive method for membrane mo Thus, porous membranes are partially differentiated mixed modified by using monomers with the help of a trans membrane flowing carrier gas to that side of the Membrane transported or guided, which modified shall be. Graft-co-polymerization can thereby any usual with any initiation of the chemi act (UV, plasma, laser, etc.). there can all the usual polymerization processes in the Introduction to the type mentioned application ge be brought.

The carrier gas can be in any direction, including in changing direction, transmembrane through the membrane stream.

The method according to the invention makes a targeted Narrowing of the pores up to the sealing against egg reached gas flowing through. Because the pores differentiate diameters within a membrane surface, there is ultimately a diameter-specific, i.e. local and staggered graft co-polymerization that begins with the larger pores and their narrowing, more and more also captured smaller, which ultimately until the closure can be continued. Taking advantage of this yourself restrictive and ultimately due to lack of monomers self-ending grafting process results in premature Un Interruption of the reaction process to one against the Output membrane narrower pore size distribution or after independent restriction to "dense" separation phase as they are used in gas parazion and pervaporation can be placed. According to the invention can thus Membranes can be partially modified by using the Po Lymerisation progress controls. Under groove generation of the transmembrane monomer stream any Direction and setting of the flowing volume per time the degree of modification can be checked. So is it is possible, for example, the modification process everyone time to interrupt and thereby mo to obtain differentiated membranes.

According to the invention, the modification to a certain point in time and thus optionally canceled become. In addition, the polymerization is more or less limited to the pore area of the membrane. Invention accordingly, a carrier gas for introducing the Mo nomers and preferably also those that may be required ten further agents for initiation and / or maintenance chemical process.

The gas stream is preferably directed from the unbe beamed, not to be modified side to the irradiated, too modifying side of the membrane. More appropriate wise one conducts the residual monomers above the membrane from. The graft-co-polymerization leads to radiation area for constriction and ultimately for closing the Membrane pores. To put it simply, one assumes a uniform bottom ren out, the grafting has the consequence that during the Po constriction less and less monomers flow through,  until finally the monomer ver supply by the gas flow and the chemical Process independently, even with continued suggestion, under is bound. Given the real distribution the pore diameter, however, can be assumed be that initially the monomer supply specific because larger pores penetrate more intensely are flowing as narrower pores. As a result, too the chemical process between pores with different chem diameter differentiated in that the Grafting progresses faster within the larger pores steps and a unification of the streams channels is effected.

However, the method according to the invention is not based on this limited that the carrier gas from the not to be modified side transmembrane to the side to be modified flows. Also an opposite flow direction and a change of flow direction is also possible. Ent the only difference is that a transmembrane carrier gas Flow takes place so that the monomers are introduced into the pores become. The carrier gas flows from the one to be modified Transmembrane side to the side not to be modified then, it may be that a polymerization also on whose places take place as in the area of the pores. Whose however, the polymerization also takes place against possibly even primarily in the area of the pores. The before part of the preferred embodiment in which the carrier gas flow from the side not to be modified to the mo flowing side, is that the graft co- Polymerization is locally limited.

The invention also relates to one according to the invention Modified Mem obtainable according to the method bran.

The monomer to be grafted on is otherwise preferred wise in gaseous form or as gas with the help of the Trä gas gases transported or to the side to be modified or introduced to and into the pores. However, it is also possible to introduce the monomers in other ways, for example as an aerosol etc.

The invention is based on one, be preferred embodiment illustrative embodiment play it out in more detail.

According to the method according to the invention, a pho chemically induced gas phase graft co-polymerization of acrylic monomers using a transmembrane stick material flow on ultrafiltration membranes made of polyacrylic performed nitrile. This will be described in more detail below Written reactor used, which in the enclosed only single figure schematically and not to scale is faithful and sketchy.

The ultrafiltration membrane 1 known per se divides a reactor 2 into two compartments 3 and 4 .

The carrier gas nitrogen used in the example described in more detail is passed together with the monomer through the feed 5 into the compartment 3 . Further carrier gas and other necessary agents (for example initiator) or a further monomer can be introduced via the further feed 6 .

The reactor 2 , which can be tempered, tei lende membrane 1 can not only be self-supporting, but also supported by a suitable carrier, for example a coarse-pored plate.

The side 7 of the membrane 1 to be modified is made accessible for the high-energy radiation 8 . The radiation source must meet the parameters (wavelength and intensity) required for the intended grafting.

The membrane 1 was previously loaded with benzophenone by soaking in methanolic benzophenone solution, which is adsorptively bound to the polyacrylonitrile within the pore structure.

The nitrogen used as the carrier gas is pressed together with the components (monomers etc.) transported by this carrier gas due to an overpressure transmem bran and thus through the membrane 1 into the compartment 4 flooded with UV light. From there, the carrier gas and residual monomer and further constituents are discharged through the discharge line 9 . The enrichment of the carrier gas with the necessary agents and the recovery of the residual monomers passing through the membrane are carried out outside the reactor 2 . Pressure and flow sensors (not shown) are available for quantitative control and reproducible design of the process.

On the side 7 of the membrane 1 to be modified, radical formation takes place via a hydrogen abstraction of the benzophenone from the polymer matrix, with other reactants (monomers and oxygen) expediently being absent. The presence of the trans membrane-guided nitrogen / methacrylic acid monomer mixture leads to a graft-co-polymerization and parallel to the homopolymerization in the exposed pore area of the membrane.

The graft efficiency (ratio of graft co-polymer to the overall yield) is both of the benzophenone concentration as well as the wavelength of UV radiation dependent. The total increases with temperature prey and the degree of grafting. Another parameter is available Controlling the process and increasing the response speed the monomer concentration in the gas phase available that increases with temperature.

Claims (9)

1. Membrane production process, in which one chemically modifies a membrane known per se by graft-co-polymerization, characterized in that the graft monomers are transported or brought to the side of the membrane to be modified with the aid of a trans-membrane flowing carrier gas and induced the graft co-polymerization on the side to be modified in a manner known per se. 2. The method according to claim 1, characterized in net that the other ones, for initiation and / or maintaining the polymerization given if necessary or desired agents with Help of the carrier gas to the side of the to be modified Membrane transported. 3. The method according to claim 1 or 2, characterized records that the carrier gas from the not too mo differentiating side of the membrane through it flow to the side of the membrane to be modified lets, especially presses. 4. The method according to any one of the preceding claims che characterized in that the monomers used in gas form. 5. The method according to any one of the preceding claims che characterized in that a porous Membrane used as a membrane known per se or modified. 6. The method according to any one of the preceding claims che, characterized in that the graft-co- Polymerization induced photochemically. 7. The method according to any one of the preceding claims che, characterized in that as monomers Uses acrylic monomers. 8. The method according to any one of the preceding claims che, characterized in that one is known as per se  Membrane from an ultrafiltration membrane Uses polyacrylonitrile. 9. Modified membrane, available by the method ren according to any one of the preceding claims.