Composite silicone membranes of high separation efficiency

Abstract

Composite membrane having a separating membrane layer characterized in that a separating membrane layer is produced by curing laterally modified silicone acrylates of the general Formula I ##STR00001##

Claims

1. A composite membrane, comprising: a separating membrane layer and a support membrane, wherein the separating membrane layer comprises a cured mixture of silicone acrylates, the mixture comprising: from 70 to 90% by weight of a component (A); and from 10 to 30% by weight of a component (B); wherein component (A) is at least one silicone acrylate of Formula I, having a silicon content of on average greater than 29% by weight, ##STR00005## wherein, a is from 25 to 500, b is 0, c is from 0 to 20, and each R.sup.2=R.sup.3, and component (B) is at least one silicone acrylate of Formula I, having a silicon content of less than 27.5% by weight, wherein, a is from 1 to 24, b is from 3 to 25, c is from 0 to 20, and each R.sup.2 is R.sup.1 or R.sup.4, each R.sup.1 is independently an alkyl or aryl radical having from 1 to 30 carbon atoms, optionally comprising an ether group, an ester group, an epoxy group, an alcohol group, or a combination thereof, each R.sup.3 is independently an organic radical comprising one or more acrylate groups, and each R.sup.4 is independently a polyether radical.

2. The composite membrane of claim 1, wherein R.sup.3 is of Formula II or III: ##STR00006## d is from 0 to 12, e is 0 or 1, f is from 0 to 12, g is from 0 to 2, h is from 1 to 3, g+h=3, each R.sup.6 is H or an alkyl or aryl radical having 1 to 30 carbon atoms, each R.sup.7 is a hydrocarbon radical.

3. The composite membrane of claim 1, wherein each R.sup.4 is independently of Formula IV:
(CH.sub.2).sub.iO(CH.sub.2CH.sub.2O).sub.j(CH.sub.2CH(CH.sub.3)O).sub.k(CH.sub.2CHR.sup.8O).sub.lR.sup.9Formula IV, i is from 0 to 12, j is from 0 to 50, k is from 0 to 50, l is from 0 to 50, each R.sup.8 independently an alkyl or aryl radical having from 2 to 30 carbon atoms, each R.sup.9 is independently H, an alkanoyl radical, or an alkyl or aryl radical having from 2 to 30 carbon atoms.

4. The composite silicone membrane of claim 1, wherein a mass ratio of (A) to (B) is from 10:1 to 1:10.

5. The composite membrane of claim 1, wherein said curing is with a photo-initiator by electromagnetic radiation having a wavelength less than 800 nm, by an electron beam, or by both.

6. The composite membrane of claim 1, wherein the support membrane is at least one solvent persistent porous three-dimensional support structure selected from the group consisting of a nonwoven membrane, a micro-filtration membrane, an ultrafiltration membrane, and a separator.

7. The composite membrane of claim 1, wherein the support membrane comprises at least one porous support material selected from the group consisting of polyacrylonitrile (PAN); polyimide (PI); polyether ether ketone (PEEK); polyvinylidene fluoride (PVDF); polyamide (PA); polyamide-imide (PAI); polyethersulfone (PES); polybenzimidazole (PBI); sulphonated polyether ketone (SPEEK); polyethylen (PE); polypropylen (PP); an inorganic porous material, ceramic membrane, or polymer ceramic membrane obtained from aluminium oxide, titanium dioxide, zirconium dioxide, silicon oxide, titanium nitrite, or a combination thereof; and mixtures, modifications or composites thereof.

8. A process for retaining dissolved molecules, comprising: retaining dissolved molecules having a molecular weight of less than 2000 g/mol with the composite membrane of claim 1, wherein a retain fraction rate of the retaining is at least 90% by weight.

9. The process of claim 8, wherein the dissolved molecules are a homogeneous catalyst system to be separated from a reaction mixture, a triglyceride to be separated from a solvent having a molecular weight of less than 200 g/mol, an oligomer to be separated from a monomer solution, or a pharmaceutical active ingredient or precursor thereof to be separated from a reaction mixture or solution.

10. The process of claim 9, wherein the dissolved molecules are to be separated from a hydrocarbon with 1 to 8 carbon atoms, an isomer or mixture thereof, or else CO.sub.2.

11. The process of claim 8, wherein the retaining comprises separating off a molecular weight fraction of less than 1000 g/mol from a solution in n-heptane at 30 C., 30 bar pressure.

12. A process for producing the composite membrane of claim 1, comprising: coating a support membrane with the mixture of silicone acrylates, to obtain a coated support membrane, and subsequently curing the coated support membrane by electromagnetic radiation, electron beam radiation, or both.

13. The composite membrane of claim 2, wherein an R.sup.7 group is CR.sup.6.sub.2-.

14. The composite membrane of claim 13, wherein an R.sup.7 group is CH.sub.2-.

15. The composite membrane of claim 3, wherein i is from 3 to 7.

16. The process of claim 12, wherein curing the coated support membrane comprises curing by electromagnetic radiation having a wavelength less than 800 nm.

Description

EXAMPLES

(1) In the examples described hereinafter, the present invention will be described for illustration of the invention, without intending to restrict the invention, the range of application of which results from the entire description and the claims, to the embodiments cited in the examples. If ranges, general formulae or classes of compound are cited hereinafter, these should comprise not only the corresponding ranges or groups of compounds that are mentioned explicitly, but also all subranges and subgroups of compounds which can be obtained by extraction of individual values (ranges) or compounds. If, in the context of the present description, documents are cited, the contents thereof shall be incorporated completely in the disclosure of the present invention. If, in the context of the present invention, compounds such as, e.g., organically modified silicone acrylate are described that can have multiple various monomer units, these can occur statistically distributed (statistic oligomer) or arranged (block oligomer) in these compounds. Statements on the number of units in such compounds must be taken to mean statistical mean values, taking the mean over all corresponding compounds.

(2) Production of the Membranes

(3) On the basis of ultrafiltration membranes available on the market that are made of polyacrylonitrile obtainable from, e.g., the company GMT, Rheinfelden or GE-Osmonics, Vista, USA, distributed by the company Desalogics, Ratzeburg, coatings were performed with TEGO silicone acrylates from Evonik Goldschmidt GmbH. The coatings were carried out in layers with a smooth-roll application appliance having 5 rolls. The coatings were performed at a coating weight of 0.6 to 1.5 g/m.sup.2. The coatings were crosslinked via a UV lamp in an inert nitrogen atmosphere. For this purpose, a suitable photoinitiator such as, e.g., a hydroxyketone, is added to the silicone acrylates in an amount of 1/100 based on the silicon mass. In this manner, on the basis of said ultrafiltration membrane, composite membranes are generated that have different mixtures and layer sequences of component a) and component b) corresponding to the silicone acrylates. The following coatings were produced having different mass fractions of the component a) and component b) in each case based on the total amount of silicone acrylate: 90% by weight a) & 10% by weight b); 80% by weight a) & 20% by weight b), with additional 3% by weight of inorganic filler based on the total amount of silicone acrylate; 70% by weight a) & 30% by weight b) with additional 3% by weight of inorganic fillers based on the total amount of silicone acrylate and without inorganic fillers and also 100% by weight b).

(4) The components a) and b) according to formula 1 as used in the examples have the following constitution: Component a) a=83, b=0, c=0, R.sup.1CH.sub.3, R.sup.2(CH.sub.2).sub.3OCH.sub.2C(C.sub.2H.sub.5)(CH.sub.2OC(O)CHCH.sub.2).sub.2 Si-content=34.2% per weight Component b) a=13, b=5, c=0, R.sup.1R.sup.2CH.sub.3 R.sup.3=substituent according to Formula II Si-content=23.8% per weight

(5) The components are produced using methods according to the prior art, as described, for example in DE 3820294 C1 (U.S. Pat. No. 4,978,726).

(6) As inorganic filler, silica was used.

(7) As a comparative type of a membrane of the prior art, a membrane was studied that was produced exclusively on the basis of TEGO RC 902 corresponding to component a).

(8) The membranes produced were characterized by what is termed the molecular weight cut-off (MWCO) method in n-heptane. The MWCO method is described, for example, in the following literature: Journal of Membrane Science 291(2007)120-125. The method is based on measuring the retention of various styrene oligomers in dependence on their molecular weight (MWCO curve).

(9) By using the MWCO method, it is possible to estimate to what extent a dissolved substance having a defined molecular weight may be separated off. In FIG. 1 and FIG. 2, the molar mass (Mw) of the dissolved substances, here polystyrenes, are plotted against the retention at the membrane studied in each case, in % by weight, derived from concentrations by mass.

(10) The stability of the separating layer was determined by determining the MWCO curve and the permeability of the membrane over a long period in n-heptane.

(11) The membranes were tested by means of a cross-flow filtration. The operating temperature was 30 C. and the transmembrane pressure (TMP) 30 bar. In the long-term experiments, a pressure of 10 bar was employed. The membranes were conditioned using pure solvents until a steady-state flux was achieved. Subsequently, the pure solvent was replaced by a mixture of solvent and oligo-styrene indicator. After a steady-state flux was again achieved, samples of permeate and feed stream were taken off and the fraction of styrene oligomer determined by analogy with the MWCO method.

(12) FIGS. 1 and 2 show the results of the retention capacity for polystyrenes having different molecular weights, and also the solvent fluxes of the silicone acrylate membranes of different composition. Permeate liquid is n-heptane.

(13) The results in FIG. 1 verify that the properties of the separating membrane layers can be set in a targeted manner by a mixture of the various TEGO RC products from a membrane having an excellent separation efficiency, but a low flux, to a membrane having a high flux, but a lower separation efficiency. In this manner by mixing the various silicone acrylates, the property profile of the membrane may be set in a targeted manner for an application.

(14) It can be seen from the MWCO curves that the membrane having the highest fraction of the component a) of 90% has the lowest relative retention and the highest permeate flux. On the other hand, a membrane that consists of 100% of component b) has virtually no longer any permeate flux for n-heptane and a very high retention. The results shown of the 20/80 and 30/70 mixtures with and without fillers show that the properties can be set virtually steplessly.

(15) The comparison test of the membranes according to the invention having a composition 30% b) & 70% a) with silicone membranes according to the prior art (100% a)) were carried out in n-heptane as described above. After a further 11 days of constant operation of the membrane at 10 bar and 30 C. in hexane, the MWCO test was carried out again.

(16) The results shown in FIG. 2 demonstrate that the membrane according to the invention has a separation limit shifted significantly to lower molecular weights.

(17) It follows from the marked shift of the separation curve of the prior art membrane to higher molecular weights and increase in permeate flux that this membrane is not stable in heptane. The membrane according to the invention shows no relevant change in permeate flux performance and in separation properties as a function of operating time, which verifies the stability of the membrane in n-heptane.