Semipermeable composite membrane

Details Semipermeable composite membrane Semipermeable composite membrane

1992-12-03

1994-09-20

Spear, Frank

Liquid purification or separation

Filter

Supported, shaped or superimposed formed mediums

210638, B01D 6118

Patent

active

053486528

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a semipermeable composite membrane having a high sucrose retention and a low salt retention, which membrane consists of a porous support substrate and a polymer film applied thereon, and also to a method for the production of such a composite membrane.
Diverse types of composite membranes for reverse osmosis and ultrafiltration are known from the prior art. For example, Netherlands Patent Application 8103550 describes a membrane having an increased resistance to oxidation and a high water permeability which is made up of a microporous substrate and a film applied thereon, said film being obtained by interfacial crosslinking of a polyvinyl alcohol and an amine containing at least two secondary amino groups per molecule, using a polyfunctional crosslinking agent which is able to react with the secondary amino groups and hydroxyl groups, and also an inner layer of a water-soluble polyvinyl alcohol, which layer is located between the porous substrate and the film. However, with regard to membranes of this type it is stated that, in addition to a very high sucrose retention of about 99%, the retention for magnesium sulphate is more than about 90% and for sodium chloride is substantial at a strongly increased operating pressure.
U.S. Pat. No. 4,769,148 relates to a polyamide membrane for use in reverse osmosis, which membrane is produced by using a cationic polymer wetting agent in an aqueous solution containing a polyfunctional amino reagent, which is polymerised interfacially using an acyl halide with the formation of a thin film on a microporous support. The polymer wetting agent contains a multiplicity of onium groups, such as, preferably, sulphonium and quaternary ammonium groups. It has been found that the membranes described in this U.S. Pat. No. 4,769,148 have a retention for magnesium sulphate of more than about 90% and according to the examples the NaCl retention thereof is virtually always substantial, that is to say >50%.
In European Patent Application 313,354 a composite membrane for use in reverse osmosis is described which is formed by interfacial polymerisation, on a surface of a microporous support, of a water-soluble polyfunctional aliphatic primary amine and a water-soluble polyfunctional secondary amine with a polyfunctional acyl halide, preferably having a functionality of >2.05. This membrane was prepared using a molar ratio of the primary amino component to the secondary amino component of less than 1:5. Membranes in accordance with this European patent application can be used for the demineralisation of cheese whey and for the treatment of the effluent from a yeast culture. It can be seen from the examples that the lactose retention is usually more than about 93%. It is also stated in the text of said European Patent Application 313,354 that only 0.6% of the sulphate can pass through the membrane.
Furthermore, EP-A 0,114,286 relates to a semipermeable composite membrane which is made up of a porous polymer substrate with a thin semipermeable film applied thereon, which film covers both the external surface and the internal pore surface. This semipermeable film consists of at least one layer, and advantageously two to three layers, of a crosslinkable hydrophilic polymer which is crosslinked with at least one polyfunctional compound having at least two functional groups. According to EP-A-0,114,286 it is possible for the polymer film to contain both anionic and cationic groups. However, it is pointed out in respect of the polymer films according to said EP-A that the distribution of the anionic and cationic groups over the polymer film is "random", which in the experience of the Applicant leads to a poor reproducibility of the test results obtained; this aspect is illustrated in Comparative Example 2 below.
The production method for the composite membrane according to EP-A 0,114,286 is also regarded as being fairly laborious. In order to coat the substrate and the wall of the pores thereof, the substrate usually has to be subjected several times to the followi

REFERENCES:
patent: 4360434 (1982-11-01), Kawaguchi et al.
patent: 4769148 (1988-09-01), Fibiger et al.
Patent Abstracts of Japan, vol. 13, No. 107, Publication No. 63-283707.

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