Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1983-02-17
1985-03-19
Cockeram, Herbert S.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
20415915, 20415917, 525276, 521134, C08J 936, C08F 800, C08F25908
Patent
active
045060355
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of rendering hydrophobic fluoropolymers hydrophilic.
In particular the invention relates to a method of preparing hydrophilic fluoropolymers suitable for use as microporous diaphragms in electrochemical cells, especially in cells electrolyzing alkali metal chloride solutions.
BACKGROUND ART
Electrolytic cells are commonly used to make chlorine and an alkali metal hydroxide solution by electrolysis of an alkali metal chloride solution. Such cells are known as chlor-alkali cells. Reference is made in this specification to chlor-alkali cells and processes as typifying electrolytic cells and processes in general.
There are three broad types of chlor-alkali cell, "mercury", "diaphragm" and the more recently developed "membrane" cells.
In membrane cells the anodes and cathodes are separated by cation-active permselective membranes; these are membranes which are selectively permeable so as to allow the passage of only positively charged ions and not the passage of bulk electrolyte. Cation-active perm-selective membranes which are suitable for this use in chlorine cells include, for example, those made of synthetic organic copolymeric material containing cation-exchange groups, for example, sulphonate, carboxylate and phosphonate. Perm-selective membranes are non-porous.
On the other hand, diaphragm cells, in which the anodes and cathodes are separated by porous diaphragms, permit the passage of both positive and negative ions and of electrolyte.
In operating a diaphragm cell for the electrolysis of alkali metal chloride solutions to give chlorine and alkali metal hydroxides, it is essential that flow of the solutions through the tortuous microporous diaphragm be unimpeded by gas voids in the porous network.
Diaphragms prepared from asbestos fibres have generally been used but these suffer from the disadvantage that is limited; and interelectrode gap can be reduced.
Alternatively diaphragms comprising fluoropolymer materials in sheet or in fibrous form which are inert to the cell liquors have been proposed. However, these diaphragms suffer from the problem that they are hydrophobic and difficult to wet with alkali metal chloride and hydroxide solutions and in consequence tend to have gas-filled voids in the porous network of the diaphragm. This can lead to diaphragm blockage, high voltages and mixing of the product gases, hydrogen and chlorine.
Several methods have been proposed for rendering such diaphragms hydrophilic. For example UK Patent 1,081,046 and Belgian Patent 794,889 to ICI Ltd describe processes for microporous sheet diaphragms in which a hydrophilic particulate inorganic additive such as titanium dioxide is added to confer hydrophilicity on the diaphragm matrix. Other additives such as surface active agents have also been proposed for this purpose.
These additives suffer from the disadvantage that into a fibrous or sheet form; achieve satisfactorily.
It is an objective of the present invention to provide hydrophilic fluorocarbon membranes for use in chlor-alkali electrolysis cells.
We have now devised a process of rendering hydrophobic fluorocarbon polymers hydrophilic by means of graft copolymerization of certain monomers to the hydrophobic fluorocarbon polymer substrate.
DISCLOSURE OF INVENTION
Accordingly the present invention provides an hydrophilic fluoropolymeric diaphragm comprising a fluorine-containing substrate to which has been radiation co-grafted a mixture of monomers comprising at least one functional monomer selected from compounds of formula I hydroxysulfonyl, fluorosulfonyl, or the group --CO--NR.sup.1 R.sup.2 wherein R.sup.1 and R.sup.2 are independently selected from hydrogen and C.sub.1 to C.sub.6 alkyl, one X is fluorine and the other X is selected from chlorine, fluorine and a trifluoromethyl group, n is an integer from 1 to 12, m is an integer from 1 to 3; and unsaturated dicarboxylic acids or derivatives thereof containing the group of formula III ##STR2## wherein R.sup.3 and R.sup.4 may be the same or different and rep
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Barnett George H.
Markus Michael V.
Cockeram Herbert S.
ICI Australia Limited
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