Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Patent
1997-06-10
1998-12-15
Phasge, Arun S.
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
204537, 204296, 204631, 521 27, B01D 6144
Patent
active
058491678
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/EP95/03596 filed Sep. 12, 1995.
The present invention relates to a process for the manufacture of bipolar membranes.
Bipolar membranes are constituent components of electrodialysis cells. The latter are well known in technology where they are especially used for the manufacture of acids and bases starting from their salts.
In processes which are generally used for manufacturing bipolar membranes, a cationic membrane and an anionic membrane, which have been subjected beforehand to a conditioning pretreatment, are joined side by side. To this end, in International Application WO 89/01059 (Unisearch Limited), a description is given of a process for the manufacture of a bipolar membrane, according to which a cationic membrane and an anionic membrane are subjected to an identical conditioning pretreatment which comprises bringing them into contact with an aqueous solution of a salt of a metal other than sodium or potassium and with an alkaline solution (generally an aqueous sodium hydroxide solution); the membranes recovered from the conditioning pretreatment are then superimposed to constitute the bipolar membrane.
The bipolar membranes obtained by means of the known process described above are generally characterized by good mechanical strength and moderate electrical resistance.
The known process which has just been described with reference to International Application WO 89/01059 necessitates, before the two unipolar membranes (the anionic membrane and the cationic membrane) are joined side by side, subjecting them to a conditioning pretreatment with a polyvalent metal salt, on the one hand, and with an aqueous alkali metal hydroxide solution, on the other hand. This known process in this way requires a large number of industrial operations, which complicates it and renders it expensive.
The objective of the invention is to simplify the abovementioned known process, without harming the performance of the bipolar membranes obtained.
Consequently, the invention relates to a process for the manufacture of a bipolar membrane, according to which an anionic membrane is joined side by side to a cationic membrane, the membranes having been subjected beforehand to a conditioning pretreatment with an aqueous medium, the conditioning pretreatment of the anionic membrane comprising bringing the latter into contact with a compound of a polyvalent metal and with an aqueous alkali metal hydroxide solution and the conditioning pretreatment of the cationic membrane with the aqueous medium essentially comprising bringing the said cationic membrane into contact with water which is essentially free from polyvalent metal and from alkali metal.
Cationic membrane is understood to denote a thin, non-porous sheet which is selectively permeable to cations and impermeable to anions. The cationic membranes which can be used in the process according to the invention must be made of a material which is inert with respect to aqueous acidic or basic solutions. Cationic membranes which can be used in the process according to the invention are, for example, sheets made from fluorinated polymer containing functional groups derived from sulphonic acids, carboxylic acids or phosphonic acids or mixtures of such functional groups, these groups acting as permanent cationic sites of the membrane. Examples of membranes of this type are those known under the name Raipore (Pall Rai) and under the trade name Morgane (Solvay), in particular the membranes Raipore R-4010, Morgane CDS and Morgane CRA.
By definition, an anionic membrane is a thin, non-porous sheet which is selectively permeable to anions and impermeable to cations. Anionic membranes which can be used in the process according to the invention are sheets made from a polymeric material which is inert with respect to aqueous acidic or basic solutions and which comprises quaternary ammonium groups acting as permanent anionic sites. The membranes Raipore R-1030, Raipore R-4030 and Morgane ADP are examples of anionic membranes which can be used in the process acco
REFERENCES:
patent: 4238305 (1980-12-01), Gancy et al.
patent: 5227040 (1993-07-01), Simons
patent: 5380413 (1995-01-01), Posar et al.
Phasge Arun S,.
Solvay ( Societe Anonyme)
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