Single-film membrane, process for obtaining it and use thereof

Details Single-film membrane, process for obtaining it and use thereof Single-film membrane, process for obtaining it and use thereof

1995-10-23

1998-11-24

Fortuna, Ana

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

21050025, 21050036, 21050042, 521 27, 204520, B01D 1504

Patent

active

058401920

DESCRIPTION:

BRIEF SUMMARY
SUBJECT OF THE INVENTION

The invention relates to a new single-film membrane, to a process for obtaining it and to its use for the production of bases and acids, for pH control and/or for the electrodialysis of an aqueous solution.
State of the art and technological background underlying the invention
Acids and bases can be produced from their salts by electrolysis or electrodialysis.
Under the effect of the application of a potential, these processes make it possible to form in an aqueous medium, starting, for example, from sodium chloride, hydrochloric acid (HCl) and caustic soda (NaOH).
Bipolar ion-exchange membranes are employed in electrodialysis for obtaining these different components.
Various types of bipolar membranes have been proposed. Membranes of double-film type consist of two monofunctional membranes, a cationic exchange membrane and an anionic exchange membrane, which are joined side by side. In another type of membrane a cationic exchange film is covered on one face with a coating including anionic exchange groups.
Bifunctional single-film bipolar membranes consist of a polymeric membrane including a cationic exchange portion and an anionic exchange portion.
Patent Application GB-2,122,543 describes a double-film membrane consisting of a cation exchange film and of an anion exchange film which are treated so that the interface of the bipolar membrane consisting of the two films which are joined together contains one or a number of inorganic compounds capable of dissociating water into its components H.sup.+ and OH.sup.-.
The compounds consist of one of the cations of group 1a to group 4a, of the lanthanides and actinides of the Periodic Table. The anion is chosen from the group of tetraborates, metaborates, silicates, metasilicates, tungstates, chlorates, phosphates, sulphates, chromates, hydroxyl, carbonates, molybdates, chloroplatinates, orthovanadates and tellurates.
Document Electrochimica Acta vol. 31, pages 1175-1176 (1986) describes a process consisting in coating the surfaces of functionalized single-film membranes before they are joined together with the aid of a solution containing at least one of the following electrolytes: sodium tungstate, chromic nitrate, sodium metasilicate, ruthenium trichloride, indium sulfate, cerous sulfate, sodium chromate, stannous chloride, sodium dihydrogenphosphate, thorium nitrate and zirconium chloride.
According to document AU-B-88/2257, bipolar membranes can be produced in various ways.
According to a first embodiment the anionic membrane and the cationic membrane are subjected to a pretreatment with an aqueous solution containing at least one monovalent or polyvalent cation other than sodium and potassium, the solution having an alkaline pH, and the pretreated membranes are next arranged together, one facing the other.
According to a second embodiment, characterized by a scission of a pretreatment into two steps, the anionic membrane and the cationic membrane are subjected to a pretreatment with an aqueous solution containing at least one monovalent or polyvalent cation other than sodium and potassium, the pretreated membranes are next subjected separately to a treatment with an alkaline solution and are arranged together one facing the other.
According to a third embodiment the anionic membrane and the cationic membrane are subjected to a pretreatment with an aqueous solution containing at least one monovalent or polyvalent cation other than sodium and potassium, the pretreated membranes are next arranged together one facing the other to form a bipolar membrane and this bipolar membrane is then treated with an alkaline solution.
In this process the pretreatment of the membranes, which can be performed at ambient temperature, is preferably performed with heating at temperatures ranging from 60.degree. C. tp 100.degree. C.
However, these types of double-film membranes exhibit the disadvantage of having an interface resulting from being joined together, which must have excellent adhesion properties, must be capable of containing a catalyst in th

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