PRODUCTION OF CHLORINE AND CAUSTIC SODA U SING A ION-EXCHANGE MEMBRANE PROCESS

In Europe, 50 % of the production of the chemical industry depends on chlorine. Elf Atochem, the french leader in chlorine, has chosen to ex tend its chlorine capacity with the ion exchange membrane (IEM) proces s. The IEM have to be resistant to the aggressive electrolyte medium, have a very high permselectivity and conductivity. The chlor-alkali me mbranes are made of perfluorocarbon polymers with cationic exchange gr oups, sulfonic on the anodic side and carboxylic on the cathodic side. Their properties are well described by the cluster network model. The electrolyser and membrane evolution allow to obtain high caustic soda current efficiency (97 %) and a voltage of about 3 V at 3 kA/m2, 90-d egrees-C and with a caustic soda concentration of about 35 wt %. Since 1990, a 50 wt % caustic soda solution can be produced directly in ele crolysers using a new generation of multilayer ion exchange membrane. Despite the unfavorable economic climate in which the chlorine industr y finds itself (overcapacity, environment), the IEM process has made a remarquable breakthrough : this technology appears to be the most eco nomic and above all the most respectful of the environment. This proce ss is already recognized as the substitute of the mercury process. Elf Atochem operates two chlor-alkali membrane plants : one of 80 kt Cl2/ year in USA and a second of 120 kt Cl2/year in France.