ELECTROASSISTED TRANSPORT PHENOMENON OF STRONG AND WEAK ELECTROLYTES ACROSS ION-EXCHANGE MEMBRANES - CHRONOPOTENTIOMETRIC STUDY ON DEACTIVATION OF ANION-EXCHANGE MEMBRANES BY HIGHER HOMOLOGOUS MONOCARBOXYLATES

The electrical responses of two interpolymer ion-exchange (anion and c ation) membranes have been investigated by chronopotentiometry in dilu te solutions of NaCl, KCI, and HCl as strong electrolytes and a 75:25 mixture of(1 mM) RCOOH-RCOONa, where R = -H, -CH3, -CH2CH3, -CH2CH2CH3 , and -CH(CH3)(2) as weak electrolytes. The behavior of both of these membranes was nearly ideal in strong electrolytes. The performance of a cation membrane in weak electrolytes R = -H and -CH3 was as good as in NaCl/KCl and less satisfactory in others. On the other hand, the pe rformance of an anion membrane in electrolytes R = -H and -CH; was nea rly identical to that in NaCl/KCl. but it steadily decreased as the le ngth and size of the alkyl (-R) chain increased. The poor performance of the anion membrane in higher homologous carboxylates with R = -CH2C H3, -CH2CH2CH3, and -CH(CH3)(2) has been attributed to fouling of the surface by the RCOO- groups next to the membrane in the interfacial zo ne on the diluate side and/or the choking of ion flow channels by thes e carboxylate ions on account of a long nonconductive alkyl chain on t hem. The parameters such as the potential drop across the membrane at the outset of each experiment, I tau(1/2), the permselectivity, and th e transference number for both types of membranes in strong as well as in weak electrolytes were measured and compared, The transport across the anion membrane of OH-ions from either water autodissociation or h ydrolysis step of RCCO- groups at the anion membrane surface was consi dered in both strong and weak electrolytes at the above optimum curren t densities. The fouled anion membrane was regenerated by rinsing with distilled water and equilibrating it with a strong electrolyte soluti on.