Application of electrodialysis within fine chemistry

Abstract

Abstract Several fine chemicals and pharmaceutical products are obtained by multi-step processes involving, amongst others, the neutralization of acid and basic solutions which lead to the formation of salts. Two routes using electrodialysis with bipolar membranes (EDBM) can be followed: (i) the conversion of the salt into the corresponding acid and basic solutions, or (ii) the neutralization of the alkali salts of the required organic acid by EDBM instead of carrying out the acid hydrolysis. Within a European Research Program the feasibility of both electrodialysis processes for amino acid production have been studied. The first type of process seemed to be not very attractive because of too high losses of amino acid and because of economical reasons. The second type of ED process was carried out in a batch mode of operation with a fixed current density of 1000 A/m2 until the stack voltage increased to 30 V, then the acidification was continued at a fixed voltage and the current density was decreased to 400 A/m2. The current efficiency found varied between 85 and 97%. The technological aspects are discussed, e.g. how to avoid precipitation of the amino acid in the membrane stack, the maximum achievable concentrations of the neutralized amino acid and of the basic solution produced.