Recovery of organic acids with high molecular weight using a combined electrodialytic process

When organic acids having molecular weights of around 200 kg kmol(-1) or more are recovered using electrodialysis with bipolar membranes (EDB) in a three compartment arrangement, mass transfer (conversion rate) is rather low and energy consumption is relatively high. One of the problems lies in the coupled system between anion exchange membranes and bipolar membranes. In order to reduce the bipolar membrane area, a high transport rate through the anion exchange membranes is necessary. This, however, leads to an unpropotionately high energy consumption. In this study an attempt was made to improve the process by splitting the three compartment EDB into a conventional ED, and a two compartment system with bipolar and cation exchange membranes. This means, the bipolar membrane area will be determined by the transport rates of Na+ through the cation exchange membrane, which is advantageous. However, the equivalent Na+ amount must be transported two times. The organic acids separated were gluconic and citric acid. The results showed that in both cases an improvement of the technology appears possible. The bipolar membrane area can be significantly reduced, which from the economic point of view is very important. Normally, energy and membrane costs are to a certain degree variable. Thus, the degree to which the process can be made more economical has to be considered case by case. (C)2000 Elsevier Science B.V. All rights reserved.