Separation of sodium sulfate and p-toluene sulfonic acid by electrodialysis

An electrodialysis process is proposed to achieve efficient separation of sodium sulfate from its mixture with p-toluene sulfonic acid. In this process, interpolymer type ion-exchange membranes were used due to their higher chemical stability and durability. Experiments were conducted in laboratory scale electrodialysis unit with an effective area of 65 cm(2) and 10 cell pairs, at different compositions of sodium sulfate and p-toluene sulfonic acid in its mixture, to see the effect of their concentration on the process efficiency. Batchwise electrodialysis experiment in four stages was also conducted to separate 12% (w/v) sodium sulfate from 2% (w/v) p-toluene sulfonic acid. Observations indicate that at higher sodium sulfate concentration, energy consumption increases while current efficiency decreases due to enhanced back diffusion from concentrate to treated compartments. Dialytic rate of sodium sulfate is also estimated under different experimental conditions. It is concluded that p-toluene sulfonic acid adsorbed or masked the surface of anion-exchange membrane, which is responsible for the increased reduction in the ionic transportation with the increase in concentration of p-toluene sulfonic acid. Adsorption/masking is completed up to its critical micelle concentration and beyond this concentration; further increase in p-toluene sulfonic acid has no more effect on ionic transportation.