Ultrafiltration: a means for decolorization of cane sugar solution

Membrane ultrafiltration was used for clarification as well as for decolorization of raw brown sugar obtained from the Indian sugar industry. Experimental results were obtained using sugar solutions of 28 and 46°Brix and mineral membranes of 20 nm, 5 and 1 kDa molecular weight cut-off (MWCO) on an industrial size pilot plant under different operating conditions. It was found that, even with the membrane of MWCO of 1 kDa, the maximum color removal was limited to 58.67% and steady-state permeate flux was only 29 1/h m² for the 46°Brix sugar solution. Empirical relationships between membrane performance (for decolorization and clarification) and membrane pore diameter were obtained from the experimental results. In order to obtain very high quality white crystalline sugar, further processing with adsorbents or use of an ion-exchange technique is required.