Analysis of retention and flux decline during ultrafiltration of limed sugarcane (clarified) juice

The flux decline behaviour of sugarcane juice solution during ultrafiltrati on (UF) process was studied both experimentally and theoretically. Rate of flux decline was analyzed under varying operating conditions such as pressu re (550, 690, and 830 kPa) and feed concentration (11, 14, 17, 20 brix). A solution of the clarified limed sugarcane juice containing low molecular we ight (LMW) solutes, mainly sucrose, and high molecular weight solutes (HMW) like proteins, fats and wax, etc., was subjected to UF in a stirred cell e mploying a cellulosic membrane (Spectra Por). Under typical experimental co nditions, solution flux was found to reach a steady state value in about th ree hours. High molecular weight solutes (e.g., proteins) retained by the m embrane formed a get like porous layer on top of the membrane surface. Rela tively lighter molecular weight solutes (e.g., sucrose) were mostly permeab le, though also partly retained within the gel layer. A mathematical model was developed to describe the flux decline behaviour during UF of sugarcane juice. The model analysis takes into account the formation of polarized co ncentration boundary layers of both types of solutes, permeable as well as non-permeable. Decline in the flux of sugarcane juice was attributed to the combined effects of gel layer formation as per the cake filtration theory and the development of osmotic pressure of sucrose in boundary layer; altho ugh contribution of osmotic pressure exerted by sucrose in flux decline was found to exist only during initial stage of filtration. The model predicti ons were found to agree well with the experimental data.