Experimental Investigation of Nanofiltration Process for the Separation of Complex Sugar Mixtures Containing Mono- and Multivalent Salts

Abstract

The energy consumption of sugar producing industry is enormous mainly due to the thermal energy demand of multi-stage evaporation. However, alternative processes have been studied to reduce the high operating cost. Membrane technology is a well-established process for water treatment. Reverse osmosis (RO) and nanofiltration (NF) have also been examined for the pre-concentration of clarified thin sugar juice to reduce the role of evaporation in the sugar production process. RO/NF can be used to remove water from the aqueous solution at a temperature below its boiling point and without phase change. It has a positive effect on the quality of the clarified thin sugar juice because sugar juice is degraded at high temperatures. The clarified thin sugar juice contains 15 °Brix (15 w%) of sugar and about 0.25 - 0.40 w% of the ionic compounds. In the present work the effect of the presence of monovalent and multivalent salts on the separation performance of a nanofiltration membrane during sugar concentration has been studied experimentally. The sugar rejection was not affected much by the salt concentration but the rejection of monovalent or multivalent ions was found to be highly dependent on the sugar concentration.