Concentration of ethanolic extracts from Sideritis ssp L. by nanofiltration: Comparison of dead-end and cross-flow modes

The present investigation considers the flux decline during concentration of ethanolic extracts from Sideritis ssp. L. by nanofiltration. Membranes Duramem with molecular weight cut-off (MWCO) 300 and 500 Da have been used. Two sets of nanofiltration experiments are performed: dead end filtration in a stirred cell and cross flow filtration in a 4 flat sheet membrane rig. Comparable fluxes and rejections are observed. The membrane behaviour with respect to the operation conditions: transmembrane pressure and feed concentration is studied. The effect of the latter is illustrated by experiments with different feed concentrations and permeate-to-feed ratios. The discussion is supported by rejections and mass balance calculations. In both modes flux decreased with concentration and the observed rejections remained constant. Better conditions for reduced flux decline and tendency to a steady value are obtained by cross-flow nanofiltration. Combined with the greater membrane area and feed volume used in these experiments, these results can be regarded as having potential for larger scale applications. (C) 2012 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.