Alistair S. Grandison, Athanasios K. Goulas, and Robert A. Rastall

pp. 915 - 928

Abstract

Nanofiltration (NF) of model sugar solutions and commercial oligosaccharide mixtures were studied
in both dead-end and cross-flow modes. Preliminary trials, with a dead-end filtration cell, demonstrated
the feasibility of fractionating monosaccharides from disaccharides and oligosaccharides in mixtures,
using loose nanofiltration (NF-CA-50, NF-TFC-50) membranes. During the nanofiltration purification of
a commercial oligosaccharide mixture, yields of 19% (w w^-1) for the monosaccharides and 88% (w w^-1) for
di, and oligosaccharides were obtained for the NF-TFC-50 membrane after four filtration steps, indicating that removal of the monosaccharides is possible, with only minor losses of the oligosaccharide content of
the mixture.
The effects of pressure, feed concentration, and filtration temperature were studied in similar experiments carried out in a cross-flow system, in full recycle mode of operation. The rejection rates of the
sugar components increased with increasing pressure, and decreased with both increasing total sugar concentration in the feed and increasing temperature. Continuous diafiltration (CD) purification of model sugar
solutions and commercial oligosaccharide mixtures using NF-CA-50 (at 25^o
C) and DS-5-DL (at 60^o
C)
membranes, gave yield values of 14 to 18% for the monosaccharide, 59 to 89% for the disaccharide and 81 to 98% for the trisaccharide present in the feed. The study clearly demonstrates the potential of cross flow
nanofiltration in the purification of oligosaccharide mixtures from the contaminant monosaccharides.