Purification of lactulose syrup by using nanofiltration in a diafiltration mode

In this study, the retention behaviours of disaccharides (lactulose and lactose) and catalysts (NaCl and H3BO3) in the prepared lactulose syrup were investigated in a pilot scale test of nanofiltration. Their retentions in the syrup by the applied membrane, ranked from high to low, were: disaccharides (94.7–98.5%) > NaCl (9.0–20.0%) > H3BO3 (−19.9–0.0%). These differences in retention were significant, which made it possible to carry out their separation in syrup. In addition, a model was utilized to simulate the purity and yield of disaccharide during the continuous diafiltration process. According to the simulation, 25.0 bar was chosen as the optimum operating pressure for a continuous diafiltration process. Based on the experimental results, it was found that more than 96.5% of NaCl and H3BO3 were removed from lactulose syrup with only a small loss (11.0%) of disaccharides when the Vc/Vf (multiple of dilution) was 5.0 for the membrane used.