Recovery of Galactose and Removal of Impurities by Nanofiltration from a Model Solution Algal Galactan Hydrolysate

Abstract

Agarose, one of algal galactan, was treated by acid catalyst such as HCl or H2SO4 to produce galactose, HMF (hydroxymethyl furfural), and levulinic acid. Since HMF and levulinic acid are inhibitors to microorganisms, they should be removed before the subsequent step of fermentation to produce bioethanol or other useful compounds. In this study, we investigated recovery of galactose and removal of impurities from algal galactan hydrolysate by nanofiltration. For a model solution containing 2 g/L galactose, 2 g/L HMF and 2 g/L levulinic acid, at an operating pressure of 200 psig, the rejections of galactose, HMF and levulinic acid were 99.3 %, 8.7 % and 37.5 %, respectively. This results clearly suggests that HMF and levulinic acid can be effectively removed into the permeate while galactose is retained in the feed solution. For the optimization of operating conditions, effects of the operating pressures (50 ~ 400 psig), the pH (4.0 ~ 8.5), temperature (20 ~ 35℃) and the concentration of each component (0 ~ 20 g/L) on the solution flux and rejection were investigated.. The pH affected the rejection of levulinic acid only. The rejection increased dramatically with pH. As the operating temperature increase, the solution flux increased rapidly, while the rejections of all the components decreased. The increase in concentration caused a decrease in the solution flux and rejection for all of the components.