Purification and fractionation of cellooligosaccharides synthesized from controlled cellulose hydrolysis by sulfuric acid using nanofiltration

Abstract

Cellooligosaccharides (COS) as potential prebiotics have drawn increasing attention. They can be synthesized from cellulose via controlled hydrolysis by sulfuric acid (SA). However, it is challenging to efficiently separate COS from the hydrolysate. In this study, nanofiltration (NF) with commercial membranes was investigated to separate COS from cellulose hydrolysate by removing SA and non-prebiotic sugars (e.g., glucose) and further fractionating COS by size. Based on water permeability, pore size, and acid stability, two membranes (Trisep® XN45 and Synder® NFG) were selected from four candidates. The effects of operation conditions (membrane and applied pressure) and feed concentrations (sugars and SA) on the COS purification and fractionation were studied. It was found that the XN45 membrane with an estimated average pore size of 0.61 nm was efficient in removing SA and glucose from COS, while NFG with a larger pore size of 0.84 nm can be used to fractionate and further purify COS based on size (degree of polymerization, DP). Four sequential batch NF operations of cellulose hydrolysate through XN45 (×3) and NFG (×1) membranes recovered 80 % of the total COS in the hydrolysate and removed 99 % of SA and 95 % of glucose. NFG membrane can roughly separate COS into two fractions, one (retentate) with more larger COS (DP ≥ 9) and another (permeate) with more smaller COS (DP 2–8). This study successfully demonstrated the feasibility of NF to purify and fractionate COS from cellulose hydrolysate.