Assessment of sugars separation from a model carbohydrates solution by nanofiltration using a design of experiments (DoE) methodology

Abstract

Nanofiltration (NF) of a model solution of different molecular weight carbohydrates (inulin, sucrose, glucose and fructose) has been studied with a pilot cross-flow unit, using a membrane with molecular weight cut off (MWCO) of 600Da. The aim of this work was to screen operational parameters and to determine the most feasible domain in order to separate inulin-type fructans from model solutions containing low molecular weight (LMW) sugars. Firstly, parameters such as transmembrane pressure (TMP), feed concentration (C0) and retentate flow (QR) were screened using a Koshal design for single-component solutions. The results indicated that the most influential parameters were TMP and C0. Then, a Doehlert design was used to improve single-inulin nanofiltration. Indeed, surface response analysis (p<0.05) revealed inulin rejection values over 90%, for high TMP (1400kPa) and low C0 (5g/100mL). In order to test the robustness of these results in presence of sugar, a full factorial design was used to evaluate the separation of a binary solution containing sucrose and inulin. In this case, the permeate flux (Jv) and inulin rejection (Rinulin) results were in agreement with those obtained with single-component solutions. Furthermore, additional experiments on a complex quaternary mixture (sucrose–glucose–fructose–inulin), confirmed that the presence of mono and di-saccharides do not modify significantly Rinulin. Actually, it is possible to obtain even slightly better results for the separation process (Rinulin=93%). All the results were statistically validated using analysis of variance (ANOVA).