From by- to bioproducts: selection of a nanofiltration membrane for biotechnological xylitol purification and process optimization

Abstract

Xylitol, an alcohol sugar with diverse applications, is commonly synthesized by chemical routes on an industrial scale. This polyalcohol can also be obtained by fermentation of lignocellulosic biomass. However, downstream purification is still a bottleneck that increases the costs and limits the yield of bioxylitol production. This study aimed to develop a novel approach for purification of xylitol obtained by fermentation of sugarcane bagasse hemicellulose hydrolysate. After nanofiltration membrane selection, process conditions were optimized by surface response methodology. Four nanofiltration membranes were tested: NF (polypiperazine amide), NF90 (fully aromatic polyamide), and NP010 and NP030 (polyethersulfones). NF had the lowest fouling tendency and provided the highest xylitol–protein separation factor and feed–permeate color difference. Factorial design studies revealed that permeate flux and color parameter a* were significantly influenced by pH and pressure. Xylitol productivity and lightness difference were affected by temperature. The best nanofiltration conditions were 40 bar, 40 °C, and pH 5.4. Fermented hydrolysate was subjected to microfiltration and ultrafiltration prior to nanofiltration to minimize fouling. Results were satisfactory, with a xylitol purification factor of 3.3, protein separation factor of 8.4, and color removal of 96.0%. Nanofiltration can be used as a preceding step to crystallization in the purification of xylitol obtained from sugarcane bagasse hydrolysate.