Value addition to wood hemicellulose hydrolysate by production of xylitol and levulinic acid

Wood based biorefineries can be developed only when they are environmentally sustainable and competitive with fossil based industries. The latter will be possible only if all streams obtained from lignocellulosics, including hemicellulose, are utilized. Most of the work reported in the literature so far that makes use of hemicellulose is bioconversion of its major sugar, xylose, to xylitol. The work reported in this paper aims to make the cost intensive downstream process economical by optimizing the upstream processes and obtain high yields and productivities of xylitol. An optimized acid hydrolysis of poplar prehydrolysate, followed by an integrated detoxification and fermentation of the hydrolysate using one of the best xylitol producing yeast, Candida guilliermondii, will be presented. The methods followed to get a very high productivity of 0.81 g/L.h and yield of 0.58 g/g after 37 hours of fermentation will be covered. Along with xylitol, efforts have been made to produce another important platform chemical, levulinic acid, from wood hydrolysate using simple chemical routes. The objective of this work is to demonstrate the usage of byproduct streams of wood based industries to produce various value added products that can generate high combined revenues and make such integrated processes economically feasible.