Process of producing xylose and dissolving pulp

A process for the production of xylose and dissolving pulp from a hardwood biomass, which has a xylan content of 10 to 35%, calculated on the dry substance (DS) of the biomass,

• comprising the steps of:
• (a) prehydrolyzing the hardwood biomass in a digester with a solution containing sulphur dioxide in a concentration of 0.1 to 2.5% based on the total liquid weight of the prehydrolysis liquid, at a temperature of 120-150° C., a liquid-to-biomass ratio of less than 6, and with a reaction time of 0.3 to 1 h, to provide (1) a dissolved hemicellulose hydrolyzate, wherein the xylose content is 25 to 55% of the dissolved solids of the hydrolyzate, the ratio of xylose to xylo-oligomers is more than 2 and the xylose yield is 30 to 80% on xylan in the biomass, and (2) a non-dissolved prehydrolyzed biomass,
• (b) separating the dissolved hemicellulose hydrolyzate from the non-dissolved prehydrolyzed biomass,
• (c) subjecting the dissolved hemicellulose hydrolyzate to chromatographic fractionation, nanofiltration or precipitation crystallization to obtain a xylose product having a xylose content of at least 55% on DS, and
• (d) subjecting the non-dissolved prehydrolyzed biomass to sulphate cooking in a digester to obtain a dissolving pulp with a viscosity of more than 600 ml/g.