Abstract: The aqueous acid-containing xylose solution is first passed through an ion exchanger to remove the strong acid which was added to the raw material in the xylane hydrolysis and xylose extraction system and then subjected to evaporation in an evaporator. The evaporated water, acetic acid and formic acid of the solution is then condensed and is partly re-cycled and partly subjected to recovery processes. The concentrated xylose solution in the evaporator is then passed through a second ion exchanger to remove any traces of acetic acid or formic acid.