Process for making xylitol

DETAILED DESCRIPTION We claim: 1.
A method for the production of xylitol on a commercial scale from a pentose-rich solution obtained by acid hydrolysis of a pentosan-containing raw material which comprises the steps of a.
removing suspended solids from the solution by mechanical filtration; b.
removing inorganic salts and the major portion of organic impurities and color from the solution by ion exclusion; c.
removing the balance of color and other organic impurities by treating the solution with a material selected from the group consisting of an ion exchange resin and activated carbon; d.
fractionating the solution thus obtained by ion exchange chromatographic techniques to provide a xylose solution of high purity; e.
catalytically hydrogenating the xylose solution; and f.
subjecting the xylitol solution thus produced to ion exchange chromatographic fractionation to recover a xylitol fraction of high purity.
2.
The process of claim 1 wherein step (d) is accomplished by: a.
providing a column of a salt of a polystyrene sulfonate cation exchange resin cross-coupled with di-vinyl benzene; b.
submerging the column of resin in water; c.
feeding the pentose-rich solution having a dry material content of 25 to 55% by weight in uniform supply to the resin surface in the column at a flow rate of 0.
2 to 1.
5 cubic meters per hour per square meter of the cross-section of the resin column; and d.
recovering successively from the downstream side of the resin bed 1.
an initial fraction containing mostly water but also containing other pentoses and a low concentration of xylose, 2.
an intermediate fraction having a high concentration of xylose and small amounts of other pentoses, and 3.
a final fraction containing other pentoses and a minor amount of xylose.
3.
The process of claim 1, wherein step (f) is accomplished by: a.
providing a column of a salt of a polystyrene sulfonate cation exchange resin cross-coupled with di-vinyl benzene; b.
submerging the column of resin in water; c.
feeding the xylitol-rich solution having a dry material content of 25 to 55% by weight in uniform supply to the resin surface in the column at a flow rate of 0