Process for separation of Ca- or Mg-sulfite spent liquor to yield crystalline xylose

A process for the separation of xylose from a feed liquor comprising a xylose-containing, lignosulphonate-containing Ca- or Mg-sulfite spent liquor having a xylose content of 14-27 wt. % based on dry solids, the process comprising:

• (A) carrying out chromatographic separation of said feed liquor using a single pass through a long resin bed chromatography column or columns, each having a strong acid cation exchange resin as a separation medium, wherein if more than one column is utilized, the feed liquor eluted from the first column is introduced with its separation profile into the subsequent column, and wherein the strong acid cation exchange resin of each column is in the ion form of Ca2+ or Mg2+ of the spent liquor, and wherein the ratio of the bed length:mean resin bead diameter of the column or columns in total is 15,500-40,000, the chromatographic separation producing fractions comprising
• a first xylose-rich fraction having a xylose content of 50-70 wt. % based on dry solids and
• a lignosulphonate-rich fraction, and
• (B) crystallizing xylose from the first xylose rich fraction by using a crystallization method comprising (i) boiling crystallization;
• (ii) cooling crystallization or (iii) a combination of (i) and (ii) to obtain a first batch of crystalline xylose and a first xylose run-off.