Production of pure sugars and lignosulfonates from sulfite spent liquor

DETAILED DESCRIPTION According to the present invention, sulfite spent liquor is subjected to a two-step chromatographic separation to form substantially purified fractions of sugars and lignosulfonates.
The process for the separation of sugars and lignosulfonates comprises the steps of (a) introducing sulfite spent liquor with a pH of 2.
5 to 3.
5 onto a chromatographic column containing a resin in metal salt form; (b) eluting the sulfite spent liquor from the column with water to recover a substantially sugar-free lignosulfonate-rich fraction and a sugar-rich fraction; (c) collecting the sugar-rich fraction for further purification; (d) adjusting the pH of the collected sugar-rich material to between 5.
5 and 6.
5 and introducing the material onto a second chromatographic column containing a resin in monovalent salt form; and (e) eluting the sugar-rich material from the second column with water, whereby a second sugar-rich fraction and a second lignosulfonate-rich fraction are formed.
By this method, essentially all of the lignosulfonate is recovered in fractions which are substantially free of sugars, and essentially all of the sugars are recovered in a fraction which is substantially free of lignosulfonates, salts and acids.
The separation process according to this invention is carried out on a sulfonated polystyrene divinyl-benzene column.
If birch wood sulfite spent liquor is used as a feedstock, the final sugar fractions is 93% by weight of dry-solids monosaccharides, and the principal sugar is xylose.
Spruce wood (soft woods) based feedstock leads to a sugar fraction in which the principal sugar is mannose.