Process for producing a pulp

Before boiling, the starting material is steam-treated. The cellulose obtained by boiling is subjected to cold alkali extraction, during further treatment. Steam treatment takes place at 120[deg]C or more, at a P factor of 50 or less. Medium pressure steam at 150[deg]C - 180[deg]C is employed. Before boiling, the raw material is impregnated. Impregnation and steam treatment take place in the same boiler in a continuous batch boiling process. Part of the press lye arising during cold alkali extraction, is purified by membrane filtration, especially by nano- or ultrafiltration. Between the two separation stages, the retentate of the first stage is diluted with water. From part of the retentate of the membrane separation stage, the hemicelluloses contained, especially xylanes, are recovered. For precipitation reversal, mineral acids, CO 2 and mono- or multivalent alcohols are used. Recovered xylanes are further processed to xylo-oligosaccharides by hydro-thermolysis or enzymatic hydrolysis. The process is couple