GB1489222A - Method of delignification of cellulosic material in alkaline medium using oxygen - Google Patents

Abstract

1489222 Delignifying cellulosic materials TOYO PULP CO Ltd 8 Oct 1974 [18 Feb 1974] 43506/74 Headings DIP and D2W A method of delignifying cellulosic material e.g. unbleached chemical pulp, semi chemical grade pulp or wood chips comprises treating the agglomerated material in a pressurised reaction vessel at an elevated temperature with an alkaline aqueous medium in which oxygen has previously been dissolved, a part of the waste liquor formed during the delignification being continuously discharged from the vessel, and being continually replaced with fresh oxygenated medium. The agglomeration of the material is brought about by selecting the concentration to be within the range in which an agglomeration is formed, which retains its structure as if it were a mat, layer or bed without any gaseous space in it. The material may be introduced into the vessel continuously or discontinuously. Waste liquor may be separately discharged from different stages of the lignification in the vessel, replacement with fresh medium also being effected at different stages of delignification, e.g. using higher pH's at earlier stages and different alkalines at lower pH's at later stages of delignification. The alkaline medium may be recovered from the discharged waste liquor, or the discharge from a later stage may be recirculated as the fresh input to an earlier stage, in countercurrent to a flow of the cellulosic material through the vessel. The preferred cellulosic material concentrations are 5-15% by weight for chemical and semi chemical grade pulp and from 10-20% by weight for wood chips; the preferred operating temperature is 80- 160‹C and the preferred oxygen partial pressure 4-12 kg/cm<SP>2</SP>.