Patent ID: 6143130
Filing Date: 2000-11-07
Classification: D21C

Abstract:
A process for producing pulp from cellulosic fiber material comprising the steps of:(a) impregnating a cellulosic fiber material with a first cooking liquor comprising polysulfide, wherein said first cooking liquor provides about 60% or less of a total effective alkali utilized for cooking said cellulosic fiber material;(b) cooking said cellulosic fiber material with a second cooking liquor in one or more cooking stages, wherein said second cooking liquor provides at least about 40% of the total effective alkali utilized for cooking said cellulosic fiber material;(c) extracting a spent cooking liquor comprising sulfide compounds from at least one of said impregnating step (a) or said cooking step (b);(d) gasifying at least a portion of said spent cooking liquor from step (c) in a gasification reactor to form a first gas stream comprising hydrogen sulfide;(e) treating said first gas stream to form an acidic gas stream comprising hydrogen sulfide and carbon dioxide;(f) reacting said acidic gas stream under conditions to provide a hot liquid stream of elemental sulfur;(g) admixing at least a portion of said hot liquid, elemental sulfur stream with an alkaline liquor containing sulfide under conditions that the elemental sulfur reacts with the sulfide to form polysulfide, whereby an alkaline liquor containing at least about 10 grams/liter of polysulfide and which is substantially free of thiosulfate is formed; and(h) adding at least a portion of said alkaline polysulfide liquor to said first cooking liquor or directly to said impregnation step (a) to stabilize carbohydrates in the cellulosic fiber material.