Patent ID: 8940130
Filing Date: 2015-01-27
Classification: C07G,C08H,D21C

Abstract:
1. In a process for removing lignin from black liquor by acidifying the black liquor with an acidifier selected from carbon dioxide or sulphuric acid and filtering the acidified black liquor, the improvement wherein the black liquor is oxidized with an oxidizing agent, in the absence of the acidifier, prior to said acidifying to eliminate total reduced sulphur (TRS) in the black liquor with oxidation of sulphides, mercaptans and disulphides by said oxidising agent at a temperature effective for oxidation to thiosulphate and other oxidized sulphur compounds and oxidation of said thiosulphate to sulphate, and such that hemicelluloses and other organics in the black liquor are oxidized by said oxidising agent at said temperature to form an acidifying agent selected from isosaccharinic acids, acetic acid, formic acid, lactic acid, oxalic acid, carbon dioxide and acidic lignin degradation products and mixtures thereof, with generation of heat through said oxidation, the generated heat leading to the creation of nucleation sites for the formation of lignin particles through lignin colloid agglomeration and coagulation, of a size easy to filter and wash, said acidifying agent reducing the acidifier requirement for said acidifying.