Method for separating lignin from black liquor

摘要

A method was developed for: a) improving the filterability of acid-precipitated lignin from kraft black liquors, b) increasing the dry solids content of the final lignin product, c) reducing the acid requirements and d) minimizing or eliminating TRS emissions during the acidification of black liquor to produce lignin and/or the subsequent suspension of the lignin in acid and/or the washing of the lignin with acid. No major difference in the chemical composition, MWD and main functional groups was found in the lignin of the present invention compared with lignins produced by conventional methods.

主权项

1. In a process for removing lignin from black liquor by acidifying the black liquor with an acidifier and filtering the acidified black liquor, the improvement wherein the black liquor is oxidized in a step consisting essentially of oxidation prior to said acidifying and filtering to eliminate total reduced sulphur (TRS) in the black liquor with oxidation of sulphides, mercaptans and disulphides by said oxidation at a temperature effective for said 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 oxidation 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.