Method for separating lignin from black liquor
AssigneeFPInnovations
InventorsLamfeddal Kouisni, Michael Paleologou
Life of this patent
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Abstract
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.
Claims20
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.
A process for separating lignin from black liquor comprising:
- a) oxidizing black liquor containing lignin with an oxidising agent, in the absence of an acidifier, to remove total reduced sulphur (TRS) in the black liquor with oxidation of sulphide in said black liquor by said oxidising agent at a temperature effective for oxidation to thiosulphate 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 with generation of heat through said oxidation, and allowing the generated heat to create a nucleation sites for the formation of lignin particles of a size easy to filter and wash,
- b) subsequently, acidifying the oxidized black liquor to precipitate lignin from the black liquor with said acidifying agent and an added acidifier, and
- c) filtering precipitated lignin particles from the acidified liquor of step b).
Dependencies are inferred from the claim text.