Method for producing pulp and lignin

Abstract

The invention provides for methods for producing pulp (comprising cellulose) and lignin from lignocellulosic material, such as wood chips. The methods involve acid catalyzed hydrolysis. Lignocellulosic material having a relatively high moisture concentration can be used as the starting material. The lignocellulosic material is impregnated with an acid (preferably nitric acid) and heated. During the heating lignin is depolymerized at relatively low temperatures, and the acid catalyst is distilled off. The acid catalyst can be collected and recycled after impregnation and heating. The lignocellulosic material is then digested in an alkaline solution under heat, dissolving the lignin and allowing the pulp to be removed. Acid is added to the black liquor to precipitate the lignin which is then removed. The resultant amber liquor can be further processed into other ancillary products such as alcohols and / or unicellular proteins.

Description

REFERENCE TO RELATED APPLICATIONS[0001] This application claims the benefit of U.S. Provisional Application No. 60 / 474,961, filed Jun. 3, 2003, and U.S. Provisional Application No. ______ unassigned, filed Oct. 6, 2003.[0002] This invention pertains to a method for producing pulp (comprising cellulose) and lignin from lignocellulosic material such as wood chips.[0003] Wood is a composite material comprising cellulose, lignin and hemicellulose.[0004] Cellulose is the strong, fibrous component which consists of long chains of glucose molecules and which is used to make paper. Lignin is a phenolic polymeric matrix which holds the cellulose fibres together. Hemicellulose is the component comprised of short, branched chains of glucose and other like molecules.[0005] In general terms, pulping processes involve converting wood chips (or other suitable vegetative material) into a fibrous form in order to produce pulp. Pulp refers to cellulose fibres or material containing cellulose fibres w...

AI Technical Summary

Benefits of technology

0029] In yet another aspect the invention provides for methods for producing pulp and lignin comprising the steps of contacting lignocellulosic material with an acid and, after removing any acid not absorbed by the lignocellulosic material, heating the lignocellulosic material at a temperature up to about 75.degree. C. to effect the acid-catalyzed hydrolytic depolymerization of the lignin in the lignocellulosic material without substantially degrading the cellulose or lignin in the lignocellulosic material, the acid-contacting and heating steps being carried out before the lignocellulosic material is digested in an alkaline liquor, the pulp being removed following the digestion of the lignocellulosic material in the alkaline liquor, the lignin being removed after being precipitated out with the addition of an acid to the black liquor produced following the digestion of the lignocellulosic material in the alkaline liquor, wherein the pulp comprises cellulose. The acid-contacting step may comprise immersing the lignocellulosic material in an aqueous solution of the acid, and wherein the acid is nitric acid and the aqueous solution comprises from about 10% to about 40% by weight of nitric acid. The lignocellulosic material may be heated, after depolymerizing the lignin but before digesting the lignocellulosic material, at a temperature above the boiling point of the acid in order to distill off the acid.

Problems solved by technology

One disadvantage with Kraft pulping is that it is carried out under extreme conditions which adversely affect yields.

These harsh conditions result in a loss of some cellulose and the destruction of much of natural form lignin from the wood chips.

Lignin typically is not recovered as an end-product in typical Kraft pulping processes.

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