Recovery of lignin
AssigneeRepap Technologies Inc.
InventorsJairo H. Lora, Raphael Katzen, Malcolm Cronlund, Chih F. Wu
Life of this patent
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Abstract
Lignin is precipitated in high yields and at high rates from a black liquor produced by pulping wood at high temperatures and pressures with an aqueous lower aliphatic alcohol solvent. The lignin is precipitated by diluting the black liquor with water and an acid to form a solution with a pH of less than about 3, an alcohol content of less than about 30% by volume and a temperature of less than about 75.degree. C. The precipitated lignin, when subsequently dried, is in the form of a powder which requires little or no crushing to convert it into a fine uniform size suitable for use without further significant processing.
Claims61
Process for precipitating lignin from a solution of lignin in a water miscible organic solvent, comprising the step of diluting the lignin-containing solution with water and an acid to form a diluted aqueous solution with:
- a pH of less than about 3, an organic solvent content of less than about 30% by volume and a temperature of less than about 75.degree. C.
A lignin having:
- a number average molecular weight of about 800 to 1500 g/mol;
- a polydispersity of less than about 4;
- and a methoxyl content approximately equal to that of native lignin.
A process for producing lignin from a black liquor comprising a solution of lignin, hemicellulose, and a water miscible organic solvent, comprising the steps of:
- precipitating lignin solids by diluting said black liquor with water and acid under conditions to form a diluted residual black liquor including a diluted residual black liquor supernatant and precipitated lignin solids which are free from the formation of tarry lignin precipitates;
- recovering said lignin by separating said lignin solids from said diluted residual black liquor supernatant.
A process for producing lignin comprising the steps of:
- containing wood or other fibrous plant material with an aqueous organic solvent to produce a cellulose pulp and a black liquor containing lignin and hemicellulose;
- separating said pulp from said black liquor;
- flashing said black liquor to form a residual black liquor with recovery of a portion of said organic solvent under conditions which cool the residual black liquor without causing premature precipitation of said lignin;
- diluting said residual black liquor with an aqueous acid to form a diluted residual black liquor supernatant and precipitated lignin solids, free from the formation of tarry lignin precipitates;
- recovering said lignin solids by separating said lignin solids from said diluted residual black liquor supernatant;
- removing said organic solvent from said diluted residual black liquor supernatant to produce residual black liquor bottoms stream;
- recycling a portion of said residual black liquor bottoms stream for use as said aqueous acid in diluting said residual black liquor whereby said residual black liquor is diluted with said aqueous acid under conditions to form a diluted residual black liquor supernatant and precipitated lignin solids, free from the formation of tarry lignin precipitates;
- recovering said lignin solids by separating said lignin solids from said diluted residual black liquor supernatant;
Dependencies are inferred from the claim text.