Method for reclaiming lignin and alkali from boiling black liquor

Abstract

The invention relates to a method for recovering lignin and alkali from the cooking black liquor of alkaline chemical pulping, which adopts the method of adding H2SO4 solution to the cooking black liquor to precipitate lignin therein, and separate and obtain high value-added lignin products. Then add NaOH solution to the black liquor to adjust the pH value, and then recover the alkali and heat energy through evaporation, combustion, causticization and other processes. The added H2SO4 reacts with NaOH to generate Na2SO4, which can partially or completely replace the added Glauber's salt in the alkali recovery process, and convert it into NaOH and Na2S, which can be reused in production as cooking medicine. It solves the problems that the lignin resources in the black liquor are not rationally utilized when the alkali and heat energy are recovered by the combustion method, the alkali and heat energy in the black liquor are not reasonably recovered by the conventional acid analysis lignin method, and the waste liquor is difficult to be further processed. The invention has remarkable economic benefits, environmental benefits and social benefits; at the same time, the method of the invention does not produce harmful substances and has no secondary pollution.

Description

Technical field: [0001] The invention relates to a method for recovering lignin and alkali from the cooking black liquor of alkaline chemical pulping. Background technique: [0002] The cooking waste liquid obtained from alkaline chemical pulping is called black liquor. The solids in black liquor include organic matter and inorganic matter. The organic matter is mainly the degradation products of lignin and carbohydrates, and the inorganic matter is mainly NaOH and Na 2 Transformation product of S. Among them, lignin accounts for 25% to 35% of the weight of black liquor solids, and 0.45 to 0.55 tons of lignin can be produced per ton of chemical pulp. Lignin is a high value-added chemical product, which has been widely used as surfactants, adhesives, flocculants, dispersants, concrete water reducers, activated carbon, dye additives, rubber additives, etc. The current market price is 2500-3000 yuan / ton; the inorganic substances in the black liquor can also be recovered by...

AI Technical Summary

Problems solved by technology

Among them, there are the following problems in the alkali recovery method of adding lime emulsion: 1. organically bound sodium cannot be converted into NaOH, and NaOH is not realized. 2 The circulation of S; ②The degradation products of carbohydrates are not removed from the black liquor, and the recovered filtrate cannot be recycled; ③The process generates more Ca 2 SO 4 Precipitation cannot be calcined into quicklime for recycling, so alkali recovery in the true sense cannot be realized; other black liquor treatment methods after acid analysis of lignin also have some technical or economic problems, and have not been able to be popularized and applied in industry

Therefore, the problem of how to economically and rationally deal with the black liquor after acid analysis of lignin has not been solved yet