Process for acidizing and recycling lignin by using pulping black liquid

Abstract

The invention discloses a process for acidizing and recycling lignin by using pulping black liquid. The process is characterized by comprising the following steps of: 1, filling 60 to 80 percent of black liquor until the black liquor is half the volume of a reaction kettle, slowly adding 30 to 40 percent of sulfuric acid solution, and simultaneously starting a stirrer; 2, when the pH value of the final point of the reaction mixture is 3.0 to 5.0, stopping adding sulfuric acid, and then continuously stirring for 5 minutes, wherein the adding of the sulfuric acid is finished in 20 minutes, and the stirring speed of the stirrer is high and then low; 3, after reaction, pumping the reaction mixture into a hot blast stove when the reaction mixture is still hot and drying at the temperature of 140 DEG C; and when the moisture content of the lignin is less than or equal to 5 percent, stopping drying and bagging the lignin; and 4, feeding tail gas produced in a drying process into a soda recovery furnace and combusting. The lignin particles produced by the process are uniform, the waste liquid amount is greatly reduced, and waste water produced after the production of the lignin is neutral and has low content of suspended matter, and low chemical oxygen demand (COD), and can be discharged under the standard.

Description

technical field [0001] The invention relates to a process for recovering lignin by acidification of pulping black liquor. Background technique [0002] At present, the treatment method of the cooking waste liquor-black liquor of domestic kraft pulp mills is mainly the traditional alkali recovery method. It is favored mainly because the production of lignin from sulfate pulping black liquor has higher economic benefits than alkali recovery and recovery of alkali, heat production and steam production. Each ton of black liquor solids can create an additional economic benefit of about 200-300 yuan. Therefore, lignin production has been widely recognized and adopted as a new growth point for processing pulping black liquor and profit. [0003] There are two main methods for producing acid-leached lignin from sulfate black liquor in China: 1. The method of mixing concentrated sulfuric acid with dilute black liquor or semi-concentrated black liquor to generate acid-leaching lignin...

AI Technical Summary

Problems solved by technology

After these two methods produce lignin, the pH value of the wastewater is low, the suspended solids are high, and the COD is high, and the wastewater cannot be discharged up to the standard.