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 technology for recovering lignin by acidifying pulping black liquor. Background technique [0002] At present, the cooking waste liquor of domestic kraft pulp mills—black liquor is mainly treated by the traditional alkali recovery method. The method of extracting acid analysis lignin through acidification is used as a supplement to the alkali recovery method, and is increasingly favored by pulp mills. It is favored mainly because the production of lignin from kraft pulping black liquor has higher economic benefits than alkali recovery, heat production, and steam production. Each ton of black liquor solids can create more economic benefits of about 200-300 yuan. Therefore, lignin production has been widely recognized and adopted as a new growth point for treating pulping black liquor and profit. [0003] There are two main methods for producing acid-analyzed lignin from sulfate black liquor in China: ①The method of mixing con...

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.