Characteristics of black liquor after alkaline delignification of paulownia wood

Abstract

The object of research is the black liquor of the alkaline pulping sample Paulownia Clone in Vitro 112® with active alkali consumption of 14, 18 and 22 % in Na2O units from the mass of completely dry raw materials. The problem solved in the work is related to the formation of waste in the form of black liquor during pulp production. It is noted that as a result of the production of 1 ton of cellulose, up to 7 tons of black liquor is formed. In the course of the work, an analysis of the total titrated and active alkalinity in the white and black liquor after cooking paulownia wood was carried out, and the pH value was determined. The dependence of the content of dry substances in black liquor on the consumption of active alkali, the duration of cooking, the presence of a catalyst, and the final temperature of the delignification process is given. The amount of organic and mineral components of dry substances of black liquor per 1 ton of air-dry fibrous semi-finished products was calculated. It was established that with an increase in temperature by 20 °C (from 150 to 170 °C) and a duration of approximately 1.5 times (from 60 to 90 min and from 90 to 150 min), with the same consumption of active alkali and the use of a catalyst in the conditions after sodium pulping, the content of dry substances in the black liquor increases by 1.5–3 %. This regularity is explained by the transition into the solution of a greater number of dissolution products of lignin, hemicelluloses, and mineral substances. Estimated values for the content of mineral and organic substances in black liquor after cooking paulownia wood for a duration of 150 min and a final temperature of 170 °C at different consumptions of active alkali and the use of catalysts in the form of anthraquinone and ethyl alcohol are within the range of 1024-1518 kg per 1 ton dry pulps of normal yield and can be used in practice. The obtained results can be used to form an assessment of the black liquor as an additional resource potential for the economy of production.