The Feasibility of Utilizing Existing Process Streams in Kraft Pulp Mills as a Source of Chemicals for Lignin Extraction

Lignin is a sustainable raw material with a high potential for use in the production of renewable products. While the market for lignin is slowly growing, lignin recovery via acid precipitation during the kraft pulping process requires the addition of chemicals that will impact the chemical balance of the pulp mill. This negatively affects both the environmental and business operations. Utilizing existing process streams as a source of chemicals will allow the mill to close the chemical loop and reduce emissions, which will have positive environmental impacts. This study investigated the internal production of sulphuric acid (H2SO4) and carbon dioxide (CO2) for use in lignin separation (also called extraction) at a Swedish kraft pulp mill. The process simulation tool CHEMCAD was used to model and analyze the wet gas H2SO4 (WSA) process to produce H2SO4. The chemical absorption process using monoethanolamine (MEA) to capturing CO2 was also analyzed. The utilization of the sulphur-containing gases to produce H2SO4 can generate an amount that corresponds to a significant lignin extraction rate. The CO2 available in the flue gases from a mill well exceeds the amount required for lignin extraction.