Techno-economic analysis of novel lignin extraction from black liquor

Abstract

Black liquor in a pulp mill is rich in lignin which is typically combusted during the kraft chemical recovery process in a kraft recovery boiler. Lignin valorization technologies such as LignoBoost have been developed which use carbon dioxide to recover lignin from black liquor. Lignin valorization may provide a platform chemical for sustainable fuels. The current work examines sodium bisulfate, a common spent acid from pulp mill bleaching operations, as an in-house alternative for pulp mills to precipitate lignin for valorization. Laboratory scale experimentation demonstrated that sodium bisulfate may substitute carbon dioxide in yielding lignin from black liquor. Empirical results informed a process simulation which demonstrated large-scale technical feasibility. For a bleaching mill producing 1,000 metric tons bleached pulp per day mill to produce 140 metric tons of lignin per day, the operational loads increase 2.3 metric tons/hour natural gas and consumption of all sodium bisulfate generated in bleaching are major process consequences. Techno-economic analysis yielded a minimum selling price of $426/ton of lignin when carbon dioxide was used and a minimum selling price of $398/ton of lignin when recycling bleaching spent acid was used. Sensitivity analysis revealed that lignin production and bisulfate usage as drivers for economic performance.