Analysis of economically viable lignin-based biorefinery strategies implemented within a kraft pulp mill

Abstract

Many pulp and paper companies are considering implementing a lignin-based biorefinery to diversify their core business to new products and improve their longer-term competitiveness. The best strategy to achieve might not be obvious, considering the lignin extraction process and derivatives to be implemented over the longer term that meet market and business objectives, and provide competitive advantage. In this article, various lignin biorefinery strategies were considered in a case study involving lignin precipitation processes integrated within an existing kraft mill, and solvent pulping processes that would be implemented in parallel to the existing mill processes using additional hardwood. The analysis aimed to identify the conditions under which various strategies would represent suitable investments. Operating constraints in the case study mill limited lignin extraction to 85 metric tons/day from 15% of the mill’s black liquor, whereas 260 metric tons/day lignin could be extracted by solvent pulping 1500 metric tons/day of hardwood. The preferred strategies identified by the study were lignin precipitation to phenolic resins production, and solvent pulping to carbon fiber production. The first product-process strategy requires lower investment, provides high returns (internal rate of return [IRR] of 39% to 43%), and is more easily implemented in the near term. Solvent pulping resulted in reasonable profitability (IRR of 18% to 25%), with higher production volumes and a diversified product portfolio, and was considered more suitable as a longer-term strategy. Business model robustness and long-term competitiveness can be better assured by combining both strategies. It was shown that 1) government support to offset capital cost, and 2) high derivatives market prices positively influence lignin valorization strategies, which are sensitive to technology and market maturity.