Process engineering for lignin value prior to pulping

Abstract

Biomass pretreatment unlocks chemical moieties for downstream valorization. This thesis focuses on organic solvent pretreatments that complement pulp production by delivering an additional lignin stream for the production of renewable chemicals. This work proposes and assesses a next-generation pulping process named Lignin Value Prior to Pulping (LVPP). Tools are developed to measure treatment efficacy, rank solvents for LVPP, and describe the process of retrofitting a pulp mill. This thesis presents Direct Yellow 11 as a replacement for Direct Orange 15 to measure cellulose accessibility, compare organic solvents, and enhance a cellulose conversion rate model. Additional screens and metrics are established to compare organic solvents within a solvent selection guide for LVPP. A set of solvents are evaluated using performance, hazard, exposure, cost, and process economic metrics. From this selection guide, 1,6 hexamethylenediamine, diethanolamine, propylene glycol, and 1-methyl piperazine are recommended for additional process development. A complete process design is presented for an LVPP treatment with 1,6 hexamethylenediamine, and a techno-economic analysis yields a minimum lignin selling price of $0.829/kg for economic viability. By incorporating an integrated computational and experimental technique, this thesis presents process and cost models that highlight feasibility constraints and technological barriers to future LVPP processes. This thesis aids the diversification of the pulp and paper industry towards new products, and it pushes the field towards favorable economics for renewable chemicals.