(24c) Exploiting the Liquid-Liquid Phase Behavior of Hybrid Poplar Lignin in Ethanol-Water Solutions to Produce Precursors for Value-Added Applications

Lignin is an abundant biopolymer with unique functionality that is a commonly produced byproduct from cellulose enrichment processes such as papermills. This aromatic polymer is synthesized by plants to add structural support and rigidity to woody biomass. Conventionally, papermills burn lignin for its heating value in order to cover the energy demands of the mill while reclaiming catalytic salts for the pulping process. While these mills are well established, bioethanol refineries are generally recognized as unprofitable, even if they could potentially produce fuels with a lower environmental impact. If the coproduct lignin could be recovered, purified, and sold at a profit, the value proposition of bioethanol refineries would be fundamentally improved. On top of supporting these refineries, finding economically feasible and renewable means of purifying/upgrading lignin opens up this currently under-utilized resource as a new feedstock for material and chemical applications. Previous work with Kraft lignins has shown that ethanol-water solvents (with specific composition, temperature, and solvent-to-lignin ratio) produce liquid-liquid phase equilibria. Titled as the ALPHA (Aqueous Lignin Purification with Hot Agents) Process, this technology has been applied to lignin sources isolated from Hybrid Poplar (HP) trees via alkaline pulping. Ethanol-water solutions have proven to be effective at simultaneously fractionating HP lignin by molecular weight and removing impurities that are harmful to downstream, value-added applications. In this work we examine the impacts of fractionation and purification on the ability for HP lignin to serve as a precursor for applications such as carbon fibers, polyurethane foams, and activated carbon.