(580b) Multi-Pass Flow-through Reductive Catalytic Fractionation Enables Minimal Solvent Usage

Reductive catalytic fractionation (RCF) is a promising biorefinery strategy to effectively extract and valorize lignin from lignocellulosic biomass. Flow-through (FT)-RCF enables physical separation of the biomass and catalyst, but this system setup typically operates at a high solvent-to-biomass ratio, precluding use of this approach at scale. Namely, FT-RCF has been reported to consume 90-360 L solvent/kg biomass, compared to batch reactions, which have been reported in the range of 4-50 L solvent/kg biomass. To that end, here we introduce the concept of multi-pass FT as a solvent reduction approach for FT-RCF. Reuse of FT-RCF effluent without additional separations could lead to a net solvent reduction on a per mass of biomass basis.

We demonstrated that multi-pass FT-RCF could enable solvent recycle without additional lignin-solvent separation steps, and the methanol in the reused RCF effluent with its lignin oil concentration up to 12 wt% could extract lignin from biomass to an equivalent or higher extent (50-70%), compared to FT-RCF with pure methanol. The cumulative monomer yields remained similar (20%) in the FT-RCF reaction with methanol or low concentration feed (0.5, 1, and 2 wt%), but feed solutions including 4-12 wt% lignin oil reduced the cumulative monomer yields, which results from operation in catalyst-limited conditions. In the presence of higher catalyst loading or additional catalysis steps, the cumulative monomer yields were maintained. The properties of the extracted lignin from each pass are statistically invariant. Additionally, the consistency of high carbohydrate retention (86-98%) during multi-pass FT-RCF enables further utilization of the pulp generated from multi-pass runs. Overall, multi-pass FT-RCF achieved a solvent reduction from 48 L/kg to 1.9 L/kg with no negative impact on biomass fractionation. This result has implications for reducing solvent usage in RCF processes, which is a key cost and energy driver.