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. In this work, we present the concept of multi-pass FT-RCF as a solvent reduction approach, wherein the solvent can be recycled after FT-RCF without lignin removal and the delignification extent and monomer yields are additive. Multi-pass FT-RCF can reduce the solvent-to-biomass ratio from 48 to 3 L/kg, which is lower than previously reported ratios in batch reactions, without a detrimental effect on delignification (50-60%). Increase in lignin concentration in the solvent requires a higher catalyst loading to avoid reduced monomer yields, and lignin oil and pulp residue samples produced during multi-pass FT-RCF are invariant. This result has implications for reducing solvent usage in RCF processes, which is a key cost and energy driver.

Multi-pass flow-through reductive catalytic fractionation

ACS Spring 2022

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