Flowthrough Reductive Catalytic Fractionation of Biomass

Abstract

Reductive catalytic fractionation (RCF) has emerged as a leading biomass fractionation and lignin valorization strategy. Here, flowthrough reactors were used to investigate RCF of poplar. Most RCF studies to date have been conducted in batch, but a flow-based process enables the acquisition of intrinsic kinetic and mechanistic data essential to accelerate the design, optimization, and scale-up of RCF processes. Time-resolved product distributions and yields obtained from experiments with different catalyst loadings were used to identify and deconvolute events during solvolysis and hydrogenolysis. Multi-bed RCF experiments provided unique insights into catalyst deactivation, showing that leaching, sintering, and surface poisoning are causes for decreased catalyst performance. The onset of catalyst deactivation resulted in higher concentrations of unsaturated lignin intermediates and increased occurrence of repolymerization reactions, producing high-molecular-weight species. Overall, this study demonstrates the concept of flowthrough RCF, which will be vital for realistic scale-up of this promising approach. As the environmental effects of mankind's energy use grow increasingly acute, economically viable and sustainable routes to carbon-neutral fuels and chemicals are critical. Biomass is an excellent feedstock for fuels and chemicals production because it is an abundant and renewable source of carbon. Biomass primarily consists of carbohydrates (cellulose and hemicellulose) and lignin. Carbohydrates have been studied and shown to be versatile feedstocks for the production of fuels and chemicals. Lignin, the largest source of natural aromatics, becomes highly recalcitrant during carbohydrate processing, hindering chemical production from lignin. Here, we demonstrate a flowthrough system for lignin fractionation from biomass into aromatics. Furthermore, flowthrough reactors allow for the measurement of critical parameters essential to the scale-up of lignin conversion, which is crucial for integration of lignin processing in the complete utilization of biomass for chemicals production. Lignin, a major component of biomass, is typically treated as waste, squandering a natural source of aromatics for high-value chemical production. Here, we demonstrate the fractionation of biomass using flowthrough reactors to semi-continuously extract and depolymerize lignin into monomeric phenols. Flow processing allows for insights into the mechanistic steps of the lignin fractionation process, which are obscured in traditional batch processing. Lignin fractionation in flow will be essential for the integration of lignin processing in the complete utilization of biomass for chemicals production.