(723c) Biomass Pyrolysis Via Liquid Metal Catalysts

Conventional biomass thermochemical conversion via heterogeneous solid catalysts has been conducted to generate fuels or specialty chemicals. However, these solid-state catalysts suffer from catalyst deactivation due to high exposed surface area and carbon layer deposition on the catalyst surface (i.e., coking), sintering and agglomeration. In addition, metals oftentimes require ceramic support that reduces the desired thermal conductivity and lowers heat transfer and consequently the liquid product yield during biomass pyrolysis. Here, we propose a single-phase liquid metal (LM) reaction system for biomass pyrolysis that overcomes the susceptibility towards deactivation from coke deposition while maintaining a high heat transfer. Bismuth (Bi), Tin (Sn), and Indium (In) were selected as the LM candidates due to their low melting points of 272, 232, 157°C, respectively. Primarily, commercial microcrystalline cellulose was selected as the biomass model compound.

Cellulose pyrolysis was conducted in a thermogravimetric analyzer to study the devolatilization kinetics with temperature increase from 30 to 650°C. It was found that bismuth increases devolatilization (95 wt% against 80 wt% for non-catalytic case), indicating preliminary evidence for its catalytic activity in volatile formation. Indium and tin enhance char formation (32-35 wt%), and lowering hydrogen production temperature (from 500 to ~300°C ), suggesting different catalytic activity. Further quantitative analysis of bio-oil through gas chromatography-mass spectrometry revealed that bismuth is selective to dehydration and functional rearrangement reactions, yielding anhydro sugars and functionalized furans, whereas, indium and tin are selective to dehydration, fragmentation reactions and Diels Alder chemistry, producing C2-C4 fragments and aromatic compounds, as further confirmed via infrared spectroscopic analysis of the obtained chars. Overall, the results showed significant promise for altering product selectivity based on catalyst choice.