With its high carbon and hydrogen content, lignocellulosic biomass presents an interesting alternative to petroleum as a nearly carbon-neutral precursor to upgraded liquid fuels. Catalytic fast pyrolysis (CFP) is one of the most promising processes to produce renewable transportation fuels and chemicals from biomass. The widely used zeolite catalysts in CFP of biomass are preferred due to their low cost, low toxicity and high effectiveness at deoxygenating pyrolysis products.<br/>Diffusion of pyrolysis vapors and their upgraded products in zeolites during CFP is an essential phenomenon, which can influence product separation and selectivity as well as coke formation. Deeper understanding of the effects of zeolite pore size and topology on diffusivity could aid in designing novel zeolites to enhance product separation and selectivity. Molecular dynamics (MD) simulation is a powerful method for addressing this challenge due to the limiation of experiemtnal measurements. In this work, we have conducted MD simulations to investigate the diffusivities of several important biofuel model compounds in H-ZSM-5. Our results demonstrate that in order to develop a correlation to relate a molecular descriptor to diffusivity within zeolites, both the molecular critical size and the molecular weight need to be considered. Furthermore, we have investigated the diffusivity in mesoporous H-ZSM-5 nanosheets, which can be shown to increase access of bulky molecules to active sites and decrease coking.<br/>Dehydration reactions represent an imporant class of chemical reactions occuring during CFP. Specifically, alcohol dehydration serves as an important, but simple, model reaction. Recent computational work has demonstrated the enhancement of Brønsted acidity by nearby extra-framework (EF) metal actives species (e.g. Liu et al. ACS Catalysis 2015). Here, we directly compare alcohol dehydration mechanisms with EF gallium species within a “bare” Brønsted acid (no EF metal), “enhanced” Brønsted acid (with EF metal), and Lewis acid contexts. We also present results on preferred binding locations for the various EF gallium species that may be present experimentally with ZSM-5. Experiments were conducted in GCMS/FID system to measure dehydration products from different alcohols. The impact of EF metal on alcohol dehydration yield, reaction rates and catalyst coking will be reported.

Revealing biomass catalytic fast pyrolysis upgrading: from diffusion to reaction classes

255th National Meeting (2018)

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