High Temperature Thermochemical Conversion of Biomass and Methane for Highly Selective Syngas

Palumbo, Aaron William

Graduate Thesis Or Dissertation

High Temperature Thermochemical Conversion of Biomass and Methane for Highly Selective Syngas Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/w6634397r

Abstract

Hybrid thermochemical routes show promise for high conversion and yield to fungible liquid hydrocarbon fuels. High temperature co-feeding of biomass and methane was shown to enable production of syngas with an enriched hydrogen content that could be used specifically for catalytic conversion to liquid hydrocarbons, increasing end-product yield compared to conventional thermochemical processes. Theoretical demonstration was performed using thermodynamic equilibrium simulations, revealing that the syngas composition is dependent on the reactant ratios. Experimental proof of concept was determined by executing a factorial experimental design in an allothermal, high temperature entrained flow reactor and revealed that temperature is the dominant factor on the major performance indicators. Reaction pathways were explored further through tests with three different biomass types and isolation of the two major heterogeneous reaction steps: pyrolysis and char gasification. Atomic balances showed hydrogen is easily evolved from both biomass and methane whereas carbon is bound in intermediate gaseous and solid species such that CO formation is the overall rate-limiting process. Biomass pyrolysis was probed in a series of drop-tube and entrained flow experiments followed by characterization of the product char morphology and reactivity. Pyrolysis was determined to be heat transfer-limited, taking place on the order of 10^-2-10⁰ seconds. The rate and reaction time were investigated through development and implementation of an integral, infinite-rate kinetic model. The char gasification rate was shown to be highly dependent on particle thermal history and biomass type based on factors such as surface area, pore size distribution, and degree of graphitization. Overall, high selectivity to enriched-H₂ syngas was achievable through rapid pyrolysis rates to increase residence time of carbonaceous intermediates char, soot, and poly-aromatic hydrocarbons.

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