Low temperature thermochemical decomposition of lignocellulosic biomass usually leads to a broad spectrum of kinetically arrested products. The desired chemicals within the mixture of products usually require separation for further use. On the other hand, high temperature gasification yields syngas, which is the product dictated by equilibrium thermodynamics. Syngas can be converted into fuels via Fischer-Tropsch synthesis, albeit the biomass-based process hasn’t been commercially explored. In contrast to the common methods of biomass valorization, low temperature plasma stands exceptional due to its nonequilibrium environment, which can provide selectivity that is unfavorable in thermal processes. In this study, we present the results on the interaction of a radio frequency low temperature plasma with switchgrass. A novel plasma-enhanced fluidized bed was designed to accomplish the plasma treatment. In an argon/hydrogen plasma, switchgrass particles were found to decompose rapidly and steadily into a narrow product spectrum composed mainly of simple hydrocarbons (e.g. C2Hx, C3Hx and C4Hx). GC/MS analysis of the small amount of oil produced by the treatment suggested that the decomposition proceeds through small oxygenated intermediates. Solid state nuclear magnetic resonance and thermogravimetric analysis both indicated that the switchgrass degraded from its surface, and the residual biomass was in fact the unreacted biomass. Considering that the plasma process does not require precious metal catalysts to perform the conversion, a feat that is very difficult in a single step by conventional thermal methods, the process shows promising results for single-step biomass valorization. The details on the operation of the reactor, a simple reaction scheme of biomass decomposition, and the effects of process parameters like plasma power and gas composition on product spectrum will be discussed.

Non-equilibrium transformation of biomass into hydrocarbons in a low temperature plasma fluidized bed reactor

2019 Spring National Meeting

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