Concerns about the environmental impacts of fossil fuels have motivated a transition towards the use of alternative energy sources, such as biofuels. Among biofuel feedstocks, agro-industrial wastes like apple pomace present an opportunity to extract useful fuel (and chemical) precursors from an underutilized by-product. However, not all thermochemical conversion techniques are appropriate for the desired feedstocks. While HTC, or wet pyrolysis, efficiently utilizes the moisture content of wet feedstocks as both solvent and catalyst, bio-oil yields are negligible at carbonization operating temperatures. Dry pyrolysis produces bio-oil yields ranging from 20-70% but requires a drying stage before reaching reaction temperatures. The resulting bio-oils from pyrolysis generally suffer from high viscosity and acidity, and low energy density and stability; traditional downstream catalytic upgrading brings bio-oil quality improvements, but at significant energetic and financial costs. One alternative is to use abundant and inexpensive clay catalysts that have previously been shown to improve bio-oil quality when added to lignocellulosic agricultural wastes during pyrolysis. This study examines the effects of using a dual HTC-pyrolysis sequential process to convert a wet agro-industrial waste into biofuels, and adding montmorillonite or attapulgite clays, before and after HTC. Hydrochars resulting from HTC were pyrolyzed at 600 °C for 1 hour and the bio-oil, biochar, and non-condensable gases were analyzed to determine the catalytic effect of the clay at various steps of the thermochemical conversion process. Bio-oil was analyzed via gas-chromatography mass-spectrometry (GC-MS), and non-condensable gases through residual gas analysis (MS) to determine the extent of oxidized species in both phases. By shifting more oxygen from the bio-oil into the non-condensable gases, the burden of upgrading bio-oils into biofuels can be lessened. This improves the economic viability and ultimately may spur the adoption of lignocellulosic biofuels into the energy market.

Enhancing pyrolysis products of apple pomace hydrochar through the addition of clay catalysts

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