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Comparative Study on the Continuous Flow Hydrothermal Liquefaction of Various Wet-Waste Feedstock Types

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journal contribution
posted on 28.12.2021, 08:43 by Dylan Cronin, Andrew J. Schmidt, Justin Billing, Todd R. Hart, Samuel P. Fox, Xavier Fonoll, John Norton, Michael R. Thorson
Hydrothermal liquefaction (HTL) liquifies wet feedstocks to produce a biocrude under moderate temperatures (300–450 °C) and high pressures (>2500 psi). The biocrude can be upgraded to transportation fuels (predominantly diesel) using typical refinery unit operations (e.g., hydrotreater and distillation). HTL of wet-wastes is a promising route to produce environmentally friendly and cost-competitive fuels; however, the feedstock significantly impacts the product quality and the process yield. Consequently, it is important to rigorously compare different feedstocks to determine the critical material attributes, which impact the biocrude yield and quality. A few published comprehensive studies evaluate the performance of numerous different wet-waste HTL feed types, processed using the same reactor configuration and analytical approach. This is particularly true for continuous flow HTL. HTL studies generally investigate one or a few surrogate feedstocks or model compound materials or attempt comparative reviews by collecting the results of numerous different research groups. Such an approach involves numerous assumptions that can significantly compromise the legitimacy of the data compared and the conclusions drawn. This work investigates HTL of 13 different real-world wet-waste feedstocks, belonging to multiple different classes of municipal wet-waste, including food waste, biosolids, sludge, fermentation residues, manure, and blends thereof. The biocrude carbon yields obtained throughout the study ranged from 39.7 to 74.3%. The biocrude yield varied through a range of different process changes, such as increasing reactor flow rate and feed solid loading, and addition of Fe-based additives. By analyzing a broad range of materials, and through the comprehensive characterization profiles prepared for both the feedstock and products, this study has produced a significant volume of data, which was then analyzed using robust statistical methods.