The effect of the reaction temperature on hydrothermal liquefaction of dried distillers grains with solubles (DDGS) was investigated using a novel stop-flow reactor system at varying temperatures (300−400°C), fixed pressure (250 bar), and fixed reaction time (15 min). The stop-flow reactor provides rapid heating of biomass feeds and the option of performing multiple sequential repetitions. This bypasses long, uncontrollable temperature gradients and unintended changes in the reaction chemistry. The product, a crude bio-oil, was characterized in terms of yield, elemental composition, and chemical composition. Higher reaction temperatures resulted in improved bio-oil yields, less char formation, and higher heating values of the bio-oil. A supercritical reaction temperature of 400°C was found to produce bio-oil in the highest yields and of the best quality.

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In this paper, we report on the construction of a novel test facility for evaluating catalytic processes at high temperature and high pressure. The design features make the facility well-suited for highly controlled studies of hydrothermal conversion of real biomasses with complex composition. The proof of concept is provided by bio-oil production from (i) Dried Distiller's Grains with Solubles (DDGS), the results serving to illustrate catalyst performance, and (ii) spent coffee grounds, which exemplify constituent analysis of the as-produced bio-oil. Both studies were carried out under near-critical conditions using both homogeneous and heterogeneous catalysts.