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This work describes the continuous hydrothermal conversion of free fatty acid and triglyceride-based feedstocks to biofuel mixtures using metal oxide catalysts, supercritical water, and high temperatures (≥500 °C) in a fixed bed reactor. A brief investigation of catalyst type indicated that zirconium dioxide (ZrO2) resulted in a biofuel mixture with similar properties to petroleum fuel products and the catalyst was stable under the supercritical water conditions used. The biofuel product is comprised of alkanes, alkenes, aromatics, and ketones. A wide variety of feedstocks were investigated, as well as the effect of temperature on yield and conversion selectivity to biofuel. The temperature study led to the identification of a set of ideal conditions (515 °C, 3:1 H2O:soybean oil mass ratio, ZrO2 catalyst, 60 s catalyst contact time, 3500 psi) where liquid yield (70%) and selectivity (99%) were maximized as well as making a biofuel product with a useful combination of functionalities. Finally, the biofuel mixture was distilled, first atmospherically and then under vacuum, to give a light fraction and a middle distillate fraction. The fractions were sent for ASTM D4814 or ASTM D975 quality testing to determine the similarities to their petroleum counterparts: gasoline (light distillate) and diesel (middle distillate). The ASTM results were promising as both biofuel distillates have similar properties to their petroleum counterparts, even meeting many of the ASTM testing specifications. © 2015 Society of Chemical Industry and John Wiley & Sons, Ltd |
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