Supercritical CO2-purification of waste cooking oil for high-yield diesel-like hydrocarbons via catalytic hydrodeoxygenation

[Display omitted] •High-yield hydrotreated biodiesel synthesized from scCO2-purified waste cooking oil.•ScCO2-purification effectively removed organic and metallic impurities in waste cooking oil.•The effect of scCO2-purification was prominent on supported metal catalysts.•The origin of catalyst deactivation by organic and metallic impurity is discussed. Waste cooking oil (WCO) was purified by supercritical carbon dioxide (scCO2) extraction and catalytic hydrodeoxygenation of fresh soybean oil, WCO and scCO2-purified oil were studied for the synthesis of diesel-like hydrocarbons. The chemical compositions of the scCO2-purified oils were very similar to those of fresh oil. Hydrotreating of WCO over the Pd and Ni catalysts showed lower conversions when compared to the NiMo and CoMo catalysts. The hydrotreating of scCO2-purified oil using a Pd/Al2O3 catalyst resulted in 85.7% conversion, which is comparable to the 91.0% conversion from fresh oil whereas only 41.8% of WCO was converted under identical conditions. Hydrotreating of the scCO2-purified oil with other catalysts including Ni/SiO2–Al2O3, CoMo/Al2O3 and NiMo/Al2O3 resulted in similar conversions in the range 84.4–92.9% compared to that from fresh oil. The scCO2-purification was effective for removing the various impurities in WCO, that were responsible for the detrimental effects on catalytic activity especially for the Pd and Ni catalysts. The origin of catalyst deactivation caused by the impurities in WCO is discussed.