Hydroprocessing of waste cooking oil over a dispersed nano catalyst: Kinetics study and temperature effect

•Hydrodeoxygenation of waste cooking oil over a dispersed nano CoMoS catalyst.•Study of kinetics over the active phase of catalyst only and without acidity.•Hydrodecarbonylation/decarboxylation (HDC) is predominant reaction pathway.•Direct hydrodecarbonylation from fatty acid is main path for HDC reaction.•Reduction of HDC activity is attributed to gradual loss of sulfur on the catalyst.

The kinetics of hydrodeoxygenation of waste cooking oil (WCO) is investigated with unsupported CoMoS catalysts. A kinetic model is established and a comprehensive analysis of each reaction pathway is carried out. The results show that hydrodecarbonylation/decarboxylation (HDC) routes are the predominant reaction pathways in the elimination of oxygen, with the rate constant three times as high as that of hydrodeoxygenation (HDO). However, the HDC activity of the CoMoS catalyst deactivates due to gradual loss of sulfur from the catalyst. HDO process is insensitive to the sulfur deficiency. The kinetic modeling shows that direct hydrodecarbonylation of fatty acids dominates the HDC routes and, in the HDO route, fatty acids are transferred to aldehydes/alcohols and then to C18 hydrocarbons, a final product, and the reduction of acids is the rate limiting step. The HDO route via alcohols is dominant over aldehydes due to a significantly higher reaction rate constant. The difference of C18/C17 ratio in unsupported and supported catalysts show that a support with Lewis acid sites may play an important role in the selectivity for the hydrodeoxygenation pathways and promoting the final product quality.

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