Catalytic hydrotreating of jatropha oil into non-isomerized renewable diesel: Effect of catalyst type and process conditions

The selective production of renewable diesel through the hydrotreating of jatropha oil was investigated to determine the effects of the catalyst type (Ni-Mo and Co-Mo) and of the variables temperature (300-370 degrees C), pressure (5.0-9.0 MPa) and time (3-6 h). Reactions were carried out in a high-pressure reactor operated in semibatch mode. The experiments also allowed to stablish the reaction pathway and to optimize the response variable (yield). A thorough characterization of the catalysts was carried out using the techniques XRF, TPR coupled to a mass spectrometer, CO-chemisorption, XRD, N-2-sorptometry and TGA/DTA. Results indicate that temperatures as high as 370 degrees C should be avoided because they induce the formation of unwanted by-products by cracking or polymerization reactions, and NiMoS was more sensitive to this effect. At intermediate temperature (350 degrees C), both catalysts behaved nearly the same. However, at the lowest temperature (300 degrees C) NiMoS was clearly more active than CoMoS. Amongst all the characterizations performed to the catalysts, only the chemisorption analyses (TPR and CO-chemisorption) showed relevant differences. TPR analyses showed that the amount of stronger sulfided sites, the ones still present at the reaction temperature, were higher in NiMoS, compared to CoMoS. Besides, CO-chemisorption revealed that Ni-Mo had a metal dispersion 75% higher than Co-Mo. Hence, these two factors could be the responsible for the better performance of NiMoS over CoMoS. The main reaction pathway was the decarboxylation/decarbonylation route. A clear optimum value for the yield of 80% (97% of theoretical) could be obtained at 300 degrees C, 9.0 MPa and 6 h with NiMoS. The variable temperature had a negative effect on yield while pressure and time had a positive effect. NiMoS did not lose activity after five re-uses.