No abstract

To produce diesel fuel from renewable organic material such as vegetable oils, it has for a number of years been known that triglycerides can be hydrogenated into linear alkanes in a refinery hydrotreating unit over conventional sulfided hydrodesulfurization catalysts. A number of new reactions occur in the hydrotreater, when a biological component is introduced, and experiments were conducted to obtain a more detailed understanding of these mechanisms. The reaction pathways were studied both in model compound tests and in real feed tests with mixtures of straight-run gas oil and rapeseed oil. In both sets of experiments, the hydrogenation of the oxygen containing compounds was observed to proceed either via a hydrodeoxygenation (HDO) route or via a decarboxylation route. The detailed pathway of the HDO route was further illuminated by studying the hydroprocessing of methyl laurate into n-dodecane. The observed reaction intermediates did not support a simple stepwise hydrogenation of the aldehyde formed after hydrogenation of the connecting oxygen in the ester. Instead, it is proposed that the aldehyde formed is enolized before further hydrogenation. The existence of an enol intermediate was further corroborated by the observation that a ketone lacking a-hydrogen (that cannot be directly enolized) had a much lower reactivity than a corresponding ketone with a-hydrogen. In real feed tests, the complete conversion of rapeseed oil into linear alkanes at mild hydrotreating conditions was demonstrated. From the gas and liquid yields, the relative rates of HDO and decarboxylation were calculated in good agreement with the observed distribution of the n-C 17 /n-C 18 and n-C 21 /n-C 22 formed. The hydrogen consumption associated with each route is deduced, and it was shown that hydrogen consumed in the water-gas-shift and methanization reactions may add significant hydrogen consumption to the decarboxylation route. The products formed exhibited high cetane values and low densities. The challenges of introducing triglycerides in conventional hydrotreating units are discussed. It is concluded that hydrotreating offers a robust and flexible process for converting a wide variety of alternative feedstocks into a green diesel fuel that is directly compatible with existing fuel infrastructure and engine technology.

Reactions of methylcyclopentane on commercial R-AI2O3-CI reforming catalysts have been studied. Kinetic data (activation energies, reaction orders for methylcyclopentane and hydrogen) are presented for the formation of: (1) cyclohexane and benzene, (2) 2-methylpentane and 3-methylpentane, and (3) n-hexane. The reactions were studied at temperatures from 470 to 515 OC, partial pressures of methylcyclopentane from 0.02 to 0.14 atm, and partial pressures of hydrogen from 6 to 40 atm. The conversion of methylcyclopentane was kept below 10%. The kinetic data combined with results from varying Pt content of the catalyst, water vapor pressure, and catalyst age imply that for the formation of (1) and (3) the rate-determining step is catalyzed by acidic centers, while the formation of (2) is catalyzed by platinum; i.e., there are two different ring opening mechanisms.