Simultaneous hydrodesulfurization and hydrodeoxygenation: interactions between mercapto and methoxy groups present in the same or in separate molecules

Simultaneous hydrodesulfurization (HDS) and hydrodeoxygenation (HDO) of mer capto and/or methoxy group containing model compounds was studied on CoMo/g amma -Al2O3 in order to find out how the interactions of the substituents a ffect the efficiency of hydrotreating. HDS of mercaptobenzene decreased in the presence of anisole compared to the reaction of pure mercaptobenzene and a less reactive sulfur compound, (met hylmercapto)benzene, was formed via methyl transfer. Simultaneously, the cl eavage of the aliphatic carbon-oxygen bond in anisole was markedly enhanced due to this methyl capture by sulfur. The apparent activation energy of ph enol formation from anisole decreased, indicating as well a change in the r eaction mechanism. HDO reactions of anisole were, however, suppressed in th e presence of mercaptobenzene. Addition of small amounts of a sulfiding age nt, CS2, to the reactor feed also had a positive effect on the total conver sion of anisole, but it did not markedly affect the HDO rates. With a methoxy group present in the same molecule as a mercapto group, both the HDS rate and the reaction selectivity were dependent on the isomer str ucture. The HDS rate of para-mercaptoanisole was about twice as high as tha t of mercaptobenzene at 225 degreesC, while the methoxy group in the ortho position did not markedly affect the rate. The HDS rate of meta-mercaptoani sole was about half of that of mercaptobenzene. phenol was formed from orth o-mercaptoanisole, while in other mercaptoanisole isomers the methoxy group remained predominantly unchanged. HDO reactions were suppressed in the pre sence of a sulfur-containing substituent but methyl transfer to. the benzen e ring was not affected. (C) 2001 Elsevier Science B.V. All rights reserved .