STUDY OF THE HYDRODEOXYGENATION OF CARBONYL, CARBOXYLIC AND GUAIACYL GROUPS OVER SULFIDED COMO GAMMA-AL2O3 AND NIMO/GAMMA-AL2O3 CATALYST .2. INFLUENCE OF WATER, AMMONIA AND HYDROGEN-SULFIDE/

The hydrotreatment of various oxygenated groups (ketonic, carboxylic, methoxyphenol) present in bio-oils in the presence of CoMo and NiMo ca talysts was studied in a batch reactor using a mixture of model compou nds mimicking the real feed. The influence of potential poisons or inh ibitors of the reactions (water, ammonia and hydrogen sulfide) was det ermined. High quantities of water had only a very slight inhibiting ef fect on the reactions. Ammonia strongly inhibited the conversion of ca rboxylic esters and the removal of the methoxy group of guaiacol, but, surprisingly, the hydrogenation of the ketonic group was not affected . Hydrogen sulfide depressed the activity of the NiMo catalyst for the conversion of the ketonic group but not that of the CoMo catalyst. It had an enhancing effect on the conversion of the carboxylic ester gro up and no effect on the removal of the methoxy group of guaiacol. The evolution of activities and selectivities as a function of the concent ration of potential inhibitors provided an indication of the catalytic sites responsible for the various reactions. The absence of the influ ence of ammonia on the hydrogenation of the ketonic group was interpre ted as resulting from the participation of nucleophilic sites and hydr idic species in the reaction mechanism. Carboxylic esters seem to reac t on electrophilic sites. Bronsted acids were thought to be responsibl e for decarboxylation, while uncoordinated metal atoms and sulfhydryl groups could be responsible for the hydrogenation of carboxylic groups . On the other hand, the surface of the alumina support catalyzes the hydrolysis of carboxylic esters into acids. The demethylation of guaia col occurs for a large part on the Lewis acid-base sites of the gamma- alumina support. The use of hydrogen sulfide and ammonia shows a high potential for controlling the selectivity of reactions occurring in bi o-oils hydrotreatment. The present results give hope that the deoxygen ation of carboxylic groups could be selectively performed through deca rboxylation thanks to catalyst selection and control of the hydrogen s ulfide pressure. Ketonic groups and aldehydic groups could be selectiv ely eliminated from complex feeds by applying a pressure of ammonia wh ich would inhibit all reactions but hydrogenation.