Aqueous Phase Hydrogenation of Acetic Acid and Its Promotional Effect on p-Cresol Hydrodeoxygenation

摘要

A systematic study of the comparative performances of various supported noble metal catalysts for the aqueous phase hydrogenation of acetic acid (as a model carboxylic add in bio-oils) by itself and in combination with p-cresol (as a model phenolic compound in bio-oils) is presented. It was found that Ru/C catalyst shows the highest activity for acetic acid hydrogenation among the tested catalysts, followed by Ru/A1_2O_3, Pt/C, Pt/Al_2O_3, Pd/Al_2O_3 and Pd/C. CH_4 and CO_2 were observed to be the major products on all of these catalysts at typical hydroprocessing temperatures (~300℃). A systematic study on parametric effects with the Ru/C catalyst shows that the product distribution is dependent upon the temperature and presence of water. At low temperatures (～150℃), acetic acid hydrogenation is favored with higher selectivity to ethaaol, while at high temperatures (~300℃), acetic acid decomposition and ethanol reforming/hydrogenolysis dominate with CO_2 and CH_4 as the major products. When water is replaced with n-heptane at otherwise similar conditions, the esterification reaction is favored over ethanol reforming/hydrogenolysis, resulting in substantial formation of ethyl acetate. With a mixed feed of acetic acid and p-cresol over the Ru/C catalyst, acetic add hydrogenation is suppressed and p-cresol hydrodeoxygenation is favored, as inferred from the observed high selectivity to methylcyclohexane.