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

• Published in: Energy & fuels 2013-01, Vol.27 (1), p.487-493
• Main Authors: Wan, Haijun, Chaudhari, Raghunath V, Subramaniam, Bala
• Format: Article
• Language: English
• Subjects: Acetic acid; Aluminum oxide; Catalysis; Catalysts; Ethanol; Ethyl alcohol; Hydrogenation; Palladium; Selectivity
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/ef301400c

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 acid 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/Al2O3, Pt/C, Pt/Al2O3, Pd/Al2O3, and Pd/C. CH4 and CO2 were observed to be the major products on all of these catalysts at typical hydroprocessing temperatures (∼300 °C). 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 °C), acetic acid hydrogenation is favored with higher selectivity to ethanol, while at high temperatures (∼300 °C), acetic acid decomposition and ethanol reforming/hydrogenolysis dominate with CO2 and CH4 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 acid hydrogenation is suppressed and p-cresol hydrodeoxygenation is favored, as inferred from the observed high selectivity to methylcyclohexane.