Catalytic hydrogenation of short chain carboxylic acids typical of model compound found in bio-oils

Due to the complexity of bio-oil many studies have focused on model compounds which mimic components in bio-oil. In this paper, the hydrogenation of short chain (C₂-C₄) carboxylic acids in hexane using a Parr reactor and commercial Pt supported on Al₂O₃, SiO₂, carbon, and graphite and prepared Pt and Pt-Re on TiO₂ catalysts was studied. With acetic acid, ethanol selectivity was found to be 80% (4%Pt-4%Re/TiO₂) and 23% (4%Pt/TiO₂), and no ethanol was observed with the other catalysts at 200 °C, 40 bar, 0.3 g of catalyst, and 1000 min^-1. A Taguchi optimization approach was carried out from temperature 80-200 °C, pressure 10-40 bar, time 1-4 h, catalyst 0.1-0.4 g, and stirring speed 400-1000 min^-1 using 4%Pt/TiO₂ . The optimum conditions determined were 160 °C, 40 bar, 4 h, 0.4 g, and 1000 min ^-1 for ethanol production. 4%Pt/TiO₂ was more selective toward esters, while 4%Pt-Re/TiO₂ increased alcohol production with increasing Re (1-4%) loading.