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.