Abstract:

In order to improve the hydrothermal deoxygenation of organic acids as well as to reduce the cost, we prepared a Cu-Ce/γ-Al₂O₃ catalyst to study the hydrothermal deoxygenation of stearic acid in the absence of H₂. The Brunauer-Emmett-Teller surface area and X-ray diffraction pattern suggest that both CuO and CeO₂ exist in the Cu-Ce/γ-Al₂O₃ catalyst. The crystals of Cu-Ce/γ-Al₂O₃ were more stable compared with those of the Cu/γ-Al₂O₃ catalyst after 12 h of hydrothermal liquefaction at 300℃, thereby indicating a better thermal stability of the former. The presence of Cu-Ce/γ-Al₂O₃ catalyst could greatly improve the conversion of stearic acid (94.71%) and the yield of hydrocarbon (81.41%). A preliminary analysis of the mechanism suggests that decarboxylation is the main step in the deoxygenation during the hydrothermal liquefaction of stearic acid. The addition of Cu/γ-Al₂O₃ and Cu-Ce/γ-Al₂O₃ decreased the yield of n-heptadecane and increased the yield of n-octadecane. Besides, the yields of n-paraffins increased drastically from 0.45% to 49.72% along the series from n-nonane to n-hexadecane. Thus, the cracking reactions could be improved in the presence of Cu-Ce/γ-Al₂O₃, suggesting that it is an efficient deoxygenation catalyst in the hydrothermal liquefaction of organic acid. In addition, the Cu-Ce/γ-Al₂O₃ catalyst could help in removing the carbonyl groups, and this effectively reduced the amounts of aldehydes and ketones in the bio-oil.

Key words: bio-oil, Cu-Ce/γ-Al₂O₃ catalyst, deoxygenation, gas chromatography-mass spectrometry (GC-MS), hydrothermal liquefaction, stearic acid