One Step Bio-Oil Upgrading through Hydrotreatment, Esterification, and Cracking

The crude bio-oil was upgraded in supercritical ethanol under hydrogen atmosphere by using Pd/SO4 2−/ZrO2/SBA-15 catalyst. This is a novel way to upgrade bio-oil with the combination of hydrotreatment, esterification, and cracking under supercritical conditions. The results indicated that the upgrading process performed effectively and the properties of the upgraded bio-oil were improved significantly. After the upgrading process, a trace amount of tar or coke was produced and most of the organic components were kept in the upgraded bio-oil. No phase separation was observed. The amount of aldehydes and ketones decreased evidently. In particular, aldehydes were almost completely removed. Most acids were converted into corresponding esters, and at the same time many new types of esters were produced. The results of TGA and DTA indicated that macromolecular compounds were decomposed and much more volatile compounds were produced after the upgrading process. The pH value and heating value of the upgraded bio-oil increased; meanwhile, the kinematical viscosity and density decreased compared to those of the crude bio-oil.