Hydrotreating of reduced oxygen content bio-oils produced by formate-assisted pyrolysis

Abstract An important aspect of the hydrotreating step is to maximize carbon retention (carbon efficiency) in the finished product. In this work, pyrolysis oils of three different oxygen contents (18, 21, and 26 wt%) prepared using formate-assisted pyrolysis were hydrotreated under similar conditions (300 °C and 52–97 bar) using a commercial nickel alumina-silica catalyst in a single-stage process. Reduced oxygen content in the feed resulted in improved hydrotreating carbon efficiencies and reduced catalyst plugging due to carbon solids formation. In the case of the 18% oxygen feedstock, the reactor was stopped due to running out of liquid feed with up to 350 h time-on-stream (TOS) whereas the 26% oxygen feed resulted in reactor plugging at 200 h TOS. For samples selected near the end of each run, hydrotreated oil yield and carbon yield in the oil improved with reduced oxygen in the feed. These yields were 79 and 92%, respectively, for the 18% oxygen feed and reduced to 52 and 61%, respectively for the 26% oxygen feed. The lower oil yields and carbon oil yields were a result of increased production of gases and unaccounted mass and carbon, possibly due to coke formation in the catalyst bed. Increasing reactor pressure from 52 to 97 bar when hydrotreating the 18% oxygen content oil also improved mass and carbon yields of the oil product after a rapid increase in oxygen content in the oil. Comparison to literature data and economic impacts is presented.