Biocoke production from heat treatment of bio-oil: Effect of temperature

Abstract

Coke formation becomes the major bottleneck issue to hinder the development of bio-oil upgrading technologies. Here, we propose to heat treat the bio-oil to simultaneously produce biocoke as a fuel or carbon-containing material and low coking tendency bio-oil for further upgrading. The effect of heat treatment temperature on the biocoke production from heavy bio-oil was investigated in this study. The results showed that the biocoke yield decreased rapidly from 67.14 to 12.85 wt% in the temperature range of 200–400 °C due to the quick releasing/evaporation of volatile compounds and the cracking of functionalities and heavy molecules in the biocoke. Various active functional groups in the heavy bio-oil including −OH, aliphatic C−H, CO, phenolic C−OH and C−O/C−O−C would be preferably retained in the lower temperature biocokes with high contents of O and H. Further increasing temperature from 500 to 800 °C, only a slight decrease in biocoke yield was obtained, but the polymerization/condensation of the biocoke was greatly enhanced as illustrated by FTIR and Raman results. The aromatic ring related functional groups in 500BC increased obviously, and the large aromatic ring systems in the biocoke increased with a higher C content as well. Biocoke was found to be a highly carbonaceous substance free of ash with imporous structure and very smooth surface, which can be potentially used as a high-quality fuel or further modified to value-added carbon materials.