Understanding the catalytic upgrading of bio-oil from pine pyrolysis over CO2-activated biochar

To understand the catalytic upgrading of bio-oil over char-based catalyst, pyrolysis of pine sawdust with various char catalysts under different reaction temperatures was performed in a fixed-bed reactor, from which the liquid product was analyzed with gas chromatography-mass spectrometry (GC/MS). The main pyrolytic liquids were ketones and acids in the non-catalytic pyrolysis run, which were mainly derived from the pyrolysis of cellulose and hemicellulose in biomass by ring opening and side chain cracking reactions, while the relative content of phenolic substances obtained from catalytic reaction at 400 °C over CO2-activated char increased from 33.79% to 78.12% with the increasing char activation time from 0.5 to 2.0 h, resulting from the formation of more multiple active sites (including surface active groups and the pore characteristics) on activated char. When the catalytic reaction temperature reached 600 °C, the quality of the bio-oil was further improved since the relative content of aromatic hydrocarbons increased from 7.30% to 21.04% at the expense of elimination of some oxygen-containing compounds (e.g., ketones, acids, aldehydes, etc). Furthermore, the content of phenol in phenolic compounds increased from 26–64% to 51–97%.