Upgrading of the bio-oil aqueous fraction (BAF) for liquid hydrocarbon production was studied in this work. Hydrotreating pretreatment and methanol cocracking were combined as a dual-stage hydrotreating–cocracking process to overcome the severe coking problem caused by the hydrogen-lacking property of BAF. The influences of hydrotreating temperature, reaction pressure, and BAF/methanol ratio in feedstock were investigated. It was found that the hydrogenation efficiencies of phenols in BAF were elevated with increases in hydrotreating temperature and reaction pressure, which were important for maintaining cracking catalyst activity. However, a too high hydrotreating temperature significantly enhanced the gasification reaction and led to reduction in the final liquid hydrocarbon yield. Meanwhile, an excessively high BAF/methanol ratio obviously accelerated the deactivation of the cracking catalyst. The comparison of different cracking processes showed that dual-stage hydrotreating–cocracking was the most superior in stable liquid hydrocarbon generation. Finally, the reaction mechanism was proposed based on experimental results.Keywords: Bio-oil aqueous fraction; Hydrogen supply; Hydrotreating−cocracking; Liquid hydrocarbon; Methanol; Upgrading;

•Hydrogenation-cocracking was developed to enhance aromatic hydrocarbons production.•Hydrogen supply was regulated in both hydrogenation and cocracking stages.•Desired aromatic hydrocarbons were obtained with a low coke yield.•Reaction mechanism of hydrogenation-cocracking was proposed.The hydrogen-lacking characteristic of bio-oil leads to a low yield of desired product and easy coke formation during its cracking for aromatic hydrocarbon generation. Therefore, an improved hydrogenation-cocracking process which could supply hydrogen in two stages to enhance aromatic hydrocarbon production was developed in this study. Furfural was chosen as the model compound of bio-oil to be coprocessed with methanol, and hydrogen supply behavior was regulated by varying hydrogenation temperature and methanol coprocessing ratio in the feedstock. The results showed that raising hydrogenation temperature in the range of 150–250 °C increased the hydrogenation degree and thus facilitated aromatic hydrocarbon production in the cracking stage. However, a further increase of temperature to 300 °C caused low-reactivity saturated gaseous hydrocarbon production, which decreased the ultimate oil phase yield. The increase of methanol coprocessing ratio in feedstock strengthened the hydrogen supply in the cracking stage, which could promote the deoxygenation of furanic ring and consequently increased aromatic hydrocarbon yield and reduced coke formation. By coprocessing 25% furfural and 75% methanol with a hydrogenation temperature of 250 °C, the oil phase yield reached 26.4% with an aromatic hydrocarbon content of 94.4%. Finally, the hydrogenation-cocracking mechanism was proposed according to the experimental results.Download high-res image (164KB)Download full-size image

•Biochar enhanced catalytic conversion of biomass pyrolytic vapor (MPV).•The catalytic conversion of MPV was promoted by the metallic elements in biochar.•The alkali and alkaline earth metals played dominating catalytic roles.•Increasing temperature and S/MPV promoted hydrogen production.The gas–solid simultaneous conversion in the integrated process means the biomass pyrolysis products, pyrolytic vapor and biochar, can be comprehensively converted for hydrogen production from biomass in the presence of steam. In order to study the catalytic conversion behavior of biomass pyrolytic vapor in this gasification process, the influence of bio-char on the conversion of model pyrolytic vapor (MPV) was investigated in a fixed bed reactor. The results showed that biochar enhanced the conversion of MPV, resulting in the increase of carbon conversion and potential hydrogen yield from 68.46% to 86.88% and 42.16% to 82.76% respectively. The catalytic activities of different metal elements in biochar were found with the following sequence: K > Ca > Mg > Fe > Zn > Al. Meanwhile, the alkali and alkaline earth metals (AAEM) like K, Ca, and Mg were found to play the dominating roles in the conversion of MPV, and especially, the catalytic effect of K was the most obvious among the metals in bio-char. Finally, the effects of temperature (750–900 °C) and steam to MPV ratio (2–5 g/g) on the catalytic conversion of MPV in the presence of biochar were investigated. The carbon conversion and potential hydrogen yield of model pyrolytic vapor were improved by increasing temperature and steam to MPV ratio (S/MPV).

•A novel integrated process was utilized to improve hydrogen yield.•The integrated process included biomass pyrolysis, gas–solid simultaneous gasification and catalytic reforming processes.•Hydrogen yield was greatly increased from 43.58 to 75.96 g H2/kg biomass.•Carbon conversion efficiency was greatly increased from 66.18% to 82.20%.A novel process, which integrated with biomass pyrolysis, gas–solid simultaneous gasification and catalytic reforming processes, was utilized to produce hydrogen. The effects of gasification temperature and reforming temperature on hydrogen yield and carbon conversion efficiency were investigated. The results showed that both higher gasification temperature and reforming temperature led to higher hydrogen yield and carbon conversion efficiency. Compared with the two-stage pyrolysis-catalytic reforming process, hydrogen yield and carbon conversion efficiency were greatly increased from 43.58 to 75.96 g H2/kg biomass and 66.18%–82.20% in the integrated process.