Effect of residence time on two-step liquefaction of rice straw in a CO2 atmosphere: Differences between subcritical water and supercritical ethanol

•Subcritical CO2-solvent pretreatment had the characteristics of hydrothermal and dilute acid.•Residence time had marginal impact on subcritical CO2-supercritical ethanol liquefaction.•CO2 promoted the carbonyl reaction in subcritical CO2-subcritical water. This study investigated the influence of t...

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Veröffentlicht in:Bioresource technology 2017-04, Vol.229, p.143-151
Hauptverfasser: Yang, Tianhua, Wang, Jian, Li, Bingshuo, Kai, Xingping, Li, Rundong
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Sprache:eng
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Zusammenfassung:•Subcritical CO2-solvent pretreatment had the characteristics of hydrothermal and dilute acid.•Residence time had marginal impact on subcritical CO2-supercritical ethanol liquefaction.•CO2 promoted the carbonyl reaction in subcritical CO2-subcritical water. This study investigated the influence of temperature and residence time on liquefaction of rice straw in subcritical CO2-subcritical water (subCO2-subH2O) and in subcritical CO2-supercritical ethanol (subCO2-scEtOH), considering the final reaction temperatures (270–345°C) and residence times (15 and 30min). Residence time was identified as a crucial parameter in the subCO2-subH2O liquefaction, whereas residence time had a marginal influence on subCO2-scEtOH liquefaction. When reaction conditions were 320°C and 15min, solvents have weak impact on the quality of bio-oil, HHV 28.57MJ/kg and 28.62MJ/kg, respectively. There was an obvious difference between the subCO2-subH2O and subCO2-scEtOH liquefaction mechanisms. In subCO2-subH2O, CO2 promoted the carbonyl reaction. In subCO2-scEtOH, supercritical ethanol have the function of donating hydrogen and promoting the reaction of hydroxyl-alkylation.
ISSN:0960-8524
1873-2976
DOI:10.1016/j.biortech.2016.12.110