Effects of Chemical–Biological pretreatment of corn stalks on the bio-oils produced by hydrothermal liquefaction

The production of bio-oils by hydrothermal liquefaction of lignocellulose is an attractive prospect. However, bio-oils produced using traditional methods have multiple components and are low grade, which limit their application. In this study, a new method was proposed to improve the quality of bio-oils. Chemical–Biological pretreatment (CB-pretreatment) was performed on fresh corn stalks to separate a partial lignin and to convert hemicellulose, generating ethanol for hydrothermal liquefaction and improving the quality of the resulting bio-oils. Furthermore, the influence of CB-pretreatment on the components of lignocellulose in corn stalks and the pretreated samples was analyzed. And the materials and bio-oils were analyzed with TGA and GC–MS. The results showed that the relative content of lignin reduced from 13.25 ± 0.87% to 8.97 ± 0.77% in the alkaline treatment. And the relative content of hemicellulose in the alkaline-acid pretreated substrates decreased from 21.65 ± 0.74% to 10.06 ± 0.48%. After the whole pretreatment, the concentrations of ethanol and remaining reducing sugar in the fermented liquor were 2.88 ± 0.09 mg/mL and 3.59 ± 0.30 mg/mL, respectively. Moreover, the pretreated substrates had a lower degradation temperature and less ash content than the corn stalks. The heating value of the bio-oil was 32.21 MJ/kg. Moreover, the number of bio-oils components was obviously reduced. Toluene and 2,6-di-tert-butyl-4-methylphenol, which are respectively used as high octane additive and antioxidant in fuels increased significantly in quantity, with their total percentage of corresponding peak area reaching 30.77%.