Investigation on Characteristics of Liquefied Products from Solvolysis Liquefaction of Chlorella pyrenoidosa in Ethanol–Water Systems

The current work presented the characteristics of liquefied products from solvolysis liquefaction of Chlorella pyrenoidosa in ethanol–water systems. The effect of different ethanol/water volume ratios on the physical and chemical characteristics of solid residue, dichloromethane-insoluble solid product (DCM-insoluble solid product), aqueous product, light bio-oil, and biocrude oil was systematically carried out. Elemental analysis and scanning electron microscopy revealed that the addition of ethanol contributed to the decomposition of solid residue. However, when the ethanol content exceeded 60%, the repolymerization of solid residue occurred. Moreover, on the basis of Fourier transform infrared spectroscopy, a plausible reaction mechanism of solid residues and DCM-insoluble solid products with respect to ethanol addition and reaction temperature was presented. The main chemical compositions of aqueous product, light bio-oil, and biocrude oil were identified by gas chromatography–mass spectrometry. It indicated that the ethanol–water cosolvent contributed to the generation of nitrogen-containing compounds in aqueous product and short-chain esters in light bio-oil, and decreased the content of toxic nitrogenous organic compounds with two or more methyl groups in aqueous product. The ethanol–water system could facilitate ester formation in biocrude oil through esterification and alcoholysis reactions. Through the thermal gravimetric analysis and thermal stability experiment of biocrude oils, it was demonstrated that the biocrude oil obtained from 60% ethanol content had the highest content of low boiling point components of C10–C20 and performed with the best thermal stability.