Oligomers obtained from sequential fractionation of lignin pyrolysis oil

Abstract

The existence of oligomers poses a huge challenge for the valorization and utilization of bio-oil, thus it is urgent to develop cost-effective fractionation techniques to improve the quality of bio-oil and realize its valorization. Herein, developed a simple and novel process based on the combination of water and organic solvents (dichloromethane and diethyl ether) extraction of AL and CHRL POs to obtain oligomer-rich fractions for qualitative and quantitative analysis. Confirmation of both the DI and EEI fractions obtained from two POs were lignin-derived oligomers by the combination of GC–MS and ESI+–HRMS analyses, where the AL- and CHRL-derived oligomers accounted for 23.4% and 14.31% of the respective PO mass, respectively. The results showed that the chemical compositions of each oligomer-rich fraction depended on the chemical nature of the extraction solvent selected and chemical compositions exerted a greater influence on thermal degradation behavior of oligomer-rich fraction than its molecular weight, and the “carbon residue” content was inversely proportional to its methoxy content. In addition, 2D HSQC NMR indicated that the side chain structures of the EEI fraction were more than the DI fraction derived from the same PO, which was attributed to the dichloromethane exhibits better δH ability with hydroxyl group than diethyl ether, while the aromatic structures were similar.