The influence of solvent on the pyrolysis of organosolv lignins extracted from willow

The targeted application of lignin needs deeper understanding of its physicochemical property. Herein, three kinds of organosolv lignin samples were obtained from willow using three typical organosolv-water co-solvents, and their properties and pyrolysis behaviors were studied by various characterization methods. It was found that the used solvents exerted different effects on lignin samples: lignin extracted from ethyl acetate-water co-solvent possessed more functional groups containing oxygen, and lignin extracted from γ-butyrolactone-water co-solvent contained more large-molecule fragments; the degradation temperature with the maximum rate in thermogravimetric analysis were 352, 384, and 398 ℃ for lignin samples extracted by ethyl acetate/tetrahydrofuran/γ-butyrolactone-water co-solvent, respectively. The cleavage of Cα-Cβ linkage performed more acutely in pyrolysis of lignin extracted from γ-butyrolactone-water co-solvent, while the linkage of C1-Cα in lignin extracted by ethyl acetate/tetrahydrofuran-water co-solvent was more fragile. With regard to the mono-phenolic products, the pyrolysis of lignin extracted from ethyl acetate-water co-solvent yielded guaiacol and 4-methylguaiacol dominantly, and lignin extracted by tetrahydrofuran-water co-solvent produced more guaiacol, 4-ethylguaiacol, and 4-methylguaiacol while lignin extracted by γ-butyrolactone-water co-solvent yielded the maximum amount of 4-methylguaiacol. In addition, the pyrolysis of lignin samples extracted by γ-butyrolactone-water co-solvent yielded only H2, CH4 and CO as gaseous products while the other two yielded H2, CH4, CO and CO2.