The performances of solvents, including γ-butyrolactone (GBL), γ-valerolactone (GVL), tetrahydrofuran (THF), ethyl acetate (EAC), 2-methyltetrahydrofuran (2-MeTHF), and the corresponding mixtures with H2 O, on the cleavage of inter- and intramolecular linkages of lignin in corncob residue were investigated. At 200 °C, miscible cosolvents (H2 O-GBL, H2 O-GVL, and H2 O-THF) exhibited much better efficiency for lignin dissolution than that of both immiscible cosolvents (H2 O-EAC and H2 O-2-MeTHF) and pure solvents. The synergetic effect between H2 O and organic solvent significantly promoted the breakage of intermolecular linkages between C6-O-H of amorphous cellulose and lignin. GBL and THF solvents preferentially dissolved lignin with H and G units, whereas GVL, EAC, and 2-MeTHF solvents exhibited high selectivity for the dissolution of lignin with S and G units. In addition to dissolution, the intramolecular β-O-4 linkage in lignin could be selectively cleaved in H2 O-GBL cosolvent, whereas the β-O-4, α-O-4, and β-5 linkages were cleaved in H2 O-EAC, H2 O-THF, and H2 O-2-MeTHF cosolvents. At 300 °C, the breakage of the β-γ bond prior to β-O-4 in H2 O-GBL, H2 O-THF, H2 O-EAC, and H2 O-2-MeTHF produced 4-ethylphenol and 4-ethylguaiacol selectively (accounting for ≈70 % of the total identified monophenols), whereas the α-1 bond was preferably broken in H2 O-GVL to form guaiacol (accounting for ≈75 % of the total identified monophenols).
Keywords: biomass; cleavage reactions; natural products; solvent effects; water chemistry.
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