Performances of Several Solvents on the Cleavage of Inter‐ and Intramolecular Linkages of Lignin in Corncob Residue

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 H 2 O, on the cleavage of inter‐ and intramolecular linkages of lignin in corncob residue were investigated. At 200 °C, miscible cosolvents (H 2 O–GBL, H 2 O–GVL, and H 2 O–THF) exhibited much better efficiency for lignin dissolution than that of both immiscible cosolvents (H 2 O–EAC and H 2 O–2‐MeTHF) and pure solvents. The synergetic effect between H 2 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 H 2 O–GBL cosolvent, whereas the β−O−4, α−O−4, and β−5 linkages were cleaved in H 2 O–EAC, H 2 O–THF, and H 2 O–2‐MeTHF cosolvents. At 300 °C, the breakage of the β−γ bond prior to β−O−4 in H 2 O–GBL, H 2 O–THF, H 2 O–EAC, and H 2 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 H 2 O–GVL to form guaiacol (accounting for ≈75 % of the total identified monophenols).