A hemicellulose and lignin-first process for corn stover valorization catalyzed by aluminum sulfate in γ-butyrolactone/water co-solvent

Abstract

A novel hemicellulose and lignin-first process for corn stover valorization catalyzed by Al₂(SO₄)₃ in GBL/H₂O co-solvent was developed in this study. In 25% GBL/H₂O at 160 °C, Al₂(SO₄)₃ assisted H₂O in breaking down intermolecular linkages of corn stover. The hydrolysis of Al₂(SO₄)₃ could produce H⁺, [Al(OH)₂(H₂O)_x]⁺ and SO₄²⁻. With the solvation of GBL, the H⁺ and [Al(OH)₂(H₂O)_x]⁺ from Al₂(SO₄)₃ hydrolysis increased the co-conversion and dissolution of hemicellulose (96.9 wt%) and lignin (68.0 wt%), while the AlHSO₄(OH)₂H₂O species formed by combining with [Al(OH)₂(H₂O)_x]⁺ and SO₄²⁻ was found to inhibit cellulose conversion (88.7 wt% kept). Expecting for H⁺ from Al₂(SO₄)₃ hydrolysis, the formed AlHSO₄(OH)₂H₂O was found to be the catalytic active species for the cleavage of glycosidic bonds in hemicellulose to produce xylose, and also acted as a “stabilizer” to prevent the further degradation of xylose to improve its yield (87.6%, based on the weight of hemicellulose). Al₂(SO₄)₃ selectively promoted lignin depolymerization to lower M_w oligomers, as well as monophenols (11.20%) with high selectivity of 70.0% to VG and VP via C_α–OH dehydration and –C_γ(O)–OH decarboxylation reaction. The obtained cellulose-rich residues show great potential for further use within many industrial processes. The developed process is recyclable, giving important insights to design new approaches for corn stover valorization.