Selective conversion of corncob hemicellulose to xylose via hydrothermal treatment with Fe2(SO4)3 and NaCl

A new catalyst (Fe₂(SO₄)₃-NaCl) was employed for the selective conversion of corncob hemicellulose to xylose via hydrothermal treatment. The optimal conditions included Fe₂(SO₄)₃-NaCl treatment for 2 h at 140 °C to achieve the selective conversion of hemicellulose (92.4 wt%) and a xylose yield of 106.8 wt%, which is based on the hemicellulose content in corncobs. These conditions led to a cellulose and lignin dissolution of 7.9 and 21.2 wt%, respectively. Fe₂(SO₄)₃ was found to play an important role, rather than NaCl, in the disruption of interactions among the three major components, while the conversion of lignin and cellulose was inhibited by NaCl and Fe₂(SO₄)₃, respectively. The co-addition of Fe₂(SO₄)₃ and NaCl promoted the selective dissolution of hemicellulose, leaving most of the cellulose and lignin unreacted in the solid residue. Additionally, Fe₂(SO₄)₃ inhibited the formation of formic and acetic acids. A second hydrothermal treatment on the hemicellulose-free residue with the same catalytic system at 140 °C for 2 h resulted in 42.2 wt% cellulose conversion and a fructose yield of 79.7 wt% based on converted cellulose. Therefore, a potential route for the comprehensive utilization of corncobs is proposed.