Revealing the mechanism of phenoxyethanol-acid pretreatment for removing lignin from bamboo: kinetic analysis and simulation analysis†

Abstract

To explore the mechanism of structural destruction of bamboo residues (BR) in a phenoxyethanol/H₂SO₄ biphasic pretreatment system, a kinetic model for removing lignin and xylan, molecular dynamics (MD) simulations, and density functional theory (DFT) calculations for delignification were investigated. The delignification and xylan removal rate for BR reached 84.1% and 92.8%, respectively at 120 °C, with 1.4% H₂SO₄ concentration, leading to an enzymatic hydrolysis yield of 97.27%. Kinetic model analysis revealed that the activation energies of delignification and xylan removal were 68.0 kJ mol⁻¹ and 77.5 kJ mol⁻¹, respectively. MD simulations and DFT calculations revealed that phenoxyethanol mainly bound the lignin compound of veratrylglycerol-β-guaiacyl ether (VG) by van der Waals forces (8900–10 100 kJ mol⁻¹), thereby enhancing the solubility of lignin during the pretreatment process. The hydroxyl group in VG and phenoxyethanol played a crucial role in their interaction. The number of hydrogen bonds formed by phenoxyethanol and the hydroxyl group in VG is ∼8. An independent gradient model based on Hirshfeld partition and electrostatic potential analysis indicated that with the increased addition of H₂SO₄ in the biphasic pretreatment system, the hydrogen bonding interactions and van der Waals forces between the H atom in phenoxyethanol hydroxyl and O atom in lignin hydroxyl groups could be enhanced, which is beneficial for the dissolution of lignin through intermolecular forces during the pretreatment process. Overall, this work provided a theoretical insight to understand the removal process of lignin during the phenoxyethanol/H₂SO₄ biphasic system.