Study on mechanism of cellulose hydrolysis during alkali thermal pretreatment of lignocellulose by density functional theory

Abstract

Alkali thermal pretreatment can effectively destroy the compact three-dimensional aggregated structure of lignocellulose, and further promote the production of high value-added chemicals. Cellulose is an important component of lignocellulose, and in this study the mechanism of cellulose hydrolysis in alkali thermal pretreatment was studied by density functional theory. The hydrolysis was divided into two steps, firstly the hydroxide ion captured a proton from the hydroxyl of which had most positive potential value of 1.23 eV. Subsequently, the glycosidic bond was cleaved to form a new C–O bond, and the hydroxide ion attacked the intermediate forming a glucose residue by a new covalent. The amount of electron transfer of the two steps were natural orbitals for chemical valence eigenvalue 0.31 and 0.34, and the corresponding energy barriers were 147.11 and 101.17 kJ/mol at 298.15 K, respectively. With the increase of pretreatment temperature from 298.15 to 413.15 K, the enthalpy and Gibbs free energy change of cellobiose hydrolysis decreased by 2.97 and 2.34 kJ/mol and the thermodynamic feasibility and reaction rate increased. This study will providing an important guidance for the process control, reactor design and performance enhancement of lignocellulose pretreatment.