Mechanism studies on β-d-glucopyranose pyrolysis by density functional theory methods

Abstract

In order to understand the pyrolysis mechanism of cellulose, the pyrolysis of β-d-glucopyranose as cellulose unit model compound was investigated by employing density function theory methods at B3LYP level with 6-31G(d,p) basis set. Two series of pyrolytic reactions containing seven possible pathways were proposed after several pathways were analyzed in detail. All the reactants, transition states, intermediates and products were optimized, also the standard thermodynamic and kinetic parameters in each reaction pathway were calculated. The calculation results indicate that the reactions of pathways 1–5 are endothermic, but ones of pathways 6–7 are exothermic. All the pathways can occur spontaneously above 400K and 1atm. We also obtain five better reaction pathways from two modes of reaction pathways. Among these five pathways, hydroxyacetaldehyde (HAA), acetol, formic acid, acetic acid and furfural are generated in pathway 2, 4, 7, 6 and 3 with the activation energy of 258.9, 291.1, 295.7, 321.5 and 360.6kJ/mol, respectively. Both thermodynamic and kinetic analyses support reaction pathways 2 and 4 as major reaction channels. It can be inferred that HAA, acetol and 5-hydroxymethylfurfural are the main products among small molecular products during cellulose pyrolysis. The formation of formic acid, acetic acid and furfural are difficult than that of former main products. The above results are in accordance with the related experimental results.