Investigation of the thermal decomposition mechanism of glycerol: the combination of a theoretical study based on the Minnesota functional and experimental support

Abstract

The multiple thermal decomposition channels of glycerol are calculated at the M06-2X-D3/6-311+G(d,p) level. In addition, the CAM-B3LYP and ωB97X-D functionals are used to show the functional influence on the free energy barrier. For the highly competitive primary channels, the DLPNO-CCSD(T)/CBS method is applied for the energy calculations. The results show that the dominant paths are: (1) breakage of the C–C, C–O, and O–H bonds of glycerol successively to form carbonyl and alkene, and then generation of water, formaldehyde, and acetaldehyde; (2) glycerol undergoing an intramolecular dehydration reaction and producing 3-hydroxypropionaldehyde; it has two subsequent reactions: ① C–C bond fracture occurring to form formaldehyde, acetaldehyde, and water; and ② intramolecular dehydration forming acrolein and water. The ΔG₁ is 65.6 kcal mol⁻¹ while the ΔG₂ is 65.5 kcal mol⁻¹ at 101 kPa and 298 K, and fitted rate equations are 1.09 × 10¹³ exp[65.6 × 10³/RT] s⁻¹ and 8.07 × 10¹² exp[65.4 × 10³/RT] s⁻¹, respectively. Besides, UPLC and TG-GC/MS are applied complementarily to investigate the anaerobic pyrolysis products of glycerol at different temperatures. The experimental results are consistent with theoretical calculations.