Insight into pyrolysis mechanism of 1,2-propylene glycol: Based on density functional theory and wavefunction analysis.

The multiple thermal decomposition mechanisms of 1,2-propylene glycol are studied through theoretical calculation and experiment, including carbon chain break, dehydrogenation and dehydration mechanism. The wavefunction is employed to analyze the decomposition process from a micro perspective. DLPNO-CCSD(T)/CBS method is engaged in establishing potential energy surface. The results reveal that the dehydration and carbon chain break mechanism are the primary pyrolysis paths, and the former is the dominant pyrolysis mechanism at low temperature, while the latter is applicable at the high temperature. The pyrolysis products are mainly acetaldehyde, propanal and acetone, which is consistent with experimental results. Besides, the comparison results of 1,2-propylene glycol and glycerol pyrolysis products indicate that the increment of hydroxyls are conducive to the generation of carbonyl compounds during the polyol thermal decomposition. This work is aimed to comprehensively investigate the pyrolysis mechanism of 1,2-propylene glycol and provide the valuable thermodynamics and kinetic data for developing efficient polyol pyrolysis technology. Furthermore, it provides a reference for choosing low-toxic tobacco humectant.