An experimental investigation of PG/VG pyrolysis combined with molecular dynamics

Propylene glycol (PG) and vegetable glycerin (VG) are common ingredients used in the preparation of various products, and notably in e-cigarette liquids. In this work, we investigated the generation of light gases from the pyrolysis of PG, VG and their mixtures. ReaxFF-MD was used to study the elementary reactions involved in the pyrolysis of PG/VG mixtures of 50/50 and 30/70 percent by volume. Main reactions included dehydration, dehydrogenation and C-C bond cleavage. In addition, we focused on the elementary reactions that form the light gases: C2 hydrocarbons, CO, CO2, and H2. Kinetic rates of PG and VG decomposition, and the Arrhenius parameters, were calculated, with errors as low as 1% with respect to pure PG and VG kinetic rate constants. Furthermore, experimental results were obtained by conducting pyrolysis experiments on PG, VG and their mixtures, in a continuous flow tube reactor at reaction temperatures ranging between 550°C and 850°C. The main gas products were predominantly CO, CH4, C2H4, in addition to C2H6, C2H2, H2, and CO2. Gas product concentrations increased with temperature except for ethane, which underwent further decomposition, as expected from the elementary reactions. Liquid mixtures proved to produce more products due to reactions taking place between the different pyrolysis products obtained from PG and VG, as shown by ReaxFF-MD simulations.