Process Hazard Assessment and Exothermic Mechanism of Propylene Glycol Butyl Ether Synthesis from Propylene Oxide

Propylene glycol ethers are a series of fine chemical products with a wide range of applications and are one of the important industrial derivatives of epoxy compounds; the thermal hazards and exothermic mechanism of the reaction process have rarely been investigated in previous studies. In this study, propylene glycol butyl ether (PNB) was prepared by the reaction of propylene oxide (PO) with n-butanol catalyzed by potassium hydroxide in semibatch mode. A Box-Behnken design (BBD) method with four factors and three levels was carried out to optimize the yield and other process parameters of the reaction. The results showed that after optimization, the maximum yield and the minimum system pressure were 85.91% and 1.752 bar, respectively, when the reaction temperature was 110 °C, the alcohol-alkane ratio was 4, the dosing rate was 10 mL/min, and the catalyst concentration was 0.5%. The thermal behavior of the propylene glycol butyl ether synthesis process was investigated by reaction calorimetry. Fourier transform infrared (FTIR) spectroscopy was used to monitor the concentration changes of the reactants and products. Differential scanning calorimetry and adiabatic calorimetry were used to study the thermal stability of the products. Meanwhile, density functional theory calculations were implemented to understand the reaction pathways and associated energies. Furthermore, the thermal runaway risk of the reaction was assessed by the risk matrix method and Stoessel criticality diagram. The results indicated that the risk level was acceptable and the critical class for this reaction was of grade 3. These findings provide guidance for the safe operation of PNB synthesis from PO, which can be used for further scale-up.