Kinetic investigations of styrene carbonate synthesis from styrene oxide and CO2 using a continuous flow tube-in-tube gas-liquid reactor

A continuous method of styrene carbonate (SC) synthesis from styrene oxide (SO) and carbon dioxide (CO2) is reported, using a semipermeable Teflon® AF-2400-based tube-in-tube gas-liquid reactor. The reaction was performed in the presence of and tetrabutylammonium bromide (TBAB) and zinc bromide (ZnBr2), acting as a highly efficient and economical homogeneous binary catalyst system. The exceptionally high permeation of CO2 through the membrane, combined with the high surface area to volume ratio in such continuous flow reactors resulted in complete SO conversion (100%) in a significantly reduced reaction time (tR) of 45 min at 120 °C and 6 bar of CO2 pressure. The effect of various operating conditions such as reaction temperature, CO2 pressure, residence time and catalyst molar ratio (ZnBr2/TBAB) was determined. Moreover, a detailed kinetic study of SC synthesis was carried out to determine the corresponding kinetic values (k and Ea) and activation parameters (ΔH‡, ΔS‡ and ΔG‡). Based on the experimental data, the reaction was found to be first-order in SO, TBAB and CO2 concentrations. The activation energy of SC synthesis in the presence of TBAB catalyst alone was calculated to be 55 kJ mol−1 over a temperature range of (90-120 °C), which was reduced to 32 kJ mol−1 as a result of using ZnBr2 as a co-catalyst.