Highly efficient synthesis of cyclic carbonate with CO2 catalyzed by ionic liquid in a microreactor

The development of highly efficient processes for the cycloaddition of CO2 with epoxides to produce five-membered cyclic carbonates is a very attractive topic. In this work, the cycloaddition of propylene oxide (PO) and CO2 to give propylene carbonate (PC) is studied in a microreactor using a HETBAB ionic liquid catalyst. The microreactor performance is evaluated by studying the effects of different operating conditions, including reaction temperature, operating pressure, residence time, molar ratio of CO2/PO, and the catalyst concentration in PO. The process characteristics of the reaction concerning the gas-liquid mass transfer and the intrinsic kinetics perspectives are discussed. The results show that the residence time can be dramatically reduced from several hours in a conventional stirred reactor to about 10 s in a microreactor. The yield of PC at 3.5 MPa can reach 99.8% at a residence time of 14 s. The turnover frequency (TOF) value varies in the range of 3000 to 14 000 h(-1) compared to 60 h(-1) in the conventional stirred reactor. The space time yield (STY) or the overall reaction rate ranges from 650 to 4500 g(prod.) (g(cat.) h)(-1), which is much larger than the value [ca. 19 g(prod.) (g(cat.) h)(-1)] for the conventional stirred reactor. To some extent, the present study has also demonstrated the concept of 'Novel Process Windows'.