Highly efficient synthesis of cyclic carbonate with CO₂catalyzed by ionic liquid in a microreactor

Abstract

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 gprod. (gcat. h)−1, which is much larger than the value [ca. 19 gprod. (gcat. h)−1] for the conventional stirred reactor. To some extent, the present study has also demonstrated the concept of ‘Novel Process Windows’.