Limonene carbonate synthesis from CO₂: Continuous high-pressure flow catalysis with integrated product separation

In this work, a proof-of-concept of a continuous flow process for the synthesis of limonene carbonate (LC) from the cycloaddition reaction between CO₂ and limonene oxide (LO) was explored. The process uses a biphasic system composed of a CO₂ mobile-phase and a stationary ionic liquid (IL)-phase used as the reaction catalyst. To determine the best conditions for integrating reaction and separation steps, high-pressure phase behaviour studies of the binary mixtures CO₂ +LO and CO₂ +LC were performed. The continuous process was carried out at a pressure of 300 bar and temperatures of 100 ºC, 120 ºC and 140 ºC, using two different ILs as catalysts, namely tetrabutylammonium bromide (TBABr) and trioctylmethylammonium chloride (Aliquat Cl). Results showed that at lower temperature conditions it was possible to continuously carry out the reaction for 45 h with moderate yields. TBABr revealed to be a more stable catalytic phase when compared with Aliquat Cl.