Optimized CO2 Cycloaddition to Epichlorohydrin Catalyzed by Ionic Liquid with Microwave and Ultrasonic Irradiation

Abstract

The capture, storage, and conversion of anthropogenic carbon dioxide (CO2) is one of the urgent environmental challenges. Among the various methods available, direct conversion is the most preferable. An example is the production of cyclic carbonates which are important products in the chemical industry. Considering that this method relies on catalysis, different catalysts can be used. Ionic liquid has been proposed as a promising candidate but the application in the process remains underexplored. Therefore, this study aimed to synthesize and comprehensively characterize ionic liquid 1-(2-hydroxyethyl)-3-methylimidazolium bromide using spectral techniques, including 1H and 13C NMR, Fourier transform infrared spectroscopy (FTIR), and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF). This compound was used as a catalyst in the cycloaddition reaction of CO2 with epichlorohydrin to produce 1-chloromethylpropylenecarbonate, comprising an important and in-demand class of organics namely cyclocarbonates. Key reaction parameters including temperature, pressure, and catalyst loading were systematically evaluated for the effects on epichlorohydrin conversion, product yield, and selectivity. The results showed that optimal conditions were found at 90 °C and 650 kPa, with a catalyst loading of 2 mol%. The main product was obtained at a yield of 94% with a selectivity of 97% within 2 hours. Additionally, methods to intensify the catalytic reaction were explored through the application of ultrasonic and microwave irradiation. Both forms of irradiation significantly accelerated the conversion of epichlorohydrin, increasing the catalyst turnover frequency (TOF) from 3.85 h-1 in the blank experiment to 4.50 h-1 and 8.38 h-1 with microwave and ultrasonic irradiation, respectively. The practical ease of integrating these approaches into industrial setups suggests promising potential for technological application. Finally, the feasibility of catalyst recycling was investigated. The 1-(2-hydroxyethyl)-3-methylimidazolium catalyst had stable catalytic activity, with only minimal activity loss observed over five consecutive cycles.

Keywords

• carbon dioxide utilization
• cyclic carbonates
• cycloaddition
• ionic liquid