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The phase diagram for the poly(ethylene glycol) dimethyl ether (PEGDE) + Na 2 SO 4 + H 2 O system at 298.15 K using PEGDE with a molar mass of 2000 was determined. Compositions of the liquid-liquid and the liquid-liquid-solid equilibria were determined using calibration curves of refractive index of the solutions, and atomic absorption (AA) and X-ray diffraction analyses were made on the solids. The solid phase in equilibrium with the biphasic region was anhydrous Na 2 SO 4 . An empirical nonlinear three-parameter expression developed by Merchuk was used for reproducing the experimental binodal data at T ) (288. 15, 298.15, 308.15, and 318.15) K, and the fitting parameters were obtained for the corresponding temperatures. The effects of temperature on the binodal curve were also studied, and it was observed that the area of the biphasic region increased slightly with an increase in temperature. The experimental tie-line compositions at the aforementioned temperatures were fitted to both the Othmer-Tobias and Bancroft and Setschenowtype equations. Correlation coefficients for all equations are reported.

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Herein, we report the application of inexpensive mesoporous melamine-formaldehyde resins (MMFR and MMFR250) obtained by a novel template-free and organosolvent-free hydrothermal method as efficient heterogeneous catalysts for direct synthesis of cyclic carbonates from CO2 and epoxides (epichlorohydrin, butylene oxide, and styrene oxide). The catalytic activities of the melamine resins were attributed to the abundant Lewis basic N-sites capable of activating CO2 molecules. Based on CO2-temperature programmed desorption, the concentrations of surface basic sites for MMFR and MMFR250 were estimated to be 172 and 56 μmol/g, while the activation energies of CO2 desorption (strength of basic sites) were calculated to be 92.1 and 64.5 kJ/mol. We also observed considerable differences in the catalytic activities and stabilities of polymeric catalysts in batch and in continuous-flow mode due to the existence of a synergism between adsorption of CO2 and cyclic carbonates (poison). Our experiments also revealed the important role of catalyst surface chemistry and CO2 partial pressure upon catalyst poisoning. Nevertheless, owing to their unique properties (large specific surface area, large mesoporous, and CO2 basicity), melamine resins presented excellent activities (turnover frequency 207–2147 h–1) and selectivities (>99%) for carbonation of epoxides with CO2 (20 bar initial CO2 or CO2:epoxide mole ratio ∼1.5) under solvent-free and co-catalyst-free conditions at 100–120 °C. Most importantly, these low-cost polymeric catalysts were reusable and demonstrated exceptional stability in a flow reactor (tested up to 13 days of time on stream, weight hourly space velocity 0.26–1.91 h–1) for continuous cyclic carbonate production from gaseous CO2 with different epoxides (conversion 76–100% and selectivity >99%) under industrially relevant conditions (120 °C, 13 bar, solvent-free/co-catalyst-free) confirming their superiority over the previously reported catalytic materials.

Compared to the large |α–β| in DESs, a relatively small |α–β| brings “synergistic interaction“ into play and allows the donor and acceptor components to react efficiently with CO2 molecules in DES.