The Effect of Alkoxide Ionic Liquids on the Synthesis of Dimethyl Carbonate from CO₂ and Methanol over ZrO₂–MgO

Abstract

The use of carbon dioxide in the synthesis of chemicals, such as dimethyl carbonate (DMC), constitutes an environmentally attractive alternative to hazardous and toxic reagents. However, the direct synthesis of DMC from methanol and CO₂ is characterized by low yields due to the reaction equilibrium and the thermodynamic limitations $\left( {\Updelta G_{298K}^{o} \; = \; + 2 6. 3 {\text{ kJ}}/{\text{mol}}} \right)$. Alkoxide ionic liquids possessing alkylimidazolium and benzalkonium cations were prepared, characterised and tested together with ZrO₂–MgO catalyst for the synthesis of DMC from methanol and CO₂. By using the novel ionic liquid as additives, ca. 12% conversion of methanol, and 90% selectivity to DMC was obtained at 120 °C and 7.5 MPa. The water abstracting potential of the ionic liquids influenced the conversion of methanol and the selectivity to DMC. The alkoxide ionic liquids were recovered and reused in DMC synthesis without loss in activity and selectivity.

Graphical abstract

Synthesis of DMC from CO₂ and methanol catalysed by ZrO₂–MgO using ionic liquid alkoxides as water abstracting additives. Comparison of the fresh and regenerated ionic liquid at 120 °C.