(677c) Carbon Dioxide Sequestration Via Zn-Catalyzed Urea Conversion to Dimethyl Carbonate

Dimethyl carbonate (DMC) is emerging as an attractive electrolyte in advanced battery technologies and as a non-toxic solvent in several applications. The production of DMC via a number of pathways is currently under investigation; we report here the reaction of urea with methanol to form DMC over a Zn-based catalyst. Urea is a low-cost commodity, commonly used as nitrogen fertilizer, produced by the reaction of carbon dioxide with ammonia. The formation of DMC from urea thus represents a carbon sequestration route to a commodity chemical.

The primary pathway for urea to DMC involves two reactions through the intermediate methyl carbamate (MC). The first reaction of urea with methanol to MC is rapid and proceeds without catalyst; DMC formation is therefore kinetically limited by the Zn-catalyzed second reaction involving MC and methanol. Prior literature suggests that Zn interacts with the amino groups in urea to form a complex that is the active species in the reaction. In this work, we show that the nature of this complex changes over the course of reaction, and that a substantial fraction of the Zn complex exists as a dissolved homogeneous catalyst. The yield of DMC is further limited in reaction by the formation of byproducts including N-methyl-methyl carbamate (NMMC), formed by the methylation of MC with DMC. A kinetic model of the overall reaction network allows prediction of optimum conditions for DMC formation, and clarifies the role of the Zn catalyst in producing DMC from urea.