Na-dawsonite derived aluminates for DMC production by transesterification of ethylene carbonate

The transesterification of ethylene carbonate with methanol to dimethyl carbonate, an alternative phosgene-free route to DMC, was investigated over aluminas derived from calcination at different temperatures of Na- and NH4-dawsonites. The influence of the monovalent cation (NH4+, Na+) on the thermal decomposition of the starting dawsonites and derived crystallinity, morphology and porosity of the resulting aluminates was studied. The physico-chemical properties of the dawsonite precursors and the derived oxides were characterized by ICP, in situ XRD, TGA-MS, TEM, N2 adsorption, FTIR, and 27Al MAS-NMR. Phase transitions during thermal decomposition are dependent on the monovalent cation in the original dawsonite, i.e. the NH4-counterpart is transformed into finely dispersed and highly amorphous aluminas with well-developed porosity in the range 473–1073 K, while Na-dawsonite exhibits an intermediate amorphous sodium-containing alumina phase at 523–773 K, which crystallizes into sodium aluminate at 773–1073 K. Tests were carried out in a parallel reactor system at 298–343 K, methanol-to-ethylene carbonate ratios of 2–12, and 0.1–10 wt.% catalyst amount. Tailoring the catalyst activation conditions is essential to optimize the transesterification performance, and consequently the production of DMC, a valuable environment-friendly chemical for many potential applications. Any of the oxides derived from NH4-dawsonite were in active in the reaction. The basicity of the Na-containing oxides, attained by calcination of Na-dawsonite at 973 K, is required to obtain an active catalyst, which rendered a maximum DMC yield ca. 65%. Recycling experiments demonstrated that activated dawsonites can be successfully reused.

Tailoring the thermal activation of Na-dawsonite is essential for the optimization of the transesterification of ethylene carbonate with methanol in the synthesis of DMC. The reaction proceeds very fast and efficiently over basic sodium aluminate obtained at temperatures above 873 K with a DMC yield up to 65%. Dawsonite-derived aluminates are prospected for multiple green catalytic processes.Figure optionsDownload as PowerPoint slide