Transesterification of dimethyl carbonate with phenol to diphenyl carbonate over hexagonal Mg(OH)2 nanoflakes

Abstract

Hexagonal Mg(OH)₂ nanoflakes were synthesized via a hydrothermal method in the presence of polyethylene glycol 20000 (PEG-20000). X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) were applied to characterize the composition, morphologies and structure of the Mg(OH)₂ nanoflakes. Brunauer–Emmett–Teller (BET) analysis was performed to investigate the porous structure and surface area of the as-obtained nanoflakes. The transesterification of dimethyl carbonate (DMC) with phenol to produce diphenyl carbonate (DPC) was carried out over the hexagonal Mg(OH)₂ nanoflakes. The evaluation results showed that the hexagonal Mg(OH)₂ nanoflakes had better activity and excellent selectivity to target products compared with many conventional ester exchange catalysts. Compared with other catalysts, such as AlCl₃, ZnCl₂, and irregular Mg(OH)₂ synthesized via a hydrothermal method without PEG-20000, which all have been widely used as catalysts for this transesterification reaction, Mg(OH)₂ nanoflakes were more stable and showed a relatively high activity with a low catalyst amount. The transesterification reaction process was also analyzed with the classic thermodynamic theory, and when the reaction was carried out at 453 K, with a molar ratio of phenol to DMC of 2 : 1, a reaction time of 13 h, and a catalyst amount of 0.2% (molar ratio to phenol), the selectivity of the transesterification reaction reached 92.3%. Moreover, the deactivated hexagonal Mg(OH)₂ nanoflakes could be easily reactivated by calcination under vacuum, and the regenerated Mg(OH)₂ nanoflakes showed the catalytic activity almost as high as that of the fresh sample.