One-step embedding method for immobilized bifunctional and alkaline ionic liquids as effective catalysts applied in transesterification

Abstract

Ionic liquids (ILs) have shown good catalytic properties in transesterification reactions, but there is still the drawback of a homogeneous state that requires high energy consumption to separate. Therefore, it is very important to acquire an efficient heterogeneous catalyst that can be applied in industrial manufacture. Herein, we propose a novel attempt to immobilize 1-ethyl-3-methylimidazole imidazolium ([Emim]Im) ILs into silica by a one-step embedding method to synthesize a series of [Emim]Im@SG-A solid catalysts. A large specific surface area of silica with a mesoporous structure can be obtained from the hydrolysis of tetraethyl orthosilicate (TEOS) catalyzed by [Emim]Im. The catalytic performance was evaluated by the transesterification of dimethyl carbonate (DMC) with ethanol (EtOH) in a fixed-bed reactor, and the cause of catalyst deactivation was analyzed. In addition, the mechanism of TEOS hydrolysis promoted by [Emim] Im as well as transesterification over [Emim]Im@SG-A was investigated. For comparison, a similar catalyst [Emim]Im/SiO₂ was prepared by an impregnation method. The results indicated that, among the as-prepared catalysts, [Emim]Im@SG-A12 exhibited the best catalytic performance with 49.0% DMC conversion and 39.0% ethyl methyl carbonate (EMC) yield under optimal reaction conditions. In addition, the results revealed that [Emim]Im can efficiently promote the hydrolysis of TEOS and enhance the transesterification of DMC with EtOH. This research provides a promising method to immobilize ILs and is enlightening for acquiring a heterogeneous catalyst.