In-depth understanding of soluble base deactivation during the carbonate transesterification process

Abstract

Soluble strong bases such as NaOH or CH3ONa were industrially applied in production of multiple carbonates via the transesterification route. However, the catalytic efficiency decreased significantly after recycling and insoluble solids were formed, leading to a complicated and non-eco-friendly manufacture process. In this study, the influence of Na-based soluble basic catalysts (C4H9ONa, C2H5ONa, CH3ONa, NaOH, Na2CO3, and NaHCO3) structures, amounts, reusability, reaction atmospheres, and different reactants treatment were systematically studied for in-depth understanding the deactivated processes and mechanism. The results indicated dimethyl carbonate (DMC) was responsible for the deactivation and with decreasing the pKb (alkalinity coefficient) value, the alkali strength, nucleophilicity, and catalyst efficiency increased. The properties of fresh, DMC-treated and recycled NaOH or CH3ONa samples were characterized by means of XRD, FT-IR, Raman, TG, and SEM. Nearly all the characterizations proved that the final deactivation species was Na2CO3 after long-time treatment or recycle. A possible deactivation mechanism of soluble bases during the transesterification process was proposed. The presence of trace H2O was the induction of CH3ONa deactivation, whereas the interaction between DMC and NaOH led to the formation of Na2CO3. This finding will contribute to the development of strategies to design homogeneous catalysts with high activity and stability for carbonate transesterification.