CO₂‑Enhanced Synthesis of Trimethyl Borate from Ulexite: Innovations in Pervaporation Separation

The primary objective of this research is to enhance a novel method for the eco-friendly production of trimethyl borate (TMB) from ulexite ore by utilizing carbon dioxide. Notably, CO₂, a major greenhouse gas, is converted into thermodynamically stable CaCO₃ following TMB synthesis. TMB, a significant organo-boron chemical, has a wide range of industrial applications. In this study, the trimethyl borate production process consists of three main steps: reaction, distillation, and pervaporation. Trimethyl borate was synthesized through the reaction of ulexite with methanol in a high-pressure reactor under a CO₂ atmosphere. The obtained liquid product was subjected to distillation to produce the TMB–methanol azeotrope. Following the distillation process, the separation of TMB from the azeotrope mixture was achieved by utilizing pervaporation. The TMB–methanol azeotrope and pure TMB were characterized and confirmed by using Fourier transform infrared (FTIR) spectroscopy and gas chromatography (GC). In this research, hydroxyethyl cellulose (HEC) and polyvinylpyrrolidone (PVP) were used as the membrane materials. Blend membranes were prepared by the solution casting evaporation method. The morphologies of the membranes were characterized by FTIR spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and contact angle assessment. The pervaporation performance of all blend membranes was evaluated for the separation of the TMB–methanol azeotrope. The effects of the operating temperature, methanol feed concentration, and PVP ratios on separation performance were investigated. The results demonstrated that a TMB purity of 97.71 wt % was achieved when the PVP–HEC-2 membrane was utilized in pervaporation. In conclusion, this study introduces an innovative and environmentally friendly process for producing valuable chemicals, highlighting its potential for industrial applications.