Transesterification of Bis 2-Hydroxyethyl Terephthalate for Production of Bis 4-Hydroxybutyl Terephthalate over Homogenous Catalysts

The vast amount of PET waste has made an enormous concern owing to its environmental pollution and human health effects. As an eco-friendly alternative option to treat plastic waste, this study investigated the transesterification of bis 2-hydroxyethyl terephthalate (BHET) into bis 4-hydroxybutyl terephthalate (BHBT) using 1, 4-butanediol (BDO) as a solvent in a typical batch reactor at various temperatures. Zinc acetate (Zn-A), antimony (III) oxide, tin (II) chloride, and titanium isopropoxide (Ti-IP) were utilized as catalysts. The effects of the experimental parameters, including the catalyst type, temperature, and catalyst loading, on the transesterification of BHET into BHBT were evaluated. Ti-IP and Zn-A showed higher catalytic activities than the other catalysts. Furthermore, Zn-A demonstrated to be a promising catalyst at lower temperatures, whereas Ti-IP exhibited higher activity at higher temperatures. An increase in temperature improved the yield of BHBT up to (0.99 mol/L) and showed the highest BHET conversion (98.93%) when Ti-IP was used as a catalyst at 210 °C. BHET conversion and the yield of BHBT were raised greatly when the catalyst amount was increased from 0.1 to 0.3 wt%. This study presents the transesterification of BHET using a Ti-IP catalyst as a novel technology for producing valuable BHBT for industrial applications.