An in-depth assessment on the non-isothermal esterification reaction for the di(2-ethylhexyl) terephthalate production: Kinetic modelling considering phase equilibria

Abstract

The di(2-ethylhexyl) terephthalate (DEHT) is an important plasticizer in the market of the polyvinyl chloride resins. DEHT can be produced by the esterification of terephthalic acid (TA) with 2-ethyl-1-hexanol (2EH), where solid TA particles react with the liquid 2EH in a heterogeneous medium. In this work, the esterification to produce DEHT catalyzed by the titanium tetraisopropoxide (TTIP) was studied in a batch reactor at reflux temperature and atmospheric pressure. A sampler device, specially designed for this purpose, was used to provide sample aliquots of the liquid phase of the reaction free of solid, which allowed to measure the solid–liquid equilibrium along the reaction, as well as to evaluate its limiting step. The reaction variables, as catalyst load and initial 2EH:TA molar ratio, were evaluated. High levels of hydrolysis were observed when TTIP was present in concentrations above 0.2% (w/w) on a total mass basis. Moreover, the reaction rate was independent on the initial molar ratio for the same catalyst load, which is an effect of the equilibrium solubility of TA in the liquid phase of the reaction. Finally, a kinetic model was proposed considering all the physical and chemical phenomena that occur in the reaction. The reaction temperature was estimated by the bubble point of the 2EH/DEHT mixture. Mass transfer rate was estimated along the reaction, by empirical equations that described the variation of the interfacial area and the Saunter mean diameter of TA particles. The model presented a good agreement with the experimental data.