Alkaline Hydrolysis of an Aromatic Ester: Kinetic Studies Using Thermal Power Profiles

Abstract

The reaction kinetics of ethyl benzoate saponification with sodium hydroxide in a heterogeneous reaction medium was investigated. The rate of reaction in a heterogeneous liquid-liquid system incorporates a chemical kinetics term as well as the mass transfer between both phases. The reaction was carried out in a reaction calorimeter and the overall reaction rate was determined from the obtained thermal profiles. The mass transfer parameters were calculated numerically, taking into account those reaction rate constants determined in our previous study, where the above-mentioned reaction was conducted in a homogeneous reaction medium. The dependence of the mass transfer parameters and reaction rates on different heterogeneity stages and temperatures is described.

Saponification reaction system: a detailed mass transfer coefficient determination

“…10 Mass transfer has to be avoided in order to study sodium benzoate's effect on chemical kinetics. Ethanol was added to the reaction media for reaching the homogeneity.…”

“…They were calculated considering k L a products from complete time range at a certain temperature and heterogeneity stage. Table 3: Comparisons between the k L a products, at different heterogeneity stages, calculated for both the simple (S) 10 and extended (EM) kinetic models at the temperature, ϑ = 30 °C. It is evident from the surface plot ( Figure 2) that a larger increase occurred in the values for mass transfer coefficient at the end of the reaction, where the masstransfer was no longer within the rate-limiting process.…”

“…10 Only a brief description will be given here. All chemicals, ethyl benzoate, ethanol, sodium benzoate and sodium hydroxide are commercially available and were used as received without further purification.…”

“…The kinetic model was presented in detail in our previous study, 10 only the major points are highlighted here. The overall rate expression regarding the base-hydrolysis of ethyl benzoate with sodium hydroxide in a heterogeneous medium incorporates two rate steps in series -mass transfer of sodium hydroxide to the surface of ethyl benzoate droplets, followed by reaction on the surface.…”

“…During this study we turned our attention towards extending a previously-simplified thermo-kinetic model valid for heterogeneous liquid-liquid reaction systems, where several assumptions were used for mass transfer estimation. 10 In this work the mass transfer coefficient, interfacial area, and the k L a product were estimated precisely using experimentally determined thermal power profiles.…”