Homogeneous Catalyzed Esterification of n-Butyric Acid with Isoamyl Alcohol: A Kinetic Study

Homogeneous Catalyzed Esterification of n-Butyric Acid with Isoamyl Alcohol: A Kinetic Study

 

Yohana Páez, Jairo Durán, Iván Darío Gil, Gerardo Rodríguez, Julio César Vargas, Álvaro Orjuela.

Grupo de Procesos Químicos y Bioquímicos, Departamento de Ingeniería Química y Ambiental, Universidad Nacional de Colombia, Bogotá D.C, Colombia.

Isoamyl butyrate, a high-valued ester widely used in fragrances and flavors industry is commonly obtained by esterification of isoamyl alcohol with n-butyric acid. Isoamyl butyrate has an enormous economic potential because it can be produced from renewable, bio-based chemicals (Isoamyl alcohol can be obtained from separation of fusel oil, a by-product from the bioethanol industry and butyric acid can be produced by fermentation), and can be used as “green solvent” to replace other petrochemical-based chemicals. In this regard, determination of the esterification kinetics is required to evaluate and design of an isoamyl butyrate production process.

In this work, an experimental kinetic study on the esterification of isoamyl alcohol and butyric acid using p-toluenesulfonic acid (PTSA) as catalyst is presented. Experiments were carried out using a response surface based method on three levels - three variable - central composite rotatable design (CCD). The influence and interaction of alcohol/acid molar ratio (1:1, 1.1:1, 1.2:1), catalyst concentration (1, 1.5, 2 wt%) and temperature (60, 70, 80°C) on the kinetics parameters and isoamyl butyrate yield were evaluated. All the experiments were carried out in a laboratory-scale stirred batch reactor without water removal during the tests. The dependency of the reaction rate constant with the temperature was fitted according to the Arrhenius equation and the experimental data were used for modeling a power law kinetic. The non-ideality of each species in the reacting mixture was considered by using the UNIFAC group contribution method. The activity model coefficients were estimated by using the commercial software ASPEN PROPERTIES^®. ANOVA analysis was performed in order to identify the variables which have the major influence on the fractional conversion. Temperature and catalyst concentration were found to have the major influence in conversion, whereas the molar feed ratio did not show significant effect. An equilibrium molar conversion of 81.6 % was obtained at 80°C, at feeding molar ratio alcohol/acid of 1.2:1 and 2% w/w catalyst. Final kinetic model agrees with experimental observations within an average deviation of around 3%.

 

KEYWORDS: Central composite rotatable design, esterification, isoamyl butyrate, kinetics, power law model.

Graphic Abstract

 

Effect of the temperature in the fractional conversion. Catalyst concentration, 1%, Alcohol/Acid molar ratio, 1:1.1. ♦ 333.15 K, ■ 343.15 K, ▲ 353.15 K.