(629an) 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.