(754g) Isoamyl Acetate Esterification: Kinetic and Adsorption Study

ISOAMYL
ACETATE ESTERIFICATION: KINETIC AND ADSORPTION STUDY

Yoshinori
Casas, Natalia Montoya, Andrés Salazar, Alvaro Orjuela, Gerardo Rodriguez¹

Departamento
de Ingeniería Química y Ambiental, Universidad Nacional de Colombia, Bogotá ?
Colombia.

In Colombia, bioethanol industry has rapidly
grown over the last decade as a result of different governmental policies that
promote the use of renewable feedstocks to produce biofuels. In fuel ethanol
production several by-products are generated, among them fusel oil. It is a
mixture of higher alcohols, mainly composed by isoamyl alcohol, which is used
as a raw material to produce several value-added products. Currently, fusel oil
is burned in furnaces as fuel and used as solvent, representing low benefits
for the overall economics of the ethanol industry. Nevertheless, considering
that fusel oil contains up to 80% of isoamyl alcohol, the use of this
by-product in the production of esters for fragrances and flavoring industries would
be an alternative to improve economical benefits.

Since esterification is a reaction limited by
chemical equilibrium, high conversions are commonly achieved using a large
excess of alcohol. This practice involves bigger equipment sizes and higher energetic
requirements in both reaction and separation steps. To solve these problems
some hybrid technologies have been used; reactive distillation is one of them.
In this case, reaction and distillation processes take place in the same unit.
Reagents react at intermediate stages of a column while products are constantly
removed; this allows to obtain high conversion and a high purity of the final
product. This approach might be useful in the production of isoamyl acetate. 

The more accurate information in terms of
kinetic and thermodynamic data, the more reliable is the modeling of the
operation. Information such as kinetic expressions, activity coefficients and
adsorption behavior on heterogeneous catalysts must be obtained from
experimental procedures, in order to get more accurate and reliable estimations
used for process design and economics.

Considering that heterogeneous catalysis is
frequently used in esterification systems, it is necessary to take into account
the adsorption phenomena that take place when reagents interact with the solid
phase. Considering the above, kinetics and adsorption constants for esterification
of isoamyl alcohol with acetic acid on a ion exchange resin were studied. A Box-Behnken
experimental design was performed to carry out the kinetic tests. Batch
isothermal reactions were performed at different temperatures (373-393 K),
alcohol:acid molar ratios (1:1-1:2) and catalyst loadings (1-2%).  Experimental
data were fitted with a non ideal pseudo-homogeneous model and LHHW model using
NRTL activity model.

Adsorption constants were determined using
two different approaches, Kippling and Pöpken models. The first one joins the
composite isotherm model with the law of mass action; while the second one joins
the overall mass balance of the binary liquid phase with Langmüir type
adsorption based on mass. The difference in the fundamentals of each model
leads to very interesting but opposite results, which are studied in this work.
Independent binary adsorption experiments were performed. Three non reactive
pairs with total solubility were used.