(91d) Simultaneous Esterification of Mixed Alcohols with Acetic Acid by Reactive Distillation

Simultaneous
Esterification of Mixed Alcohols with Acetic Acid by Reactive Distillation

Karen Cañón-Rubio, Jairo Duran, Gerardo Rodríguez, Alvaro Orjuela

Grupo de Procesos Químicos y Bioquímicos. Department of Chemical and
Environmental Engineering. Universidad Nacional de Colombia. Bogotá. Colombia.

Reactive
distillation (RD) is a multifunctional operation that enhances selectivity and
conversion through product removal in systems where conversion is limited by
chemical equilibrium. Similarly, RD prevents the formation of undesired
products, hot spots, avoiding azeotropic conditions, among other benefits. In
this direction, RD become a potential processing alternative to overcome
equilibrium limitations observed in esterification systems, primarily in those
where high molecular weight and branched alcohols or acids are involved. Some
of these branched, high molecular weight alcohols are present in bio-based
products such as fusel oil, a well known by-product in bioethanol production.
In Colombia Fusel oil is used as fuel in bioethanol plants, but its main
components, isoamyl alcohol, ethanol and water can be separated and upgraded to
produce fragrances and flavors additives, among other products with high value.

In this work the mixed
esterification of isoamyl alcohol and ethanol with acetic acid was studied by
simulation using a RD process. Also, ethanol dehydration was considered as a
feasible reaction. Design specifications were focused on obtaining high purity
streams of ethyl acetate and isoamyl acetate, which are widely used in industry
as paint solvent and artificial flavors, respectively.

Thermodynamic data
for the 21 binary systems were obtained from literature and experiments.
Vapor-Liquid equilibrium data were fitted with NRTL activity model.  A kinetic
study was performed with a synthetic mixture of isoamyl alcohol, ethanol and
water resembling commercial fusel oil, and it was compared with ethanol and
isoamyl alcohol rate expressions, considering each reaction, separately. The
esterification was made using Amberlyst 70 cation exchange resin as catalyst,
and runs were performed in a stainless steel batch reactor between 353 ? 373K.
A full factorial experimental design with three levels was used. Kinetic data
were fitted with a pseudo-homogeneous model; the pre-exponential factor,
activation energy and equilibrium constant were obtained.

RD simulation was
made using Aspen Plus® 7.2, and Radfrac model was used to simulate the
catalytic column. Equilibrium stage model was assumed along the column, including
reactive, stripping and rectifying stages. Concentration and temperature
profiles were calculated based on simulation results. Sensitivity analyses were
made to determine optimum number of reactive and non-reactive stages, reflux ratio,
feed stage and feed ratio using minimization of Total Annual Cost (TAC) as
objective function.

Economic analysis
took into account fixed and variable costs related with equipment and energy
requirements by using equations and heuristics from literature. TAC has been
used to evaluate the performance and cost of this configuration.

Keywords: reactive distillation, fusel
oil, mixed esterification, ion exchange resin, total annual cost.