250025 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.