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The extractive distillation of ethanol using glycerol as entrainer is studied in order to find its optimal design and operating conditions. The optimization is formulated as a mixed integer nonlinear programming (MINLP) problem. The discrete variables determine the number of stages of the columns and their feed stage locations. The continuous variables include the variables of the equilibrium model and operating variables. The solution of the optimization problem is achieved through a two-level strategy that combines stochastic and deterministic algorithms. The result obtained establishes the process that maximizes an economic criterion for the industrial production of bioethanol satisfying the problem constraints.

-The aim of this work is to simulate and analyze an extractive distillation process for azeotropic ethanol dehydration with ethylene glycol and calcium chloride mixture as entrainer. The work was developed with Aspen Plus® simulator version 11.1. Calculation of the activity coefficients employed to describe vapor liquid equilibrium of ethanol -water -ethylene glycol -calcium chloride system was done with the NRTL-E equation and they were validated with experimental data. The dehydration process used two columns: the main extractive column and the recovery column. The solvent to feed molar ratio S/F=0.3, molar reflux ratio RR=0.35, number of theoretical stages Ns=18, feed stage Sf=12, feed solvent stage SS=3, and feed solvent temperature TS=80 ºC, were determined to obtain a distillate with at least 99.5 % mole of ethanol. A substantial reduction in the energy consumption, compared with the conventional processes, was predicted by using ethylene glycol and calcium chloride as entrainer.

-Extractive distillation is an alternative for ethanol dehydration processes that has been shown to be more effective than azeotropic distillation and, in close proximity, to be very competitive against the process that uses adsorption with molecular sieves. Glycols have been shown to be the most effective solvents in extractive distillation, mainly ethylene glycol and glycerol. In this work, an extractive distillation column was simulated with the Aspen Plus software platform, using the RadFrac module for distillation columns, to investigate the effect on the separation of the ethylene glycol-glycerol mixture composition, the separating agent feed stages, the separating agent split stream feed, and the azeotropic feed temperature. The NRTL model was used to calculate the phase equilibrium of these strongly polar mixtures. A rigorous simulation of the extractive distillation column finally established was also performed, including a secondary recovery column for the mixture of solvents and a recycle loop, to simulate an industrially relevant situation. This simulation allowed establishing the complete parameters to dehydrate ethanol: the optimal stage for separating agent feed is stage 4; the most adequate composition for the glycols mixture is 60 mol% ethylene glycol and 40 mol% glycerol. Finally, energetically efficient operating conditions for each one of the columns were established through a preliminary pinch analysis.

In this work, the production of tributyl citrate via catalytic and self-catalyzed esterification of citric acid with 1-butanol was studied. Both, methanesulfonic acid (MSA) and Amberlyst 70 ion-exchange resin were evaluated as catalysts in the reaction. The kinetic effects of the temperature (353–393 K), the feed molar ratio of alcohol to acid (8:1 to 16:1), and catalyst loadings (0.5–1.5 wt % of MSA, and the equivalent amount of Amberlyst 70) were evaluated. Experiments were carried out using stirred batch reactors under isothermal operation. A Box–Behnken design was used to optimize the number of experiments required to obtain a valid kinetic model. Chemical equilibrium conditions were evaluated independently from kinetic experiments, reducing the number of parameters to adjust during data regression. Self-catalytic rate of reaction was also evaluated, and it was included within the overall kinetic model. The obtained models show good agreement with experiments, and they can be used for process analysis and simulation.

In this work, isobaric vapor–liquid equilibrium data for the binary mixtures of the isobutyl acetate + isoamyl acetate and isobutyl acetate + ethyl acetate were measured using an all-glass dynamic-recirculation still equipped with a Cottrell circulation pump (Labodest VLE 602D). For the system of isobutyl acetate + isoamyl acetate the measurements were carried out at 100 and 150 kPa, while for the system isobutyl acetate + ethyl acetate they were performed at 50, 100, and 150 kPa. Vapor pressures of the pure components were also measured to verify the performance and reliability of the equilibrium still, and data were correlated with an Antoine-type expression. The equilibrium data for the pure components were in agreement with literature reports and the data for the binary solutions show a fairly ideal behavior. Binary parameters for nonrandom two liquid (NRTL) and universal quasichemical (UNIQUAC) equations were correlated with experimental data, and both models showed good agreement with experiments and can be used for process design. It was found that, in the absence of experimental data, phase equilibrium in mixtures of acetates formed in the direct esterification of the fusel oil can be confidently predicted using the UNIFAC-DMD model or even the Ideal Model.

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