(445a) Ethyl Acetate Synthesis Using Semi-Batch Reactive Distillation

Batch reactive distillation (BRD) is an integrated process which combines the advantages of reactive distillation and the flexibility of batch processes. Semi-batch reactive distillation (SBRD) is a design alternative for BRD in which one reactant is fed continuously into the column during the batch. Esterifications of low molecular weight alcohols (methanol–amyl alcohol) with acetic acid have been studied as model systems for the design and optimization of BRD and SBRD processes.

For such esterification processes the lowest-boiling stationary point is an azeotrope. If the azetrope is located in a two-liquid region and the aqueous phase is nearly pure water, (n-butanol and amyl alcohol), a BRD process is feasible because water (a product) can be removed from the column by a decanter.¹ Furthermore, Qi and Malone² showed that for the more difficult isopropyl acetate system in which the ternary azeotrope lies just inside the liquid-liquid zone, semi-batch reactive distillation (SBRD) operation can improve the production efficiency. Using acetic acid as an entrainer and continuously feeding it into the column during the batch can reduce the concentration of isopropyl alcohol in the distillate so that the distillate composition is closer to the water-acetate edge. Therefore the concentration of water in the aqueous phase is higher.

     In this work, the more challenging ethyl acetate process is investigated. Unlike the isopropyl acetate process, BRD with a decanter is not feasible for the ethyl acetate process because the minimum-boiling ternary azeotrope is not located in the two-liquid region. To overcome this problem, researchers have considered the use of a middle-vessel column³ and a two-column pressure swing BRD process.⁴ In this work, we consider another possibility, which is the application of SBRD. Similar to the isopropyl acetate process, acetic acid is fed continuously near the top of the column to reduce the ethanol concentration in the distillate and move the distillate composition into the two liquid-liquid region. After the liquid split, high purity water can removed from the column, and the organic phase containing mainly ethyl acetate and water is collected. High purity of ethyl acetate (99 mol %) can be obtained from the separation of the collected organic product using a batch stripper with a decanter. The two step process is discussed in this work, and some important design variables including the number of reactive trays, initial amount of acetic acid added, side feed policy, reflux ratio policy, and reboiler heating policy are studied to improve the production efficiency.

References

1. Venimadhavan G, Malone MF, Doherty MF. A novel distillate policy for batch reactive distillation with application to the production of butyl acetate. Ind Eng Chem Res. Mar 1999;38(3):714-722.
2. Qi W, Malone MF. Semibatch Reactive Distillation for Isopropyl Acetate Synthesis. Ind Eng Chem Res. Feb 2 2011;50(3):1272-1277.
3. Steger C, Lukacs T, Rev E, Meyer M, Lelkes Z. A Generic Feasibility Study of Batch Reactive Distillation in Hybrid Configurations. Aiche Journal. May 2009;55(5):1185-1199.
4. Modla G. Reactive pressure swing batch distillation by a new double column system. Computers & Chemical Engineering. Nov 15 2011;35(11):2401-2410.