Contribution to the Study of Methyl Acetate Transesterification by Reactive Pressure-Swing Distillation

Abstract

Distillation is the most widespread operation used to separate homogeneous mixtures since it is a mature industrial technology and offers advantages over other separation methods. However, when thermodynamic conditions are unfavorable, i.e. close-boiling systems or azeotropes, other techniques that are ultimately also based on distillation are used: enhanced distillation operations. Pressure-swing distillation is the only enhanced distillation technique that solely depends on an energy-separating agent. Nevertheless, this process is only feasible when the composition of species to be separated is significantly sensitive to pressure variation. Methyl acetate–methanol system is the case study used as an example of a mixture that forms an azeotrope with a pressure-sensitive composition. This mixture is collected in large amounts from a residual stream of polyvinyl alcohol production process. Accordingly, methods to separate and convert this components into more valuable chemicals are being studied. One of the most attractive possibilities is transforming methyl acetate into isobutyl acetate via transesterification with isobutanol, since methanol, which is a reactant for the polymer synthesis, is also generated as by-product. Due to the nature of methyl acetate–methanol mixture, pressure-swing distillation can be used to separate both species. In addition, this technology can be performed jointly with reactive distillation, another enhanced distillation technique, to carry out separation and reaction operations simultaneously and, thus, reduce capital and energy costs. Therefore, in this report, transesterification of methyl acetate using the reactive and pressure-swing distillation process is developed. Transesterification, catalyzed by the ion-exchange resin Amberlyst 15, is described using the pseudohomogeneous kinetic model. The process is simulated in Aspen Plus using a vapor–liquid equilibrium-stage approach and optimized to obtain products with commercial specifications. The design procedure involves finding the optimal number of stages for rectifying, stripping and reaction sections and the most appropriate operating pressure considering design factors such as heat duties, available pressure-levels of hot utilities and the recommended operating temperature for the catalyst