Abstract
In the acetic acid esterification, ethanol (EtOH) in excess is used to produce ethyl acetate (EtAc), which is commonly used as an organic solvent in biochemical and food industries. On the other hand, EtOH is useful considering the growing production of bioethanol for the fuel market. The resulting mixture of EtAc with unreacted EtOH forms an azeotrope which is difficult to separate by conventional distillation. Literature data shows that the azeotropic binary mixture EtOH – EtAc is separated mostly through extractive distillation. Unfortunately, this procedure has some drawbacks, such as high energy cost and environmental concerns (quite related to the extracting agent recovery). However, taking advantage of the azeotrope sensitivity on pressure, the extracting agent use can be avoided. This paper presents an optimal design for the separation of the above-mentioned mixture, using pressure-swing distillation (PSD) as separation process. In order to achieve a fully optimised system in terms of energy and capital, the method followed consists in simulating the process with Aspen Plus® and making use of genetic algorithms (GAs) to optimise the process variables, including, among others, the pressure of the high-pressure column. This process variable is of great importance, and from our point of view, this factor has not been properly studied nor discussed in literature so far. The starting population consists of points that group a set of values for all the design variables. These sets are a mixture of random and calculated values, obtained by application of heuristics, so that the initial population contains some potentially good initial individuals. The optimisation code is written in Visual Basic language and the link between Aspen Plus® and Visual Basic is also programmed so that a continuous connection can assure information flow from the optimisation program to Aspen Plus® and vice-versa.
