Optimal Pressure for Pressure Swing Distillation

Abstract

Distillation is the most common unit operation for separation used in the industry. Many times, the mixtures to be separated have closely related boiling points or are azeotropic systems. In these cases, the conventional distillation doesn’t work. In order to achieve the separation different forms have been developed to solve these cases. This work focus on azeotropic systems where the separation is achieved without the use of external agents. The pressure-swing distillation (PSD) allows the separation of the different components of the mixture making use of the sensitivity in the azeotropic composition which some mixtures have in front of different pressures. An exhaustive bibliographic study is presented on no reactive binary mixtures where the separation is being achieved by PSD. Out of this search 180 articles were selected which in a first selection have been reduced to 140. Of these 140 a synthesis and a critical analysis was conducted of each article followed by a classification applying different criteria. As consequence of the analysis more articles have been excluded for not complying with the specific conditions of the search leading to a final number of 49 articles. PSD has not been intensively studied, most of the publications in this field following the same criteria. This work will show that the majority of the investigations have been made following the criteria of the working pressure of the columns at 1 and 10 atmospheres and will be explained the considerations that have been taken in the investigations of the column pressures which have been optimized. Will also be explained the other classifications that have been applied at making the survey and will be concluded the general lines that have to be applied at selecting de PSD as method for the separation of the present mixture. Once the study had been concluded was found that there are very few cases in which the selection of the pressures had been made optimizing the process according the energetic cost of the reboiler. From the articles that have followed this criterium has been selected one and made the simulation to compare the results: the ethyl acetate - ethanol mixture studied by Zhang et al. (2017) was selected to study. A simulation of the mixture was conducted, using the program AspenPlus V10 with the parameters of the article and realizing the optimization with different pairs of pressures. Once the optimized values were obtained a total annual costs (TAC) was conducted in order to compare the results with those of the articles