Optimization and feasibility analysis of pressure swing distillation for the separation of formic acid, propionic acid, and water azeotropic mixture

Abstract This study evaluates the performance of Pressure-Swing Distillation (PSD) applied to the separation of a ternary azeotropic mixture composed of formic acid, propionic acid, and water. Two pressure levels — atmospheric and a reduced pressure of 0.133 bar — were selected based on the relative volatilities of the components, in order to overcome azeotropic constraints. It was observed that formic acid is more effectively separated at low pressure, while propionic acid is efficiently recovered at atmospheric pressure. Water can be extracted at either pressure depending on its concentration in the feed mixture. Successive four-column configurations enabled effective component separation. Formic acid reached a purity of 99.9% with an overall recovery rate of 86%, accounting for 50.1% of the total energy consumption. Propionic acid was recovered at over 92%, consuming 54.57% of the energy, while water—though more energy-intensive—achieved 97.2% purity with an 89% recovery rate. Feed composition and operating conditions strongly influence both the reflux ratio and energy requirements, especially when the mixture approaches azeotropic composition. Depending on the scenario, the components were recovered in one to three steps, based on their physicochemical properties. Although four columns proved sufficient in the base configurations, the targeted addition of extra columns helped enhance overall separation efficiency. Overall, the results confirm that the PSD process is a robust, adaptable, and industry-relevant method for purifying complex mixtures containing carboxylic acids.