Feasibility Study of for Separation of Formic Acid – Water- Propionic Acid By Pressure-Swing Distillation

The separation of the mixture formic acid - propionic acid - water into three high-purity products is difficult due to the presence of two binary and one ternary azeotropes that divide the ternary diagram into four distinct distillation regions. Fortunately, the compositions of these azeotropes change significantly with pressure. The pressure-swing distillation process was proposed for the separation of this ternary system. The process simulations were carried out using Aspen Plus 10 software. The effects of the number of theoretical stages (NT), feed stage (NF) and reflux ratio (R) were investigated to optimize the operating parameters of the pressure-swing distillation. The best operating process parameters were defined for systems containing 70% mol. in formic acid, 20% mol. in water and 10% mol. in propionic acid, It has been found that, the formic acid can be obtained in the distillate product in the first column operating at the pressure of 0.133 bar, then the water can be separated at pressure 1.013 bar in the distillate product in  second one and propionic acid can be obtained in the bottom product of the third column operating at 1.013 bar. Formic acid is recovered a second time from the distillate product of the fourth column operating at 0.133 bar to increase its yield. The carboxylic acid obtained products in the four distillation columns have a purity of more than 99.9% mol. and the water product have a purity more than 97.0% mol. The residue stream from the fourth column is recycled to the first column.