Extractive Distillation of Acetic Acid from its Dilute Solution using Lithium Bromide

Separation and purification are an integral part and a major cost factor in the chemical industry. Distillation is a very commonly used for solvent separation and purification process. It is neither cost effective nor process efficient when dealing with close-boiling and azeotropic solvent mixtures without modifying the relative volatility of the solvent components with an extraneous solvent or a non-volatile solute electrolyte or nonelectrolyte. The selection of a suitable modifier generally depends on the experimental determination of its effect on the Vapour–Liquid Equilibrium (VLE) of the solvent mixture. Acetic acid is most widely used as aliphatic carbonic acid. It is frequently used as a solvent like in manufacture of cellulose acetate or in manufacture of many pharmaceutical products. Aqueous acetic acid is obtained during these processes and recovery of which is of great significance. Separation of pure water from dilute solution of Acetic acid –water mixture in the concentration range of 1 % to 30 % Acetic acid by simple rectification is almost impossible as relative volatility of the mixture in this range approaches unity.We would then require towers with large number of stages which would be operated with high reflux ratio and required high energy costs and operating costs. In practice extraction with suitable solvent is carried out before pure recovery occurs during the rectification of azeotropic mixture. An alternative separation process is the addition of Lithium Bromide(LiBr) salt into acetic-acid water solution . Lithium bromide is largely soluble in water. Addition of salt will increase the boiling point of salt-water solution, there by separating comparatively pure acetic acid as overhead product. LiBr–water solution remains as residue from which LiBr can be readily separated by evaporation and reused. Experiments are carried out in laboratory with different concentrations of Acetic acid-water, in Othmer still which is vapor-liquid equilibrium apparatus. An Extractive distillation column will be designed based on experimental results. Cost analysis of this new separation technique will be carried out. The experimental data will be correlated to any model to calculate activity coefficients. Words: Vapor liquid Equilibrium, Lithium bromide, Extractive distillation, recovery of acetic acid, Othmer still