Studies on transport properties of short chain aliphatic carboxylic acids in electrodialytic separation

An electrodialysis process was employed to investigate the concentration of formic, acetic and propionic acid solutions under different experimental conditions. In this process interpolymer-type ion-exchange membranes were used due their high chemical stability and durability. The effects of concentration, electric current and time on the electrodialysis process were studied. A mathematical equation representing the water transport behavior of the electrodialysis process for concentrating acids under the influence of different current densities was developed. This equation is valid for any electrodialysis process with ion-exchange membranes used under similar operating conditions. The reliability of the water transport equation was tested through comparison with the experimental data. Results indicate that electrodialysis is an effective method for concentrating shorter chain aliphatic carboxylic acid solutions. Ionic transportation, power consumption and current efficiency data reveal the following trend of the electrodialysis process’s efficiency during concentration of carboxylic acid solutions: formic acid > acetic acid > propionic acid.

— E — F i I n — — — — Q — t v dV/dt — — — Carboxylic acid concentration at time t in the CS, M Carboxylic acid initial concentration in the CS, M Carboxylic acid concentration at time t in the DS, M Carboxylic acid initial concentration in the DS, M Power consumption in kWh/kg of acid removed Faraday constant Current density, A/cm2 Current, A Number of ion-exchange membranes cell pairs in ED unit Amount of electricity passed, Coulomb Time Applied potential, Volt Slope of the variation of volume of CS with time, ml/s VCt VC0 Vdt Vd0 — — — — Volume of CS at time t, ml Initial volume of CS, ml Volume of DS at time t, ml Initial volume of DS, ml Greek " $ — — Phenomenological coefficient Phenomenological coefficient