Investigation of Breakthrough Curves of Citric Acid Adsorption

Citric acid is the most widely used organic acid in the field of foods and beverages as an acidulant as well as in pharmaceutical and chemical products. Generally, surface or submerged fungal fermentation mainly with aspergillus niger is utilized for citric acid production. However, the submerged fermentation method is the most used method for citric acid production.1,2 The method of calcium salt precipitation is an established process for citric acid purification. a series of precipitation and isolation reactions using Ca(OH)2 and H2SO4 can be exploited for citric acid separation from fermentation broths.3,4 However, this process includes several batch treatments in which huge amounts of chemical reagents and a large amount of heat are required. These negative factors have directed many investigators to find new techniques to separate or purify citric acid from fermentation broths, such as adsorption and electro-dialysis.5,6 Electro-dialysis as an electrochemical separation process charged the membranes electrically. For separation of ionic species from aqueous solutions, electrical potential difference is used. The electro-dialysis was used in citric acid recovery. However, the main problem is that the costs of this technique were determined to be approximately 50 % higher compared to the current industrial citric acid recovery process. The use of electro-dialysis requires the development of new processes to decrease waste formation and enhance productivity.7 Purification of organic acids, particularly citric acid, by adsorption process has lower production costs compared to other methods. Attention has been drawn to the novel use of synthetic ion-exchange resins in separation and purification of organic acids.8,9 This set of adsorbents acts selectively and other components of solution remain intact. After saturation of solid adsorbent at the end of a separation operation period, it is recovered by elution with water, acid or base. Although the principle of organic acids separation by ion-exchange method is known, there are many details that require development and increment. Thus, it seems that Simulated Moving Bed (SMB) by using chromatography method on the base of countercurrent continuous contact between feed and adsorbent is appropriate and effective.10,11 SMB is a continuous chromatographic method which requires determined parameters like ion-exchange resins properties, adsorption equilibrium data, and operating characteristics of bed. One of the best methods to specify and optimize operating parameter is to prepare a fitting mathematical model from actual processes. Generally in such models, mass transfer in liquid layer outside the resin particles is negligible. The general ion-exchange reaction of resin is presented in eq. 1.12–14