Application of an Air-Operated Impinging Streams Contactor in Liquid-Liquid Extraction By Asghar Molaei Dehkordi,* Tahereh Kaghazchi, and Morteza Sohrabi An experimental study was conducted on the liquid-liquid extraction of isobutyric acid by means of cumene from its aqueous solutions in an air-operated impinging streams contactor (AOISC) with spray nozzles. Aqueous and organic streams may or may not contact one another inside the spray nozzles depending on the modes of operation. The overall volumetric mass transfer coefficient, K L a, determined enabled us to evaluate the performance capability of the contactor. The effects of air and solution flow rates, contactor length and diameter, impingement zone as well as modes of operation have been investigated. These experimental results verify the capability of the method of impinging streams in liquid-liquid extraction. 1 Introduction The separation of the constituents of a homogeneous liquid mixture is a problem frequently encountered in the chemical processing industry. Liquid-liquid extraction has been used as a very important method for separating such liquid mixtures. The industrial applications of liquid-liquid extraction are extensive. Typical applications of such a process are in hydrometallurgy, polymer processing, effluent treatment, pharmaceutical, food and petroleum industries. Impinging streams (IS), used as a method for enhancing heat and mass transfer processes, have been studied by Elperin [1] and further developed by Tamir [2]. It provides a powerful technique for intensifying transfer processes. The principle of impinging streams is to bring the two streams, flowing along the same axis in opposite directions, into collision. As the result of such a collision, a relatively narrow zone, called the impingement zone of high turbulent intensity, is created which offers excellent conditions for intensifying heat and mass transfer rates. In this zone, the number density of drops is the highest and continuously decreases towards the inlet point of streams. This technique can be implemented in gas-liquid, solid-liquid and liquid-liquid systems. At the zone of impingement, drops penetrate into the opposite stream due to their inertia and decelerate until stagnation due to the gas drag force. Afterwards, the drops accelerate and penetrate into the original stream, and so forth. Thus, drops perform damped oscillations. After performing several oscillatory motions as such, the particle velocity eventually vanishes before it is withdrawn from the system. The latter might occur even earlier due to either interdroplet collisions or collisions with contactor walls. The method has been successfully applied for absorption and desorption of gases [3–7], dissolution of solids [8], drying of solids [9], dust collection [10], absorption with chemical reactions [11,12], two-phase chemical reaction [13], mixing [14], evaporative cooling of air [15], bioreaction [16], and extraction in thin film generated by impinging streams [17]. On the basis of Tamir’s extensive investigations, it may be concluded that almost all processes in chemical engineering can be carried out by applying the IS method presumably with a higher efficiency in comparison with conventional methods. The great potential of the IS technique in chemical processes, on the one hand, and the absence of its application (air operated) in liquid extraction, on the other hand, was the major motivation for the present investigation. It should be noted that the application of such a technique in liquid extraction using spray nozzles operated with compressed liquids finds elsewhere [2]. The major objective of the present study was to apply and test an air-operated impinging streams contactor (AOISC) for extraction processes. In order to achieve this goal, an experimental investigation on the extraction of isobutyric acid from water using cumene applying an AOISC with spray nozzles has been conducted. In our experiments, the effec- tiveness of the two impinging streams contactor was tested by placing a partition in the middle of the extraction compart- ment that divided the latter into two halves. Thus the two opposed streams entering the contactor did not interact. 2 Experimental Section 2.1 Apparatus The experimental apparatus, shown in Fig. 1, consists of the following parts: (1) a cylindrical vessel made of Pyrex glass with various dimensions of D (m)  L (m) = 0.064  0.60, 0.078  0.60, 0.094  0.60, 0.11  0.60, 0.12  0.60 in order to study the effect of contactor diameter and contactor length on the extraction efficiency; (2) spray nozzles made of stainless steel (SS), by which liquids could be sprayed using air. The latter were placed on the two movable coaxial circular plates made of Teflon, positioned against each other at the two ends of the contactor. By moving the plates away from or towards each other the length of the contactor could be varied. The design of nozzles has some significant effects on the drop size distribution and the velocity of phases. A schematic diagram of the nozzles is given in Fig. 2. Each nozzle consists of two basic sections: the main body and the middle part. The latter is Chem. Eng. Technol. 24 (2001) 2, Ó WILEY-VCH Verlag GmbH, D-69469 Weinheim, 2001 0930-7516/01/0202-0173 $ 17.50+.50/0 173 – [*] A. M. Dehkordi (author to whom correspondence should be addressed), T. Kaghazchi, M. Sohrabi, Chemical Engineering Department, Amirkabir University ofTechnology, Tehran, Iran; Fax: +98212071251 0930-7516/01/0202-0173 $ 17.50+.50/0 Full Paper