Analysis of Competition between Multicomponent BTX Compounds for the Active Site of Adsorption in a Fixed-Bed Column Adriana Dervanoski da Luz,* ,† Selene Maria de Arruda Guelli Ulson de Souza, † Cleuzir da Luz, † Josiane Maria Muneron de Mello, ‡ and Antônio Augusto Ulson de Souza † † Chemical Engineering Department, Federal University of Santa Catarina, Laboratory of Numerical Simulation of Chemical Systems, Campus Universita ́ rio, 88040-900 Florianó polis, SC, Brazil ‡ Environmental Sciences Postgraduate Program, Chapecó Region Community University. PO Box 1141, 89809-000, Chapecó , SC, Brazil ABSTRACT: An experimental and numerical study of the individual and competitive adsorption of BTX compounds (benzene, toluene, and o-xylene) in aqueous solution was carried out in a fixed-bed column filled with activated carbon. The equations of transport were discretized using the finite volumes method and an algorithm was implemented in the Fortran programming language. The results obtained in all cases showed that o-xylene is the contaminant which is most competitive for the active site of the adsorbent, and over time it is able to desorb the compounds which have a lower affinity and adsorb to the free active sites. The result is that the local concentration of the weakly adsorbed component in the fluid phase is higher and surpasses the dimensionless concentration. This finding appeared to be related to the Biot number. As the Biot number increased the rate of competitive adsorption decreased, and the form of the breakthrough curves is flat with a lower breakpoint. This is due to the low intraparticle resistance and also the reduced contact time required to reach saturation. 1. INTRODUCTION The removal of volatile organic compounds (VOCs), such as benzene, toluene, and xylenes, collectively known as BTX, from effluents produced by the petrochemical industry is of considerable interest because of the harmful effects of these contaminants. 1-4 BTX compounds are powerful central nervous system depressants, with chronic toxicity and mutagenic potential even at low concentrations. Benzene is among the most toxic compounds due to its carcinogenic activity, causing leukemia and tumors in multiple organs. Acute exposure by inhalation or ingestion can even cause death in humans. 5-7 Environmental legislation, monitoring instruments, and economic implications have been key instruments of environ- mental policy related to the release of these effluents. Thus, studies have been directed to the treatment of polluted streams (integrated approach) and the final effluent treatment (end-of- pipe approach), for which the adsorption method has been used quite effectively. 8-11 Investigations on the removal of most hydrocarbon groups, particularly VOCs, by adsorption have focused on the individual components. 10-16 However, in industrial effluents there is a mixture of toxic compounds to be removed. The experimental measurement of the multicomponent adsorption equilibrium is complex, especially when the number of components exceeds two. 17-20 An optimized design for multicomponent adsorption must take into account the interactions between the mixture of compounds and various factors associated with the physical and chemical nature of the adsorbent and the adsorbate. Thus, the design process must proceed through experimentation with the subsequent development of rigorous mathematical models that can be used to validate the numerical methodology and prediction of different operational conditions. 21 The study of these effects is of great importance for obtaining the appropriate operating conditions in an adsorption column for multicomponent removal in a continuous process. Studies to determine the characteristics of the adsorption process in relation to the removal of VOCs in multicomponent solutions showed very good performance when activated carbon was used as the adsorbent. 2,22,23 According to Wibowo et al., 13 Leitã o and Rodrigues 24 and Chatzopoulos et al., 25 adsorption with activated carbon is a proven and reliable technology for removing small amounts of soluble organic compounds from water and wastewater, which can thus be reused several times in the same process. The aim of this study was to investigate the single- component and multicomponent adsorption of BTX com- pounds using thermally activated carbon (obtained from coconut shell) as the adsorbent. The parameters of the thermodynamic equilibrium were obtained from Luz et al. 2 and the isotherm model which best represented the equilibrium data was the Langmuir model (mono- and multicomponent). Multicomponent adsorption tests were carried out in a fixed- bed column in order to verify the competition between contaminants for the active site of the adsorbent. The results for the multicomponent adsorption were compared with those obtained for the individual compounds. In the case of the bicomponent mixtures, all combinations were tested and the concentration of each contaminant was 50 mg/L. The same concentration was used for each contaminant in the Received: July 29, 2013 Revised: October 25, 2013 Accepted: November 15, 2013 Published: November 15, 2013 Article pubs.acs.org/IECR © 2013 American Chemical Society 16911 dx.doi.org/10.1021/ie402452h | Ind. Eng. Chem. Res. 2013, 52, 16911-16921