Breakthrough analysis for adsorption of sulfur-dioxide over zeolites Arun Gupta, Vivekanand Gaur, Nishith Verma * Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 2028016, India Received 31 July 2002; received in revised form 13 December 2002; accepted 15 December 2002 Abstract The adsorption experiments were carried out under dynamic conditions for the removal of trace sulfur-dioxide (SO 2 ) in nitrogen by 5A zeolites. The experiments were conducted to characterize the breakthrough characteristics of SO 2 in a fixed bed under different operating conditions including temperature, pellet size, concentration levels, and gas flowrate. At a reaction temperature of 70 8C, the breakthrough time was found to be maximum. The adsorption isotherm was found to be linear over the gas concentration range from 1000 to 10 000 ppm. The exothermic heat of adsorption assuming Arrehenius type of temperature dependence of the equilibrium constant was determined to be 9.8 kc/mol. The mathematical model was developed to predict the breakthrough profiles of SO 2 during adsorption over the biporous zeolites (containing both macro and micro-pores). The model incorporates all resistances to mass transfer, namely: diffusion in the gas film around pellets in the bed, diffusion in the binder-phase of zeolites and within the crystals, and adsorption/desorption at the interface of binder-phase and crystals. The model was successfully validated with the observed experimental breakthrough data. The study showed potential application of 5A zeolites in controlling SO 2 emissions at trace levels. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Zeolites; Breakthrough; Adsorption; SO 2 ; Air pollution 1. Introduction There are two types of solid (ad)sorbents commonly used in controlling SO 2 emissions: one is non-regenera- tive. The common examples are CaO and MgO obtained from different sources such as hydroxide, carbonate and acetates. The other is regenerative, such as zeolites, silica gel, and charcoal. A number of studies pertaining to the use of non-regenerative type of sorbents have been reported in open literature [17  /20]. These range from the theoretical analysis for understanding the mechan- ism and kinetics of the sorption process to the develop- ment of novel materials having relatively higher reactivity for SO 2 , to the improvement in the solid  / gas contact patterns. Despite significant progress made over the last few years in exploiting the non-regenerative type of materials, the premature termination of the sorption process due to pore-blocking by the product sulphate layers remains the major inherent drawback of these materials. The chemical reaction being irreversible, the commercial value of the spent solids is also often marginal. It is in this context that zeolites have been in the recent forefront of many researchers. The major advantage of using zeolites is their ability for the successive regeneration. The reaction temperature is also relatively lower. Successfully commercialized in early seventies in the area of bulk gas separation due to their molecular sieving properties, the application of zeolites in air pollution control has just begun to emerge. It may, however, be pointed out that zeolites in the latter application are used due to their adsorption character- istics rather than molecular sieving actions. Reviewing recent works reported in open literature, it is fair to say that a limited number of studies have been carried out on the adsorption of SO 2 over zeolites. Among some of the pertinent studies, Kopac [1] has investigated adsorption properties of SO 2 on molecular sieve 13X under equilibrium conditions in a temperature range of 523  /673 K and reported a significant adsorp- tion of SO 2 below 523 K. The adsorption equilibrium constants were experimentally determined over the * Corresponding author. Tel.:  /91-512-597629; fax:  /91-512- 590104. E-mail address: nishith@iitk.ac.in (N. Verma). Chemical Engineering and Processing 43 (2004) 9  /22 www.elsevier.com/locate/cep 0255-2701/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0255-2701(02)00213-1