A. D~browski and V.A. Tertykh (Editors) Adsorption on New and Modified Inorganic Sorbents Studies in Surface Science and Catalysis, Vol. 99 9 1996 Elsevier Science B.V. All rights reserved. 629 Chapter 2.12 Drying of gases and liquids by activated alumina S. Sircar, M. B. Rao and T. C. Golden Air Products and Chemicals, Inc., 7201 Hamilton Boulevard, Allentown, PA, 18195, USA 1. INTRODUCTION Removal of trace and bulk water from a fluid (gas or liquid) stream is a major unit operation in the chemical and petrochemical industries [1-3]. The drying process is neces- sary to (a) prevent condensation and freeze-out of water in plant pipeline and equipment, (b) eliminate corrosion in process equipment, (c) protect against undesirable chemical reactions such as hydration, hydrolysis, etc., (d) prevent catalyst poisoning, and (e) meet product fluid composition specification. Selective adsorption of water on a solid desiccant such as zeolites, silica gels and activated aluminas is often used as the method of drying the fluid stream. Various forms of cyclic pressure swing adsorption (PSA) and thermal swing adsorption (TSA) concepts are generally used as the drying process. These pro- cesses utilize regenerative schemes consisting of adsorption and desorption steps so that the adsorbent can be repeatedly used for drying the fluid stream. The design and cost of operation of these processes demand certain properties for adsorption of water by the adsorbent which facilitate the adsorption and desorption steps. Activated aluminas often provide a large spectrum of desirable adsorptive properties for such drying applications. These properties include adsorption equilibria, adsorption kinetics, heats of adsorption, and adsorption and desorption column dynamics which govern the performance of the drying process. This chapter briefly describes these properties for adsorption of water on various forms of alumina and illustrates several conventional drying processes using alumina. 2. PHYSICOCHEMICAL STRUCTURE OF ALUMINA Most aluminas are produced by precipitation from an aluminate solution using the well-known Bayer process [4]. Numerous stable and transitional forms of alumina can be formed. The thermodynamically stable forms such as alpha alumina are of little use for drying application because of their low surface areas and porosities. The transitional aluminas such as gamma and eta which are formed by thermal dehydration of aluminum hydroxides are mostly used as desiccants. They consist of A1 +3 and 0 .2 ions bonded in either tetrahedral or octahedral coordination. The resulting crystal structure is cubic or hexagonal closed packed. Generally, the oxygen sublattice is fairly well organized and