Desiccants

Abstract Desiccants are classified by four drying mechanim: chemical reaction, physical absorption with constant relative humidity, physical absorption with variable relative humidity, and physical adsorption. Desiccants are further categorized by their use in static or dynamic drying applications. Various desiccants are discussed. Testing the compatibility of desiccants with the material being dried is briefly covered. The water capacity of some static desiccants and the efficiency (or effectiveness) of various desiccants in drying air and laboratory solvents are discussed. The dynamics of closed‐system drying is covered in some detail. Desiccants used in dynamic applications include both liquids (sulfuric acid, glycols) and solids (activated alumina, silica gel, molecular sieves). Solid adsorbent drying systems with multiple beds are described. The use of adsorption equilibrium plots and the influence of desiccant properties on mass transfer and useful dryer capacity is covered. The factors affecting cost‐effectiveness of desiccants are discussed, and some market data are given for solid adsorbent desiccants. Finally, the emerging uses of desiccants for energy storage and cooling are mentioned.