Contactors for Chemical Separation

Abstract

In the chemical process industry, separation of mixtures into streams of high purity compounds is frequently necessary. Mixtures may originate from feedstock impurities, incomplete conversion of the reactants, and/or occurrence of undesirable side reactions. Feedstocks for the process industry are often complex mixtures such as mineral oil, coal, petroleum distillates, or vegetable fats. It is often desirable to separate the components of these mixtures prior to use. For the separation of mixtures a large number of processes and techniques have been developed. These are divided into two classes. The first is composed of separations based on differences in physiochemical properties, eg, boiling point in the case of distillation, and diffusivity in some membrane applications. The second class of separation is achieved by means of a selective chemical reaction. Examples include removal of acidic gases, carbon dioxide, and hydrogen sulfide, and hydrogen. This article discusses the second class with emphasis on contactor selection. The implementation of a chemical reaction is rarely simple. Reactor selection, regeneration of intermediate products, and possible degradation of the various components must be considered. The selection or design of a contactor is also complicated, even when the a classical contactor is used. For new processes, the various steps in the chemical reaction must be identified, eg, mass transfer, diffusion and chemical reaction, reaction schemes or networks, by product formation, etc, must all be considered. This identification is often too expensive to follow in commercial development so only partial knowledge of the elementary process may be obtained before proceeding. When more detailed knowledge of the reaction is available, selection or design of a special contactor exclusively devoted to the duty of the chemical separation process is possible. This article gives details for separation processes involving gas‐liquid systems, gas‐solid systems, and slurry contactors