Process Design Aspects of Gas Absorbers

Abstract

Equipment which is used in contacting a gas with a reactive liquid can be gas absorber or a gas-liquid reactor. This terminology itself shows the interdisciplinary nature of the process which involves both chemical (i.e. reaction kinetics) and physical (molecular diffusion, fluid mechanics etc.) phenomena. Thus the subject does not fall entirely within the province of either the chemist or the conventional engineer. The classical literature on this area (Astarita (1), Danckwerts (2), Sherwood et al. (3) etc.) has mainly dealt with gas absorption, in which the reaction is applied merely to enhance the rate of mass transfer. In such cases, there is also always a physical gas absorption process to refer to and the reactions are usually “fast”. On the other hand, many industrial reactions in organic chemistry such as oxidations and chlorinations (4), are relatively slow and the main emphasis is the conversion of the liquid phase product. Therefore, two approaches may be used to characterize the interaction of mass transfer and chemical reaction between components of a gas and a liquid, one expressing the enhancement effect of a relatively fast reaction on the physical mass transfer leading to the classical concept of the “enhancement factor” (1–3) and a second, a relatively new one, expressing of slowing down of the already slow reaction rate by mass transfer and leading to the “Utilization factor” (5,6).