Isotherms are of paramount importance for the interpretation of adsorption and ion exchange mechanisms and the design of separation and catalytic processes. Although the literature on sorption isotherms is rich, most of experiments and models employed are limited to systems that obey simple equilibrium isotherms, such as linear, favorable (convex-upward) or unfavorable (concave-upward). This paper deals with the rather overlooked S-shaped isotherms and their dimensionless forms, which are of great importance for the modeling of separation processes and interpretation of equilibrium data. A review on the physical significance and applications of S-shaped isotherms in adsorption and ion exchange process is also presented.

等温线对于解释吸附和离子交换机理以及分离和催化过程的设计至关重要。尽管关于吸附等温线的文献很多，但大多数采用的实验和模型都限于遵循简单平衡等温线的系统，例如线性，有利（凸上）或不利（凹上）。本文讨论了被忽略的S形等温线及其无量纲形式，这对于分离过程的建模和平衡数据的解释非常重要。综述了S形等温线在吸附和离子交换过程中的物理意义及其应用。