HYSTERESIS-DEPENDENT ADSORPTION-DESORPTION CYCLES - GENERALIZATION FOR ISOTHERMAL CONDITIONS

Hysteresis-dependent adsorption-desorption equilibrium cycles are measured for the systems water vapor-silica gel at 25-degrees-C. Various and distinct types of equilibrium cycles are observed, depending on the relative positions of the limiting partial pressures with respect to the closure points of the main hysteresis loop as well as the history of the cycle. Hysteresis-dependent cycles are classified accordingly. The simple theoretical model based on the network pore blocking theory for predicting primary and secondary adsorption and desorption isotherms (Rajniak and Yang, 1993) is extended for predicting isotherms of higher orders and equilibrium cycles of all types. Only primary adsorption and desorption isotherms are needed for the predictions. Furthermore, there exists an infinite number of equilibrium cycles between any two partial pressures within the main hysteresis loop; the exact path of the cycle depends on the history before the cycle is initiated-it is memory-dependent.