Universal solution of a family of sorption kinetic models which are based on superposition principle has been developed to describe sorption experiments in a closed system. The models account for the interactions of a sorbate-sorbent system with the apparatus which arise (i) from the mass balance condition in a closed system and (ii) from a finite rate of sorbate supply to the sorbent, the latter effect being of importance particularly in rapid nonstationary kinetic processes. Theoretical uptake curves for the intracrystalline sorption kinetics in zeolite crystals are exemplified using numerical solution of the corresponding Volterra integral equations which represent kinetic models of the overall transient sorption process in the apparatus. The approach appears to be promising for treatment of sorption kinetics in multi component systems. The Volterra Integral Equation (VIE) approach has recently been proposed to solve mathematical models of sorption kinetics from the gas phase measured under constant volume/variable pressure conditions 1. For fast sorption kinetics with characteristic times amounting to about one second, one arrives at the limits of the experimental method and thus, the valve used to start the experiment may distort the uptake curves considerably. In a previous publication 2 , the valve effect was analyzed thoroughly for a special type of sorption kinetics. The use of the VIE approach 1,3,4, offers a general way to compute sorption uptake curves affected by the limited rate of sorbate supply through valves and tubings of the experimental apparatus. In such a manner the limits of the experimental methods can in principle be displaced about one order of magnitude to lower intrinsic time constants of sorption kinetics whatever type of valve may be used. DESCRIPTION OF THE EXPERIMENT The principal scheme of the experimental piezometric apparatus is given i
