A change in the composition (accompanied perhaps by a change of flow rate) of a binary gas mixture flowing into a column which can adsorb both species gives rise to a chromatographic transient. Observed at the outlet, this is seen as the concentration varying sigmoidally with time; there is also a flow-rate fluctuation. A theory has been developed which relates these transients to the phase-equilibrium properties. A retention time is defined for the concentration transient and another for the flow transient; the slopes of the equilibrium curves are shown to be explicit functions of these retention times. Experiments to determine the slopes at infinite dilution of the equilibrium curves for the simultaneous adsorption of argon and nitrogen on Linde 5A molecular sieve by measuring both the retention times are reported.

A simple model for describing residence time distributions (RTD) in packed beds is derived and applied to a trickle flow system. It is based on the concept of fluid elements being randomly delayed in time on their passage through the bed and leads to a simple and flexible rnathematical description.In this paper, we take a fresh look at factors governing the distribution of residence times of material flowing continuously through packed bed systems. The picture presented is simple and physically plausible with obvious application in a wide variety of continuous processes. It is based on the abstraction that material would flow uniformly (in plug flow) through the system were it not that elements have a chance of being detained at all points of their passage; an element so detained eventually rejoins the main stream after a period of time, the time delay, has elapsed. The cumulative effect of the individual time delays is to distribute the total residence times in some manner.For the most simple case in which delayed elements are all delayed for the same time tD, a mass balance on a differential element of bed length (Figure 1) yields This description leads to a family of models mutually differentiated by their delay time distributions. For any particular distribution, the model parameters will depend solely on the probability of a delay occurring and the average time for which elements are delayed. The mechanism is analogous to that of surface renewal in the penetration theories of mass transfer, in which fluid elements that find their way to the surface are detained and then returned to the bulk fluid. In the time-delay model, this effect is distributed through the system; bulk material flows at a uniform rate, while the delayed elements have negligible velocity in the direction of the main flow.This way of looking at the problem has certain very clear advantages over the usual models based on analogies with diffusion theory. These are discussed later, and it will be shown that time-delay models retain their mathematical simplicity when elaborated to suit particular physical situations. This is not so with diffusion models. The mathematically delicate (although often physically irrelevant) problems concerning choice of boundary conditions for diffusion models do not arise in the time-delay treatment. Also, the physical mechanisms resulting in the spread of residence times are often more accurately described by time delays then by diffusion. M. N. Rathor is with the

A new method to determine binary adsorption isotherms from a set of binary chromatographic retention-time experiments is proposed. It differs from existing methods in two main ways. The first is that a functional form is assumed for the isotherms. The second is that it does not require supplementary measurements to be made. The isotherm parameters are found by a computer search. Any other available data may be incorporated into the method. The method is tested on retention-time data for the coadsorption of nitrogen and argon on 5A molecular sieves and of ethane and ethylene on 13X molecular sieves. Very precise experimental data are required if the isotherms are to be reconstructed solely from retention data.

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