Theory of zero length column chromatography with the condition of a well-stirred sorbing zone

The zero length column technique to measure adsorption equilibrium and kinetics: lessons learnt from 30 years of experience

“…They used a numerical software tool to fit the entire desorption curve, but what was surprising was the fact that the slopes of the long-time asymptotes were concentration dependent. This is contrary to the basic theory, considering that the system follows a Langmuir isotherm (Micke et al 1993(Micke et al , 1994). This example makes it possible to discuss the importance of the correct choice of the baseline of the signal.…”

“…The importance of understanding the qualitative behaviour of a ZLC under nonlinear conditions becomes more evident with two examples from experienced adsorption groups. Micke et al reported ZLC experiments where they measured concentration dependent diffusivities for benzene in H-ZSM5 (Micke et al 1993(Micke et al , 1994. They used a numerical software tool to fit the entire desorption curve, but what was surprising was the fact that the slopes of the long-time asymptotes were concentration dependent.…”

On the Diffusion of Cyclohexane in ZSM-5 Measured by Zero-Length-Column Chromatography

“…Conflicting work has been published on the effect of a nonlinear adsorption isotherm , on the ZLC. It would appear that the earlier work was in error, the latter paper providing an intuitively more correct result, i.e., that the low-concentration region of the desorption curve is similar to that for a linear isotherm and the zero loading diffusivity may still be measured.…”

“…The effect of external film mass-transfer resistance on the desorption curve has been briefly mentioned, 6 and the effect of incomplete saturation during the equilibration stage of the experiment has been analyzed. 7 Conflicting work has been published on the effect of a nonlinear adsorption isotherm 8,9 on the ZLC. It would appear that the earlier work was in error, the latter paper providing an intuitively more correct result, i.e., that the low-concentration region of the desorption curve is similar to that for a linear isotherm and the zero loading diffusivity may still be measured.…”

Determination of Diffusion Coefficients in Porous Media

“…(19). Analytical solutions for various models may be found in the literature [115,[120][121][122][123], including the application to liquid-phase counter-diffusion measurements [124]. In this technique, which has proved to be particularly useful for the observation of fast sorption phenomena, a small sample of adsorbent (in general only consisting of microparticles of radius R) is equilibrated at a uniform sorbate concentration and then desorbed by purging with an inert gas at a flow rate high enough to maintain essentially zero sorbate concentration at the external surface of the particles.…”