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

Abstract

The zero length column technique has been developed over the past 30 years as a versatile experimental method to measure adsorption equilibrium and kinetics. In this review we discuss in detail the theory that forms the basis for the technique in order to understand how to design and operate efficiently a system. Experimental checks that should be performed to ensure the correct interpretation of the dynamic response are presented and examples are used to identify how to avoid major errors in determining diffusion time constants. The review concludes with an overview of all experimental studies available in the literature to date and a set of recommendations that should help improve the standard in the reported equilibrium and kinetic properties.

Cation Ordering and Exsolution in Copper‐Containing Forms of the Flexible Zeolite Rho (Cu,M‐Rho; M=H, Na) and Their Consequences for CO2 Adsorption

“…The ZLC method is in essence a chromatographic technique, whereby the desorption of a previously equilibrated adsorbent is monitored. [48,49] Equilibration occurs in the dilute mixture of adsorbate in inert carrier, whereas desorption takes place in the pure inert carrier. The small amount of sample allows for neglecting external mass and heat transfer resistances and the short length of the column allows for treating the system as a well-mixed cell (CSTR), due to negligible axial concentration gradients.…”

Material Screening for Gas Sensing using an Electronic Nose: Gas Sorption Thermodynamic and Kinetic Considerations

“…This is analogous to a packed bed in chromatography/adsorption when the length of the column tends to zero. 43 Therefore, the component mass balance for the gas j is written as…”

Diffusion in Nanoporous Solids in the Focus of IUPAC – A Tribute to Jens Weitkamp

“…Attribution of the macroscopically observed features to their ''microscopic'' origin needs particular care. The spectrum of techniques applicable for this purpose includes uptake and release measurements with loose beds of particles [92], liquid-phase batches [93] and packed-bed columns [94], as well as their ''variants'' such as the zero-length column (ZLC [95]) and the frequency response (FR [96]) techniques. Macroscopic diffusion measurements are also possible via NMR imaging (MRI) [97] and X-ray computed tomography (XCT) [98].…”

“…A given technique of measurement may, correspondingly, under certain conditions happen to be more properly assigned to another category. This refers to, e.g., uptake and release measurements [92,95,96] if performed with only a small amount of adsorbent particles so that bed effects may be excluded. The thus attainable information may indeed be referred to as meso-rather than macroscopic.…”