New adsorption studies with different adsorptives: investigation of ultramicropores (Zeolite 4A)

Zeolites are often used for moisture removal, e.g. in filter dryers. The high drying performance of zeolite 4A illustrates that water molecules with a critical molecular diameter of 0.26 nm can easily penetrate the 0.4 nm (4 Å) pores of the zeolite at room temperature, but also smaller molecules such as N2, O2 or CO2.

Looking at the adsorption isotherms of N2 at 78 K, H2 at 78 K, and of CO2 at 195 K (see figure), it is evident that zeolite 4A adsorbs very little nitrogen under these conditions, whereas significant adsorption is evident with H2 and CO2.

Zeolite 4A isotherms of H2 at 78 K, CO2 at 195 K, and N2 at 78 K

Zeolite 4A isotherms of H2 at 78 K, CO2 at 195 K, and N2 at 78 K

The reason for this is that during the N2 adsorption experiment at 78 K, kinetic hindrance of the adsorptive occurs and therefore no significant amounts of N2 are adsorbed by zeolite 4A, as also shown by other scientific studies. Nitrogen is not suitable as an adsorptive for pore sizes below 0.5 nm. Ultramicropores should therefore always be characterized using CO2 or H2 as adsorptive. Until now, this has been a challenge, since the temperature control of such measurements was only possible with the use of a cryocooler (very energy- and cost-intensive).

3P Instruments now offers a cost-effective and easy way to temper adsorption measurements in the range 82 K – 323 K with an accuracy of ± 0.004 K: the cryoTune temperature controller. Find out the possibilities in our video:

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