Will the zeolite be considered hydrated during adsorption isotherm calculations?
Experimentally, the zeolite should be degassed thoroughly before adsorption measurements to remove any moisture or adsorbed gases. Any adsorbed water will affect the pore volume and surface area results. For the benchmark studies, the degassing procedure mentioned in the BCR-704 certificate of analysis has been used. The procedure is based on thermogravimetric investigations of the zeolite material. The important steps of the procedure are described as below.
-
Starting at room temperature, the zeolite was heated up to about 80˚C under vacuum.
-
When a low residual pressure was achieved, the temperature was increased slowly up to 120˚C at about 1 Kelvin per minute. In this temperature range, the main portion of water was expelled.
-
Slowly increased the temperature up to 350˚C and continued evacuating between 5-16 hours. Overnight degassing is preferable.
The physisorption instrument works based on static volumetric method and there is no hydration during the analysis provided the adsorbate being used is of ultra high purity and free of moisture. (2012/08/22)