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Abstract:
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A stepped isothermal pressure change method for the investigation of water desorption from zeolites has been developed. Stepped isothermal evolved gas analysis (SI-EGA) utilizes static methods, in a unique way, to determine kinetic data. This method produces isothermal kinetic data. The problems associated with dynamic methods are reduced by the use of an isothermal method. Zeolites NaY, NaX, and CaX have been investigated to determine if the SI-EGA method yields reliable kinetic data. This method consists of multiple expansions into vacuum carried out through a temperature range. The results of the SI-EGA experiments show water desorbing from zeolites NaY, NaX, and CaX with apparent energies of desorption (Ea) of 34 ± 3 kJ/mol, 16.9 ± 0.4 kJ/mol, and 40 ± 1 kJ/mol respectively. The results also give preexponential factors (Aa) of 156 ± 121 sec-1, 0.5 ± 0.1 sec-1, and 744 ± 295 sec-1 for zeolites NaY, NaX, and CaX, respectively. The results confirm that the SI-EGA method produces reliable kinetic data for water desorption from zeolites. A refinement of the SI-EGA method could be useful for the investigation of desorption from microporous solids. |
