Deactivation modeling for the adsorption isotherm of deactivated adsorbents used in natural gas dehydration process

Abstract

Two types of adsorbents, activated alumina and molecular sieve zeoite 4A, used in the natural gas dehydration process were studied for their adsorption behaviour, both static and dynamic along the adsorption process. Deactivation by hydrothermal steaming was employed for deactivating the adsorbents. The effect of the deactivated adsorbents on the adsorption capacity was then studied. The results showed a decrease in the specific surface area of activated alumina, when hydrothermally steamed at 300 to 500C, from 200.2 to 124.0 m2/g. The adsorption capacity of the activated alumina decreased linearly with surface area. The adsorption capacity of the molecular sieve zeolite was also decreased by steaming, but not in a linear fashion, SEM analysis indicated a decrease in average crystal size from about 2 to 1 microns with the increase of steaming time. The adsorption isotherms of fresh and deactivated adsorbents were examined at 25C, latm, and it was found that Freudilch model gave good agreement for alumina, and aranovich and Donohue (A-S) for Toth model fitted the data of molecular sieve zeolite. Also, the adsorption isotherms are used in a previously developed mathematical model to predict the breakthrough time of the multi-layered adsorber. From the dynamic adsorption of a packed column with the fresh and deactivated adsorbents, it was found the breakthrough time of the deactivated bed was shorter than the fresh one. The predicted breakthrough time agrees well with the experimental one