Experimental study on adsorption characteristics of SAPO-34 zeolite and silica gel in vacuum condition

Using the gravimetric method the adsorption characteristics of SAPO-34 zeolite and silica gel to water vapor in vacuum condition have been experimentally studied. Comparisons of the result in vacuum condition to the result in moist air condition were carefully conducted. It was found that the equilibrium adsorption concentration of the two materials in vacuum condition was higher than the equilibrium concentration in moist air under the same condition. Also, the adsorption time to reach the equilibrium state was greatly shortened in vacuum cases. The maximum time shortening was up to 48.1% for the SAPO-34 zeolite and 38.8% for the silica gel as compared to the time of the moist air cases. With an anti-S type of the adsorption isotherm curve the concentration change of the SAPO-34 zeolite was insensitive in the middle pressure range, while the concentration change of the silica gel was more sensitive in the middle pressure range with a S type isotherm curve. The existing Freundlich equation and S-B-K equation did not fit well the adsorption isotherm of the SAPO-34 zeolite and the silica gel. Therefore novel correlations were proposed and they fitted the experimental data with much better accuracy.