Adsorption and separation properties of n-pentane/isopentane on ZIF-8

Adsorption equilibrium and kinetic data is essential for the design of an adsorption process. In this work, the adsorption isotherms of n-pentane/isopentane on zeolitic imidazolate framework material (ZIF-8) were measured at 308, 343 and 373   K over the pressure range from 0 to 9.7   kPa by a gravimetric system. The equilibrium adsorption capacity at 303   K and 9.7   kPa is 0.2504   g   g −1 for n-pentane and 0.1439   g   g −1 for isopentane. Langmuir model was used to fit the adsorption isotherms. The adsorption kinetics of n-pentane/isopentane was studied at 308   K in the pressure range from 0 to 69.9   kPa. The data was well fitted with linear driving force model (LDF) model. The adsorption rate constant of n-pentane is from 0.0019 to 0.0326   s −1 , which is higher than that of isopentane, represented 0.0007–0.0036   s −1 . The adsorption selectivity of n-pentane/isopentane on ZIF-8 was contrast by the measurement of the binary breakthrough experiments at 343   K, 363   K and 393   K in the partial pressure of 7   kPa. When the adsorption temperature is 363   K, the adsorption selectivity of n-pentane/isopentane on ZIF-8 reaches the maximum 55. Compared with 5A molecular sieve, the desorption temperature of n-pentane on ZIF-8 was analyzed by temperature-programmed-desorption (TPD) method. The peak temperature of n-pentane desorption on ZIF-8 is 361   K. However are 392   K and 443   K on a 5A molecular sieve. Thus, ZIF-8 is more selective or preferential adsorption for n-pentane in comparison to isopentane molecules at low temperature.