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.