Effect of coke in the equilibrium and kinetics of sorption on 5A molecularsieve zeolites

Porosimetric, gravimetric, zero length column (ZLC), and fixed-bed studies on coked pellets of 5A molecular sieve zeolites were performed. From porosi metric studies it seems that the coke is located in the microporous structu re of 5A zeolite or as layers covering all crystals. The gravimetric studie s between 473 and 573 K using n-pentane as a probe molecule show that Henry 's constants in coked pellets are much smaller than those in fresh ones. Th e kinetics of sorption measured by the ZLC technique is also significantly modified. The results show that the system changes from a macropore control resistance with the reciprocal of time constant D-p/R-p(2)(1 + K) on the o rder of 0.002-0.02 s(-1) in fresh pellets to a micropore control resistance system with reciprocal time constant D-c/r(c)(2) 1 Order of magnitude lowe r in coked pellets. The effect of temperature on the behavior of a fixed be d is also shown. A simple mathematical model with equilibrium and diffusivi ty parameters obtained from independent experiments predicts with good accu racy all fixed-bed adsorption and desorption runs.