Effect of Coke in the Equilibrium and Kinetics of Sorption on 5A Molecular Sieve Zeolites

Porosimetric, gravimetric, zero length column (ZLC), and fixed-bed studies on coked pellets of 5A molecular sieve zeolites were performed. From porosimetric studies it seems that the coke is located in the microporous structure of 5A zeolite or as layers covering all crystals. The gravimetric studies 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. The 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 order 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 lower in coked pellets. The effect of temperature on the behavior of a fixed bed is also shown. A simple mathematical model with equilibrium and diffusivity parameters obtained from independent experiments predicts with good accuracy all fixed-bed adsorption and desorption runs.