EFFECT OF COKE DEPOSITION ON TRANSPORT AND ADSORPTION IN ZEOLITES STUDIED BY A NEW MICROBALANCE REACTOR

Coke formation and the effect of coke on transport and adsorption beha viour of a commercial HZSM-5 zeolite has been studied by means of an o scillating microbalance. This transient technique provides a powerful tool for in situ studies of adsorption and diffusion in coked zeolites . Adsorption experiments at 30 degrees C involving ethane, toluene and n-hexane were carried out before and after coke formation during ethe ne oligomerization at 475 degrees C using a partial pressure of ethene of 0.8 bar. Both adsorption rates and equilibrium adsorption were stu died. Information about the location of coke was obtained from changes in characteristic diffusion time and adsorption capacity with coke co ntent. Distinct deactivation modes such as site coverage, pore blockin g and external coking were identified at different coke levels. Change s in characteristic diffusion time were found to depend on both coking level and coke location, which influenced either the diffusivity or t he diffusion path.