Evolution of Coke Formation and Its Effect on β-Zeolite in Catalytic Cracking

Deactivation by coke formation is a very important feature in catalytic cracking. The evolution of coke and its effect on the catalyst need further clarification. This was studied by using a recycle electrobalance reactor with various hydrocarbon feeds over a β-zeolite catalyst. The coking rate was measured online. The effects of the deactivation on the physical properties of the catalysts and the cokes produced at different stages were characterized. It could be confirmed that light olefins were the key components in coke formation, leading to coke contents up to 9.68 wt %. Aromatics had strong synergistic effects on coking. The coke formation did not change the intrinsic structure of the catalysts, but mainly functioned by blocking the entrance to the pores of the catalysts. The large molecules could accelerate the pore blockage and lead to sharply decrease of the BET surface area. The nature of the coke in paraffin cracking mainly consisted of polyaromatics with 3–5 rings and an average molecular weight from 231.0 Da to 337.9 Da. The reaction routes of coke formation were depicted based on the experimental results. These data are the basis upon which the effects of deactivation on different types of elementary steps in catalytic cracking could be estimated.