Effect of Si/Al2 Ratio Over Zeolite Beta in Steam and Direct Catalytic Cracking of n-dodecane

Abstract

To achieve a higher light olefin yield for the catalytic cracking of kerosene and diesel, the effect of the Si/Al2 ratio (SAR) of zeolite beta (BEA) in steam catalytic cracking (SCC) and direct catalytic cracking (DCC) of n-dodecane (n-C12) was investigated in a fixed bed reaction system over zeolite beta with SAR in a range of 25–360. The catalysts were characterized by XRD, NH3-TPD, pyridine FT-IR, N2-sorption, SEM, and TGA. In both DCC and SCC, n-C12 conversion showed a tendency to decrease linearly as the BA (Brønsted acidity) of the zeolite beta catalyst increased. Both the light olefin yield and the light olefin/paraffin ratio in SCC were higher than that in DCC, where the steam in SCC acts as a diluent, thereby decreasing the partial pressure of the reactants and reducing the formation of paraffins. Through optimization of the operation variables, light olefin yield exceeding 74.3 wt% was obtained in SCC using high silica zeolite beta catalysts with SAR = 300 at TOS = 1 h, 650 °C, and 4.2 h−1.