Grant Campbell Edwards

Influence of zeolite particle size on selectivity during fluid catalytic cracking

Abstract NaY zeolites of varying average particle size were synthesized and incorporated into fluid cracking catalysts. Scanning Electron Micrographs showed that these zeolites exhibited agglomeration and intergrowths. Hence, external surface area measured by N2 adsorption t plot was used to calculate effective particle size. Effective particle size of these zeolite samples ranged from 0.06 to 0.65 μm. The t plot micropore volume was determined to be the appropriate method of characterization of crystallinity of these zeolites. Cracking of West Texas Heavy Gas oil is limited by zeolitic diffusion at 500°C for a zeolite with 0.65 μm effective particle size. Hence, the catalyst containing smaller particle zeolite exhibited improved activity and selectivity to intermediate cracked products like gasoline and light cycle oil. Selectivity differences can be explained by considering the effect of diffusion resistance on the rate constants for cracking of gas oil and gasoline.

Penta-co-ordinated aluminium in zeolites and aluminosilicates

Solid state 27Al n.m.r. spectroscopy of various aluminosilicates (zeolites, clays, amorphous SiO2–Al2O3) shows that upon thermal or hydrothermal treatment a line appears at ∼30 p.p.m.; the position of this line suggests that penta-co-ordinated Al is present in all these aluminosilicates.