Catalytic cracking of gasoil: Benefits in activity and selectivity of small Y zeolite crystallites stabilized by a higher silicon-to-aluminium ratio by synthesis

Abstract

Catalytic cracking of a vacuum gasoil has been carried out on USY zeolites with unit cell size in the range 24.50–24.25Å. The starting materials were NaY zeolites with average crystal size 0.30–1.0 μm and silicon-to-aluminium ratios by synthesis of 2.4–3.1. It is shown that smaller crystal sizes produce more gasoline and diesel, and less coke and gases. However, smaller crystals are less hydrothermally stable than bigger crystals when the zeolite is synthesized with a silicon-to-aluminium ratio of 2.4, and the activity and selectivity benefits are lost after steaming. However, if NaY zeolite is made with a silicon-to-aluminium ratio ≥ 3.0, the smaller crystals are hydrothermally stable and show a higher activity and a better selectivity than bigger crystals, even after steaming at 750°C for five hours.