Effect of the Zeolite Type on Catalytic Performance in Dewaxing of the Diesel Fraction under Sour Conditions

Dewaxing by isomerization is widely used to produce winter and arctic grades of diesel fuel. Preliminary feed hydrotreatment and pure hydrogen are usually used in order to avoid poisoning of the catalyst by sulfur and nitrogen. However, combining hydrotreatment and dewaxing in one reactor has some advantages, such as lower capital and operating costs. In such a configuration, a dewaxing catalyst works in sour environments, defined by sulfur and nitrogen presented in the feed stream. In the presented work, Pt-containing catalysts based on commercial zeolites with one-dimensional channels and their mixtures (ZSM-23, ZSM-22, ZSM- 12, EU-2, SAPO-11, ZSM-23+ZSM-12, and ZSM-23+ EU-2) were prepared, characterized using different analytical techniques (X-ray diffraction, scanning electron microscopy, transmission electron microscopy, inductively coupled plasma atomic emission spectroscopy, N-2 sorption, and infrared spectroscopy), and tested in dewaxing of the diesel fraction under sour conditions. It was found that catalyst activity, dewaxed product yield, and quality indicators (aromatic hydrocarbon content and density) were highly sensitive to zeolite channel size, while catalyst acidity and zeolite crystal size were less important factors. The highest activity was shown by catalysts based on EU-2 and ZSM-12, which had the widest channels. The highest product yield was observed for the catalyst based on EU-2, which had a medium channel size among compared zeolites. Wider zeolite channels promoted the metal function of catalysts that led to a decrease in the aromatic hydrocarbon content of dewaxed products. Using the mixtures of ZSM-23+ZSM-12 and ZSM-23+EU-2 did not lead to visible synergetic effects. Using different binder materials (Al2O3, TiO2, and ZrO2) did not significantly affect the quality or yield of dewaxed products.

Automated summary

Research shows that catalyst activity, dewaxed product yield, and quality indicators are highly sensitive to zeolite channel size. Catalysts based on EU-2 and ZSM-12 with wider channels exhibit the highest activity. Wider zeolite channels promote the reduction in aromatic hydrocarbon content of dewaxed products.