Preparation and n-hexadecane hydroisomerization properties of SAPO-11-based composite molecular sieve

Abstract

In this work, SAPO-11, SAPO-11-γ-Al₂O₃ and SAPO-11-ZSM-5-γ-Al₂O₃ molecular sieve supports were prepared by static hydrothermal synthesis, which SAPO-11-γ-Al₂O₃ and SAPO-11-ZSM-5-γ-Al₂O₃ supports were loaded with Co and Mo as active metal components. The hydroisomerization properties of n-hexadecane on SAPO-11, SAPO-11-γ-Al₂O₃ and SAPO-11-ZSM-5-γ-Al₂O₃ molecular sieves were investigated, as well as the effects of reaction temperature, reaction time, solid–liquid ratio and reaction pressure on the hydroisomerization properties. The results demonstrated that the SAPO-11 molecular sieves synthesized under the ratios of 1Al₂O₃:2P₂O₅:0.6TEOS:1.2DPA:55H₂O, crystallization time of 48 h, and crystallization temperature of 180 °C had high crystallinity and uniform size distribution, and the pore structure was more obvious. After loading metals onto the SAPO-11-γ-Al₂O₃ molecular sieves, the charged metals partially block the pores or pore openings of the molecular sieves, leading to a reduction in specific surface area and pore volume. As a result, some acidic sites become occupied by the metals, weakening the acidity. The results of the hydroisomerization experiments showed that the SAPO-11 molecular sieves achieved maximum isoparaffin selectivity and isoparaffin yield, reaching values of 31.26% and 28.32%, respectively, at 340 °C over a reaction time of 60 min. The selectivity and yield reached maximum of 51.02% and 43.76% at liquid–solid ratio up to 25:1. The selectivity and yield reached maximum values of 55.82% and 51.2% at an initial reaction pressure of 5 MPA. For the SAPO-11-γ-Al₂O₃ supports, the selectivity and yield the maximum values of 79.50% and 71.49% at a metal Co: Mo loading ratio of 1:3 was achieved. For the SAPO-11-ZSM-5-γ-Al₂O₃ supports, the selectivity and yield the maximum values of 55.44% and 54.05% were achieved with ZSM-5 loading of 30 wt%. These catalysts have the potential for a wide range of applications.