Upgrading The Structure And Performance Of Hierarchical Zeolite Y

Nowadays the consumption ratio of diesel to gasoline is decreasing in China,the environmental laws are more and more rigorous,and the gasoline standards are increasing rapidly.It is imperative to improve the production of clean gasoline.Hydrocracking process is one of the ideal ways to achieve this goal.The key of hydrocracking process is catalyst.Zeolite Y is widely used as the cracking active component and carrier in hydrocracking catalyst,its pore structure and acid property directly impact the hydrocracking precess.But commercial USY zeolites are not perfect in the hydrocracking industry,since the mesopore volume is too small and also the weak acid site is too high,which leads to seriously secondary cracking.Hydrocracking technology can be used to treat heavy oil and to poor processing capacity of heavy oil.It is believed that the introduction of mesopores through the modification will improve substantially the pore structure and acidity property of Y zeolite,thus,the catalytic performance of hydrocracking catalysts is improved.In order to prepare the USY with rich secondary pores,several compound modification methods were studied,such as inorganic-organic acid,hydrothermal-acid,and inorganic acid-base,then a better method was established.Subsequently,the reagent concentration,reaction time,reaction temperature and other conditions were investigated,so as to optimize the condition of modification.The results indicated that a large number of mesopores were introduced into USY zeolites by using combined nitric acid-sodium hydroxide treatment,and the method has less pollution and low cost.The secondary pores content could be adjusted by changing the condition of modification,its surface area increased obviously by increasing sodium hydroxide concentration and prolonging nitric treatment time.Nitric acid-sodium hydroxide modified system had increased the acidity,reduced the unit cell parameters of Y zeolites,and had kept good crystallinity while the mesopores were introduced.Fluid dynamic simulation using Fluent was applied to modeling the preparation of hierarchical zeolites in a pilot-scale,which provided that the unsteady simulation results at different rotational speeds showed that the increase of rotational speed in a certain range was beneficial to the uniform mixing of solid and liquid,and can reduce the side wall effect effectively,so the appropriate stirring speed should be chosen in the process of industrialization.At the same time,another simulation result showed that the larger the volume,the longer the steady time,the more homogeneous the solid-liquid mixture.The solid-liquid distribution can be controlled by adjusting the rotational speed and solid-liquid ratio.The catalyst was prepared using modified Y zeolite with high secondary pores content,which catalytic performance of hydrocracking was investigated by using n-dodecane as model reactant.The results showed that the conversion and yield of C4?C8 was significantly higher than the commercial USY.The results provide a reference for the preparation of hydrocracking catalyst.It is expected that the Y zeolites modified by nitric acid-sodium hydroxide can meet the requirements of hydrocracking to produce clean gasoline,which has a high research value.