Computer Simulation Of The Adsorption And Diffusion Of Organic Molecules In Zeolite

Recently, with increasing attention has been paid to the environmental protection, the product of clean fuel has been the focus which people are concerned about. The deep desulfurization of gasoline and incrase of the octane number of lead free gasoline have become the emphosis of investigation. Zeolites are microporous materials that have been found widespread useing in several technological fields. These materials have outstanding properties due to their regular structure and high internal surface areas, and they have been used as catalysts ino exchangers, and adsobents. The adsorption of thiophene in zeolite microporous materials is of great scientific interest in the context of separation and catalysis processes. For instance, the separation of thiophene from gasoline is performed by using selective adsorption in synthetic-type zeolites. MOR and MCM-22 are two kinds of microporous materials. MOR zeolite possesses 12-MR(member rings) channel systems; and MCM-22 zeolite possesses an interesting and unusual framework structure: two independent pore systems formed by interconnected sinusoidal 10-MR(member rings) pores with a 0.41×0.51 nm diameter and an independent 12-MR supercage with 1.82×0.71 nm linked by 10-MR windows with 0.40×0.55 nm diameter. The organic molecules can adsorb and diffuse in two independent pore systems because of their large surface area and the high thermal stability of the framework. It is very important to understand the adsorption and diffusion of the pure organic molecules and the mixture of organic molecules in MCM-22 zeolite. But it is very difficult or impossible to be interpreted by the experimental and theoretical study. It is of great importance to investigate that by molecular simulation techniques.In this paper, we employed Monte Carlo and Dynamic technique to simulate the adsorption and diffusion of thiophene/isooctane, thiophene/benzene and their mixtures, and 1-butene and n-butane in MCM-22 zeolite; and obtained the the adsorption isotherms, the heat of adsorption, mass cloud and diffusion coefficients. Then the located sites and the mainly diffusion channel can be predicted. The fellowing results can be drawn:1. Adsorption of thiophene and thiophene/iso-octane mixtures in MOR zeolite by Monte Carlo simulationAt first, the adsorption isotherm of thiophene in MOR zeolite was studied with CVFF and COMPASS forcefield by Monte Carto simulation. The simulated results showed that the result with compass is more exactly than that with CVFF compared with the reference. Thus, the COMPASS force field was used to simulate. The adsorption of thiophene/iso-octane mixtures in MOR zeolite was studied by Monte Carlo simulation. The results showed that Thiophene and iso-octane can be separated effectively by MOR zeolite.2. Adsorption and diffusion of thiophene and thiophene/iso-octane mixtures in MCM-22 zeolite by Monte Carlo simulation and dynamic simulationThe adsorption isotherm, the heat of adsorption and the located sites of the pure thiophene and iso-octane molecules can be obtained by MC simulation. It can be showed that thiophene can be adsorbed in 10-MR channel and 12-MR supercage system, but iso-octane mainly is adsorbed in supercage system. And the adsorption capacity and the adsorption sites can be affected by the temperature and the pressure. The binary mixtures obey competition classification, and thiophene is adsorbed more strongly than iso-octane. The diffusion coefficients of iso-octane are larger than these of thiophene, and the result is in agreement with that of GCMC simulation. The molecules of thiophene and iso-octane can be segregated by MCM-22 zeolite.3. Adsorpion of thiophene and thiophene/benzene mixture in MCM-22 zeolite by Monte Carlo simulationThe adsorption tendencies of thiophene and benzene are similar in MCM-22 zeolite, which can be adsorbed in two independent channel systems. On the other hand, the binary mixtures have competition adsorption, and thiophene adsorbs more strongly than benzene. The adsorption of the ternary mixtures of thiophene, benzene and iso-octane in MCM-22 was studied by MC simulation. The results showed that the adsorptive capacity of thiophene in MCM-22 zeolite is strongest, and the iso-octane is weakest. Then MCM-22 zeolite is a eximious sorbent of deep desulfurization of gasoline.4. Adsorption and diffusion of 1-butene and n-butane in MCM-22 zeolite were studied by Monte Carlo and Monte Carlo simulationThe adsorption and diffusion of 1-butene and n-butane in MCM-22 zeolite were studied by Monte Carlo and Molecular Dynamic simulation. The calculated results showed that 1-butene and n-butane can be adsorbed in two independent channel systems, and can be preferentially adsorbed in 10-MR channel systems. The dynamic simulation was performed at 400K and 673K, and the two kinds of molecules can diffuse in two independent channel systems and mainly diffuse in the center of the supercage systems. It can be predicted that the catalytic reactions mainly happen in 10-MR channel, and the upper and lower of the supercage systems.