Adsorption, Diffusion On Zeolite And It's Application

Zeolites are widely used in selective adsorption for removing sulfur from fuels and separation of aromatic hydrocarbon and alkane. An accurate knowledge of adsorption and diffusion on zeolite is very important to separation technology and developing a new kind of sorbent due to intracrystalline diffusion is always a key factor for separation. Compared with other sorbents, ion-exchanged Y zeolite is best for selective adsorption desulfurization. Contracdictory results can be obtained although there are a few of papers about the desulfurization mechanism. There are also contracdictory consequences on the mechanism of adsorption, diffusion of aromatic hydrocarbon and alkane on Silicalite-1.In this work, two studies have been firstly performed combining thermodynamics, kinetics and temperature programmed desorption (TPD):1) NaY was firstly modified using two ion-exchange and two calcinations method. The specific area, average pore size of NaY, Ce(IV)Y, Cu(I)Y, Ag(I)Y were obtained based on the nitrogen adsorption experiment. The isotherms, adsorption selectivity, TPD, thermodynamics, dynamics of thiophene, benzene, n-octane, 1-octene on NaY and ion-exchanged NaY were further studied using Intelligent Gravimetric Analyser (IGA) and Molecular Simulation choosing thiophene, benzene, n-octane and 1-octene as the representation of sulfur-contained compounds, aromatic hydrocarbons, alkane, alkene in fuels respectively.2) The isotherms and temperature programmed desorption (TPD) of benzene, cyclopentane, cyclohexane and p-xylene on Slicalite-1 were firstly measured using IGA, and then the adsorption and diffusion mechanism were studied according to thermodynamics, kinetics and TPD.All the isotherms can be well fitted by Langmuir equation other than the isotherms of 1-octene on CeY at low teperature. The deviation from Langmuir was caused by the strong σ-Ï€ coordinations between 1-octene and Ce⁴⁺. The isotherms of cyclopentane, benzene, p-xylene changed from Type I to Type IV with decreasing temperature. The isotherms at higher temperature can be well fitted by Langmuir equation. Stepwise isotherms, which cannot be fitted by the Langmuir equation, showed up at low temperature.