Adsorption Diffusion And Reaction Behaviors Of Thiophenic Organosulfurs And Hydrocarbons On Y Zeolites

Catalytic cracking(FCC) gasoline with high sulfur content is a major component of commercial gasoline in china,which is the primary factor leading to lower standards for the sulfur content of fuel than the high standards of the United States and Europe. Deep desulfurization of FCC gasoline, therefore, is the key issue of clean fuel production in china.Focus on the main problems of the selective adsorption desulfurization technology that sulfur adsorption capacity of the current adsorbents is too low to be industrialized for FCC gasoline, the desulfurization performances of three kinds of typical zeolite adsorbent, such as Cu(I)Y, NiY and L-CeY, in model gasolines and FCC gasoline are compared in this paper. The results show that the desulfurization performances of these modified zeolite adsorbents for FCC gasoline are far worse than those for model gasoline. Adsorptive selectivity of different thiophenic organosulfurs of FCC gasoline and HDS gasoline was investigated. It is clearly that the adsorptive selectivity of various thiophenic organosulfurs is quite different. Selectivity of alkylthiophene substituted in α sites is worst due to the steric effects of alkyl groups. While, 3,4-alkylthiophene derivatives show better selectivity thanks to the hyper conjugation effect of alkyl groups to thiophene ring.The effect law of olefins and aromatics on thiophenic organosulfurs adsorption on zeolites were investigated by using model gasoline, revealing that the desulfurization property of "π complexion" adsorbent significantly affected by aromatics but "S-M" mode sorbents effectively relieve the impact of aromatics. The strong adsorption of olefins over Br?nsted acid sites on the surface of L-CeY which was prepared by liquid phase ion exchange will seriously disturb the removal of sulfide by adsorption. The solid state ion exchange method was utilized to prepare S-CeY zeolites with little B acid sites to avoid the adverse influence of olefins. However, affinity of aromatics on S-CeY zeolites is enhanced, resulting in an increase of the competitive adsorption of aromatics 。 An in situ infrared spectroscopic investigation of the nature of the effect of aromatics and olefins on the adsorption of thiophenic organosulfurs was further carried out. It is proved that the influence mechanism of aromatics is mainly the competitive adsorption "π complexion", while the strong adsorption and catalytic reactions of olefins on B acid sites of the zeolite adsorbent is the key factor of adsorption capacity of thiophenic organosulfurs.Sulfur species on surface of the sorbents were analyzed by using in situ infrared spectroscopy, temperature programmed desorption(TPD)- mass spectrum(MS) and GC-SCD. It is initially confirmed that the protonation and oligomerization thiophene which occur on the B acid sites of surface of zeolite adsorbent under mild conditions. Furthermore, the produce of H2 S by cracking reaction of sulfur species on surface of L-CeY sorbent was found at lower temperatures(below 200 oC).The phenomenon that thiophene can be activated on B acid sites of L-CeY at ambient temperature was then associated with in situ reduction of sulfur in fluid catalytic cracking. The catalytic conversion of thiophene over a series of FCC catalysts(LDO-70 and LDO-70S), rare earth modified molecular sieve(HRSY-1 and HRSY-3)(Lanzhou Chemical Research Center) and other modified Y zeolite(Cu(I)Y and L-CeY) was explored by in situ FTIR and TPD-MS methods. The results preliminary prove that protonation of thiophene on B acid sites occur. Subsequently, protonated thiophene further converts to polymers which is easy to produce H2 S by cracking reaction. In addition, the role of rare earth ion in cracking reaction of thiophene was also studied by the comparison of the conversion behaviors of thiophene over Cu(I)Y and L-CeY. The results indicate that the synergistic effect between “S-Ce” adsorption model and B acid site can promote the hydrogen transfer reaction via intermolecular and the oligomerization, thus, it is helpful to the cracking reaction of sulfides.The adsorption and diffusion behaviors of benzene, p-xylene, cumene, n-octane and thiophene in Y- based zeolite and Fluid Catalytic Cracking catalyst particles were studied by an intelligent gravimetric analyzer(IGA) and frequency response(FR) method. It is confirmed that the diffusion time constants of guest molecules in FCC catalyst particles are all larger than those in Y zeolite by measuring of the adsorption rate. Besides, the results from frequency response method further prove diffusion time constants in FCC catalyst particles are larger than Y zeolite and the adsorption process on the active site of Y zeolite component can disturb the diffusion processes in the macropores of the matrix in the catalyst particles. In summary, it is possible that the diffusion process in intraparticle of the catalyst particles and zeolite-matrix interfaces play a dominant role in transport limitation rather than the intracrystalline diffusion process.