Desulfurization Of Gasoline Distillation By Adsorption And Its FT-IR Spectroscopic Study

Ultra-deep desulfurization of fuel oils has become an urgent subject worldwide. Desulfurization via selective adsorption is considered as one of the most promising methods, since it can remove organic sulfur compounds from oils under mild conditions. However, there are few researches dealing with the adsorption mechanism of organic sulfur compounds. In this dissertation, the effect of coadsorption of molecules present in oil, such as aromatics and olefins, on thiophene adsorption is investigated by fixed-bed adsorption experiments, the adsorption modes of thiophene on zeolite Y modified by Cu or La are systematically studied by FT-IR spectroscopy, and the relationship of different adsorption modes and adsorptive selectivity are discussed.For Cu modified zeolite Y, the adsorbents prepared by mechanical mixture shows evidently enhanced breakthrough capacity for thiophene removal from model gasoline, since the cooperative interaction of highly dispersed CuO and NaY zeolite;the adsorbents prepared by aqueous ionic exchange shows decreased sulfur removal ability, owing to the decreased numbers of cations in zeolite. The addition of cyclohexene and toluene in model gasoline reduce the adsorptive selectivity of thiophene removal. Adsorbed thiophene inteacts with Na⁺ via Ï€ electronic interaction on NaY, and the introduction of Cu⁺ or CuO does not change this adsorption mode. Thiophene adsorbed through Ï€ electronic interaction can be easily affected by benzene co-adsorption, which leads to the poor adsorption selectivity for removing organic sulfur compounds from FCC gasoline.For La modified zeolite Y, the adsorbents prepared by mechanical mixture and ionic exchange shows similar tendency in thiophene removal when they are used in the desulfurization of model gasoline. However, a noticeable difference observed in La³⁺ exchanged zeolite Y is that it shows a much higher adsorptive selectivity in sulfur removal from FCC gasoline. FT-IR data demonstrate that there appears a new mode of thiophene adsorption after the introduction of La³⁺ ions, i.e., a direct interaction of adsorbed thiophene with La³⁺ ions by sulfur atoms. Thiophene adsorbed via the direct interaction of La³⁺ ions and sulfur atoms is relatively less affected by the presence of aromatic compounds like benzene.This is responsible for the improved selectivity of LaNaY zeolite in the adsorption of organic sulfur compounds from FCC gasoline.MCM-41 shows significantly increased sulfur removal ability for model gasoline with aluminum content in the framework, which is directly related to the enhanced acidity. FT-IR spectra show that thiophene is adsorbed on MCM-41 via n electronic interaction, and the adsorption is much weaker than that on microporous zeolites.