Adsorptive Desulfurization Of Gasoline Distillation Over Zeolite Modified By Lanthanum

SO2 from the combustion of fuels containing organic sulfur compounds is the main reason for acid rain, and it can also poison the catalysts used in the engines'exhaust treatment. With the improvement of people's environmental protection, more stringent restrictions about the sulfur content in fuel oil have been mandated in many countries. Although traditional hydro-desulfurization (HDS) can desulfurize gasoline deeply, but it can also lead to octane reduction, more hydrogen consumption and equipment investment. Adsorption desulfurization technology is simple, easy, fast, and it can not reduce the octane number of gasoline. Now, a variety of molecular sieves have been studied for adsorption desulfurization, however, there is little research on the adsorption mechanism of organic sulfur compounds on adsorbents. This dissertation involves two parts:for microporous zeolite adsorbents, the effect of olefins on the desulfurization of model gasoline and the adsorption mechanism of thiophene and cyclohexene are studied; for micro-mesoporous zeolite adsorbents, the effect of pore structure on adsorption desulfurization are discussed.LaNaY adsorbents are prepared by liquid ion-exchanging La(NO3)3 solution with NaY zeolite. For model gasoline without cyclohexene, the desulfurization capacity of LaNaY is lower than that of NaY, because of the decrease of the number of cations and the partly broken lattice structure. In static adsorption, NaY shows declined sulfur removal with the addition of cyclohexene, while LaNaY displays evident improvement in sulfur removal with the addition of a certain amount of cyclohexene. FT-IR results demonstrate that thiophene is adsorbed on NaY byπcomplexation, but a new adsorption mode, the direct S-La3+interaction, appears on LaNaY. Cyclohexene is adsorbed on NaY byπ-OH interation and is partly adsorbed on LaNaY by alkyl-OH. It is woth noting that carbenium is detected on LaNaY. Combined with GC-FPD analysis, it can be deduced that alkylation between thiophene and cyclohexene occurs on the acidic sites of LaNaY, the lager size of alkylated thiophene enhances the micropore-filling effect, and thus promotes adsorption desulfurization. This may be one of the reasons for LaNaY shows improved sulfur removal from model gasoline containing olefin.Besides the effect of adsorption mode on desulfurization selectivity, we should also consider the role of the adsorbent's pore size plays in desulfurization. In this dissertation, the micro-mesoporous molecular sieve NaY/MCM-41 is synthesized by the assembly of protozeolitic nanoclusters, and La3+is introduced into NaY/MCM-41 zeolite by liquid ion-exchange. The characterization results show that the systhesized NaY/MCM-41 contains the structure units of zeolite Y in its wall, and the micro-mesoporous structure of LaNaY/MCM-41 is maintained after the introduction of La3+, even though the surface area is decreased. Comparing the sulfur capacity of microporous LaNaY and composite LaNaY/MCM-41, both of them show decreased tendency with the addition of toluene, but the drop rate of the latter is lower than that of the former. The desulfurization of FCC gasoline by microporous LaNaY, mesoporous LaMCM-41 and composite LaNaY/MCM-41 also displays that the sulfur capacity of LaNaY/MCM-41 is superior to that of the other two adsorbents. These results show that the pore structure of the adsorbents is one of the key factors of the desulfurization capacity.