Ultra-deep adsorptive removal of thiophenic sulfur compounds from FCC gasoline over the specific active sites of CeHY zeolite

Abstract

Abstract Adsorption desulfurization performance of NaY, HY and CeHY zeolites is evaluated in a miniature fixed-bed flow by model gasoline containing with thiophene, tetrahydrothiophene, 2-methylthiophene, benzothiophene or mixed sulfur compounds. The structural properties of adsorbents are characterized by XRD, N2-adsorption and XPS techniques. Adsorption desulfurization mechanisms of these sulfur compounds over the specific active sites of adsorbents as a major focus of this work, have been systematically investigated by using in situ FT-IR spectroscopy with single and double probing molecules. Desulfurization experimental results show that the CeHY adsorbent exhibits superior adsorption sulfur capacity at breakthrough point of zero sulfur for ultra-deep removal of each thiophenic sulfur compound, especially in the capture of aromatic 2-methylthiophene (about ca. 28.6 mgS/gadsorbent). The results of in situ FT-IR with single probing molecule demonstrate an important finding that high oligomerization ability of thiophene or 2-methylthiophene on the CeHY can promote the breakthrough adsorption sulfur capacity, mainly resulting from the synergy between Bronsted acid sites and Ce(III) hydroxylated species active sites located in the supercages of CeHY. Meanwhile, the result of in situ FT-IR with double probing molecules further reveals the essence of oligomerization reactions of thiophene and 2-methylthiophene molecules on those specific active sites. By contrast, the oligomerization reaction of benzothiophene molecules on the active sites of CeHY cannot occur due to the restriction of cavity size of supercages, but they can be adsorbed on the Bronsted acid sites via protonation, and on Ce(III) hydroxylated species and extra-framework aluminum hydroxyls species via direct “S-M” bonding interaction. As to the tetrahydrothiophene, adsorption mechanism is similar to that of benzothiophene, except in the absence of protonation. The paper can provide a new design idea of specific adsorption active sites in excellent desulfurization adsorbents for elevating higher quality of FCC gasoline in the future.