Desulfurization of Tier 2 gasoline by divalent copper-exchanged zeolite Y

The desulfurization of Tier 2 gasoline (<30 ppmw S) by divalent copper-exchanged zeolite Y (Cu(II)Y) zeolite was examined. Sulfur removal was found to be greater at 150 °C than at lower temperatures for Cu(II)Y adsorbents containing as the secondary cation either Na+ (CuNaY) or H+ (CuHY). Capacities on the order of 60 ml gasoline/g adsorbent were obtained with both materials before the sulfur concentration in the effluent exceeded 3 ppmw. Overall, the CuHY zeolite showed somewhat better desulfurization performance. It is proposed that acid sites (H+) that are present play a role in the desulfurization process, facilitating chemical reactions involving the sulfur-containing molecules. This leads to the generation of sulfur-bearing compounds having molecular weights and sizes greater than those present in the initial feed. Some of these heavier sulfur species are eluted but many do not elute. The net effect is a desulfurization pathway that is the result of entrapment of sulfur-containing molecules in addition to a desulfurization pathway involving direct interaction between the copper and sulfur atoms.