Adsorptive Separation of Infinitesimal Sulfur Oxide in Naphtha —Reactivation of Silica Gel Using Toluene and Dimethyl Ether—

Adsorption of sulfur oxide is one of the key techniques for producing extra-low-sulfur content naphtha during oxidative desulfurization. Reactivation and repeated use of adsorbent are quite important for practical and economic reasons. The reactive performance of silica gel (SIL), an excellent adsorbent for the adsorption of benzothiophene-1,1-dioxide (BTDO), a model sulfur oxide, was evaluated using toluene and dimethyl ether (DME) by multicycle adsorption-reactivation tests. In an 8-cycle adsorption-reactivation test using toluene as a reactivation agent, the breakthrough amount after 8 cycles was reduced to 68% of the first cycle. Using DME, the breakthrough amount was reduced to 87% at the second run based on the first run, but this level was maintained throughout the remaining cycles. Three types of naphtha, Naphtha A, hydrotreated naphtha (Naphtha B), and a 50% mixture, were tested in 8-cycle tests using DME as a reactivation agent. The breakthrough amount of SIL was as high as 1300-1700 g/g-SIL for Naphtha A, and 500-1000 g/g-SIL for Naphtha B containing 13 wt% of aromatics. The breakthrough amount for the mixture was almost the same as for Naphtha A. These results suggest that SIL is suitable for naphtha containing up to 7 wt% of aromatics. A 25-cycle adsorption-reactivation test was performed using Naphtha A by limiting the throughput to 1300 g/g-SIL. During the 25 cycles, no significant amount of BTDO was observed in any of the treated naphtha products.