Reactivation of spent S-Zorb adsorbents for gasoline desulfurization

Abstract

Spent adsorbents from the S-Zorb technology are hazardous wastes. Reactivating and recycling the spent S-Zorb adsorbents is of great significance to environmental protection. However, no report concerning this subject has been found yet. Herein, we have developed an acid-base coupling method to reactivate the spent S-Zorb adsorbents. To achieve this goal, the deactivation factors of the adsorbents were studied. The results show that the formation of Zn2SiO4 phase, which results in loss of active phase (ZnO) for sulfur storage, is the main deactivation factor. The acid-base coupling method can transform Zn2SiO4 into soluble Zn2+ via nitric acid, followed by precipitation as Zn(OH)2 with sodium hydroxide addition. After calcination, the loss of ZnO can be supplemented. The newly formed ZnO bears a willow-leaf shape that is remarkably different from the original one. Also, it has smaller particle size compared to that of fresh adsorbents. Of note is that mesopores and Lewis acid sites are created over the adsorbents via the acid-base coupling method, accelerating the mass transfer and conversion of sulfur compounds. Carbon deposited over the adsorbent surface is removed and metal sulfides (ZnS and NiS) are oxidized into metal oxides (ZnO and NiO) via calcination of the spent adsorbents. The desulfurization efficiency of the reactivated adsorbent is superior to that of the regenerated adsorbent and reaches a level comparable to that of the fresh adsorbent in gasoline desulfurization.