Adsorptive removal of dimethyl disulfide and thiophene from liquefied petroleum gas by zeolite-based adsorbents

NaX- and NaY-based adsorbents were used for desulfurization of Liquefied Petroleum Gas (LPG). Zeolites were modified by incorporation of Cu²⁺, Zn²⁺ and Cu²⁺-Zn²⁺ metal ions through liquid phase ion-exchange (LPIE) and characterized for their crystal structure, surface area, acidity, ion-exchange rate, and adsorption mechanism. Desulfurization experiments were carried out by static and dynamic methods using dimetyhl disulfide (DMDS) and thiophene (TP) dosed LPG containing 196 mg/L total sulfur as the feed. The sulfur removal performance of zeolites increased after modification and the adsorption capacities of the modified zeolites for DMDS and TP removal were found in the order of Cu > Cu-Zn > Zn for both NaX and NaY zeolites. The breakthrough DMDS adsorption capacities of modified zeolites were 14–37% and 16–45% higher than those of the original NaX and NaY zeolites, respectively. As for TP, modified NaX and NaY zeolites displayed 9–22% and 10–25% increase in breakthrough capacity compared to original zeolites, respectively. The modification did not cause any degradation in the zeolite crystal structure and the metal ions were successfully dispersed in zeolites. The incorporation of Cu²⁺ ions enhanced the Lewis acid sites of zeolites. The Cu-X and Cu-Y adsorbents binded DMDS by direct sulfur-metal (S-M) interaction while both direct S-M interaction and π-complexation were effective in TP adsorption onto zeolites. The adsorption of DMDS and TP over Cu-X and Cu-Y followed pseudo-second-order kinetics and was best described by the Langmuir isotherm model. The best performing adsorbent, Cu-Y, is promising for industrial scale LPG desulfurization.