Adsorptive desulfurization of jet and diesel fuels using Ag/TiOx–Al2O3 and Ag/TiOx–SiO2 adsorbents

The objective of this work is to examine the performance of Ag/TiOx–Al2O3 and Ag/TiOx–SiO2 for adsorptive desulfurization of JP5, JP8, Off-Road Diesel (ORD), and Ultra Low Sulfur Diesel (ULSD) at ambient conditions. These adsorbents were observed to be effective for desulfurizing liquid hydrocarbon feeds that ranged from 7.5 to 1172 ppmw S and comprised of diverse sulfur compositions. In fixed bed continuous adsorption tests, 4 wt.%Ag/TiOx–Al2O3 demonstrated saturation capacities of 10.11, 6.11, and 7.4 mg S/g adsorbent for JP5 (1172 ppmw S), JP8 (630 ppmw S), and ORD (452 ppmw S), respectively. In equilibrium saturation experiments, the adsorbent was able to desulfurize ULSD down to less than 75 ppbw S and this was achievable even when the initial concentration of non-sulfur aromatics was greater than 25,000 times higher. Dispersing TiOx onto high surface area alumina and silica substrates increased the sulfur adsorption capacities of both. This enhancement in adsorption capacity increased still further with silver addition. Higher Ag loading (up to ∼12 wt.%Ag) on TiOx–Al2O3 proved beneficial to sulfur adsorption capacity when compared to TiO2 (up to ∼4 wt.%Ag), indicating that the mixed oxide supports were able to host more active silver oxides. The adsorption selectivity toward different sulfur compounds present in the fuels varied during the fixed bed adsorption tests. The adsorbent had the greatest affinity for BT’s and the least for TMBT’s and DMDBT’s (the selectivity order from the strongest to weakest adsorption was: BT > MBT > DMBT > DBT ≈ MDBT > TMBT ≈ DMDBT). Ag/TiOx–Al2O3 was thermally regenerable in air for multiple cycles at temperatures ranging from 110 to 450 °C. The effects of titanium loading, silver loading, and titanium precursor on sulfur adsorption capacity are also presented.