Ultra-Deep Desulfurization of Hydrocarbon Fuels Using TiO2 and Ag-TiO2 Adsorbents Assisted By UV Irradiation

Fuel cell (FC) technologies have attracted dramatic research interests in recent years to achieve clean electric power for the “hydrogen economy”. However, the development of fuel cell systems is restricted because of the demand of ultra clean fuels. Considering the protection of fuel cells, ultra-deep desulfurization of liquid fuels is an important task. Adsorptive desulfurization (ADS) is considered as a promising method for producing ultra-low sulfur fuels under ambient operation conditions. The Ag/TiO₂ and Ag/TiO₂—Al₂O₃ adsorbents developed by our research group exhibited high selectivity and sulfur capacity and can be regenerated for multiple cycles. In our previous work, the desulfurization mechanism was investigated based on the role of surface acidity and surface hydroxyl groups. In the present work, UV assisted adsorptive desulfurization technique was developed for the first time by applying TiO₂/UV system into dynamic breakthrough process. Results showed that both breakthrough and saturation capacities of TiO₂ based adsorbents were improved as observed from  UV-assisted breakthrough experiments using model fuels (3500 ppmw S as benzothiophene in n-octane). The breakthrough capacity of blank TiO₂ was increased from 2.45 mgS/g to 4.05 mgS/g under UV irradiation. It is known that H₂O impurities in fuels can decrease the activity of TiO2 based adsorbents. But the sulfur removal capacities were increased by adding water as fuel additive during UV adsorptive desulfurization based on our studies. The breakthrough capacity of blank TiO₂ was further increased to 5.00 mgS/g with H₂O under UV environment. Moreover, H₂O helped maintain the activity of Ag-TiO₂ adsorbent during multiply UV adsorption-regeneration cycles. No photo-oxidation products of sulfur aromatic compounds were formed during UV-assisted adsorptive desulfurization (ADS) process, as confirmed by GC-PFPD and GC-FID.