Static and Dynamic Catalytic Adsorptive Desulfurization (CADS) of Real Diesel Using Low-Cost TiO2/Fumed Silica

The catalytic adsorptive desulfurization (CADS) has been developed as a promising approach for ultra-deep desulfurization of diesel with low energy comsumption (Ren, X.; Miao, G.; Xiao, Z.; Ye, F.; Li, Z.; Wang, H.H.; Xiao, J. Catalytic Adsorptive Desulfurization Using TiO₂/SBA-15 under Mild Conditions. Fuel, 2016, 174, 118-125.). In this work, low-cost fumed silica were screened as the supporting substrate for TiO₂ for effective CADS of real diesel (~35 ppm-S). Effect of TiO₂ loading and CADS temperature were optimized in batch reactor. The dynamic breakthrough performance was evaluated in fixed-bed reactor. The sorbent was regenerated by solvent wash followed by air oxidative treatment, and its regenerability was assessed in multiple adsorption-regeneration cycles. Results suggested that TiO₂/fumed silica (300-400 mesh) with higher surface area and larger amount of Si-OH groups showed higher desulfurization capacity. The TiO₂ loading was optimized to 13% with the maximized utilization of Ti catalytic sites and Si-OH adsorption sites on TiO₂/fumed silica for CADS. While the CADS temperature was optimized to 35°C with the balanced catalytic activity for the oxidation of dibenzothiophenes (and their derivatives, 4,6-DMDBT mainly) and minimized desorption of yielded dibenzothiophene sulfones. With a suitable O/S ratio of 5, and overall aspect ratio of 10, the TiO₂/fumed silica showed the maximal desulfurization capacity of 1.44 mg-S/g-A of real diesel at the breakthrough concentration of 5 ppm-S. Considering the effect of the dimension of fixed bed, the dynamic desulfurization performance with varied aspect ratio followed the order of H/R=10 > H/R=22 ~ H/R=5. The S-breakthrough concentration decreased with increased O/S ratio. The superior regenerability of TiO₂/fumed silica was suggested by no loss on desulfurization capacity was observed after six adsorption-regeneration recycles. The CADS using the low-cost TiO₂/fumed silica adsorbent with superior desulfurization capacity and remarkable stability provide an effective and economic approach for ultra-deep desulfurization of real diesel with low energy consumption.

Keyword: catalytic adsorptive desulfurization, TiO₂/fumed silica, diesel, dynamic adsorption.