Ultra-Deep Desulfurization of Real Diesel Using Two-Layer Silica Gels under Mild Conditions

The objective of this work is to explore ultra-deep oxidative desulfurization (ODS) of real diesel using two-layer silica gels as both the guard adsorbent and oxidation catalyst under mild conditions. A series of commercial silica gels were screened for ODS in the presence of cumene hydrogen peroxide, with the dibenzothiophene conversion varying diversely from 1.2 to 99.8%. The best silica gel SC-2 is capable of treating >375 cm 3 of simulated diesel per gram of catalyst with ∼3 ppmw S at 373 K. Fairly trace Ti species of ∼0.02 wt % in silica gel was detected and quantified by inductively coupled plasma, which was identified as the major Lewis acidic species correlating to the high ODS conversion. Moreover, the effects of real diesel composition, including model aromatics, olefin, oxygen fuel additive, and trace organonitrogen compounds, on ODS using silica gel were investigated, where nitrogen compounds, such as indole, were identified as major inhibitors, even at a low concentration of 150 ppmw. Accordingly, guard adsorbents were investigated for adsorptive denitrogenation prior to ODS, the N-capacity followed the order of SC-2 ∼ AC > Al 2 O 3 > 13X. The layered-bed combination for deep desulfurization was optimized to be 5 and 2.5 mg/mL of SC-2, respectively, as the guard adsorbent and oxidation catalyst. The matrix is capable of processing deep-desulfurized diesel below 10 ppm with the total sulfur capacity of up to 4.2 mg-S/g. The process using two-layer commercial silica gel beds provides a new path for ultra-deep oxidative desulfurization of diesel under mild conditions.