Preparation And Sulfur Removal Performance Of Adsorbent For Deep Desulfurization Of Diesel Fuel

In recent years, to meet more stringent criterion for sulfur in diesel, deep desulfurization of diesel fuel has become a more important subject around the world. Adsorption desulfurization is a new method with broad application prospect because of its high desulfurization rate, simple operation, low investment cost and no pollution, etc.In this paper, modified MCM-41 adsorbents based onπ-complexion adsorption mechanism were prepared by impregnation method with transition metal salt. The effects of preparation conditions of adsorbent and operating condition on desulfurization performance were investigated, such as the kind of transition metal, heat treating temperature, impregnation concentration of transition metal and adsorption temperature. The desulfurizatin performance of the adsorbent was evaluated by both static adsorption and dynamic adsorption methods. The results show that MCM-41 modified with AgNO3(Ag/MCM-41) exhibits the best adsorption performance. MCM-41 impregnated with 20 wt% AgNO3 aqueous solution at 40℃for 12 h has better desulfurization performance after being treated at 110℃overnight when the adsorption operated at 25℃, the saturated sulfur capacity was 0.814%(sulfur content of diesel fuel is 1037 mg/L), the volume of treated diesel reached 14.5 mL-D/g-A. The results of desulfurization of model diesel indicate that the breakthrough sulfur capacity for DBT and 4,6-DMDBT reached 2.55% and 2.59% respectively without naphthane existed in model diesel. When naphthane content was 5 wt% and 10 wt% in DBT model diesel respectively, the saturated capacity of Ag/MCM-41 for DBT was reduced dramaticly to 0.652% and 0.534% respectively, which expresses a poor adsorption selectivity between DBT and naphthane.Based on reaction adsorption mechanism, Ni/ZnO/Al2O3-SiO2 adsorbent was prepared and the desulfurization performance was evaluated in a fixed bed reactor. The effect of preparation method, type of SiO2 source and the composition of the adsorbent on desulfurization performance were discussed. The optimized preparing conditions were as follows:Na2Si03 as SiO2 source, the adsorbent with the composition of 20% Ni,50% ZnO, 10% SiO2,20% Al2O3, which was coprecipitated by Na2CO3, and calcined at 400℃for 4 h, prereduced at 450℃for 3 h in hydrogen. The prepared Ni/ZnO/Al2O3-SiO2 exhibits a strong desulfurization performance. The effect of operating conditions were also investigated, the tedults of sulfur removal performance from hydrotreated diesel(sulfur content is 1037 mg/L) show that high temperature, high pressure, high volume ratio of hydrogen/oil and low weight hourly space velocity are favorable to improve the desulfurization ability of adsorbent. The proper operating congotions as follows:adsorption temperature,420℃, adsorption pressure: 2.0 MPa, volume ratio of hydrogen/oil:200～300, WHSV:6～7 h-1, under which the saturated sulfur capacity reached 3.1%, the volume of treated diesel was 30 mL-D/g-A.The regeneration of adsorbent was also studied, the results show that the aggregation effect of NiO, ZnO, Al2O3 and SiO2 particles in the process of calcination in air+reduction in H2, which makes the grains growth, crystallinity becomes bigger, homogeneous dispersion becomes worse, pore blockage and the decrease of specific surface area. All these factors caused the decrease of the desulfurization performance.