Study On Sulfur Removal From Diesel Oil Over Activated Carbon Based Adsorbent And Characterization Of Physical And Chemical Properties

The desulfurization of diesel fuel is of great significance while the regulation of sulfur content in liquid transportation fuel is becoming more and more stringent. At present, the main way to reduce sulfur content in diesel oil is hydrodesulfurization (HDS) and non-hydrodesulfurization. Hydrodesulfurization technology needs harsh conditions as follows: high temperature, high pressure, hydrogen environment, the noble metal catalysts and high operating costs. Furthermore, removal of thiophene sulfide and its derivatives are more difficult. However, adsorptive desulfurization is a new and effective method of removing sulfur from FCC diesel oil, which has some advantages as follows: simple operation, low investment, no pollution and suitable for deep desulfurization. Therefore, adsorptive desulfurization is a broad space for development and application.In this paper, activated carbon based adsorbent, loaded with copper oxide, zinc oxide and nitric acid was prepared by incipient wetness impregnation methods. Removal performance of sulfur from FCC diesel oil was evaluated using the two methods of static adsorption and dynamic adsorption in a fixed bed reactor. The effects of preparation parameters of adsorbents and operating conditions on sulfur removal performance of diesel oil were intensively discussed, such as the kind and granularity of activated carbon, loading amount of active component, calcination temperature and time, desulfurization temperature, space velocity and ratio of oil to adsorbent were studied, and the saturation sulfur capacity of desulfurizers was calculated. In the present study, the operation parameters on sulfur removal performances and optimal adsorbents were chosen, the disabled adsorbents were regenerated and physical and chemical properties of adsorbents were characterized. The practice experiences were provided for the industrialization of adsorptive desulfurization.The results indicated that, the sulfur compounds in diesel oil were effective to remove over activated carbon based adsorbent. Desulfurization performance was enhanced when active component was supported with active component, the sulfur removal efficiency decreased in the order of activated carbon loaded with CuO>ZnO, denoted as AC-A and AC-B respectively. When activated carbon was loaded with CuO/ZnO, denoted as AC-C, the sulfur removal efficiency is similar to AC-A and AC-B. When activated carbon was pretreated by nitric acid before loaded with CuO, denoted as AC-N-A, its sulfur removal efficiency was greatly enhanced comparing to AC-A. The GC-FPD chromatograms of FCC diesel oil showed that activated carbon loaded with CuO or ZnO preferred to adsorbe dibenzothiophene and its derivatives compared with other sulfur components.The content of surface basicity functional groups on desulfurizers was more than the contents of surface acidity functional groups, the content of surface basicity functional groups decreased in the order of AC-N-A>AC-C>AC-A>AC-B>AC, and the content of surface basicity functional groups decreased in the order of AC-C> AC-B>AC-A>AC-N-A>AC. Calcination and nitric acid activation did not change the surface area, pore volume and average pore diameter, and most probable pore diameters were in 20-30?. DTA-TG analysis showed that when the temperature reached 350°C, copper nitrate crystals and zinc nitrate crystals were decomposed into CuO and ZnO completely. Activated carbon was stable from 200°C to 550°C. X-ray diffraction analysis indicated that Cu2O diffraction peaks were found in desulfurizer AC-A under calcination temperature of 350°C, and Cu diffraction peaks were found under calcination temperature of 500°C and 700°C, because some copper oxide was deoxidize to copper. After desulfurization Cu2O diffraction peaks disappeared, it is probably because Cu2O participated in adsorption. Diffraction peaks in any form of Zn were not found in desulfurizer AC-B, because active component was dispersed on activated carbon.The results of removal performance of sulfur from FCC diesel oil and model diesel oil showed that, the saturation sulfur capacities over AC-A, AC-B, AC-C and AC-N-A was 0.587%, 0.531%, 0.596% and 0.808% respectively, the saturation sulfur capacities of thiophene over AC, AC-A, AC-B and AC-N-A was 0.261%, 0.325%, 0.298% and 0.470% respectively, the saturation sulfur capacities of benzothiophene over was 1.076%, 1.354%, 1.251% and 1.826% respectively. The desulfurizers prefer to selectively remove benzothiophene compared with thiophene. The saturation sulfur capacities of desulfurizers decreased in the order of AC-N-A> AC-C>AC-A>AC-B>AC.The static adsorption results indicated that when loading amount of CuO and ZnO, desulfurization temperature and time, ratio of diesel oil to adsorbent were 4.0%, 2.0%, 80°C, 2.0 h, 1.0, the sulfur removal efficiencies over AC-A, AC-B, AC-C and AC-N-A reached the maximum of 45.27%, 44.40%, 45.76% and 60.95% respectively. The dynamic adsorption results showed that, when loading amount of CuO and ZnO, calcination temperature and time, desulfurization temperature, space velocity, ratio of diesel oil to adsorbent were 4.0%, 2.0%, 350°C, 2h, 80°C, 2.0h-1, 1.0, the sulfur removal efficiencies over AC-A, AC-B and AC-C reached the maximum of 46.98%, 43.91% and 47.82% respectively. When loading amount of CuO, calcination temperature and time, desulfurization temperature, space velocity, ratio of diesel oil to adsorbent were 4.0%, 350°C, 2h, 100°C, 2.0h-1, 1.0 respectively, the sulfur removal efficiency over AC-N-A reached the maximum of 70.60%. Thermal regeneration at gas atmosphere and organic solvent washing regeneration were effective to the disabled desulfurizer AC-N-A.