Deep Desulfurization Of Diesel Fuel By Highly Selectively Photocatalytic-Adsorptive Technologies

Sulfur in diesel caused environment and human health issues and attracted worldwide attention. Therefore, The government has enacted more and more strict regulations, from low-sulfur diesel to near zero-sulfur diesel. The refineries have facing the great challenge to meet the requirement. Among the current desulfurization technologies, adsorptive desulfurization(ADS) has been considered as a promising desulfurization technology because of its simple operation under mild conditions. In this work, Metal-Organic Frameworks(MOFs) and Ti O2/Si O2 were chosen as the adsorbents, the ADS performance and adsorption mechanism were further discussed.In the first part, three kinds of MOFs were compared and their adsorption capacity and selectivity of thiophenic compounds were assessed. The combined experimental and simulation approach was employed to illustrate the ADS mechanism over MOFs. Results showed that:(1) adsorption capacity and selectivity for DBT and 4,6-DMDBT followed the order of Cu-BTC > MIL-101(Cr) > MIL-100(Fe);(2) Other components in real diesel fuels, such as trace amount of organic nitrogen, water and large amount of aromatic hydrocarbons, competed with the thiophenic compounds for adsorption sites to different extents;(3) The combined experimental and computational results suggested that the adsorption of thiophenic compounds over Cu-BTC was dominated by the interaction between the conjugated π system and the lone pair of electrons on sulfur atom of thiophenes, and the coordinatively unsaturated sites on Cu-BTC. Alkyl groups of thiophenic compounds functioned as both electron donor and steric inhibitor on ADS.A novel approach of photocatalytic adsorption based on the bifunctional Ti O2/Si O2 was proposed for the selective adsorption of thiophenic compounds from diesel. Results showed:(1) Highly dispersed Ti O2 served as the photocatalytic sites and Si O2 acted as the selective adsorption sites for the corresponding oxidized DBT. These two types of active sites worked cooperatively to achieve the high adsorption selectivity of Ti O2/Si O2 and the kinetic rate-determining step for the adsorption was DBT oxidation;(2) With the employment of UV-irradiation, high organosulfur uptake of 5.12 mg/g was achieved on the optimized 0.3Ti O2/0.7Si O2 adsorbent at low sulfur concentration of 15 ppm, and its adsorption capacity of thiophenic compounds over naphthalene was twice as that of Cu-BTC, suggesting photocatalytic adsorption can be a suitable approach for deep desulfurization of diesel. In the adsorption of the real diesel, the process can remove the sulfur in real diesel fuel to below 6 ppm, and reached the requirement. Consecutive adsorption-regeneration cycles suggested that the 0.3Ti O2/0.7Si O2 adsorbent can be regenerated by acetonitrile washing followed with oxidative air treatment.Novel bifunctional Ti O2@mesoporous silica and Ti O2-C3N4/Si O2 adsorbents were also studied for the photocatalytic adsorption. Results showed that:(1) Under UV-irradiation, all of the four Ti O2@ mesoporous silicas were capable of effectively removal of more than 85% of thiophenic compounds from model fuels. Among these, Ti O2@SBA-15 was able to remove the thiophenic compounds in real diesel fuel to as low as 1.31ppm;(2) Under visible light-irradiation, the desulfurization capacity of the novel Ti O2/C3N4@SBA-15 was able to desulfurize the fuel with the ADS capacity of 3.22mg/g.