Pollution in the atmosphere has been an issue to be resolved by the government of every nation. Sulfur-containing compounds (e.g. SOx) in air, in particular, are harmful gases affecting human health. Therefore the governments or international organizations have established emission control legislations and/or measures for sulfur-containing compounds in order to control their emission. The gasoline and diesel oils for industrial applications as well as the gasoline and diesel oils for use as fuels in automobiles contain compounds of sulfur, and combust to generate gases including sulfur dioxide. This is the major polluting source generating sulfur-containing compounds. So the petroleum refining industry generally requires a desulfurization process to reduce sulfur content of the petroleum.
As is well known, gasoline and diesel oils generally contain 300 to 500 ppmw of sulfur-containing compounds, and combust to generate sulfur compounds harmful to automobile engines, human health and the environment. So in recent years more attention is devoted to low-sulfur automobile fuels. One of desulfurization technologies is hydrodesulfurization, which may effectively remove certain sulfur-containing compounds, such as thiols and sulfides. Although the hydrodesulfurization method may lower a part of the sulfur content in gasoline and diesel oils, there are limitations in this method, for example it is unable to remove thiophenic compounds such as alkyl dibenzothiophenes (DBTs) bearing one or more alkyl groups at 4- and/or 6-position(s). Thus it is not possible for deep desulfurization. Besides, the hydrodesulfurization method requires to be carried out at a high temperature such as 320-380° C. and a high pressure such as 3-7 Mpa. Hence a great amount of energy needs to be consumed. Also, equipments capable of withstanding the high temperature and the high pressure need to be made, so the cost of equipment is high.
Another desulfurization technology is the use of desulfurizing adsorbents, such as reduced metals, metal oxides, metal loaded zeolite-based materials, activated alumina, carbonaceous materials, and the like. However, low sulfur adsorption capacity of these adsorbents is their major defect because of low pore volume and low surface area to volume ratio. This defect has limited their applications.
Nanotechnology has in recent years found applications in many areas. Since nanomaterials possess surface effect, volume effect and quantum size effect, they exhibit many surprising physical and chemical properties. Of these materials, magnetic nanoparticles (MNPs) may form a core-shell structured composite microsphere together with organic compounds, polymers or inorganic materials by surface copolymerization and surface modification, wherein the core is magnetic, and the shell possesses surface-active functional groups able to couple with various organic and inorganic species. Under the action of an externally-applied magnetic field, the magnetic nanoparticles may be conveniently separated from the base solution. The separation is simple, costs little and has high separation efficiency. Moreover, the magnetic microspheres possess a large specific surface area, so they have the advantages including high adsorption capacity, fast adsorption rate, and the like. They show very good prospects for applications in the separation, adsorption and purification of substances.
Chinese patent application No. 200510019060.9 discloses a Fe3O4/Au core-shell structured magnetic nanogranule and a method of its preparation. The method comprises adding a mixture of aqueous ammonia and sodium citrate to a mixed solution of FeCl2 and FeCl3, controlling the growth of an iron oxide nanogranule, then adding sodium citrate solution and HAuCl4 solution, and growing on the Fe3O4 nanogranule a Au shell layer to form a Fe3O4/Au core-shell structured magnetic nanogranule. The nanogranule may be used in biology and medicine.
International patent application No. WO 01/78506A1 discloses an oxide nanoadsorbent and a method of its preparation. The oxide nanoadsorbent may destroy biological reagents such as toxins. The oxide may be MgO, CaO, TiO2, ZrO2, FeO, Fe2O3, NiO, CuO, Al2O3, ZnO, Mn2O3, V2O3, V2O5 and mixtures thereof. The particle surface of the oxide nanoadsorbent disclosed in this application may be modified by a metal oxide different from itself.
Presently, in order to reduce damages to the industrial production and the environment by sulfur-containing compounds and safeguard human health, researchers have conducted substantial research work on the desulfurization of substances containing sulfur-containing compounds. In particular, extensive attempts have been made to the deep desulfurization (removing thiophenic compounds) of gasoline and diesel oils for use as fuels in automobiles. There are now some compound adsorbents for thiophenic compounds being tried for deep desulfurization, but their small specific surface area limits their loading capacity. So their desulfurizing ability is not high.
People are becoming more concerned with the design and manufacture of magnetic nanoparticles which find a wide range of applications in many areas such as magnetic separation, magnetic probing, biomedicine. However, application of magnetic nanoparticles in deep desulfurization has not been known yet.