The Application Of Carbon Nitride Material In Oxidative Desulfurization

SO_x is released by burning sulfur in fuel oil, which not only pollutes the atmosphere, but also harms people’s health. Countries around the world have also issued relevant laws and regulations to limit the sulfur content in fuel oil. Due to the mild operating condition, low in production cost and environmentally friendly of oxidative desulfurization, it attracts the attention of researchers in recent years. There are mainly two problems in oxidative desulfurization technology at present:（1） heteropoly acid catalyst has high catalytic activity, but it is difficult to recycle, so the cost of catalyst is very high.（2） the oxidation efficiency of hydrogen peroxide is very high, but it is decomposed into oxygen easily above 60 oC. So it is very dangerous in storage, transportation and industrial application. Therefore, there are two problems to solve in preparing high efficient supported heteropoly acid catalysts and choosing green safety oxidizing agent. According to the above two science problem, this paper studies the following three parts.（1） Mesoporous carbon nitrogen material（mpg-C₃N₄） is prepared. The phosphotungstic acid/mesoporous graphitic carbon nitride catalyst was successfully prepared by immobilizing phosphotungstic acid（H3PW12O40, HPW） on mpg-C₃N₄. The catalyst HPW/mpg-C₃N₄ is characterized by X-ray diffraction（XRD）, nitrogen adsorption/desorption isotherms（BET）, thermogravimetric analysis（TGA）, transmission electron microscopy（TEM）, Fourier transform infrared spectroscopy（FT-IR） and inductively coupled plasma atomic emission spectroscopy（ICP-AES）. Characterization results show that the carrier（mpg-C₃N₄） is mesoporous structure（pore diameter, 15.3 nm） and HPW is immobilized on mpg-C₃N₄ successfully. Different sulfide oxidation reactivity sequence is as follows: DBT（dibenzothiophene） >4,6-DMDBT（4,6-dimethyldibenzothiophene） >BT（benzothiophene）. The stability of HPW/mpg-C₃N₄ is very excellent. The desulfurization rate is still above 98.7% after 15 recycles.（2） PPy-MWCNT was prepared by polypyrrole（PPy） modifying multiwalled carbon nanotube（MWCNT）. HPW/PPy-MWCNT was prepared by immobilizing HPW on PPy-MWCNT. The N species that exist on the NCNT surface are mainly pyridinic, pyrolic, graphitic, quaternary, and nitrogen oxides from the deconvolution of the N1 s XPS, and the average N content is around 5.26%. By measuring HPW/PPy-MWCNT, HPW/MWCNT-HNO₃ and HPW/MWCNT surface potential, we do not found that the relationship between performance of the reclaimed catalyst and electric potential of catalyst, due to the low initial activation of HPW/PPy-MWCNT.（3） Mpg-C₃N₄ was used as catalyst for fuel oil with visible light irradiation and O₂ atmosphere. The desulfurization rate was 100% with the visible light. Howerver, the desulfurization rate was only 41% under dark. In the presence of oxygen, the desulfurization rate can reach 100%. Under the condition of nitrogen（N2）, the desulfurization rate was only 41%. The mechanism of photocatalytic reaction is that the electron of valence band leaps into the conduction band with the visible light to reduce the molecular oxygen and form the superoxide radical anion(·O^2-). DBT was oxidized to sulfone by the superoxide radical anion.