Study On Photocatalytic Oxidation Desulfurization Of Fluid Catalytic Cracking Gasoline

Along with more attention being paid to environment protection worldwide, most countries have made laws or regulations to restrict the sulfur content in fuel oil with a more rigorous standard. Photochemical oxidation is a new technology to degrade sulfur-containing compounds in oil, and has received much attention as a new technology for deep desulfurization of light oil in recent years because of its advantage such as low cost, mild reaction condition and high desulphurization effect. In previous, people have mostly researched desulfurization of fuel oil phtooxidized by H₂O₂. In the paper, photocatalytic oxidation desulfurization of fluid catalytic cracking (FCC) gasoline and thiophene as its model sulfur-containing compound phtooxidized by O₂ was investigated, mechanisms of photooxidation of thiophene by O₂ were speculated, and kinetics equations were also established.Thiophene was dissolved in n-octane to form model gasoline and mixed vigorously with water. The combined solution was UV irradiated by a high-pressure mercury lamp. During photoirradiation, air was introduced by a gas pump to dissolve O₂ as oxidant. By this method, Thiophene dissolved in n-octane was photodecomposed and removed into the water phase at ambient temperature and atmosphere pressure. Thiophene was photooxidized to sulfone and ethanedioic acid,SO4₂- and CO₂. Desulfurization yield was improved by adding zeolite with high specific surface area and suitable pore size as sorbent for O₂ from 58.9% to 9₂.3%.Nano-TiO₂ was prepared by sol-gel method and used as photocatalyst in desulfurization of FCC gasoline. The results showed that the photooxidation kinetics of thiophene with TiO₂ as photocatalyst was the first-order by differential method. Desulfurization yield of model gasoline which initial sulfur content was 800μL·L-1 reached 96.0% and the kinetic equation was ln(C0/Ct)=0.6405t+0.3441.Nano-F-/Zn₂+/TiO₂ particles were prepared via the sol-gel reaction of Ti(i-OC4H9)4 in an aqueous solution of CF3COOH and Zn(NO3)₂ and the appropriate doping content were n(F)/n(TiO₂)=₂%, n(Zn)/n(TiO₂)=3%. Specific surface area, crystal size and photocatalytic activities of F-/Zn2+/TiO₂ were investigated. The powders were characterized by energy dispersion X-ray spectrum (EDS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and brunauer–emmett–teller (BET). The results showed that F- and Zn2+ were doped into TiO₂. Desulfurization yield of thiophene was improved from 96.0% to 99.2% using F-/Zn2+/TiO₂ as photocatalyst and half-time was shortened from 1.08h to 0.95h.To disperse TiO₂ in the oil phase, nano-TiO₂ was modified by Span60 and Span40 which were non ionic surfactant in ethanol. The result obtained by FT-IR and transmission electron microscopy (TEM) showed that there were Span60 or Span40 on the surface of TiO₂ nanoparticles and the degree of aggregation of nano-particles has been improved effectively. And sulfur content of FCC gasoline was decreased from 550μg·g-1 to 10μg·g-1.Riboflavin was added into the reaction system to improve light quantum efficiency as a kind of photosensitizer. And the photooxidation of thiophene sensitized by riboflavin was conducted by singlet state oxygen. It was founded that riboflavin and nano-TiO₂ showed combined catalytic effects and desulfurization yield of thiophene reached 99.1%.