Research On Different Catalytic Oxidation Methods For Ultra Deep Desulfurization Of Diesel Fuel

As people pay more attention to the serious pollution and harm produced by SO2 from combustion of fuels containing high proportion of sulfur to environment, ultra-deep desulfurization of fuel oil has become an environmentally urgent subject due to the very stringent environmental regulations that limit the sulfur levels in diesel fuels to less than 15ppm. Conventional hydro-treating process can remove the most of the organic sulfur compounds present in the fuels. However, it also results in a significant reduction of octane number due to the saturation of olefins. The refractory benzothiophenic sulfur compounds in diesel are very difficult to desulfurize to achieve a total sulfur level of less than 15μg/g using conventional hydro-treating processes. Catalytic oxidation desulfurization technology may prove to be the most economical method among different deep desulfurization technologies since it needn't to operate under the high pressure and temperature.This work is mainly concerned with the removal of thiophenic sulfur in diesel fuel using catalytic oxidation method with activated carbon, the modification of solid super acid catalyst SO42-/ZrO2 and its catalytic activity for oxidation reaction of thiophene, the aerobic oxidative desulfurization of thiophenic sulfur in diesel fuel over Ce, La -based catalysts and coupling with adsorption of super surface area activated carbon was also investigated. It is not only of great important scientific significance but also of great prospect in practice application.The removal of thiophenic sulfur in diesel fuel using catalytic oxidation method with activated carbon was investigated. The kind and concentration of thiophenic sulfur in diesel was determined separately by gas chromatography with a sulfur chemiluminescence detector. The composition of diesel being sold at market was determined by gas chromatography-mass spectrometry. H2O2-HCOOH-AC catalytic oxidation system was used to remove the thiophenic sulfur in diesel fuel. Results showed the organic sulfur in real diesel contained mainly BT, BT alkylated derivatives, dibenzothiophene (DBT) and DBT alkylated derivatives. The BT, BT alkylated derivatives,DBT and DBT alkylated derivatives can all be oxidized;The more the electron density on sulfur atom is, the faster the oxidation velocity is,and the larger the removal selectivity is. The order of catalytic oxidation selectivity is followed as: DBT alkylated derivatives > DBT > BT alkylated derivatives> BT. With this method, the concentration of total sulfur in diesel reduced to less than 10μg/g from original 1200μg/g. H2O2-HCOOH-AC system could reduce the content of arene and alkene in diesel, so the proportion of saturated hydrocarbons increased, which was positive for the quality of diesel. This is a new point of this work. The solid super acid catalyst SO42-/ZrO2 was modified by doping with different metal oxides, and then a series of modified solid super acid catalysts such as, SO42-/ZrO2 , SO42-/ZrO2-ZnO, SO42-/ZrO2-Fe2O3, SO42-/ZrO2-CuO and SO42-/ZrO2-Al2O3 were obtained by coprecipitation method. With oxygen as oxidant, the catalytic oxidation kinetic experiments of thiophene over the modified solid super acid catalysts were carried out. Results showed that doping Zn, Fe, Cu metal oxides to SO42-/ZrO2 can improve the catalytic oxidation activity of the catalysts,of which the catalytic activity of SO42-/ZrO2-ZnO was the highest and the conversion efficiency of thiophene can reach very high at 50℃. The characterization results of the catalysts by powder X-ray diffraction(XRD) and temperature programmed desorption of ammonia(NH3-TPD) showed that the more the content of T-ZrO2 on the catalyst surfaces was, the more its acid amounts was, and thus it had higher catalytic activity.In this paper, we wish to oxidize desulfurization of thiophenic sulfur in diesel fuel over Ce, La-based catalysts at high pressure and then couple with adsorption of super surface area activated carbon to achieve the ultra deep desulfurization of diesel. It was found that the catalytic activity of La-based catalyst is much larger than the Ce-based catalyst. La2O3 /γ- Al2O3 can reduce the concentration of total sulfur to 350μg/g from original 1200μg/g at 200℃. In order to get ultra-clean diesel (<5μg/g), the super surface area activated carbon was used next. More importantly, this technology can avoid waste water which exsit with conventional oxidation desulfurization technology. The breakthrough capacity was 4.704mg of sulfur per gram of adsorbent (mg-S/g-adsorbent). This is an important new point of this work.