Effect of Olefins on Formation of Sulfur Compounds in FCC Gasoline

The effect of olefins on formation of sulfur compounds in FCC gasoline was studied in a small-scale fixed fluidized bed （FFB） unit at temperatures ranging from 400℃ to 500℃, a weight hourly space velocity （WHSV） of 10 h-1, and a catalyst/oil ratio of 6. The results showed that C4--C6 olefins contained in the FCC gasoline could react with HzS to form predominantly thiophenes, alkyl-thiophenes as well as a fractional amount of thiols, while large molecular olefins such as heptene could react with hydrogen sulfide to form benzothiophenes. The amount of sulfur compounds formed at different tem- peratures over different catalysts were in proportion to the mass fractions of olefins in the feedstock, with the amount of sulfur compounds formed over REUSY catalyst exceeding those formed over the shape selective zeolite catalyst owing to the effect of catalyst performance and the impact of catalyst on the degree of olefin conversion. The amount of sulfur compounds generated and their increase reached a maximum at 450℃ and a minimum at 400℃ because of the influence of temperature on the thermodynamic and kinetic constants for formation of sulfur compound as well as on the olefin conversion degree. Based on the above-mentioned study, a reaction network and a model for prediction of sulfur compounds generated upon reaction of olefins in FCC gasoline with HES were established.

The role of the sulfur 3d orbitals in bond formation in sulfur-containing compounds

The role of the sulfur 3d orbitals in bond formation is discussed by taking into account the influence of the environment on the orbitals of the sulfur atom in the molecules. The ca cula- tion results of a series of prototype molecules containing sulfur such as SF_2, SF_4, NSF_3, SF_1, H_2S are reported. It is convincingly shown that in highly electronegative environment the energy levels of the sulfur 3d orbitals are reduced to the vicinity of those of the ligand valence orbitals and their spatial distributions are contracted to the bonding area, and therefore they can participate in bond formation to a certain extent, which is enhanced by the formation of the d-p π back bonds. It seems that the result reported in this paper is helpful for the solution of the long-standing debate about the sulfur 3d orbital participation in bond formation.

Role of secondary aerosols in haze formation in summer in the Megacity Beijing

A field experiment from 18 August to 8 September 2006 in Beijing, China, was carried out. A hazy day was defined as visibility 〈 10 km and RH（relative humidity） 〈 90%. Four haze episodes, which accounted for ～ 60% of the time during the whole campaign, were characterized by increases of SNA（sulfate, nitrate, and ammonium） and SOA（secondary organic aerosol） concentrations. The average values with standard deviation of SO2-＋4, NO-3, NH4 and SOA were 49.8（± 31.6）, 31.4（±22.3）, 25.8（±16.6） and 8.9（±4.1） μg/m3, respectively, during the haze episodes, which were 4.3, 3.4, 4.1, and 1.7 times those in the non-haze days. The SO2-4,NO-3, NH＋4, and SOA accounted for 15.8%, 8.8%, 7.3%, and 6.0% of the total mass concentration of PM10 during the non-haze days. The respective contributions of SNA species to PM10 rose to about27.2%, 15.9%, and 13.9% during the haze days, while the contributions of SOA maintained the same level with a slight decrease to about 4.9%. The observed mass concentrations of SNA and SOA increased with the increase of PM10 mass concentration, however, the rate of increase of SNA was much faster than that of the SOA. The SOR（sulfur oxidation ratio） and NOR（nitrogen oxidation ratio） increased from non-haze days to hazy days, and increased with the increase of RH. High concentrations of aerosols and water vapor favored the conversion of SO2 to SO2-4and NO2 to NO-3, which accelerated the accumulation of the aerosols and resulted in the formation of haze in Beijing.