Pyrolysis of petroleum fractions

Dynamic kinetic analyses were performed on different Brazilian petroleum fractions by thermogravimetry. The data were treated by a multiple heating rate methodology. The apparent activation energies for the light and middle fractions within the range of 62–74 kJ mol⁻¹ and for heavy distillation residues were within the range of 80–100 kJ mol⁻¹ at lower conversions and 100–240 kJ mol⁻¹ at higher conversions. The kinetic study can be a criterion for tells apart the main phenomena involved in the thermal behavior of the refinery feedstock.     

Geminate recombination processes induced by rare gas collisions with predissociating NaI molecules prepared by femtosecond excitation

NaI molecules predissociate after excitation with ultrashort pulses at a peak wavelength of 320 nm. In rare gas environments at higher pressures the process of geminate recombination is likely to occur. We studied the dynamics of these processes under various pressure conditions and for different collision partners. The calculations were performed within a three-dimensional statistical model which simulates the NaI wave-packet dynamics with classical trajectories and the collisions via an instantaneous hard-sphere scattering. Received: 4 May 1998 / Accepted: 27 July 1998 / Published online: 28 September 1998     

毛细管色谱法在苯产品馏程分析中的应用研究

 对苯产品中的烃类杂质含量与苯的馏程之间的相关性进行研究。结果表明 ,当苯中烃类杂质含量在一定范围内时 ,根据毛细管色谱法对苯中烃类的分析结果 ,可以准确地反映出苯馏程是否合格 ,从而提出了以苯中烃类杂质含量的测定取代苯馏程的测定。使苯馏程分析由经典的蒸馏法改为毛细管色谱分析法 ,并在实际生产分析中得以实施应用。     

用气相色谱-质谱和气相色谱-红外联用技术分析热裂解汽油C9馏分中的组成

采用气相色谱-质谱和气相色谱-红外联用技术对热裂解汽油C9馏分中的组分进行分离和定性分析。实验使用了50m聚甲基硅氧烷毛细管色谱柱,EI电离源,电离能70eV和10eV,红外光谱仪的检测器为MCT。通过分析确定了热裂解汽油C9馏分中52个化合物的结构。降低质谱的电离能有利于确定组分的分子量。质谱可以提供被测组分的裂解碎片离子和分子量的信息,红外在确定官能团和同分异构体时要优于质谱。两种联用技术的使用较好地解决了单一方法测定复杂混合物中组分结构所存在的缺陷。     

Participation of preadsorbed atoms in heterogeneous recombination of hydrogen atoms on semiconductor surfaces

Atoms trapped from the vapor phase in the preadsorbed state were found to provide the catalytic activity of semiconductors in the heterogeneous recombination of hydrogen atoms.     

Genetic characterization of Escherichia coli RecN protein as a member of SMC family of proteins

The proteins of SMC family are characterized by having Walker A and B sites. The Escherichia coli RecN protein is a prokaryotic member of SMC family that involved in the induced excision of Tn10 and the repair of the DNA double strand breaks. In this work, the Walker A nucleotide binding site of the E. coli RecN protein was mutated by changing the highly conserved lysine residue 35 to the aspartic acid (D), designated as recN_K35D. Reverse genetics was utilized to delete the entire recN gene (ΔrecN108) or introduce the recN_K35D gene into the E. coli chromosomal DNA. The recN_K35D cells showed decrease in the frequency of excision of Tn10 from gal76::Tn10 after treatment with mitomycin C compared to recN⁺ cells. The ΔrecN108 cells showed an un-induced increase in the frequency of Tn10 excision from gal76::Tn10 in rec⁺ background while, recBC sbcBC ΔrecN108 cells are completely deficient in Tn10 excision. The recombination proficiency is reduced in cells carrying recBC sbcBC cells in addition recN_K35D mutation. We observed that the Walker A nucleotide binding site is important for the RecN protein. Strains that deleted recN gene are recombination deficient and more sensitive to mitomycin C than strains carrying recN_K35D.     

Post-modification using aluminum isopropoxide after dye-sensitization for improved performance and stability of quasi-solid-state solar cells

In this study, dye-sensitized TiO₂ electrodes were immersed into a solution of aluminum isopropoxide and after hydrolysis quasi-solid-state solar cells were fabricated. The interaction between the dye and the resulting Al₂O₃ overlayer was investigated by ultraviolet–visible (UV–vis) spectrum, Fourier transform infrared (FTIR) spectrum and X-ray photoelectron spectrum (XPS). The current density–voltage (I–V) characteristics showed that the overlayer increased the photovoltage and decreased the photocurrent under low intensity irradiation, and increased both the photovoltage and photocurrent under AM 1.5 irradiation. The Al₂O₃ overlayer at the dye/electrolyte interface resulted in a 28% improvement in overall photo-to-electrical conversion efficiency from 2.60 to 3.32%. Dark current measurements showed that Al₂O₃ acted as an insulator barrier to retard recombination between the TiO₂ and dye/quasi-solid-state electrolyte interface. Without encapsulation, dye-sensitized solar cells with Al₂O₃ coating after sensitization also exhibited improved stability compared to cells without coating.