含缺陷位TS-1催化氧化噻吩及甲基噻吩反应机理的量子化学研究

用ONIOM2方法 7T/45T模型优化了含缺陷位TS-1分子筛(TS-d)催化氧化噻吩及甲基噻吩各步反应的反应物、过渡态、中间体和产物的结构.我们结合实验数据,得到的路线如下:首先,TS-d吸附H2O2,然后经历质子转移生成单齿或双齿超氧化物中间体.质子转移有两条途径,单质子和双质子转移.研究表明双齿比单齿超氧化物中间体的能量更低,是更稳定的中间体.因此采用双齿中间体继续反应.噻吩和甲基噻吩氧化先形成亚砜,再进一步氧化生成砜.计算数据与实验结果一致.     

Mechanisms for the reaction of thiophene and methylthiophene with singlet and triplet molecular oxygen

Mechanisms for the reaction of thiophene and 2-methylthiophene with molecular oxygen on both the triplet and singlet potential energy surfaces (PESs) have been investigated using ab initio methods. Geometries of various stationary points involved in the complex reaction routes are optimized at the MP2/6-311++G(d, p) level. The barriers and energies of reaction for all product channels were refined using single-point calculations at the G4MP2 level of theory. For thiophene, CCSD(T) single point energies were also determined for comparison with the G4MP2 energies. Thiophene and 2-methylthiophene were shown to react with O(2) via two types of mechanisms, namely, direct hydrogen abstraction and addition/elimination. The barriers for reaction with triplet oxygen are all significantly large (i.e., >30 kcal mol(-1)), indicating that the direct oxidation of thiophene by ground state oxygen might be important only in high temperature processes. Reaction of thiophene with singlet oxygen via a 2 + 4 cycloaddition leading to endoperoxides is the most favorable channel. Moreover, it was found that alkylation of the thiophene ring (i.e., methyl-substituted thiophene) is capable of lowering the barrier height for the addition pathway. The implication of the current theoretical results may shed new light on the initiation mechanisms for combustion of asphaltenes.     

Pyrolysis of asphaltenes and biomarkers for the fingerprinting of the Amoco-Cadiz oil spill after 23 years

The geochemical technique of asphaltenes pyrolysis was successfully applied to the long-term monitoring of the Amoco-Cadiz oil spill 23 years after the wreck in the salt marshes of Île Grande, Northern Brittany, France. This method allows the reconstitution of the saturated fraction of the original oil from the asphaltenes fraction of severely degraded oil residues. The results showed that the oil reached a degradation rate of 60% relatively to the initial oil. The asphaltenes pyrolysis generated a gas chromatographic profile very similar to the original Amoco-Cadiz oil. In the biomarkers fraction, gas chromatographic/mass spectrometric (GC-MS) analyses demonstrated that terpanes were conserved whereas steranes were partly degraded. We also showed that the class of seco-hopanes biomarkers are conserved and can be used in the long-term monitoring of oil pollutions.     

甲基噻吩在HY分子筛上的吸附、脱附及转化行为

由NH₄Y分子筛制备了HY分子筛,运用N₂吸附、NH₃-TPD和Py-FTIR等手段表征HY分子筛的物化性能;采用智能重量分析仪(IGA)方法研究了甲基噻吩(2-甲基噻吩、3-甲基噻吩)在HY分子筛上的吸附-脱附行为;采用程序升温脱附-质谱(TPD-MS)联用手段研究了甲基噻吩在HY分子筛上的转化行为。结果表明,在200 ℃下 2-甲基噻吩和3-甲基噻吩在HY分子筛中的强B酸上发生强化学吸附作用,与B酸结合后生成了甲基噻吩的碳正离子结构进而发生了歧化反应、脱烷基反应以及裂化反应;与2-甲基噻吩不同的是,3-甲基噻吩与HY通过一定的氢转移反应生成了3-甲基四氢噻吩,且200 ℃吸附条件下3-甲基噻吩比2-甲基噻吩更容易发生裂化反应。     

Phase composition of asphaltenes

The phase composition of asphaltenes taken from oils of Romashskino field (Russia) was studied with calorimetry. It was found that in asphaltenes there are ordered amorphous phases which break in the temperature ranges 70–130 and 130–170 °C. Polarization microscopy data show that the liquid crystal phase appears at temperatures from 180 to 190 °C. Moreover, it is shown that in asphaltenes the crystal phases of co-precipitated paraffinic hydrocarbons and salts can be present.     

Kinetic studies of methylthiophene hydrogenation on sulfurized aluminopalladium catalysts

Kinetic studies of methylthiophene hydrogenation by dihydrogen in the presence of sulfurized aluminoppalladium catalysts were carried out at T=220–300°C and =3.3–9.5 MPa. An equation is suggested that accounts for the retarding effect of the product.

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T=220–300°C, 3,3–9,5 . , - .

     

Interaction between asphaltenes and fatty-alkylamine inhibitor in bulk solution

In the present work, the mechanism of interaction between asphaltenes and a commercial fatty-alkylamine inhibitor was investigated by a combination of techniques. The “macro” properties, like the asphaltene precipitation onset and the amount of asphaltenes precipitated, were measured by near-infrared (NIR) and UV-vis spectroscopy, respectively, while the interaction enthalpy between asphaltenes and inhibitor was measured by isothermal titration calorimetry (ITC). Asphaltenes subfractions and derivatives were also used to identify the mechanism.

ITC indicated that only a small fraction (～6%) of asphaltenes interacts strongly with the inhibitor. The proportion of interacting species was found to be higher in irreversibly adsorbed asphaltenes subfraction. These 6% are mostly composed of acidic asphaltenes, as indicated by measurements involving ester asphaltenes. However, the measurement of precipitation onset and amounts precipitated for whole and ester asphaltenes indicated that the acid–base interaction was not the main interaction responsible for the inhibitory action. Other type(s) of interaction is/are responsible for the inhibition properties of the inhibitor, which are not detected by ITC. The nature of other interactions is not known for the moment, but it was shown that irreversibly adsorbed asphaltene fraction contains a higher concentration of the functionality (ies) responsible for the “other” type of interaction.     

Predicting adsorption isotherms of asphaltenes in porous materials

In this paper we present a molecular thermodynamics approach for the modeling of adsorption isotherms of asphaltenes adsorbed on Berea sandstone, Bedford limestone and dolomite rock, using a model for bulk asphaltenes precipitation and a quasi-two-dimensional approach for confined fluids [E. Buenrostro-González, C. Lira-Galeana, A. Gil-Villegas, J. Wu, AIChE J., 50 (2004) 2552–2570; A. Martínez, M. Castro, C. McCabe A. Gil-Villegas, J. Chem. Phys. 126 (2007) 074707, respectively], both based on the Statistical Associating Fluid Theory for Potentials of Variable Range [A. Gil-Villegas, A. Galindo, P.J. Whitehead, S.J. Mills, G. Jackson, A.N. Burgess, J. Chem. Phys. 106 (1997) 4168–4186]. The theory is applied to model adsorption isotherms from experimental data of asphaltenes extracted from a dead sample of heavy crude oil from a Mexican reservoir. The theoretical results give the right Langmuir Type II adsorption isotherms observed experimentally. The model requires the determination of ten molecular parameters related to the size of the particles and the square-well potentials used to describe the particle–surface and particle–particle interactions at the bulk and adsorbed phases. Nine parameters are taken from previous published results about the behavior of asphaltenes in bulk phases and the adsorption of several molecular fluids onto activated carbon and graphite surfaces. The remaining parameter, the energy strength of the particle–surface interaction, is adjusted to reproduce the experimental data, obtaining values that are consistent with Molecular Mechanics calculations for asphaltenes adsorbed on different surfaces and solutions. Although the agreement between theory and experiments shows some deviations at low bulk concentrations, the model reproduces adsorption data at high concentrations where other semi-empirical approaches fail.     

Two-step laser mass spectrometry of asphaltenes

Defined by their solubility in toluene and insolubility in n-heptane, asphaltenes are a highly aromatic, polydisperse mixture consisting of the heaviest and most polar fraction of crude oil. Although asphaltenes are critically important to the exploitation of conventional oil and are poised to rise in significance along with the exploitation of heavy oil, even as fundamental a quantity as their molecular weight distribution is unknown to within an order of magnitude. Laser desorption/ionization (LDI) mass spectra vary greatly with experimental parameters so are difficult to interpret: some groups favor high laser pulse energy measurements (yielding heavy molecular weights), arguing that high pulse energy is required to detect the heaviest components of this mixture; other groups favor low pulse energy measurements (yielding light molecular weights), arguing that low pulse energy is required to avoid aggregation in the plasma plume. Here we report asphaltene mass spectra recorded with two-step laser mass spectrometry (L2MS), in which desorption and ionization are decoupled and no plasma is produced. L2MS mass spectra of asphaltenes are insensitive to laser pulse energy and other parameters, demonstrating that the asphaltene molecular weight distribution can be measured without limitation from insufficient laser pulse energy or plasma-phase aggregation. These data resolve the controversy from LDI, showing that the asphaltene molecular weight distribution peaks near 600 Da and previous measurements reporting much heavier species suffered from aggregation effects.     

Aggregation and solubility behavior of asphaltenes and their subfractions

Asphaltenes from four different crude oils (Arab Heavy, B6, Canadon Seco, and Hondo) were fractionated in mixtures of heptane and toluene and analyzed chemically, by vapor pressure osmometry (VPO), and by small angle neutron scattering (SANS). Solubility profiles of the asphaltenes and their subfractions indicated strong cooperative asphaltene interactions of a particular subfraction that is polar and hydrogen bonding. This subfraction had lower H/C ratios and modestly higher N, V, Ni, and Fe contents than the less polar and more soluble subfraction of asphaltenes. VPO and SANS studies indicated that the less soluble subfractions formed aggregates that were considerably larger than the more soluble subfractions. In general, asphaltene aggregate size increased with decreasing solvent aromaticity up to the solubility limit, beyond which the aggregate size decreased with heptane addition. The presence of a low wavevector Q feature in the scattering curves at 25 degrees C indicated that the individual aggregates were flocculating; however, the intensity of the feature was diminished upon heating of the samples to 80 degrees C. The solubility mechanism for Canadon Seco asphaltenes, the largest aggregate formers, appears to be dominated by aromatic pi-bonding interactions due to their low H/C ratio and low nitrogen content. B6 and Hondo asphaltenes formed similar-sized aggregates in heptol and the solubility mechanism is most likely driven by polar interactions due to their relatively high H/C ratios and high nitrogen contents. Arab Heavy, the least polar asphaltene, had a H/C ratio similar to Canadon Seco but formed the smallest aggregates in heptol. The enhancement in polar and pi-bonding interactions for the less soluble subfraction indicated by elemental analysis is reflected by the aggregate size from SANS. The less soluble asphaltenes contribute the majority of species responsible for aggregation and likely cause many petroleum production problems such as pipeline deposition and water-in-oil emulsion stabilization.     

Synthesis and reactivity of thiophene palladium and thiophene dipalladium complexes with unsaturated molecules

Reactions of 2,5‐dibromothiophene, 1 , with [Pd₂(dba)₃]^?dba [Pd(dba)₂; dba = dibenzylideneacetone] in the presence of N‐donor ligands such as 2,2′‐bipyridine (bpy) and 4,4′‐di‐tert‐butyl‐2,2′‐bipyridine (dtbbpy) give arylpalladium complexes of cis‐[2‐(5‐BrC₄H₂S)PdBrL₂], 2a, b [L₂ = bpy ( 2a ), L₂ = dtbbpy ( 2b )], and cis‐cis‐L₂PdBr[2,5‐(C₄H₂S‐)PdBr(L₂)], 3a, b [L₂ = bpy ( 3a ), L₂ = dtbbpy ( 3b )]. Treatment of cis complexes 2a, b and 3a, b with CO causes the insertion of CO into the Pd? C bond to give the aroyl derivatives of palladium complexes of cis‐[2‐(5‐BrC₄H₂S)COPdBrL₂], 4a, b [L₂ = bpy ( 4a ), L₂ = dtbbpy ( 4b )], and cis‐cis‐[(L₂)(CO)BrPdC₄H₂S‐PdBr(CO)(L₂)], 5a, b [L₂ = bpy ( 5a ) and L₂ = dtbbpy ( 5b )], respectively. Treating complexes 2a, b with 1 mole equivalent of isocyanide XyNC (Xy = 2,6‐dimethylphenyl) gave iminoacyl complexes cis‐[2‐(5‐BrC₄H₂S)C?NXyPdBrL₂], 6a, b [L₂ = bpy ( 6a ), L₂ = dtbbpy ( 6b )], and a 3‐fold excess of isocyanide XyNC (Xy = 2,6‐dimethylphenyl) gave triiminoacyl complexes [2‐(5‐BrC₄H₂S)(C?NXy)₃ PdBr], 7 . Cyclization reactions of 6a, b with 3 mole equivalents of isocyanide XyNC (Xy = 2,6‐dimethylphenyl) or cyclization reaction of 7 with 1 mole equivalent of isocyanide XyNC (Xy = 2,6‐dimethylphenyl) both gave tetraiminoacyl complexes of [2‐(5‐BrC₄H₂S)(C?NXy)₄PdBr], 8 , which was also obtained by the reaction of 1 or 2a, b with a 4‐fold excess of isocyanide XyNC with or without add Pd(dba)₂. Similarly, complexes 3a and b were also reacted with 2 mole equivalents of isocyanide XyNC (Xy = 2,6‐dimethylphenyl) to give iminoacyl complexes cis‐cis‐[(L₂)(CNXy)BrPdC₄H₂S‐PdBr(CNXy)(L₂)], 10a, b [L₂ = bpy ( 10a ), L₂ = dtbbpy ( 10b )] and an 8‐fold excess of isocyanide XyNC (Xy = 2,6‐dimethylphenyl) afforded tetraiminoacyl complexes of [2,5‐(C₄H₂S)(C?NXy)₈Pd₂Br₂], 11 . Complexes 2a, b and 3a, b reacted with TlOTf [(TfO = CF₃SO₃)] in CH₂Cl₂ to give 9a, b and 12a, b , respectively, in a moderate yield. Copyright © 2007 John Wiley & Sons, Ltd.     

Structure of molecular nanoparticles of petroleum asphaltenes

Ab initio RHF/3-21G** and MM+ molecular mechanics method are employed to calculate the structural chemical parameters of molecular nanoparticles of petroleum asphaltenes. It is found that naphtheno-aromatic rings have a non-planar cup-like character. The values of dihedral angles α ₁ between the planes of aromatic and naphthene rings, which are calculated by the RHF/3-21G** method, are within 156–163°. The values of dihedral angles α₂, which were calculated by the molecular mechanics method, are within 156–164°.     

Flocculation behavior of asphaltenes in solvent/nonsolvent systems

Diffusion coefficients of asphaltenes dissolved in two aromatic solvents, toluene-d(8) or ethylbenzene-d(10), were measured with the pulsed-field gradient spin echo nuclear magnetic resonance (PFG-SE NMR) technique upon addition of flocculant (pentane-d(12) or heptane-d(16)). It was observed that the change in the diffusion coefficients, as a function of amount of added flocculant, was small in the concentration interval studied (up to 30 wt% alkane). Complementary kinetic flocculation studies were made at alkane additions above 55 wt%. The initial change in turbidity upon the addition of alkane was measured with an UV-VIS spectrophotometer. The obtained stability ratio, W, showed that asphaltenes were least stable in the ethylbenzene-pentane system and most stable in the toluene-heptane system. These findings were in agreement with the PFG-SE NMR. When combining the results from the two different techniques it appeared as if there was a dramatic increase in flocculation above a certain "threshold concentration" of added alkane. Furthermore, the flocculation appeared to be reaction controlled until as much as 63 wt% of n-pentane or, alternatively, 68 wt% of n-heptane had been added to the systems, after which the flocculation became primarily diffusion controlled. Finally, careful relaxation measurements showed that the asphaltenes displayed two distinctly different transverse (T(2)) relaxation times (most probably averages), one at 0.6 ms and the other at 7 ms.     

Interaction of asphaltenes with nonylphenol by microcalorimetry

This paper shows the work performed in the study of the capability of isothermal titration calorimetry (ITC) to characterize the interaction between petroleum asphaltenes with a model molecule, namely, nonylphenol. ITC is widely used in biochemistry to study the interaction of proteins with ligands. The intention is to transfer the knowledge into the asphaltene field, with the aim of getting a better understanding of the mechanism of interaction, as well as the energies involved in this process. Calorimetric experiments show that nonylphenol has a complex mechanism of interaction with asphaltenes in toluene, including more than one process. Several models have been used to fit the experimental data. The enthalpies calculated with a model based on polymerization are in the order of -1 to -7 kJ/mol, which are very close to the hydrogen bond energies. This shows the capability of ITC to provide experimental data to the modeling of asphaltene behavior. The number of sites of interaction has been inferred by means of a model taken from protein-ligand science. The values obtained are in the range two to five sites per molecule, assuming an average Mw of 1000 units.