HZSM-5沸石中Lewis酸与Brönsted酸协同作用下的甲基环己烷开环反应

由于水蒸气处理HZSM-5生成的骨架外铝在分子筛中体现Lewis酸性, 分子筛中骨架外铝物种的可移动性导致Lewis酸与分子筛本身的Brönsted酸在空间上具有临近性. 当甲基环己烷分子在HZSM-5的笼中转化时, Lewis酸与Brönsted酸的协同作用加快了甲基环己烷分子的转化速率, 且骨架外铝物种浓度越高, 这种协同效应越明显. 而产物的选择性只与催化剂的孔道结构有关, 与水蒸气处理所导致的酸性质的变化无关.     

Densities,refractive indices,and derived excess properties of the binary systems tert-butyl alcohol+toluene, +methylcyclohexane,and +isooctane and toluene+methylcyclohexane,and the ternary system tert-butyl alcohol+toluene+methylcyclohexane at 298.15 K

This paper reports experimental densities and refractive indices of the binary systems tert-butyl alcohol (TBA)+toluene, +isooctane, and +methylcyclohexane, and toluene+methylcyclohexane, and the ternary system TBA+toluene+methylcyclohexane, over the entire range of composition at 298.15 K. Excess molar volumes and changes of refractive indices were evaluated from the experimental data obtained. These derived properties were fitted to variable-degree polynomials. The experimental values of physical properties were compared with the values estimated by different methods of prediction.     

Adsorption of toluene, methylcyclohexane and neopentane on silica MCM-41

Adsorption-desorption isotherms of toluene, methylcyclohexane and neopentane were determined on a silica MCM-41 material of pore diameter ∼3.4 nm over the temperature range 258 K to 308 K (278 K for neopentane). The isosteric enthalpies of adsorption were determined from the isotherms at the various temperatures. It was found that the isotherms of toluene and methylcyclohexane have a similar variation with the temperature, exhibiting hysteresis at 268 K and at lower temperature, while the adsorption of neopentane is reversible at all temperatures. The three organic adsorptives interact differently with the silica surface and the isosteric enthalpies of adsorption indicated that methylcyclohexane has the weakest interaction and toluene the strongest. A slight increase in the adsorption enthalpy at the beginning of the capillary condensation step is observed with methylcyclohexane and neopentane but not with toluene.     

Volumetric Properties of Ternary-Pseudobinary Mixtures Containing Benzene and Cyclohexane

Densities have been measured as a function of composition for ternary-pseudobinary mixtures of [(benzene + toluene or methylcyclohexane) + (cyclohexane + toluene or methylcyclohexane)] by means of a vibrating-tube densimeter at atmospheric pressure and the temperature 298.15 K. The excess molar volumes, V_m^E, were calculated from the densities and correlated using the Redlich–Kister equation to estimate the coefficients and standard errors. The experimental and calculated quantities are used to discuss the mixing behavior of the components. The results show the third component, toluene and methylcyclohexane, influences the interaction between benzene and cyclohexane.     

The equilibrium phase properties of selected naphthenic binary systems: Carbon dioxide-methylcyclohexane,hydrogen sulfide-methylcyclohexane

Vapor and liquid equilibrium phase compositions have been determined at temperatures ranging from 310 to 478 K for two binary systems. Measurements were made at 311.0, 338.9, 394.0, and 477.2 K for the carbon dioxide—methylcyclohexane system and at 310.9, 352.6, 394.3 and 477.6 K for the hydrogen sulfide—methylcyclohexane system. At each temperature, pressures ranged from the vapor pressure of methylcyclohexane to the vapor pressure of hydrogen sulfide, or to a pressure near the critical for the system, whichever was higher. The data were used to calculate equilibrium ratios for each component in the binary system.     

Effect of hydrogen bonding on the intramolecular charge transfer fluorescence of 6-dodecanoyl-2-dimethylaminonaphtalene

The effect of hydrogen bonding on the intramolecular charge transfer (ICT) of 6-dodecanoyl-2-dimethylaminonaphtalene (laurdan) in neat and binary solvent mixtures has been investigated by using steady-state and time-resolved spectroscopic techniques. The different features of ICT emission of laurdan in methylcyclohexane–tetrahydrofuran and methylcyclohexane–ethanol are explained by the absence and presence of hydrogen bonded ICT. The presence of isosbestic point in absorption spectra of laurdan in methylcyclohexane–ethanol confirms the formation of 1:1 complex between laurdan and ethanol. The obtained data were used to determine the stoichiometric equilibrium constants. In protic rigid (77 K) the fluorescence spectra of laurdan show excitation wavelength dependence (the red-edge effect). Moreover, we reported the decay characteristics of laurdan molecule in locally excited (LE) and ICT state in methylcyclohexane–ethanol.     

Effects of the Presence of Cyclohexane or Methylcyclohexane on the Densities and Volumetric Properties of the Mixture (Benzene + Propionitrile)

Excess molar volumes, V_m^E, have been obtained as a function of composition for ternary-pseudobinary mixtures of [(benzene + cyclohexane or methylcyclohexane) + (propionitrile + cyclohexane or methylcyclohexane)] from the densities measured by means of a vibrating-tube densimeter at atmospheric pressure and a temperature of 298.15 K. The values of V_m^E have been correlated using the Redlich–Kister equation to estimate the coefficients and standard errors. The experimental and calculated quantities are used to discuss the mixing behavior of the components. The results show that the third component, cyclohexane or methylcyclohexane, has a significant effect on the interaction between benzene and propionitrile.     

负载型Pt/CeO_2-Al_2O_3催化剂的制备及其脱氢性能

通过超声辅助共沉淀法制备了具有高比表面积、大孔容和大孔径的CeO_2-Al_2O_3复合载体,并以此制备了一系列负载型Pt/CeO_2-Al_2O_3催化剂,采用XRD、氮吸附、NH3-TPD、SEM和TEM等方法对复合载体和催化剂进行了表征;以甲基环己烷为模型化合物,考察了Pt/CeO_2-Al_2O_3催化剂的脱氢性能,研究了载体中Ce/Al物质的量比及反应温度对其催化脱氢性能的影响。结果表明,当Ce/Al物质的量比为0.5时,Pt/CeO_2-Al_2O_3催化剂在450℃下具有较高的脱氢性能;甲基环己烷转化率达到88.53%,甲苯的选择性达94.63%。     

Characterization of the ground state pyrene complex in ethylene-propylene copolymer solutions

Pyrene-labeled functionalized ethylene-propylene (EP) copolymer was prepared by grafting 1-pyrenebutyrylhydrazine onto EP copolymer through maleic anhydride pendants. The EP copolymer contained 60 mol % ethylene; its weight-average molecular weight (M^w) was 148,000. The pyrene-labeled amide functionalized EP copolymer, PA-EP(60/40), was made to simulate the amine functionalized EP copolymers that are commonly used as dispersant additives in motor oils. UV absorption spectra, fluorescence emission and excitation spectra, and fluorescence decay profiles of the pyrene were studied to determine the copolymer conformation and dynamics in methylcyclohexane and tetrahydrofuran (THF). The pyrene fluorescence characteristics of PA-EP(60/40) were highly dependent on the solvent. The dependence of fluorescence emission intensity on the excitation wavelength was large in methylcyclohexane and moderate in THF. A frequency shift of about 2 nm was observed between the excitation spectrum obtained with the emission line at 377 nm and that at 550 nm in the methylcyclohexane solutions, but no shift was found in the corresponding tetrahydrofuran solutions. The ratios of the preexponential factors (a₂₁/a₂₂) of the excimer decays obtained in both methylcyclohexane and THF solutions were different from ?1.0. However, the deviation of the excimer formation process from the Birks scheme is small in THF but large in methylcyclohexane. In addition, the Huggins constants obtained from intrinsic viscosity measurements of the PA-EP(60/40) copolymer solutions suggest that copolymer aggregation occurs in methylcyclohexane but not in THF. H-bonding between two pyrene-containing pendants is apparently the main driving force for the formation of the ground state pyrene complex. THF is found to be effective in inhibiting the H-bonding formation. © 1995 John Wiley & Sons, Inc.     

Liquid-liquid equilibria of (cyclohexane + acetonitrile + methylcyclohexane + toluene) and of {(acetonitrile + methylcyclohexane) + benzene or + toluene or + cyclohexane or + chlorobenzene} at 298.15 K

Tie-line results at 298.15 K and atmospheric pressure are reported for (cyclohexane + acetonitrile + methylcyclohexane + toluene) and for {(acetonitrile + methylcyclohexane) + benzene or + toluene or + cyclohexane or + chlorobenzene). The extended UNIQUAC and UNIQUAC equations are used to correlate binary vapour-liquid equilibria and mutual solubilities for 10 mixtures constituting the ternary mixtures and to predict the ternary and quaternary liquid-liquid equilibria by use of only binary parameters.     

Direct electrochemical hydrogenation of toluene at Pt electrodes in a microemulsion electrolyte solution

In the present study, we demonstrated a new concept for the direct electrochemical hydrogenation of toluene using an acidic microemulsion electrolyte with active Pt electrodes to pave the way for efficient methylcyclohexane mass production. We have achieved a Faradaic efficiency of 80% for the toluene/methylcyclohexane conversion at a Pt black electrode, under galvanostatic conditions and in a one-compartment cell. The reaction rate and selectivity of the toluene reduction were found to depend strongly on the surface structure of the Pt electrodes.     

The Anomalous Emission Characteristics of the Cyalume Fluorescer: 9,10-Bis (Phenylethynyl) Anthracene

A fancy emission behavior was found in the light carrier of the commercial Cyalume light stick, 9,10-bis (phenylethynyl) anthracene (BPEA). The yellowish-orange emission is noted from BPEA in methylcyclohexane matrix. Nitrogen laser time-resolved spectroscopy and excitation luminescene studies of BPEA in methylcyclohexane showed that the different emission behavior is probably due to the different conformation of the ground state of the BPEA in solid and in solution.     

Separation of Aromatics/Cyclic Aliphatics by Nonporous Adaptive Pillararene Crystals

The separation of cyclic aliphatics of high purity, which are produced from hydrogenation of the corresponding aromatics, is highly desired in the chemical industry. An energy‐efficient and environmentally friendly adsorptive separation method using nonporous adaptive crystals of perethylated pillar[5]arene (EtP5) and pillar[6]arene (EtP6) is described. Adaptive EtP5 crystals separate toluene from methylcyclohexane with 98.8 % purity, while adaptive EtP6 crystals separate methylcyclohexane from toluene with 99.2 % purity. The selectivities come from the stability of new EtP5 and EtP6 crystal structures upon capture of toluene and methylcyclohexane, respectively. The reversible transformations between nonporous guest‐free EtP5 or EtP6 structures and guest‐loaded structures make them highly recyclable.     

Partial hydrogenation of toluene over a ruthenium catalyst — A model treatment of a deactivation process

Hydrogenation of toluene to methylcyclohexene and methylcyclohexane was performed over a commercial 5% Ru/act. charcoal catalyst. The reaction was strongly affected by deactivation of the catalyst. The complete reaction model was examined together with a number of its simplified versions regarding their ability to fit experimental data. On the basis of the regression analysis results it was shown that methylcyclohexene could be thought as the main source of the strongly and irreversibly adsorbed surface deposits responsible for activity decrease of the catalyst. Direct transformation of toluene to methylcyclohexane was found to be insignificant. On the other hand substantial role of disproportionation of methylcyclohexene was proved.     

On the mechanism of alkane S1 decay

Results of photodecomposition studies of liquid cyclohexane n-octane, n-decane and methylcyclohexane with 7.6 eV photons are reported for various temperatures. In all cases the yield of molecular elimination decreases with decreasing temperature. In the presence of xenon this yield is also found to decrease. The fluorescence decay rate of cyclohexane and methylcyclohexane as obtained from pulse radiolysis measurements, shows a considerable temperature dependence, and is increased in the presence of xenon. The results of the photodecomposition experiments and of the fluorescence experiments are compared and discussed.     

Excess Molar Enthalpies of Cyclic Ethers with Cyclohexane, Methylcyclohexane, or Chlorocyclohexane

Excess molar enthalpies for mixtures of tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran or 2,5-dimethyltetrahydrofuran with cyclohexane, methylcyclohexane, or chlorocyclohexane were determined at 25°C. The excess enthalpies are positive for the mixtures containing cyclohexane or methylcyclohexane, but negative for the mixtures containing chlorocyclohexane. The results were used with the Prigogine–Flory–Patterson theory to predict the corresponding excess molar volumes.     

Study on volatility and flash point of the pseudo binary mixtures of sunflower-based biodiesel + methylcyclohexane

The transesterification of sunflower seed oil was carried out in supercritical ethanol without using any catalyst to produce biodiesel. In the present work, methylcyclohexane was added to enhance the vapor pressure of biodiesel. The vapor pressures of mixtures of biodiesel + methylcyclohexane as a function of temperature were measured by comparative ebulliometry with an inclined ebulliometer. The vapor pressures versus composition at different temperatures were obtained. Experimental data of vapor pressures and equilibrium temperatures were correlated by the Antoine equation. A mathematical model was used to predict the flash point of the pseudo binary mixtures. With the regular solution theory, the predictive flash point displays agreement with the experimental data obtained by closed cup test.     

Excess Enthalpies of 2-Methyltetrahydrofuran + (2,2,4-Trimethylpentane or n-Heptane) + Methylcyclohexane at 25°C

Measurements of excess molar enthalpies at 25°C in a flow microcalorimeter, are reported for the two ternary mixtures 2-methyltetrahydrofuran + 2, 2, 4-trimethylpentane + methylcyclohexane and 2-methyltetrahydrofuran + n-heptane + methylcyclohexane. Smooth representations of the results are described and used to construct constant-enthalpy contours on Roozeboom diagrams. It is shown that useful estimates of the ternary enthalpies can be obtained from the Liebermann–Fried model using only the physical properties of the components and their binary mixtures.     

Proprietes physico-chimiques de reseaux polymeriques modeles—II. Influence de la temperature

Polystyrene gels were prepared by anionic copolymerization of styrene and divinylbenzene in dilute solution. There has been a study of the stress-birefringence, as a function of temperature, of these networks swollen to equilibrium in cyclohexane and methylcyclohexane.     

环庚烷正离子重排反应的从头算研究

先采用HF方法,基组采用STO-3G,对环庚烷正离子的重排机理进行了初步粗略的从头算研究,较快地找到了反应过程中的部分过渡态。然后再采用MP2/3-21G方法精确计算了整个重排过程中的各个过渡态的几何构型、零点能,同时对反应路径也进行了计算,以作进一步的过渡态验证。得出的结论是:环庚烷正离子的重排是环的缩小过程,在生成甲基环己烷叔正碳离子的过程中,经历了2个过渡态;首先是C(1)C(7)的键长变长、C(1)C6的键长变短,β位H(20)逐渐远离与之相连的C(1),与C(7)形成化学键;然后是与C+相连的H(16)逐渐远离C+,与β位的C(1)形成化学键,产生稳定的甲基环己烷叔正碳离子椅式结构,甲基环己烷叔正碳离子还有可能进一步重排为一个含伯正碳离子的甲基环己烷结构,计算了每一步重排反应所需的活化能。