Formation of the structure-Ⅱ gas hydrate from low-concentration propane mixed with methane

It has been recognized that a small amount of propane mixed with methane can change greatly in not only the thermodynamics but also the structural properties of gas hydrate. However, its mechanism is still not well understood yet. In this research, structure-Ⅱ(sⅡ) hydrate is synthesized using a methanepropane gas mixture with an initial mole ratio of 99:1, and it is found that large(5¹²6⁴) cages are cooccupied by multiple gases based on the rigid structure analysis of neutr...     

Liquid–liquid equilibria of ternary mixtures of methanol + MEG + n-C5, ethanol + MEG + n-C5, and n-butanol + MEG + n-C5

New liquid–liquid equilibrium data of ternary systems of mono ethylene glycol + n-pentane + methanol, mono-ethylene glycol (MEG) + n-pentane + ethanol, and mono ethylene glycol + n-pentane + n-butanol from 283.15 to 293 K are presented in this work. Binodal curves were obtained by the cloud point titration method. Tie-line compositions were obtained through density and sound velocity measurements of phases in equilibrium. Results show that the solubility increases with temperature in all systems and decreases as the alcohol chain increases. The relative solubility data indicate that the alcohols are more soluble in MEG than in n-C5. The obtained experimental data were successfully correlated using the CPA and the PC-SAFT equation with appropriate binary interaction parameters.     

Screening of ionic liquids as entrainers for the separation of 1-propanol + water and 2-propanol + water mixtures using COSMO-RS model

The COSMO-RS model was used to screen potential ionic liquids for the separation of aqueous azeotropic mixtures 1-propanol?+?water and 2-propanol?+?water. A combination of 22 cations (involving imidazolium, pyridinium, pyrrolidinium, quinolinium, and ammonium) and 36 anions were investigated. The anions chloride [Cl] and dihydrogen phosphate [H₂O₄P] were found to strongly influence the vapor liquid equilibrium behavior, whereas the ammonium-based cations diethanol ammonium [(Et)₂AMM]⁺ and tetra methyl ammonium [M₄AMM]⁺ were the most promising cations. In addition, the study of mixing enthalpy and excess Gibbs free energy confirmed that the molecular interaction of ionic liquids with water was found to be much larger than that with alcohols 1-propanol and 2-propanol, indicating the presence of a strong hydrogen bonding between the ionic liquids and water. Further, the addition of ionic liquids to the alcohol–water mixture reduces the activity coefficient of water and increases the relative volatility of the mixture, facilitating easier separation. Ionic liquids [(Et)₂AMM][Cl], [(Et)₂AMM][H₂O₄P], [M₄AMM][Cl], and [M₄AMM][H₂O₄P] are expected to be effective entrainers for the separation of the industrially important 1-propanol?+?water and 2-propanol?+?water systems.     

Thermodynamic data for separation of ternary mixture (1,2-propanediol + 1,3-butanediol + 1,4-butanediol) by distillation

Thermodynamic behaviors of ternary system (1,2-propanediol (1,2-PG)?+?1,3-butanediol (1,3-BD)?+?1,4-butanediol (1,4-BD)) were studied in this paper. Vapor–liquid equilibria (VLE) data of systems (1,2-PG?+?1,3-BD), (1,2-PG?+?1,4-BD), (1,3-BD?+?1,4-BD), and (1,2-PG?+?1,3-BD?+?1,4-BD) were measured at 101.3?kPa. The binary interactive parameters were obtained by regressed the binary VLE data with different models. The results have shown that the Wilson model, the NRTL model and the UNIQUAC model are suitable to describe the ternary system, but the UNIFAC model is not appropriate; the residue curve map of the ternary system was obtained on the basis of the binary interactive parameters. Finally, the design and optimization of the two-column sequence distillation process were completed for separation of the ternary system. Under the optimized conditions, product amounts of 1,2-PG, 1,3-BD, and 1,4-BD can be up to 0.98, 0.90, and 0.98, respectively, after separation.     

The absorption of propane and ethene in slurries of activated carbon in water—I

A gas mixture of propane and ethene was absorbed batchwise in a stirred cell in a slurry of activated carbon in water. The selectivity of the absorption process was investigated. Experiments were performed in which the influence of carbon particle size, and especially the addition of a small amount of fines, was studied. It was found that at the beginning of the experiments ethene was absorbed more readily than propane; later the adsorbed ethene was driven away from the carbon by propane. Addition of small amounts of carbon-fines resulted in an increase of the observed gas—liquid mass-transfer coefficients and also in the selectivity of the process changes. A new continuous ultrasonic gas analyser for high-resolution determination of the gas mixture composition has been developed.     

Facilitated transport separation of propylene–propane: Experimental and modeling study

Supported liquid membrane, as one type of facilitated transport membranes, was used for the separation of propylene–propane mixtures. The effect of trans-membrane pressure and carrier concentration on membrane separation performance were evaluated in terms of mixed-gas selectivity, propylene and propane permeances and propylene and propane permeation fluxes. A general dimensionless model for the transport of components across the membrane was proposed and solved numerically by orthogonal collocation method. Experimental results showed that for a 70:30 (vol.%) propylene–propane mixture, at pressure 120 kPa and carrier concentration 20 wt.%, a propylene permeation flux of 1.46 × 10⁻⁴ mol/m² s was obtained. Mathematical results are in well agreement with experimental results. The average deviation between experimental and modeling results was found to be 5.3% for propylene permeation flux and 0.03% for propane permeation flux.     

The reversibility of the adsorption of methane–methyl mercaptan mixtures in nanoporous carbon

The results of extensive molecular dynamics simulations and theoretical considerations of the adsorption of methane–methyl mercaptan mixtures in slit-shaped carbon nanopores are presented. We observe significant mobility of both methane and mercaptan molecules within the pore volume, between pores, and between adsorbed and gas phases for a wide range of temperatures and pressures. Although mercaptans adsorb preferentially relative to methane, the process remains reversible, provided non-oxidizing conditions are maintained. A mercaptan/methane ratio of the order of 200 ppm in the adsorbed phase is sufficient for the gas phase to have a mercaptan concentration above the human threshold for detection. The reversibility of the adsorption process and low concentration of mercaptans makes it unlikely that these would be harmful for adsorbed natural gas storage systems.     

The IR spectroscopy of methane and hydrogen adsorbed on α-chromia

The vibrational perturbations induced in the IR spectra of methane and of dihydrogen by the non-dissociative adsorption on the (01 2) and (11 0) faces of -chromia are illustrated and compared. It is concluded that both molecules are adsorbed on Cr³⁺ sites and that the involved forces are mainly of the electrostatic type. The resulting situation is compared with that found on the more basic MgO. The problems associated with the C–H and H–H bond activations on transition metal oxides are also discussed.     

Kinetics of methane combustion over Pt and Pt–Pd catalysts

A kinetic study was performed over thermally aged and steam-aged Pt and Pt–Pd catalysts to investigate the effect of temperature, and methane and water concentrations on the performance of catalysts in the range of interest for environmental applications. It was found that both catalysts permanently lose a large portion of their initial activity as result of exposure to 5 vol.% water in the reactor feed. Empirical power-law and LHHW type of rate equations were proposed for methane combustion over Pt and Pt–Pd catalysts respectively. Optimization was used to determine the parameters of the proposed rate equations using the experimental results. The overall reaction orders of one and zero in methane and water concentration was found for stabilized steam-aged Pt catalyst in the presence and absence of water. The apparent self-inhibition effect caused by methane over Pt–Pd catalyst in the absence of water was associated with the inhibiting effect of water produced during the combustion of methane. A significant reversible inhibition effect was also observed over steam-aged Pt–Pd catalyst when 5 vol.% water vapor was added to the reactor feed stream. A significant reduction in both activity and activation energy was observed above temperatures of approximately 550 °C for steam-aged Pt–Pd catalyst in the presence of water (the activation energy dropped from a value of 72.6 kJ/mol to 35.7 kJ/mol when temperature exceeded 550 °C).     

Combustion and emission characteristics of a diesel engine fuelled with diesel–propane blends

In this paper, the combustion and emission characteristics of a direct injection diesel engine operating on diesel–propane blends were investigated. The results showed that under the same operating condition, the effective thermal efficiency increased with the increase of propane proportion in the blends. Ignition delay and combustion durations of diesel–propane blends were decreased with the increase of propane proportion in the blends. Maximum cylinder pressure, maximum rate of pressure rise, maximum rate of heat release and maximum mean combustion temperature of the diesel–propane blends increased with the increase of propane proportion in the blends. Simultaneous reduction in exhaust CO, HC and smoke emissions could be realized when operating on the diesel–propane blends. Exhaust NO_x emission gave an increasing trend when operating on the diesel–propane blends.     

Kinetics of copolymerization of styrene-isoprene-butadiene rubber with2,2-di(tetrahydrofuran-2-yl)propane as polar modifier

SIBR is a new-style rubber with an excellent combination of low rolling resistance and high wet skid resistance,and could be applied to making high performance tires.2,2-di (tetrahydrofuran-2-yl) propane(DTHFP),as a new kind of polar modifier for terpolymerization of styrene(St),isoprene(Ip) and butadiene (Bd),has not been reported.In this paper,the anionic terpolymerization of St,Ip,Bd was conducted with DTHFP as polar modifier,n-BuLi as initiator,hexane/cyclohexane as solvent at different temperatures.The kinetics of anionic copolymerization of St,Ip,Bd was investigated using the method of gas chromatography.     

Oxidative coupling of methane at 600 °C on CaNiK oxide catalysts

We are herewith reporting new data which modifies, explains and extends our earlier work on this subject. Previous observations of low CH₄ conversion and high selectivity to C₂ hydrocarbons were erroneous due to the formation of bulk CaCO₃ in the catalyst. The carbonate was detected by powder X-ray diffraction and was shown to accumulate during the reaction and decompose during regeneration. Catalytic runs which incorporated an internal standard revealed a deficit in the C balance consistent with carbonate formation. Actual CH₄ conversions were 20% with 15% selectivity to hydrocarbons. The effect of steam in promoting coupling over combustion was affirmed.     

Rate oscillations during partial oxidation of methane over chromel–alumel thermocouples

A chromel–alumel thermocouple has been found to catalyse the methane/oxygen reaction, the main products being CO, H₂ with some CO₂ and H₂O. Regular oscillations in both reactants, products and temperature have been observed at temperatures around 700C. Similar behaviour has been obtained using nickel wires.     

Dry reforming of methane over palladium–platinum on carbon nanotube catalyst

A dry reforming (DR) catalyst based on bimetallic Pd–Pt supported on carbon nanotubes is presented. The catalyst was prepared using a microwave-induced synthesis. It showed enhanced DR activity in the 773–923?K temperature range at 3 atm. Observed carbon balances between the reactant and product gases imply minimal carbon deposition. A global three-reaction (reversible) kinetic model—consisting of DR, reverse water gas shift, and CH₄ decomposition (MD)—adequately simulates the observed concentrations, product H₂/CO ratios, and reactant conversions. Analysis shows that, under the conditions of this study, the DR and MD reactions are net forward and far from equilibrium, while the RWGS is near equilibrium.     

Oxidative coupling of methane over LaCoO3−δ-based mixed oxides

The catalytic activity of LaCoO_3–-based mixed oxides for the oxidative coupling of methane has been tested by TPR and cyclic reaction. Characterization has been done by XRD, TGA and Mössbauer spectrometry. It is likely that the perovskite-crystal structure containing hypervalent metal ions has an important role and that unique structural oxygen species in the perovskite contribute to the partial oxidation of methane.     

Enhancement of the activities with feedstream doping by tetrachloromethane in the oxidative dehydrogenation of propane on α-magnesium pyrovanadate

The oxidative dehydrogenation of propane to propylene has been investigated on -magnesium pyrovanadate (Mg₂V₂O₇) at 723 K in the presence and absence of tetrachloromethane (TCM). Under the present conditions, the conversion of propane and the selectivity to propylene were 5.0 and 74.5%, respectively, in the absence of TCM while those were 14.0 and 70.2%, respectively, upon addition of a small amount of TCM (P(TCM) = 0.34 kPa) into the feedstream on the catalyst. The conversion of propane on Mg₂V₂O₇ without oxidant in the presence and absence of TCM revealed that a contribution of lattice oxygen in the catalyst to the oxidation was strongly controlled by the addition of TCM, resulting in the enhancement of the activity with TCM.     

Effects of Ga content and reaction pressure upon the aromatization of propane over H–Ga–Al-bimetallosilicate catalysts

Aromatization of propane has been investigated at 540 °C in a reaction pressure range up to 0.686 MPaG over MFI-type H–Ga–Al-bimetallosilicates having various Ga/(Ga + Al) atomic ratios but a constant Si/(Ga + Al) ratio of 15. Both the propane conversion and the aromatic selectivity increased with increasing the Ga/(Ga + Al) ratio up to 0.25. Further increase in the Ga content decreased the propane conversion, although the aromatic selectivity increased. Of the catalysts examined, the H–Ga–Al-bimetallosilicate sample having the Ga/(Ga + Al) ratio of 0.25 showed the highest performance for propane aromatization. The effect of reaction pressure was investigated using this catalyst. With increasing the reaction pressure, the propane conversion increased, but the aromatic selectivity decreased. The reaction pressure was also found to strongly influence the cracking activity and the deactivation rate of the catalyst. From the analysis of the gaseous products, it was concluded that the aromatization reaction was suppressed under high reaction pressure conditions because of the formation of methane and ethane by protolytic cracking and hydrogen transfer from aromatic precursors to olefinic intermediates.     

Performance of Ni/MgO–AN catalyst in high pressure CO2 reforming of methane

The catalytic activity of 8.8 wt Ni/MgO–AN prepared from alcogel derived MgO was studied for the dry reforming of methane under high pressure (1.5 MPa). The catalyst showed a self-stabilization process during the reaction that lasted for 50 h, in which the catalytic activity decreased with increasing the reaction time on stream (TOS) up to 12 h, and then became stabilized thereafter. The activity decline during the initial 12 h of the reaction was found closely related to an increase in the amount of carbon deposits on the catalyst, which also became stabilized after the catalyst had served the reaction for 12 h. Comprehensive characterizations of the coked catalyst with Temprature programmed hydrogenation (TPH), X-ray photoelectron spectroscopy (XPS) and X-ray diffractometer (XRD) techniques revealed two kinds of carbon deposits (-carbon and -carbon) on the used catalyst. The -carbon deposits were found to be produced from CH4 decomposition while the -carbon deposits from CO disproportionation. It was revealed that the accumulation of -carbon deposits was a key cause for the activity decline and the self-stabilized catalysis during the initial 12 h of the high-pressure reaction. Moreover, it was also observed that an unavoidable sintering of metallic Ni particles from 6.5 to 11 nm, which happened within the very first hour of the reaction, was not directly related to the catalyst stability.