Permeation of N-butane,propane and ethane through ethylcellulose

The permeation of n-butane, propane, and ethane in ethylcellulose has been measured over a pressure range from 25 to 200 mm Hg and over the temperature range from 30 to 70°C. The permeation and diffusional time lag of each of the three gases in ethylcellulose is pressure dependent. Transport of the gases through ethylcellulose can be described by the partial immobilization model. It was found that, in general, the Langmuir-mode species diffusion coefficients are lower than the Henry's law species diffusion coefficients. The logarithm of diffusion coefficients at zero penetrant concentration varies linearly with the square of the molecular diameter of n-butane, propane, and ethane permeating through ethylcellulose. This relationship suggests that the diffusion process depends upon the availability of sufficient cross-sectional area for the penetrant to diffuse. An Arrhenius temperature dependence was observed for permeation coefficients and diffusion coefficients for n-butane, propane, and ethane in ethylcellulose. The activation energy of diffusion at zero penetrant concentration is directly proportional to the square of the gas molecular diameter and the entropy of activation. This observation is consistent with the view that the activation energy of diffusion is associated with the energy required to produce a space of sufficient cross-section for the diffusion molecule to pass.     

Effect of ethane addition on propane pyrolysis

Pyrolysis of propane/argon mixture in the presence of trace quantities (0.1% and 0.9%) of ethane was investigated at reflected shock wave temperatures between 1200 and 2000K. Traces of ethane accelerated propane decomposition at high temperature. However, increase in the quantity of ethane added to propane/argon mixture did not result in the same increase of its accelerating influence. Ethylene, methane and acetylene were the main hydrocarbon reaction products, with small quantities of propylene and ethane detected only at lower temperatures. Below 1500K, addition of ethane slightly enhanced the yields of ethylene and methane at the expense of propylene and ethane respectively. The selectivity for acetylene increased with increasing temperature and with the decline of those for the other products. For none of the products, did the presence of ethane alter the relationship between product formation rates and temperature. The influence of ethane addition on propane pyrolysis at high temperatures was explained in terms of increased radical concentrations, especially hydrogen atoms and vinyl radicals, formed at high conversions. These accounted for the rapid acceleration of propane decomposition and the high yield of acetylene at high temperatures.     

Viscosities of moderately concentrated solutions of polyethylene in ethane,propane, and ethylene

The viscosities of moderately concentrated solutions of low-density polyethylenes in ethane, propane, and ethylene have been measured at low shear rate in the temperature range of 150–250°C and in the pressure range of about 15000–30000 psi. Within the precision of the measurements, the relative viscosity is independent of pressure over the range investigated but increases as the solvent is changed from propane through ethane to ethylene. The activation energy for the relative viscosity in ethane varies from about 0.5 to 2.5 kcal/mole as the concentration changes from 5 to 15 g/dl. Effects of polymer concentration and molecular weight on solution viscosity in ethane at 150°C have been determined, and all of the data can be represented by a single straight-line plot of the logarithm of relative viscosity versus the intrinsic viscosity (in p-xylene at 105°C) times concentration. This simple relation is valid over wide ranges of polymer concentration and molecular weight and over more than two orders of magnitude of relative viscosity. The solution viscosities of the polyethylenes in the three supercritical fluid solvents used appear surprisingly low at first sight. This behavior is partly a result of the low solvent viscosities but also might mean that the polymer has an abnormally low segmental friction factor compared to that in solutions under more familiar conditions.     

Oxidative dehydrogenation of ethane and propane over Mn-based catalysts

The catalytic performances of Mn-based catalysts have been investigated for the oxidative dehydrogenation of both ethane (ODE) and propane (ODP). The results show that a LiCl/MnO_x/PC (Portland cement) catalyst has an excellent catalytic performance for oxidative dehydrogenation of both ethane and propane to ethylene and propylene, more than 60% alkanes conversion and more than 80% olefins selectivity could be achieved at 650°C. In addition, the results indicate that Mn-based catalysts belong to p-type semiconductors, the electrical conductivity of which is the main factor in influencing the olefins selectivity. Lithium, chlorine and PC in the LiCl/MnO_x/PC catalyst are all necessary components to keep the excellent catalytic performance at a low temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

乙烯装置自产丙烷掺入循环乙烷共裂解

阐述了中国石化扬子石化股份有限公司烯烃厂1#乙烯装置自产丙烷作为裂解原料掺入循环乙烷共裂解运行情况，分析了对裂解炉运行周期及分离系统操作的影响，并指出该举措给装置带来的经济效益。     

乙烷丙烷单独及混合裂解相互作用机理的模拟研究

作者提出了将分子模拟和自建的一维工艺数学模型模拟计算相结合的研究速度快,结果详细的新的烃类热裂解自由基反应机理的理论研究方法。并以乙烷、丙烷及混合物相互作用机理的研究为例对该方法进行了论证。结果表明,该方法可以得到与实验研究相同的乙烷、丙烷的反应机理,并对研究较困难的乙烷和丙烷相互作用机理进行了详细研究,揭示了不同自由基相互作用的规律,同时也证明该方法是可行的。     

Kinetic modelling of the gas phase ethane and propane oxidative dehydrogenation

Gas phase thermal and oxidative dehydrogenation of ethane and propane are explored experimentally and mikrokinetically. Kinetic data for the elementary reactions postulated were adopted from the literature. The results show that oxygen plays a dominating role in the primary activation of the alkanes by producing an HO₂ and a hydrocarbon radical. The kinetic sequences developed predict satisfactorily conversion and products yields for ethane and propane oxidative dehydrogenation.     

Oxidative dehydrogenation and cracking of ethane and propane over LiDyMg mixed oxides

The oxidative dehydrogenation and cracking of ethane and propane over LiDyMg mixed oxides is reported. High yields of olefins and only moderate formation of carbon oxides was observed. Both are primary products that hardly interconvert under the reaction conditions used. Addition of chloride increases the rate of reaction, while slightly decreasing the selectivity to olefins. The addition of carbon dioxide strongly decreases the rate of reaction, the negative order of 0.5 indicating that two active Li⁺sites are blocked by the adsorption of one CO₂molecule. The reaction proceeds at low oxygen pressure primarily via elimination of dihydrogen, while at higher oxygen partial pressure the hydrogen elimination occurs via water formation. It is speculated that dehydrogenation and cracking involve Li⁺and a rather nucleophilic oxygen site.     

Spectroscopic evidences of the double hydrogen hydrates stabilized with ethane and propane

Hydrogen molecules are known to occupy the small cages of structure I (sI) and II (sII) hydrates with the aid of coguests, leading to the highly stable state of their crystalline framework. For the first time, we synthesized the double hydrogen hydrates incorporated with ethane and propane that play a special role as the hydrate promoters or stabilizers. The resulting hydrate structures cage occupancy was identified by the spectroscopic methods of the PXRD and solid-state NMR. In addition, direct GC analysis confirmed that the encaged hydrogen amounts are 0.127 for sI ethane and 0.370 for sII propane at 120 bar and 270 K. The proper hydrate thermodynamics particularly focusing on the cage occupancy estimated that 0.17 and 0.33 wt% of hydrogen are observed in small cages of sI and sII hydrates. The overall spectroscopic and physicochemical analysis strongly imply that the sII cages act as much more favorable sites than sI cages in storing hydrogen.     

Sorption of propane in poly(ethyl methacrylate) near Tg

The sorption of propane in poly(ethyl methacrylate) was investigated above and below the polymer T_g and the dual-mode sorption model parameters were evaluated. The Langmuir capacity decreased as the temperature was raised to T_g and the apparent Henry's law constant exhibited a discontinuity at T_g. The enthalpy of microvoid filling ΔH_H is more exothermic than the enthalpy of dissolution at T < T_g by about 8 kJ/mol.     

Oxidative dehydrogenation of ethane and propane: How far from commercial implementation?

This review examines the recent literature on the oxidative dehydrogenation (ODH) of ethane and propane, which aims for the synthesis of the corresponding alkenes. The following aspects are discussed: (a) the main features affecting the catalytic properties of systems based on supported vanadium oxide and molybdenum oxide; (b) the characteristics of catalysts producing outstanding olefin yields; (c) advantages in selectivity gained by means of either special reactor configurations or non-conventional conduction of the reaction; (d) the contribution of homogeneous reactions to the formation of olefins during the oxidation of alkanes.     

Modeling of thermal cracking kinetics—I: Thermal cracking of ethane,propane and their mixtures

Molecular reaction schemes for the thermal cracking of ethane, propane and their mixtures have been derived from observed product distribution, radical mechanisms, and thermodynamic principles. The rate parameters were determined in a systematic way by estimation techniques minimizing a multi-response objective function. Discrimination between rival models was based upon physical criteria and statistical tests. The reaction scheme obtained by the superposition of single component cracking also satisfactorily fits the data for the cracking of mixtures of ethane and propane.     

Silica-supported tantalum clusters: catalysts for conversion of methane with n-butane to give ethane, propane, and pentanes

Si0₂-supported tantalum clusters were prepared by adsorption of the precursor Ta(CH₂Ph)₅ (Ph is phenyl) on the support followed by treatments in H₂ at 523, 623, and 723 K. The resultant clusters, had approximate average diameters of 0.3, 0.8, and 2 nm, as determined by extended X-ray absorption fine structure (EXAFS) spectroscopy. The samples were tested as catalysts for conversion of methane with n-butane in a once-through flow reactor operated at atmospheric pressure and 523 K, and EXAFS spectroscopy was used to characterize the used catalysts. The results show that (a) the catalysts are active for the conversion of methane with n-butane to give ethane, propane, and pentanes; (b) catalytic activity decreased to nearly zero over a time on stream of 22 h; (c) the catalyst incorporating the smallest clusters exhibited the highest initial activity and that incorporating the largest clusters exhibited the lowest activity; (d) each used catalyst contained clusters of approximately the same nuclearity as the respective fresh catalyst, but with Ta–Ta bond lengths approximately 0.17 ? longer than those found in the fresh catalysts. The data are consistent with catalysis by the supported clusters, and the product distributions are consistent with disproportionation of n-butane accompanied by the reaction of methane with propane to give other alkanes.     

Solid–fluid phase behaviour of linear polyethylene solutions in propane, ethane and ethylene at high pressures

The solid–fluid phase transitions for a series of linear polyethylene fractions (M_w: 800, 7000, 23 625, 52 000, 59 300 g/mol) in propane, ethane and ethylene were measured in the temperature range from 360 to 423 K and at pressures up to 2000 bar. Conditions of precipitation of the solid polyethylene from supercritical solutions seem to have minor influence on dissolution of the solid polymer in supercritical solvents. In general, an increase of pressure results in a shift of the solid–fluid phase transition to higher temperatures, i.e. solubility of polyethylene decreases. The solid–fluid phase boundaries for systems composed of low-molecular weight polyethylene and propane show temperature minima. The effect is not observed in the high-molecular weight polyethylene + propane systems and systems with ethane or ethylene as solvents. It was observed that the temperature of the solid–fluid phase transition measured at a constant pressure and a constant composition is not a monotonic function of molecular weight of the polymer. The order of the dissolution temperatures depends on pressure.     

乙二胺双-2-羟基丙磺酸(EDHPS)的合成及阻垢缓蚀性能研究

以亚硫酸氢钠、环氧氯丙烷为主要原料,合成中间体3-氯-2-羟基丙磺酸钠(ES),ES与乙二胺反应生成乙二胺双-2-羟基丙磺酸(EDHPS).通过元素分析、红外光谱、核磁共振等手段对合成的产物进行了结构鉴定.用静态阻垢法和旋转挂片失重法对产物的阻垢性能、缓蚀性能进行了评价.结果表明:EDHPS具有优良的阻垢、缓蚀性能,属于一种低氮、无磷的新型水处理剂.     

Equilibrium isotherms and adsorption heats analysis for ternary mixture of methane,ethane, and propane on 4A zeolite

Equilibrium isotherms were obtained experimentally and theoretically for adsorption of methane, ethane, and propane mixtures on 4A zeolite at 301 K. The experimental data were measured using constant volume method and analyzed by extended Langmuir, modified extended Langmuir, and extended Freundlich isotherm models. The best correlation was achieved with the extended Freundlich isotherm equation and the negative values for heats of adsorption indicate exothermic adsorption nature for these gases on 4A zeolite. The selectivity of 4A zeolite to adsorb gases was also studied with the observation that ethane was more selectively adsorbed than methane on 4A zeolite, while propane was less selectively adsorbed on this zeolite at the studied temperature. Also, it was found that an increase in initial partial pressure of ethane decreases the adsorbed amount of methane, while the increase in partial pressure of methane had no effect on adsorbed amount of ethane.     

Polyethylene exposed to liquid propane: Sorption and permeation kinetics and mechanical properties

Data obtained by sorption and permeation measurements of liquid propane in medium-density polyethylene were analyzed with an analytical diffusion model, assuming a constant diffusion coefficient, and a numerical model, based on the free volume theory of Fujita. The stress-strain properties of propane-swollen medium-density polyethylene were recorded in an Instron tensile tester. The sigmoid sorption curves (modeled here for the first time) were adequately described using nonstationary boundary conditions. The numerical model was capable of representing sorption, desorption, and permeation data, whereas the analytical technique gave satisfactory results only for sorption/desorption data in the initial, transient stage. The difference between diffusion coefficients determined from sorption and desorption measurements and the time dependence of the modulus-solute concentration relationship can be explained by assuming a relaxation of constrained amorphous chain segments. The penetrant-induced structure rearrangement is, according to differential scanning calorimetry measurements, confined to the amorphous phase.     

Oxidation of propane to acetone and of ethane to acetaldehyde by O2 in zeolites with complete selectivity

Oxidation of propane by O₂ to acetone was observed in solvent-free BaY and CaY under irradiation with visible light as well as under dark thermal conditions. The reaction was monitored in situ by FT-infrared spectroscopy. In the case of the photochemical oxidation, isopropyl hydroperoxide was detected as reaction intermediate. No byproduct was observed even upon > 50% conversion of the alkane. Ethane was oxidized completely selectively to acetaldehyde in CaY under irradiation with blue light. This revised version was published online in July 2006 with corrections to the Cover Date.     

Modeling of thermal cracking kinetics—II: Cracking of iso-butane,of n-butane and of mixtures ethane—propane—n-butane

Molecular reaction schemes for the pyrolysis of isobutane and normal butane were derived from experimental products distributions, radical mechanisms and thermodynamic principles. The associated parameters were estimated by non linear regression using a Marquardt routine for the minimization of a suitable objective function. The discrimination between the rival models was based on physical criteria, statistical tests and the closeness of fit. The prediction of the product distributions of the cracking of binary mixtures of normal and isobutane, n-butane and ethane, n-butane and propane and the ternary mixtures of n-butane, propane and ethane was based upon a model obtained from the superposition of the models for single component cracking.     

Selective oxidation of propane and ethane on diluted Mo–V–Nb–Te mixed-oxide catalysts

Te-free and Te-containing Mo–V–Nb mixed oxide catalysts were diluted with several metal oxides (SiO₂, γ-Al₂O₃, α-Al₂O₃, Nb₂O₅, or ZrO₂), characterized, and tested in the oxidation of ethane and propane. Bulk and diluted Mo–V–Nb–Te catalysts exhibited high selectivity to ethylene (up to 96%) at ethane conversions <10%, whereas the corresponding Te-free catalysts exhibited lower selectivity to ethylene. The selectivity to ethylene decreased with the ethane conversion, with this effect depending strongly on the diluter and the catalyst composition. For propane oxidation, the presence of diluter exerted a negative effect on catalytic performance (decreasing the formation of acrylic acid), and α-Al₂O₃ can be considered only a relatively efficient diluter. The higher or lower interaction between diluter and active-phase precursors, promoting or hindering an unfavorable formation of the active and selective crystalline phase [i.e., Te₂M₂₀O₅₇ (M = Mo, V, and Nb)], determines the catalytic performance of these materials.