Stability of acetylene/methane and acetylene/hydrogen/methane gas mixtures at elevated temperatures and pressures

Hydrogen-enriched natural gas (HENG) containing a mixture of acetylene, hydrogen, and methane is produced from natural gas feedstock in our plasma dissociation process. Storage of this HENG fuel at pressures up to 4000 psig is required for rapid vehicle refueling. Little information on the stability of acetylene mixtures at elevated pressures is presently available; therefore we have performed stability testing on gas mixtures that simulate our HENG fuel. This report describes the stability testing of binary gas mixtures of acetylene and methane containing up to 10%(v) acetylene, and a ternary gas mixture of 4%(v) acetylene, 20%(v) hydrogen, and 76%(v) methane, at pressures up to 3600 psig and temperatures up to 200 °C. The mixtures tested were found to be stable to rapid spontaneous decomposition at all test conditions; however, some degree of hydrogenation of acetylene to ethylene may have occurred in an intermediate mixture of acetylene and hydrogen while preparing the highest pressure ternary test mixture.     

Mechanical properties and permeability of polypropylene and poly(ethylene terephthalate) mixtures

The synthetic membranes currently used for soil stabilization and road construction are mainly made of polypropylene and of polyesters. They are used separately for each application. The polymer used has an effect on the wettability and, the permeability of the membrane. The polypropylene membranes, for instance, have a zero wettability, whereas it is high for polyester membranes. This paper reports on the mechanical properties and the permeability of mixtures of polypropylene (PP) and poly(ethylene terephthalate) (PET). The elastic modulus of the mixture was at a minimum for a 50/50 mixture. For the other compositions, the moduli gave a positive deviation as compared with the additivity equation results. This is probably due to the fact that pure PET has a fragile behavior at the temperature at which the mechanical tests were run. This 50/50 composition corresponds to the domain where a phase inversion occurs. The permeability to water vapor gave an S-shape curve that is typical of a “mixture” of immiscible polymers. The diffusion of the water molecules is controlled by the continuous phase. To compatibilize the two homopolymers, a 94/6 copolymer of PP and of polyacrylic acid was added, at various levels, to a 60/40 mixture of PET and PP: This did not affect markedly the elastic modulus. The yield stress increased, however, indicating that we had a better adhesion and that the copolymer seems to have a certain emulsifier effect, increasing the quality of the dispersion.     

Evaluation of extraction properties of N-methylpyrrolidone and ethylene glycol mixtures by gas chromatography

Gas chromatography has shown that the selectivity of binary mixtures of N-methylpyrrolidone with ethylene glycol for aromatic hydrocarbon extraction purposes increases with increasing amounts of ethylene glycol in the mixture and is optimum in the range of 50–70% (w/w) of ethylene glycol. This was attributed to hydrogen bonding between the two solvents used.     

PEBA/EPH热可逆凝胶膜的制备及其气体分离性能

通过热致相分离法制备了具有高气体渗透性能的聚醚共聚酰胺/乙二醇苯醚凝胶膜(PEBA/EPH),并探讨了EPH含量对其物理化学结构及CO2/N2渗透性能的影响。结果表明,PEBA/EPH凝胶膜具有良好的力学性能及优异的气体渗透性能,EPH的添加使得膜结晶度及熔融温度下降,从而CO2、N2在凝胶膜内的渗透系数显著增加。同时,由于EPH对于CO2具有优先吸附性,凝胶膜的CO2/N2选择性也相应增加。当EPH含量从0%增加到60%时,凝胶膜的CO2渗透系数由234 barrer增加到1 040 barrer,CO2/N2的气体选择系数从22.5增加到40.5。     

溶解乙炔气回收技术在湿法乙炔气生产中的成功应用

介绍了溶解乙炔气回收技术的先进性和回收装置的建设方案,评估了对溶解乙炔回收技术应用创造的经济效益.     

Dust/gas mixtures explosion regimes

The explosion features of nicotinic acid dust in atmosphere of methane and air at different concentrations of either dust or gaseous fuel are studied. Experimental measurements of the pressure history, deflagration index and flammability limits are performed by the standard 20 l Siwek bomb though adapted for such hybrid mixtures.Data show non linear effect of explosion severity and the synergistic effects when hybrid mixtures explode. Results allow the definition of five different regimes of the gas/dust/air mixture explosion in the plane dust concentration vs. fuel concentration.     

Calculation of the detonation parameters of acetylene mixtures

The detonation parameters of mixtures of acetylene with oxygen and air are calculated over a wide rage of concentrations. The heat of condensation of carbon is shown to be a major source of energy supply to the detonation wave at high acetylene contents.     

PU-EVA共混膜的制备及其气体性能研究

采用溶剂挥发法制备了不同组成聚氨酯(PU)/聚乙烯-聚醋酸乙烯酯共聚物(EVA)及与聚醋酸乙烯酯(PVAc)共混膜,并研究了聚合物种类和添加量对膜的化学结构、表面形貌及O2和N2渗透性能的影响。结果表明,EVA和PVAc与PU的相容性良好。添加EVA28和EVA40后,PU-EVA28和PU-EVA40共混膜的O2和N2气体渗透系数均明显增加;当EVA28的添加量为50%时,膜的O2和N2渗透系数分别可达到25.84 Barrer和8.58 Barrer。添加PVAc后,O2和N2渗透系数呈下降趋势,而PU-PVAc共混膜的O2/N2的选择性随着PVAc的添加量增加而增大,由5.70增加到6.21。     

Morphology and permeability in extruded polypropylene/ethylene vinyl-alcohol copolymer blends

Studies of the morphology of extruded polymer blend systems have shown that it is feasible to produce a laminar structure of an ethylene vinyl-alcohol copolymer (EVOH) dispersed phase in a polypropylene (PP) matrix phase. The laminar structure forms in the core of the extrudate when a slit die is incorporated into the extrusion process. Morphological studies, including a study of morphology development inside the die and studies of the effect of processing conditions on the morphology of the final product, revealed that the laminar structure is a result of die design. Processing conditions influence mainly the shape and dimensions of the laminar core region of the extrudate. Oxygen permeation tests have shown that the blend exhibits lower oxygen permeability than pure PP, when EVOH is incorporated as a dispersed phase into the system. Oxygen transmission rates obtained with a blend system approach those obtained with a multilayer coextrusion product, although only at high EVOH concentrations. Comparison of experimental data with theoretical permeation predictions shows that, up to 20 wt% EVOH, the reduction in oxygen transmission rate follows the prediction for a homogeneous system. At 25 wt%, a considerable decrease in oxygen transmission rate is noticeable, and the trend for higher EVOH contents is towards the behavior of a multilayer system.     

PU-EVA共混膜的制备及其气体性能研究

采用溶剂挥发法制备了不同组成聚氨酯(PU)/聚乙烯-聚醋酸乙烯酯共聚物(EVA)及与聚醋酸乙烯酯(PVAc)共混膜,并研究了聚合物种类和添加量对膜的化学结构、表面形貌及O2和N2渗透性能的影响。结果表明,EVA和PVAc与PU的相容性良好。添加EVA28和EVA40后,PU-EVA28和PU-EVA40共混膜的O2和N2气体渗透系数均明显增加;当EVA28的添加量为50%时,膜的O2和N2渗透系数分别可达到25.84 Barrer和8.58 Barrer。添加PVAc后,O2和N2渗透系数呈下降趋势,而PU-PVAc共混膜的O2/N2的选择性随着PVAc的添加量增加而增大,由5.70增加到6.21。     

乙炔电还原制备乙烯的反应机理

选择钯电还原乙炔制备乙烯并通过气相色谱法对产品进行表征,利用第一性原理计算方法探讨乙炔在催化剂Pd (111)表面的吸附情况,采用循环伏安法研究钯电极在硫酸溶液中还原乙炔的电极过程,测定电极的稳态极化曲线并根据极化曲线推算Tafel斜率,重点结合表观传递系数及反应级数对拟定的乙炔电还原制备乙烯的反应机理进行验证。实验结果表明:乙炔分子在Pd (111)面上呈平行桥键构型时最稳定;钯电极在硫酸溶液中可将乙炔电还原为乙烯;得出了反应最可能的速率控制步骤。     

Pressure measurements at the combustion front of gas-free pyrotechnic mixtures with low gas permeability

It is shown that the method of continuous measurement of pressure at the combustion front using an axial-force gauge is applicable to gas-free pyrotechnic systems producing solid reaction products and characterized by low gas permeability of specimens in the initial state. Small inclusions of a high-energy material producing gas combustion products are placed in the specimens to check the reliability of the result. These inclusions are located near the inlet to the main line going to the pressure gauge. The results of experiments on Ti+C+20% TiC specimens containing inclusions of pyroxylin powder are given. Institute of Experimental Physics, Sarov 607190. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 2, pp. 76–80, March–April, 1997.     

Basic self-ignition regimes and conditions for their realization in combustible gas mixtures

Self-ignition of hydrogen-air mixtures has been studied experimentally. This process was initiated behind a reflected shock wave at an initial pressure of up to0.5 MPa and with hydrogen volume contents ranging from9.5–20 and40–60%. Simultaneous recording of pressure and temperature profiles near the end of a shock tube made it possible to reveal the specific features of various self-ignition regimes and the regions of their existence. The peculiarities of the realization and evolution of mild and strong self-ignition processes are discussed, and a comparison with self-ignition of carbon-air mixtures is done. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow 117977. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 2, pp. 3–10, March–April, 1997.     

The permeability of quaternary particulate mixtures

The fall of small particles through a bed of large ones under the influence of gravity has been termed interparticle percolation and is a fundamental process that contributes to bulk segregation in free-flowing powders. For particles larger than the minimum interstices of the bed, percolation is induced only under shear.The bed of particles under shear is modelled as a series of layers in which the percolating particle moves from one layer to the next.A prediction for the Péclet number is made and is in good agreement with experiment. As the number of layers in the failure zone increases, the percolation behaviour becomes well described by a convective diffusion equation. Comparisons with a series of well-mixed reactors and axial mixing of a liquid flowing through a packed bed are made.     

The permeability of ternary coke mixtures

Experimental measurements are reported of permeabilities of beds of ternary mixtures of 27.6, 17.4 and 5.1 mm coke particles under turbulent gas flow regime. The results obtained are presented in the form of ternary diagrams of isopermeabilities from which the standard permeability of any mixture in the ternary system used can be read off directly. As no ternary permeability data exist in the literature, no comparison with other work could be made. It is however, concluded that the standard permeability of any ternary and higher order mixtures of any particulate solids may be obtained from eqn. (3) by inserting appropriate values of the mean particle size and bed porosity.