High flux freeze-dried cellulose acetate reverse osmosis membranes as microporous barriers in gas permeation and separation

The permeations of helium, hydrogen, methane, ethylene, nitrogen, and argon, and helium–methane, nitrogen–ethylene, oxygen–nitrogen, and sulfur dioxide–nitrogen mixtures have been studied using freeze-dried porous cellulose acetate reverse osmosis membranes. The results illustrate the existence of mobile and immobile sorbed layers and the governing influence of surface flow in gas-phase reverse osmosis separations. Preshrunk freeze-dried porous cellulose acetate membranes seem to offer a practical means of utilizing the reverse osmosis process for recovering helium from natural gas and separating sulfur dioxide from flue gases.     

Computerized Solution of the Dynamic Sorption Process for a Ternary System in a Heterophase Medium

A mathematical model equation for the ternary adsorption–reaction process was developed and illustrated for the catalytic dehydrogenation of cyclohexane to benzene with the adsorption of hydrogen atoms as a monomolecular species on platinum–rhenium/alumina catalyst in inert and active carrier gases using pulse and continuous flow techniques. An optimization routine of the Nelder–Mead simplex method was used to estimate the surface reaction rate constant and adsorption equilibrium constant at different temperatures. These constants were then used to determine activation energies and adsorption equilibrium energies for cyclohexane dehydrogenation in inert (argon, helium) and active (hydrogen) carrier gases using pulse and continuous flow techniques. Numerical solutions for the ternary adsorption–reaction scheme were compared with the binary adsorption–reaction case where hydrogen adsorption is ignored. The predicted results for the ternary adsorption–reaction revealed that hydrogen adsorption during cyclohexane dehydrogenation is significant.     

Composition and volume of gas released by crushing coal from West Virginia,Kentucky and Alabama

Analyses of the composition and volume of gaseous inclusions in samples of coal from West Virginia, Alabama and Kentucky have been made at room temperature by mass spectrometric techniques. This was done by crushing the coal in the high-vacuum inlet system of a research mass spectrometer. The gases observed were composed of C, S, H, O, N, He and Ar atoms. Water was the most abundant gas; others were hydrogen, helium, methane, ammonia, methanol, ethanol, carbon monoxide, nitrogen, ethane, oxygen, hydrogen sulphide, argon and carbon dioxide. Gas compositions were found to be a function of the source of the coal. For example, over 6% of the gas from Alabama coal was methane, but West Virginia coal contained only 0.1% methane. The volume of gas also was a function of the coal source. Coal from Kentucky contained 2.3 cm³ g^?1 (STP), whereas coal from West Virginia contained 0.4 cm³ g^?1.     

Low-temperature filtration of gases using multilayer cermet filters

The performance characteristics of highly efficient cermet filters with a multilayer membrane structure used for the treatment of nitrogen, argon, helium, methane, carbon monoxide and dioxide at temperatures up to 75 K are studied. It is shown that as the temperature decreases, their collection efficiency with respect to a finely dispersed aerosol decreases. At low Reynolds numbers, the variation of the gas-flow pressure drop through the filters is determined by the gas viscosity. The multilayer nickel-based membrane structure is stable to substantial temperature gradients and can be regenerated by blowing and heating. It is found that the filter collection efficiency for liquid gases is determined by the pore size of the fine-pore selective layer of the filters according to the sieving mechanism of collecting dispersed particles.     

Some features of spinning hollow fibres from polycarbonatesiloxane melts

Conclusions The following parameters have been determined as a result of calculations: fibre tension, solidification path length, and the change along the spinning path of the following: stretching stresses, speed, radius, wall thickness, and fibre temperature.It has been shown that, with increase in take-up speed, the length of the section of fibre deformation is reduced, varying practically proportionally to the flow rate of the polymer system.Stability of the process of spinning hollow fibres from polycarbonatesiloxane melts is assured within a narrow range of stretching force.Translated from Khimicheskie Volokna, No. 3, pp. 41–43, May–June, 1989.     

Oxyfuel combustion using a catalytic ceramic membrane reactor

Membrane catalytic combustion (MCC) is an environmentally friendly technique for heat and power generation from methane. This work demonstrates the performances of a MCC perovskite hollow fibre membrane reactor for the catalytic combustion of methane. The ionic–electronic La_0.6Sr_0.4Co_0.2Fe_0.8O₃₋ (LSCF6428) mixed conductor, in the form of an oxygen-permeable hollow fibre membrane, has been prepared successfully by means of a phase-inversion spinning/sintering technique. For this process polyethersulfone (PESf) was used as a binder, N-methyl-2-pyrrollidone (NMP) as solvent and polyvinylpyrrolidone (PVP, K16-18) as an additive. With the prepared LSCF6428 hollow fibre membranes packed with catalyst, hollow fibre membrane reactors (HFMRs) have been assembled to perform the catalytic combustion of methane. A simple mathematical model that combines the local oxygen permeation rate with approximate catalytic reaction kinetics has been developed and can be used to predict the performance of the HFMRs for methane combustion. The effects of operating temperature and methane and air feed flow rates on the performance of the HFMR have been investigated both experimentally and theoretically. Both the methane conversion and oxygen permeation rate can be improved by means of coating platinum on the air side of the hollow fibre membranes.     

合成催化剂升温还原气水汽浓度及氨含量测定

氨合成催化剂升温还原气中含有氢气、氮气、氩气、氨及微量水。其中的微量水与电石反应,转化成乙炔;氢气、氮气、氩气及氨气与电石不反应。转化后的气体经ＰｏｒａｐａｋＮ柱分离、ＳＰ３４３０型气相色谱仪串联的ＴＣＤ、ＦＩＤ检测器,在ＴＣＤ上检测出氨气,在ＦＩＤ上检测出乙炔。用外标法计算出乙炔及氨含量,并经换算计算出水汽浓度。     

Nonisothermal flow of polymer melts and solutions in spinneret channels

Conclusions The effect of dissipation of mechanical energy on the temperature fields of polymer melts and solutions in the channels of spinnerets for fibre spinning has been investigated.It has been shown that the flow of polymer melts in spinneret channels takes place with only slight heat evolution, that is, practically under isothermal conditions. The flow of polymer solutions takes place significantly under nonisothermal conditions, with a large drop in temperature over the channel radius.Translated from Khimicheskie Volokna, No. 4, pp. 42–44, July–August, 1986.     

Separation of gas mixtures using hollow fibre membranes

Conclusions Dependences have been derived for the enrichment of a binary gas mixture with the easily penetrating component on initial concentrations and the stream ratio, and also of specific permeability on the length of the active part of hollow gas-separation fibre.The calculated data agree with experimental data obtained in apparatus employing Graviton hollow fibre in enrichment of air with oxygen.Translated from Khimicheskie Volokna, No. 6, pp. 26–27, November–December, 1988.     

Composition and volume of gas released by ‘melting’ coal from West Virginia and Alabama

Analyses of the composition and volume of gases released by ‘melting’ samples of coal from West Virginia and Alabama under vacuum have been made by mass spectrometric techniques. This was done by melting the coal in a quartz tube attached to the highvacuum inlet system of a research mass spectrometer. The gases observed were composed of C, S, H, O, N, He and Ar atoms. Hydrogen was the most abundant gas; others were helium, methane, ethylene, ethane, carbon monoxide, nitrogen, hydrogen sulphide, propane, argon, carbon dioxide and sulphur dioxide. Gas compositions were found to be a function of the source of the coal. For example, over 65% of the gas from Alabama coal was hydrogen, but West Virginia coal yielded only about 30% of hydrogen. All coals released about 100 cm³ g^?1 (STP) (about 2300 ft³ (short ton)^?1) of combustible gas. An additional observation was the fact that about 90% of the sulphur was physically separated from the coal in the vacuum melting process.     

Supercritical adsorption of ‘permanent’ gases under corresponding states on various carbons

Adsorption isotherms at 298 K have been measured on four different carbons for six gases: argon, carbon monoxide, hydrogen, methane, nitrogen and oxygen at pressures up to 7 MPa. For all the carbons, methane, on a molar basis, was adsorbed to a greater extent than all the other gases and hydrogen the least. These same gases were then adsorbed using the same carbons at temperatures corresponding to a reduced temperature of 2.36 up to reduced pressures of about 1.0. Under those conditions, five gases presented very similar uptakes on any given carbon although the porous nature of these carbons was very different. The exceptional gas was hydrogen. For every carbon, hydrogen was adsorbed to a much greater extent than the other gases. In all cases, the isotherms were reversible suggesting that only physisorption was involved. It would appear that hydrogen can penetrate into pores within the structure of carbons that go undetected by conventional pore or surface characterisation techniques. The carbon with the highest 77 K N₂ D-R micropore volume, AX-21, still showed the greatest hydrogen uptake under these reduced conditions.     

Gas transport in ethylene-propylene-diene (EPDM) elastomer: Molecular simulation and experimental study

Time lag permeation measurements with ethylene-propylene-diene (EPDM) elastomer have been undertaken in an effort to characterize the gas transport properties of this barrier material. The derived solubility and diffusivity of a series of probe gases including helium, hydrogen, neon, argon, krypton, oxygen, nitrogen, carbon dioxide and methane were measured and compared with molecular simulation predictions. Molecular Dynamics (MD) and Grand Canonical Monte Carlo (GCMC) calculations were performed to provide estimates for diffusivity and solubility, respectively. Agreement between the molecular simulations and experimental data is obtained for simple spherical monatomic probe gases, with greater deviation observed for non-spherical polyatomic gases. Additionally, agreement between semi-empirical correlations based on the effective cross-sectional area of the diffusing species and the effective Lennard-Jones interaction constant of the sorbed species is better than widely used correlations based on gas critical properties. Furthermore, the molecular simulations provide a meaningful representation for the elastomer studied and additionally appear to capture the fundamental principles of sorption and diffusion of the chosen probe gases.     

Evaluation of the mixing performance of three passive micromixers

This work presents a numerical investigation on mixing and flow structures in microchannels with different geometries: zig-zag; square-wave; and curved. To conduct the investigation, geometric parameters, such as the cross-section of the channel, channel height, axial length of the channel, and number of pitches, are kept constant for all three cases. Analyses of mixing and flow fields have been carried out for a wide range – 0.267–267 – of the Reynolds number. Mixing in the channels has been analyzed by using Navier–Stokes equations with two working fluids, water and ethanol. The results show that the square-wave microchannel yields the best mixing performance, and the curved and the zig-zag microchannels show nearly the same performance for most Reynolds number. For all three cases, the pressure drop has been calculated for channels with equal streamwise lengths. The curved channel exhibits the smallest pressure drop among the microchannels, while the pressure drops in the square-wave and zig-zag channels are approximately the same.     

Comparison of the Pyrolysis Products of Dichlorodimethylsilane in the Chemical Vapor Deposition of Silicon Carbide on Silica in Hydrogen or Argon

A chemical analysis of the pyrolysis gases and solids formed during the deposition of silicon carbide from the decomposition of dichlorodimethylsilane in argon and hydrogen is reported. Depositions were performed at 1 atm pressure, temperatures from 700° to 1100°C, and a mean residence time of approximately 1 min. The chemical analysis shows that, under reactor conditions, the gases formed were mainly methane, hydrogen, silicon tetrachloride, trichloro-silane, and trichloromethylsilane. The presence of hydrogen chloride was not examined. The use of hydrogen, as a carrier gas, decreased the trichloromethylsilane and solid aerosol (smoke) in the reaction products, compared to that present in the argon system, and increased methane, trichlorosilane, and silicon production. Primarily, silicon and silicon carbide were deposited when hydrogen was used as the carrier gas. When argon was used, a complex mixture of silicon carbide and organosilicon compounds was formed. It is hypothesized that, when hydrogen was used as the carrier gas, silicon carbide formed from chlorosilanes and methane, which were products from the decomposition of dichlorodimethylsilane. These products subsequently reacted to form silicon, which then reacted with methane to form silicon carbide. In argon, however, it is hypothesized that silicon carbide can be formed in two ways: (1) from the pyrolysis of solid organosilicon compounds which are products from the pyrolysis of dichlorodimethylsilane in argon and (2) as the reduction of dichlorodimethylsilane to chlorosilanes and methane, caused by the hydrogen produced from the pyrolysis of dichlorodimethylsilane in argon.     

Gas transport through ceramic membranes under super-critical conditions

In order to select and to apply a porous membrane under supercritical conditions, it is necessary to understand the transport mechanism affecting the permeation behaviour.This paper describes the investigation of gas transport through micro porous ceramic membranes consisting of several layers. The separation layer is made from TiO² with a nominal pore size diameter of 0.9 nm. Single gas permeation of helium, nitrogen, argon, methane, and carbon dioxide was measured in the temperature range of 293-443 K and in the pressure range of 1-10 MPa.Observation of the permeability of these membranes revealed that the transport of non?adsorbing gases under these conditions is governed by Knudsen diffusion and viscous flow.     

布朗深冷净化工艺综述

布朗合成氨工艺是当今世界先进水平的低能耗合成氨工艺,深冷净化是其中的核心,也是其独特之处。它利用原料气自身过量的氮,对原料气进行洗涤,除去几乎全部的甲烷、60%的氩气及过量的氮气,以使出口气体氢氮比达到3∶1。深冷净化的作用主要是把新鲜气的制备和氨的合成这两个系统完全分开,显著地提高了整套装置的操作弹性,使工艺操作更为灵活、方便、稳定。本工艺现已在大型合成氨装置中得到了很好的应用,未来可以将其应用于中小型合成氨厂,以降低生产合成氨的能耗。     

利用吸收-水合耦合法从氨弛放气中回收氢气的研究(英文)

In this work, the absorption-hydration hybrid method was used to recover (hydrogen + nitrogen) from (hydrogen + nitrogen + methane + argon) tail gas mixtures of synthetic ammonia plant through hydrate forma-tion/dissociation. A high-pressure reactor with magnetic stirrer was used to study the separation efficiency. The in-fluences of the concentration of anti-agglomerant, temperature, pressure, initial gas-liquid volume ratio, and oil-water volume ratio on the separation efficiency were systematically investigated in the presence of tetrahydro-furan (THF). Anti-agglomerant was used to disperse hydrate particles into the condensate phase for water-in-oil emulsion system. Since nitrogen is the material for ammonia production, the objective production in our separation process is (hydrogen + nitrogen). Our experimental results show that by adopting appropriate operating conditions, high concentration of (hydrogen + nitrogen) can be obtained using the proposed technology based on forming hydrate.     

Pressure distribution in a channel of a spinneret for spinning polymer melts

Conclusions The pressure distribution of a polycaproamide melt along the length of the spinneret channel has been studied.In the case of flow of a polycaproamide melt, a dependence of pressure drop on the flow rate of the melt through the spinneret hole and on the length of the capillary has been shown.Translated from Khimicheskie Volokna, No. 2, pp. 49–51, March–April, 1986.     

Products from the rapid pyrolysis of a brown coal in inert and reducing atmospheres

Yallourn brown coal and its calcium form have been pyrolysed in three different gas mixtures: 23% methane in argon, 50% hydrogen in argon, and 9.4% toluene in argon, at heating rates of 10⁷Ks^?1 and residence times of ≈2 ms. The products have been compared with those obtained in pure argon. The highly reactive molecule, ketene, was detected in the pyrolysate gases from both the ‘raw’ and calcium-form coals when pyrolysed in the above mixtures. Ketene was not detected in the pyrolysate gases, however, when the coals were pyrolysed in argon alone. When pyrolysed in 23% methane/argon the maximum yield of carbon monoxide from the ‘raw’ coal was found to be much lower than when pyrolysed in pure argon. The fully exchanged calcium-form coal when pyrolysed in pure argon, gave a maximum yield of carbon dioxide of oxygen content equal to the total oxygen content of the carboxyl groups originally present in the coal; the C0₂ yield from the ‘raw’ coal was about half that from the calcium-form in pure argon.     

The influence of inert retardants on the combustion of hydrogen-oxygen mixtures under elevated temperatures and pressures

The experimental values of the flammability limits in hydrogen-oxygen-inert diluent (helium argon, carbon dioxide, steam) mixtures at temperatures up to 523 K and pressures up to 2 MPa as well as of the burning velocities of H₂–O₂–N₂ mixtures at 293 K and 4 MPa are reported. An anomalous effect of helium on the lower flammability limit in a hydrogen-oxygen-helium mixture is shown. The synergistic effect observed for helium-carbon dioxide and helium-steam mixtures used as inert retardants is noted. The data are interpretea theoretically on the assumption of the important role of the selective diffusion of hydrogen and helium from the initial mixture to the flame.VNIIPO, 143900 Balashikha. Translated from Fizika Goreniya i Vzryva, Vol 30, No. 2, pp. 51–57, March–April, 1994.