The influence of inert gases on the high-pressure phase equilibria of EH-copolymer/1-hexene/ethylene-mixtures

The influence of the addition of several inert compounds on the phase equilibria of poly(ethylene-co-1-hexene) copolymer solutions in 1-hexene and ethylene was determined at the conditions of the industrial high-pressure copolymerization process. Using a high-pressure autoclave we measured cloud point pressures in dependence on temperature and mixture composition. The temperature was varied in the range of 393 to 493 K. We present the results for quasi-ternary mixtures consisting of a poly(ethylene-co-1-hexene) copolymer (EH), ethylene and an inert compound (helium, nitrogen, CO₂, methane, ethane, propane, n-butane). Also the quasi-quaternary system EH-copolymer/ethylene/1-hexene/nitrogen is discussed. Experiments were carried out at 1-hexene:ethylene mass ratios between 0 and 85:15. Helium, nitrogen, methane and carbon dioxide lowered the copolymer solubility. The antisolvent effect decreases in the order helium>nitrogen>methane>CO₂. In contrast, ethane, propane and especially n-butane were found to act as cosolvents.     

脉冲电晕等离子体作用下甲烷偶联反应的研究 Ⅱ.反应添加气的影响

脱氢偶联;脉冲电晕等离子体作用下甲烷偶联反应的研究 Ⅱ.反应添加气的影响     

Development of a new gas sensor for binary mixtures based on the permselectivity of polymeric membranes: Application to carbon dioxide/methane and carbon dioxide/helium mixtures

Membrane-based gas sensors were developed and used for determining the composition on bi-component mixtures in the 0-100% range, such as oxygen/nitrogen and carbon dioxide/methane (biogas). These sensors are low cost and are aimed at a low/medium precision market.The paper describes the use of this sensor for two gas mixtures: carbon dioxide/methane and carbon dioxide/helium. The membranes used are poly(dimethylsiloxane) (PDMS) and Teflon-AF hollow fibers. The response curves for both sensors were obtained at three different temperatures. The results clearly indicate that the permeate pressure of the sensors relates to the gas mixture composition at a given temperature. The data is represented by a third order polynomial. The sensors enable quantitative carbon dioxide analysis in binary mixtures with methane or helium. The response of the sensors is fast (less than 50 s), continuous, reproducible and long-term stable over a period of 2.3×10⁷ s (9 months). The absolute sensitivity of the sensors depends on the carbon dioxide feed concentration ranging from 0.03 to 0.13 MPa.     

The effect of inert gases on the yield and morphology of carbon deposits resulting from methane pyrolysis on fechral catalyst under direct current resistive heating

The effect of the inert component nature (argon, helium) in a gas mixture on the morphology and the amount of carbon deposits formed upon methane pyrolysis on a resistive fechral wire catalyst heated by direct current was studied. The carbon deposits had a similar morphology with fibrous texture in all cases. By varying the gas medium composition, one can obtain either fibers with up to 150 μm length and 2–3 μm diameter or short fibers of 8–10 μm length formed from a dense surface carbon layer. In the presence of helium, the amount of carbon deposited on the surface was virtually proportional to the methane content in the gas mixture, while in argon medium, the carbon formation was markedly retarded.     

The magnetic suspension balance in high pressure measurements of pure gases

In the present work the supercritical fluids argon, methane, nitrogen, carbon dioxide, ethane, ethylene and propane were picked out as examples, and the results of analysis concerning the adsorption of these fluids at activated carbon Norit R1 (Norit Company, Germany) and SCS-3 (ISPE, Kiev) at different temperatures up to a pressure of 50 MPa are presented and discussed in this paper. The principle of working of the measuring device is described in this context as well.A three-parameter isothermal equation is used to represent the adsorption equilibrium. The isothermal equation is based on a physical model concept which has already been used for the modelling of adsorption processes with a pressure up to 15 MPa.This revised version was published online in November 2005 with corrections to the Cover Date.     

Wet Conversion of Methane and Carbon Dioxide in a DBD Reactor

The influence of water on the plasma assisted conversion of methane and carbon dioxide in a dielectric barrier discharge (DBD) plug flow reactor was studied. The plasma at atmospheric pressure was ignited by a power supply at a frequency of 13.56?MHz. Product formation was studied at a power range between 35 and 70?W. The concentrations of the three gases were altered and diluted with helium to 3?%. FTIR spectroscopy and mass spectroscopy were applied to analyze the inlet and the product streams. The main product of this process are hydrogen, carbon monoxide and ethane. Ethene, ethine, methanol and formaldehyde are generated beside the main products in this DBD in lower concentrations. The conversion of methane, the ratio of the synthesis gas components (n(H₂):n(CO)), and the yield of oxygenated hydrocarbons and hydrogen increases by adding water. The total consumed energy reaches lower values for small amounts of water. Additional water does not influence the generated amount of C2 hydrocarbons and of CO, but decreases the carbon dioxide conversion.     

Modeling of gas adsorption equilibrium over a wide range of pressure: a thermodynamic approach based on equation of state

A thermodynamic approach based on the Bender equation of state is suggested for the analysis of supercritical gas adsorption on activated carbons at high pressure. The approach accounts for the equality of the chemical potential in the adsorbed phase and that in the corresponding bulk phase and the distribution of elements of the adsorption volume (EAV) over the potential energy for gas-solid interaction. This scheme is extended to subcritical fluid adsorption and takes into account the phase transition in EAV. The method is adapted to gravimetric measurements of mass excess adsorption and has been applied to the adsorption of argon, nitrogen, methane, ethane, carbon dioxide, and helium on activated carbon Norit R1 in the temperature range from 25 to 70 degrees C. The distribution function of adsorption volume elements over potentials exhibits overlapping peaks and is consistently reproduced for different gases. It was found that the distribution function changes weakly with temperature, which was confirmed by its comparison with the distribution function obtained by the same method using nitrogen adsorption isotherm at 77 K. It was shown that parameters such as pore volume and skeleton density can be determined directly from adsorption measurements, while the conventional approach of helium expansion at room temperature can lead to erroneous results due to the adsorption of helium in small pores of activated carbon. The approach is a convenient tool for analysis and correlation of excess adsorption isotherms over a wide range of pressure and temperature. This approach can be readily extended to the analysis of multicomponent adsorption systems.     

分子筛对微量二氧化碳的吸附

本文研究了分子筛对氦气中微量二氧化碳的静态吸附和对氩气中微量二氧化碳的连续动态吸附，及格连续流动法测定了载气氩和氦对分子筛吸附微量二氧化碳的影响。     

Homogeneous Pyrolysis of Anisole

Homogeneous pyrolysis of anisole in argon (1 : 25 volume ratio) at 750-900°C and contact time of 1.5-4.5 s was studied. The conversion and group composition of the tar and component composition of the gaseous pyrolysis products, phenols, and hydrocarbons were determined; asphaltenes and neutral oxygen-containing compounds were characterized. The kinetic parameters of formation of methane, hydrogen, and carbon monoxide and dioxide were calculated; mechanisms of their formation are proposed.     

Investigation of drift gas selectivity in high resolution ion mobility spectrometry with mass spectrometry detection

Recent studies in electrospray ionization (ESI)/ion mobility spectrometry (IMS) have focussed on employing different drift gases to alter separation efficiency for some molecules. This study investigates four structurally similar classes of molecules (cocaine and metabolites, amphetamines, benzodiazepines, and small peptides) to determine the effect of structure on relative mobility changes in four drift gases (helium, nitrogen, argon, carbon dioxide). Collision cross sections were plotted against drift gas polarizability and a linear relationship was found for the nineteen compounds evaluated in the study. Based on the reduced mobility database, all nineteen compounds could be separated in one of the four drift gases, however, the drift gas that provided optimal separation was specific for the two compounds.     

Dilute Methane Treatment by Atmospheric Pressure Dielectric Barrier Discharge: Effects of Water Vapor

Oxidation of dilute methane in oxygen containing mixtures by atmospheric pressure dielectric barrier discharge at moderate temperature (below 150°C) has been studied with regard to the effect of water vapor. First, the impact of water vapor on methane conversion was studied in nitrogen. In dry nitrogen, methane was converted into hydrogen cyanide and hydrogen in the absence of oxidant. When water was added, it both acted as a scavenger in competition with methane for reactive nitrogen species and changed the reaction product speciation from HCN to carbon monoxide and carbon dioxide. The addition of water also led to the formation of hydrogen and nitrogen oxides. In the presence of oxygen, the addition of 1% water vapor enhanced methane conversion. Increasing water vapor content above 1% had a slight positive effect on methane conversion, and was found to enhance selectivity of the reaction products toward carbon dioxide over carbon monoxide.     

Fe-Containing Intermetallic Compounds As Catalysts of Methane Conversion with Carbon Dioxide

Systems based on iron and aluminum were studied in methane conversion with carbon dioxide. The systems were prepared by the method of self-propagating high-temperature synthesis. Massive iron did not exhibit noticeable catalytic activity in methane conversion with carbon dioxide. The deactivation of iron-containing intermetallic compounds was shown to occur because of the formation of the FeC and FeO phases, which screened the active centers of the catalyst surface. The suggestion was made that the active center of the dissociative adsorption of methane was the γ-Fe phase, which existed at the working temperature of methane conversion with carbon dioxide.     

Separation and permeation characteristics of a DD3R zeolite membrane

Permeation of various gases (carbon dioxide, nitrous oxide, methane, nitrogen, oxygen, argon, krypton, neon) and their equimolar mixtures through DD3R membranes have been investigated over a temperature range of 220–373 K and a feed pressure of 101–400 kPa. Helium was used as sweep gas at atmospheric pressure. Adsorption isotherms were determined in the temperature range 195–298 K, and modelled by a single and dual site Langmuir model. The permeation flux is determined by the size of the molecule relative to the window opening of DD3R, and its adsorption behaviour. As a function of temperature, bulky molecules (methane) show activated permeation, weakly adsorbing molecules decreasing permeation behaviour and strongly adsorbing molecules pass through a maximum. Counter diffusion of the sweep gas (helium) ranged from almost zero up to the order of the feed gas permeation and was strongly influenced by the adsorption of the feed gas.

DD3R membranes have excellent separation performance for carbon dioxide/methane mixtures (selectivity 100–3000), exhibit good selectivity for nitrogen/methane (20–45), carbon dioxide and nitrous oxide/air (20–400), and air/krypton (5–10) and only a modest selectivity for oxygen/nitrogen (2) separation. The selectivity of mixtures of a strongly and a weakly adsorbing component decreased with increasing temperature and pressure. The selectivity of mixtures of weakly adsorbing components was independent of pressure.

The permeation and separation characteristics of light gases through DD3R membranes can be explained by taking into account: (1) steric effects introduced by the window opening of DD3R leading to molecular sieving and activated transport, (2) competitive adsorption effects, as observed for mixtures involving strongly adsorbing gases, and (3) interaction between diffusing molecules in the cages of the zeolite.     

Raman study of the dissolution of gases under high pressure on conformational equilibria of some n-alkanes

The conformational changes of some odd-numbered n-alkanes by increasing pressure agree with a greater volume of the trans conformations. Dissolving nitrogen, helium, argon or carbon dioxide displaces the conformational equilibria. The evolution is sensitive to the nature of the gas. For solutions of nitrogen or argon, all-trans forms appear with increasing pressure just before the solid organized phase. We show the effect of the quantity of dissolved gas on the conformational equilibria from the study of the vibrational spectrum of nitrogen. The interaction between the nitrogen molecules and the conformations of alkanes is also discussed.     

Effect of buffer gas on the fluorescence yield of trapped gas-phase ions

We investigated the dependence of three different gases, helium, argon, and nitrogen, on the fluorescence signal intensity of rhodamine 6G cations in the gas phase. The method is based on laser-induced fluorescence of ions trapped in a Fourier transform ion cyclotron mass spectrometer. We found that the use of helium results in the highest fluorescence signal, while no fluorescence was detected when using argon under the same conditions.     

Critical evaluation of gas standards based on hydrogen

Summary Six commercial hydrogen standards containing helium, oxygen, nitrogen, methane and carbon dioxide at trace levels were analyzed by gas chromatography, for periods up to 105 days. The concentrations, in the range of 0–120 μmol mol⁻¹, were stable (with the exception of oxygen) but often significantly different from the certified values provided by the suppliers, especially for helium, oxygen and nitrogen. Concurrently, some experiments were carried out to verify the stability of gas mixtures based on hydrogen stored in cylinders submitted to different chemical and physical treatments. The causes that led to the deviations observed, as well as the decreases in oxygen, are discussed. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996.     

Characterization of new catalysts based on uranium oxides

Catalysts based on uranium oxides were systematically studied for the first time. Catalysts containing various amounts of uranium oxides (5 and 15%) supported on alumina and mixed Ni-U/Al₂O₃ catalysts were synthesized. The uranium oxide catalysts were characterized using the thermal desorption of argon, the low-temperature adsorption of nitrogen, X-ray diffraction analysis, and temperature-programmed reduction with hydrogen and CO. The effects of composition, preparation conditions, and thermal treatment on physicochemical properties and catalytic activity in the reactions of methane and butane oxidation, the steam and carbon dioxide reforming of methane, and the partial oxidation of methane were studied. It was found that a catalyst containing 5% U on alumina calcined at 1000°C was most active in the reaction of high-temperature methane oxidation. For the Ni-U/Al₂O₃ catalysts containing various uranium amounts (from 0 to 30%), the introduction of uranium as a catalyst constituent considerably increased the catalytic activity in methane steam reforming and partial oxidation.     

Matrix effect in the cryotrapping of gas samples in the ppbv range

A gas mixture containing ppbv concentrations of volatile chlorinated and aromatic hydrocarbons was prepared in helium, nitrogen, or argon in a plastic (Nalophan) bag, in which it was found the mixture could be safely stored for several days. Samples of the mixture were subsequently analyzed by gas chromatography after direct cryotrapping in an empty metal U-tube. The cooling medium used was liquid nitrogen, liquid argon, or a dry ice-acetone slurry (197 K). The efficiency of cryotrapping in liquid nitrogen was over 90% when the aromatic hydrocarbon mixture was prepared in the helium matrix, but between 50 and 70% when it was prepared in nitrogen or argon, the recovery from the argon matrix being somewhat higher. The poor recovery in nitrogen at 77 K and argon at 87 K was explained by the reduced rate of diffusion to the wall owing to mist or aerosol formation. At 197 K condensation was negligible if the partial pressures were lower than the saturated vapor pressures.     

Electrochemically-controlled generation of small amounts of carbon monoxide

The generation of carbon monoxide is based on oxidation of carbon at a temperature of 920-950 degrees by electrolytically generated oxygen. The rate of production of CO is a linear function of the oxygen generating current over a range of 5-60 mA and corresponds to the theoretical value. By the method described it is possible to obtain CO concentrations from 0.0075 to 2.5% in an inert gas (nitrogen, argon and helium).     

Adsorption of gases on layered silicates at high pressures

Equilibrium adsorption of nitrogen, carbon dioxide, and argon was examined on the sodium and pyridinium forms of montmorillonite and on the hydrogen form of bentonite. The measurements were carried out at 303, 343, 373, and 400 K over pressure ranges of 0.1–90 MPa (Ar and N₂) and 0.1–6 MPa (CO₂). The amount of nitrogen vapor adsorbed was determined at 77 K and pressures from 0 to 0.1 MPa. The porous structure parameters of the studied samples were determined using adsorption isotherms of nitrogen, argon, and carbon dioxide vapors. At elevated temperatures and pressures >10 MPa, Ar and N₂ adsorption processes on the Na-form of montmorillonite and Ar adsorption on bentonite are activated, since the amounts of the gases adsorbed and adsorption volumes increase with temperature. No activated adsorption is observed for carbon dioxide adsorption on these adsorbents. A comparison of the excess adsorption isotherms of gases on the Py-form of montmorillonite and H-form of bentonite shows that adsorption in micropores predominates for the Py-form of montmorillonite, whereas for the Na-form of bentonite and H-form of bentonite adsorption occurs mainly in meso- and macropores.