Composition Of Gas Mixture Research Articles

Mixed gas sorption in glassy polymeric membranes. III. CO2/CH4 mixtures in a polymer of intrinsic microporosity (PIM-1): Effect of temperature

We have explored the effect of temperature on the mixed gas CO2/CH4 sorption in a polymer of intrinsic microporosity (PIM-1) in the range between 25 and 50°C. The new data obtained in this work at 25 and 50°C were combined with previously published data obtained at 35°C, to determine the temperature-dependence of mixed gas solubility and solubility-selectivity, a type of information that has not been obtained before in the literature. The data were collected at different total pressures and gas mixture compositions using a pressure decay − gas chromatographic device. The data collected indicate that the sorption of such mixture in PIM-1 is dominated by competition, whose major effect is to reduce the solubility of gases with respect to the pure gas value at same fugacity. The competitive phenomena follow a generalized trend that is not dependent on total gas pressure, composition and gas type but is only a function of the second gas concentration in the polymer and temperature. In particular the competition, expressed as reduction of gas solubility with respect to pure gas value, decreases with the concentration of the second gas, and increases with increasing temperature. Such effects are generally favourable to separation, with positive deviations of the CO2/CH4 solubility-selectivity from ideal values calculated from pure gas solubility, by factors as high as 4. As a rule of thumb, observed at all temperatures and similarly to other glassy polymers, the real solubility-selectivity deviates positively from ideal value calculated from pure gas behaviour if the molar content of CO2 in the membrane is higher than that of methane, which is usually the case, unless low CO2 gas fractions are considered. A new type of generalized plot, reporting departures of multicomponent properties from the corresponding pure gas values, has been traced for this system and indicates that solubility selectivity departure is univocally correlated to CH4 solubility departure, independent of the operative conditions (pressure, composition, temperature) explored during the experiments.

Non-equilibrium of charged particles in swarms and plasmas—from binary collisions to plasma effects

In this article we show three quite different examples of low-temperature plasmas, where one can follow the connection of the elementary binary processes (occurring at the nanoscopic scale) to the macroscopic discharge behavior and to its application. The first example is on the nature of the higher-order transport coefficient (second-order diffusion or skewness); how it may be used to improve the modelling of plasmas and also on how it may be used to discern details of the relevant cross sections. A prerequisite for such modeling and use of transport data is that the hydrodynamic approximation is applicable. In the second example, we show the actual development of avalanches in a resistive plate chamber particle detector by conducting kinetic modelling (although it may also be achieved by using swarm data). The current and deposited charge waveforms may be predicted accurately showing temporal resolution, which allows us to optimize detectors by adjusting the gas mixture composition and external fields. Here kinetic modeling is necessary to establish high accuracy and the details of the physics that supports fluid models that allows us to follow the transition to streamers. Finally, we show an example of positron traps filled with gas that, for all practical purposes, are a weakly ionized gas akin to swarms, and may be modelled in that fashion. However, low pressures dictate the need to apply full kinetic modelling and use the energy distribution function to explain the kinetics of the system. In this way, it is possible to confirm a well established phenomenology, but in a manner that allows precise quantitative comparisons and description, and thus open doors to a possible optimization.

The phase composition and physicochemical properties of transparent nanocomposite films of silicon oxycarbonitride

Films of hydrogenated SiCxNyOz:H obtained by plasma-enhanced chemical vapor deposition from a mixture of 1,1,3,3-tetramethyldisilazane with oxygen and nitrogen (TMDS+ O2+xN2) in the temperature range 373-973 K are nanocomposites in whose amorphous part nanocrystals belonging to phases of the Si–C–N: α-Si3–xCxN4 system and graphite are distributed. A change in the chemical composition of gas mixtures enables the preparation of SiCxNyOz:H films with a broad variation range of functional properties, such as the 1.45-2.15 variation of the refractive index; the controlled transparency (T ~ 92-99.7%) in the UV, visible, and IR spectral ranges; tunable characteristics of the band gap (3.5-5.4 eV), and dielectric constants (5.2-5.8).

Influence of Anodic Gas Mixture Composition on Solid Oxide Fuel Cell Performance: Part 1

Influence of Anodic Gas Mixture Composition on Solid Oxide Fuel Cell Performance: Part 1

Influence of Anodic Gas Mixture Composition on Solid Oxide Fuel Cell Performance: Part 2

Influence of Anodic Gas Mixture Composition on Solid Oxide Fuel Cell Performance: Part 2

Influence of anodic gas mixture composition on solid oxide fuel cell performance: Part 1

Influence of anodic gas mixture composition on solid oxide fuel cell performance: Part 1

Influence of anodic gas mixture composition on solid oxide fuel cell performance: Part 2

Influence of anodic gas mixture composition on solid oxide fuel cell performance: Part 2

Determination of Individual Diffusion Coefficients of C3H8/n-C4H10/CO2/Heavy-Oil Systems at High Pressures and Elevated Temperatures by Dynamic Volume Analysis

SummaryBy coupling heat and mass transfer for C3H8/n-C4H10/CO2/heavy-oil systems as well as by treating heavy oil as multiple pseudocomponents, a new technique together with its computational scheme has been developed to determine individual diffusion coefficients of alkane solvents and CO2 in heavy oil at high pressures and elevated temperatures by dynamic volume analysis (DVA). Experimentally, well-designed diffusion tests have been conducted for an n-C4H10/heavy-oil system, a CO2/heavy-oil system, an n-C4H10/CO2/heavy-oil system, and a C3H8/n-C4H10/CO2/heavy-oil system by using a visualized pressure/volume/temperature (PVT) setup. The volume change of liquid phase is monitored and recorded during the measurements, whereas the gas-chromatography (GC) method is used to determine the compositions of gas mixtures at the beginning and the end of the diffusion tests. Theoretically, the volume-translated Peng-Robinson (PR) equation of state (EOS) characterizing heavy oil as multiple pseudocomponents has been incorporated to develop a 2D heat-and-mass-transfer model for the aforementioned systems. The alternating-direction-implicit algorithm is applied to solve the 2D difference equations into which a moving gas/liquid interface has been successfully incorporated. The discrepancy between the measured and calculated dynamic-volume change and the discrepancy between the measured and calculated gas compositions at the end of diffusion tests have been minimized to determine the individual diffusion coefficients. Alkane solvents diffuse faster than CO2 in heavy oil, whereas addition of alkane solvent(s) into the CO2 stream not only enhances mass transfer, but also achieves an improved swelling effect of heavy oil. Among the four diffusion tests, the largest dynamic swelling factor at the end of the diffusion test is measured to be 1.118 for the C3H8/n-C4H10/CO2/heavy-oil system.

Development of KSVGRNN: A hybrid soft computing technique for estimation of boiler flue gas components

Abstract In this research paper, a novel hybrid technique named KSVGRNN, which combines a multi-class support vector machine (SVM) and a generalized regression neural network (GRNN), has been developed for obtaining the composition of boiler flue gas mixtures. This hybridization was made by the support of K-means clustering algorithm and grid search technique. In the first phase, K-Means clustering technique has been utilized and the size of the training vectors has been reduced by employing a multiclass SVM. In the second, a GRNN has been trained for estimating the individual gas concentration in the flue gas mixture. The reduction of training vectors through SVM has been shown to improve the generalization capability of GRNN. Grid search has been utilized to obtain the optimal parameters of SVM. This hybrid technique has been validated by measuring its performance by processing volatile organic component (VOC) data acquired from quartz crystal microbalance (QCM) and SnO2 semiconductor type sensors utilized by other researchers in this domain. Further studies have been carried out to assess the discriminating and estimation capability of the proposed hybrid technique for real-time flue gas data obtained from two different analyzers namely ORSAT® and KANE®. The outcome of these studies, observations and analysis clearly indicate the exceptional performance of the proposed hybrid model in classifying and estimating the flue gas components in the machine (Analyzer) independent manner.

Effective ionisation coefficients and critical breakdown electric field of CO2 at elevated temperature: effect of excited states and ion kinetics

Electrical breakdown by the application of an electric field occurs more easily in hot gases than in cold gases because of the extra electron-species interactions that occur as a result of dissociation, ionization and excitation at higher temperature. This paper discusses some overlooked physics and clarifies inaccuracies in the evaluation of the effective ionization coefficients and the critical reduced breakdown electric field of CO2 at elevated temperature, considering the influence of excited states and ion kinetics. The critical reduced breakdown electric field is obtained by balancing electron generation and loss mechanisms using the electron energy distribution function (EEDF) derived from the Boltzmann transport equation under the two-term approximation. The equilibrium compositions of the hot gas mixtures are determined based on Gibbs free energy minimization considering the ground states as well as vibrationally and electronically excited states as independent species, which follow a Boltzmann distribution with a fixed excitation temperature. The interaction cross sections between electrons and the excited species, not reported previously, are properly taken into account. Furthermore, the ion kinetics, including electron–ion recombination, associative electron detachment, charge transfer and ion conversion into stable negative ion clusters, are also considered. Our results indicate that the excited species lead to a greater population of high-energy electrons at higher gas temperature and this affects the Townsend rate coefficients (i.e. of electron impact ionization and attachment), but the critical reduced breakdown electric field strength of CO2 is only affected when also properly accounting for the ion kinetics. Indeed, the latter greatly influences the effective ionization coefficients and hence the critical reduced breakdown electric field at temperatures above 1500 K. The rapid increase of the dissociative electron attachment cross-section of molecular oxygen with rising vibrational quantum number leads to a larger electron loss rate and this enhances the critical reduced breakdown electric field strength in the temperature range where the concentration of molecular oxygen is relatively high. The results obtained in this work show reasonable agreement with experimental results from literature, and are important for the evaluation of the dielectric strength of CO2 in a highly reactive environment at elevated temperature.

Dependence of characteristics of MSiBCN (M = Ti, Zr, Hf) on the choice of metal element: Experimental and ab-initio study

The paper deals with MSiBCN (M=Ti, Zr, Hf) thin films prepared by pulsed dc reactive magnetron sputtering of M15Si20(B4C)65 targets. We focus on the effect of M choice and N2+Ar discharge gas mixture composition. The experimental results are complemented and explained by ab-initio calculations. We find that the transition from Ti through Zr to Hf leads to (i) increasing driving force towards segregation, (ii) weaker role of M around the Fermi level and opening of a wider band gap in N-rich compositions, (iii) higher electrical resistivity and lower extinction coefficient in N-rich compositions, (iv) increasing energy resulting from the oxidation of constituent M-containing phases, and consequently decreasing oxidation resistance of N-poor compositions and (v) increasing oxidation resistance of N-rich compositions. The results are important for the design of future coatings with tailored combinations of mechanical, electrical and optical properties and oxidation resistance.

Effect of active gas mixture composition on tribological behavior of coatings obtained by reactive magnetron sputtering of chromium in acetylene–nitrogen and acetylene–air gas mixtures

The tribological properties of chromium-based coatings deposited by reactive magnetron sputtering in argon–acetylene–nitrogen and argon–acetylene–air mixtures of different volume compositions have been studied. The coatings acquired in acetylene–nitrogen gas mixture have DLC structure and demonstrate high mechanical characteristics and low coefficient of friction values in dry friction. Although the coefficient of friction of these coatings has a tendency to decrease with the increasing nitrogen volume concentration in the mixture (until the values below 0.1 in dry friction in pair with silicon nitride), their performance diminishes at high contact pressures. This decrease was maximal for coatings deposited in acetylene–nitrogen gas mixture, with 80 vol % of nitrogen. The substitution of nitrogen with air is shown to considerably improve the performance, but a further increase in the air volume fraction above 85 vol % provokes a drastic decrease in the efficiency, especially at high contact pressures. The possible mechanisms of these effects and the abilities of their elimination are discussed, as well.

Time-resolved electron temperature and electron density measurements in a nanosecond pulse filament discharge in H2–He and O2–He mixtures

Time evolution of electron density and electron temperature in a nanosecond pulse, diffuse filament electric discharge in H2–He and O2–He mixtures at a pressure of 100 Torr is studied by Thomson/pure rotational Raman scattering and kinetic modeling. The discharge is sustained between two spherical electrodes separated by a 1 cm gap and powered by high voltage pulses ~150 ns duration. Discharge energy coupled to the plasma filament 2–3 mm in diameter is 4–5 mJ/pulse, with specific energy loading of up to ~0.3 eV/molecule. At all experimental conditions, a rapid initial rise of electron temperature and electron density during the discharge pulse is observed, followed by the decay in the afterglow, over ~100 ns–1 µs. Electron density in the afterglow decays more rapidly as H2 or O2 fraction in the mixture is increased. In He/H2 mixtures, this is likely due to more rapid recombination of electrons in collisions with and ions, compared to recombination with ions. In O2/He mixtures, electron density decay in the afterglow is affected by recombination with and ions, while the effect of three-body attachment is relatively minor. Peak electron number densities and electron temperatures are ne = (1.7–3.1) · 1014 cm−3 and Te = 2.9–5.5 eV, depending on gas mixture composition. Electron temperature in the afterglow decays to approximately Te ≈ 0.3 eV, considerably higher compared to the gas temperature of T = 300–380 K, inferred from O2 pure rotational Raman scattering spectra, due to superelastic collisions. The experimental results in helium and O2–He mixtures are compared with kinetic modeling predictions, showing good agreement.

Development of a robust refrigerant mixture for liquefaction of highly uncertain natural gas compositions

To export natural gas to overseas, it has to be liquefied and transported by the LNG tankers. Some LNG plants will receive their natural gas from different shale gas reservoirs so that one of the key challenges in developing a refrigerant mixture is the variation the of natural gas compositions. Previous attempts to create refrigerant mixtures for LNG plants were focused on implementing deterministic optimization methods. However, we demonstrate in this paper that these optimized refrigerants are so sensitive to natural gas composition that a slight variation in natural gas composition makes them unsuitable for the liquefaction process. To demonstrate the Gradient Assisted Robust Optimization technique capabilities, we developed a refrigerant mixture for propane precooled mixed refrigerant natural gas liquefaction cycles with an exaggerated variation in feed gas composition. This refrigerant is relatively unaffected by the variation of the natural gas compositions. We compared the performance of the new refrigerant to five other refrigerants found in literature and found the newly developed refrigerant is the only one satisfying the design constraints for all of the tested natural gas mixture compositions. This technique can be used for developing refrigerant for any LNG cycle that has a variation in feed composition.

An intelligent optimization–based prediction model for natural gas hydrate formation in a deepwater pipeline

ABSTRACTTemperature, pressure, and composition of gas mixtures in deepwater pipelines promote rapid formation of gas hydrates. To avert this dilemma, it is more significant to find out the temperature and pressure limits in gas hydrates formation of the deepwater pipeline. The objective of this research is to develop an optimization method that finds the optimal temperature and pressure profile for natural gas hydrate formation conditions and an error calculation method to find the realistic approach of the hydrate formation prediction model. A newly developed correlation model is computing the hydrate formation pressure and temperature for a single component of methane (CH4) gas. The proposed developed prediction model is based on the 2 and 15 constant coefficients and holds a wide range of temperature and pressure data about 2.64 to 46°C and 0.051 to 400 MPa for pure water and methane, respectively. The reducing error discrepancies are 1.2871, 0.35012, and 1.9052, which is assessed by GA, PSO, and GWO algorithms, respectively. The results show the newly developed optimization algorithms are in admirable compliance with the experimental data and standards of empirical models. These correlations are providing the capability to predict gas hydrate forming conditions for a wide range of hydrate formation data.

Effect of Argon during Diamond Deposition by Hot Filament Chemical Vapor Deposition

The effect of argon content upon the growth rate and the properties of diamond thin films grown with different grains sizes are explored. An argon-free and argon-rich gas mixture of methane and hydrogen is used in a hot filament chemical vapor deposition reactor. Characterization of the films is accomplished by scanning electron microscopy, Raman spectroscopy and high-resolution x-ray diffraction. An extensive comparison of the growth rate values and films morphologies obtained in this study with those found in the literature suggests that there are distinct common trends for microcrystalline and nanocrystalline diamond growth, despite a large variation in the gas mixture composition. Included is a discussion of the possible reasons for these observations.

X-ray photoelectron study of the effect of the composition of the initial gas phase on changes in the electronic structure of hexagonal boron nitride films obtained by PECVD from borazine

Hexagonal boron nitride films are synthesized by plasma enhanced chemical vapor deposition (PECVD) from a gas mixture of borazine and ammonia or helium on Si(100) substrates. X-ray photoelectron spectroscopy is used to study changes in the electronic structure and chemical composition of the films depending on the composition of the initial gas mixture. It is found that the chemical composition of the samples depends on the gas used. The use of helium results in an excess of boron atoms on the film surface, the appearance of B–B bonds, and a decrease in the contribution of B–N bonds in the hexagonal structure. The preparation of h-BN films close to the stoichiometric composition by PECVD methods with the use of borazine is shown to be possible with the addition of ammonia. Based on the literature data, the binding energies in the B 1s XPS spectra are calculated for different boron environments in the hexagonal lattice.

Improvement in methanol production by regulating the composition of synthetic gas mixture and raw biogas

Raw biogas can be an alternative feedstock to pure methane (CH4) for methanol production. In this investigation, we evaluated the methanol production potential of Methylosinus sporium from raw biogas originated from an anaerobic digester. Furthermore, the roles of different gases in methanol production were investigated using synthetic gas mixtures of CH4, carbon dioxide (CO2), and hydrogen (H2). Maximum methanol production was 5.13, 4.35, 6.28, 7.16, 0.38, and 0.36mM from raw biogas, CH4:CO2, CH4:H2, CH4:CO2:H2, CO2, and CO2:H2, respectively. Supplementation of H2 into raw biogas increased methanol production up to 3.5-fold. Additionally, covalent immobilization of M. sporium on chitosan resulted in higher methanol production from raw biogas. This study provides a suitable approach to improve methanol production using low cost raw biogas as a feed containing high concentrations of H2S (0.13%). To our knowledge, this is the first report on methanol production from raw biogas, using immobilized cells of methanotrophs.

Hydrate phase equilibrium for CH4‐CO2‐H2O system in porous media

CO2/CH4 replacement in hydrate exploitation is considered a promising method to enhance natural gas production and mitigate the greenhouse effect. Since the gas concentration in mining hydrate sediment changes with the displacement process, it is crucial to investigate the hydrate formation and dissociation characteristics with the presence of different gas mixtures. To obtain fundamental thermodynamic data, CO2/CH4 gas mixture hydrate phase equilibrium conditions in porous media were experimentally investigated. The experiments were conducted at 276.55–284.85 K and 2.10–6.80 MPa using an isochoric method with different CO2/CH4 gas mixture compositions (CO2 mole fractions were 0.798, 0.499, and 0.199 mol/mol (79.8, 49.9, and 19.9 mol%)). The results showed that gas mixtures with higher CO2 mole fractions had lower hydrate equilibrium pressure (p) under the same temperature (T) according to the experimental data. The two different porous media used in the experiments had a slight influence on gas mixture hydrate phase equilibrium conditions. An improved thermodynamic model was proposed to calculate the CO2/CH4 hydrate phase equilibrium conditions in porous media, and the prediction results fitted closely to the experimental data.

Repetitively pulsed cryogenically cooled quasi-sealed-off slab RF discharge first-overtone CO laser

A slab first-overtone CO laser of improved design excited by repetitively pulsed RF discharge was researched and developed. Its quasi-sealed-off operation appeared to be possible only by using active gas mixture composition with extremely high content of oxygen — up to 50 % with respect to CO concentration. Average output power of the first-overtone CO laser came up to ~2 W with the efficiency of ~2 %. The laser spectrum obtained by using three sets of output couplers consisted of more than 100 vibrational–rotational spectral lines in 28 vibrational first-overtone bands of CO molecule within 2.55÷3.90 μm wavelength range. The number of laser radiation pulses which could be produced by the laser in sealed-off mode of operation (without gas mixture renovation) reached ~5×105 at the averaged output power near its maximum, and ~106 at lower (near its half-maximum) averaged output power. Special features of laser radiation temporal behavior were discussed. Under repetitively pulse pump with repetition rate from 300 up to 7500 Hz, a temporal profile of the CO laser radiation changed from the train of time-separated laser pulses with high peak power to quasi-CW mode of operation.