A GC-system for the analysis of residual geothermal gases

Summary The gases evolved from geothermal fields, after condensation of H₂O, CO₂, H₂S and NH₃ in caustic solution, contain He, H₂, Ar, O₂, N₂, CH₄ and higher hydrocarbons. The analysis for the major components in these residual gas mixtures can be achieved by use of two simple gas chromatographs in parallel, and using 5Å molecular sieve. The separation of He and H₂ to baseline is achieved by using low temperatures (30°C) coupled with a relatively long column; and the difficult separation of Ar and O₂ is achieved by use of a cryogenically cooled column. The use of switching valves to backflush and bypass columns ensures that a minimum time for analysis can be achieved whilst retaining baseline separations of the He/H₂ and Ar/O₂ pairs.     

Mechanisms of the IR laser initiation of combustion in a supersonic H2/O3/O2 flow

The ignition of a supersonic H₂/O₃/O₂ flow by the λ_I = 9.7 μm laser excitation of asymmetric vibrations in O₃ molecules is considered. The O₃ molecules vibrationally excited by laser radiation dissociate more readily to generate active O atoms, thus accelerating the ignition/combustion process. Even at a low input of radiation energy (～7 × 10^?4 J/cm³), combustion in the supersonic flow can be initiated at a short distance (<1 m) from the irradiation zone and at a low gas temperature (～300 K).     

Effect of Ar/H2 and Kr/H2 mixtures as discharge gas on the ion intensity in dc glow discharge mass spectrometry

 In dc glow discharge mass spectrometry, the addition of small amounts of H₂ to pure Ar as discharge gas has greatly increased the ion intensities of elements compared with the conventional method using pure Ar. This phenomenon was also observed for the addition of H₂ to pure Kr. The reason for the increase of the ion intensities of elements was studied by using a Kr gas mixture containing 0.2% (v/v) H₂. The ion intensities of the elements P, Se and As (whose first ionization potentials are higher than the energy levels of the excited state of Kr) did not increase even if the Kr/H₂ gas mixture was used. The results show that the addition of H₂ significantly contributed to increasing the number of metastable argon or krypton atoms (Penning ionization). Received: 4 November 1995/Revised: 5 January 1996/Accepted: 10 January 1996     

Effect of Ar/H2 and Kr/H2 mixtures as discharge gas on the ion intensity in dc glow discharge mass spectrometry

 In dc glow discharge mass spectrometry, the addition of small amounts of H₂ to pure Ar as discharge gas has greatly increased the ion intensities of elements compared with the conventional method using pure Ar. This phenomenon was also observed for the addition of H₂ to pure Kr. The reason for the increase of the ion intensities of elements was studied by using a Kr gas mixture containing 0.2% (v/v) H₂. The ion intensities of the elements P, Se and As (whose first ionization potentials are higher than the energy levels of the excited state of Kr) did not increase even if the Kr/H₂ gas mixture was used. The results show that the addition of H₂ significantly contributed to increasing the number of metastable argon or krypton atoms (Penning ionization). Received: 4 November 1995/Revised: 5 January 1996/Accepted: 10 January 1996     

An optimized kinetics model for OH chemiluminescence at high temperatures and atmospheric pressures

Chemiluminescence from the OH(A → X) transition near 307 nm is a commonly used diagnostic in combustion applications such as flame chemistry, shock‐tube experiments, and reacting‐flow visualization. Although absolute measurements of OH(X) concentrations are well defined, there is no elementary relation between emission from the electronically excited state (OH*) and its absolute concentration. Thus, to enable quantitative emission measurements, a kinetics model has been assembled and optimized to predict OH* formation and quenching at combustion conditions. Shock‐tube experiments were conducted in mixtures of H₂/O₂/Ar, CH₄/O₂/Ar, and CH₄/H₂/O₂/Ar with high levels of argon dilution (>98%). Elementary reactions to model OH*, along with initial estimates of their rate coefficients, were taken from the literature. The important formation steps follow: (R0) (R1) Sensitivity analyses were performed to identify experimental conditions under which the shape of the measured OH* profiles and the magnitude of the OH* emission would be sensitive to the formation reactions. A fitting routine was developed to express the formation rate parameters as a function of a single rate, k₁ at the reference temperature (1490 K). With all rates so expressed, H₂/CH₄ mixtures were designed to uniquely determine the value of k₁ at the reference temperature, from which the remaining rate parameters were calculated. Quenching rates were fixed at their literature values. The new model predicts the experimental data over the range of conditions studied and can be used to calibrate the emission diagnostic for other applications, such as measurements in real combustion environments, containing higher order hydrocarbon fuels and lower levels of dilution in air. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 714–724, 2006     

Detailed combustion kinetics of cyclopentadiene studied in a shock‐tube

Mixtures of cyclopentadiene and oxygen diluted in argon were used to obtain ignition delay data in a single pulse shock‐tube. The temperatures ranged from 1278–2110 K and the experimental pressures were between 2.43 and 12.45 atm. The fuel concentrations ranged from 0.5 to 2.5% and the oxygen concentrations were between 3.3 and 16.6%. A Semenov ignition delay expression was determined: τ = 10^?12.5 exp(+34500/RT) [C₅H₆]^0.06 [O₂]^?0.95 [Ar]^0.29 sec The concentrations are in mol/cc and the activation energy is in cal/mol. Gas‐chromatographic analyses were run on samples quenched before the ignition. The kinetics of combustion of cyclopentadiene was modeled with a full scheme containing 439 elementary reactions and a reduced scheme containing 125 reactions. Both ignition delay times and product distribution served as modeling targets. The mechanism of combustion of cyclopentadiene is discussed in connection to the combustion of aromatic fuels. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 491–508, 2001     

TG and DTA Evaluation of Cobalt Salts and Complexes Mixed with Activated Carbon

The thermal decomposition process of mixtures of CoC₂O₄⋅2H₂O (COD) or Co(HCOO)₂⋅2H₂O (CFD) or [Co(NH₃)₆]₂(C₂O₄)₃⋅4H₂O (HACOT) with activated carbon was studied with simultaneous TG–DTG–DTA measurements under non-isothermal conditions in argon and argon/oxygen admixtures. The results show that the thermal decomposition of the studied mixtures in Ar proceeds in the same manner. It begins with the salt decomposition to Co_met+CoO mixture followed by (T>680 K) the simultaneous reduction of CoO to Co_metand carbon degasification. The final product of the thermal decomposition of COD-C and CFD-C mixtures, identified by XRD, is β-Co. Cobalt contents determined in the final products fall in the range 71–78 mass%. The rest is amorphous residual carbon. In Ar/O₂ admixtures the end product is Co₃O₄ with ash admixture. This revised version was published online in July 2006 with corrections to the Cover Date.     

Rate constant for H+H+Ar = H2 + Ar from 1300 to 1700 K

Shock tube experiments on the decay of OH-radical concentration after shock-initiated combustion of H₂:O₂:Ar = 10:1:89 mixtures were analyzed to give the rate constant 1 × 10¹⁵ cm⁶mol^?2s^?1for the reaction H + H + Ar = H₂ + Ar overthe temperature range 1300 to 1700 K.     

Effect of reducing gas on the hydrogen production by thermo-oxidation of water over 1%Rh/Ce0.6Zr0.4O2

We have studied the effect of the reducing gas (H₂, CO and CH₄) on the hydrogen production by thermo-oxidation of water over the 1%Rh/Ce_0.6Zr_0.4O₂ catalyst prepared by impregnation. The catalyst is characterized by hydrogen chemisorption (Hc), before and after catalytic decomposition of water, temperature-programmed desorption, temperature-programmed reduction, X-ray diffraction and scanning electron microscopy. The catalyst is reduced in situ at 500 °C (4 h) under H₂, CO or CH₄ flows and flushed with Ar gas. Then, pulses of water (1 μL/pulse) are injected at 500 °C under Ar flow (30 mL/min). The results show clearly that the reducing gas has a strong effect on the H₂ production which follows the order: H₂?>?CH₄?>?>?CO. H₂ chemisorption measurements at room temperature highlight a strong metal–support interaction over fresh reduced catalysts which decreases after water decomposition (reduced centers?+?H₂O?→?oxidized centers?+?H₂).

     

Single-walled carbon nanotubes as stationary phase in gas chromatographic separation and determination of argon, carbon dioxide and hydrogen

A chromatographic technique is introduced based on single-walled carbon nanotubes (SWCNTs) as stationary phase for separation of Ar, CO₂ and H₂ at parts per million (ppm) levels. The efficiency of SWCNTs was compared with solid materials such as molecular sieve, charcoal, multi-walled carbon nanotubes and carbon nanofibers. The morphology of SWCNTs was optimized for maximum adsorption of H₂, CO₂ and Ar and minimum adsorption of gases such as N₂, O₂, CO and H₂O vapour. To control temperature of the gas chromatography column, peltier cooler was used. Mixtures of Ar, CO₂ and H₂ were separated according to column temperature program. Relative standard deviation for nine replicate analyses of 0.2 mL H₂ containing 10 μL of each Ar or CO₂ was 2.5% for Ar, 2.8% for CO₂ and 3.6% for H₂. The interfering effects of CO, and O₂ were investigated. Working ranges were evaluated as 40-600 ppm for Ar, 30-850 ppm for CO₂ and 10-1200 ppm for H₂. Significant sensitivity, small relative standard deviation (RSD) and acceptable limit of detection (LOD) were obtained for each analyte, showing capability of SWCNTs for gas separation and determination processes. Finally, the method was used to evaluate the contents of CO₂ in air sample.     

Gamma-radiolysis of hydrogen—Oxygen-mixtures— Part I. Influences of temperature,vessel wall,pressure and added gases (N2, Ar,H2) on the reactivity of H2/O2-mixtures

The influence of pressure, temperature, of “matrix gases” N₂, Ar, H₂ and of the pretreatment of the vessel wall on the rate of reaction from ⁶⁰Co γ-radiolysis of hydrogen—oxygen-mixtures, in the region of slow reaction, was investigated. The G(-H₂)-value2 of H₂/O₂-mixtures (H₂:O₂ = 1:9−2:1) ranges from 1 to 14 with only slight dependence on pressure, temperature, H₂/O₂-ratio, and surface/volume ratio (S/V). The temperature has little influence (35–210°C). Replacing most of the O₂ in the H₂:O₂ (1:9)-mixtures with N₂, Ar or excess H₂ at higher temperature, causes the G(-H₂)-values to increase. The influence of these matrix gases increases with increasing temperature (35–210°C) and decreasing S/V ratio (0.59 and 3.8 cm^-1) of the reaction vessel; it depends also on the pretreatment of the wall surface. Varying the total pressure, the G(-H₂)-values show a temperature and gas mixture dependent maximum between about 20 and 200 mb. At higher temperature (210°C) we observed an influence of dose for 50 mb H₂/air-mixtures, whereas at 1 b and 35–90°C no influence of the dose on the rate of reaction of such mixtures was found.The activation by N₂, Ar, H₂ is discussed on the base of the H₂/O₂-reaction being a radical-chain reaction, built up by at least 38 coupled elementary steps (Ref⁽¹⁾ or see part 2). O₂ reacts with H₂, at increased rates of conversions (> 25%), in the expected stoichiometric ratio of 2:1. Oxygen may however also be converted in non-stiochiometric amounts under certain conditions.     

The solubility of Co in TiO2 anatase and rutile and its effect on the magnetic properties

Co-doped anatase and rutile bulk-samples prepared by the sol-gel technique are found to be paramagnetic at room-temperature. Only further annealing in Ar/H₂ gas results in a ferromagnetic behavior. X-ray diffraction and electron-microscope studies reveal for low doping levels <4% the formation of Co-doped rutile samples and the formation of CoTiO₃ as a new phase. Co₃O₄ can be detected in anatase samples with Co doping levels ?4%. The observed Co oxides are reduced by Ar/H₂ to Co metal. The room-temperature ferromagnetism can therefore be traced back to a segregation of metallic Co.     

PAHs Formation in the Depositions in a Methyl tert-Butyl Ether/Ar,a Methyl tert-Butyl Ether/O2/Ar and a Methyl tert-Butyl Ether/H2/Ar RF Plasma Environment

Contents and distributions of polycyclic aromatic hydrocarbons (PAHs) in the depositions were investigated and discussed in a MTBE/Ar, a MTBE/O₂/Ar and a MTBE/H₂/Ar plasma systems. A radio-frequency (RF) plasma system was used to produce the depositions under the designed operational condition. The identification and quantification of PAHs was accomplished by using a GC with a mass selectivity detector (GC/MS). Results indicated that when the input power controlled at high wattage (70 W) in the three systems, the contents of total-PAH in the MTBE/Ar system are higher than those of total-PAH in other system with adding O₂ or H₂. The comparison of three systems indicated the formation and accumulation of PAHs in the MTBE/Ar system is easier than other systems. At high input power wattage, when the MTBE/Ar mixture added O₂ or H₂, the domain pattern was shifted from both 3- and 4-ring PAH to 2-ring PAH. As far as the total-PAH content is concerned, the MTBE/Ar system at 70 W was found to have the highest mean total-PAH content (1540 g/g), while the MTBE/O₂/Ar system at 20 W had the lowest mean total-PAH content (44.4 g/g).     

Properties of low-molecular-weight polyethylene treated with gas plasma

Polyethylene films were evaporated in gas plasmas of Ar, N₂, O₂, and H₂O. The deposits were analyzed by infrared (IR) spectroscopy to determine the concentration of characteristic functional groups. The deposit prepared in Ar-atmosphere had a rather high concentration of methyl group and many double bonds were produced in the film. The deposits prepared in Ar- and N₂-plasmas produced similar spectra, which showed twice the concentration of methyl group than the deposit in Ar-atmosphere and also contained a few carbonyl and hydroxyl groups. The film treated in O₂-plasma contained the largest amount of carbonyl group and the lowest number of double bonds among the plasma-treated deposits. Dielectric loss curves against temperature for the deposits treated in these plasmas showed a broad peak near 20°C. For O₂-plasma-treated film the loss tangent curves showed a sharp maximum. The activation energy for the relaxation of Ar-, O₂-, and H₂O-plasma-treated films had the same value of 50.6 kcal/mol. The observed relaxation in the films prepared in gas plasmas was considered due to the β process and was attributed to the motion of oxidized branched polyethylene.     

Etching Characteristics and Mechanisms of Mo and Al2O3 Thin Films in O2/Cl2/Ar Inductively Coupled Plasmas: Effect of Gas Mixing Ratios

An investigation of etching behaviors for Mo and Al₂O₃ thin films in O₂/Cl₂/Ar inductively coupled plasmas at constant gas pressure (6 mTorr), input power (700 W) and bias power (200 W) was carried out. It was found that an increase in Ar mixing ratio for Cl₂/Ar plasma results in non-monotonic etching rates with the maximums of 160 nm/min at 60 % Ar for Mo and 27 nm/min at 20 % Ar for Al₂O₃. The addition of O₂ in the Cl₂/Ar plasma causes the non-monotonic Mo etching rate (max. 320 nm/min at 40–45 % O₂) while the Al₂O₃ etching rate decreases monotonically. The model-based analysis of etching kinetics allows one to relate the non-monotonic etching rates in Cl₂/Ar plasma to the change in the etching regime from the ion-flux-limited mode (at low Ar mixing ratios) to the neutral-flux-limited mode (for high Ar mixing ratios). In the Cl₂/O₂/Ar plasma, the non-monotonic Mo etching rate is probably due to the change in reaction probability.     

The Formation of OH*(<Superscript>2</Superscript>Σ<Superscript>+</Superscript>) Radical in the Reaction of Hydrogen with Oxygen behind a Shock Wave in Nonequilibrium Conditions

The mechanism of formation of the electronically excited radical OH*(A²Σ⁺) has been studied by analyzing calculations quantitatively describing the results of shock wave experiments carried out in order to determine the moment of maximum OH* radiation at temperatures T < 1500 K and pressures P ≤ 2 atm in the H₂ + O₂ mixtures diluted by argon when the vibrational nonequilibrium is a factor determining the mechanism and rate of the overall process. In kinetic calculations, the vibrational nonequilibrium of the initial H₂ and O₂ components, the HO₂, OH(X²Π), O₂*(¹Δ) intermediates, and the reaction product H₂O were taken into account. The analysis showed that under these conditions the main contribution to the overall process of OH* formation is caused by the reactions OH + Ar → OH* + Ar, H₂ + HO₂ → OH* + H₂O, H₂ + O*(¹D) → OH* + H, HO² + O → OH* + O² and H + H²O → OH* + H², which occur in the vibrational nonequilibrium mode (their activation barrier is overcome due to the vibrational excitation of reactants), and by H + O₃ → OH* + O₂ and H + H₂O₂ → OH* + H₂O, which are reverse to the reactions of chemical quenching.     

Comparison of pulverized coal combustion in air and in O2/CO2 mixtures by thermo-gravimetric analysis

Thermo-gravimetric technique was used to study the combustion characteristics of pulverized coal in different O₂/CO₂ environments. The effects of combustion environment, oxygen concentration, particle size and heating rate were considered and the differences of pulverized coal pyrolysis, combustion and gaseous compounds release under two environments were analyzed. Results show that the coal pyrolysis in CO₂ environment can be divided into three stages: moisture release, devolatilization and char gasification by CO₂ in higher temperature zone. In the lower temperature zone, the mass loss rate of coal pyrolysis in CO₂ environment is lower than that in N₂ environment. The burning process of pulverized coal in O₂/CO₂ environment is delayed compared with that in O₂/N₂ environment for equivalent oxygen concentrations. With the oxygen concentration increase or the coal particle size decrease, the burning rate of coal increases and burnout time is shortened. As the heating rate increases, coal particles are faster heated in a short period of time and burnt in a higher temperature region, but the increase in heating rate has almost no obvious effect on the combustion mechanism of pulverized coal. During the programmed heating process, species in flue gas including H₂O, CO₂, CO, CH₄, SO₂ and NO were determined and analyzed using the Fourier-transform infrared (FTIR) spectrometer. Compared with pulverized coal combustion in O₂/N₂ environment, much more CO is produced in O₂/CO₂ coal combustion process, but the releases of SO₂ and NO are less than those released in O₂/N₂ environment. The present results might have important implications for understanding the intrinsic mechanics of pulverized coal combustion in O₂/CO₂ environment.     

Influence of dielectric barrier plasma treatment of ZnMgAl alloy-coated steel on the adsorption of organophosphonic acid monolayers

The adsorption of octadecyl phosphonic acid (ODPA) on oxide-covered surfaces of ZnMgAl alloy coatings is described as a function of a dielectric barrier discharge (DBD) pretreatment step. The ODPA monolayer formation enables the investigation of the influence of the DBD treatment on the resulting interfacial bond formation and surface coverage. Surface characterisation by means of surface spectroscopy (PM-IRRAS, XPS) and surface electrochemistry (cyclic voltammetry) showed that the DBD pretreatment with Ar, Ar/O₂ and Ar/H₂O gas mixtures leads to improved barrier properties of the adsorbed ODPA monolayer. Moreover, during ODPA monolayer formation from ethanolic solution, a partial etching of the surface oxide layer occurs.     

The vibrational relaxation of H2. I. Experimental measurements of the rate of relaxation by H2, He,Ne, Ar,and Kr

The vibrational relaxation of gaseous H₂ in mixtures with He, Ne, Ar, and Kr was studied by the laser Schlieren technique in incidents shock waves at 1350–3000 K. From the results of 155 experiments the following standard relaxation times for self-relaxation of H₂ and relaxation of H₂ by He, Ne, Ar and Kr were obtained:

pτ is in atm s, and the qouted uncertainties are standard deviations. The results for H₂/H₂ and H₂/Ar are in very good agreement with previous results of Kiefer and Lutz, and the extrapolated for H₂/H₂, H₂/He and H₂/Ar agree very well with low temperature data Ducuing.The linear mixture rule for a additivity of relaxation rates was found to hold, to within experimental accuracy, for the mixtures studied in the present work.     

Autoignition of heptanes; experiments and modeling

There is much interest in determining the influence of molecular structure on the rate of combustion of hydrocarbons; the C₇H₁₆ isomers of heptane have been selected here as they exemplify all the different structural elements present in aliphatic, noncyclic hydrocarbons. With the exception of n‐heptane itself, no autoignition studies have been carried out to date on the other isomers of heptane at high temperatures. Therefore, ignition delay times were measured for the oxidation of four isomers—n‐heptane, 2,2‐dimethylpentane, 2,3‐dimethylpentane, and 2,2,3‐trimethylbutane—under stoichiometric conditions at a reflected shock pressure of 2 atm, within the temperature range of 1150–1650 K. Measurements under identical conditions reveal that they all have essentially the same ignition delay time; this confirms earlier theoretical predictions based purely on detailed chemical kinetic modeling. The variation of ignition delay times for n‐heptane with changing oxygen concentrations and reflected shock pressure was determined and shown to follow expected trends. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 728–736, 2005