Atm Range Research Articles

The refinement of the rate determining process in sulfur trioxide electrolysis using the electrolysis cell

We are developing a new hydrogen production process, named a hybrid thermo-chemical process, which is based on H 2 SO 4 synthesis and decomposition, and SO 3 electrolysis with a solid electrolyte at 500 – 550 ∘ C . In order to improve the energy efficiency, it is necessary to reduce SO 3 electrolysis resistance. For refining the rate determining process of SO 3 electrolysis, we performed SO 3 electrolysis with YSZ solid electrolyte, and it was found that YSZ solid electrolyte resistance was small enough to be regarded as unimportant, and that SO 3 electrolysis resistance was almost due to the electrode reaction, which meant the rate determining process was involved in the electrode reaction. In order to analyze this experiment, we created an analytical model. With this model , we concluded that the rate determining process was the adsorption and dissociation reaction near the three phase boundary at 450 – 500 ∘ C and the surface diffusion on the electrode at 500 – 600 ∘ C , and it was important to encourage the adsorption and dissociation reaction near the three phase boundary in order to improve SO 3 electrolysis in low temperature ( 450 – 500 ∘ C ) or SO 3 high pressure ( 0.5 – 1.0 atm ) range.

Investigation of ZrMn 2+ x-H 2 by means of calorimetric method

The interaction of hydrogen with the ZrMn 2+ x ( x = 0, 0.7) Laves phase compounds at pressure up to 50 atm and temperature range from 75 to 305 °C were studied by means of calorimetric and P– C-isotherm methods. On the base of obtained results it can be assumed that in the ZrMn 2+ x -H 2 system one or two hydride phases exist according to experimental temperature.

Reduction of nitrobenzene catalyzed by immobilized copper catalyst under carbon monoxide and water

Catalytic activity for reduction of nitrobenzene to aniline (98%) and azobenzene (2%) using a poly(4-vinylpyridine)-immobilized Cu catalyst [Cu(II)/P(4-VP)] under a CO atmosphere in aqueous 2-ethoxyethanol was studied as a function of the various reaction parameters ([Cu], P(CO), T, and nitrobenzene/Cu molar ratio). Reaction rates were first-order in [Cu]tot over 1.0–12.0 wt.% range and in P(CO) over the 6.8–27.2 atm range. The catalytic activity proved to be non-linear in nitrobenzene/Cu ratio over 41–500 molar ratio range. These results suggest that the rate-limiting step is preceded by reversible coordination of nitrobenzene to a carbonyl–Cu(I) immobilized species. A catalytic mechanism consistent with the data is proposed.

Theoretical study on the mechanism of cycloaddition between dimethyl methylene carbene and acetone

The mechanism of the cycloaddition reaction of singlet dimethyl methylene carbene and acetone has been studied by using second-order Moller-Plesset perturbation and density functional theory. The geometrical parameters, harmonic vibrational frequencies and energy of stationary points on the potential energy surface are calculated by MP2/6-31G* and B3LYP/6-31G* methods. The results show that path b of the cycloaddition reaction (1) would be the major reactive channel of the cycloaddition reaction between singlet dimethyl methylene carbene and acetone, which proceeds in two steps: i) The two reactants form an energy-rich intermediate (INT1b), which is an exothermic reaction of 23.3 kJ/mol with no energy barrier. ii) The intermediate INT1b isomerizes to a three-membered ring product (P1) via transition state TS1b with energy barrier of 22.2 kJ/mol. The reaction rate of this reaction and its competitive reactions do greatly differ, with excellent selectivity. In view of dynamics and thermodynamics, this reaction is suitable for occurring at 1 atm and temperature range of 300–800 K, in which the reaction will have not only the larger spontaneous tendency and equilibrium constant but also the faster reaction rate.

Shock tube determination of ignition delay times in full-blend and surrogate fuel mixtures

Autoignition characteristics of n-heptane/air, gasoline/air, and ternary surrogate/air mixtures were studied behind reflected shock waves in a high-pressure, low-temperature regime similar to that found in homogeneous charge compression ignition (HCCI) engine cycles. The range of experiments covered combustion of fuel in air for lean, stoichiometric, and rich mixtures ( Φ = 0.5 , 1.0, 2.0), two pressure ranges (15–25 and 45–60 atm), temperatures from 850 to 1280 K, and exhaust gas recirculation (EGR) loadings of (0, 20, and 30%). The ignition delay time measurements in n-heptane are in good agreement with the shock tube study of Fieweger et al. (Proc. Combust. Inst. 25 (1994) 1579–1585) and support the observation of a pronounced, low-temperature, NTC region. Strong agreement was seen between ignition delay time measurements for RD387 gasoline and surrogate (63% iso-octane/20% toluene/17% n-heptane by liquid volume) over the full range of experimental conditions studied. Ignition delay time measurements under fuel-lean ( Φ = 0.5 ) mixture conditions were longer than with Φ = 1.0 mixtures at both the low- (15–25 atm) and high- (45–60 atm) pressure conditions. Ignition delay times in fuel-rich ( Φ = 2.0 ) mixtures for both gasoline and surrogate were indistinguishable in the low-pressure (15–25 atm) range, but were clearly shorter at high-pressures (45–60 atm). EGR loading affected the ignition delay times similarly for both gasoline and surrogate, with clear trends indicating an increase in ignition delay time with increased EGR loading. This data set should provide benchmark targets for detailed mechanism validation and refinement under HCCI conditions.

Catalytic wet oxidation of phenol in a trickle bed reactor

Catalytic liquid phase oxidation of aqueous phenol was studied in a pilot plant trickle bed reactor using a copper oxide catalyst supported on alumina. Catalysts were prepared by impregnating CuO on alumina extrudates and on computer designed shape (CDS) alumina pellets. Phenol oxidation was carried out in a 2.54 cm diameter reactor with a catalyst bed length of 60 cm and in the pressure range of 1–15 atm and temperature range of 373–403 K Compared to alumina extrudates higher phenol conversion was achieved over CDS pellets under identical conditions. Phenol oxidation reaction was strongly affected by the temperature and pressure, however, pressure had less effect. Hydrodynamics of the reactor had strong influence on phenol oxidation reaction. A one dimensional axial dispersion model was proposed to simulate the experimental results. The model satisfactorily explains the experimental results with a deviation of ±15%.

Investigation of the spatial profile of stimulated Raman scattering beams in D2 and H2 gases using a pulsed Nd:YAG laser at 266 nm

The stimulated Raman scattering (SRS) beam spatial mode structure is studied in H2 and D2 gases, in a 60 cm-long high-pressure Raman cell, using a pulsed Nd:YAG laser at 266 nm. The conversion efficiencies of the first and second Stokes in H2, D2 and H2/D2 mixtures have been measured precisely in the 1–14 atm range. The SRS beam profiles were recorded for different gas pressures in the high-pressure Raman cell and interesting behaviour is revealed. Homogeneous SRS spatial profiles were obtained only for pressures higher than 7 atm. For lower pressures the profiles are either in the form of a ring or of a more complicated shape. The results are explained in terms of nonlinear self-focusing processes during the pump beam propagation in the Raman cell. Also, from our measurements, a more precise value of the nonlinear index of refraction for the H2 and D2 at 266 nm is proposed.

Particulate Emission from Combustion of Diesel and Fischer−Tropsch Fuels: A Shock Tube Study

Motor vehicle emissions have been identified as a major source of particulates, and have been associated with adverse health effects and decreased ambient air quality. Recent published studies have shown that Fischer−Tropsch fuels can reduce particulate emissions. The fuel composition, temperature, and pressure affect the kinetics of a chemical reaction and ultimately the yield of end products. To see how the above factors impact the particulate yields, D-2 diesel and two Fischer−Tropsch fuels, Shell MDS and Mossgas COD, were investigated in this study over a pressure range of 5 to 24 atm and temperature range of 1000 to 2300 °C. All experiments were conducted in a modified single-pulse reflected shock tube. Fuels were injected using a high-pressure liquid injector. The results from Leco carbon analysis indicated that for most test conditions, Shell MDS had the lowest particulate yield compared to D-2 diesel followed by Mossgas COD. At relatively low temperatures (∼1150 °C) and high temperatures (∼2250 °C) the particulate yields decreased for all fuels tested. At higher pressures an increase in particulate yield was observed. An attempt was made to correlate the observed difference in soot yields to physical properties and chemical composition of the investigated fuels. The results are well in agreement with previous studies that relate lower sulfur and aromatic contents to lower particulate yields for the test conditions studied. No direct benefit was seen from a high cetane number on particulate emissions.

Vibrational relaxation in methyl hydrocarbons at high temperatures: propane, isobutene, isobutane, neopentane, and toluene.

Vibrational relaxation has been seen in shock waves in propane, isobutene, isobutane, neopentane, and toluene dilute in krypton with the laser-schlieren technique. These experiments cover about 600-2200 K and post-shock pressures from 5 to 29 Torr. The process cannot be resolved in any for T<600 K, or in any for large molecule fraction. All the ultrasonic measurements of relaxation in these at room temperature show characteristic times in the 1-5 ns atm range, corresponding to fewer than five collisions, whereas the relaxation times in the shock waves range from 20 to 200 ns atm, with a clearly defined negative or "inverted" temperature dependence. It would seem the observed slowdown of relaxation with increasing T is simply a consequence of the much increased energy transfer required at high temperature in such large polyatomics when this is combined with a collision efficiency, here interpreted as <DeltaE>down, already so large it cannot much increase. The simple method for the extraction of a <DeltaE>down from relaxation data offered here by consideration of the energy relaxation equation for Evib=0 appears to be original and should prove quite useful in connecting thermal relaxation data to values obtained from spectroscopy and master-equation analyses. Here it is found that the derived <DeltaE>down extrapolate well to room temperature ultrasonic measurements, showing a slight increase with temperature.

Reduction of aromatic nitro compounds as catalyzed by rhodium trichloride under water–gas shift reaction conditions

Abstract Described are quantitative studies of the CO/H 2 O reduction of various nitroaromatics to the respective anilines under water–gas shift reaction (WGSR) conditions catalyzed by solutions of RhCl 3 in aqueous amines. The most active media were aqueous tetramethylethylenediamine and 2-picoline solutions. The reduction rates exhibited first-order dependence on P (CO) over the 0.3–1.5 atm range, but turnover frequencies decreased as the total rhodium concentration increased over the range 5–40 mM. The latter behavior was interpreted in terms of the coexistence of mononuclear and polynuclear Rh species in the system, the mononuclear being the more catalytically active. Relative shift reaction and reduction rates indicate that the nitroaromatics must be reduced by an independent catalytic cycle rather than by the WGSR produced H 2 .

XPS characterization of adsorbed reaction intermediates on automotive exhaust gas catalysts: NO and CO + NO interactions with Pd

AbstractNitrous oxide (NO) adsorption and the CO + NO reaction have been investigated on bulk and alumina‐supported Pd catalysts by XPS at various temperatures between 25 and 300°C with PNO in the 0.5–5.0 (×10−2) atm range and PCO = 5 × 10−3 atm. A catalytic reactor settled in the preparation chamber coupled to the spectrometer allows surface changes occurring under catalytic conditions on these catalysts to be characterized. Various nitrogen‐containing species have been detected, which depend on the oxidation state of Pd. The results have been explained tentatively in the light of a mechanism proposed for NO transformation. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Electrical conduction and oxygen sensing mechanism of Mg-doped SrTiO 3 thick film sensors

The dependencies of the electrical conduction of Mg-doped SrTiO 3 thick film samples on temperature and oxygen partial pressure have been studied. The Mg contents in SrTiO 3 were 10 mol%, 20 mol%, 30 mol%, 40 mol% and 50 mol%, respectively. The experimental results show that all samples exhibit p-type semiconduction in the p O 2 region 3.8×10 −4–2.6×10 −1 atm and temperature range 500–900°C. The temperature at which a maximal resistance is observed decreases from 300°C to 100°C in Mg-doped SrTiO 3 samples. The 40 mol% Mg-doped SrTiO 3 sample reveals the best oxygen sensing properties. Results are discussed based on the X-ray diffraction and the analysis of defect chemistry.

Dry melting of high albite

The properties of albitic melts are central to thermodynamic models for synthetic and natural granitic liquids. We have analyzed published phase-equilibrium and thermodynamic data for the dry fusion of high albite to develop a more accurate equation for the Gibbs free energy of this reaction to 30 kbar and 1400 °C. Strict criteria for reaction reversal were used to evaluate the phase-equilibrium data, and the thermodynamic properties of solid and liquid albite were evaluated using the published uncertainties in the original measurements. Results suggest that neither available phase-equilibrium experiments nor thermodynamic data tightly constrain the location of the reaction. Experimental solidus temperatures at 1 atm range from 1100 to 1120 °C. High-pressure experiments were not reversed completely and may have been affected by several sources of error, but the apparent inconsistencies among the results of the various experimentalists are eliminated when only half-reversal data are considered. Uncertainties in thermodynamic data yield large variations in permissible reaction slopes. Disparities between experimental and calculated melting curves are, therefore, largely attributable to these difficulties, and there is no fundamental disagreement between the available phase-equilibrium and thermodynamic data for the dry melting of albite. Consequently, complex speciation models for albitic melts, based on the assumption that these discrepancies represent a real characteristic of the system, are unjustified at this time.

Pressure and composition dependences of acetone laser-induced fluorescence with excitation at 248, 266, and 308 nm

In previous studies, acetone has been successfully applied as a tracer for planar laser-induced fluorescence (PLIF) measurements of concentration and temperature. The desire to extend acetone PLIF capability to conditions of varying pressure and composition has motivated studies of the effects of these quantities on fluorescence yield. The present work explores pressure and composition effects over a 0.5 to 16 atm range for the three excitation wavelengths of greatest interest for diagnostics: 248, 266, and 308 nm. In accord with previous studies, fluorescence per acetone molecule is seen to increase with pressure, apparently towards a high-pressure limit for each wavelength, with the most significant effect observed at short wavelengths. Bath gas composition is also seen to affect fluorescence intensity, with an impact related to the effectiveness of the bath gas species at vibrationally relaxing excited acetone. A model of fluorescence yield considering the relative rates of intersystem crossing and vibrational relaxation for excited singlet acetone describes the measured pressure and composition dependences well. To explain an oxygen fluorescence quenching effect that is observed experimentally, a term is added to the model to represent oxygen-assisted intersystem crossing. The data and model results provide useful guidance for diagnostic applications. A key conclusion is that long excitation wavelengths are preferable from the standpoint of minimizing pressure and composition dependences.

Preliminary experience with the V-flex plus coronary stent: immediate and one-month clinical outcome.

Procedural and 1-month outcome data following implantation of the V-Flex Plus stent in our first 54 consecutive patients (35 male; mean age, 62 years) are described. Sixty-four stents were implanted for 60 mainly complex lesions; 48% were left anterior descending; 20%, circumflex; 27%, right coronary artery; and 5%, saphenous vein graft. The Indication for stenting was elective in half of the patients and for a suboptimal result or as a bailout procedure in the other half. The stents were deployed at a mean of 12 atm (range, 6-18) and postdilatated to a mean of 15 atm (range, 8-20). Pre- and postdilatation balloon sizes were 2.96 +/- 0.57 mm and 3.16 +/- 0.34 mm, respectively. The procedural success rate was 98%. There were no deaths or Q-wave myocardial infarctions. One patient suffered a non-Q-wave myocardial infarction and another developed a femoral false aneurysm. At 1-month follow-up, there were no additional events, in particular no revascularization procedures. Eighty-nine percent of patients were free of angina. Implantation of the V-Flex Plus stent is safe and effective with an excellent early success rate comparable to that of published randomized trials and registries of carefully selected patients.

Oxidative coupling of methane – the transition from reaction to transport control over La 2O 3/MgO catalyst

A 10% La 2O 3 supported on fused MgO (periclase) catalyst has been studied in the 0.45–3.04 atm range for methane partial oxidation to ethane plus ethylene. X-ray diffraction showed that this catalyst, operated by a mechanism La 2O 3→2La 3+O 2−e −+[O], provides active oxygen and vacancies e − for the surface reaction. Four independent reactions were found that allowed calculation of the rates and approximate kinetics of every species in the reacting system: 2CH 4+1/2O 2→C 2H 6+H 2O; C 2H 6+1/2O 2→C 2H 4+H 2O; 2CH 4+3O 2→2CO+4H 2O; 2CO+2H 2O⇌2CO 2+2H 2.The equilibrium proceeds so fast that it is not possible to distinguish whether CO or CO 2 is the primary product. It was found that oxygen conversion was in a transition regime between surface reaction and mass-transport control in the 700–825°C range. Oxygen conversion is strictly transport controlled at 850–875°C while methane reaction rate remains surface controlled. It is in this oxygen-transport controlled regime at 875°C that our highest yield of 16.2 mol% C 2 was obtained. We have fitted kinetics in both transition- and transport-controlled regimes. Finally, it should be noted that catalyst surface temperatures were calculated to be far above than those of the bulk gas temperatures as a consequence of the transport control; as much as 222°C temperature rise at 875°C gas temperature was observed.

Defect structure and oxygen sensing properties of Mg-doped SrTiO 3 thick film sensors

The preparation of oxygen sensors based on Mg-doped SrTiO 3 thick film is described briefly. The oxygen sensing properties and the defect structure of the samples have been investigated as a function of the Mg content. The results show that all samples exhibit p-type semiconduction in the P O 2 region 3.8 × 10 −4 − 2.6 × 10 −1 atm and temperature range 400–1000 °C. A sensor prepared from the pre-calcined powder of Sr(Mg 0.4Ti 0.6)O 3 − δ revealed the best oxygen sensing properties. When the temperature is between 500 and 800 °C, its sensitivity to the change of P O 2 is 7–8.5 and its response and recovery times are 3 and 28–32 s, respectively. It can be used for monitoring and controlling the combustion processes under excess air (lean-burn) conditions. In addition, its approximate dependence of σ ∝ P O 2 1/3 was observed at intermediate temperature. To explain this result a new defect structure is proposed, in which a double ionized oxygen vacancy, V " o, double ionized acceptor of Mg, Mg″ Ti, and an association defect formed by Mg″ Ti, trapping one hole, (Mg″ Tih .), are the important defects.

High pressure studies of moist carbon monoxide / nitrous oxide kinetics

Flow reactor experiments were performed over the pressure range of 3–15 atm and temperature range of 950–1123 K to study the reaction kinetics of CO/N 2O/H 2O/N 2 mixtures. Experimentally measured profiles of CO, CO 2, N 2O, NO, O 2, H 2O, and temperature were used to constrain the development of a detailed chemical kinetic mechanism. For the first time, the catalytic effect of water vapor has been clearly measured and a quantitative treatment of its influence on the overall reaction rate has been possible. Even at the lowest level of water vapor achievable in the experiments (∼ 10 ppm), the reaction proceeded through the two-step straight-chain sequence of hydrogen atoms reacting with nitrous oxide, producing hydroxyl radicals, which then reacted with carbon monoxide to reform H-atoms and continue the chain. The direct reaction of carbon monoxide with nitrous oxide was found to be insignificant and not necessary in the model to predict the observed species profiles. However, the high-temperature rate constant of this reaction still remains in question. The results also show that pressure fall-off behavior of the reaction CO + O + M = CO 2 + M must be included in the mechanism at intermediate temperatures and superatmospheric pressures. Finally, the detailed kinetic model developed predicts the measured species profiles over the entire range of conditions studied here, and is consistent with previously and concurrently studied mechanisms for N 2O decomposition and reacting H 2/N 2O mixtures.

Results of Coronary Stenting for Restenosis

Objectives. This study attempted to analyze immediate and long-term angiographic and clinical results of coronary stent implantation for restenosis in a consecutive group of patients.Background. The rate of stent utilization in patients with coronary artery disease has increased exponentially in recent years. There are many unanswered questions about the use of stenting in patients with restenosis, particularly with respect to late clinical and angiographic results.Methods. A total of 159 stents were implanted in 128 consecutive patients with 139 lesions (mean 1.3 stents/patient). A technique of optimal stent expansion was used in all patients, and intravascular ultrasound guidance with no subsequent anticoagulation was performed in 41 patients.Results. Stent implantation was successful in 126 patients (98%). Four patients (3.1%) had complications (in two after successful stenting): death in one, emergency bypass surgery operation in two and subacute stent thrombosis in one. Stents were implanted with a final balloon size (mean ± SD) of 3.5 ± 0.5 mm and a mean maximal pressure of 11 ± 4 atm (range 8 to 20). Angiographic restenosis occurred in 27 patients (25%). Regression analysis on clinical and angiographic variables for prediction of restenosis showed no statistical significance for any variable. Late events occurred in 23 patients (19%). The actuarial survival rate was 98% at 1 year and at 3 years, and the event-free survival rate including freedom from repeat angioplasty for restenosis was 95% and 76%, respectively.Conclusions. The late angiographic outcome, restenosis rate and total clinical events are favorable for selected patients undergoing stent implantation for the indication of restenosis.

Line-Mixing Effects in the RotationalrQ-Branches of16O3Perturbed by N2and O2

Line-mixing effects have been studied in therQ5torQ12rotational subbranches of16O3. Far-infrared Fourier transform measurements have been made in the 30–90 cm−1spectral region for mixtures of ozone with N2and O2at room temperature and total pressures in the 0.5–1.3 atm range. A careful analysis of the experimental data evidence, for the first time, the effects of line interferences on absorption in the far-infrared ozone branches. Modifications with respect to additive Lorentzian line contributions are on the order of 15% at the[formula]peaks under atmospheric conditions. A simple model is proposed in order to account for these line-mixing effects. It successfully predicts the spectral shape in the 0.05–1.3 atm total pressure range for both O3–O2and O3–N2collisions.