High-temperature Oxidation Reactions Research Articles

Limitations and potentials of oxygen transport dense and porous ceramic membranes for oxidation reactions

This overview focuses on both dense and porous ceramic membranes for high temperature oxidation reactions, i.e. partial and total oxidations. Non-permselective porous membranes are efficient contactors for total oxidation of VOC or soot. They are also still attractive as oxygen distributors for the partial oxidation of long chain alkanes, although dense mixed conducting membranes are now on the way to be commercialized for methane involving reactions. By a proper selection of the ion conducting materials composition, structure and thickness, and by combining in a suitable way both dense and porous layers, the oxygen flux, performance and stability of dense ceramic membranes can be considerably improved. In view of the large number of material challenges and scientific approaches found in the literature, it is clearly difficult to be exhaustive. New developments in the field of advanced membranes constantly contribute to improve the potential of membrane reactors, through the development of new preparation methods, of optimized layer stacking and of new membrane materials with original or improved properties. After a rapid overview on both dense and porous membranes used for oxidation reactions, examples of the developments in the field of membrane materials, structures, architectures, synthesis methods and reactor designs are reported, coming from either our Institute or from the recent literature on both membrane reactors and SOFCs.

Microfabricated high-temperature reactor for catalytic partial oxidation of methane

A new setup using microfabricated silicon reactors for studying high-temperature partial oxidation reactions is described in this paper. Methane oxidation is chosen as a test reaction. The system is completely safe to operate due to the small size and the temperature is easy to control even for the highly exothermic reaction. The activation energy obtained for full oxidation of methane on Pd/Al 2O 3 catalyst is similar to the values reported in the literature for the case of oxidized Pd particles. The simplicity of depositing the catalyst, bonding and mounting the microreactor, gives a fast, safe, and easy way for reliable catalyst screening in studying partial oxidation reactions.

Combustion Reaction Kinetics Studies of Turkish Crude Oils

In this research, sixteen experiments were conducted to study the combustion reaction kinetics of Turkish crude oils (Batı Raman, Çamurlu, Raman, Adıyaman, Garzan, Karakuş, and Beykan) in a limestone medium. A mixture of the limestone and the crude oil was subjected to a controlled heating program under a constant flow rate of air. The produced gas was analyzed for its oxygen and carbon oxides contents. Although the molar CO2/CO ratios vary during low-temperature oxidation (LTO), for fuel deposition (FD) and high-temperature oxidation (HTO), these values can be indicated at different temperatures. A decrease in the atomic H/C ratio with an increase in temperature was observed for all runs. The activation energies of the Çamurlu, Batı Raman, and Raman crude oils for both fuel deposition and high-temperature oxidation reactions were observed to be similar. For medium-gravity oils (Adıyaman and Garzan), the activation energies for the high-temperature oxidation reaction is higher than that for the fuel deposition reaction. For the LTO reaction, the activation energies are almost twice those of FD and HTO reactions for each crude oil. The activation energies are almost independent of the gravity of the oil used. The Arrhenius constant is not affected by the API gravity of the oils.

Laser cutting quality assessment and thermal efficiency analysis

Lasers are widely used in industry as cutting tools due to ultra flexibility of the cutting conditions, obtaining high quality end product, quick set up, non-mechanical contact between the workpiece and the tool, and small size of the heat affected zone. In the present study, laser gas assisted cutting process is examined. Statistical method based on factorial analysis is introduced to identify the influence of cutting parameters on the resulting cut quality. International standards for thermal cutting is employed to identify the measurable variables when assessing the cut quality. Kerf width size is presented using scaling laws. Contribution of high temperature oxidation reaction in cutting due to assisting gas is accommodated in the analysis. First and second law efficiencies for laser cutting process are formulated. An experiment is conducted to assess the cutting quality and validate the Kerf width predictions. It is found that increasing laser beam scanning speed reduces the Kerf width while Kerf width increases with increasing laser output power. The main effects of all the parameters employed have significant influence on the resulting cutting quality. First law efficiency increases with increasing laser scanning speed, which substantiates as the workpiece thickness is doubled.

Effects of metal salts on char oxidation in pectins/uronic acids and other acid derivative carbohydrates

Extensive experimental investigations on oxidative reactivity of pectins and related carbohydrates have revealed a high temperature oxidation reaction above 600 °C. Most biomass chars typically oxidize in the temperature range from 400 to 500 °C. This work reports characterization of this high temperature oxidation process, which is not limited to pectins, but seems to be specific to acid carbohydrate salts. Oxidation studies were conducted with a thermogravimetry/differential scanning calorimetry/mass spectrometry instrument. Significant temperature variations in pectin oxidation behavior were dependent on free sugar content, inorganic content, degree of esterification, and pyrolysis conditions. Results indicate alkali metals, such as sodium or potassium, bound in pectins initially as the salt of the uronic acid groups, decompose during pyrolysis between 200 and 400 °C to produce a metal complex in the char which apparently inhibits/shields the carbon char from oxidation at the ‘typical’ oxidation temperatures. Temperatures in excess of 600 °C are needed, in either oxygen or inert gas, to decompose the metal–char complex and allow oxidation of surrounding carbon to proceed.

Metallurgical Considerations for Life Assessment and the Safe Refurbishment and Requalification of Gas Turbine Blades

Metallurgical analysis of rotating blades operating in advanced gas turbine engines is important in establishing actual operating conditions, degradation modes, remaining life, and most importantly, the proper repair and rejuvenation techniques to be used in developing optimum component life strategies. The elevated firing temperatures used in the latest engine designs result not only in very high metal surface temperatures but also in very high temperature gradients and concommitant thermal strains induced in part by the complex and efficient cooling systems. This has changed the primary function of today’s superalloy-coating systems from one of hot corrosion protection to moderating high temperature oxidation reactions. Furthermore, as a result of the high thermal strains induced by the cooling systems, long-term metallurgical structural stability issues now revolve around optimizing both thermal mechanical fatigue (TMF) resistance and creep life. Thus the gradual change to directionally solidified (DS) and single crystal (SC) alloys throughout the industry. The use of DS and SC alloys coated with state of the art TBC, platinum modified aluminide and MCrAlY coatings with or without subsequent aluminizing applied by vacuum plasma spray (VPS), high velocity oxygen fuel (HVOF), physical vapor deposition (PVD), air plasma spray (APS), and by chemical vapor deposition (CVD) methods along with the widespread use of internal aluminide coatings have made today’s rotating components prohibitively expensive to replace after only one cycle of operation. It is therefore, or should now be a high priority for all cost conscious gas turbine users to help develop reliable repair and rejuvenation strategies and techniques to minimize their operating cost. Traditional metallurgical considerations required for life assessment and the reliable refurbishment and requalification of gas turbine blades are reviewed along with some new exciting techniques. Examples of component degradation modes are presented. Appropriate attention to metallurgical issues allows turbine users to more successfully and economically operate their turbines.

Microemulsion-Templated Synthesis of Highly Active High-Temperature Stable Partial Oxidation Catalysts

ABSTRACTHighly active catalysts for high-temperature partial oxidation reactions have been synthesized based on a microemulsion-templated sol-gel synthesis. The catalysts were tested with the direct catalytic oxidation of methane to synthesis gas and showed excellent selectitivites towards syngas combined with very high activity and low ignition temperatures. Furthermore, a surprisingly high long term stability was observed at these high-temperature conditions of T > 900°C. The catalyst therefore seem very promising candidates for high-temperature partial oxidation and hydrogen production from hydrocarbon fuels.

EVALUATION OF TURKISH OIL SHALES – THERMAL ANALYSIS APPROACH

In this research, thermal characteristics of three Turkish oil shales (Himmetoglu, Beypazaro and Hatoldag) were studied by thermal analysis techniques (differential scanning calorimetry, thermogravimetry and pressurised differential scanning calorimetry) Two distinct exothermic peaks were identified in all experiments known as low-temperature oxidation and hightemperature oxidation reaction regions. Kinetic data were analysed by Arrhenius, and Coats and Redfern models and the results are discussed.

Characterization of oil shales by high pressure DSC

Pressurised differential scanning calorimeter (PDSC) has been used to obtain information on the pyrolysis and combustion characteristics of oil shales. Two distinct exothermic peaks were identified in combustion experiments known as low temperature oxidation (LTO) and high temperature oxidation (HTO) reaction regions. The pyrolysis process of all studied oil shale samples showed one exothermic effect at each total pressure studied. Kinetic data were analysed by Roger & Morris and Arrhenius methods and the results are discussed.

Thermodynamic properties of silicides. VI. Pentamolybdenum trisilicide (Mo 5Si 3). Fluorine combustion calorimetric determination of the standard molar enthalpy of formation at the temperature 298.15 K

The standard molar enthalpy of formation Δ f H m oof pentamolybdenum trisilicide Mo 5Si 3has been determined by fluorine combustion calorimetry to be −(314.3 ± 8.3) kJ·mol −1at T= 298.15 K and p o= 101.325 kPa. Conventional thermodynamic properties of Mo 5Si 3are tabulated to T= 2100 K. Thermodynamic quantities to the same temperature maximum are also given for the high-temperature oxidation reactions: 2MoSi 2(s) + 70 2(g) = 2MoO 3(s) + 4SiO 2(s), and 5MoSi 2(s) + 70 2(g) = Mo 5Si 3(s) + 7SiO 2(s) on the basis of the most up-to-date thermodynamic values.

Interaction of oxygen with silver at high temperature and atmospheric pressure: A spectroscopic and structural analysis of a strongly bound surface species.

X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), and ion scattering spectroscopy (ISS) have been used to study the Ag(111) single-crystal surface after exposure to ${\mathrm{O}}_{2}$ at high temperature and at atmospheric pressure. The activated formation of a strongly bound surface layer has been observed, as identified by an asymmetry of the Ag 3${\mathit{d}}_{5/2}$ core-level peak at 367.3 eV and an O 1s peak at 529.0 eV (${\mathrm{O}}_{\ensuremath{\gamma}}$). In addition, oxygen was found to be dissolved in the bulk (${\mathrm{O}}_{\mathrm{\ensuremath{\beta}}}$), exhibiting an O 1s binding energy between 531 and 530 eV depending on its abundance. X-ray-excited oxygen KVV Auger electron spectroscopy revealed the presence of ${\mathrm{O}}_{\ensuremath{\gamma}}$ by additional peaks at 514.8 and 494.7 eV. UPS displayed oxygen-derived bands located above the emission from the Ag 4d band at 3.2 and 2.5 eV. Oxygen-related peaks below the Ag 4d band were identified as resulting from OH groups formed by reaction of surface oxygen (${\mathrm{O}}_{\mathrm{\ensuremath{\alpha}}}$) with residual hydrogen. The incorporated oxygen caused a pronounced charge separation as reflected by a 1 eV increase in the work function. ISS measurements revealed that ${\mathrm{O}}_{\ensuremath{\gamma}}$ is incorporated in the topmost surface layer, shielding underlying Ag atoms from the ${\mathrm{He}}^{+}$ beam. All spectroscopic data point to the presence of one monolayer of silver-embedded oxygen, which is in dynamic equilibrium with surface atomic oxygen segregated from the bulk at high temperature. The oxygen embedded in the topmost silver layer is strongly bound to the metal, with its interaction being different from adsorbed atomic oxygen and bulk ${\mathrm{Ag}}_{2}$O. It is stable up to 900 K, in contrast to the binary silver oxides, and relevant for high-temperature oxidation reactions catalyzed by Ag. A qualitative analysis is presented of the chemical bonding of the different surface species in comparison to the situation of a complex silver oxide reference. \textcopyright{} 1996 The American Physical Society.

High-temperature oxidation of Ti3Al−Nb alloys

Titanium aluminide (Ti3Al−Nb) has potential for high-temperature applications because of its low density and high-temperature strength. This research is aimed at improving the high-temperature oxidation resistance of a Ti3Al−Nb alloy by modification of its composition. The oxidation rates of Ti3Al−Nb alloys were measured from 600 to 900°C in air. The oxide layer was examined by X-ray diffraction, scanning electron microscopy, and electron probe microanalysis. The experimental results reveal that alloys with added Nb tend to form denser oxide layers and that oxidation rate can be reduced by increasing Nb content (up to 11 at.% in this study), which is in good agreement with other investigators. The only exception is a Ti65Al25Nb10 alloy, which shows better oxidation resistance than the commercial Ti65Al24Nb11 alloy. The oxidation resistance of Ti65Al25Nb10 alloy can also be improved slightly by the addition of small amounts of Si or Cr. An increase in the oxidation resistance of Ti65Al25Nb10 alloy containing Y was observed at 900°C but not at 800°C or below. The parabolic oxidation rate equation is adequate to describe the high-temperature oxidation reaction of the Ti3Al−Nb alloys in the atmosphere.

Phosgene formation from 1,1,1-trichloroethane oxidation

The high-temperature oxidation of 1,1,1-trichloroethane can, under certain conditions, form the highly toxic byproduct phosgene. Potential routes of phosgene formation during the high temperature post-flame oxidation of 1,1,1-trichloroethane are investigated. These include photolysis reactions, heterogenous wall reactions, reactions of carbon monoxide and molecular chlorine, and high temperature oxidation reactions. Experiments using both extractive and in situ measurement techniques, along with chemical kinetic studies, indicate that phosgene is formed directly in the gas phase as a product of 1,1,1-trichloroethane oxidation. We measured up to 29% conversion of 1,1,1-trichloroethane to phosgene at an injection temperature of 1160K and a residence time of 0.1 s. The chemical kinetic model suggests that 1,1,1-trichloroethane conversion to phosgene is strongly dependent on temperature and is weakly dependent on initial concentration, equivalence ratio, and residence time.

Mechanisms of Autoignition of Finely Divided Steel

Autoignition of direct reduced iron (DRI) that leads to severe warming or even to uncontrollable metal fires has always been linked with the presence of moisture, being particularly severe in the presence of sea water. This is of considerable concern in view of the regular transportation of DRI across the oceans. In spite of the very high specific surface area and high reactivity of DRI, oxidation reactions cannot alone proceed to autoignition in the absence of water. Reactions involved in aqueous corrosion appear to be a necessary precursor for autoignition. But there has been no satisfactory explanation of how aqueous corrosion reactions that must terminate at 100°C, can initiate high temperature oxidation reactions. It has also been reported that, although most DRI cargos and piles show some warming, autoignition to an uncontrollable situation or a metal fire is observed only in case of relatively large or deep piles. The present work suggests that while thermal insulation is necessary, the size of the...

Laser-induced decomposition of ammonium perchlorate. Identification of nascent products from emission spectroscopy

The decomposition of ammonium perchlorate by a pulsed excimer laser at reduced pressures has been studied. Transient emission spectra from nascent products are presented and OH, NH, ClO radical species are positively identified. From the temporal behavior of the emission bands, the high-temperature oxidation reaction pathways are inferred.

Partial oxidation of fuel-rich mixtures in a spouted bed combustor

It is shown that stable combustion can be maintained in spouted beds at fuel concentrations greatly in excess of the rich limit of flammability. This makes it possible to minimize the fraction of fuel used for heat release in any high-temperature partial oxidation, pyrolysis, or other reaction in which the remainder of the fuel is to be processed. Thus, combustion of methane/oxygen/nitrogen mixtures at equivalence ratios of up to 2.34 is shown to yield large proportions of hydrogen and carbon monoxide, as well as appreciable amounts of higher hydrocarbons. In view of the ability of spouted beds to handle solid and heavy liquid fuels, a wide range of potential applications of the method is envisaged, ranging from less polluting combustion systems to processing inexpensive fuels to more desirable products.

Kinetic Parameters For The High-Temperature Oxidation Of In-Situ Combustion Coke

Abstract Coke combustion plays a vital role in many thermal recovery methods, whether in-situ or otherwise. Due to this importance, much research has been done into high-temperature coke oxidation. Notwithstanding the extensive studies undertaken to determine the high-temperature coke oxidation model and its kinetic parameters, almost all have used differential analysis in (lie parameter estimation procedure. In addition, the adequacy of the commonly accepted model has never been statistically tested. Because differential analysis requires subjective data manipulation and because a statistical evaluation was sought, an integral-analysis method was developed and applied, with multi-response parameter estimation techniques, to differential reactor data. Kinetic parameters were found for the coke oxidation model using two types of petroleum cokes. It was determined that the commonly accepted coke oxidation model was statistically adequate and that the objective integral-analysis method was superior to the differential analysis technique. Introduction and Literature Survey Thermal recovery methods, including in-situ combustion, the fluidized solids technique(18), the Lurgi Ruhrgas Process(19) and the Taciuk Process(20) depend on high-temperature coke oxidation for their commercial viability. In light of this, much research has been done to determine the form of the combustion model and to estimate the kinetic parameters involved. There have been two approaches to these investigations: a petroleum perspective, done in porous media, and secondly an idealized approach-using a sphere or plate coated with carbon. Dart et al.(18), Lewis et al.(11) and Metcalfe(13), although not done in a porous medium, conducted their experimentation from a global reaction perspective. That is, they analyzed effluent gas compositions and, on that basis, determined reaction rates and the dependence of reaction rate on oxygen and coke concentration. They concluded that the high-temperature coke oxidation reaction is first-order with respect to coke concentration and oxygen partial pressure. Further research was done by Bousaid ef al.(3), Dabbous et al.(7) and Fassihi et al.(9), who conducted their work in porous media, within now-through reactors. In general, their findings indicate that the coke combustion reaction was first-order with respect to coke and oxygen concentration. The reported activation energies varied from 58,850 J/gmole up to 157,300 J/ gmole and the pre-exponential factors ranged from 2.0e-03 to 6.67e05 (g carbon /100 gsand-s). In these studies the reaction rate parameters were obtained by graphical means assuming a differential reactor system. Allag(2) studied coke oxidation from a more numerically rigorous viewpoint. He modelled coke production and burn-off simultaneously and compared the difference between these two (being the residual coke) to his data. He numerically integrated these terms but eventually had to resort to graphical means to minimize convergence problems. Ozomarot(17) investigated the controlling mechanism to coke combustion and the adequacy of the model describing it. He developed a solution routine which solved for the coke combustion parameters by minimizing the error between experimental and calculated reaction rates. However, it was concluded that the technique did not overcome the disadvantages of haphazard data selection and that, judicious choices had to be made as to which data points to include and which to discard.

Hazardous Waste Incineration: A Progress Report

Safe, effective treatment of hazardous wastes has emerged as a national priority. Advances in technology and testing methods have increased credibility and public acceptance of incineration as a means of destroying chemical wastes. The incineration process, a high temperature oxidation reaction, offers many advantages over other methods of treatment. The quantity of the waste is immediately reduced to a fraction of its original state and toxicity is greatly reduced or eliminated. Existing technology can achieve essentially complete destruction of even the most hazarous materials while effectively controlling emissions to the atmosphere for minimal environmental impact. Incineration requires a relatively small process area; wastes often can be treated at or near the site of generation. While capital and operating costs are high in comparison to other means of disposal, they often can be offset by some form of heat or metals recovery.

Description of ignition and combustion of gas mixtures with solid particles by methods of the mechanics of continuous media

DESCRIPTION OF IGNITION AND COMBUSTION OF GAS MIXTURES WITH SOLID PARTICLES BY METHODS OF THE MECHANICS OF CONTINUOUS MEDIA A. E. Medvedev, A. V. Fedorov, and V. M. Fomin Let us examine a mixture of gas with solid particles in which particle oxidation and combustion reactions can proceed. We take the usual assumptions [i] relative to the inter- penetrating gas and particle continua being studied for the mathematical description of the motion of such a mixture, and we append the apparent kinetics of the chemical reactions. We consider the first phase (gaseous, subscript i) to consist of oxidizer, inert gas, and gaseous reaction products (subscripts ii, 12, 13). The second phase (condensed, sub- script 2) is the metal particles with the condensed reaction products (subscripts 22 and 23). We consider the high-temperature oxidation and combustion reactions to be purely hetero- geneous and described by the stoichiometric equations

Enthalpies of pyrolysis and oxidation of Athabasca oil sands

Thermal degradation of Athabasca oil sands, bitumen, and its fractions have been investigated in N 2and in air, at 25–600 °C and at pressures up to 6.9 MPa, using thermogravimetry (TG) and high pressure differential scanning calorimetry (PDSC). These conditions are likely to occur during in-situ recovery of bitumen by underground combustion processes. Two regions of weight loss are detected using both gases. The endothermic low temperature volatilization reactions (150–400 °C) absorbed +26 mJ mg −1 for oil sand to +2319 mJ mg −1 for medium oil. The heats of reaction for high-temperature cracking and volatilization reactions (400–550 °C) were similar. The heats of reaction for the low-temperature oxidation reactions (150–375 °C) were −405 mJ mg −1 for oil sand to −30200mJ mg −1 for medium oil. Values for the high-temperature oxidation reactions (400–550 °C) were slightly higher. Increasing the pressure of nitrogen and air caused an increase in the endothermicity and exothermicity of the respective reactions.