Kinetic Parameters For Oxidation Research Articles

Study on effect of coal treatment with blast furnace slag on char reactivity in air

Waste heat of the blast furnace slag might be recovered in an allothermal coal gasification process to produce an alternative fuel for ironmaking. The effect of heat treatment of brown and sub-bituminous coals mixed with blast furnace slag on the properties of the produced chars was studied. More porous chars were formed at charring in contact with the slag. The development of better porosity in sub-bituminous coal chars was observed in contrast to brown coal, where charring was followed by cracking. Thermal analysis was used to study the behaviour of chars and to derive Arrhenius kinetic parameters for oxidation in air. The behaviour of chars is affected by the simultaneous development of thermally activated oxidation and decomposition processes. Higher volatile ignition temperature for chars produced with slag was observed. The activation energy for the combustion of chars produced with slag was essentially lower, while the pre-exponential factor is higher for chars produced without slag.

Growth stress in SiO2 during oxidation of SiC fibers

A method to calculate growth stress in SiO2 scales formed during SiC fiber oxidation was developed. Calculations were done for Hi-NicalonTM-S SiC fibers using previously measured Deal-Grove oxidation kinetics parameters. Initial compressive stresses in SiO2 of ∼25 GPa from the 2.2× oxidation volume expansion are rapidly relaxed to lower levels by flow of silica with a shear-stress dependent viscosity. At >1200°, viscous flow of silica relaxes stress to negligible levels. At 700° – 900 °C, compressive axial and hoop stress at the GPa level persist, but radial stresses are much smaller. The decrease in growth stress with increase in temperature is a consequence of larger activation energy for silica viscosity than for oxidation kinetics. Radial expansion of the outer scale eventually causes hoop stress to become tensile in the outer scale, and axial stress becomes tensile from the Poisson effect. Tensile hoop stresses can be >1 GPa for thick scales formed at <1000 °C. Approximate analytical expressions for growth stress for some limiting cases are discussed. Growth stresses were also calculated for crystallized SiO2 scales; these were qualitatively consistent with microstructural evidence of stress. Assumptions and limitations of the calculation method are discussed, along with the possible effects of growth stress on SiC oxidation kinetics and on SiC fiber strength.

Redox-cycling studies of anode-supported microtubular solid oxide fuel cells

Accidental reoxidation is one of the most critical issues of SOFC anodes, leading to performance degradation or even producing catastrophic failure of the cell. In this work several redox cycling experiments over microtubular SOFC cells are reported. Oxidation kinetic parameters have been determined for this geometry by Thermogravimetric Analysis (TGA). Oxidation kinetics is known to be diffusion limited at typical operation conditions and, for this reason, strictly dependant on geometry. A linear relationship was found between expansion kinetics and damage on SOFC anodes in a series of dilatometric experiments for the same temperature. A microtubular Ni-YSZ/YSZ/LSM-YSZ cell was also redox cycled several times at partial oxidation conditions (22% oxidation) and performance degradation was measured by j-V characterization and the loss was found to be approximately 2% in performance per cycle.

SIFAT SELF-IGNITION PADA GAMBUT, SABUT KELAPA SAWIT DAN KAYU

Self-ignition properties of peat, palm shell fibre and woods. Forest fire is one of the greatest environmental problems faced by Indonesia. Forest fires have destroyed million hectares of forest and land which cause economic loss, social problems including smoke related diseases and environmental disaster with long time consequences. The exothermic reactions of forest fuels that lead to fire can be initiated by a piloted flame and low-temperature oxidation mechanism. This paper presents the results of low temperature oxidation studies using forests fuel samples i.e. palm shell fibre, peat, woods and low-rank coal. The measured values of the critical oven temperatures and the kinetic oxidation parameters are used to analyze the intrinsic properties of the samples to self-ignite. Thermal runaway reactions leading to ignition are indicated for all forest fuels tested. This reaction is affected by various factors including oven temperature, moisture content, chemical and physical properties as well as basket sizes. Attempt to extrapolate the results of these laboratoryscaled experiments for real fires still require further tests and assessments.

A novel adaptive differential evolution algorithm with application to estimate kinetic parameters of oxidation in supercritical water

A new version of differential evolution (DE) algorithm containing the adaptive mutation and crossover operators, named adaptive differential evolution (ADE), is proposed. In ADE, the control parameters of ADE are generated for each individual and the value of the parameters are based on individual's current generation number and parent's fitness value. With population evolution, the ADE algorithm gradually changes from being exploratory at the early stages to being exploitationary at the later stages. At the same time, in certain generations, low fitness individuals or high fitness individuals are assigned with small parameters to accelerate the convergence of these individuals. The experiments conducted show that the ADE generally outperforms the original DE algorithm and other existing self-adaptive DE algorithms for 11 benchmark functions. Furthermore, ADE is applied to develop the global kinetic model of the 2-chlorophenol oxidation in supercritical water, and satisfactory results are obtained.

Enhancement of oxidative stability of the subtilisin nattokinase by site-directed mutagenesis expressed in Escherichia coli

Nattokinase (subtilisin NAT, NK) is a bacterial serine protease with strong fibrinolytic activity and it is a potent cardiovascular drug. In medical and commercial applications, however, it is susceptible to chemical oxidation, and subsequent inactivation or denaturation. Here we show that the oxidative stability of NK was substantially increased by optimizing the amino acid residues Thr 220 and Met 222, which were in the vicinity of the catalytic residue Ser 221 of the enzyme. Two nonoxidative amino acids (Ser and Ala) were introduced at these sites using site-directed mutagenesis. Active enzymes were successfully expressed in Escherichia coli with periplasmic secretion and enzymes were purified to homogeneity. The purified enzymes were analyzed with respect to oxidative stability, kinetic parameters, fibrinolytic activity and thermal stability. M222A mutant was found to have a greatly increased oxidative stability compared with wild-type enzyme and it was resistant to inactivation by more than 1 M H 2O 2, whereas the wild-type enzyme was inactivated by 0.1 M H 2O 2 ( t 1/2 ∼ 11.6 min). The other mutant (T220S) also showed an obvious increase in antioxidative ability. Molecular dynamic simulations on wild-type and T220S mutant proteins suggested that a hydrogen bond was formed between Ser 220 and Asn 155, and the spatial structure of Met 222 was changed compared with the wild-type. The present study demonstrates the feasibility of improving oxidative stability of NK by site-directed mutagenesis and shows successful protein engineering cases to improve stability of NK as a potent therapeutic agent.

Oxidation of copper nanopowders on heating in air

The morphology and structure of copper nanopowders produced by electrical explosion of conductors are considered. The regularities of nanopowder oxidation in air were studied during linear and isothermal heating. The characteristics of initial powders in relation to the kinetic oxidation parameters were determined and the dependence of phase composition of the products of nanopowder oxidation on the heating conditions and dispersity of initial powders was found.

Effect of the Addition of a Cocoa Butter–Like Fat Enzymatically Produced from Olive Pomace Oil on the Oxidative Stability of Cocoa Butter

A cocoa butter (CB)-like fat was produced in a packed bed enzyme reactor using sn-1,3 specific lipase, and its blends with CB were prepared at different ratios (CB: CB-like fat; 100: 0, 90: 10, 80: 20, 70: 30, 60: 40, 50: 50, 0: 100). The oxidation kinetics of CB: CB-like fat blends was studied by differential scanning calorimeter (DSC). Samples were heated in DSC at different temperatures (130, 140, 150, 160 degrees C) under 100 mL/min oxygen. From DSC exotherms, oxidation induction times (OIT) were determined and used for the assessment of the oxidative stabilities of the blends. Oxidation kinetics parameters (activation energy, E(a); preexponential factor, Z; and oxidation rate constant, k) were calculated. In general, it has been observed that above 110 degrees C increasing the ratio of CB-like fat in the blend increased the k value with increasing temperature. It has been observed that for all blends the increase in k value with temperature was significant (P < 0.05). Increasing CB-like fat ratio in the blend decreased the content of major TAGs (1,3-dipalmitoyl-2-oleoyl-glycerol [POP]; 1[3]-palmitoyl-3[1]stearoyl-2-oleoyl-glycerol [POS]; 1,3-distearoyl-2-oleoyl-glycerol [SOS]), and decreased the oxidative stability of the blends.

Morphology influence of the oxidation kinetics of carbon nanofibers

This paper reports the stability and oxidation rate of five types of carbon nanofiber (CNF) with distinctly different orientation of their graphite sheets based on conversion to CO 2 when heated in the presence of oxygen. A non-isothermal technique was used to determine the oxidation kinetic parameters including the activation energy ( E a). Graphite shows a similar activation energy ( E a = 158 kJ/mol −1) to CNF with longitudinal alignment ( E a = 156 kJ/mol −1). CNF type herringbone ( E a = 126 kJ/mol −1) and platelet ( E a = 145 kJ/mol −1) show the lowest oxidation resistance which improved dramatically after a heat treatment at 3023 K of the herringbone ( E a = 216 kJ/mol −1) and platelet ( E a = 174 kJ/mol −1) structures.

CH 3OH oxidation over well-defined supported V 2O 5/Al 2O 3 catalysts: Influence of vanadium oxide loading and surface vanadium–oxygen functionalities

A series of supported V 2O 5/Al 2O 3 catalysts were synthesized by incipient wetness impregnation with vanadium isopropoxide in isopropanol solutions and subsequent calcination. The vanadium surface density was varied from 0.3 to 11.4 V atoms/nm 2 spanning the sub-monolayer and above-monolayer regions. The resulting supported vanadium oxide catalysts were physically characterized with in situ Raman spectroscopy and chemically probed by CH 3OH TPSR and steady-state methanol oxidation. The Raman characterization under dehydrated conditions revealed that the supported vanadium oxide catalysts contained only surface vanadia species below monolayer coverage (100% dispersed) and both surface vanadia species and crystalline V 2O 5 nanoparticles (NPs) above monolayer coverage. The CH 3OH oxidative dehydrogenation kinetic parameters were found to be independent of the surface bridging V O V bond concentration (polymerization extent), surface V O bond length/strength, vanadium surface density on the alumina support, surface acidity, and surface vanadia reduction characteristics during H 2-TPR. The crystalline V 2O 5 NPs above monolayer coverage were relatively inactive and served only to decrease the number of exposed catalytic active surface vanadia sites by covering them.

Iron Redox Reactions in Model Nuclear Waste Glasses and Melts

AbstractThe influence of boron on the kinetics of oxidation of iron in silicate melts relevant to nuclear waste storage has been investigated by XANES experiments. The measurements have been performed isothermally as a function of time at the iron K-edge. The redox kinetics become slower with increasing B2O3 content either close to the glass transition range, where the redox kinetics are controlled by diffusion of network-modifying cations, or at superliquidus temperatures where oxygen diffusion is the rate-limiting factor. In both ranges the kinetics can be interpreted in terms of boron speciation and interaction with alkali cations. Below the liquidus, however, the long times needed to reach redox equilibrium allow sintering of the powders investigated to take place so that the resulting changes in sample geometry prevent determinations of oxidation kinetic parameters from being made.

Oxidation kinetics of soybean oil/anhydrous milk fat blends: A differential scanning calorimetry study

The oxidation kinetics of soybean oil (SBO)/anhydrous milk fat (AMF) blends was studied by differential scanning calorimetry (DSC). Lipid blends containing 0–100% of SBO in AMF at 10% intervals were analyzed. Samples were heated in the DSC at different heating rates (2.5, 5.0, 7.5, 10.0 and 12.5 � C/min) and oxidation kinetics parameters from the Arrhenius equation (activation energy, preexponential factor and oxidation rate constant) were calculated using the Ozawa–Flynn–Wall method. Results show a significant increase in the oxidation rate (k) with temperatures for 60–90% SBO blends. The increase in k with SBO addition was only significant for 240 and 250 � C. A significant correlation between the rate constant and the chemical composition of the samples was not observed. This behavior suggests possible interactions among fatty acids present in the blends. Published by Elsevier Ltd.

An Improved Desulfurization Process Based on H2O2/Formic Acid Oxidation and Liquid-Liquid Extraction 2. FCC Diesel Oil Feedstocks

Semi-empirical molecular orbital theory and parametric model 3 methods were used to calculate the quantum chemistry properties of dibenzothiophene (DBT) and its corresponding sulfone compounds to investigate the essential theory of a formic acid/H2O2 oxidation desulfurization system. To study oxidation kinetics of the oxidation desulfurization reaction, DBT was also employed as a model compound to obtain the oxidation kinetic parameters. Desulfurization of fluid catalytic cracking (FCC) diesel was also performed in this process, and the sulfur content was reduced from 7,200 μg·g−1 to 598 μg·g−1 after being extracted by polyethylene glycol 200.

High-temperature oxidation of titanium, zirconium, and hafniyum in steam

The influence exerted by the nature of titanium, zirconium, and hafnium on the kinetic parameters of oxidation and on the diffusion mechanism of scale formation in steam at 973–1473 K is analyzed. The results obtained are compared with the data for the air medium.

Oxidation behavior of biomass chars: pectin and Populus deltoides

Biomass chars of pectin and cotton wood ( Populus deltoides) were prepared by using a heating rate of about 1 °C/s, peak pyrolysis temperatures of 400–800 °C, and residence times of 10–60 min at peak temperatures. Char samples were pyrolyzed in a helium atmosphere using a thermogravimetric analyzer (TGA). Oxidation reactivity measurements of the same char samples in the TGA were collected after converting the helium atmosphere to an oxygen containing atmosphere. Reactivities were measured using an isothermal method at various reaction temperatures from 400 to 700 °C and oxygen concentrations of 2–21%. Oxidation kinetic parameters such as apparent reaction order and apparent activation energies were obtained. Scanning electron microscopy (SEM) was employed to study morphological and structural development in the char samples as a function of heat treatment temperature. An interesting morphological development on the surface of the char was observed by SEM, which showed evolution of vesicle formation and whisker growth as heat treatment temperatures increased. Its implication on char reactivity is discussed. Preliminary results showed decreasing reactivity with increasing peak heat treatment temperatures. Char reactivity was affected more by the heat treatment temperature than by the hold times (10–60 min).

Kinetic parameters associated with self-heating of New Zealand coals under adiabatic conditions

AbstractAdiabatic self-heating tests were carried out on five New Zealand coal samples ranging in rank from lignite to high-volatile bituminous. Kinetic parameters of oxidation were obtained from the self-heating curves assuming Arrhenius behaviour. The activation energy E (kJ mol–1) and the pre-exponential factor A (s–1) were determined in the temperature range of 70–140°C. The activation energy exhibited a definite rank relationship with a minimum E of 55 kJ mol–1 occurring at a Suggate rank of ∼6.2 corresponding to subbituminous C. Either side of this rank there was a noticeable increase in the activation energy indicating lower reactivity of the coal. A similar rank trend was also observed in the R70 self-heating rate index values that were taken from the initial portion of the self-heating curve from 40 to 70°C. From these results it is clear that the adiabatic method is capable of providing reliable kinetic parameters of coal oxidation.

Oxidation kinetics of the nitrided TiAl-based alloys

The oxidation kinetics of the nitrided TiAl-based alloys have been investigated at 800–1000 °C in hot air. It is concluded that nitridation is detrimental to the oxidation resistance of TiAl-based alloys under the present conditions. The nitrided alloys exhibited increased oxidizing rate with the prolongation of nitridation time at 800 °C. However, alloys nitrided at 940 °C for 50 h displayed a sign of better oxidation resistance than the other nitrided alloys at more severe oxidizing conditions. The parabolic rate law was considered as the basis of the data processing and interpretation of the mass gain vs. time data. As a comparison with it, attempts were made to fit the data with the power law. The oxidation kinetic parameters k n , k p and n were measured and the trends were discussed.

Screening of Three Light-Oil Reservoirs for Application of Air Injection Process by Accelerating Rate Calorimetric and TG/PDSC Tests

Abstract A series of Accelerating Rate Calorimeter (ARC) and Thermo Gravimetric Pressurized Differential Scanning Calorimeter (TG/PDSC) tests was conducted on oil-rock systems from three light-oil reservoirs (Oils A, B and C) to screen and evaluate the potential of the air injection process. ARC tests helped determine, a priori, whether the test oils would autoignite under reservoir conditions of pressure and temperature. Also, the limits of the low temperature range were established and Arrhenius oxidation kinetics parameters were estimated. The goals of the TG/PDSC tests were to identify temperature ranges over which the oil reacted with oxygen in the injected air, and to determine the fraction of the sample responsible for the reactivity. ARC and TG/PDSC tests demonstrate that Oils A and C offer favourable exothermic behaviour in the low temperature range with lower activation energies and low orders of reactions?the conditions typically favouring autoignition. The presence of rock material lowered the ignition temperature, confirming its impact on O2 uptake. Oil A had a lower energy generation (ignition) temperature, and a stronger and smoother transition to the higher temperature region. Both oils responded favourably during isothermal aging with air as manifested by a drop in the initial self-heating temperature (a 15 °C drop for Oil A and a 10 °C drop for Oil C). The third oil, Oil B, showed unusual characteristics, with almost no impact of the core material on the starting temperature of the exotherm; rather, the core material appeared to have acted as a heat sink. Overall, Oil B needed a much higher activation energy to ignite, and its order of reactions was very high. Furthermore, it showed no response to isothermal aging, and hence, it is less likely to autoignite in the reservoir. esults revealed that ARC and TG/PDSC tests could be an effective tool to rank and study the oxidation characteristics in the low temperature range of the candidate oils. Also, it was observed that the oil composition and rock mineralogy are important factors affecting the type and rate of the oxidation reactions occurring in the low temperature range. Introduction The air injection process is now a proven and viable process in improving oil recovery from several light-oil reservoirs. As a result, it has generated much interest in recent years(1–5). Cheap and abundant, air is also touted as a possible alternative to highcost hydrocarbon and CO2 gases in certain circumstances or locations where water is scarce(6–10). Moore et al(11) suggest that in an air injection process in lightoil reservoirs, both oxygen addition and bond scission reactions take place. Oxygen addition reactions are believed to occur at temperatures between 100 °C and 150 °C. These reactions are characterized by heavier oxygenated hydrocarbon products. Bond scission reactions for light oils typically occur at temperatures in the 150 to 300 °C and the 350 to 700 °C range. These reactions produce carbon oxides, water (steam) and heat, which contribute significantly towards mobilizing oil.

Oxidation of Carbon Monoxide on Cr-, Mn-, Fe-, Co-, and Ni-containing Catalysts on a Foamed Ceramic Support

A series of oxide catalytic systems with a new foamed ceramic support were suggested for oxidation of CO with atmospheric oxygen. The activity of the catalysts was studied by the pulse procedure; the reagents were analyzed by gas chromatography. The kinetic parameters of oxidation were determined for each catalyst. The systems were ranked with respect to their activity. The systems developed ensure high conversion of CO (∼98%) and show promise for industry.

Chemiluminescence study of thermal and photostability of polyethylene

The oxidation stability of low density polyethylene to UV light has been studied in the presence of various types of antioxidants (hindered phenols, HALS and synthetic N-alkylamines). A chemiluminescence procedure has been applied. Kinetic parameters of oxidation are obtained from isothermal measurements at 180°C. The synergistic effect of antioxidant couples is examined and a stabilisation order is determined.