Unreacted Oxygen Research Articles

Integrated Hydrogen and Power Production with CO2 Capture Using Chemical-Looping ReformingRedox Reactivity of Particles of CuO, Mn2O3, NiO, and Fe2O3 Using SiO2 as a Support

A concept for combined hydrogen and power production from natural gas with CO2 capture is presented. The process involves the use of a metal oxide in fluidized bed reactors; the metal oxide is reduced by a mixture of natural gas and steam in a fuel reactor and oxidized by air in the air reactor. The natural gas is partially oxidized in the fuel reactor, resulting in a mixture of CO2, H2, H2O, and CO from the exit. If no hydrocarbons are present in this stream, it can be sent to a water gas shift reactor to get an undiluted stream of CO2 and H2. The product stream from the air reactor contains mostly N2 and some unreacted oxygen. The oxidation reaction is exothermic with resulting heat production in the air reactor; this heat is used to maintain the oxygen carrier particles at the high temperature necessary for the endothermic reaction in the fuel reactor. The hot gases from the air reactor could be used for power production. Metal oxides of Ni, Cu, Mn, and Fe were prepared by impregnation on a SiO2 suppor...

Gas leakage measurements in a cold model of an interconnected fluidized bed for chemical-looping combustion

In chemical-looping combustion (CLC) a gaseous fuel is burnt with inherent separation of the greenhouse gas carbon dioxide. The oxygen is transported from the combustion air to the fuel by means of metal oxide particles acting as oxygen carriers. A CLC system can be designed similar to a circulating fluidized bed, but with the addition of a bubbling fluidized bed on the return side. Thus, the system consists of a riser (fast fluidized bed) acting as the air reactor. This is connected to a cyclone, where the particles and the gas from the air reactor are separated. The particles fall down into a second fluidized bed, the fuel reactor, and are via a fluidized pot-seal transported back into the riser. The gas leaving the air reactor consists of nitrogen and unreacted oxygen, while the reaction products, carbon dioxide and water, come out from the fuel reactor. The water can easily be condensed and removed, and the remaining carbon dioxide can be liquefied for subsequent sequestration. The gas leakage between the reactors must be minimized to prevent the carbon dioxide from being diluted with nitrogen, or to prevent carbon dioxide from leaking to the air reactor decreasing the efficiency of carbon dioxide capture. In this system, the possible gas leakages are: (i) from the fuel reactor to the cyclone and to the pot-seal, (ii) from the cyclone down to the fuel reactor, (iii) from the pot-seal to the fuel reactor. These gas leakages were investigated in a scaled cold model. A typical leakage from the fuel reactor was 2%, i.e. a CO 2 capture efficiency of 98%. No leakage was detected from the cyclone to the fuel reactor. Thus, all product gas from the air reactor leaves the system from the cyclone. A typical leakage from the pot-seal into the fuel reactor was 6%, which corresponds to 0.3% of the total air added to the system, and would give a dilution of the CO 2 produced by approximately 6% air. However, this gas leakage can be avoided by using steam, instead of air, to fluidize the whole, or part of, the pot-seal. The disadvantages of diluting the CO 2 are likely to motivate the use of steam.

Thermal stability of the exchange-biased NiFe/IrMn/CoFe electrode in the magnetic tunnel junctions

The exchange-biased electrode of the magnetic tunneling junction (MTJ), consisting of Ta/NiFe/IrMn/CoFe/AlO x /Ta layer was annealed at 300 °C to study the extent of interdiffusion within the electrode. The tunnel barrier, AlO x was also under- and over-oxidized in the oxygen plasma in order to elucidate the effects of plasma oxidation on the interdiffusion. A significant amount of Mn diffusion into the AlO x layer was observed in the over-oxidized electrode from the depth profiles using Auger electron spectroscopy (AES) while the under-oxidized electrode exhibited a minimal amount of Mn diffusion after annealing at 300 °C. X-ray photoelectron spectroscopy (XPS) proved that the Mn found at the CoFe/AlO x interface and in the CoFe layer of the over-oxidized electrode was in the form of MnO 2 while Co at the CoFe/AlO x interface remained unoxidized. The XPS data suggests that the Mn diffusion was accelerated by the preferential oxidation of Mn. The results indicate that the oxidation condition of the insulator will influence the Mn diffusion and subsequent post-annealing response of MTJ as the plasma oxidation provides inherently meta-stable AlO x layer, creating a source for the unreacted oxygen radicals.

A Kinetic Analysis of the Thermal-Oxidative Decomposition of Polypropylene

The kinetics of the thermal-oxidative decomposition of poly propylene (PP) was studied by a conventional thermogravimetric technique in pure nitrogen and various concentrations of oxygen ranging from 5-21%. The kinetic model that accounts for the effects of oxygen concentration was proposed to describe the thermal decomposition of PP. The thermogravimetric analysis curve and its derivative have been analyzed using the differential and integral methods with modification of the Friedman and Coats-Redfern methods. The activation energy, the pre-exponential factor, and the reaction order for unreacted material and oxygen concentration have been determined. When oxy gen was present, the activation energy was reduced significantly.

Autocatalytic behavior and role of oxygen diffusion in the hydrogen-oxygen reaction on Pt(111)

A short review of the hydrogen-oxygen reaction on Pt(111) is given in which the emphasis is put on the apparent contradictions between experiments reported in the literature. We consider these results in the light of our recent observation that certain defects appear to be very active sites for this reaction. Making the basic assumption that the reactive sites play the central role in the hydrogen-oxygen reaction, it is concluded that two fundamentally different mechanisms for the overall reaction are possible: (1) A process in which diffusion of oxygen to the reactive sites is essential for the reaction, and (2) an autocatalytic process in which hydrogen reacts at the reactive sites and is transferred to oxygen on the terrace via molecular reactions between adsorbed H 2O, the reaction intermediates and unreacted oxygen. Based on these ideas, a model for the hydrogen-oxygen reaction on Pt(111) is proposed. With the model a consistent explanation of the reported measurements can be given, i.e., it can resolve the apparent contradictions between the different experiments. A transition between these mechanisms is expected in the temperature range where H 2O starts to desorb and adsorbed oxygen atoms become mobile, i.e., around 250 K. We present experiments obtained in this temperature range using molecular beam titration and helium diffraction. The measurements clearly show the transition between the autocatalytic and the diffusion controlled mechanism and they are considered, therefore, as a strong support for the model.

Partial oxidation of municipal solid waste

Municipal solid waste fraction of average particle size 0.42 mm and a uniformity coefficient of 1.65 was partially oxidized in a continuous reactor in the temperature range of 973 to 1123 K and the variation in gas yields, composition and product heating values with temperature and oxygen/feed ratio was investigated. The main components of the product gases were hydrogen, methane, carbon monoxide and carbon dioxide. In some runs, unreacted oxygen was also present in the off gases. The heating value of the product gases varied from 14.1 to 20.0 MJ/Nm 3 and the energy production efficiency varied from 34 to 50%. At a constant oxygen/feed mass ratio, thermal efficiency increased with temperature. The highest energy production efficiency was obtained at 1123 K and an oxygen to feed ratio of 0.17 kg/kg (d.a.f.).

Simultaneous microdetermination of sulphur, carbon and nitrogen by reaction gas chromatography

A simultaneous microdetermination of C, N and S, based on reaction GC, with a commercial analyser for the microdetermination of C, H, N and O, is described. The sample, covered with a mixture of WO3 and SnO2, is combusted in a stream of helium with added oxygen, and the mixture of pyrolysis products is oxidized completely by passage through a layer of granulate SnO2. Conversion of SO3 into SO2, reduction of nitrogen oxides and absorption of unreacted oxygen proceed in a layer of Cu, and halogens are trapped by metallic antimony. Particular attention is paid to determination of sulphur in liquid samples without weighing.

The adsorption, desorption, and exchange reactions of oxygen, hydrogen, and water on platinum surfaces: IV. Field emission studies on the adsorption of water, hydrogen and the reaction between hydrogen and adsorbed oxygen

Field electron emission microscopy has been used to study the adsorption of water on platinum and its production by the reaction of hydrogen with adsorbed oxygen. Techniques are described whereby clean reproducible Pt field emitters can be produced without irreversible contamination or excessive tip blunting. Direct water adsorption always led to emitter failure, consequently adsorbed water was produced by the reaction of hydrogen with adsorbed oxygen. This reaction occurred from 100 to 175 K with a decrease in work function from Δφ = +0.6 eV, for oxygen adsorption, to a minimum work function, Δφ = −0.55 eV, at 175 K. From 175 to 300 K the work function increases and reattains a positive shift, Δφ ∼ + 0.2 eV, and a field emission pattern characteristic of adsorbed oxygen which are uninfluenced by further H 2 interaction up to 600 K. There is little change in emission anisotropy, but enhanced emission from Pt(110) planes suggests that the reaction is particularly facile on this plane. The work function shifts indicate the formation of adsorbed water up to 175 K, which therefore forms an electropositive adsorbed state, followed by desorption of water in the interval 175 to 300 K from an adlayer stabilised by the presence of unreacted oxygen. These observations are in agreement with thermal desorption results, although the observation that part of the oxygen adlayer could not be reduced was surprising since thermal desorption studies suggested that this efficient reaction proceeded to completion. Rationalisation requires that the unreactive oxygen is undetected in the thermal desorption experiments and supporting evidence is given from oxygen adsorption, desorption and exchange, field emission and Auger electron spectroscopy experiments.

The adsorption, desorption, and exchange reactions of oxygen, hydrogen, and water on platinum surfaces IV. field emission studies on the adsorption of water, hydrogen and the reaction between hydrogen and adsorbed oxygen

Abstract Field electron emission microscopy has been used to study the adsorption of water on platinum and its production by the reaction of hydrogen with adsorbed oxygen. Techniques are described whereby clean reproducible Pt field emitters can be produced without irreversible contamination or excessive tip blunting. Direct water adsorption always led to emitter failure, consequently adsorbed water was produced by the reaction of hydrogen with adsorbed oxygen. This reaction occurred from 100 to 175 K with a decrease in work function from Δφ = +0.6 eV, for oxygen adsorption, to a minimum work function, Δφ = −0.55 eV, at 175 K. From 175 to 300 K the work function increases and reattains a positive shift, Δφ ∼ + 0.2 eV, and a field emission pattern characteristic of adsorbed oxygen which are uninfluenced by further H2 interaction up to 600 K. There is little change in emission anisotropy, but enhanced emission from Pt(110) planes suggests that the reaction is particularly facile on this plane. The work function shifts indicate the formation of adsorbed water up to 175 K, which therefore forms an electropositive adsorbed state, followed by desorption of water in the interval 175 to 300 K from an adlayer stabilised by the presence of unreacted oxygen. These observations are in agreement with thermal desorption results, although the observation that part of the oxygen adlayer could not be reduced was surprising since thermal desorption studies suggested that this efficient reaction proceeded to completion. Rationalisation requires that the unreactive oxygen is undetected in the thermal desorption experiments and supporting evidence is given from oxygen adsorption, desorption and exchange, field emission and Auger electron spectroscopy experiments.

Effect of cleavage of ether linkages on physicochemical properties of coals

Coals of different rank were treated with naphthalene anion in tetrahydrofuran. It was found that, as in the case of coal of 87.8% C (daf), large amounts of unreactive oxygen bonds, possibly of the ether type, were cleaved. Cleavage of these ether linkages led to a lowering of the melting point and, in some types of coals, to a large increase in dilatation and a substantial increase in Gieseler fluidity.

Polymer combustion

AbstractExperimental conditions have been defined for the steady‐state combustion of vertically positioned polymer rods burning at the top surface. Temperature and composition profiles through solid and gas phases of the system, polymer consumption rate, and flame height were measured, and the response of these parameters to changes of the oxygen concentration in the environment were determined. Measurements showed that unreacted oxygen diffused from the environment to the burning surface and was absorbed into the polymer, forming a well defined oxygen‐rich layer. Concentration of chemically bound oxygen at the surface of this layer were high, e.g., with polypropylene ca. 26 wt‐%, and identical with the stoichiometry of the gases leaving the surface and serving as fuel for the flame. The composition of the gas phase at the surface indicated the conversion of 11.4% of the hydrocarbon fuel to CO, CO2, and H2O. An energy balance for the system confirmed that fuel production in this surface layer takes place via simultaneous oxidative and pyrolytic degradation of the polymer, with exothermic processes supplying the energy for endothermic processes. Conductive and radiative contributions from the gas phase were found to play a minor role in maintaining fuel formation. The rate of degradation of a polymer to fuel, normalized to the area of the burning surface, was found to be independent of polymer supply rate and to increase with the oxygen concentration in the environment. The degradation process was successfully modeled in TGA experiments at temperatures and oxygen concentrations representative of the burning surface. The existence of an oxidative surface layer was confirmed and the TGA degradation rate related to the surface‐to‐volume ratio of the polymer sample. Compositional analysis of a methane diffusion flame of a geometry identical to that of the polymer flame, revealed the presence of unreacted oxygen throughout the preheating zone and at the surface of the burner. Conversion of fuel to final combustion products at the surface was 6.3%. Temperature and composition changes as a function of oxygen concentration in the environment were determined and compared with the polymer diffusion flame. It was concluded that a polymer flame, because of its autogenerative fuel production, possesses only one degree of freedom, viz., the oxygen concentration in the environment, in contrast to the conventionally fueled diffusion flame for which fuel supply rate is an additional independent parameter. Due to this single degree of freedom, the sensitivity of the polymer flame to environmental influences is increased. Effects caused by these extrinsic factors will be the subject of a separate report.

A Study on the Qxygen-Containing Groups in Pyridine Extracts from Coals

The oxygen-containing functional groups and their contents in pyridine extracts prepared from a series of twelve Japanese coals were investigated toobtain some insight into their structures.The estimation of the oxygen-containing functional groups (-OH, C=O, COON) in pyridine extracts was made by chemical methods which were applied previously to parent coals. The variation of thecontents of the oxygen-containing functional groups in pyridine extracts with respect to the carbon contents of parent coal was compared with those of parent coals. It was found that, in the case of relatively lower carbon content of coal, the contents of the hydroxyl and carbonyl groups in pyridine extract were lower than those of parent coals. As the coalification proceeded, the difference in thecontents between the parent coals and pyridine extracts diminished to disappear approximately at about 80% carbon or thereabouts.It is to be mentioned that, in the proton NMR spectra of the pyridine extract of coal, the signals at c 3. 5to 5. 0 are assigned to the aliphatic hydrogens at the a position to the oxygen atom in the alkyl ethers. It may be concluded on this basis that the unreactive oxygen groups such as dialkyl and alkylaryl ethers are not important in coal andcoal derivatives with the exception of Ishikari peat pyridine extract which has the lowest carbon content. Therefore, it can be assumed that almost all unreactive oxygen functions in coal consist of heterocyclic or diphenyl ether types. By considering the results of structural analysis of aromaticity f in parent coal and their pyridine extracts, it can also be concluded that the hydroxyl groupsconsist of phenolic group.Moreover, in the fraction isolated by various solventsfrom Sumiyoshi coal, the content of oxygen-containing groups was correlatedwith the character of these structures, especially with aromaticity. The conclusionsimilar to the one obtained above was found to hold true for the structure of the hydroxyl and unreactive oxygen functions in solvent fractionation products.

Chemical Structure and Properties of Heat Treated Coal in the Early State of Carbonization (VI)

The measurments of hardness are a very available mean in the study of rheological properties of coal. It is well known that the hardness of coal, changes with rank and that the hardness of heat-treated coals has a maximum at heat treatment temperature (HTT) of about 1, 200°C. It apPears, however, that very few detailed inves tigations of hardness of heat-treated coals in the early state of carbonization have yet been made. The present authors measured the Knoop hardness of 17 coals of every rank and that of coals heat-treated over the range from HTT 200°C to HTT 500°C.The relation between Knoop hardness number of original coals and rank shows in Fig. 5.The cohesive energy density of coals has a minimum at about 85-90% C. It is supposed, therefore, that the hardness of coals shows a minimum at about 90%C. Although the intermolecular forces tend to increase below about 85%C, the hardness shows a maximum at about 80%C and decreases with the decrease of rank. This phenomenon may be explained by the increase of micro-pore structure or texture in the lower rank coals. On the other hand, the unreactive oxygen has a maximum at about 80%C (Fig. 8). Assu ming that the major part of the unreactive oxygen is an ether-type, it is supposed that the other-type oxygen in coals increases with rank up to about 80%C. It may be said, therefore, that the oxygen bridge in coals increases and the hardness of coals increases with rank in the range of about 70%C to about 80%C.The Knoop hardness number of heat-treated non-caking coals below about 80%C is almost the same as that of original coals over the range of HTT about 200-250°C and then increases suddenly with the increase of HTT. It seems that this sudden increase of hardness depends on the chemical change of constitution in original coals caused mainly by dehydration.The Knoop hardness number of heat-treated caking coals in the range of about 80% C to about 90%C is almost the same as that of original coals up to HTT about 300°C, gradually decreases with the increase of HTT, reaches a minimum at HTT about 400-450°C, and then suddenly increases with HTT. It is seen that the Knoop hardness of heat-treated caking coals is closely related to the lower molecular substances in original coals and to the thermal softening and thermal fusing properties of original coals.The Knoop hardness number of heat-treated anthracite above about 90%C is almost the same as that of original coal up to HTT about 450°C and then increases with HTT. It is suggested that the sudden increase of Knoop hardness in heat-treated coals above a certain HTT depending on the rank of original coals has an intimate relation with the development of cross-linking, aromaticity and ring condensation in heat-treated coals.

Fractionation of Oxygen Isotopes in the Formation of Oxide Films on Copper

The fractionation of the oxygen isotopes in the formation of oxide films on copper has been measured at 0, 25, and 100°C on granular copper and copper foil by determining the O18/O16 isotope ratio in the residual unreacted oxygen gas after a fraction of the oxygen has reacted. An analysis is given of the mixing problem and of the kinetics of the reaction. Two fractionation factors, one of unity or less than unity for an initial rapid reaction and one greater than unity for the slower and (approximately) steady state reaction are required to explain the data. The fractionation factor for the steady state reaction is calculated to be 1.045, 1.042, and 1.037 at 0, 25, and 100°C, respectively. All of these values are greater than the lower limit of 1.029 given by the rate theory of Bigeleisen in contrast to an earlier conclusion of Bernstein.