Showing papers on "Partial oxidation published in 1995"

Dense ceramic membranes for partial oxidation of methane to syngas

Abstract: Several perovskite-type oxides (ABO3) containing transition metals on the B-site show mixed (electronic/ionic) conductivity. These mixed-conductivity oxides are promising materials for oxygen-permeating membranes that can operate without electrodes or external electrical circuitry. Oxides in the system LaSrFeCoO permeate large amounts of oxygen, and extruded tubes of these materials have been evaluated in a reactor operating at ca. 850°C for direct conversion of methane into syngas (CO + H2) in the presence of a reforming catalyst. Methane conversion efficiencies of > 99% were observed, and some of the reactor tubes have been operated for over 1000 h. Membrane tubes were fabricated from calcined powders by a plastic extrusion technique. Ceramic powders in the LaSrFeCoO system were made by solid-state reaction of the constituent carbonates, oxides, and/or nitrates. The chemical-phase behavior of the ceramic powders with varying stoichiometries were studied by high-temperature in-situ X-ray diffraction (XRD) as a function of oxygen partial pressure. The sintered extruded tubes were also characterized by XRD and scanning electron microscopy.

Carbon dioxide reforming of methane over nickel alkaline earth metal oxide catalysts

Abstract: The CO2 reforming of CH4 over reduced NiO/alkaline earth metal oxide catalysts was investigated. A CO yield of 95% was obtained from a stoichiometric feed mixture of CH4 and CO2, at high GHSV (60 000 cm3 g−1 h−1), over a reduced NiOMgO with a weight ratio of 0.2. In addition, the catalyst had excellent stability, since the CO yield remained unchanged during 120h. Compared to the reduced NiOMgO catalyst, the reduced NiOCaO,NiO SrO NiO BaO catalysts had low CO yields and very low stabilities. The TPD of CO over the reduced NiOMgO catalyst indicated a lower decomposition of CO to CO2 than over the other catalysts investigated, hence that MgO inhibits the disproportionation reaction 2CO → C + CO2 over Ni. The behavior of the reduced NiOMgO catalyst is probably due to the formation of a NiOMgO solution, as a result of the similar crystalline structures of NiO and MgO.

Solid multi-component membranes, electrochemical reactor components, electrochemical reactors and use of membranes, reactor components, and reactor for oxidation reactions

Abstract: Solid membranes comprising an intimate, gas-impervious, multi-phase mixture of an electronically-conductive material and an oxygen ion-conductive material and/or a mixed metal oxide of a perovskite structure are described. Electrochemical reactor components, such as reactor cells, and electrochemical reactors are also described for transporting oxygen from any oxygen-containing gas to any gas or mixture of gases that consume oxygen. The reactor cells generally comprise first and second zones separated by an element having a first surface capable of reducing oxygen to oxygen ions, a second surface capable of reacting oxygen ions with an oxygen-consuming gas, an electron-conductive path between the first and second surfaces and an oxygen ion-conductive path between the first and second surfaces. The element may further comprise (1) a porous substrate, (2) an electron-conductive metal, metal oxide or mixture thereof and/or (3) a catalyst. The reactor cell may further comprise a catalyst in the zone which comprises a passageway from an entrance end to an exit end of the element. Processes described which may be conducted with the disclosed reactor cells and reactors include, for example, the partial oxidation of methane to produce unsaturated compounds or synthesis gas, the partial oxidation of ethane, substitution of aromatic compounds, extraction of oxygen from oxygen-containing gases, including oxidized gases, ammoxidation of methane, etc. The extraction of oxygen from oxidized gases may be used for flue or exhaust gas cleanup.

Failure mechanisms of ceramic membrane reactors in partial oxidation of methane to synthesis gas

Abstract: In the course of generating synthesis gas (H2, CO) from methane, we have observed two types of fractures occurring on the Sr(Co, Fe)Ox-type oxygen membrane reactors The first type occurred shortly after the reaction started and the second type often occurred days after the reaction To determine the causes of these fractures, we have examined the starting material and fractured membranes using a combination of X-ray diffraction and thermogravimetric analyses We found that the first type of fracture was the consequence of an oxygen gradient in the membrane, pointing from the reaction side to the air side This causes a lattice mismatch inside the membrane, leading to fracture The second type of fracture, however, was the result of a chemical decomposition We found that the Sr(Co, Fe)Ox-type membrane had been reduced to SrCO3, and elemental Co and Fe by the synthesis gas generated in the reaction The decomposition causes enormous expansion leading to a large crack along the axis of tube

Catalytic supercritical water oxidation: phenol conversion and product selectivity.

Abstract: Catalytic supercritical water oxidation (SCWO) has been demonstrated as an effective method of destroying organic compounds contained within an aqueous waste stream. Whereas SCWO is effective in the destruction of the original organic compound, incomplete conversion to low molecular weight partial oxidation products may be achieved. In all cases, enhanced phenol conversion and CO 2 yield were obtained relative to the homogeneous case. Under selected operating conditions (temperature 450 °C, 500% excess oxygen), the addition of MnO 2 /CeO or V 2 O 5 catalysts can enhance the conversion to CO 2 such that essentially quantitative conversion is obtained. The MnO 2 /CeO catalyst is stable in the harsh reaction environment, at least to the limits of detection of the analytical instruments. A simple kinetic model, based on parallel reaction pathways, was used to evaluate the experimental data. Rate constants were obtained that adequately modeled the experimental results. The values of the rate constants were higher in the catalytic experiments compared with the homogeneous runs, further indicating that the addition of the heterogeneous catalyst promoted the oxidation pathways at the expense of the oligimerization pathway.

Catalytic oxidation : principles and applications

Abstract: Mechanism of heterogeneous catalytic oxidation, J. Haber industrial oxidation processes, J. Lerou et al high temperature oxidation processes - oxidative coupling of methane, G.B. Marin metal ion co-ordination catalysis, I.I. Moiseev metal catalysis, R.A. van Santen partial oxidation on noble metals at high temperatures, L.D. Schmidt and M. Huff free radical oxidation in the liquid phase, R.A. Sheldon liquid phase heterogeneous oxidation, R.A. Sheldon fine chemicals and gas phase processes, R.A. Sheldon heterogeneous oxidation catalysts on metallic oxides, J.C. Vedrine electrocatalytical oxidation, J.A.R. van Veen fuel cells, J.A.R. van Veen.

Evolution of the active surface of the vanadyl pyrophosphate catalysts

Abstract: Bulk crystallinity of vanadyl(IV) pyrophosphate catalysts forn-butane partial oxidation increased up to 23 days on stream as determined by XRD and Raman spectroscopy, while selectivity reached steady state after 8–10 days. Electron microscopy detected a 15 A amorphous layer terminating the (200) planes of (VO)2P2O7 in fresh catalysts that was not observed in the equilibrated catalysts. It is suggested that ordering of (200) planes at the surface of (VO)2P2O7 is responsible for selective oxidation.

Stable, ultra-low residence time partial oxidation

Abstract: A process for the catalytic partial oxidation of methane in gas phase at very short residence time (800,000 to 12,000,000 hr-1) by contacting a gas stream containing methane and oxygen with a metal supported catalyst, such as platinum deposited on a ceramic monolith.

On the relation between catalytic performance and microstructure of polycrystalline silver in the partial oxidation of methanol

Abstract: Electrolytic silver was investigated as partial oxidation catalyst for the conversion of methanol to formaldehyde. Using the mass spectrometric technique as on-line detector the relation between feed composition and temperature was determined allowing us to conclude that two simultaneous reaction pathways operate under steady state conditions. The microstructure was analysed by XRD and STM. A pronounced restructuring of the surface on the mesoscopic scale was detected. The atomic structure of the γ oxygen phase was determined on the (111) face of facets grown during reaction. The two reaction pathways find their counterparts in two distinctly different surface microstructures providing different geometries for the respective active sites. After prolonged time on stream the high surface mobility of the silver atoms removes all mesoscopic restructuring without changing the conversion characteristics. The observed restructuring is thus considered as a frozen large scale image of the continuously changing surface under reaction conditions.

A Novel Solid Oxide Fuel Cell System Using the Partial Oxidation of Methane

Abstract: A novel solid oxide fuel cell (SOFC) system, which does not need to separate the supply of fuel and oxidant gases and generates electric power as well as chemicals, was studied. The fuel cell consisted of Pt{vert_bar}BaCe{sub 0.8}Y{sub 0.2}O{sub 3{minus}{alpha}}{vert_bar}Au, in which two electrodes were exposed to the same mixture of CH{sub 4} and air. Electromotive forces (EMFs) were about 700--800 mV at operating temperatures between 750 and 950 C, and terminal voltages were about 420 mV with discharge a current density of about 400 mA/cm{sup 2} (0.17 W/cm{sup 2}) at 950 C and 350 mV with 75 mA/cm{sup 2} (0.03 W/cm{sup 2}) at 750 C. The working mechanism of the fuel cell was clarified to be based on the difference in catalytic activity for the partial oxidation of methane between two electrode materials: the Pt catalyzes the partial oxidation of methane to form hydrogen and carbon monoxide, while the Au is inactive to this reaction. Therefore, the Pt acts as a fuel electrode, while the Au acts as an oxygen electrode at which electrochemical reduction of oxygen takes place on discharging the cell.

Pulse-MS study of the partial oxidation of methane over Ni/La2O3 catalyst

Abstract: The CH4 direct oxidation reaction was studied at 600°C by the pulse-MS transient method over the Ni/La2O3 catalyst. Over the freshly prepared catalyst (which contains NiO), the CO selectivity and CH4 conversion increased and attained constant values as the number of CH4/O2 pulses increased. Over the reduced catalyst (containing Ni), as the number of CH4/O2 pulses increased, the CO selectivity and CH4 conversion decreased before they reached the same constant values as over the fresh catalyst. The CO selectivity increased as the residence time of the reactants shortened, implying that CO was directly generated without the preformation of CO2. The activation energies of CH4 dehydrogenation in the presence and absence of oxygen have been calculated using the bond-order conservation Morse-potential approach. The results indicate (1) the direct dehydrogenation steps are more likely to occur; (2) the transient oxygen species adsorbed on-top of the metal atoms promote dehydrogenation; (3) the oxygen species adsorbed on bridge or hollow sites do not promote dehydrogenation.

Process for production of high-purity hydrogen

Abstract: There is a system for producing high-purity hydrogen by reforming a hydrocarbon and/or an oxygen atom-containing hydrocarbon to form a reformed gas containing hydrogen and separating the hydrogen from said gas. The system includes a hydrocarbon source, a water source, an oxygen source, a vaporization chamber connecting with the hydrocarbon source, the water source and the oxygen source, and a reforming chamber provided with a catalyst for steam reforming and partial oxidation and a hydrogen-separating membrane. The reforming chamber is thermally connected with the vaporization chamber. A process for producing high-purity hydrogen includes heating a reforming chamber provided with a hydrogen-separating membrane, feeding, into the reforming chamber, hydrocarbon, steam and oxygen or air to give rise to steam reforming and partial oxidation therein to produce a reaction gas, and passing the reaction gas through the hydrogen-separating membrane to recover high-purity hydrogen. The heat possessed by the portion of the reaction gas not permeable into the hydrogen-separating membrane and the heat generated by the partial oxidation are utilized for the heating and reforming of the hydrocarbon, water and oxygen or air.

Selective oxidation of toluene over V2O5/TiO2 catalysts. Effect of vanadium loading and of molybdenum addition on the catalytic properties

Abstract: The influence of vanadium loading and molybdenum presence on the catalytic performance of vanadia-titania (anatase) catalysts for the selective oxidation of toluene was investigated. Two series of V2O5/TiO2 and V2O5-MoO3/TiO2 catalysts were prepared. In the first series the loading of vanadium varied from 0 to 8 mole %, whereas in the second the atomic ratio V/(V + Mo) varied from 0 to 1 while the total loading of active elements (V + Mo) was kept constant and equal to 8 mole %. The samples were characterized by XPS, TPR, XRD and BET measurements. It was found that the activity for the oxidation of toluene and the selectivity for side chain partial oxidation products (benzaldehyde and benzoic acid) exhibited by V2O5/TiO2 catalysts increased with the vanadium loading up to monolayer coverage. This increase was attributed to the parallel increase of the surface concentration of easily reducible isolated vanadium species interacting with the anatase surface. When the vanadium content increased above monolayer coverage both activity and selectivity decreased. V2O5-MoO3/TiO2 catalysts were found to be less active and selective than the corresponding V2O5/TiO2 ones. Molybdenum species supported on anatase were less active for this reaction than vanadium and, in addition, the presence of molybdenum inhibited the interaction between vanadium and anatase leading to a poor vanadium dispersion.

Effect of pressure on three catalytic partial oxidation reactions at millisecond contact times

Abstract: The effects of pressure on reactant conversion and product selectivities in three catalytic oxidation systems have been examined at pressures between 1 and > 5 atm Reaction was sustained autothermally near adiabatic operating conditions at temperatures of ∼1000°C with residence times over the noble metal catalysts between 10−4 and 10−2 s The three systems investigated were (1) HCN synthesis over Pt-10% Rh gauze catalysts, (2) methane oxidation to synthesis gas (CO and H2) over rhodium-coated monoliths, and (3) ethane conversion to ethylene over platinum-coated monoliths We find that selectivities in all three reactions do not change dramatically with approximately a five-fold increase in pressure This strongly suggests that free radical homogeneous chain reactions are not significant in these processes and that they can be operated reliably above atmospheric pressure For the synthesis of HCN over Pt-10% Rh gauzes, the selectivity to HCN can be maintained above 075 at pressures up to 55 atm Selectivities to synthesis gas (CO and H2) from a methane-air mixture over a Rh-coated foam monolith at pressures up to 55 atm were maintained above 090 Over a Pt-coated foam monolith, the selectivity to ethylene from ethane-air and ethane-O2 mixtures was independent of pressure up to 65 atm and conversion rose slightly although it was necessary to maintain constant velocity and residence time over the catalyst to avoid carbon formation

Modeling and simulation of a nonisothermal catalytic membrane reactor

Abstract: A two-dimensional nonisothermal mathematical model has been developed to simulate a tube-and-shell configuration, catalytic membrane reactor. The three-layer membrane consists of an inert large-pore support, an o2 semipermeable dense perovskite layer and a porous catalytic layer. The model is applied to the simulation of the partial oxidation or methane to syngas (oxyreforming). The membrane reactor simultaneously supplies oxygen to the catalytic reaction along the reactor length, and separates oxygen from the air feed, using a dense perovskite layer which is a mixed conductor, thus allowing rapid oxygen permeation without the use of an external circuit. Two configurations of catalytic membrane reactors are simulated, for both bench-scale and industrial-scale conditions. Comparisons are made to the conventional fixed-bed reactor, and to membrane reactors which are isothermal, adiabatic or wall-cooled. The simulation results imply that the temperature rise in exothermic partial oxidation reactions...

In situ surface Raman spectroscopy studies of oxygen adsorbed on electrolytic silver

Abstract: In situ Raman spectroscopy has been employed to investigate oxygen adsorption on electrolytic silver catalyst under industrial conditions for methanol oxidation to formaldehyde. Both adsorbed atomic and molecular oxygen species are shown to exist on the silver surface in O2 flow above 870 K. The peroxide species is determined to be a precursor to atomic adsorbed oxygen. In consideration of the industrial process, the molecular mechanism of the partial oxidation of methanol and the adsorption mechanism of oxygen on electrolytic silver surface are discussed.