Showing papers on "Partial oxidation published in 1993"

Synthesis gas formation by direct oxidation of methane over Rh monoliths

Abstract: The production of H2 and CO by catalytic partial oxidation of CH4 in air or O2 at atmospheric pressure has been examined over Rh-coated monoliths at residence times between 10−4 and 10−2 s and compared to previously reported results for Pt-coated monoliths. Using O2, selectivities for H2 ( $$S_{H_2 }$$ ) as high as 90% and CO selectivities (S CO) of 96% can be obtained with Rh catalysts. With room temperature feeds using air, Rh catalysts give $$S_{H_2 }$$ of about 70% compared to only about 40% for Pt catalysts. The optimal selectivities for either Pt or Rh can be improved by increasing the adiabatic reaction temperature by preheating the reactant gases or using O2 instead of air. The superiority of Rh over Pt for H2 generation can be explained by a methane pyrolysis surface reaction mechanism of oxidation at high temperatures on these noble metals. Because of the higher activation energy for OH formation on Rh (20 kcal/mol) than on Pt (2.5 kcal/mol), H adatoms are more likely to combine and desorb as H2 than on Pt, on which the O+ H→ OH reaction is much faster.

A study of carbon deposition on catalysts during the partial oxidation of methane to synthesis gas

Abstract: The deposition of carbon on catalysts during the partial oxidation of methane to synthesis gas has been investigated and it has been found that the relative rate of carbon deposition follows the order Ni>Pd>Rh>Ir. Methane decomposition was found to be the principal route for carbon formation over a supported nickel catalyst, and electron micrographs showed that both “whisker” and “encapsulate” forms of carbon are present on the catalyst. Negligible carbon deposition occurred on iridium catalysts, even after 200 h.

Partial Oxidation of Methane Using the Redox of Cerium Oxide

Abstract: Direct conversion of methane into synthesis gas of H2/CO ratio of 2 has been demonstrated using CeO2 as an oxidant at 873–1073 K. The reaction was accelerated in the presence of Pt black (1 wt%). The reduced cerium oxide after the oxidation of methane can be used to convert carbon dioxide into carbon monoxide.

Heterogeneous Catalytic Oxidation of Acrolein to Acrylic Acid: Mechanism and Catalysts

Abstract: Partial oxidation of acrolein is a commercially important reaction, its product—acrylic acid—being widely used industrially for producing resins, dyes, glues, nonwoven fabrics, etc. Partial oxidation of acrolein is also a convenient model reaction because: (1) the number of reaction products is moderate (CO, CO2, acrylic acid) and (2) their difference in acid-base properties from the starting material makes it possible to select desirable catalysts by applying directly and efficiently Boreskov's concept of intermediate chemical interaction of a catalyst with reaction mixture components. According to this concept [1], the transformation of surface intermediates (SI) formed in the interaction of reactants with a catalyst's surface is determined by the structure and bond energy of these SI. The study of the reaction mechanism includes determination of structures and energy characteristics of the surface intermediates and the elucidation of their connection with catalyst chemical composition and reac...

Selective oxidation of methane to CO and H2 over unreduced NiO-rare earth oxide catalysts

Abstract: NiO-LnO x (Ln = lanthanide) catalysts (with Ni∶Ln=1∶1) without prereduction show high activity/selectivity and very high productivity in the oxidative conversion of methane to CO and H2. The catalysts are first activated in the initial reaction, which is started at 535–560°C, by the reduction of NiO and creation of active sites. The carbon deposition on the catalysts in the reaction, particularly for the NiO-Gd2O3, NiO-Tb4O7 and NiO-Dy2O3 catalysts, is quite fast but it has caused a little or no influence on the catalytic activity/selectivity. Pulse reaction of pure methane on NiO-Nd2O3 (at 600°C) shows involvement of lattice oxygen in the initial reaction and also reveals formation of carbon from CO on the catalyst reduced in the reaction.

Partial oxidation of methane to syngas over Co/MgO catalysts. Is it low temperature?

Abstract: Co/MgO catalysts with high Co-loading (>28 wt%) are able to initiate the reaction of methane with oxygen at temperatures around 500 °C. High conversions of methane (∼ 70%) and very high selectivities for hydrogen and carbon monoxide (∼ 90%) are obtained at very high reactant gas space velocities (105–106 h−1). The temperature of the catalyst at the conditions of partial oxidation of methane to form syngas was found to be extremely high (1200–1300 °C); it is about 600–850 °C higher than that previously reported by others. At these temperatures, high temperature homogeneous reactions may prevail. It is suggested that combustion of methane to carbon dioxide occurs on the catalyst with major heat release and that methane and water, respectively methane and carbon dioxide are reformed thermally in an endothermic reaction leading to syngas.

Investigation of zeolite catalysts for the direct partial oxidation of benzene to phenol

Abstract: The direct oxidation of benzene to phenol using nitrous oxide as an oxidant has been investigated on a range of zeolite catalysts. It has been found that ZSM-5 type zeolites are excellent catalysts for this reaction, giving up to 99% selectivity at high conversions. Zeolites having theEU-1 type structure had low activities and selectivity, and amorphous acidic silica-alumina catalysts were inactive. The acidity of the various catalysts has been assessed using FT-IR of adsorbed pyridine coupled with thermal desorption, and by temperature-programmed desorption of adsorbed ammonia. It has been found that all the types of catalysts have similar acidities even though they have very different catalytic activities. Elimination of Bronsted acid sites has demonstrated that such sites are a necessary but not sufficient requirement for high activity and selectivity in the benzene-to-phenol reaction. The possible role of iron ions has been investigated and it has been concluded that these are not involved in the catalytic reaction on these particular materials. Possible reaction mechanisms have been considered and the importance of the detailed structure of the zeolite has been examined.

Simplification of Solid Oxide Fuel Cell System Using Partial Oxidation of Methane

Abstract: The solid oxide fuel cell, Ni–YSZ cermet |YSZ| Au, could supply the stable electric power in an uniform atmosphere, namely, a methane + air mixture. At operating temperature of 950 °C, the electromotive force (EMF) was 350 mV, and the terminal voltage was 159 mV at 14.7 mA cm−2 with 2.36 mW cm−2. The working mechanism of the fuel cell was based on the difference in catalytic activity for partial oxidation of methane between Ni–YSZ cermet and Au electrode materials.

Oxidation catalyst and process for the partial oxidation of methane

Abstract: The invention relates to a catalyst for the partial oxidation of methane or a gaseous mixture containing methane, said catalyst which preferably has a perovskite structure has the following composition: Ln.sub.x A.sub.1-y B.sub.y O.sub.3 in which x is a number such that 0

Partial oxidation of low rank coal

Abstract: Abundant low cost low rank coal may now be gasified by partial oxidation or burned in a furnace or boiler. About 30 to 45 parts by wt. of comminuted low rank coal is mixed and reacted in the reaction zone of a partial oxidation gas generator with a free-oxygen containing gas and (a) about 0.5 to 30 parts by wt. of a liquid hydrocarbonaceous fuel selected from the group consisting of residual fuel oil, shale oil, waste hydrocarbon oil, asphalt and mixtures thereof, and (b) about 70 to 55 parts by wt. of water. The hot effluent stream of synthesis gas, reducing gas or fuel gas from the partial oxidation gasifier may be purified to provide a gas stream which will not pollute the environment.

Partial oxidation process and burner with porous tip

Abstract: A partial oxidation process and a novel burner are provided for simultaneously introducing two or three separate feedstreams into a free-flow partial oxidation gas generator for the production of synthesis gas and fuel gas, or reducing gas. The reactant feedstreams include a liquid hydrocarbonaceous fuel or a pumpable slurry of solid carbonaceous fuel, and a free-oxygen containing gas e.g. air or oxygen. The burner comprises a central conduit and a plurality of spaced concentric coaxial conduits with down-flowing annular passages. A flat annular-shaped disc or cup-shaped porous ceramic or porous metal cooling means of uniform composition, wall thickness and porosity with the various pores interconnecting is attached to the downstream tip of the burner. A controlled amount of liquid coolant under pressure is passed successively through the porous inside surface, porous core and porous outside surface of the cooling means is vaporized. The tip of the burner is thereby cooled. Stress cracking of the burner tip is prevented; and the life of the burner is extended. Further, deposition of ash on the face of the burner is prevented.

Effect of carbon dioxide on the selectivities obtained during the partial oxidation of methane and ethane over Li+/MgO catalysts

Abstract: AtT ⩽ 650 °C carbon dioxide either formed during reaction or added to the system increases the selectivity for the desired hydrocarbon products during the oxidative coupling of methane and the oxidative dehydrogenation of ethane reaction over Li+/MgO catalysts. Similarly, CO2 inhibits secondary reactions of CH3-radicals with the surface of the Li+/MgO. The improved selectivities are attributed to the poisoning effect that CO2 has on the secondary reactions of alkyl radicals with the surface.

Effect of surface species on activity and selectivity of MoO3/SiO2 catalysts in partial oxidation of methane to formaldehyde

Abstract: The effect of the nature of surface species on the activity and selectivity of MoO3/SiO2 catalysts has been investigated for the partial oxidation of methane to formaldehyde. Characterization techniques including BET surface area, ambient and in situ Raman spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed reduction were used in conjunction with steady-state reaction studies to relate the presence of different surface species to the activity and selectivity of the catalyst. Results of these experiments indicate the presence of a highly dispersed silicomolybdic species with terminal Mo=O sites appearing at lower MoO3 loadings. As the weight loading increases, these sites are transformed into polymolybdate species, forming more Mo-O-Mo bridging sites at the expense of Mo=O sites. At high weight loadings, crystalline MoO3 begins to form. The abundance of the Mo=O sites is believed to affect activity and selectivity in the partial oxidation of methane to formaldehyde.

Homogeneous gas-phase oxidation of methane using oxygen as oxidant in an annular reactor

Abstract: The gas-phase partial oxidation of methane with oxygen has been investigated in a high-pressure quartz-lined annular reactor. The work undertaken consists of a systematic investigation of the effects of reactor tube wall temperature, pressure, feed oxygen concentration, and gas flow rate on methane conversion and methanol yield and selectivity. Methanol yields in the range of 1.5-2.3 mol % and selectivities in the range of 23-47 mol % have been observed, depending on the process parameters used. Increasing the oxygen concentration in the feed is found to decrease methanol selectivity dramatically, while yield exhibits a trade-off between decreasing selectivity and increasing conversion. The influence of pressure is most noticeable between 1.5 and 3.0 MPa, where substantially more methanol is produced at the higher pressure. The effect is less pronounced as the pressure is increased further. The most significant outcome of this study is the recognition of the importance of the interaction of the chemistry of the system and the heat-transfer properties of the reactor system. The system is very sensitive to heat release rate and exhibits a discontinuity in methane conversion, with hysteresis being observed under process conditions employing high feed oxygen concentrations and total gas flow rates. More importantly, highestmore » methanol yields are observed on the downward sweep of reactor wall temperature, reinforcing the concept that the reaction is most sensitive to temperature and that low temperatures favor methanol production.« less

Process for production of desulfurized synthesis gas

Abstract: A process for the partial oxidation of a sulfur- and silicate-containing carbonaceous fuel to produce a synthesis gas with reduced sulfur content which comprises partially oxidizing said fuel at a temperature in the range of 1900 DEG -2600 DEG F. in the presence of a temperature moderator, an oxygen-containing gas and a sulfur capture additive which comprises a calcium-containing compound portion, a sodium-containing compound portion, and a fluoride-containing compound portion to produce a synthesis gas comprising H2 and CO with a reduced sulfur content and a molten slag which comprises (1) a sulfur-containing sodium-calcium-fluoride silicate phase; and (2) a sodium-calcium sulfide phase.

Phosphorous/vanadium oxidation catalyst

Abstract: An improvement in the oxidation catalyst used for the partial oxidation of n-butane and containing vanadium and phosphorus, zinc, lithium and molybdenum mixed oxides which comprises adding the molybdenum as a compound which is dissolved in a solvent during the manufacture of the catalyst.

Partial oxidation of methane over ruthenium catalysts

Abstract: The catalytic partial oxidation of methane with oxygen to produce synthesis gas was studied under a wide range of conditions over supported ruthenium catalysts. The microreador results demonstrated the high activity of ruthenium catalysts for this reaction. A catalyst having as little as 0.015% (w/w) Ru on Al2O3 gave a higher synthesis gas selectivity than a catalyst having 5% Ni on SiO2. XANES measurements for fresh and used catalyst samples confirmed that ruthenium is reduced from ruthenium dioxide to ruthenium metal early during the experiments. Ruthenium metal is thus the active element for the methane partial oxidation reaction.

Novel high activity catalyst for partial oxidation of methane to formaldehyde

Abstract: Vanadium oxide–silica catalyst can effect the partial oxidation of methane to formaldehyde with extremely high activities and the space time yield (STY) can reach a value in excess of 800 g kg–1cath–1; bare silica also shows apprecible STY value upto ca. 300 g kg–1cath–1.

Carbon pathways for the partial oxidation of methane

Abstract: The partial oxidation of methane to formaldehyde was studied at 1-atm pressure using a 2% V[sub 2]O[sub 5]/SiO[sub 2] catalyst with molecular oxygen as an oxidant. As methane conversion increased, formaldehyde selectivity decreased rapidly while CO[sub x] selectivity increased, indicating that formaldehyde was a primary product of the reaction, while CO[sub x] formation occurred apparently in large part by secondary reaction. Using steady-state isotopic transient kinetic analysis technique, carbon transients were obtained by switching from [sup 12]CH[sub 4] to [sup 13]CH[sub 4] at steady state, permitting the determination of surface residence times and surface concentrations of various carbon-containing intermediates. It was possible to observe detectable reversible chemisorption of methane on the catalyst studied and other reference oxides only at conditions where significant reaction took place. For the partial oxidation of methane over the 2% V[sub 2]O[sub 5]/SiO[sub 2] catalyst, it was found that HCHO and CO did not exhibit significant reversible readsorption under the reaction conditions used. It is suggested that the formation of CO involves a sequential pathway wherein an irreversible readsorption of HCHO is involved. A carbon pathway consistent with the observations is proposed. It is speculated that different types of sites involved in the formation of HCHO,more » CO and C[sub 2]H[sub 6] may correspond to vanadium oxide species in different redox states. 30 refs., 6 figs., 5 tabs.« less

Factors affecting the deactivation of various zeolites used as catalysts for the direct partial oxidation of benzene to phenol

Abstract: The way in which zeolites ZSM-5 and EU-1 deactivate when exposed to a mixture of benzene and nitrous oxide has been studied. The deactivation has been shown to be due to the deposition of carbonaceous material within the zeolite structure. It has been shown that upon exposure to the reaction mixture a substantial amount of the internal surface area of the zeolites is lost. The decrease in surface area accessible to the reactant molecules has been measured by the adsorption of nitrogen at −196 °C; polyaromatic molecules such as biphenyl and 2-phenoxyphenol are thought to be responsible for this decrease. This material has been found to be removable by treatment in nitrogen at 500 °C, causing the zeolites to be partially regenerated. In addition, it has been shown using the temperature-programmed desorption of ammonia that Bronsted acid sites are also blocked by polymeric carbonaceous material. This material is not removeable in nitrogen, the activity of the zeolites being totally regained after treatment in oxygen at 500 °C.

Partial oxidation of methane on mo/sn/p silica supported catalysts

Abstract: In this paper the partial oxidation of methane on a series of silica supported Mo/Sn/P catalysts has been studied. It is shown that tin promotes the activity of a Mo/SiO2 catalyst, and phosphorus improves its selectivity. The results obtained for a Mo/2Sn/P catalysts were among the highest reported in the literature corresponding to a formaldehyde selectivity of 64.8% at a methane conversion of 7.2%. Characterization of the catalysts indicates that an interaction between molybdenum and tin is responsible for the high activity-selectivity found.

The role of chlorine in the partial oxidation of methane to ethene on MgO catalysts

Abstract: The effect of dichloromethane on the activity and selectivity of an MgO catalyst in the methane coupling reaction has been investigated. The results indicate that the primary role of chlorine is to modify the surface of the catalyst so as to enhance the selectivity to ethane and ethene. The response of ethene and ethane to the introduction of dichloromethane is different, and this is taken as evidence that the dehydrogenation of ethane to ethene is not due to gas-phase reactions involving chlorine radicals. The physical properties of the catalyst before and after treatment with dichloromethane have been investigated using surface area measurements, X-ray diffraction and analytical transmission electron microscopy. Substantial changes in the morphology of the catalyst particles are observed but these do not account for the trends in catalytic properties. X-ray photoelectron spectroscopy has been used to determine the surface composition of the catalysts before and after treatment. Chlorine is observed in the treated catalyst at a surface concentration of 3%.