Methane combustion with oxides

Total carbon in beryUium is determined by combustion of the sample, along with an accelerator mixture of tin, iron, and copper, in a stream of oxygen (15,16). The evolved carbon dioxide is usuaUy measured by infrared absorption spectrometry. BeryUium carbide can be determined without interference from graphitic carbon by dissolution of the sample in a strong base. BeryUium carbide is converted to methane, which can be determined directly by gas chromatography. Alternatively, the evolved methane can be oxidized to carbon dioxide, which is determined gravimetricaUy (16). 

The SOFC module is set (sized) to operate at 0.69 volts per cell. The spent fuel and air effluents of the SOFC are combusted within the module to supply heat for oxidant preheating. Unlike the natural gas case, the fuel does not require a pre-reformer with only 0.3% methane along with 36% hydrogen and 43% carbon monoxide. The carbon monoxide will be either water gas shifted to hydrogen or utilized directly within the fuel cell. A gas recirculation loop for the... 

Seshadri, K., and N. Ilincic. 1995. The asymptotic structure of nonpremixed methane-air flames with oxidizer leakage of order unity. Combustion Flame 101 69-80. 

Another related problem is associated with over-oxidation of the substrate, in the extreme case resulting in complete combustion. In the case of methane oxidation by FeO", for example, the activation of methane occurs with about 10% of the gas-kinetic collision rate, whereas those of the putative oxygenation products CH3OH, CH2O, and HCOOH occur on every collision [60]. With regard to applied catalysis this would imply that the oxidation products are oxidized faster by about one order of magnitude compared to methane as the initial substrate. In the particular context of heterogeneous oxidation... 

Methane is an important starting material for numerous other chemicals. The most important of these are ammonia, methanol, acetylene, synthesis gas, formaldehyde, chlorinated methanes, and chlorofluorocarbons. Methane is used in the petrochemical industry to produce synthesis gas or syn gas, which is then used as a feedstock in other reactions. Synthesis gas is a mixture of hydrogen and carbon monoxide. It is produced through steam-methane reforming by reacting methane with steam at approximately 900°C in the presence of a metal catalyst CH4 + H20 —> CO + 3H2. Alternately, methane is partially oxidized and the energy from its partial combustion is used to produce syn gas ... 

The main problems associated with the direct oxidation of methane are the higher reactivity of the products (methanol and formaldehyde) compared to methane, and the thermodynamically more favorable complete combustion of methane to carbon oxides and water ... 

A convenient method to produce porous surfaces is the anodic oxidation of aluminum plates. Such microstructured aluminum platelets have been coated by wet impregnation with Pt-, V- and Zr-precursors [35], and tested under catalytic methane combustion conditions. The conversion rate of oxygen followed directly the platinum content in the catalysts. These data were well reproducible even after five different runs. 

In the case of catalytic methane combustion, aluminum was chosen as an appropriate material for the catalyst wafers since anodic oxidation of aluminum can be used to obtain porous surfaces. Such micro structured aluminum platelets were coated by wet impregnation with Pt, V and Zr precursors [50],... 

CH4 oxidation has been experienced for ceria supported on a barium hexaaluminate, an heat resistant support. Preparation by a new reverse microemulsion method leads to ceria nanoparticles deposited on support and having a BET area close to 100 mVg after calcination at 1000 0 [72]. Such ultrahigh disperse nanoparticles show exceptional thermal resistance the authors mentioned that ceria particles prepared with a size of 6 nm sinters only to 18 nm after a calcination at 1IOO°C under a water containing atmosphere. Of course excellent activity in methane combustion has been observed. According to their experimental conditions calculated specific activity expressed as mol(CH4).h. m was estimated to 6.4x10 at 500°C whereas Bozo [44J reported a value of 1.5x1 O at the same temperature both values look similar. Thus the difference in methane conversion may be related to BET area only which is spectacularly preserved using the reverse micro-emulsion method for synthesis. 

Another relevant issue in methane combustion over palladium is the significant increase in activity that is observed with lime on stream [46,49]. This may be explained by the removal of chloride ions from palladium precursor [46] but was also observed for chlorine-free precursors [49]. A change in the morphology of the palladium oxide on the surface during operation may be the cause for the activity enhancement. 

CAS 1333-86-4. A finely divided form of carbon, practically all of which is made by burning vaporized heavy-oil fractions in a furnace with 50% of the air required for complete combustion (partial oxidation). This type is also called furnace black. Carbon black can also be made from methane or natural gas by cracking (thermal black) or direct combustion (channel black), but these methods are virtually obsolete. All types are characterized by extremely fine particle size, which accounts for their reinforcing and pigmenting effectiveness. 

The flame temperature increases significantly when air is replaced with oxygen because N2 acts as a diluent that reduces the flame temperature. Figure 1.13 is a plot of the adiabatic equilibrium flame temperature for CH4 combustion, as a function of the oxidizer composition, for a stoichiometric methane combustion process. The flame temperature varies from 3600 to 5000°F (2300 to 3000 K) for air and pure... 

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