Methane sensing

Dutronc P, Lucat C, MenU F, Loesch M, Combes L (1993b) A new approach to selectivity in methane sensing. Sens Actuators B 15-16 24-31... 

A base material used for alcohol sensing is the perovskite oxide with rare-earth elements, which shows p-type semiconducting properties. The most commonly used rare earth is lanthanum. In this case, to retain a perovskite structure with semiconducting characteristics is important. Other rare earths are used instead of lanthanum. However, lanthanum is the most reasonable choice of the rare-earths series from the expense viewpoint. Methane sensing is also attempted by using the rare-earth-containing perovskite oxide. The perovskite oxide does not act as base material but as the auxiliary electrode to accelerate methane combustion. 

Table 6 shows the effect of varying coil oudet pressure and steam-to-oil ratio for a typical naphtha feed on the product distribution. Although in these tables, the severity is defined as maximum, in a reaUstic sense they are not maximum. It is theoretically possible that one can further increase the severity and thus increase the ethylene yield. Based on experience, however, increasing the severity above these practical values produces significantly more fuel oil and methane with a severe reduction in propylene yield. The mn length of the heater is also significantly reduced. Therefore, this is an arbitrary maximum, and if economic conditions justify, one can operate the commercial coils above the so-called maximum severity. However, after a certain severity level, the ethylene yield drops further, and it is not advisable to operate near or beyond this point because of extremely severe coking. 

In the narrow sense, bis-maleimide resin means the thermosetting resin eom-posed of the bis-maleimide of methylene dianiline (BMI, bis(4-maleimidophenyl)-methane) and methylene dianiline (MDA, bis(4-aminophenyl)methane) (Fig. 1). Beeause of the addition meehanism, the resin is eured without elimination, whieh is a eharacteristic of this resin. Bis-maleimide resin is used as a thermally stable matrix up to 204°C (400 F) whieh typical epoxy resins may not normally be used. However, in spite of having an imide structure, bis-maleimides are classified as being moderately thermally stable resins. The aliphatic structure of the resin is not stable for long periods above 232°C (450°F.) If a highly aromatic thermally stable thermosetting resin is necessary, acetylene end-capped aromatic imide-based oligomers should be used. 

This result makes sense because the equation now represents the burning of twice as much methane. 

A very recent example of the first case is presented by Vilaseca et al. [71] where an LTA coating on a micromachined sensor made the sensor much more selective to ethanol than methane. Moos et al. [72, 73] report H-ZSM5 NH3 sensor based on impedance spectroscopy using the zeolite as active sensing material. At elevated temperatures (>673 K) NH3 still adsorbs significantly in contrast to CO2, NO,... 

This presentation reports some studies on the materials and catalysis for solid oxide fuel cell (SOFC) in the author s laboratory and tries to offer some thoughts on related problems. The basic materials of SOFC are cathode, electrolyte, and anode materials, which are composed to form the membrane-electrode assembly, which then forms the unit cell for test. The cathode material is most important in the sense that most polarization is within the cathode layer. The electrolyte membrane should be as thin as possible and also posses as high an oxygen-ion conductivity as possible. The anode material should be able to deal with the carbon deposition problem especially when methane is used as the fuel. 

We know that methane normally is a gas at 298 K and atmospheric pressure, so it makes sense that the gas behaves ideally under these conditions. A pressure above 100 atm, on the other hand, is substantially higher than normal conditions, so we expect to see deviations from ideality. 

Chisholm and his group recently succeeded in transforming a metal carbonyl into a stable fi4-carbido complex W4( 4-C)(/t-NMe)(0-i-Pr)12 1 The 13C-NMR signal for the (/ 4-C)4 ligand is 366.8 ppm [5] which can be considered as a realistic model of a surface bound carbido species in the sense of the original proposal by Fischer and Tropsch (Fig. 2). Upon addition of hydrogen, surface bound carbide can be stepwise transformed into methane. 

Fiber optics have been used mainly to remotely sense chemical species via their intrinsic absorption or fluorescence. Methane and other hydrocarbons were a target analyte from the beginning. They can detected by infrared spectroscopy in the gas phase, as impressively shown by the... 

Chan K., Ito H., Inaba H., Humio H., Remote sensing system for near-infrared differential absorption of methane gas using low-loss optical fiber link. Appl. Optics 1984 23 3415. 

Displacing the methane tied up in deep unmineable coal adds another small carbon sink to the portfolio of options and this process is called enhanced coal bed methane recovery. When injected into a coal bed, C02 can replace adsorbed methane. By doing so, coal beds can serve as a C02 reservoir and a source for methane production (Parson and Keith, 1998). This method is attractive in the sense that most of the injected C02 will be immobilized by either physical or chemical adsorption on the coal surface. 

As usual, you need to begin with a balanced chemical equation. If a given reactant or product has a molar coefficient that is not 1, you need to multiply its AH°f by the same molar coefficient. This makes sense because the units of Aff°f are kj/mol. Consider, for example, the complete combustion of methane, CH4(g). 

A second set of experiments further supported the surface carbon route to methane. In these experiments a Ni(lOO) surface was precarbided by exposure to CO and then treated with hydrogen in the reaction chamber for various times. Steps (3) and (4) above were then followed to measure the carbide level This study showed that the rate of carbon removal in hydrogen compared favorably to the carbide formation rate in CO and to the overall methanation rate in H2/CO mixtures. Thus in a H2-CO atmosphere the reaction rate is determined by a delicate balance of the carbon formation and removal steps and neither of these is rate determining in the usual sense. 

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