Combustion at higher temperature

Secondary reactions manifest, as explained next An amount of ethylene is lost by combustion at higher temperature ... 

AEROTHENE (71-55-6) Combustible at higher temperatures above 995°F/535°C. Forms explosive mixture with air (range 7.5— 12.5% by volume in air). The sensitivity of these limits may be widened by pressure, oxygen, aluminum, magnesium, zinc, and their alloys. Reacts, possibly violently, with strong caustics, strong oxidizers, acetone, sodium, amides, chemically active metals, metal powders of aluminum, bronze, copper, magnesium. 

It was reported that CeOg-FcgOg mixed oxides improve the kinetic performance of soot combustion. The reaction proceeds through a redox cycle between Ce VFe and Ce VFe ", and FcgOg has been shown to exhibit a push-pull redox mechanism for soot combustion at higher temperatures. The active sites involved are Fe-O-Ce-type species. The mechanism shown in Fig. 8.29 involves the surface oxide anion bound to the Fe , which reacts with the soot... 

Black carbon is operationally defined on the basis of its relative resistance to oxidation in combustion experiments it is typically considered to be the carbon that survives oxidation in air at 375 °C but combusts at higher temperatures. However, because of variations in protocols, different laboratories may measure somewhat different values for /be in the same sediment. In sediments, values of /be are t)q)ically somewhat less than 1%. In the atmosphere, black carbon also has a significant role in atmospheric transparency and thus in the radiation balance of Earth (see Section 4.7). 

The syngas obtained from gasification is potentially more efficient than direct combustion of the original fuel because it can be combusted at higher temperatures or even in fuel cells. Syngas may be used to produce methanol and hydrogen, or converted via the Fischer-Tropsch process into synthetic fuel. 

Although Hitec is nonflammable, it is a strong oxidizer and supports the combustion of other materials. Consequendy, combustible materials must be excluded from contact with the molten salt. Hitec is compatible with carbon steel at temperatures up to 450°C. At higher temperatures, low alloy or austenitic stainless steel is recommended. Adding water to Hitec does not appreciably alter its corrosion behavior. 

No SCR catalyst can operate economically over the whole temperature range possible for combustion systems. As a result, three general classes of catalysts have evolved for commercial SCR systems (44) precious-metal catalysts for operation at low temperatures, base metals for operation at medium temperatures, and 2eohtes for operation at higher temperatures. 

Figure 19.1 indicates the flue losses to be expected for different temperatures and excess air. It is seen that considerable savings can be made, particularly at higher temperatures, by reducing excess air levels to a practical minimum. It is also evident that a reduction in air/gas ratio to below stoichiometric will cause a rapid deterioration in efficiency caused by the energy remaining in the incomplete combustion of fuel. 

At higher temperatures e.g. 230°C, the hardboards at Infinite time have lost less than half their total combustion heat while semi-hardboards will have lost all, if the extrapolation used is valid. Table II includes the total calculated heat release at 230 and 160°C respectively. 

Pellistors are used to detect flammable gases like CO, NH3, CH4 or natural gas. Some flammable gases, their upper and lower explosion limits and the corresponding self-ignition temperatures are listed in Tab. 5.1. This kind of gas sensor uses the exothermicity of gas combustion on a catalytic surface. As the combustion process is activated at higher temperatures, a pellistor is equipped with a heater coil which heats up the active catalytic surface to an operative temperature of about 500 °C. Usually a Platinum coil is used as heater, embedded in an inert support structure which itself is covered by the active catalyst (see Fig. 5.33). The most frequently used catalysts are platinum, palladium, iridium and rhodium. 

H2 production from ethanol (as well as methanol) employs these methodologies either as such or after slight modifications, especially in the ATR process, wherein a separate combustion zone is usually not present (Scheme 3). A mixture of ethanol, steam and 02 with an appropriate ethanol steam 02 ratio directly enters on the catalyst bed to produce syngas at higher temperature, around 700 °C.18,22 The authors of this review believe that under the experimental conditions employed, both steam reforming and partial oxidation could occur on the same catalyst surface exchanging heats between them to produce H2 and carbon oxides. The amount of 02 may be different from what is required to achieve the thermally neutral operation. Consequently the reaction has been referred to as an oxidative steam reforming... 

In fuel cells, the combustion energy of hydrocarbons can be converted directly into electrical energy. At the fuel cell anode, the hydrocarbon is in most cases converted to carbon dioxide because the intermediates are more easily oxidized than the starting hydrocarbon (Eq. 9a) at the fuel cell cathode oxygen is reduced to water (Eq. 9b). Most fuel cell research has involved the use of hydrogen as fuel. However, solid oxide fuels cells (SOCFs) can operate at higher temperature and can... 

At higher temperatures (T>1320 °C) and larger particles, combustion regime (II) prevails [75], Regime (II) is controlled by both intraparticle diffusion and chemical kinetics. In this case the density and diameter decrease, see Figure 55. 

At temperatures below 400 C no flames were observed. At higher temperatures stationary flames were formed at the tip of the oxygen nozzle, depending on the pressure of the reaction cell. No electric spark or other means were necessary. The flame ignition started spontaneously. The flame and the combustion space can be illuminated from behind with a simple lamp giving diffuse light. 

Consequently, the benzene oxidation mechanism was further developed by considering additional decomposition and oxidation steps. Sethuraman et al. proposed that phenyl radical decomposition can occur by either of two key pathways (3-scission of phenyl radical or by breakdown of the phenylperoxy radical formed by the oxidation of phenyl radical (Fig. 9). Using PM3 calculations,which were ultimately verified by DFT studies,Carpenter predicted that another species, 2-oxepinoxy radical (3 in Fig. 9b), is an important intermediate due to its relative stability, formed via a spirodioxiranyl intermediate (2 in Fig. 9b) from phenylperoxy radical. Pathway A in Fig. 9b is the thermodynamically preferred pathway at temperatures increasing up to 432 K, while pathway B has an entropic benefit at higher temperatures. While pathway B essentially matched the traditional view of benzene combustion, pathway A introduced a new route for phenylperoxy radical, which could resolve discrepancies observed using previous models. 

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