Combustion hydrocarbon

Mass spectrometry has been used to determine the amount of H2 in complex gas mixtures (247), including those resulting from hydrocarbon pyrolysis (68). Mass spectrometry can also be used to measure hydrogen as water from hydrocarbon combustion (224,248). Moreover, this technique is also excellent for determining the deuterium hydrogen ratio in a sample (249,250). 

D. J. McCracken, Hydrocarbon Combustion and Physical Properties Rep. No. 1496, Ballistic Research Laboratories, Sept. 1970. 

Hydrocarbon combustion Contaminated with other gases No 85% ca 14% CO 0.5% Oo 0.5% HaO saturated Small Simple process can use combustion products from engines or boilers, or dedicated burner less reliability of control maybe very economical used on tanker ships... 

Table II. Some Important Ions in Hydrocarbon Combustion...

Ethylenic and acetylenic hydrocarbons combust spontaneously when they come into contact with nitric acid, within a millisecond. 

Volume of effluent gas Small volume because of absence of nitrogen and hydrocarbon combustion products Large volume because of presence of air and fuel combustion products... 

The reaction 0(3P) + C2H2 plays a key role not only in the combustion of acetylene itself,53 but also in the overall mechanism for hydrocarbon combustion, since acetylene is an important intermediate in the combustion of methane, larger aliphatic hydrocarbons, and aromatics.54-57 There are two energetically-allowed channels ... 

D. J. Hucknall, Chemistry of Hydrocarbon Combustion (Chapman Hall, New York, 1985), p. 199. 

For most hydrocarbon combustion explosions in air the change in the number of moles is small. For example, consider the combustion of propane in air. The stoichiometric equation is... 

BPR [By-Product Recycle] A process for recycling the chlorine-containing by products from the manufacture of vinyl chloride, 1,2-dichloroethane, and other chlorinated hydrocarbons. Combustion with oxygen converts 90 percent of the chlorine to anhydrous hydrogen chloride, and 10 percent to aqueous hydrochloric acid. Developed by BASF and licensed by European Vinyl Corp. 

Westbrook, C.K. and Dryer, F.L., Chemical kinetic modeling of hydrocarbon combustion, Prog. Energy Combust. Sci., 1984, 10, 1-57. 

Although it is expected that for the next 50 years the world economy, especially the United States, will remain dependent on hydrocarbon combustion, there is no certainty about whether this long-term requirement can be met. 

The ODH of ethylbenzene to styrene is a highly promising alternative to the industrial process of non-oxidative dehydrogenation (DH). The main advantages are lower reaction temperatures of only 300 500 °C and the absence of a thermodynamic equilibrium. Coke formation is effectively reduced by working in an oxidative atmosphere, thus the presence of excess steam, which is the most expensive factor in industrial styrene synthesis, can be avoided. However, this process is still not commercialized so far due to insufficient styrene yields on the cost of unwanted hydrocarbon combustion to CO and C02, as well as the formation of styrene oxide, which is difficult to remove from the raw product. 

Thus, one observes that the rate expression can be written in terms of readily measurable stable species. One must, however, exercise care in applying this assumption. Equilibria do not always exist among the II2 02 reactions in a hydrocarbon combustion system—indeed, there is a question if equilibrium exists during CO oxidation in a hydrocarbon system. Nevertheless, it is interesting to note the availability of experimental evidence that shows the rate of formation of C02 to be (l/4)-order with respect to 02, (l/2)-order with respect to water, and first-order with respect to CO [17,18], The partial equilibrium assumption is more appropriately applied to NO formation in flames, as will be discussed in Chapter 8. 

The solution procedure to this equation is the same as described for the temporal isothermal species equations described above. In addition, the associated temperature sensitivity equation can be simply obtained by taking the derivative of Eq. (2.87) with respect to each of the input parameters to the model. The governing equations for similar types of homogeneous reaction systems can be developed for constant volume systems, and stirred and plug flow reactors as described in Chapters 3 and 4 and elsewhere [31-37], The solution to homogeneous systems described by Eq. (2.81) and Eq. (2.87) are often used to study reaction mechanisms in the absence of mass diffusion. These equations (or very similar ones) can approximate the chemical kinetics in flow reactor and shock tube experiments, which are frequently used for developing hydrocarbon combustion reaction mechanisms. 

It is apparent that in any hydrocarbon oxidation process CO is the primary product and forms in substantial amounts. However, substantial experimental evidence indicates that the oxidation of CO to C02 comes late in the reaction scheme [13]. The conversion to C02 is retarded until all the original fuel and intermediate hydrocarbon fragments have been consumed [4, 13]. When these species have disappeared, the hydroxyl concentration rises to high levels and converts CO to C02. Further examination of Fig. 3.6 reveals that the rate of reaction (3.44) does not begin to rise appreciably until the reaction reaches temperatures above 1100K. Thus, in practical hydrocarbon combustion systems whose temperatures are of the order of 1100K and below, the complete conversion of CO to C02 may not take place. 

It is essential to establish the specific mechanisms that explain the cool flame phenomenon, as well as the hydrocarbon combustion characteristics mentioned earlier. Semenov [14] was the first to propose the general mechanism that formed the basis of later research, which clarified the processes taking place. This mechanism is written as follows ... 

Since the system requires the buildup of ROOH and R CHO before chain branching occurs to a sufficient degree to dominate the system, Semenov termed these steps degenerate branching. This buildup time, indeed, appears to account for the experimental induction times noted in hydrocarbon combustion systems. It is important to emphasize that this mechanism is a low-temperature scheme and consequently does not include the high-temperature H2—02 chain branching steps. 

The evidence in Figs. 3.11 and 3.12 [12, 30] indicates three distinct, but coupled zones in hydrocarbon combustion ... 

The relative importance of these three mechanisms in NO formation and the total amount of prompt NO formed depend on conditions in the combustor. Acceleration of NO formation by nonequilibrium radical concentrations appears to be more important in non-premixed flames, in stirred reactors for lean conditions, and in low-pressure premixed flames, accounting for up to 80% of the total NO formation. Prompt NO formation by the hydrocarbon radical-molecular nitrogen mechanism is dominant in fuel-rich premixed hydrocarbon combustion and in hydrocarbon diffusion flames, accounting for greater than 50% of the total NO formation. Nitric oxide formation by the N20 mechanism increases in importance as the fuel-air ratio decreases, as the burned gas temperature decreases, or as pressure increases. The N20 mechanism is most important under conditions where the total NO formation rate is relatively low [1],... 

Jones, W. P., and Lindstedt, R. P., Global reaction schemes for hydrocarbon combustion, Combust. Flame 73, 233 (1988). 

Thorslund, T.W. and D. Farrar. 1990. Development of relative potency estimates for PAH and hydrocarbon combustion product fractions compared to benzo[a]pyrene and their use in carcinogenic risk assessment. EPA/600/R-92/134, Dept. Commerce, NTIS. 

The re-oxidation of lead was expected to occur rapidly at 600 K the surface of the lead oxide would then remain unchanged in the presence of oxygen. The authors concluded that, as a consequence, general hydrocarbon combustion in which formaldehyde is a degenerate branching intermediate is inhibited in the presence of PbO by the rapid removal of formaldehyde. 

It is known that a small amount of lead tetraethyl is effective as an anti-knock agent in gasoline engines. This effect is due to the inhibition of the gas-phase reaction by the lead or lead oxide derived from the lead tetraethyl.l o.si] The inhibitory action of lead compounds on hydrocarbon combustion is largely exerted in the gaseous phase of the combustion zone. 

Automobile tires are the largest-volume mbber material manufactured, and they are formed from natural or synthetic monomers with sulfur compounds added to crosslink the polymer within the tire mold. Tires also contain large amounts (typically 35%) of carbon black particles, which are made by hydrocarbon combustion in excess fuel, as we have considered previously in Chapters 9 and 10. 

Iceland escapes this dilemma because most of their energy is from clean sources, hydropower and geothermal, rather than from hydrocarbon combustion. Since there are few emissions in the production of their electricity, providing hydrogen by electrolysis does not spoil the zero-emission advantage for Iceland s fuel cells. 

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