Combustion, of hydrocarbons

Although essentially inert m acid-base reactions alkanes do participate m oxidation-reduction reactions as the compound that undergoes oxidation Burning m air (combus tion) IS the best known and most important example Combustion of hydrocarbons is exothermic and gives carbon dioxide and water as the products... 

The third characteristic of interest grows directly from the first, ie, the high thermal conductance of the heat pipe can make possible the physical separation of the heat source and the heat consumer (heat sink). Heat pipes >100 m in length have been constmcted and shown to behave predictably (3). Separation of source and sink is especially important in those appHcations in which chemical incompatibilities exist. For example, it may be necessary to inject heat into a reaction vessel. The lowest cost source of heat may be combustion of hydrocarbon fuels. However, contact with an open flame or with the combustion products might jeopardize the desired reaction process. In such a case it might be feasible to carry heat from the flame through the wall of the reaction vessel by use of a heat pipe. 

H. C. Barnett and R. R. Hibbard, Basic Considerations in the Combustion of Hydrocarbon Fuels with Air, NASA Technical Report, 1959, p. 1300. 

Catalyst Function. Automobile exhaust catalysts are perfect examples of materials that accelerate a chemical reaction but are not consumed. Reactions are completed on the catalyst surface and the products leave. Thus the catalyst performs its function over and over again. The catalyst also permits reactions to occur at considerably lower temperatures. For instance, CO reacts with oxygen above 700°C at a substantial rate. An automobile exhaust catalyst enables the reaction to occur at a temperature of about 250°C and at a much faster rate and in a smaller reactor volume. This is also the case for the combustion of hydrocarbons. 

Maurice, L.Q.W., and Blust, J.W., Emission from Combustion of Hydrocarbons in a Well Stirred Reactor, AIAA 1999. 

Carbon dioxide has been implicated as a contributing factor in global warming. Increased global warming has been associated with increased release of carbon dioxide into the atmosphere attributed in part to an increase in the combustion of hydrocarbon fuels. Carbon dioxide is an inevitable consequence of the complete combustion of hydrocarbons in air. If combustion devices are made more efficient, less fuel is required and less carbon dioxide is released into the atmosphere. 

Unlike carbon dioxide and water that are the inevitable by products of complete combustion of hydrocarbons, species such as carbon monoxide, ethene, toluene, and formaldehyde can be emitted because combustion has been interrupted before completion. Many factors lead to emissions from incomplete combustion. Emitted unburned hydrocarbons and carbon monoxide are regulated pollutants that must be eliminated. In automobiles with spark ignited engines, these emissions are almost entirely removed by the catalytic converter. 

F.19 The CO, produced by the combustion of hydrocarbons contributes to global warming. Rank the following fuels according to increasing mass percentage of carbon (a) ethene, C2H4 (b) propanol, C3H-OI I (c) heptane, C-Hl6. 

Methyl and ethyl nitrates are promoters of the combustion of hydrocarbons. Nitrobenzene and aromatic nitrated explosives are mostly insensitive to impact. They become sensitive when potassium or Na-K alloy is present. 4-Nitrotoluene with sodium in diethyl ether medium forms a black residue that combusts spontaneously in air. 

The two most important environmental hazards faced by humankind today are air pollution and global warming. Both have a direct link with our current overdependence on fossil fuels. Pollutants produced from combustion of hydrocarbons now cause even more health problems due to the urbanization of world population. The net increase in environmental carbon dioxide from combustion is a suspect cause for global warming, which is endangering the Earth—the only known place to support human life. In addition, the import of expensive hydrocarbon fuel has become a heavy burden on many countries, causing political and economic unrest. 

Notwithstanding the intellectual challenges posed by the subject, the main impetus behind the development of computational models for turbulent reacting flows has been the increasing awareness of the impact of such flows on the environment. For example, incomplete combustion of hydrocarbons in internal combustion engines is a major source of air pollution. Likewise, in the chemical process and pharmaceutical industries, inadequate control of product yields and selectivities can produce a host of undesirable byproducts. Even if such byproducts could all be successfully separated out and treated so that they are not released into the environment, the economic cost of doing so is often prohibitive. Hence, there is an ever-increasing incentive to improve industrial processes and devices in order for them to remain competitive in the marketplace. 

Combustion reactions are redox reactions in which the chemical species rapidly combines with oxygen and usually emits heat and light. Reactions of this type are extremely important in our society as the sources of heat energy. Complete combustion of carbon yields carbon dioxide, and complete combustion of hydrogen yields water. The complete combustion of hydrocarbons, organic compounds containing only carbon and hydrogen, yields carbon dioxide and water ... 

Satisfactory combustion of hydrocarbon gases depends on the matching of burner and appliance design with certain gas characteristics. Various types of test methods are available for the direct determination of calorific value (ASTM D900,... 

In the next investigation, you will carry out several redox reactions, including reactions of acids with metals, and the combustion of hydrocarbons. 

The products of complete combustion of hydrocarbons in air are water and carbon dioxide. However, combustion is rarely complete and byproducts... 

Fomi, L. and Rossetti, I. Catalytic combustion of hydrocarbons over perovskites. Appl. Catal, B Environmental, 2002, Volume 38, Issue 1,19-211. 

The chosen combinations of these chemicals and metals depend on the requirements of the specific application. Gasless combustion prevents pressure increase in a closed combustion chamber. Some combinations of metal particles and metal oxide particles or of metal particles and crystalline oxidizers are chosen as chemical ingredients of gasless pyrolants. On the other hand, hydrocarbon polymers are used to obtain combustion products of low molecular mass, such as H2O, CO, CO2, and H2. High pressure is thus obtained by the combustion of hydrocarbon polymers. Table 10.6 shows the chemical ingredients used to formulate various types of pyrolants. 

Fullerene generation by vaporization of graphite or by combustion of hydrocarbons is very effective and certainly unbeatable what facile production in large quantities is concerned. However, total synthesis approaches are attractive because (a) specific fullerenes could be made selectively and exclusively, (b) new endohedral fullerenes could be formed, (c) heterofullerenes and (d) other cluster modified fullerenes could be generated using related synthesis protocols. 

The products of complete combustion of hydrocarbons are carbon dioxide and water. 

CA 49,7391(1955)(Explosive combustion of hydrocarbons — comparative investigation and study of continuous spectra) llJH.M.Hershen-son, "Ultraviolet and Visible Absorption Spectra , Index for 25 years — 1930 to 1954, Academic Press, NY(1956) I2)A.Gillam ... 

Effect of Hydrocarbon Molecular Structure on Ionization from Catalytic Oxidation in Air. Figure 1 shows the data for the ion yields obtained for several hydrocarbons during oxidation in air over a platinum filament in the approximate temperature range of 400° to 900°C. The hydrocarbons fall into two broad categories those which produced about 0.04 coulomb per mole of hydrocarbon oxidized, and those which produced about 1.0 coulomb or more per mole. The latter yield is similar to that obtained during combustion of hydrocarbons in a hydrogen flame... 

Reactions (Rl) and (R12) are the two most important elementary reactions in combustion. H + O2 is the essential chain-branching reaction, while CO + OH is a chain-propagating step that regenerates the H atom from OH. Furthermore the CO + OH reaction is highly exothermic and responsible for a large fraction of the heat release that occurs in combustion of hydrocarbon fuels. Under moist conditions, reactions of CO with O and O2 are not competitive, but (RIO) may serve as an initiation step. 

The mechanism of formation of the initial benzene molecule in combustion of hydrocarbons depends on both the fuel and the reaction conditions. Two classes of ring-forming reactions have been proposed. The first class involves addition of acetylene to vinyl-type radicals (i.e., short-chain radicals containing a double-bond), with subsequent cyclization to a five or six membered ring, depicted in Fig. 14.8. In these reactions the adduct does not require intramolecular rearrangements prior to cyclization [318]. However, under most conditions these reactions are thought to be of secondary importance. 

E. Ranzi, M. Dente, A. Goldaniga, G. Bozzano, and T. Faravelli. Lumping Procedures in Detailed Kinetic Modeling of Gasification, Pyrolysis, Partial Oxidation, and Combustion of Hydrocarbon Mixtures. Prog. Combust. Sci. Techn., 27 99-139, 2001. 

E. Ranzi, A. Sogaro, P. Gaffuri, G. Pennati, C.K. Westbrook, and W.J. Pitz. A New Comprehensive Reaction Mechanism for Combustion of Hydrocarbon Fuels. Combust. Flame, 99 201-211,1994. 

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