Carbon compounds, combustibility

The carbon residue is a measure of the carbon compounds left in a fuel after the volatile components have vaporized. Two different carbon residue tests are used, one for light distillates, and one for heavier fuels. For the light fuels, 90% of the fuel is vaporized, and the carbon residue is found in the remaining 10%. For heavier fuels, since the carbon residue is large, 100% of the sample can be used. These tests give a rough approximation of the tendency to form carbon deposits in the combustion system. The metallic compounds present in the ash are related to the corrosion properties of the fuel. 

The chief source of such energy is the combustion of carbon compounds to C02. You know that man exhales more carbon dioxide than he inhales in the air he breathes. This extra carbon dioxide is one of the products of the oxidation processes by which food is oxidized and energy is liberated. 

Carbon monoxide (CO) is a colorless and odorless gas molecule. This inorganic compound, at standard temperature and pressure, is chemically stable with low solubility in water but high solubility in alcohol and benzene. Incomplete oxidation of carbon in combustion is the major source of environmental production of CO. When it burns, CO yields a violet flame. The specific gravity of CO is 0.96716 with a boiling point of -190°C and a solidification point of-207°C. The specific volume of CO is 13.8 cu ft/lb (70°F). 

If nitrogen or sulphur is present in the fuel then the mixture of combustion products may include oxides of these elements. In the absence of excess oxygen incomplete oxidation occurs to produce partially oxidized carbon compounds such as aldehydes, ketones, phenols, and carbon monoxide. Carbon monoxide is extremely toxic and some of the other compounds are respiratory irritants. 

Carbon monoxide is produced when carbon and carbon compounds undergo incomplete combustion. The inefficient combustion of carbon fuels for heating results in the production of carbon monoxide, which may result in high CO concentrations in indoor environments. The use of carbon fuel heaters without adequate ventilation can result in deadly conditions. Each year several hundred people in the United States die from CO poisoning, and 10,000 patients are treated in hospitals for CO exposure. Most of these cases result from faulty heating systems, but barbeques, water heaters, and camping equipment (stoves, lanterns) are also sources of CO. 

Since the time of the earliest work concerned with the reaction of hydrocarbons and fluorine in 1890 by Moissan (who isolated fluorine in 1886), numerous difficulties have been reported. According to Lovelace et al the action of fluorine on a carbon compound can be likened to a combustion process where the products are carbon tetrafluoride and hydrogen fluoride (1). 

Combustibility of Carbon Compounds. Place successively a few drops of gasoline, carbon disulphide (CS2), carbon tetrachloride (CCI4), and chloroform in a porcelain dish and apply a lighted match. 

The varied properties of organic bodies explain this unequal treatment and the result. The reduction of carbon compounds occurs usually at certain reducible groups in the molecule without destroying this latter. The whole molecule is usually exposed to the action of the electrolytic oxygen. The final product of a reduction is closely related chemically to the material started out with the end result of an oxidation is often the complete combustion of the molecule. Quite a number of possibilities exist between a slight attack by oxygen upon and the complete destruction of a compound by oxidation. A realization of these, if at all possible, depends upon most painstaking observations of fixed experimental conditions, which are often difficult to determine. Hence oxidation processes are much more com-... 

The carbon-hydrogen combustion analyzer works because we know that compounds containing carbon and hydrogen will burn in a stream of pure oxygen, O2, to yield only carbon dioxide and water. If we can find the mass of the carbon dioxide and water separately, we can determine the mass percent of carbon and hydrogen in the compound. 

The carbon-hydrogen combustion analyzer can also be used to find the empirical formula of a compound that contains carbon, hydrogen, and one other element, such as oxygen. The difference between the mass of the sample and the mass of the hydrogen and carbon produced is the mass of the third element. 

Examine the following Sample Problem to learn how to determine the empirical formula of a compound based on carbon-hydrogen combustion data. 

A 1.000 g sample of a pure compound, containing only carbon and hydrogen, was combusted in a carbon-hydrogen combustion analyzer. The combustion produced 0.6919 g of water and 3.338 g of carbon dioxide. 

Explain how a carbon-hydrogen combustion analyzer can be used to determine the mass percent of carbon, hydrogen, and oxygen in a compound. 

Menthol is a compound that contains C, H and O. It is derived from peppermint oil and is used in cough drops and chest rubs. When 0.2393 g of menthol is subjected to carbon-hydrogen combustion analysis, 0.6735 g of C02 and 0.2760 g of H20 are obtained. 

Related problems must be considered in individual products. Bromine, chlorine, and antimony add to the smoke of a fire, while phosphorus and water do not, and some metal oxides can actually reduce it. Toxicity of combustion gases is a major concern but the main problem is that oxidation of carbon compounds in an enclosed space—indoors— produces carbon monoxide, no matter whether the carbon compounds are wood or plastics. Other problems include the cost of flame-retardants, difficulties in processing, and loss of mechanical or thermal properties. 

Petroleum is a diverse mixture of hydrocarbons—chemical combinations of primarily hydrogen and carbon. Complete combustion of hydrocarbons yields the end products of carbon dioxide (C02) and water (H20). However, incomplete combustion results in a composite mixture of other products such as C02, H20, carbon monoxide (CO), and various oxygenated hydrocarbons. Since burning petroleum consumes air, nitrogen compounds are also formed. In addition, other elements are associated with hydrocarbon compounds such as sulfur, nickel, and vanadium. 

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