Carbonaceous fuel molecules

This section addresses the role of chemical surface bonding in the electrochemical oxidation of carbon monoxide, CO, formic acid, and methanol as examples of the electrocatalytic oxidation of small organics into C02 and water. The (electro)oxidation of these small Cl organic molecules, in particular CO, is one of the most thoroughly researched reactions to date. Especially formic acid and methanol [130,131] have attracted much interest due to their usefulness as fuels in Polymer Electrolyte Membrane direct liquid fuel cells [132] where liquid carbonaceous fuels are fed directly to the anode catalyst and are electrocatalytically oxidized in the anodic half-cell reaction to C02 and water according to... 

Combustion. Combustion is a chemical reaction between a material and oxygen. The reaction is an oxidation-reduction process in which one material becomes chemically oxidized and the other becomes chemically reduced. In the context of fossil fuels, the material that becomes oxidized is coal, fuel liquids, or natural gas. Combustion of these carbonaceous materials converts each atom of carbon in the fuel molecules to a molecule of carbon dioxide, according to the general equation ... 

Kerosene, gas oils and full oils can be partly cracked into gasolines, where their heavy hydrocarbon molecules are broken down into light hydrocarbon molecules. This is done with coil furnaces, at a temperature above 750°F. Then at a pressure of 10 to 17 pounds per square inch they are sent into reaction chambers, where the molecules are broken down. The gasoline yield from this thermal cracking is 55-70% for kerosene, 40-55% for gas oils, 30-40% for fuel oils. The residues are bitumens and carbonaceous products similar to coke. 

An alternative starting point in chemically reacting fossil fuels is to treat them as if they were graphite. As noted earlier, graphite and larger polynuclear aromatic hydrocarbons are far from inert with respect to electron-transfer reactions, and thus the use of chemistry known to work for graphite may be of possible use in the investigation of coal, petroleum, and their derivatives. In the next two sections, we will discuss aspects of reduction and oxidation of carbonaceous solids and thereby parallel the chapters in this book on the reduction and oxidation of polynuclear aromatic hydrocarbon molecules. 

The majority of solids will undergo a chemical decomposition, better known as pyrolysis. Pyrolysis is the chemical decomposition of the solid fuel by the apphcation of a heat source. As the molecular bonds begin to break down, smaller molecules (lower molecular weights) are released in the gaseous form and ignited if released from the solid at a sufficient rate that the flammable limit is reached. Most solids will undergo this process of pyrolysis when exposed to a sufficient heat source some, however, may melt first and vaporize like a liquid. For example, cellulosic materials (i.e., wood, paper) and thermoset polymers will undergo pyrolysis and leave behind a carbonaceous residue (char) in the presence of a sufficient heat source, but thermoplastics (plastic bottles) will melt when exposed to heat and vaporize similar to liquids. 

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