A hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. The hydrocarbons are the most broadly used organic compounds known, and are quite literally the driving force of western civilization. The greatest amounts of hydrocarbons are used as fuel for combustion, particularly in heating and motor fuel applications. The primary components of natural gas are methane and ethane. We are all familiar with the use of propane in gas barbecues, lanterns, and as a fuel for internal combustion engines and heating systems. Butane is also a readily available fuel, familiar to everyone in the form of the pocket lighter.
With pentane, the saturated hydrocarbons enter the realm of room-temperature liquids. This makes them useful as organic solvents, cleaners, and transport fuels. Petrol (Gasoline) for internal combustion engines in cars, trucks, tractors, lawnmowers, and so on, is rated in combustion properties relative to octane. It is in fact a combination of liquid hydrocarbons ranging from hexanes to decanes. Slightly larger hydrocarbons are known as kerosene or jet fuel, diesel fuel and heating oil. Still larger hydrocarbon molecules serve as lubricating oils, and greases. Eventually a point is reached at which the materials are solids at room temperature. These are the waxes. Hydrocarbon molecules larger than those of the waxes are the heavy greases and the tars commonly used in roofing applications and highway construction.
Most hydrocarbons are generated from the thermal 'cracking' and fractional distillation of crude oil. Another major source is the industrial alteration of ethanol to produce ethylene. The ethylene so produced becomes a feedstock for the industrial synthesis of other hydrocarbons up to and including polyethylene.
Environmental Problems Associated With the Combustion of Hydrocarbons
Hydrocarbons are burned, or combusted, primarily in engines, power plants and heating systems. Known more commonly as fossil fuels, the hydrocarbons humans burn are coal, natural gas and petroleum products. If combustion were 100 percent efficient and all hydrocarbons contained only hydrogen and carbon, the sole byproducts would be water and carbon dioxide. There are unintended waste products, however, and they cause environmental harm. Even carbon dioxide, which is a natural part of the atmosphere, becomes a pollutant when released in excessive amounts. The environmental liabilities associated with hydrocarbons provide incentives for the development of alternative energy sources.
Polycyclic Aromatic Hydrocarbons
The incomplete combustion of hydrocarbons, especially coal and diesel fuel, causes the release of altered hydrocarbons. These hydrocarbon pollutants, known collectively as polycyclic aromatic hydrocarbons, take a variety of forms. Some are quite toxic, known to harm aquatic life and cause cancer.
Oxides of Carbon, Nitrogen and Sulphur
Incomplete combustion of hydrocarbons also results in carbon monoxide pollution. An odorless, colorless gas, carbon monoxide causes headaches and complications for people with heart disease. Carbon dioxide is always released when hydrocarbons are burned. It is a leading cause of global climate change and the acidification of oceans. Combustion of oil and coal, in particular, causes the release of nitrogen oxides and sulfur dioxide. These oxides combine with water and oxygen in the atmosphere, creating nitric and sulfuric acids, which return to Earth's surface as acid deposition, or "acid rain." Acid deposition harms aquatic organisms and kills trees. Because it makes certain nutrients, such as calcium and phosphorus, less available to plants, it reduces the productivity of ecosystems and farms. An additional problem associated with nitrogen oxides is that they, along with hydrocarbon pollutants, contribute to the formation of tropospheric ozone, a major component of smog.