Chapter 22: Hydrocarbon Compounds

Cracking

A controlled process by which hydrocarbons are broken down r rearranged into smaller, more useful molecules. For example, fractions containing compounds of higher molar mass are "cracked" to produce the more useful short-chain components of gasoline and kerosene. Hydrocarbons are cracked with the aid of a catalyst and heat to produce low molar mass alkanes.

Coal Distillation

Coal may be distilled to obtain a variety of products: coal gas, coal tar, ammonia, and coke. Coke is the solid material left after coal distillation. It is used as a fuel in many industrial processes and is the crucial reducing agent in the smelting of iron ore. Coal gas consists mainly of hydrogen, methane, and carbon monoxide. Coal tar can be distilled further into benzene, toluene, naphthalene, phenol, and pitch. The ammonia from distilled coal is converted into ammonium sulfate for use as a fertilizer.

Natural Gas

Composed of about 80% methane, 10% ethane, 4% propane, and 2% butane. The remaining 4% consists of nitrogen and hydrocarbons of higher molar mass. Natural gas also contains a small amount of helium. Propane and butane are separated by liquefaction and sold in liquid form in pressurized tanks as liquid petroleum gas (LPG).

Petroleum and Crude Oil

Composed of mostly straight-chain and branched-chain alkanes. Also contains small amounts of aromatic compounds and sulfur-, oxygen-, and nitrogen- containing compounds. Crude oil is a mixture of hydrocarbons having anywhere from 1 to more than 40 carbon atoms.

Coal Composition

Consists largely of condensed aromatic compounds of extremely high molar mass. Due to the high proportion of carbon compounds, coal leaves more soot when burned than the more aliphatic fuels obtained from petroleum. Coal also contains a small amount of sulfur which oxidizes to form SO2 and SO3 when coal burns. In order to reduce air pollution, the majority of sulfur is removed before burning.

Refining

Crude oil is refined into parts called fractions. Petroleum refining begins with the distillation of crude oil into fractions according to boiling point.

Coal formation

First stage is an intermediate material known as peat. Peat is a soft, brown, spongy, fibrous material with a high water content. After it drys, it produces a low-cost but smoky fuel. Second stage is lignite (brown coal) which is much harder than peat but still has a high water content. Third stage is bituminous coal (soft coal) which is harder than lignite and has a lower water content and higher carbon content. Fourth stage is anthracite (hard coal) which has a carbon content that exceeds 85%, making it an excellent fuel source. Coal is classified by its hardness and carbon content.