Betty Hess, age 13, of Henderson, Nev., for her question:
HOW IS PETROLEUM REFINED?
Petroleum comes from the earth as a dark liquid and from it man makes thousands of useful products. Petroleum is composed of thousands of different combinations of just two elements: hydrogen and carbon.
Refineries and chemical plants account for about a fifth of the industry's total investment in property and equipment. The United States has about 350 refineries that range in capacity from 40 to 165,000 barrels of oil a day.
The combinations of hydrogen and carbon are called hydrocarbons, and they give special characteristics to the fractions or parts of petroleum. Some of these fractions, such as gasoline and kerosene, are valuable products in themselves. Refineries must change other fractions of the petroleum before they can be used.
Separating the fractions and converting them to useful products are the chief jobs of an oil refinery. Distillation, or "fractionating," is the first step in the refining process. It separates the fractions of crude oil.
The fact that different hydrocarbons vaporize or boil at different temperatures makes possible the process of distillation. In a pipe still, oilmen start the distillation by running crude oil into pipes that pass through a furnace.
As the oil is heated, gasoline is one of the first fractions to vaporize. Kerosene is next. At higher temperatures, such fractions as diesel oil and lubricant stocks boil.
The mixture of hot vapors and liquid goes into a fractionating tower, or bubble tower. The vapor rises through the tower, which separates the fractions in a continuous process. Different fractions cool and condense at different levels in the tower and are drawn off. Heavy fuel oils condense at the bottom of the tower and gasoline condenses at the top.
In early times, the refining process consisted chiefly of distillation.
As automobiles became popular, the petroleum industry found new ways of changing less useful fractions into gasoline and other valuable products.
These products changed the molecules of the fractions by heating them under pressure, or by contact with a catalyst.
The chief conversion methods included thermal cracking, catalytic cracking, polymerization, alkylation, hydrogenation and reforming.
Thermal cracking is the application of steady heat and pressure to crack or break down heavier hydrocarbons into lighter ones such as gasoline. Catalytic cracking, sometimes called "cat cracking," uses a catalyst to help break down petroleum fractions.
A newer type of catalytic cracking, called fluid cat cracking, is the most widely used process. Refineries use it to produce aviation gasoline, raw materials for synthetic rubber and other petroleum products.
In fluid cat cracking, a powdered catalyst flows through the petroleum like a fluid. Refineries started using this method in 1942.