Jeffrey Cook, age 11, of Tucson, Ariz.,
How do they get gasoline?
An active oil field is a forest of stately derricks and solemn pumps, all working to extract petroleum from the ground. The petroleum is piped to a cluster of strange buildings ‑ sturdy domes and giant bubbles, stacks of tall towers and mazes of metal pipes. This Martian city is an oil refinery, working to extract crystal‑clean gasoline from the dark, syrupy petroleum.
T o the oil man, petroleum is crude oil, ready to be separated into gasoline, lubricating oils, kerosene, paraffin wax and a host of other useful substances. T o the chemist, it is a complex hydrocarbon made from atoms of hydrogen and carbon. Various molecules are made from different combinations of these atoms and linked together in long chains. Gasoline is a mixture of molecules which contain from 12 to 20 atoms of hydrogen and from six to 10 atoms of carbon. Other molecules in petroleum contain 50 atoms or more.
The different compounds are called fractions and all of them are mixed together in the crude oil which comes from the ground. The work of the oil refinery is to separate the useful fractions, such as gasoline, and remake some of the less useful ones. Some of the processes used are distillation, cracking, polymerization and hydrogenization and they are as complex as their names suggest.
Distillation requires heat and it works because each fraction has its own boiling point, the temperature at which the liquid becomes vapor. The crude oil is piped into a tall metal tower and heated from below, The fraction with the lowest boiling point turns to vapor first and rises to the top of the tower. There it is run off through a pipe and chilled to liquid. The fractions with higher boiling points collect at lower levels in the tower.
The gasoline fraction vaporizes at between 80 and 220 centigrade degrees and rises high in the tower. Below it is the kerosene which vaporizes at between 204 and 300 degrees. Then come the fuel oils. The heavy lube oils collect at lower levels. After this general separations each fraction may be refined and purified again and again.
Some of the less useful fractions are re‑.made into gasoline. Larger molecules are cracked or broken down and smaller molecules polymerized or joined together to make gasoline. Cracking may be done under heat and pressure or by using a catalyst. The catalyst used to break the larger mclecules of petroleum into molecules of gasoline is usually a compound of aluminum and silica. Smaller molecules, often from waste gases, are made into gasoline under heat and pressure. In‑the hydrogenization process, hydrogen is added to molecules which need only an atom or two of this gas to become atoms of gasoline.
The refinery also must separate impurities mixed with the valuable fractions in the crude oil. Acids and sulphur are removed by various chemical processes. Clays and muddy sludge are removed by complex filter systems. ,Many of these complicated Jobs are done automatically and a sizable oil refinery can process 300,000 barrels of crude oil in a single day.