Petrochemicals

Petrochemicals are derived from a variety of sources, including coal and natural gas, though the majority of the petrochemicals we use today are made from petroleum. Understanding how petroleum—also known as crude oil—is transformed into petrochemicals begins with a basic understanding of petroleum itself. Petroleum is found deep in the Earth's crust, beneath land and ocean alike, and it is formed from decaying plant and animal matter. While not considered a chemical compound in and of itself, petroleum is instead composed of scores of individual chemical compounds, all of which contain carbon and hydrogen atoms, which are referred to as hydrocarbons. These hydrocarbons can either be simple or quite complex, ranging from a few atoms to nearly 100 atoms. Once petroleum is extracted from the Earth, it is sent, via pipeline or ship, to refineries. Through various physical and chemical processes, such as fractional distillation—which is the heating of petroleum to different temperatures in order to “boil off” specific hydrocarbons—refineries alter the petroleum so that the more complex hydrocarbons can be separated from the less complex ones. The resulting compounds are known as fractions, and it is from these fractions that petrochemicals are derived.

Petrochemicals are derived from coal, natural gas, and petroleum and converted into useful compounds in refineries like this one. A mere handful of petrochemicals contains the building blocks for creating more than 4,000 other compounds and products.

These initial fractions, often referred to as feedstocks, include gasoline, kerosene, diesel oil, lubricating oils, and heavy gas oils. In the fractional distillation tower, the lighter, shorter-chained hydrocarbons, like gasoline and kerosene, make their way to the top, while the heavier, longer-chained hydrocarbons settle near the bottom. These heavier hydrocarbons—the lubricating and heavy gas oils—are converted into other chemical compounds through a process known as cracking. Cracking uses heat and steam, and sometimes a catalyst, to alter the molecular structure of these heavier fractions into an assortment of simpler fractions, or petrochemicals; these petrochemicals now become the feedstocks used for creating an astounding array of other chemical compounds and products. Petrochemical feedstocks fall into one of three following classes:

• Olefins: propylene, ethylene, and butadiene
• Aromatics: benzene, toluene, and xylene
• Synthesis gas: used to make ammonia and methanol

This handful of petrochemicals, in combination with each other or with other chemicals, contains the building blocks for creating more than 4,000 other compounds and products. [Page 365]In the nearly 100 years since petrochemical manufacture began in earnest, these petroleum-derived compounds have profoundly impacted almost everything we interact with in our daily lives, including clothes, food, cosmetics, plywood, water hoses, food packaging, artificial limbs, paint, disposable diapers, crayons, water and soda bottles, toothpaste, flooring, blankets, building insulation, heart valves, candles, fertilizers, surgical gloves, kitchenware, toys—the list goes on and on. It is no exaggeration to say that petrochemicals are found in nearly every conventionally made product found inside and outside our homes.