How is Petroleum Used to Make Plastic?

The process of converting petroleum and natural gas into plastic involves a series of chemical reactions known as polymerization. These reactions allow for the creation of a wide range of plastic materials with diverse attributes, all driven by the intricate world of organic chemistry. The polymerization process can be simple or complex, but it primarily involves the manipulation of hydrocarbons to produce various plastic types.

Raw Materials and Energy Requirements

Petroleum and natural gas are the primary sources for the carbon and hydrogen needed in plastic production. These raw materials are essential as they are the backbone of synthetic polymers. However, the process may also require additional chemicals to provide necessary elements such as oxygen, nitrogen, or chlorine. Moreover, petroleum can provide the energy needed for the chemical processing involved in making plastics. This dual role as both a raw material and an energy source is crucial in the manufacturing of plastics.

Recycling and Pyrolysis

Interestingly, there is a correlation between the use of petroleum in plastic production and its potential use as a fuel. A study suggests that approximately one gallon of petroleum distillates can be recovered from every 8 and 1/3 pounds of waste plastics, based on the pyrolysis process. While the distillates may need refining or re-refining to be marketable as fuel, the pyrolysis process also demonstrates the potential for recycling waste plastic into useful materials.

Common Misconceptions

It's important to clear up some common misconceptions about the production of plastic. Contrary to popular belief, plastics are not indeed made from oil residue or crude oil. The key molecule in plastic production is a gas called ethylene, also known as ethene. Ethylene is derived from a process where naphta, a type of crude gasoline, is treated with very hot steam at 800C°, resulting in a mixture of unsaturated hydrocarbons. The ethene is then separated and further purified to ensure it is of high quality for plastic production.

In recent years, a more cost-effective method has been adopted in North America, where ethane is used instead of naphta. This results in a product that requires less purification before polymerization. The ethylene gas undergoes polymerization through various methods, often involving high pressures and catalysts, to produce polyethylene granules. Other plastic types are made in a similar fashion, using small molecule unsaturated hydrocarbons known as olefins as intermediates.