Petrochemistry is a branch of chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

 that studies the transformation of crude oil (petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

) and natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 into useful products or raw materials. These petrochemicals have become an essential part of the chemical industry today.

Origin of Petroleum

It may be possible to make petroleum from any kind of organic matter under suitable conditions. The concentration of organic matter is not very high in the original deposits, but petroleum and natural gas evolved in places that favored retention, e.g., sealed-off porous sandstones. Petroleum, produced over millions of years by natural changes in organic materials, accumulates beneath the earth's surface in extremely large quantities.

Basics of Crude Oil

Crude oils are compounds that mainly consist of many different hydrocarbon compounds that vary in appearance and composition. Average crude oil composition is 84% carbon, 14% hydrogen, 1%-3% sulphur, and less than 1% each of nitrogen, oxygen, metals and salts.

Crude oils are distinguished as sweet' or sour, depending upon the sulphur content present. Crude oils with a high sulphur content, which may be in the form hydrogen sulphides, are called sour, and those with less sulphur are called sweet.


A process called fractional distillation separates crude oil into various segments. Fractions at the top have a lower boiling points than fractions at the bottom. The bottom fractions are heavy, and are thus "cracked" into more lighter and useful products.

Raw or unprocessed ("crude") oil is not useful as it comes directly from the ground. Though light sweet oil has been used directly as a burner fuel, these lighter fragments form explosive vapors in fuel tanks, and thus are dangerous. The oil must be separated into various parts and refined before used in fuels and lubricants, and before some of the byproducts form materials such as plastics, detergents, solvents, elastomers, and fibers such as nylon and polyesters.


The first oil commercial was set up in 1859, two years after which the first oil refinery was set up. The industry grew in the late 1940s. Demand for products from the petrochemical industry grew during the World War II. The demand for synthetic materials increased, and this rising demand was met by replacing costly and sometimes less efficient products with these synthetic materials. This caused petrochemical processing to develop into a major industry.

Before this, petrochemical industry was a tentative sector where various experiments could be carried out. The industry used basic materials: synthetic rubbers in the 1900s, Bakelite, the first petrochemical-derived plastic in 1907, the first petrochemical solvents in the 1920s, polystyrene in the 1930s. After that period, the industry produced materials for a large variety of areas—from household goods (kitchen appliances, textile, furniture) to medicine (heart pacemakers, transfusion bags), from leisure (running shoes, computers) to highly specialized fields like archaeology and crime detection.


Crude oil and natural gas are extracted from the ground, on land or under the oceans, with oil wells. Ships, trains, and pipelines transport extracted oils and gasses to refineries.

Refineries then execute processes that cause various physical and chemical changes in the crude oil and natural gas. This involves extremely specialized manufacturing processes. One of the important process is distillation, i.e., separation of heavy crude oil into lighter groups (called fractions) of hydrocarbons. There are two processes of distillation: CDU process and VDU process. The objective of the CDU process is to distill and separate valuable distillates(naphtha, kerosene, diesel) and atmospheric gas oil (AGO) from the crude feedstock. The technique used to carry out the above process is called complex distillation. On the other hand, the objective of the VDU process is to recover valuable gas oils from reduced crude via vacuum distillation. Two of the fractions of distillation are fuel oil and naphtha, which are familiar to consumers. Fuel oil, is used for heating for diesel fuel in automotive applications. Naphtha is used in gasoline and also used as the primary source for petrochemicals.

Refining is the processing of one complex mixture of hydrocarbons into a number of other complex mixtures of hydrocarbons. Refining is where the job of oil industry stops and that of petrochemical industry starts. The raw materials used in the petrochemistry industry are known as feedstocks. These are obtained from the refinery:naphtha, components of natural gas such as butane, and some of the by-products of oil refining processes, such as ethane and propane. These feedstocks then undergo processing through an operation called cracking.
Cracking is defined as the process of breaking down heavy oil molecules into lighter, more valuable fractions. There are two kinds: steam cracking and catalytic cracking. In steam cracking, high temperatures are used. Catalytic cracking is when a catalyst is being used. The plant where these operations are conducted is called a 'cracker'.
Once these operations complete, new products are obtained that serve as building blocks of the petrochemical industry: olefins, i.e., mainly ethylene, propylene, and the so called C4 derivatives, including butadiene—and aromatics, so called because of their distinctive perfumed smell, i.e., mainly benzene, toluene and the xylenes.

Then petrochemicals go through various processes that eventually contribute to the final output of products like plastics, soaps and detergents, healthcare products like aspirin, synthetic fibres for clothes and furniture, rubbers, paints, insulating materials etc.


The global demand for petrochemical products continuously rises. One of the major concerning issues in today's world is the dependence of the modern society on oil and gas and various other petroleum products. Besides this, there are problems relating to the increasing scarcity of workable hydrocarbon deposits and global warming.
Thus, solutions must be found in the next few years. For example, we need to make more efficient use of the energy available and use more renewable energy sources in addition to hydrocarbons.

See also

  • Oil refinery
    Oil refinery
    An oil refinery or petroleum refinery is an industrial process plant where crude oil is processed and refined into more useful petroleum products, such as gasoline, diesel fuel, asphalt base, heating oil, kerosene, and liquefied petroleum gas...

  • Petrochemical
    Petrochemicals are chemical products derived from petroleum. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sources such as corn or sugar cane....

  • Petroleum product
    Petroleum product
    Petroleum products are useful materials derived from crude oil as it is processed in oil refineries.According to crude oil composition and demand, refineries can produce different shares of petroleum products. The largest share of oil products is used as energy carriers: various grades of fuel...

  • Cracking (chemistry)
    Cracking (chemistry)
    In petroleum geology and chemistry, cracking is the process whereby complex organic molecules such as kerogens or heavy hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products...

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