Omar Khalid
Plastics are derived from natural, organic materials such as cellulose, coal, natural gas, salt, and crude oil. Crude oil is a finite fossil fuel made from animal and plant matter that has endured heat and pressure underground for millions of years. The largest crude oil reserves as of 2023 are in Venezuela, Saudi Arabia, and Iran. Crude oil is a complex mixture of thousands of compounds and needs to be processed before it can be used to create plastic. This process, called fractional distillation, breaks the oil into smaller pieces called fractions. One of these fractions, naphtha, is the crucial compound for the production of plastics. Naphtha is composed of many different hydrocarbons, including ethane and propene, which are the critical components of synthetic plastics. The next step in the process is called polymerisation, in which simple molecules like ethylene and propylene are chemically bonded into chains.
| Characteristics | Values |
|---|---|
| Molecules from crude oil that become plastics | Naphtha, ethylene, propylene, ethane, and propene |
| Crude oil distillation products | Petroleum, gasoline, paraffin, kerosene, naphtha, light oil, heavy oil |
| Crude oil distillation process | Heating oil in a furnace, separating hydrocarbons by molecular weight, and feeding them into a distillation tube |
| Plastic production process | Polymerisation, polycondensation |
| Plastic composition | Polymers, monomers |
| Polymer composition | Carbon and hydrogen |
| Plastic types | Synthetic plastics, bio-based plastics |
| Synthetic plastic sources | Crude oil, natural gas, coal |
| Bio-based plastic sources | Carbohydrates, fats, oils, cornstarch, vegetable fats, bacteria |
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What You'll Learn
Crude oil is heated and separated into fractions
Crude oil is a complex mixture of thousands of compounds that need to be processed. It is composed of hydrocarbons and other organic matter that has endured heat and pressure underground for millions of years.
Crude oil is heated to around 600 degrees Celsius (1112 Fahrenheit) in a furnace and then sent to a distillation unit. This process is called fractional distillation, which breaks the oil into smaller pieces called fractions. The distillation column is filled with trays or plates that collect the liquids as the vapour condenses. The trays collect the various liquid fractions, which then follow pipework outside the column. The collected liquid fractions may pass to condensers, which cool them further, and then go to storage tanks, or to other areas for further chemical processing.
The fractions contain hydrocarbons, including gasoline, kerosene, diesel fuel, bitumen (or asphalt), lubricating oil, residual fuel oil, and naphtha—the chemical that goes on to become plastic. Naphtha is composed of many different hydrocarbons, including ethane and propene, which are the critical components of synthetic plastics.
Synthetic plastics are derived from crude oil, natural gas, or coal, while bio-based plastics come from renewable products such as carbohydrates, fats, and oils. The largest group of plastics is synthetic plastics, which are made with petroleum in China, Europe, Southeast Asia, and Japan.
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Naphtha, a crucial fraction, is further decomposed
Naphtha is a crucial fraction of crude oil that is further decomposed to produce plastics. It is a flammable liquid hydrocarbon mixture that is separated from crude oil through fractional distillation. This process involves heating the crude oil to vaporize it and then feeding it into the bottom of a distillation tower. As the vapour rises through the tower, the temperature decreases, causing certain hydrocarbons to condense and run off at different levels. This results in the separation of crude oil into several distinct groups of chemicals, including naphtha.
Naphtha is composed of many different hydrocarbons, including ethane and propene, which are critical components of synthetic plastics. To produce plastics, naphtha undergoes a process called steam cracking, which breaks it down into its component compounds. This is followed by polymerization, where simple molecules like ethylene and propylene are chemically bonded into chains to form plastics.
Naphtha can be further classified into light and heavy naphtha based on its boiling point. Light naphtha has a boiling point between 30 and 90 °C and consists of molecules with 5-6 carbon atoms. Heavy naphtha, on the other hand, has a boiling point between 90 and 200 °C and consists of molecules with 6-12 carbon atoms. Heavy naphtha is a crude oil fraction that generally contains cycloalkane and alkane, and sometimes aromatics.
The treatment process is then applied to refine the fraction by removing contaminants such as sludge, sulfur, and paraffin. This results in standardized quality naphtha that can be used in various manufacturing processes. Naphtha is a crucial feedstock not only for plastic production but also for the synthesis of other synthetic materials, solvents, fuels, and rubbers.
Overall, the decomposition of naphtha through processes like distillation, cracking, and polymerization plays a vital role in the production of plastics and other synthetic materials, making it a crucial step in the utilization of crude oil.
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Naphtha forms ethylene and propylene
Naphtha is a crucial compound in the process of making plastic. It is a chemical that is separated from crude oil through fractional distillation, which involves heating the oil to 600-750 degrees Fahrenheit. Naphtha is composed of many different hydrocarbons, including ethane and propene, which are essential components of synthetic plastics.
To create the monomers (basic building blocks of polymers) needed for plastic production, naphtha undergoes a process called steam cracking. This process breaks naphtha down into ethane and propene, which are then further broken down into simpler molecules like ethylene and propylene. These molecules are then chemically bonded to form chains, a process known as polymerization.
The thermal cracking of naphtha to produce ethylene is energy-intensive, requiring up to 40 GJ of heat per tonne of ethylene produced. It also leads to the formation of coke and nitrogen oxide (NOx), as well as carbon dioxide (CO2) emissions. To address these issues, an alternative process called redox oxy-cracking (ROC) has been proposed. This two-step process involves the selective combustion of hydrogen (H2) from naphtha cracking using a redox catalyst, followed by the re-oxidation of the catalyst by air to release heat for the cracking reactions. The ROC process can significantly reduce energy consumption and CO2 and NOx emissions while increasing the yield of ethylene and propylene.
The demand for propylene and ethylene is high, with propylene demand increasing faster than ethylene demand before the 2008-2009 recession. Steam cracking of naphtha and gas oils is a traditional method for producing propylene, contributing about 60% of the global propylene demand. However, the P/E (propylene/ethylene) ratio indicates that heavier feeds produce a higher ratio of propylene to ethylene, and the demand for propylene is expected to exceed the P/E ratios produced by cracking naphtha and gas oil feedstocks. This has led to a focus on investing in on-purpose propylene production (OPP) technology.
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Ethylene and propylene are bonded into chains
Crude oil is a fossil fuel that is made from animal and plant matter that has endured heat and pressure underground for millions of years. It is a finite resource, with the global supply expected to last only through 2050. Crude oil is extracted and sent to refineries, where it is heated to high temperatures and distilled. This process, called fractional distillation, breaks the oil into smaller pieces called fractions. These fractions contain hydrocarbons, including gasoline, kerosene, diesel fuel, bitumen, lubricating oil, residual fuel oil, and naphtha.
Naphtha is a crucial compound in the creation of plastics. It is composed of many different hydrocarbons, including ethane and propene, which are the critical components of synthetic plastics. A process called steam cracking breaks the naphtha down into these components.
The next step in the process is called polymerisation, in which simple molecules like ethylene and propylene are chemically bonded into chains. Ethylene (IUPAC name: ethene) is a hydrocarbon with the formula C2H4 or H2C=CH2. It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon–carbon double bonds). Propylene has a similar structure, with the formula CH2=CH-CH2.
During polymerisation, the double bonds in ethylene and propylene molecules are opened so that one single bond can be used to link to a carbon atom of another molecule. In this way, thousands of molecules can be joined together, or copolymerised, to produce very long chain-like ethylene-propylene molecules. These molecules can also include dienes, which are hydrocarbons with two pairs of carbon atoms joined by a double bond. The resulting copolymers are known as EPM (ethylene-propylene monomer) or EPDM (ethylene-propylene-diene monomer).
The polymerisation process generates thick, viscous substances known as resins, which are used to make plastic products. For example, when ethylene is subjected to heat, pressure, and a catalyst, it joins together into long, repeating carbon chains, forming a plastic resin called polyethylene (PE).
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The process is called polymerisation
The process of turning crude oil into plastic is called polymerisation. Crude oil is a fossil fuel made from animal and plant matter that has endured heat and pressure underground for millions of years. It is a finite resource, with the global supply expected to last only until 2050.
The process of polymerisation involves reacting monomer molecules together to form polymer chains or three-dimensional networks. Monomers are small molecules that are the basic building blocks of polymers. Polymers, on the other hand, are molecules comprising many repeating units, giving plastics qualities such as flexibility, malleability, and strength. The name 'polymer' comes from the Greek 'polymeres', meaning 'having many parts'.
There are two major types of polymerisation: addition polymerisation and condensation polymerisation. In addition polymerisation, monomers are added together to form polymers, and in condensation polymerisation, monomers condense together to form polymers with by-products. An example of addition polymerisation is the formation of polyethylene from ethylene molecules. In this reaction, the double bond in each ethylene molecule opens up, and two of the electrons originally in this bond are used to form new carbon-carbon single bonds with two other ethylene molecules. An example of condensation polymerisation is the formation of nylon-6,6 from hexamethylene diamine and adipic acid.
There are also two main classes of polymerisation reaction mechanisms: step-growth and chain-growth. The former is often easier to implement but requires precise control of stoichiometry, while the latter more reliably affords high molecular-weight polymers but only applies to certain monomers.
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Frequently asked questions
The first step is the extraction of raw materials, which are largely crude oil and natural gas, but also coal.
The raw materials are then heated in a furnace and sent to a distillation unit, where they are separated into lighter components called fractions. One of these fractions, called naphtha, is the crucial compound for making plastic.
The final step is called polymerisation, where simple molecules like ethylene and propylene are chemically bonded into chains.
