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.
Two petrochemical classes are olefins including ethylene and propylene, and aromatics including benzene, toluene, and xylene isomers. Oil refineries produce olefins and aromatics by fluid catalytic cracking of petroleum fractions. Chemical plants produce olefins by steam cracking of natural gas liquids like ethane and propane. Aromatics are produced by catalytic reforming of naphtha. Olefins and aromatics are the building-blocks for a wide range of materials such as solvents, detergents, and adhesives. Olefins are the basis for polymers and oligomers used in plastics, resins, fibers, elastomers, lubricants, and gels.12
Global ethylene and propylene production are ~115 million tonnes and ~70 million tonnes per annum, respectively. Aromatics production is ~70 million tonnes. The largest petrochemical industries are located in the USA and Western Europe; however, major growth in new production capacity is in the Middle East and Asia. There is substantial inter-regional petrochemical trade.
Primary petrochemicals are divided into three groups depending on their chemical structure:
- Olefins includes ethylene, propylene, and butadiene. Ethylene and propylene are important sources of industrial chemicals and plastics products. Butadiene is used in making synthetic rubber.
- Aromatics includes benzene, toluene, and xylenes. Benzene is a raw material for dyes and synthetic detergents, and benzene and toluene for isocyanates MDI and TDI used in making polyurethanes. Manufacturers use xylenes to produce plastics and synthetic fibers.
- Synthesis gas is a mixture of carbon monoxide and hydrogen used to make ammonia and methanol. Ammonia is used to make the fertilizer urea and methanol is used as a solvent and chemical intermediate.
The prefix "petro-" is an arbitrary abbreviation of the word "petroleum"; since "petro-" is Ancient Greek for "rock" and "oleum" means "oil". Therefore, the etymologically correct term would be "oleochemicals". However, the term oleochemical is used to describe chemicals derived from plant and animal fats.
- Methane, ethane, propane and butanes: Obtained primarily from natural gas processing plants.
- Naphtha obtained from petroleum refineries.
- Benzene, toluene and xylenes, as a whole referred to as BTX and primarily obtained from petroleum refineries by extraction from the reformate produced in catalytic reformers.
- Gas oil obtained from petroleum refineries.
Methane and BTX are used directly as feedstocks for producing petrochemicals. However, the ethane, propane, butanes, naphtha and gas oil serve as optional feedstocks for steam-assisted thermal cracking plants referred to as steam crackers that produce these intermediate petrochemical feedstocks:
- Butenes and butadiene
In 2007, the amounts of ethylene and propylene produced in steam crackers were about 115 Mt (megatonnes) and 70 Mt, respectively.5 The output ethylene capacity of large steam crackers ranged up to as much as 1.0 – 1.5 Mt per year.67
The following is a partial list of the major commercial petrochemicals and their derivatives:
- ethylene - the simplest olefin; used as a chemical feedstock and ripening stimulant
- polyethylene - polymerized ethylene
- ethanol - via ethylene hydration (chemical reaction adding water) of ethylene
- ethylene oxide - via ethylene oxidation
- vinyl acetate
- propylene - used as a monomer and a chemical feedstock
- isopropyl alcohol - 2-propanol; often used as a solvent or rubbing alcohol
- acrylonitrile - useful as a monomer in forming Orlon, ABS
- polypropylene - polymerized propylene
- propylene oxide
- acrylic acid
- allyl chloride -
- C4 hydrocarbons - a mixture consisting of butanes, butylenes and butadienes
- isomers of butylene - useful as monomers or co-monomers
- 1,3-butadiene (or buta-1,3-diene) - a diene often used as a monomer or co-monomer for polymerization to elastomers such as polybutadiene, styrene-butadiene rubber, or a plastic such as acrylonitrile-butadiene-styrene (ABS)
- synthetic rubbers - synthetic elastomers made of any one or more of several petrochemical (usually) monomers such as 1,3-butadiene, styrene, isobutylene, isoprene, chloroprene; elastomeric polymers are often made with a high percentage of conjugated diene monomers such as 1,3-butadiene, isoprene, or chloroprene
- higher olefins
- polyolefins such poly-alpha-olefins, which are used as lubricants
- alpha-olefins - used as monomers, co-monomers, and other chemical precursors. For example, a small amount of 1-hexene can be copolymerized with ethylene into a more flexible form of polyethylene.
- other higher olefins
- detergent alcohols
- benzene - the simplest aromatic hydrocarbon
- ethylbenzene - made from benzene and ethylene
- cumene - isopropylbenzene; a feedstock in the cumene process
- phenol - hydroxybenzene; often made by the cumene process
- acetone - dimethyl ketone; also often made by the cumene process
- bisphenol A - a type of "double" phenol used in polymerization in epoxy resins and making a common type of polycarbonate
- solvents - liquids used for dissolving materials; examples often made from petrochemicals include ethanol, isopropyl alcohol, acetone, benzene, toluene, xylenes
- cyclohexane - a 6-carbon aliphatic cyclic hydrocarbon sometimes used as a non-polar solvent
- adipic acid - a 6-carbon dicarboxylic acid, which can be a precursor used as a co-monomer together with a diamine to form an alternating copolymer form of nylon.
- caprolactam - a 6-carbon cyclic amide
- nitrobenzene - can be made by single nitration of benzene
- alkylbenzene - a general type of aromatic hydrocarbon, which can be used as a presursor for a sulfonate surfactant (detergent)
- toluene - methylbenzene; can be a solvent or precursor for other chemicals
- mixed xylenes - any of three dimethylbenzene isomers, could be a solvent but more often precursor chemicals
- ortho-xylene - both methyl groups can be oxidized to form (ortho-)phthalic acid
- para-xylene - both methyl groups can be oxidized to form terephthalic acid
- dimethyl terephthalate - can be copolymerized to form certain polyesters
- purified terephthalic acid - often copolymerized to form polyethylene terephthalate
- Petroleum products
- Instrumentation in petrochemical industries
- Organization of the Petroleum Exporting Countries
- Asia Petrochemical Industry Conference
- Sami Matar and Lewis F. Hatch (2001). Chemistry of Petrochemical Processes. Gulf Professional Publishing. ISBN 0-88415-315-0.
- Staff (March 2001). "Petrochemical Processes 2001". Hydrocarbon Processing: pp. 71–246. ISSN 0887-0284.
- SBS Polymer Supply Outlook
- Jean-Pierre Favennec (Editor) (2001). Petroleum Refining: Refinery Operation and Management. Editions Technip. ISBN 2-7108-0801-3.
- Hassan E. Alfadala, G.V. Rex Reklaitis and Mahmoud M. El-Halwagi (Editors) (2009). Proceedings of the 1st Annual Gas Processing Symposium, Volume 1: January, 2009 - Qatar (1st Edition ed.). Elsevier Science. pp. 402–414. ISBN 0-444-53292-7.
- Crackers capacities From the website of the Association of Petrochemicals Producers in Europe (APPE)
- Steam Cracking: Ethylene Production (PDF page 3 of 12 pages)
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