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© Photo: Alan Clements
A complete petrochemical plant site at Teesside, England.

Petrochemicals are chemical products made from the hydrocarbons present in raw natural gas and petroleum crude oil. The largest petrochemical manufacturing industries are to be found in the United States of America, Western Europe, Asia and the Middle East.

A relatively small number of hydrocarbon feedstocks form the basis of the petrochemical industries, namely methane, ethylene, propylene, butanes, butadiene, benzene, toluene and xylenes.[1][2]

As of 2007, there were 2,980 operating petrochemical plants in 4,320 locations worldwide.[3] The petrochemical end products from those plants include plastics, soaps, detergents, solvents, paints, drugs, fertilizer, pesticides, explosives, synthetic textile fibers and rubbers, flooring and insulating materials and much more.

Petrochemicals are found in such common consumer products as aspirin, cars, clothing, compact discs, video tapes, electronic equipment, furniture, and a great many others.[4]

Feedstocks sources

(PD) Image: Milton Beychok
Petrochemical feedstock sources.

The adjacent diagram schematically depicts the major hydrocarbon sources used in producing petrochemicals are:[1][2][5][6]

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:

  • Ethylene
  • Propylene
  • Butenes and butadiene
  • Benzene

In 2007, the amounts of ethylene and propylene produced in steam crackers were about 115 Mt (megatonnes) and 70 Mt, respectively.[7] The output ethylene capacity of large steam crackers ranged up to as much as 1.0 – 1.5 Mt per year.[8][9]

Steam crackers are not to be confused with steam reforming plants used to produce hydrogen and ammonia.

Worldwide usage of optional steam cracking feedstock sources

As of 2004, the percentage of the worldwide steam cracking plants using each of the optional steam cracking feed sources was:[10]

  • Ethane: 35%
  • Propane: 9%
  • Butanes: 3%
  • Naphtha: 45%
  • Gas oil: 5%
  • Other: 3 %

The effect of feedstock on the steam cracking yields of intermediate petrochemical products

The effect of feedstock selection upon the yields of steam cracking products is summarized in the table below:

Steam cracking feedstocks versus yields of intermediate petrochemical products[2]
  Product Yields
weight %
weight %
weight %
Aromatics (a)
Other (b)
weight %
Ethane 84.0 1.4 1.4 0.4 12.8
Propane 45.0 14.0 2.0 3.5 35.5
Butane 44.0 17.3 3.0 3.4 32.3
Naphtha (c) 34.4 14.4 4.9 14.0 32.3
Gas oil (d) 25.5 13.5 4.9 12.8 43.3
(a) Includes benzene, toluene, xylenes and any other aromatics.

(b) Includes hydrogen, methane, butenes, non-aromatic portion of pyrolysis gasoline and fuel oil.
(c) Full-range naphtha (as differentiated from light or heavy naphtha).
(d) The portion of petroleum crude oil that has a boiling range of about 250 to 550 °C (480 to 1020 °F).
That encompasses the boiling range of atmospheric gas oil (AGO) produced by the atmospheric distillation
of petroleum crude oil and the boiling range of vacuum gas oil (VGO) produced by the vacuum distillation
of petroleum crude oil.

Feedstocks and example petrochemical products

The table below includes some representative examples of the petrochemical end products produced from the eight hydrocarbon feedstocks – methane, ethylene, propylene, butenes, butadiene, benzene, toluene and xylenes:

Feedstocks and example petrochemical products
methane ethylene propylene butenes and butadienes benzene toluene xylenes
hydrogen polyethylene polypropylene styrene-butadiene rubber (SBR) styrene benzoic acid phthalic anhydride
ammonia ethanol isopropanol methyl tert-butyl ether (MTBE) polystyrene toluene diisocyanate polyesters
methanol ethylene glycol propylene glycol polybutadiene phenol polyurethanes dimethyl terephthalate
methyl chloride vinyl acetate allyl chloride acrylonitrile-butadiene-styrene (ABS) cumene caprolactam terephthalate acid
carbon black perchloroethylene acrylonitrile polybutenes aniline nylons polyethylene terephthalate
acetylene polyvinyl acetate acrylic acid methyl ethyl ketone (MEK) adipic acid polyureas dioctyl phthalate
formaldehyde glycol ethers epoxy resins tert-butanol nylons  

The chemicals that can be produced from each of the major petrochemical feedstocks can be depicted as "network diagrams". For example, these are the network diagrams for the chemicals that may be derived from ethylene and from propylene as the petrochemical feedstocks:

(CC) Diagram: Milton Beychok
Petrochemicals that may be produced from ethylene.
(CC) Diagram: Milton Beychok
Petrochemicals that may be produced from propylene.

As another example, this is the network diagram for the chemicals that may be derived from benzene as the petrochemical feedstock:

(CC) Diagram: Milton Beychok
Petrochemicals that may be produced from benzene.

As more examples, these are the network diagrams for the chemicals that may be derived from toluene and from xylenes as the petrochemical feedstocks:

(CC) Diagram: Milton Beychok
Petrochemicals that may be produced from toluene.
Petrochemicals that may be produced from xylenes.


  1. 1.0 1.1 Sami Matar and Lewis F. Hatch (2001). Chemistry of Petrochemical Processes. Gulf Professional Publishing. ISBN 0-0-88415-315-0. 
  2. 2.0 2.1 2.2 Staff (March 2001). "Petrochemical Processes 2001". Hydrocarbon Processing: pp. 71-246. ISSN 0887-0284.
  3. Petrochemical Industry – Worldwide
  4. Petrochemicals Chart From the website of the National Petrochemical & Refiners Association
  5. SBS Polymer Supply Outlook
  6. Jean-Pierre Favennec (Editor) (2001). Petroleum Refining: Refinery Operation and Management. Editions Technip. ISBN 2-7108-0801-3. 
  7. 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. Elsevier Science, pp. 402-414. ISBN 0-444-53292-7. 
  8. Crackers capacities From the website of the Association of Petrochemicals Producers in Europe (APPE)
  9. Steam Cracking: Ethylene Production (PDF page 3 of 12 pages)
  10. Richard Meyers (2003). The Basics of Chemistry. Greenwood Press. ISBN 0-313-31664-3.