Editing Polyethylene (section)

==Manufacturing process==

===Monomer===
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The ingredient or [[monomer]] is [[ethylene]] ([[IUPAC]] name ethene), a [[gas]]eous [[hydrocarbon]] with the formula C<sub>2</sub>H<sub>4</sub>, which can be viewed as a pair of [[methylene group]]s (−{{chem|CH|2}}−) connected to each other. Typical specifications for PE purity are <5&nbsp;ppm for water, oxygen, and other [[alkene]]s contents. Acceptable contaminants include N<sub>2</sub>, ethane (common precursor to ethylene), and methane. Ethylene is usually produced from [[Cracking (chemistry)|petrochemical sources]], but is also generated by [[Ethanol#Dehydration|dehydration of ethanol]].<ref name="Ullmann"/>

===Polymerization===
[[File:CNX Chem 20 01 monomer.png|thumb|500x500px]]
Polymerization of ethylene to polyethylene is described by the following [[chemical equation]]:

: {{var|n}} {{chem|CH|2|{{=}}CH|2}} (gas) → {{chem|[−CH|2|−CH|2}}−{{chem|]|{{var|n}}}} (solid){{pad|2em}}[[Standard enthalpy of reaction|Δ{{var|H}}]]/{{var|n}}&nbsp;=&nbsp;{{convert|-25.71|+/-|0.59|kcal/mol|kJ/mol|abbr=on}}<ref>Victor Ostrovskii et al. [https://www.researchgate.net/publication/255729774_Ethylene_Polymerization_Heat Ethylene Polymerization Heat] (abstract) in Doklady Chemistry 184(1):103–104. January 1969.</ref>

Ethylene is a stable molecule that polymerizes only upon contact with catalysts. The conversion is highly [[exothermic]]. [[Coordination polymerization]] is the most pervasive technology, which means that metal chlorides or metal oxides are used. The most common catalysts consist of [[titanium(III) chloride]], the so-called [[Ziegler–Natta catalyst]]s. Another common catalyst is the [[Phillips catalyst]], prepared by depositing [[chromium trioxide|chromium(VI) oxide]] on silica.<ref name="Ullmann"/> Polyethylene can be produced through [[radical polymerization]], but this route has only limited utility and typically requires high-pressure apparatus.