1-Hexene

1-hexene is a higher olefin, or alkene, with a formula C₆H₁₂. 1-hexene is an alpha-olefin, meaning that the double bond is located at the alpha (primary) position, endowing the compound with higher reactivity and thus useful chemical properties. 1-hexene is an industrially significant linear alpha olefin.

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Synthesis

Industrially, 1-hexene is commonly manufactured by two main routes: oligomerization of ethene and by Fischer-Tropsch synthesis followed by purification. Another route to 1-hexene, used commercially on small scale, is dehydration of alcohols. Prior to the 1970's 1-hexene was also manufactured by the thermal cracking of waxes. Linear internal hexenes were manufactured by chlorination/dehydrochlorination of linear paraffins.

There are five commercial processes which oligomerize ethene to 1-hexene. Four of these processes produce 1-hexene as a part of a wide distribution of alpha-olefins. Typically, 1-hexene content ranges from about twenty percent distribution in the Ethyl (Innovene) process, whereas only twelve percent of distribution in the Gulf (CP Chemicals) and Idemitsu processes.

The only commercial process to isolate 1-hexene from a wide mixture of C₆ hydrocarbons is practiced by Sasol Ltd., a South African oil and gas and petrochemical company. Sasol commercially employs Fischer-Tropsch synthesis to make fuels from synthesis gas derived from coal. The synthesis recovers 1-hexene from the afformentioned fuel streams, where the initial 1-hexene concentration cut may be 60% in a narrow distillation, with the remainder being vinylidenes, linear and branched internal olefins, linear and branched paraffins, alcohols, aldehydes, carboxylic acids and aromatic compounds.

Synthesis of 1-hexene as a part of multi-product ethene oligomerization process or a Fischer-Tropsch process is covered in an article on Linear alpha olefins.

One process, the Phillips ethene trimerization process, produces only 1-hexene.

Applications

The primary use of 1-hexene is as a comonomer in production of polyethene. High density polyethene (HDPE) and linear low density polyethene (LLDPE) use approximately 2-4% and 8-10% of comonomers.

Another significant use of 1-hexene is the production of linear aldehyde via hydroformylation ( oxo synthesis ) for later production of the short-chain fatty acid heptanoic acid.

References