Chemical News

Monday, December 17, 2007

“On-purpose” 1-octene process is under development

Manufacturers use 1-octene primarily as a comonomer for making linear low-density polyethylene. The current technology standard for producing linear α-olefins such as 1-octene is based on ethylene oligomerization. However, the relatively fixed distribution of full-range oligomerization products creates supply–demand imbalances and requires comonomer producers to cross-subsidize the lower-value products in their sales schemes.


A third “on-purpose” 1-octene process is under development. Manufacturers use 1-octene primarily as a comonomer for making linear low-density polyethylene. The current technology standard for producing linear α-olefins such as 1-octene is based on ethylene oligomerization. However, the relatively fixed distribution of full-range oligomerization products creates supply–demand imbalances and requires comonomer producers to cross-subsidize the lower-value products in their sales schemes.

Sasol’s coal-based high-temperature Fischer–Tropsch (F–T) technology produces an Anderson–Schulz–Flory distribution of hydrocarbons with high α-olefin content. Sasol commissioned its first commercial on-demand 1-octene plant in Secunda, South Africa, in 1998. Depletion of the 1-octene capacity of Sasol’s Secunda complex, coupled with rapidly increasing global demand for 1-octene, has spurred the search for alternative “on-purpose” production routes to 1-octene. The Sasol F–T process is the only 1-octene on-purpose process in commercial operation.

Sasol has a second synthesis gas–based process that produces 1-octene from 1-heptene. The product from its Secunda complex is rich in α-olefins of all carbon numbers (odd and even) from ethylene through 1-decene. This product stream is prefractionated to provide a C7 stream that the manufacturer further purifies to give 1-heptene, which then undergoes hydroformylation to produce aldehydes. Sasol then hydrogenates the aldehyde mixture to 1-octanol, and, in the final step of the 1-heptene-based process, dehydrates 1-octanol to produce 1-octene. The plant for this process is currently under construction.

A third approach to 1-octene production under development by Sasol is selective ethylene tetramerization. K. Blann and 10 co-inventors disclose catalysts that are effective for tetramerizing ethylene in ~50–65% selectivity. The other major product is 1-hexene, also a valuable α-olefin comonomer.

Here is a description of the best results given in the patent: The inventors prepared a solution of 16.4 mg of the ligand (4-MeOC6H4)2PN(i-Pr)P(4-MeOC6H4)2 in 10 mL of toluene and added it to a solution of 5.2 mg Cr(III) acetylacetonate in 10 mL of toluene. They stirred the solution for 5 min, then transferred it to a pressure vessel containing 80 mL of toluene and 4.5 mmol of modified methylaluminoxane at 40 ˚C. They charged the reactor with hydrogen at 250 kPa and then with ethylene at 4500 kPa.

The inventors terminated the reaction after 15 min and then analyzed the products. They obtained 82.71 g of product, and of this only 1.46 g was solid polyethylene. The liquid fraction contained 63.2% octenes and 32.6% hexenes. The octene fraction consisted of 98% of the desired 1-octene.

Source: ACS/Sasol

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