Patent Watch

February 6, 2012

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Oligomerize ethylene to 1-hexene and 1-octene. Sasol is building a first-of-its kind plant for making 1-hexene and 1-octene in Lake Charles, LA. This plant will use Sasol’s recently developed ethylene trimerization–tetramerization process to make 100,000 t/year of a 1-hexene–1-octene mixture. These olefins are used as comonomers for manufacturing linear low-density polyethylene.

Sasol is already in the 1-hexene–1-octene business because of their proprietary technology for extracting them from their coal-derived synthetic fuel streams in Secunda, South Africa. This is an inexpensive source of the olefins, but production is limited to the amounts available from the synthetic fuel streams. Demand is greater than production, so to increase its capacity, Sasol developed a unique catalyst system that can oligomerize ethylene to 1-hexene and 1-octene.

A. Bollmann, H. Maumela, and K. Blann disclose catalyst systems that promote ethylene trimerization and tetramerization. In one example, a solution 0.015 mmol Ph2PN(i-Pr)P Ph2 (the tetramerization ligand) and 0.015 mmol (o-EtC6H4)2PNMeP(o-EtC6H4)2 (the trimerization ligand) in 10 mL toluene is added to a solution of 0.02 mmol Cr(acac)3 in 10 mL toluene; acac is acetylacetonate. The mixture is stirred for 5 min and then transferred to a 300-mL autoclave that contains a mixture of 80 mL toluene and 4 mmol methylaluminoxane at 40 °C. The autoclave is charged with ethylene at 4500 kPa pressure and maintained at 45 °C for 13.5 min. After workup, the 68.58-g product mass consists of 38.7% C6 hydrocarbons, of which 98.3% is 1-hexene, and 51.4% C8 hydrocarbons, of which 98.8% is 1-octene.

In other experiments, the inventors varied the ligands to alter the hexene/octene product ratio. In almost all cases, however, the α-olefin concentration of each fraction is >93%. (Sasol Technology [Johannesburg, South Africa]. US Patent 8,076,523, Dec.13, 2011; Jeffrey S. Plotkin)

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