March 21, 2011
This catalyst converts midrange olefins to longer ones. Converting low-demand linear α-olefins to those in greater demand has important commercial implications. So-called full-range linear α-olefin (LAO) processes, such as operated by Ineos, Shell, and Chevron Phillips, produce LAO products from 1-butene to C20 and even longer. The problem with this process is that the end-use markets of the products are growing at different rates. The consequence is undersupply of some olefins and oversupply of others.
One way to mitigate this supply–demand imbalance is to convert the olefin fractions in low demand to those in high demand. For example, Shell, in its Shell Higher Olefin Process (SHOP), metathesizes low–carbon number olefins with longer olefins to produce midrange olefins to serve the detergent alcohol market.
B. L. Small discloses a catalyst system that dimerizes midrange LAOs to higher olefins in good conversion, with good selectivity to dimers and a high percentage of linear products. A hexadentate bimetallic catalyst is used in conjunction with a modified methylalumoxane (MMAO) cocatalyst.
In the lone example, the hexadentate ligand is prepared by dissolving 5.0 g 2-diacetylpyridine in 75 mL MeOH containing 0.3 mL HCO2H. In a separate container, 2.17 g o-toluidine is dissolved in 75 mL MeOH, and this solution is slowly added to the first solution at 25 °C over 12 h. The yellow precipitate has the empirical formula C22H30N4O2, consistent with the desired hexadentate diketone. The bimetallic catalyst is made by adding the diketone to FeCl2, followed by adding o-toluidine dissolved in anhydrous n-BuOH. The catalyst precipitates and is isolated by filtration.
To test the catalyst’s efficacy, a sealed NMR tube containing 50 mg of the catalyst is attached to the stirrer shaft of a 2-L ZipperClave reactor (Autoclave Engineers, Erie, PA). The reactor is sealed, evacuated, and loaded with 400 g 1-decene, 400 g 1-dodecene, and 8.6 mL of a MMAO-3A solution (7 wt% Al). The stirrer is started, breaking the NMR tube and releasing the catalyst. Stirring is continued overnight with a starting temperature of 23 °C; the maximum temperature reached is 31 °C.
The starting olefin conversion is 64.1 wt%. The product contains 77.4% dimers, 22.2% trimers, and 0.4% tetramers. The dimer fraction contains 75.4% linear olefins. Unfortunately, no data are given for the percentage of α-olefins in the linear olefins. (Chevron Phillips Chemical [The Woodlands, TX]. US Patent 7,902,415, March 8, 2011; Jeffrey S. Plotkin)