February 10, 2014
This ethylene dimerization catalyst produces 1-butene in high yields. 1-Butene is a key comonomer used in the production of linear low-density polyethylene. Typically, 1-butene is copolymerized with ethylene in 7–8% concentration.
The three commercial sources of 1-butene are
- extraction from the crude C4 cut from a naphtha-fed steam cracker for ethylene production;
- one of the fractions produced in full-range α-olefin processes; and
- on-purpose production by selective ethylene dimerization.
The on-purpose process is becoming important in the United States as ethylene producers opt to crack more and more ethane instead of naphtha because of the economics of inexpensive shale gas–based ethane. Ethane-based steam crackers produce small amounts of C4 olefins.
The most widely used on-purpose ethylene dimerization process is Axens’s AlphaButol process. Inventors F. Grasset and L. Magna at IFP Energies Nouvelles (Axens’s parent company) point out that one obstacle to the ethylene dimerization processes is the propensity to form ethylene-based oligomers and polymers that deactivate the catalyst and complicate the operability of the overall process.
The inventors disclose catalysts that significantly reduce polymer formation. One of the more selective, active catalysts they describe is (L16)2Ti(O-n-Bu)2, in which ligand L16 is Ph2P(CH2)3OH.
In one example, 0.15 mmol of this catalyst and 0.45 mmol AlEt3 were dissolved in cyclohexane in an autoclave. Ethylene was introduced at 2 MPa pressure. After 15 min, C4 olefins were produced in 93% yield, of which>99% was 1-butene. The byproducts were 7% C6 hydrocarbons and<0.5% polyethylene. The productivity was 9700 g ethylene consumed/(g Ti·h). (IFP Energies Nouvelles [Rueil-Malmaison, France] US Patent 8,624,042, Jan. 7, 2014; Jeffrey S. Plotkin)