Published December 1997
Phillips Petroleum Company (Phillips) has developed a catalyst technology to produce 1-hexene, a comonomer used in producing linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) resins. The process, which uses a proprietary chromium-based catalyst system, converts ethylene gas to an olefinic product containing about 93 wt% 1-hexene. Small amounts of coproducts, such as 1-octene and 1-decene, are also formed. The catalyst system has a 95-99 wt% selectivity for C6-C10 linear a-olefins. Solid product formation is negligible. The technology employs milder process conditions than those used in competing processes, with the trimerization of ethylene taking place at 115°C (239°F) and 45-50 kg/cm2.
The catalyst system, a product of a pyrrole compound and chromium salt with triethyl aluminum (TEA) and ethyl aluminum dichloride (EADC) added as modifiers, is dissolved in cyclohexane. The catalyst solution is pumped into a reactor where ethylene at 115°C (239°F) and 48.5 kg/cm2 trimerizes in a solution phase to produce C4-C10 linear a-olefins. n-Octanol is added to reactor effluents to inhibit polymerization. The products are then fractionated to obtain 1-hexene, 1-octene, and 1-decene. Chromium and aluminum are precipitated from the process effluents by adding NaOH and H2SO4 before effluent disposal. The cyclohexane and n-octanol are recycled.
Phillips intends to build a production line by 1999 near the U.S. Gulf Coast with capacity targeted at about 200 million lb/yr (90,700 t/yr). Plans for another project in Qatar of 100 million lb/yr (45,400 t/yr) capacity have also been completed. In addition, Phillips is considering building a 20,000 t/yr plant in Asia.