α-Olefin Trimerization for Lubricant Base Oils with Modified Chevron–Phillips Ethylene Trimerization Catalysts

Abstract

α-Olefin trimers are used at a bulk scale as top-tier lubricant base oils, with putative future applications as diesel fuels obtainable from renewable ethylene. α-Olefin trimers are conventionally obtained in the cationic oligomerization process, during which a range of n-mers are simultaneously generated alongside severe skeleton rearrangement. In this context, catalysts that can selectively convert α-olefin to its trimers are valuable. However, few examples have been reported. Herein, we report selective α-olefin trimerization catalysts constructed via the modification of the Chevron–Phillips ethylene trimerization catalytic system and avoiding the use of expensive activators, such as methylaluminoxane (MAO), B(C6F5)3, and [B(C6F5)4]− salt, despite the typical Chevron–Phillips system being inactive for α-olefin. A catalytic system Cr(acac)3/[2,5-Me2C4H2N–Al(iBu)3]−Na+/(iBu)3Al demonstrating high turnover numbers exceeding 10,000 (31 kg/g-Cr for 1-decene), generating trimers selectively without other higher or lower fractions, was developed, confirmed by simulated distillation gas chromatography analysis. The hypothesized η5-pyrrolide chromium active species was partially confirmed by the structure elucidation of [η5-Me2C4H2N–AlMe3]Cr(Me)[CH2C6H4(ortho-NMe2)-κ2C,N]. The prepared 1-decene trimers (after hydrogenation) exhibited an advantageously higher viscosity index than the commercial product PAO-4.0 (128 vs 123). Fluids demonstrating similar lubricant characteristics to either the 1-decene trimers or PAO-4.0 were obtained by using a 1-octene/1-dodecene blend.