Towards understanding low-viscosity poly-α-olefin production from Fischer-Tropsch alpha-olefin-rich distillate by [Al2(Ga/Ti/Zr)xCl7+nx]--based ionic liquids: Lewis acidity and PAO structure

Lewis acid imidazolium-based ionic liquids (ILs) with inorganic anions of [Al₂Cl₇]^-, [Al₂Ti_xCl_7+4x]^-, [Al₂Zr_xCl_7+4x]^-, and [Al₂Ga_xCl_7+3x]^- have been synthesized in good yields and used as the catalysts for the polymerization of Fischer-Tropsch (FT) mixed α-olefins. The poly alpha-olefins (PAO) products have been tuned through various bimetallic Lewis-acid ionic liquids (ILs). A high PAO yield of 95 % and excellent selectivity to trimers & tetramers of 65 % were achieved at 100 °C for 120 min using 3 wt% [Bmim][Al₂Ga_0.1Cl_7.3] as the catalyst. The bimetallic Lewis acid ILs are easily separated from the reaction mixture and recycled with good stability. Molecular orbital studies show the LUMOs of IL anions have changed from Al to the other metal site (Ga/Ti/Zr), leading to a weakened Lewis acidity, finally making the PAO structure tunable. Notably‌, the synthesis of PAO products by bimetallic ILs from Fischer-Tropsch (FT) mixed α-olefins, instead of 1-decene from ethylene production, was demonstrated to be effective, ensuring a green, low-cost, and recyclable technology industrially. Furthermore‌, the IL catalysts demonstrated‌ inherent safety and environmental compatibility, ‌positioning them as promising alternatives to conventional BF₃ catalysts.