Highly Efficient Zirconium-Catalyzed Batch Conversion
of 1-Butene: A New Route to Jet Fuels
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Abstract
Quantitative conversion of 1-butene to a Schultz−Flory distribution
of oligomers has been accomplished by use of Group 4 transition-metal
catalysts in the presence of methylaluminoxane (MAO). The oligomerization
reaction was carried out at ambient temperature in a sealed reaction
vessel with complete conversion of 1-butene at catalyst turnover numbers
of >17 000. The combination of high catalyst activity without
concomitant production of high polymer led to a highly efficient production
of new hydrocarbon jet fuel candidates. The reaction proceeds with
high regioselectivity; however, because achiral catalysts were used,
several diastereoisomeric structures were produced and observed in
the gas chromatography−mass spectrometry (GC−MS) chromatograms.
The single and specific dimer formed in the reaction, 2-ethyl-1-hexene,
was easily removed by distillation and then dimerized using acid catalysis
to afford a mixture of mono-unsaturated C<sub>16</sub> compounds.
Changes in the oligomerization catalyst led to production of fuels
with excellent cold-flow viscosity without the need for a high-temperature
distillation. Thus, removal of the dimer followed by catalytic hydrogenation
(PtO<sub>2</sub>) led to a 100% saturated hydrocarbon fuel with a
density of 0.78 g/mL, a viscosity of 12.5 cSt at −20 °C
(ASTM 445), and a calculated heat of combustion of 44+ MJ/kg. By back-addition
of hydrogenated dimer in varying amounts (6.6, 11.5, and 17 wt %),
it was possible to tailor the viscosity of the fuel (8.5, 7, and 6.5
cSt, respectively)
