(206b) Conversion of Ethanol to Distillate Fuels through Guerbet Condensation

Ethanol is currently the most common liquid fuel derived from biomass in the world and is used as a blendstock in gasoline-powered vehicles. In the next 20 years demand is anticipated to grow in heavier, distillate-range fuels such as diesel and jet while that of gasoline is projected to decrease.¹ Ethanol can be catalytically converted into distillate fuels by several different catalytic routes that involve C-C bond forming reactions such as acid-catalyzed olefin oligomerization, metal-catalyzed olefin oligomerization, aldolization, and ketonization reactions and may also include dehydration (to olefins), dehydrogenation (to aldehydes), and hydrogenation (of C=C and C=O bonds) reactions.^2-8 In this presentation we will review routes to convert ethanol into distillate fuels and then discuss Guerbet conversion of ethanol—a route involving aldolization chemistry.

We have investigated Guerbet conversion of ethanol over various catalysts such as hydroxyapatite (HAP) and transition-metal-promoted metal oxides. HAP can be used to produce C₄₊ alcohols with stable performance over 200 h after an initial period of deactivation. A kinetic model shows that the rate constants for formation of linear and branched alcohols are equal. The lower activity for further conversion of branched alcohols compared to the conversion of linear alcohols results in an increased selectivity to branched products at elevated conversions. We additionally show that Cu doping of AlMgO and AlCaO supports promotes production of C₄₊ alcohols at higher rates than achieved with HAP with higher preference toward linear alcohols. At low pressures, the main role of Cu is to promote dehydrogenation of ethanol to acetaldehyde which remains largely unconverted but also undergoes further condensation to yield C₄₊ alcohols. Operation at elevated pressures promotes condensation, increasing selectivities toward C₄₊ alcohols and aldehydes. Minimal deactivation was observed with time-on-stream. Water and other co-products have an inhibiting effect on ethanol conversion making operation at elevated conversions difficult. We will additionally show how these Guerbet products can be further converted into distillate fuels.

References

1. Outlook for Energy: A View to 2040. In ExxonMobil, 2017.
2. Zhang, M. H.; Yu, Y. Z., Dehydration of Ethanol to Ethylene. Industrial & Engineering Chemistry Research 2013, 52 (28), 9505-9514.
3. Kozlowski, J. T.; Davis, R. J., Heterogeneous Catalysts for the Guerbet Coupling of Alcohols. ACS Catal. 2013, 3 (7), 1588-1600.
4. Dagle, V. L.; Smith, C.; Flake, M.; Albrecht, K. O.; Gray, M. J.; Ramasamy, K. K.; Dagle, R. A., Integrated process for the catalytic conversion of biomass-derived syngas into transportation fuels. Green Chemistry 2016, 18 (7), 1880-1891.
5. Derouane, E. G.; Nagy, J. B.; Dejaifve, P.; van Hooff, J. H.; Spekman, B. P.; Védrine, J. C.; Naccache, C., Elucidation of the mechanism of conversion of methanol and ethanol to hydrocarbons on a new type of synthetic zeolite. Journal of Catalysis 1978, 53 (1), 40-55.
6. Nicholas, C. P., Applications of light olefin oligomerization to the production of fuels and chemicals. Applied Catalysis A: General 2017, 543 (Supplement C), 82-97.
7. Moore, C. M.; Staples, O.; Jenkins, R. W.; Brooks, T. J.; Semelsberger, T. A.; Sutton, A. D., Acetaldehyde as an ethanol derived bio-building block: an alternative to Guerbet chemistry. Green Chemistry 2017, 19 (1), 169-174.
8. Sun, J.; Zhu, K.; Gao, F.; Wang, C.; Liu, J.; Peden, C. H.; Wang, Y., Direct conversion of bio-ethanol to isobutene on nanosized Zn x Zr y O z mixed oxides with balanced acid–base sites. Journal of the American Chemical Society 2011, 133 (29), 11096-11099.