(329a) Catalytic Conversion of Ethanol to 1-Butanol and Higher Alcohols

With the recent increase in demand for renewable fuels, there has been a surge in corn-based bioethanol production.  Unfortunately, the energy density of ethanol is much lower than gasoline, resulting in poor fuel economy. Gas mileage could be improved if ethanol was upgraded to 1-butanol and other higher alcohols, as these alcohols have energy values close to gasoline [1]. Bioethanol thus has potential to be a platform feedstock for higher alcohol production, which have broad applications as both fuels and chemicals. The current method for producing higher alcohols is the oxo process, which uses petroleum-derived propylene as the feedstock [2]. The oxo process is complicated, requires high energy input, and is costly [2].

A greener process needs to be realized that directly converts ethanol to higher alcohols.  Carbon-carbon coupling of alcohols is commonly regarded as the Guerbet reaction [2].  In the ethanol Guerbet reaction, ethanol is oxidized to acetaldehyde, the acetaldehyde undergoes an aldol condensation to crotonaldehyde, and then the crotonaldehyde is hydrogenated to butanol [3].  Formed higher alcohols can subsequently undergo Guerbet reactions with themselves and ethanol.  The literature shows the highest higher alcohol yields have been obtained with hydrotalcite-derived mixed oxides, hydroxyapatite, iridium complexes, and alumina- supported nickel catalysts [2-6].

Ethanol Guerbet reactions were performed in a 300ml Parr reactor where reaction times were between two and ten hours.  An in-house prepared alumina-supported catalyst was used.  Liquid reaction products were analyzed with a Varian 450 gas chromatograph.  High selectivity (67%) and high yield (38%) towards higher alcohols have recently been obtained. Higher alcohol products consist of 1-butanol, 1-hexanol, 2-ethyl-1-butanol, 1-octanol, and 2-ethyl-1-hexanol.  The kinetics of 1-butanol and higher alcohol formation from ethanol via the Geurbet reaction are being characterized. 

References

[1]  R. Cascone, Chemical Engineering Progress, 104 (2008) S4.

[2] T. Tsuchida, S. Sakuma, T. Takeguchi, W. Ueda, Industrial & Engineering Chemistry Research, 45 (2006) 8634-8642.

[3] A.S. Ndou, N. Plint, N.J. Coville, Applied Catalysis a-General, 251 (2003) 337-345.

[4]  K. Koda, T. Matsu-Ura, Y. Obora, Y. Ishii, Chemistry Letters 38 (2009) 838-839.

[5] M.J.L. Gines, E. Iglesia, Journal of Catalysis, 176 (1998) 155-172.

[6] K.W. Yang, X.Z. Jiang, W.C. Zhang, Chinese Chemical Letters, 15 (2004) 1497-1500.