272986 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 . 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 . The oxo process is complicated, requires high energy input, and is costly .
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 . 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 . 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.
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