Condensed phase conversion of bioethanol to 1-butanol and higher alcohols.

摘要

Higher alcohols are important chemical feedstocks as well as potential fuels. With the recent surge in bioethanol production, it would be advantageous to convert bioethanol to butanol and higher alcohols. Results by various authors for a wide range of reaction conditions are presented. For butanol specifically, the highest yields have been obtained with hydroxyapatite, hydrotalcite and alumina-supported nickel catalysts. The literature shows it is a challenge to convert ethanol to butanol, since no one has achieved butanol yields higher than ~30%.;In this research project, attention is focused on alumina-supported nickel, since it is robust, stable, and well suited for condensed phase ethanol Guerbet chemistry. Catalyst screening of different compositions was performed and higher alcohol selectivities were analyzed. The 8%Ni/8%La-Al2O 3 was proven to produce over 80% selectivity to higher alcohols at 50% ethanol conversion. The impacts of water removal on target alcohol yield with the 8Ni/8La catalyst were investigated in a batch reactor. Removing water decreased selectivity to CH4 and CO2 from 15% without water removal to 8% with water removal.;Preliminary kinetics of 1-butanol and 1-hexanol formation were investigated by looking at initial rates of their formation at 215°C, 230°C, and 239°C. Runs with ethanol/acetaldehyde/H2 were performed to investigate the steps of the ethanol Guerbet reaction mechanism. Runs completed at 150°C and 200°C were modeled and rate constants were determined for acetaldehyde hydrogenation, acetaldehyde condensation, and butyraldehyde hydrogenation. It was found ethanol dehydrogenation is in equilibrium and is the rate limiting step of the ethanol Guerbet mechanism. The activation energy for ethanol dehydrogenation was calculated to be 150 KJ/mol. Therefore, the effect of H2 on a neat ethanol run was examined and found to have little effect on ethanol conversion rate. Ethanol conversion rates were the same due to the side reaction of H2 with ethanol to CH 4 and water, which offsets the negative effect of hydrogen on acetaldehyde formation rate. The presence of excess H2 was found to decrease 1-butanol and 1-hexanol formation rates.