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Converting the acetone-butanol-ethanol mixture to drop-in hydrocarbons

Researchers at Auburn University report on the catalytic dehydration of the acetone-butanol-ethanol (ABE) mixture produced by fermentation by genetically modified Clostridium acetobutylicum. Their paper appears in the ACS journal Energy & Fuels.

C. acetobutylicum produces a mixture of acetone, butanol and ethanol via fermentation. While the catalytic dehydration of the individual components—n-butanol, acetone, and ethanol—has been studied, not much work has been reported on the dehydration or deoxygenation of the mixture as produced from the ABE fermentation process, Shaima Nahreen and Ram Gupta note in their paper.

Two main challenges of the ABE production by fermentation are low yield and contamination by aerobic and acid producing anaerobic bacteria. The low yield is being addressed by continuous separation of ABE from the bioreactor, and the toxicity tolerance is being addressed by genetic improvement in the microorganism.

The ABE mixture can become a compatible fuel if it is transformed into a drop-in fuel for the replacement of gasoline, diesel, or jet fuel. For upgrading ABE to be used in automotive engines, dehydration or deoxygenation of the ABE mixture to produce a higher energy content hydrocarbon chain is the most promising route. Dehydration or deoxygenation can be aided by inorganic catalysts containing acid sites. However, to date, not much work has been done on the conversion of the ABE mixture.

...This work examines the dehydration of the ABE mixture. In this work, the mixture of acetone, n-butanol, and ethanol has been taken in a mass ratio of 3.7:8:1, which implies a composition of 29.3, 62.9, and 7.8 wt %, respectively, a typical composition obtained from genetically modified clostridium bacteria. The main objective of this work is to dehydrate the ABE mixture to long chain hydrocarbons.

—Nahreen and Gupta

In their experiments, they preheated a feed of the ABE mixture and pumped it through a catalytic packed bed tubular reactor in a continuous process at pressures of 3−13 bar. Using different operating temperatures and feed flow rates, they observed the effect on the dehydration products, which are mixtures of three phases:

  1. a gas phase consisting of light hydrocarbons and carbon dioxide;
  2. an organic liquid phase consisting of heavy hydrocarbons; and
  3. an aqueous phase with dissolved oxygenated hydrocarbons.

The dehydration products from the ABE mixture are mostly unsaturated hydrocarbon chains in the range of C2−C16.

They analyzed the products and compared them to those from the dehydration of pure n-butanol, acetone, and ethanol feedstocks. On the basis of the higher heating values (HHV) of the liquid products and infrared spectra of the gas products, they concluded that the products from the ABE feedstock are different from those from the individual components, which suggests a cross reactivity of the components during the reaction.

Catalytic dehydration of the ABE mixture reveals an interesting synergy of the reacting components. The product from the ABE mixture is not a simple sum of the products from the individual feed components, acetone, 1-butanol, and ethanol. The inter-reactivity of the components contributed to a liquid product with a high heating value.

Out of the conditions studied here, γ-Al2O3-catalyzed dehydration at 400 °C produced the highest amount of useful hydrocarbon products in terms of butene and high HHV organic liquid.

—Nahreen and Gupta


  • Shaima Nahreen and Ram B. Gupta (2013) Conversion of the Acetone–Butanol–Ethanol (ABE) Mixture to Hydrocarbons by Catalytic Dehydration. Energy & Fuels doi: 10.1021/ef302080n



whats the advantage over regular yeast used in common ethanol mills?

Shaima Nahreen

In this work,process of fermentation was not studied, but ABE fermentation product have been upgraded to hydrocarbons in catalytic process. the ABE fermentation product composition was taken from recent studies (referred in the paper),where genetically modified 'Clostridium Acetobutylicum' microbial strain was used as the bio-catalyst and found to increase the yield of acetone-butanol-ethanol (ABE) in the fermentation process compared to the conventional processes.

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