Strategy for production of chemicals and fuels employing acetone upgrading as a key step. Moore et al. Click to enlarge.

…methyl ketones have shown promise as bio-derived synthons for the production of chemical/fuel precursors because their carbon chain can be readily extended through aldol condensation. Acetone, the simplest ketone building block, has been industrially produced for nearly a century by the microbial fermentation of biomass through the acetone–butanol–ethanol (ABE) fermentation process, with the products obtained in roughly a 3:6:1 ratio, respectively. Recently, however, metabolically engineered microorganisms were developed that can produce mixtures of isopropanol and acetone in high titers from carbohydrate inputs using strains that have the potential to be scaled up industrially.

These isopropanol/acetone mixtures are much more attractive from a technoeconomic perspective because 1) the output stream from fermentation contains a larger fraction of isopropanol/acetone, and 2) in situ de-hydrogenation of the isopropanol fraction can be performed to provide the system with bio-derived H₂ sufficient for acetone upgrading. This is an advantage over other processes that incorporate acetone from ABE fermentation, such as furfural–acetone condensation and acetone alkylation using other bio-derived alcohols because an isopropanol feed could supplement an H₂ supply required for further processing steps.

—Moore et al.

To assess the potential for drop-in fuel replacements, the team predicted the corresponding derived cetane numbers (DCNs) and research octane numbers (RONs) for some of the product molecules, thereby yielding a first approximation of the suitability of a given molecule for either gasoline or diesel applications.

The results (depicted in the figure below), showed that the C₆, C₉ and C₁₂ ketones and alcohols were suitable for gasoline replacement. The branched C₉ and C₁₂ alkanes were suitable for diesel replacement.

Predicted DCN and RON for select molecules that can be produced using this process. DCN measured using ASTM D6890 and corresponding calculated RON are bolded and presented in parentheses. Moore et al. Click to enlarge.

Testing using the Ignition Quality Tester (IQT) strongly agreed with the predictions.

By evaluating the chemical market and the initial fuel properties, we are confident that this process supplies relevant molecules to both sectors rather than presuming a certain class of molecule is inherently important. By doing this initial analysis, we have also determined that the drive towards hydrocarbons is not always necessary and in certain cases will lead to more expensive processes, using more resources to produce a product with less value than the starting material. Current efforts are focused on developing this chemistry in flow, full fuel-property testing, and technoeconomic and life-cycle analyses, and will be described in due course.

—Moore et al.

Resources

• Moore, C. M., Jenkins, R. W., Janicke, M. T., Kubic, W. L., Polikarpov, E., Semelsberger, T. A. and Sutton, A. D. (2016) “Synthesis of Acetone-Derived C₆, C₉, and C₁₂ Carbon Scaffolds for Chemical and Fuel Applications” ChemSusChem doi: 10.1002/cssc.201600936