Waste water streams can serve as a valuable source for the production of renewable value-added chemicals, together with simultaneous minimization of waste. Waste water fermentation results in the production of short-chain carboxylic acids, so-called volatile fatty acids (VFAs). These carboxylic acids can be upgraded catalytically to a wide range of compounds, e.g. mixed ketones, which can in turn serve as valuable bio-based platform chemicals. The low concentration of the VFAs in the fermentation broth makes direct conversion unfeasible and efficient extraction is required first. Different separation techniques are known to be effective for the VFAs separation from dilute aqueous solution, including extraction by an ionic liquid or by adsorption on a polymeric resin. The extracted acids can subsequently be easily recovered from the resin by stripping with hot nitrogen, followed by in-line catalytic gas-phase ketonization. Amphoteric reducible metal oxides are known to possess high ketonization activity and selectivity towards the ketones. Although the gas-phase ketonization of single acids has been extensively studied in the past, the conversion of VFAs mixtures has only received limited attention. In addition, little attention has been paid to the influence of feed impurities or co-extracted water on catalyst performance. Here, we report on the efficient catalytic ketonization of VFAs (C2-C4 acids, in particular) extracted from the fermentation broth over TiO2-based catalysts. Catalyst performance, including stability of the solid catalyst was studied as function of increasing feed complexity from single acids to VFAs mixture extracted from a real feed. Stability towards water, found to strongly inhibit the catalyst, was improved by dispersing TiO2 on a hydrophobic carbon support. The influence of TiO2 phase and addition of dopants will also be discussed, as will a coupled, cascade conversion of the VFA-derived ketones to other valuable chemicals.

Ketonization of volatile fatty acids recovered from waste water streams

255th National Meeting (2018)

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