Valorization of aqueous streams via catalytic hydrogenation of carboxylic acids

The aim of this work consists in the study of carboxylic acids hydrogenation in the aqueous phase. This kind of reaction is of relevant importance in the context of biorefinery processes such as the upgrade of pyrolysis bio-oil or for the valorization of waste streams generated during the process of bioethanol production via fermentation of aqueous broths. The target compound was represented by the respective alcohol, derived from the acid present in the solution (acetic, propionic and butyric acid hydrogenation have been performed). This aspect has to do with the fact that alcohols represent building blocks both for biorefinery operations and for the sector of green chemistry. To perform our study, a doscontinuous reactor has been used and the analysis of the gas and the liquid phases have been performed using a gas chromatogram and a HPLC instruments. The most relevant aspect individuated during our study is that the target compound (the alcohol) represented an intermediate molecule of a complex system of reactions. Moreover the catalyst used, that was 5%Ru/C, was more selective towards the production of gaseous compounds (mainly alkanes) that with respect to liquid ones. Nevertheless, other type of catalyst used (Pt/Al2O3, Pd/Al2O3, Ir/C) showed limited activity, leading to unsatisfactory values of the acid conversion. A proposed way to overcome the difficulties to reach good values for alcohol yield, in an optic of an industrial process, could be to operate with a continuous reactor, with high recirculation flows.