Brewing sustainability: Continuous flow Ru-supported hydrochar from bagasse beer waste for renewable N-containing chemicals via reductive amination of biomass-derived platform molecules

This research aligns with sustainability goals, wherein hydrochar derived from the hydrothermal treatment of brewing industry waste was employed as a support for a ruthenium-based catalyst. Hydrochar-supported Ru metal (Ru-HC) was synthesized and applied in the reductive amination pathway within the H-cube, a flow reactor coupled with a hydrogen source. The reductive reaction between levulinic acid and n-butylamine was chosen as a model reaction. High conversion and high selectivity were obtained after optimization with temperature, flow rate, hydrogen pressure and solvents. At 40 bar of hydrogen pressure, 80 °C of temperature, with a flow of 0.1 mLmin-1, 99% conversion with selectivity of 98% towards the hydrogenated product was obtained. The catalytic ability of Ru-HC was investigated across a variety of substrate scopes. Several biomass-derived molecules such as furfural, 5-hydroxymethylfurfural, furfurylamine etc. were employed in the reductive amination process to yield diverse valuable N-containing products. The possible mechanism was further proved with the formation of an intermediate and a recyclability study proved the robust nature of Ru-HC. Overall, the established pathway for reductive amination with Ru-HC as a heterogeneous catalyst provides a sustainable protocol for the synthesis of N-containing molecules, which is highly valuable for our society.