A Multiphase Protocol for Selective Hydrogenation and Reductive Amination of Levulinic Acid with Integrated Catalyst Recovery

Graphical Abstract

It's a phase: Two reactions of levulinic acid (LA), hydrogenation and reductive amination with cyclohexylamine, are explored in a multiphase system. By tuning the relative volume of the immiscible water/hydrocarbon phases and the concentration of the aqueous solution, quantitative conversion of LA can be achieved with formation of γ-valerolactone (GVL) or N-(cyclohexylmethyl)pyrrolidone in >95 and 88 % selectivity, respectively.

Abstract

At 60–150 °C and 15–35 bar H₂, two model reactions of levulinic acid (LA), hydrogenation and reductive amination with cyclohexylamine, were explored in a multiphase system composed of an aqueous solution of reactants, a hydrocarbon, and commercial 5 % Ru/C as a heterogeneous catalyst. By tuning the relative volume of the immiscible water/hydrocarbon phases and the concentration of the aqueous solution, a quantitative conversion of LA was achieved with formation of γ-valerolactone or N-(cyclohexylmethyl)pyrrolidone in >95 and 88 % selectivity, respectively. Additionally, the catalyst could be segregated in the hydrocarbon phase and recycled in an effective semi-continuous protocol. Under such conditions, formic acid additive affected the reactivity of LA through a competitive adsorption on the catalyst surface. This effect was crucial to improve selectivity for the reductive amination process. The comparison of 5 % Ru/C with a series of carbon supports demonstrated that the segregation phenomenon in the hydrocarbon phase, never previously reported, was pH-dependent and effective for samples displaying a moderate surface acidity.