Innovative catalytic processes for the continuous-flow valorization of C5 esters and lactones

This work focused on the investigation of the continuous-flow, gas-phase conversion of γ-valerolactone (GVL) and related C5 esters over ZrO2 catalysts. The objective of this study is to develop a process to produce valuable ketones and aromatics from renewable C5 building blocks. Different reaction conditions were studied in a fixed-bed reactor, and the effects of temperature, contact time, co-feeding of steam, and the C5 substrate structure were analysed. The products of the reaction were identified by GC and GC-MS, and the spent catalyst was analysed by TGA. The best compromise between GVL conversion and product quantification was achieved over monoclinic ZrO2 at 440 ˚C and a nominal contact time of 1 second, with near-complete conversion of GVL maintained for approximately 7 to 8 hours and an overall yield of valuable products of approximately 55%. Control experiments with methyl pentanoate and ethyl pentenoate demonstrated substrate dependence and generated multiple overlapping C5-C9 oxygenated products. Methyl-substituted phenols and other aromatic oxygenates were also observed. This prompts consideration of the potential of the catalytic system to manufacture other aromatic chemicals. The variety of oxygenated products and the complexity of the overall product distribution suggest that the reaction is not sufficiently understood to simplify it to a single pathway.