Interconversion between γ-valerolactone and pentenoic acid combined with decarboxylation to form butene over silica/alumina

Reaction kinetic studies were carried out of the reversible interconversion between γ-valerolactone (GVL) and pentenoic acid (PEA) combined with the irreversible decarboxylation of both species to form butene and CO2 over a SiO2/Al2O3 catalyst at pressures from atmospheric to 36 bar, temperatures from 498 to 648 K, different concentrations of GVL and PEA, as well as in the presence of water. The catalyst exhibited reversible deactivation within the initial 24 h on stream (losing about 50% of the initial catalytic activity), followed by a slower rate of deactivation of roughly 0.4–0.5% per hour on stream. Decarboxylation of γ-valerolactone, producing equimolar quantities of butene and CO2, may possibly occur by two distinct pathways: a direct route from the lactone and an indirect route from PEA. 1-butene is the primary product of decarboxylation, formed via β-scission of intermediate carbenium ions. The apparent activation barrier for decarboxylation of GVL (175 kJ mol−1) is higher than for decarboxylation of PEA (142 kJ mol−1). A simple kinetic model with rate expressions accounting for adsorption and unimolecular surface reactions of GVL and PEA is sufficient to describe the trends measured for the rates of GVL ring opening to PEA, GVL decarboxylation, PEA cyclization to GVL, and PEA decarboxylation at different reaction conditions.

Graphical abstractThe conversion of γ-valerolactone over SiO2/Al2O3 for the production of butenes or pentenoic acid represents an important application of heterogeneous catalysis in bio-refining practice. In this study, we present a reaction kinetics study of key transformations and provide a simple kinetic model that captures the reactivity trends.Figure optionsDownload full-size imageDownload high-quality image (126 K)Download as PowerPoint slideResearch highlights► Elucidated pathways for γ-valerolactone decarboxylation. ► Demonstrated significance of direct γ-valerolactone decarboxylation. ► Quantified the nature of water inhibition on silica/alumina catalyst. ► Kinetic modeling for interconversion between γ-valerolactone and pentenoic and their decarboxylation.