Esterification of valeric acid and glycerol via various acidic zeolites

Biomass-derived green esters can be produced from the esterification of valeric acid and glycerol. In this work, various zeolites (ZSM-5, Y, and BEA) were examined, specifically targeting divalerin and trivalerin esters. A direct link between pore size and esterification performance was not evident. This outcome can be attributed to the combined influence of various characteristics such as acidity, hydrophobicity and mesoporous structure. Among the zeolite types tested, HZSM-5, HY, and HBEA with SiO 2 /Al 2 O 3 ratios of 87, 88.6, and 45.2, respectively, showed the best performance. The Y-zeolite with a SiO 2 /Al 2 O 3 atomic ratio of 88.6 produced the lowest amount of by-products. This sample had a combination of low acidity (indicating high hydrophobicity), the highest mesoporous area and a relatively high mesoporous volume. These balanced properties rendered Y zeolite with active acid sites that were easily accessible, and facilitated effective pore diffusion properties for both the reactants and products during the esterification of glycerol and valeric acid. This zeolite achieved complete glycerol conversion and a 52.9% yield of divalerin and 25% of trivalerin at 130 °C after 6 h, using 1 wt.% catalyst, a 5:1 acid-to-glycerol mole ratio, and continuous water removal. Additionally, the reusability of the zeolite was demonstrated, as the Y zeolite could be recycled four times with only a minimal decrease in glycerol conversion. Complete regeneration of the zeolite was also achieved through re-calcination. This study demonstrates that acidic commercial zeolites are a promising option for esterification processes due to their good catalytic performance, long-term stability and easy regeneration. • Acidic zeolites screened for esterification of glycerol and valeric acid. • HY zeolite (SiO₂/Al₂O₃ = 88.6) achieved 77.9% di- and trivalerin yield at 130 °C. • High Si/Al ratio and mesoporosity boosted ester yields with improved site access. • HY-80 zeolite showed full regeneration and reuse potential via re-calcination.