One-pot directly conversion of passion fruit husk to levulinic acid using highly efficient and recyclable SO3H-functionalized ionic liquids

In this study, hydrothermal conversion of passion fruit husk powder (PFHP) into levulinic acid (LA) was achieved using SO₃H-functionalized ionic liquids (ILs) as catalyst. The investigation focused on the impact of IL types and reaction conditions (temperature, time, water quantity and catalyst loading) on LA yield. Among the selected ILs, [C₄SO₃Hmim][HSO₄] exhibited the highest LA yield at 66.6%, achieved under specific conditions: 4 h of reaction time, 180 °C temperature, 0.2 g of PFHP, 1.5 g of IL, and 6.0 g of deionized water. Remarkably, [C₄SO₃Hmim][HSO₄] displayed consistent stability and catalytic efficiency throughout four recycling cycles. Comprehensive analyses, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD), were conducted on the solid residues of passion fruit husk obtained at different reaction times. These analyses revealed significant alterations in surface morphology, functional groups, and crystallinity index of the solid residues with prolonged reaction times. Notably, hemicellulose and lignin removal occurred within the first 0.5–1 h of the reaction, leading to the formation of by-products after 3 h. This one-pot process for LA production from agricultural waste showcases a promising avenue for converting sustainable biomass resources into valuable chemicals, emphasizing the potential for future biomass utilization.