A Clever Application of a Recycled Waste Solution for Levulinic Acid and Adsorbent Production from Apple Pomace Using a Hydrothermal Process

We investigated the hydrolysis of apple pomace in subcritical water conditions, with a focus on efficiently producing levulinic acid (LA) by utilizing a waste solution derived from the electronics industry’s dashboard printing, containing iron (Fe2 + and Fe3+), copper (Cu2+), and chloride ions as a catalyst. We also explored the impact of subcritical water alone on apple pomace hydrolysis.

The composition of apple pomace was determined through neutral and acid detergent fiber, and lignin in acid detergent analyses. Hydrothermal reactions were conducted in a Parr reactor at temperatures ranging from 160 to 200ºC and catalyst concentrations from 0.1 to 0.3 M. Analysis was performed using HPLC to measure sugars, aldehydes, and organic acids. The resulting hydrochar was characterized for elemental composition, thermogravimetry, porosity, SEM, IR spectroscopy, and X-Ray analysis.

In reactions using only water, we observed the production of 5-hydroxymethyl furfural (HMF) with no humins formation. We systematically investigated the impact of different oxidation states of iron, copper ions, and chloride ions on LA yield at a fixed temperature. The highest LA yield was achieved when combining copper (Cu²⁺) and iron (Fe³⁺) ions as catalysts. Remarkably, at an ion concentration of 0.3 M and operating at 200 °C, the waste solution yielded 55.3% of levulinic acid. Copper and chloride ions notably played key roles in facilitating the breakdown of biopolymers into monomers while preventing humins formation. Our findings demonstrate the potential of using waste solutions from electronics board production as catalysts for apple pomace hydrolysis under subcritical water conditions, offering an efficient route to levulinic acid production.