Valorization of pomegranate waste through green solvent extraction and biochar production: a zero-waste biorefinery approach

Abstract

This study introduces a sustainable, zero-waste biorefinery approach for the valorization of pomegranate (Punica granatum) waste, focusing on the sequential extraction of anthocyanins, ellagic acid and its derivatives using environmentally friendly solvents, followed by biochar production. Initially, a COSMO-RS in silico analysis was conducted, screening 10 512 combinations of hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) typically used in eutectic solvent formulations, along with 49 bio-based solvents, to identify the most efficient green solvents for recovering anthocyanins, ellagic acid and its derivatives. In the first step, an aqueous solution of gamma-valerolactone (GVL) (2900 mM, pH 2) was used for solid–liquid extraction; this led to the optimization of extraction conditions (solid–liquid ratio of 0.07 g_biomass mL_solvent⁻¹, at 25 °C for 55 minutes) yielding 38.52 ± 0.06 mg_anthocyanins g_biomass⁻¹. Subsequently, the residual biomass underwent a second extraction using an aqueous solution of the ionic liquid (IL) cholinium acetate (2900 mM, pH 13) under similar conditions, yielding a rich fraction of ellagic acid and its derivatives (21.82 mg_{ellagic acid} g_biomass⁻¹). The remaining biomass was then converted into activated biochar using a eutectic solvent composed of cholinium chloride and oxalic acid (molar ratio 1 HBA : 2 HBD), providing a greener alternative to traditional biochar production methods. The resulting biochar was utilized as an adsorbent for removing synthetic dyes (food and textile) from aqueous solutions, presenting new opportunities for the remediation of contaminated water effluents. This zero-waste process fully valorizes pomegranate residues, adhering to green extraction principles and achieving a Path2Green score of 0.401 (corresponding to around 288.50 g_CO2 g_biomass⁻¹), underscoring its eco-friendliness. By minimizing waste and reducing the need for harmful organic solvents, this biorefinery model highlights the potential for greener industrial practices through the use of bio-based solvents and the complete utilization of biomass.