Integrated valorization of pineapple peel by coupling levulinic acid production with CO2-mediated pyrolysis

Abstract

Levulinic acid (LA) is a platform chemical derived from C6 mono-/poly-saccharides in lignocellulosic biomass, serving as a versatile precursor for the synthesis of various chemicals. However, its production unavoidably remains lignin-rich residues during the recovery of C6 carbohydrates, which undermines the environmental sustainability of LA production. To address this challenge, this study proposed an innovative strategy that converts hydrolysis residue into both syngas and CO2 sorbent to enhance the sustainability of LA production. Pineapple peel (PP) was employed as the feedstock. Acid-catalyzed hydrolysis of PP produced LA with a maximum concentration of 11.19 g L⁻¹ under 2 M H₂SO₄. The resulting PP residue was subsequently subjected to CO2 mediated pyrolysis. CO2 acts as both a reaction medium for gas-phase reactions and activation agent for pore development of biochar. To promote these gas-phase reactions, catalytic pyrolysis over Ni/Al₂O₃ was performed, which accelerated CO generation under CO₂ condition (46.38 mmol) compared to N2 condition (6.74 mmol). To maximize carbon utilization, the biochar generated from CO₂-mediated pyrolysis was evaluated as a CO₂ sorbent. Compared with N₂-derived biochar, the CO₂-derived biochar exhibited more developed meso- and microporous structures. Although both biochars achieved comparable CO₂ adsorption capacities (39.33 mg g⁻¹), the CO₂-derived biochar showed a faster adsorption rate. Overall, this work demonstrates an integrated approach to valorizing hydrolysis residues in LA production, coupling syngas generation with biochar-based CO₂ capture to improve carbon efficiency and process sustainability.