Biomass waste-derived recyclable heterogeneous catalyst for aqueous aldol reaction and depolymerization of PET waste

In this work, we discuss the valorization of biomass waste-derived orange peel ash (OPA) by exploring its applicability as a heterogeneous catalyst in aqueous aldol reactions and demonstrating its versatility by promoting the methanolysis of poly(ethylene terephthalate) (PET) waste. The catalyst was characterized using Fourier-transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) analysis, X-ray powder diffraction (XRD), X-ray fluorescence (XRF), energy dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and thermal gravimetric analysis (TGA) to decode its chemical composition. The aldol reactions were carried out at ambient temperature in the presence of water as a solvent. PET depolymerization was performed in an autoclave for 1 h using only 6% w/w OPA. The catalyst was recovered and reused in both the reactions for up to four successive cycles with minimal loss in the catalytic activity. The use of OPA as a cost-free, eco-friendly and effective recyclable catalyst enables a greener route for C-C bond formation and PET waste recycling.

Automated summary

This study explores the valorization of biomass waste-derived orange peel ash (OPA) as a heterogeneous catalyst in aqueous aldol reactions and in promoting the methanolysis of poly(ethylene terephthalate) (PET) waste. The catalyst was characterized using various techniques to decode its chemical composition and was found to be effective in catalyzing reactions with minimal loss in catalytic activity over multiple cycles. The use of OPA offers a cost-free, eco-friendly and recyclable catalyst for greener C-C bond formation and PET waste recycling.