Plastic production has increased by almost 200-fold annually from 2 million metric tons per year in 1950s to 359 million metric tons in 2018. With this rapidly increasing production, plastic pollution has become one of the most demanding environmental issues and tremendous efforts have been initiated by the research community for its disposal. In this present study, we reported for the first time, a biomass-waste-derived heterogeneous catalyst prepared from waste orange peel for the depolymerisation of poly(ethylene terephthalate) (PET) to its monomer, bis(2-hydroxyethyl terephthalate) (BHET). The prepared orange peel ash (OPA) catalyst was well-characterised using techniques such as IR, inductively coupled plasma (ICP)-OES (Optical Emission Spectrometry), XRD, X-ray fluorescence (XRF), SEM, energy-dispersive X-ray spectroscopy (EDX), TEM, BET (Brunauer-Emmett-Teller) and TGA. The catalyst was found to be composed of basic sites, high surface area, and a notable type-IV N2 adsorption–desorption isotherm indicating the mesoporous nature of the catalyst, which might have eventually enhanced the rate of the reaction as well as the yield of the product. The catalyst completely depolymerises PET within 90 min, producing 79% of recrystallised BHET. The ability of reusing the catalysts for 5 consecutive runs without significant depreciation in the catalytic activity and its eco- and environmental-friendliness endorses this protocol as a greener route for PET recycling.

Decomposition of used poly(ethylene terephthalate) (PET) bottles was accomplished by methanolytic degradation using bamboo leaf ash (BLA) as a green and highly efficient heterogeneous catalytic system. The reaction at 200 °C in an autoclave reactor gave dimethyl terephthalate (DMT) and ethylene glycol (EG) in 78% and 76% yields, respectively. The chemical and physical characteristics of the prepared catalyst were studied using X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), X-ray diffractograms (XRD), Energy dispersive X-ray spectrometry (EDX), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Thermal Gravimetric Analysis (TGA) and Brunauer-Emmett-Teller (BET) analyses. The conversion of PET to DMT and EG was completed within 2 h, and the crude as well as the recrystallized products were characterized using HPLC, NMR and IR. The catalyst, owing to its excellent thermal stability, mesoporous nature, bio-compatibility, cost free, easy preparation, recyclability and efficacy make it an attractive alternative and greener solid catalyst for PET depolymerization.

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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 reaction and demonstrating its versatility...

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