Catalytic upgrading of polyethylene plastic waste using GMOF catalyst: Morphology, pyrolysis, and product analysis

Abstract

Since 2000, global plastic waste production and consumption have doubled, escalating from 250 to 500 million tonnes. Merely 9 % of plastic waste undergoes global recycling, leaving the majority either in landfills or poorly managed. This research introduces a new catalyst, GMOF, created by growing Metal-Organic Framework (MOFs) rods on the flaked, carpet-like structure of Graphene Oxide (GO) nanosheets. The aim is to enhance the quality of pyrolysis products derived from high-density polyethylene (HDPE) and low-density polyethylene (LDPE) waste using this GMOF catalyst. HDPE and LDPE, sourced from post-consumer plastic packaging, underwent specific treatment involving cleaning, drying, and shredding. Morphological and property evaluations of GO nanosheets before and after MOF decoration employed techniques including Field-Emission Scanning Electron Microscopy (FE-SEM), Energy-Dispersive X-ray Spectroscopy (EDS), and Fourier Transform Infrared Spectroscopy (FTIR). Flash pyrolysis at 500 °C for 1 min using a sample-to-catalyst ratio of 4:1 in a Quartz Wool Matrix (QWM) reactor was conducted via a Thermogravimetric Analyzer (TGA) and Frontier LAB pyrolizers. Thermal stability and characteristics of feedstocks and catalysts were assessed using TGA. Gas Chromatography-Mass Spectrometry (GC–MS) analyzed and quantified pyrolysis product compounds, while a Micro GC Fusion system determined non-condensable pyrolyzate permanent gas distribution. Results showcased that the GMOF catalyst's unique morphology efficiently captured smaller radicals on its surface, providing increased surface area for effective radical–radical interactions during pyrolysis. In HDPE pyrolysis, the GMOF catalyst notably decreased selectivity of C21-C40 and C40 + wax fractions to 49.07 % and 7.73 %, respectively, while boosting C1-C20 olefin production by 2.54 %. Conversely, LDPE pyrolysis with the GMOF catalyst notably amplified the CO2 peak intensity by 3.17 %, signifying a gasification phase. Primary gases produced were C3 aliphatic hydrocarbons, propane, and propylene, yielding 79.46 % collectively.