Upcycling of Contaminated Plastics Recovered Through Landfill Mining and Pyrolysis to High-Value Products

Lead Research Organisation: Cranfield University
Department Name: School of Water, Energy and Environment

Abstract

Pyrolysis is known for yielding condensable volatile organic vapours of varying chain length and complexity depending on process configuration and operating conditions. Although the process has been known for decades, significant challenges need to be addressed in order to deploy economic commercial systems. Given that plastics are manufactured from fossil feedstock, the properties of the pyrolysis liquids are expected to be similar to those of conventional chemicals and fuels. However, the wide range of non-standardised mixed waste plastics and presence of organic additives enhance secondary reactions during thermal conversion processes. While these issues need to be addressed in conventional processes of valorisation of plastics, more uncertainties and challenges are encountered in the case of advanced thermal conversion of plastics recovered through landfill mining because the presence of contaminants and chemical degradation result in more variability of the composition.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509450/1 01/10/2016 30/09/2021
1819284 Studentship EP/N509450/1 03/10/2016 02/10/2019 Luisa Canopoli
 
Description This research provided a comprehensive detailed characterisation of recovered plastics, identifying the plastic types and examining the physico-chemical properties through a series of analyses. Then, the potential valuable products from the pyrolysis were investigated using a combination of modelling prediction and pyrolysis using Pyrola 2000 system connected to a gas chromatography-mass spectrometry (Py-GC-MS). The literature review described the most common produced plastic types and their typical degradation process. It explored the current limitation of enhanced landfill mining (ELFM) feasibility related to the lack of knowledge on recovered material condition and how to upcycle it. After overviewing the different recycling strategy, the potential upcycling of recovered plastics was identified in the chemical and thermochemical recycling (tertiary recycling) of this material. Few studies have investigated the application of tertiary recycling to recovered plastics from landfill. The analysis of genuine plastics from MSW landfills is very limited in the literature and most of the studies conducted to date only evaluated the plastics as a whole stream without identifying the different polymers for energy recovery. In this study, the recovered plastic from landfill was analysed to investigate the extent of degradation and chemical composition of main plastic types such as polyethylene (PE) and polypropylene (PP) which represented 64 wt% of total recovered plastics. Overall, PE and PP with storage of more than 10 years in landfill showed a greater extent of degradation compared to newer samples with fewer years of storage and fresh plastic waste samples. The recovered plastics pyrolysis was simulated with a model built in ASPEN Plus software for predicting the pyrolysis products yields. Commodity chemicals such as olefins and BTX were further analysed in order to give information on related potential income. The recovery of these materials could help to mitigate the utilisation of virgin fossil resources. The pyrolysis of recovered plastics was performed using a Py-GC-MS at a temperature between 350 and 800°C. Detailed information of potential recyclable chemicals compounds was given suggesting the inclusion of recovered plastics into the new circular plastic economy point of view. Most compounds were identified in the products fitted within the naphtha range (C6-C10) which has a high potential to be used in the petrochemical cluster. Further studies should analyse the cost and benefits and life cycle of the whole process from excavation to the production of valuable chemicals through pyrolysis.
Exploitation Route This research highlights the urgency of considering the new management of disposed plastics important as the management of new plastics waste. The material present in landfills can be valorised through ELFM. Due to the high percentage of plastics in landfills, the feasibility of ELFM depends also to the valorisation of this material. The data on chemical compounds derived from pyrolysis of recovered plastics can help to evaluate the feasibility of ELFM projects, introduce the recovered plastics into the circular economy and reduce the use of virgin fossil resources.
Sectors Chemicals,Energy,Environment,Government, Democracy and Justice,Manufacturing, including Industrial Biotechology