Technical aspects of marine plastic litter treatment by pyrolysis, for material and energy recovery

Abstract

Marine plastic pollution is a serious problem the world is currently facing. Due to the long exposure to the marine environment and contamination from salts and microorganisms, the properties of marine plastic litter would potentially differ from conventional plastic waste. This could affect the downstream treatment of marine plastic waste. Pyrolysis is a recycling technique often adopted in the treatment of plastic wastes, converting plastic into coke, oil and gas that can be reused as fuel or intermediates for manufacturing. Catalytic chemical vapour deposition (CCVD) is one method that has been widely researched for the up-cycling of plastic pyrolysis products into valuable carbon nanomaterials. Hence, this study investigated: 1) technical aspect of marine plastic recovery in terms of energy and material recovery and 2) the feasibility of using non-condensable gas from marine plastic litter pyrolysis for up-cycling into carbon nanotubes (CNTs). Marine plastic litter obtained from 2 sources were sorted and divided into ‘washed’ and ‘raw’ samples. The samples were characterised for ion chromatography, ash content and calorimetry prior to pyrolysis. Pyrolysis was conducted at 600℃ and non-condensable gases were passed through Ni-Ca catalyst at 600℃ for one hour during CCVD for CNT synthesis. Analysis of pyrolysis oils revealed its potential to be recovered as fuels due to the high proportion of short chain hydrocarbons. The presence of large fractions of ethylene, propylene, C4 and C5 hydrocarbons suggested the ability of non-condensable pyrolysis gas to be converted into CNTs via CCVD. The formation of CNTs affirmed the feasibility of using pyrolysis gas from using marine plastic waste as feedstock.