Chemical recycling of waste plastics: The role of catalysts Pyrolysis oil from plastics enables the integration of the circular economy for sustainable chemicals and energy
Tooran Khazraie Valmet Guillaume Vincent BASF
Background The mounting issue of plastic waste represents a significant global challenge, calling for the development of creative and enduring solutions for its management. Since the 1960s, the production and use of plastic have escalated dramatically, increasing more than 20 times, mainly due to the demand for single- use packaging. Presently, less than 20% of plastic waste is recycled worldwide. The vast majority ends up in landfills, is incinerated, or unintentionally ends up in natural habitats ( Gao, et al., 2022 ). Mechanical recycling is often considered the optimal solution for recycling plastics. However, its effectiveness is constrained, especially when dealing with plastics that are mixed or contaminated with unwanted substances like metals, paper, other types of polymers, or fillers. Additionally, the limited number of times that plastics can be mechanically recycled – due to the breakdown of polymer chains during the extrusion process – eventually leads to their disposal as waste, thereby continuing the cycle of environmental contamination. This issue is further aggravated by the predominant use of fossil fuels in plastic production ( Musso, et al., 2022 ). Due to these limitations, chemical recycling is emerging as a viable alternative, capable of transforming mixed and contaminated plastics into valuable commodities. While there are various chemical recycling techniques, including gasification, pyrolysis, and solvolysis, this work focuses on pyrolysis. In fast pyrolysis, waste plastics are quickly (within a few seconds) heated to around 600°C in the absence of
oxygen. The vapours produced are then condensed to give a dark brown fast pyrolysis oil product. In certain cases, a catalyst, often zeolite-based, might be employed to improve the quality and yield from the pyrolysis process. Ideally, pyrolysis can revert polyolefin plastics to their monomeric forms, which are then utilised within refinery or petrochemical processes. However, the process yields a wide spectrum of products, including gases, naphtha, heavy oils, and waxes. In the decentralised concept of chemical recycling of plastic through pyrolysis, production of liquids is favoured, given the economic advantage for transportation of liquids over wax or gaseous products. This article investigates two innovative approaches using catalysts to upgrade plastic waste at two different points in the chemical recycling of plastic value chain: • Maximising naphtha yield in pyrolysis oil through catalytic pyrolysis treatment from waste plastics using BASF’s proprietary catalysts. • Cracking of a waxy fraction produced in the fast thermal pyrolysis of low-density polyethylene (LDPE) using BASF’s commercial fluid catalytic cracking (FCC) catalysts. The main objective of this work was to increase the amount of condensable vapours generated by the pyrolysis process, particularly in the naphtha range. Pyrolysis was performed in a small-scale unit equipped with two fixed-bed reactors ( Stefanidis, et al., 2011 ) developed by the Chemical Process and Energy Resources Institute (CPERI). Catalytic and thermal pyrolysis of waste plastic
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