Pyrolytic Conversion of Plastic Waste to Value-Added Products and Fuels: A Review

Abstract

Plastic production has been rapidly growing across the world and, at the end of their use, many of the plastic products become waste disposed of in landfills or dispersed, causing serious environmental and health issues. From a sustainability point of view, the conversion of plastic waste to fuels or, better yet, to individual monomers, leads to a much greener waste management compared to landfill disposal. In this paper, we systematically review the potential of pyrolysis as an effective thermochemical conversion method for the valorization of plastic waste. Different pyrolysis types, along with the influence of operating conditions, e.g., catalyst types, temperature, vapor residence time, and plastic waste types, on yields, quality, and applications of the cracking plastic products are discussed. The quality of pyrolysis plastic oil, before and after upgrading, is compared to conventional diesel fuel. Plastic oil yields as high as 95 wt.% can be achieved through slow pyrolysis. Plastic oil has a heating value approximately equivalent to that of diesel fuel, i.e., 45 MJ/kg, no sulfur, a very low water and ash content, and an almost neutral pH, making it a promising alternative to conventional petroleum-based fuels. This oil, as-is or after minor modifications, can be readily used in conventional diesel engines. Fast pyrolysis mainly produces wax rather than oil. However, in the presence of a suitable catalyst, waxy products further crack into oil. Wax is an intermediate feedstock and can be used in fluid catalytic cracking (FCC) units to produce fuel or other valuable petrochemical products. Flash pyrolysis of plastic waste, performed at high temperatures, i.e., near 1000 °C, and with very short vapor residence times, i.e., less than 250 ms, can recover up to 50 wt.% ethylene monomers from polyethylene waste. Alternatively, pyrolytic conversion of plastic waste to olefins can be performed in two stages, with the conversion of plastic waste to plastic oil, followed by thermal cracking of oil to monomers in a second stage. The conversion of plastic waste to carbon nanotubes, representing a higher-value product than fuel, is also discussed in detail. The results indicate that up to 25 wt.% of waste plastic can be converted into carbon nanotubes.

Transforming Plastic Waste into Porous Carbon for Capturing Carbon Dioxide: A Review

“…This is because not all types of plastic are suitable for pyrolysis. For example, as reported by Papari et al [109], waste PVC produces a significant amount of benzoic acid and hydrochloric acid during the pyrolysis process, which can cause corrosion problems to the equipment. The pyrolysis process can generate high aromatic contents of oil, but some of the aromatic hydrocarbons are toxic and can have a negative impact on the environment and cause serious human health issues.…”

Innovations in applications and prospects of bioplastics and biopolymers: a review

“…Conventional petrochemical-based plastics are non-biodegradable because of which they last in landfills and oceans for thousands of years, thus affecting soil quality, microbial activity, flora and fauna. However, the overuse of petrochemically derived plastics, rubbers and synthetic polymers along with their inferior recycling techniques has made their remediation more difficult (Nanda et al 2019 ; Nanda and Berruti 2021c ). Alternative and sustainable methods for recycling or valorizing plastic wastes should be established instead of their pervasive disposal into landfills and oceans.…”

Advanced Biofuels Based on Fischer–Tropsch Synthesis for Applications in Gasoline Engines

“…Another widespread method is chemical recycling of waste using pyrolysis by producing pyrolysis oil. Sources for this process can be waste tyres [ 10 ], plastic waste [ 11 ], municipal solid waste [ 12 ] or lignocellulosic biomass [ 13 , 14 ]. Last but not least, in this category is also hydrogen produced from renewable energy sources [ 15 ].…”