Plastic waste is one of the most pressing environmental issues of our time. According to the World Bank, the global generation of plastic waste was 242 million tons in 2016, and it is expected to increase to 417 million tons by 2030. Most of this waste ends up in landfills, incinerators, or the oceans, causing pollution, greenhouse gas emissions, and harm to wildlife and human health.
One way to address this problem is to recycle plastic waste into valuable products, such as fuels, chemicals, or new plastics. This can reduce the demand for fossil resources, lower the carbon footprint of the plastics industry, and create a circular economy for plastics. Among the various technologies for plastic recycling, pyrolysis is a promising option that can convert mixed and contaminated plastic waste into liquid oils, gases, and char.
Pyrolysis is a thermal decomposition process that occurs in the absence of oxygen. It breaks down the long polymer chains of plastics into smaller hydrocarbon molecules, mainly in the range of C5-C20. The composition and quality of the pyrolysis oil (pyoil) depend on the type and purity of the plastic feedstock, the pyrolysis temperature and residence time, the catalyst used, and the post-treatment applied.
Pyoil can be used as a feedstock for steam crackers, which are industrial plants that produce ethylene and propylene, the main building blocks for most plastics. By using pyoil instead of conventional naphtha or gas oil, steam crackers can reduce their dependence on fossil fuels and lower their greenhouse gas emissions. Moreover, pyoil can potentially increase the yield of ethylene and propylene, as it contains a higher fraction of olefins than naphtha.
However, there are also significant challenges and barriers for the application of pyoil as a feedstock for steam crackers. Some of the main ones are:
- Quality and consistency: Pyoil is a complex and heterogeneous mixture of hydrocarbons, oxygenates, aromatics, and contaminants, such as water, ash, metals, halogens, and nitrogen. These impurities can cause corrosion, fouling, coking, and poisoning of the steam cracker equipment and catalysts, leading to reduced performance, increased maintenance, and higher costs. Therefore, pyoil needs to meet strict specifications for steam cracking, such as low water, sulfur, and chlorine content, narrow boiling range, and high olefin-to-paraffin ratio. However, achieving these specifications requires extensive and costly upgrading and purification processes, such as hydrotreating, distillation, dehalogenation, and filtration. Moreover, the quality and consistency of pyoil can vary depending on the source and composition of the plastic waste, which can affect the steam cracker operation and product distribution.
- Supply and demand: Pyoil is a relatively new and niche product, with limited availability and market demand. According to a recent study, the global production capacity of pyoil was estimated at 1.5 million tons per year in 2020, which is only 0.4% of the global steam cracker feedstock demand. The majority of the pyoil producers are small and medium-sized enterprises, located mainly in Asia and Europe, with varying technologies and standards. The lack of a stable and reliable supply chain, as well as a clear regulatory framework and incentive scheme, hinders the integration of pyoil into the existing steam cracker infrastructure and market.
- Economics and sustainability: Pyoil is not necessarily cheaper or greener than conventional steam cracker feedstocks. The production cost of pyoil depends on several factors, such as the plastic waste collection and sorting cost, the pyrolysis plant capital and operating cost, the pyoil upgrading and transportation cost, and the price and availability of competing waste disposal options. The environmental impact of pyoil also depends on several factors, such as the life cycle emissions of the plastic waste, the energy consumption and emissions of the pyrolysis and upgrading processes, the displacement of fossil fuels and virgin plastics, and the potential leakage of pollutants and microplastics. A comprehensive and comparative assessment of the economic and environmental performance of pyoil is needed to evaluate its viability and attractiveness as a steam cracker feedstock.
In conclusion, pyoil is a potential alternative feedstock for steam crackers that can contribute to the circular economy of plastics and the decarbonization of the petrochemical industry. However, it also faces significant technical, logistical, and regulatory challenges that need to be overcome to achieve commercial and sustainable deployment. Further research and development, as well as collaboration and coordination among the stakeholders, are required to address these challenges and unlock the opportunities of pyoil for steam cracking.
