Pyrolysis represents the thermal degradation of materials at high temperatures within an inert atmosphere. The process has several industrial uses and applications. Nonetheless, plastic pyrolysis is one of the processes or techniques used in converting waste plastics into energy in the form of solid, liquid, or gaseous fuels. Hence, it is an energy recovery method and a more specific type of waste-to-energy conversion.
Different Fuel Byproducts of Plastic Pyrolysis
Specific types of plastic such as polyethylene plastics and polypropylene plastics can be processed to extract fuels simply because they are fundamentally made from petrochemicals and other hydrocarbon compounds. However, take note that there are specific types of fuels that can be extracted through the pyrolysis of plastics. Take note of the following:
• Hydrogen: Several techniques and processes have been utilized to extract hydrogen from discarded plastics. These include a two-step process that involves pyrolysis and catalytic steam reforming of pyrolysis gases and vapors. The recovered hydrogen can be used for aircraft propulsion and fuel cell vehicles.
• Diesel: The thermal degradation of waste plastics can also produce liquid oil. The high temperature and high pressure break down the plastics and convert them into oils. The extracted liquid oil can be processed further through oil refinery distillation. Distillation converts the liquid oil into diesel.
• Other Hydrocarbons: Energy recovery from plastics by pyrolysis also produce other hydrocarbon compounds such as kerosene, as well as hydrocarbon gas including butane and propane. These byproducts can be recovered and processed further for use in heating systems, kitchen stoves, and smaller vehicles, among others.
Pros: What Are the Advantages of Plastic Pyrolysis
The main advantage of plastic pyrolysis centers on energy recovery that in turn, has specific environmental, economic, and social advantages. Furthermore, processing waste plastics into useful sources of energy promotes the concept of a circular economy and might be a solution to the ongoing climate emergency.
Below are the specific benefits and applications:
1. Waste Management via Upcycling
Pyrolysis is fundamentally a process for upcycling waste plastics or more specifically, for transforming unwanted and discarded plastic materials into newer and usable byproducts. The facilities used for processing these wastes also use discarded combustible non-recyclable materials. Hence, plastic pyrolysis prevents waste materials from ending up in landfills.
Findings from a study by R. Geyer, J. R. Jambeck, and K. L. Law revealed that of the 8.3 billion metric tons of plastics that have been produced, 6.3 billion metric tons have become plastic waste. These discarded plastics end up in landfills, in seas and oceans, washed ashore, or partially degraded into microplastics, thus polluting the environment. Advanced recycling and recovery technologies should be part of the integrated solid waste management of a community.
2. Alternative Source of Energy
Remember that the thermal degradation of waste plastics produces fuel byproducts. Thus, it is important to highlight the fact that pyrolysis, particularly when applied in plastics, is an energy recovery method. The technology can supplement the energy supply of a specific community while reducing the need to extract, transport, and burn fossil fuels to maintain energy security. Note that the upstream, midstream, and downstream activities of the hydrocarbon industry are energy intensive.
Energy recovery via plastic pyrolysis has also specific advantages over fossil fuels. Researchers P. T. Benavides et al. from the Argonne National Laboratory conducted a life-cycle analysis of fuels from post-use non-recycled plastics. Their findings showed that when compared to ultra-low-sulfur diesel derived from post-use plastics with the same fuel from conventional sources, pyrolysis technique reduced greenhouse gas emissions by up to 14 percent, water usage by 58 percent, and fossil fuel-derived energy usage by 96 percent.
3. Source of Economic Activity
The operation of pyrolysis facilities, as well as the activities built around energy recovery from waste plastics by pyrolysis, can have economic and social benefits. These facilities can generate jobs, become a source of livelihoods in communities, and become a primary industry. Apart from the labor requirements of building and operating pyrolysis plants, community members can immerse themselves in enterprises involved in collecting and sorting solid waste materials.
A factsheet published by the American Chemistry Council mentioned that plastic-to-fuel facilities in the United States could employ 39,000 individuals and produce nearly USD 9 billion in economic output. The energy produced in these facilities can help national governments save money from reduced fossil fuel importation while promoting energy diversification.
Cons: What Are the Disadvantages of Plastic Pyrolysis
Despite the aforementioned advantages or benefits and applications, energy recovery via plastic pyrolysis has several disadvantages. Critics are also concerned about its possible negative environmental impacts that could offset its environmental gains.
The following are the specific drawbacks and limitations:
1. A Possible Source of Emissions
The study of I. Kalargaris, G. Tian, and S. Gu showed that fuel oils from plastic pyrolysis produced higher exhaust emissions than diesel obtained directly from hydrocarbon processing. In addition, fuel oils extracted using higher temperatures also produce higher emissions than those produced using low temperatures.
Nevertheless, using waste plastics as fuels is not a completely clean source of energy. Subjecting these materials to high temperatures can result in the release of nitrous oxides, sulfur dioxides, particulate matter, and other harmful pollutants. The use of complementary technologies, alongside the inclusion of strict government regulation, should be put in place to minimize the environmental drawbacks of plastic pyrolysis.
2. Further Technological Development
Conversion technologies and some of the more specific waste-to-energy conversion methods and techniques are relatively new. Furthermore, the technologies and processes used for recovering energy from plastics via pyrolysis are still emerging. More research or studies are needed to come up with an industrial and commercialized guideline that would standardize energy recovery activities via the pyrolysis of plastics.
In addition, because of the relative novelty of plastic pyrolysis, the cost of implementation remains high. Constructing facilities and maintaining their operations are still unaffordable for developing and underdeveloped countries, as well as for jurisdictions without access to financial and technical resources, as well as with poor economic outlook.
3. Concerns Over Sustainability
Some countries that partially depend on waste-to-energy technologies might encounter problems in their supply chain. For example, Sweden depends heavily on importing trash from other European countries to keep their waste-to-energy facilities operational. A shortage in wastes would disrupt the operations of these facilities and create energy security problems. Hence, one of the disadvantages of plastic pyrolysis, particularly when used as a method for producing energy, is its dependence on the required waste plastic raw materials.
Others are also worried that specific energy recovery via plastic pyrolysis would undermine other solid waste management activities and practices, as well as other waste-to-energy processes such as waste incineration or waste-to-energy incineration. The inclusion of pyrolysis in an integrated solid waste management strategy would require careful planning and implementation of appropriate policies and regulations.
FURTHER READINGS AND REFERENCES
- American Chemistry Council. 2019. “Economic Potential of Advanced Recycling Technologies in the U.S.” American Chemistry Council. Available online
- Benavides, P. T., Sun, P., Han, J., Dunn, J. B., and Wang, M. 2017. Life-cycle Analysis of Fuels from Post-use Non-recycled Plastics.” Fuel. 203: 11-22. DOI: 1016/j.fuel.2017.04.070
- Czernik, S. and French, R. J. 2006. “Production of Hydrogen from Plastics by Pyrolysis and Catalytic Steam Reform.” Energy & Fuels. 20(2): 754-758. DOI: 1021/ef050354h
- Geyer, R., Jambeck, J. R., and Law, K. L. 2017. “Production, Use, and Fate of all Plastics Ever Made.” Science Advances. 3(7): e1700782. DOI: 1126/sciadv.1700782
- Kalargaris, I., Tian, G., and Gu, S. 2017. “The Utilization of Oils Produced from Plastic Waste at Different Pyrolysis Temperatures in a DI Diesel Engine.” Energy. 131: 179-185. DOI: 1016/j.energy.2017.05.024
- Miandad, R., Rehan, M., Barakat, M. A., Aburiazaiza, A. S., Khan, H., Ismail, I. M. I., Dhavamani, J., Gardy, J., Hassanpour, A., and. Nizami, A.-S. 2019. “Catalytic Pyrolysis of Plastic Waste: Moving Toward Pyrolysis Based Biorefineries.” Frontiers in Energy Research. 7. DOI: 3389/fenrg.2019.00027
- Thahir, R., Altway, A., Juliastuti, S. R., and Susianto. 2019. “Production of Liquid Fuel from Plastic Waste Using Integrated Pyrolysis Method with Refinery Distillation Bubble Cap Plate Column.” Energy Reports. 5: 70-77. DOI: 1016/j.egyr.2018.11.004