Oil has played a crucial role in the energy sector for centuries, powering everything from domestic cooking to industrial engines and boilers. Its high energy density, simplicity, and availability worldwide have made it a staple in energy production. Traditionally, oil was derived from natural biomass and used extensively, but the advent of crude oil refined into petrol fuels like petrol and diesel gradually dominated the market. However, growing concerns over climate change and the greenhouse effect are leading to a resurgence in using biomass-based oils as alternatives to fossil fuels. While edible biomass oils are primarily reserved for food and medicinal purposes, non-edible biomass oils are increasingly being used for industrial and energy applications. Pyrolysis is gaining momentum among the methods for extracting oil from non-edible biomass. This thermal decomposition process converts complex macromolecules in biomass into bio-oil, offering a renewable alternative to fossil fuels.
What is Pyrolysis?
Pyrolysis is a thermal decomposition process that occurs in the absence of air. It is the initial stage in combustion and gasification reactions, where biomass breaks down at the molecular level. Pyrolysis of biomass typically yields three primary products: solid biochar, liquid bio-oil, and gases such as methane (CH4), hydrogen (H2), carbon monoxide (CO), and carbon dioxide (CO2). These products’ proportions vary depending on the operating temperature and heating rate.
Solid Biochar: Produced at temperatures below 450°C, biochar is a solid residue rich in carbon.
Bio-Oil: Yield increases with higher temperatures, providing a liquid fuel alternative.
Gaseous Byproducts: Including methane, hydrogen, and carbon monoxide, these gases can be used for energy generation.
Pyrolysis of Plastics and Rubber Tyres
In recent years, pyrolysis has expanded beyond biomass to include waste plastics and rubber tyres as feedstocks. This approach addresses the growing environmental problem of plastic and rubber waste disposal. However, the process also poses significant risks, including the release of harmful emissions such as hydrogen sulfide (H2S), methane (CH4), and carbon monoxide (CO). Additionally, the high heat required for pyrolysis can contribute to environmental warming.
Plastics, which take an extended period to degrade naturally, are affected by various factors such as sunlight, air, moisture, and thermal stress. Due to their durable molecular structure, they resist degradation under normal conditions, making pyrolysis an effective method for breaking them down into more minor, combustible compounds. Similarly, rubber tyres, which also degrade slowly, require high temperatures for pyrolysis.
However, not all plastics yield the same products during pyrolysis. The type of plastic and the operating temperature significantly influence the composition of the resulting bio-oil and gases. Common hydrocarbons produced include polyaromatic hydrocarbons (PAHs), polyaromatic nitrogen hydrocarbons (PANHs), and polyaromatic sulfur hydrocarbons (PASHs), with carbon chains ranging from C5 to C20.
A Scientific View On Pyrolysis of Plastics and Rubber Tyres:
Pyrolysis offers a promising solution for converting non-edible biomass, plastics, and rubber tyres into biofuels. The process can produce a variety of hydrocarbons suitable for combustion, effectively mimicking the fractional distillation of crude oil. However, it’s essential to acknowledge the environmental and safety concerns associated with pyrolysis, including the potential release of toxic emissions and the significant heat required for the process.
While pyrolysis can produce high-quality combustible chemical compounds, it is also time- and resource-intensive. This raises questions about the overall environmental friendliness of the process. As we continue exploring renewable energy alternatives, it’s crucial to weigh the benefits and drawbacks of pyrolysis and consider its long-term impact on the environment and energy sustainability.
Table 1: Chemical compounds obtained during the pyrolysis of different types of plastics (Qureshi et al., 2020)
Table 2: products produced during pyrolysis of different types of tyre materials (Alsaleh and Sattler, 2014)
From table 1 and 2, it is evident that pyrolysis of both plastics and rubber tyres yields a higher number of hydrocarbons like polyaromatic hydrocarbons (PAHs), polyaromatic nitrogen hydrocarbon (PANH), and polyaromatic sulphur hydrocarbons (PASHs); with their carbon chain length ranging between 5 and 20. On the other hand, aliphatic hydrocarbons were reported as straight-chain alkanes with carbon chain length ranging between 6 and 37. Most commonly occurring aromatic HCs include benzene, indene, limonene, styrene, toluene and xylenes. Moreover, upon distilling the pyrolysis oil, light fraction yielded BTEX and styrene, while heavy fractions yielded chemical compounds similar to asphalt. Also, high sulphur content is reported for pyrolysis oil at processing temperatures near 400OC and 650OC. However, intermediate temperatures reported minimal sulphur content (Williams, 2013). Likewise, major gas constituents include hydrogen (H2), methane (CH4), ethane (C2H6), ethene (C2H4), propane (C3H8), propene (C3H6), butane (C4H10), butene (C4H8), butadiene (C4H6), carbon dioxide (CO2), carbon monoxide (CO), and hydrogen sulfide (H2S) (Kaminsky et al., 2009).
Conclusion
One can appreciate the benefits reaped from the pyrolysis of plastic and rubber tyres, which produced varieties of hydrocarbons that can be used for fuelling engines. In fact, this technique redemonstrates the fractional distillation of crude oil, except it is replaced with plastic or rubber wastes. Chemical compounds produced during this process can be processed according to their requirement and are almost the same as the products developed during fractional distillation of crude oil. However, not all products are desired and environmental friendly; instead have the ability to produce high toxic emission which can be harmful to both living beings and environment.
If you’re interested in learning more about biofuel production and the potential of pyrolysis or if you have any questions, please call +91-9315124803.
References;
Alsaleh, A., & Sattler, M. L. (2014). Waste tire pyrolysis: influential parameters and product properties. Current Sustainable/Renewable Energy Reports, 1(4), 129-135.
Kaminsky, W., Mennerich, C., & Zhang, Z. (2009). Feedstock recycling of synthetic and natural rubber by pyrolysis in a fluidized bed. Journal of Analytical and Applied Pyrolysis, 85(1-2), 334-337.
Martínez, J. D., Puy, N., Murillo, R., García, T., Navarro, M. V., & Mastral, A. M. (2013). Waste tyre pyrolysis–A review. Renewable and Sustainable Energy Reviews, 23, 179-213.
Qureshi, M. S., Oasmaa, A., Pihkola, H., Deviatkin, I., Tenhunen, A., Mannila, J., … & Laine-Ylijoki, J. (2020). Pyrolysis of plastic waste: opportunities and challenges. Journal of Analytical and Applied Pyrolysis, 152, 104804.
Reddy, B. R., & Vinu, R. (2018). Feedstock characterization for pyrolysis and gasification. In Coal and biomass gasification (pp. 3-36). Springer, Singapore.
Shah, A. A., Hasan, F., Hameed, A., & Ahmed, S. (2008). Biological degradation of plastics: a comprehensive review. Biotechnology advances, 26(3), 246-265.
Vijayakumar, A., & Sebastian, J. (2018, August). Pyrolysis process to produce fuel from different types of plastic–a review. In IOP Conference Series: Materials Science and Engineering (Vol. 396, No. 1, p. 012062). IOP Publishing.
Williams, P. T. (2013). Pyrolysis of waste tyres: a review. Waste management, 33(8), 1714-1728.
