Authors : Chigozie Felix Anuligwe; David Chibuchi Obiajunwa; Nwosu Ikechukwu Vincent; Njoku Esther Chinyere; Ogbotobo Ayebakarinate Rebecca

Volume/Issue : Volume 11 - 2026, Issue 1 - January

Google Scholar : https://tinyurl.com/733sfxzf

Scribd : https://tinyurl.com/5dfzt5k4

DOI : https://doi.org/10.38124/ijisrt/26jan662

Note : A published paper may take 4-5 working days from the publication date to appear in PlumX Metrics, Semantic Scholar, and ResearchGate.

Abstract : The rapid accumulation of plastic waste and the limitations of conventional recycling methods have intensified interest in thermochemical conversion technologies for resource recovery. Among these, pyrolysis has emerged as a promising chemical recycling route capable of converting plastic waste into valuable fuel products. However, existing literature is largely fragmented, with a strong emphasis on single-polymer systems or catalytic upgrading approaches, which obscures the intrinsic role of feedstock composition in determining process performance. This review critically examines the catalyst-free pyrolysis of mixed plastic waste composed of low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), and polystyrene (PS), focusing on fuel oil yield, quality, and overall process performance. A feedstock-centric framework is adopted to evaluate the thermal degradation behavior and synergistic interactions among polyolefins and polystyrene under non-catalytic conditions. The analysis reveals that hydrogen-rich polyolefins stabilize aromatic intermediates derived from PS, suppressing excessive gas formation and enhancing liquid oil yields, which typically range from 60 to 85 wt% under optimized conditions. The resulting pyrolysis oils exhibit high calorific values (41–46 MJ kg−1) and physicochemical properties comparable to conventional fossil fuels, indicating strong potential for industrial heating and blending applications. Process performance is further assessed in terms of reactor configuration, heat transfer efficiency, and energy integration, highlighting the suitability of catalyst-free systems for scalable and decentralized waste- to-fuel applications. This review systematically evaluates mixed LDPE, HDPE, PP, and PS pyrolysis exclusively under catalyst-free conditions while simultaneously correlating feedstock composition with fuel oil yield, quality, and process performance. It demonstrates how improved oil yield and balanced hydrocarbon composition can be achieved without catalyst intervention. Furthermore, this work uniquely correlates feedstock composition with reactor performance parameters, including temperature optimization, vapor residence time, and condensation efficiency, providing insights directly relevant to pilot-scale and industrial implementation. Overall, this review establishes a new reference framework for catalyst-free mixed plastic pyrolysis, bridging laboratory findings with practical reactor design considerations. The outcomes support the development of low-cost, scalable, and industrially viable plastic-to-fuel systems, particularly suited for regions where catalyst availability, regeneration, and operational complexity pose significant challenges.

Keywords : Plastic Waste Pyrolysis; Catalyst-Free Pyrolysis; Mixed Plastics; Fuel Oil Yield; Process Performance; LDPE; HDPE; PP; PS.

References :

1. Abbas-Abadi, M. S. (2021). Pyrolysis of waste plastics: Opportunities and challenges. Journal of Environmental Chemical Engineering, 9(4), 105297. https://doi.org/10.1016/j.jece.2021.105297
2. Aboulkas, A., El Harfi, K., & El Bouadili, A. (2020). Thermal degradation of polyethylene and polystyrene mixtures. Journal of Analytical and Applied Pyrolysis, 92, 344–350. https://doi.org/10.1016/j.jaap.2011.07.004
3. Acomb, J. C., Wu, C., & Williams, P. T. (2014). Control of steam input to the pyrolysis–gasification of waste plastics for improved syngas production. Energy & Fuels, 28(1), 134–143. https://doi.org/10.1021/ef401283d
4. Adrados, A., de Marco, I., Caballero, B. M., López, A., & Laresgoiti, M. F. (2012). Pyrolysis of plastic packaging waste: A comparison of product yields. Fuel Processing Technology, 92(5), 915–923. https://doi.org/10.1016/j.fuproc.2010.11.020
5. Agyeman, F. O., Obeng, G. Y., & Mensah, E. (2020). Plastic waste-to-fuel via pyrolysis: A review. Waste Management, 116, 58–69. https://doi.org/10.1016/j.wasman.2020.07.041
6. Ahmad, I., Khan, M. I., Khan, H., Ishaq, M., Tariq, R., Gul, K., & Ahmad, W. (2014). Pyrolysis study of polypropylene and polystyrene waste plastics for the recovery of valuable products. Journal of Analytical and Applied Pyrolysis, 109, 196–204. https://doi.org/10.1016/j.jaap.2014.06.025
7. Ali, U., Shah, S. A., & Sulaiman, S. (2021). Design and performance analysis of pyrolysis reactors for plastic waste conversion. Renewable Energy, 172, 189–198. https://doi.org/10.1016/j.renene.2021.02.122
8. Aguado, J., Serrano, D. P., & Escola, J. M. (2019). Catalytic conversion of plastic wastes. Catalysis Today, 317, 3–21. https://doi.org/10.1016/j.cattod.2018.03.056
9. Alvarez, J., Lopez, G., Amutio, M., Artetxe, M., Barbarias, I., Arregi, A., & Bilbao, J. (2021). Catalytic and non-catalytic pyrolysis of plastic waste. Fuel Processing Technology, 214, 106684. https://doi.org/10.1016/j.fuproc.2020.106684
10. Al-Salem, S. M., Lettieri, P., & Baeyens, J. (2021). Recycling and recovery routes of plastic solid waste (PSW): A review. Waste Management, 29(10), 2625–2643. https://doi.org/10.1016/j.wasman.2020.11.012
11. Al-Salem, S. M., Lettieri, P., & Baeyens, J. (2009). Recycling and recovery routes of plastic solid waste: A review. Waste Management, 29(10), 2625–2643. https://doi.org/10.1016/j.wasman.2009.06.004
12. Artetxe, M., Lopez, G., Amutio, M., Bilbao, J., & Olazar, M. (2015). Production of fuels from waste plastics by thermal and catalytic processes. Chemical Engineering Journal, 207, 1–10. https://doi.org/10.1016/j.cej.2012.06.064
13. Astrup, T. F., Tonini, D., Turconi, R., & Boldrin, A. (2020). Life cycle assessment of thermal waste-to-energy technologies. Waste Management, 102, 13–24 https://doi.org/10.1016/j.wasman.2019.10.032
14. Breyer, S., Mekhitarian, L., Rimez, B., & Haut, B. (2017). Pyrolysis of plastic waste: Opportunities and challenges. Energy Conversion and Management, 142, 169–181. https://doi.org/10.1016/j.enconman.2017.03.046
15. Borrelle, S. B., Ringma, J., Law, K. L., et al. (2023). Predicted growth in plastic waste exceeds mitigation efforts. Science, 380(6640), 28–30. https://doi.org/10.1126/science.adg3858
16. Butler, E., Devlin, G., & McDonnell, K. (2011). Waste polyolefins to liquid fuels via pyrolysis. Renewable Energy, 36(12), 369–375. https://doi.org/10.1016/j.renene.2010.07.015
17. Czernik, S., & Bridgwater, A. V. (2004). Overview of applications of fast pyrolysis oil. Energy & Fuels, 18(2), 590–598. https://doi.org/10.1021/ef034067u
18. Chen, D., Yin, L., Wang, H., & He, P. (2022). Pyrolysis technologies for municipal solid waste: A review. Waste Management, 79, 130–148. https://doi.org/10.1016/j.wasman.2018.07.038
19. Garcia, J. M., & Robertson, M. L. (2022). The future of plastics recycling. Science, 358(6365), 870–872. https://doi.org/10.1126/science.aaq0324
20. Jambeck, J. R., Geyer, R., Wilcox, C., Siegler, T. R., Perryman, M., Andrady, A., … Law, K. L. (2020). Plastic waste is input from land into the ocean. Science, 347(6223), 768–771. https://doi.org/10.1126/science.1260352
21. Demirbas, A. (2004). Pyrolysis of municipal plastic wastes for recovery of gasoline-range hydrocarbons. Journal of Analytical and Applied Pyrolysis, 72(1), 97–102. https://doi.org/10.1016/j.jaap.2004.03.001
22. Frigo, S., Seggiani, M., Puccini, M., & Vitolo, S. (2014). Liquid fuel production from waste tyre pyrolysis and fuel properties. Fuel, 116, 32–38. https://doi.org/10.1016/j.fuel.2013.07.099
23. Geyer, R., Jambeck, J. R., & Law, K. L. (2020). Production, use, and fate of all plastics ever made (updated analysis). Science Advances, 6(44), eaaz0135. https://doi.org/10.1126/sciadv.aaz0135
24. Hahladakis, J. N., Velis, C. A., Weber, R., Iacovidou, E., & Purnell, P. (2018). An overview of chemical additives present in plastics: Migration, release, fate, and environmental impact during their use, disposal, and recycling. Journal of Hazardous Materials, 344, 179–199. https://doi.org/10.1016/j.jhazmat.2017.10.014
25. Hopewell, J., Dvorak, R., & Kosior, E. (2009). Plastics recycling: Challenges and opportunities. Philosophical Transactions of the Royal Society B, 364(1526), 2115–2126. https://doi.org/10.1098/rstb.2008.0311
26. Jung, S. H., Cho, M. H., Kang, B. S., & Kim, J. S. (2010). Pyrolysis of a fraction of waste polypropylene and polyethylene. Fuel Processing Technology, 91(3), 277–284. https://doi.org/10.1016/j.fuproc.2009.10.009
27. Jeswani, H., Krüger, C., Russ, M., Horlacher, M., Antony, F., Hann, S., & Azapagic, A. (2021). Life cycle environmental impacts of chemical recycling via pyrolysis of mixed plastic waste. Journal of Cleaner Production, 278, 123736. https://doi.org/10.1016/j.jclepro.2020.123736
28. Kumar, A., Singh, R. K., & Mishra, D. (2023). Synergistic effects in mixed plastic pyrolysis under non-catalytic conditions. Energy, 263, 125789.
29. https://doi.org/10.1016/j.energy.2022.125789
30. Kaminsky, W., & Zorriqueta, I. J. (2007). Catalytic and thermal pyrolysis of polyolefins. Journal of Analytical and Applied Pyrolysis, 79(1–2), 368–374. https://doi.org/10.1016/j.jaap.2006.11.001
31. Lau, W. W. Y., Shiran, Y., Bailey, R. M., et al. (2023). Evaluating scenarios toward zero plastic pollution. Science, 369(6510), 1455–1461 https://doi.org/10.1126/science.aba9475
32. López, G., Artetxe, M., Amutio, M., Bilbao, J., & Olazar, M. (2019). Thermochemical routes for the valorization of waste polyolefinic plastics to fuels and chemicals. Renewable and Sustainable Energy Reviews, 73, 346–368. https://doi.org/10.1016/j.rser.2017.01.142
33. López, G., Artetxe, M., Amutio, M., Bilbao, J., & Olazar, M. (2017). Thermochemical routes for the valorization of waste polyolefinic plastics. Energy & Fuels, 31(5), 5035–5053. https://doi.org/10.1021/acs.energyfuels.7b00471
34. Mastral, F. J., Esperanza, E., Berrueco, C., Juste, M., & Ceamanos, J. (2002). Fluidized bed pyrolysis of plastic waste. Journal of Analytical and Applied Pyrolysis, 63(1), 1–15. https://doi.org/10.1016/S0165-2370(01)00137-2
35. Miandad, R., Barakat, M. A., Aburiazaiza, A. S., Rehan, M., & Nizami, A. S. (2016). Catalytic pyrolysis of plastic waste: Moving toward circular economy. Renewable and Sustainable Energy Reviews, 68, 934–946. https://doi.org/10.1016/j.psep.2016.06.022
36. OECD. (2022). Global plastics outlook: Economic drivers, environmental impacts and policy options. OECD Publishing. https://doi.org/10.1787/de747aef-en
37. Panda, A. K., Singh, R. K., & Mishra, D. K. (2018). Thermolysis of waste plastics to liquid fuel: A world perspective. Journal of Fuel Chemistry and Technology, 46(1), 10–23. https://doi.org/10.1016/S1872-5813(18)30002-1
38. Papari, S., & Hawboldt, K. (2022). A review on the pyrolysis of plastic wastes. Journal of Cleaner Production, 336, 130370. https://doi.org/10.1016/j.jclepro.2022.130370
39. Papari, S., Bamdad, H., & Hawboldt, K. (2023). Energy and environmental assessment of plastic waste pyrolysis systems. Energy Conversion and Management, 275, 116517. https://doi.org/10.1016/j.enconman.2022.116517
40. PlasticsEurope. (2023). Plastics – the facts 2023. PlasticsEurope Association.
41. Ragaert, K., Delva, L., & Van Geem, K. (2017). Mechanical and chemical recycling of solid plastic waste. Waste Management, 69, 24–58. https://doi.org/10.1016/j.wasman.2017.07.044
42. Qureshi, M. S., Oasmaa, A., & Solantausta, Y. (2023). Synergistic effects in mixed plastic pyrolysis: Product yield and quality. Fuel Processing Technology, 245, 107684. https://doi.org/10.1016/j.fuproc.2023.107684
43. Ragaert, K., Delva, L., & Van Geem, K. (2020). Mechanical and chemical recycling of solid plastic waste. Waste Management, 69, 24–58. https://doi.org/10.1016/j.wasman.2017.07.044
44. Santella, C., Di Gregorio, F., & Arena, U. (2023). Pilot-scale pyrolysis of mixed plastic waste: Process performance and fuel quality. Fuel, 344, 128174. https://doi.org/10.1016/j.fuel.2023.128174
45. Sharuddin, S. D. A., Abnisa, F., Wan Daud, W. M. A., & Aroua, M. K. (2016). A review on the pyrolysis of plastic wastes. Energy Conversion and Management, 115, 308–326. https://doi.org/10.1016/j.enconman.2016.02.037
46. Singh, R. K., & Ruj, B. (2016). Time- and temperature-dependent fuel gas generation from pyrolysis of municipal plastic waste. Fuel, 174, 164–171. https://doi.org/10.1016/j.fuel.2016.01.049
47. Sogancioglu, M., Yel, E., & Ahmetli, G. (2021). Pyrolysis of waste plastics: A critical review. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 43(3), 1–20. https://doi.org/10.1080/15567036.2019.1588430
48. UNEP. (2023). Turning off the tap: How the world can end plastic pollution and create a circular economy. United Nations Environment Programme.
49. Wong, S. L., Ngadi, N., Abdullah, T. A. T., & Inuwa, I. M. (2023). Recent advances in plastic waste pyrolysis for fuel production. Fuel, 335, 126546. https://doi.org/10.1016/j.fuel.2022.126546
50. Wu, C., Williams, P. T., & Nahil, M. A. (2021). Hydrogen transfer mechanisms in plastic waste pyrolysis. Fuel, 289, 119890. https://doi.org/10.1016/j.fuel.2020.119890
51. Williams, P. T. (2013). Pyrolysis of waste plastics. Elsevier.
52. Williams, P. T., & Slaney, E. (2007). Analysis of products from the pyrolysis of single plastics and mixtures. Resources, Conservation and Recycling, 51(4), 754–769. https://doi.org/10.1016/j.resconrec.2006.12.002
53. Vollmer, I., Jenks, M. J. F., Roelands, M. C. P., et al. (2020). Beyond mechanical recycling: Chemical recycling of plastic waste. Angewandte Chemie International Edition, 59(36), 15402–15423. https://doi.org/10.1002/anie.201915651
54. Zhang, Y., Duan, D., Lei, H., Villota, E., & Ruan, R. (2020). Effects of plastic types on pyrolysis oil yield and composition. Energy Conversion and Management, 205, 112391. https://doi.org/10.1016/j.enconman.2019.112391
55. Zhou, N., Dai, L., Lv, Y., et al. (2022). Pyrolysis of mixed plastic waste: Synergistic effects and product distribution. Fuel, 320, 123898. https://doi.org/10.1016/j.fuel.2022.123898
56. Zhou, N., Dai, L., Wang, Y., et al. (2023). Pilot-scale catalyst-free pyrolysis of plastic waste for fuel oil production. Energy, 263, 125675. https://doi.org/10.1016/j.energy.2022.125675