Plastic recycling for liquid fuel production and its use in thermal engines

Abstract

Pyrolysis is a thermochemical degradation process that has become one of the most promising methods for converting plastic waste into valuable alternative fuels, offering a dual environmental benefit by reducing solid emissions. This review examines the advancements in pyrolysis over the past decade, focusing on the efficiency of different plastics in producing fuels such as diesel, gasoline, and high-calorific-value gases. A systematic analysis is conducted, emphasizing the thermochemical pyrolysis of polypropylene (PP), high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polystyrene (PS). Critical parameters evaluated include conversion yields, physicochemical properties of the products, residence times, and reactor configurations. Furthermore, studies comparing the performance and emission characteristics of pyrolysis-derived fuels with conventional fossil fuels are reviewed. Findings indicate that pyrolysis can achieve cumulative yields exceeding 80 wt%, producing fuel products with properties closely resembling those of commercial diesel and gasoline under optimized conditions. Additionally, emission studies suggest that these fuels exhibit environmental performance comparable to conventional fuels, reinforcing pyrolysis as a viable recycling alternative. However, challenges remain in scaling up this technology, primarily due to the variability in plastic feedstock composition and processing conditions, including reactor type and mode of operation, which significantly influence product yield and quality. Addressing these challenges requires further research into process optimization and feedstock pre-treatment. Despite these limitations, pyrolysis represents a promising solution for plastic waste management, contributing to the development of sustainable waste-to-energy strategies aligned with circular economy principles. This review synthesizes findings from multiple studies, bridging existing knowledge gaps while highlighting the critical role of thermochemical conversion in advancing sustainable waste management and alternative fuel development. Unlike previous reviews, this one provides a more comprehensive and nuanced perspective on the subject.