Abstract
Increasing awareness regarding fossil fuel dependence, waste valorization, and greenhouse gas emissions have prompted the emergence of new solutions for numerous markets over the last decades. The tire industry is no exception to this, with a global production of more than 1.5 billion tires per year raising environmental concerns about their end-of-life recycling or disposal. Pyrolysis enables the recovery of both energy and material from end-of-life tires, yielding valuable gas, liquid, and solid fractions. The latter, known as recovered carbon black (rCB), has been extensively researched in the last few years to ensure its quality for market applications. These studies have shown that rCB quality depends on the feedstock composition and pyrolysis conditions such as type of reactor, temperature range, heating rate, and residence time. Recent developments of activation and demineralization techniques target the production of rCB with specific chemical, physical, and morphological properties for singular applications. The automotive industry, which is the highest consumer of carbon black, has set specific targets to incorporate recycled materials (such as rCB) following the principles of sustainability and a circular economy. This review summarizes the pyrolysis of end-of-life tires for the production of syngas, oil, and rCB, focusing on the process conditions and product yield and composition. A further analysis of the characteristics of the solid material is performed, including their influence on the rCB application as a substitute of commercial CB in the tire industry. Purification and modification post-treatment processes for rCB upgrading are also inspected.
Highlights
IntroductionThe worldwide production of tires is estimated to reach 2.4 billion units per year by
This is mostly due to European Union regulations [4] for end-of-life tires (ELT) management that cover the collection of tires by particular entities and their valorization and recycling
This review focuses and systematizes the manufacture of syngas, oil, and recovered carbon black as products obtained from ELT pyrolysis
Summary
The worldwide production of tires is estimated to reach 2.4 billion units per year by. Part-worn tires may be retreaded (i.e., the tire tread and sidewall rubber are replaced) and reintroduced in the market, contributing to 70% material savings (due to material recovery and extended lifespan) and lower CO2 emissions (24%), water consumption (19%), and air pollution by particulate matter (21%) when compared to non-retreadable tires [6] This strategy is not the solution for ELT management because tires are not retreadable forever, and retreaded tires present poorer quality and safety when used at high speed [7]. A literature search was performed in the Web of Science platform with the following keywords: “end-of-life tires”, “waste tires”, “used tires”, “pyrolysis”, “recovered carbon black”, “carbon activation”, and “carbon demineralization” The importance of this subject can be inferred by the increasing number of publications over the years. It has been reported that high temperatures lead to a reduction in the C5 –C10 fraction and an increase in the C10 + aromatic compounds due to Diels–Alder reactions [23]
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