Production and Upgrading of Recovered Carbon Black from the Pyrolysis of End-of-Life Tires

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.

Keywords: activation; demineralization; end-of-life tires; pyrolysis; recovered carbon black.

Figure 1

Number of publications on the subject—selected from Web of Science, with the keywords: “pyrolysis” and “end-of-life tires”, “waste tires”, or “used tires”. (a) Number of publications between 1991 and 2021; (b) Number of publications per year between 2016 and 2022 (March).

Figure 2

Schematic representation of ELT pyrolysis and ensuing products.

Figure 3

Pyrolysis process: from ELT to rCB, oil, and syngas, and applications thereof.

Figure 4

Prospective application fields of rCB.