Weibold Academy article series discusses periodically the practical developments and scientific research findings in the end-of-life tire (ELT) recycling and pyrolysis industry.

Mohamed Khloufi
Mohamed Khloufi

This article is a review by Mohamed Khloufi, Market Research Associate at Weibold. This review aims to provide industry entrepreneurs, project initiators, investors, and the public with a better understanding of a rapidly growing circular economy. At the same time, this article series should stimulate discussion.

For completeness, we would like to emphasize that these articles are no legal advice from Weibold or the author. Please refer to the responsible authorities and specialist lawyers for legally binding statements.

Introduction

For much of its commercial development, ELT pyrolysis has been framed primarily as a liquid-oriented business. Process design, commercial discussions, and investor narratives have traditionally focused on oil yield optimization and gas utilization. Solid char, despite representing roughly 30–35% of the original tire mass, was often treated as a secondary output with limited strategic relevance.

As global ELT pyrolysis capacity expands, this view is increasingly misaligned with operational reality. Char volumes are no longer marginal; they are structural. Managing char in a credible, scalable, and economically defensible manner has become a prerequisite for long-term project viability. In this sense, char is no longer a by-product to be addressed post hoc, but a core design parameter that must be integrated into project development from the outset.

Char as a Material: Constraints Define Opportunities

Tire pyrolysis char is frequently simplified as a generic carbon material. In practice, it is a heterogeneous solid containing high fixed carbon, along with zinc, sulfur, silica, and other inorganic residues from tire formulations. These constituents are intrinsic and directly influence feasible end uses.

Applications that tolerate compositional variability, ash content, and performance dispersion tend to exhibit higher technology readiness and lower scale-up risk. By contrast, applications requiring high purity, tightly controlled surface chemistry, or advanced nanostructures generally sit at lower TRLs and entail greater technical and economic uncertainty. A realistic char strategy, therefore, starts with aligning material properties with application maturity rather than pursuing theoretical maximum value.

Established and Near-Commercial Applications (TRL 6–9)

Several char applications are already commercial or near-commercial and form the backbone of today’s char valorization strategies:

  • Recovered carbon black (rCB) for use in rubber compounds, plastics, and construction materials
  • Solid fuel substitution in cement kilns and industrial boilers
  • Asphalt modification and construction fillers

These outlets are robust because they leverage existing industrial infrastructure, established standards, and mature supply chains. They are generally tolerant of material variability and, most importantly, capable of absorbing meaningful volumes of char today. While margins may be modest compared to more speculative applications, these routes provide operational stability and near-term risk mitigation, placing them firmly in the TRL 6–9 range.

Emerging and Experimental Applications (Typically TRL 2–5)

In parallel, research institutions and technology developers continue to explore more advanced and potentially higher-value applications for tire-derived char, including:

  • Activated carbons for adsorption and environmental remediation
  • Catalysts for bio-oil upgrading and chemical processing
  • Electrochemical materials and hydrogen-storage systems
  • Graphene and graphene-like carbon additives

Most of these pathways remain at TRL 2–5. While they demonstrate scientific feasibility and, in some cases, compelling performance enhancements, they should be viewed as long-term innovation efforts rather than near-term commercial solutions. Scale-up complexity, feedstock variability, regulatory acceptance, and limited market capacity remain key constraints.

Graphene-Type Upgrading: Targeted Potential, Limited Volume (TRL 3–5)

Graphene-type upgrading deserves specific attention due to the level of interest it attracts. In the context of ELT char, “graphene” typically refers to graphene oxide (GO), reduced graphene oxide (rGO), or turbostratic graphene-like platelets used as functional additives in bulk materials such as cement, rubber, polymers, asphalt, and coatings.

Chemical oxidation–reduction routes are scientifically mature but operationally complex and generally sit at TRL 3–4. Emerging dry or flash-conversion processes show promise at pilot scale, often reaching TRL 4–5, but still face challenges related to continuous operation, quality control, and reproducibility. Strategically, these routes are best positioned as margin-enhancing, additive-driven applications rather than primary volume outlets.

Metallurgical Applications: Volume-Oriented Maturity (TRL 6–7)

Metallurgical uses, particularly in iron ore sintering and related steelmaking processes, represent one of the most mature non-rubber outlets for tire pyrolysis char. Semi-industrial trials indicate that partial substitution of conventional coke breeze is feasible without compromising process stability, with zinc and sulfur content defining practical limits.

These applications require little upgrading, operate close to industrial conditions, and can absorb significant volumes, placing them at TRL 6–7. From a strategic standpoint, they address the scale challenge more directly than most advanced material routes.

Toward a TRL-Aware Portfolio Strategy

No single application will resolve the char challenge on its own. Sustainable ELT pyrolysis projects are likely to combine:

  • High-TRL, volume-relevant outlets (rCB, fuels, metallurgy) to ensure baseline material flow;
  • Medium-TRL upgrading pathways (e.g., graphene-type additives) to improve margins and strategic positioning; and
  • Select experimental applications to maintain innovation optionality.

Such a portfolio-based approach aligns technical maturity with economic expectations and reduces dependency on any single outlet.

Conclusion: Designing Char into the Business Model

Tire pyrolysis char should neither be dismissed as waste nor overstated as an inherently high-value product. It is a complex material whose role must be deliberately designed into pyrolysis projects. Understanding the application landscape, associated TRL levels, and realistic market absorption is essential for credible project development.

From a Weibold Academy perspective, the conclusion remains pragmatic: char does not need to become perfect carbon. It needs to become useful carbon—matched to appropriate applications, deployed at the right maturity level, and managed consistently at scale. Projects that internalize this TRL-aware mindset will be best positioned for sustainable growth as the ELT pyrolysis industry continues to mature.

If you would like to gain deeper insights into this topic, please don't hesitate to contact the author, mohamed@weibold.com.