Refining of Recovered Carbon Black Moves Toward Large-Scale Production

Within the waste tire pyrolysis value chain, the refining of recovered carbon black is emerging as a critical link connecting raw pyrolysis products to high-value-added applications. Historically, the crude carbon black generated by pyrolysis—characterized by high impurity levels and uneven particle sizes—was relegated to low-end filler applications or direct incineration, resulting in a significant undervaluation of its resource potential. However, this landscape is shifting thanks to advancements in milling, activation, and granulation technologies.

From Crude Carbon Black to a Substitute for Commercial Carbon Black

The primary objective of a recovered carbon black refining plant is to systematically remove residual steel wire, rust, incompletely pyrolyzed rubber fragments, and ash. Through subsequent particle size control and surface treatment, the material is processed to achieve reinforcing properties comparable to those of conventional commercial carbon black. Unrefined crude carbon black typically contains 5% to 15% ash and trace metal impurities; direct incorporation into rubber formulations can lead to uneven vulcanization and inconsistent mechanical properties. Consequently, the stability of the refining process directly determines whether the final product can access key markets such as tires and conveyor belts.

Four Key Processes Determine Product Quality

Magnetic separation and impurity removal mark the beginning of the refining workflow. Upon discharge from the pyrolysis furnace, crude carbon black passes through multi-stage magnetic separation equipment to extract residual steel wire and ferromagnetic impurities. Some production lines also incorporate air classification or screening units to remove large rubber fragments and grit. While seemingly straightforward, this stage is essential for the stable operation of downstream milling equipment; the entry of hard metal objects into the grinding chamber can cause abnormal wear on grinding discs and contaminate batches of the finished product.

Ultrafine milling is the core step in enhancing carbon black quality. Crude carbon black typically has an initial particle size exceeding several tens of microns and exhibits significant agglomeration. Refineries commonly employ centrifugal pulverization, roller milling, or jet milling to reduce the material to micron-level fineness. Industry standards often target a 99.9% pass rate through a 325-mesh screen, with some high-end products requiring fineness exceeding 1,000 mesh. Milling fineness directly influences dispersion within the rubber matrix; finer particles provide more reinforcement sites, resulting in superior tensile and tear strength. It is worth noting that grinding accounts for a significant portion of the total energy consumption in the refining process; production lines utilizing staged grinding and closed-loop airflow designs can achieve energy savings of 40% to 50% compared to traditional ball milling.

The activation and modification stages determine the practical utility of the carbon black. Pyrolysis carbon black often retains tar-like volatiles and oxygen-containing functional groups on its surface, resulting in surface activity characteristics that differ from those of commercial carbon black. Physical activation removes volatiles through high-temperature treatment, while chemical modification introduces specific functional groups to the surface, enhancing compatibility with rubber molecules. Properly modified recovered carbon black exhibits improved dispersion (rising by one or two grades) in natural rubber and styrene-butadiene rubber systems, along with a reduced Payne effect and mitigated vulcanization reversion.

Granulation and drying constitute the final steps before the finished product leaves the plant. Ultrafine carbon black powder has a low bulk density and generates significant dust, posing occupational health risks during direct transport and handling. Refineries typically employ wet granulation—using only water as a binding agent—to roll the powder into spherical granules, followed by drying to reduce moisture content to below 1%. Granulated carbon black offers good flowability, facilitating pneumatic conveying and automated weighing while simultaneously lowering dust concentrations in the workshop.

Product Performance and Application Scope

The performance profile of refined recovered carbon black must be viewed objectively. Test data indicate that its reinforcing effect is comparable to N550 carbon black; its modulus is on par with N772, and its tear strength falls within the same range as N330. This implies that recovered carbon black is not intended for wholesale replacement but rather for equal-mass or partial substitution based on specific product performance requirements. Currently, grades such as EN550 and EN330 have achieved substitution rates of 20% to 50% in applications including tire sidewalls, inner liners, conveyor belt cover rubber, and vibration-damping components. In applications requiring high aging resistance—such as seals and hoses—substitution rates must be determined cautiously in conjunction with formulation adjustments.

Regarding market capacity, my country generated over 16.4 million tons of waste tires in 2024, with a recovery rate of only about 50%, ensuring an abundant supply of feedstock for pyrolysis carbon black production. The steadily rising demand from downstream tire manufacturers for low-carbon materials has opened a market entry window for recovered carbon black. Producers such as Klinteer have achieved scaled production capacity and established partnerships with multiple tire companies, while Jiangsu Wilson Carbon Black Technology focuses on deep processing at the nanoscale. On the equipment front, companies like Jinan Hengyu Environmental Protection and Qingdao Dehuixin Environmental Protection provide continuous production lines covering everything from pyrolysis to refining, with single-line processing capacities steadily increasing.

Refining Depth Determines Industry Potential

Refining recovered carbon black is not merely a process of crushing and classification; it is a systematic operation involving magnetic separation, grinding, activation, and granulation. The greater the depth of refining, the closer the product comes to mainstream commercial carbon black grades, thereby offering greater potential for price premiums. Although the industry currently faces practical challenges—such as batch-to-batch consistency, modification costs, and lengthy downstream certification cycles—advancements in continuous processing equipment and the accumulation of formulation application data are driving a shift in the role of recovered carbon black from a simple "cost-reducing filler" to a "low-carbon reinforcing material." For refining plants, perfecting and stabilizing these four core processes offers greater long-term value than blindly expanding production capacity.