Until now, waste tires have been used mainly for recovering energy. Only small proportions of the carbon black contained in these tires are recycled, since the mineral ash generated by pyrolysis consists of about 20 wt.% of additives used to make the tires. A new process developed by the Fraunhofer Institute for Building Physics (IBP; Valley, Germany; www.ibp.fraunhofer.de) is able to isolate almost all of this ash, allowing both the carbon black and the minerals from the ash to be reused. The process was developed on behalf of RCB Nanotechnologies GmbH (Munich, Germany; www.recovered-carbon-black.com).
To purify the carbon-black/ash mixture created during the pyrolysis process, a wet chemical method is used. The (raw) carbon-black/ash mixture, together with various additives and a liquid, are blended in a reactor, and taken through a defined pressure and temperature curve. The parameters and additives are adjusted in such a way that only one particular mineral is selectively extracted from the mixture at a time. This demineralization process produces high-purity, recycled carbon black for use in tires and other rubber products, as well as colorants (masterbatch) for plastic applications, silicates, which can be used in the building materials industry or for dyes, for example, and also zinc salts for a broad range of applications.
A 200-L pilot plant will operate for the next two years at Fraunhofer IBP, aiming to make recovered carbon black usable for other industrial applications besides tires. The basic process has already been patented, and RCB Nanotechnologies GmbH is the exclusive licensee. The company is currently working on scaling up the process and the production hall is already built. The reactor volume for one production line is expected to be around 4,000 L, which will produce 400 kg/h of recycled carbon black from the ash, or 2,500 ton/yr. In the final expansion stage, the plant will have a capacity of 30,000 ton/yr.