New use of waste tyres

Tyres are made primarily from natural and synthetic rubber (consisting of hydrocarbon polymers) along with other compounds and materials such as carbon black, metal oxides and steel. Despite the attempts of reusing them in many different ways, a relevant fraction (nearly 13%) of waste tyres is still landfilled.

Pyrolysis and gasification are a promising way for high-efficiency material and energy recovery; nevertheless, inability to exploit the solid by product does not make recycling cost effective or sustainable. In this frame the EU-funded project 'High added value materials from waste tyre gasification residues' (TYGRE) was designed to expand the material outputs of tyre recycling by providing a valuable material with a broad array of applications, silicon carbide (SiC).

A prototype plant, able to treat 20 kg/h of scrap tyres, has been assembled at ENEA Research Centre in Southern Italy and the proposed process has been tested.

Furthermore, thanks to the multidisciplinary partnership, a sustainability analysis allowed the assessment of the pilot plant and also a scaled-up model of the technology, through Life-cycle assessment (LCA), life-cycle costing and social LCA studies.

To improve the powder grade and enlarge the range of market applications, project partners developed a new purification method to produce high quality SiC powders. Results demonstrated that the SiC produced by TYGRE project (TyGReSiC) is suitable for industrial purposes.

From the product point of view, TyGReSiC is a valuable material for a broad range of applications. At the end of 2012 the global SiC capacity highly increased, rising up to 2,500,000 tonnes per year. The market is mainly shared by the following sectors: Metallurgical Industry (refractory and foundry) 60%; Abrasive and Ceramics 28 %; Electro-products 12 %.

The grade and price increase going down in the list, ranging from a few euros per tonnes to hundreds of thousands of euro per tonnes. TyGReSiC was successfully tested in the formulation of structural ceramics and membranes.

Very good results (sintered density was 98 % of theoretical density), in comparison with commercial powders, have been obtained. The mechanical properties of sintered TyGReSiC were similar to commercial SiC powder considered as the benchmark, so it can be concluded that TyGReSiC is suitable for structural applications.

Tests demonstrated that the TyGReSiC powder could be successfully used in the production of membranes for water filtration. Other applications are under investigation.