Recycling of Scrap Tires to Oil and Carbon Black by Vacuum Pyrolysis
Tire recycling has become a necessity because of the huge piles of tires that represent a threat to the environment. There is about one worn tire produced per year and per person in the developed countries. The used tires represent a source of energy and valuable chemical products. By thermal decomposition of rubber under reduced pressure, it is possible to recover the useful compounds. A step-by-step approach has been used, from bench-scale batch systems, to process a development unit and finally a pilot plant, to experiment and develop vacuum pyrolysis of used tires. Yields are 55% oil, 25% carbon black, 9% steel, 5% fiber and 6% gas. The maximum recovery of oil was performed at 415°C below 2 kPa abs. The specific gravity of this oil was 0.95, its gross heating value was 43 MJ/kg and total sulfur content about 0.8%. It was rich in benzol and other petrochemical components. The carbon black favorably compared with the low standard grades and may find an application in lowgrade rubber goods following further research and development. The heat of pyrolysis for the reactions is low, estimated around 700 kJ/kg. The process has been tested in a 200 kg/h pilot plant, which positively demonstrated the possibility of continuously feeding large chunks of rubber under vacuum. The process feasibility is promising, with returns on the investment of 31% after three years of operation.