Recovery of carbon black from scrap rubber

A hydrogenation process has been developed to recover carbon black from rubber crumbs prepared from scrap tires. A semi-batch 2 L autoclave was used, with hydrogen continuously bubbled through a slurry of rubber crumbs and a paraffinic dissolution oil under pressures from 300 to 1500 psig and temperatures of about 400 °C. The dissolution oil dissolved the rubber and allowed the carbon-black particles to be freed from the polymer matrix. The carbon black then acted as a hydrogenation/cracking catalyst. Under optimal reaction conditions, the yield of carbon black+inorganic additives was approximately 36%, the gas yield 1-2%, naphtha yield 8%, and the balance a product oil, part of which can be recycled as the dissolution reagent. The carbon-black product after filtering and drying had properties which were an average of those of the various grades added during tire manufacture. One-half of the inorganics could be removed by a simple acid wash if desired. The carbon black has a value more than twice that of the other products and could be the factor which would allow this process to be economically viable without subsidies.