Center for Environmental Science and Technology, University of Missouri-Rolla, Rolla, MO, 65401
Scrap tires represent a major environmental problem. It is estimated that approximately 2.5 million tons of scrap tires are generated each year in North America. Most of these materials are discarded and have found little use through reclamation. The reclaimed rubber and other materials are not suitable for production of tires or other durable rubber goods. As a result, most of the scrap tires accumulate in dumps and create hazards for infestation, water pollution and fire.
Automobile tires are composed of carbon black reinforced rubber. Typical composition of tires is 62% styrene butadiene copolymer rubber, 31% carbon black, and other materials, such as extender oils, sulfur, zinc oxide and stearic acid, which are present in smaller amounts. Potential reuse of the polymeric contents of tires has received considerable attention. Processes have been evaluated for production of goods such as construction fillers; however, fillers and other reclamation applications have shown relatively small economic potential. Another process of interest is the pyrolysis of tires to produce liquid hydrocarbons and gases with high calorific values. Pyrolysis yields solid char residues which generally contain higher amounts of elemental carbon than the original tires. Most studies on conversion of tire char to activated carbon rely on further pyrolysis at 600-850ºC under nitrogen atmosphere followed by activation with acid for reaction with superheated steam. All of the processes are energy intensive.
An alternative low energy conversion process has been evaluated in our laboratory. The process is based on a counterflow oxidative technique. The technique utilizes a flame front which propagates in a direction counter to the oxygen flow. The results obtained show that, under optimal conditions, the process yields carbon with adsorptive characteristic similar to those of commercially available activated carbons. Breakthrough curves for toluene, phenol and aniline were found to be comparable to those obtained with commercial carbons. Similarly, comparable adsorptive capacities were obtained for polychlorinated biphenyls (PCBs) in mineral oils.
One of the major concerns for scrap tire derived carbon is the presence of leachable materials. Initial results of the U.S. EPA extraction procedure and soxhlet extraction are very encouraging and show that the material is essentially free of leachable chemicals.
scrap tires, carbon, counterflow oxidation
This paper is from the Proceedings of the 10th Annual Conference on Hazardous Waste Research 1995, published in hard copy and on the Web by the Great Plains/Rocky Mountain Hazardous Substance Research Center.