The present invention relates to a process for the treatment of used rubber tires by vacuum pyrolysis to produce liquid and gaseous hydrocarbons and a solid carbonaceous material.
The accumulation of large quantities of scrap tires has become a major environmental problem. Because of their resistance to biodegradation, used automobile tires provide a favourable environment for vermin, rodents and fire. Environmental regulations, on the other hand, prohibit the disposal of such waste materials by burning outdoors or by burial underground.
One possible solution to the above problem is to convert the tires into fuels and other useful hydrocarbon products, for instance by thermal decomposition. In order to avoid side reactions and cross-reactions among product species when heating the tires under atmospheric or superatmospheric pressure, which results in a very inefficient conversion process, U.S. Pat. No. 4,235,676 has proposed to conduct the pyrolysis of rubber tires under sub-atmospheric pressure. According to this patent, the vacuum pyrolysis of tires is effected by moving a mass of shredded tires through an elongated tubular member maintained at a temperature between about 400.degree. C. and 800.degree. C., in the absence of air and/or oxygen, with the material being turned or stirred as it passes through the tubular member, and withdrawing the gases and vapors produced by means of a vacuum of from about 4 inches to about 6 inches of mercury (i.e. an absolute pressure of from about 608 mm Hg to about 658 mm Hg). The process conditions, however, are such as to promote the formation of gaseous hydrocarbons to the detriment of the more highly desirable hydrocarbon oils.