The Recycling ofTires

Another consumer commodity that presents a waste-management headache is vehicle tires. In North America, about one 10-kg rubber tire per person per year on average is discarded; thus about one-third of a billion tires are added to the supply of approximately 3 billion tires presently stored in mountainous piles, awaiting ultimate disposal! Because the tires are made primarly from oil and consequently are flammable, tire fires in these huge piles are not uncommon and produce tremendous amounts of smoke, carbon monoxide, and toxins such as polynuclear aromatic hydrocarbons (PAHs) and dioxins (Chapters 11 and 12). The fires are difficult to extinguish because of air pockets in and between the tires.

There have been efforts to use tires either as fuel or as a filler for asphalt, but currently such applications consume only about 10% of the tires that are discarded annually. Some used tires are also utilized for their rubber content, to produce landscaping products.

a number of attempts have been made to commercially reprocess shredded scrap tires by pyrolysis—the thermal degradation of a material in the absence of oxygen. The resulting products are low-grade gaseous and liquid fuels and a char containing minerals and a low-grade version of the material called carbon black, which can be further treated and converted into activated carbon (Chapter 14). It may eventually be possible to convert the liquid component into high-grade char, thereby making the process economically profitable. The "rubber" in tires consists of about 62% of a hydrocarbon polymer and 31% of carbon black—added to strengthen the tires and reduce wear—so there is a ready market for the latter. Using the liquid component as a fuel is problematic because of its high content of aromatic hydrocarbons.

Continue reading here: The Recycling of Plastics

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