Devulcanization and Demineralization of Used Tire Rubber by Thermal Chemical Methods: A Study by X-ray Diffraction

摘要

The use of novel methods for the devulcanization and demineralization of used tire rubber (UTR) based on the thermal chemical treatment of this material with LiCl-KCl, LiCl-KCI-KOH, or KOH at relatively low temperatures is investigated. The influence of composition of the reactive system, ratio of reactants to UTR, and maximum heat treatment temperature (i.e., 300, 400, or 500 ℃) is studied. For comparison purposes, a HNO_3 solution is also used. The changes produced in the chemical composition of UTR as a result of the devulcanization and demineralization processes are studied by X-ray diffraction. Sulfur of UTR usually transforms into a metal sulfide or a variety of sulfur chemical species [i.e., Na_2Zn-(S_2O_4)-H_2O, KA1(SO_4)_2, etc.] depending upon the composition of the reactive system. A combination of the treatments of UTR with LiCl-KCl, LiCl-KCI-KOH, or KOH and with HNO_3 in aqueous solution is more effective to reduce the ash content in the resultant products. The most promising results are obtained when UTR is treated first with the LiCl-KCI-KOH mixture and then with HNO_3 solution. For the resultant product, the ash content is as low as 4.9 wt %, whereas for UTR, it is 7.0 wt %, and for the HNO_3 solution-treated product, it is 5.8 wt %. The preparation of carbonaceous materials with a low ash content may promote the recovery and use of UTR, and this leads to a decrease in its environmental impact.