Hydrocracking of Rubber and Used Tyres

The most commonly used rubber in tyre manufacture is styrene-butadiene copolymer containing about 25 wt% of styrene. The presence of a high concentration of double bonds in the rubber backbone makes the alternative of degrading rubber wastes by treatment in hydrogen atmospheres very attractive. Moreover, because used tyres contain significant amounts of sulfur, hydrogenation also favours the removal of this undesired element as H2S, which allows oils to be produced with lower S content than those derived from tyre pyrolysis. 

Shabtai, page 31. 1996, with permission from Elsevier Science) 

A number of patents have been filed claiming the processing of waste rubber, either vulcanized or unvulcanized, by hydrocracking.10-13 The degradation usually proceeds in the presence of catalysts CoNi/Al203, FeMo/Cr203, Mo acetates, Cp2ZrCl2, etc. In some cases, a certain positive effect has been derived from the presence of sulfur compounds, which may either be the sulfur contained in the used tyre or H2S added to the reaction mixture. 

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