Abstract
The application of hydrothermal solution containing NaOH under supercritical conditions to convertsion of the scrap vulcanized ethylene-propylene-diene terpolymer (EPDM) rubber into reusable oily materials as softeners for the rubber synthesis was verified through batch process experiments using a microautoclave.In this paper, the properties of resultant oily materials from a rubber by the hydrothermal treatment under supercritical conditions were compared with those by pyrolysis.In addition, effects of reaction pressure on the desulfurization, and liquefaction in hydrothermal solution and pyrolysis were investigated. These results lead to the followings:(1) Remarkable desulfurization takes place with cracking in hydrothermal solution, (2) Desulfurization and depression of liquefaction in hydrothermal solution are not caused by the increase of reaction pressure but are attributed to the characteristic reactivity of hydrothermal solution, (3) All resultant oily materials were composed of paraffinic hydrocarbons, (4) Resultant oily materials by hydrothermal treatment are more homogeneous than those by pyrolysis. The rubber compound mixed with the resultant oily material by hydrothermal treatment showed the same properties as one mixed with a paraffinic softener commercially available.Since the resultant oily materials by hydrothermal treatment can be used as a softener in a cyclic manner, a closed rubber manufacturing process can be established. These findings and those previously reported motivate us to develop a new recycle process by hydrothermal treatment; the process can simplify hitherto known complex purification steps and facilitate the control of reactions without damaging to the present earth environment.
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