Beneficial migration of sulfur element during scrap tire depolymerization with supercritical water: A molecular...

Complete depolymerization of scrap tires (ST) to valuable oil products and fuel gas could be achieved by supercritical water (SCW) technology. For implementing this promising technology, migration mechanism of sulfur element during the entire ST-SCW depolymerization process was identified to reduce the sulfur pollutions. In the depolymerization process of ST, OH radicals released from SCW molecules could enhance cleavage of CS bonds, resulting sulfur-containing intermediates. The intermediates could be further oxidized by free OH radicals and transformed into inorganic sulfur molecules mainly consisting of SO₄^2-, S₂O₃^2-, SO₃^2- and S^2-. In this study, a combined ReaxFF-MD and DFT method was performed to study the detailed sulfur migration mechanism during ST depolymerization in the presence of SCW and provided a strategy to fix low-valent sulfur in aqueous solution for separation of sulfur from the oil & gas products. This work provides a guidance to make ST-SCW technology cleaner and cheaper.