Treating waste tire to prepare high-yield sulfur-doped porous char via ZnCl2–KOH heat treatment method

As a typical solid municipal waste, waste tire (WT) needs to be efficiently treated for high-value utilization due to its large production capacity. ZnCl2–KOH heat treatment method was developed to treat WT to prepare high-yield sulfur-doped porous char. The treatment effect was the best when the additive mass ratios of ZnCl2/WT and KOH/WT were both 1, every g WT produces capacitance of 25.7 F/gWT (much higher than 9.2 F/gWT of pyrolysis and K2FeO4-activation). The effects of different ratios of ZnCl2/WT were found: For the activated char structures, more ZnCl2/WT decreased micropores, smaller pores turned to larger when the ratio increased from 1/3 to 1 and larger pores formed with some pores blocking as it further rose to 3 for mesopores + macropores; higher ratio (<1) resulted in more graphitic microcrystals, further increased ratio generated aromatic rings; 1 time of ZnCl2/WT promoted formations of both sulphide and sulphone bridges most powerfully. The roles of ZnCl2 and KOH in pyrolysis and activation processes were revealed: During pyrolysis process, ZnCl2 promoted polymerization reactions, huge generation of pores, disordered carbon skeleton structures turned to graphitic microcrystals. During activation process, ZnCl2 inhibited the oxidation reactions of KOH on char, promoted formations of mesopores + macropores, converted inorganic sulfur to doped sulfur, weakened the reactions between KOH and doped sulfur.