Desulfurization of pyrolysis oil from waste tires via photocatalytic oxidation using titanium dioxide

Abstract

The aim of this research was to study the desulfurization of waste tire pyrolysis oil via photo-oxidation catalyzed by titanium dioxide (TiO₂ or Degussa P-25) at mild reaction condition. The starting waste tire pyrolysis oil contained 0.84 wt% of sulfur content. The photo-oxidation of the pyrolysis oil was carried out by using a 400 W of high-pressure mercury lamp for 1-7 h. The oxidized sulfur compounds were then removed into the extracting phase. The effects of TiO₂ content (1-7 g/L), TiO₂-calcination temperature (400-800℃), reaction temperature (30-70℃), pyrolysis oil/extracting solvent (1/1-1/5 (v/v)), type of extracting solvent (distilled water, methanol and acetonitrile), air flow rate (0-150 mL/min) hydrogen peroxide concentration (0-30 wt%) and stages of the reaction (1-3 stages) on the %sulfur removal were also investigated. The maximum %sulfur removal at 47.5% was achieved when 7 g/L of uncalcined TiO₂ was loaded into the system containing 1/4 (v/v) of pyrolysis oil/acetonitrile at 50℃ for 7 h after 3 stages of reaction. The oxidation of sulfurous compounds in the pyrolysis oil before and after photocatalytic desulfurization was detected by using gas chromatography equipped with a flame photometric detector (FPD) and high performance liquid chromatography (HPLC). The results indicated that the photocatalytic desulfurization using TiO₂ was effective to reduce the sulfurous compounds in the pyrolysis oil; especially, benzothiophenes by converting to sulfones or sulfoxides with higher polarity which was easier to be dissolved into the extracting phase.