XANES measurements of sulfur chemistry during asphalt oxidation
Date of Original Version
Sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy is used to measure how the speciation of sulfur compounds evolves within a warm-mix asphalt as a consequence of the Rolling Thin-Film Oven (RTFO) and Pressure Aging Vessel (PAV) oxidative aging procedures. Identifying the types of sulfur compounds present is important for quantifying the growth in polar sulfur-containing species that can alter the asphalt's mechanical properties over time. Elemental analysis indicates that the sulfur content of the asphalt holds constant at 5 wt% during aging. XANES analysis indicates that thiophenic sulfur compounds are most prevalent (62%), followed by sulfide and elemental sulfur compounds. RTFO and PAV aging cause smaller and larger shifts, respectively, from sulfide to sulfoxide. The amount of unreacted sulfide remains larger than the amount of sulfoxide, even with PAV aging. The XANES spectra lack features that would be expected if engine oil additives indicative of recycled engine oil bottoms were present. The results indicate the importance of including thiophene, sulfide, and sulfoxide chemistries within molecular asphalt models.
Greenfield, Michael L., Michael Byrne, Sudipa Mitra-Kirtley, Eric M. Kercher, Trudy B. Bolin, Tianpin Wu, Paul R. Craddock, Kyle D. Bake, and Andrew E. Pomerantz. "XANES measurements of sulfur chemistry during asphalt oxidation." Fuel 162, (2015): 179-185. doi:10.1016/j.fuel.2015.08.074.