The chemical transformation of hydrocarbons to carbon using SO3 sources

To develop low-cost carbon fiber, The Dow Chemical Company and others have explored the sulfonation of polyethylene fibers as an alternative to the incumbent poly(acrylonitrile) route. Although the process of polyethylene sulfonation and subsequent thermal carbonization in an inert atmosphere has been known to provide carbonaceous material for over 35 years, we have found the chemical understanding of this transformation to be insufficient. Herein, we report a series of studies that have led to our current understanding for both the sulfonation and subsequent thermal treatment steps. Sulfonation of hydrocarbon model compounds yields completely conjugated and functionalized products. Spectroscopic data suggest that sulfonated polyethylene is similar; containing extended conjugated systems with sulfonic acids and various other oxygen-containing functional groups. Near-Edge X-ray Absorption Fine Structure data have identified that between 150 and 200 °C the polymer undergoes a cross-linking step, while evolved gas analysis has identified concomitant release of SO2 and H2O. Above 600 °C, H2 is produced and a graphenic carbon microstructure is obtained.