Upgrading of coal-tar pitch in supercritical water

Conversion of coal-tar pitch in supercritical water (SCW) was researched using a batch reactor. The effects of temperature (400°C–480°C), pressure (25 MPa–40 MPa), and residence time (1 min–80 min) on product composition were investigated. When compared with pyrolysis under N2 atmosphere, the conversion of asphaltene to maltene was enhanced, whereas, the formation of gas and char were restrained in SCW. Moreover the yields of high value chemicals were higher than those obtained via pyrolysis. The results suggest that SCW promotes the decomposition of coal-tar pitch into maltene and enhances the yields of high value chemicals. It is also observed that asphaltene is the main active component and it is converted to maltene, gas, and char in SCW. High temperature promotes the reactions of both asphaltene to light components and the formation of char. The results indicate that temperature appears to be the important parameter for coal tar pitch conversion, whereas, the effects of pressure and time are less significant.