Transformation of Lewis acid during the carbonization and graphitization of mesophase pitches

In this work, we examine the poly-condensation of anthracene mixed with aluminum trichoride (AlCl3) or zirconium tetrachloride (ZrCl4) at 350 °C and 1.5 MPa, investigating the catalyst transformations during poly-condensation and through further heat treatment to 1000 °C (carbonization) and 2800 °C (graphitization). The mesophase transformation reveals that AlCl3 exhibits a higher catalytic activity than ZrCl4, while the ash content indicates that the resulting pitches perfectly retain both AlCl3 and ZrCl4 after poly-condensation and carbonization. X-ray diffraction (XRD) pattern and X-ray photoelectron spectroscopy (XPS) show the details of the catalyst transformation. The AlCl3 deliquesces into hydroxides during poly-condensation, and a part of Al(OH)3 decomposes into Al2O3 at 1000 °C, while the ZrCl4 converts into ZrO2 during poly-condensation and carbonization. The graphitization volatilizes the Al component and results in no aluminum detected. A part of ZrO2 retained in the pitch transforms into ZrC after graphitization. The results of this investigation are beneficial for optimizing the removal of Lewis catalysts, and the prepared mesophase pitch, which containing ZrC and ZrO2, could be used as a functional material precursor.