Investigation of the separation method of mesophase pitch by two-stage thermal sedimentation

Mesophase pitch (MP) derived from fluid catalytic cracking (FCC) aromatic-enriched oil exhibits polydisperse molecular architecture, which impairs the spinnability of the resultant carbon fibers. The separation of mesophase pitch has garnered significant attention due to its critical role as a premium precursor for advanced carbon materials. In this study, a mesophase pitch with a softening point of 151 °C was prepared from FCC aromatic-enriched oil through a two-stage thermotreatment process preparation. The anisotropic phase in the mesophase pitch was collected at the bottom of the samples by thermal sedimentation, while the anisotropic phase was collected at the top of the samples. To investigate the temperature-dependent phase separation behavior between the anisotropic phase and isotropic phase, the two phases were systematically characterized using polarized light microscopy, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Results indicated that the optimal sedimentation effect occurred when the sedimentation temperature exceeded the softening point of mesophase pitch by approximately 50 °C. The superior sedimentation product exhibited enhanced structural ordering with an aromaticity of 0.4354 as measured by FTIR and an order degree of 0.9230, an interlayer spacing of 3.4477 Å as measured by XRD. The ordering degree and thermal stability of the sedimented anisotropic phase were significantly enhanced. During heat treatment, distinct phases of separation occurred between anisotropic and isotropic components, driven by molecular differences: aliphatics migrated upward while condensed aromatic clusters sank. This study showed that thermal sedimentation at the appropriate temperature and time could effectively developed the properties of the mesophase pitch.