Molecular growth from coal-based asphaltenes to spinnable pitch

The chemical composition of spinnable pitch determined the performance of resultant carbon fiber. Three spinnable pitches were prepared from asphaltenes by a modified air-blowing method and their component and structural differences were comparatively investigated using MALDI-TOF and Q-TOF MS. The three spinnable pitches had insignificant changes in elemental compositions, while the molecular species and their relative content varied significantly, and the molecular weight growth of spinnable pitches was consistent with the 24/50 rule of aromatic annelation. Dominant compounds in the molecular weight range of 250-600 Da showed a clear growth tendency via alternate additions of C4H2 and C-2, and species of larger molecular weight grew mainly in conjunction with C-2. As an excellent precursor for pitch-based carbon fiber, spinnable pitch derived from asphaltenes should have a uniform molecular weight distribution and high number-average molecular weight (1672.6 Da), good thermal stability, high polycondensation degree and aromatic hydrocarbons with the short or few chains in its light fraction. This work systematically analyzed spinnable pitch composition and shed light on the controllable synthesis of pitch-based carbon fiber.