Effect of thermal modification on molecular structure of mesophase pitch precursor and subsequent liquid-phase carbonization behaviour

Abstract

The quality and performance of mesophase pitch are significantly influenced by the structure and composition of its precursor. This study, the thermal modification method was proposed for preparing petroleum pitch, which serves as precursors for the preparation of mesophase pitch via low-temperature condensation. The internal structure of modified pitch molecules is reconstructed to form condensed aromatic macromolecules, increasing aromaticity and reducing the number and length of side chains. The precursor pitch possess higher molecular weight and more concentrated distribution. By analsing the pyrolysis kinetics, it was concluded that the differential form of the second-order chemical reaction mechanism function is applicable to the non-isothermal pyrolysis of precursor pitch. The temperature range of 350–440℃ represents the primary stage of condensation and mesophase transformation, with E_a and lnA reaching 80–90 kJ/mol and 13–16 min⁻¹, respectively. Additionally, the isotropic and anisotropic phases of MP-P400–380℃ exhibit a ‘cliff-like’ development due to the significant difference in reactivity between the components with a wide molecular weight distribution of P-400. P420 has moderate aromaticity (f_a=0.71), aliphatic structure (H_α= 27.58 wt%), and HI-TS components (41.9 wt%), resulting in a uniform wide-area optical texture and highest stacking order (L_c = 4.5463 nm, N = 15.2854) for MP-P420–380℃. In contrast, MP-P430–380℃ exhibits a rough mosaic optical texture due to the low alkyl structure content, poor fluidity, and high viscosity of P430. This study has enhanced the liquid-phase carbonization theory, providing a unique and feasible method for the synthesis of pitch-derived carbon material precursors.