Pyrolysis Behaviour and Kinetic of Coal Tar Pitch Modified with Paraformaldehyde

Coal tar pitch (CTP) was modified with paraformaldehyde (POM) within the presence of p-toluene sulfonic acid (PTS). CTP and the modified CTP (MCTP) were characterized by elemental analysis, X-ray diffractometer, scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). The pyrolysis behaviors of CTP and MCTP were studied by thermogravimetric analysis (TGA), and the pyrolysis kinetics were analyzed via Coats-Redfern method which based on the TGA data. Experimental results demonstrated that MCTP had a higher polymerization degree, leading to an increase in carbonization yield by 14 wt%. The anisotropic degree of CTP was increased after modification by POM. New phases were formed during modification, and their decomposition was to be suppressed when pyrolyzed, while they underwent more polymerisation reactions at higher temperatures. CTP had a single pyrolysis stage, which can be described by the second order reaction model (F2). And the activation energy of CTP pyrolysis was 38.32 kJ mol−1. The pyrolysis of MCTP contained three stages, which the third order reaction model (F3), the fourth order reaction model (F4) and the one-dimensional diffusion (D1) model were the most probable mechanisms for the three stages, respectively. The activation energies of the three stages were 56.20, 86.89 and 9.10 kJ mol−1, respectively.