Effect of polymerization with paraformaldehyde on thermal reactivity of >300 °C fraction from low temperature coal tar

>300 °C fraction obtained by distillation of heavy tar of low temperature coal tar was reacted with paraformaldehyde. After reaction, toluene soluble (TS-tar) and toluene insoluble (TIS-tar) fractions were collected. Their structures were confirmed by gas chromatography–mass spectroscopy (GC–MS), gel permeation chromatography (GPC) and Fourier transformed infrared (FTIR). The degradations under nitrogen atmosphere of >300 °C fraction and TIS-tar were investigated by thermogravimetric analyzer coupled with Fourier transform infrared spectroscopy (TG-FTIR). Based on the above analyses, polymers were generated and the carbonization yields were increased by polymerization reaction. The degradation process of TIS-tar was divided into two stages, 118–248 °C and 248–700 °C. In the pyrolysis process of >300 °C fraction, CO has no significant absorbency for infrared at 2060–2240 cm−1, but there are obvious absorption peaks in TIS-tar. Polymerization reaction of paraformaldehyde and compounds with carboxyl, short-chain fatty and ester group in >300 °C fraction generates polymers and fixes these compounds.