Effect of addition of K2CO3 on the structure of coals with different ranks by FTIR and TG/MS

K2CO3 was considered as the effective catalyst on the pyrolysis performance of coal, however, its effect on coals with different ranks and coalification jumps is unknown until now. This study aims to explore the catalytic mechanism of K2CO3 on coals with different ranks. 8 coals with a vitrinite reflectance (Ro,max) ranging from 0.68% to 1.71% were catalyzed by K2CO3. Thermogravimetric-Mass spectrometry analyzer (TG/MS) and Fourier Transform Infrared (FTIR) spectroscopy were used to characterize the structural variation before and after the addition of K2CO3. FTIR results showed that the length of aliphatic chains (CH2/CH3) decrease and then increase with the turning point near Ro,max = 1.53%, the degree of condensation of aromatic ring (DOC),aromaticity (I) decreased and the concentration of aliphatic hydrogen (Hal/H) increased for all coal samples except for DQ coal (Ro,max = 1.53%) after the addition of K2CO3, indicating the abrupt changes occurred at Ro,max = 1.53%. TG/MS results showed that both the weight loss rate and the maximum weight loss rate temperature exhibit reflection changes near 0.68% and 1.2% of Ro,max. The evolution rate of hydrogen and ethane showed turning changes near Ro,max = 1.21%, while the evolution rate of methane and benzene present transitive changes near Ro,max = 1.53%. Ro,max = 1.21% and Ro,max = 1.53% are consistent with the second and the third coalification jump, respectively. Both TG/MS and FTIR results demonstrated that the effect of K2CO3 is related to coal rank, especially the coalification jump. K2CO3 may tend to act on CC structures furthermore promote the evolution of gaseous products during pyrolysis. The results provide deeply understanding for the coalification jumps and theoretical basis for the selection of suitable catalysts with different coal ranks. •Both the TG/MS and FTIR results indicated that the effect of K2CO3 on the coal is related to the first three coalification jumps.•After the addition of K2CO3, the generation of hydrogen and ethane showed turning changes near Ro,max = 1.21%, while the methane and benzene present transitive changes near Ro,max = 1.53%.•K2CO3 may tend to act on CC structures and furthermore promote the evolution of gaseous products during pyrolysis.