Study on the evolution of the char structure during hydrogasification process using Raman spectroscopy

In the present study, the hydrogasification of chars produced from different rank coals was carried out in temperature up to 1123 K and in the pressure of 5 MPa using a high pressure fixed bed reactor. The experimental results show that the char hydrogasification process can be divided into two stages: an initial stage with sharp decline in hydrogasification rate and a stable stage with slower decline one. To further explore the hydrogasification mechanism, Raman spectroscopy was used to investigate the evolution of the char structure during hydrogasification. The initial stage can be attributed to the rapid reaction of hydrogen and the functional groups, amorphous carbon remaining in char. The stable stage owes to the gradual consumption of amorphous carbon and the ordering of the microstructure, which was indicated by the decrease in ID3/IG and the increase in IG/IALL with the increasing carbon conversion. Good linear correlations were found between the hydrogasification reactivity and the band area ratios of (ID3 + ID4)/IG and ID1/IG, which denote the active sites and the degree of graphitization of chars, respectively.