Changes in char properties after catalytic reforming volatiles from pyrolysis of brown coal

To decrease tar yield and thus improving gasification efficiency, tar from pyrolysis of Shengli brown coal was catalytically reformed in situ in a two-stage quartz reactor using char (as catalyst) prepared from the pyrolysis of same coal. The properties of char catalysts before and after reactions were analyzed and compared. The results show that the mass of char generally decreases after the reforming reactions, which means that char is a kind of consumptive catalyst. The maximum reduction in specific surface area after reactions is from 422 to 231.8 m²/g. Results from Raman spectroscopy show that the O-containing functional groups, as well as the ratio of small aromatic rings (3-5 aromatic rings) to big aromatic rings (more than 5 aromatic rings) in char, decrease after the reactions. Besides, it appears that during the interaction between char and volatile, char from fast-heating pyrolysis mainly cracks the volatiles into small-molecule gases, while char from slow-heating pyrolysis removes the volatiles by coking on its surface.