Effect of catalysts on the reactivity and structure evolution of char in petroleum coke steam gasification

Petroleum coke was gasified using non-isothermal thermogravimetric analysis (TGA). The catalytic effects of FeCl3, CaCl2, KCl, K2CO3, K2SO4, KAC and KNO3 were studied. It was found that the gasification of petroleum coke was inefficient at temperature <1000 °C. However, with the addition of catalysts, the efficiency greatly improved. In particular, with the addition of K2CO3, gasification was completed quickly in 10 min and the final temperature was about 900 °C. To further uncover the catalytic mechanism, the structures of char samples at various conversions were investigated with Raman spectra (Raman) and X-ray diffractometry (XRD). The Raman spectra showed that with K2CO3 catalyst, the formation of active intermediates C(O) and M-C-O were enhanced by the relatively small aromatic ring systems with 3-5 fused benzene rings, alkyl-aryl C-C structures and methyl carbon dangling onto an aromatic ring. K2CO3 could stimulate the crackdown of big aromatic ring systems into small aromatic ring systems. Thereby, the addition of K2CO3 could increase the steam gasification rate of petroleum coke. XRD analysis indicated that with char conversion increasing, char structure became more ordered with a large amount of aromatic ring formed in original samples, while the degree of graphitization was lowered with K2CO3 addition, which is favorable for char gasification.