Graphite and Graphite Oxide: New Models to Analyze the Calcium Catalytic Effect on Steam Gasification of Lignite and Char

Graphite oxide (GO) and graphite (G) were used as Shengli lignite (SL) and char (SL+-T) models to study gasification reactivity for the first time. The steam gasification performance of SL+, SL+-T, G, GO and the corresponding Ca-added samples was evaluated in a fixed bed reactor equipped and linked with a downstream GC system. The samples were comprehensively characterized by Fourier transform infrared, XRD, Raman, X-ray photoelectron spectroscopy, and C-13 NMR. Results show that calcium exerted a significant catalytic effect on the steam gasification of SL+ and GO but had a limited impact on high-temperature char and G. Once the char was oxidized using a similar liquid oxidation method to prepare GO, the steam gasification rate of the oxidized Ca-added char presented higher reactivity at low temperature, which was similar to the gasification behavior of GO with calcium addition. Characterization results show that the oxygen-containing functional group of SL is similar to GO. By comparing the catalytic effect of calcium of oxidized char and GO with that of char and G, it was further demonstrated that the oxygen-containing functional group was the key structure for Ca-catalyzed coal gasification. These results suggest that GO is similar to SL not only in terms of its oxygen structure but also in its steam gasification reactivity. Thus, GO is an excellent model of lignite. This study provides a new lignite modeling approach with a more accurate structure than reported lignite models and is suitable for precise investigations of the structural evolution of lignite as well as the catalytic mechanism of calcium in steam gasification.