Effect of metal ions on the steam gasification performance of demineralized Shengli lignite char

Abstract

Lignite is considered to be a promising coal to obtain H2 or H2-rich synthesis gas. In order to investigate which metal ions promote its high H2 production, Shengli lignite after partial demineralization followed by addition metal ions were mainly studied. The steam gasification reaction with temperature programmed was tested by using fixed-bed reactor. XRD, Raman, XPS and FTIR were used to do the research on microcrystalline structure changes of the Shengli lignite. The results proved that the gasification reactivity of HCl treatment samples were poor. The addition of alkali metal and alkaline earth metal had a distinguished catalytic effect on the steam gasification. Nevertheless, transition metal had a slight catalysis. The metal ions added into the acid treatment lignite decreased initiating gasification temperatures, increased H2 cumulative yield and H2/CO ratio in the syngas from the steam gasification, especially for Ca, K and Na. The XRD and Raman results revealed that the addition of alkali metal and alkaline earth metal made the char structure disorderly, and hindered chemical structure of coal changes towards graphitization. The XPS results indicated that the content of CO increased significantly after adding metal ions, which could contribute to opening the loop of aromatic nucleus. The reaction mechanisms about how metal ions catalyzed low-rank coals in steam gasification were proposed.