Soluble conversion of Zhaotong lignite by ammonolysis and the occurrence forms of oxygen and nitrogen in soluble portion

Lignite is of high carbon content, rich in oxygen and nitrogen, and other heteroatoms, thereby is treated as an important raw material for the preparation of carbon materials. However, the preparation of carbon materials from lignite is faced with many challenges, due to the low soluble organic carbon content and the irregular distribution of heteroatoms. Therefore, it is necessary to achieve the soluble transformation of lignite. In this investigation, ammonia was applied to achieve the solubilization of Zhaotong lignite, and also the regulation of oxygen and nitrogen in soluble portion from lignite under mild conditions. As a result, Zhaotong lignite exhibits efficient thermal dissolution with a soluble portion yield of 76.66%, at the condition of ammonium concentration of 15%, temperature of 160 ℃, and reaction time of 3 h. Based on the characterization and analysis of soluble portion, the macromolecular structure of coal is changed by ammonolysis, mainly displaying the replacement of the hydroxyl group by the amino group or the formation of organic nitrogen groups by the direct reaction between the carboxyl or carbonyl groups with the amino group. By contrast, the occurrence forms of nitrogen in raw coal are mainly quaternary nitrogen and pyrrole nitrogen, while they in soluble matter are mainly amino nitrogen and pyridine nitrogen, indicating that amino or amide groups are formed during the thermal dissolution of lignite.