The characterization of organic nitrogen and sulfur functional groups in coals after biomethane production.

To study the change characteristics of nitrogen and sulfur functional types in the raw coal and coal residues after anaerobic fermentation, three different rank coals from Baiyinhua mine (BY coal), Qianqiu mine (QQ coal), and Malan mine (ML coal) in China were collected and treated with methanogenic microorganisms, then X-ray photoelectron spectroscopy (XPS) was used to test the nitrogen and sulfur functional types in raw coals and coal residues. The results show that the pyrrolic nitrogen (N-5) and aromatic sulfur are the main nitrogen type and sulfur type in three coals. The N-5 increases by 17.42% in BY coal residue and decreases by 2.37% and 8.51% in QQ and ML coal residues, respectively. The pyridinic nitrogen (N-6) in BY, QQ, and ML coal residues decreases by 2.18%, 5.44%, and 2.75%, respectively. The aromatic sulfur increases by 2.13%, 3.14%, and 4.02% in BY, QQ, and ML coal residues, respectively. The aliphatic sulfur has obvious changes in BY and QQ coal residues with the increment of 9.17% and decrement of 11.64%, respectively. The results reveal that the nitrogen and sulfur types have changed in the coal residues after the biomethane production, and the instable types such as N-5 and aliphatic sulfur have obvious changes in the low-rank BY and QQ coals. The research provides a sight to the changes about nitrogen and sulfur types after biomethane yield and more deep thoughts about the clean and effective utilization of coals.