Distribution characteristics and differences of oxygen-containing functional groups in macerals of low rank coal

Composition of oxygen-containing functional groups is considered as a critical factor in determining the sorting strategy and separating efficiency of macerals in low rank coal,and a significant role in their subsequent processing and transforming as well,therefore it is particularly indispensable to ascertain the distribution characteristics and differences of oxygen-containing functional groups in macerals of low rank coal.By using elemental analysis,XPS,13C-NMR and chemical titration in combination,the distribution characteristics and differences of oxy-gen-containing functional groups of macerals in Shenhua (vitrinite-rich) and Zhundong (inertinite-rich) low rank coal were investigated from surface and inner structure respectively.The research findings are as follows:the elemental analysis shows the oxygen content of macerals in Zhundong coal is higher than those in Shenhua coal,and the O/C atomic ratio of vitrinite are higher than inertinite in both coals.However,vitrinite and inertinite share a similar surface O/C ratio in XPS test,which indicates the oxygen-containing functional groups are mainly concentrated on the surface of inertinite while these groups are much well distributed inside and outside of vitrinite.CO (carbonyl or O—C—O) and COOH are the typical oxygen-containing group of vitrinite and inertinite respectively based on quantitative analysis of XPS,while the dominant oxygen-containing group in vitrinite and inertinite are CO and —OH respectively.According to 13C-NMR measurement,all macerals have the same proportion rank of oxygen-containing groups:aromatic oxygen-containing groups＞carbonyl＞COOH＞aliphatic oxygen-containing groups except that aliphatic oxygen-containing groups in Shenhua vitrinite ranked up to second.There is a lower percentage of COOH in vitrinite whereas aliphatic oxygen-containing groups possess the least distribution in inertinite even disappeared in Zhundong inertinite.Results of chemical titration show that the acid oxygen-containing groups are more easily gathered on the surface of inertinite,and the distribution of acid oxygen-containing groups varies according to the type of coal and maceral,for instance,the inertinite in Zhundong has obviously high content of phenolic hydroxyl group.