褐煤中有机氮的赋存形态分布和分子结构特征

Occurrence forms and molecular structural characteristics of the organic nitrogen in lignite

利用X射线光电子能谱(XPS)分析了先锋褐煤(XL)、小龙潭褐煤(XLT)和胜利褐煤(SL)及其萃取残渣表面有机氮的形态分布。结果表明,三种萃取残渣表面五种有机氮的含量分布各异,但均以吡咯型氮为主。考察了在300℃下Na OH催化的褐煤萃取残渣的超临界甲醇解反应,XL、XLT和SL萃取残渣超临界甲醇解所得石油醚可溶物的收率分别为46.0%、43.8%和47.6%(质量分数)。用傅里叶变换离子回旋共振质谱(FTICR/M S)分析石油醚可溶物中的含氮化合物(NCCs)。结果表明,NCCs主要包括N1、N1O1-N1O5、N2、N2O1-N2O4、N3O2和N5O2-N5O4类化合物。根据不饱和度和碳原子数的分布推测了NCCs的分子结构特征,表明绝大部分NCCs含羟基和羧基等含氧官能团,氮原子主要以吡咯、吡啶和氨基的形式存在于芳环结构中,以1-3个芳环的结构为主。褐煤中的-C-O-桥键的断裂是生成NCCs的一个重要路径。

The occurrence forms of organic nitrogen in Xianfeng lignite(XL),Xiaolongtan lignite(XLT) and Shengli lignite(SL) as well as their extraction residues were characterized by X-ray photoelectron spectroscopy(XPS).The results show that the content distributions of organic nitrogen in the three extraction residues are different,but all are mainly dominated by pyrrole nitrogen.The NaOH-catalyzed supercritical methanolysis of lignite extraction residues at 300℃ was then investigated,which indicates that the yields of petroleum ether soluble portions from supercritical methanolysis of extraction residues derived from XL,XLT and SL are 46.0%,43.8%,and 47.6%(mass ratio),respectively.The characterization of nitrogen-containing compounds(NCCs)in petroleum ether soluble portions by Fourier transform ion cyclotron resonance mass spectrometry(FTICR/MS) indicates that NCCs are mainly composed of N1, N1 O1-N1 O5, N2, N2 O1-V2 O4,N3 O2 and N5 O2-N5 O4 class species.The molecular structural characteristics of NCCs were speculated according to the distributions of double bond equivalent values and carbon numbers,which shows that most of NCCs contain oxygen-functional groups like hydroxyl and carboxyl groups,and the nitrogen atoms are mainly present in aromatic structures(mainly 1-3 aromatic rings) in the forms of pyrrolic,pyridinic and amino groups.The cleavage of C-O bridged bonds in lignite is an important pathway for producing NCCs.