褐煤中有机氮的赋存形态分布和分子结构特征

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N_1、N_1O_1-N_1O_5、N_2、N_2O_1-N_2O_4、N_3O_2和N_5O_2-N_5O_4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。

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

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, N₁O₁-N₁O₅, N₂, N₂O₁-N₂O₄, N₃O₂ and N₅O₂-N₅O₄ 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.