用固体^(13)C核磁共振技术研究黄县褐煤的化学结构

STUDY ON THE STRUCTURALS FEATURES OF HUANGXIAN LIGNITE BY SOLID STATE ^(13)C NMR

应用高磁场(75.46MHz)固体^(13)C核磁共振仪与交叉极化,魔角自旋,旋转边带全抑制、偶极相移等核磁技术,对黄县褐煤的化学结构进行了研究。结合元素分析与一些含氧基团的化学分析,得出了碳、氢、氧在各种基团中的分布,并据此计算了芳碳率、芳氢率、芳氢取代率、未取代芳核氢碳比和平均结构单元芳环数等一系列化学结构参数。据此,提出了一个该褐煤有机质的假想化学结构模型。

Huangxian lignite was studied by high field (75.46 MHz) solid state ^(13)C nmr (CP/MAS) with TOSS technique for suppression of spinning sidebands. In addition to the carbon aromaticity, functional groups including methyl carbons, methylene carbons, O-bonded aliphatic carbons, prolonated and bridgehead aromatic carbons, alkyl substituted aromatic carbons, O-bonded aromatic carbons, carboxyls and carbonyls can be distinguished from the spectra. Dipolar dephasing technique has been employed in order to measure the protonatcd and nonprotonated carbons along with the mobile methyl or methylene groups. Chemical analyses have been supplemented for determination of carboxylic, phenolic and alcoholic hydroxyl groups. Based on these data, the distribution of carbon, hydrogen and oxygen in different functional groups has been deduced. Main structural parameters of this lignite are found to be carbon aromaticity, f_(ar)~c=0.59; hydrogen aromaticity, f_(ar)^(II)=0.22; degree of substitution of the aromatic system, σ=0.54; aromatic hydrogen to carbon ratio of the hypothetical unsubstituted aromatic structure, (H/C)_(aru)=0.78 and average number of aromatic ring per structural unit, R_(ar)=2. In the light of elemental distribution and structural parameters, a hypothetical model of the Huangxian lignite is proposed.