Characterization And Modeling Of Coal High Molecular Weight Components

Now the structure of coal extracts, especially that of the higher molecular weight (HMW) parts (>500amu), which determinate the skeleton frame of coal is still ambiguous problem. These parts in coal structure decide the whole structure thermal stability and affect the features of coal during the further processing.To obtain the structure and composition of the HMW components, the Column Chromatographic (CC) method was employed to extract ten Chinese typical coal samples from different Chinese regions with different ranks. By using acetonitrile (ACN), tetrahydrofuran (THF), pyridine and N-methyl -pyrrolidinone (NMP) as solvents in sequence order the different polarity range of extracts were acquired. Synchronous fluoresce (Syn-F) spectroscopy and gel permeation chromatography (GPC) were used to analyze the aromatic feature and MW distributions of extracts. The separation type and adsorbent influence were compared for the HMW components collection. Furthermore, the model of HMW components in coal structure was constructed. The detailed information was shown as followings:1. NMP could form complexes with coal organic matters, and more than one NMP molecule could be combined during solvent extraction and produce the MW difference of 97amu. ACN extracts were mainly consisted of 2-3 rings aromatic systems; THF and pyridine extracts were of 3-5 rings systems. 5 or larger than 5 rings systems were found in NMP extracts. ACN extracts and methanol soluble parts of THF, pyridine and NMP were the small molecular phases of coal, mainly composed of small aromatic hydrocarbons and polar aromatics.2. The Syn-F shifted to long wavelength with the increase of extraction solvent polarity, the spectra of pyridine and NMP extracts extended to 650nm. The MW distributions were continuous for extracts with different polarity. The MW of ACN extracts was from 110amu to 2200amu, mainly consisted of two double-bond conjugate system and polyene conjugate system. The MW of THF extracts were below 3390amu, mainly consisted of aromatic and aliphatic species (MW below 110amu). Pyridine extracts were consisted of polar compounds with high aromaticity whose MW was less than 9650amu.3. Small MW components accounted for a significant amount of the extracts, and no relations was found with the coal types or coal ranks. GPC with a mixture of THF and NMP as eluent showed that the macromolecular weight components were dissolved further in the mixed solvent, and the association of the polar components decreased or vanished. The profiles of pyridine and NMP extracts were consisted of two parts. The MW of the first part was above 29,900amu; and the second part was from 110amu to 13,300amu. The relative amounts of the first part increased with the contents of carbon, about 15% for PS-C and YZ-C, about 50% for PS-D and YZ-D, and decreased rapidly with the contents of carbon, about 6.5% for CC-C and CC-D.4. The components were purity and could be identified clearly after prepared by Solid phase extraction (SPE) whatever the absorbent used, C18 or polymer. However, it could not collect the HMW components from coal extracts. The HMW components were enriched in the fraction of chloroform/ethanol (F3) prepared by CC method using silica as absorbent. Except for HLH-C and XLT-C, there was one porphyrin series (I) in pyridine extracts with the MW increased every 74amu regularly there from MW 592.5amu to 1932.0amu. The 74amu are attributed to the functional groups containing oxygen, butanol (C₄H₁₀O) or acetic acid, methyl ester or formic acid, ethyl ester (C₃H₆O₂). And there was another series (II) in HDG-C there from MW 535/540amu to 1950.6amu, which was corresponding to poly(dimethylsiloxane).5. The Syn-F results suggested that three to five rings polyaromatics of anthracene, phenanthrene and pyrene, and a little aromatic heterocycles of benzofuran, porphyrin and thiophene are the main body in coal structural unit.6. Combined characterization results from the Syn-F and LC/MS, the coal macro-structure model was built to represent the feature of coal during extraction.