Solvent Extraction Of Shengli Lignite And Structure Characterization Of Its Small Molecular Compounds

Structures of the small molecular compounds of shengli lignite were studied bysolvent extraction method in this paper. Acetone, methanol, THF and DMF were usedto extract the small molecule compounds of shengli lignite by Soxhlet extraction,ultrasonic-assisted extraction and microwave-assisted extraction.The extracts andresidues were analyzed by FT-IR, BET and GC/MS. By comparing the differences ofextracts of different extraction methods and changes in the pore structure of coalresidues, the effects on the dissolution process of small molecules were explored andthe occurrences of small molecules were deduced, so as to provide some basis for themodel building of the molecular structure of lignite.The extraction yields of four solvents by different extraction methods were:DMF> THF> methanol> acetone, indicating the nature of the solvent itself was themain factor in extraction process. Effects of different extraction methods on extractionyield varies due to solvents.the regulation of extraction yield was: Soxhletextraction> microwave-assisted extraction> ultrasonic-assisted extraction.Considering the extraction efficiency, the amount of solvent, environmental and otherfactors, microwave-assisted extraction was considered optimal process.The extracts were analyzed by GC/MS. The results show that theGC/MS-detectable species can be classifed into aliphatic hydrocarbons、Aromatichydrocarbons and Heteroatom-Containing Compounds. Aliphatic hydrocarbons weremainly composed of C10~C24n-alkanes、small amounts of olefins and substitutedcycloalkanes. Aromatic hydrocarbons mainly were short-chain substituted benzeneand naphthalene, only very small amount of phenanthrene and pyrene were detected.Heteroatom-Containing Compounds were variety, containing some long chain alkylacid methyl ester, alcohol, phenol, aldehyde, ketone and nitrogen compounds.Extracts species varied with extraction methods, ultrasonic-assisted extractioncontributed to accelerate the dissolution of aliphatic hydrocarbons,while Soxhletextraction and microwave-assisted extraction had obvious advantage on the extractionof Heteroatom-Containing Compounds.By FT-IR, the specific surface area and pore size distribution measurementanalysis of coal residues，it found that extraction process had no significant effect onfunctional group of lignite, but had larger impacts on the pore structure.Ultrasonic-assisted extraction and microwave-assisted extraction not only increased the number of pores but also changed the pore size distribution, especially thenumber of micropores of about0.92nm，indicating the small molecules in this kind ofpores were extracted.The small molecules may exist in three states based on my study method:“freestate”,“micropore-bounded state”and“cross-association state”.Different extractionmethods had different effects on the dissolution behavior of the small molecules.Ultrasonic-assisted extraction and microwave-assisted extraction had advantage toextract the small molecules in the “micropore-bounded state” while Soxhlet extractionhad advantage to extract the small molecules in the “cross-association state”. Theextracts of different extraction methods by THF as solvent were summarized and theirpossible occurrences were deduceded: low carbon number of alkane mostly existed inthe “free state”，Aromatic substances were likely existed in micropores,which were inthe“micropore-bounded state”; cyclic alkanes, olefins, amine and oxygenatedsubstances with long-chain were probably in the “cross-association state”.