Fractional Extraction And Sequential Thermal Dissolution Of Zhundong Subbituminous Coal And Shengli Lignite

Understanding of organic spices in low-rank coals at the molecular level, which is a keyproblem needed to be solved urgently for coal chemistry, is the main research topic ofmolecular coal chemistry, and is the scientific foundation for efficient, clean and value-addutilization of coals. Hence, it is of crucial importance to develop a method to understandcoal structure at the molecular level.A “fractional dissolution, finely separable and non-(low-)destructive” analytical methodto analyze low-rank coals was put forward in this dissertation. This method combinesfractional extraction of coals at room temperature, sequential thermal dissolution of theextraction residues and fine column separation of the mild and thermal extracts, andprovides an effective way to analyze organic matter in coals at the molecular level. Usingthis method, Zhundong subbituminous coal (ZSBC) and Shengli lignite (SL) were mildlyextracted with isometric carbon disulfide (CS2) and acetone mixed solvent (CDSAMS) toobtain the extracts (EM-Zand EM-S) and exraction residues (ERZand ERS), respectively. Thetotal yields of ZSBC and SL are2.8%and2.9%, respectively. Some copounds in coal show“wave-like dissolution” and “group component dissolution” characteristics duringextraction process. Low-and non-polar components (e.g., aliphatic compounds) could beextracted out firstly with CDSAMS, then aromatic compounds. Polar components andmacromolecules are most aboundent compounds and could be extracted out throughoutwhole extraction process. Water content of SL was reduced from12.52%to0.58%afeter18cycles of solvent extraction. Therefore, lignite extraction with CDSAMS might be a novelmethod for mild upgrading of lignite. EM-Zand EM-Swere fractionally extracted withpetroleum ether, CS2, methanol, acetone and CDSAMS. Fractional extraction yields of EM-Zand EM-Swith methanol both are highest, up to38.5%and49.7%, respectively. Atmosphericsolid analysis probe/time-of-flight mass spectrometry (ASAP/TOF-MS) results indicate thatmolecular weight distribution of petroleum ether-soluble portions of EM-Zand EM-Sshowdouble peaks distribution, while other fractional extracts show approximate normaldistribution.Thermal dissolution of EM-Sin methanol was carried out to offer thermal extract (TDE6).4possible structure units of soluble macromolecules in SL were put forward according tothe difference in chemical compositions of EM-Sand TDE6. Sequential thermal dissolutionof ERZand ERSin cyclohexane, benzene, methanol and ethanol was performed. Totalthermal dissolution yields of ERZand ERSin cyclohexane, methanol and ethanol are2.5% and2.9%,12.3%and12.9%, and3.3%and4.3%, respectively. In addition, thermaldissolution of raw coals and their extraction residues in methanol, ethanol, phenol and ethylacetate, and so on was also investigated, and found that ethanol have better desulfurizationeffect than other solvents. Some unreported or seldom reported compounds were detected inthermal extracts, for example,34-hydroxyltetrakishomohopane,35-hydroxylpentakis-homohopane, cyclopropa[9,10]lanostan-3-one, stigmast-4-en-3-one and two silicon con-taining organic compounds. Structure unit of (-O(CH2)2)2CHCH3may exist in SL deducedfrom3-methyl-1,5-pentanediol which was detected in large amount. Nearly100%oxidationproducts of thermal dissolution residue with NaOCl are benzene-polycarboxylic acids.Many unreported or seldom reported group compounents were enriched from mild andthermal extracts via columm separation. Unreported group compounents include8cyclizedhopanoids and many polycyclic aromatic lactones. Seldom reported group compounentsinclude13arenes with7rings,8series of long-chain alkyl benzenes,10alkansls,22alkylbenzyl carbonates,1trialkyl benzene-tricarboxylate,8benzohopane and2macromolecularsulfur-containing hopanoids. Most of them are important biomarkers.8pure compounds were isolated from ZSBC and SL. They are5H-phenanthro[1,10,9-cde]chromen-5-one (),4H-benzo[5,10]anthra[1,9,8-cdef]chromen-4-one (П),3-ethyl-8-methyl-2,3-dihydro-1H-cyclopenta[a]chrysene (Ш), diethylhexylnaphthalene, retene,palmitic acid, bis(2-ethylhexyl) phthalate and octathiocane. Diethylhexylnaphthalene,compounds П and Ш are unreported compounds. Compound Ш was purified up to99.8%via preparative medium-pressure liquid chromatography, Sephadex LH-20gelatin columnand recrystallization, and its high resolution Fourier transform infrared (FT-IR),1H nuclearmagnetic resonance (NMR) and13C NMR spectra were provided. Two possible formationpathways of compound Ш were put forward according to the intermediates.General fragmentation rules in mass spectrometer of long-chain alkanals, polycyclicaromatic lactones, hopanoids and long-chain alkyl benzenes were summarized. For example,peaks m/z [M-18]，82and44, m/z [M-28] and [M-28-29], and m/z191(strong) and369(weak) are the characteristic of long-chain alkanals, polycyclic aromatic lactones andhopane, respectively. Base peaks of C35and C3622-aryl-30-norhopanes are m/z105and m/z119, respectively. Summarization of fragmentation rules for all kinds of compounds is theimportant scientific foundation for developing molecular coal chemistry.