Dissociation And Compositional Features Of Organic Matter In Xilinguole Lignite

Lignites is abundant coal resources in China,while the disadvantages,such as lower calorific value,higher mineral matter and moisture contents,of lignites limit its utilization.On the other hand,the structural advantages of aromatic and heterocyclic ring in lignites are unvalued in current utilization of lignite.Therefore,revealing the compositions and structural features of organic matter in lignite at molecular level will facilitate the efficient utilization of lignite.As we all know,the oxygen content exceed 20%,due to lignite retains partial macromolecular structure of coal-forming plants.Taking this feature into account,organic matter in XL can be dissociated into soluble portions,which can be characterized with advanced mass spectrometer.In this study,alkanolysis and catalytic methanolysis were used to investigate molecular compositional features of organic matter in XLThe direct characterizations of Xilingol No.6 lignite?XL?and its methanolysis residue?R_M?shows that XL mainly consists of aliphatic?37.4%?and aromatic?59.3%?carbons and each aromatic cluster contains 2 rings on average,while the content of aliphatic carbons and the degree of condensation from R_M decreased.The XRPES and FTIR analysis of XL and R_M show that the O atom in XL mainly existed in the form of>C-O-,but the relative content of>C-O-significantly decreased after XL methanolysis.According to the fitting curves of differential thermogravimetric profiles from XL,peak around 320? should result from the cleavages of>C_al-O-,>C_al-N-and>C_al-S-linkages,resulting in the highest yield?34.4%?of soluble portions from XL methanolysis at 320?.The yields of soluble portions from catalytic methanolysis of R_M with CH₃ONa and Ni_10%/Si_xAl_yO_z are 28.28%and 54.72%,respectively.About 90%of organic matter are dissolved after XL methanolysis and catalytic methanolysis of R_M with Ni_10%/Si_xAl_yO_z,which provides a basis for comprehensive analysis of the compositional features of organic matter in XL.The extracts from the methanolysis of XL were analyzed with Curie point pyrolysis-gas chromatography/mass spectrometer and the main group components were alkanes,alkenes,arenes,phenols,ketones and esters.The carbon number of n-alkanes and n-alkenes demonstrate continuous distributions ranging from 9 to 31 and 9 to 23,respectively.The n-alkenes may released from the pyrolysis and methanolysis of long chain structures.Arenes mainly contain 1-2 ring and 1-3 substituents which are methyl,ethyl and isopropyl.Phenols and esters are the most abundant oxygen-containing compounds,which generated from the breakage of>C-O<in lignites.In addition,a large number of alkanoates intermittently distribute in the range of C₈-C₃₀,which could be ascribed to transesterification during methanolysis of XL.In addition,E_M/320-1 and the extractable portions from catalytic methanolysis of R_M with CH₃ONa were analyzed with a quadrupole-orbitrap mass spectrometer coupled with an atmospheric pressure chemical ionization and electrospray ionization source.The results show that the oxygen atoms may exist in-OH,>C=O,-COO-,R-O-and furans in lignite.Pyridine and aromatic amine nitrogen are the dominant nitrogen forms in extracts,while thiophenes are the main form of sulfur atom.Among them,methoxyquinoline?N₁O₁?,methylfuropyridinate?N₁O₃?and alkylbenzoylimidazole?N₃O₁?could be generated by cleaving>C-O-linkage between nitrogen-containing aromatic rings and macromolecular groups in lignites.The Ni_10%/Si_xAl_yO_z were characterized by N₂ adsorption/desorption,Transmission electron microscopy-Energy dispersive spectrometer,X-ray diffraction,and X-ray photoelectron spectrometer.The analysis indicate that nickel nanoparticles were successfully supported on the surface of Si_xAl_yO_z.The particle size of nickel nanoparticles range from 3 to7 nm,and there is no obvious agglomeration of nickel nanoparticles.Compared to the analysis of extracts from XL methanolysis,fewer phenolic compounds and a large number of esters were identified in the soluble portions from catalytic methanolysis of R_M with Ni_10%/Si_xAl_yO_z.The results show that weak covalent bonds such as aromatic ether bonds were broken during the alkanolysis of XL,and the strong covalent bonds were mostly dissociated in the alkanolysis of R_M.