Study Of Organic Matter Of Composition And Molecular Structure Characteristics Of Hefeng Subbituminous Coal In Xinjiang Besad On Gental Dissolution

Hefeng subbituminous coal（HSBC）from Hoxtolgay coalfield in Xinjiang（China）was selected as the research object in this paper.Firstly,ultrasonic dissolution of HSBC at room temperature in petroleum ether（PE）,carbon disulfide（CDS）,acetone（A）,methanol（M）and carbon disulfide/acetone mixed solvent（IMCDSAMS）was conducted,respectively.Secondly,thermal dissolution（TD）of HSBC at 300 ℃ was carried out with cyclohexane（CH）,benzene（B）,methanol M,ethanol（E）and isopropanol（IP）as the solvent.Furthermore,HSBC was subjected to variable temperature thermal dissolution and different energy field treatment with IP as solvent.Then,a series of organic matter components can be obtained.The components were characterized by fourier transform infrared spectrometer（FTIR）,thermogravimetry-derivative thermogravimetry（TG-DTG）,nuclear magnetic resonance(¹³C NMR),gas chromatograph/mass spectrometer（GC/MS）and orbitrap mass spectrometry（Orbitrap MS）.Based on the cluster analysis from chemometrics method,the molecular structure model of HSBC was constructed.And then,the coal quality characteristics of HSBC are summarized via the comparison between HSBC molecular structure model and other coal models,and its possible suitable development and utilization are given out.Specific research contents and results are as follows.（1）With PE,CDS,A,M and IMCDSAM as the solvent,HSBC was dissolved by ultrasonic dissolution at room temperature under the condition of F=100 k Hz,P=210 W,t=1 h and T=25 ℃.Results showed that the yield of soluble portion（SP_i）was in the order of SP_IMCDSAM（3.90%）>SP_M（2.73%）>SP_A（2.18%）>SP_CDS（0.65%）>SP_PE（0.21%）.From FTIR analysis,by ultrasonic dissolution of HSBC,PE can destroy weak hydrogen bond,and CDS can not only destroy the weak hydrogen bond,but also slightly destroy C-O bond,while M and IMCDSAM can destroy the twining effect of alkanes in coal,C-O bond and C=C bond in HSBC.Results from GC/MS analysis showed that alkanes are predominantly abundant in the five soluble portion.（2）Analysis from Quadrupole/electrostatic field orbitrap mass spectrometry（Orbitrap MS）for SP_i showed that,except for IMCDSAM,with the enhancement of the polarity of PE,CDS,A and M,the solubility parameter increased and the content of heteroatomic compound in the four soluble portion was increased in turn.For IMCDSAM,heteroatomic compound is more abundant among its group components since the significant“synergistic effect”.Cluster analysis from Orbitrap MS results showed that,on the one hand,SP_PE and SP_CDS can be clustered into one class,mainly composed of hydrocarbons（HC）and oxygen-containing hydrocarbons（O_n）,and SP_Mand SP_IMCDSAM can be clustered into one class,mainly composed of O_n,hydrocarbons containing O and N（ON）and hydrocarbons containing O,N and S（ONS）.While SP_Ais clustered as another class,which not only contains ON and ONS but also adds n nitrogen-containing hydrocarbons（N_n）and hydrocarbons containing N and S（NS）,and the content is similar to ON and ONS.On the other hand,for the O_n class of SP_Mand SP_IMCDSAM,the content of O₃ and O₄ in SP_M is higher,while the content of O₅-O₆in SP_IMCDSAM is higher,and both of them are diverse.（3）Thermal dissolution of HSBC with IP as the solvent at 220 ℃,240 ℃,260 ℃,280 ℃ and 300 ℃ indicated that,with the increase of thermal dissolution temperature,yield of thermal dissoluble component(SP_TDj)increased from 1.97%to 13.53%.Especially,the yield increased by 70.1%from 280 ℃ to 300 ℃,illustrating that macromolecular cluster in HSBC could be dissolved partially as the temperature as high as 280 ℃.GC/MS results from SP_TDj shows that as the thermal dissolution temperature increased from 260 ℃ to 280 ℃,SP_TDj contains not only alkanes,esters,ketones and carboxylic acids,but also aromatics,alkenes,aldehydes and phenols.As the temperature up to 300 ℃,alcohols and ethers appeared with 11 compounds.Obviously,with the increase of thermal dissolution temperature,the covalent bond in HSBC is more easily to be broken,and esterification with IP or ring opening hydrogenation could be occurred.The results can be derived from that,with the thermal dissolution temperature increases from 240 ℃ to 260 ℃,the content of carboxylic acids and esters in SP_TD changed from 91.65%and 2.66%to 33.13%and49.61%;with the thermal dissolution temperature increased from 280 ℃ to 300 ℃,the content of alkanes and aromatics in SP_TDchanged from 13.59%and 48.69%to45.90%and 18.86%.Results from Orbitrap MS for SP_TDj showed that with the increase of thermal dissolution temperature,the content of O_n decrease firstly and then increase,down to the lowest at 240 ℃,and there are benzyl alcohol and（E）-cinnamaldehyde appeared in SP_TDj.The content changes of N_n and ON are opposite,and pyrrole nitrogen and pyridine nitrogen are the main forms of nitrogen atoms.TG-DTG analysis showed that the maximum weight loss rate peak temperature of ISP_TD220-260 is the same as that of HSBC（440 ℃）,while the temperature of ISP_TD280 and ISP_TD300 was increased to 450 ℃ and 455 ℃,respectively.Above results indicate that TD process slightly destroys the network structure of HSBC as the temperature was up to 280 ℃.（4）HSBC was dissolved at 300 ℃ with CH,B,M,E and IP as the solvent,respectively.The yield order of SP_TDk is SP_TD/IP（13.53%）>SP_TD/E（10.51%）>SP_TD/CH（5.72%）>SP_TD/B（5.36%）>SP_TD/M（3.40%）.GC/MS results of SP_TDk shows that the ester compounds in SP_TD/M,SP_TD/E and SP_TD/IP are 66.89%,38.06%and 6.32%respectively,indicating that the intensity of esterification between three alcohol solvents and HSBC in the process of TD is followed by M>E>IP.According to Orbitrap MS analysis of SP_TDk,aliphatic compounds containing heteroatoms are mainly found in SP_TD/CH and SP_TD/B,while aromatic compounds such as benzene,biphenyl,naphthalene and fluorene are mainly discovered in SP_TD/M,SP_TD/E and SP_TD/IP.Compared with SP_TD/CH and SP_TD/B,the contents of O_n and ONS compounds in SP_TD/M,SP_TD/E and SP_TD/IP are higher,while those of HC,N_n and NS are lower,indicating that the three alcohol solvents presented higher damage to the oxygen-containing bridge bond in HSBC in the TD process.In addition,it can be seen that oxygen atoms from ON compounds in SP_TDk are mainly carbonyl and ester groups,while nitrogen atoms are mainly amino,pyrrole nitrogen and pyridine nitrogen.ISP_TDk was also tested by FTIR and TG-DTG.FTIR analysis shows that compared with HSBC,not only self-associated hydroxyl peak at 3420 cm^-1disappear in ISP_TDk,but also the C-O bond at 1110 cm^-1,and the benzene ring disubstituted absorption peak at 797 cm^-1 are weakened.TG-DTG results shows that the maximum weight loss rate peak temperature of ISP_TDk increases from 440 ℃ to 455 ℃.The above results suggest that the TD process under the five solvents can not only affect the weak bonds such as hydrogen bond and C-O in HSBC,but also slightly affect its network structure.（5）With IP as solvent,HSBC was treated with three single energy field of USI,microwave radiation（MWI）and mechanochemical activation（MCA）)and three coupling energy fields of ultrasonic-microwave coupling（USI/MWI）,ultrasonic-mechanical activation coupling（USI/MCA）and microwave-mechanical activation coupling（MWI/MCA）,respectively.The treated samples were subjected to300 ℃ TD.According to CG/MS detection results of SP_TDs,the oxygen-containing compounds（esters,alcohols,carboxylic acids,phenols,ketones and ethers）in SP_TD/MAC are the most compounds,and their content is as high as 59.90%,indicating that MCA energy field treatment intensified the fracture of oxygen-containing bridge bonds in HSBC.The aromatics in SP_TD/MWI and SP_TD/USI are the most compounds,with 49.48%and 43.56%,respectively,indicating that MWI and USI energy fields mainly destroy theπ-πinteraction between HSBC aromatic rings.The Orbitrap MS result of SP_TDs shows that O_n compounds are most enriched in SP_TD/USI/MWI and SP_TD/MWI/MCA,with 59.11%and 49.73%respectively.And the O_n compounds in SP_TD/MCA is 30.99%.It can be speculated that MWI plays a dominant role in both USI/MWI and MWI/MCA,and the treatment of these two coupled energy fields significantly enhance the dissolution of O_n compounds in HSBC.It can also be seen that the contents of NS and ONS compounds in SP_TD/USI/MWI and SP_TD/MWI/MCA are significantly lower than those in SP_TD/USI,SP_TD/MWI and SP_TD/MCA,indicating that HSBC inhibits the dissolution of NS and ONS compounds by these two energy field coupling treatments.In addition,the oxygen atoms of O_n compounds in SP_TDs are mainly carbonyl,ester and ether oxygen bonds,while the nitrogen atoms are mainly amino nitrogen.TG-DTG results show that the maximum weight loss rate peak temperature of ISP_TDs increases from 440 ℃ for HSBC to 450 ℃.The above results indicate that different energy field treatment-TD processes can not only affect the C-O weak bonds in HSBC,but also slightly affect its network structure.（6）In view of the composition features of aliphatic compounds and short chain alkanes in total soluble matter from HSBC,the aromatic compounds are mainly phenanthrene,fluorene,naphthalene and their derivatives,and heteroatomic compounds are mainly oxygen-containing and nitrogen-containing compounds.Combined with proximate analysis,ultimate analysis,FTIR,¹³C NMR,XPS and TG-DTG analyses,the molecular formula of HSBC can be fitted as C₂₃₀H₂₀₉O₃₉N₄S and the molecular weight of which is 3685.44.The inactive heteroatom functional groups in the model are mainly hydroxyl groups,and the model also contains heteroatom containing units such as condensed pyran,pyridine and pyrrole.The aromatic ring units are mainly connected by short aliphatic chain and ether bond.And the model presents the characteristics of Shinn model.It is speculated that HSBC is suitable for coal liquefaction,coal-oil co-liquefaction,pyrolysis and other processing processes to prepare high-grade lubricating oil or fine aromatic chemicals.