Characterization Of Organic Component In Medium-and Low-rank Coals Based On Ionization Methods Of Mass Spectrometry

Due to their low calorific value,high contents of moisture,and high ash yield,etc.,medium-and low-rank coals have not been reasonably utilized.Extensive separation and characterization techniques have been applied to obtain the structures of medium-and low-rank coals to provide the theoretical basis for the high value-added utilization of coals.Mass spectrometry(MS)is proven to be one of the effective methods to investigate on coal structure.The complexity of coal molecular composition makes it difficult to obtain adequate molecular information of coals through single MS ionization mode.Therefore,MS analyses with multiple ion sources are necessary for investigating complex compositions of organic matters in coals at the molecular level.In the thesis,Dayanhe lignite(DL)and Shenfu long flame coal(SLF)were selected as the coal samples and sequentially thermal dissolution of coal samples at 300 oC using cyclohexane,acetone,and methanol afforded thermal dissolution products(TDPs).The total yields of TDPs in DL and TDP are 41.6% and 32.7%,respectively.Fourier transform infrared spectrometer(FTIR)and MS systems equipped with different ion sources,such as gas chromatography/mass spectrometry(GC/MS),atmospheric pressure photoionization time of flight MS(APPI-TOF MS),electrospray ionization TOF MS(ESI-TOF MS),and direct analysis in real time TOF MS(DART-TOF MS)were used to characterize compositions and structure features of the soluble organic components in coals,and the significant otherness analysis were carried out.GC/MS mainly obtained structural information of compounds with small molecule mass and low polarity in TDPs.The relative abundance of arenes in FDL is much higher than that in FSLF,and most of the arenes are 1-2 aromatic-ring compounds.Compounds with small molecule mass,including aliphatic hydrocarbons,arenes,and phenols,can be dissolved out efficiently with cyclohexane.Acetone is an effective solvent to extract furan and nitrogen-containing compounds(NCCs)from the coal samples,especially NCCs with more than 2 nitrogen atoms owing to the strong hydrogen bonds between acetone and NCCs,which mainly exist in pyrazole,imidazole,quinoxaline,indole,pyridine and amino species.With strong nucleophilicity and hydrogen donor ability,methanol can easily penetrate into the network structure of coals under supercritical condition,and alcoholysis and alkylation reaction release abundant oxygen-containing compounds with increased yields of alcohols and ethers.Compared with GC/MS,APPI-,ESI-,and DART-TOF MS greatly extend the range of detectable compound,double bond equivalent(DBE),and carbon number.APPI-TOF MS is available for analyzing thermally labile and weak/non-polar compounds in TDPs,especially for arenes which are poorly ionized by conventional ionization methods.Toluene dopant was used in conjunction with the APPI method to further enhance the ionization efficiency of analyte,afterwards identify more species and obtain more information about the composition and structure of coals.Compared with GC/MS and ESI-TOF MS,APPI-TOF MS detected more arenes over 2 rings and compounds with molecular mass over 500 u.ESI-TOF MS has advantage in the ionization of polar species in TDPs,which mainly consist of compounds with DBE<8.The polar species mostly contain oxygen or nitrogen atoms,and N1 and N1O1 species are the main NCCs which mainly exist in the forms of amino groups,pyrrole rings,and hydrogenated quinolone rings.As an ambient ionization technique,DART speeds up the analysis process,and greatly improves the range of detectable compound and DBE.Noteworthily,a small amount of dimers and other hydrocarbon compounds which cannot be detected by other ionization techniques are identified in the TDPs with methanol.