Molecular Characterization Of Extracts And Liquefication Products Of Low-rank Coal

In order to achieve the goal of clean utilization of low-rank coal and optimization of coal tar hydrogenation process,it is essential to get a clear analysis of their compositions.Low-rank coal and its low-temperature coal tar were treated by extraction,separation and hydrogenation.The molecular compositions of the products were detected by Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS),the transformation of heteroatomic components were revealed as well.The heteroatomic composition of a lignite was recognized by the characterization of the pyridine extract,N-methyl-pyrrolidone(NMP)extract and thermal dissolved product.a complex composition of small molecules(less than 700 Da)with multi-nitrogen and oxygen atoms species were discovered in NMP extract.The maximum nitrogen and oxygen number reach 6 and 11 respectively,which are much higher than the reported coal extracts composition.The nitrogen isotope detection shows a large amount of nitrogen in the extract were from NMP solvent.The result of thermogravity analysis,hydrolysis reaction and collision-induced dissociation indicate that no free NMP and associated NMP were existed in the extract,which demonstrate NMP were reacted with the soluble matters of coal during the extraction process.The results would be valuable for the understanding of molecular composition of coals,as well as the interactions between NMP and molecules of low-rank coal relative materials.The coal tar was separated into fractions by SARA separation,acid-base extraction and supercritical CO2 fluid extraction,followed with characterization of the fractions.The extraction selectivity of supercritical fluid CO2 extraction was revealed on the molecular level,it prefers to extracting compounds with low condensed degree and low carbon numbers.In addition,it is effective for the separation of components of similar molecule composition but with different functional groups.Therefore supercritical fluid CO2 extraction can provide great convenience for the separation of coal tar and introduce a new solution for the differentiation of similar molecules with different functional groups.Meanwhile,a method of using Ag+-SPE to physically separate olefins from coal tar was devoleped.After separation,high purity olefin fractions were obtained and a clear identification of olefins was shown on GC chromatogram.None or negligible amounts of iso-α-olefins were found in coal tar.The coal tar and its hydrogenated products were detected by negative and positive ESI FT-ICR MS.The character of heteroatomic compounds were obtained on the molecular level.The transformation rule of heteroatomic compounds were obtained depending on the composition difference.Under this experiment conditions,the heteroatom removal rate of coal tar from high to low is S>N>O.Compared to petroleum,the coal tar contains a large amount of highly condensed nitrogen-containing compounds,which have strong ability to resist hydrogenation and are difficult to be removed.Basic nitrogen-containing compounds rather than non-basic nitrogen-containing compounds are liable to be hydrogenated under mild condition.In pre-hydrogenation process,basic nitrogen–containing compounds can be hydrogenated and generate amine substances,while negligible new matters were appeared in non-basic nitrogen–containing compounds.Compounds with one or two oxygen atoms were existed in the final hydrogenated product.Hydrogenation has different influence on the distribution of different oxygen functional group matters.negligible changes were occurred on mono-phenol,however the distribution of furans narrowed down.The study on the transformation of heteroatomic compounds in coal tar can promote optimization of hydrogenation process,meanwhile provide reference to the hydrotreating of biomass oil and petroleum.