Change Of Chemical Composition Of Solvent Extraction From Coals And Its Kinetics Mechanism

In the process of coal-forming,the coalification and destructive effect of tectonic stress,not only make metamorphic grade,macro profile,structure and physical mechanic property of coal change,but also changes the chemical composition of coal.In order to investigate the difference of chemical composition of coal under the influence of coalification and tectonic deformation,by means of solvent extraction,the coal of different metamorphic and destruction degrees was fractionally extracted.The kinetics of the dissolution of small molecule compounds in the extraction process and the variation rules of the chemical composition were analyzed to provide a theoretical basis for the efficient and clean conversion of coal and the development of coalbed methane.This paper took different metamorphic grades of brown coal,long flame coal,1/3coking coal,meager coal,anthracite and different destruction degrees of primary structure coal,cataclastic coals,granulated coal and mylonitized coal as the research object,which were fractionally extracted with tetrahydrofuran?THF?and carbon disulfide?CS₂?sampled in batches with time intervals.By means of column chromatography and gas chromatography-mass spectrometry?GC-MS?,the difference and mechanism of dissolution behavior of small molecule compounds,group composition and chemical composition of coals were analyzed.The results show that:?1?In the total extraction yield of coals with different ranks,the highest extraction yield is long flame coal?9.97%?,the lowest is anthracite?4.19%?,while brown coal,1/3 coking coal and meager coal are the middle.The total extraction yield of tectonic coals from high to low are mylonitized coal,granulated coal,cataclastic coals,primary structure coal.?2?The extraction process of coals can be divided into two stages,and the extraction yield of stage I is much higher than stage II,and k_I,k_II values in different solvents and coal samples showed different changes.?3?The results of group composition test show that stage II compared with stage I,different rank coals and tectonic coals under the THF solvent disposition,the hydrocarbon content decreased,the non-hydrocarbon content increased,while under CS₂ solvent disposition,the hydrocarbon content increased,the non-hydrocarbon content decreased,and with the change of the degree of coalification and destruction,the content of hydrocarbon and non-hydrocarbon is also changed.?4?The detectable small molecule compounds of GC-MS are composed of aliphatic hydrocarbons,aromatic hydrocarbons and heteroatomic compounds,among them,aliphatic hydrocarbons are mostly long-chain alkanes and alkenes,aromatic hydrocarbons are mainly 2⁵ cyclic aromatic hydrocarbons and their alkyl substituents,and heteroatomic compounds are mainly oxygen and nitrogen compounds;Heteroatomic compounds are abundant in the extract of different coals and have many types.The content of long-chain alkanes of aliphatic hydrocarbons in the extract of low-medium rank coals is larger,while the aromatic hydrocarbons only appear in the bituminous coal,and the content of aromatics hydrocarbons in the extract of intermediate bituminous coal is higher,which type content increased with the increase of the destruction degree of coal.