Study On The Pyrolysis Characteristics Of Low Metamorphic Coal/swelling Coal With Metal Ions In Situ

Coal pyrolysis is an important means for clean and efficient utilization of low rank coal.Coal pyrolysis reactions are closely concerned with the coal structure.Studying the coal structure and the coal pyrolysis characteristics is helpful to reveal the relationship between the structural characteristics of coal and the composition and distribution of pyrolysis products,and is of great significance for realizing the directional regulation of coal conversion process.In this study,FTIR,SEM-EDS,XRD and ¹³C-CP/MAS-NMR were used to investigate the effect of different pretreatments,including demineralization,swelling?methanol/THF?,the impregnation of metal ions and swelling with metal ions(Li⁺,Ca²⁺,Mn²⁺,Cu²⁺,Co²⁺)in-situ impregnated,on the physical and chemical structure of coal.TG-FTIR,Py-GC/MS and quartz retort reactor were also applied to study the effect of different pretreatments on the pyrolysis characteristics,the composition and distribution of pyrolysis products.A summary of the results obtained in this study is as follows.?1?The absorption intensity of-COOH was reduced by the methanol swelling with metal ios impregnated.The results of ¹³C-CP/MAS-NMR showed that demineralization and methanol/THF swelling had little effect on the carbon structure of the coal.?2?The conversion of demineralized coal could be improved by swelling.The impregnation of Cu²⁺and Co²⁺and swelling with Cu²⁺and Co²⁺impregnated could also promote the conversion of the demineralized coal.The in-situ loading of Cu²⁺made the DTG curves of coal changed dramatically.The swelling with metal ions impregnated could further promote the conversion of the coal,compared with that of the impregnation of metal ions.?3?The impregnation of Li⁺and Ca²⁺and swelling with Li⁺and Ca²⁺impregnated had negative effect on the emission of CO.The impregnation of Cu²⁺and Co²⁺and swelling with Cu²⁺and Co²⁺had catalytic effect on the emission of CO₂.The emission peaks of CH₄ and aliphatic hydrocarbons were observed during the low temperature region?150-380??derived from the CH₃OH+THF swelling coal samples with metal ions impregnated.Swelling with Ca²⁺?Mn²⁺?Cu²⁺and Co²⁺impregnated had promoting effect on the emission of aromatics. ?4?The tar yield of demineralized coal could be increased by swelling.The impregnation of Li⁺and Ca²⁺and swelling with Li⁺and Ca²⁺impregnated could decreased the tar yield of coal.However,the impregnation of transition metal ions and swelling with transition metal ions impregnated had positive effect on the tar yield of coal.The swelling with metal ions impregnated could further increased tar yield of the coal,compared with that of the impregnation of metal ions.?5?Swelling increased the relative content of the acidic compounds of the coal tar.However,the impregnation of metal ions and swelling with metal ions impregnated decreased the relative content of the acidic compounds and increased the relative content of aromatics.The swelling with metal ions impregnated could further promote the formation of aromatics,compared with that of the impregnation of metal ions.The impregnation of Cu²⁺and Co²⁺and swelling with Cu²⁺and Co²⁺impregnated had positive effect on the formation of benzene.The swelling with Cu²⁺and Co²⁺impregnated could further increased benzene yield of the coal,compared with that of the impregnation of Cu²⁺and Co²⁺.The impregnation of Li⁺and Ca²⁺and swelling with Li⁺and Ca²⁺impregnated had positive effect on the formation of phenol,but decreased the content of cresol and xylenol.?6?The absorption intensity of-COOH,-C-O-C,-C=O and aliphatic side chains was reduced by the impregnation of metal ions and swelling with metal ions impregnated.The C=C stretching vibration of char shifted to higher wave numbers because of the impregnation of metal ions and swelling with metal ions impregnated.The impregnation of metal ions and swelling with metal ions impregnated could inhabit the growth of graphite structures in char.?7?The kinetic results showed that the impregnation of metal ions and swelling with metal ions impregnated could result in a decrease of activation energy at the corresponding temperature range of the first and the second prolysis stage.The functional mechanism of the metal ions in-situ impregnated during coal pyrolysis was discussed and proposed based on the pyrolysis characteristics and the composition and distribution of pyrolysis products.