Study On The Structure And Composition Of Low Temperature Pyrolysis Products Of Lignite Saturated By K⁺?Ca²⁺ And Mg²⁺

Lignite reserved in China is abundant,the research spots focuses on drying,pyrolysis,combustion and et al.The catalytic pyrolysis process of lignite by low-temperature is also a research hotspot.In this paper,the pyrolysis and drying experiment of the lignite saturated by the K⁺,Ca²⁺ and Mg²⁺ solution were carried out.The influence of K⁺,Ca²⁺ and Mg²⁺ on lignite drying and pyrolysis process were studied.What's more,the fractal characteristics of char were also researched using the FHH?Frenkel-Halsey-Hill?method.The results show that:In the process of dewatering?100-300??,the macromolecule framework and pore structure of lignite samples doesn't vary noticeably as a whole,mesopores and macropores are mainly the open cylindrical pores and cracks pores,and the diameter distribution of mesopores are unimodal in 2.65¹0nm;micropores and mesopores are mainly one dead end pores,and the diameter distributed of micropores appears to be multimodal in 0.5¹.5nm.In the process of pyrolysis?350-600??,char yield reduced while the yield of pyrolysis water and gas increased when the temperature rose,and the tar yield increased at first and then decreased,and the transition temperature was 500?.K⁺,Ca²⁺ and Mg²⁺can catalyze the pyrolysis process of lignite in defferent degrees,because K⁺,Ca²⁺ and Mg²⁺loaded on the carboxyl,participated in the pyrolysis reaction,and then played a catalytic role.After ash handling,the yields of hydrogen,methane and C2 substance in pyrolysis gas were enhanced because the catalytic function of metal ions.In the pyrolysis tar,phenol,toluene,ethyl benzene,paraxylene,the methyl ethyl benzene,isopropyl benzene,three methyl benzene,the methyl isopropyl benzene,the hydrogenated indene,benzofuran,naphthalene,two methyl naphthalene,phenanthrene and other substances,came from the coal macromolecular structure.Nevertheless,with multiple substituent naphthalene,biphenyl and with two benzofuran,phenanthreneand and anthracene,and four ring pyrene,were generated from the process of pyrolysis tar material of secondary reaction.There are two different fractal dimensions in the pyrolysis char,D1 and D2 varing from 2 and 3,D2 indicated the roughness of micropore volume,and was controlled by micropore volume in the process of pyrolysis.Ca²⁺ and Mg²⁺ enhanced the number and specific surface area of micropore,and made the pore structure of char rougher.And conversely,K⁺ reduced the number and specific surface area of micropore,and made the pore structure of char smoother.