Investigation on pore structure evolution in metaplast from pyrolysis of vitrinite in bituminous coals
It is of great significance for regulating the pore structure of coal-based carbon materials to investigate the pore structure evolution in metaplast during the pyrolysis of bituminous coals.In this study,three kinds of bituminous coals with different metamorphic degrees,enriched in vitrinite,were pyrolyzed to their characteristic temperatures point(softening temperature,tp;maxi-mum fluidity temperature,tm,and solidification temperature,tk).Nitrogen adsorption method was used to investigate the evolution behaviors of pore structure for the metaplast.The results show that the isothermal adsorption-desorption curves of the metaplast derived from vitrinites in three kinds of bituminous coals with different metamorphic degrees at the characteristic temperature are of type-Ⅲ,with a hysteresis loop.During the pyrolysis of vitrinite,the specific surface area of the metaplast ini-tially increases and then decreases,with the rate of change in the generation phase being slower than that in the shrinkage and solidification phase.As the characteristic temperature in the pyrolysis process increases,the vitrinite in the low-metamorphic-degree Tangkou gas coal(TK)initially exhibites pore growth and pore enlargement,followed by pore merging and interconnection,forming mesopores and macropores.In the medium-metamorphic-degree Huozhou fat coal(HZ),a large number of micro-pores gradually formed in the vitrinite,with a specific surface area as high as 5.97 m2/g,followed by merging and interconnection of the micropores into mesopores or larger pores.However,In the high-metamorphic-degree Scarlat coking coal(SK),the vitrinites first formed more mesopores or macro-pores,with an average pore diameter of 13.93 nm,and then shrank into smaller pores.
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