Supercritical CO₂/CH₄ Adsorption Desorption Characteristics Of Tectonically Deformed Coals And Its Control Mechanisms

In this paper,five medium rank tectonically deformed coals with different deformation degree in Huaibei area are taken as research objects.Based on the isothermal adsorption/desorption experiments of supercritical CO₂and CH₄at 45?and drying condition to study the adsorption/desorption characteristics of tectonically deformed coals.Besides,according to the experiments of mercury injection,low temperature liquid nitrogen and carbon dioxide adsorption,XRD and FTIR results of structural analysis.The control mechanisms of the evolution of pore structure and chemical structure on the supercritical adsorption/desorption characteristics of tectonically deformed coals are revealed.The main achievements are as follows:?1?The adsorption/desorption curves of supercritical CO₂excess?absolute?are two-stage evolution.Before mutational pressure 8 MPa?adsorption?/10 MPa?desorption?,the curves rise first and then fall,with the feature of type I isotherm.After that,with the increase of pressure,the curves ascend sharply and have the feature of type?isotherm.And negative adsorption occurs in the process of adsorption/desorption.The excess adsorption/desorption curves of supercritical CH₄rise first and then drop with the increase of pressure,and there are maximum adsorption capacity.However,the absolute adsorption/desorption curve go up rapidly and then slow down gradually,both of them have the feature of type I isotherm.With the increase of deformation degree,the maximum adsorption capacity of supercritical CO₂for tectonically deformed coals?the limit adsorption capacity of supercritical CH₄?have an increasing trend,while the reversibility of adsorption/desorption of supercritical CO₂and CH₄show the opposite evolution law.?2?With the increase of deformation degree,the total pore volume and total specific surface area of macropore and ultramicropore in the tectonically deformed coals show an increasing trend.The pore volume and specific surface area of pores in each stage show a different evolution,which the ultramicropore is the most developed,and the fractal dimension of each diameter of aperture also has an increasing trend.The adsorption capacity of tectonically deformed coals to supercritical CO₂?CH₄?increases with the increase of ultramicropore?micropore?content.The key physical factor controlling the reversibility of adsorption/desorption of supercritical CO₂and CH₄is ultramicropore,however,due to the difference of main adsorption space and adsorption mechanism between them,the reversibility of adsorption/desorption enhanced and attenuated with the increase of ultramicropore content.?3?With the increase of deformation degree,the fatty side chains and oxygen-containing functional groups in the tectonically deformed coals gradually fall off,the aromatization and ring condensation degree increase,the aromatic carbon mesh layer in the coal crystal core increases rapidly,and the coal crystal core tends to flatten.Functional groups are the key chemical factors to control the adsorption capacity of supercritical CO₂?CH₄?.With the increase of aromatic structure,fat structure and the decrease of oxygen-containing functional groups,the adsorption capacity of tectonically deformed coals to supercritical CO₂?CH₄?is increasing.The adsorption/desorption reversibility of supercritical CO₂and CH₄are controlled by chemical structure evolution of tectonically deformed coals which have different control functions.There are 36 figures,29 tables and 159 references in this thesis.