Dependence Of Methane Absorption On Microstructure Of Tectonic Caol

The structure of tectonic coal determines its properties such as low strength,poor permeability,large specific surface area,high adsorption capacity and fast desorption.It is easy to cause coal and gas outburst,so the study that the relationship between the microstructure of coal and gas adsorption is of great significance.In this paper,three kinds of tectonic coals with different degrees of coalification were selected and extracted with pyridine as the solvent by Soxhlet extraction.The extracts and coal residue with pyridine extraction of different metamorphic structural coals were obtained,and the relationship between the degree of coalification and the extraction rate was analyzed.Fouriertransforminfraredspectroscopy?FTIR?andgas chromatography-mass spectrometry?GC/MS?experiments were used to analyze the structural characteristics of surface functional groups and constituents of the extract family of tectonic coals with different degrees of coalification.The micro-pores structural characteristics of tectonic coal and coal residues are analyzed by low pressure CO₂ adsorption experiment.Methane adsorption isotherm experiments were carried out to discuss the methane adsorption characteristics and influencing factors of tectonic coal and coal residues.The main conclusions are as follows:?1?There are significant differences in the pyridine extraction rates of tectonic coals.The order of the extraction rates?Edaf?of tectonic coals with different degrees of coalification is:fat coal>gas coal>anthracite coal.The presence of small molecules in coal restricts the gas adsorption capacity of coal.The greater the pyridine extraction rate of the tectonic coal,the weaker the methane adsorption capacity,and vice versa.After the extraction,the free low-molecular materials in the coal are removed and their adsorption capacity changes,and the effects of tectonic coal with different degrees of coalification are different;the differences in the species,quantity,and nature of the low-molecular compounds dissolved in different solvents make the change of the residues,gas adsorption capacity different.?2?The composition of pyridine extracts from tectonic coal is controlled by the degree of coalification.Saturated hydrocarbons in tectonic coal can be divided into three categories:naphthenes,isoparaffins,and normal alkanes.From gas coal to anthracite,the relative content of n-alkanes and naphthenic hydrocarbons in tectonic coal all show a tendency to increase first and then decrease with the increase of coalification,while the alkanes decrease first and then increase with the increase of coalification.The composition of aromatic hydrocarbons in tectonic coal is closely related to the degree of coalification.The lower the coal grade,the more abundant the constituents are,and the composition of gas coal and fat coal is not much different.Both are rich in condensed ring compounds and aldehydes,ketones,and esters.The composition of aromatic hydrocarbons detected in anthracite is simple.?3?The functional group structure in coal has an important influence on gas adsorption.The basic functional groups of coal are the same,and the extraction of pyridine does not change the main molecular structure of coal.The intensity of absorbance of aliphatic hydrocarbons and oxygen-containing functional groups in coal is controlled by coal rank.The higher the coal rank,the weaker the intensity of infrared spectrum absorbance.The aliphatic components and oxygen-containing functional groups in tectonic coals decrease as the degree of coalification deepens.The functional group structure affects the gas adsorption,and the ultimate adsorption capacity of methane in tectonic coal decreases with the proportion of-CHx containing functional groups and oxygenated functional groups increasing.?4?Organic solvent extraction can change the pore structure of coal.Borth of the pore volume and specific surface area can change regularly with the increase of coalification,which shows that the pore volume and specific surface area of the coals increase with the increase of coalification,while the pore volume and specific surface area of the coal residue with pyridine extraction decrease with the increase of coalification.The effect of pyridine extraction on pore volume and specific surface of tectonic coal with different degrees of coalification is different.The extraction of coal samples through organic solvent can expand pores,increase pores and sparse pores.In the gas coal and the fat coal,the main performance is increase pores and sparse pores.In the anthracite coal,the main performance is the expand pores.?5?The gas adsorption capacity of tectonic coal is controlled by both pore structure and molecular structure.Pore structure provides space and channel for the adsorption and migration of methane molecules in coal.Gas adsorption occurs mainly in micropores.When the micropores are more developed,there are more methane adsorption spaces,and the low molecular compounds will affect the adsorption sites of methane molecules,thereby enhancing or reducing the effect of microporous adsorption.Gas adsorption is mainly based on microporous adsorption,and low molecular weight compounds in coal also affect adsorption capacity of coal.