Study On The Pore Structure Of Coals And Characteristics Of Gases Adsorption On Coals

Pore structure and adsorption characteristics of CH₄, CO₂, N₂ single and CH₄/CO₂ binary gas on coals have been studied comprehensively on the basis of experimental data with computer program from the point of view of Physical Chemistry, Interface Chemistry, Coal Chemistry, Coal Petrology and so on in this paper. It is highly important to enrich the theoretics on pore structure of coal, Coalbed Methane and gas, especially in the fields of Enhanced Coalbed Methane (ECBM) recovery and CO₂ sequestration using CO₂ injection.Mercury Porosimetry and Nitrogen Adsorption at lower temperature were employed to investigate the pore structure of coal, which is characterized with the distribution of pore diameter, pore volume and specific surface area. The results in Mercury Porosimetry show that there is abundant macropore and micropore in coal, injection-Hg is retained in micropore as Hg is ejected, the pore volume and specific surface area for anthracite is greater than that bituminous coal. Abnormal nitrogen adsorption on coal is observed, in which coal is a kind of nonrigid sorbent and swelling/shrinkage of coal matrix occur with abnormal nitrogen adsorption/desorption. In order to express the pore structure of coal with the abnormal nitrogen adsorption, processing method (including normal and special one) and adjusting method (including linear adjustment and maximum one) for experimental data were employed to obtain the distribution of pore volume and specific surface area with pore equivalent model of columnar and parallel-plate. The results show that maximum adjustment is suited to adjust the experimental data, and the micropore in coals is the main adsorption space of coals.Adsorption/desorption characteristics of CH₄, CO₂, N₂ pure and CH₄/CO₂ binary gases adsorption on Jincheng coal and Luan coal has been studied, and then, the four different models viz. Langmuir, BET, D-A and D-R were used to fit the experimental data of CH₄, CO₂, N₂ adsorption on coals by SPSS software, linear regression and EXCEL method. The results show there is preferential adsorption behaviour of CO₂ on coals, and CH₄ preferentially adsorbed in coals in some cases. Fitting parameters could be employed to explain the adsorption characteristics and the changed-pore structure during adsorption/desorption to a certain extent. The fitting parameters could not be used to provide quantitative results on pore structure and its change as interaction between fitting parameters, matrix change during gas adsorption/desorption on coals and uncertainness of the physics meaning for saturated vapor pressure.