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Abstract
The paper presents a numerical approach to the analysis of the statistical effect of functional groups on the sorption of methanol and water on hard coal samples. The material used for the analysis was obtained from numerous samples of hard subbituminous and bituminous coals up to anthracite from different Polish coal mines and includes sorption isotherms of water and methanol vapors, as well as carbon dioxide and methane on these samples. Measurements were made of the sorption isotherms of water and methanol vapors and the data set has been supplemented with the sorption isotherms of water, methane and carbon dioxide taken from the literature for the precise estimation of the model parameters. More precise estimation is reached by using a strong setting of the coal structure parameters for a bigger number of sorption system, and in each case the same parameters of coal geometry are constant with an exact fitting of sorption isotherm. The adsorption-absorption model of the sorption in coal (Multiple Sorption Model-MSM) is used in the numerical experiments and the parameters of hard coal structure and the sorption systems are estimated. It has been stated that water as a polar substance together with methanol, as well as carbon dioxide and methane give good estimates of coal structure and let us quantify the polar effect of surface groups present in hard coal. The polar effect is introduced in the model in the range of adsorption and expansion sub-processes. The presence of oxygen groups in the bulk of coal matter has no significant effect and can be neglected. A weak decreasing tendency of polar factors ratio for water and methanol is discovered.
Highlights
Hard coal is a very complex substance containing copolymer matter which is partially rigid and partially elastic
More precise estimation is reached by using a strong setting of the coal structure parameters for a bigger number of sorption system, and in each case the same parameters of coal geometry are constant with an exact fitting of sorption isotherm
The comparison of energetic and geometric parameters of sorption on the same coal sample for water, methanol and the other apolar substances simultaneously gives a better estimation of the structure and energy properties of the surface than the estimation of the individual sorption system
Summary
Hard coal is a very complex substance containing copolymer matter which is partially rigid and partially elastic This problem is further complicated by functional groups present on the surface (Hao et al 2013). Surface groups of coal have a small effect on the liquefaction, gasification, pyrolysis (Feng et al 2013; Lin et al 2014; Yu et al 2013) and wettability (Zhou et al 2015b) of coals They play a important role in the competitive adsorption of H2O, CH4 and CO2 molecules in coals (Gensterblum et al 2014). The idea of presenting the interactions of polar substances by the factor describing the excess forces compared to apolar ones led to the analysis of the statistical influence of functional groups on the adsorption of small molecule polar substances. An analysis of the entered parameters for the energy formula obtained through the simulation of isotherms using a model based on the measurement data is presented in this paper
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