Structural Characterization Of Coals With Different Rank And Molecular Simulation Of Interaction Between Coal And CH₄/CO₂/H₂O

In order to reduce the environmental pollution and improve coal bed methane?CBM?production rates,the improvement of CO₂-ECBM technology and the geological disposal of CO₂ in the deep unminerable seam have become a significant research subject.In order to implement the CO₂-ECBM process,the structural characteristics of coal is predominant to deeply understanding the interaction micromechanism between coal and CH₄/CO₂/H₂O to solve some fundamental subjects,such as the improvement of coal reservoir structure,the increasement of CH₄ recovery and the evaluation of safety for C02 in the coal reservoir.The paper aims at understanding molecular mechanism on the interaction between the macromolecular structure of coal and CH₄/CO₂/H₂O,and analysing the structural characteristics of WMC-YM(R^o_max=0.457%),YZ-YM(R^o_max=0.620%),LL4-YM(R^o_max=1.287%),LL3-YM(R^o_max=1.294%),CZ-YM(R^o_max= 3.210%)and SH-YM?Rmax0=3.355%?,based on which,the molecular mechanism on the interaction between CH₄/CO₂/H₂O and Yanzhou gas coal and Chengzhuang anthracite by molecular simulation method is mainly researched in this paper.The conclusions are as follows:1.Based on true relative density,XRD spectrum,proximate and ultimate analysis,13C-NMR spectrum,FTIR spectrum and XPS spectrum,the structural characteristics of WMC-YM,YZ-YM,LL4-YM,LL3-YM,CZ-YM and SH-YM are represented in the three dimensions.Furthermore,the structural characteristics of different rank coals are known and can provide comprehensive information for the construction of macromolecular structure model.2.According to the structural characteristics in the three dimensions,the construction method and the three-dimensional criterion of the macromolecular structure of coal are established.Then the structure models of YZ-YM and CZ-YM are constructed,respectively.The main composition of aromatic compound in YZ-YM is benzene with less naphthaline and the anthracene.Aliphatic structure exists in the form of side chain and cycloalkanes.Oxygen atoms mainly exist in the form of carboxyl,carbonyl and hydroxy while nitrogen atoms mainly exist in the form of pyridine and pyrrole and sulphur atoms mainly exist in the form of thiophene.The numbers of rings of aromatic compound in CZ-YM were 2/3/4 ring-based and 5 rings is the biggest ring.Oxygen atoms mainly exist in the form of carboxyl,carbonyl and hydroxy and nitrogen atoms mainly exist in the form of pyrrole.However,sulphur atoms is not appear in the model because its concentration was lowest.We found that the short-range ordering in low-rank coal structure was mainly attributed to the oriented arrangement of intramolecular or little intermolecular aromatic layers while the oriented arrangement of intermolecular aromatic layers is largely contributed to the short-range ordering in high-rank coal structure.According to the simulation results,densities of YZ-YM and CZ-YM are 1.20g/cm³,1.40g/cm³,respectively.And the values are smaller than experiment.3.Monte Carlo simulation method is used to investigate isothermal adsorption characteristics of CH₄/CO₂/H₂O.?1?The results show that the one-component adsorption quantities is CH₄<CO₂<H₂O in YZ-YM and CZ-YM and the adsorption quantities are well suit to the Langmuir model for the individual sorption of the coal molecules to CH₄/CO₂/H₂O.Furthermore,the higher temperature is,the lower the adsorption quantity is.?2?For the muti-component adsorption,the situation is the same to one-component adsorption in YZ-YM.But for CZ-YM,the adsorption of H₂O is lower than CO₂ because it breaks the ability to make hydrogen bond,.4.Molecular Dynamics was performed to study the energy changes before and after adsorption.?1?The results indicate that the different degrees of variation are occurred for valence energy when lots of micromolecules enter into the model,which indicates the strong interaction is occurred between CH₄/CO₂/H₂O and coal molecules and the stable configurations are formed.The changes of adsorption configurations may be the inner mechanism of adsorption giving rise to swelling.?2?The non-valence energy variation before and after adsorption show that the adsorption mechanism of the coal to CH₄/CO₂/H₂O is different.CH₄ represents the obvious physical absorption while CO₂ is given priority to the physical adsorption companies with weak chemical adsorption.On the contrary,the absorption behavior of the coal to H₂O is physical and chemical.Compared to the YZ-YM,the ?-? electrostatic energy arising from plenty of aromatic structure play a large role in the adsorption of the coal to micromolecules in the CZ-YM.5.?1?In YZ-YM,the adsorption of CH₄ is suit to the space which the aromatic functional groups with high polycondensation enclose and the adsorption of CO₂ is suit to the space which aromatic functional groups with plenty of side chains and oxygen-containing functional groups enclose.However,the environment which can easily form plenty of hydrogen bond with H₂O molecules is suitable for adsorption of H₂O.Besides,the type of functional groups has an important effect on the adsorption of micromolecules.?2?Compared to YZ-YM,the above-mentioned functional groups have more important effect on the adsorption of three components because of extensive existence of micropore in CZ-YM.Micropore theory is the main adsorption mechanism of CZ-YM.