| The study of trace elements in coal was an important subject for coal science research. Since the occurrences of trace elements in coal were complicated and various, the research literatures about trace elements in coal were more and its contents were also widespread, but were lack of understanding the occurrence mechanism of those trace elements in coal molecular structure from microscopic perspective, especially why trace elements were enriched in low rank coal, how to explain the phenomenon and what relationship between these metal ions and coal molecular. This paper mainly found a new understanding mode and research methods to study the occurrence of the trace elements in coal, which was based on constructing the coal molecular structure model and stimulating those structures from microscopic perspective.The samples what the paper adept were Yimin15#coal and their vitrinite reflectance was0.268%, the humic acid was extracted.The paper constructed the structure models of the raw coal(M) and humic acid(HA) molecular and adopted Grand Canonical Mote Carlo(GCMC) to simulate those structures adsorption alkali metal ions K+and alkaline earth metal ions Mg2+under25℃-200℃temperature conditions, Main conclusion were drawn as follows: 1. By twelve structural parameters analysis, Yimin15#coal(M) and humic acid (HA) molecular structure model were constructed using the ACD/ChemSketech and ACD/CNMR predictor software. Then using molecular dynamics(MD) and molecular mechanics(MM) methods to stimulate its geometry optimization, the structure transfer from the original plane configuration to the three-dimensional spatial configuration and formed a certain angle aromatic layer, Van der Waal affect the potential energy of the system in the processes. The density of M is1.15g/cm3, HA is1.13g/cm3by the stimulation of the density and the ideal lattic configuration were obtained under those density conditions that provided the prerequisite and foundation in processes of the stimulation of adsorption of metal ions in next work. Through the calculation of the bond length of M and HA structure model, the results showed that the bond length distribution characteristics are that the longest bond length are alicyclic and methyl side chain, followed by the aromatic ring, carbon oxygen bond and carbon-oxygen double bonds, the shortest is nitrogen bond lengths.2. The adsorption stimulation of HA and M adsorption the alkali metal K+and the alkali metal Mg2+were used Grand Canonical Mote Carlo(GCMC) under different temperature conditions, the changes of system energy, the saturated adsorption amount and the density of the mixture were obtained, the main conclusion were drawn as follows: (1) The adsorption behavior of HA and M adsorption K’and Mg2+can be divided into three stage, the first stage shows that system energy is linear decreased, system energy is ups and downs in second stage, system energy appear to rise in third stage.(2)The adsorption behavior of HA and M adsorption K+showed the charge of the oxygen atoms and K+was decreased, then the carbon atomic charge was increased or decreased, these can showed that the charge happened transferring among K+, oxygen and carbon atoms, carbon atomic charge volume changes was slightly lower than oxygen atomic charge volume changes, those illustrate that the adsorption process is mainly linked with oxygen-containing functional groups.(3) Because of the different of the structural system or the occurrence mechanism of different metal ions, the adsorption behavior of HA and M adsorption K+and Mg2+, the temperature have a different affection. the system energy does not have apparent changed with the temperature changing when the K+concentration is low in the processes of HA and M adsorption K+, illustrates that the temperature does not affect the adsorption amount of K+, but the system energy can change through changing the temperature when K+reaches a certain concentration, namely the temperature influences on the adsorption capacity of K+. while in the process of HA and M adsorption Mg2+, the average energy decreased with the temperature increasing when the Mg2+amount was less, but the adsorption energy had no necessarily changing rule, when the adsorption capacity of Mg2+gradually increased and increase the system temperature, then the system average energy and adsorption energy can appear obvious fluctuation and had no certain rules.(4) The phenomenon can be found that metal ions can move from the system boundary bias into the internal system with the temperature increasing in the process of the stimulation when the amounts of adsorption K+and Mg2+are the same time, when the temperature is the same time, K+and Mg2+will move from system boundary bias into the internal system with the amounts of K+and Mg2+increasing, its spatial distribution have three forms,①Hanging within the internal system space in system,②Back and forth concussion around the benzene ring or fat groups,③Back and forth concussion around the oxygen-containing functional groups.3.The simulation of kinetic parameters of HA and M adsorption K+and Mg2+calculation were used molecular dynamics method, the results showed that HA and M adsorption K+and Mg2+were mainly related to electrostatic force. Through a combination of the analysis of Monte Carlo and Molecular Dynamic methods, the results showed, the system energy of HA and M adsorption Mg2+will lower than the system energy of HA and M adsorption K+, and the system is more stable, which is can explain the relative performance of the system adsorption K+is weak than adsorption Mg2+, but indicating that the catalytic performance of K+has a higher than Mg2+, making the system energy to be able to remain high, the catalytic mechanism will be subject to further investigate. Through the radial distribution function of the oxygen atom and K+as well as Mg2+, first coordination number reduces first then increases with the increase of the numbers of adsorption metal irons, when the number reached to a certain amount, first coordination number will increase and due to the repulsive interaction in metal ions. |
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