Quantum Chemistry Studies On The Interactions Of CS₂/NMP With Hydrogen Bonds Of Coal In The Process Of Coal Extraction

Coal is an important and unregenerated fossil resource. In order to develope more cleaning coal chemical technology and take more advantage of coal, it is important to study the structure and property of coal. Meanwhile, solvent extraction is an effective method to investigate the composition and structure of coal. By extraction, solvent can damage the weak interactions (mainly hydrogen bonds) of coal macromolecule. As a result, small molecules are obtained and used to study coal macromolecular structure. At present, CS2/NMP (1:1, v/v) is an excellent mixed solvent for extraction of coal at room temperature.The quantum chemistry calculation method has been gradually used in coal and become an effective tool for studying the structure and reactivity of coal. Based on the specific attributes of coal, the corresponding models are constructed, of which the theoretical calculation can reasonably illustrate experimental facts and provide a good guidance for further experiment.Therefore, on the basis of previous experimental facts and theoretical calculations, by the premise of keeping the main chemical properties of objects, this paper simplifies the models of trace amounts of NMP, pure NMP solvent and CS2/NMP(1:1, v/v) mixed solvent in the real process of coal extraction to S-NMP, D-NMP and IM, which can be easily operated in quantum chemistry calculation. Then, the interactions of extraction solvents with the hydrogen bonds of coal macromolecule involving in the OH—N, OH—ether O and Cyclic OH, are investigated. The research results are expected to solve the following issues:how does the solvent weaken hydrogen bonds, as well as what types of hydrogen bonds does the solvent damage during the extraction. Further, the microscopic explanations for the excellent extraction yield of this mixed solvent can be obtained.The main conclusions obtained in this paper are listed as follows:1) CS2/NMP(1:1, v/v) mixed solvent can weaken two types of hydrogen bonds of OH—N and OH—ether O in coal macromoleculer. In this way, this mixed solvent achieves the excellent extraction yield.2) By comparing the interactions of trace amounts of NMP, pure NMP solvent with two types of hydrogen bonds of OH—N and OH—ether O, respectively, we can find that CS2 added into the pure NMP solvent plays the role of releasing the original capacity of NMP, which can damage above two types of hydrogen bonds in coal.3) Because of the existence of the hydrogen bond of Cyclic OH, which is a very stable structure, CS2/NMP(1:1, v/v) mixed solvent can damage or even weaken the hydrogen bond of Cyclic OH. This may be one of the microscopic reasons that why the mixed solvent can not achieve complete performance in the process of coal extraction.