Research On The Structure Of Mengdong Lignite And Its Molecular Simulation

Coal is the main energy of China,at present,high-quality coal resources are gradually depleted.China is relatively abundant of lignite resources,but because of high moisture,inflammable,low calorific value etc,the defects have brought great difficulties to its industrial applications.To clean and efficient utilization of lignite’s resources,much attention has been attracted on the characteristics of lignite’s organic matters.So this paper researched on domestic Mongdong lignite,by solvent extraction,coal quality analysis and FTIR analysis of coal and extraction residual coal,as well as GC/MS analysis of the extract,chemical composition and distribution of lignite’s small moleculars were studied;while 13C-NMR measurement techniques were used to analyze macromolecular structure of lignite,then macromolecular structural model of lignite were constructed.Finally,molecular simulation techniques were applied to explore the relationship between the structure and reactivity of lignite,providing a reference for the pyrolysis of lignite’s utilization.The main conclusions are as followed:(1)The extract mainly consists of heteroatom-containing compounds and aliphatic hydrocarbons,besides,there are small amounts of aromatic hydrocarbons.Oxygen-containing compounds are mainly composed of phenols and alcohols,ketones and acids;nitrogen emeries in the extract as amine,amide forms;only one mercaptan is detected.Coal macromolecular skeleton structure has not been fundamentally changed during the process of extraction,carbon content increases,while hydrogen and oxygen content reduce in the extracted residue coal;aromatic carbon rate increases;CH2/CH3 increases,aliphatic chain becomes longer and branched chain shorter.(2)The aromatic structural units of lignite’s macromolecular are benzene and naphthalene,the numbers are both two;oxygen atoms exist in the forms of hydroxyl groups,ether bonds,carbonyl groups,carboxyl groups;the nitrogen atoms exist in the forms of the pyridine and the pyrrole respectively;sulfur atom exists in the forms of sulfide.On this basis,the molecular structural model of lignite was constructed and Materials studio software was applied to amend the model;finally,lignite structural model in good agreement with the experimental 13C-NMR spectrum was obtained.(3)Molecular simulations of structural model indicate that the van der Waals energy plays a major role in stabilizing the macromolecular structure of coal;aromatic layers are in quasi-parallel arrangement;calculated infrared spectrum and experimental spectrum are in good agreement;alkyl ether bond,C-C bond linked with oxygen and carbonyl carbon are highly active,which break easily in the pyrolysis process.In MD structure model,there are more negative charges in the N,O and edge methyl C atoms,which are more prone to oxidation;aromatic ring plays a stabilizing role in lignite’s structure,at the same time,the aromatic ring itself is also ver y stable,which hardly occurs pyrolysis reaction.(4)The molecular simulations of structural model explain the generation phenomenon of CO2 during pyrolysis,CO2 is mainly generated by decomposition of carboxyl groups of fatty acids and aromatic acids,a structural model of aromatic acid is much more stable than fatty acid in structural model,resulting in CO2 generating curve been divided into two sections.