| According to the structure and trend of primary energy consumption in China,lignite,as a kind of low rank coal,has been playing an increasingly important role in the energy supplying process.And in order to improve the cleanness and efficiency of the utilization of lignite resource,it is necessary to have a deep understanding of the macromolecular structure characteristics of the lignite.In this paper,a series of testing methods including industrial and elemental analysis,13 C NMR,XRD,Raman,XPS and FTIR were used to obtain the necessary parameters for the construction of molecular model,and the molecular structure models of holinhe(HLH)raw coal,Microwave modified HLH coal and Ultrasonic modified HLH coal were constructed respectively.The effects of Microwave modification and Ultrasonic modification technology on the molecular structure of HLH lignite were compared.Finally,the model was optimized and quantum chemistry calculation was carried out by using the Material Studio 8.0 software.The conclusion is as follows:(1)The existent form of N and O were determined by XPS detection,in which N mainly exist in the form of N-5,N-6 and N-Q in different proportions,and O mainly exist in the form of C-O and COO-structure.Eleven kinds of basic structural parameters of HLH lignite and XBP of aromatic bridge carbon to surrounding carbon ratio before and after upgrading were confirmed through 13 C NMR,among which the XBP of HLH raw coal,coal sample after microwave upgrading and coal sample after ultrasonic upgrading were 0.26,0.29 and 0.28,respectively.The combination of Raman spectrum and XRD spectrum showed that the degree of arrangement and ordering of aromatic ring increased,and the content of fat chain and side chain decreased after Microwave and Ultrasonic modification.(2)The average formula of HLH raw coal is C167N3O27H149,where the aromatic node part includes 5 benzene rings,6 naphthalene rings,2 pyrrole rings and 1 pyridine ring;In addition,the average molecular formula of microwave modified HLH coal sample is C148H129N3O20,where the aromatic part includes 3 benzene rings,4 naphthalene rings,1 anthracene ring,1 pyridine ring and 2 pyrrole rings;Furthermore,the average molecular formula of ultrasonic modified HLH coal sample is C155H131O23N23,and the aromatic part includes 3 benzene rings,5 naphthalene rings,1 anthracene ring,1 pyridine ring and 2 pyrrole rings.Modification of Microwave and Ultrasonic provided the energy for the combination of aromatic rings,which results in the increasing number of aromatic rings in the structure and higher stability of the structure.Meanwhile,the content of aliphatic chain and side chain in the aliphatic structure of lignite powder decreased after the modification.(3)According to the molecular dynamics simulation method,the minimum energy configuration is obtained,which is the stable configuration of lignite after annealing.The aromatic lamellae of the modified model have obvious bending and twisting,and the angle of C-C bond between the aromatic lamellae have increased,where the position of tertiary carbon and quaternary carbon is more twisted,resulting in the optimized structure more stereoscopic.(4)The bond length and bond order of three kind of configuration are calculated by quantum mechanics.It can be seen that the stability of the C-C chemical bond between aliphatic hydrocarbons is the lowest.In addition,it is difficult to destroy the benzene ring in the process of upgrading due to its stability;Furthermore,the existence of benzene ring may reduce the reactivity of the carbon oxygen(C-O)bond connected with it,resulting in the fracture of the aliphatic chain and the side chain in the process of upgrading,which is consistent with the experimental results.Therefore,quantum mechanical calculation can be used to provide a new breakthrough point for the study of lignite quality improvement. |
PDF Full Text Request