Study On Mechanism,Kinetics Of Coal Pyrolysis Based On Functional Groups And Its Impact Factors

As one of the main energy in China,large quantity of pollutants are emitted during coal comsumption,which results in a series of enviromental problems.Clean coal is an important subject in the researches of coal utilization.Because of complex composition and molecular structure,it is necessary for good controlling of the pollutants emitted during the use of coal to focus on studies on the molecular structure and mechanism of coal pyrolysis,which bennifit the clean utilization of coal resources and have important theoretical and environmental significance.Lignite,gas coal,1/3 coking coal and coking coal were sampled to be determined mainly by in-situ FTIR and Thermogravity Analysis?TGA?.The coal pyrolysis was carried out in the fixed heating rate under N₂ flow in the temperature range of 20?500?.Microwave assisted extraction of gas coal sample by pyridine was also conducted.Mechanism and kinetics of coal pyrolysis was deeply discusssed by application of deconvolution technique conjuncted with the theories in coal chemistry,environmental science and thermodynamics.The main influence factors on the coal pyrolysis were investigated based on evolution of functional groups during pyrolysis.The main conclusions include:?1?the evolution of functional groups was divided into several stages according to the mechanism of their pyrolysis;the aliphatic groups decomposed mainly above 400?;the aromatic C-H increase with rising temperature caused by split of the aliphatic substituent groups;aromatic C=C,C-O and OH decreases with rising temperature;C=O begins to decompose obviously from 370?and ester increased in the lower temperature in the lower rank of coal;pyrolysis of low rank coal undergo crack of hydrogen bond and oxygen-containing functional groups,while that of high rank coal experience crack of covalent bond and small amount of oxygen-containing functional groups;?2?the activation energy of pyrolysis of aliphatic groups,C-O,C=O and OH in coal range from 32.9?219.4 kJ·mol^-1,16.0?45.7kJ·mol^-1,12.3-44.7 kJ·mol^-1 and 8.6 to 258.3 kJ·mol^-1,respectively;the activation energy in the higher temperature stage is higher than that in the lower temperature stage;preliminary kenitics model of functional groups during coal pyrolysis was established based on the activation energy and kinetics equations fitting for the various functional groups;?3?the effect of coal rank on the pyrolysis of coal is significant;C=O,C-O and aromatic functional groups is sensitive to coal rank reflected by evolution of functional groups and the activation energy during pyrolysis,while aliphatic groups and OH is not;?4?the order of sensitivity to pyridine extraction is C=O>aromatic C-H,aromatic C=C and OH>aliphatic groups and C-O;in addition,the small molecules extractable is main reacting matter in the free radical reactions,which further revealed the effect of pyridine extraction on the coal pyrolysis;?5?the interaction between coal molecules and interaction between coal molecules and solvent changed after C=O is partly reduced by KBH₄,resulting in the various extraction ratio and different extract compositions,which reflects some information of coal structure.