Evolution And Kinetic Analysis Of Functional Groups During Pyrolysis Of Low Rank Coal

The oil-rich property of low rank coal in Northern Shaanxi is very outstanding.The gas and tar produced by pyrolysis are ideal materials to replace natural gas and oil,which can effectively alleviate China’s dependence on oil resources.The quality of tar is directly related to the evolution of functional groups during pyrolysis,and the kinetics reflects the reaction mechanism of functional group evolution.Therefore,this paper takes the low rank coal（HCG coal,ZJM coal,SJC coal）in Northern Shaanxi as raw materials,carries on the thermogravimetry analysis,In-situ FTIR analysis,TG-IR-MS analysis experiment,studies the main functional group change and the product formation mechanism.FWO method,Kissinger method,the general integration method and Mac Callum-Tanner method were used to analyze the kinetic mechanism.It provides theoretical guidance for improving the yield and quality of tar.The main conclusions are as follows:The activation energy was 158.59-240.47 k J/mol in the main stage of coal pyrolysis,and the reaction rate was controlled by chemical reaction.The content of oxygen functional group in coal was the most,and it had a positive correlation with the content of oxygen in coal.The contents of aromatic-C-H and-C=C in three kinds of coal were HCG,ZJM and SJC coal in order from large to small.The evolution activation energies of aliphatic groups,-C=O,-C-O,aromatic-C-H and-C=C were 65.03-84.64 k J/mol,106.59-116.48 k J/mol,107.99-126.46 k J/mol,131.78-213.00k J/mol and 107.99-126.46 k J/mol,respectively.The mechanism functions were all Avrami-Erofeev equation（n=2/3）.There were three stages in the evolution of-OH:in the first stage,-OH decreases,the activation energy was 38.31-46.37 k J/mol,and the mechanism function was Avrami-Erofeev equation（n=4）.In the second stage,the conversion of-C=O and-C-O resulted in the increase of-OH.In the third stage,the combination of-OH and hydrogen results in the rapid decrease of-OH,the activation energy was 295.31-561.11 k J/mol,and the mechanism function was Avrami-Erofeev equation（n=2/3）.The reaction mechanism was random nucleation and subsequent growth.The release of CO₂ consisted of three stages,of which the maximum rate was due to decomposition reaction in the temperature range of 300-580℃.CO began to release at400℃,the main release temperature range was 400-750℃,which came from the pyrolysis of aliphatic groups and oxygen-containing functional groups,the fracture of aromatic weak bonds,and the fracture of hydroxyl and oxygen-containing heterocycles.The main reason for the separation of H₂ from 300℃to 520℃was the cracking or aromatization of alkanes and the dehydrogenation of aromatic structures.The temperature range of CH₄ release was 290-740℃,the release temperature range of C₂-C₅ was 342-520℃,289-535℃,334-452℃,340-447℃,and the maximum release rate temperature of C₃-C₅ was about 400℃.In C₆,the release temperature of aliphatic C₆ was 332-490℃,and that of benzene was 342-715℃,benzene release was the largest.