Ultrasonic Extraction And Exothermic Characteristics Of Active Groups During Coal Spontaneous Combustion Process

According to compound theory of coal and oxygen,coal spontaneous combustion is the result of accumulated heat released during reactions of oxygen and combination small molecules of coal.It is fact that some functional groups of coal can be extracted by some specific organic solvents.Effects of functional groups on oxidation characteristics of coal spontaneous combustion are comprehensively studied in this thesis by comparatively analyzing differences between raw coal and coal samples subjected by organic solvents.In this thesis,seven organic solvents were selected on the basis of the organic chemistry theory.Coal samples were ultrasonic extracted by seven single organic solvents and four mixed organic solvents,respectively.Extraction rates of different organic solvents were analyzed.Responses of functional groups in coal samples to the organic solvents were studied as well.Experimental results indicated that the highest extraction rates,which were 65.9%,62.87%and 57.38%,were obtained by using acetone+ethylenediamine,DMAC and NMP,.FTIR spectrogram illustrates that,generally,-CH3?C-O and-OH were efficiently extracted by selected solvents.Nevertheless,acetone?cyclohexanone?DMAC and ethylenediamine can effectively extract-CH3 and C-O in coal,while-OH group in coal were more sensitive to DMAC?NMP and ethylenediamine.Obviously,concentrations of free radicals for coal samples extracted by acetone+ethylenediamine,DMAC,NMP,CS2+DMAC,CS2+NNMP,and ethylenediamine were lower than raw coal and other coal samples subjected to ultrasonic experiments.The oxidation characteristics of five representative coal samples and raw coal sample were studied by the TG/DSC-FTIR technique.It was found that-OH,C-O bond and-CH3 were the key active functional groups during the coal oxidation process.Further,-OH was believed to be the most important functional group of coal oxidation.By comparing the oxidation characteristics of extracted coal and raw coal,it was found that decreased C-O bond,-CH3 and-OH in coal samples led to a decrease in the mass of extracted coal in the stage of oxygen absorption.Compared to C-O bond and-CH3,decrement of coal mass were higher at the stage of oxygen absorption when-OH was decreased.Also,the maximum combustion reaction rate,the gas release amount,maximum mass temperature,net heat release amount,and combustion characteristics index of these extracted coals all decreased as the decrease of the active functional groups during the coal oxidation process.In general,effectiveness of these active groups on these parameters from high to low were in the order of-OH,C-O bond,and the-CH3.