Effect of alkyl glycoside on coal structure modification and methane desorption characteristics

Coal seam water injection is one of the effective methods to slow down the gas desorption rate and reduce the over-limit gas concentration in the working face. The addition of surfactants can change the chemical structure of coal and enhance the gas desorption inhibition effect. Coal samples from typical high gassy coal mines are used,and the alkyl glycoside surfactant with different mass fractions are prepared. The effects of alkyl glycoside surfactant on functional groups,free radicals and Zeta potential before and after coal modification were studied by means of infrared spectrometer(IFTR),EPR spectrometer (EPR)and microelectrophoresis apparatus. The impact of alkyl glycoside surfactants on the contact angle of coal was analyzed by using the contact angle measurement. The gas desorption law of coal samples under the conditions of drying,water injection and the injection of alkyl glycoside surfactant was studied by using the self developed dynamic experimental system of post solution inhibition of gas desorption. The experimental results show that:the total content of oxygen containing functional groups in coal shows an exponential function relationship with the mass fraction of APG0810. The Zeta potential of coal sample is a negatively exponential function with the mass fraction of APG0810. The concentration of free radical (Ng) increases with the mass fraction of APG0810 first and then flattens out,and the concentration of unpaired electrons increases 4.18 times. The relationship between coal contact angle and APG0810 mass fraction is negative exponential function,and the contact angle decreases from 79.15° to 25.63°,decreasing by 67.62%. The maximum gas desorption capacity and desorption rate of APG0810 showed a negative exponential relationship with the mass fraction of APG0810. The maximum gas desorption capacity and the maximum desorption rate decreased by 31.59% and 78.23% respectively. The coal contact angle,maximum gas desorption capacity and gas desorption rate are negatively correlated with the total area of oxygen containing functional groups and free radical concentration,and positively correlated with Zeta potential. The physical chemical reaction between APG0810 and coal contact increases the oxygen containing functional groups and hydrogen bonds on the coal surface,and the negative electrical properties of the coal surface,and the concentration of free radicals,decreases the contact angle,and improves the wetting characteristics of the coal.Thus,it slows down the rate of gas desorption,with a view to providing some basis for the prevention of disaster accidents such as gas overrun or coal and gas protrusion.