Experimental And Mechanism Study On The Influence Of Electrochemical Action On The Gas Adsorption And Desorption Characteristics Of Lean Coal

China is rich in gas resources of lean coal and and has great development potential,but the production of experimental mining is not ideal.The existing research results show that electrochemical modification can reduce the adsorption capacity of coal gas and improve the gas desorption rate,but it is rare to take lean coal as the research object.In view of this,the electrochemical modification experiment on the lean coal samples collected from No.9 coal seam of Dongqu mine of Shanxi Coking Coal Group Co.,Ltd.was carried out,the influence of potential gradient and electrolyte acid-base on the electrochemical change of the gas adsorption and desorption characteristics of lean coal was analyzed,and the influence mechanism from the perspective of pore structure and surface characteristics was explained.The main work and conclusions are as follows:(1)Under the condition of Na₂SO₄ electrolyte,the electrochemical modification experiments of lean coal samples were carried out with the potential gradients of 1 V/cm,2 V/cm and 4 V/cm,respectively,and the gas adsorption and desorption characteristics of the samples before and after modification were tested.The results show that the saturated adsorption capacity of natural lean coal samples is 30.03 ml/g,Langmuir pressure is 0.88 MPa,and the final gas desorption rate is 83.20%.The greater the potential gradient during modification,the lower the ability of the lean coal samples to adsorb gas after modification,and the higher the final gas desorption rate.When the potential gradient is 4 V/cm,the saturated adsorption capacity of modified coal samples in anode area and cathode area decreases to 26.67ml/g and 27.25ml/g respectively,Langmuir pressure rises to 1.05 MPa and 1.03 MPa respectively,and the final gas desorption rate rises to 87.84%and 86.90%respectively.The mechanism of the influence of potential gradient on the electrochemical change of the gas adsorption and desorption characteristics of lean coal is as follows:under the condition of Na₂SO₄ electrolyte,the greater the potential gradient during modification,the greater the amount of charge transfer during the modification process,resulting in the stronger"pore expansion"effect of electrochemical modification on the lean coal samples,the greater the content of oxygen-containing functional groups in the lean coal samples after modification,the fewer aliphatic hydrocarbon branches,the lower the surface free energy,and the better effect of inhibiting gas adsorption and promoting gas desorption.(2)Under the potential gradient of 4 V/cm,the electrochemical modification experiments of lean coal samples were carried out with H₂SO₄,Na₂SO₄ and Na OH electrolyte respectively,and the gas adsorption and desorption characteristics of the modified lean coal samples were tested.The results show that the lean coal samples electrochemically modified with H₂SO₄electrolyte have the lowest ability to adsorb gas,and the final desorption rate of gas is the highest,the saturated adsorption capacity of the modified coal samples in anode area and cathode area is 23.70 ml/g and 24.33 ml/g respectively,Langmuir pressure is 1.15 MPa and 1.12 MPa respectively,and the final desorption rate of gas is 90.10%and 89.28%respectively;the trend of modification with Na₂SO₄ electrolyte is basically the same as that with H₂SO₄electrolyte,but the effect is second;the lean coal samples modified with Na OH electrolyte have stronger ability to adsorb gas,and the final desorption rate of gas decreases,the saturated adsorption capacity of modified coal in anode area and cathode area is 31.85 ml/g and 32.79 ml/g respectively,Langmuir pressure is 0.81 MPa and 0.80 MPa respectively,and the final desorption rate of gas is82.12%and 81.71%respectively.The mechanism of the influence of the acid-base property of electrolyte on the electrochemical change of the gas adsorption and desorption characteristics of lean coal is as follows:under the potential gradient of 4 V/cm,the charge transfer during modification with H₂SO₄electrolyte is the largest,which results in the most obvious"pore expanding"effect on the lean coal samples,the most content of oxygen-containing functional groups in modified lean coal samples,the least aliphatic hydrocarbon branched chains,the least surface free energy,and the effect of inhibiting gas adsorption and promoting gas desorption is also the best;the trend of modification with Na₂SO₄ electrolyte is basically the same as that with H₂SO₄electrolyte,but the effect is second;after electrochemical modification of Na OH electrolyte,the specific surface area of lean coal samples increases,the average pore diameter decreases,the content of oxygen-containing functional group decreases,the number of aliphatic hydrocarbon branches increases,the surface free energy increases,and the adsorption capacity of gas increases,which is not conducive to gas desorption.(3)Under the condition of the same potential gradient and the same electrolyte,compared with the modified coal samples in cathode area,the modified coal samples in anode area has smaller specific surface area,larger average pore diameter,more oxygen-containing functional group content,less aliphatic hydrocarbon branch chain and smaller surface free energy,so the adsorption point of methane molecule is less,the binding capacity of methane molecule is weaker,and the gas is harder to be adsorbed and easier to desorb.