Experimental and mechanistic research on methane adsorption in anthracite modified by electrochemical treatment using selected electrode materials

Abstract

The strong adsorption capacity of methane in anthracite can seriously affect the methane extraction. Electrochemical treatment is an effective way to weaken the capacity of methane adsorption in coal. Iron, copper, aluminum and graphite as four kinds of electrode materials were selected to modify anthracite by electrochemical treatment. The adsorption of methane in anthracite, before and after modification, was tested under different adsorption pressure. Based on the changes of pore characteristics and chemical groups of anthracite, the modification process of different electrode materials was analyzed. The results showed that after electrochemical modification, the adsorption of methane decreased, when the graphite electrode was used, the methane adsorption decreases the most, followed by copper and iron electrodes, and the aluminum electrode decreased the least. After electrochemical modification using aluminum, iron, copper and graphite electrodes, the Langmuir constant a reduced by 5.22%, 8.48%, 9.24% and 11.33%, respectively, and the degree of reduction is graphite > copper > iron > aluminum. After electrochemical modification using the graphite electrode, the Langmuir constant b was reduced by 23.52%. On the contrary, after electrochemical modification using the mental electrodes, the Langmuir constant b was increased by about 5%. The surface free energy of anthracite decreased with the adsorption of CH4, the higher the pressure, the more the free energy decreased, and the reduction of surface energy decreased after electrochemical modification. The difference of the electrode reactions was the main reason for the electrochemical results, the Mn+ ions generated in the anode changed the properties of the clay mineral in the coal, and the H+ ions corroded the calcite minerals in the coal. The results obtained from this work indicate that the selection of electrode materials is crucial for the electrochemical modification, and graphite electrode is optimum for anthracite when accelerating methane extraction by electrochemical method.

Effect of Electric Potential Gradient on Methane Adsorption and Desorption Behaviors in Lean Coal by Electrochemical Modification: Implications for Coalbed Methane Development of Dongqu Mining, China

“…The calculation results of the Δγ of lean coal samples are shown in Figure 2 , which shows that the Δγ increased after methane is adsorbed, while the Δγ decreased after modification, and the decrease in Δγ increased with an increase in potential gradient up to 4 V/cm. Besides, the coal samples from the anode zone ( Figure 2 a) decreased larger than coal samples from the cathode zone ( Figure 2 b) at the same electric potential gradient, and the same results were also found by ref ( 23 ). The pressure and temperature of methane adsorption tests were the same; so, the reduction of coal surface energy can only be caused by electrochemical modification.…”

Experimental and mechanistic research on modifying the mechanic properties of the high water backfill material by electrochemical treatment

“…It can be observed that the electrical resistivityof the samples first decreased rapidly when the measurement frequency increased from 50 Hz to 5 kHz, then decreased slowly, and finally tended to be stable when the measurement frequency was increased from 5 to 200 kHz. This result is consistent with the research on zinccontaminated soil solidified by cement 30 . The electrical resistivity measurements indicate that the frequency used to measure the electrical resistivity of HWBMs should exceed 5 kHz.…”

“…In recent years, the electrochemical method has been successfully applied to many fields of geotechnical engineering, such as the electrochemical consolidation of weak rock [10][11][12] , the electrochemical desalination of rock or soil [14][15][16][17][18][19][20] , the drainage and consolidation of soil by electro-osmosis [21][22][23][24][25][26][27] , and the acceleration of methane desorption in lump anthracite by the electrochemical treatment [28][29][30] . Meanwhile, the electrochemical treatment was used to accelerate the hydration reaction rate to enhance the strength and deformation characteristics of fly-ash-cemented filling materials 31 .…”

Response of Molecular Structures and Methane Adsorption Behaviors in Coals Subjected to Cyclical Microwave Exposure

“…Samples with sizes of 60−80 mesh were used, and the operations met the requirements of the tests. 23 A Nicolet iS5 FTIR instrument produced by Thermo Fisher was used to carry out the FTIR tests. The detection wavenumber range of the device was 400−4000 cm −1 with a solution of 4 cm −1 .…”

“…17−19 The other is external field stimulation, including ultrasonic, 20 electric field, 21,22 and electrochemical field stimulation. 23,24 These approaches have achieved some positive results; however, limitations such as complex operations, construction costs, and environmental damage still exist.…”