“…24 . Electrochemical modification is better than just chemical treatment because it not only increase acidic groups, also reaction with mineral matters in coal and migration them 6 .Figure 4Dynamics of pH in anode and cathode areas during the electrochemical modification process.…”
Section: Discussionmentioning
confidence: 99%
“…The high degree of metamorphism and wildly development of micro-pore in anthracite lead to strong adsorption capacity and low desorption rate of methane, which seriously restrict the efficiency of methane extraction. Thus, researchers around the world have conducted numerous studies focused on the change of methane adsorption/desorption characteristic in coal, such as pressure relief of reservoirs 1 , and the application of heated hydro-fracture technology 2 , sound field effect 3 , electric field effect 4 , the action of electromagnetic field 5 and electrochemical treatment 6 optimizes methane adsorption/desorption performance in coal and helps to promote the methane extraction. The existing researches show that electrochemical treatment can significantly change the methane adsorption/desorption and seepage characteristics in coal 6–8 .…”
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.
“…24 . Electrochemical modification is better than just chemical treatment because it not only increase acidic groups, also reaction with mineral matters in coal and migration them 6 .Figure 4Dynamics of pH in anode and cathode areas during the electrochemical modification process.…”
Section: Discussionmentioning
confidence: 99%
“…The high degree of metamorphism and wildly development of micro-pore in anthracite lead to strong adsorption capacity and low desorption rate of methane, which seriously restrict the efficiency of methane extraction. Thus, researchers around the world have conducted numerous studies focused on the change of methane adsorption/desorption characteristic in coal, such as pressure relief of reservoirs 1 , and the application of heated hydro-fracture technology 2 , sound field effect 3 , electric field effect 4 , the action of electromagnetic field 5 and electrochemical treatment 6 optimizes methane adsorption/desorption performance in coal and helps to promote the methane extraction. The existing researches show that electrochemical treatment can significantly change the methane adsorption/desorption and seepage characteristics in coal 6–8 .…”
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.
“… 7 In the electrochemical modification method, the acidic and alkaline treatments on coal samples were conducted in the anode and cathode environment, respectively, in which the electrokinetic characteristics of coal were changed. 8 , 9 …”
The
application of electrochemical modification for accelerating
methane extraction in lean coal seams is limited due to the lack of
experimental and theoretical research studies. Therefore, electrochemical
modification with different electric potential gradient values was
selected to modify lean coals in this study; meanwhile, the amount
of methane adsorption and the methane desorption ratio were tested
and analyzed. The results showed that the maximum amount of methane
adsorption in coal samples decreased after electrochemical modification
and the decrease in methane adsorption increased with an increase
in electric potential gradient. The methane desorption ratio increased
from 83.20% up to 87.84 and 86.90% at the anode and cathode zone,
respectively, after electrochemical modification using a 4 V/cm electric
potential gradient. A higher electric potential gradient performs
better in the electrochemical modification. The mechanism of electrochemical
modification using different electric potential gradients was revealed
based on the measurements of Fourier transform infrared spectroscopy
and liquid nitrogen adsorption. It is due to an increase in acid groups
in coal molecular structure and the change of the specific surface
area of coal after modification. The results obtained from this work
contribute to the methane extraction via the electrochemical method
in lean coal seams.
“…erefore, an exploratory study on intensifying methane desorption and seepage from coal modified by electrochemical treatment was proposed [12]. Guo et al [13] found that the average desorption rate of methane from 130 to 140 mm lump coal after electrochemical treatment increased by 1.68 times reaching desorption equilibrium. In general, the electrochemical method is applicable to soft coal seam [14].…”
The electrochemical method can strengthen gas desorption and seepage from coal. The study on change of the pore-fracture structure of coal after electrochemical modification can help to reveal the mechanism. Anthracite was modified by the electrochemical method using our own self-developed experiment apparatus. The pore-fracture structure of modified samples was measured by micro-CT. Combined with the Matlab software, its characteristics such as pore number, porosity, and average pore diameter were analyzed. The results show that (1) the number of fractures in modified coal samples increases. The shape of new fractures in samples in the anodic and cathodic zones was irregular voids and striola, respectively. The effect of electrochemical treatment on the section of samples close to the electrode is relatively obvious. (2) With increasing pore size, the number of pores in samples changes according to negative exponential rules. After electrochemical modification, the porosity of modified samples in the anodic zone increases from 11.88% to 31.65%, and the porosity of modified samples in the cathodic zone increases from 12.13% to 36.71%. (3) The main reason for the increase in the number of pores of coal samples in the anodic and cathodic zones is the treatment of electrolytic dissolution of minerals and electrophoretic migration of charged particles, respectively.
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