Abstract
Coalbed methane (CBM) primarily exists in the adsorbed state within
coalbeds. Understanding adsorption/desorption of coal to CH4 is highly important for estimating CBM reserves, predicting productivity and enhancing CBM extraction. In this work, the properties of coal, with the o,m=0.50%-2.54%, adsorb/desorb CH4 were quantitatively evaluated. Moreover, the variation characteristics were analyzed utilizing the theory of isosteric heat of adsorption, adsorption potential and surface free energy. The results show that the D-A and Weibull function have better fitting accuracy, indicating there are multilayer adsorption or micropore filling, while considering the physical significance of the formula parameters, the Langmuir and the desorption equation are more practical, and as the Ro,m increasing, the VL of samples to CH4 present a “U-shape” change. The isosteric heat of adsorption is proportional to the adsorption amount, but the change rates vary due to the different coverage of CH4, showing that the low and medium metamorphic degree coals changes faster. The adsorption potential exhibits a negatively correlation with the adsorption volume, and the adsorption potential of high metamorphic coal is higher, owing to the higher proportion of micropores. As the adsorption progresses, the cumulative decrease in surface free energy of samples rises, but the rate of change gradually decreases. The adsorption heat and potential of the desorption are higher than adsorption process and the variation of surface free energy is lower, as well as the differences become greater with more CH4
desorption, reveling the mechanism of the adsorption hysteresis.
coalbeds. Understanding adsorption/desorption of coal to CH4 is highly important for estimating CBM reserves, predicting productivity and enhancing CBM extraction. In this work, the properties of coal, with the o,m=0.50%-2.54%, adsorb/desorb CH4 were quantitatively evaluated. Moreover, the variation characteristics were analyzed utilizing the theory of isosteric heat of adsorption, adsorption potential and surface free energy. The results show that the D-A and Weibull function have better fitting accuracy, indicating there are multilayer adsorption or micropore filling, while considering the physical significance of the formula parameters, the Langmuir and the desorption equation are more practical, and as the Ro,m increasing, the VL of samples to CH4 present a “U-shape” change. The isosteric heat of adsorption is proportional to the adsorption amount, but the change rates vary due to the different coverage of CH4, showing that the low and medium metamorphic degree coals changes faster. The adsorption potential exhibits a negatively correlation with the adsorption volume, and the adsorption potential of high metamorphic coal is higher, owing to the higher proportion of micropores. As the adsorption progresses, the cumulative decrease in surface free energy of samples rises, but the rate of change gradually decreases. The adsorption heat and potential of the desorption are higher than adsorption process and the variation of surface free energy is lower, as well as the differences become greater with more CH4
desorption, reveling the mechanism of the adsorption hysteresis.
| Original language | English |
|---|---|
| Pages (from-to) | 269-284 |
| Number of pages | 16 |
| Journal | Energy & Fuels |
| Volume | 38 |
| Issue number | 1 |
| Early online date | 21 Dec 2023 |
| DOIs | |
| Publication status | Published - 4 Jan 2024 |
Bibliographical note
We acknowledge financial support from National Natural Science Foundation of China (grant nos.41922016, 42130806 and 41830427), and Fundamental Research Funds for the Central Universities (No.2652022207).Data Availability Statement
Conflict of Interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.Keywords
- CBM
- adsorption/desorption characteristics
- isosteric heat of adsoprtion
- adsorption potential
- surface free energy