Effect of Electrolyte pH on CH₄ Adsorption and Desorption Behavior in Electrochemically Modified Lean Coal

Practical application of the electrochemical method for enhancing coalbed methane (CBM) extraction is limited due to the insufficiency of in-depth experimental and theoretical research. Therefore, H₂SO₄, Na₂SO₄, and NaOH electrolytes with different pH values were selected to electrochemically modify lean coals and their CH₄ adsorption and desorption behaviors were tested. The experimental results showed that the amount of CH₄ adsorption decreased after modification using H₂SO₄ and Na₂SO₄ electrolytes, and increased after electrochemical modification using the NaOH electrolyte. The ratio of CH₄ desorption increased from 83.20 to 90.10 and 87.84%, respectively, after electrochemical modification using H₂SO₄ and Na₂SO₄ electrolytes, and decreased to 81.71% after electrochemical modification using the NaOH electrolyte. The pore volume and average pore size increased, and the specific surface area decreased with the decrease of electrolyte pH. Lower pH electrolytes perform better and the mechanism was analyzed by the change of surface energy, surface groups, and pore structures. The work will provide a basis for the reasonable selection of electrolyte pH when using in situ electrochemical methods for enhancing CBM extraction.