Effect of microwave-assisted acidification on the microstructure of coal: XRD, 1H-NMR, and SEM studies

Microwave heating contributes to coal fracturing and gas desorption. However, problems of low penetra-tion depth, local overheating and fracture closure exist. Coal demineralisation by acids has advantages in coal unblocking and permeability improvement, while it is difficult for acid to enter microcracks. Microwave-asisted acidification may offer an alternative. In this work, XRD, 1H-NMR, and SEM were used to evaluate the effect of microwave-assisted acidification on the microstructure of coal. Results show that kaolinite, calcite, and dolomite can be dissolved by acid. After microwave irradiation, the graphitization of microcrystalline structure of carbon improves. Microwave-assisted acidification erodes minerals in coal and enhances the graphitization degree of microcrystalline structure. Compared to individual micro-wave irradiation or acidification, the pore volume and pore connectivity can be greatly enhanced by microwave-assisted acidification. The NMR permeability of coal increased by 28.05%. This study demon-strates the potential of microwave-assisted acidification for coalbed methane recovery.& COPY; 2023 Published by Elsevier B.V. on behalf of China University of Mining & Technology. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Microwave heating can facilitate coal fracturing and gas desorption, but it has issues such as low penetration depth, local overheating, and fracture closure. Acid treatment of coal has advantages in unblocking and permeability improvement, but it struggles to enter microcracks. Microwave-assisted acidification may provide an alternative solution.