The production of ash-free coal in closed vessels with the microwave method

This work focuses on reducing the ash content in coal via the microwave-assisted extraction (MAE) method using the closed vessel system. Ash-free coal (AFC) was produced from three variously ranked Turkish coals through microwave-assisted extraction in N-methyl-2-pyrrolidone (NMP) containing a small amount of ethylenediamine (EDA) or tetralin. The extraction yield of these coals was found to depend on the related coal, temperature, and co-solvent type. The results showed that the extraction yield of these coals in NMP increased with the increase in the extraction temperature. When EDA was used as co-solvent, the extraction yields increased depending on the coal type and the increase in the extraction yield varied between 1.8% and 7.3%. However, when there was the usage of tetralin as a co-solvent, the extraction yield of uzulmez coal increased and the extraction yields of the other two coals decreased, and AFCs containing less than 0.62% ash were obtained in this study.