Optimization of solvent extraction process of some Turkish coals using response surface methodology and production of ash-free coal

In order to produce ash-free coal (AFC) from three Turkish coals, solvent extraction of coals using 1-methylnaphthalene (1-MN) at different temperatures were conducted. The extraction yield of coals was found dependent on coal, temperature, and solvent type. When there was usage of 1-MN as solvent, the extraction yield was low. However, on addition of N-methyl-2-pyryrolidone (NMP) or quinoline (QN) into 1-MN, the extraction yield increased. Following the extractions, we obtained AFC with less than 0.65% ash content for the three coals used in this study. The response surface methodology (RSM) was employed to investigate the solvent extraction conditions. The factors investigated were extraction temperature and additional polar solvent ratio. The obtained results demonstrated that either excess amount of polar solvent into 1-MN should be added at low temperatures or extraction should be done at high temperatures using less polar solvent to obtain an increase in extraction efficiency. The sensitivity and validity of results obtained by RSM were confirmed through validation experiments. The results of validation experiments showed a good agreement between the experimental and predicted values (relative error <1.2) and that indicated the robustness of the models. (C) 2016 Curtin University of Technology and John Wiley & Sons, Ltd.