Response Surface Methodological Approach to Optimize Microwave-assisted Extraction of Cayirhan Lignite

Microwave-assisted extraction of Cayirhan lignite was investigated using N-methyl-2-pyrrolidinone. The response surface methodology was employed to optimize the microwave-assisted extraction conditions. The controllable factors selected in the present investigation included the extraction temperature, extraction time, and solvent-to-coal ratio. The obtained results demonstrated that the extraction temperature was the most important factor, which had a positive influence on the extraction yield. The statistical model predicted that a higher extraction yield of up to 28% would be obtained at the following optimized conditions: an extraction temperature between 217-230 degrees C, a solvent-to-coal ratio of 13.5, and an extraction time of 28-30 min.