Investigation of parameters affecting atmospheric extraction yields and extract qualities of two Turkish lignites

Abstract

Four sets of extractions of two Turkish lignites have been performed at atmospheric pressure in Soxhlet-type extractors varying the time of extraction, particle size of the lignite, its moisture, and the solvent. Extractions performed in small-size Soxhlet extractors (capacity 90 g coal) with benzene as the solvent have shown that for the Mengen lignite the most appropriate size range is 20–60 Tyler mesh and the moisture content leading to highest yield is 10–12 per cent. For the Elbistan lignite the corresponding values are 10–60 Tyler mesh and 20 per cent moisture. Extractions carried out with benzene in a larger-size Soxhlet apparatus (capacity 1–1.5 kg coal) have shown that Mengen lignite should be extracted for 30 hours and Elbistan lignite for 24 hours for exhaustion. Most of the extractable material can be obtained in the first five hours in the case of Elbistan lignite and in the first 10 hours in the case of Mengen lignite; the difference is attributed to different porosities. Extractions carried out using various solvents in larger-size Soxhlet extractors under the most appropriate conditions as determined from the first three sets of experiments have indicated that Mengen lignite may be a promising raw material for industrial-scale montan wax production. Yields varying between 10 and 14 per cent on dry basis have been obtained from Mengen lignite with benzene—ethanol, benzene—methanol and tetrahydrofuran as solvents. Elbistan lignite gives a maximum yield of 3.5 per cent with tetrahydrofuran. Solvents characterized by a high substitution ability yield more extract. Montan waxes obtained from Mengen and Elbistan lignites are found to be richer in free acids and esters compared with commercially available ones. Infrared spectra results indicate the raw wax to be predominantly aliphatic. The melting points of the waxes obtained with various solvents are generally found to increase as the asphaltic matter content increases and resinous matter content decreases.