Abstract
We have presented a new coal solvent extraction method that enhances the extraction yield dramatically by using a flowing stream of a solvent at high temperature. The extract yield reached 65 to 80% for bituminous coals using tetralin as a solvent under 10 MPa at 350°C, and the extract was separated into about 25 to 40% of soluble fraction at room temperature (soluble) and about 40% of solid fraction (deposit) which precipitated from the extract at room temperature. It was found that the soluble and the deposit were almost free from inorganic materials. To utilize these clean carbonaceous materials for specific purposes, their fractionation and more detailed characterization are essential. Then the deposit, which is soluble at 350°C but insoluble in tetralin at 25°C (Frac.+25-350), was further extracted at several different temperatures below 350°C. It was found that five extraction steps could fractionate the coal into 8 fractions. Ultimate analysis and molecular mass measurement showed that the fractions obtained at lower temperature consisted of smaller molecular mass compounds which were existent in the parent coal and have larger atomic H/C ratio. Furthermore, the fractionation behaviors are discussed in terms of the solution theory by using solubility parameters. From a practical viewpoint, the melting and plastic behavior of Frac.+25-150 (softening temperature: 270°C) was very close to that of a naphthalene-based pitch (softening temperature: 223°C) which was synthesized for producing high performance carbon materials. This result suggested a possibility of utilizing the fraction as a feedstock of high performance carbon materials.
