| Abstract: | The solubilization of small molecules from coal by solvent extraction and the resulting effects on the pore distribution of a low rank coal were studied. Samples were extracted, in succession, with petroleum ether and with CS2. Extract and residue frac-tions collected during the solubilization process were analyzed by FTIR and by surface area and porosimetry. The results show that an obvious inflection point exists that allows separating the dissolution sequence into stages. Small molecules are first extracted from the free state, then molecules trapped in micropores are extracted and, finally, molecules trapped in the coal-matrix network are extracted. This is indicated from the extraction yield curves. Chain-like carbonyl compounds, -OH (or-NH) containing com-pounds that are hydrogen bonded and phenolics dominate the petroleum ether extracts. Chain-like carbonyl components and ether compounds (aliphatic ethers and aromatic ethers) dominate the CS2 extracts. A solvent dissolution mechanism and the effect of small molecule extraction on the pore structure are put forward. Diffusion, dissolution, pore opening, pore shrinking or even col-lapsing caused by swelling, creating of new micropores, pore opening and, finally, colloidallization of some micropores occurs. In the later stages of the extraction the internal structure of the coal is colloidallized due to swelling and the pore number or volume is greatly reduced. |
