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Direct coal liquefaction residue (DCLR) could be extracted using dipropylamine (DPA) to afford extract with polycyclic aromatic structures, and the separation of extract and DPA as well as the recovery of DPA could be achieved by the nonthermal CO2-trigger at room temperature and atmosphere pressure, which would potentially gain huge energy savings. On the basis of preliminary single factor experiment, response surface methodology was used for optimizing DCLR extraction, and Box–Behnken experimental design was adopted, where extraction time, extraction temperature, and ratio of DPA to DCLR were chosen as the three independent variables, and extract yield was chosen as response variable. Among the three independent variables, DCLR extraction was mainly affected by extraction time and ratio of DPA to DCLR, and the two variables exhibited an interaction effect on the extract yield. The predicted extract yield would reach the peak under the optimized conditions, i.e., extraction time of 48 min, extraction temperature of 25°C, and DPA to DCLR ratio of 39 mL/g. In the practical experiment under the optimal conditions, the real extract yield was up to 29.42%, which was similar to the expected one. Response surface methodology proved to be applicable and useful for optimization of DCLR extraction. [ABSTRACT FROM PUBLISHER]

The effect of small molecular compounds in coal on quick direct coal liquefaction at high temperature was studied. The results showed that extraction with tetrahydrofuran just removed a portion of organic compounds, which were free or embedded in the macromolecular network structure in coal, without changing the macromolecular network of coal. However, removal of small molecular compounds in coal influenced the pyrolysis behavior and liquefaction performance of coal. The extracted coal exhibited better liquefaction activity in good donor solvent. The liquefaction conversion and yield of oils were higher than that of raw coal. The reason was that extraction with tetrahydrofuran made the relaxation of coal macromolecular network, and increased average pore size of extracted coal, which favored the diffusion of hydrogen-donating solvent into coal macromolecular network, thus increased the probability of collision of radicals and active hydrogen. The quick liquefaction experiment of extracted coal in poor hydrogen-donating solvents showed that the small molecular compounds played an important role as hydrogen donor during the quick liquefaction at high temperature without external active hydrogen resource. [ABSTRACT FROM PUBLISHER]