Extracting Coal Liquids from Direct Coal Liquefaction Residue Using Subcritical Water

Efficient recovery of coal liquids from direct coal liquefaction residue (DCLR) is beneficial for improving the economics of the direct coal liquefaction process. An attempt was made to evaluate the possibility of extracting coal liquids from DCLR using subcritical water (SBCW). The properties of water are compared with those of typical organic solvents. With regard to the ability of dissolving/emulsifying organic components, SBCW compares favorably with some typical organic solvents under certain conditions. This is evidenced by the fact that the SBCW3 (320 °C/11.7 MPa) extraction yield is similar to the n-hexane extraction yield, although the SBCW1 (250 °C/5.2 MPa) and SBCW2 (300 °C/8.9–11.6 MPa) extraction yields are lower than the n-hexane extraction yields under comparable conditions. The recovery rate of coal liquids from DCLR by SBCW3 extraction can be higher than the maximum recovery rate by n-hexane or methanol extraction when the (SBCW3/DCLR)mass is high enough. In comparison with n-hexane-extra...