Determination of surface properties of direct coal liquefaction residue before and after solvent extraction by inverse gas chromatography

Direct coal liquefaction residue (DCLR) is deashed by hydrochloric acid and hydrofluoric acid to obtain ACLR. The ACLR was extracted with n-hexane, toluene and tetrahydrofuran to obtain n-hexane insoluble matter (HCLR), toluene insoluble matter (TCLR), tetrahydrofuran insoluble (FCLR). The surface properties of ACLR, HCLR, TCLR and FCLR were characterized by inverse gas chromatography (IGC). Based on net residual volume V_n of the non-polar probe, surface dispersion free energy were calculated by Dorris-Gray and Schultz method respectively. The adsorption enthalpy △H^sp of the polar probe on surface of the 4 insoluble solids was obtained by V_n of the polar probe, and the acid constant K_a and the base constant K_b of the 4 insoluble solids were calculated by △H^sp. The results show that the surface dispersion free energy of ACLR are obviously changed after solvent extraction, and the dispersion free energy on surface of the 4 insoluble solids is decreasing from 60 to 100℃. By K_b/K_a> 1 and △H^sp analysis, 4 insoluble solids surfaces are both amphoteric and the alkaline effect is stronger than that of the acid effect. As a kinetic adsorption technique, IGC can quickly and accurately characterize change of surface properties of DCLR during fractionated extraction. At the same temperature the surface dispersion free energy obtained by the Dorris-Gray method is slightly higher than that by the Schultz method.