Study On The Structure And Association Of Preasphaltene From The Direct Hydro-liquefaction Of Shenfu Coal

Direct coal liquefaction is an important clean coal technology. It can produce directly transportation fuel and fine chemicals to make up for the shortage of the petroleum resources. So the basic research focused on the direct coal liquefaction is very significant. In this paper, two different preasphaltenes (PA) were firstly prepared by the hydro-liquefaction of Shenfu coal in a batch autoclave (SF-PA) and the liquefied residue of PDU of Shenhua group in Shanghai (RP-PA), respectively. Subsequently, the PAs were separated into seven sub-fractions by the column chromatography. The structures, compositions and molecular weights of two PAs and their sub-fractions were determined by element analysis, FTIR, UV-vis, FL, GPC and MALDI-TOF-MS techniques. These results from two PAs and their sub-fractions were further compared. Finally, the association in PA and its sub-fraction solutions were investigated by Uv-vis, FL and GPC analyses.Results indicate that two PAs all show higher condensation degree of aromatic rings and average molecular weight than corresponding asphaltenes. The aromatic nucleus in PA mainly consist of3-5ring condensed aromatic nucleus. The average molecular weights of RP-PA determined by MALDI-TOF-MS and GPC are800aum and1291aum, respectively. These of SF-PA are807aum and1394aum. Compared with SF-PA, RP-PA contains more aromatic structures and less aliphatic structures, and shows higher regular structure. All sub-fractions separated from two PAs have similar structural characteristics with parent coal. The molecular weight distributions of RP-PA and its sub-fractions determined by MALDI-TOF-MS are narrower than those of SF-PA and corresponding sub-fractions. The differences of average molecular weight between RP-PA sub-fractions lower than those between SF-PA sub-fractions. Except of Ⅵ and Ⅶ sub-fractions, the average molecular weights of SF-PA sub-fractions are in range of549～837aum, but those of RP-PA sub-fractions are in range of585～786aum. However, the average molecular weights of RP-PA sub-fractions are obviously higher than those of SF-PA sub-fractions. Meanwhile, the average molecular weights of all sub-fractions determined by GPC are significantly higher than those determined by MALDI-TOF-MS, especially those of strong polar sub-fractions. It suggested that there are obvious association in PA and its sub-fraction solutions. Their "critical association concentration" determined by FL are between10mg/L and20mg/L in THF solvent. The aggregate scales of RP-PA sub-fractions are larger than those of SF-PA sub-fractions. Finally, based on the results of structural characterization and association research, an association mechanism of PA and its sub-fraction in solution were proposed and used to explain the fluorescent characteristics observed in this paper.