Study Of Association Properties And Aggregation Process Of The Heavy Products From The Liquefaction Residue Of Shenhua Coal

As we all known, the aggregation behaviors of heavy intermediate products(HIP) of direct coal liquefaction have important effects on the technology and efficiency of liquefaction. In order to study the association properties of HIP and its structural dependences, the asphalt(PAS), asphaltene(AS) and preasphaltene(PA) were separated from the liquefaction residue in this paper. In addition, the aggregation kinetic process of PAS was also explored. Firstly, the structures and associations of these HIPs were characterized by FTIR, UV-vis spectroscopy, fluorescence spectroscopy and surface tension methods. Secondly, the effects of HIPs concentration, temperature, solvent composition and precipitator on the aggregation behaviors of HIPs in solvent were investigated by a series of chemical analysis methods. Further, combining with dynamic chemical calculation of model compounds, the non covalent nature in association process of PAS was studied. What's more, the paper also studied the aggregation kinetics process of PAS in solution. Meanwhile, the multi-scale aggregation/conglomeration process and mechanism of PAS by the dynamic analyses of conglomeration were investigated.Results indicated that the HIPs from the liquefaction of Shenhua PDU consist of multiple aromatic structures linked by methylene, ether bond etc. bridge bonds or connection by direct covalent bond. The composition and structure of HIPs are extremely complex and the aromatic structure mainly composes of benzene and naphthalene ring. The PAS mainly consists of 2~3 fused aromatic rings, and a lot of functional groups, in which hydroxyl group and aliphatic side chains are abundant, a certain amount of ester base is also exist. The AS mainly consists of aromatic compounds with lower condensation degree containing a certain amount of long alkyl side chains. The PA contains more condensed aromatic rings structure and less aliphatic structure, which is mainly methyl group. The PA also shows much more hydrogen bonding hydroxyl groups. The HIPs show very complex non-covalent bond associations to form different sizes of associates, in which include intramolecular and intermolecular aggregations. The association is related to its structure, and the ?-? interaction is the main factor to form the association between aromatic rings compared with the hydrogen bond. Moreover, the content of aromatic structure, the condensation degree of aromatic and the substituent group are also the important factors to influence the aggregation ability of HIPs. At low concentration, except the PA can generate intramolecular association, the AS and the PAS almost exist in the form of molecule. But at the high concentration(?25 mg/L), these three components generally can form intermolecular aggregates consisted of about hundreds of nanometer particle size by non-covalent bond associations with increasing solution concentration. In the solution, the molecules of HIPs firstly form a mesoscopic nano-aggregate, and further form micro-scale agglomerates, which finally were precipitated. What's more, the PAS gathered by very fast dynamics process, and then released some molecules with higher solubility to improve selectivity of precipitation by dissolving-precipitation equilibrium. Because of the complexity of the PAS structures, PAS can gather to form precipitation by some conjugate system of aromatic compounds with ?-? interaction. The aggregation and solvation of HIPs are the key factors to influence the aggregation and conglomeration.