| Lignite is rich reserves of low quality coal, high moisture content was an important factor to interfere the mention mass use of liginite. The causes of high moisture content of lignite lies in its diversity of oxygen containing functional groups and the complexity of pore structure. This text constructed a macromolecular structure model(C169H140O44N3S2) of SL that was consistent with the structural analysis and optimized by the quantum chemical calculation. The effects of pore size and oxygen containing functional groups on the properties of lignite hold water was studied by experiment and theoretical calculation. The main results are summarized as follows:(1)The results suggested that SL was rich in aromatic ring compounds and oxo-bridged oxygen bond,-S-S- was a crossed linkage connecting aromatic rings in SL. The pyrolysis of SL resulted in a light volatile GC/MS detected heterocyclic compounds consisting of furan, indole, quinoline, indene, et al. Meanwhile, the oxygenic groups were mainly composed by hydroxyl, carboxyl,carbonyl group and ether. In addition, C169H140O44N3S2 was identified as the formula of macromolecular structure model of SL, of which the FTIR spectrum by structural calculation was highly correlated with that of by experimentally determined.(2)44 kinds of model compounds were selected to study substituent effects on water-holding properties of oxygen containing functional groups. Graphene oxide structure model was selected to research the relationship between the structure and water holding properties of complex system. The results show that as far away from the substituent, the effect on the binding energy is more and more small. Substituents have different effects on the binding energy between compounds and water, the sequence is carboxyl >methoxy>hydroxyl>methyl> benzene. Electron donating groups can reduce the binding energy between compound and water, and electron withdrawing group can increase the binding energy, while the number of substituents is not the main factor influencing the binding energy. Binding energy exists differences between water molecule and various oxygen containing functional groups in graphene oxide model, the sequence is carboxyl> the phenolic hydroxyl on the edge of model > interlayer hydroxyl > epoxy group. With the increase of the number of water molecules on the compound model, interaction energy between water molecule and compound model(EC) can significantly decrease.(3)The wate-holding properties of graphite oxide and graphene oxide with different functional group content was studied. As the oxidant concentration increased, carboxyl group content and total oxygen content became higher, and the variation of hydroxyl content was not obvious. We choose KCl as flocculants to make suspended sedimentary and got large number of graphene oxide solid, the thickness of the graphene oxide films was 0.6~1.6 nm. Water holding capacity of grapheme oxide and graphite oxide increased with the content of oxygen containing functional groups. Water holding capacity and the carboxyl group content had significantly positive correlation, and the change of hydroxyl content has little effect on water holding capacity.(4)Multi-walled carbon nanotubes(MWCNTs) was selected as a model compound to research on the influence of pore size on the water holding properties. The results show that a large amount of reactive functional groups such as carboxyl was obtained on the surface of the MWCNTs. The most suitable oxidative reflux time was 1.5 h. And in this condition, the O-MWCNTs has the highest equilibrium re-adsorption water content(493%). The synergistic effect of oxygen containing functional groups and the pore structure, can significantly improve the water holding properties of compounds. The theoretical study shows that, with the increase of diameter, EC/EB will decrease gradually. Diameter increased to more than 1 nm, the effect of delocalized pi-bond played a major role in the interaction energy. This fits the experimental results. |
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