| As important chemical raw materials and chemical intermediates, benzene polycarboxylic acids have an wide range of uses in synthetic fibers, plastics, pesticides, pharmaceuticals, plasticizers, adhesives, fragrances, dyes intermediates, and so on. Currently, benzene polycarboxylic acids (BPCAs) are mainly obtained by the oxidation of the corresponding aromatics and more than70%aromatics come from petroleum. With petroleum resources diminishing, direct preparation of BPCAs using coal as raw materials by the method of alkali-oxygen oxidation show a prospect in the future. Therefore, in the work, we mainly studied the separation of12kinds of BPCAs, products of coal alkali-oxygen oxidation, and alkali-oxygen oxidation of multiple coals with different coal ranks. Through the yield and product distribution of BPCAs from different rank coals, we hope to get some information about coal structure evolution.At present, it has been made some progress in alkali-oxygen oxidation of lignite as raw material to yield BPCAs. However, BPCAs were obtained in the form of mixtures of potassium. Therefore, the separation and purification of BPCAs is an major problem of the efficient use of coal by alkali-oxygen oxidation. This work attempts to separate mixtures of BPCA models using anti-solvent method. Some anti-solvent systems, such as butanone-hexane, butanone-petroleum ether (60℃-90℃boiling rang), butanone-petroleum ether (30℃-60℃boiling rang), ethanol-water, acetone-petroleum ether and butanone-cyclohexane, have been invesitgated. The results indicate that butanone-petroleum ether (60℃-90℃boiling rang) and butanone-hexane anti-solvent systems have some effect for separating the mixture of benzene polycarboxylic acids.As the anti-solvent method is difficult to completely separate the mixture of BPCAs, so it has been considered to roughly divide the mixture into two parts:BPCAs with a small number of carboxyl attached to the benzene ring and with a large number of carboxyl attached to the benzene ring. Then the two parts are treated with different ways, like separation and purification. For the part of BPCAs with a small number of carboxyl (from benzoic acid to trimellitic acid), Henkel reaction was applied to yield a single product, terephthalic acid (TPA). For the part of BPCAs with a large number of carboxyl, which mainly consist of pentacarboxylic acid and mellitic acid, it is expected to selectively remove off one or two carboxyl to obtain high purity pyromellitic acid by decarboxylation. The results indicate that TPA can be produced via Henkel reaction, but the yield of TPA did not meet the expectations. By trying different anti-solvent systems, we founa that butanone-petroleum ether (60℃-90℃boiling rang) and butanone-hexane anti-solvent systems have positive effect for separating the mixture of BPCAs. Then the solubility of BPCAs in the three anti-solvent systems was studied. The solubility of BPCAs has been measued in the solvent with ratios of antisolvent to solvent volume ratio of1,3,5,7and10, under temperatures of20℃,30℃,40℃,50℃and60℃Up to now, study of coal alkali-oxygen oxidation is mainly for lignite that has a low coalification, and the data about bituminous coal or anthracite coal is few. So it is necessary to examine alkali-oxygen oxidation of coals with different coal ranks. Meanwhile, the results of alkali-oxygen oxidation of coals with different coal ranks may provide some information on coal structure and its evolution. Hence this work studies the alkali-oxygen oxidation of10kinds of coals from Xiaolongtan Lignite to Taixi Anthracite coal at240℃and5MPa initial oxygen pressure. |
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