Separation of Nitrogen Heterocyclic Compounds Contained in Coal Tar Absorption Oil Fraction by Solvent Extraction

摘要

The liquid-liquid equilibrium properties (distribution coefficient and separation selectivity) between the feed of coal tar absorption oil fraction and the solvent (aqueous solution of methanol or that of tetrahydrothiophene-1, 1-dioxide (sulfolane)) were experimentally measured with changing various conditions (water content in the solvent, etc.) in order to study the performance of operation and of separation. Nitrogen heterocyclic compounds (2,3-benzopyridine (quinoline), 3,4-benzopyridine (isoquinoline), and 2,3-benzopyrrole (benzo[b] pyrrole, indole)) were extracted perferentiaaly to aromatic hydrocarbon (2-methylnaphthalene) in all cases. The distribution aoefficients of heterocyclic compounds and aromatic hydrocarbon decreased, and the separation selectivities of the heterocyclic compounds relative to the aromatic hydrocarbon increased with the water content in the extract. The aqueous solution of methanol was superior as a solvent to that of sulfolane in terms of both operation and separation performances. The above distribution coefficients were used to carry out the simple process simulation of extraction operation where the solvent was the aqueous solution of methanol. The multi-stage structure of equilibrium stage and countercurrent contact between the feed and the solvent improved the concentrations and yields of the heterocyclic compounds in the product that indicated process feasibility of the separation technique.