The principle of the step-by-step product separation and refining method for industrial naphthalene is based on the liquid-solid phase equilibrium of the material system. The main impurities in the industrial naphthalene produced by distillation are thionines, phenols, broken nitrogen-containing compounds, and neutral oils, with impurities accounting for about 5% of the total amount. The phase diagram of the mixed system composed of naphthalene and other tar components shows that naphthalene, aromatics, and
The system composed of acidic and alkaline aromatic compounds forms simple low eutectic melts, and the low eutectic points all appear in the low concentration zone of tea. In theory, these impurities undergo a single pass
The final product can be removed, especially the complex system formed by tea and sulfhydrin. The two can not only form a co melt, but also form a solid melt in the high concentration zone of sulfhydrin. Analyzing the two-phase equilibrium diagram of naphthalene and methanol, theoretically, the required separation effect can be achieved by processing several equilibrium sample stages. However, due to the decreasing separation efficiency of each stage near the narrow region tip, in actual production, it is necessary to determine the appropriate number of separation stages and the purity index that the product needs to achieve. By controlling certain temperature conditions.
Place the industrial Cai in the two-phase zone, and the components in the system will be redistributed in the coexisting two phases. The concentration of each component in the two phases depends on the distribution coefficient K of the component: experimental measurement, in the phase
In the high concentration zone, the distribution coefficients K of phenols, pipettes, and neutral oils are all approximately zero, so these impurities are basically retained in the liquid phase.
For thionines, the distribution coefficient K value is approximately, indicating that thionines have a lower content in the solid phase compared to the liquid phase in the equilibrium phase. Therefore, by separating the liquid phase, a solid phase with higher purity than the original industrial tea can be obtained. The solid phase crystals obtained after separation are melted again, and some of the products are controlled. After separating the liquid phase again, a higher purity solid phase crystal will be obtained than the previous one. By repeating the process of melting a portion of the crystals and separating the liquid phase, we can obtain crystals with higher purity of naphthalene each time, until we meet the required indicators. The production of refined naphthalene from industrial naphthalene generally requires 5 repeated product processes.
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