Study On The Continuous Multistage Countercurrent Fractional Crystallization For Naphthalene-Thionaphthene

Continuous multistage countercurrent fractional crystallization is a new and potential technique for separation and purification, and the evolvement of exploitation work in foreign countries has been rather active in recent years. Compared with traditional crystallization and distillation, it has more advantages, not only it has higher separation efficiency, lower energy consumption, fewer investment for equipment, and higher product purity, but also it deal with the difficulty for distillation to separate the azeotropic and thermosensitive mixtures. As the highest operation temperature was around the melting point of the material, it lowers the requirement for equipments, moreover, the process of crystallization and melting was carried out in the tower column, so the structure of equipment and operation procedure were simplified obviously. Otherwise, the feature of large production capacity determined it was suitable for large-scale continuous production. Therefore, the new separation technique has more extensive application prospect and important industrial value.In this work, the process of continuous multistage counter-current fractional crystallization was investigated; also the achievement of predecessors was summarized, and based on the combination with practice the crystal column was developed independently. In the column with the length1350mm and the inner diameter50mm, the experiments took the isomer mixture of naphthalene-thionaphthene as material, and studied the impact factors such as effect of stirring, height of crystal bed, feed compositionre, and flux ratio, meanwhile large amount of experimental data was collected and analyzed after repeated experiments. Further, satisfactory results were achieved that the concentration of the crystal was purified from90.85%to99.99%. In the experiment, the principles were mainly countercurrent washing and sweating, and based on the two principles the mathematic model was established about the relationship of the concentration of key component in column and the height of the column. Through lots of experiment, the distributing curve which reflects the relation of concentration and height z in different conditions was exhibited in the paper. And the correctness of the mathematic model was testified, besides, it also provided credible sustainment for the next enlargement to industrial scale.As the process of industrial crystallization based on the theory of solid-liquid phase equilibrium, so the research of solid-liquid phase equilibrium has important theoretic and practical significance. The solubility of naphthalene in N, N-dimethylformamide, n-butanoic acid, ethyl acetate, butyl aetate, tetrahydrofuran and N-methyl-2-pyrrolidone was measured using laser technique. Based on the theory of solid-liquid phase equilibrium, the solubility equation has been deduced and measured solubility values were correlated by the modified Apelblat equation. During the process of industrial crystallization, the binary mixed-solvent has been used for choosing a high efficient solvent of separating property. Thus thermodynamic property of the binary solvents will provide basic data for industrial crystallization and other chemical processes. Liquid densities of the binary glycerol and1-propanol,2-propanol,1,2-propanediol,1,3-propanediol mixtures were measured at the temperatures in the range from298.15K to333.15K. From these data, the excess molar volunes have been calculated and correlated using the Redlch-Kister equation.