Research Of The Process Of Continuous Multistage Countercurrent Fractional Crystallization For4-Nitrochlorobenzene And2-Nitrochlorobenzene

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 same equipment, 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.As the process of crystallization based on the theory of solid-liquid phase equilibrium, so the research of solid-liquid phase equilibrium has important theoretic and practical significance. But this research was proved unenlightened because it was in the state of semi-empirical and semi-theoretic. However, along with the rapid development of medicines and fine chemicals, we believe the research of solid-liquid phase equilibrium would inevitably gain more regards and development. We have studied many kinds of organics using laser technique, especially the solubility of D-(-)-p-Hydroxyphenylglycine Dane Salt in mixtures of methanol and ethanol, lots of data was gained and this research won broad approval in the area of international academe.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 diameter φ=50mm, we took the isomer mixture of4-Nitrochlorobenzene and2-Nitrochlorobenzene as input material, and studied the impact factors such as feed composition, reflux ratio, height of crystal bed, and effect of stirring, 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 effect of 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 z. 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.