Study On The Process Of Monomehypo Crystallization

The final process of the industrial production of monomehypo is crystallization. For a long term, the factory can not get a desired product with sufficient quality, crystal size distribution, shape and purity for the lack of study on the crystallization process. So, it is very important to study the crystallization in order to improve the product quality.In this thesis, the author studied the crystallization of monomehypo hi four aspects. Firstly, the metastable zone width was measured through experiments and predicted by theoretical computation respectively. The results of the two methods were comparable and could provide a criterion for the control of the supersaturation in the industrial crystallization. At the same time, the theoretical computation method could be applied to other high-viscous, diffussion-controled crystallization of some organic system. Secondly, the effects of some additives on the morphology of the crystal were studied. One anionic surfactant(L5) was very effective at the concentration of 30 ppm. At the presence of additive L5, the monomehypo crystal became course and the water entrainment decreased by almost 50%. The changes of the crystal morphology were because of the selected-adsorption of additives on different faces of the crystal. Through the comparison of the temperature at which the solution turned turbid with or without additives, it was proved that the metastable zone width was enlarged at appropriate additive concentration. This could partly account for the enlargement of the crystalsize and the author suggested some unclear changes of the thermodynamic parameters might play an important role too. Thirdly, the phase diagram of the ternary system monomehypo-NaCl-ItO was plotted through experiment. By analyzing the phase diagram, the author advised to use NaCl as saltingout agent to increase the yield. The experiments showed that the productivity could be increased to as high as 80% and at the same time, combined with the effects of the additive that was added, the purity of the product was increased to 95%. Finally, the author carried out the continuous crystallization experiments. The CSD of the product were simulated though discretized model of the Equation of Population Balance(EPB) which included the aggregation and breakup effects. It was proved more accurate than linear simulation of the CSD and the actual growth rate and nucleation rate were obtained. All of these were very important for the design of the continuous crystallizer.