Research On Spherical Ni（OH）₂Production Using A Oscillatory Baffled Crystallizer

The oscillatory flow reactor (OFR) is a novel chemical process equipment for its unique advantage in transfer intensification including efficient transport of mass and energy, and good fluid mixing. The control of OFR is simple and precise, and now be-comes the new research focus of reaction equipment. The industrial application field of OFR has expanded to polymerization reaction, suspension separation, flocculation, so-lution crystallization and so on.Crystallization is an important operation unit in chemical process. Crystallization is used in the production of some chemical products, and also has wide applications in separation, purification and so on. Currently the OFR’s application in crystallization field is limited to solution crystallization system; the application in reactive crystalliza-tion system has not been reported yet. Therefore, this thesis explores the application of OFR in reactive crystallization system through the synthesizing of spherical nickel hy-droxide.The control crystallization method was used to synthesize spherical nickel hy-droxide. This thesis researched the effect of process parameters in a remodeled four-mouth flask on product’s sooth density, tap density and average particle size. These parameters encompass reaction time, pH value, ammonia concentration, stirring intensity and reaction temperature. The results showed that the extension of reaction time (0-20h), the decrease of pH value (10.6-11.4), the increase of ammonia concen-tration (0.2-0.8mol/L), stirring intensity (200-800rpm), reaction temperature (45-60degC) could improve the quality of products. In the actual production process, the parameters’setting should also consider energy consumption, operation environ-ment, equipment depreciation and material liquid loss.The research on the original OFR shows that, the materials that added into the re-actor could not been well dispersed, the smaller volume of a single cell would cause the local high supersaturation and fail to form spherical nickel hydroxide. Thus when OFR is applying in reactive crystallization system, it is necessary to set a specific re- gion for the rapid dispersion of added material.Based on the research of the process parameters and the original OFR experiment, this thesis designed and set up the oscillatory baffled crystallizer (OBC). It integrates a stirring tube (dispersion region) on the top of the OBC. The experiment result shows, the product of OBC has a higher quality than the original one. The effect of oscillation frequency, mean residence time, initial concentration, pH value and ammonia concen-tration on product’s sooth density, tap density and average particle size were studied in OBC. The results showed that the increase of oscillation frequency and the extension of mean residence time could improve the quality of products; for this reactor, there was an optimum initial concentration; the variation trend of pH value and ammonia concentration on products quality is similar to flask experiment, but the products qual-ity was lower in OBC than in flask, which turned to be the future improvement of OBC.