| P-chlorobromobenzene is a key intermediate used in the synthesis of boscalid and p-chlorophenylboronic acid.It is obtained by the bromination reaction between chlorobenzene and bromine using iron as a catalyst.However,in the production process of p-chlorobromobenzene,side reactions are prone to produce o-chlorobromobenzene,which results in higher impurity content and lower product purity.Therefore,it is important to develop an appropriate method to accomplish the effective separation of o-chlorobromobenzene and p-chlorobromobenzene.At present,rectification and solution crystallization are mostly used to separate the two isomers.However,the slight difference in the boiling points of the two isomers makes it very difficult to separate them by rectification,because the multiple vaporizations and condensations result in high content of by-products as well as high valuable operating costs and energy consumption.In addition,the solution crystallization process requires the addition of solvents,resulting in higher product impurities.In order to overcome the shortcomings of traditional methods,this paper developed a melt crystallization technology to acheive the high-efficiency separation of o-chlorobromobenzene and p-chlorobromobenzene.The p-chlorobromobenzene product obtained in the experiment was analyzed by X-ray powder diffraction technique to obtain the crystal diffraction pattern.Materials Studio software was used to analyze the powder diffraction data and further index the powder diffraction results to obtain its unit cell parameters.Then,crystal structure of the p-chlorobromobenzene was refinded through the construction and optimization function of Materials Studio,Rietived refinement and other processes.The density and viscosity of p-chlorobromobenzene at different temperatures and different mass fractions were measured with a pycnometer and Ubbelohde viscometer.The obtained density and viscosity data were fitted and mathematical models were established to obtain the responding model parameters.The thermal conductivity of p-chlorobromobenzene was obtained by the longitudinal comparison heat flow method in the steady-state method.The fusion enthalpy of p-chlorobromobenzene was measured by a differential scanning calorimeter.The above results provide basic physical property data for exploring the melt crystallization kinetics of p-chlorobromobenzene.The macro kinetics of static melt crystallization was thoroughly studied.The change rule of the thickness of the static molten crystal layer with time were incestigated under different refrigerant temperatures,different cooling rates and different concentrations.The obtained data is correlated with the heat transfer model,and the heat transfer model is solved by analytical and iterative methods.According to the relevant parameters,a kinetic model is established.Based on the mathematical model,the effects of different refrigerant temperatures,cooling rates and concentrations on the growth of the crystalline layer were studied,and the growth trend of the crystalline layer was predicted.The separation and purification process of p-chlorobromobenzene and o-chlorobromobenzene was developed and systematically optimized.The optimal process conditions for suspension melt crystallization and static melt crystallization are determined.Finally,the suspension melt crystallization was chosen to conduct the separation of p-chlorobromobenzene and o-chlorobromobenzene taking yield and purity as target parameters,in which the economic cost was treated as an important parameter.The optimized process parameters of the suspension melt crystallization are:cooling rate of 0.2°C·min-1,crystallization temperature of-2°C,and crystallization time of 5h.Under the best operating conditions,the primary crystallization yield reached 62.74%,the product purity reached 99.15%,the removal rate of impurity A and impurity B were both close to 100%,the removal rate of impurity C reached 99.62%,and the effective partition coefficient was 0.0166. |
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