层熔融结晶法制备高纯度磷酸

Preparation of high purity phosphoric acid by layer melt crystallization

动态层熔融结晶技术净化磷酸,具有分离效率高、能耗低、无污染等优点,绿色环保。采用程序冷冻法研究了动态层熔融结晶净化磷酸过程中的传质、传热、结晶动力学和杂质分布。研究表明,磷酸晶层生长速率随磷酸熔体起始浓度和冷端降温速率的增加而增加,达结晶平衡态时,晶层平均厚度随磷酸熔体起始浓度的增加和降温终点温度的降低而增加,研究建立了晶层的增长速率和平均厚度与过程操作参数的关联模型;晶层传热能力和杂质的分离效率随着磷酸熔体起始浓度和降温终点温度的降低而增加;采用优化的工艺条件,通过一次结晶纯化,可将质量分数为86.79%的磷酸溶液纯度提高至90.8%,杂质氟离子的质量分数由3×10^(-5)下降到4.5×10^(-6),杂质去除率达85%。

Phosphoric acid was purified by layer melt crystallization,which is an environmental friendly technology with high separation efficiency,low energy consumption and less pollution.Kinetics,mass-transfer,thermodynamics and impurity distribution of dynamic layer melt crystallization were studied by the gradual freezing method.Research showed the growth rate of the crystal layer increased with the increase of initial melt concentration and the cooling rate of the cold end,and the average thickness of the crystal layer increased with the increase of the initial melt concentration and the decrease of the temperature of the end of cooling when the crystal was completely crystallized,and the correlations between growth rate,average thickness and operating parameters were established respectively.The effective thermal conductivity of the crystal layer and the separation efficiency of impurities increased with the decrease of the initial melt concentration and the decrease of the temperature of the end of cooling.By optimized process conditions of layer melt crystallization,the mass concentration of phosphoric acid was improved from 86.79%to 90.8%,the content of impurity ion F-was reduced from 3×10^-5 to 4.5×10^-6.The removal rate of impurities reached 85%.