熔融悬浮结晶法提纯湿法磷酸

使用熔融悬浮结晶法分离提纯湿法磷酸,研究了全回流稳态操作条件下重力洗涤塔内磷酸的纯化过程,考察了原料质量分数、洗涤塔中搅拌转速等操作条件对塔中产品纯度、杂质质量分数沿塔高分布的影响,并用发汗提纯模型进行了拟合。研究结果表明:采用的悬浮结晶装置对湿法磷酸有良好的分离提纯效果;结晶器进料质量分数、洗涤塔搅拌速率对熔融液中杂质质量分数沿塔高的分布有很大影响,进料质量分数增加,则产品纯度增加,适度的搅拌有助于保证洗涤塔的纯化效率,而过高的搅拌速率对分离提纯效果影响不大。在结晶器H3PO4进料质量分数为84%—86%、洗涤塔搅拌速率为10—20 r/min范围内,产品磷酸纯度可达到食品添加剂的标准,发汗提纯模型能很好地描述稳态操作时塔内的杂质质量分数分布规律,在半对数坐标中,杂质质量分数沿塔高呈线性分布。

Purification of wet-process phosphoric acid by melt suspension crystallization

By melt suspension crystallization,the purification process of wet-process phosphoric acid was studied in a vertical agitated cylindrical column at total reflux.The profiles of the mass fraction of impurities in the column were also investigated as a function of the feed mass fraction and stirring speed in the column,which was correlated with the axial dispersion model modified by sweating mechanism.The results indicate that the suspension crystallization equipment presented has strong adaptability for purifying phosphoric acid;both feed mass fraction and stirring speed have a great influence on the profiles of the mass concentrations of impurities in the column,the higher feed mass concentration,the purer product is,and the moderate agitation is beneficial for the purification of phosphoric acid,however,overhigh stirring speed is unnecessary.The product stream of phosphoric acid withdrawn from the column can meet the standard of food-grade when the process is operated with H3PO4 feed mass concentrations of 84%—86% and stirring speed of 10—20 r/min in the column.The model modified can be used to explain the impurities mass concentration distributions along the column satisfactorily,which are linear in the logarithmic coordinates.