| At present, the use of fluoride resources is irrational. The byproduct fluorine acid of the phosphorus fertilizer industry is used to produce sodium fluoride. As an important fluoride salt, sodium fluoride is used as the toothpaste additive because of its better anti caries effect. The market supply and demand imbalance of sodium fluoride Market in the toothpaste grade is outstanding. In view of those problems, this paper proposed the idea of sodium fluoride preparation of toothpaste grade, combined with the production characteristics of Yuntianhua International chemical Co., Ltd.This paper hope to explore a production line with green, environmental protection, energy saving for sodium fluoride of toothpaste grade.The experimental use the raw material purification treatment, product synthesis and washing as routes to explore the synthesis process,and to find out the appropriate technological conditions by optimizing the technological conditions.1.The purification treatment of raw materials including two parts:the The treatment of desilication of hydrofluoric acid and sodium sulfate removal of iron ion, magnesium ion, calcium ion.(1) The raw material of hydrofluoric acid has 0.5% fluosilicic acid which has effects on the quality of sodium fluoride product.It is necessary to do a desilication experiment of hydrofluoric acid. Used the desilication rate as the index, to determine the optimum conditions for the desilication process:sodium carbonate as desiliconization agent, room temperature (25±5℃), the amount of sodium carbonate is the theoretical amount in excess of 5%, reaction time is 30min.(2) Sodium sulfate of industrial grade has a lot of iron ions, magnesium ion, calcium ion which have a certain effect on the quality of sodium fluoride product.Adding sodium hydroxide in sodium sulfate solution at 60 ℃,and controlling the pH above 11.5～12.0, reaction time at 30min, stirring intensity at 100r/min.The sodium sulfate solution of calcium, magnesium and iron ions content reached 0.032%, 0.021%,0.0042%.2.The synthesis process for sodium fluoride were discussed mainly in the experimental process by thermodynamic analysis and experimental methods.(1)Whether the main reaction could work,we can do a thermodynamic Analysis for it. By calculating,we konw that △rHmθ>0,△rSmθ<0、△rGmθ<0.The driving force of the reaction is the difference of solubility, the reaction temperature has greatly effect of on experimental result.(2) Through analysis,it determined the product yield and the sodium fluoride purity as index for single factor experiments. Through the single factor experiment and orthogonal experiment, the process parameters have been optimized:the hydrofluoric acid concentration is 18mol/L, the reaction temperature is 40 ℃, the reaction time in the 60min, the aging temperature is 10 ℃, the aging time was 15min.In this conditions, obtained the crude product with the average yield of 98.338% and the average purity of 96.578%.Then, washing the crude product. Washing the single factor experiment was carried out, to determine the optimum process conditions:volume of distilled water is the product of 2 L/kg, wash water temperature 35-40 ℃. The content of sodium fluorideis more than 98.5%, sulfate content is less than 0.05% in the products after washing.Through the process synthesis sodium fluoride of toothpaste grade, the reaction yield was above 95%, the products can better meet the requirements of the company standard of Q/XWJ114-2007. |
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