响应面法优化氟硅酸铵制备白炭黑和氟化铵

本文以氟硅酸铵和碳酸氢铵为原料制备白炭黑和氟化铵(NH₄F)。根据单因素实验并结合Box-Behnken响应面法建立二次回归模型进行方差分析和验证,考察了液固比、配料比、反应温度、反应时间四个因素对白炭黑收率和NH₄F浓度的影响,通过响应面法优化得到较优工艺条件:液固比8,配料比5.49,反应温度76.5 ℃,反应时间49.08 min。在该工艺条件下进行验证实验得到白炭黑收率为96.90%,NH₄F浓度为2.02 mol/L,预测值与实验值无显著差异,验证了二次回归模型的可靠性。对产品白炭黑进行XRD、IR、TG-DSC、SEM、BET表征,及粒度分析和性能测试,对于产品NH₄F,采用氟离子选择性电极法测定其浓度,并对其性能进行检测。证实了白炭黑产品粒度为微米级,且是一种比表面积达316.83 m²/g的介孔材料,其中SiO₂的质量分数高达97.77%,外观、加热减量、灼烧减量、pH值、重金属含量和吸油值均达到行业标准。NH₄F产品中氟化铵含量、游离酸含量和氟硅酸盐含量均达到国家标准。

Response Surface Methodology to Optimize Process of Preparing Silica and Ammonium Fluoride from Ammonium Hexafluorosilicate

Ammonium hexafluorosilicate and ammonium bicarbonate as raw materials were used to prepare silica and ammonium fluoride (NH₄F).Based on the single factor experiment and Box-Behnken design response surface methodology, a quadratic regression model was established for variance analysis and verification. The influences of four single factors (liquid-solid ratio, ingredient ratio, reaction temperature and reaction time) on silica yield and NH₄F concentration were investigated. By the response surface analysis, the better process conditions are as follows: liquid-solid ratio 8, ingredient ratio 5.49, reaction temperature 76.5 ℃, reaction time 49.08 min. Under these conditions, the verification experiment was carried out. The silica yield is 96.90%, and the NH₄F concentration is 2.02 mol/L. There is no significant difference between the predicted value and the experimental value, which verifies the reliability of the quadratic regression model. XRD, IR, TG-DSC, SEM, BET characterization, particle size analysis and performance test of the product silica were carried out. The concentration of the product NH₄F was measured by the fluoride ion selective electrode method, and its performance was tested. It is confirmed that the particle size of silica product is micron-sized, and silica is a mesoporous material with specific surface area of 316.83 m²/g. The mass fraction of SiO₂ is as high as 97.77%, and the appearance, heating loss, ignition loss, pH value, heavy metal content, and oil absorption value all meet industry standards. The content of ammonium fluoride, free acid and fluorosilicate in NH₄F product all meets the national standard of the People's Republic of China.