| Ammonium polyphosphate (APP) has a lot of advantages, such as non-toxic, biodegradability, polyion, and anti-bacterial, and it has been widely used in water treatment, fertilizers, flame retardants and food additives. Therefore, ammonium polyphosphate has a very broad application prospects and potential for development, which has been sought after by domestic and foreign scholars. The preparation for high-purity phosphate from wet process acid, especially for the ammonia polyphosphate, is in line with the national energy conservation, the sustainable resource development and the upgrading of the industrial structure requirements. This paper studied the preparation process for high value ammonium polyphosphate, based on the study of the preparation of high purity diammonium phosphate using the purified wet process phosphoric acid and phosphorus pentoxide as raw materials. The main contents and conclusions are as follows:(1) The preparation of the high purity of diammonium phosphate was studied. The effects of the initial simulated phosphoric acid (with or without impurities) concentration and the pH on the purity and yield of the products were examined. And the two step neutralization process was obtained in sequence. Then, the the industrial extraction purified wet process acid was used as raw materials to prepare the diammonia phosphate by using the two-step neutralization process. The arsenic and lead ions in the acid were removed by the precipitation. The results showed that the diammonium phosphate prepared by the two-step neutralization process was food grade, and it could be used to produce high degree of polymerization ammonium polyphosphate.(2) A novel preparation for n-APPs has been proposed by using diammonium hydrogen phosphate (DAP) and dicyandiamide (DICY). The preparation can be divided into two steps, the reaction and the crystallization. First, the reaction pathway has been studied by FTIR techniques. Then, the crystallization mechanism has been investigated. Accordingly, crystal form Ⅱ and crystal form V were obtained under their specific conditions. The shrinking core model was used to explain the effect of the crystallization time on the pH and solubility of the products. Finally, the linear structure of the n-APPs products has been confirmed by the liquid P31-NMR techniques; TG analysis showed that the products had high thermal stability with less than 2% wight loss below 250℃.(3) The phosphorus pentoxide and diammonium phosphate melt polycondensation reaction kinetic was studied. The monomer content in the condensation product was measured under different conditions by using exchange chromatography. The reaction mechanism was obtained as well as the activation energy.The effects of the vacuum and the thickness of the materials on the rection were examined. Finally, the Flory-huggins model was used to predict the solubility of water in polyphosphate melt. The results showed that the predicted values and the experimental values were close, and it was satisfied to use the model to predict the water content in polyphosphate melt within the reaction temperature.(4) Diammonium phosphate and urea were used to synthesis the different molecular weight and low polymerization degree ammonium polyphosphates. The BP network modeling method was used to predict the number average molecular weight of the products. The network input variables were temperature, residential time and the molar ratio, respectively, and the output variable was the number-average molecular weight. By preprocessing the experiment data and optimizing the network parameters such as the number of nodes in the hidden layer, the number of hidden layers, transfer function and learning rate, this paper built a neural network with first layer nodes of 12 and a second layer of 15. The predicted values were close with the 10 random experimental samples and it verified the feasibility of the network.(5) The crystallization of APP-Ⅱ and APP-Ⅴ as well as crystal transformation between the two crystal forms were studied. Introduction of water resulted in the generation of amorphous APP, and it also promoted the generation of APP-Ⅱ and inhibited the growth of APP-Ⅵ. The crystal transformation of APP-Ⅴ was studied. Effects of the heating time and water content in the reactor were explored. The results showed that APP-Ⅴ underwent complete conversion to crystalline form Ⅱ (APP-Ⅱ) when heated at 200℃. However, the TG analysis showed APP-V had high thermal stability over the range of 300 to 580℃.(6) The industrial scale preparation of high degree of polymerization of APP using phosphorus pentoxide and diammonium hydrogen phosphate from solvent extraction wet process acid was studied in a 1000 L kneader. The effect of phosphorus pentoxide activity on the polymerization reaction was studied, and the results showed that the high activity of phosphorus pentoxide was due to its high degree of crystallinity, which resulted in the better performance for the preparation of high-quality APP. The influence of charge amount, content of melamine, ammonia flow rate, ammonia flow rate in curing stage were investigated. The optimum process parameters were obtained.The process could stablely produce high-quality, low water solubility and high degree of polymerization of ammonium polyphosphate, which built the foundation for the high-quality ammonium polyphosphate industrial production. |
PDF Full Text Request