The Study Of Industrial Preparation Process Of Low Water Solubility Ammonium Polyphosphate(form Ⅱ)

Ammonium polyphosphate is a halogen-free flame retardant with the characteristics of low hygroscopicity and high thermal stability, it contains both phosphorus and nitrogen, and was thought to be effective flame retardant. II-APP is mainly produced by P2O5-DAP or P2O5-DAP-Urea process at present. In terms of this process, the degree of industrialization is not high, and the quality-controlling factors remain to be groping. In this paper, preparation technology of Ⅱ-APP was investigated trough pilot plant experiments. The contents and results are as follows:(1) Ⅱ-APP was synthesized by using DAP and P2O5with the existence of NH3in100L reactor. The factors such as reaction temperature, ammonia flow that influence crystal form and property of APP were investigated. It was found that the quality of APP had not much to do with the activity value of P2O5, and ammonia flow is the key factor that influences the crystal form of APP. The optimum conditions were obtained and showed as follows:DAP and P2O5with molar ratio1:1were mixed in reactor and then heated to To+75℃, keeping this temperature for15min. And then ammonia with the flow of2.5m3/h was passed into the reactor. When the solidification was finished, the ammonia flow was reduced to2.0m3/h, keeping this flow for90min at250～270℃. In the end, Ⅱ-APP with good quality was prepared.(2) According to the optimum conditions of pilot scale test, repeated experiments were carried out, and the synthesized products was characterized by XRD and FTIR, their properties such as water solubility and thermal stability were tested. And the results shows that the products all reached the standard.(3) Based on the previous experiments in100L reactor, industrial experiments was operated in1000L reactor, Ⅱ-APP was prepared.(4) The degree of polymerization of the synthesized product and merchant product was characterized by31P-NMR, their properties such as water solubility and thermal stability were tested. And based on these information, it was considered that it is more practical to choose water solubility, thermal stability and pH as the criterion instead of the degree of the polymerization to evaluate the quality of Ⅱ-APP.The mainly operating parameters were investigated in both the pilot plant and the industrial device. These technological parameters will be saved for the industrial production of Ⅱ-APP.