The Study And Process Design For Preparation Of High Purity Silicon Dioxide And Ammonium Bifluoride Without Water

High purity silicon dioxide (high purity silica) is used in electronics industry for itsinsulation. Ammonium bifluoride is widely utilized in surface treatment for aluminiumproduct and glass carving. The process of preparation of carbon-white co-generatingammonium bifluoride is applicated in several manufacturers. However, the ammoniumbifluoride from this process is more susceptible to moisture deliquescence andcarbon-white with low added value can not be widely used. Therefore, it is significant todevelop a process to generate high purity silicon dioxide and ammonium bifluoride.Ammonification of fluosilicic acid to get high purity silica is studied first in this text.The influences of various factors on the reaction is explored through single factor andorthogonal experiments. It is clearly to get that the ratio of ammonia and fluosilicic acid isthe most important factor to the yield; reaction temperature is the most important factor tothe purity, stirring speed and the dropping rate of ammonia come second, the optimumcondition of the reaction is: the molar ratio of ammonia and fluosilicic acid is18:1, theyield gets98.4%, reaction temperature is40℃, dropping rate of ammonia is6mL/min,stirring speed is500rpm, the aging time is2.0hours. The purity of this product is beyondto99%under this condition.Ammonium bifluoride is obtained throngh thermolysis or acidulation of ammoniumfluoride which can get from the filtrate of ammonification reaction. By comparing the twokinds of methods, it can be get that thermolysis of ammonium fluoride gives low-contentproduct, low usage of raw material, high energy consumption, however, acidulation ofammonium fluoride shows low energy consumption, high-content product that meets theindexs of the national superior product. The best condition of the reaction is: theconcentration of ammonium fluoride is30%, the pH value of the ending of solution is3.The purity of this product is beyond to98%, and the yield gets95%. The final product isget through crystallization by cooling or flaking. The product get through flaking showslow-deliquescence and good chemical stability. It can also achieve the national superiorproduct the standard after3months preservation.The process design of2000t/a high purity silica co-generating ammonium bifluoridetakes place after the experiment. Following the finalise of process flow, material balancefor the total flow and energy balance for representative equipment are completed. The listof the equipments is getted after type-choosing for standard equipments and process calculation for non-standard equipments. This paper gives the control scheme for typicalequipment in unit operations of chemical engineering, and the design for pipe. On thebasis of above, the piping and instrumentation diagram(P&ID) is accomplished. Workshopequipment layoutment and piping for the process equipments are present after P&ID.Finally, this paper gives simple general layout of the total factory.