Study On The Process Of Degradation Of Food Grade Phosphoric Acid By Dehydration Of Wet - Process Phosphoric Acid

Phosphoric acid as the key intermediates in the process of phosphorus chemical industry production,is one of the main raw material for the production of phosphate fertilizer.With the development of phosphorus chemical industry refinement,various levels of phosphate market demand continues to increase,in recent years,there has been some of China’s phosphorus chemical industry defect,such as overcapacity,low product quality,single structure,the degree of precision is also not enough,the international market less competitive.In order to achieve sustainable development of phosphorus chemical industry,wet phosphoric acid purification technology has become the hotspot and focus of scientific research.Yuntianhua three circle branch produced by wet process phosphoric acid are also have problem such as many impurities and low content of P2O5.Currently three circle branch has worked with SichuanUniversity,which mainly use the pretreatment,solvent extraction(tributyl phosphate),washing and stripping obtained refined phosphoric acid,in addition to the fluorine,other indexes can reach the food grade quality standards.Firstly,this paper selects the single factor experiment which used diluted lye washing extracted acid organic phase defluorination,through experiments it was concluded that the optimum conditions are as follows:dilute alkali concentration was 20%,dilute alkali dosage was 1.4%,dilute lye washing temperature was 45℃.Then orthogonal and validation experiment was carried out,it was found that the optimal operating conditions were as follows:dilute alkali concentration was 20%,dilute alkali dosage was 1.4%,dilute lye washing temperature was 45℃,defluorination rate was 67.75%,organic phase P2O5 yield was 95.50%. After stripping by distilled water fluorine contend in the phosphoric acid decreased to 272ppm.This suggest that single dilute alkali washing defluorination effect can’t reach the standard of food grade phosphoric acid.Then carried out vacuum concentration defluorination experiment to the refined phosphate.Through the single factor experiment obtains the optimal conditions as follows:concentration time was 120min,optimized addition was 200% of the theoretical amount of fluorine in phosphoric,concentrated temperature was 85℃.Then orthogonal and validation experiment was carried out5the test results show that the optimum process conditions is concentration time was 120min,the optimized diatomite addition was 200% of the theoretical amount of fluorine in phosphoricconcentration temperature was 90 "C,fluorine rate reached 66.72%,fluorine content decreased to approximately 160ppm,concentrated acid phosphorus concentration up to 67.53%.This show that single vacuum concentration defluorination experiment effect can’t reach the standard of food grade phosphoric acid.So choice the nitrogen stripping deep defluorination experiment,the test results show that the optimized process conditions are as follows:the stripping time was 120min,the optimized diatomite addition was 200% of the theoretical amount of fluorine in phosphoric,the stripping temperature was 90℃,nitrogen flow was appropriate for 0.5-0.6L/min,stirring speed was 300r/min.In the above analysis of the optimal single factor condition,high fluorine removal rate can reach above 85%,the fluorine content was reduced to approximately 110ppm,concentrated acid phosphorus concentration was about 70%.This show that the nitrogen stripping deep defluorination experiment effect also can’t reach the standard of food grade phosphoric acid.Through the above test data,using a single method to removing fluorine,although can achieve a certain defluorination effect,raw acid containing a variety of impurities such as iron, aluminum, magnesium, sulfate and other ions,these impurity ions can affect the existence form of fluoride in phosphate,diversify the the existence form of fluoride in phosphate,so it is difficult to design effective experiment method to remove fluorine,as a result defluorination effect is difficult to achieve food grade standards.In view of this, finally design the three methods above are integrated, the preliminary test results showed that fluorine content can be reduced to about lOppm, the mass concentration of phosphorus in phosphate after stripping can reached to 72%. The integrated technology can effectively remove fluoride in extracting phosphoric acid, and provides a new train of thought of deep defluorination to achieve food grade phosphoric acid standard.This study is not only beneficial to widen the Yuntianhua industrial phosphoric aicd production utilization way,improve the enterprise’s own economic benefits and market competitive power,fully realized the competitive use,it can also provide some technical support for phosphorus fine chemical products and professional development.