Study On The Preparation Of Industrial Urea Phosphate With Wet Phosphoric Acid

The application of urea phosphate has gradually developed from being mainly used as animal husbandry feed additive,agricultural high efficiency nitrogen,phosphorus compound fertilizer to other fields.It has gradually developed into other fields,with broad market prospects.Urea phosphate in China is mainly produced by thermal phosphoric acid.However,the price of hot process phosphoric acid is too high,low output,unable to meet market demand.To use low-priced wet process phosphoric acid and industrial urea as raw materials is the direction of development and research of urea phosphate product in the future to develop the technological process of producing urea phosphate from wet phosphoric acid.In this thesis,the process of preparing industrial urea phosphate by wet phosphoric acid was studied.The main contents of this thesis are as follows:（1）Purification of wet process phosphoric acid.The purification of wet phosphoric acid was carried out.The influence of impurity ions such as Fe³⁺,Mg²⁺,Al³⁺,Ga²⁺,SO₄^2-,F^-on the yield of urea phosphonate was studied,and the optimum conditions for impurity of sodium dodecyl benzene sulphonate and phthalic acid as impurity remover were studied.（2）The preparation of industrial urea phosphate by wet phosphoric acid was studied.The effects of the molar ratio of urea to phosphoric acid,reaction time,reaction temperature,crystallization time and crystallization mode on the yield and grade of the product were studied.（3）Recycling of mother liquor.Effect of different dosage and cycle times on product yield and quality were investigated.It was found that the increase of cations reduced the yield of urea phosphate.The presence of SO₄^2-inhibited the production of urea phosphate crystals.However,with the increase of the content of SiF₆^2-ions,the yield of the product increased slightly.In order to increase the yield of the product and improve the purity of the product,the content of impurity in wet process phosphoric acid should be reduced as far as possible.The optimal conditions for the purification of wet-process phosphoric acid using sodium dodecyl benzene sulphonate was 0.8 times the theoretical value,the reaction time was 50 minutes,and the stirring strength was 400 rpm.Under this condition,the purification rate of iron ions was 54.23%,the purification rate of aluminum ions was 41.42%,the purification rate of magnesium ions was 38.37%,the purification rate of calcium ions was 36.62%,and the purification rate of fluoride ions was 47.01%.And purification of wet-process phosphoric acid using phthalic acid was1.5 times the theoretical value,the reaction was 40 minutes,and the stirring intensity was 500 rpm.In this process,the purification rate of iron ion was 68.94%,the purification rate of aluminum ion was 55.18%,the purification rate of magnesium ion was 53.02%,and the purification rate of calcium ion was 46.9%.Considering comprehensively,choosing phthalic acid to purify wet-process phosphoric acid is more reasonable and effective.The optimum technological process for the preparation of industrial urea phosphonate by wet process phosphoric acid are as follows:using phthalic acid as the impurity remover to purify the wet process phosphoric acid,molar ratio of urea to purified phosphoric acid was 1:0.95,reaction for 60 min at 80℃,and crystallization for 60 min by vacuum filtration and crystallization.The yield of the product reached80.2%,and the indexes met the requirements of GB/T 27805-2011 industrial urea phosphate.Without affecting the content of P₂0₅ and the content of N in the product,the maximum ratio of mother liquor to wet phosphoric acid was 2:23（mass ratio）,product yield reached 71.3%.The maximum ratio of the second mother liquor to wet phosphoric acid was 1:19（mass ratio）,and the product yield reached 72.5%.The maximum ratio of the third mother liquor to wet phosphoric acid was 1:99（mass ratio）,and the product yield reached 76.5%.However,the product prepared by mixing4th times of mother liquor which is excessively high in impurity content with wet phosphoric acid at a certain mass ratio could not meet the standard of industrial urea phosphate.Therefore,the number of cycles in whichthe mother liquor is added to the wet-process phosphoric acid to prepare urea phosphate should be controlled within three times.