Study On The Process Of Urea-sulfuric Acid Decomposing Potassium Chloride

As the decrease of cultivated area and the increase of population, fertilizer isbecoming the effective measure to increase the production of crops, so that it canmeet the requirement of human for more agricultural products. At present, a largeamount of application of high concentration compound fertilizer, it causes soil hardenand salinization, crop malnutrition, decline in quality, vulnerable to disease invasion,and high-yield crops are becoming easy lodging. Preparation of S-based compoundfertilizer by urea-sulfuric acid decomposing potassium chloride（USK compoundfertilizer for short）is a kind of concentration and multi-nutrients compound fertilizer.Besides containing NPK, it contains calcium, magnesium, sulfur, iron, zinc,manganese and other medium and trace nutrient elements, and it can promote thebalanced fertilization.The process of USK compound fertilizer uses urea sulfuric acid to decomposepotassium chloride, through the ratio of urea sulfuric acid to control the conversionrate of potassium chloride. The fertilizer contains both potassium chloride andpotassium sulfate, which can meet the variety of nutrition needs of crop. At the sametime, by the late dosing and process adjustment, can meet the requirement of S-basedcompound fertilizers. It can be expected to solve the problem of traditional lownitrogen content of S-based compound fertilizer and the problem of by-producthydrochloric acid generation. In this paper, the process of the urea sulfuric aciddecomposing potassium chloride was researched systemically.The process of sulfuric acid decomposing potassium chloride of the S-basedcompound fertilizer was experimental researched systematically. By single factorexperiment, the ratio of sulfate and potassium chloride, reaction temperature andreaction time on the influence of the potassium chloride conversion rate wereresearched. The optimum conditions of this experimental are the ratio of sulfuric acidand potassium chloride is1.4:1, the reaction time is40min, and the reaction temperature is130℃. In this optimal condition, the conversion rate of potassiumchloride is83%.On the basis of this process condition, the process of urea sulfuric aciddecomposing of potassium chloride was experimental researched. By single factorexperiment and orthogonal experiment, the proportion of the urea sulfate andpotassium chloride, reaction temperature, reaction time and particle size of potassiumchloride to potassium chloride conversion rate and the influence of the biuret contentwere mainly researched. The optimum conditions for this experimental were obtained:the ratio of urea, sulfuric acid potassium chloride is0.5:1.4:1, the reaction time is40min, the reaction temperature is145℃, and particle size of potassium is0.18mm.In this optimal condition, the conversion rate of potassium chloride is78%, the biuretcontent is0.122%. Biuret content of USK product increases with the increase ofdrying time and drying temperature.In this article，the performance of S-based product and USK product wererespectively characterized by Fourier infrared （FTIR） and XRD, and comparativestudy was carried out. From infrared spectroscopy, it can be seen that it only existsabsorption peak of hydrogen sulfate root in the S-based product. Beside theabsorption peak of hydrogen sulfate root, the absorption peak of C=O groups, C-Nbond and N-H bond are showed in the infrared spectroscopy of USK product,indicating that it may contain urea. XRD diffraction patterns show that compositionsof S-based sample are potassium hydrogen sulfate and potassium chloride,compositions of USK product are mainly potassium hydrogen sulfate and chloride,urea may exist in a new material form or masked by other material’s peak, biuretcontent is extremely low, don’t show in the XRD diffraction patterns.This article tries to study the reaction principle of the process of urea sulfuricacid decomposing potassium chloride. Crystalline forms of urea, potassium chloride,potassium hydrogen sulfate, mixing of urea and potassium chloride, mixing of ureaand potassium hydrogen sulfate, potassium sulfate were investigated by photographicmicroscope. What’s more, mixing of urea and potassium hydrogen sulfate ischaracterized by XRD. The result shows that urea was not exist in the form ofcomplex CO（NH2）2·KCl and CO（NH2）2·KHSO4. In the laboratory conditions, using the secondary absorption device to study the amount of hydrogen chloride gasescapes of the process of S-based compound fertilizer and USK compound fertilizer.The result show that the amount of hydrogen chloride gas escapes of process of USKcompound fertilizer is18.3%less than the amount of S-based compound fertilizer,and the subsequent processing of by-product hydrochloric acid are proposed.The thermal decomposition kinetics of USK product was studied in this paper.The USK product was analyzed by thermogravimetry （TG） at four heating rates. Themechanism of reaction mechanism was determined to be accordance with23functionAvrami-Erofeev equation, of which integral and differential form is G（α）=[ln（1α）]4and f（α）=（1/4）（1α）[ln（1α）]3. Thermal decomposition of the average activationenergy E of USK product is39.53KJ·mol-1and pre-exponial factor lgA is3.53. Theequation of thermal decomposition kinetics is listed as follow:dα/dt=847.1/βe^4754.6/T（1-α）[ln（1-α）]^-3...