Study On Catalytic Thermal Decomposition Of Ammonium Sulfate And Ammonium Bicarbonate Mixture

Fluosilicic acid is one of the important byproduct of phosphate fertilizer enterprise, which is focused for its use by researchers. According to the company’s development strategy, the research of technology in the production of hydrofluoric acid from fluoride acid-byproduct of wet process phosphoric acid (WPA) was launched by Yuntianhua International Chemical Co.,. Although the technology can produce high standard anhydrous hydrogen fluoride, but its development is limited, because in the production process for one ton of anhydrous hydrofluoric acid, a byproduct mixture of ammonium sulfate and ammonium bisulfate which cannot be used directly is about 2.2 tons. In recent years, The decomposition of ammonium sulfate and ammonium bisulfate mixture was studied in the case of their market conditions and company’s specific production needs, to provide new ideas and technical support for the company in the new field and create new ways to get more economic benefits.At first, in the study, the factors, like catalyst, reaction temperature, the ratio of starting material, the reaction residence time, the size of the crucible, the particle size of raw material and the reactive atmosphere, were discussed by the single factor test. The results show that the significantly affected factors are catalyst, reaction temperature, the ratio of starting material, the reaction residence time and the reactive atmosphere.Secondly, chromium oxide was selected as the preferred catalyst for the catalytic thermal decomposition of ammonium bisulfate and ammonium sulfate mixture, by thermal decomposition rate test and the orthogonal test. The results showed as follows the preferred operating:reaction temperature is 700℃, the ratio of starting material is 1:1, reaction residence time is 60min, carrier gas flow rate is 5L/min. In the recovery process of chromium oxide was preliminary discussed. The sample was calcined 60min at the temperature of 1000～1100 ℃, then dissoluted, filtrated, washed and dried. The product obtained in the above manner complies with HG/T2775-2010 standards, and no activity changes.Finally, the instrumental analysis methods, such as thermogravimetry (TG), mass spectrometry (MS), fourier transform infrared spectroscopy (FT-IR), X-ray diffraction analyzer (XRD), and chemical analysis are used for the reaction residue and the gaseous products. According to the experimental data and the literatures, the kinetics and mechanism of thermal decomposition for the ammonium sulfate and ammonium bisulfate mixture catalyzed by chromium oxide were studied, the results are as follows:The first stage is the generation of ammonium pyrosulfate, with activation energy (E) is 112.3105 kJ.mol-1, pre-exponential factor (lgA) is 10.3874, the most probable mechanism function is G (α)=-ln (1-α);The second stageis the thermal decomposition of ammonium pyrosulfate catalyzed by chromium oxide, with activation energy (E) is 120.1150kJ.mol-1, pre-exponential factor (lgA) is 7.1508, the most probable mechanism function is G(α)=[1-(1-α)1/3]2;The third stage is the generation of chromium sulfate, with activation energy (E) is 130.3200kJ.mol-1, pre-exponential factor (lgA) is 8.5958, the most probable mechanism function is G(α)=[-ln(l-α)]1/3;The fourth stage is the thermal decomposition of chromium sulfate, with activation energy (E) is 174.1806kJ.mol-1, pre-exponential factor (lgA) is 10.3538, the most probable mechanism function is G(α)=[-ln(l-α)]1/2;...