Study On Thermal Decomposition Behavior Of Ammonium Sulfate

Alumina is an important industrial material in our country.Due to the lack of bauxite resources,about 50%of bauxite needs to be imported.Our country is a large coal-consuming country,and therefore the fly ash produced by coal-fired power plants in northern Shanxi and the central and western regions of Inner Mongolia contains a large amount of aluminum,which is a high-value secondary resource.Currently,there are many researches on the process of extracting alumina from high-alumina fly ash,among which the leaching method of ammonium hydrogen sulfate solution boasts the most industrialized prospect.This paper takes the ammonium hydrogen sulfate solution leaching fly ash to extract alumina as the research background.The circulation of materials and thermal decomposition process of ammonium sulfate were studied with the purpose of making ammonium sulfate decompose to form a certain concentration of ammonium bisulfate solution and ammonia,which was returned to the leaching process for recycling.The main research contents and conclusions were as follows:（1）The instrumental analysis methods,such as thermogravimetry（TG）,fourier transform infrared spectroscopy（FT-IR）,X-ray diffraction analyzer（XRD）and mass spectrometry（MS）were used for the reaction residue and the gaseous products and the decomposition process of ammonium sulfate was obtained as follows:246°C-328°C:（NH₄）₂SO₄=NH₄HSO₄+NH₃（g）328°C-346°C:2NH₄HSO₄=（NH₄）₂S₂O₇+H₂O（g）346°C-430°C:3（NH₄）₂S₂O₇=2NH₃（g）+2N₂（g）+6SO₂（g）+9H₂O（g）（2）The thermal analysis kinetics of ammonium sulfate was studied by thermogravimetric data.The results showed that the activation energy of the first stage reaction was 125.218KJ·mol^-1,the pre-exponential factor was 18.36,and the most probable mechanism function was G（α）=(1-(1-α^1/3)²;the activation energy of the second stage reaction was 110.214 KJ·mol^-1,the pre-exponential factor was 13.94,and the most probable mechanism function was G（α）=（-ln（1-α））^1/4;at the third stage,the reaction activation energy was 97.7062 KJ·mol^-1,the pre-exponential factor was 8.44,and the most probable mechanism function was G（α）=α^1/2.（3）The effects of different temperatures,different reaction times,and different material layer thicknesses on the decomposition rate of ammonium sulfate were investigated through single factor experiments,and the macro kinetics of ammonium sulfate at different decomposition stages were calculated.The results were demonstrated as follows:The first kinetic equation was 1-（1-α）^1/3=5.24×10⁸exp（-1222036/（RT））t;The second kinetic equation was 1-2α/3-（1-α）^2/3=1.79×10⁵exp（-88287/（RT））t;The third kinetic equation was 1-（1-α）^1/3)^1/2=7.0087×10⁴exp（-93347.9/（RT））t.（4）Aspen plus simulation software was used to optimize the decomposition cycle process of ammonium sulfate.Under the condition of ammonium sulfate flow rate of 10000 kg·h^-1,the optimal decomposition temperature and decomposition pressure of ammonium sulfate were300°C and 1.0 bar respectively.In addition,the optimum temperature of water absorption in ammonia absorption tower was 15°C,and the optimum water consumption was 1000 kmol·h^-1;as a consequence,the ammonia absorption tower was demonstrated to be a one-stage packed tower that has a height of 12 m,a diameter of 1.5 m,and the number of trays 25.