Mass Transfer And Reaction Process Of Sulfuryl Fluoride Removal By Chemical Absorption Using Sodium Hydroxide Solution

Along with the phasing out of methyl bromide as the traditional fumigant,sulfuryl fluoride(SO₂F₂)has been widely used as the alternative to methyl bromide in various fields,owing to its excellent characteristics in fumigation.Meantime,its greenhouse effect and toxictity have been gradually recognized and become the focus of attention.However,SO₂F₂ after fumigation is directly emitted into the atmosphere at present.Therefore,it is increasingly important to find a reasonable way to remove SO₂F₂after fumigation effectively.According to the fact that SO₂F₂ can be hydrolyzed in alkaline aqueous solution,SO₂F₂removal by chemical absorption was developed in this paper.Firstly,fundermental research including the solubility of SO₂F₂ in water,mass transfer-reaction kinetics of SO₂F₂ absorption with aqueous Na OH solution was conducted.Secondly,lab-scale tests were performed in a packed column for absorption of SO₂F₂ by aqueous Na OH solution,and a method for harmless treatment of SO₂F₂ by chemical absoption was developed.Thirdly,overall volumetric mass transfer coeffecient K_Ga was investigated in the packed column and zigzag high-gravity rotating beds.The data of K_Ga obtained would provide foundermental data for industrial applications.Finally,large-scale tests were performed in a custom packed column for recyclic treatment of simulated exhaust SO₂F₂ gas.The main conclusions presented in this thesis are as follows:a)The solubilities of SO₂F₂ in water at 10-35?and 0-600 k Pa were measured using the isochoric saturation method.According to the solubility data of SO₂F₂ obtained,the solubilities of SO₂F₂ in water at 10-35?and atmospheric pressure were determined.Meanwhile,the Henry's law constants E_x(E_m)at 10-35?were acquired.From the correlation between Henry's law constants E_x and temperature T,the standard Gibbs free energy change,enthalpy change and entropy change of SO₂F₂ dissolution in water were calculated.b)According to the two-film theory,the mass transfer and reaction kinetic zone of SO₂F₂absorption with aqueous Na OH solution was determined to be fast pseudo-first-order reaction zone using a double-stirred cell at 25?and atmospheric pressure.The average second-order reaction rate constant k₂ between Na OH and SO₂F₂ was determined to be 1.258×10³ m³/(kmol·s)at 25?.Moreover,a mathematical model between enhancement factor and Na OH concentration was obtained.c)The lab-scale tests of absorption of simulated exhaust SO₂F₂ gas by aqueous Na OH solution were performed in a random raschig ring column with the diameter of 100 mm.Results showed that the harmless treatment of simulated exhaust SO₂F₂ gas was achieved by chemical absorption using Na OH solution(the volume concentration of SO₂F₂ was lower than 5 ppm).Moreover,the removal efficiency of SO₂F₂ increased from 75.5%to 96.1%when the Na OH concentration increased from 0.11 to 0.95 mol/L.And the removal efficiency of SO₂F₂ increased from 94.1%to 96.0%when the liquid spray density increased from 9.55 to 22.31 m³/(m²·h).However,the removal efficiency of SO₂F₂ decreased from 99.9%to 89.5%when the gas flow rate increased from 0.12 to 0.48 m³/h.The inlet SO₂F₂ volume concentration had almost no influence on the removal efficiency of SO₂F₂.According to the two-film theory,a mathematical model based on Onda correlation was developed to describe the removal efficiency of SO₂F₂.Comparison between the calculated and experimental data proved that the predictability of the proposed model was within the maximum deviation of 8.0%.Aqueous Na OH solution after absorption was analyzed by ion chromatography.It was found that the SO₂F₂was mainly converted to Na F,Na SO₃F and a little Na₂SO₄.The Na OH solution after absorption was acidified by hydrochloric acid and then heated,followed by addition of Ca Cl₂ and Ca O mixture,and hence the harmless treatment of absorption liquid was achieved.Finally,a method of harmless treatment of SO₂F₂ by chemical absoption was obtained.d)At 25?and atmospheric pressure,the overall volumetric mass transfer coefficients K_Ga of three different kinds of packings were investigated in a packed column with the diameter of 100 mm.Packings included stainless steel corrugated plate packing with punctures(700Y),raschig ring packing(12×12×2 mm)and stainless steel wire mesh packing(700Y).The effects of liquid spray density,gas flow rate,concentration of Na OH solution,temperature of absorption,and inlet SO₂F₂ volume concentration on overall volumetric mass transfer coefficient K_Ga were investigated.Results showed that the overall volumetric mass transfer coefficients K_Ga of the three different packings increased with the increase in liquid spray density,gas flow rate,concentration of Na OH solution,and absorption temperature.Moreover,the inlet SO₂F₂ volume concentration had almost no influence on the K_Ga of the three packings.Under the experimental conditions,mass transfer performance of stainless steel corrugated plate packing with punctures was better than that of raschig ring packing which was then better than that of stainless steel wire mesh packing.Furthermore,the overall volumetric mass transfer coefficient K_Ga in zigzag rotating bed BZ750-III was determined.The effects of liquid spray density and gas flow rate on K_Ga were investigated with the rotating speed of the rotating bed of800 r/min.Results showed that the overall volumetric mass transfer coefficient K_Ga increased with the increase of the liquid spray density and the gas flow rate,and the K_Ga of zigzag rotating bed was 5-10 times that of the packed column.e)The large-scale tests of recyclic treatment of simulated exhaust SO₂F₂ gas were performed in a custom packed column with the volume of 13 m³.Results showed that at 25?and atmospheric pressure,for the container with the volume of 13 m³ and SO₂F₂ volume concentration of 4500 ppm(SO₂F₂ addition rate of 18.8 g/m³),the time needed for recyclic treatment and volume concentration reduction of simulated exhaust SO₂F₂ gas in the container to be lower than 5 ppm were 40 min and 30 min when the gas flow rate were 230 m³/h and 450m³/h,respectively.According to continuous stirred tank reactor model,a mathematic model was developed to predict the SO₂F₂ volume concentration in the container during the recyclic treatment of simulated exhaust SO₂F₂ gas.The reliability of model was validated by experimental results.Furthermore,model analysis for recyclic treatment of simulated exhaust SO₂F₂ gas was performed.Results showed that the suitable gas flow rate was in the range of400-600 m³/h.Parallel connection was recommended when more than one absorption apparatus was used to treat exhaust SO₂F₂ gas.The increase in overall volumetric mass transfer coefficient K_Ga favored the removal of simulated exhaust SO₂F₂ gas.Therefore,process intensification equipment could be used to improve the recyclic treatment of simulated exhaust SO₂F₂ gas.