The mechanism of ultrasonic desorption of sulfur dioxide from citrate solution was investigated mathematically based on the characteristics of ultrasonic wave.The factors influencing ultrasonic desorption of sulfur dioxide were discussed theoretically and the mechanism was verified by experiments.The results showed that it was feasible to remove sulfur dioxide from citrate solution with ultrasonic field in theory and on the laboratory scale.There was a greater effect of ultrasonic frequency and gas content in solution as well as solution properties on sulfur dioxide desorption.The sulfur dioxide desorption efficiency could be improved rapidly by introducing cavitation bubble nucleus,such as adding trace argon gas.A lower ultrasonic frequency might result in higher desorption efficiency.Giving a proper stirring to the solution,the SO2 desorption efficiency enhancement could be increased by 20%—30% over the control value.The higher the initial concentration of sulfur dioxide in citrate,the higher the desorption efficiency.
A new flue gas desulphurization (FGD) technology was developed to absorb SO2 by using citrate solution as absorbing agent, with hollow fiber membrane and ultrasonic enhancement.Ultrasonic treatment and membrane technology were introduced into the process of FGD.Ultrasonic cavitation and its enhancement of the mass transfer process were discussed.By using the self-designed reactor,the effects of ultrasonic treatment on the stability of citrate solution and hollow fiber membrane for FGD were studied.The results showed that under the condition of frequency 20 kHz, citrate concentration 0.5 mol·L-1 and pH 4.5, the absorption of sulfur dioxide from flue gas in the hollow fiber membrane module could be enhanced by ultrasonic treatment, but the solution could be heated up,which caused inhibition of absorption.In the process of ultrasonic treatment,citrate solution and hollow fiber membrane remained stable.
Using a sonochemical reactor designed by the authors,the process of removing sulfur dioxide from cit- rate solution simulating the flue gas desulfurization was studied.The influence of ultrasonic frequency,ultrasonic power,reaction temperature,stirring speed,inert gases,initial concentration of sulfur dioxide and concentration of citrate on the efficiency of sulfur dioxide desorption,the stability of citrate solution and the concentration of sulfate radical was examined systematically.By comparing the desorption of sulfur dioxide with and without ultrasonifica- tion,it was concluded that(1)lower ultrasonic frequency results in a better degassing efficiency;(2)the use of ul- trasonification in desorbing sulfur dioxide from citrate solution improves the desorbing efficiency in some condi- tions,without changing the essence of chemical reactions;(3)sparging inert gas into the liquid can lower the vis- cosity of solution and the cavitating threshold,and raise the desorption efficiency.These results demonstrate a technical way for deep desorption of sulfur dioxide and provide the fundamental data for future industrial disposal of sulfur dioxide.
