Study On SO₂ Desorption From Aqueous High-Efficiency Organic Amine Solutions

The flue gas desulfurization（FGD）with organic amine has the advantages of highdesulfurization efficiency,low corrosivity,and no secondary pollution,etc.,which has attracted full attention.First,the effects of four kinds of desorption methods on desorption were studied,including the static desorption process with water supplement,the dynamic continuous desorption process,the dynamic semi-continuous desorption process,and the dynamic semi-continuous desorption process with water supplement.The results indicate that the static desorption process with water supplement is stable and has a high desorption efficiency.The dynamic continuous desorption process runs stably,but it requires high regeneration energy.During the operation of the dynamic semi-continuous desorption,the amine concentration continues to increase,and the process is non-stationary.The dynamic semi-continuous desorption with water supplement is not as stable as the static desorption with water replenishment,and the regeneration energy is also higher.Then,the desulfurization performances of piperazine-based organic amines were studied experimentally by the dynamic absorption of SO₂from the simulated flue gas in a packed column.The solvent was regenerated by the static with water supplement,and the regeneration energy of the organic amine was analyzed.The evaluation was done for five kinds of organic amines,including piperazine（PZ）and its derivatives1-（2-hydroxyethyl）piperazine（HEP）,N,N′-bis（2-hydroxyethyl）piperazine（BHEP）,N,N′-bis（hydroxypropyl）piperazine（HPP）,1-（2-hydroxyethyl）-4-（2-hydroxypropyl）piperazine（HEHPP）.The p K_a values of piperazine organic amines were determined at 50℃by potentiometric titration,and the sterically hindered energy was calculated by Chem Bio 3D 19.0 software.The results of the four times absorption-desorption cycles indicate that the desulfurization performances of organic amines are depended on its alkaline strength and steric effects.The sterically hindered energy of BHEP,HPP,HEHPP,HEP,PZ is 14.3 kcal·mol^-1,16.1 kcal·mol^-1,15.1 kcal·mol^-1,8.2kcal·mol^-1,2.0 kcal·mol^-1,and the alkaline strength sequence of the organic amines is PZ>HEP>HPP>HEHPP>BHEP.The p K_a of PZ is the largest and has the highest absorption capacity of 0.8428mol·mol^-1 to SO₂ for the first time.However,it is not easy to desorption with the first desorption efficiency of 78.9%and requires the highest regeneration energy.The saturated absorption capacity decreased by 54.3%after four cycles,and the cyclic absorption performance is the worst.The absorption efficiency of HEP is inferior to that of PZ,but desorption performance is improved.The bis-substituted piperazine diamines with lower p K_a have relatively low the saturated absorption capacities and high desorption efficiencies.After the four cycles,the average absorption capacities are not less than 0.4 mol·mol^-1,and the average desorption rates are above 95%.Meanwhile,they have the lowest regeneration energy.The desulfurization performances of HEHPP are between those of BHEP and HPP.Finally,the desorption properties of two kinds of the blended amines of HPP-HEP and HEHPP-HEP were studied.For the HPP-HEP blended amines,the higher content of HEP,the greater absorption capacity,and the longer breakthrough time.The desorption efficiency of the blended amines and the regeneration energy declined slightly.Among them,the blended solution with the mass ratio of HPP to HEP equals9:1 shows better desulfurization performance.The desorption performance of HEHPP-HEP blended amines was studied at the same SO₂ loading of 0.5 mol·mol^-1.The results showed that with the increase of HEP,the desorption efficiency and rate of the blended amines both decrease,and the regeneration energy increases proportionally.