Oxidation And Its Inhibition Of SO₂ During Flue Gas Desulfurization By Ionic Liquids

Sulfur dioxide（SO₂）is the main air pollutant in China,which is mainly produced by coal combustion.It will do harm to human beings and nature.Due to the complex composition of coal-fired flue gas,desulfurization side reactions often occur in flue gas desulfurization technologies.The common desulfurization side reaction is the oxidation of SO₂ by O₂ in coal-fired flue gas.The oxidized SO₂ can reduce the absorption and regeneration performance of absorbents.Previous studies have found that ionic liquids,as new absorbents,also have side reactions in the process of flue gas desulfurization.The oxidized SO₂ reduces the SO₂ absorption capacity of ionic liquids,and the regeneration of ionic liquids are difficult.Hence,this paper explored the oxidation laws of SO₂ during desulfurization by ionic liquids,and inhibited the oxidation of SO₂by adding anti-oxidants.The main research contents and results are as follows:（1）Tetramethylguanidine lactate（[TMG][Lac]）,ethanolamine lactate（[MEA][Lac]）and triethanolamine lactate（[TEOA][Lac]）were selected for SO₂ absorption.The influence of O₂ on ionic liquids desulfurization processes were explored.The results showed that O₂ has no effect on the absorption of SO₂ by pure ionic liquids,but oxidized the absorbed SO₂.The oxidation rate of[TMG][Lac]is the highest,and the oxidation rate after one cycle is 6.2%.Because the flue gas also contains water,this paper explored the influence of O₂ on the removal of SO₂ by ionic liquid aqueous solutions.The oxidation degree order of SO₂ in the desulfurization processes of three ionic liquid aqueous solutions is the same as that of pure ionic liquids,which are:[TMG][Lac]>[MEA][Lac]>[TEOA][Lac].NMR results showed that when SO₂ was absorbed under the condition of containing O₂,the structure of pure ionic liquids did not change,but the structure of ionic liquid aqueous solutions changed.The reason is that water changed the absorption mechanism,thus affecting the oxidation mechanism.When the absorption temperature raised and the absorption time raised,the oxidation rate raised immediately.（2）An aqueous solution of[TMG][Lac]ionic liquid with a mass fraction of 50%was selected to absorb SO₂ in simulated flue gas,and the effect of added anti-oxidants on the oxidation of SO₂ during the desulfurization process was investigated.It was found that the addition of anti-oxidants could inhibit the oxidation of SO₂.Ethylene glycol was selected as an anti-oxidant for ionic liquids desulfurization process.When the amount of ethylene glycol increased,the oxidation rate of SO₂ decreased.The inhibition of ethylene glycol on SO₂oxidation decreased with the increase of absorption temperature and absorption time.Infrared spectrum showed that the hydroxyl group on ethylene glycol molecule was the reason for inhibiting SO₂ oxidation.