Effect Of SO₂in Flue Gas On Degradation Of Mea In CO₂Capture

Among the variety of CCS technologies, chemical absorption using an aqueousmonoethanolamine （MEA） is the most widely applied and commercialized one for largestationary sources. The degradation of MEA makes an important contribution to thehigh cost of the system and the composition of the flue gas leads to the complexity ofthe degradation process. The objective of this study is to evaluate the influence of sulfurdioxide （SO₂） to MEA degradation on both oxidative degradation and thermal-oxidativecycle.The oxidative degradation experiments were performed in a rotary-type stainlesssteel semi-batch reactor, using30w.t.%aqueous MEA with0.4CO₂loading at55℃and1.2atm. Theaqueous MEA was degraded with7.5L/min mixed gas （Air/2%CO₂/0-200ppm SO₂） under55oC. Degraded samples were analyzed by ionchromatography （IC） and element analyzer. It suggests that SO₂is a potent inhibitor ofMEA oxidative degradation by scavenging the active oxide in the solution. A turningpoint of SO₂concentration exists at approximately20ppm, which is determined by theO₂percentage, gas flow rate and the mass transfer in the reactor. With SO₂concentration less than20ppm, MEA degradation degree changes evidently with SO₂concentration changes, while the excess part of SO₂makes little difference in inhibitioneffect. The SO₂concentration over the turning point will aggravate the corrosion of theequipment. When the equipment has a good corrosion resistance, the Fe²⁺concentrationin the solution has a linear relationship with SO₂concentration.For the thermal-oxidative degradation cycle,250g MEA was degraded at120oCin an airtight reactor for2weeks, then was mixed with300g fresh MEA for theoxidation. It suggests that MEA thermal degradation productN-（2-hydroxyethyl）ethylenediamine （HEEDA） will be consumed in the oxidativeprocess and MEA oxidative product nitrite will be further oxidized into nitrate with thethermal-oxidative cycle. Besides, MEA total degradation rate will increase with thecycle. SO₂is suggested to have multiple effects during the cycle process.