Investigation of degradation inhibitors on CO2 capture process

In this study we have used sodium sulfite (Na2SO3), potassium sodium tartrate tetrahydrate (KNaC4H4O6⋅4H2O), ethylenediaminetetraacetic acid (EDTA), and hydroxylamine (NH2OH) to effectively inhibit O2-SO2 induced degradation of amines such as monoethanolamine (MEA) during CO2 capture from flue gases (i.e. the degradation systems of MEA-O2-SO2-H2O-CO2). The ranges of experimental conditions were such as to duplicate the extremes normally encountered in a typical CO2 capture process in a coal fired power plant. MEA concentration, O2 concentration, SO2 concentration, CO2 concentration and degradation temperature were respectively in the range of 3–7 kmol/m3, 6–100%, 0–196 ppm, 0–0.52 loading, and 393 K. There were optimum concentrations of these inhibitors that best prevented the degradation; namely, 0.05, 0.01, 0.0025, and 0.025 kmol/m3 respectively for Na2SO3, NaKC4H4O6⋅4H2O, EDTA, and NH2OH. Outside these concentrations the inhibitors were not very effective. The blend of Na2SO3-KNaC4H4O6⋅4H2O was the most effective inhibitor either in the absence or presence of CO2. Based on the evaluation of the inhibition mechanisms, Na2SO3 works as an O2 and SO2 scavenger, while KNaC4H4O6⋅4H2O, EDTA, and NH2OH function as radical scavengers. It was also observed that CO2 alone works on the basis of the salting out effect whereby CO2 goes into the aqueous amine solution in preference to O2 and SO2.