NO2 Absorption in Aqueous Solutions with Phenolic Additives : Hydroquinone and 4-Methylaminophenol Sulfate

Abstract

<p>NO₂ absorption has recently gained attention as a promising alternative to conventional NO_<em>x</em> reduction methods. One key challenge in NO₂ absorption is that high amounts of additives are required to maintain satisfactory absorption efficiency. The present study investigates the absorption of NO₂ from flue gases in aqueous solutions with low concentrations of phenolic additives. Absorption tests with hydroquinone and 4-methylaminophenol sulfate were performed in a laboratory-scale absorption system with test gases containing 0 or 5% O₂ (N₂ as a balance gas) and 50, 100, or 150 ppm of NO₂, representing typical flue gas conditions in a range of industrial processes. The results show that NO₂ was absorbed efficiently with small concentrations of 4-methylaminophenol sulfate, both with 0 or 5% O₂ in the test gas. Hydroquinone also enhanced NO₂ absorption but to a lesser degree than 4-methylaminophenol sulfate. Interestingly, the presence of O₂ did not influence the consumption of the phenolic additives, in contrast to commonly used additives such as sulfite that require oxidation inhibitors such as thiosulfate. With a 2 mM solution of 4-methylaminophenol sulfate, more than 90% of the incoming NO₂ was absorbed. Thus, NO₂ absorption with 4-methylaminopheno sulfate appears to be able to remove NO_<em>x</em> emissions from flue gases with high efficiency.<br></p>