Effect of amino acid additives in ammonia solution on SO₂ absorption and ammonia escape using bubbling reactor for membrane contactor applications

Controlling the SO₂ emissions is crucial because they result in several environmental problems and affect human health. Several techniques have been proposed for controlling SO₂ emissions. Limestone or lime-based absorbents are widely used for SO₂ removal. However, their low solubility limits their applications. Ammonia solution has attracted attention owing to its higher SO₂ removal efficiency. However, owing to its high volatility, it has the propensity to escape, which can cause secondary environmental pollution. Therefore, we investigated the effect of six amino acid additives to improve the SO₂ absorption performance and inhibit the ammonia escape in aqueous ammonia solution. The surface tension and theoretical breakthrough pressure of the amino acid-containing ammonia solutions was investigated to evaluate their applicability to a membrane contactor process. L-histidine (His) exhibited the best performance. Therefore, the effect of His concentration, inlet SO₂ concentration, and absorption temperature on SO₂ absorption performance was explored. The ¹³C nuclear magnetic resonance (NMR) and ¹H NMR analyses were used to study the SO₂ absorption mechanism. This study provides a strategy for preparing an eco-friendly and highly efficient SO₂ absorbent that can overcome the disadvantage of current ammonia solutions for the removal of low-concentration SO₂ from industrial gas emissions for the membrane contactor process application.