(126c) Absorption with Photochemical Oxidation of Sulfur Dioxide in Sulfuric Acid

Absorption of sulfur dioxide in aqueous hydrogen peroxide is a state of the art desulfurization process. Performance of the absorption process is limited by a maximum concentration of sulfuric acid of less than 70 % by weight. Concentration of sulfuric acid above 70 % by weight needs an additional distillation step. In this project extended oxidative absorption of sulfur dioxide has been investigated. The process is based on absorption of SO₂ from highly concentrated off-gas in medium concentrated sulfuric acid and photochemical oxidation in the liquid phase in a first step, followed by absorption of the residual sulfur dioxide from the tail gas with H₂O₂ in a second step. The laden absorption liquor of the second absorption step with a sulfuric acid concentration of less than 70 % by weight is fed to the first desulfurization step. In principle photochemical oxidation of sulfur dioxide in humid carrier gas can be carried out in the gaseous phase. But this process route causes the formation of an aerosol. Oxidation must therefore be followed by precipitation of the aerosol in a wet electrostatic precipitator. Alternatively photochemical oxidation can also be carried out in the liquid phase after absorption of sulfur dioxide. Subject of this project was investigation and modeling of sulfur dioxide absorption in H₂O₂ as well as absorption with photochemical oxidation in sulfuric acid. The experiments were carried out in a film absorption column and in a bubble column which was equipped with a medium pressure Hg-lamp. The maximum concentration of sulfuric acid obtained by this dual step process was 95 % by weight. From the technical point of view applicability of this dual step process has been confirmed in lab scale.