Development of a compact MnO2 filter for removal of SO2 from diesel vehicle emissions

Abstract

Increasing concern about sulfur dioxide (SO₂) from diesel vehicle exhausts causing detrimental effects on NO_x removal catalysts has resulted in the development of dry desulfurization filters for complete removal of SO₂. In this study, a compact MnO₂ filter was developed for diesel emission control. The SO₂-capture behavior of the compact MnO₂ filter was investigated by using a volumetric device in a low temperature range (200–400 °C) and low SO₂ pressure conditions. The maximal capacity of the MnO₂ filter was 304.1 mg_SO2 per g_MnO2 at 400 °C. Based on the experimental results, the required volume of the MnO₂ filter was estimated as only 0.6 L for a diesel car with 30 000 km distance traveled per year. The thickness of the MnO₂ filter had significant influence on its SO₂-capture performance. The sulfate reaction mechanism was also discussed by using a grain model under four reaction temperature conditions for improving the efficiency of the design of the desulfurization filter. The sulfate process can be divided into two control stages (the chemical reaction control stage and the solid diffusion control stage) and the prediction models fit the experimental data well for both control stages, indicating that the two-stage grain model is suitable for the sulfate reaction between the MnO₂ filter and SO₂. The calculated apparent activation energy of 18.8 kJ mol⁻¹ indicates that the MnO₂ filter exhibits high activity for SO₂ adsorption in a pure SO₂ atmosphere.