SOx, Effect on Membrane Properties

The combustion of sulfur-containing fuels, such as coal, results in the production of SO₂ and SO₃, commonly collectively referred to as SOx. The typical coal-fired power station flue gas has SOx concentrations between 1000 and 5000 ppm in their untreated flue gas, dependent on the sulfur content of the coal, of which the main component is SO₂. The contribution of SOx to acid rain has meant that their emissions have been heavily regulated for over 30 years. The similar chemical properties between SOx (in particular SO₂) and CO₂ also correlate into the behavior of SOx in membrane separation processes.

The high molecular weight of SO₂ and SO₃ relative to other components of flue gas means that for Knudsen diffusion-based membranes, the SOx components will remain in the retentate. Similarly, the large kinetic diameters of SO₂ and SO₃, both greater than CO₂, means for molecular sieve based membranes the SOx components of flue gas will leave the membrane module mainly in the retentate...