Desulfurization processes to limit SO₂ emissions

   Current awareness of the effects of environmental pollution has been instrumental in the development of desulfurization processes; this includes desulfurization of fossil fuels and flue gases from a variety of sources. The aim in a flue gas desulfurization process, for example, is to optimize the removal of SO₂ from emissions into the atmosphere. One important method of desulfurization in commercial operation throughout the world is based upon the neutralization reactions between Ca(OH)₂ or CaCO₃ and sulfuric acid. Flue gases containing SO₂ are passed through absorbers containing slaked lime or limestone. The reactions occurring are:

An advantage of the system is that CaSO₄.2H₂O, gypsum, is non-toxic and is not a waste product; it has a number of commercial applications, for example in the production of plaster of Paris and cement. In an alternative desulfurization process, NH₃ replaces Ca(OH)₂ or CaCO₃ and the final sulfur-containing product is [NH₄]₂[SO₄]. Again, the sulfur is removed in the form of a commercially desirable chemical, since [NH₄]₂[SO₄] has applications as a fertilizer.