Sulfur dioxide removal from industrial exhaust

One way to control gaseous pollutants like SO2 and SO3 is to remove the gases from fuel exhaust systems by absorption into a liquid solution or by adsorption onto a solid material. Absorption involves dissolving the gas in a liquid while adsorption is a surface phenomenon. In each case, a subsequent chemical reaction can occur to further trap the pollutant. Lime and limestone are two solid materials that effectively attract sulfur dioxide gas to their surfaces. The ensuing chemical reaction converts the gaseous pollutant to a solid nontoxic substance that can be collected and disposed or used in another industry. 

Calcium hydroxide, Ca(OH)2, often called slaked lime, is widely used in industry because it is inexpensive and plentiful. For example, slaked lime is used in scrubbing stack gases to remove sulfur dioxide from the exhaust of power plants and factories. In the scrubbing process a suspension of slaked lime is sprayed into the stack gases to react with sulfur dioxide gas according to the following equations ... 

For fuel applications, a popular SBO derivative is methyl soyate (SBO methyl ester, also known as Soy Gold) (J). This biodiesel has several advantages over diesel fuel from petroleum sources because it is biodegradable, has a high flash combustion temperature, contains negligible amount of sulfur, is neutral with respect to carbon dioxide emission, and can potentially reduce many harmful exhaust emissions. Methyl soyate is also an increasingly useful industrial solvent for grease removal. 

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