Rectisol

Rectisol is the trade name for an acid gas removal process that uses methanol as a solvent to separate acid gases such as hydrogen sulfide and carbon dioxide from valuable feed gas streams. By doing so, the feed gas is made more suitable for combustion and/or further processing. Rectisol is used most often to treat synthesis gas (primarily hydrogen and carbon monoxide) produced by gasification of coal or heavy hydrocarbons, as the methanol solvent is well able to remove trace contaminants such as ammonia usually found in these gases.

Process description
In the Rectisol process (licensed by Lurgi AG), cold methanol at approximately –40 °F (–40 °C) dissolves (absorbs) the acid gases from the feed gas at relatively high pressure, usually 400 to 1000 psia (2.76 to 6.89 MPa). The rich solvent containing the acid gases is then let down in pressure and/or steam stripped to release and recover the acid gases. The Rectisol process can operate selectively to recover hydrogen sulfide and carbon dioxide as separate streams, so that the hydrogen sulfide can be sent to a Claus unit for conversion to elemental sulfur, while at the same time the carbon dioxide can be sequestered or used for enhanced oil recovery.

Rectisol, like Selexol, is a physical solvent, unlike amine based acid gas removal solvents that rely on a chemical reaction with the acid gases. While the methanol solvent is inexpensive compared to the proprietary Selexol solvent, the Rectisol process is relatively complex and requires costly refrigeration to maintain the low temperatures required.