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.
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, mercury, and hydrogen cyanide usually found in these gases.
In the Rectisol process (licensed by both Linde AG and Air Liquide), 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 Rectisol process can operate selectively to recover hydrogen sulfide and carbon dioxide as separate streams, so that the hydrogen sulfide can be sent to either a Claus unit for conversion to elemental sulfur or a WSA Process unit to recover sulfuric acid, while at the same time the carbon dioxide can be sequestered (CCS) or used for enhanced oil recovery.
It is very suitable to complex schemes where a combination of products are needed, such as for example hydrogen, carbon monoxide, ammonia and methanol synthesis gases and fuel gas side streams.