Amines are formed when hydrogen atoms of ammonia (NH3) are swapped with one or more hydrocarbon groups. The more hydrogen swapped out, the less reactive the resulting amine will be. Numerous types of amines are made and used specifically for treating natural gas, which contains relatively weak acid gases like hydrogen sulfide (H2S) and carbon dioxide (CO2) when extracted. Those gases can adversely affect processing equipment (corrosion and stress cracking) if not removed. As such, amines are placed in an aqueous solution ranging from 10 to 65 percent amine by weight, depending on the intended application. (The amine methyl diethanolamine [MDEA] is good at bulk removal of CO2 and selective H2S removal but isn’t optimal for carbon disulfide (CS2) removal, for example.)
Amine solutions are typically used in the gas treatment process via a scrubbing device sometimes referred to as an absorber. The lean amine solution is introduced at the top of the absorber tower and flows down. Natural gas is introduced and rises up the column. As the gas makes contact with the solution, acid gases in the natural gas stream are weakly dissolved, with the amines assisting in making those gases more soluble in the solution. That they’re weakly dissolved is advantageous to processors because the rich solution can then be passed through a secondary tower and heated. The weakly dissolved H2S and CO2 readily escapes upon being heated and can be captured, while the amine solution can then be regenerated for reuse.
Primary manufacturers of natural gas treatment amines include U.S.-based Dow Chemical Company and Switzerland-based INEOS. Both companies have worked to produce acid-gas-removing solvents for a wide variety of scenarios. Dow, for example, announced in 2011 the release of a special amine blend — UCARSOL Shale H-100 — for processing natural gas from Haynesville Shale plays, offering more efficiency and reduced corrosion rates. And INEOS’ GAS/SPEC TG-10 is designed to realize near 99.9% sulfur conversion from tail gas treatments.