Amine-Treated LPG is an intermediate refinery LPG stream that has undergone acid gas removal via amine treating (also known as gas sweetening in the H₂S-removal sense), but which has not yet passed through caustic sweetening (e.g., Merox). It represents the first purification step in the LPG treatment sequence, positioned between raw straight-run or cracked LPG and the fully sweetened/refined product.
Treatment process:
The raw LPG is contacted in a liquid-liquid amine contactor (typically using MDEA, DEA, or DGA solutions), where the amine selectively absorbs hydrogen sulfide (H₂S) and carbon dioxide (CO₂) from the liquefied hydrocarbon phase. The rich amine is regenerated in a separate stripping column, and the recovered acid gases are routed to the sulfur recovery unit (Claus) or, in integrated complexes such as the proposed Prayagraj configuration, to sulfuric acid production.
Characteristics:
- H₂S content: Reduced to very low levels, typically < 10 ppm (often < 5 ppm), eliminating toxicity and the primary corrosion hazard.
- Mercaptans (RSH): Still present — standard amine treating does not remove mercaptans (MDEA is largely non-reactive toward them; DEA removes only a minor fraction). Consequently, the stream will typically still fail the copper strip corrosion test and the doctor test, and retains the characteristic mercaptan odor.
- CO₂: Substantially removed, which matters for downstream processing (e.g., preventing dry ice formation in cryogenic sections or caustic consumption in Merox).
- Moisture: May carry some water from the aqueous amine contact, requiring drying later if destined for petrochemical feedstock use.
Position in the value chain:
Amine-treated LPG is not a finished product. It is typically routed onward to caustic/ Merox sweetening for mercaptan removal, followed by water washing and drying to produce sweetened or refined LPG. In some configurations, amine-treated LPG from cracking units may alternatively be sent directly to olefin recovery units (propylene splitters) or hydrotreating, where sulfur removal occurs as part of the catalytic processing step.
Distinction: Unlike sweetened or refined LPG, amine-treated LPG is defined by the partial completion of the treating sequence — acid-gas-free but not yet mercaptan-free — and is therefore generally restricted to internal refinery processing rather than sale or use in corrosion-sensitive service.
