Amine Solvent Selection: MEA, DEA, MDEA, or Blend?

An opinionated decision guide for picking the right amine solvent for acid gas removal. Based on 30+ years of refinery and NG treating experience distilled into a page.

The Short Answer

If you only read one paragraph: pick MDEA if you need H2S selectivity with CO2 slip, pick MDEA + piperazine (PZ) if you need bulk CO2 removal with low reboiler duty, pick DEA or MEA only if you are stuck with an existing unit or ultra-low-pressure service where MDEA kinetics fall apart. Pick DGA or DIPA in niche COS / mercaptan services.

If someone shows up pitching MEA for a new CO2 capture unit in 2026, ask how they're paying the reboiler bill. Unless the contract is already signed, you're better off with a formulated MDEA/PZ blend.

Decision Matrix

Scenario	First Choice	Second Choice	Why
Refinery sour gas scrubbing (H2S + CO2 mixed)	MDEA (activated or formulated)	DEA	MDEA gives H2S selectivity + lower circulation + lower duty
Natural gas pipeline specification (<4 ppmv H2S)	MDEA	DEA	Kinetics sufficient at high pressure; easy lean loading
Bulk CO2 capture (post-combustion, >85% removal)	MDEA + PZ 5-8 wt%	MEA 30 wt%	PZ activator cuts circulation ~15% and duty ~10%
Claus tail gas treating	MDEA (Shell FLEXSORB)	DIPA (Sulfinol-D)	Need H2S selective with very low CO2 pickup to avoid SRU overload
Low-pressure atmospheric service (stoichiometric)	MEA 20 wt%	DGA 50 wt%	Fast kinetics critical at low P; DGA has lower circulation
COS / mercaptan / CS2 in feed	DGA or DIPA (Sulfinol-M)	MEA + primary co-solvent	Physical solvent component helps with heavy sulfur
Revamp — existing DEA plant, higher throughput	Formulated MDEA	MDEA/PZ blend	Drop-in solvent swap, ~20% capacity boost, lower corrosion

Trade-offs by Solvent

MEA (Monoethanolamine) — Primary Amine

The old workhorse. Fast kinetics, cheap, and will absorb anything with a lone pair — but you pay for it in energy, corrosion, and degradation. Reboiler duty runs 1,550 Btu/gal vs ~900 for MDEA. Needs a reclaimer above 250 F. Don't use for new-build unless regulatory or contract requirements force your hand.

DEA (Diethanolamine) — Secondary Amine

Most common refinery solvent through the 1990s. Slight H2S-over-CO2 kinetic selectivity. Lower corrosion than MEA but still requires full metallurgy attention. In 2026, DEA is usually kept because someone bought the piping 20 years ago and the operators know it.

MDEA (Methyldiethanolamine) — Tertiary Amine

The default for new units. Tertiary nitrogen means no direct reaction with CO2 — CO2 must first hydrate to bicarbonate, which is slow. That's a feature: you get natural H2S selectivity and save the duty you'd have spent stripping CO2 that you didn't want to capture in the first place. Low corrosion, tolerates high concentrations (up to 50 wt%), stable under oxidation.

MDEA + Piperazine (PZ)

PZ is a fast-kinetics cyclic diamine. Adding 3-8 wt% to MDEA restores the CO2 absorption rate (bypassing the slow bicarbonate pathway) while keeping MDEA's low regen energy. This is what Shell ADIP-X, BASF activated MDEA, and most post-combustion capture processes use.

DGA (Diglycolamine) — Primary Amine

Fluor's Econamine process. 50-65 wt% concentration, lower circulation than MEA. Better with COS and mercaptans. Degrades to BHEP; vacuum reclaim required. Niche application.

DIPA (Diisopropanolamine) — Secondary Amine

Shell Sulfinol-D uses DIPA + sulfolane + water. Sulfolane is a physical solvent — the blend handles high H2S partial pressures with low CO2 co-absorption, plus picks up COS and mercaptans. Used in SRU tail gas and natural gas when feed has heavy sulfur.

Sizing Heuristics (Quick Screen)

Parameter	MEA 20%	DEA 30%	MDEA 45%	MDEA+PZ 40/5%
Reboiler duty (Btu/gal solvent)	1,550	1,100	900	1,200
Circulation (gal/mol acid gas)	135	113	110	95
Lean loading (mol/mol)	0.10-0.15	0.05-0.10	0.005-0.010	0.02-0.05
Rich loading target (mol/mol)	0.40-0.50	0.35-0.45	0.30-0.40	0.40-0.50
Corrosion risk	High	Medium	Low	Low
H2S/CO2 selectivity	No	Mild	Strong	Moderate

Traps to Avoid

Running MEA above 250 F in reboiler — thermal degradation to oxazolidone and bicine accelerates. Use a reclaimer and keep bulk <240 F.
Oxygen ingress on MDEA — oxidative degradation to bicine is slow but cumulative; put a nitrogen blanket on the storage tank.
Assuming MDEA gives H2S selectivity at low pressure — at low pressure (<50 psig contactor) CO2 kinetics catch up and selectivity degrades. Use DEA or MEA instead.
Forgetting antifoam — heat-stable salts and degradation products foam; keep a metered antifoam injection ready.
Undersizing the reclaimer — heat stable salts above 2 wt% will cause corrosion and foaming; plan reclaimer capacity for 3-5% of lean flow continuous.

References

Kohl, A.L. & Nielsen, R. (1997). Gas Purification, 5th Ed. Gulf Publishing.
GPSA Engineering Data Book 13th Ed., Section 21 — Gas Treating.
Polasek & Bullin (1994). "Selecting amines for sweetening units." GPA Proceedings.
Rochelle, G.T. (2009). "Amine scrubbing for CO2 capture." Science 325, 1652.
API 945 — Avoidance of environmental cracking in amine units.