MEA vs DEA vs TEA: Alkanolamine Selection for Acid Gas Treating

Meta description: A technical comparison of monoethanolamine (MEA), diethanolamine (DEA) and triethanolamine (TEA) for natural-gas and refinery acid-gas treating — reactivity, selectivity, degradation and corrosion.

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Primary keyword: MEA vs DEA vs TEA
Secondary keywords: alkanolamine gas treating, amine selection, acid gas removal

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When engineers specify an amine-treating unit for natural gas, refinery off-gas or flue gas, the first decision is usually which alkanolamine to use. The three workhorses — monoethanolamine (MEA), diethanolamine (DEA) and triethanolamine (TEA) — share the same functional group (an amine + an alcohol) but behave very differently depending on how many hydroxyethyl groups are attached to the nitrogen. This article compares them on the parameters that actually drive plant performance.

Structural Difference in One Picture

Amine	Formula	Hydroxyethyl groups	N-substitution
MEA	HO–CH₂CH₂–NH₂	1	Primary
DEA	(HO–CH₂CH₂)₂NH	2	Secondary
TEA	(HO–CH₂CH₂)₃N	3	Tertiary

Adding hydroxyethyl groups increases molecular weight and boiling point, but decreases alkalinity. MEA is the strongest base of the three; TEA is the weakest.

Comparison Table

Parameter	MEA	DEA	TEA
CAS	141-43-5	111-42-2	102-71-6
MW (g/mol)	61.08	105.14	149.19
pKa (25 °C)	~ 9.5	~ 8.9	~ 7.8
Typical conc. in solution	15–20 wt%	25–30 wt%	20–35 wt%
CO₂ reactivity	Fastest	Moderate	Slow
H₂S selectivity	Low	Moderate	High
Heat of regeneration	Highest	Medium	Lowest
Degradation rate	Highest	Medium	Low
Corrosion rate	Highest	Medium	Lowest

Detailed Differences

1. CO₂ Reactivity and Loading

MEA reacts rapidly with both CO₂ and H₂S because the primary amine forms carbamates readily. This makes MEA the standard solvent for post-combustion CO₂ capture, where high CO₂ removal is the goal. The downside is that MEA's high heat of regeneration (~ 85 kJ/mol CO₂) drives reboiler energy use.

DEA reacts more slowly with CO₂ and cannot form carbamates to the same extent. It is often preferred in refinery applications where H₂S and CO₂ coexist and steam cost matters.

TEA is a tertiary amine. It cannot form carbamates directly with CO₂ (only through base-catalysed hydration), so it is slow to react with CO₂. It is, however, highly selective for H₂S — it reacts instantaneously with H₂S via proton transfer while leaving CO₂ largely untouched. This makes TEA useful for "sweetening" where H₂S must meet spec but CO₂ can slip.

2. Degradation and Corrosion

MEA's high reactivity is a double-edged sword: it degrades faster in the presence of oxygen, SOx and heat-stable salts (formate, acetate, oxalate, chloride). MEA plants need reclaimer systems and corrosion allowances.

DEA degrades more slowly and is less corrosive, but it forms N-nitrosodiethanolamine under certain conditions — a regulatory concern in some jurisdictions.

TEA is the most stable and least corrosive, but its low alkalinity means it is unsuitable for deep CO₂ removal. It is commonly used in lower-pressure systems or as a complement to stronger amines.

3. Operational Trade-offs

• Deep CO₂ removal (e.g. post-combustion capture, LNG feed gas): MEA is still the default.
• Selective H₂S removal (e.g. refinery Claus feed): DEA or tertiary amines (MDEA, TEA) are preferred.
• Low-energy regeneration: Lean, CO₂-slip-allowed processes benefit from DEA or TEA.
• Low steam budget / fouling service: TEA or blended amines (e.g. MDEA + piperazine activator) are common.

Which One Should You Choose?

• Choose MEA when you must hit < 50 ppm CO₂ in treated gas and energy cost is secondary.
• Choose DEA when H₂S and CO₂ are both present and you want a balanced solvent with lower corrosion than MEA.
• Choose TEA when you primarily need H₂S removal, CO₂ slip is acceptable, and corrosion/steam budgets are tight.

In modern plants, pure MEA/DEA/TEA are increasingly replaced by formulated blends (MDEA + piperazine, or sterically hindered amines) that combine the selectivity of tertiary amines with the reactivity of activators. But the three traditional ethanolamines remain the reference point for any amine-treating design.

Closing Thought

For engineers selecting an amine solvent, the question is rarely "which is best" — it is "which best matches our gas composition, treated-gas spec and steam budget". If you are specifying a new unit or evaluating a solvent switch, run a lab slip test on your actual feed gas rather than relying on generic vendor brochures.

*This article is a technical reference, not procurement advice. For sample data sheets or COA for MEA, DEA or TEA, contact the ChinaAmines engineering team through the link below.