In gas sweetening, MDEA is the default and aminoethoxyethanol wins in only three cases

Your natural gas sweetening unit is at its circulation limit. The rich amine pumps are at capacity, the reboiler has no spare steam, and the inlet gas carries more acid gas than the design case. Someone proposes changing the amine, and the proposal reaches procurement as a price per pound, the least useful number in the decision. The amine sets the circulation rate, stripping heat, corrosion program and degradation chemistry for the life of the charge; the purchase price is the smallest of those costs.

This page sets out what each common treating amine is good at, why MDEA has become the default, and the three cases where aminoethoxyethanol is the better buy. In a request for quotation, name it by its generic, 2-(2-aminoethoxy)ethanol (CAS 929-06-6). The page closes with its purchase specification, including an identity check a total-amine titration cannot make.

What the amine does in the absorber and the stripper

Amine gas sweetening runs a reversible reaction in a loop. In the absorber, a water solution of an alkanolamine meets the sour gas, and the amine, a weak base, takes up hydrogen sulfide and carbon dioxide as dissolved salts. The rich solution flows to the stripper, where reboiler heat reverses the reaction, sends the acid gas overhead and returns lean amine to the absorber.

The amine is a working fluid, not a consumable. After the initial fill, what you buy is makeup: amine lost to vaporization, entrainment, degradation and filter changes. Two properties of each amine drive everything downstream: how fast it reacts with CO2, and how much heat it takes to give the acid gas back.

Why does MDEA let CO2 slip when MEA and aminoethoxyethanol do not?

Hydrogen sulfide reacts with any amine almost instantly, by simple proton transfer. Carbon dioxide behaves differently. A primary amine such as monoethanolamine (MEA) or aminoethoxyethanol, and a secondary amine such as diethanolamine (DEA), carries a hydrogen on the nitrogen and reacts with CO2 directly to form a carbamate. That reaction is fast, so these amines pull CO2 out of the gas alongside the H2S whether your specification needs it removed or not.

Methyldiethanolamine (MDEA) is a tertiary amine with no hydrogen on the nitrogen, so it cannot form a carbamate. CO2 has to dissolve and hydrate to bicarbonate first, and that step is slow. In an absorber with short gas contact time, the H2S is captured and much of the CO2 passes through. The selectivity is kinetic, not thermodynamic: give the gas more trays or more residence time and MDEA will pick up more CO2.

The same chemistry sets the energy bill. Carbamate formation releases more heat than the bicarbonate route, so a primary amine needs more reboiler heat to strip each unit of acid gas it carries. When the CO2 must come out as well, MDEA is run with an activator such as piperazine, which restores fast CO2 uptake while keeping much of the energy advantage. That flexibility is why MDEA and formulated MDEA solvents became the default for new units.

MEA, DEA, MDEA and aminoethoxyethanol side by side

Read the table as constraints, not a ranking: each amine trades reaction speed against stripping heat and corrosion, and the right one is the one whose weakness your unit can live with.

The three cases where aminoethoxyethanol is the better buy

Aminoethoxyethanol is a primary amine with an ether link in the chain. In the absorber it behaves like MEA: fast, non-selective, and it removes CO2 with the H2S. Its advantages are physical and operational, and they decide the purchase in three situations.

The unit is circulation-limited and both acid gases must come out. Aminoethoxyethanol is run at a far higher solution strength than MEA, so each gallon circulated carries more amine and picks up more acid gas. Lower circulation means smaller pumps and exchangers, and less sensible heat spent warming solution in the stripper. For a high acid-gas load that needs CO2 removed as well as H2S, this is the strongest case for aminoethoxyethanol, and it is a capital argument as much as an operating one.

The site is cold or remote. Neat aminoethoxyethanol freezes at -12.5 °C and boils at 221 °C, according to its PubChem record. MEA freezes in an unheated winter store, which turns each drum or tote receipt into a thawing job. Its solutions at operating strength freeze lower still, the root of its cold-climate reputation, though neat stock held below -12.5 °C still needs heat. The 221 °C boiling point sits well above MEA’s, so less amine leaves overhead as vapour, which matters most where makeup shipments are infrequent.

The feed gas carries carbonyl sulfide. COS reacts slowly with tertiary amines, so an MDEA unit removes little of it. Primary amines react with COS, and aminoethoxyethanol does so in a way that can be partly undone. Its degradation product from CO2 and COS is a urea, N,N’-bis(hydroxyethoxyethyl)urea, which a thermal reclaimer converts back to amine. MEA’s degradation products from COS are largely irreversible, which is why MEA is a poor choice for COS-bearing gas.

Outside those three cases, MDEA usually wins. If your pipeline specification tolerates CO2 and you only need the H2S off, an aminoethoxyethanol unit spends steam stripping CO2 you never had to remove.

What should an aminoethoxyethanol purchase specification say?

Start with identity. Aminoethoxyethanol and DEA are isomers: both have the formula C4H11NO2, so both have a molecular weight of 105.14 g/mol, and a total-amine titration cannot tell you which one is in the drum. Density and freezing point can screen a delivery, because DEA is denser and solid or nearly so at room temperature. Ask for CAS 929-06-6 on every certificate of analysis (CoA), with gas chromatography against a reference standard or an infrared spectrum match to confirm identity.

Then put the physical basis of the quote on paper.

The density line matters more than it looks. Quotes arrive per pound, per gallon or per tote, and a gallon of the neat amine weighs slightly more than a gallon of water. Convert every quote to price per pound of active amine before you compare them.

Because the amine is miscible with water, buying it neat and diluting on site with the makeup water quality your licensor specifies saves freight on water, provided storage stays above the -12.5 °C freezing point or is heated. At a cold site where winter storage falls below that, price heated neat storage against a pre-diluted delivery at the licensor’s strength.

Before you buy aminoethoxyethanol neat for on-site dilution, read the hazard statements in the supplier’s current safety data sheet (SDS) and the safety section of its product page; they, not the freezing point alone, set the handling, storage and dilution rules. Request the current SDS with the first quote, check the PubChem safety section against it, and re-check on every revision.

Sizing the makeup order

Makeup is the recurring buy, and it is the line you can measure. Track solution strength by titration and solution inventory by level; the gap between what the unit should hold and what it does hold is your loss rate. Order to that observed rate, with an allowance for reclaimer bottoms in an aminoethoxyethanol unit. Investigate any step change, because a rising loss rate is an operating signal, such as foaming, entrainment or a leaking exchanger, before it is a purchasing one.

The decision itself fits in four lines:

1. H2S must come out and CO2 may stay: MDEA.

2. Both must come out and steam is the limit: activated MDEA.

3. Both must come out and circulation is the limit, the site is cold or remote, or COS is in the feed: aminoethoxyethanol, with a reclaimer in the budget.

4. A small low-pressure unit with cheap steam and no COS: MEA still earns its low price.

Whichever line you land on, compare quotes on cost per unit of acid gas removed at your unit’s loading. Your process engineer can supply that loading; the price per pound is only the input.

Methodology: property values for aminoethoxyethanol come from its PubChem record (CID 13578) and the product catalog record for CAS 929-06-6. Process chemistry is standard gas-treating practice and is stated without figures where no primary source was in hand; hazard information is left to the current SDS.