Acid gases, such as hydrogen sulphide and carbon dioxide, must be removed from natural gas through amine gas treatment to prevent pipeline damage and toxicity. Sweetening with ethanolamine is a common method.
The term acid gas covers any type of gas or gaseous mixture which forms an acidic compound when mixed with water. The most common types of acid gases are hydrogen sulphide (H2S) and carbon dioxide (CO2). Acid gases are found in natural gas and must be removed through a process known as amine gas treatment before the natural gas is usable. While the terms sour gas and sour gas are often used incorrectly to describe sour gases, the terms are not the same thing. An acidic gas contains high amounts of hydrogen sulfide, while a true acidic gas contains any of the acidic gases.
When found in natural gas, hydrogen sulfide can be considered both a sour gas and a sour gas. Carbon dioxide, however, is an acidic gas but not technically an acidic gas. Gases must remove these acidic materials before being used. This is achieved using the amine gas treatment process, called softening. The process takes certain liquids and uses them to remove harmful hydrogen sulfide and carbon dioxide, or other combination of acidic gases, from natural gas.
Sweetening causes the hydrogen sulphide and carbon dioxide to separate from the natural gas. This is crucial because, being acidic gas types, these two substances will become acidic when they come into contact with water. Any building that runs a pipeline will have problems with these acid gases if it is not removed. The acid will begin to eat through the pipes and cause leaks. The presence of these gases also limits the types of materials that can be used when installing gas lines.
To sweeten natural gas using the amine gas treatment process, an ethanolamine is added. Ethanolamine is a solvent that scrubs or scavenges acid gases; it absorbs carbon dioxide and hydrogen sulphide but leaves the other gases intact. There are several types of the organic compound ethanolamine. Common compounds used in the sweetening process include monoethanolamine (MEA) and methyldiethanolamine (MDEA).
Aside from the risk of damaging the pipeline, hydrogen sulphide is highly toxic and dangerous, even fatal, to animals or people exposed to it. It is also flammable and produces a foul odor, hence the name “acid gas”. Carbon dioxide is not an acidic gas and, unlike hydrogen sulphide, is an odorless gas.
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