In the following table, the first, second and third types of amines are compared in terms of commonly used concentrations and adsorption capacity of acid gases:
|
Amine name |
Molecular Weight |
Normal concentration (weight percentage) |
Acid adsorption capacity (IB MOL / T) |
|
Monoethanolamine |
61 |
15-20 |
2.53 |
|
Diethanolamine |
105 |
25-35 |
2.52 |
|
Methyl diethanolamine |
119 |
35-50 |
4.16 |
Also, the first and second type amines react directly and rapidly with hydrogen sulfide and carbon dioxide. The third type of amine reacts directly and rapidly with hydrogen sulfide, but reacts slowly with carbon dioxide in two steps. Therefore, by limiting the contact time of amines and acid gases, hydrogen sulfide can be selectively separated.
Properties of monoethanolamine
|
Advantages |
Disadvantages |
|
High reactivity |
Wasted up due to evaporation |
|
low price |
High energy required for regeneration |
|
Possibility of separation of carbonyl sulfide and carbon disulfide |
Impossibility of selective separation of hydrogen sulfide in the presence of carbon dioxide |
Properties of Diethanolamine
|
Advantages |
Disadvantages |
|
Less reactivity compared to monoethanolamine |
High chemical stability |
|
Impossibility of selective separation of hydrogen sulfide in the presence of carbon dioxide |
Low wastage due to evaporation |
|
higher price |
Less energy needed for regeneration |
|
Lower adsorption capacity of acidic gases resulting in higher circulating flow rate (compared to monoethanolamine) |
No decomposition and decomposition in the presence of carbonyl sulfide and carbon disulfide |
Properties of methyl diethanolamine
|
Advantages |
Disadvantages |
|
Selective separation ability |
High price compared to other amines |
|
Hydrogen sulfide in the presence of carbon dioxide |
Low reaction speed with carbon dioxide and lower adsorption capacity |
|
Low energy required for reduction compared to other amines |
——— |
|
Low corrosion compared to other amines |
——— |
|
Low evaporation loss |
———- |
|
High stability |
———- |
Amines based on methyl diethanolamine
As mentioned above, methyl diethanolamine, for all its important advantages, has one major drawback, which is its low rate of reaction with carbon dioxide and consequently the low rate of carbon dioxide uptake by this solvent. To solve this problem and take advantage of this solvent, in recent years the use of solvents or amines based on methyl diethanolamine (MDEA-based Amines) including formulated amines and mixed amines has been expanded. Has found. These amines are added to methyl diethanolamine, an activator, or an amine of the first or second type.
Mixtures of amines
In mixtures of amines, a type II amine (diethanolamine) or a type 1 amine (monoethanolamine) is added to methyldiethanolamine, thus preserving the benefits of methyl diethanolamine, the rate and extent of carbon dioxide uptake. Increased by this solvent. In fact, in a mixture of amines, by combining the advantages of both amines in the mixture, ie the high adsorption capacity of acidic gases by methyl diethanolamine and the high rate of reaction of the first or second type amines with acidic gases, both the rate and rate of acidic adsorption (especially di (Carbon monoxide) increases and the amount of energy required to reduce the solvent is significantly reduced. In addition these solvents have the ability to selectively separate hydrogen sulfide in the presence of carbon dioxide in a very desirable way. Also less corrosion and less solvent flow rate are other advantages of using amine mixtures. These factors have led to the use of amine mixtures, especially during the last decade, a significant expansion in the global gas industry.
