Process for increased selectivity and capacity for hydrogen sulfide capture from acid gases
A process for selectively separating H 2 S from a gas mixture which also comprises CO 2 is disclosed. A stream of the gas mixture is contacted with an absorbent solution comprising one or more amines, alkanolamines, hindered alkanolamines, capped alkanolamines, or mixtures thereof. The H 2 S/CO 2 selectivity of the absorbent solution is preferably greater than about 4.0 for an acid gas loading [mol(CO 2 +H 2 S)/mol(amine)] between about 0.2 and about 0.6, and is achieved by reducing pH of the absorbent solution.
1. A method for increasing the selectivity of an absorption process for H 2 S absorption from a gas mixture which also comprises CO 2 , the absorption process having an absorbent solution comprising one or more sterically hindered alkanolamines selected from methoxyethoxyethoxyethanol-t-butylamine (M3ETB) and ethoxyethanol-t-butylamine (EETB), the method comprising reducing the pH of the absorbent solution;
wherein the pH reducing step comprises adding an acid to the absorbent solution;
wherein the H 2 S/CO 2 selectivity of the absorbent solution is greater than about 5.0 for the acid gas loading [mol(CO 2 +H 2 S)/mol(amine)] range between about 0.2 and about 0.55.
2. The method of claim 1 , wherein the pH reducing step further comprises diluting the absorbent solution.
3. The method of claim 2 , wherein the diluted absorbent solution is less than 36 wt %.
4. The method of claim 2 , wherein the diluted absorbent solution is less than 30 wt %.
5. The method of claim 1 , wherein the acid is selected from phosphoric acid and sulfuric acid.
6. The method of claim 1 , wherein the H 2 S/CO 2 selectivity of the absorbent solution is greater than about 6.0 for the entire acid gas loading [mol(CO 2 +H 2 S)/mol(amine)] range between about 0.2 and about 0.55.
7. The method of claim 1 , wherein the H 2 S/CO 2 selectivity of the absorbent solution is greater than about 7.0 for the entire acid gas loading [mol(CO 2 +H 2 S)/mol(amine)] range between about 0.2 and about 0.55.
8. A method for increasing the selectivity of hydrogen sulfide (H 2 S) separation from a gas mixture comprising H 2 S and carbon dioxide (CO 2 ), the method comprising:
providing an absorbent solution comprising one or more sterically hindered alkanolamines, wherein the one or more sterically hindered alkanolamines is selected from methoxyethoxyethoxyethanol-t-butylamine (M3ETB) and ethoxyethanol-t-butylamine (EETB), and wherein the absorbent solution has a pH;
contacting the gas mixture with the absorbent solution;
reducing the pH of the absorbent solution by adding an acid to the absorbent solution to provide an H 2 S/CO 2 selectivity of the absorbent solution greater than about 5.0 for an acid gas loading [mol(CO 2 +H 2 S)/mol(amine)] range between about 0.2 and about 0.55.