Removal of hydrogen sulphide and carbon dioxide from a stream of fluid
A process for removing hydrogen sulfide and carbon dioxide from a fluid stream comprises a) an absorption step in which the fluid stream is contacted with an absorbent comprising an aqueous solution (i) of an amine of the general formula (I) in which R 1 , R 2 and R 3 are each independently selected from C 1-4 -alkyl and C 1-4 -hydroxyalkyl; each R 4 is independently selected from hydrogen, C 1-4 -alkyl and C 1-4 -hydroxyalkyl; each R 5 is independently selected from hydrogen, C 1-4 -alkyl and C 1-4 -hydroxyalkyl; X is OH or NH(CR 1 R 2 R 3 ); m is 2, 3, 4 or 5; n is 2, 3, 4 or 5; and o is 0 or 1; and optionally (ii) at least one tertiary amine, where the molar ratio of (i) to (ii) is greater than 0.05; wherein at least 90% of the hydrogen sulfide is removed from the fluid stream and selectivity for hydrogen sulfide over carbon dioxide is not greater than 8, wherein a CO 2 — and H 2 S-laden absorbent is obtained; b) a regeneration step in which at least a substream of the CO 2 — and H 2 S-laden absorbent is regenerated and a regenerated absorbent is obtained; and c) a recycling step in which at least a substream of the regenerated absorbent is recycled into the absorption step a). The process allows a high level of hydrogen sulfide removal with a simultaneously high coabsorption of carbon dioxide.
1. A process for removing hydrogen sulfide and carbon dioxide from a fluid stream, the process comprising
(a) contacting the fluid stream, having a hydrogen sulfide pressure of at least 0.1 bar, a partial carbon dioxide pressure of at least 1 bar, and a total pressure of at least 20 bar, with an absorbent comprising an aqueous solution comprising (i) 2-(2-tert-butylaminoethoxy)ethanol and (ii) methyldiethanolamine, at a molar ratio of (i) to (ii) in a range of from 0.1 to 0.9, to obtain a CO 2 — and H 2 S-laden absorbent and a treated fluid stream, having at least 90% of the hydrogen sulfide removed relative to the fluid stream;
(b) regenerating at least a substream of the CO 2 — and H 2 S-laden absorbent to obtain a regenerated absorbent; and
(c) recycling at least a substream of the regenerated absorbent into the contacting (a),
wherein a selectivity S for hydrogen sulfide over carbon dioxide in the contacting is not greater than 8, calculated as follows:
S
=
y
(
H
2
S
)
feed
-
y
(
H
2
S
)
treat
y
(
H
2
S
)
feed
y
(
CO
2
)
feed
-
y
(
CO
2
)
treat
y
(
CO
2
)
feed
,
in which y(H 2 S) feed is a molar proportion of H 2 S in the fluid stream, y(H 2 S) treat is a molar proportion in the treated fluid stream, y(CO 2 ) feed is a molar proportion of CO 2 in the fluid stream and y(CO 2 ) treat is a molar proportion of CO 2 in the treated fluid stream, and
wherein the selectivity S is less than that of methyldiethanolamine in a process performed under the same conditions.
2. The process of claim 1 , wherein a total concentration of (i) and (ii) in the aqueous solution in the contacting (a) is 10% to 60% by weight.
3. The process of claim 1 , wherein the absorbent in the contacting (a) does not comprise any sterically unhindered primary or secondary amines.
4. The process of claim 1 , wherein the absorbent in the contacting (a) comprises an organic solvent.
5. The process of claim 1 , wherein the fluid stream in the contacting (a) comprises a hydrocarbon.
6. The process of claim 1 , wherein the CO 2 — and H 2 S-laden absorbent is regenerated in the regenerating (b) to an H 2 S loading corresponding to an equilibrium loading for an H 2 S content of less than 90% of a H 2 S content of the treated fluid stream.
7. The process of claim 1 , wherein a cumulated CO 2 and H 2 S loading of the CO 2 — and H 2 S-laden absorbent is at least 0.25 mol/mol and a cumulated CO 2 and H 2 S loading of the regenerated absorbent is less than 0.20 mol/mol.
8. The process of claim 1 , wherein the regenerating (b) comprises heating, decompressing, and/or stripping with an inert fluid.
9. The process of claim 1 , further comprising:
(d) passing at least a substream of the CO 2 — and H 2 S-containing gas stream released in the regenerating (b) into a Claus plant to obtain a Claus tail gas, which is hydrogenated to obtain a hydrogenated Claus tail gas;
(e) treating the hydrogenated Claus tail gas with the regenerated absorbent to obtain a first H 2 S-laden absorbent; and
(f) passing the first H 2 S-laden absorbent into the regenerating (b) and/or into the contacting (a).
10. The process of claim 9 , wherein the treating (e) is effected at a lower pressure than a pressure in the contacting (a).
11. The process of claim 1 , further comprising:
(d′) treating a substream of a CO 2 — and H 2 S-containing gas stream released in the regenerating (b) with the regenerated absorbent to obtain a second H 2 S-laden absorbent; and
(e′) passing the second H 2 S-laden absorbent into the regenerating (b).
12. The process of claim 11 , wherein the substream of the CO 2 — and H 2 S-laden absorbent is passed into the treating (d′).
13. The process of claim 11 , further comprising:
(f′) passing the substream of the CO 2 — and H 2 S-containing gas stream released in the regenerating (b) into a Claus plant to obtain a Claus tail gas, which is hydrogenated to obtain a hydrogenated Claus tail gas;
(g′) treating the hydrogenated Claus tail gas with the regenerated absorbent to obtain a first H 2 S-laden absorbent; and
(h′) passing the first H 2 S-laden absorbent into the regenerating (b) and/or into the contacting (a).
14. The process of claim 13 , wherein the treating (g′) is effected at a lower pressure than a pressure in the contacting (a).
15. The process of claim 1 , further comprising
(i″) recycling and passing into the contacting (a) a substream of the CO 2 — and H 2 S-containing gas stream released in the regenerating (b).
16. The process of claim 1 , wherein the regenerating (b) comprises:
(b1) decompressing the CO 2 — and H 2 S-laden absorbent to obtain a CO 2 — and H 2 S-containing gas stream and a partly regenerated absorbent; and
(b2) heating and/or stripping the partly regenerated absorbent to obtain the regenerated absorbent;
and wherein the process further comprises:
(d″) treating the CO 2 — and H 2 S-containing gas stream with the regenerated absorbent of the regenerating (b) to obtain a third H 2 S-laden absorbent and a CO 2 — enriched gas stream; and
(e″) passing the third H 2 S-laden absorbent into the regenerating (b).
17. The process of claim 16 , further comprising:
(f″) decompressing the CO 2 — and H 2 S-laden absorbent to a pressure between a pressure in the contacting (a) and a pressure in the decompressing (b1), in order to release gas constituents other than carbon dioxide and hydrogen sulfide from the CO 2 — and H 2 S-laden absorbent.
18. The process of claim 1 , wherein the absorbent in the contacting (a) consists of:
(i) the 2-(2-tert-butylaminoethoxy)ethanol;
(ii) the methyldiethanolamine; and
optionally 0.01 to 3 wt. % of one or more additives, based on absorbent weight,
in the aqueous solution optionally with an organic solvent which is sulfolane, ethylene glycol, diethylene glycol, ethylene glycol dimethyl ether, triethylene glycol, triethylene glycol dimethyl ether, di-(C 1-4 -alkyl ether) monoethylene glycol, mono-(C 1-4 -alkyl ether) monoethylene glycols, di-(C 1-4 -alkyl ether) polyethylene glycol, mono-(C 1-4 -alkyl ether) polyethylene glycol, N-methylpyrrolidone, N-methyl-3-morpholine, N-formylmorpholine, N-acetylmorpholine, N,N-dimethylformamide, N,N-dimethylimidazolidin-2-one, N-methylimidazole, or a mixture thereof,
wherein a total concentration of (i) and (ii) in the aqueous solution in the contacting (a) is 20% to 50% by weight.
19. The process of claim 1 , wherein the absorbent does not comprise phosphonic acid, sulfonic acid, or carboxylic acid groups.
20. The process of claim 1 , wherein a total concentration of (i) and (ii) in the aqueous solution in the contacting (a) is 30% to 50% by weight.