CA1149136A

CA1149136A - Method for removing carbonyl sulfide in gas treating processes

Info

Publication number: CA1149136A
Application number: CA000349517A
Authority: CA
Inventors: Mark Mackles
Original assignee: Ralph M Parsons Co
Current assignee: Parsons Government Services Inc
Priority date: 1979-04-27
Filing date: 1980-04-10
Publication date: 1983-07-05
Also published as: ZA802436B; JPS565120A; DE3015739A1

Abstract

Abstract Gas streams containing carbonyl sulfide are contacted with an aqueous alkanolamine hydrolysis medium flowing through a closed-loop hydrolysis zone at a temperature sufficient to hydrolyze, in the presence of water, carbonyl sulfide to hydrogen sulfide and carbon dioxide. The aqueous alkaline hydrolysis medium is in equilibrium with hydrogen sulfide and carbon dioxide. As a consequence, the formed hydrogen sulfide and carbon dioxide pass through the closed-loop hydrolysis zone and at least the hydrogen sulfide is extracted from the gas stream by contact with a second acid gas lean absorbent. The gas stream may be pre-treated to remove hydrogen sulfide, carbon dioxide, or both.

Description

3Çi ~3209 -1-5ULFID~ IN GAS TREATING PROCESSES

~ackground of the Invention . The present invention relates to a vapor liquid absorption process for the treatment of gas stxeams such as natural gas streams, and particularly to the treatment 20 of such gas streams ~or elimination of caxbonyl sulfide by its conversion to hydrogen sulfide and removal at least o~
the formed hydrogen sulfide.
In ~he processing of natural gas ~treams and the like for the removal of the acid gases hydrogen sulfide and 25 carbon dioxide, alone or.in combination, a wide variety of absorbents can be used. Typically in such processe~, the gas stream is passed countercuxrent to the liquid flow of the absorbent in an absorption tower such that the gas stream rich in the impurity to be removed is initially contacted 30 with nearly or partially spent absorbent; while as the gas progresses through the absorption tower~ it meets an increasingly lean absorbent having a greater absorptive potential for the impurity, As a consequence/ a high degree of ex~rao~iGn of a gaseous constituent can be realized. -35 The spent absorbent from the base vf ~he absoxption toweris no~mally passed to regenerakion ox stripping facilities ~ 3 l for removing the absorbed acid gases to enable re~ycling of the absorbent to the system. A~sorbents may be lost by entrainment in the gas stream during regene~ation practices; by virtue of irreversible reactions with some of the constituents and by normal degradation.
A particularly difficult to remove sulfur compound is carhonyl sulfide and is an undesirable constituent ln most gas streams containing it, including natural gas streams.
io In U.S. Patent 3,961,015 to Dailey, there is described a continuous process for txea~ing natural gas containing carbonyl sulfide, carbon dioxide and hydrogen sulfideO
The process comprises the step of contacting the gas stream in countercurrent flow with an aqueous ethanol-15 amine solution as an absorbent for carbon dioxide - and hydrogen sulfide in a first absorbtion zone at a net temperature at which the capacity o the absorbent for hydrogen sulfide and carbon dioxide per unit volume is high. The gas stream is passed from the 20 first absorbent zone to a second absorption-reaction zone where it is brought into countercurrent contact with an aqueous ethanolamine solution maintained at a higher temperature and at a temperature at which carbonyl sulf ide will hydrolyze in the presence of water 25 present or provided by the gas stream to hydrogen ~ulfide and carbon dioxide. Reaction occurs with some absorption of the formed hydrogen sulfide and carbon dioxide.
The gas stream is then passed to a third absorptiQn 30 zone where it is placed in countercurrent contact with a cooled, lean aqueous ethanolamine solution for absorption of the residual formed hydrogen sulfide and carbon dioxide either present in the initlal gas feed or formed in the absorption-reaction zoneO
3~ The solutions from the third absorption zone and the .

1320g -3 1 second absorptlon~reaction zone are then combined to become the absorptlon solution in the irst absorption zone.
. The practice of the invention requires the ùse of a 5 single absorption medium, albeit at different temperatures, capable of not only absorbing the undesired original constituents but also the reaction products of one or more of the original constituents.
Another limitation in the practice of U.S~ Patent 10 No. 3,961!015 is the limitation on the quantity and temperature of the hot absorption reactive medium that can be used in the second stage. If the temperature i~
too high or the volume too great, the first-stage absorption medium is less effective in its capacity to 15remove the acid gases, increasing thereby the total requirement of the circulating ab~orption medium.
- There is a need, therefore, ~or a process ln which a hot intermediate reaction absorption mPdium does not affect ~he overall operating capacity ~or the sys~em~
20increase circulation rates and tower sizesO

Summary of the Invention The present invention pertains to improvements in vapor-liquid absorption systems for treatment of gas streams 25containing carbonyl sulfide. ~he improvement resides in providing a closed-loop hydrolysîs system containing an aqueous alkanolamine hydrolysIs medium prior to a stage of absorption or between stages o~ absorption in which the gas stream containing carbonyl sulfide is ~ed and where 30hydrolysis of carbonyl sulfide into absorbable constituent~
occurs, and from which the gas stream sweeps the products of the hydrolysis into an absorption stage where absorption occurs.
More particularlyp the present invention provides a 3scon~inuous process or purifying gas streams contai~ing ., ~g~36 1 carbonyl sulfide and as acid gas constituents, hydrogen sulfide or mixtures of hydxogen sulfide and carbon dioxide.
As an essential step of the prscess,.the gas stream 5 to be treated is passed ~hrough a circulating closed-loop hydrolysis zone containing an aqueous alkanolamine hydrolysis medium capable of accepting and promoting thermal hydrolysis of car~onyl sulfide maintained at a temperature sufficient to hydrolyze substantially all o~
the carbonyl sulfide to form a resultant gas stream containing the formed hydrogen sulfide and carbon dioxide.
~ he resultant gas stream is then passed ~rom the hydrolysis 20ne to an absoprtion zone containing an absorbent for and which is lean with respect to at least hydrogen sulfide where the foxmed hydrogen sulfide alone or with carbon dioxide is removed from the gas ~tream.
As a first step in the process~ the gas stream may be passed through a first absorptio~ zone containing an absorbent for at-least hydrogen sulfide, preferably in zocountercurrent flow to the absorbent, to extract substantially all of the hydrogen sulfide presen~ in the gas stream t~ leave a gas stream substantially free of hydrogen sulfide but still containin~ carbonyl sulfide.
Carbon dioxide~ if present, may, depending on ~he a~sorbent 25U5ed, be extracted with the hydrogen sulfide. If this step is employed; the absorbent of the absorption zone following hydrolysis is preferably the same as the first and passed from the second absorption ~one to the first absorption zone. The spent absorbent from the 30process is normally stripped of the acid gases and recycled back to the processO

~ 9~

13209 _~_ Drawings ~ IG. 1, illustrates a simplified apparatu~ which may be used to carry out the practice of the invention~
FIG. 2, is a modifica~ion of FIG. l, illustrating a 5 system for heating the gas ~tream prior to ~ntroduction to the hydrolysis zone and for cooling the gas stream containing the products of reaction before it enters the second absorption zone.

, . ' , . ~, ' . ' ' ' .
. , ' " ' ' s l36 1 etailed Description According to the present invention, there is provided a continuous proces 5 for treating of gas streams wherein one constituent, in the present instance carbonyl sulfide~
then passed through an essentially closed-loop hydrolysis zone containing an aqueous alkanolamine hydrolysis medium for promoting hydrolysis of carbonyl sulfide and maintained at a temperature sufficient to cause hydrolysis of carbonyl sulfide into the readily absor~able constituents, hydrogen 10 sulfide and carbon dioxide, which are swapt from the hydrolysis zone by gas ~low into a following absorption zone where the products of the hydrolysis reaction, namely hydrogen sulfide and carbon dioxide~ may be readily removed from the gas stream.
An essential step of the process of the invention i5 to employ in the closed-loop hydrolysis zone an "aqueous alkanolamine hydrolysis medium" which means an aqueous alkanolamine composition in equilibrium wi~h carbon dioxide nd hydrogen sulfide, the products of hydrolysis, and 20 which will take up by some mechanism carbonyl sulfide and promote its hydrolysis to hydrogen sulfide and carbon dioxide at the ~emperlture employed during its residence in the medium. Also essential is that the medium be contained in a sepa~ate closed-loop reaction zone and not 25 intermixed with the absorbents used in the following absorption zone and, if used, a preceding absorption æone.
In operation, the products of hydrolysis are cantinuously removed from the aqueous alkanolamine hydrolysis medium such that the capacity of the medium to promote hydrolysis 30 will not be lost, nor will the medium ~e irreversibly consumed. Although not`required, the medium can ~e the same absorbent as that employed in other absorp~ion zones used in the processO
The presently contemplated aqueous alkanolamine 35 hydrolysis medium includes ethanolamine solutions such a5 ~9~6 13209 ~7~
1 solutions of monoethanolamine, diethanolamine, methyldi-ethanolamine, propanolamine, diisopropanolamine and the like~ -The absorbents employed have a limited capacity for carbonyl sulfide and provide the alkaline conditions essential to promote its hydrolysis. This condition may require pxomotion with a base or the like. Typically, the alkanolamines can comprise from 1% to about 50% by weight of the aqueous alkanolamine hydrolysis medium.
The ethanolamines are preferred.
An ethanolamine which may be used directly is an aqueous solution of diethanolamine, preferably one containing from about 10% to a~out 30% by welght diethanolamine. If monoethanol~mine is employe~, it i5 intrc~uced with an alkali metal hydroxide or salt such as sodium hydroxide, 15 potassium hydroxide, sodium carbonate, potassium carbonate and the like, which revert to the carbonate or bicarbonate state to inhibit or pr~vent irreversible reaction between the carbonyl sulfide and the monoethanolamine. A typical solution is an aqueous solution containing from about ~0 10% to abou~ 20% by weight monoethanol~nine and from about

2% to about 5% by weight OL an alkali metal hy~roxide or alkali metal salt, or their mixtures, reported as the alkali metal hydroxide, the balance being water.
It is presently preferred that the aqueous alkanolamine 25 hydrolyis medium be at a pH from about 8 to about 12 maintained at a temperature from about 150F to about 300F, preferably rrom about 150F to about 280Fo The absorption solutions employed for extraction of the acid gases in the absorption towers may be the same or 30 different than the aqueous aklanolam~ne hydrolysis m~dium. , 1 ~he~ may have the capacity to absorb hydrogen sulfide and carbon dioxide or be selective to the absorption of hydrogen sulfide. Selective absorbents include Selexol, a mixture of dimethyl ethers of propylene glycol, diisopropano~amine; methyl diethanolamine and the like.
The absorbents are normally employed at ambient temperature to maximize their absorpti~e capacity.
While the gas stream to undergo treatment may ~e fed directly to a hydrolysis reactor containing the aqueous i0 alkanolamine hydrolysis medium, more typically as illustrated in FIGS. 1 and 2, the ~as stream is pre- .
processed to remove free hydrogen sulfide alone or with carbon dioxide if present.
With reference now to FIG. 1 in the process of the 15 invention, the gas stream to undergo treatment may pass by line 10 to the base of absorption tower 12~ then by line 14 j~
to the closed-loop hydrolysis system containing in hydrolysis reactor 16 the aqueous alkanolamine absorption .
medium, and then following hydrolysis of carbonyl sulfide, 20 by line 18 to the second absorption tower 20. Lean absorbent enters the second absorption tower by line 22, collects at its base 24, and passes ~y liq~lid seal ~6 to absorption tower 1?, and is removed by line 28 as spent absorbent for regeneration. The treated gas leaves by 25 line 30.
If absorption tower 12 is eliminated the fe~d gas passes directly to hydrolysis reactor 16 and the spent solution from absorption tower 20 is regenerated for recycle~
If desired, separate absorbents may be employed in 30 towers 12 and 20 necessitating separate regeneration facilities with the eliminatîon of flow communication between the towers.

, .

1320~ _g_ 1 As an alternate embodiment, only a portion of the lean absorbent may be fed to tower 20, with the balance ~o tower 12.
The instant invention will be described in greater 5 detail in terms of the treatment of gas streams, such as natural gas streams, containing readily removable acid gas constituents such as hydrogen sulfide and carbo-n dioxide and the more difficult to remove the sulfur species, carbonyl sulfide.
I0 With reference to FIGS. 1 and 2, the feed gas, such as natural gas, is fed to the base of absorption tower 12 countercurrent ~o the flow of an absorbent liquid there-through. Absorption tower 12 as well as absorption tower 20, are vessels containing trays or packing and stagewise 15 contact is made by the countercurre~t flow of gas and absorbent. Lean, or relatively lean absorbent enters at the top of each ~tower, absorbs one or both of the acid gas components from the gas stream as lt flows downward through the trays or packing, and spent absorbent leaves 20 by line 28 to a regeneration, reactivation, flashing or stripping section (not shown) where the acid gases are removed and the lean absorbent retu-.ned for service by its addition in line 2~ to upper absorption tower 2~ Where vessels contain packing, the packing is frequen~ly divided 25 into two or more beds of packing to reduce mechanical loads which would tend to crush the packing at the bo~tom of ~he tower as well as provide for redistribution o th~ absorbent 10wing downward, which in tall packed sections, may have a tendency to flow in channels rath~r than egually dLstributed 30 across the cross~section of the packed towerO
In the practice of the invention, the gas flowing upward to absorption tower 12, is deple~ed of the bulk o~ ~he acid gases which are absorbable ln the absorbent used. Massive absorption of ~he absorbable acid gas cons~ituen~s origin-35 ally prcsen~ in the gas prior to allowing the ga~ to ~ ~ ~9~ 3 132~9 10-1 enter the hydrolysis reaction zone 16 is required to permit more complete hydrolysis of carbonyl sulfide. Carbonyl sulfide will hydrolyze in accordance with .~he reaction-. ~OS t ~2 = ~25 ~ C2 The reaction is reversible but favored in the forwarddirection at the temperatures employed, as indicated by the equilibrium constants at various temperatures:
io ;. . ~.
' lH25] [C2]
1COS j IH201 15 .

where~ `
.
at 100F K ~ 63,330 20 at 200F K ~ 12~951 at 300~ X = 3,272 Despite Eavorable equilibrium driving the r~action 25forward or to the risht, the reaction proceeds very slowly at low temperatures. At higher temperatures and in an aqueous alkanolamine hydrolysis medium~ the reaction proceeds more rapidly and will go to essential completion if the initial concentrations of hydrogen sulfide or 30carbon dioxide are not too high~ ~his may necessitate mass removal of the bulk of at least one of these constituents, usually hydrogen sulfide, in tha first absorption tower 12.

L3E;

1 The gas then leaves bulk absorption tower 12 and .
passes by line 14, with or without heat exchange to hydrolysis reaction zone 16 for contact with, preferably in countercurrent flow, the aqueous alkanolamine hydrolysis S medium. Contact is for a time sufficient to achieve essentially complete hydrolysis of carbonyl sulfide.
Residence times of from about 2 to about 5 seconds, depend~
ing on temperature, will suffice. ' ~owever, in many commercial installations the hydrogen 10 sulfide and carbon dioxide appear, in .the gas to ~e treated, in concentrations sufficiently low as not to inhibit materially the''completeness of the hydrolys.is reaction rate, with reaction rate rather than equiiibrium being the controlling fac~or. 'In such instances the first 15 absorber 12 for the bulk of hydrogen sulfide, carbon dioxide, or both, is eliminated. The gas with or without heat exchange is fed directly to hydrolysis reactor 160 With re~erence 'to FIG5. 1 and 2, the aqueous alkanolamine hydrolysis medium entsrs hydrolysis reactor 16 by line 40 20 at a temperature suitable to the hydrolysis of carbonyl sufide, passes downward in countercurrent flow to the gas stream and exits at the Dase by line 42. It is pumped by pump 44 through heat exchanger 46 which adds heat as required to maintain the aqueous alkanolamine hydrolysi's 25 medium at the desired operating temperature for use in hydrolysis reactor 16. The agueous alkanolamine hydrolysis medium returns to hydrolysis reactor 1~ by line 42 to close the loop. A suitable heating medium is steamO
Because the aqueous alkanolamine hydrolysis medium is in 30 equilibrium with hydrogen sulfide and carbon dioxide; as . ..
well as the other consti~uents of ~he gas stream~ the absorbent is not consumed and regeneration is not required.
In operation, the products of hydrolysis leave with the flow of process gas ~hrough hydrolysis reactor 160 .
.

1 Stated another way, as the gases pass up through hydrolysis reactor 16 in countercurrent to the aqueous alkanolamine hydrolysis medium, carbonyl sulfide reacts with water present in the gas stream and/or in the aqueous alkanolamine hydrolysis medium and is converted to hydrogen sulfide and carbon dioxide which are stripped by the flowing gas from the aqueous alkaline hydrolysis medium, except for the small equilibrium quantities which remain dissolved in the aqueous alkanolamine hydrolysis medium at lO the operating conditions.
The reaction products, along with the balance of the gas stream, leave through line 18 and pass to absorption tower 22 in countercurrent flow to the absorbent fed thereto which serves to strip one or both of the acid 15 gases ~rom the gas stream. The absorben~ from tower 20 is, as shown, passed by liquid seal ~6 to absorption tower 12 and, in the case of FIG. 2~ by line 38 and pump 36 to absorption tower 12, ~he conditions for employing the apparatus shown in 20 FIG. 2 are to meet the requirement of a low temperature gas entering absorption tower 20 to maximize removal of the acid gas constituents,as the capacity of most absorbents for the acid gases are inverse functions of temperature. It can serve to meet the situation where 25 low temperature is required by the concentration of the acid gas constituents, or by greater economy of size of absorbing facilities, or greater energy conservation.
In the arrangement of FIG. 2~ the gas leaving bu1k absorption zone 12 is passed by ~ine 14 in indirect heat 30 exchange with the gas leaving hydrolysis reactor 16 in heat exchanger 32. The gas entering reactor 16 is partially heated to the hydrolysis temperature while the gas leaving the hydrolysis rea~tor 16 is partially cooled in exchanger 32 for ~eed to absorption tower 20~ Any 35 additional hea~ to be removed from the ~as stream i9 ~9~36 1 removed by passage of a cooling medium such as water through heat exchanger 34.
Since heat exchangers 32 and 34 create pressure losses in gas flow, a long pipe seal 26, as shown in FIG. 1, may be required. To avoid its use, there may be employed a pump 36 to pump the partially spent absorben~ from the base of absorption tower 20 to the upper ~eed level of absorption tower 12.

9~36 1320~ -14-CONTROLS A AND E~ ~ND EXAMP~E 1 There is processed a gas stream of the feed gas composition as shown in Table I below. Employing a conventional ambient temperature selective absorbent for hydrogen sulfide in each instance, for other than ~he hydrolysis zone, Control A shows 'che total sulfur removed and C3S removed from the gas stream for a given absorbent flow rate.
10 For Control B, the absorbent ~low rate was doubled, almost making the gas treating facility twice as large.
As shown, this increases total ~ulfur removal to 97.5%~
but only 72.4% of the COS is removed.
Instead of increasing the absorbent flow ratet the 15 absorption is ~plit between the two absorption zones with an intermediate closed-loop hydrolysis zone operated at 200F. The aquesus alkanolamine hydrolysis medium is a 35% by weight diethanolamine solution~ With the same net flow of absorbent as in Control A, tokal sulfur 20 removal is increased to 99~3% and the amoun~ of COS
remaining is nil~

$~g~36 Trea~ed Cas~
Component Feed Gas Control A Control B Exam~le 1 .. .

~2S123.28 1.02 0.35 1.02 .
COS11.16 6.Z9 3.~8 c 5 pp,m ~' :
C0~1,887.~81,598.4g 1,198.55 1,598.44 CO5,236.955,235.2~ 5,2~9.99 5,~35.24 ~23,651.303,647.91 3,650.27 3,647.91 CH410.30 10.27 10~23 lC.27 N241.21 41.21 41~21 41.21 Ar~on17.6717.67 17.67 __17.67 Total10,~79.3510,558.0510,151.3510,551.76 % S Removed - 94.6 97.5 99.3 % COS Removed - 43.6 7204 100.0 ~5 * Moles per hour~ dry basis .

-

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A continuous process for treating gas streams containing carbonyl sulfide:
(a) contacting the gas stream with an aqueous alkanolamine hydrolysis medium flowing through in a closed-loop hydrolysis zone and maintained at a temperature sufficient to hydrolyze, in the presence of water, the carbonyl sulfide contained in the gas stream to hydrogen sulfide and carbon dioxide and hydrolyzing carbonyl sulfide contained in gas stream in the hydrolysis zone to form a residual gas stream and (b) contacting the residual gas stream containing at least the formed hydrogen sulfide and carbon dioxide with an acid gas lean absorbent for at least hydrogen sulfide in an absorption zone to remove the hydrogen sulfide from said residual gas stream.

2. A process claimed in Claim 1 in which the aqueous alkanolamine hydrolysis medium is an aqueous ethanolamine solution.

3. A process as claimed in Claim 1 in which the aqueous alkanolamine hydrolysis medium is an aqueous solution of diethanolamine.

4. A process as claimed in Claim 3 in which the aqueous solution of diethanolamine contains from about 10% to about 30% by weight diethanolamine.

5. A process as claimed in Claim 1 in which the aqueous alkanolamine hydrolysis medium is an aqueous solution of monoethanolamine and at least one alkali metal compound selected from the group consisting of an alkali metal hydroxide, water soluble salts of an alkali metal and mixtures thereof.

6. A process as claimed in Claim 5 in which the aqueous solution of monoethanolamine contains monoethanolamine in an amount of from about 10% to about 20% by weight and in which the alkali metal compound calculated as the alkali metal hydroxide is present in an amount of from about 2% to about 5% by weight.

7. A process as claimed in Claim 5 in which the alkali.
metal is selected from the group consisting of sodium, potassium and mixtures thereof.

8. A process as claimed in Claim 6 in which the alkali metal is selected from the group consisting of sodium, potassium and mixtures thereof.

9. A process as claimed in Claim 1 in which the aqueous alkanolamine hydrolysis medium is maintained at a temperature from about 150°F to about 300°F.

10. A process as claimed in Claim 1 in which the aqueous alkanolamine hydrolysis medium is maintained at a temperature from about 150°F to about 280°F.

11. A continuous process for treating gas streams containing carbonyl sulfide and at least the acid gas, hydrogen sulfide which comprises:
(a) contacting the gas stream with an aqueous absorbent for at least hydrogen sulfide in a first absorption zone to remove substantially all of the hydrogen sulfide from the gas stream and form a first residual gas stream containing carbonyl sulfide, (b) contacting the first residual gas stream with an aqueous alkanolamine hydrolysis medium flowing through in a closed-loop hydrolysis zone and maintained at a temperature sufficient to hydrolyze, in the presence of water, the carbonyl sulfide contained in the first residual gas stream to hydrogen sulfide and carbon dioxide and hydrolyzing carbonyl sulfide contained in the first residual gas stream in the hydrolysis zone to form a second residual gas stream, and (c) contacting the second residual gas stream containing at least the formed hydrogen sulfide and carbon dioxide with an acid gas lean absorbent for at least hydrogen sulfide in a second absorption zone to remove the hydrogen sulfide from said second residual gas stream.

12. A process as claimed in Claim 11 in which the absorbent in the first and second absorption zones is the same, and the absorbent flows from the second absorption zone to the first absorption zone.

13. A process claimed in Claim 11 in which the aqueous alkanolamine hydrolysis medium is an aqueous ethanolamine solution.

14. A process as claimed in Claim 11 in which the aqueous alkanolamine hydrolysis medium is an aqueous solution of diethanolamine.

15. A process as claimed in Claim 14 in which the aqueous solution of diethanolamine contains from about 10% to about 30% by weight diethanolamine.

16. A process as claimed in Claim 11 in which the aqueous alkanolamine hydrolysis medium is an aqueous solution of monoethanolamine and at least one alkali metal compound selected from the group consisting of an alkali metal hydroxide, water soluble salts of an alkali metal and mixtures thereof.

17. A process as claimed in Claim 16 in which the aqueous solution of monoethanolamine contains monoethanolamine in an amount of from about 10% to about 20% by weight and in which the alkali metal compound calculated as the alkali metal hydroxide is present in an amount of from about 2% to about 5% by weight.

18. A process as claimed in Claim 16 in which the alkali metal is selected from the group consisting of sodium, potassium and mixtures thereof.

19. A process as claimed in Claim 17 in which the alkali metal is selected from the group consisting of sodium, potassium and mixtures thereof.

20. A process as claimed in Claim 11 in which the aqueous alkanolamine hydrolysis medium is maintained at a temperature from about 150°F to about 300°F.

21. A process as claimed in Claim 11 in which the aqueous alkanolamine hydrolysis medium is maintained at a temperature from about 150°F to about 280°F.

22. A continuous process for treating gas streams containing carbonyl sulfide and at least the acid gas, hydrogen sulfide which comprises.
(a) contacting the gas stream in countercurrent flow with an aqueous absorbent for at least hydrogen sulfide in a first absorption zone to remove substantially all of the hydrogen sulfide from the gas stream and form a fast residual gas stream containing carbonyl sulfide;
(b) contacting the first residual gas stream with an aqueous alkanolamine hydrolysis medium flowing through a closed-loop hydrolysis zone and maintained at a temperature sufficient to hydrolyze, in the presence of water, the the carbonyl sulfide contained in the residual gas stream to hydrogen sulfide and carbon dioxide and hydrolyzing carbonyl sulfide contained in the first residual gas stream in the hydrolysis zone to form a second residual gas stream;
(c) passing the second residual gas stream containing at least the formed hydrogen sulfide and carbon dioxide in countercurrent flow to an acid gas lean absorbent for at least hydrogen sulfide in a second absorption zone to remove the hydrogen sulfide from said second residual gas stream and (d) passing the absorbent from the second absorption zone to the first absorption zone.

23. A process claimed in Claim 22 in which the aqueous alkanolamine hydrolysis medium is an aqueous ethanolamine solution.

24. A process as claimed in Claim 22 in which the aqueous alkanolamine hydrolysis medium is an aqueous solution of diethanolamine.

25. A process as claimed in Claim 24 in which the aqueous solution of diethanolamine contains from about 10% to about 30% by weight diethanolamine.

26. A process as claimed in Claim 22 in which the aqueous alkanolamine hydrolysis medium is an aqueous solution of monoethanolamine and at least one alkali metal compound selected from the group consisting of an alkali metal hydroxide, water soluble salts of an alkali metal and mixtures thereof.

27. A process as claimed in Claim 26 in which the aqueous solution of monoethanolamine contains monoethanolamine in an amount of from about 10% to about 20% by weight and in which the alkali metal compound calculated as the alkali metal hydroxide is present in an amount of from about 2% to about 5% by weight.

28. A process as claimed in Claim 26 in which the alkali metal is selected from the group consisting of sodium, potassium and mixtures thereof.

29. A process as claimed in Claim 27 in which the alkali metal is selected from the group consisting of sodium, potassium and mixtures thereof.

30. A process as claimed in Claim 22 in which the aqueous alkanolamine hydrolysis medium is maintained at a temperature from about 150°F to about 300°F.

31. A process as claimed in Claim 22 in which the aqueous alkanolamine hydrolysis medium is maintained at a temperature from about 150°F to about 280°F.