CA1069680A - Method of removing hydrogen sulfide from a gas containing carbon dioxide - Google Patents

Abstract

METHOD OF REMOVING HYDROGEN SULFIDE
FROM A GAS CONTAINING CARBON DIOXIDE
(D#73,028-Cl-FB) ABSTRACT OF THE DISCLOSURE
A process wherein hydrogen sulfide present in a gas mixture comprising hydrogen sulfide and carbon dioxide is preferentially removed from the gas stream into an aqueous solution where the hydrogen sulfide is oxidized. The aqueous solution has dissolved therein either bicarbonate ions or bicarbonate ions with transition metal ions, and oxygen.

-I-

Description

106g680 This invention ls concerned with the removal of hydrogen sulfide from a mixture o~ gases.
In many industrial processes and in the oil production industry, concern over pollution has compelled the more complete removal of harmful and/or o~fensive components from effluent gas streams before release into the atmosphere. Also, many chemlcal processes demand gas streams of specilic composltion.
The problem is to separate gases rrom each other efficiently and economlcally and to dispose of any unwanted gas efflciently and economically.
A gas which i8 0~ particular concern as a pollutant is hydrogen sulfide. Hydrogen sulfide and other sulfur compounds are both offensive and harmful.
Hydrogen sulfide, for example, can cause corrosion problems and is also toxic in concentrated amounts.
Even ln conslderably less than toxic concentrations, hydrogen sulflde ha~ an offensive odor.
The removal of hydrogen sulride ls complicated by the fact that lt often occur~ as a component in a mlxture of gase~. One frequently occurring gas mixture contains hydrogen sulfide and carbon dioxide along with perhsps other gases. Carbon dioxide is usually tolerated and not cons~dered as a pollutant. Thus~
lt may be released into the atmosphere. There are many proce~ses which will remove both hydrogen sulride and carbon dloixde from gas stre~ms and a few which m~y be ~ d~ to preferentially remove hydrogen sul~ide.
Some of these processes use, in combination or alone, .
*

~0696~30 monoethanolumlne and diethanolamlne. Others use propylene carbonate, a combinatlon Or an alkali metal carbonate and an alkali metal arsenate, and others u~e a mixture of tetrahydrothiophene-l, l-dioxlde and alkanolamines. ~-It 18 also known in the art to use an aqueous basic solutlon to remove both carbon dloxlde and hydrogen sulflde since both gases lncrea~e ln solubility ln aqueous solutlons as the pH Or the solution rlse~.
Detall~ Or several prlor art processes for treatlng mlxture~ Or hydrogen sulflde and other gAses are dlsclosed ln the llterature. See for example, "The 011 and Gas Journal", August 14, 1967, p. 131;
"The 011 and Gas Journal", June 3, 1968, p. 90; and "Chemlcal Englneerlng", May 15, 1972, p. 66.
These prlor art processes have disadvantages such as requirlng addition Or rresh reagents as the active lngredients ~re used up in the proce6s or regeneratlon Or these actlve ingredlents. Al~o, the pH o~ ~ome systems 18 requlred to be ~alntalned at a predetermined level requlrlng constant ~urvelllance and manlpulatlon. Also, many prlor art processe~ do not adequately provlde for dlsposal Or the hydrogen sulride arter lt le in ~olutlon.

, .. ~ .. .. . . -- ` ~. ' .'' . , ~ ' ' ' ' ' ' ' .: , .

:1069680 A proce~s whlch provides for catalytic oxidation of hydrogen sulfide dls~olved in an aqueous medlum i6 disclosed ln U.S. P~tent 3,576,738. However~ thi~ process is not directed to separat~ng hydrogen ~ulfide from a mixture of gases but is concerned only with hydrogen sulfide already present in an aqueou~ solution.
The present lnventlon overco~es many problems ol the prlor art by providing a proce~s whereby hydrogen sulrlde is preferentially ab~orbed ~rom a gaseous mixture compr~elng hydrogen sulfide and carbon dioxide into an aqueous solution. In one preferred embodlment, the hydrogen 8Ulflde i8 catalytlcally oxidlzed to elemental sulfur whlle in solutlon.
The lnventlon 18 a process whereln hydrogen sulrlde pre~ent ln a gas mixture comprlslng hydrogen sul~ide and carbon dloxide i8 preferentlally removed from the ga~ stream, and may, ir deslred, be converted to elemental sulfur.
The present inventlon provldes a method for ao preférentlally removlng hydrogen sulflde from a gas mixture comprlslng hydrogen sulflde and carbon dloxlde whlch comprlses contactlng the gas mixture wlth an aqueous solution containlng bicarbonate ions ln sufflcient concentration to establlsh an equillbrium imbalance preventing substantial solution o~ carbon dio~de.
The aqueous ~olution may also contain lnert salts.

30~

.

.
.
-In a pre~erred embodlment, hydrogen sulflde~
dissolved ln the aqu-ous solution by the contacting, is oxidized to sulfur by reaction in aqueous medium with dissolved oxygen catalyzed by transition metal lons .
U.S. Patent No. 1,918,153, indicates th~t the reactlon NaHS + C02 NaHC03 + H2S
proceeds from left to right, due to the fact that carbon dioxide iB a slightly stronger acid that hy~rogen sulfide, but it has now been found that the above reactions will proceed from rlght to left un~er conditions wh~ h maintaln a high level of con-centratlon of blcarbonate ions in the aqueous medium at atmospherlc pressure. Required blcarbonate ConCentrati3ns are presented herelna~ter. Next, the dis301ved hydrogen SUlride i8 catalytically oxidized to elemental sulfur by dissolved transition metal ions and dissolved oxygen, lf desired.
In one typical embodlment of this invention the gas mixture comprislng hydrogen sulfi~e and carbon dioxlde is treated with one solutlon contalning dissolved blcarbonate ions, dl~solved transition metal ions and dlssolved oxygen. Since the catalytlc reaction of hydrogen sulfide to sulfur takes place rapidly, the dissolutlon of hydrogen sulfide precedes the catalytic reaction by only a very short time. In another typical embodlment of this invention the dissolution o~ the hydrogen sulfide takes place flr~t and the aqueou~
solution contalnlng t~e dissolved gas is transferred 1069~0 to another facllity where the catalytic oxldatlon o~ -hydrogen sulride to sulfur takes place.
The Dissolution of Hydrogen Sulfide The process of this invention is particularly applicable to the sltuatlon where hydrogen sulfide and carbon dioxide are ln a gas mixture and lt is deslred to be rid of the hydrogen sulflde while the carbon dloxlde ma~ be allowed to escape.
~ he process of this lnvention læ of particular advantage where the concentratlon or carbon dloxide 18 relatively hlgh with respect to the concentratlon o~
hydrogen sulfide. This i8 60 because ln conventional baælc system~ th~ carbon dioxide iB adsorbed in proportlon to its concentratlon and reduce6 the pH
of the system to the point that hydrogen sulfide 18 no longer absorbed necessitating the additlon o~ more baslc materlal to the aqueous solutlon. The process .
Or the present lnventlon prevents maJor ~luctuatlons in the pH of thO agueous solution by the presence of bicarb~nate ions ln the aqueous medlum. While there 18 no lntentIon to llmlt the success of the present lnventlon to a speclrlc mechanism the following i8 believed to be explanatory of the operatlve chemlcal ~: . .
actlon Or the dissolution 6tep in the present inventlon.
When carbon dloxide dlssolves in water the followlng equillbrlum reaction takes place:
~ C2 + H20 H2CO H+ + HCO-r ~ 3 ~ 3 xcess~blcarbonate~ion is present in the aqueous solutlon~ as~ln thls lnventlon, the equilibrlum solublllty or carbonlc acid (H2C03) decreaseæ and, , , -: ~ : -~ ' . ' .

1~69~

consequently, the carbon dioxide i~ reduced in solubllity and the pH of the solution remQins stable.
The solubility ln water of hydrogen ~ulfide ls governed by the following equilibrium:
H2S H+ + H8 The equilibrium solubility of hydrq~en sul~ide decreases as the pH of the solution decrea~es. Since the pre~ence of the bicarbonate ion~ in effect, keeps the pH high and prevents carbon dioxide from dlssolving, the hydrogen ~ulfide is preferentlally absorbed into the aqueous solution. That is, a greater percentage of hydrogen sulfide than carbon dloxide is dissolved.
The dissolution step or the invention entall~
contacting the gas contalnlng hydrogen sulfide and carbon dioxide with a blcarbonate rlch aqueous ~olutlon.
The contact may be carried out in any conventional ~as liquid contactor. For example, the aqueous solution may be sprayed over the ga~ mlxture Or a packed tower may be u~ed. The gas may also be bubbled through a vessel contalnlng the aqueous solution of bicarbonate lon~.
The particular manner of cont~cting the aqueou~ solution o~ bicarbonate ion~ and the hydrogen sulfide-carbon dioxide containing gas i~ left to the choice of one ~killed in the art. Therefore, any conventional manner of contacting found convenient and effecient i~ suitable for the operation of this inventlon. It i~ wlthin the capabllity of one ~kllled in the art to choose a method e~ricient enough to remove the required amount of hydrogen ~ulfide from a glven stre~m or gas input.

.
.

1069~

- The bicarbonate ions in the aqueou~ solutlon may be derlved from any one or a mlxture of water soluble salts of bicarbonate anlons such as ammonium bicarbonate, ~ -sodlum bicarbonate, potassium bicarbonate, magnesium blcarbonate, calclum bicarbonate and transition metal salts of the blcarbonate anions to name only a ~ew.
Sodlum and potassium bicarbonate salts are preferred because they are very soluble in water and are extremely stable and do not tend to form mlneral scale on the surrace of the gas-liquld contactor and assoclated equlpment.
If a blcarbonate salt as above 18 used, the blcarbonate lons are present immedlately upon dlssolutlon o~ the sa}t ln the water and, therefore, the selectlvlty of the solutlon ror hydrogen sulfide wlll be establlshed from the beglnnlng of carbon dioxide-hydrogen sulflde , contact.
Alternatively, in another embodiment of thls ~ ~ invention water soluble carbonate salts of various catlons may be used ln the process Ot- this lnvention.
In this embodiment the water soluble carbonate salts are dissolved in an aqueous medium and are contacted with a source of c~rbon dioxlde to convert the carbonate ; ions to blcarbonate lons according to the following react~on:
C03 + C2 + H20 HC03 ~`~ The resulting solution of bicarbonate lons will then selectively ab~orb hydrogen sulfide.
~ ~ .
The carbon dioxide to convert the carbonate lon to bicarbonate ion may be ln pure form in which .

. .

iO~96~30 case a short preconditioning ~tep comprislng conversion o~ carbonate to bicarbonate ions wlll precede the process of separatlng hydrogen sulfide from a mixture o~ hydrogen sulfide and carbon dioxide. However, since the conversion o$ carbonate to bicarbonate ion~ i8 very rapld the gas mixture of hydrogen sulfide and carbon dioxide may be used as a source of carbon dioxlde. Thus, eliminating the need for pretreatment with a pure carbon dlo~lde source.
In yet another embodiment of this invention water soluble acid phosphate salts of ammonla, alkali metals and alkallne earth metals may be used. For example, ammonlwm orthophosphate (dl- and trlbaslc), sodium phosphate (dl- and tribaslc, potasslum phosphate (di- and trlbaslc), calclum phosphate (dl- ana tribasic), ma~neslum phosphate (di- and tribasic) and barium pho~phate (dl- and trlbasic) are sultable.
When these phosphate salts are used, carbon dioxlde ls absorbed In the solutlon for a time forming bicarbonate ions. The proces6 may proceed as ~ollows for a typical salt:
Na2HP04 2Na+ + HP04 HP04Z + H20 H2P4 + OH-OH + CO HCO

2 3 ~hus, the bicarbonate ion is formed which wlll lnhlblt further carbon dloxlde dissolutlon.
Other sources o~ bicarbonate ions may occur to those skllled in the art wlthout departing from the scope of this invention.

.
, . . . .
.

.
, ., ~. . . . .... .. . ~ , Irlert or neutral salt~, that is ~alts whlch do not impart an acidlc or basic c~laracter to an aqueous solution may also be present along with the bicarbonate salts in the aqueous solution of my invention. However, salt~ which do impart a basic or acidic character to an aqueous ~olution such as carbonate salts are not acceptable ln the aqueous solution of my invention except in trace amounts which have minuscule effect on the 301ution.
The concentration of bicarbonate forming salt required mu~t be large enough to establlsh an equilibrium imbalance which will prevent carbon dioxide from dissolving in the aqueous solutlor) in substantial amounts. The hi~her the concentration of bicarbonate ions, the more readlly hydrogen ~ulflde will be dissolved. The maxlmum concentratlon of blcarbonate ions 18 dictated by practical conslderatlons such a~ the maximum 601ubllity of the partlcular blcarbonate salt, the most deslrable concentratlon of hydrogen sulfide in the aqueous solution from the llquld-gas contactor, the desired llquid clrculation rate through the liquid-ga~ contactor and desired scrubblng efflciency. Bicarbonate ion containing solutions having from 0.01 g-moles/l to 0.25 g-moles/l of aolublllzed blc~rbonate or equlvalent amount of other bicarbonate ~alts are preferred.
The dlssolution step of the proces~ of thls lnvention may be operated at ambient condition~ of temperature and pressure. Severe conditions are not necedsary for the successful operation of thl~ inventlon.

- . : . . . . . . - -:
. ... : .: . . .
.
.. : ', ~ ~ ' ;',, -10~96~30 The Catalytic Oxidation of Hydrogen Sulfide Once dis~olved, the hydrogen sul~ide is free to react with dissolved oxygen to form elemental sulfur in the second broad step of this invention. As pointed out earlier, both the di~solution of hydrogen sulflde and the oxidation of hydrogen ~ulfide may take place in the sAme facility, such as a liquid filled ves~el.
In thie ca~e, the dissolution and oxidation of hydrogen sulfide wlll be occurring ~imultaneously as the proces~
proceeds. In another possible case mentioned, the hydrogen sulfide dlssolut$on step takes place in a facllity ~eparate from the oxidation step. In either case the oxldation step must take place ln an aqueous solutlon contalning in addition to the hydrogen sulflde, di~solved transition metal ions as catalyst and dissolved oxy~en.
The preferred cataly~t for the reaction ls a soluble transition metal catalyst, more specifically an ion of a transition metal i8 preferred. The usual form or ~uch a catalyst ls a salt. Soluble salts of niekel, cobhlt, manganese, copper and iron, for example, are suitable ~or the operation of my lnvention.
The amount of catalyst to be used must be l~rge enough to lmpart catalytic activity and promote the reaction between hydrogen sulflde and oxygen. Amounts as low a8 1 part by weight of catalyst per 2000 parts of hydrogen sulflde to be treated may be used. Any amount up to the limit of solubility of the catalyat in the aqueous solution may be used. As a practical matter amounts mu~h above 1 part of cataly~t per 20 parts of : ,' . . . ~ :

.

1069~;~0 hydrogen sul~ide may not appreciably improve catalytic actlvity. It 1~ preferred to use from about 1 part of catalyst to 50 parts of hydrogen sulfide to about 1 part of catalyst to about 200 parts of hydrogen sulfide.
The water must contain dissolved ~ ygen in an amount at least sufficient to stoichiometrically convert all of the dlsEolved hydrogen sulfide to elemental sulfur. An excess may be required to insure more complete reaction. The oxygen may be dissolved in the aqueous solution in any convenient manner. For example, the oxygen may be bubbled through the aqueous solutlon or the solution may be aerated by dividing it into a fine mist or spray and passing it through a source o~ oxygen. Any number of ways to dissolve oxygen in an aq~eo~ medium are avallable and the method u~ed is not criticalto the proces~ of this inventlon.
The source oi` oxygen may be any convenient source including, but not limited to, pure oxygen and alr.
The process of my invention may be carried out at ~mbient condition~ of temperature and pressure, if deslred.
The proces~ of my invention may be carried out at embient conditions of temperature and pressure, if deslred. Severe conditions are not required for the p~ocess or this lnvention. As a result, the invention may be practiced in inexpensive equipment.
The contact time between the hydrogen sulfide~

3~ carbon dioxide g~s and the aqueous solution must be adequate for equilibrll~ to be obtained so that a . . ,- , - . . . . --10~96~30 maximum amount of hydrogen sulflae will be di~solved.
In general, with adequate mixing, more than-twenty seconds are seldom needed to reach equilibrium and equillbrium ls orten reached in a second or less. The necessary contact time is largely dependent on many other varlables such as bubble size and mlxing efficiency.
The greater the efflclency the shorter the contact tlme may be. These are engineering details to be included in the design o~ each unlt.
Experimental Example 1 Thls example illustrates the abilIty or an unaerated aqueous solutlon of blcarbonate lons to selectlvely remove hydrogerl sul~lde ~rom a mlxture of hydrogen sulflde and carbon dloxlde.
An aqueous solution was passed through the top o~ the contactor and out the bottom. A two component ~s conslstlng of 96.33~ carbon dloxide and 3.67%
hydrogen sulflde was bubbled into the bottom of the con-tactor in a counter current manner to the ~low of the aqueous solutlon.
Two runs were made. In the ~irst run the aqueou6 solution $ontained no bicarbonate. In the second run the aqueous solutlon contained sodium blcarbonate. The contact tlme of the gas and llquid wa8 about 3 ~econds ln both runs.
The result indicate that the addition of bicarbonate ion increased the ability of the aqueous solutlon to dlssolve hydrogen sulflde in preference ~ to carbon dioxide.

, '.

io69~0 Composltion of gas Composltion of Gas before treatment after treatment Content of aqueous solution contacting 3.67% H~S and Run %H2S %Co2 %H2S %C02 96.33% ~2 1 3.~7 9~.33 1.8 98.2 2 3.67 96.33 o.76 99.24 Sodlum bicarbonate Example 2 A contactor comprising a vertical glass tube fllled with glass beads was used as follows:
An aqueous solutlon was passed through the top of the contactor and proceeded through the contactor and out the bottom. A gas comprising 95.5% carbon dloxlde and 4.5% hydrogen sulflde was bubbled into the bottom of the contactor ln a counter current manner to the flow of the aqueous solution.
Five runs were made. In the first the aqueous solutlon was aerated containing only oxygen. In the second and thlrd runs the aqueous solution contained ~ -oxygen and sodlum bicarbonate. In the fourth run the aqueous solutlon contained oxygen and nickel chlorlde cataly~t. In the flfth run the aqueous solutlon contalned ~ ;
oxygen, a nlckel chloride catalyst and sodium bicarbonate.
$he contact time between the sour gas and aqueou~ solution wa3 approxlmately two second~.
.
As 1B evident~ the ability of the aqueous solutlons to remove hydrogen sulfide increase from runs one to flve.

~ 3~

: .

H S H~S Content of aqueous o~ gas of gas solution contacting 95-5%
before after carbon dloxide, 4.5% hydrogen Run treatment treatment sulfide ~a~
1 4.5 2.92 oxygen 2 4.5 2 05 oxygen, sodium bicarbonate 3 4.5 2.02 oxygen, sodlum bicarbonate

4 4.5 1.70 oxygen, nickel chloride 4.5 0.27 oxygen, nickel chloride, sodium bicarbonate Ex~mple 3 Fleld Data A process for oxidlzing gaseous hydrqgen ~ulfide with an aqueous solution and air was operated on a pilot scale at a gas point. In this proce6s, an aqueou6 ~olution containing bicarbonate ion alkallnity (HC03 ) was used to absorb hydrogen sulflde from acid gas. The absorbed hydrogen sulfide was oxidlzed to elemental sulfur. A nickel catalyst was u~ed to promote the hydrogen sulfide-oxygen reaction.
The absorption solution was prepared by adding soda ash (Na2C03) to fresh water and bubbling gaseous carbon dioxide (from acid ~as) through the solution ~-until all of the soda a~h was converted to sodium bicarbonate.
The Pilot Unit Acld gas from amine regeneration was pas~ed into a 2.4 m (8 ft.) diameter by 8.5 m (28 ft.) tall absorption-reaction vessel which wa~ fabricated from a heater treater from which the fire tubes and spreader plate ha~ been removed. The acid gas was bubbled into the ~olution contained within the vessel through 2.54 cm (1 ln.) pipe perforated with eight, ~0696~30 7.9 ~ (5/16 lt~. ~ holes. Alr from a blower was passed through an ori~ice plate flowmeter and into the reactlon ve~sel through 2.54 cm (1 in.) pipe perforated wlth thirteen, 7.9 mm (5/16 in.) holes. Valves and a pressure regulator were used to control the air and acld gas flow rates; 5.o8 cm (2 in.) pipe was used as acld gas and air flowllnes.
The solutlon flowed from the adsorption-renctlon vessel to a 3.0 m (10 ft.) diameter by 4.6 m (15 ft.) tall settling vessel. Piping and valving were arranged so that the solution coul~ be dralned from the bottom, or 3.2 m (10.5 ft.), 4.4 m (14.5 ft.), 5.6 m (1~.5 ft.) or 6.8 m (22.5 ~t.) levels. Solution ~rom the settllng vessel was recycled to the reactlon ve~sel by a po~itive displacement pump. sludge ~rom the settllne ve~sel was drained lnto 0.21 m3 (55 gal.) drums.
A nickel chlorlde (catalyst) solutlon wa~
added dlrectly to the adsorptlon-reactlon vessel pump.
Test Procedure Approxlmately 40 m3 (250 bbls) or fresh water, 227 kg (500 lbs.) of soda ash and 0.45 kg (1 lb) of catalyGt (nlckel chloride hexahydrate) were added to the test unit. ~he catalyst solution for the chemlcal metering pump was prepared by addlng 0.03 kg/m3 (0.25 lb/gal) : ~ or nickel chloride hexahydrate to ~resh water. The .
clrculation pump was started and draln valves were adJusted co that tho depth of solution in the reactlon vessel was 5.~m (18.5 ft). Acid gas, alr and catalyst flows ~ ~ to the~ adeorptlon-reaction ve~sel were then started. --LQboratory test data indicated that solid .

- : . . . .. .. , . .
- . .. ~ . .. , .- . - ~, ....... .

106~6~30 sulfur and spent catalyst need not be purged from the solutlon more than once per d~y; consequently, attempts were made to run the solution circulation pump so that the daily solution circulation rate was equal to the volume contained in the reaction vessel~ 25.4 m3 (160 bbls), when the solution depth was 5.6 m (18.5 ft).
In practlce, the pump would not operate at such a low clrculatlon rate. In all tests prior to May 19, the clrculatlon rate was 2.0-2.6 m3hl (300 - 400 bbl~/day);
after May l9, the clrculation pump was run only 30 min/day ancl, durlng pumplng periods, solùtlon from the reactlon ve~sel was dralned through the bottom valve.
Solutlon samples, from the absorption-reactlon vessel, were taken once or twlce dally to determlne ~ree carbon dloxide, bicarbonate lon alkalinlty (Analysis of 011 Field Water, API RP45, Second Editlon, MethOds 3.5 and 2,2) and pH. The vent gas was analyzed once or twlce daily uslng the Unico Hazardous Gas Detector;
the acid gas was analyzed for hydrogen sulfide content by the Tutweller method.
~ .
Test Results The acid gas wa~ sampled on three occa~ions and found to cont~in 0.041 (4.1% ~/v), o.o46 (4.6% v/v) and 0.042 m3/m3 (4.2~ v/v~ hydrogen sulflde. The pH
o~ the solutlon ranged from 6.4 to 7.7 and lncreased with the bicarbonate lon alkalinlty. The free cerbon .
dioxide concentratlon varied from 0.156 ta 0.360 kg/m3 ;(156-360 mg/ ). Thé hydrogen sulfide content in the~vent gas~and the bicarbonate lon alkalinity in the 30`~ solution under test conditions are reported in Tables I
and II.

.~ . .. . .. , .,. . ~ .. ~ ., .. , . . - . . ,, , . . . , -, ~ . . . .
. . . ., ~, . . . .

~069~i~0 Discus~ion Or Test Results In all subsequent calculation~ and dlscusslons, acid gas from the gas treatlng plant was assumed to contaln 0.043 m3/m3 (4.3%) hydrogen sulfide. Thl~
value was derived by averaging the values obtained in - the three acid gas analyses.
The gas vented ~rom the absorption-reactlon ve~sel was a mixture of sweetened acid and air. There-fore, to calculate the percentage hydrogen sulflde removed from the acid gas by using the vent gas and acid gas hydrogen sulflde concentrations, allowance was made for dilutlon of gas with air. The equation used in the calculations was as follows (Tables I and II~.
ppm H2S ln vent gas % H2S removed = 100 - [~ x 10-2 x bc~ + ~lr rates)]
QCI~
Laboratory te~t data showed that the primary hydrogen sulfide oxidation product is sulfur, but thiosul~ate lons and acld (H+) were also formed by the ~ollowing secondary reactlon:
2H2S + 202 ~ 2H+ ~ S2o32 + H20 Acid neutralized blcarbonate ion alkAlinlty according to the following reaction:
H+ + HC03 ~ H20 ~ C02 Supplementary soda ash was added to the solution ~hlch was rapidly converted to bicarbonate to replace neutralized blcarbonate ion alkalinity.
,, .
- The soda ash consumption rates in the hourly ~ ~tests varied ~rom 0 to 0.072 kg/m3 (0 to 4.5 lbs/MSCF).

~ _17-. , . .. - - . .

:1069680 'lhe lAtter rate was observed ln the first test only and the high rate was probably due, in part, to alkalinity losses by calcium and magnesium carbonate preclpltation due to the hardness of the water used.
Tests 1-13 from May 2 to May 8 showed that o.96-0.98 kg/kg (96-98~) hydrogen sulride was removed when (1) the air/acid gas flow rate ratio was one, (2) the acid gas treating rate was 76 m3/h (45 ft3/min), and (3) the solutlon depth was 5.6 m (18.5 ft).
Decreaslng the air/acid gas flow rate ratlo ~rom 3 to l increased the percentage hydrogen sulride removed.
Tests 13-18 demon~trated that when the air/acid gas ratio was about one and the acid gas treating rate was 70 to 75 m3/h (41-44 ft3/min), the percent~ge hydrogen sulride removed decreased with solution depth.
Test~ from May 15 to May 18 demonstrated that the percentage hydrogen sulride decreased only slightly wlth ~olution depth provided that the alr rate per surface area of solution, 12-14 m3/h/m2 (o.6-o.7 ft3/min/ -~
rt )~ and acid gas rate per volume o~ solution, 1.7-1.9 m3/hjm3 (0.18-0.19 ft3/min/bbl), remalned constant.
When the acld gas to air flow rate ratio was about one, the percentage hydrogen sul~ide removed decreased only slightly as the flow rate increased ~ (Table II)-'. ~ ~, . , ~ ' . ....

~, .. . . , . ~
. . .
,. -: , . : . .

1069~30 Lr l z~
H H ` 0000000000000000000 ~\ N ~1 Uo~ D ~N (~'~r:) ~co C--C--H ~ ~ _ ,~ f) N ~=~ ~ ~1 N N N N N N N ~1~ ~D
.¢

Z 000 0000000000000 Lr ~n ~ Q. $,,~0 u~ ~2~0~oo~0 ~ ~ N ~1 ~ 0~ r--H
h Q ~:~ O oa~ o~0 ~),~ o ~10 ~1 ~ cq ~ , E~ O ' , ' .~' ~ H ~^
U~ ~ ~_ 000~C0000000000~ 00~00 H - OQ
~ ' ~ ^
~ ~ ~ ~U~OOOU~OOOOOO~O
. ~ . ~ ~ HH~NHH~NNN~NNNNNN~N
E~ ~ :~
' ~3 ~
o H~ ~O~N~NN~
NN~ J~

H I ~ ~N ~ N 00 ~o o~
¢ ~ I ~ ~ ~) ~ ~ ~ ~ ~J J ::~ J ~ ~ ~ N
:.

OOOO~OOOOOOOO~OOU~ OO
;~: o ~0 ~)~Y)~)~r)~r)O ~o ~o ~1 ~J
l N 0 N 0 H 8 ,, o ,, o ,, o ,, o , o , o o ,, :

. ~ ~_____~ N ~ ~ ~ ~ ~ N0 :; ., .

~19- :

10696t30 :~: ~c~ ~ ~ 0 ~0 ~ o~

I ~Z H
0 0 ~; _ al H H O~CU u~ J C-- ~ ~ 2 c~ 0 ~u c~- ~
¢ ~q ¢ ~ ~D ~ ~CO ~ a~O J O 1~ ~
cC ' " -U~ . ", .
Z ~ ~3 H Q~ Ll~ O O O O O O O O O O 0 3 ~ t 0 0 0 E~ ~ ~ "~ O C~l O O ~D O O CU ~
~ P
O --H j~ 1~ ~ N ~0 CU O O O Lr~ CU ~ L~
~æ ~ ~000~ 0, U~

~u~ ~ ~ ~ 00000~0~ 00~ .
O P .
~- ~ ~
H ~~ ~ ~ ~ ll~ 0 0 0 0 0 0 ~ 0~ 0 ~ 0 00 0 C~
~ 3 ~0 ~ i O O O O O O O O O O
.
3 ~ ..
~ ~ 0 ~ 1 ~o ~ O O O O
~ ~~3 C~ ~ ~, N N N ~1 N _I t~ ~) tr) ~ t~) N Ir) ~) tr~ ~ ~)tY-) ~ .. ' ' ~ ~ N 0 0~D 0 0 ~1~ N 0 ~1 0~ 0 0 0 0 0 0 ~ ~ ~
~ o a~ ~000oo~
: O ~ rl O N O H O ~1 O ~ r-l ~I N r~ -1~1~1 - :
Nl ~NI Nl N~ N ~ ~ N N~ N~
rl N ~* ~ D ~X) ~O ~1 N ~)~ D ~0 : : : 20 -' : .. '' ' . ' : ' , : : . . - .

10696~0 TABLE II
Hydrogen Sulfide Removal a~ a Functlon o~ Acid Ga~ R~tes No. of A~e. Air Rate6 ~e. Acid Gas ~te6 % H2S
Test8 m /hr Ft /min m /hr Ft /mln Removed 14 51 30 51 30 99.4 -. .... . . . . ..
.

Claims (13)

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

1. A method for preferentially removing hydrogen sulfide from a gas mixture comprising hydrogen sulfide and carbon dioxide which comprises contacting the gas mixture with an aqueous solution containing bicarbonate ions in sufficient concentration to establish an equilibrium im-balance preventing substantial solution of carbon dioxide.

2. A method as claimed in Claim 1 wherein the aqueous solution contains from about 0.01 to about 0.25 gram moles per litre of bicarbonate ions.

3. A method as claimed in Claim 1 or 2 wherein the bicarbonate ions in solution are obtained by dissolving a bicarbonate salt.

4. A method as claimed in Claim 1 wherein the bicarbonate ions in solution are obtained by reaction be-tween carbon dioxide and dissolved carbonate or acid phos-phate ions in the aqueous solution.

5. A method as claimed in Claim 4 wherein the carbonate or acid phosphate ions are reacted with carbon dioxide employed in a preconditioning step.

6. A method as claimed in Claim 4 wherein the carbonate or acid phosphate ions are reacted with carbon dioxide from the gas mixture.

7. A method as claimed in Claim 1 wherein the aqueous solution comprises alkali metal cations.

8. A method as claimed in Claim 1 wherein hydro-gen sulfide, dissolved in the aqueous solution by the con-tacting, is oxidized to sulfur by reaction in aqueous medium with dissolved oxygen catalyzed by transition metal ions.

9. A method as claimed in Claim 8 wherein the transition metal ions are contained in the aqueous solution.

10. A method as claimed in Claim 8 wherein the transition metal ions are contained in a second solution which is mixed with the aqueous solution containing dis-solved hydrogen sulfide after the contacting.

11. A method as in Claim 8 wherein l part by weight of a soluble transition metal salt is employed per 20 to 2000 parts by weight of dissolved hydrogen sulfide.

12. A method as claimed in Claim 11 wherein 1 part by weight of soluble transition metal salt is employed per 50 to 200 parts by weight of dissolved hydrogen sulfide.

13. A method as claimed in Claim 8 wherein the transition metal ions are provided by nickel chloride.