CA1084687A

CA1084687A - Quaternary pyridinium salt inhibitor system for gas conditioning solutions

Info

Publication number: CA1084687A
Application number: CA299,197A
Authority: CA
Inventors: Robert C. Clouse; Robert G. Asperger
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1977-03-28
Filing date: 1978-03-17
Publication date: 1980-09-02
Also published as: FR2385812A1; NL7803292A; AU3451378A; AU519454B2; NO780989L; FR2385812B1; MY8200232A; ES468254A1; JPS53119739A; DE2813126A1; GB1597038A; GR64223B

Abstract

A B S T R A C T
The present invention resides in the area of corrosion inhibition in gas conditioning where CO2 and small amounts of H2S are removed by an absorbent.
The invention is an inhibitor composition for alkanolamine solutions and other absorbents for removing CO2 and small amounts of H2S from gas streams, comprising an inhibiting concentration in the absorbent of a combination of one part by weight of a quarternary pyridinium salt and either (1) 0.001-10 parts of a thio compound which is a water-soluble thiocyanate, a water-soluble sulfide, or an organic thioamide, or (2) 0.01-10 parts of a lower alkylene-polyamine, a corresponding polyalkylenepolyamine or mixture thereof, wherein the alkylene units contain 2-3 carbon atoms.
The advantages obtained over the prior art are less corrosion than results from numerous known inhibitor combinations, and the claimed inhibitor systems are essentially non-toxic, in contrast with previous inhibitor systems using arsenic, antimony or vanadium.

Description

~0l~6~

The presen-t invention relates to a new inhibitor composition useful for preventing corrosion by solvents used in treating sour gas streams and to the inhibited solvent.
The conditioning of naturally occurring and ; 5 synthetic gases by absorbing acidic gases such as CO2, H2S, COS, and HCN in an absorbent solution has been practiced commercially for many years. Gases such as `~ feed gas for an ammonia plant, natural gas, and fluegas are examples. Aqueous solutions of various compounds such as alkanolamines, sulfolane (tetrahydrothiophene-l,l-dioxide), potassium carbonate, and mixtures of two or more of these have been used for the purpose.
The water may be replaced partly or entirely by a ~-glycol. All of these systems are plagued by corrosion 15 ~ of metal equipment which can be caused by products ~; of degradation of the absorbent, by acidic components, or by products of reaction of these acidic components with the absorbent. For example, although aqueous alkanolamine itself is not particularly corrosive toward .
iron and steel equipment, it becomes highly corrosive when there are dissolved CO2 and minor amounts of H2S
present, particularly when it is hot. To combat this problem, various metal compounds have been used alone or in combination with other compounds as corrosion inhibitors, for example, compounds of arsenic, antimony, and vanadium.
While such metal compounds are effective corrosion inhibitors~
they have the disadvantages of low solubility in most gas conditioning solutions and of relatively high toxicity.

18,313A~

- . ' .,: , : , . .
, . .

~V1~68'7 The latter property is particularly undesirable since it affects both the handling of the solvent and the disposal of waste material. ~hey are also ineffective in the presence of H2S.
The problems of toxicity and corrosion described above have been subs-tantially overcome by the present invention, which is a composition for inhibiting corrosion .
of iron and steel by carbon dioxide and optionally a minor quantity of hydrogen sulfide in gas conditioning solutions, 10 compri.sing an inhibiting concentration in said solu-tion of a combination of one part by weight of a quaternary pyridinium salt and (1) 0.001-10 parts of a thio compound which is a water-soluble thiocyanate, a water-sol~lble -.
sulfide, or an organic thioamider or (2) 0.01-10 parts of a lower alkylenepolyamine, a corresponding polyalkylene~
; polyamine, or a mixture thereof wherein the alkylene units contain 2-3 carbon atoms. - .
Essentially any pyridinium salt which is sta~le in the gas conditioning solution is operable in the .
~ 20 invention. Preferably, this salt.has the formula:
. lR ' ' , R' ~ ~ R' X ~, R' ~ R' ~.

' where R is an alkyl radical of 1-20 carbon atoms, a benzyl radical, or an alkylated benzyl radical wherein the,aromatic ring has one or more alkyl substituents 25 . totaling 1-20 carbon atoms~ each R' is a hydrogen atom 18,313A~F -2-.

: , , '~` ':
, ' ' . ' lL6~37 or an alkyl radical of 1-6 carbon atoms, and X is any convenient anionic radical such as halide, sulEate, aceta-te, or nitrateO In the above general formula, X is preferably a bromine or chlorine atom and most preferably bromine. sest results are obtained when at least one R' represents an alkyl radical and par- -ticularly good inhibition has been found when the pyridine ring has multiple alkyl substi-tuents.
Preferably, R is a higher alkyl radical of about 10-18 carbon atoms.
The thio eompound in -the inhibitor combination is preferably a water-soluble thiocyana-te such as an alkali metal thiocyanate or, most preferably, ammonium thiocyanate. It can also be an organic thloamide and -essentially any such compound is operable. This class of compounds includes thiourea, a polythiourea, a - ~ -hydrocarbon substituted derivative thereof, or a thioamide having the formula:
,S, R"
A-C-N
R
; 20 wherein A is a hydrocarbon radieal o~ 1-12 carbon atoms or a pyridyl radical and each R" is a hydrogen atom or an alkyl radical of 1-8 earbon atoms. Thioamides such as thiourea, 1~2-diethylthiourea, propylthiourea, l,l-diphenylthiourea, thiocarbanilide, 1,2-dibutyl-thiourea, dithiobiurea, thioacetamide, thionico-tinamide, and thiobenzamide are representative o~ this class.
Water-soluble sulfides such as ammonium sulfide, an alkali metal sulfide, or corresponding hydrosulEide ineluding H2S are other operable thio compounds.
:

- ': ' 18,313A-F _3_ ..
- . . : , , ``` ~
~0~ 87 While any significant quantity of the combination of the pyridinium salt and the thio compound will provide some degree of inhibition of corrosion, at least about 100 parts per million concentration of the combination in -the gas conditioning solution is usually required to provide practical protection. More than about 2,boo ppm of the inhibitor combination usually provides little or no added protection. Either the thio compound or the pyridinium salt alone will provide no inhibition or only partial inhibition. It appears that very little of the thio compound is usually needed in the presence of the pyridinium salt, however, concentrations as low as one part per million of thio compound in the presence of 50-100 parts per million of pyridinium salt having been found to give effective - 15 inhibition in some cases. About the maximum degree of inhibition obtainable with a particular combination is usually found when the concentration of the thio compound reaches a concentration of 10-100 parts per million.
Higher concentrations of this component appear to offer -little or no added benefit under most conditions but may help ~hen the quaternary salt concentration is at a disproportionately higher level.
On the other hand, it has been found that at least about 50 parts per million and preferably 100-1000 parts of the pyridinium salt is required to obtain optimurn results. For each combination, a maximum degree ` of inhibition seems to occur at a particular level within the preferred ranges described above and higher concentra-tions of either component or of the combined components :. :
13,313A-F`
' ' :

6~

provide slight added pro-tection, if any. In many cases, higher concentra-tions seem to cause a slight decline in the degree of inhibition after a maximum has been reached.
- The polyamine component includes ethylenediamine, propylene diamine, the various polymeric forms of these such as tetraethylenepentamine, hexaethylenehepta~ine tripropylenetetramine, dipropylenetriamine, the higher molecular weight compounds of the same type and also the closely related polymers of ethylenimine and propylenimine as well as mixtures of any of these including polyalkylene polyamines containing mi~ed ethylene and propylene groups.
These straight chain and branched chain polyamines can have molecular weights running as high as several hundred thousand.
The term polyalkylenepolyamine is used herein to mean all of - 15 these polymeric forms and mixtures thereof. Polyethylene-polyamines are preferred, particularly those having an average molecular weight of about 100-1000.
~ While any significant quantity of the combination - of the pyridinium salt and the polyamine will provide some degree of inhibition of corrosion, at least about 100 parts per million concenLration of the combination in the gas conditioning solution is usually required to provide practical protection. Either the polyamine or the pyridinium salt alone will provide no inhibition or only partial in-: ~ .
hibition. It appears that relatively little of the poly-amine is usually needed in the presence of the pyridinium salt, however, concen-trations as low as 50 parts per million of polyamine in the presence of 50-100 parts per million of pyridinium salt having been found to give effective inhibition 18,313A~ _5_ ,, .: , ,, ~ , ' ' , ..
,, , ,. , . , .. ~ , i,. . .... .. . .

~08~6~37 in some cases. About ~he maximum degree o~ inhibition obtainable with a particular combination is usually found when the concentration of the polyamine reaches a con-centration of 50-500 parts per million. Higher concentra-tions of this component appear to offer little or no added benefit.
On the other hand, it has been found that at least about 50 parts per million and preferably 100-1000 parts of the pyridinium salt is required to obtain optimum results.
The present invention afEords effective inhibition of iron and steel corrosion by sour gas ~ -conditioning solutions containing dissolved CO2 and H2S
; using relatively low concentrations of an inhibitor combina-tion which is easily handled and convenient to use.
A concentrate of the combined compounds when the -thio compound is a thioamide or a sulfide can be made up in aqueous alkanolamine, aqueous giycol, or lower -~ ~ alkanol and this concentrate can be added to the gas treating solvent as required to make up or to maintain a desired concentration. Since thiocyanates tend to react on standing with the quaternary salt to form a difficultly soluble, less active product, these thio compounds are best added separately to the gas treating solution, thereby forming the combination in si-tu a-t higher dilution.
When a polyamine is the co-inhibitor, any con~
centrate should contain about 0.01-10 parts of the polyamine per part of pyridinium salt and a concentra-te containing 0.1-1 part by weight of polyamine per part of salt is most preferred 18,313A~F ~6-.

This inhibitor combination is particularly useful in aqueous lower alkanolamine solutions known as sour gas scrubbing solvents. Preferred lower alkanolamines ca~ be defined as those having the formula:
~, R R
~ N-C-C-OH
R R
wherein R' and R" independen-tly represent hydrogen or ; -CR2CR2-OH and wherein each R may be hydrogen or an ~ alkyl radical of 1-2 carbon a-toms. Representative ,~ .
alkanolamines are ethanolamine, diethanolamine, tri--~ 10 ethanolamine, isopropanolamine, diisopropanolamine, :.
`~ and N-methyldiethanolamine. Related alkanolamines which are useful acidic gas absorbents are Methicol (3-dimethylamino-1,2-propanediol) and diglycolamine :;
J (2-(2-aminoethoxy)ethanol). Other gas treating ab-lS ~ sorbents in which this inhibi-tor combination is effec-tive include suLfolane (tetrahydrothiophene~ dioxide) and aqueous potassium carbonate. These absorbents - ;~ can be employed alone or in combinations of two or more, usually in aqueous solution although the water may be replaced partly or entirely by a glycol.
The inhibitor combination of this invention . .
is also effective to inhibit corrosion of iron and ~
, ~ .
steel by a gas-treating solution containing both CO2 -, ::
and ~2S when the ~l2S is present in the solution at ; 25 limited concentration, up to about 500 ppm, for example, and preferably not more than about 150 ppm. The inhibitor combination is thus of wider applicability than many known inhibitors which are not effective in the presence - of dissolved H2S. ~ ~
.,, . ' .
.' '' :.. ~' . :
', ::',, :, 18,313A-F _7_ ... . . . .
- ,. .. ; . .. , .. . . , ,. . :
', ~ ' . , . , ' ' ' , , ' ' . ~ ' ' ' ' ', ' ' ', ~ .

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

Testing Procedure :
The corrosion of mild steel by aqueous alkanol-amine solutions saturated with CO2 for 7 hours at 10-20C
was measured at elevated temperat~res and moderate S pressure. Loosely capped bottles each containing 120 ml of test solution and a totally immersed 1 x 2.5 x 0.0625 inch coupon (2.54 cm. x 6.35 cm. x 0.16 cm.) of mild steel were put in a modified pressure filter for a ` period of 16-18 hours, at 125C and 40 psig (2.8 kg./cm~2) unless otherwise specified. The test solvent was 30%
; by weight aqueous ethanolamine unless o-therwise specified.
The steel coùpons were previously cleaned with 5N HCl by~
immersion for 30 minutes at room temperature, followed by a soap and water wash, a water rinse, then an acetone rinsa and air drying. At least two bottles of each trial solution were tested in each experiment along with three bottles of solution containing no lnhibitor which served as controls.
After testing, the same cleaning procedure was used except ~ ~
that the HCl treatment was 15 minutes with SN HCl inhibited -with a commercial HCl inhibitor in order to remove any -'' :
corrosion deposits. The corrosion rate and efflciency of inhibition were calculated according to the following formulas using the average weight loss of the test coupons:
Rate in mils/yr (cm./yr.j =
(0.025~) x 534 x mgs weight loss of coupon (coupon density, g/cc)(coupon surface, sq in) (6.45cm. /in. ~(hrs) % Inhibition = -Corrosion rate of blanks - rate of test coupons x 100 .. .. . . _ . ............. . _ _ .
corrosion rate of blanks 18,313A-F -8-: . , .

Preparation of Qua-ternary Salts The qua-ternary pyridinium salts used in the inhibitor compositions were made by heating a mixture of the pyridine compound with excess alkyl halide or benzyl halide at 90C for two hours. The reaction mixture was then cooled and the quaternary salt was recovered as a solid or viscous liquid precipitate.
The inhibitor compositions were added to -the . aqueous ethanolamine as a solution in a small amount 10 of 60% by weight aqueous ethylene glycol or isopropyl alcohol.
~ Example 1 -.
: The pyridinium quaternary salt used in these tests was the reaction product of tetradecyl bromide . .
and high boiling alkylpyridine still bottoms (HAP).
These still bottoms were from processes for making various ~ .
lower alkyl substituted pyridines wherein most of the components were pyridines having multiple lower alkyl ~
:. substituents, particularly methyl and ethyl groups. ~his :
~: mixed quaternary salt was tested in combination with ~
NH4SCN, thioacetamide, thiourea, thionicotinamide, and ; .
thioisonicotinamide at various concentrations as noted.
., , , ': ' ' '.', .

. ~ -.....
1~,313A-F -9- -. . .

' Thio Concentration, ppm by wt.
Compound Quat. Salt Thio Compound % Inhibition N~I~SCN 100 10 82.5 100 25 86.8 500 25 91.6 500 50 93.9 Thioacetamide 100 25 88.3 -- 100 50 83.2 ~ 500 50 89.5 .... _ Thiourea 100 50 72.5 , 500 50 77.6 _.. __ . . .. _ . _ Thionicotinamide 100 25 92.2 100 50 92.2 Thioisonieotin-amide 100 25 92.2 -; 100 S0 - 92.2 ~
: . .
`~ 15 Example ? ~: -....
Combinations of thiourea with benzyl pyridinium ',~ ehloride and with dodeeylbenzyl alkylpyridinium ehloride ~ (made from the alkylpyridine still bottoms described in ,; . . .
Example 1) were -tested for inhibition as described above. A eombination of dodecylbenzyl alkylpyridinium ~ -ehloride with thioacetamide was also tested.
Pyridinium Coneentration, ppm by wt.
Chloride ~ ~O Inh~bition . . .
- Benzyl 1000 none 11 1 Dodeeylbenzyl 1000 none 66.6 1000 1 89.7 1000 5 90.3 .: :
Dodecylbenzyl 1000 1* 91.5 1000 5* 90.6 1000 25* 90.6 - * Thio compound was thioacetamide - .

~ 18,313A-F -10-- - .

.

Example 3 Quaternary salts made from various higher alkyl bromides and alkylpyridine still bottoms were tested as inhibitors with and without NH4SCN as in the foregoing examples.
Pyridinium Concentration, ppm by wt Bromide Quat. Sal-tNH SCN~ Inhibition --~

Dodecyl 100 none 7.2 100 50 64.4 500 10073.1 :
Cetyl 100 none-34.4 100 50 59.7 500 10062.3 Octadecyl 100none -14.3 ~- 100 50 43.8 -500 10053.9 -,, _ ..... . .. . . ..
Example 4 Quaternary salts made by reacting tetradecyl bromide with different alkylpyridines were tested as ` inhibitors in combina-tion with NH4SCN by the procedure ~-0 F~eviously : . .

18~313A-F

., .
. , . :,, , , : .
, . .. . . .

Concentration, ppm by wt.
Alkylpyridine Quat. Salt NH4SCN ~ Inhibi-tion

2-methyl- 100 50 27.0

3-me-thyl- 1000 none 54.5 1000 50* 88.8 2-ethyl- 50 50 3.2 100 50 31.1 ~ -:, ~
3-ethyl- 100 50 83.7 500 50 93.6 .
2,4-dimethyl- 100 50 83.9 ' 500 5~ 8307 ~' ..: ' , ,, , ,. . ,, ,.,_ __ ,, .
- 3,5-dimethyl- 100 50 60.8 ~
:
500 50 73.3 ., .. _ ., .... - ------ . , 5-ethyl-2-methyl- 100 50 82.5 500 50 90.9 ., _ , ,, __~
3-ethyl-4-methyl- 100 50 88.1 ~ 100 100 89.9 500 100 95.7 , .. ...
2,4,6-trimethyl- 100 50 73.5 500 50 84.9 , ,, ., . . _ _ ,, . . . , , ,, .. , ., . _ . _ * Thio compound was thioace-tamide 18,3J3~-F -12-, , ' . ' . .

~3 61~7 E~ample 5 The quaternary salt of Example l (tetra~ecyl alkylpyridinium bromide) was tested in combination with N~4SCN as before excep-t for using 35~ by weight aqueous etllanolamine. Blanks were also run for comparison.
Concentration, ppm by wt Quat. Salt NH4SCN% Inhibition 100 none -24.2 lO00 ,none -36.9 .... _.
none lO0 - 8.4 10 none 500 -20.2 39.3 500 26.4 ~-- - - :
lO0 25 88.5 lO0 50 94.5 lO0 500 92.3 ~ . :. . . :
500 lO 87.4 500 50 92.6 500 lO0 96.4 500 500 92.0 , 20 lO00 25 8l.0 ;` lO00 50 87.6 1000 lO0 89.2 lO00 500 89.5 ... .
.: . ...

:: .
i '~

. .
.

18,313~-F -13-:, . :. -, - .: , ;: , : , . . . .. ..
: '-:, :., . ' , . ' .,, . . ,, '' . : , , :
. ,. , . . , ,. , , . ,: . :, , ,. ".. . ..

E~ample 6 ~8~6~7 The same quaternary salt described in Examples 1 and 5 was tested as before in combination with NH4SCN at various concentrations using 15% by weight aqueous ethanolamine as the test sol~ent.
Concentration, p_m by wt.
; Quat. Salt NH4SCN % Inhibition :' , ' 68.3 91.9 ~ -- . 50 500 95.9 . . .
100 10 96.4 100 50 95.8 : 100 500 96.2 ~: 500 10 9~.2 500 50 93.3 500 500 9~.8 ... ... . . .. _ _ . . _ . .
-~ : 1000 10 89.0 1000 50 87.6 1000 500 91.7 , "' " ' ' , , , , ' ' ' ;' ;~ ' ' ,: .. .

; 18,313A-P -14- :
~ . ,.: .. .. ..

,.''.. ' ', .' .~.', ~'. "' ', . , , ' ' .

Examples 7-10 The quaternary salt describ~d in Examples 1 and 5-6 was tested in combination with NII4SCN as before using various aqueous alkanolamine-containing solutions as test solvent.
Concentration, ppm by wt. Corrosion Quat._Salt. NH4SCNSolvent (mm./yr ) % Inhibition 70% TEA 10.1 ---100 50 " 0.3 92.6 500 100 " 0.7 93.1 _ _ _ (0.02) --- --- 50~ DEA 10.4 --- -100 50 " 0.6 93 500 100 " i~o 90.4 (0.03) --- --~ 60~ DEA2 27.1 --- -500 50 ~ 1-1 96.1 , (o . 03?
-- _ :
--- --- Mixed 19.0 ---100 --- " 2.6 86.5 500 ___ ~ (0 07) 89 4 100 50 " (i.65) 91 8 ` 500 100 " ~i.5) 92.1 (0.04) lTEA - Tr1ethanolam1ne, by weight DEA = Diethanolamine, by weight Mixed = 45% diisopropanolamine, 35% sulfolane 20~.water, by weiyht ' ~ .. ' .: ' ~ ' ' ~'"'"' ' '~

18,313A-F -15-:'. ', -:. , - . , ' -, , ,.. , , ' , ' " , ': . ' ' ' ' . ' ,'-':" ' ~' "'' ' ' ''"' ' ' ~ "'' '''' ' ' '' 6a~
Example 11 Combinations of tetradecyl alkylpryidinium bromide and NH~SCN were tested in 30% by weight aqueous ethanolamine saturated with CO2 and containing 100 ppm by weight of sulfide ion added as ammonium sulfide under test conditions otherwise as previously described.

Concentration, ppm Qua-t. Salt NH~SCN % Inhibition 100 --- 76.5 500 ___ 94.1 100 50 76~6 500 50 89.2 100 100 77.1 500 100 93.3 ;~ 15 In the above tests, the ammonium sulfide present in the alkanolamine solution to simulate the presence of H2S served as the thio compound and so the quaternary salt was active even in the absence `~ of NH4SCN.
Examples 12-17 -~
In the following examples, the quaternary salts ~ere prepared as in Examples 1-11 and the same test pro-cedure was used, except that an H2S equivalent was added to the aqueous alkanolamine. The H2S was added to the CO2-saturated aqueous alkanolam;.ne as an amount of aqueous (NH~)2S sufeicient to supply sulfide and hydro-sulfide ions in.about the same concentrations as the ~1 listed.H2S concen-tration would provide. In Examples 12 to 14 the corrosion inhibition testing was done at 125C
: 30 in 30 percent by weight aqueous ethanolamine saturated :~.
with CO2 and containing the equivalent of, by weight, 100 ppm, 300 ppm, and 500 ppm H2S as (NH~)2S, respecti~ely.

~ ' 18,313A-~ -16-' ,~ .. . .. . .
,, . ~ . , . . ' ' ' : . : .

08~6 Example 12 (100 ppm H2S) :
Quat.Concentration, ppm by wt.
Salt Polyamine Quat. Salt Polyamine ~ Inhibition TAPB(l) PEI_3(2) 100 -- 76.5 500 -- 9~.2 -- 100 64.3 -- 500 49.1 -100 100 94.3 -500 100 95.5 ` 100 500 94.2 `--- _____________________ :
TAPB(l) E-100(3) -- 100 47.5 ` ` `
~~ 500 57-7 100 100 94.9 500 100 95.2 -~ (1) TAps = Tetradecyl bromide salt of polyalkylpyridines in lower alkylated pyridine still bottoms (HAP).
These still bottoms were ~rom processes for making various lower alkyl substituted pyridines wherein most of the components were pyridines having multiple lower alkyl substituents r particularly methyl and ethyl groups.
( ) PEI-3 = Polyethylenimine of about 300 average molecular - weight. - -(3) E-100 = Ethylenediamine plant still bottoms containing 85-90% pentaethylenehexamine and hexaethyleneheptamine with some tetraethylenepentamine and small-amounts o~ branched and cyclic isomers and derivatives.

Example 13 (300 ppm H~S~

'7 ` ' Quat. Concentration, ppm, by wt.
Salt Polyamine Quat. Sa~r-~-Polyamïne % Inhibi-tion TAPB E-100 100 - 72.6 500 -- 86.0 i 1000 -- 83:7 -- 100 - 4.6 500 100 88.7 `
100 500 gO.l :~' ~, : ' , . - .. . - . , ~:
18,313A-F -17- `
.~ ~
.. . . .. . . .
' " ' ' ' ' ', .

6~37 Example 14 (500 ppm H2S) . , .
Quat. Concen-tration, ppm, by wt.
Sal-t Polyamine Quat. Sal-t Polyamine % Inhibi-tion TAPB E-100 100 -- 57~1 500 _- 84.8 100 100 89.0 500 100 88.1 500 500 91.3 Examples 15-17 are essentially a repeat of Examples 12-14 using 60 percent by weight aqueous diethanol-amine as the éthanolamine solution. Equivalent amoun-ts of ~:
aqueous (NH4)2S were added as before to the CO2-sa-turated alkanolamine to provide about the concentrations of sulfide and hydrosulfide ions formed by the listed amounts of ~. 15 H2S .
Example 15 (100 ppm H2S) .~ .
Quat. Concentration, ppm, by wt.
Salt Polyamine Quat. Salt Polyamine % Inhibi-tion TAPB E-100 100 -- 92.8 ~ ~ 500 -- 93.6 - 20 1000 -- 92.3 - -- 100 25.8 A; . 500 55.8 100 100 96.2 500 100 96.2 , .
Example 16 (300 ppm H2S) :. . .
Quat. Concentration, ppm! by ~t. _ Salt Polyamine Quat. Salt Polyamine ~ Inhibitio~
TAPB E-100 100 -- 88.6 5~0 -- 90.3 ~- 10 0 ~9 . 1 -- 500 ~0.2 100 100 93.2 500 100 91.8 -- 100 500 92.6 18,313A-F -18-. .. ... .
:. ~
. .

3fl6~7 Example 17 (500 ppm H2S) Quat. Concentration, ppm, by wt.
Salt Polyamine Quat. Salt Polyamine % Inhibition TAPs E-100 100 -- 8~.0 500 -~ 83.2 ~ -1000 -- 84.0 -- 100 39.6 -- 500 46.3 -- 1000 27.6 100 100 86.6 500 100 85.5 Similar effective inhibition o~ corrosion is found when the quaternary salt of the above examples is replaced by the same amount of other pyridinium salts as previously defined, for example, dodecylbenzyl 3-ethyl-

4-methylpyridinium chloride, dodecyl alkylpyridinium bromide (made from HAP alkylpyridine still bottoms), tetradecyl 3-ethylpyridinium bromide, and tetradecyl trimethylpyridinium bromide. Similarly, closely comparable :
results are obtained when the polyamine component in these examples is replaced by the same concentration ~
of polypropylenimine of 500 average molecular weight, -triethylenetetramine, hexapropyleneheptamine, or other such polyamine as defined above.
In the same way, ef~ective inhibition o~ ferrous metal corrosion is also obtained when these quaternary pyridinium salt-polyamine combinations are Inaintained at the disclosed concentration in other sour yas conditioning solutions such as previously described. For example, aqueous or glycol-containing solutions o~ diethanolamine, ~ ~
.. , ~ ,.
~. , ' .~ ' .'' . ~ .
', '.-''".

~' ' ' 1~,313A-F -19-~ . :
~'' ~ ; ;

~0~;8~

N-me-thyldiethanolamine, diisopropanolamine, and mixtures of these including mixtures with sulfolane and-other known gas conditioning solvents, also aqueous potassium carbonate are all pro-tected by these inhibitor combinations.

~ .

~', ~,. .
;' , ' ' '.
' :~ ' ' ' ' ' -'"
~-'. .
.
- ' ' ' ,;

18,313A-F -20- :

,', . . .
. . .
' . ' ' . , .
.

Claims

1. A composition for inhibiting corrosion of iron and steel by carbon dioxide and optionally a minor quantity of hydrogen sulfide in gas conditioning solutions, comprising an inhibiting concentration in said solution of a combination of one part by weight of a quaternary pyridinium salt and (1) 0.001-10 parts of a thio compound which is a water-soluble thiocyanate, a water-soluble sulfide, or an organic thioamide, or (2) 0.01-10 parts of a lower alkylenepolyamine, a corresponding polyalkylene-polyamine, or a mixture thereof wherein the alkylene units contain 2-3 carbon atoms.

2. A composition as in Claim 1 wherein the pyridinium salt has the formula:

wherein R is an alkyl radical of 1-20 carbon atoms, a benzyl radical, or an alkylated benzyl radical wherein the aromatic ring has one or more alkyl substituents totaling 1-20 carbon atoms, each R' is a hydrogen atom or an alkyl radical of 1-6 carbon atoms, and X is an anionic radical.

3. A composition as in Claim 2 wherein the in-hibitor is said pyridinium salt and said thio compound.

4. A composition as in Claim 3 wherein thio compound is thiourea.

5. A composition as in Claim 3 wherein the thio compound is ammonium thiocyanate.

6. A composition as in Claim 2 wherein R is an alkyl radical of 10-18 carbon atoms.

7. A composition as in Claim 6 wherein the pyridinium salt is tetradecyl polyalkylpyridinium bromide.

8. A composition as in Claim 2 wherein the in-hibitor is said pyridinium salt and said alkylenepolyamine or polyalkylenepolyamine.

9. A composition as in Claim 8 wherein the alkylenepolyamine or polyalkylenepolyamine is polyethylene-polyamine having an average molecular weight of from 300 to 1000.

10. A composition as in Claim 8 wherein the pyridinium salt and the polyamine are present in weight proportions of 1 to 0.01-10.