DE2134798B2 - Process for inhibiting corrosion in the removal of acidic gases from a gas stream - Google Patents

Description

Gases such as natural gas, exhaust gas and synthesis gas are available through the use of aqueous alkanolamine solutions Absorption of the acidic gases contained in the gas stream has been cleaned. Usually a 5-30% flow Alkanolamine solution (e.g. a monoethanolamine solution) in countercurrent to the gas flow in an absorption column, to remove the acidic gases. One advantage of such a system is that the method is a continuous cycle and so the reaction can be reversed at higher temperatures to achieve the to release acidic gases from the solution.

Using steel parts or components in such a system has found that both a general as well as locally corrosive attack can occur. This is a particular problem in Cookers and heat exchangers where the steel is exposed to a hot, protonated alkanolamine solution. A heat transferring metal surface appears to be particularly vulnerable. Investigations have in the Past established that under certain eo conditions corrosive products such as aminoacetic, Glycolic, oxalic and formic acid. The monoethanolamine salts of these acids give the Possibility of increased attack against ferrous metals. Furthermore, the carbonate t> 5 salt of monoethanolamine can be converted into other products such as N- (2-hydroxyethyl) ethylenediamine, which have been found to affect the corrosiveness of steel, particularly under heat transfer conditions, raise.

There are several alternatives for reducing corrosion rates, such as, among others (1) the installation of a sidestream collection device to remove corrosive degradation products, (2) the use of more corrosion resistant construction materials, (3) better control of process conditions and (4) the use of corrosion inhibitors. From the cost and effectiveness standpoint the latter alternative is preferred. Certain corrosion inhibitors stated to be effective however, have not gained industry-wide adoption, possibly because they are unable to provide lasting protection in any particular respect.

The present invention now relates to a method of inhibiting corrosion in the removal of acids Gases from a gas stream by absorption of the gases in aqueous alkanolamine solutions, which is characterized is that one of the aqueous alkanolamine solution

1) in a weight ratio of 9: 1 to 1: 9 vanadate and antimonyl salts, the vanadate salt from the Group of sodium metavanadate, potassium pyrovanadate and potassium orthovanadate and the antimonyl salt is selected from the group of potassium antimonyl tartrate and sodium antimonyl gluconate, or

2) Stannous salts from the group of stannous tartrate, stannogluconate, stannous chloride, stannous acetate and Stannofluoborate or

3) organic tin compounds from the group of di-n-butyltin dimethoxide, n-butylstannonic acid, Dimethyl tin oxide and diethyl tin dichloride or

4) aromatic nitro compounds from the group of sodium m-nitrobenzoate, sodium 4-nitrophthalate, Nitroterephthalic acid and p-nitrocinnamic acid

admits.

Antimony compounds are already used as inhibitors to prevent attack by ferrous metals has been used by aqueous monoethanolamine solutions. A hypothesis from working with Compounds containing antimony in acid solutions were used as iron or steel corrosion inhibitors act by reducing and causing a deposit of antimony to form on the metal surface that the inhibition of cathodes with local effect results. There is also the possibility an additional secondary anodic effect.

Vanadates were known in the past as iron or steel corrosion inhibitors, but they became too not used much for this purpose. The oxidation states of vanadium suggest that the vanadates as Oxidant-type inhibitors work.

If it has now been found that despite the different inhibition mechanisms by certain Antimonyl and vanadate compounds are a combination of these compounds gives a synergistic effect, this is to be regarded as surprising.

The preferred antimony compound is potassium antimonyl tartrate having the formula

K (SbO) C ₄ H ₄ O ₆ '/ 2H ₂ O.

Where this compound is used in the combination according to the invention, there is an improvement Stability still tartaric acid is used in an amount equal to / to the antimonyl concentration. Suitable Va-

nadat compounds are ζ. Β. Sodium metavanadate, Potassium pyrovanadate and potassium orthovanadate. The preferred one Vansdat compound is sodium metavanadate.

The compounds are mixed together so that there is a ratio of the antimonyi compound to the Vanadate compound yields from about 1 to 9 parts by weight to about 9 to 1 part by weight. The preferred one The ratio is between 4: 6 to 6: 4 parts, with equal parts being very particularly preferred.

The combination is preferably in an amount of 0.01-1.0% by weight, based on the weight of the aqueous alkanolamine solution including the weight of water and alkanolamine added. These Percentages apply to all corrosion inhibitors according to the invention.

Other compounds that can be used are tin compounds, such as stannous salts from the group of stannous tartrate, Stannogluconate, stannous chloride, stannous acetate and stannofluoborate, as well as organic tin compounds from the group of di-n-butyltin dimethoxide, n-butylstannonic acid, Dimethyl tin oxide and diethyl tin dichloride. Stannotartrate and stannogluconate are preferred, especially stannotartrate.

Stannotartrate and stannogluconate are the preferred compounds as they are present in amounts of at least 1% and up to 2% by weight have been found to be soluble in concentrated Alkanolamirien.

Other compounds that can be used are the nitro-substituted ones aromatic acids from the group of sodium m-nitrobenzoate, sodium 4-nitrophthalate, nitroterephthalic acid and p-nitrocinnamic acid. These compounds can be oxidizer-type inhibitors by causing a certain anodic polarization, the mechanism perhaps also being a Chemisorption exercises together with an oxidation. The result of using these compounds as a The protection exerted by inhibitors appears to be relatively dependent on temperature.

Alkanolamine systems that can be improved by the process according to the invention are mono- and polyalkanolamines having 2-4 carbon atoms per alkanol part. Typical alkanolamines are monoethanolamine, Diethanolamine and monoisopropanolamine.

The corrosion inhibitors used according to the invention were in monoethanolamine / water-carbon dioxide solutions tested, because although aqueous monoethanoiamine solutions per se compared to iron-containing ones Metals are not corrosive, they become strong against mild steel after saturation with carbon dioxide corrosive. Electrochemical corrosion is believed to occur with the anodic reaction of the They can be expected to have products such as ferrohydroxide, ferrocarbonate, or certain complexes forms.

In some of the examples, metal strips measuring 76 38 χ 1.6 mm were made using a mild one Cleaned with abrasive clean by scrubbing with a brush and then rinsed with water and acetone. The dry, clean metal strips were then weighed and placed upright in a 600 cc glass cell given, whereupon the strips were separated by means of Z-shaped glass rods. The strips were through Addition of 400 ecm of the monoethanolamine test solution completely covered previously at room temperature had been saturated with carbon dioxide. Then each cell was equipped with a reflux condenser, a sprinkler tube and thermometer and placed in a constant temperature bath. The solution was Maintained at test temperature for 72 hours with carbon dioxide being released at a standard rate of 100ccm / min was initiated. The metal strips were inhibited by briefly immersing them in a j Hydrochloric acid solution cleaned, rinsed with water and acetone and air-dried. Then there was weight loss certainly.

The heat transfer effects relative to corrosion of the steel were measured as follows: One

κι weighed steel plate of 76 χ 76 χ 4.8 mm was attached to a 1000 cc flask using a 1/2 '' pipe connector. The plate was with a 500 watt soldering iron for which a special head had been made to heat the unit to stick together. A variac device was used to regulate the heat input; for recording the corresponding metal temperature was a thermocouple half the distance from the Plate edge drilled into it. The flask was fitted with a reflux condenser, thermometer, and Sprinkler pipe fitted. In all tests, the heat input was sufficient to last for the 72 hour test duration to maintain violent boiling, releasing carbon dioxide at a standard rate of 100ccm / min was initiated. About the effect of the steel heating by the soldering iron heating device described above to be compared with that which is created simply by immersing a steel plate, became a 38 38 χ 1.6 mm plate of the same steel

ju hung in the solution by means of a hook. As was found to be the rate of corrosion of the heat transfer plate in dilute monoethanoiamine solutions significantly larger than that of the immersed plate (in the examples »suspended-

called j5th stripe ”). The metal strips and plates were cleaned after the test by brief immersion in an inhibited hydrochloric acid solution, in water and Acetone rinsed and air dried. The corrosion of the steel was due to both weight loss and weight loss determined by appearance.

Corrosion of mild steel and Type 304 stainless steel from monoethanoiamine solutions has been observed Conditions of Higher Temperatures and Pressures Using a Parr 4500 Series Pressure Reactor, examined. Cleaned and weighed metal plates Mild steel and stainless steel 76 19 χ 1.6 mm hung on hooks in the reactor were used completely covered by monoethanolamine solution treating with carbon dioxide at room temperature had been. After closing the reactor with its pressure lid, carbon dioxide was released through the Solution passed to decrease the available oxygen. Then the plant was under for 24 hours heated to the desired temperature using the natural pressure developed by the solution. After that were the metal strips are cleaned by briefly immersing them in an inhibited hydrochloric acid solution, with water and Acetone rinsed and air dried.

The above test procedures were used in the following examples embodying the present invention illustrate without limiting them.

example 1

In this example the system was designed in such a way that the steel plate in question also used the heat source Maintaining a violent boil of the solution. A thermocouple reading showed that the

5 6

The temperature of the heat transfer ^{plate was 120 0} C for all experiments with the introduction of carbon dioxide was a 15% monoethanolamine solution, which was 72 hours. The percent protection was as follows: Melt temperature was ^{approximately 101 ° C.} The test duration calculates:

Uninhibited weight loss inhibited weight loss Uninhibited weight loss

KK).

The results are summarized in the table below. The following abbreviations were used used:

MEA = iVsonoethanolamine; HEED = N- (2-hydroxyethyl) -a'thy! Enediamine. Protection of mild steel in%

Inhibitor and amount in% 0.1 Amine solution
in % worm over
tragur.gs-
platle Suspen
dated
Stripes Appearance of the heat transfer
platle after the test Sodium metavanadate 0.1 ! 5MEA
30 MEA
15 HEED 85
94
0 85
95
0 well maybe some small holes
like New
heavy crevice pits,
those for weight loss
are responsible Potassium antimonyl tartrate 0.01 30 MEA 83 80 light general attack Tartaric acid 0.05 15 HEED 95 28 like New Sodium metavanadate 0.05 15 MEA 93 92 like New Potassium antimonyl tartrate 0.005 30 MEA 96 97 like New and tartaric acid 15 HEED 97 90 like New Example 2

Aqueous Monoäthanolaminlösur.gen with a content of 15 wt .-% monoethanolamine, which at room temperature treated with carbon dioxide were placed in a small Parr 4500 series pressure reactor, placed; then the reactor was sealed, heated, and the natural pressure of the solution was released let develop. The corrosion studies

i ¹ ) Done with an uninhibited solution and one with 0.04% sodium metavanadate, 0.05% potassium antimonyl tartrate and 0.005% tartaric acid on samples of cold rolled mild steel and stainless steel, Type 304. The working conditions and results were as

40 follows:

Uninhibited 125 Inhibited 125 Evaluation conditions 14th 17.5 Temperature, &quot; C 100 24 100 24 Pressure reading, kg / cm ² 8.4 7.7 Time, st 24 0.5 24 <0.025 Corrosion losses, mm per year <0.025 none cold rolled mild steel 0.5 <0.025 stainless steel, type 304 <0.025 none Example 3

In order to test the effect of the corrosion inhibitors according to the invention under more severe conditions, e> o was the antimonyl vanadate combination with the individual additives in the corrosion test with aqueous Monoethanolamine solutions compared the 65 wt .-% monoethanolamine at the boiling point of the solutions contained, which passed through at the same time with carbon dioxide *> ■> were rinsed. The purpose of these conditions is that they provide faster and more stringent evaluation measures of inhibitors offer. After 72 hours under these

Conditions were the corrosion of steel strips as in the above examples by comparing the Weight losses determined with similar strips immersed in uninhibited solutions. From the following Results with duplicate and sometimes triple tests can be seen that with the combination, however, a reproducible, satisfactory Schulz cannot be achieved with the individual additives could.

Inhibitor and amount in%

Sodium- Potassium antimonyl Protection area mctavanadat tarlrat with mild steel in % 0.1 0 42-99 0 0.1 0-16 0.05 0.05 99 ± 1 0.05 - 70-99 0 0.05 0 0.025 0.025 99 ± 1

The poor reproducibility with sodium metavanadate alone is a hallmark of anodic inhibitors at a limit concentration, which is sometimes shown by a severe, local attack.

Example 4

Here was one of the tin compounds according to the invention, namely Stan notary Trat, monoethanolamine, tested at different concentrations _s under heat transfer conditions on their protection for mild steel in two different systems of water, carbon dioxide and Stan notary Trat. All solutions were constantly flushed through with carbon dioxide. The results were as follows:

Stannotartrate
Wt%

Percentage protection ^A )

0.005

0.01

0.025

0.05

0.1

0.005

0.01

0.025

0.05

0.1

66

73 77 87 87

85 92 95 93

^Λ ) l'ro / cntualci school / from immersed l'lulklahlplatlcn. calculated by

uninhihicrlcr (icwichtsvcrlusl

more inhibited

iiniiiliihicrler (icuichtsvcrlusi

KX).

¹¹ I! '. Inc solution with lü (iew .- "/ n Moiioaihaiiolamin« urile λ Tnpc

to about K) I (° crhit / l. 'I I.inc Ii) MITIU with fö (ieu .-' Ί. Momiälhannlamin was 3 Jane to about ID7 C crhil / l.

The following example was performed using the sodium octavanadate / potassium antimonyl tartrate / tartaric acid inhibitor system to test under the conditions of an industrial plant.

Example 5

An ammonia plant with a capacity of 1000 t / day using the Girbitol process was examined to absorb the remaining carbon dioxide from the hydrogen stream with an 18% aqueous mono-

Ethanolamine solution used as an acidic gas absorption medium.

The inhibitor combination consisted of 0.05% each of sodium metavanadate and potassium antimonyl tartrate and 0.005% tartaric acid.

The first method of evaluating corrosion was to determine the weight loss of Metal samples held in racks strategically placed in the plant's streams. It ίο the following results were obtained before and after the addition of the inhibitor combination:

Attachment of the corrosion frame ') (4 metal samples each)

Average rate of steel corrosion mm / year ² )

before after

the addition of inhibitor

At the heat exchanger between the 0.071 0.020 amine-rich and amine-poor solution on the side poor in Amin

Amine-rich solution, after the 5.77

hydraulic turbine

0.010

') Flow rate of about 19 l / min, caused by the Corrosion racks was maintained.

² ) mm / year, calculated from the weight loss after 5-22 days.

A second method of evaluation used a "Corrosometer", model CK-2. There were Probes of the metal in question were immersed in the stream of the plant, and the metal was lost through Change in the electrical resistance of the probes measured. The following readings, which have a Period of several months, confirm the effectiveness of the inhibitor combination for both Mild steel as well as stainless steel, type 304.

Corrosometer readings with probes in the amine solution

Metal type Average from
read corrosion
speed
mm / year before after the inhibitor addition c Mild steel 14.0 none Stainless steel, type 304 0.044 none

The same plant was continued to check for signs of corrosion during the Reverse Period examined 5 months after the addition of the inhibitor. The tube side of the heat exchanger between the at The amine-poor and amine-rich solution was investigated, since with the uninhibitable amine solution the corrosion, especially the baffle plate, was a problem. After 5 months of working with the inhibitor, it became apparent

none of the parts any attack. Furthermore, the upper sections of the stripping columns and developed Branch lines to the pipe side of the heat exhaust

10

exchangers, which were frequently perforated by the uninhibited solution, did not leak any leaks during the entire working time with the inhibitor combination.

Example 6

Following the procedure of Example 4, additional samples of tin compounds were evaluated for their ability to inhibit steel corrosion under heat exchanger conditions,
obtained the following test results:

The

Tin compound Wt% % Amine solution Percentage protection 80 Heat over- suspen-
support plate dated
Stripes 80 Stannotartrate 0.025 15 MEA ¹ ) 75 90 Stannogluconate 0.025 15 MEA 75 95 Stannogluconate 0.05 30 MEA ² ) 80 90 Stannotartrate 0.05 30 MEA 90 90 Stannous chloride 0.05 30 MEA 85 85 Stannous acetate 0.05 30 MEA 70 0 Stannofluoborate 0.05 30 MEA 70 0 Potassium stannate 0.1 30 MEA 0 85 Stannous chloride 0.05 30 MEA 0 70 Di-n-butyltin dimethoxide ³ ) 0.05 30 MEA 85 80 n-butylstannonic acid ³ ) 0.05 30 MEA 45 15th Stannotartrate 0.05 30 1: 1 MEA: HEED ⁴ ) 90 Stannogluconate 0.05 30 1: 1 MEA: HEED ⁴ ) 5

') Aqueous monoethanolamine solution containing 15% by weight of monoethanolamine.
² ) Aqueous monoethanolamine solution with 30% by weight of monoethanolamine.

³ ) Incompletely soluble in the test solution.

⁴ ) Aqueous solution with 30% by weight of a 1: 1 weight mixture of monoethanolamine and N- (2-hydroxyethyl) ethylenediamine.

It is noted that inorganic tin salts with a valence state of +4, such as stannous chloride and potassium stannate, often do not appear to be inhibitory.

Example 7

The tests of Example 6 were carried out using certain nitro-substituted aromatic acids and / or salts repeatedly. The results were as follows:

Inhibitor

Amount of test tem- perature%

% bond "C protection

Sodium-m-nitro- 0.5 65 ') 107 80 benzoate 0.5 15 ² ) 101 95 0.05 15th 80 95 Sodium-4-nitro- 0.5 15th 80 95 phthalate 0.5 15th Zimmerert. 90 0.05 15th 80 90

') Aqueous monoethanolamine solution with 65 wt .-% monoethanolamine for 3 days at the specified temperature.

² ) Aqueous monoethanolamine solution with 15% by weight of monoethanolamine for 3 days at the specified temperature.

Example 8

Under heat transfer conditions as in Example 4, certain other corrosion inhibitors were used evaluated. The results were as follows:

Inhibitor Amine Amine Percentage Protection

% solution of mild steel

Heat transfer plate strips

Sodium m-nitro-0.5 15 89 50

benzoate

Nitroterephthalic 0.1 15 87 0

acid

Claims (3)

Patent claims: 1. Method of corrosion inhibition in the removal of acidic gases from a gas stream by Absorption of the gases in aqueous alkanolamine solutions, characterized in that one of the aqueous alkanolamine solution (1) in a weight ratio of 9: 1 to 1: 9 vanadate and antimonyl salts, whereby the Vanadate salt from the group of sodium metavanadate, potassium pyrovanadate and potassium orthovanadate and the antimonyl salt selected from the group consisting of potassium antimonyl tartrate and sodium antimonyl gluconate is selected, or 1> (2) stannous salts from the group of stannous tartrate, Stannogluconate, stannous chloride, stannous acetate and stannous fluorate or (3) organic tin compounds from the group of di-n-butyltin dimethoxide, n-butylstannonic acid, Dimethyl tin oxide and diethyl tin dichloride or (4) aromatic nitro compounds from the group of sodium m-nitrobenzoate, sodium 4-nitrophthalate, Nitroterephthalic acid and p-nitro- 2 ~> cinnamic acid admits. 2. The method according to claim 1, characterized in that the {combination of vanadate and Antimonyl salts is a combination of sodium metavanadate and potassium antimonyl tartrate. 3. The method according to claim 1 or 2, characterized in that the corrosion inhibitor is added in an amount of 0.01 to 1.0 wt .-%, based on the weight of the aqueous alkanolamine solution, y .