JPS604272B2 - Corrosion inhibitor for alkanolamine gas processing systems - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel corrosion inhibitor for systems treating gases with alkanolamines.

Gases such as natural gas, fuel gas and synthesis gas contain CO2, 2S, COS in these streams.
It has traditionally been purified by the use of aqueous solutions of alkanolamines for the absorption of acidic gases such as alkanolamines. Usually a 5-30% by weight solution of alkanolamine (eg monoethanolamine) flowing countercurrently with the gas stream in the absorption column is used to remove the acid gases. The process is continuous and cyclical, with the alkanolamine solution being counterflowed at elevated temperatures in order to desorb the absorbed acid gases from the alkanolamine solution. When steel components or construction materials are used in such systems, they are susceptible to general or localized corrosive damage.

This is particularly problematic in reboilers and heat exchangers where the steel is exposed to hot protonated alkanolamine solutions. Metal surfaces that conduct heat are particularly susceptible to damage. Previous studies conducted by various people have shown that under certain conditions corrosive products such as aminoacetic acid, glycolic acid, oxuic acid and formic acid are produced. The alkanolamine salts of these acids can severely damage ferrous metals. Furthermore, the carbonate of monoethanolamine can be converted to addition products such as N-(2-hydroxyethyl)-ethylenediamine, which are useful for steels, especially for steels under thermally conductive conditions. It has been found that the corrosive properties of the amine solution are increased. There are various effective proposals for reducing the degree of corrosion.

Among them {1) the provision of a side stream collector to remove corrosive products, ``2'' the use of materials that are more resistant to corrosion, and ``3'' more stringent operating conditions. and {4) the inclusion of corrosion inhibitors. Of these, method (4) is preferred from the viewpoint of cost and efficiency. Various corrosion inhibitors have been proposed to prevent the corrosion that occurs when metals come into contact with acidic gas absorbers. For example, in the United States No. 4,071,47, Utako adds a monoalkanolamine to the acid gas absorbent medium to inhibit corrosion when the metal contacts the acid gas absorbent medium.
sulfur or sulfide and an oxidizing agent together with copper or a salt or sulfide or oxide of copper at 0.1°C to about 100°C until the mixture is stable when diluted with water.
A method for recirculating absorbed soot bodies is disclosed, which consists of introducing a compound obtained by reacting for an hour to about two feeding hours. U.S. Pat. No. 4,096,085 discloses that an amine compound or a mixture of amine compounds selected from a specific class of amine compounds is present in an amount of from about 1 part to about 200 parts per million parts of the solution to be treated; 2) Aqueous N-methyl fluoride with inhibited corrosive power, consisting mainly of a compound that yields 0 to 100 parts of copper or steel ions and a compound that yields 0 to 100 Q of sulfur or sulfur atoms. Tanolamine or jetanolamine acid gas treatment solutions are disclosed.

Nos. 4,100,099 and 4,100,10}, a sour gas conditioning solution is disclosed.

Of these, 1 part by weight of a quaternary pyridium salt according to US Pat. containing 2 to 4 carbon atoms). U.S. Pat. No. 4,100,010 discloses a quaternary pyridium salt, about 0.001 to 10 parts of a thio compound such as a water-soluble thiocyanate or an organic thioamide, and cobalt, which is a divalent cobalt compound when dissolved in the above. and a small but effective amount of. U.S. Patent No. 41431
No. 1y discloses a corrosion-inhibiting composition for absorbing alkanolamine solutions in contact with ferrous metals and their alloys, which compositions are primarily selected from the group consisting of {a} metallic steels, sulfide steels, and copper salts. copper ion source and [b'
'Eiow and Z are {ro}hydrogen sulfide and (or)
a sulfur atomic source selected from the group consisting of COS;
} It consists of an oxidizing agent capable of producing iodine atoms in solution and at least some polysulfide.

In addition to the techniques described above, two compositions which inhibit the effects of corrosion are disclosed in U.S. Pat. Nos. 3,896,044 and 3,808,14.

No. 3,896,044 discloses a method of inhibiting corrosion, consisting essentially of an aqueous solution of an alkanolamine and a corrosion inhibitor selected from nitro-substituted aromatic acids and nitro-substituted acid salts. Compositions are disclosed. U.S. Pat. No. 3,808,140 also discloses an anti-corrosive composition consisting primarily of an aqueous solution of an alkanolamine, a vanadium compound in the 15-valent state, and an antimony compound.

However, the various U.S. patents cited above describe the synergistic combination of the present invention, i.e., an organic compound selected from the group consisting of nitro-substituted aromatic acids, nitro-substituted acid salts, 1,4 naphthoquinones, and mixtures thereof; There is no disclosure of a synergistic combination with a specific vanadium compound, which is vanadium in the 15-valent state.

In fact, U.S. Pat. No. 3,808,14 discloses the use of vanadium compounds in the 15-valent state as effective corrosion inhibitors only when used in combination with antimony compounds. According to the invention, the corrosion of metal surfaces by an aqueous solution of an alkanolamine used for the removal of acid gases, in particular when at least a portion thereof is hydrogen sulfide, can be prevented by vanadium.
a specific vanadium compound in a valence state; and an organic compound selected from the group consisting of nitro-substituted aromatic acids, acid salts of nitro-substituted aromatic acids, 1,4-naphthoquinone, and mixtures thereof. It has been found that inhibition can be achieved by an effective amount of a corrosion inhibitor comprising a co-active combination of: The organic compound is p-nitrobenzoic acid,
It is preferably selected from m-nitrobenzoic acid, 3,5-dinitrobenzoic acid, p-nitrophenol, m-nitrophenol, m-nitrobenzenesulfonic acid, 1,4-naphthoquinone and mixtures thereof.

The corrosion-inhibiting amounts of these vanadium compounds and organic compounds used may be lower than the respective amounts when used alone for corrosion protection purposes. However, it is believed that other beneficial results occur when both of these compounds are used together at higher concentrations. The corrosion inhibitors described herein are particularly useful in aqueous monoethanolamine gas purifiers (scrapers) employed in the removal of hydrogen sulfide and carbon dioxide in natural gas processing systems. According to the present invention, when the vanadium compound and the organic compound are roughly combined at a specific concentration, an amazing corrosion protection effect is achieved, whereas these two compounds individually It has been found that corrosion protection is not achieved at amounts below these combined concentrations.

Vanadium compounds, if the vanadium in these compounds has a valence of 14 or +5, preferably 15, exhibits exceptional corrosion-preventing power when combined with the specific organic compound. According to the present invention, no special restrictions are necessary for the selection of a particular vanadium.

Thus, for example, V24, NaV03, Na3V04, K
V03, N ratio V03, VOC13, VOS04, V02
, VOC12 and others and mixtures thereof can be used. The organic compounds used as corrosion inhibitors in combination with the vanadium compounds mentioned above are nitro-substituted aromatic acids, acid salts of nitro-substituted aromatic acids,
and 1,4 naphthoquinones, and preferably p-nitrobenzoic acid, m-nitrobenzoic acid, 3,5
-Dinitrobenzoic acid, p-nitrophenol, m-nitrophyl, m-nitrobenzenesulfonic acid, 1,4
selected from the group consisting of naphthoquinones and mixtures thereof;

For a particular corrosion inhibitor, the effect of the corrosion inhibitor concentration is generally monotonic. That is, the inhibitor has no corrosion-preventing effect below a certain minimum concentration, but always exhibits an inhibitory effect when the concentration is higher than that. This critical concentration is referred to as the minimum effective concentration for preventing corrosion (hereinafter referred to as m.e.c.). m. of the individual inhibitors. e. c. can be easily determined by testing a given corrosion inhibitor at various concentrations and determining its minimum concentration required for it to exhibit inhibitory power. In the present invention, when the vanadium compound and the organic compound are combined at concentrations below these minimum effective concentrations, these components have a surprisingly superior corrosion-preventing effect than when used individually at the concentrations mentioned above. It has been found.

Furthermore, it is believed that still other advantageous results may be obtained when the vanadium compound(s) and the organic compound(s) are combined in amounts greater than or equal to their respective minimum effective concentrations. The concentration of the vanadium compound and the organic compound may range from about 0.01 mmol to about 50 mmol.

The synergistic combination of these particular vanadium compounds and organic compounds generally involves an amount of the vanadium compound to produce a concentration of about 0.01 mmol to about 1 mmol, and about 0.01 mmol to about 1 mmol.
and preferably the vanadium compound(s) and the organic compound(s) in an amount to produce a concentration of 1 mmol to about 10 mmol.
and are added in corrosion-inhibiting amounts such that the concentrations are less than their respective minimum effective concentrations. Preferred alkanolamine systems for inclusion in the combined corrosion inhibitors of this invention are mono- and polyalkanolamines containing from 2 to 4 carbon atoms per unit of hydroxyalkyl moiety; Typical alkanolamines are monoethanolamine, diethanolamine and monoisopropanolamine.

The corrosion inhibitor of the present invention was tested in a monoethanolamine-water carbon dioxide-hydrogen sulfide solution. This is because an aqueous solution of monoethanolamine is not corrosive to ferrous metals, but when saturated with carbon dioxide and/or hydrogen sulfide, it becomes highly corrosive to mild steel. . In this case, it is believed that the anodic reaction causes electrochemical corrosion, resulting in products such as ferrous hydroxide, ferrous carbonate, ferrous sulfide, or certain complex compounds. It is believed that if hydrogen sulfide is present in this inhibitory alkanolamine solution, a complex series of reactions occurs to produce sulfur, at least a portion of which is present as polysulfides in this solution.

The sulfur form in this alkanolamine solution also acts as a passivating agent. The protective power of a given corrosion inhibitor is determined by measuring the relative degree of protection of the alkanolamine solution containing the inhibitor and whether the steel was active (enteric) or inactive at the end of the test. This was determined by measuring the potential of the steel to see if it was active (negative). The relative degree of corrosion for a particular alkanolamine solution is the degree of corrosion of the alkanolamine solution divided by the degree of corrosion of the alkanolamine solution without corrosion inhibitor. The degree of corrosion in a particular case is calculated by measuring the weight loss of the metal specimen after carrying out the test for a defined period of time. A relative degree of corrosion greater than about 0.5±0.1 is considered to be indicative of an inhibitor lacking protective ability. The potential difference across the steel was measured at the end of each test. 2
A voltage greater than about 1500 millivolts (mV) at 0° C. is considered to indicate that the steel is inert and the inhibitor provided effective protection.

The thermal conduction corrosion test was conducted as follows. Diameter approx. 3.
A 5-inch, 1/32-inch thick cross-rolled mild steel disc was cleaned and weighed.

This iron disk was then clamped into a shelf silicate glass corrosion cell to form the bottom of the cell. A 3% by weight monoethanolamine solution saturated with carbon dioxide gas was added to the corrosion cell. Residual air was vented from the cell with carbon dioxide gas. The steel billet was then activated by electrochemically reducing the inert film created by the air. Alternatively, if an inert steel plate is desired, this electrochemical reduction operation is omitted. A sample of a 3% by weight monoethanolamine solution saturated with hydrogen sulfide is then introduced into the corrosion cell in an air-tight manner. The volume of this sample is approximately 25% of the volume of monoethanolamine-carbon dioxide gas used to initially charge the corrosion cell. (The monoethanolamine saturated with hydrogen sulfide was prepared by the use of hydrogen sulfide that had been carefully purified to ensure that there was no sulfur present therein that would act as a beneficial inhibitor. ) By this method, a mixture of about 2% by weight hydrogen sulfide and about 8% by weight carbon dioxide is used, with careful exclusion of air that might oxidize the hydrogen sulfide to sulfur. in,
Activated steel is prepared under saturated 30% monoethanolamine. Therefore, the release gas is introduced from the carbon dioxide gas into a gas containing about 2% by volume of hydrogen sulfide and about 8% by volume of carbon dioxide gas. This corrosion cell can then be subjected to a cold activation prevention test. And when it is desired to test this, the inhibitor is added under exclusion of air and the cell is heated to reflux temperature through a test steel plate.
Alternatively, hot activated steel corrosion protection may be tested by heating the corrosion cell to reflux prior to introduction of the inhibitor to be tested. After the test time has elapsed, the release gas obtained by mixing hydrogen sulfide and carbon dioxide is replaced with carbon dioxide to cool the cell. The potential difference across this steel test disk is then measured. The steel piece is also cleaned and the degree of corrosion is calculated. The test method described above was employed in carrying out the following examples representative of the present invention.

Comparative examples are also listed. The defects of a given concentration of inhibitor are shown in Tables 1 and 2 with the concentration of the inhibitor in parentheses. Examples 1-24 In these examples, corrosion inhibitors of the present invention are tested.

Examples 1-24 were all carried out on hot activated steel for two hours under hydrogen sulfide and carbon dioxide according to the method previously described. In each example, vanadium was added before any other inhibitors were added. The degree of corrosion of the monoethanolamine-water-carbon dioxide-hydrogen sulfide solution without the addition of an inhibitor was determined by first testing it on 29 steel billets without the addition of a corrosion inhibitor.

In this test, each specimen lost a weight corresponding to a corrosion rate of 9.0 ± 1.4 mils per year for the 1-day test and 4.1 ± 1.0 mils per year for the 8-day test. showed a corrosion rate of These corrosion rates are shown in Tables 1 and 0.
was used to calculate the relative corrosion rates of all examples. These corrosion rates indicate that efforts to eliminate adventitious inhibitors from these tests were successful. Examples 1-4
The vanadium compound used in 7 is V205 or NaV03.
It was either

Table 1 shows the results obtained by using the combined corrosion inhibitor of the present invention at various concentrations, which do not exhibit an inhibitory effect when used alone, but do exhibit an inhibitory effect when used in combination. Show the results. Examples 1-7 demonstrate the excellent protection exhibited by these silk-combined inhibitors. Examples 1-3 show that vanadium (V) has m.m. e. c. is between about 0.2 mmol and about 0.3 mmol.

Examples 4 to 6 show m.p. of p-nitrobenzoic acid. e. c. is between about 10 and 20 mmol for hot activated steel. Example 7 shows that the combination of 0.1 mmol vanadium (V) and 1.0 mmol p-nitrobenzoic acid provides excellent protection against hot activated steel. Similar results were obtained using vanadium(V) in combination with m-nitrophenol/m-nitrobenzenesulfonic acid, 1,4-naphthoquinone/p-nitrophenol, m-nitrobenzoic acid, or 3,5-dinitrobenzoic acid. Illustrated by Examples 8-24. Table 1 Notes (1) The numbers in parentheses indicate that the concentration of the inhibitor has no inhibitory effect.

(2) P-nitrobenzoic acid (3) m-nitrophenol (4) m-nitrobenzenesulfonic acid (5) 1,4-naphthoquinone (6) p-nitrophenol (7) m-nitrobenzoic acid (8) 3,5-dinitrobenzoic acid (9) Steel voltage was not measured in this example.

(10) A indicates activity (positive) and P indicates inactivity (negative). Examples 32-47 In these examples vanadium (
The preventive effect of the combination of V) and p-nitobenzoic acid was evaluated by the general method described above.

However, in this case, the heat conduction test was conducted for 8 days, or 19 hours. Figure 3 shows the preventive effect achieved by the combination of vanadium (V) and p-nitrobenzoic acid. Moreover, this figure shows the case where the combination inhibitor is used in a concentration that is in excess of the amount in which the individual use of these components has no inhibitory effect. Examples in Table 0 are this vanadium (V)
The combination of p-nitrobenzoic acid and vanadium (
V) at a concentration of about 0.02 mmol to about 0.25 mmol and the p-nitrobenzoic acid at a concentration of about 0.6 mmol to about 8.0 mmol.

When using such concentrations, the m. e. c. Vanadium (V) and p-
The combination with nitrobenzoic acid exhibits a preventive effect. Table 0

Claims (1)

[Scope of Claims] 1. At least one vanadium compound containing vanadium in a +5 valence state in an aqueous solution of an alkanolamine, a nitro-substituted aromatic acid, or a nitro-substituted aromatic acid. an inhibitory amount of an organic compound selected from the group consisting of acid salts and 1,4-naphthoquinones, or a combination thereof, for inhibiting the corrosive action of aqueous alkanolamine solutions when in contact with metal surfaces; Corrosion inhibitor suitable for. 2 The organic compound is p-nitrobenzoic acid, m-nitrobenzoic acid, 3,5-dinitrobenzoic acid, p-nitrophenol, m-nitrophenol, m-nitrobenzenesulfonic acid, 1,4-naphthoquinone, and mixtures thereof. A composition according to claim 1, which is selected from the group consisting of: 3 Vanadium compounds are V_2O_5, NaVO_3,
Na_3VO_4, KVO_3, NH_4VO_3, V
A composition according to claim 1 selected from the group consisting of OCl_3 and mixtures thereof. 4. The composition according to claim 2, wherein the organic compound is p-nitrobenzoic acid. 5 Vanadium compounds and organic compounds are 0.01 to 50. 3. A composition according to claim 1 or 2 in millimolar amounts. 6 a concentration of a vanadium compound in which vanadium is in the +5 valence state from 0.02 mmol to 0.25 mmol and a concentration of p-nitrobenzoic acid from 0.6 mmol to 8.6 mmol.
A composition according to claim 1, comprising a concentration of 0 mmol. 7. The composition according to claim 1, wherein the alkanolamine aqueous solution is a monoethanolamine aqueous solution. 8 A vanadium compound or a mixture thereof in which vanadium is in a +5 valent state in an aqueous solution of a corrosive alkanolamine, a nitro-substituted aromatic acid, an acid salt of a nitro-substituted aromatic acid, 1,4-naphthoquinone, and 0.01 to 50% of a corrosion inhibitor selected from combinations with organic compounds selected from the group consisting of mixtures thereof;
A method for preventing corrosion of a metal surface by a corrosive alkanolamine aqueous solution, which comprises adding a millimolar preventive amount to the corrosive alkanolamine aqueous solution. 9 The organic compounds to be added are p-nitrobenzoic acid, m-nitrobenzoic acid, 3,5-dinitrobenzoic acid, p-nitrophenol, m-nitrophenol, m-nitrobenzenesulfonic acid, 1,4-naphthoquinone and their 9. The method of claim 8, wherein the method is selected from the group consisting of mixtures. 10. The method according to claim 8, wherein the aqueous solution of alkanolamine is an aqueous solution of monoethanolamine. 11. According to claim 8, the vanadium (V) compound is used in a concentration of 0.01 mmol to 0.2 mmol and p-nitrobenzoic acid is used in a concentration of 0.6 mmol to 8.0 mmol. the method of. 12 Vanadium compounds are V_2O_3, NaVO_3
, Na_2VO_4, KVO_3, NH_4VO_3,
9. A method as claimed in claim 8, selecting from the group consisting of VOCl_3 and mixtures thereof.