JP2823137B2 - Composition for inhibiting corrosion of iron metal and method for inhibiting corrosion - Google Patents

Abstract

Compositions comprising certain amino acids such as aspartic acid, when fully ionized at alkaline pH, function effectively as corrosion inhibitors for ferrous metals in the presence of an aqueous medium. This effect is enhanced with increased fluid velocity.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to novel and improved corrosion inhibiting compositions, unexpectedly novel methods of using biodegradable corrosion inhibitors, and the use of aqueous media in the presence of aqueous media. And to an improved method for inhibiting the corrosion of ferrous metal surfaces (prone to corrosion). More specifically, the present invention uses an amino acid that has a corrosion inhibiting effect and a corrosion inhibiting amino acid that is effective in inhibiting the corrosion of iron metal under use conditions in the presence of an otherwise corrosive aqueous medium. And how to.

Description of the Related Art An important mechanism for protecting metals against corrosion degradation is achieved by using inhibitors. Unfortunately, certain conventional corrosion inhibitors, such as formulations containing nitrogen and aromatics, are widely used as corrosion inhibitors in aqueous heating and cooling systems, but have the disadvantage of the public. Has been found to be dangerous to human health and the surrounding environment. Removing such potentially dangerous compounds by sedimentation or other treatment is complex and expensive. For example, other corrosion inhibitors such as chromium salts have been banned from use because they are suspected of being carcinogenic. As a result, it has become desirable to study the inhibitory properties of biologically compatible and / or biodegradable compounds. Such compounds are non-toxic, easy to produce with high purity, and, if biodegradable, can dramatically reduce the cumbersome task of removal and recovery. Limited uses of amino acids have been proposed.

For example, Japanese Unexamined Patent Publication (Kokai) No. 50-091546, dated July 22, 1975, by Nippon Kaishi Paper Co., Ltd. discloses that a mixture that requires an amine and an amino acid or a salt thereof is a 20% aqueous solution. It is disclosed that when dissolved in water, atmospheric corrosion of many ferrous and non-ferrous metal plates was suppressed. It is believed that the pH of the water adsorbed on the metal plate was about 5.5 or less.

However, a closer look at ordinary amino acids alone did not prove promising. For example, V. Hluchan et al., "Amino Acids as Corrosion Inhibitors in Aqueous Hydrochloric Acid" (Warkstoffeund Korr, published in 1988)
osion, Vol. 39, pages 512-517), studied the 22 most common amino acids as inhibitors of iron corrosion in 1.0 molar hydrochloric acid at a pH of about 0. In general, these amino acids, which have inhibitory properties at the pH of the acid, have not proved to have a corrosion inhibitory effect that is sufficient for immediate commercial use. Amino acids having a long hydrocarbon chain and amino acids having additional amino groups or amino acids having a group capable of increasing the electron density of the amino groups merely exhibited an effective corrosion inhibition tendency.

In particular, the preferred amino acids for use in the present invention, aspartic acid and glutamic acid, did not fall within the above "trends". In conclusion, these amino acids are particularly poor inhibitors because they have a single amino group, a short carbon chain and have additional carboxyl groups.

Further, the use of aspartic acid as an inhibitor above the pH of the acid is considered a disadvantage by those skilled in the art. This is because aspartic acid is known to be essentially corrosive under somewhat alkaline pH conditions. K.
"Role of Biologically Important Compounds on Mild Steel and Copper Corrosion in Sodium Chloride Solutions," by K. Ramarkrishnaiah, Bullet, 1986.
ine of Electrochemistry, Volume 2 (January), 7-1
See page 0). The article discloses that aspartic acid actually accelerated corrosion at pH 8 (inhibition efficiency -25.4%). Indeed, even in combination with a good corrosion inhibitor for mild steel such as papaverine, the presence of aspartic acid retained the corrosiveness of the solution.

A related problem in the industry is that moving fluids are known to increase the corrosion rate of ferrous metals when exposed to an aqueous environment. Thus, any corrosive effects expected from an amino acid, such as aspartic acid, in an aqueous medium will result in the presence of such an amino acid in the vehicle's cooling or heating system, where such a medium will be in motion. Then, in fact, it should be even bigger.

Therefore, amino acids such as aspartic acid have been avoided as corrosion inhibitors, despite being non-toxic and biodegradable.

The use of amino acids having only one amino group and having an additional carboxyl group (eg, aspartic acid) in a state where the amino acids are sufficiently ionized to inhibit the corrosion of ferrous metal is surprisingly surprising. It is a discovery that fulfills a long-felt need in industry. In addition, ferrous metal corrosion inhibitors, which reduce the rate of corrosion even in large fluid flow conditions, provide a significant improvement in the art.

SUMMARY OF THE INVENTION It is a primary object of the present invention to provide a new and improved corrosion inhibiting composition for ferrous metals in the presence of an aqueous medium.

It is a primary object of the present invention to provide a new and improved method for inhibiting ferrous metal corrosion in the presence of an aqueous medium.

To provide a new and improved method of inhibiting corrosion of ferrous metal in the presence of an aqueous medium at rest,
It is another main object of the present invention.

It is yet another primary object of the present invention to provide a new and improved method for inhibiting the corrosion of ferrous metals in the presence of an aqueous medium in the motion of a fluid.

It is a further object of the present invention to provide a new and improved method of using amino acids having one amino group as corrosion inhibitors for ferrous metals in the presence of an aqueous medium.

Other and further objects of the present invention will become apparent from the description and claims that follow.

Certain amino acids, especially aspartic acid, are known to accelerate metal corrosion in slightly alkaline aqueous media, but function effectively as corrosion inhibitors when sufficiently ionized under conditions of use. I understood.
Such amino acids can increase the corrosion rate of iron metal by 100-1000
Reduce by a factor of two. Surprisingly, this corrosion inhibiting effect
It improves as the fluid velocity increases.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a plot of the impedance spectrum for a mild steel electrode rotating at 200 rpm in a 90 ° C. aqueous solution containing 1000 ppm of aspartic acid at pH 10 in real and imaginary coordinates.

FIG. 2 shows a plot of the impedance spectrum in real and imaginary coordinates for a mild steel electrode rotating at 200 rpm in an aqueous solution at pH 10 and 90 ° C., the conductivity of which was adjusted with sodium sulfate without using aspartic acid.

FIG. 3 shows the magnitude of the impedance spectrum for the mild steel electrode of FIGS. 1 and 2 plotted against the logarithm of the frequency.

FIG. 4 shows a plot of the phase angle for the mild steel electrode shown in FIGS. 1 and 2 against the logarithm of the frequency.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Useful in the present invention are amino acids having one amino group and salts thereof. Suitably, the ratio of carboxyl groups / amino groups is 1, but preferably these compounds have more carboxyl groups than "free" amino groups, for example two carboxyl groups and one amino group. Having. Suitable amino acids are represented by the formula: Where R ¹ is H, Or _{H 2 N- (CH 2 -)} y) -; R 2 is, HO-, Or HOOC— (CH ₂ —) _y —NH—; R ³ represents H, —COOH, —CH ₂ COOH, or —CH ₂ CH ₂ COOH, and x and y are each independently an integer from 1 to 3. And n represents an integer corresponding to the number of aminoacyl units that are repeatedly present.

Examples of suitable compounds are glycine, polyglycine, aspartic acid, polyaspartic acid, glutamic acid, polyglutamic acid, and salts thereof. Without limitation, preferred salts are, for example, an alkali metal, soluble alkaline earth metal, and C ₁ -C ₄ salts of alkyl amines.

These compounds are readily available from a number of sources and can be produced using either chemical synthesis or microbial fermentation.

These compounds tend to be ineffective as corrosion inhibitors when in the fully protonated cationic form, and become worse enough to actually accelerate corrosion as the pH increases from the acid side to the alkali side. However, once these compounds were sufficiently ionized under sufficiently alkaline use conditions, they were found to dramatically reverse the corrosion rate of ferrous metals. In general, depending on the temperature and the particular compound employed, a calcareous pH of at least about 8.9 is preferred. Under such conditions of use, the corrosion rate is 100 to 1000 times lower than the corrosion rate of ferrous metals under equivalent pH conditions without using these compounds.

The corrosion inhibitors of the present invention can be used (in aqueous media) at concentrations as low as 100 ppm, as high as 5.0 wt% and more. Particularly preferably, the corrosion inhibitors of the present invention are used at a concentration of about 1000 ppm to about 3.3% by weight. However, it is determined that concentrations above 5.0% of the corrosion inhibitor can be used, if desired, unless such a high concentration is disadvantageous to the system in which the corrosion inhibitor is used.

The corrosion inhibiting effect of the composition of the present invention is at room temperature, that is, about 25 ° C.
Alternatively, it may be expressed at a lower temperature, or lower, and at a higher temperature of about 90 ° C. or more.

Temperature is known to accelerate metal corrosion,
It is particularly noted that as temperature increases, the corrosion inhibiting properties of the present invention are not affected, beyond any effect of temperature on pH. For example, the pH of this system may decrease by one unit from the measurement at 25 ° C. when comparing the measurements at 90 ° C. The fully ionized pK of the amino acid also decreases with increasing temperature. However, as long as the temperature does not reduce the pH to a value below the point at which the corrosion inhibitor completely ionizes, the compositions of the present invention will continue to maintain efficacy.

In a particularly preferred embodiment, the compositions of the present invention are used in dynamic, flowing systems. It is surprising that the rate of corrosion of ferrous metals in such systems does not increase with increasing flow rate. In fact, as the flow rate increases, the corrosion rate tends to decrease to a significant degree. Typically, in the absence of the composition of the present invention, the flow rate will be, for example, 200 revolutions / min (r
From pm) to about 1000 rpm, the presence of such an aqueous medium in at least 24 hours results in an increase in the corrosion rate of ferrous metals. Such increased corrosion rates are common for steels in water or other aqueous systems. This is because the reduction of oxygen is often the rate-limiting step. That is, the mass transfer rate of oxygen to the corroding surface increases as the flow rate increases.

PH of aqueous medium under use conditions of the corrosion inhibiting composition of the present invention
Is about 8.9 when measured at ambient or room temperature (about 25 ° C)
To about 14, preferably from about 9.5 to about 12. It is particularly preferred that the compositions of the present invention be used at a pH of about 10 or higher when measured at ambient or room temperature. However, as already mentioned, it is understood that the pH changes depending on the temperature measured.

Thus, where the aqueous medium is essentially acidic, one of the preferred embodiments of the present invention is to use a suitable amine acid, preferably aspartic acid. The composition includes a total pH of the aqueous medium of about 9.5 or higher, most preferably about 9.9.
Includes an effective amount of base to raise to ~ 10 or more. At such a pH, the amino acids are present in a fully ionized form (conjugate base).

The pH of the aqueous medium is a hydroxide of an alkali metal, for example,
It can be adjusted by adding a suitable base such as sodium hydroxide or potassium hydroxide. Bases that can be used in the present invention further include alkali metal carbonates, hydrocarbylamines, alkaline earth metal hydroxides, and ammonium hydroxide.

It is possible that the pH of a corrosive environment is essentially alkaline. For example, in the case of aqueous solutions or automotive antifreeze in contact with lime deposits, concrete and fertilizers.
In such systems, a suitable amino acid or salt thereof is
Corrosion inhibition can be performed by simply adding a sufficient amount to the above concentration to the aqueous medium without adding other bases.

Many inorganic and / or organic materials, in particular all materials or substances used in the water treatment industry, the automotive industry,
It is also within the scope of the invention to use the corrosion inhibitor in aqueous media containing other materials or substances, including antifreeze compositions, metal detergent compositions and radiator cleaning compositions.

The effectiveness of corrosion inhibition on metal surfaces is usually determined by measuring the corrosion rate of the test metal under certain conditions. Here, two methods for measuring the corrosion rate were employed. For convenience, they are referred to as (1) a standard metal strip corrosion weight loss test (also referred to as a static immersion test), and (2) an electrochemical impedance method.

In the standard metal strip corrosion weight loss test method, a metal strip of known mass is immersed in an aqueous solution whose corrosion inhibition properties are to be determined. The aqueous medium is maintained under specific conditions for a specific period. At the end of the exposure period, remove the metal pieces from the aqueous solution, wash in an ultrasonic bath containing soap, rinse with deionized water, rinse with acetone, and pat dry with a lint-free paper towel. Blow a stream of nitrogen, weigh and measure the weight loss by corrosion, observe with a stereoscope of appropriate magnification, and measure the degree of erosion of the metal surface due to corrosion.

However, corrosion is an electrochemical process rather than a strict chemical reaction. Thus, electrochemical techniques, for example,
Use of the electrochemical impedance method provides a useful and convenient indicator of the rate of corrosion. In the electrochemical impedance method, a corroding metal surface is composed of a number of local anodes and a number of local cathodes, and these positions actually move or are in the same place, and a corrosion reaction occurs Useful for predicting At the anode, the metal is being oxidized, while at the cathode, reduction is taking place, and in acidic solutions, reduction of hydrogen ions is taking place. The magnitude of the current, or amperes per square centimeter (A / cm ² ) of the open circuit potential measured relative to the reference electrode, is a measure of the tendency for each reaction to occur. ". In many instances, the corrosion rate is converted to the "erosion rate" of corrosion in mils per year (mpy), or loss of corrosion, for example, by assuming two electrons per ionized atom.

The “electrochemical impedance method” is applied by changing the frequency at the electrode interface using a low-voltage amplitude wave, for example, 5 to 10 millivolts (mV). This response is
It is used to estimate the corrosion rate and draw some conclusions about the corrosion mechanism. When analyzing the spectrum of the impedance, those measured in ohms per square centimeter (ohm-cm ²⁾ referred to as "polarization resistance" is obtained. This is inversely proportional to the corrosion current density (corrosion rate). Therefore, the corrosion rate is equal to the proportionality factor (for the test metal) divided by the polarization resistance, measured in volts, according to Ohm's law (i = v / R _p ). For example, the proportionality factor for carbon steel is typically 0.025 volts. And since the polarization resistance is inversely proportional to the corrosion rate, the relative magnitude of the polarization resistance is
Many compositions are used to determine whether or not they have a low or high corrosion rate. Thus, the polarization resistance of 100 ohm-cm ² is caused by even greater corrosion rate about 100 times higher than the corrosion rate with a polarization resistance of 10,000ohm-cm ^2. The polarization resistance of 100 chm-cm ² is
A corrosion rate on the order of about 100 mpy is exhibited, and a polarization resistance of 1000 ohm-cm ² indicates a corrosion rate on the order of about 10 mpy. The conversion of polarization resistance to corrosion rate (in mpy) can be done by assuming a proportionality constant of 25 mV and Faraday's law.

For an introduction to the electrochemical impedance method, see "Introduction to the AC Impedance Method," by Silverman, DC (1986, National Association of Corrosion Engineers in Houston, Houston).
osion Engineering), published on pages 73-79 in "Electrochemical Techniques for Corrosion Engineers" (edited by R. Baboian).

The following examples illustrate the best known ways of practicing the invention and are described in detail to facilitate a clear understanding of the invention. It should be understood, however, that the detailed disclosure of the application of the invention, while indicating a preferred embodiment, is for illustrative purposes only and should not be construed as limiting the invention. is there. Many variations and modifications within the spirit of the invention will be apparent to those skilled in the art from this detailed description.

In the following examples, all parts and percentages are by weight and all temperatures are in degrees Celsius (° C.) unless otherwise specified;
The pH was measured at 25 ° C. and “loss on corrosion” means average “erosion”.

Reference Example 1 Corrosion was estimated for two mild steel (C1018) electrodes labeled Samples A and B using the electrochemical impedance method. Each factor and its results are shown in Tables 1 and 2.

The billet was manufactured for use as an electrode in a rotating cylindrical electrode device. This device is DC Silverman (Silv
erman), “Rotary cylindrical electrode for speed sensitivity test” (1
Corrsion, 984, Vol. 40, May 220-226 in May
Page)). The electrochemical impedance method is based on DC Silverman and J.
E. Carrico, "Electrochemical Impedance Method-A Practical Tool for Predicting Corrosion" (Corrosion, 1988), Vol. 44, May, pages 280-287. Published).

The cylindrical electrode was made of mild steel (C1018). 600 electrodes
It was polished with a #silicon carbide paper file and then immersed in the test solution. The solution was also heated to the desired temperature of 90 ° C., after which the electrodes were immersed therein. The electrodes are mounted on a cylindrical shaft, then immersed and 200 rpm to ensure turbulent conditions
Was set to rotate. The water level is determined by the upper Lulon (registered trademark (Rulon) [poly (tetrafluoroethylene) impregnated with graphite), EIdu Pont de Nemou
rs & Company)] in the middle of the spacer to prevent hydrodynamic effects from interfering with the results and to ensure optimal flow and streamlines.

The data of Sample A shown in Table 1 was measured using a rotary cylinder device.
Obtained by exposing mild steel electrodes to 10 sodium aspartate solutions. Its pH is sodium hydroxide
Adjusted to 10. The concentration of sodium aspartate was about 1000 pm. pH was measured at 25 ° C but temperature was 90
Adjusted to ° C.

Similarly, the data shown in Table 2 was obtained for sample B. However, there is no sodium aspartate,
Instead, the same ionic strength was achieved using sodium sulfate, which had substantially no effect on corrosion.

The corrosion potential of the steel electrode used for each of Sample A and Sample B was measured by measuring the voltage between the steel electrode and the saturated calomel electrode. The electrodes for each of Sample A and Sample B rotated at different speeds at the same exposure time. The polarization resistance was measured as described in the above-mentioned literature co-authored by Silverman and Calico and used to estimate the corrosion rate. Corrosion rates were converted to erosion or loss in mils per year (mpy).

Impedance spectra for billet electrodes (Samples A and B) were obtained at 200 rpm and pH 10 in each of the aqueous solutions used for Samples A and B using a rotating cylindrical electrode device. These spectra (curves) are shown in Figures 1,2,3
And 4. The agreement between the calculated curves and the actually obtained data demonstrates that the model used to obtain the polarization resistance is in good agreement with the actual results. The local nature of corrosion found in the static immersion test under comparative conditions (test numbers 4 and 5 in Example 2 below) was not observed for the rotating cylindrical electrode. This behavior suggests that the presence of a uniform velocity field advantageously allows aspartic acid to more uniformly inhibit corrosion. In addition, due to the increased uniform suppression effect, the method is aided by the smoother 600 grit finish used on the electrodes than the 120 grit finish on the test specimens used in the static immersion test. It is suggested that. The end result of a smoother finish is that the surface microstructure of the electrode was less heterogeneous than that of the static immersion specimen. As such, a more uniform rate and smoother steel surface would require a lower concentration of aspartic acid to uniformly inhibit corrosion of all parts of the surface.

As shown in Tables 1 and 2, the corrosion potential of sample A against sodium aspartate was −310 mV (SCE), while the corrosion potential of sample B without sodium aspartate was −630 mV (SCE). SCE) and is much more active. This difference in corrosion potential suggests that sodium aspartate has a greater tendency to oxidize the steel surface.

However, it has been clarified that the corrosion rate of each of the above samples has a relation opposite to the tendency of oxidation. The magnitude of the difference between the corrosion rates of Sample A versus Sample B after the same exposure time demonstrates that aspartate inhibits corrosion by a factor of 100-1000. The corrosion started at about the same rate for both sample A (32 mpy) and sample B (45 mpy), but in the presence of sodium aspartate,
The speed rapidly decreased, and was almost constant in its absence.

Furthermore, in the absence of aspartate, the rotational speed,
That is, in the experimental example, the corrosion rate increases at least up to 24 hours as the fluid velocity increases. No change is observed after 48 hours, probably due to corrosion products accumulating on the surface. This behavior is normal for carbon steel and water. This is because the reduction of oxygen is the rate-determining step. The rate of mass transfer of oxygen to the corroded surface is often determined by the rate of corrosion, which is the rate at which corrosion products accumulate on the surface. The opposite is affected. However, in the presence of aspartate, the corrosion rate did not increase with increasing flow rate. In fact, the corrosion rate decreased significantly with increasing rotation speed throughout the Reference Examples and Examples. The phenomenon of reduced corrosion rate, which is obtained by increasing the speed of the flow, seems to be irreversible. Even after reducing the rotation speed to 200 rpm (exposure time 46 ~
As can be seen from the corrosion rates shown in Table 1, measured at 48, 49, and 50 hours), the corrosion rate was 1000 rpm at fluid speed.
0.13mpy at 200rpm showed the sample before increasing to
Because he did not return to that speed.

Thus, the sodium salt of aspartic acid, under basic conditions, functions in an unexpected way as a corrosion inhibitor for ferrous metals.

The impedance spectrum itself was studied as a function of rotational or fluid velocity, and a rotating cylindrical electrode was used for over 48 hours. The plots at 200 rpm and 24 hours are shown in Tables 1, 2, 3 and 4.

There are two peaks in the phase angle plot for mild steel in contact with sodium aspartate. This is shown in FIG. Such behavior suggests that there are two relaxation time constants, which are due to the fact that either strongly adsorbed intermediates or firmly attached films are involved in the corrosion mechanism. It suggests that High frequency peaks are due to intermediates adsorbed on the film, and low frequency peaks contribute to the corrosion rate. Thus, while not wishing to be bound by theory about the corrosion mechanism or to limit the invention in any way, if the mechanism is not fully understood, aspartate ions may remain on the metal surface. Is believed to form some kind of adsorption layer. Another evidence of the presence of certain adsorbed layers on metal surfaces when aspartate ions are present is that the phase angle for mild steel under mild conditions under comparative conditions when no aspartate ions are present. Given by plot. In such a plot (also shown in FIG. 4), there is only one peak which suggests that only a charge transfer corrosion reaction has occurred.

Reference Example 2 The same 14 specimens of mild steel (C1018) were
Grit sanded, rinsed with deionized water, dried and weighed. Thereafter, the specimen was subjected to a static immersion test. The parameters varied and the results obtained are shown in Table 3 below. Specimens were subjected to the respective L- aspartic acid test solution to about 600 cm ³ (or cc) of the glass in the glass bottle containing hooks. This solution was prepared using deionized water and a sufficient amount of aspartic acid to obtain the desired aspartic acid concentration. The hook was attached through a rubber stopper that sealed the top of the bottle. Gas spray water,
It was placed beside the stopper and blown for aeration of a solution with air saturated with water, excluding carbon dioxide. These bottles were placed in a constant temperature bath where the temperature was maintained at 90 ° C. The exposure time of these specimens was between 5 and 7 days, during which period deionized water was periodically added to the aspartic acid test solution to compensate for water loss due to evaporation at constant temperature. The pH of each solution was adjusted at the beginning of the test using sodium hydroxide and measured at room temperature (RT, about 25 ° C) and test temperature.

At the end of the test piece exposure time, the test pieces were removed from the solution, washed in an ultrasonic bath with a soap solution, rinsed with deionized water, rinsed with acetone, dried and weighed. The surface of the test piece was inspected using a stereoscope at a magnification of 10 to 30 times after exposure. Corrosion imposition measures the change in weight (before and after exposure to aspartic acid solution) and then measures the degree of erosion or corrosion loss in mpy or g.
Estimated according to the method previously described by calculating in / h. If the corrosion was significantly non-uniform and appeared locally on the surface, only the corrosion loss in grams was divided by the total exposure time in hours. The reason is that the corrosion rate averaged over the entire surface area does not accurately indicate the magnitude of the corrosion if the corrosion occurs in a very localized area. However, Table 3, which shows the results from the static immersion test, compares Tables 1 and 2 which show the results from a constant flow system, to achieve the same level of corrosion inhibition under no flow conditions. It has been shown that the required concentration of aspartic acid required is increased.

Reference Example 3 Reference Example 2 except that the solution did not contain aspartic acid and only three steel specimens were subjected to the static immersion test.
Was used. The solution was adjusted to have the same conductivity as that containing aspartic acid by adding sodium sulfate. By doing so, corrosion was limited to corrosion caused only by oxygen contained in water at a given pH. Table 4 shows the results.
Is shown in

Comparing Test Nos. 2 and 3 in Table 3 with Test No. 1 in Table 4, the corrosion rate at pH 8 is higher with aspartic acid than with no aspartic acid. This helps to confirm that at pH 8, aspartic acid does not provide a beneficial corrosion inhibitory effect, but instead acts as a corrosion promoter. Similar behavior is observed when the pH is 9.5 and the concentration of aspartic acid is 3% by weight (test number 10 in Table 3). This behavior is due to the fact that aspartic acid does not exist in a completely or fully ionized (conjugate base) form at pH below 9.5. This means that at a pH higher than 9.5, e.g.
Even concentrations as low as 1000 ppm are clearly evidenced by the observed change. At a concentration of 1% by weight and a pH of 10 (test number 9), almost all of the corrosion disappears under the static test conditions in Table 3. Therefore, when the pH is measured at 90 ° C, 8.5
Aspartic acid inhibits corrosion under static conditions in the range of about 9.0, ie at room temperature (about 25 ° C.) at pH 10 or higher, but at lower pH it increases or promotes corrosion.

The fact that some attack or corrosion is observed at concentrations between 1000 ppm (test numbers 4 and 5) and 5000 ppm (test number 8) in the pH range 9.9 to 10 indicates that aspartic acid does not inhibit corrosion at these concentrations. That doesn't mean that. The fact that there is a large area where no corrosion is observed strongly suggests that aspartic acid actually inhibits corrosion. This apparent inconsistency is due to the fact that there is no flow during the immersion test, that is, it is impossible to uniformly disperse aspartic acid in the test piece under static conditions.

REFERENCE EXAMPLE 4 A steel test piece was prepared for use as the electrode of the rotary cylindrical electrode device described in Reference Example 1, and the pH was changed at three different levels (8, 10) using an aspartic acid solution containing 1000 ppm of aspartic acid. , And 12). The fourth specimen was also subjected to the same procedure at pH 10 (for comparison). However, without using aspartic acid, the solution was adjusted with sodium sulfate so as to have the same conductivity as when aspartic acid was present. Corrosion was estimated using the electrochemical impedance method described in Reference Example 1. The results are shown in Table 5.

Electrochemical impedance spectra were generated after about 30 minutes to 0.01 Hertz (hz) to estimate the corrosion rate with short-term exposure. Then the spectrum is 200r daily
Generated for 0.001hz at pm. In addition, spectra were generated at 1000 rpm for 0.01 hz to estimate the effect of fluid velocity on corrosion. The tests were carried out at pH 8, 10, and 12 with 1000 ppm of aspartic acid and at pH 10 without aspartic acid. Perturbation voltage (perturbi
(ng voltage) signal magnitude was small (5 mV) to ensure linearity between perturbation and response. The steel electrode was weighed twice before and after the experiment. The purpose of the corrosion weight loss measurement is to extrapolate the corrosion rate.
Note that at pH 10, especially at pH 12, corrosion weight loss was affected by water leaking behind the electrodes. The polarization resistance was estimated using the circuit analog method shown in FIG. 2 of the above-mentioned document co-authored by Silverman and Calico.

The results of the rotating cylindrical electrode test show that under ideal conditions of fluid velocity, if the concentration of aspartic acid is at least 1000 ppm, then it is shown (at pH 10) in the absence of 50-100 mpy
It shows that the corrosion rate can be reduced to about 0.1 to 0.5 mpy compared to In the absence of aspartic acid, fluid movement increases corrosion, erodes the surface completely, and ultimately affects the velocity profile of the fluid near the surface. This tendency is expected for corrosion of mild steel and low alloy steel in water. However, pH 9.5
(Measured at room temperature)
Corrosion is reduced in the presence of fluid movement.

Example 5 This example demonstrates that previously corroded surfaces can be protected with the corrosion inhibitors of the present invention. The results shown in Table 6 were obtained in the rotary cylindrical electrode device described in Reference Example 1.
Measured by exposing a previously corroded steel cylindrical electrode to deionized water containing 2000 ppm sodium sulfate and 50 ppm sodium chloride (to have approximately the same conductivity as 1000 ppm aspartic acid at pH 10) Was done. At 24 hours, the electrode broke significant corrosion weight loss and formed a reddish brown rust layer. The electrode was immersed in an aqueous solution having an aspartic acid concentration of 500 ppm, adjusted to a pH of about 10 with sodium hydroxide, and maintained under constant rotation. The polarization resistance increased sharply over 24 hours, indicating that the corrosion rate decreased with exposure time. The corrosion rate did not decrease to the values of electrodes exposed to 1000 ppm aspartic acid, which had not previously undergone corrosion, eg, the results shown in Table 1. This difference suggests that the concentration was not optimal for this particular system. More important, however, is the observation that even 1000 ppm aspartic acid can inhibit the corrosion of steel (even steel that has previously been corroded) under suitable conditions.

Reference Example 6 A static immersion test was performed as described in Reference Example 2. However, glutamic acid, glycine, and certain acids commonly used in antifreeze formulations were used in place of aspartic acid. The parameters used and the results obtained are shown in Table 7. It can be seen that glutamic acid and glycine each show behavior and corrosion inhibition similar to aspartic acid. Although slightly more spots were observed on the specimens, the weight loss was similar to that with aspartic acid at the same pH.
Furthermore, these results demonstrate that aspartic acid behaves at 90 ° C. equivalent to a mixture of benzoic, sebacic, and octanoic acids. Since acids such as the latter name are commonly used in antifreeze formulations, the results for aspartic acid (Test Nos. 11 and 12 in Table 3 of Reference Example 2) indicate a suitable alternative for such acids. This shows that aspartic acid can be used as a product. As can be seen from Table 7, the ammonium salt of aspartic acid does not appear to perform as well as the sodium salt. Because the pH drops to 7.7, a pH below the pH value at which aspartic acid exists (in conjugate base) in a fully ionized form.

Example 1 A static immersion test was performed as described in Reference Example 2. However, instead of aspartic acid, polyaspartic acid at a concentration of 2000 ppm to 3.3% and polyaspartyl hydroxamic acid (to show the effect in the absence of amino groups of amino acids) were used.
The parameters and results are shown in Table 8. The concentration of 2000 ppm means that the concentration of carboxyl groups at this time is 1000 pp
m was selected to be similar to that of aspartic acid.
The corrosion inhibiting effect was observed at pH 9.5 when measured at 25 ° C. (changes to about pH 8.4 when measured at 90 ° C.).
This is very close to the pH threshold of aspartic acid, suggesting that higher amounts of polyaspartic acid are required to completely suppress all points on the surface that result in a heterogeneous surface. However, a significant degree of suppression was obtained at 2000 ppm. However, it is expected that at high fluid velocities, such as those imparted to rotating electrodes, the corrosion inhibiting properties of polyaspartic acid will increase.

Although polyaspartic acid / hydroxamic acid does not contain an amino group, the corrosion inhibitory effect was inferior at the same concentration as aspartic acid.

Example 2 This example demonstrates that the compositions of the present invention are effective as corrosion inhibitors at relatively low temperatures.

Static immersion tests on steel in water at pH 10 were carried out as described in Example 2 at 30 ° C., without inhibitors, with the addition of 3% aspartic acid or with 3% polyaspartic acid. The parameters and results are shown in Table 9.
Both aspartic acid and polyaspartic acid showed a significant corrosion inhibitory effect (10.0 mpy was reduced to less than 0.1 mpy without local corrosion) under relatively low temperature conditions.

Thus, it is apparent that there has been provided, in accordance with the present invention, a composition and method for inhibiting ferrous metal corrosion in the presence of an aqueous medium that fully satisfies the objects and advantages set forth above. Although the present invention has been described with respect to many specific examples and embodiments, the present invention is not limited thereto, and many alternatives, partial modifications and variations will occur to those skilled in the art in light of the above description. It will be understood that this will be obvious. Accordingly, the present invention includes all alternatives, modifications and variations that fall within the spirit and scope of the invention.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor: Silverman, David, Charles Strawbridge Court, Chesterfield, Missouri, USA 63017 14314 (56) References JP-A-49-26145 (JP, A) 50-91546 (JP, A) JP-A-56-98482 (JP, A)

Claims (26)

(57) [Claims] A composition for inhibiting corrosion of ferrous metal in the presence of an aqueous medium, comprising: (Where R ¹ is H, Or H ₂ N— (CH ₂ —) _y ) —; R ² represents HO—, Or HOOC— (CH ₂ —) _y —NH—; R ³ represents H, —COOH, —CH ₂ COOH, or —CH ₂ CH ₂ COOH, and x and y are each independently from 1 to 3 And n is an integer greater than 1 and represents a repeating integer of aminoacyl units in an amount effective to inhibit corrosion of ferrous metal. The above-described corrosion-inhibiting composition, comprising an amino acid represented by) and (b) an amount and a base effective to provide the amino acid in a form that is sufficiently ionized under the conditions of use. 2. The composition of claim 1, wherein the amino acid is selected from the group consisting of polyglycine, polyaspartic acid, polyglutamic acid, and salts thereof. 3. The method according to claim 1, wherein the amino acid is present in an aqueous medium under the conditions of use.
The composition of claim 1, wherein the composition is present in an amount sufficient to provide an amino acid concentration of 0 ppm to greater than or equal to 5.0% by weight. 4. An amino acid is present in an aqueous medium under the conditions of use.
4. The composition of claim 3, wherein the composition is present in an amount sufficient to provide an amino acid concentration between 00 ppm and 3.3% by weight. 5. The composition according to claim 1, wherein the base is an alkali metal hydroxide, an alkali metal carbonate, an alkaline earth metal hydroxide, an ammonium hydroxide, and hydrocarbylamine. Stuff. 6. The base is a hydroxide of an alkali metal,
A composition according to claim 5. 7. The composition of claim 6, wherein the alkali metal hydroxide is selected from the group consisting of sodium hydroxide and potassium hydroxide. 8. The composition according to claim 1, wherein the pH in the aqueous medium under the conditions of use is at least 8.9. 9. The pH in an aqueous medium, measured at room temperature, of 9.9
The composition of claim 1, wherein the composition is -12. 10. The pH in an aqueous medium when measured at room temperature is 10
The composition of claim 1, wherein the composition is 11. A method for inhibiting the corrosion of ferrous metal in the presence of an aqueous medium, the aqueous medium comprising: (Where R ¹ is H, Or _{H 2 N- (CH 2 -)} y) - indicates, R ² is, HO-, Or HOOC— (CH ₂ —) _y —NH—, R ³ represents H, —COOH, —CH ₂ COOH, or —CH ₂ CH ₂ COOH, and x and y are each independently 1 to 3 Represents an integer, and n is an integer greater than 1, indicating a repeating integer of an aminoacyl unit in an amount effective to inhibit corrosion of ferrous metal. ), And (b) a base in an amount effective to provide the amino acid in a sufficiently ionized form under the conditions of use. 12. The method of claim 11, wherein the amino acid is selected from the group consisting of polyglycine, polyaspartic acid, polyglutamic acid, and salts thereof. 13. The method according to claim 12, wherein the amino acid is in an aqueous medium under the conditions of use.
12. The method of claim 11, wherein the amount is present to provide an amino acid concentration of 100 ppm to 5.0% by weight or more. 14. The method according to claim 1, wherein the amino acid is present in an aqueous medium
14. The method of claim 13, wherein the method is present in an amount sufficient to provide an amino acid concentration of 1000 ppm to 3.3 wt% or more. 15. The method according to claim 11, wherein the base is an alkali metal hydroxide, an alkali metal carbonate, an alkaline earth metal hydroxide, an ammonium hydroxide, or hydrocarbylamine. 16. The method according to claim 11, wherein the base is a hydroxide of an alkali metal. 17. The alkali metal hydroxide is selected from the group consisting of sodium hydroxide and potassium hydroxide.
The method according to claim 16. 18. The method according to claim 11, wherein the pH in the aqueous medium under the conditions of use is at least 8.9. 19. The pH in an aqueous medium, when measured at room temperature, is 9.
The method of claim 11, wherein the method is 9-12. 20. When measured at room temperature, the pH in an aqueous medium is 10
20. The method of claim 19, wherein 21. The method of claim 11, wherein the corrosion rate of the ferrous metal is reduced by a factor of 100 to 1000 compared to the corrosion rate in the absence of amino acids. 22. The aqueous medium is substantially stationary.
The method according to claim 11. 23. The method according to claim 11, wherein the aqueous medium is in a dynamic fluid state. 24. The method according to claim 11, wherein the aqueous medium under the conditions of use is at ambient or room temperature. 25. The method according to claim 11, wherein the temperature of the aqueous medium is at least 25 ° C. 26. The temperature of the aqueous medium is 30 ° C.
The method according to 25.