JPH0593287A - Corrosion inhibitor for metal - Google Patents

Abstract

PURPOSE:To produce the corrosion inhibitor for inhibiting the corrosion of the metal surface in the hydrocarbon distillation tower and steam condensation part by preparing the inhibitor contg. the amines shown by a specified formula as the effective component. CONSTITUTION:A corrosion inhibitor for metal contg. at least one kind of the amine (N,N-dimethylethyleneamine, N,N-dimethylethylenediamine) shown by the formula (n is an integer of 1 to 6, m is an integer of 2n or 2n-2, and R<1> and R<2> are independently 1-4C alkyls) as the effective component is prepared. The inhibitor is injected into the initial condensation part or its upstream side so that the condensed water is kept substantially at >=pH 4 in the hydrocarbon distillation tower. The corrosion problem of the condensation part is solved in this way.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a metal corrosion inhibitor. More specifically, the present invention relates to a corrosion inhibitor that suppresses corrosion that occurs on the metal surface of the steam condensation section of a hydrocarbon distillation column containing an acidic substance.

[0002]

2. Description of the Related Art When distilling hydrocarbons in a petroleum refining / chemical plant to separate and refine the hydrocarbons, when steam contained in the hydrocarbons is condensed,
The acidic substances existing in the hydrocarbons are dissolved therein, and the pH of the condensed water is lowered, resulting in severe corrosion on the metal surface of the apparatus in this portion. It is well known that corrosion is particularly severe in the initial condensed portion of water.

In order to suppress this kind of corrosion, the condensed water p
It is well known to add basic substances such as ammonia, morpholine, ethylenediamine, cyclohexylamine and methoxypropylamine for the purpose of increasing H. [For example, "Corrosion and Anticorrosion Society", "Handbook of Metal Corrosion Technology", page 735 (1981, Nikkan Kogyo Shimbun), Japan Petroleum Institute, "New Petroleum Encyclopedia," page 736 (1982, Asakura Shoten), JP-B-52-3896, USP 3,447. 891
It is described in the description etc.].

[0004]

However, in the petroleum refining / chemical plants, there have been cases where conventional corrosion inhibitors cannot provide sufficient corrosion inhibiting effect due to changes in operating conditions of the plant. A typical example of this is an atmospheric distillation unit for crude oil in an oil refinery plant. In recent years, there has been a tendency to keep the overhead temperature lower than before due to the demand for increased production of petroleum middle distillates, and as a natural consequence, the temperature of the initial condensation section has become lower than before. as a result,
Although a severe corrosion problem that has not been seen before has occurred in this part, it is hard to say that an effective corrosion suppression method has been established.

[0005]

Means for Solving the Problems The present invention has been achieved as a result of intensive studies to solve the above problems. (In the formula, n is an integer of 1 to 6, m is 2n or 2n-2.
And R ¹ and R ² each independently have 1 to 4 carbon atoms.
Which is an alkyl group of) and which has at the same time a primary amino group and a tertiary amino group in one molecule, and / or an amine represented by the general formula (I) as an active ingredient. It is an inhibitor. Specific compounds represented by the general formula (I) include N, N-dimethylethylenediamine, N, N-diethylethylenediamine,
N, N-dimethyl-1,3-propylenediamine, 1-
(N, N-diethylamino) -2-aminopropane,
Examples thereof include N, N-dibutyl-ethylenediamine and N, N-dimethyl-1,4-cyclohexanediamine.

The corrosion inhibitor described in the present invention is used by mixing one or more of the compounds represented by the general formula (I), and further dissolving them in water or a suitable organic solvent, if necessary. You can do it. Further, if necessary, they may be used in combination with or mixed with conventionally known amines such as ammonia, morpholine, ethylenediamine, cyclohexylamine, and methoxypropylamine. Further, the combined use with the film-forming corrosion inhibitor does not impose any limitation.

The injection of the corrosion inhibitor of the present invention is carried out upstream of the initial condensation part or the target corrosion problem point,
And it is desirable to have a place near the corrosion problem.

Generally, the corrosion inhibitor reacts with an acidic substance (mainly hydrochloric acid) existing around the corrosion inhibitor immediately after being injected into the process to form a neutralization salt (hydrochloride). The neutralized salt exists as a solid or in a liquid state at the upstream of the point where the steam condenses, but when the steam condenses, the water generated and the neutralized salt coexist. Since the amount of condensed water is small in a very initial condensed portion of water vapor, the neutralized salt contains a small amount of water, so that the corrosiveness of the neutralized salt containing a small amount of water becomes a problem. When the water is highly condensed, the neutralized salt dissolves in the condensed water in a very high concentration. Then, because of the high temperature there, part of the neutralized salt dissociates in water, and the hydrochloric acid produced remains in the water, but part of the free amine moves to the gas phase and the balance of neutralization is disrupted, causing condensation of condensed water. Will decrease the pH. This is the cause of corrosion occurring in the steam condensation part, especially in the initial condensation part. Therefore, the amine used as a corrosion inhibitor stays in distilled water as much as possible in the free state,
Those that are difficult to move to the gas phase are desirable. In any case, in the condensing part, the neutralized salt is repeatedly formed, dissolved and dissociated, and the stability and behavior of the neutralized salt greatly affect the corrosion. On the other hand, the condensed water during the process varies depending on the location such as temperature and amount of condensation, but it is desirable to keep the pH constant at any location. This will cause corrosion. P from the process management side
It is an important factor that it is easy to keep H constant.

The corrosion inhibitor according to the present invention is intended to solve such problems. That is, a neutralization salt (mainly a hydrochloride salt) of the amine of the general formula (I), which is the active ingredient of the present invention, and an acidic substance in the process.
Was significantly improved in its corrosiveness at a high temperature containing a small amount of water. Regarding the corrosiveness of the neutralized salt, the hydrochloride obtained by adding hydrochloric acid to the above-mentioned substances of the general formula (I) mentioned in the present invention is ammonia, ethylenediamine, cyclohexylamine, triethylamine which has been conventionally used for this purpose. It has the feature of being less corrosive than hydrochlorides such as methoxypropylamine.

Further, the corrosion inhibitor described in the present invention has excellent transferability to condensed water, and does not cause a pH decrease due to dissociation of the hydrochloride even when dissolved in water at high temperature. this is,
This is because the free amine generated by dissociation in water is difficult to transfer to the gas phase. Therefore, it is possible to exhibit a far superior corrosion inhibiting effect to ammonia, morpholine, cyclohexylamine, triethylamine, etc., which have been conventionally used for this purpose.

Furthermore, the corrosion inhibitor according to the present invention has an excellent pH adjusting function, and is substantially 4 or more, which is generally used as a set value of the final pH, and is particularly desirable for suppressing corrosion.
It is easy to keep between 5 and 6.5.

As described above, the amines represented by the above general formula (I) according to the present invention, which simultaneously have a primary amino group and a tertiary amino group in one molecule, can be used as an initial condensation part of steam in a hydrocarbon distillation column. It was found that the various points required for suppressing the corrosion occurring in the above can be satisfied and the corrosion can be effectively suppressed.

[0013]

EXAMPLES The present invention will be described below with reference to examples. However, the present invention is not limited by the experimental examples and use examples in the following examples.

Example 1 An experimental distillation column 2 as shown in FIG. 1 was assembled to evaluate a corrosion inhibitor. This device vaporizes naphtha, water and hydrochloric acid, adds a corrosion inhibitor to the vapor, and then gradually condenses the temperature, the amount of condensed water, and the p of condensed water.
It measures H and corrosion rate, and has a good correlation with the initial condensation of the actual equipment.

The naphtha heating furnace 1 was set at 125 to 140 ° C., and naphtha was added thereto at 1.7 l / hr. One after the other was poured continuously and evaporated. On the other hand, in the steam generator 3, 0.2 l / hr. Then, it was supplied from a pipe 7 to generate water vapor, and hydrochloric acid was added from a pipe 8 to mix it with the vapor of naphtha, and sent to the condensing pipe 4. Immediately after the mixed vapor entered the condensing pipe 4, the corrosion inhibitor was injected from the pipe 9, but at this time, the pH measuring device 5 attached to the receiver of the condensed water should keep the pH at 6.5. The amount of corrosion inhibitor injected was controlled. The condensing tube 4 has a total length of 1.2 m and is designed to be gradually cooled from 105 ° C. to 80 ° C. The test pieces 12 for measuring the corrosion degree were attached at four places on the way. The test piece 12 is made of mild steel and has a size of 25 × 15 × 2.
The size is mm.

For each corrosion inhibitor, the experiment was repeated for 48 hours under the same conditions, and the results shown in Table 1 were obtained. The corrosion rate is
Calculated from the corrosion weight loss of the test piece, MD
D is the corrosion weight loss per day expressed in mg for a surface area of 1 dm ² .

[Table 1]

When the water condensation rate is 0.1% or less, a small amount of water is contained in the neutralizing salt (hydrochloric acid salt), and the corrosion rate here depends on the corrosiveness of the neutralizing salt (hydrochloric acid salt). Comes from. on the other hand,
The corrosion rate at a water condensation rate of 10% and 25% is that after the neutralization salt (hydrochloride) is dissolved in the condensed water, it is dissociated and the hydrochloric acid in the water is increased to cause corrosion. In addition, the magnitude of the pH fluctuation can be read from the pH of each part. It can be seen that the amines of the examples are superior to any of the amines listed in the comparative examples.

(Example 2) In the experiment of Example 1, a corrosion inhibitor was injected to control the pH of the condensed water to 6.5. However, depending on the amine of the corrosion inhibitor, the pH may be 6.5. It was difficult to keep the pH value constant and the pH fluctuated considerably.
Table 2 shows the results of reading the pH every 5 minutes in this experiment and comparing the magnitude of the variation with the value of the standard deviation.

[Table 2]

It can be seen that the amines shown in the examples have a predetermined pH controlled and little fluctuation.

Example 3 N, N-dimethylethylenediamine according to the present invention was used in an atmospheric distillation column (110,000 barrels / day) for petroleum refining so that the final pH of the condensed water was 6.5. When the continuous operation was carried out for one year while adjusting the injection amount, the corrosion at the top of the column and the initial condensation part was significantly reduced, and there was no problem such as accumulation of neutralized salt.

[0021]

As described above, the corrosion inhibitor according to the present invention significantly reduces the corrosion of the initial condensation part as compared with the conventional neutralizing corrosion inhibitor used for the same purpose.
The neutralization salt is not deposited, and the pH of the condensed water can be stably controlled, so that the corrosion problem of the steam condensation section of the hydrocarbon distillation column in the petroleum refining / chemical plant can be solved.

[Brief description of drawings]

FIG. 1 is a system diagram showing an experimental distillation column for evaluating the method of the present invention.

[Explanation of symbols]

 1: Naphtha heating furnace 7: Distilled water supply pipe 2: Distillation tower 8: Hydrochloric acid supply pipe 3: Steam generator 9: Corrosion inhibitor supply pipe 4: Condensation pipe 10: Condensed oil removal 5: Condensed water pH meter 11: Condensed water removal 6: Naphtha supply pipe 12: Test piece

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukio Matsui 9 Yokkaichi, Mie Prefecture, 6th place, 6-chome 6 Hakka East Co., Ltd. Yokkaichi Laboratory

Claims (2)

[Claims] 1. A general formula (In the formula, n is an integer of 1 to 6, m is 2n or 2n-2.
And R ¹ and R ² each independently have 1 to 4 carbon atoms.
Which is an alkyl group of 1) is contained as an active ingredient at least one kind of amines. 2. The corrosion inhibitor according to claim 1 is injected into the initial condensation part or upstream thereof so that the pH of the condensed water of steam in the hydrocarbon distillation column is maintained at substantially 4 or more. A method for inhibiting metal corrosion, which is characterized in that