JPH0720530B2 - Corrosion control method for steel in carbon dioxide absorption process - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for inhibiting corrosion of steel used in a process of absorbing and separating carbon dioxide gas.

[Background of the Invention] When producing city gas, hydrogen gas, ammonia synthesis gas, and other raw material gases from a hydrocarbon such as petroleum as a raw material by a steam reforming method, a partial oxidation method, etc., unnecessary carbon dioxide gas produced as a by-product is produced. It will need to be removed.

These syngas are produced in large quantities, have high flow rates, and
The carbon dioxide content is also high at 20-30%. This flow rate is also large,
In addition, in order to economically remove carbon dioxide gas from synthesis gas, which also contains a large amount of carbon dioxide gas, with a low residual concentration,
A process using an aqueous solution of potassium carbonate as the absorbing liquid and a process using an aqueous solution of amines such as monoethanolamine and diethanolamine as the absorbing liquid are adopted.

The process using an aqueous solution of amines is suitable for treating a gas having a low carbon dioxide gas content to reduce the residual carbon dioxide gas concentration, but the absorption liquid is cooled and used, so that the thermal economy is not good. On the other hand, the process using an aqueous solution of potassium carbonate has a high concentration of residual carbon dioxide gas, but basically, the absorption liquid is circulated without being cooled, and therefore, the thermal economy is excellent.

The process of using an aqueous solution of potassium carbonate as the absorbing liquid is performed by absorbing and releasing carbon dioxide gas according to the following formula.

In the absorption tower, K ₂ CO ₃ in the aqueous solution is converted to KHCO ₃ and chemically absorbs carbon dioxide gas. In the regeneration tower, KHCO 3 in the aqueous solution is absorbed.
Carbon dioxide is released by regenerating ₃ into K ₂ CO ₃ .

Aqueous potassium carbonate solution that has absorbed carbon dioxide is corrosive, and corrodes steel materials used in absorption towers, regeneration towers, or piping connecting them, such as piping, pumps, and control valves, albeit slightly. There was a problem.

To prevent these corrosions, vanadium pentoxide (V
₂ O ₅ ), sodium chromate (Na ₂ CrO ₄ ) and other corrosion inhibitors have been developed.

Although these vanadium pentoxide (V ₂ O ₅ ) and sodium chromate (Na ₂ CrO ₄ ) are excellent in suppressing corrosion well, they are targets for pollution control, so these compounds are used for suppressing corrosion. Doing so is not preferable. In addition, steel materials used in absorption towers, regeneration towers, piping connecting them, etc.
Although it was attempted to suppress corrosion by replacing carbon steel with stainless steel, it is still not sufficient to suppress corrosion, and vanadium pentoxide, which is a target of pollution control,
It has been desired to develop a pollution-free corrosion inhibitor that replaces sodium chromate.

[Object of the Invention] Accordingly, it is an object of the present invention to provide a method of suppressing corrosion of a steel material in a carbon dioxide absorption process using a pollution-free corrosion inhibitor.

[Constitution of Invention] The above objects of the present invention are: (1) In a carbon dioxide gas absorption process using an aqueous solution of carbonate as an absorbent, adding 1-hydroxyethylidene-1,1-diphosphonic acid to the aqueous solution of carbonate. A method for suppressing corrosion of steel material, characterized by:

(2) A method for inhibiting corrosion of steel material, which comprises adding 1-hydroxyethylidene-1,1-diphosphonic acid to an aqueous solution of carbonate in a carbon dioxide separation process using an aqueous solution of carbonate as an absorbent.

(3) The method for inhibiting corrosion according to (1) and (2) above, wherein the carbonate is potassium carbonate.

(4) The method for inhibiting corrosion of steel according to the above (1) to (3), wherein the amount of 1-hydroxyethylidene-1,1-diphosphonic acid added is 50 ppm or more.

(5) The method of inhibiting corrosion of steel according to any one of claims (1) to (3), wherein the amount of 1-hydroxyethylidene-1,1-diphosphonic acid added is 100 to 500 ppm.

(6) 1-hydroxyethylidene-1, in an aqueous solution of carbonate,
The method for inhibiting corrosion of steel according to the above (1) to (5), characterized in that diethanolamine is added together with 1-diphosphonic acid.

Achieved by

[Specific Configuration of the Invention] The carbon dioxide absorption process using an aqueous solution of carbonate as an absorbent is a process of selectively absorbing carbon dioxide using an aqueous solution of carbonate as an absorbent of carbon dioxide. The carbon dioxide gas separation process using an aqueous solution of carbonate as an absorbent means that the aqueous solution of carbonate is used as an absorbent of carbon dioxide, selectively absorbs carbon dioxide, and the carbon dioxide is absorbed from the aqueous solution of carbonate. Is a process in which carbon dioxide gas is separated and recovered.

These processes are industrially known as Benfield processes and are widely practiced.

Potassium carbonate is used as the carbonate in the Benfield process.

When potassium carbonate is used as the carbon dioxide absorbent, the carbon dioxide is absorbed and regenerated by the equilibrium reaction represented by the following formula.

In this reaction system, increase the partial pressure of carbon dioxide gas, or
When the temperature is lowered, the reaction proceeds to the right, carbon dioxide is absorbed, and when the partial pressure of carbon dioxide is decreased or the temperature is raised, the reaction proceeds to the left and carbon dioxide is regenerated. Is done.

It is thermo-economically advantageous to increase the partial pressure of carbon dioxide and lower the partial pressure of carbon dioxide to absorb and regenerate carbon dioxide, rather than raising or lowering the temperature of the absorbing liquid. Is.

A conventionally known method can be adopted for absorption and regeneration of carbon dioxide gas from the raw material gas.

For example, it can be carried out by using an absorption tower and a regeneration tower filled with packing materials such as Rahi ring, saddle, and pole ring.

Usually, the raw material gas is fed from the bottom of the absorption tower, the absorbing liquid is allowed to flow down from the top, and the gas-liquid is countercurrently contacted on the packing to cause an absorption reaction, and the carbon dioxide gas in the raw material gas is removed to purify the raw material gas. Is taken out from the top of the absorption tower, and the absorption liquid absorbing the carbon dioxide gas coming out from the bottom of the absorption tower is supplied to the top of the regeneration tower by utilizing the pressure of the absorption tower. Part of the carbon dioxide gas absorbed in the absorption liquid is removed by a vacuum flash at the top of the regeneration tower, and flows down over the packing. The partial pressure of carbon dioxide in the absorbing liquid flowing down over the packing is lowered by the steam rising from the bottom of the regeneration tower, and potassium hydrogen carbonate in the absorbing liquid is decomposed into potassium carbonate and carbon dioxide. The produced carbon dioxide gas is taken out from the top of the regeneration tower. The steam is supplied by indirectly heating the absorbing liquid by a reboiler installed at the bottom of the regeneration tower or by directly blowing raw steam into the bottom of the regeneration tower. The steam also replenishes the energy lost due to the regeneration of carbon dioxide.

As the absorption tower and the regeneration tower, other known absorption towers and regeneration towers can be used.

The pressure and temperature at which carbon dioxide is absorbed are not particularly limited, but for industrial use, it is generally 10 to 30 kg / cm ² , 100 to 1
20 ° C is used. Further, the concentration of the absorbing solution is not particularly limited, but for industrial use, it is generally selected in the range of 20 to 40%.

The carbon dioxide absorption process using the aqueous carbonate solution of the present invention as an absorbent and the carbon dioxide separation process using the carbonate aqueous solution as an absorbent use another carbon dioxide absorption process or carbon dioxide separation process, for example, amines. It may be used in combination with a carbon dioxide absorption process or a carbon dioxide separation process.

1-Hydroxyethylidene-1,1-diphosphonic acid is added to an aqueous solution of carbonate.

The addition amount is preferably 50 ppm or more. More preferably, it is 100 to 500 ppm.

Further, the corrosion inhibitory effect of 1-hydroxyethylidene-1,1-diphosphonic acid is further increased by the simultaneous presence of DEA.

[Effects of the Invention] (1) Test of Corrosion Inhibition Effect (Stationary System) 1-Hydroxyethylidene-1,1-diphosphonic acid (hereinafter referred to as HEDP), monoethanolamine (hereinafter referred to as ME)
A. ), Diethanolamine (hereinafter referred to as DEA), triethanolamine (hereinafter referred to as TEA), propanolamine, Na ₂ CrO ₄ , V ₂ O ₅ , sodium molybdate (Na ₂ MoO ₄ ), sodium silicate (Na ₂
SiO ₃ ) was added, and the surface of the eggplant-shaped flask filled with a 23% by weight aqueous solution of potassium carbonate saturated with carbon dioxide (temperature 50 ± 1 ° C) was polished with emery paper (# 1500) and then with methanol and acetone. The treated test piece of 20 × 50 × 1.6 mm (steel material, SS 41) was immersed under atmospheric pressure for 7 days to perform a corrosion weight reduction test.

MEA, DEA, TEA, propanolamine, Na ₂ MoO ₄ , Na ₂ SiO
_In No. ₃ , black-brown iron carbonate was produced on the surface of the steel material, and an excellent anticorrosion effect was not obtained.

FIG. 1 shows the results of those having a corrosion inhibiting effect.

HEDP is a target for Na that is a conventionally used pollution control item.
_{Although not as high as 2} CrO ₄ and V ₂ O ₅ , it exhibited a corrosion inhibition effect with an inhibition rate (η) of 80% near a HEDP concentration of 200 ppm.

(2) Corrosion inhibition test (fluid system) HEDP, MEA, DEA, TEA, propanolamine, Na ₂ CrO ₄ ,
V ₂ O _5, sodium molybdate (Na ₂ MoO _4), circulates sodium silicate (Na ₂ SiO ₃₎ 40 wt% aqueous potassium carbonate was added (temperature 94 ± 4 ℃), pressure 10 kg / cm ^The bench scale device shown in Fig. 2 maintained at 2 (hereinafter,
BF device), the surface was polished with emery paper (# 1500) and treated with methanol and acetone.
0.8mm thick, 25.0mm high test piece (steel, SUS 304)
Was immersed for 30 days, and the corrosion weight reduction test was conducted.

Carbon dioxide was introduced into the BF device, and the potassium carbonate aqueous solution was saturated with carbon dioxide.

The test piece 1 is inserted into the BF device 2, and the potassium carbonate aqueous solution is circulated through the BF device 2 by the circulation pump 3. The potassium carbonate aqueous solution is saturated with the carbon dioxide gas introduced from the carbon dioxide gas inlet 4. (FIG. 2) In FIG. 2, 5 is a motor for driving the circulation pump 3, 6 is a tray for evenly flowing the potassium carbonate aqueous solution saturated with carbon dioxide into the test piece 1, and 7 is a pressure gauge. ,
8 is a safety valve, 9 is a thermometer, 10 is a sight glass, and 11 is a discharge valve.

The flow system test also showed the static test, while at the same time MEA, DEA, TEA, propanolamine, Na ₂ MoO ₄ , Na
_{2 With} SiO ₃ , blackish brown iron carbonate was produced on the surface of the steel material, and an excellent anticorrosion effect was not obtained.

Table 1 shows the results of those having a corrosion inhibiting effect.

HEDP is similar to the result of the test in the stationary system, Na ₂ CrO ₄ and V ₂ O _{5 which} are the targets of the conventionally used pollution control substances.
However, it showed an excellent corrosion inhibition effect.

Also, the corrosion inhibition effect is further increased by the simultaneous presence of DEA.

As described above, according to the present invention, the corrosion of the steel material in the carbon dioxide absorption process, the use of Na ₂ CrO ₄ and V ₂ O ₅ which are the targets of the conventionally used pollution control substances is reduced, or It can be suppressed without using.

[Brief description of drawings]

FIG. 1 is a diagram showing a result of a test of a corrosion inhibition effect in a stationary system, and FIG. 2 is a diagram showing an outline of a BF device.

Claims (6)

[Claims] 1. A method for inhibiting corrosion of steel material, comprising adding 1-hydroxyethylidene-1,1-diphosphonic acid to an aqueous solution of carbonate in a carbon dioxide absorption process using an aqueous solution of carbonate as an absorbent. 2. A method for inhibiting corrosion of steel material, comprising adding 1-hydroxyethylidene-1,1-diphosphonic acid to an aqueous solution of carbonate in a carbon dioxide separation process using an aqueous solution of carbonate as an absorbent. 3. The method for inhibiting corrosion according to claim 1, wherein the carbonate is potassium carbonate. 4. The method for inhibiting corrosion of steel according to any one of claims 1 to 3, wherein the amount of 1-hydroxyethylidene-1,1-diphosphonic acid added is 50 ppm or more. 5. The method for inhibiting corrosion of steel materials according to claim 1, wherein the amount of 1-hydroxyethylidene-1,1-diphosphonic acid added is 100 to 500 ppm. 6. The method of inhibiting corrosion of steel according to claim 1, wherein diethanolamine is added together with 1-hydroxyethylidene-1,1-diphosphonic acid to an aqueous solution of carbonate.