JPH01254293A - Corrosion-resistant treatment of metal - Google Patents

Abstract

PURPOSE:To prevent the corrosion of a metal material, by adding a specific reducing agent to an aqueous solution containing an oxoacid salt of halogen to hold the redox potential thereof to the corrosion generating potential of a metal or less and allowing said aqueous solution to flow through a metal container or metal flow passage. CONSTITUTION:A reducing agent generating only one or more kind of carbon dioxide, water and nitrogen by decomposition or reaction is added to an aqueous solution containing an oxoacid salt of halogen to bring the redox potential of the aqueous solution to the corrosion generating potential of a high corrosion- resistant metal. This aqueous solution having the reducing agent added thereto is supplied to a metal container or metal flow passage to perform metal corrosion-resistant treatment. As the reducing agent, there are hydrazine, hydrogen peroxide and formalin. As mentioned above, by adding the reducing agent, the oxoacid salt of halogen is reduced to decrease the corrosion of the metal by the aqueous solution.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention is directed to the storage or distribution (hereinafter simply referred to as a flow path) of an aqueous solution containing a halogen oxoacid salt in a metal container or channel (hereinafter referred to as a channel, etc.). The present invention relates to a metal corrosion prevention treatment method for preventing corrosion of metal materials that come into contact with the aqueous solution during distribution (referred to as distribution).

"Prior art and its problems" Hypobromite, hypochlorite, and bromate produced from various organic or inorganic compound production processes, such as the bromination process in the production of methyl bromide, have traditionally been produced. ,
An aqueous solution containing a halogen oxoacid salt such as chlorate,
When flowing through a channel made of a highly corrosion-resistant metal, there is a problem in that the metal material of the channel or the like that comes into contact with this aqueous solution is likely to be corroded.

For example, in the bromination process for producing methyl bromide, when bromine is added to the raw methanol to perform bromination,
Clean exhaust gas. The cleaning liquid generated by this cleaning is
Contains bromine oxoacid salts, mainly hypobromite, which is highly corrosive to metals, and may cause corrosion to metal channels when the cleaning solution is transported to other parts. be.

Therefore, as a measure to prevent corrosion of flow channels, etc., 5US3 is added to the material.
Attempts have been made to use stainless steel with excellent corrosion resistance, such as 29J2L, but even this stainless steel cannot completely prevent corrosion caused by the above cleaning solution, especially in partially deep areas. There have been problems in that pitting corrosion occurs in which holes are formed and corrosion progresses, and crevice corrosion occurs in the joints of the stainless steel plates. This phenomenon becomes particularly noticeable as the alkaline concentration of the cleaning solution decreases.

As a means to completely prevent corrosion caused by this cleaning liquid, there are methods to use expensive metal materials such as Inconel 625, Hastelloy C-275, Ni alloy, Ti, etc. as materials for the flow passages, and methods to completely prevent corrosion caused by the cleaning liquid for the flow passages. Methods such as coating the contact surfaces with corrosion-resistant lining materials are considered, but these methods cannot completely prevent corrosion, and all of these methods require a significant amount of production equipment. There was a problem that led to an increase in costs.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for preventing corrosion of metal materials by an aqueous solution containing a halogen oxoacid salt without using expensive metals.

"Means for Solving the Problems" In order to achieve the above object, in the metal corrosion protection treatment method of the present invention, carbon dioxide, water and nitrogen are removed by decomposition or reaction into an aqueous solution containing a halogen oxoacid salt. A reducing agent that produces only one or more of the following is added to keep the oxidation-reduction potential of the aqueous solution below the corrosion potential of the metal, and the aqueous solution is supplied to a flow path or the like.

"Operation" By adding the reducing agent to the aqueous solution, the halogen oxoacid salt is reduced, and the corrosiveness of the aqueous solution to metals is reduced.

In addition, a reducing agent is added while measuring the amount of the halogen oxoacid salt in the aqueous solution, and after the oxidation-reduction potential of the aqueous solution is lower than the corrosion potential of the metal material such as the flow path, it is poured into the flow path etc. The amount of reducing agent added can be adjusted to the required minimum amount by allowing the amount of reducing agent to be added to the amount of the reducing agent.

"Example" Examples will be described with reference to the drawings.

FIG. 1 is for explaining one embodiment of the method of the present invention, and reference numeral 1 indicates a reducing agent addition mechanism.

This example shows an example in which the method of the present invention is applied to the reduction treatment of a cleaning solution containing hypobromite, such as a cleaning solution discharged from the methanol bromination process during the production of methyl bromide. .

This reducing agent addition mechanism 1 is equipped with a stirring device and includes a cleaning liquid 2 containing hypobromite sent from the bromination process etc.
A reduction tank 3 stores a certain amount of water, and the oxidation-reduction potential of the cleaning liquid 2 in this reduction tank 3 or the Br0 in the cleaning liquid 2.
A measuring device 4 for measuring the concentration of - and the oxidation-reduction potential of the cleaning liquid 2 measured by this measuring device 4
The configuration 1 includes an automatic addition device 5 for adding the amount of hydrazine necessary for reducing the cleaning liquid 2 into the reduction tank 3 depending on the concentration. Further, reference numeral 6 indicates the automatic addition device 5.
This is a hydrazine tank for storing hydrazine added from.

The measuring device 4 includes an ultraviolet absorption photometer that can measure the absorbance of Br0-, which has absorption in the near-ultraviolet region with a wavelength of 331 nm, and an oxidation-reduction potential measurement device that measures the potential difference between a reference electrode and an indicator electrode such as a platinum electrode. A meter is used. Note that the reference electrode when measuring the redox potential is a normal hydrogen electrode (NHE) or a saturated calomel electrode (SCE).
is preferably used.

In addition, as an indicator electrode, various metals can be used instead of platinum electrodes.
Although electrodes made of alloys can be used, platinum electrodes have a faster potential response than electrodes made of other metals, such as stainless steel, and have a high detection sensitivity of B on the order of ppm.
Since the presence of r0- can also be detected sensitively, it is particularly suitable for use when directly measuring Br0- in the cleaning solution.

The cleaning liquid 2 is continuously reduced by the above-mentioned reducing agent addition mechanism 1 as follows. First, the cleaning liquid 2 is continuously supplied into the reduction tank 3. In this reduction tank 3, the B ro-a degree in the liquid or the oxidation-reduction potential of the liquid is constantly measured by the measuring device 4, and the B ro-a degree in the liquid or the oxidation-reduction potential of the liquid is below a predetermined level. As shown, hydrazine is added to the liquid by the automatic addition device 5. Br0- in the cleaning liquid 2 is reduced to Br- by the hydrazine added to this liquid, and the redox potential of the liquid decreases. Therefore, the liquid in the reduction tank 3 is reduced to a predetermined level or lower, such as a Br0- concentration of 10 ppm or less and an oxidation-reduction potential of less than the corrosion potential of stainless steel, and becomes the treated liquid 7.
is discharged from. The amount of hydrazine added by the automatic addition device 5 is automatically adjusted based on the measurement result of the amount of Bro- in the liquid or the oxidation-reduction potential of the liquid by the measuring device 4. When the oxidation-reduction potential of N or the liquid reaches a predetermined level or higher, hydrazine is supplied into the reduction tank 3.
It is desirable to automatically adjust the amount of hydrazine added or stop adding hydrazine when the amount of Br0- in the liquid or the oxidation-reduction potential of the liquid falls below a predetermined level.

According to this example, B, which is involved in corrosion of stainless steel,
Adding hydrazine to the washing solution containing r0-
Since this treatment liquid 7 is discharged into the flow path etc. after reducing it to Br-, this treatment liquid 7 has excellent effects such as not corroding the metal materials such as stainless steel used in the flow path etc. Since reducing agent addition mechanism I was used as a means for adding, the amount of Br0- in cleaning liquid 2 or cleaning liquid 2
While measuring the oxidation-reduction potential of Since the reduction treatment of the cleaning liquid 2 can be performed continuously by adding hydrazine, it is possible to save labor in the anticorrosion treatment of the flow path, etc., and the running cost of the anticorrosion treatment can be reduced.

In this example, hydrazine was used as the reducing agent, but the reducing agent used in the method of the present invention is not limited to this, and carbon dioxide, water, and nitrogen can be removed by decomposition or reaction of hydrogen peroxide, formalin, etc. Reducing agents that produce only one or more of the following can be used. The above-mentioned reducing agents such as hydrazine, hydrogen peroxide, and formalin all have reducing properties even in alkaline conditions, and when decomposed in the presence of oxygen, they become gaseous components such as water, nitrogen, and carbon dioxide gas. Since it does not remain in the processing solution,
When the treatment liquid is reused, it does not affect the process reaction and does not cause problems such as scale formation.

Further, in the above-mentioned embodiment, stainless steel such as 5US329 J 2 L was used as the metal material forming the flow path etc., but the metal material to be subjected to anti-corrosion treatment is not limited to stainless steel, and may be, for example, N of inconel etc.
Even with other metal materials such as i-based alloys and Ti, corrosion prevention treatment can be performed by checking the lower limit potential of corrosion of the target metal and adding a reducing agent to keep the potential below that lower limit. can.

In addition, in the above-mentioned example, the cleaning solution containing Br0- discharged from the methyl bromide production process by bromination of methanol was used as the aqueous solution to be treated. Without being limited to this, for example, an aqueous solution containing one or more halogen oxoacid salts such as Cl0- generated during cleaning of waste gas containing chlorine gas such as in the phosgene production process may be used. good.

(Experimental Example) First, the corrosion potential of stainless steel used as a metal material for flow channels and the like was measured. 5US3 for stainless steel
Using 29J2L, the two stainless steel plates are partially joined to form a gap and used as a sample.
pi-(9,
A constant potential crevice corrosion test (holding time: 16 hours) was conducted in a liquid at a temperature of 90°C. As a result of this test, it was confirmed that in the presence of a high concentration of 01- or Br-, crevice corrosion occurs in the above sample at a potential of +0,15V or higher, as shown in FIG. Note that the ○X shown in FIG. 2 represents the potential at which crevice corrosion occurred in the stainless steel sample, and O indicates the potential at which crevice corrosion did not occur.

In addition, the three concentrations of Br0− shown on the right side of FIG.
The potential range shown by 10000 ppm Br-
The aqueous solution containing Br0-;Oppm is defined as Br0-;
The results show the results of measuring the corrosion potential (natural immersion potential) of the above-mentioned sample by immersing it in each solution which was added so as to have a concentration of 0 ppm, pH 12.5, and temperature 90°C. In addition, when measuring this corrosion potential, a saturated calomel electrode was used as a reference electrode, and the above sample was used as an indicator electrode.

From the results of each of the above tests, the stainless steel sample (SUS
329 J 2L) in a solution containing a high concentration of Br" or CI-, crevice corrosion occurs at a potential of O,I5V or more, and the corrosion potential of the stainless steel increases as the concentration of Br0- increases. Shift to the side, Br0-
The corrosion potential of B in an aqueous solution is 0.15 V or higher under conditions of a concentration of 310 ppm or 620 ppm.
It was confirmed that a cleaning solution with an r0- concentration of about several 100 ppm could cause crevice corrosion in the stainless steel.

In addition, since the corrosion potential of stainless steel is 0.15 V or less under conditions where Br0- is Oppm, even an aqueous solution containing high concentrations of Br- and Br0-, such as a cleaning solution, cannot reduce Br0-. It was confirmed that corrosion prevention treatment of stainless steel is possible by reducing the B ro -8 degrees in the aqueous solution and bringing the potential below the lower limit potential for corrosion of the target metal.

Next, using the cleaning solution collected from the methanol bromination process, B to -
While measuring @ or the redox potential of this solution using a saturated calomel electrode and a platinum electrode, hydrazine is added to this cleaning solution, and the amount of hydrazine added and Br0-
The relationship between concentration or redox potential was investigated. Note that the Br0− concentration in this cleaning solution is I 2 , 5 mmol/ρ
, Br concentration is 100 mmol/12, pH 1
2.5 tears.

Then, while measuring the concentration of Br0− in the cleaning solution using an ultraviolet absorption photometer at a measurement wavelength of 33 nm, hydrazine was added to the cleaning solution, and the amount of hydrazine added and Br0− were measured.
-The relationship between concentrations was investigated. The results are shown in Table 1.

table ! As shown in Table 1, as hydrazine is added to the cleaning solution, Br0- decreases, and this Br0-0 degree can be accurately monitored. It was confirmed that it is fully applicable.

Next, while measuring the redox potential of the cleaning solution mentioned above using the redox potential method that measures the redox potential of an aqueous solution, hydrazine was added to the cleaning fluid to investigate the relationship between the amount of hydrazine added and the redox potential of the cleaning fluid. Ta. Note that a saturated calomel electrode was used as a reference electrode, and a platinum electrode was used as an indicator electrode. The results are shown in Table 2 and Figure 3.

Table 2 (*Br0-concentration and Br0-removal rate are measured by ultraviolet absorption spectrophotometry shown in Table 1.) As is clear from Table 2 and Figure 3, as hydrazine is added to the cleaning solution, the oxidation-reduction rate of the cleaning solution increases. When the potential decreases and fluctuates from 10Ω, for example, a particularly sharp potential change is shown. Therefore, it has been confirmed that changes in the oxidation-reduction potential of the cleaning liquid can be monitored extremely accurately, and that the method can be sufficiently applied to corrosion protection for metal materials such as channels through which the cleaning liquid flows.

In addition, as a result of conducting a reduction treatment test of a cleaning solution similar to that described above using each of hydrogen peroxide and formalin instead of the above-mentioned hydranone as a reducing agent, it was found that no matter which reducing agent was used, the same results as with the above-mentioned hydrazine were obtained. It was possible to reduce Br0- in the cleaning solution, and to accurately monitor changes in the Br0- concentration in the solution or the redox potential of the solution. Therefore, it was confirmed that even if a reducing agent other than the above-mentioned hydrazine is used, it can be sufficiently applied to the corrosion protection of metal materials such as channels through which cleaning liquid flows, in the same way as when the above-mentioned hydrazine is used.

"Effects of the Invention" As explained above, in the metal corrosion protection treatment method of the present invention,
A reducing agent that generates only one or more of carbon dioxide gas, water, and nitrogen through decomposition or reaction is added to an aqueous solution containing a halogen oxoacid salt to remove halogen oxoacids that are involved in corrosion of metal materials in the flow path. Since the acid salt is decomposed and then supplied to the flow path, there is no possibility of corrosion of the metal materials of the flow path etc. when this treatment liquid is circulated through the flow path. Therefore, it is possible to prevent corrosion of the flow path, etc. without using expensive metal materials such as Ti or Ni-based alloys for the metal material of the flow path, etc., and it can be used in various manufacturing equipment that requires the above-mentioned aqueous solution to flow through the flow path. It is possible to reliably protect the flow path, etc. from corrosion, and also to reduce the cost of the manufacturing equipment.

In addition, in this metal corrosion prevention treatment method, by adding the above-mentioned reducing agent to the aqueous solution, the halogen oxo acid salt can be decomposed and removed regardless of its concentration, and the concentration of the halogen oxo acid salt fluctuates greatly. Even in this case, the aqueous solution can be reduced. In addition, these reducing agents do not oxidize and decompose to produce water or gas that remains in the processing solution, so even if the processing solution is re-supplied into the manufacturing process after adding the reducing agent, it will not affect the process reaction. Therefore, it can be applied to various manufacturing processes with different processing conditions, such as when the treatment liquid is used again in the manufacturing process.

Further, when the treatment liquid is to be used again in the manufacturing process, metal corrosion prevention treatment can be performed not only on the flow path through which the treatment liquid flows, but also on the entire process in which the treatment liquid is reused.

Furthermore, when adding the reducing agent to the aqueous solution, the reducing agent is added while measuring the amount of the halogen oxoacid salt in the aqueous solution, and the oxidation-reduction potential of the aqueous solution is measured to prevent corrosion of the metal. By supplying the aqueous solution to the flow path after reducing the potential to below the potential, the reduction process of the aqueous solution can be automated and continuous, making it possible to save labor in the corrosion prevention treatment of the flow path, etc., and reduce the running cost of the corrosion prevention treatment. You can do it.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining one embodiment of the present invention, and is a schematic configuration diagram showing one example of a reduction processing mechanism, and FIGS. 2 and 3 are diagrams for explaining the present invention in detail. It is. l... Reducing agent addition mechanism 2... Cleaning liquid (aqueous solution) 7... Processing liquid.

Claims (1)

[Scope of Claims] A metal corrosion prevention treatment method when an aqueous solution containing a halogen oxoacid salt is accommodated or distributed in a container or flow path made of a highly corrosion-resistant metal, wherein carbon dioxide gas is generated in the aqueous solution by decomposition or reaction. , water, and nitrogen, to maintain the redox potential of the aqueous solution below the corrosion potential of the metal, and supply the aqueous solution to the container or flow path. Metal corrosion protection treatment method.