JP2003119581A - Corrosion inhibition method for metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a corrosion inhibition method which enables continuous operation of an apparatus in manufacturing a vinyl compound such as acrylic acid, or the like, by inhibiting corrosion in the manufacturing apparatus. SOLUTION: This corrosion inhibition method is characterized by adding copper acetate into a system including the vinyl compound containing copper dithiocarbamate of a polymerization inhibitor, concretely into a manufacturing apparatus or the like for the vinyl compound containing copper dithiocarbamate. In the above addition, the ratio of the above copper dithiocarbamate to copper acetate is preferably 2 mol% or higher in terms of copper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corrosion suppressing method for suppressing corrosion of a manufacturing apparatus for a vinyl compound such as acrylic acid.

[Prior art]

Acrylic acid, a type of vinyl compound, is
Generally, it is produced by a catalytic gas phase oxidation reaction of propylene or acrolein. In this catalytic gas-phase oxidation reaction, the obtained reaction product gas is cooled and collected with water to obtain an aqueous solution of acrylic acid containing by-products such as acetic acid and aldehyde, and acrylic acid is separated from this aqueous solution by distillation. , Concentrate and purify.

However, since acrylic acid has a property of being easily polymerized by light or heat, it is polymerized in a device used in the manufacturing process of acrylic acid, for example, a device such as a distillation column treated in a high temperature atmosphere. Things may be generated. Examples of the production site of the polymer include a manhole of a distillation column, a reflux pipe, a condenser for condensing vapor containing acrylic acid discharged from the distillation column, and the like. In these places, a polymer of acrylic acid is very likely to be formed, and once formed, it becomes a nucleus to gradually grow and accumulate the polymer, and finally the inside of the distillation column is blocked. This is a major factor that hinders continuous operation of the distillation column. Further, it is very difficult to remove the produced polymer, and the removal cost is great.

Therefore, when distilling acrylic acid,
Hydroquinone, methoquinone (p-
Methoxyphenol), copper dimethyldithiocarbamate, etc. have been used for a long time, and at least one compound selected from hydroquinone, metoquinone, cresol, phenol, t-butylcatechol, diphenylamine, phenothiazine and methylene blue and dimethyl A method using a combination with at least one compound selected from copper dithiocarbamate, copper diethyldithiocarbamate, copper dibutyldithiocarbamate, and copper salicylate (Japanese Patent Publication No. 52-34606),
A method using a manganese salt such as manganese acetate, or a method using the manganese salt and hydroquinone and / or metoquinone (JP-A-51-98211), and further a method using a dithiocarbamic acid manganese salt or thiurams (JP-A-5-51403). Gazette) etc. are used.

However, among the above, when a polymerization inhibitor containing copper dithiocarbamate such as copper dimethyldithiocarbamate, copper diethyldithiocarbamate and copper dibutyldithiocarbamate is used, the effect of suppressing the polymerization of acrylic acid can be obtained. However, there is a problem that devices such as a distillation column are easily corroded. Therefore, the corrosion of the device progresses and continuous operation becomes impossible, and the material of the device is changed from SUS304 to SUS316L or SUS329.
Since it is necessary to improve corrosion resistance by changing to J4L or the like, there is a problem that the cost increases.

[0006]

DISCLOSURE OF THE INVENTION An object of the present invention is to suppress corrosion of a production apparatus when producing a vinyl compound such as acrylic acid, thereby enabling continuous operation of the apparatus. Is to provide.

[0007]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors in order to solve the above problems, a system in which a vinyl compound containing copper dithiocarbamate as a polymerization inhibitor is present, specifically, For example, they have found that the corrosion of the device is suppressed by adding copper acetate into the device for producing a vinyl compound containing copper dithiocarbamate, and have completed the present invention.

That is, the metal corrosion inhibiting method of the present invention is characterized in that copper acetate is added to a system in which a vinyl compound containing copper dithiocarbamate is present, and the ratio of the copper dithiocarbamate to copper acetate is equivalent to copper. It is preferably 2 mol% or more.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail below. The metal corrosion inhibiting method of the present invention is to add copper acetate to a system in which a vinyl compound containing copper dithiocarbamate is present.

Examples of the copper dithiocarbamate include copper dimethyldithiocarbamate, copper diethyldithiocarbamate, copper dipropyldithiocarbamate, copper dibutyldithiocarbamate and the like, copper dialkyldithiocarbamate, copper ethylenedithiocarbamate, copper tetramethylenedithiocarbamate, pentamethylene. Cyclic alkylenedithiocarbamate such as copper dithiocarbamate and copper hexamethylenedithiocarbamate, cyclic oxydialkylenedithiocarbamate copper such as copper oxydiethylenedithiocarbamate, copper diphenyldithiocarbamate and the like can be mentioned.

Examples of the vinyl compound include, in addition to acrylic acid, conjugated acids such as methacrylic acid or derivatives thereof such as esters, amides and nitriles (methyl acrylate, methyl methacrylate, acrylamide, acrylonitrile, etc.),
Conjugated aldehydes and ketones (acrolein, methacrolein, methyl vinyl ketone, etc.), vinyl halides (vinyl chloride, etc.), vinyl group-substituted aromatic compounds (styrene, etc.), vinyl carboxylates (vinyl acetate, etc.), vinyl ethers (methyl vinyl ether, etc.) ), 1,3-diolefin (butadiene, isoprene and the like), ethylene and alkyl-substituted ethylene (propylene and the like) and the like.

The system in which the vinyl compound containing copper dithiocarbamate is present corresponds to, for example, the inside of a distillation column used in the step of purifying acrylic acid. As described above, acrylic acid is a substance that is very easily polymerized, so the polymerization inhibitor such as copper dithiocarbamate is added to the distillation column. As the material of the liquid contact surface of this distillation column, for example, stainless steel such as SUS304 and SUS316 is used. The distillation temperature is usually 50 ° C to 100 ° C.
It is controlled to about ℃.

The amount of copper dithiocarbamate added depends on the amount of impurities contained in the aqueous solution of acrylic acid and is not particularly limited, but is usually about 10 ppm to 3000 ppm relative to acrylic acid. When the amount of copper dithiocarbamate is very small, the effect of preventing polymerization is not sufficient especially at the initial stage of distillation. Further, when the amount of copper dithiocarbamate is excessively large, the function of corroding the apparatus is strengthened, and accordingly, it is necessary to increase the amount of copper acetate to be added, which is unfavorable because it causes an increase in cost.

The copper acetate acts as a corrosion inhibitor in the distillation column where acrylic acid containing copper dithiocarbamate is present. The addition amount of this copper acetate is not particularly limited because it exhibits a corrosion inhibiting effect even if added in a very small amount, but the ratio of the copper dithiocarbamate to copper acetate is preferably about 2 mol% or more in terms of copper (that is, (acetic acid The number of moles of copper derived from copper / the number of moles of copper derived from copper dithiocarbamate) is about 2
Mol% or more), more preferably about 10 mol% or more. There is no particular upper limit to the amount of copper acetate added in terms of the corrosion inhibition effect.

The method of adding copper dithiocarbamate and copper acetate is not particularly limited, but, for example, a method of directly adding to acrylic acid or a method of adding after dissolving in a suitable organic solvent can be used. The temperature at the time of addition can also be appropriately determined. These can be added, for example, immediately after synthesizing acrylic acid, or can be added immediately before performing distillation. From an industrial point of view, it is preferable to dissolve the acrylic acid in the stock solution to be supplied to the distillation column or to the solution which is refluxed to the distillation bottom liquid side by distillation and supplied.

In the present invention, as the polymerization inhibitor, in addition to the above-mentioned copper dithiocarbamate, other known polymerization inhibitors can be used in combination, if necessary. Specific examples thereof include hydroquinone, metoquinone (p-methoxyphenol), cresol, phenol, t-butylcatechol, diphenylamine, phenothiazine, methylene blue, and copper salicylate.

In order to prevent the polymerization of vinyl compounds such as acrylic acid in a distillation column or the like, the acrylic acid vapor is condensed by heating the manhole or the top of the column or by heating the reflux liquid. Can also be used in combination.

[0018]

The present invention will be described in detail below with reference to test examples, but the present invention is not limited to the following examples.

Test Example 1 In order to confirm the anticorrosion effect of copper acetate, a stainless steel plate was immersed in an aqueous acrylic acid solution containing copper dibutyldithiocarbamate (hereinafter referred to as CBSC), and its corrosion degree was measured. The test conditions are shown below. The term "corrosion" refers to the amount of weight loss of a stainless steel plate after immersion, converted into a unit time and a unit area. In addition, the immersion test
The test solution was subjected to vacuum boiling at 85 ° C.

<Test conditions> Test liquid: 99% acrylic acid aqueous solution CBSC addition amount: Copper acetate addition amount so that the CBSC concentration is 100 ppm with respect to acrylic acid: Copper acetate concentration is 0 to acrylic acid Added so as to be 154 ppm (Table 1) Test liquid temperature: 85 ° C. (boiling under reduced pressure) Immersion time: 6 hours Stainless steel plate material: SUS304 Stainless steel plate Size: 25 mm × 20 mm, thickness 2 m
m Test conditions and test results of Test Example 1 are shown in Table 1 and FIG. Note that FIG. 1 is a graph in which the horizontal axis and the vertical axis show the copper acetate concentration and the corrosion degree shown in Table 1, respectively.

[0021]

[Table 1]

As shown in Table 1 and FIG. 1, it can be seen that the corrosion of the stainless steel sheet is suppressed by adding copper acetate to the test solution.

Test Example 2 The immersion test of a stainless steel plate was conducted in the same manner as in Test Example 1 except that the addition amount of CBSC was 2000 ppm with respect to acrylic acid and the addition amount of copper acetate was 0 to 770 ppm with respect to acrylic acid. went. Test example 2
The test results of are shown in Table 2 and FIG.

[0024]

[Table 2]

As shown in Table 2 and FIG. 1, when 2 ppm of copper acetate was added to the test solution, that is, the ratio represented by (the number of moles of copper derived from copper acetate / the number of moles of copper derived from CBSC) was 0. In the case of 0.26 mol%, the corrosion degree is slightly lower than that in the case where copper acetate is not added, but when the ratio is 2.6 mol% or more, some corrosion is not observed on the stainless steel plate. However, it can be seen that the corrosion degree is clearly reduced as compared with the case where copper acetate is not added. When the ratio was 10.8 mol% or more, almost no corrosion was observed on the stainless steel sheet.

[0026]

INDUSTRIAL APPLICABILITY According to the present invention, copper acetate is used in a system in which a vinyl compound containing copper dithiocarbamate, which is a polymerization inhibitor, is present, and specifically, for example, in an apparatus for producing a vinyl compound containing copper dithiocarbamate. The effect of adding corrosion is that the corrosion of the device can be suppressed.

[Brief description of drawings]

FIG. 1 is a graph showing the test results shown in Test Examples 1 and 2.

Claims (2)

[Claims] 1. A method for inhibiting metal corrosion, which comprises adding copper acetate to a system in which a vinyl compound containing copper dithiocarbamate is present. 2. The method for inhibiting metal corrosion according to claim 1, wherein the ratio of the copper dithiocarbamate to the copper acetate is 2 mol% or more in terms of copper.