JP2574109B2 - Method for preventing polymerization of (meth) acrylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to (meth) acrylic acid (in this specification, when describing matters common to acrylic acid and methacrylic acid, these acids are collectively referred to as "(meth) acrylic acid"). ).

[0002]

2. Description of the Related Art Vinyl compounds have the property of being easily polymerized by light, heat, or the like. Among vinyl compounds, (meth) acrylic acid is particularly easily polymerized. Therefore, conventionally, in order to prevent polymerization of (meth) acrylic acid, various polymerization inhibitors have been used alone or in combination of two or more depending on the conditions in which (meth) acrylic acid is placed.

Conventionally, as a method for producing (meth) acrylic acid, for example, a method for producing acrylic acid by a catalytic gas-phase oxidation reaction of propylene and / or acrolein, a catalytic gas-phase oxidation reaction of isobutylene and / or methacrolein And a method of producing methacrylic acid by the method described above. In these methods, the reaction product gas obtained in the catalytic gas phase oxidation reaction is cooled and collected with water,
After obtaining an aqueous solution of (meth) acrylic acid containing by-products such as acetic acid and aldehyde, the (meth) acrylic acid is separated and purified from the aqueous solution by combining steps such as distillation and solvent extraction. In addition, the method for producing (meth) acrylic acid by the above-mentioned catalytic gas phase oxidation reaction includes a step of separating, concentrating, purifying, etc., (meth) acrylic acid by distillation. In addition, as a method for producing (meth) acrylic acid other than the above, a method of producing acrylic acid by a Reppe method, a method of producing methacrylic acid by an acetone cyanohydrin method, and the like are also known. These production methods also include a step of separating, concentrating, purifying, etc., (meth) acrylic acid by distillation.

[0004] As described above, (meth) acrylic acid is
It is very easy to polymerize by light or heat. Therefore, the polymerizability of (meth) acrylic acid becomes extremely large particularly in a treatment in a high temperature state such as the above-mentioned distillation step. Therefore, when such a polymerizable (meth) acrylic acid is industrially produced, preventing troubles due to polymerization of these acids in the distillation step is a very important item in the process operation. In particular, establishing an effective polymerization prevention technology in a distillation step in which these acids are treated at a high temperature requires that the process be continuously performed for a long period of time.
And it is an indispensable matter for stable operation.
According to the findings of the present inventors, among the above-described distillation steps,
In the dehydration step (water separation step), polymerization is most likely to occur,
This is a major factor preventing continuous operation of the manufacturing apparatus including the distillation column.

[0005] When (meth) acrylic acid is subjected to operations such as separation, concentration and purification using a distillation column, these acids are likely to polymerize to form a polymer at the back of the tray, at the bubble bell. In most places where liquid is difficult to get wet, such as the inside of a downcomer, the backside of a downcomer, the inside of a tower, etc., or where there is a tendency for liquid to stagnate, such as tray mounting hardware (bolts, nuts, etc.) or packing parts. It is. The polymer is hardly soluble in (meth) acrylic acid, water, ordinary organic solvents, and the like,
Further, once formed in the column, it becomes a nucleus of polymerization and gradually accumulates, and finally, the inside of the column is blocked thereby, making it impossible to continue the operation of the production apparatus. Moreover, these accumulated polymers are very difficult to remove.

Conventionally, as a measure for preventing polymerization of (meth) acrylic acid in a distillation step in producing (meth) acrylic acid, a method of performing distillation in the presence of a polymerization inhibitor has been adopted. Examples of such polymerization inhibitors include at least one compound selected from the group consisting of hydroquinone, methoquinone (also referred to as p-methoxyphenol), cresol, phenol, t-butylcatechol, diphenylamine, phenothiazine, and methylene blue. And a polymerization inhibitor (A) comprising molecular oxygen and at least one copper dithiocarbamate selected from the group consisting of copper dimethyldithiocarbamate, copper diethyldithiocarbamate, and copper dibutyldithiocarbamate. (For acrylic acid, refer to JP-A-49-85016, and for methacrylic acid, refer to JP-B-57-61015). Also, (meta)
Examples of the polymerization inhibitor other than the above for acrylic acid include a polymerization inhibitor (B-1) composed of a manganese salt such as manganese acetate, and a polymerization inhibitor (B-) composed of a manganese salt such as manganese acetate and hydroquinone and / or methoquinone. 2) a polymerization inhibitor comprising a manganese salt such as manganese acetate and molecular oxygen (B-3); a polymerization inhibitor comprising a manganese salt such as manganese acetate and hydroquinone and / or methoquinone and molecular oxygen (B- 4) is known (for all, see JP-A-51-98211).

[0007]

However, in the subsequent study, it was found that the above-mentioned known polymerization inhibitors (A) and (B-
It has been found that 1) to (B-4) have the following problems. That is, the above-mentioned JP-A-49-8501 was used.
No. 6 and JP-B-57-61015, the polymerization inhibitor (A) is prepared by the catalytic gas-phase oxidation reaction.
As in the azeotropic separation tower (water separation tower) of the aqueous solution of (meth) acrylic acid in the distillation step when producing acrylic acid,
In the case where polymerization of (meth) acrylic acid is extremely likely to occur due to the presence of water, acetic acid, and aldehydes in the feed composition, the polymerization inhibitory effect is low, so that popcorn polymer and viscous polymer are generated during distillation. ,
There has been a problem that long-term continuous operation of the manufacturing apparatus including the distillation column cannot be performed.

On the other hand, the polymerization inhibitors (B-1) to (B-4) described in JP-A-51-98211 have a sufficient polymerization inhibitory effect on (meth) acrylic acid products. However, as in the case of the polymerization inhibitor (A), as in the azeotropic separation column of the aqueous solution of (meth) acrylic acid in the distillation step of producing (meth) acrylic acid by catalytic gas phase oxidation reaction, In the case where polymerization of (meth) acrylic acid is extremely likely to occur, the effect of preventing polymerization is not sufficient, so that popcorn polymer or viscous polymer is generated during distillation, and the long-term continuous operation of the manufacturing apparatus cannot be performed. there were.

In view of such circumstances, the present invention enables a long-term continuous operation of a production apparatus for (meth) acrylic acid, which is particularly easy to polymerize among vinyl compounds, and provides a (meth) acrylic acid product An object of the present invention is to provide a method excellent in preventing polymerization during transportation and storage.

[0010]

Means for Solving the Problems In order to solve the above problems, the inventors have made various studies. As a result, as a polymerization inhibitor, manganese salt, copper dialkyldithiocarbamate, a phenolic compound, and phenothiazine, which will be described in detail later, are used in combination. Compared to polymerization prevention method,
The present invention was completed after confirming by experiments that the polymerization inhibitory effect of the above four polymerization inhibitors was improved by a synergistic effect far exceeding the expectation, thereby enabling long-term continuous operation of the manufacturing apparatus.

Therefore, the method for preventing polymerization of (meth) acrylic acid according to the present invention comprises the steps of: preparing a manganese salt comprising at least one of manganese acetate and manganese octanoate; a dimethyldithiocarbamate copper salt; a diethyldithiocarbamate copper salt; Polymerization of phenothiazine with copper dialkyldithiocarbamate composed of at least one of copper dipropyldithiocarbamate and copper dibutyldithiocarbamate, phenolic compound composed of at least one of methoquinone and hydroquinone, and phenothiazine In this method, an inhibitor is used in combination.

In the present invention, as described above, a manganese salt, a copper dialkyldithiocarbamate, a phenolic compound and a phenothiazine are used in combination. Details of the polymerization inhibitors other than phenothiazine among these four polymerization inhibitors are as follows.

As the manganese salt, at least one of manganese acetate and manganese octoate is used, which may be a hydrated salt or an anhydrous salt.
As the dialkyldithiocarbamic acid copper salt, at least one of dimethyldithiocarbamic acid copper salt, diethyldithiocarbamic acid copper salt, dipropyldithiocarbamic acid copper salt and dibutyldithiocarbamic acid copper salt is used.

As the phenolic compound, at least one of methoquinone and hydroquinone is used. In the present invention, a sufficiently excellent polymerization inhibitory effect can be obtained even when only the above four members are used as the polymerization inhibitor.However, if necessary, molecular oxygen may be further used as the polymerization inhibitor. Due to the synergistic effect, a more excellent polymerization preventing effect can be obtained.

The present invention is suitably used for (meth) acrylic acid which is particularly easily polymerized among vinyl compounds. The conditions under which the (meth) acrylic acid to which the present invention is applied are not particularly limited.
The present invention can be applied to a reactor, a distillation tower, a condensation tower, a storage tank of purified (meth) acrylic acid, or the like at the time of producing (meth) acrylic acid. More specifically, for example, the case where (meth) acrylic acid is produced by a catalytic gas phase oxidation reaction will be described.
In various distillation processes such as an azeotropic separation column for acrylic acid, a column for separating (meth) acrylic acid and light components such as acetic acid, and in various processes including a distillation operation such as a stripper for light components such as acrolein and methacrolein, polymerization is carried out. It is effectively applied by allowing the inhibitor to coexist with (meth) acrylic acid.

In the present invention, each polymerization inhibitor is usually used by adding it to (meth) acrylic acid or a solution thereof.
The method of adding each polymerization preventing component is not particularly limited. For example, it may be added directly in the form of solid or powder,
It may be added in a form dissolved in an appropriate organic solvent. In addition,
The molecular oxygen used as necessary may be directly mixed into (meth) acrylic acid or a solution thereof by an air bubbling method or the like, or may be dissolved in a solution of another polymerization preventing component in (meth) acrylic acid. It may be indirectly incorporated into the acid or its solution. In addition, each polymerization preventing component is (meth)
It may be added separately to acrylic acid or its solution,
It may be added in the form of a mixture of a plurality of polymerization inhibiting components.

Specifically, for example, in the distillation step in the production of (meth) acrylic acid, the polymerization preventing component other than molecular oxygen is used in the production step of (meth) acrylic acid and these acids. Since it is relatively easy to dissolve in the organic solvent to be obtained, it can be dissolved in the supply liquid or reflux liquid and introduced into the process. The molecular oxygen is supplied in gaseous form from a distillation tower, a separation tower, the bottom of a stripper and / or a reboiler.

The amount of the polymerization inhibitor used in the present invention generally varies depending on the operating conditions and the like, and is not particularly limited. Specifically, the amount of the manganese salt and the dialkyldithiocarbamic acid copper salt described above may be used. , The total amount of the four polymerization inhibitors of phenolic compound and phenothiazine is
100 to 10 with respect to the evaporation vapor amount of (meth) acrylic acid
It is preferably 00 ppm (by weight).

Further, the amount of each of these four polymerization inhibitors used is 15 to 300 ppm as a manganese salt.
, As a dialkyldithiocarbamic acid copper salt, 10 to 2
00ppm, 30-600ppm as phenolic compound
And phenothiazine is preferably in the range of 30 to 600 ppm (in each case, "ppm" is a weight ratio to the amount of vaporized vapor of (meth) acrylic acid).

Further, when the present invention is carried out, as described above, the effect tends to be significantly increased when carried out in the presence of molecular oxygen. Therefore, it is desirable to introduce about 0.1 to 1.0% by volume of molecular oxygen with respect to the evaporation vapor amount of (meth) acrylic acid.

[0021]

The manganese salt described above as a polymerization inhibitor,
When the dialkyldithiocarbamic acid copper salt, the phenolic compound, and the phenothiazine are used in combination, the combination of the four polymerization inhibitors is used as compared with the case where at least one of the four polymerization inhibitors is lacking. In order to significantly improve the polymerization prevention effect due to the synergistic effect of (meth) acrylic acid and sufficiently prevent the polymerization of (meth) acrylic acid even under conditions where (meth) acrylic acid is extremely easy to polymerize, a (meth) acrylic acid distillation column is included ( It enables long-term continuous operation of the (meth) acrylic acid production equipment, and exhibits an excellent polymerization prevention effect during transportation and storage of (meth) acrylic acid products.

[0022]

EXAMPLES Specific examples of the present invention will be described below together with comparative examples, but the present invention is not limited to the following examples. The unit ppm in the following Examples and Comparative Examples is based on weight. -Examples 1-2 and Comparative Examples 1-4 The product acrylic acid from which a polymerization inhibitor was previously removed by distillation was used as a test blank solution. This blank liquid 2
ml was placed in a test tube, and the type and amount of the polymerization inhibitor shown in Table 1 were added thereto to prepare a prepared solution. Next, after reducing the pressure in the test tube, the test tube was immersed in an oil bath kept at 100 ° C., and the time from the start of immersion to the polymerization of acrylic acid (polymerization time) was visually measured. The results are shown in Table 1.

[0023]

[Table 1]

In the above Table 1, the amount of the polymerization inhibitor added (ppm) is based on the amount of acrylic acid before polymerization, and CB,
HQ, MnAc and PTZ represent copper dibutyldithiocarbamate, hydroquinone, manganese acetate and phenothiazine, respectively. As shown in Table 1, even if any one of CB, HQ, MnAc, and PTZ is missing as a polymerization inhibitor, the polymerization time is shorter than when all four are used, The effect of preventing polymerization is reduced. From this, it was confirmed that it is preferable to use the above four polymerization inhibitors. In particular, Example 2
In this case, the polymerization time is longer than in Comparative Examples 1 to 4 in spite of the fact that the total amount of the polymerization inhibitor is small, and the polymerization prevention effect is high.

Example 3 and Comparative Examples 5 to 8 Using a packed tower equipped with a distilling pipe at the top and a raw material supply pipe at the center, in the presence of molecular oxygen and other polymerization inhibitors A distillation experiment of azeotropic separation of acrylic acid aqueous solution was performed. After operating at an operating pressure of 160 mmHg, the polymer generated in the tower during an operation time of 8 hours was dried under reduced pressure to a constant weight, and the effect of the polymerization inhibitor was observed by measuring the amount.

The polymerization inhibitors other than molecular oxygen were added to the column from the reflux solution in the form of the kind and amount shown in Table 2 and dissolved therein. The amount of molecular oxygen shown in Table 2 was supplied to the bottom of the column. The amounts of the polymerization inhibitor other than molecular oxygen and the molecular oxygen are based on the amount of vaporized acrylic acid vapor. As a feedstock, an aqueous solution of acrylic acid containing 30% by weight of water and 2.5% by weight of acetic acid obtained by a catalytic gas phase oxidation reaction of propylene is used. As a reflux liquid, methyl isobutyl ketone is used. And the bottom temperature was 97 ° C.

The composition of the liquid withdrawn from the bottom in the steady state is as follows:
1. Acrylic acid 97% by weight, acetic acid 0.5% by weight, others
It was 5% by weight. The reflux liquid was obtained by recycling the distillate composition. The results are shown in Table 2.

[0028]

[Table 2]

In Table 2, CM, HQ, MnOc and PTZ represent copper dimethyldithiocarbamate, hydroquinone, manganese octoate and phenothiazine, respectively. As shown in Table 2, even if any one of the polymerization inhibitors CM, HQ, MnOc, and PTZ other than the molecular oxygen is missing, the amount of generated polymer is smaller than the case where all of them are used. And the effect of preventing polymerization is reduced. From this, CM, HQ, MnOc and P
It has been confirmed that it is preferable to use TZ for all four members.

Examples 4 to 5 and Comparative Examples 9 to 12 A methacrylic acid product from which a polymerization inhibitor was previously removed by distillation was used as a test blank. 2 ml of this blank solution was placed in a test tube, and the kind and amount of the polymerization inhibitor shown in Table 3 were added thereto to prepare a prepared solution. Next, after reducing the pressure in the test tube, the test tube was immersed in an oil bath kept at 130 ° C., and the time from the start of immersion to the polymerization of methacrylic acid (polymerization time) was visually measured.
Table 3 shows the results.

[0031]

[Table 3]

In Table 3, the amount (ppm) of the polymerization inhibitor is based on the amount of methacrylic acid before polymerization.
E, MQ, MnAc, and PTZ represent copper diethyldithiocarbamate, methoquinone, manganese acetate, and phenothiazine, respectively. As shown in Table 3, even if any one of CE, MQ, MnAc, and PTZ is missing as a polymerization inhibitor, the polymerization time is shorter than when all four are used, The effect of preventing polymerization is reduced. From this, it was confirmed that it is preferable to use the above four polymerization inhibitors. In particular, Example 5
In this case, the polymerization time is longer than in Comparative Examples 9 to 12 in spite of the fact that the total amount of the polymerization inhibitor is small, and the polymerization prevention effect is high.

Example 6 A 50-stage stainless steel sieve tray was installed at a step interval of 147 mm, and a distillation column with an inner diameter of 105 mm equipped with a distilling tube at the top and a raw material supply tube at the center was used. Continuous operation of azeotropic separation of the aqueous solution was performed. The polymerization inhibitors used were manganese acetate, copper dibutyldithiocarbamate,
Hydroquinone, phenothiazine and molecular oxygen. Manganese acetate, copper dibutyldithiocarbamate, hydroquinone and phenothiazine were all introduced into the tower from the top. A predetermined amount of molecular oxygen was supplied to the bottom of the column. The amount of each polymerization inhibitor used was 45 ppm of manganese acetate, 30 ppm of copper dibutyldithiocarbamate and 100 parts of hydroquinone, based on the amount of vaporized acrylic acid vapor.
ppm and phenothiazine were 100 ppm. Further, the input oxygen amount was set to 0.3% by volume with respect to the acrylic acid evaporation vapor amount.

The effect of preventing polymerization was confirmed by pressure loss in the column, flooding or dismantling inspection of the column. As a feedstock, acrylic acid containing 30% by weight of water and 2.5% by weight of acetic acid obtained by a catalytic gas-phase oxidation reaction of propylene is used, and methyl isobutyl ketone is used as a refluxing liquid. Bottom temperature 97 ° C, Top pressure 112
mmHg, supply liquid amount 10.56 l / hr, reflux ratio (R /
Distillation was performed under the condition of D) = 0.92 (on a molar basis).

The composition of the liquid withdrawn from the bottom in the steady state is as follows:
The content was 97.0% by weight of acrylic acid, 0.5% by weight of acetic acid, and 2.5% by weight. As the reflux liquid, the distillate oil phase was recycled and used. After continuous operation for about 14 days under these conditions, a stable state was always obtained, and after the operation was stopped, the inside of the distillation column was inspected. As a result, no generation of polymer was observed at all.

[0036]

According to the present invention, since the above-mentioned four specific polymerization inhibitors are used in combination, it is particularly easy to polymerize (meth) among the vinyl compounds as compared with the case where at least one of them is missing. The effect of preventing polymerization of acrylic acid is greatly improved, and the polymerization of (meth) acrylic acid is sufficiently prevented even under conditions in which (meth) acrylic acid is extremely easily polymerized. Long-term continuous operation of the production equipment for containing (meth) acrylic acid becomes possible. The present invention can be applied not only to the production of (meth) acrylic acid but also to the transportation and storage of the product.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoji Akazawa One of 992, Nishioki, Okihama, Himeji-shi, Hyogo Prefecture Nippon Shokubai Himeji Works Co., Ltd. (72) Inventor: Masao Baba 1 Himeji Works, Nippon Shokubai Co., Ltd. (56) References JP-A-2-209842 (JP, A) JP-A-64-42443 (JP, A) JP-A-51-98211 (JP, A) JP-A 50 -101313 (JP, A) JP-A-49-85016 (JP, A)

Claims (1)

(57) [Claims] 1. A manganese salt comprising at least one of manganese acetate and manganese octanoate, and a copper salt of dimethyldithiocarbamate, a copper salt of diethyldithiocarbamate, a copper salt of dipropyldithiocarbamate and a copper salt of dibutyldithiocarbamate. A method for preventing polymerization of (meth) acrylic acid, which comprises using at least one of a dialkyldithiocarbamic acid copper salt, a phenolic compound comprising at least one of methoquinone and hydroquinone, and phenothiazine, a polymerization inhibitor of four types.