JP2000034267A - Prevention of polymerizing nitriles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress polymer formation, reduce the pressure difference rise, enable long-term continuous operation for a purification process and cut cleaning operation involved in the process by preventing nitriles from being polymerized by adding piperidine-oxyl compounds to a (meth)acrylonitrile purification process liquor. SOLUTION: Nitriles are prevented from being polymerized by adding a piperidine-oxyl compound to a (meth)acrylonitrile purification process liquor containing 5-100 ppm of aldehyde(s) and/or 0.0005-10 wt.% of hydrogen cyanide; where it is preferable that the piperidine-oxyl compound is a compound of the formula (R1 is a 1-3C alkyl; R2 is H, O, OH or the like) (pref. 2,2,6,6- tetramethylpiperidine-1-oxyl), its amount being >=5 ppm based on the liquor flow in the purification process, and its concentration being 1-50 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to the prevention of polymerization of nitriles in the purification process of acrylonitrile or methacrylonitrile.

[0002]

2. Description of the Related Art The conventional techniques in the production and purification of acrylonitrile or methacrylonitrile by ammoxidation of propane, propylene or isobutylene are as follows. The above reaction product is usually introduced into the absorption tower after cooling and washing, and acrylonitrile or methacrylonitrile, acetonitrile, hydrogen cyanide and other reaction products are absorbed by a large amount of water. This absorbed water is supplied to a water extraction distillation column, and acrylonitrile or methacrylonitrile and hydrogen cyanide are distilled off from the top of the column. This distillate is supplied to the next purification step,
Using two or more distillation columns, impurities such as hydrocyanic acid, water, and aldehyde are removed to obtain acrylonitrile or methacrylonitrile as products.

[0003] In the purification step of acrylonitrile or methacrylonitrile, the addition of a polymerization inhibitor is indispensable. If the addition is not performed, a polymer obtained by polymerization of acrylonitrile or methacrylonitrile in the distillation column and in the reboiler in the purification step Is generated in a large amount, so that the continuous operation period of the process is limited to a maximum of one month.

As a conventional measure for preventing polymerization in the acrylonitrile or methacrylonitrile purification step, there is a method of adding hydroquinone or pyrogallol. Although these are already known, they cannot be said to have a sufficient polymerization inhibitory effect, and the continuous operation period in the distillation column in the purification step can be extended to one year, but the continuous operation of the reboiler in the purification step is not possible. The operating period can be extended to 3 to 6 months.

Another method for preventing polymerization is described in JP-A-6-345681 or JP-A-8-486 as a method for preventing polymerization of (meth) acrylic acid and its ester, which are the same vinyl compounds as acrylonitrile or methacrylonitrile.
50, with the N-oxyl compound proposed as an essential condition, this compound and a manganese salt compound and / or
Alternatively, there is a polymerization prevention method using a copper salt compound and / or a 2,2,6,6-tetramethylpiperidine compound and / or a nitroso compound in combination, but there is no description about a reaction system of acrylonitrile or methacrylonitrile in this publication. And piperidine-1-piperidine-1-hydrogen cyanide and / or aldehyde, which is determined from the range of operating conditions of the acrylonitrile purification step, and
There is no description of a method for preventing polymerization using oxyls.

[0006]

SUMMARY OF THE INVENTION The present invention provides a method for further exerting the effect of preventing polymerization when the above-mentioned piperidine-1-oxyls are added as a polymerization inhibitor in the step of purifying acrylonitrile or methacrylonitrile. In addition, it suppresses the production of acrylonitrile, methacrylonitrile, and polymers caused by hydrogen cyanide or aldehyde generated inside the distillation column and in the reboiler used in the purification step.

[0007] By suppressing the formation of the polymer, the pressure difference between the top and the bottom of the process distillation column is reduced, so that long-term continuous operation is possible, and the cleaning work of the process distillation column is reduced. Can be. Further, in the reboiler of this step, the operation of the acrylonitrile or methacrylonitrile purification step is facilitated by slowing down the rate of decrease in the overall heat transfer coefficient to achieve a reduction in cleaning work and a longer life.

[0008]

Means for Solving the Problems In view of these circumstances, the present inventors have conducted intensive studies on an effective method for suppressing polymerization and reducing the amount of generated polymer in the purification step of acrylonitrile or methacrylonitrile. It has been found that the presence of piperidine-1-oxyls in a liquid of acrylonitrile or methacrylonitrile containing aldehydes and / or aldehydes further improves the effect of preventing polymerization of piperidine-1-oxyls.

That is, according to the present invention, in the step of purifying acrylonitrile or methacrylonitrile, the aldehyde contains 5 to 100 ppm by weight, preferably 5 to 50 ppm by weight.
A nitrile characterized in that a piperidine-1-oxyl is present in an acrylonitrile or methacrylonitrile purification step solution in which hydrogen cyanide is present at 0.0005 to 10% by weight, preferably 0.005 to 5% by weight. Are methods of preventing polymerization. If the concentrations of the aldehyde and hydrogen cyanide are out of the above ranges, the polymerization preventing effect required in the present invention cannot be sufficiently achieved.

The piperidine-1-oxyls used in the present invention are represented by the general formula (I) wherein R1 is an alkyl group having 1 to 3 carbon atoms, R2 is an H, O, OH, OR3 group (R3 is An alkyl group of the formulas 1-3 or a phenyl group) or CO
OR4 group (R4 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms)], for example, when piperidine-1-oxyl is 2,2,6,6-tetramethylpiperidine-1- Oxyl, 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl,
2,2,6,6-oxopiperidine-1-oxyl, 2,2,6,6-tetramethyl-4-methoxypiperidine-1-oxyl, 2,2,6,6-tetramethyl-4- Ethoxypiperidine-1-oxyl, 2,2,
6,6-4-phenoxypiperidine-1-oxyl,
2,2,6,6-4-carboxypiperidine-1-oxyl and the like.

The amount of the piperidine-1-oxyl is 1 weight pp with respect to the liquid flow rate in the purification process.
m or more, more preferably 5 ppm by weight or more. In the present invention, the number of distillation columns used in the distillation operation in the acrylonitrile or methacrylonitrile purification step is generally two or more. The gas-liquid contacting device used in this distillation column may be a commonly used plate or packed type, and the reboiler type at the bottom of the distillation column may be either a vertical type or a horizontal type.

The piperidine-1-oxyl in the present invention is used as a solid or a solution, and the solvent for the piperidine-1-oxyl in the solution may be water or acrylonitrile or methacrylonitrile. -The concentration of oxyls is preferably 1 to 50% by weight. Further, as a method of controlling the amount of addition, for example, a method of injecting a fixed amount by a quantitative injection device or the like is used.

In the present invention, the piperidine-1-oxyl is preferably added at the feed of the distillation column, the top of the distillation column, the bottom of the distillation column, and / or the intermediate portion thereof. 5 to 100 weight p as aldehyde
It is sufficient that piperidine-1-oxyls can be present in the acrylonitrile or methacrylonitrile purification step solution present at pm and / or 0.0005 to 10% by weight of hydrogen cyanide.

Further, substances other than acrylonitrile, methacrylonitrile, hydrogen cyanide, and aldehyde may be present at the location where the piperidine-1-oxyls are added.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to examples. First, the length of the polymerization start time is described as an index of the polymerization inhibitory effect of acrylonitrile. As the polymerization initiation time described here is longer, the generation of polymer in the acrylonitrile purification step is suppressed, and it can be determined that the effect is greater. In addition, 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl of piperidine-1-oxyls was used as a polymerization inhibitor.

In Examples 1 to 3, an oxygen stability test was carried out using a gum tester, and the time until the start of polymerization of acrylonitrile was measured as the polymerization start time. The method for measuring the polymerization start time is as follows. (1) The outline of the method is an acrylonitrile polymerization test under accelerated polymerization conditions.
Here, the time required for heating to cause a sudden pressure change indicating polymerization was measured. (2) As a measuring device, an oxygen stability measuring device according to ASTM-D-525-55 was used. (3) Prepare a glass sample container which has been washed and dried in advance and an oxygen cylinder into which the sample container is to be inserted. (4) A glass sample container is placed in this cylinder, and 25 ml of the sample is injected into the glass container with a pipette. (5) Close the cylinder and supply oxygen with 7.0 to 7.2 kg / cm.
Press up to 2G. Then, the relief valve is opened slightly by the operation of expelling the internal air. (6) After oxygen is added again to the pressure of (5), the leakage of the cylinder is checked. At this time, the initial pressure drop caused by the sample dissolving oxygen can be ignored if it does not exceed 0.42 kg / cm2G. Thereafter, if the pressure drop after 10 minutes does not exceed 0.14 kg / cm2G, it is recognized that there is no leakage, and the test is continued as it is. (7) While taking care not to spill the sample and the cylinder containing oxygen, put the sample in a boiling water bath, and use this time as the test start time. (8) At this time, the temperature in the hot water bath should be from 98 degrees Celsius to 100 degrees Celsius.
Continue the test, keeping it in good condition. (9) The time from the start of the test to the time at which a rapid pressure change indicating polymerization is observed is shown on the chart of the measuring device as the oxygen stability time. This is read and recorded as the polymerization start time.

The analysis of hydrogen cyanide, aldehyde present in acrylonitrile and 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl present in the acrylonitrile purification step was carried out as follows. (1) Hydrogen cyanide: Measured with a 0.05 N silver nitrate solution using LIEBIG-DENIGES titration method. (2) Aldehyde; measured by gas chromatography with a hydrogen flame detector. The filler here is SEPABEAD G
HP-1 or its equivalent was used. (3) 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl; measured by gas chromatography with a hydrogen flame detector. The column used here was a non-polar capillary column.

In Examples 4 and 5, piperidine-1 was used as a polymerization inhibitor in the actual acrylonitrile purification step.
The amount of polymer generated when 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl of oxyls was added and the pressure difference between the top and bottom of the acrylonitrile purification step distillation column and the pressure of the distillation column 1 The behavior of the overall heat transfer coefficient of each of the reboiler and the reboiler of the distillation column 2 will be described.

[0019]

Example 1 In the acrylonitrile purification step, the product acrylonitrile was subjected to simple distillation, and acrylonitrile excluding other components was used to obtain a solution containing 99.9% by weight or more of acrylonitrile, 20 ppm of aldehyde, and 40 ppm of hydrogen cyanide.
The liter was adjusted. To the prepared solution, 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl was added as a powder corresponding to 10 ppm, and an oxygen stability test was carried out on a part of 1 liter using a gum test device. The time required until the start of polymerization was measured, and the required time was 420 minutes.

[0020]

Example 2 Acrylonitrile The product obtained in the acrylonitrile purification step was subjected to simple distillation, and 1 L of a solution containing 99.9% by weight of acrylonitrile and 40 ppm of hydrogen cyanide was prepared using acrylonitrile excluding other components. The same test as in Example 1 was carried out by adding 10 ppm of 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl as a powder to the prepared solution, and the time required until the start of polymerization was as follows. 385 minutes.

[0021]

Example 3 Acrylonitrile A product obtained in the acrylonitrile purification step was subjected to simple distillation, and 1 liter of a solution containing 99.9% by weight of acrylonitrile and 20 ppm of aldehyde was prepared using acrylonitrile excluding other components. The same test as in Example 1 was carried out by adding 10 ppm of 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl as a powder to the prepared solution, and the time required until the start of polymerization was as follows. 395 minutes.

[0022]

Example 4 Purification was performed by supplying acrylonitrile having an aldehyde concentration of 20 ppm and a hydrogen cyanide concentration of 5% by weight to a distillation column 1 through a conduit 5 shown in FIG. 2,2,6,6-Tetramethyl-4-hydroxypiperidine-1-oxyl was added as a polymerization inhibitor to adjust the concentration at the bottom of the distillation column 1 to 10 ppm. The addition method in this case is a pump capable of supplying a constant amount of a 5% by weight aqueous solution of 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl to the conduit 5 of the distillation column 1 per unit time. Was added.

After 24 hours from the start of the addition of 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, the bottom liquid of the distillation column 1 is sampled,
The amount of polymer present in the liquid was measured. The method for measuring the amount of the polymer here is as follows. (1) Stir the sample after heating for 1 hour with a glass rod,
Disperse the precipitate in the liquid so that no precipitate is deposited on the bottom of the sample container, and weigh 200 ml with a measuring cylinder. (2) The filter paper is used to filter the above sample using five kinds A for quantitative analysis described in JIS standard P3801-1976. (3) The residue on the filter paper is washed three times with 30 ml of pure water. (4) After drying the aluminum evaporating dish at 105 degrees Celsius for 60 minutes, it is cooled in a desiccator for 40 minutes, and the residue on the filter paper is weighed to 0.1 mg and washed with pure water while washing the residue. . (5) The above evaporating dish is evaporated to dryness in a water bath at 100 degrees Celsius, and the residue on the evaporating dish is dried with a dryer at 105 degrees Celsius for 60 minutes. (6) The evaporating dish is cooled in a desiccator for 40 minutes and then weighed. (7) The difference in weighing due to the presence or absence of the residue is calculated, and this is defined as the amount of polymer.

When 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl is added in an amount of 10 ppm, the amount of polymer present is 0.1 mg or less per liter of the bottom liquid of the distillation column 1. It was confirmed that it was. Similarly, the polymer content of the distillation column 2 was measured by the same operation as described above. As a result, the weight of the polymer in 1 liter of the bottom liquid of the distillation column 2 was 5 mg.

[0025]

Example 5 Purification was performed by supplying acrylonitrile having an aldehyde concentration of 20 ppm and a hydrogen cyanide concentration of 5% by weight to a distillation column 1 through a conduit 5 shown in FIG. 2,2,6,6-Tetramethyl-4-hydroxypiperidine-1-oxyl was added as a polymerization inhibitor to adjust the concentration at the bottom of the distillation column 1 to 10 ppm. The method of addition in this case is
Using a 5% by weight aqueous solution of 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, an amount corresponding to 3 ppm of the concentration at the bottom of the distillation column 1 was added to the conduit 5 of the distillation column 1; An amount corresponding to a concentration of 7 ppm at the bottom of the column was added from the top of the distillation column 1. These addition methods were performed using a pump capable of supplying a constant amount per unit time, as in Example 4.

After the addition of 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl by the above method, the top of the distillation column 1 in the acrylonitrile purification step,
The pressure difference at the bottom of the column and the overall heat transfer coefficient of each of the reboiler of the distillation column 1 and the reboiler of the distillation column 2 were measured. The pressure difference was measured by the method described below. (1) A stainless steel conduit is attached to the gas layer pressure measurement nozzle at the top of the distillation column 1 and connected to one of the diaphragm type differential pressure gauges installed in the middle portion of the distillation column 1. (2) A stainless steel conduit is attached to the gas pressure measuring nozzle at the bottom of the distillation column 1, and is connected to the other end of the diaphragm type differential pressure gauge installed at the middle part of the distillation column 1. (3) Read the indicated value of the diaphragm type differential pressure measuring instrument.
It should be noted that the diaphragm type differential pressure measuring instrument and the conduit used here have a structure that can withstand rupture or the like at the time of measurement and have been subjected to standard calibration. May be used.

At the top and bottom of the distillation column 1, the pressure difference caused by the adhesion of the polymer to the internal tray due to the polymerization of acrylonitrile caused by 0.02 kg / cm 2 per year.
Thus, a long-term continuous operation of two years was possible for the distillation column. In addition, the overall heat transfer coefficient of the reboiler of the distillation column 1 is such that the overall heat transfer coefficient decreasing rate is 0.10 K / day.
cal / m 2 · Hr · ° C., and the reboiler could be operated continuously for one year.

Like the reboiler of the distillation column 1, the distillation column 2
Also, the overall heat transfer coefficient of the reboiler was 0.20 Kcal / m 2 · Hr · ° C. per day, so that the reboiler could be operated continuously for one year. The overall heat transfer coefficient is a heat transfer coefficient in consideration of all heat transfer resistances when heat is transferred from a high-temperature fluid to a low-temperature fluid. The indicated value of the thermometer installed in each of the pipe and the outlet pipe is read, and the average temperature difference is calculated from the indicated value.
This average temperature difference is calculated by the following equation.

[0029]

(Equation 1)

The names of the symbols used here are as follows. Δt; average temperature difference T1; pipe-side inlet pipe internal temperature T2; pipe-side outlet pipe internal temperature T3; barrel-side inlet pipe internal temperature T4; barrel-side outlet pipe internal temperature ln; natural logarithmic sign The value calculated by dividing the heat transfer area of the reboiler by the above average temperature difference is the overall heat transfer coefficient, and is represented by the following equation.

[0031]

(Equation 2)

The names of the symbols used here are as follows. U: Overall heat transfer coefficient Q: Heat supply amount of reboiler A: Heat transfer area of reboiler Δt; Average temperature difference As in Example 5, piperidine-1-piperidine-1- as a polymerization inhibitor in an acrylonitrile purification step in which aldehyde and / or hydrogen cyanide coexists. It was proved that the presence of oxyls can reduce the cleaning work inside the distillation column and the cleaning work of the reboiler in this step.

[0033]

[Comparative Example 1] Acrylonitrile product in the acrylonitrile purification step was subjected to simple distillation, and aldehyde and hydrogen cyanide excluding other components were both 0 ppm acrylonitrile, and 2,2,6,6-tetramethyl-4- The same test as in Example 1 was carried out with the addition of 10 ppm of hydroxypiperidine-1-oxyl. The required time until the start of polymerization was 108 minutes.

[0034]

Comparative Example 2 Acrylonitrile The product obtained in the acrylonitrile purification step was subjected to simple distillation, and acrylonitrile obtained by excluding other components was 99.9% by weight or more, and aldehyde and hydrogen cyanide were both 0 ppm. The same test as in Example 1 was carried out with considerable addition, and the time required until the start of polymerization was 45 minutes.

[0035]

Comparative Example 3 Acrylonitrile A product obtained in the acrylonitrile purification step was subjected to simple distillation, and a liquid containing 99.9% by weight of acrylonitrile, 20 ppm of aldehyde, and 40 ppm of hydrogen cyanide was prepared using acrylonitrile excluding other components. 2,2,6,6-tetramethyl-4-
When the same test as in Example 1 was performed without adding hydroxypiperidine-1-oxyl, the required time until the start of polymerization was 15 minutes.

[0036]

Comparative Example 4 2,2,6,6-
Without adding tetramethyl-4-hydroxypiperidine-1-oxyl, 10 ppm of hydroquinone was added, and an oxygen stability test using a gum test device was performed on a part of 1 liter of the solution. The measured time was 42 minutes.

[0037]

Comparative Example 5 2,2,6,6-
Without adding both tetramethyl-4-hydroxypiperidine-1-oxyl and hydroquinone, an oxygen stability test was performed using a gum tester, and the time required until the start of polymerization was measured, and the required time was 18 minutes. .

[0038]

Comparative Example 6 2,2,6,6-
Without adding tetramethyl-4-hydroxypiperidine-1-oxyl, 10 ppm of hydroquinone was added, and an oxygen stability test using a gum test device was performed on a part of 1 liter of the solution. The measured time was 40 minutes.

[0039]

[Comparative Example 7] 2,2,6,6-
Without adding tetramethyl-4-hydroxypiperidine-1-oxyl and hydroquinone together, an oxygen stability test was performed using a gum tester, and the time required until the start of polymerization was measured, and the required time was 15 minutes. .

[0040]

Comparative Example 8 The product acrylonitrile in the acrylonitrile purification step was subjected to simple distillation, and acrylonitrile excluding other components was used.
When the same test as in Example 1 was conducted without adding 4-hydroxypiperidine-1-oxyl and hydroquinone, the required time until the start of polymerization was 20 minutes.

Table 1 shows the results of Examples 1 to 3 and Comparative Examples 1 to 8. In Table 1, the substance names are abbreviated as follows. ACN; acrylonitrile HCN; hydrogen cyanide HQ; hydroquinone 4HTMP; 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl

[0042]

[Table 1]

[0043]

Comparative Example 9 Acrylonitrile having an aldehyde concentration of 20 ppm and a hydrogen cyanide concentration of 5% by weight was supplied from the conduit 5 shown in FIG. 1 to the distillation column 1 for purification. Hydroquinone was added as a polymerization inhibitor to adjust the concentration at the bottom of the distillation column 1 to 200 ppm. In this case, a 4 wt% aqueous solution of hydroquinone was added to the conduit 5 of the distillation column 1 using a pump capable of supplying a constant amount of hydroquinone per unit time, and the concentration of hydroquinone in the supplied liquid was adjusted to 100 ppm. The remaining 100 ppm of hydroquinone was added simultaneously from the top of the distillation column 1. The addition equipment and the aqueous hydroquinone solution were of the same type and concentration as the equipment for adding hydroquinone to the feed solution.

After 24 hours from the start of hydroquinone addition, the bottom liquid of the distillation column 1 was sampled, and the amount of polymer present in the liquid was measured. The same method as in Example 4 was used for measuring the amount of the polymer. Further, under the same conditions, the pressure difference at the top and bottom of the process distillation column 1 and the overall heat transfer coefficient of the reboiler and the overall heat transfer coefficient of the reboiler of the distillation column 2 were measured.

The amount of polymer was 2.5 mg despite the presence of 200 ppm of hydroquinone. Similarly, the amount of polymer in the distillation column 2 was measured.
3 mg. Further, the pressure difference of the distillation column 1 measured by the same measuring method as in Example 5 was 0.0
5 kg / cm @ 2, and the continuous operation period of the process distillation column 1 was limited to one year.

Further, the overall heat transfer coefficient of the reboiler installed in the distillation column 1 is 0.36 Kcal / day.
m2.Hr..degree. C., and the continuous operation period of the reboiler was limited to 6 months. The overall heat transfer coefficient of the reboiler installed in the process distillation column 2 is 1.
At 50 Kcal / m 2 · Hr · ° C., the continuous operation period of the reboiler was limited to 3 to 4 months.

[0047]

According to the method for preventing polymerization of nitriles of the present invention, acrylonitrile in the distillation column and in the reboiler in the step of purifying acrylonitrile or methacrylonitrile,
The production of polymers caused by methacrylonitrile and hydrogen cyanide or aldehyde is suppressed, and the pressure difference between the top and bottom of the distillation column in the process is also reduced, enabling long-term continuous operation. Cleaning work in the distillation column, which has been performed, can be reduced.

Further, it is possible to slow down the rate of reduction of the overall heat transfer coefficient of the reboiler, and to reduce the cleaning work which has been performed every three to six months.
The life of the reboiler can be extended. The operation of the acrylonitrile or methacrylonitrile purification step is facilitated by the reduction of the inside of the distillation column and the reboiler in this step.

[Brief description of the drawings]

FIG. 1 shows the flow of an acrylonitrile purification step used in the present invention.

[Explanation of symbols]

 1,2 distillation column 3,4 reboiler 5 conduit from water extraction distillation column 6 conduit for acrylonitrile product

Claims (3)

[Claims] In the purification step of acrylonitrile or methacrylonitrile, the aldehyde is contained in an amount of 5 to 100 ppm by weight and / or the hydrogen cyanide is added in an amount of 0.0005 to 10 ppm.
A method for preventing polymerization of nitriles, characterized in that piperidine-1-oxyls are present in a acrylonitrile or methacrylonitrile purification step solution present in a percentage by weight. 2. A compound of the formula (I) wherein R1 is an alkyl group having 1 to 3 carbon atoms, R2 is an H, O, OH, OR3 group (R3 is a group having 1 to 3 carbon atoms). An alkyl group or a phenyl group) or a COOR4 group (R4 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms).
A method for preventing polymerization of nitriles as described above. Embedded image 3. The method of claim 2, wherein the piperidine-1-oxyl is 2,2,
6,6-tetramethylpiperidine-1-oxyl, 2,
2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, 2,2,6,6-4-oxopiperidine-1-oxyl, 2,2,6,6-tetramethyl-4
-Methoxypiperidine-1-oxyl, 2,2,6,6
-Tetramethyl-4-ethoxypiperidine-1-oxyl, 2,2,6,6-phenoxypiperidine-1-
The method for preventing polymerization of nitriles according to claim 2, wherein the method is at least one selected from oxyl and 2,2,6,6-4-carboxypiperidine-1-oxyl.