JPH0710910A - Production of ethylene copolymer - Google Patents

Abstract

PURPOSE:To provide a method for stably and efficiently producing an ethylene copolymer through the high-temp. and high-pressure polymerization of ethylene with a radical-polymerizable monomer (a) copolymerizable therewith by preventing the heat polymerization of the monomer (a). CONSTITUTION:This production method comprises polymerizing ethylene with a radical-polymerizable monomer (a) copolymerizable therewith in the presence of a polymerization initiator at 100-300 deg.C and 500-3,000kg/cm<2> or higher and introducing a polymerization inhibitor into the system in the range of from the polymerization zone to the inlet of a first separator.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing an ethylene copolymer. More specifically, the present invention relates to a method for stably producing an ethylene copolymer by preventing thermal polymerization of a radically polymerizable monomer capable of copolymerizing with ethylene in a pipe after a reaction zone.

[0002]

2. Description of the Related Art A method for obtaining an ethylene copolymer by polymerizing ethylene and a radical-polymerizable monomer copolymerizable with ethylene at high temperature and high pressure in the presence of a polymerization initiator is known. In such a method for producing an ethylene copolymer, ethylene and a radical-polymerizable monomer are pressurized to a predetermined pressure by multi-stage compression, and polymerization is carried out at a high pressure. In order to separate the radical-polymerizable monomer, it is separated by multistage depressurization. This multi-stage compression (decompression) means increasing the pressure (reducing pressure) to a predetermined pressure by dividing it into several stages without depending on only one-stage compression (reducing pressure). In the case of multistage depressurization, the unreacted ethylene and the radical-polymerizable monomer separated by depressurization in each stage are reused by a circulation line. When a radically polymerizable monomer having high heat-polymerizability and high homo-polymerizability is used in such a polymerization step, the radical-polymerizable monomer gas produces a homopolymer by heat in this multistage compression and reduced pressure purification step. Form and adhere to the inside of the pipe. If this accumulates, the pipe will be clogged and the pressure will rise, making stable manufacture for a long time difficult. Further, such a polymer may be mixed into the produced ethylene copolymer to cause a quality problem. Therefore, under high temperature and high pressure conditions, the number of types of radically polymerizable monomers that can be copolymerized with ethylene is practically limited.

Regarding the prevention of thermal polymerization in the step of compressing ethylene and a radical-polymerizable monomer gas to a predetermined pressure before polymerization, 1. Method of adding polymerization inhibitor to ethylene 1. Method of dissolving the polymerization inhibitor in a solvent and injecting it into the system. 3. A method of adding a polymerization inhibitor to the lubricating oil of a reciprocating ultra-high pressure compressor (JP-A-52-33986). There are various reported examples such as a method of injecting a polymerization inhibitor into a polymerization reactor (JP-A-1-156309). However, these methods suppress the polymerization and cannot obtain a practically sufficient high molecular weight substance. In addition to problems, it was not sufficient as a method for preventing thermal polymerization in the vacuum purification step after the polymerization reactor. Further, in ionic polymerization under high temperature and high pressure using a metal catalyst, a method of adding a saturated fatty acid of an alkaline earth metal or an aromatic carboxylic acid near the outlet of the reactor in order to inactivate the residual catalyst after the reaction. (JP-A-51-11128
2), a method of adding polyalkylene glycol to the reaction mixture (Japanese Patent Laid-Open No. 59-22910) and a high-pressure radical polymerization method, a compressor for repressurizing the circulating gas from the first separator to the reaction pressure. As a lubricant for paraffins by dissolving one polymerization inhibitor from quinones, phenol derivatives, phosphites and thiodicarboxylic acid alkyl esters to prevent clogging of the circulation line after the reactor. 58-103593), etc., but in this case, the type and amount of the polymerization inhibitor that can be used are limited depending on the solubility of the polymerization inhibitor in paraffins, and sufficient results were not always obtained, and production was difficult.

[0004]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention The thermal polymerization which is the cause of the blockage of the pipe in the circulation line of the monomer gas separated by the separator after the polymerization reactor as described above is prevented, and long-term stable production is enabled. It proposes a method.

[0005]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have found that ethylene and a radical-polymerizable monomer are mixed at 10 to 10 at 500 to 3000 kg / cm ² .
In a method for producing an ethylene copolymer by radical polymerization at a temperature of 0 to 300 ° C., a polymerization reaction system is prepared by injecting a polymerization inhibitor into the system from the outlet of the polymerization reactor to the inlet of the first separator. A process has been developed to prevent undesired thermal polymerization of ethylene and radically polymerizable monomers as a whole, especially in the circulation line from the post reactor separator.
According to this method, it is possible to prevent thermal polymerization of the radically polymerizable monomer after the polymerization reactor and to stably produce an ethylene copolymer of excellent quality for a long period of time.

The present invention will be described in detail below. The radical-polymerizable monomer used in the ethylene copolymer according to the present invention is a vinyl monomer having radical-polymerizability, and examples thereof include (meth) acrylates, vinyl esters, and (meth) acrylamides. be able to. Specific examples of the (meth) acrylate include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate and methacrylic acid. Isodecyl,
Lauryl methacrylate, lauryl methacrylate-tridecyl, tridecyl methacrylate, cetyl methacrylate-
Stearyl, stearyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, glycidyl methacrylate, tetrahydrofurfuryl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, acrylic acid Butyl, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, isodecyl acrylate, lauryl acrylate, lauryl-tridecyl acrylate, tridecyl acrylate, cetyl-stearyl acrylate, acrylic acid Stearyl, cyclohexyl acrylate, benzyl acrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate,
Examples thereof include glycidyl acrylate, tetrahydrofurfuryl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate and hydroxyethyl acrylate.

Specific examples of vinyl esters include vinyl acetate and vinyl propionate.

Specific examples of (meth) acrylamide include acrylamide and methacrylamide. N
Specific examples of the substituted (meth) acrylamide include N
-Methyl methacrylamide, N-ethyl methacrylamide, N-propyl methacrylamide, N-isopropyl methacrylamide, N-butyl methacrylamide, N-
Tertiary butyl acrylamide and N-methyl acrylamide, N-ethyl acrylamide, N-propyl acrylamide, N-isopropyl acrylamide, N-
Butyl acrylamide, N-tertiary butyl acrylamide, N, N-dimethyl acrylamide, N, N-diethyl acrylamide, etc. can be mentioned.

In particular, when hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, N, N-dimethylacrylamide, or N, N-diethylacrylamide is used among the radical-polymerizable monomers described above, The effect of suppressing thermal polymerization after the polymerization reactor by the production method of the present invention is higher than that of the above-mentioned polymerization method.

In the present invention, a polymerization inhibitor selected from phenol compounds, nitrosamine compounds and phosphite compounds can be used. As the phenol-based compound, a monophenol-based compound, a bisphenol-based compound, or a polymer type phenol-based compound can be used. Specifically, para-hydroxybenzaldehyde,
In addition to hydroquinone monomethyl ether and p-aminophenol, especially 3,5-xylenol, 2,6-diisopropylphenol, 2-tert-butylhydroxyanisol, 4-tert-butylhydroxyanisol, 4-tertiary-
Butyl pyrocatechol, 2,4 bis (1,1 dimethyl-
Propylphenol), 4,4'-thiobis- (6-tert-butyl-meta-cresol), 4,4'-methylenebis (6-tert-butyl-ortho-cresol), 4,4 '.
Preference is given to using compounds such as methylenebis (2,6-di-tert-butylphenol) and 2,6-di-tert-butyl-4-methylphenol.

In the case of the above antioxidants, 3,5-xylenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol or 2-tertiary. The use of mononuclear phenols such as butylhydroxyanisol is particularly effective.

The nitrosamines polymerization inhibitor used in the present invention is specifically N-nitrosodiphenylamine,
N-nitroso-N-cyclohexylaniline and N-nitroso-N-methylaniline.

Specific examples of the polymerization inhibitor of the phosphite ester compound referred to in the present invention include triphenylphosphite, tris (nonylphenylphosphite), triethylphosphite, tris (2-ethylhexyl) phosphite and triphenylphosphite. Decyl phosphite, tris (tridecyl) phosphite, diphenyl mono (2-ethylhexyl) phosphite, diphenyl monodecyl phosphite, diphenyl mono (tridecyl) phosphite, dilauryl hydrogen phosphite, tetraphenyl dipropylene glycol diphosphite,
Tetraphenyl tetra (tridecyl) pentaerythritol tetraphosphite, tetra (tridecyl)-
4,4′-isopropylidenediphenyl diphosphite, trilauryl trithiophosphite, bis (tridecyl) pentaerythritol diphosphite, tristearyl phosphite, distearyl pentaerythritol diphosphite, bis (nonylphenyl) pentaerythritol diphosphite Fight, Tris (2,4
-Di-t-butylphenyl) phosphite.

Further, when a phosphite compound and a phenol compound are used together as a polymerization inhibitor, more preferable effects can be obtained. When a phenolic compound is used alone as a polymerization inhibitor, the phenolic compound remaining in the product is oxidized, causing yellowing and deterioration of quality. The combined use of the phosphite compound and the phenol compound makes it difficult for the phenol compound to have a color-developing structure even when it is oxidized, and it is effective for preventing yellowing of the product.

These polymerization inhibitors can be used alone or as a solution dissolved in a solvent such as a low molecular weight ketone or ester. Specific examples of the solvent used here include acetone, 2-butanone, methyl acetate, and ethyl acetate. In some cases, two or more kinds of these solvents may be used in combination. The solvent used here is preferably a good solvent for the polymerization inhibitor and does not adversely affect the polymerization system. Further, in consideration of the boiling point and the efficiency of separation from the polymer, it is preferable to select one having the smallest amount remaining in the copolymer.

The polymerization inhibitor used in the present invention is 300 pp with respect to the expected total amount of unreacted radical-polymerizable monomer.
m to 20000 ppm, more preferably 3000 ppm
Add in the range of up to 1000 ppm. If the added amount is less than 300 ppm, the expected effect does not appear, and 2000
When it is 0 ppm or more, the polymerization inhibitor in the circulating gas hinders the polymerization reaction when the circulating gas is fed again, which is not preferable.

The polymerization inhibitor is preferably fed after the outlet of the polymerization vessel and before the inlet of the first separator. Before the polymerization reactor, there is a risk of inhibiting the polymerization reaction, and after the first separator, it is not possible to prevent the blockage of the circulation line piping from the first separator, making it difficult to stably manufacture for a long time. Because. Here, the first separator is installed after the pressure control valve of the reactor, and the copolymer produced from the reactor and the unreacted ethylene or radical polymerizable monomer are pressurized to 100%.
This is a device for separating under reduced pressure at up to 300 atm, and the separated ethylene and radically polymerizable monomer gases are reused through a circulation line. Similarly, the second separator is a device for separating the unreacted ethylene or radical-polymerizable monomer from the copolymer produced from the first separator under reduced pressure at a pressure of 10 atm or less. A flow sheet of the high pressure method plant is shown in FIG.

The production of the ethylene copolymer according to the present invention is carried out in the presence of at least one free radical polymerization initiator. Free radical polymerization initiators are compounds that generate free radicals, such as oxygen, ditert-butyl peroxide, tert-butyl peroxide, tert-butyl cumyl peroxide, dialkyl peroxides such as dicumyl peroxide, acetyl peroxide, Isobutyl peroxide, diacyl peroxide such as octanoyl peroxide, diisopropyl peroxydicarbonate, peroxydicarbonate such as di-2-ethylhexyl peroxydicarbonate, tert-butyl peroxyisobutyrate, tert-butyl peroxy Peroxyesters such as pivalate and tert-butyl peroxylaurate, ketone peroxides such as methylethylketone peroxide and cyclohexanone peroxide, 1,1-bisterchari Cylperoxycyclohexane, peroxyketals such as 2,2-bistershabutylbutyloxyoctane, hydroperoxides such as tert-butyl hydroperoxide and cumene hydroperoxide, and 2,2-azobisisobutyronitrile Azo compounds may be mentioned.

It is also possible to use various chain transfer agents as molecular weight regulators. Examples of chain transfer agents include olefin compounds such as propylene, butene and hexene, paraffins such as ethane, propane and butane, and aromatic hydrocarbons such as toluene, xylene and ethylbenzene.

According to the above-mentioned production method, the ethylene copolymer can be produced stably, there is no limitation on the radical-polymerizable monomer to be used, and unfavorable thermal polymerization in the steps after the polymerization reactor. Thus, it is possible to produce an ethylene copolymer having excellent quality. Hereinafter, the present invention will be specifically described with reference to examples.

[0021]

EXAMPLES In the following Examples and Comparative Examples, an autoclave type reactor having a volume of 4 l and divided into two zones was used. <Example 1> Monomer composition at the inlet of the reactor was 96% by weight of ethylene and β-hydroxyethyl methacrylate (H
EMA) 1.9% by weight and acetone 1.9% by weight to prepare a mixed solution, which is injected upstream of the second stage compressor,
After compression with ethylene gas, it was fed to the first zone of the reactor. A radical copolymerization reaction was carried out in the reactor using ditertiarybutyl peroxypivalate as an initiator.
Further, a solution prepared by dissolving a mixture of diphenylmonodecyl phosphite and hydroquinone as a polymerization inhibitor in acetone between the reactor outlet and the first separator inlet was adjusted to 5000 ppm based on expected unreacted HEMA. While injecting, the first separator (pressure 200 Kg / cm
² , temperature 220 ° C.) second separator (pressure 3 Kg / cm ² ,
A product was obtained by separating the produced polymer and the unreacted monomer at a temperature of 200 ° C.). The polymerization temperature is 201 to 204 ° C.,
The reaction was carried out under the condition of a pressure of 1550 Kg / cm ² , but the reaction was sufficiently stable and there was no particular problem and long-term operation was possible. The obtained copolymer was a binary copolymer of ethylene and HEMA, and the composition determined using infrared absorption spectrum and ¹³ C-NMR spectrum was 92.6% by weight of ethylene and 7.4% by weight of HEMA. It was MI13. The results are shown in Table 1.

<Examples 2 to 6> Polymerization was carried out in the same manner as in Example 1 except that the type and composition of the radical-polymerizable monomer and the amount of the polymerization inhibitor in Example 1 were changed. The results are shown in Table 1. In both cases, the reaction stability was good and continuous operation was possible for a long time.

Comparative Examples 1 to 4 Copolymerization of ethylene with some radically polymerizable monomers was carried out under the same conditions as in Example 1 except that a polymerization inhibitor was not injected after the polymerization reactor. In this case, the pipe was clogged in the circulation line from the first separator due to the deposits, which are considered to be thermal polymerization products of the radical-polymerizable monomer, and the pressure increased. For this reason, it became difficult to use the separator, and stable operation for a long time was difficult. The results are shown in Table 2.

Comparative Example 5 The polymerization inhibitor of Example 4 was injected in front of the reactor, and the polymerization was carried out in the same manner as in Example 4 under other conditions. In this case, the amount of catalyst consumed in the reactor increased, and deposits, which were considered to be thermal polymerization products of radical-polymerizable monomers, were generated in the circulation line from the first separator.
The MI of the obtained polymer was larger than that in Example 4.

Comparative Example 6 The polymerization inhibitor of Example 4 was injected after the first separator and before the second separator, and the polymerization was carried out in the same manner as in Example 4 under other conditions. In this case, deposits that appeared to be thermal polymerization products of radically polymerizable monomers were generated in the circulation line from the first separator.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

EFFECTS OF THE INVENTION According to the production method of the present invention, it is possible to prevent thermal polymerization of a radical-polymerizable monomer and stably and efficiently produce an ethylene copolymer.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a process flow of an ethylene copolymer.

Front page continuation (72) Inventor Katsuaki Tsutsumi Oita City, Oita Prefecture No. 2 Nakasu, Showa Denko Oita Research Center

Claims (5)

[Claims] 1. Ethylene and a radical-polymerizable monomer copolymerizable with ethylene are added under a pressure of 50 in the presence of a polymerization initiator.
0 to 3000 Kg / cm ² or more, temperature 100 ° C. to 300
A method for producing an ethylene copolymer by polymerizing at 0 ° C., wherein a polymerization inhibitor is injected into the system after the polymerization reaction region and before the entrance of the first separator. 2. The ethylene copolymer according to claim 1, wherein the polymerization inhibitor is at least one compound selected from phosphite ester compounds, nitrosamine compounds and phenol compounds. Production method. 3. The ethylene copolymer according to claim 1, wherein the polymerization inhibitor is a mixture of at least one compound selected from phosphite compounds and at least one compound selected from phenol compounds. Method for producing polymer. 4. A radical-polymerizable monomer copolymerizable with ethylene is (meth) acrylate, vinyl ester, N-
The method for producing an ethylene copolymer according to any one of claims 1 to 3, wherein the ethylene copolymer is substituted (meth) acrylamide or N, N-substituted (meth) acrylamide. 5. The radically polymerizable monomer is β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, β-hydroxypropyl methacrylate, N, N′-
It is dimethyl acrylamide, The manufacturing method of the ethylene copolymer of Claim 4 characterized by the above-mentioned.