JPS6220512A - Production of deodorized ethylene copolymer - Google Patents

Abstract

PURPOSE:To obtain the titled copolymer for use in food packaging, etc., by high-pressure radical polymerization between ethylene and a polar comonomer, making the resultant reaction mixture put under reduced pressure to add specific amount of ethylene to the system followed by separation and purification of the unreacted monomer to return it to the polymerizer. CONSTITUTION:Ethylene 1 and a polar comonomer 2 are put in a high-pressure state by compressors 3 and 4 to feed them to polymerizer 5 to carry out high- pressure radical polymerization. The resulting reaction mixture is put at a reduced pressure state by reducing valve 6, and such an amount of ethylene as to be >=2.0 in the weight ratio; ethylene/copolymer is newly fed to the system in a molten state of the copolymer under a pressure 1-500kg/cm<2> to come into contact with the copolymer. The reaction mixture is then fed to separator 7 to separate the unreacted monomer. Following that, the ethylene newly brought into contact with the copolymer and said unreacted monomer separated are both purified by purification process 12, being returned to the polymerizer 5, thus obtaining the objective copolymer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing copolymers of deodorized ethylene and polar comonomers, such as acrylic esters, by high-pressure radical polymerization.

[Prior art and its problems] Conventionally, it has been widely practiced industrially to copolymerize ethylene and a polar comonomer, such as an acrylic ester, by high-pressure radical polymerization to obtain a copolymer.

However, although these copolymers are essentially odorless, they actually have an odor (° C.), which is said to have delayed their advancement into the food packaging field in particular.

It has been proposed to wash and deodorize the copolymer pellets with an n52 odor agent, but this is not preferred because the deodorizer remains in the copolymer.

Copolymers with vinyl acetate etc. as polar comonomers (
In the case of EVA (hereinafter referred to as EVA), the odor-causing substance (hereinafter referred to as odorous substance) is mainly acetic acid. However, for example, copolymers with acrylic esters, E
In EA), the main odorous substances are thought to be the residual monomer acrylic ester, as well as its simple decomposition products such as acrylic acid and alcohol. In addition to these, for example, various carboxylic acids that are used to cleave the polymer main chain, further decomposition of these acids, decomposition products of radical polymerization initiators during polymerization, and even oligomers that are quarters of low molecules are also odorous. At present, not only all of them have been identified, but also the causes of their occurrence have not been completely elucidated. Therefore, I+ such as EEA
! 2 deep is generally considered more difficult than IB 2 deep such as EVA.

All of the 11 Iλ methods that have been proposed so far are EVA
These deodorizing methods are not necessarily satisfactory as deodorizing methods for EEA and the like.

[Means for Solving the Problems] The object of the present invention is to provide an ethylene/polar comonomer copolymer!
The objective is to obtain a deodorized copolymer during production. Other purposes are listed below as appropriate.

The method for producing a deodorized ethylene/polar comonomer copolymer of the present invention includes the following steps: (a) supplying ethylene and a polar comonomer to a polymerization vessel and performing high-pressure radical polymerization; ) reducing the pressure of the reaction mixture from the polymerization vessel using a pressure reducing valve, and then separating unreacted monomers from the mixture; (c) melting the copolymer between the pressure reducing step and the separation step; a step of newly supplying ethylene in an amount such that the ethylene/copolymer ratio (weight pressure) is at least 52.0 and bringing it into contact with the copolymer under a pressure of 1 to 500 kg/cm2; (d) A step of returning the contacted 1-tyrene and the separated unreacted monomer to the polymerization vessel through an ethylene purification step.

The following provides a further detailed description of the invention.

Examples of the polar comonomer of the present invention include α,β-unsaturated carboxylic acids such as acrylic acid and methacrylic acid, and esters thereof with lower alcohols such as methanol and ethanol. Furthermore, vinyl esters of lower carboxylic acids such as acetic acid and propionic acid, styrene,
Also included are styrenes such as α-methylstyrene and vinyl l-toluene. Polar comonomers particularly suitable for the present invention are acrylic acid, methacrylic acid, and esters thereof.

If arbitrarily selected depending on the copolymer obtained, J, I,
The ratio of the polar comonomer to ethylene in the polymerization vessel is suitably 1 to 50% by weight, particularly 5 to 40% by weight.

Generally, the polymerization temperature is 100 to 350°C, and the pressure is 50°C.
High pressure radical polymerization is carried out at 0 to 3500 kg/ci. In particular, for copolymerization of polar comonomers such as acrylic acid and its salts, the temperature is 100 to 300°C and the pressure is 100°C.
0 to 3 (loOKg/ci is preferred.

In addition, in high-pressure radical chassis, radical polymerization 1;n
Initiators are commonly employed. Any conventionally known radical combination initiator can be used, but for example,
Diethyl peroxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, dicumyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxy acetate, tert-butyl peroxy-2-
Peroxides such as ethylhexanoate, tert-butyl peroxypivalate, 2-ethylhexanoyl peroxide, bivalyl peroxide, 1-pyl peroxydicarbonate, oxygen, azoisobutyronitrile, azobis Azo compounds such as -2,2-diphenylacetonitrile and 1-tert-butylazo-1-cyanocyclohexane are used. These initiators are 1
species or mixtures of two or more species, with the usual amount of polymerization initiator;
For example, 0.00 parts by weight of initiator per 100 parts by weight of ethylene
It is supplied to the polymerization vessel at a ratio of 0.5 to 0.5 polymer tails.

After the ethylene and polar comonomer are mixed, they are compressed to the pressure necessary to cause the copolymerization reaction and fed to the polymerization vessel. The polymerization initiator can be added to either ethylene, polar comonomer, or a mixture thereof before the polymerization vessel. It can also be added to one or more locations in the polymerization vessel.

The polymerization vessel can be either a tubular type or an autoclave type with a stirrer.

The polymerization time is not particularly limited, but is generally in the range of 1 to 60 seconds, for example.

Note that the conditions inside the polymerization vessel are harsh because of the high temperature and the presence of radicals, and a decomposition reaction, which can be called a reverse reaction of polymerization, is likely to occur. Therefore, it is thought that the decomposition products as the material on the right are mainly produced in the polymerization vessel. It is also thought that low molecular weight molecules such as oligomers are formed here.

After polymerization, the reaction mixture is depressurized through a pressure reducing valve or other pressure reducing device before entering the separator.

This separation can also be carried out in two or more stages. From the reaction mixture in a 1 ift vessel,
Unreacted monomers and waxes other than the ethylene/polar comonomer copolymer are separated and removed.

For example, in the case of separation in two stages, the pressure is reduced by the first pressure reducing valve, and substances with relatively high boiling points are separated in the first separator. The substances separated here are typically unreacted monomer wax such as ethylene. Next, the pressure is further reduced by the second pressure reducing valve, and the pressure is further reduced by the second separator. Here too, unreacted monomers such as ethylene are separated, but also low-boiling substances are separated. It is thought that these low boiling point substances mainly form the right back substance. However, it is difficult to completely remove the material contained in the copolymer by simply reducing the pressure. Therefore, in the present invention,
Between the depressurization process and the unreacted monomer separation process, the ethylene/copolymer ratio (weight) is small (both 2 ．．
On the day of zero, ethylene is freshly fed and brought into contact with the molten copolymer.

An ethylene content of less than 2.0 is not preferred because deodorization becomes insufficient. The temperature may be set as long as the copolymer melts, but if the temperature exceeds the decomposition temperature, deodorization will still be insufficient. Therefore, ethylene and the copolymer are brought into contact at a temperature arbitrarily selected from a temperature range of not less than the melting temperature of the copolymer and not more than the decomposition temperature.

Contact with the supplied ethylene may take place in the conduit during transportation, or it may be forced into contact using a suitable mixer. For example, a static mixer can be used as such a mixer.

Furthermore, an appropriate standing tank may be provided between the pressure reducing valve and the separator, and ethylene may be supplied to the standing tank and brought into contact there. Further, the number of contact points may be two or more.

In this way, odorous substances in the copolymer are removed by ethylene.

Ethylene after contact is separated in the reactor and returned to the polymerization reactor together with unreacted monomers for copolymerization.

By the way, the ethylene that has come into contact with the unreacted monomer and the copolymer returns to the polymerization vessel as described above, but the substance removed from the copolymer is also taken with it. Since these odorous substances do not have radical polymerization ability, they are not consumed in the polymerization vessel. An ethylene M manufacturing process is provided for the purpose of removal. The conventional purification steps provided for recovered unreacted monomers are merely aimed at removing high boilers such as waxes.

Such an ethylene purification process must aim at removing substances with relatively high boiling points, such as odorous substances. Therefore, it is appropriate to use, for example, a cryogenic separator, a scrubber, etc. The cleaning liquid for the scrubber is preferably liquid paraffin, which is a saturated hydrocarbon, for example. In addition, an ethylene rectification apparatus having an appropriate structure for ethylene rectification can also be employed in the ethylene purification process.

These cryogenic separation devices, scrubbers, and ethylene rectification devices can be installed in appropriate combinations. The purified ethylene and unreacted monomers are returned to the polymerization vessel.

Next, the present invention will be explained in more detail with reference to FIG.

Ethylene from source 1 and comonomer (eg ethyl acrylate) from source 2 are sent to feed lines 21 and 22, respectively. Compressor 3 and J: and compression 1
14 to the copolymerization initiation pressure. The compressed high-pressure gas is supplied to the polymerization vessel 5 through lines 22 and 23, and an ethylene/polar comonomer copolymer is produced by high-pressure radical polymerization.

After polymerization, the reaction mixture 81 is sent to the first pressure reducing valve 6 via the inlet 24. The reaction mixture whose pressure has been reduced by the pressure reducing valve 6 is
It is fed via line 25 to the first separator 7. In the separator 7, high boiling point substances such as waxes are mainly separated along with unreacted ethylene. This separated product is cooled by a heat exchanger 13 via a line 29, and the precipitated waxes are separated by a lever 10 and a filter 11. The gas from which waxes have been separated is sent through line 30 and from line 22 to second compressor 4.

The copolymer leaving the minute 1ift unit 7 is transferred from the line 26 to the second
The pressure is further reduced by the pressure reducing valve 8, and the second
Minute 11 [Enter V5.9. Here, unreacted monomers and unreacted monomers dissolved in the copolymer are further separated. Odorous substances with low boiling points are also mainly separated here and sent to the ethylene purification step 12 via line 31. In this ethylene purification process, ethylene is purified,
Odorous substances are removed and ethylene is recovered. The recovered ethylene is sent to the first compressor 3 from the line 21 via the line 32 and fed to the polymerization vessel 5.

The copolymer that has come out of the atomizer 9 is pelletized by a pelletizer 13 through a line 28, and stored as appropriate.

Furthermore, the newly supplied ethylene for deodorizing purposes is
In FIG. 1, either line 25 or line 27 or both are fed. Also, line 25,
or a mister installed in line 27 (not shown)
Alternatively, the copolymer can be forced into contact with the ethylene. After coming into contact with the copolymer, this newly supplied ethylene is separated in the subsequent separators 7 and 9, and is recovered together with unreacted monomers and waxes via line 29 or line 31, and filtered into filter 11.
Then, it is purified through an ethylene purification step 12. After purification, it is supplied to OII line 22 or 23 of compressor 3 or 4 via line 30 or 32, compressed again, and returned to polymerization vessel 5.

[Effects of the Present Invention] According to the method of the present invention, a deodorized ethylene/polar seven-mer copolymer is produced during radical copolymerization. In addition, unreacted monomers and newly supplied ethylene can be completely reused.

The present invention will be explained below using examples.

[Example] High-pressure radical polymerization of ethylene and ethyl acrylate was carried out according to FIG.

′! In other words, 100 parts of ethylene and 4 parts of ethyl acrylate as a polar comonomer were fed into a polymerization reactor with a population temperature of 175°C, and the pressure was 250 (1Ng/c#).
Copolymerized with i. Polymerization time was 5 seconds. The reaction mixture was then fed through a first pressure reducing valve, a first separator, and into a second pressure reducing valve and a second separator.

In Example 1, L run was fed into the conduit of line 25 between the first pressure reducing valve and the first separator.

In Example 2, a line mixer (not shown) was installed at the same location, and agielene was supplied immediately upstream of the line mixer (not shown).

In Example 3, ethylene was fed into the conduit of line 27 between the second pressure reducing valve and the second separator.

Furthermore, in Example 4, a Lysimi 1cer (not shown) was installed at the same location as in Example 2, and ethylene was supplied immediately upstream thereof.

Temperature and pressure during contact with ethylene in each example,
The ethylene/copolymer ratio (weight ratio) is summarized in Table 1.

EEA obtained in each example after 10 days of continuous operation (
20% by weight of ethyl acrylate (M, 1.10) was allowed to stand overnight, and its deodorizing effect was evaluated by 10 odor judges. The evaluation criteria were -1 for "strong unpleasant odor", 01 for "unpleasant odor but tolerable", and 1 for "almost no unpleasant odor". The results are shown in Table 1 as a combined score of 10 people.

The new deodorizing ethylene feed location is the same as in Example 1.
Similarly, the results of a comparative example in which the ethylene purification step was bypassed are also listed in Table 1.

Since it is clear that widely different embodiments may be constructed without departing from the spirit and scope of the invention,
The invention is not limited to its particular embodiments, except as limited in the claims.

[Brief explanation of drawings]

FIG. 1 is a schematic system diagram for carrying out the present invention.

Claims (3)

[Claims] (1) A method for producing a deodorized ethylene/polar comonomer copolymer, comprising: (a) supplying ethylene and a polar comonomer to a polymerization vessel;
a step of performing high-pressure radical polymerization; (b) a step of reducing the pressure of the reaction mixture from the polymerization vessel using a pressure reducing valve, and then separating unreacted monomers from the mixture; (c) a step of performing the pressure reducing step and unreacted monomers. During the separation process, ethylene is added to the molten state of the copolymer in an amount such that the ethylene/copolymer ratio (weight ratio) is at least 2.0 under a pressure of 1 to 500 kg/cm^2. (d) returning the contacted ethylene and the separated unreacted monomer to the polymerization vessel through an ethylene purification process. Production method. (2) The ethylene purification step uses any one of an ethylene rectifier, a cryogenic separator, and a scrubber for the purpose of separating low-boiling point impurities. Production method. (3) The manufacturing method according to claim 1, wherein the polar comonomer is selected from acrylic acid, methacrylic acid, or an ester thereof.