JPS5950244B2 - How to clean polymeric substances - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cleaning a polymeric substance adhering to equipment for producing or molding an aromatic vinyl-acrylonitrile copolymer.

It is known that during the production or molding of aromatic vinyl-acrylonitrile copolymers, polymeric substances that are insoluble or sparingly soluble in monomers and polymerization solvents adhere to the inside of the apparatus.

This polymer substance adheres to the inside of the reaction tank and the walls of heat transfer devices, causing a decrease in heat transfer performance and clogging of piping.

This has led to a decrease in reaction controllability and a decrease in productivity, which has become a major obstacle to stable operation. Furthermore, a part of the attached polymer substance mixes into the product, causing deterioration of the product appearance and color. Therefore, it was often necessary to shut down operations and remove this polymeric material. As a method for removing this polymer substance, removal work by inputting information has been carried out, but it requires a large amount of manpower and time, and also causes damage to the equipment and contamination by residual chemical substances from the operator, so this is the preferred method. It can not be said.

A method of peeling and removing using high-pressure fluid is also known, but this cannot be applied when there are locations where high-pressure fluid cannot be directly sprayed due to the structure of the device, or when the strength is insufficient.

For this reason, a cleaning removal method using a solvent is generally used.

When cleaning with monomers, the dissolving ability is poor at low temperatures, and polymerization of the monomers tends to occur at high temperatures, making the cleaning effect small.
A solvent that can dissolve the polymer is used. Alkyl amides such as dimethylformamide and alkyl sulfoxides such as dimethyl sulfoxide are good solvents for aromatic vinyl-acrylonitrile copolymers; Since some solvents cannot be dissolved, they cannot be completely dissolved and removed even if the manufacturing equipment is cleaned using these solvents.

It is known that if a small amount of this unremovable polymeric material remains in the device, it becomes a nucleus and causes new polymeric material to be formed and not deposited. A method is known in which the gelled product produced during the production of high nitrile gas is dissolved and removed using a solvent containing hydroxides of alkali metals and alkaline earth metals (Japanese Patent Publication No. 55-8087). ).

However, it has been found that this method has poor dissolving power even when applied to polymeric substances produced during the production of low nitrile resins. The present inventors have discovered a solvent system that can easily and almost completely remove polymeric substances adhering to aromatic vinyl-acrylonitrile polymer manufacturing equipment in a shorter time than conventional methods, and have completed the present invention. did. That is, the present invention provides a method for cleaning polymeric substances that adhere to the inside of an apparatus during production or molding of an aromatic vinyl-acrylonitrile copolymer using at least one solvent selected from alkylamides and alkyl sulfoxides and at least one metal. This is a method for cleaning polymeric substances characterized by using an alcoholate at the same time.

The aromatic vinyl-acrylonitrile copolymer to which the present invention can be applied is one that contains 5 weight or more of acrylonitrile in the polymer, and may also contain a nitrile monomer such as methacrylonitrile instead of acrylonitrile. Examples of group vinyl monomers include styrene, α-methylstyrene, etc., and methods such as suspension polymerization, solution polymerization, and bulk polymerization can also be applied as production methods.

Examples of the solvent selected from alkylamides and alkylsulfoxides used in the present invention include solvents such as dimethylformamide, dimethylacetamide, dimethylsulfoxide, and mixtures thereof, and monomers such as acrylonitrile, methacrylonitrile, styrene, and α-methylstyrene. It may also contain a small amount of water, aromatic hydrocarbons such as benzene and toluene, other solvents such as acetone and methyl ethyl ketone, and water.

Particularly regarding water, even if it is contained in the range of several Ppn to 1% by weight, the cleaning effect is not affected. Further, the metal alcoholate that is present simultaneously with the above solvent is a compound represented by formula (1).

(R-0) an alkaline earth metal (X-2) or aluminum (X-3),
In the case of X-2 and X=3, R may be a different alkyl group.

More specifically, sodium methylate, sodium ethylate, potassium methylate, potassium ethylate,
Suitable metal alcoholates include potassium t-butylate, magnesium methylate, magnesium ethylate, and aluminum ethylate.

The amount of metal alcoholate to be present at the same time as the melting stage is 1 x 1
0-4 to 1.0 gram equivalent/l is preferred, 1X10-
3 to 1×10 −2 gram equivalents/l are preferred.

As a method for making the metal alcoholate exist simultaneously with the solvent, methods such as adding it to the solvent in advance or adding it during washing with the solvent may be used.

For example, a method is used in which the interior of the polymerization apparatus is filled with a solvent, and then a metal alcoholate is added and the mixture is heated and stirred. Furthermore, it is also possible to use a solvent containing the metal alcoholate of the present invention after removing a portion of the previously attached polymeric substance with a monomer or a suitable solvent. In the cleaning method of the present invention,
The cleaning temperature is not particularly limited and can be selected depending on the location and equipment to which the polymeric substance is attached.

However, by selecting a temperature near or above the glass transition temperature of the polymer material, the cleaning effect can be further increased. The method for cleaning polymeric substances of the present invention requires extremely short dissolution time compared to conventional methods using solvent systems, and the polymeric substances are completely removed, so it can be applied on an industrial scale. It is highly effective in cleaning copolymer manufacturing equipment or molding equipment.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Examples 1 to 5 In an apparatus for producing styrene-acrylonitrile copolymers, styrene-acrylonitrile copolymers having different acrylonitrile contents were each produced by a continuous bulk polymerization method for one month.

Stainless steel test pieces of 3 (V! This test piece was placed in a flask with a capacity of 1000 g, and CH3ONa was added at 4.0 x 10-3 gram equivalent/l.
Add 500ml of dimethylformamide containing 130ml
Washing was carried out at .degree. C. with stirring.

The results of this cleaning test are shown in Examples 1 to 5 in Table 1. Comparative Examples 1 to 5 For test pieces obtained in the same manner as Examples 1 to 5, CH3O
NaOH instead of dimethylformamide containing Na
A cleaning test was carried out using dimethylformamide containing 4.0 x 10-3 gram equivalents/l.

The results are shown in Comparative Examples 1 to 5 in Table 1. Comparative Example 6 For a test piece obtained in the same manner as in Example 3, CH3ONa
Table 1 shows the results of a cleaning test using only dimethylformamide instead of dimethylformamide containing .

Examples 6 to 18 The same test pieces as used in Example 3, i.e., the acrylonitrile content was 24% by weight, were installed in an apparatus for producing a styrene-acrylonitrile copolymer, and the obtained polymeric substance was attached. The test pieces were subjected to a cleaning test in the same manner as in Examples 1-6.

Dimethylformamide, dimethylsulfoxide, dimethylacetamide and a mixture of dimethylformamide and dimethylsulfoxide were used as solvents, and CH3ONa, C2H, OK, (CH
3) 3C0K, (CH2())2kg and (C2H5O
) 3A1 were used in various combinations. The results are shown in Table 2. Examples 19-20 Instead of the solvents shown in Examples 6-18, a mixed solvent of acrylonitrile, ethylbenzene, styrene, etc. was used, and CH2ONa and 4.0
A washing test was carried out at 130° C. by adding 103 gram equivalents/l.

The results are shown in Table 3. Example 23 Acrylonitrile 2
3-32 weight? A polymerization tank (inner capacity 50w) was used for two months to produce a styrene-acrylonitrile copolymer containing
The cleaning method of the present invention was applied to 1').

This polymerization tank was charged with 4.5 times of dimethylformamide having a CH3ONa concentration of 1.times.10@-2 gram equivalent/l, heated to 130 DEG C. with stirring, and washed for 5 hours. Thereafter, when the solvent was discharged and the inside was inspected, metallic luster was observed on the inner surface of the polymerization tank, and no polymeric substance was observed to be attached at all. Comparative Example 7 Acrylonitrile monomer was charged into a polymerization tank similar to that in Example 23 to which a polymeric substance was attached, heated to 70° C. with stirring, and washed for 40 hours.

Claims (1)

[Scope of Claims] 1. One or more solvents selected from alkylamides and alkyl sulfoxides and at least one solvent for cleaning and removing polymeric substances adhering to equipment during production or molding of aromatic vinyl-acrylonitrile copolymers. 1. A method for cleaning a polymeric substance, characterized by simultaneously using a metal alcoholate. 2. The method according to claim 1, wherein the metal alcoholate is represented by general formula (I). (R-O)_XM・・・・・・・・・(I) However, R
is an alkyl group such as methyl group, ethyl group, propyl group or butyl group, M is an alkali metal (X=1), alkaline earth metal (X=2) or aluminum (X=3), and X= 2 and when X=3, R may be a different alkyl group.