JPS6168441A - Polymerization inhibitor for acrylic compound - Google Patents

Abstract

PURPOSE:To obtain the titled inhibitor having excellent solubility in acrylic acid, acrylic acid ester, etc., and effective to prevent the polymerization of the monomer, by using a copper salt of dithiocarbamic acid having cyclic amine skeleton, as an active component. CONSTITUTION:The copper salt of the dithiocarbamic acid of formula I (R is 2-8C alkylene which may contain atoms other than carbon and hydrogen), preferably the copper hexamethylenedithiocarbamate of formula II is used as an active component. The amount of the copper salt to be added to the monomer depends upon the kind of the acrylic acid and acrylic acid ester and the treatment condition of the production process, and usually, it is 0.0001-0.2wt%, preferably 0.0005-0.1wt% in the case of an acrylic compound. The copper dithiocarbamate may be used in combination with other polymerization inhibitor such as hydroquinone.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a polymerization inhibitor for acrylic compounds such as acrylic acid and methyl methacrylate.

[Prior art]

In the process of producing acrylic acid by catalytic gas phase oxidation reaction of propylene or acrolein, and acrylic ester by esterification reaction of this acrylic acid and alcohol, the separation and purification process of acrylic acid and acrylic ester involves distillation. Towers are commonly used.

As is well known, these acrylic acids and acrylic esters are unstable compounds that easily polymerize due to heat, light, peroxides, etc., or the presence of impurities. When υ, acrylic acid, and acrylic acid ester, which have extremely high polymerizability, are industrially produced, these polymerizations occur in the distillation column, and the aggregates accumulate in the distillation column, reducing the distillation efficiency. Problems may occur, such as a decrease in the product recovery rate of acrylic acid or acrylic acid ester.

Therefore, prevention of troubles caused by polymerization in the industrial production process of acrylic acid and acrylic esters is
This is a very important item in process operation, and is particularly effective in the distillation process where acrylic acid and acrylic esters are handled at high temperatures. It is indispensable in order to have a good time. However, no method has yet been established to effectively prevent the polymerization of acrylic acid and acrylic esters in industrial practice.

BACKGROUND ART Conventionally, as one method for preventing polymerization of acrylic acid or acrylic ester, adding a polymerization inhibitor has been proposed and practiced for a long time. For example, phenol, hydroquinone, hydroquinone monoethyl ether, phenothiazine, and amines have been proposed as typical heavy inhibitors, and these are used alone or in combination with these compounds.

However, the polymerization inhibitory effects of conventionally used polymerization inhibitors on acrylic acid and acrylic esters are
This is not satisfactory in industrial practice. These polymerization inhibitors are particularly impractical in high-temperature conditions such as distillation columns in the acrylic acid and acrylic acid ester production process, and must be added in large quantities to the distillation process, for example, to prevent polymerization. Since the agent is volatile, it is mixed in small amounts into the product acrylic (drying or acrylic ester).

If even a small amount of these polymerization inhibitors is present when producing useful polymers by polymerizing acrylic acid or acrylic acid esters, it may delay the finishing time, reduce the reproducibility of the polymerization reaction,
This results in unfavorable results such as deterioration of the 1-combination yield, adversely affecting the molecular weight distribution of the obtained polymer, and coloring of the polymer.

Instead of such a polymerization inhibitor, a method using dimethyldithiocarbamic acid copper salt was proposed (Japanese Patent Publication No. 43-299).
No. 25). Although this product has a good polymerization-preventing effect, it has the disadvantage of being limited in practical use due to its small solubility i and T in acrylic acid and acrylic esters.

That is, by the method abbreviated above, acrylic, 'l
! These non-volatile polymerization inhibitors used in the production and use of esters thereof are added to the reflux liquid of each distillation column, solvent separation column, acetic acid separation column, and purification column.
During operation, it will gradually accumulate at the bottom of the tower. In particular, in the final purification tower, the feed liquid is condensed 30 to 40 times at the bottom of the tower. The polymerization inhibitor will precipitate, forming scale in the reboiler, etc., making it impossible to continue distillation. In order to avoid this risk, if distillation is carried out by reducing the amount of the polymerization inhibitor added to an extent that does not precipitate the polymerization inhibitor, a decrease in the yield of acrylic acid or its ester cannot be avoided. As described above, the polymerization prevention 1'711 used in these steps is subject to various limitations due to its anti-compatibility effect and solubility.

A method has also been proposed in which copper dibutyldithiocarbamate, which has excellent solubility in acrylic acid and acrylic esters, is used as a polymerization inhibitor (Japanese Patent Publication No. 3514/1983).

However, even if copper dibutyldithiocarbamate or copper dimethyldithiocarbamate is used, polymerization of acrylic acid and acrylic acid ester cannot be completely prevented.

[Problem that the invention seeks to solve]

The present invention utilizes a polymerization inhibitor that has better polymerization inhibitory properties than conventional dialkyldithiocarnocarnomate copper salts, thereby making it possible to prevent acrylics, acrylic esters, acrylamide, and their methacrylates. A method of preventing polymerization of compound analogs is provided.

[Specific measures to solve the problem]

The object of the present invention is achieved by using a copper dithiocarbamate salt having a cyclic amine skeleton as a polymerization inhibitor.

[Structure of the Invention] The present invention provides a copper dithiocarbamate salt represented by the following formula, which is an inhibitor of acrylic compounds such as acrylic acid, methacrylic acid, acrylic ester, methacrylic ester, acrylamide, and methacrylamide. A certain U\/1/ヮS [wherein R is an alkylene group having 2 to 8 carbon atoms, and may contain atoms other than carbon and hydrogen].

(Copper dithiocarbamate salt) Examples of the copper dithiocarbamate salt represented by the above formula include copper ethylenedithiocarbamate, copper tetramethylenedithiocarbamate, copper pentamethylenedithiocarbamate, steel hexamethylenedithiocarbamate, copper oxydiethylenedithiocarbamate, and the like.

This polymerized anti-cutting material is used in the acrylic dredging process of the acrylic acid production process, which is produced by catalytic gas-phase oxidation reaction of propylene or acrolein, and in the distillation process in each process of producing acrylic acid ester from this acrylic acid and alcohol. The present invention can be effectively carried out by having this polymerization inhibitor present in the evaporation and condensation operations. As a preferred example, in a distillation column, the anti-coupling agent can be dissolved in the feed liquid or reflux liquid and introduced into the process.

The amount of the copper salt of dithiocarbamic acid composed of a cyclic amine varies depending on the type of acrylic acid and acrylic ester, or the processing conditions of the manufacturing process, but usually o, o o o
i~0.2% by weight, preferably 0.0005~0.1
It is used in concentrations in the range of % by weight.

The copper dithiocarbamate may be used in combination with other polymerization inhibitors, such as hydroquinone.

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

Example 1 10 CC of acrylic acid and various polymerization inhibitors shown in Table 1 were placed in a glass ampoule, and the angle was immersed in an oil bath at 95°C and shaken. The polymerization initiation time was determined from the time when acrylic acid in the ampoule began to dry up or the viscosity increased. The results are shown in Table 1.

(Margin below) Table 1 Example 2 As in Example 1, acrylic acid 2-
The test was carried out using ethylhexyl at an oil bath temperature of 140°C. The results are shown in Table 2.

Table 2 Example 3 In the same manner as in Example 1, butyl acrylate was used in place of acrylic acid and the oil bath temperature was 135°C.

The results are shown in Table 3.

Table 3 *Example M Example 4 After carrying out an esterification reaction of acrylic acid and 2-ethylhexanol according to a conventional method using para-toluenesulfonic acid as a catalyst, the reaction solution was mixed with 10% by weight of 7% caustic soda aqueous solution and water. The catalyst and acrylic acid were removed.

To this reaction washing solution, 0.01% by weight of hexamethylene dithiocarbamine was added, and a glass batch distillation column (bottom flask capacity: 2 t, column diameter: 50 m) was used to carry out 5 to 6 Raschig rings.
0. It is filled to a height of . ) was prepared and distilled. At this time, the pressure at the top of the column was set to 20 Tarr, and distillation was carried out until the bottom of the column reached 140°C. The recovery rate of acrylic 2-ethylhexyl was 99%, the bottom residue was 2.3% based on the charge liquid, and the viscosity of the residue liquid was not particularly changed.

Ratio example 1 Real: gm [! The procedure was carried out in the same manner as in IIJ 4, except that 0.05 wt. It was rising markedly.

Example 5 Acrolein was catalytically oxidized in the vapor phase with air using an oxidation catalyst mainly composed of molybdenum oxide in the presence of water vapor, and the resulting reaction gas was cooled and condensed and collected. Ethyl acetate (1:1
) to extract the acrylic component, and then operate a distillation column under reduced pressure so that the bottom temperature of the column reached 80° C. to separate ethyl acetate and acrylic acid.

At this time, 0.01% by weight of copper hexamethylene dithiocarbamate was added to the feed solution from the reflux solution.

When the apparatus was dismantled after continuous distillation for one month, only traces of the polymer were found. Further, there was no precipitate.

Claims (1)

[Claims] 1) Polymerization inhibitor for acrylic compounds consisting of copper dithiocarbamate salt represented by the following formula ▲ Numerical formulas, chemical formulas, tables, etc. are available ▼ [In the formula, R is alkylene having 2 to 8 carbon atoms] group and may contain atoms other than carbon and hydrogen]. 2) The polymerization inhibitor according to claim 1, wherein the copper dithiocarbamate salt is copper hexamethylene dithiocarbamate represented by the formula ▲ Numerical formula, chemical formula, table, etc. ▼.