JPH10158309A - Purification of monomer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To purify a monomer by bringing a monomer solution containing sulfur compounds into contact with an aqueous solution of an alkali(ne earth) metal hypochlorite, then extracting the monomer thereby obtaining the monomer of high quality having no foreign smell. SOLUTION: A plastic waste that contains sulfur compounds and a resin containing more than 50wt.% of methyl methacrylate units or styrene units is thermally decomposed to prepare a monomer solution. This monomer solution is treated with an aqueous solution of an alkali(ne earth) metal hypochlorite and extracted or distilled thereby purifying the monomer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying a monomer solution containing a sulfur compound, and more particularly, to efficiently and economically advantageously use a small amount of a sulfur compound contained in a decomposition solution obtained by thermally decomposing waste plastic. The present invention relates to a method suitable for purifying a monomer with an emphasis on removal.

[0002]

[Technology of the United States] Methyl methacrylate (hereinafter, referred to as
This may be abbreviated as MMΛ) or methacrylic resin, styrene resin, MS resin, and the like obtained by polymerizing a monomer containing styrene as a main component are widely used as home electric appliances, automobile parts, and optical materials. It is known that these resins are easily depolymerized into monomers by thermal decomposition. However, when these resins are thermally decomposed, impurities mainly composed of sulfur compounds added at the stage of resinification remain and cannot be removed by the distillation operation, so that an unpleasant odor remains. Could not be monomer. Also, trace amounts of sulfur compounds contained in the decomposition solution could not be sufficiently removed with activated carbon or molecular sieve used as an impurity remover. For this reason, these waste plastics have conventionally been incinerated or landfilled.

[0003]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a monomer solution containing a sulfur compound, in particular, a decomposition solution containing a trace amount of a sulfur compound obtained by thermally decomposing waste plastic to purify a monomer solution having no sulfur odor. The purpose is to provide a method of obtaining.

[0004]

Means for Solving the Problems The present inventors have intensively studied a method for removing a sulfur compound contained in a pyrolysis solution, and as a result, the sulfur compound reacts with an oxidizing agent to react with the water-soluble compound. It has been found that since the compound is converted into a high-boiling compound, it can be easily removed by extraction and distillation. Furthermore, among the oxidizing agents, it has been found that an aqueous solution of an alkali metal salt or an alkaline earth metal salt of hypochlorous acid has high reactivity with a low-molecular-weight sulfur compound, thereby completing the present invention.

That is, the present invention provides a method for purifying a monomer solution containing a sulfur compound, particularly a monomer solution containing a sulfur compound obtained by thermally decomposing waste plastic.
A method for purifying a monomer, comprising subjecting a monomer solution to a contact treatment with an aqueous solution of an alkali metal salt or an alkaline earth metal salt of hypochlorous acid, followed by extraction and / or distillation.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention will be described below in detail. The present invention is a method for purifying a monomer solution containing a sulfur compound, particularly a monomer solution containing a trace amount of a sulfur compound obtained by thermally decomposing waste plastic.

[0007] The monomer solution used in the method of the present invention is not particularly limited as long as it is a monomer solution containing a monomer component containing a sulfur compound as a main component, but a sulfur compound obtained by thermally decomposing waste plastic is used. It is preferable that the decomposition solution is contained.

The waste plastic is not particularly limited, but may be methacrylic resin, styrene resin or MMA.
A waste plastic of another copolymer resin containing 50% by weight or more of a styrene unit or a styrene unit is preferably used. The present invention is effective as a method for using a decomposition solution obtained by thermally decomposing these as a monomer solution and purifying MMA and / or styrene monomer from the monomer solution. The decomposition solution usually contains a monomer such as MMA or styrene as a main component, and a sulfur compound (eg, methyl mercaptan, dimethyl sulfide, dimethyl disulfide, etc.) composed of various forms of organic sulfur compounds of about 1 to 100 ppm. And various other impurities such as plasticizers.

According to the present invention, by subjecting a odorant such as a sulfur compound to a water-soluble compound or a substance having a greatly different boiling point without losing monomers, the present invention provides a contact treatment with an aqueous oxidizing agent prior to extraction and distillation. In this method, a monomer which can be easily separated by ordinary extraction and distillation operations to obtain a monomer having substantially no off-flavor, particularly, a MMA and / or styrene monomer is obtained.

In the method of the present invention, an alkali metal salt or an alkaline earth metal salt of hypochlorous acid is used as an oxidizing agent, and among them, sodium, potassium and calcium salts are particularly preferable. These hypochlorites are used in aqueous solution. For example, the amount of 10% aqueous sodium hypochlorite used is generally 0.1 to 4 parts by weight, preferably 0.3 to 2 parts by weight, per 100 parts by weight of a monomer solution such as a pyrolysis solution. It is.

The contact treatment method and the reaction apparatus are not particularly limited, and it is sufficient to stir and contact the monomer solution and the aqueous solution in a kettle equipped with a stirrer, for example. The contact time is usually 0.1 to 30 minutes,
The temperature is not particularly limited, and it is advantageous to carry out the reaction at room temperature.

In the method of the present invention, an extraction step and / or a distillation step is applied after the contact treatment. However, no special extraction equipment or distillation equipment is required. It can be fed to an extraction and / or distillation process in a purification facility for purification and recovery of the target monomer. Of these, the use of a distillation step is preferred from the viewpoint of reducing the number of steps. For example, distillation and purification can be performed by mixing with a produced crude monomer.

[0013]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples, but the scope of the present invention is not limited by these examples. In addition,
In the following Examples and Comparative Examples, the purity of the monomer was determined by gas chromatography [GC-1 manufactured by Shimadzu Corporation].
4A].

Example 1 1 kg of waste acrylic resin was heated to 500 ° C. in a reaction vessel and distilled to obtain 1 liter of a decomposed liquid (specific gravity 0.98; MMA 9
0.7% by weight, containing 56 ppm of methyl mercaptan, 15 ppm of dimethyl sulfide, 35 ppm of dimethyl disulfide, etc.) were charged into a 2 liter flask equipped with a stirrer. 10 ml of a 10% aqueous solution of sodium hypochlorite and 90 ml of distilled water are added to the flask, and the mixture is stirred at room temperature for 5 minutes. After completion of the stirring, the mixture was allowed to stand and the lower aqueous phase was separated, and 100 ml of water was further added and stirred for 5 minutes.
The lower aqueous phase was separated. The obtained crude monomer liquid is transferred to a tray 2
A distillation apparatus incorporating a 0-stage Oldershaw rectification column was charged, and distilled under a normal pressure at a reflux ratio of 1.1.
750 ml of a 100.6 ° C. fraction were obtained. Purified M obtained
The purity of the MA monomer is 99.8%, and the odor is MMA.
No peculiar smell. No peak was detected by FPD-gas chromatography (gas chromatography with a flame photometric detector equipped with a sulfur filter), and the content of sulfur compounds was 0.01 ppm or less.

Comparative Example 1 In Example 1, 1 liter of the pyrolysis liquid of waste acrylic resin was charged into a distillation apparatus without treatment with an aqueous solution of sodium hypochlorite, and a fraction at 99.8 to 100.6 ° C. 750 ml were obtained. Although the purity of the obtained MMA monomer was 99.8%, an odor different from that of the MMA monomer was felt. According to the measurement by FPD-gas chromatography, 28
A peak corresponding to ppm was measured.

Example 2 1 kg of MS resin containing 65% of MMA and 35% of styrene
Was heated to 500 ° C. in a reaction vessel to distill 950 ml of a decomposition solution (specific gravity 0.95; MMA 55.3% by weight, styrene 22.9% by weight, methyl mercaptan 89 ppm, dimethyl sulfide 12 ppm, dimethyl disulfide 21 ppm, etc.). Was charged into a 2 liter flask equipped with a stirrer. 6 ml of a 10% aqueous solution of sodium hypochlorite and 100 ml of distilled water were added to the flask and stirred for 5 minutes. After completion of the stirring, the lower aqueous phase was separated, and 100
After addition of ml and stirring for 5 minutes, the lower aqueous phase was separated. The obtained crude monomer liquid was charged into the same distillation apparatus as in Example 1, and distilled under a normal pressure and a reflux ratio of 1.7, and the boiling point was 99.8 to 99.8.
At 100.6 ° C., a fraction of 520 ml was obtained. Purified M obtained
The purity of the MA monomer was 99.8%, and there was no off-odor. The presence of the sulfur compound was not recognized by FPD-gas chromatography.

Example 3 1 kg of waste styrene resin was heated to 500 ° C. in a reaction vessel and distilled out to 950 ml of a decomposition solution (specific gravity 0.92; styrene 7
2 wt%, containing 18 ppm of methyl mercaptan, 21 ppm of dimethyl sulfide, 44 ppm of dimethyl disulfide, etc.) were charged into a 2 liter flask equipped with a stirrer. In this flask, an aqueous solution of 0.5% hypochlorous acid was used, which was prepared by using a reagent powder [Ca (OCl) ₂ ].
Then, the mixture was stirred at room temperature for 5 minutes. After completion of the stirring, the mixture was allowed to stand, and the lower aqueous phase was separated. Further, 100 ml of water was added and the mixture was stirred for 5 minutes, and the lower aqueous phase was separated. The obtained crude styrene monomer liquid was charged into a distillation apparatus incorporating an Oldershaw rectification column having 20 trays, and distilled under a normal pressure at a reflux ratio of 1.4 to obtain a fraction having a boiling point of 144.8 to 145.5 ° C. 670 ml were obtained. The purity of the obtained styrene monomer was 99.7%, and the odor was peculiar to styrene, and there was no off-odor. Also, the presence of the sulfur compound was not recognized by FPD-gas chromatography.

[0018]

According to the present invention, it is possible to recover a high-quality monomer having no off-odor from waste plastics by converting sulfur compounds and the like into substances that can be selectively separated, which is industrially effective. It is.

Claims (3)

[Claims] In purifying a monomer solution containing a sulfur compound, the monomer solution is contacted with an aqueous solution of an alkali metal salt or an alkaline earth metal salt of hypochlorous acid, followed by extraction and / or distillation. A method for purifying a characteristic monomer. 2. The method according to claim 1, wherein the monomer solution is a decomposition solution obtained by thermally decomposing waste plastic. 3. The method for purifying a monomer according to claim 2, wherein the waste plastic is a resin containing at least 50% by weight of a methyl methacrylate unit or a styrene unit.