JP2000256221A - Purification of easily polymerizable compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently, safely and inexpensively purifying an easily polymerizable compound having a polymerizable double bond in the molecule, such as acrylic acid, methacrylic acid, an acrylate ester, a methacrylate ester or styrene by the vacuum-distillation of the compound. SOLUTION: This method for purifying an easily polymerizable compound comprises distilling a liquid containing the easily polymerizable compound such as acrylic acid, methacrylic acid, an acrylate ester, a methacrylate ester or styrene under vacuum. Therein, a water-sealed vacuum pump 1 is used as a pressure-reducing device. When the sealing water of the water-sealing vacuum pump is maintained at a temperature of <=30 deg.C and further when a process drain 7 is used as the sealing water, the effect of the purification is further improved. The sealing water is suitably cooled using a circulation line having a cooling device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to acrylic acid and methacrylic acid (both of which are collectively referred to as "(meth) acrylic acid").
And a method for purifying an easily polymerizable compound having a polymerizable double bond in the molecule, such as (meth) acrylic acid ester and styrene. More specifically, the present invention relates to a purification method for efficiently and safely purifying an easily polymerizable compound by distillation under reduced pressure.

[0002]

2. Description of the Related Art Compounds having a double bond, particularly a carbon-carbon double bond, in the molecule are generally rich in reactivity and easily polymerized. If polymerization occurs in the process of handling such compounds, especially in the purification process, it may cause a product yield decrease and equipment operation troubles due to adhesion of the polymer and clogging of piping etc. due to it. There is.
Therefore, when such an easily polymerizable compound is purified by distillation, phenothiazine,
A method in which methoxyhydroquinone, hydroquinone, various metals or their compounds, or a polymerization inhibitor such as oxygen or an oxygen-containing gas is added and distilled, and in addition, under a high vacuum to suppress the polymerization by lowering the processing temperature and suppressing the polymerization. A method of performing distillation and the like are widely used.

However, when distillation is performed under high vacuum, there are the following problems. (1) The structure of the distillation apparatus is complicated, and the airtightness of the joints such as the distillation tower and the pipes and the sealing parts of the equipment such as the pump is insufficient, and the air is usually slightly sucked into the system. . In a large-sized device, the amount of intake air is large, and the equipment is likely to be excessively large. (2) The non-condensable gas such as nitrogen inhaled in (1) is not preferable from the viewpoint of environment because it may accompany an organic component distilled off at the top of the tower when it is discharged out of the system. To prevent this, an exhaust treatment device must be added. Also,
Even in the case where distillation is performed by adding a polymerization inhibitor, it is more preferable to perform distillation at a low temperature. Therefore, distillation is generally performed under reduced pressure. Vacuum distillation and vacuum decompression devices for performing vacuum distillation include dry mechanical pumps such as reciprocating type (piston type) and roots type, wet mechanical pumps such as oil-sealed liquid Nash pump, oil-sealed rotary vacuum pump, and the like. Steam ejectors are widely used.

[0004]

However, in the case of ordinary dry mechanical vacuum pumps and wet mechanical vacuum pumps, even if a cooling device is provided in the front stage of the pump to condense and remove easily polymerizable compounds, the suction of the same is not possible. Since a small amount of easily polymerizable compound is mixed in the gas, the easily polymerizable compound accumulates in the pump and polymerizes, which may lead to troubles such as adhesion and blockage of the polymer, and eventually, equipment shutdown. . In addition, when a steam ejector is used, wastewater corresponding to the amount of drive steam is generated, and in the wastewater, an easily polymerizable compound that is an organic substance is dissolved.
A treatment facility such as an activated sludge facility for safely discharging this is required. In order to prevent the formation of an explosive mixed gas due to the condensation of organic substances and the formation of a polymer, a method of reducing the pressure with a water ejector has also been proposed (JP-A-10-204)
No. 030). However, in this case, as in the case of the steam ejector described above, the problem of drainage remains. An object of the present invention is to provide a method for efficiently, safely and inexpensively purifying an easily polymerizable compound from the above viewpoint.

[0005]

Means for Solving the Problems The present inventors have conducted various studies and evaluations on the above points and found that these problems can be solved by using a specific pressure reducing device. The invention has been reached. That is, the gist of the present invention is to provide an easily polymerizable compound, particularly (meth) acrylic acid and / or
Or a method for purifying an easily polymerizable compound using a water ring vacuum pump as a depressurizing device when distilling a liquid containing a (meth) acrylic acid ester under reduced pressure. Another gist of the present invention resides in that the temperature of the water seal liquid of the water ring vacuum pump is set to 3 degrees.
The above method of maintaining the temperature at 0 ° C. or lower, the above method of using process wastewater as a water sealing liquid, and the above method of cooling the water sealing liquid by a circulation line having a cooling device also exist.
Still another aspect of the present invention is the above-described method of continuously or periodically extracting a water sealing liquid and recovering organic components from the extracted water sealing liquid, and supplying an inert gas to the exhaust of a water sealing vacuum pump. The method for purifying an easily polymerizable compound described above also exists.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The water ring vacuum pump used in the present invention uses water as a sealing liquid (sealing liquid). As used herein, “water” can be used as long as it contains water as a main component, as long as the object of the present invention is not hindered. As a vacuum pump that can be used in this manner, a Nash type vacuum pump can be exemplified, and specifically, ANVH manufactured by Awamura Seisakusho
Mold, SONIT type, SLPH type manufactured by Shin Nippon Machinery Co., Ltd. and the like. In the vacuum distillation of the easily polymerizable compound, the easily polymerizable compound corresponding to the vapor pressure that cannot be completely condensed by the condenser from the overhead distillate gas enters a vacuum pump through a pressure reducing line, and a part or almost all of the compound is here. Condense.
In the present invention, since water is used as the sealing liquid in the vacuum pump, the condensed easily polymerizable compound is dissolved or dispersed in water to form a dilute aqueous solution or aqueous dispersion. Therefore,
Polymerization is less likely to occur, and the risk of trouble due to the formation of the polymer is reduced.

However, if driving is continued for a long time,
Since the easily polymerizable compound accumulates in the water-sealing liquid, and as a result, a polymer is likely to be formed, it is preferable to continuously or periodically extract the water-sealing liquid. The water-sealed liquid containing the extracted easily polymerizable compound can be recovered by supplying it to a distillation column or the like. When extracting the water seal liquid, if the distillate gas at the top contains moisture, etc., it may not be necessary to add the water seal liquid. Need additional supply. When there is water by-produced in the process, it is preferable to use this by-produced water as a water sealing liquid to be supplied, because the amount of drainage can be reduced. Examples of the by-product water from such a process include water generated in an oxidation step in the production of (meth) acrylic acid and water generated in an esterification reaction in the production of (meth) acrylic acid ester.

The lower the temperature of the water sealing liquid, the lower the vapor pressure of water and easily polymerizable compounds dissolved and dispersed in water, so that the ultimate vacuum of the vacuum pump can be increased. It is preferable because operation becomes possible. In the vacuum pump, the temperature tends to increase due to adiabatic compression of the compressed gas. Therefore, in order to prevent polymerization of the easily polymerizable compound in the vacuum pump, the temperature of the water seal liquid is kept low. Is preferred.

In the present invention, the water-sealed liquid is kept at 30 ° C. or less,
It is effective to keep the temperature preferably at 25 ° C. or lower, more preferably at 20 ° C. or lower, for preventing the formation of a polymer or the like. Further, the temperature control of the water sealing liquid is preferably performed by a method using a thermometer installed inside the vacuum pump or a method of measuring the outlet temperature of the water sealing liquid from the vacuum pump because the temperature of the water sealing liquid can be directly controlled. However, the management may be performed based on the correlation between the temperature of the above-described portion of the vacuum pump and the temperature and amount of the water seal liquid to be supplied.

In order to efficiently perform the above-described extraction of the water sealing liquid and control of the temperature, for example, as shown in FIG. 1, “drawing of water sealing liquid from vacuum pump (1) —gas-liquid separation” It is preferable to provide a circulation line for performing “(2) -cooling (3) -supply to vacuum pump”. This circulation line may be provided with a pipe (5) for discharging the water seal liquid outside the system and adding / supplying the water seal liquid from outside the system as necessary. The temperature control of the water-sealing liquid may be performed by a method of supplying and mixing a water-sealing liquid that has been cooled in advance, in addition to the above-described heat exchanger provided in the circulation line. The water-ring vacuum pump has a limit to the degree of vacuum that can be reached due to the vapor pressure of the water-sealing liquid. The same applies hereinafter)
It can be operated at the following pressure, usually 50 torr or less. If it is necessary to operate at a lower pressure than this, for example, a water ring vacuum pump and a pressure reducing device such as a steam ejector may be used in combination. In order to prevent the water seal liquid from freezing, for example, an inorganic compound having a small wastewater load such as sodium chloride, magnesium chloride, calcium chloride, sodium sulfate, and magnesium sulfate, or ethylene glycol, methanol, or the like may be added to the water seal liquid. . However, when a large amount of alcohol having a low boiling point is added, the vapor pressure of the water sealing liquid increases, and the degree of reduced pressure that the vacuum pump can reach decreases. When an aqueous solution is used as the water sealing liquid, it is preferable to use one having a vapor pressure at 30 ° C. of 70 torr or less.

When an organic solvent is used as the sealing liquid, there is a possibility that an explosive mixed gas may be formed by the vapor. In addition, the cost of the organic solvent itself and an apparatus for recovering the organic solvent used as the sealing liquid may be used. Expensive and not economical. In order to more effectively suppress the polymerization reaction of the easily polymerizable compound, it is preferable to previously dissolve the polymerization inhibitor in the water sealing liquid. As the polymerization inhibitor that can be used here, the above-mentioned hydroquinone, methoxyhydroquinone and the like may be appropriately selected and used. Withdrawal of the water seal liquid may be performed from a part of the circulation pipe,
When the gas-liquid separator is in the circulation line, it is common to withdraw the liquid phase while monitoring the liquid level. When the easily polymerizable compound is a compound having low solubility in water such as styrene, butyl (meth) acrylate, and 2-ethylhexyl acrylate, phase separation occurs in the gas-liquid separator to form an oil layer. May be done. In this case, an oil layer can be efficiently collected by providing an overflow pipe from the gas-liquid separator.

Normally, the extracted water-sealed liquid is used to separate and recover organic components using a distillation column or the like, and the organic components are returned to an appropriate step in the process. And discharge it out of the system. The recovery of the organic substance component from such a water sealing liquid is performed, for example, when a device such as a distillation column for collecting the organic substance component from the reaction product water is used, as in a process for producing a (meth) acrylate ester. It is reasonable to carry out in the distillation facility.

As the easily polymerizable compound to which the method of the present invention can be applied, unsaturated carboxylic acids such as acrylic acid and methacrylic acid, methyl methacrylate, butyl acrylate, octyl acrylate, 2-hydroxyethyl acrylate, Examples thereof include unsaturated carboxylic esters including (meth) acrylic esters such as 2-hydroxypropyl acrylate and butyl methacrylate, acrylic compounds such as acrylonitrile and acrylamide, and aromatic vinyl compounds such as styrene. The method of the present invention is particularly effective when the boiling point of the easily polymerizable compound is 80 ° C. or higher. When the boiling point of the easily polymerizable compound is 80 ° C. or lower, it is often unnecessary to perform the distillation under reduced pressure.

In the distillation, a method using an organic solvent such as toluene or methyl isobutyl ketone as an azeotropic solvent is also employed. When purifying a mixture containing such a compound or a compound having a flash point of 30 ° C. or lower such as methyl methacrylate, a gas mixture in an explosive range may be formed on the exhaust side of the vacuum pump. To prevent this, take measures such as supplying an inert gas such as nitrogen or carbon dioxide to the exhaust gas of the vacuum pump to lower the oxygen concentration in the exhaust gas and avoid the gas composition in the explosion range. Is preferable for safety. The gas discharged from the gas-liquid separator in the circulation line contains a large amount of components distilled at the top of the distillation column. Further, when an oxygen-containing gas is supplied to the bottom of the column for preventing polymerization, such as a distillation column for (meth) acrylic acid or (meth) acrylate, oxygen is also contained in the exhaust gas. Therefore, by supplying this exhaust gas to the distillation column, it becomes possible to reduce the amount of exhaust gas at the same time as the recovery of organic components. The method for purifying an easily polymerizable compound of the present invention is applicable not only when the target substance is an easily polymerizable compound, but also when removing and purifying light impurities in a reaction product liquid, or when separating an easily polymerizable compound from water. It can also be applied to the separation of heavy impurities in easily polymerizable compounds.

[0015]

EXAMPLES Hereinafter, the present invention will be described in more detail and specifically with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. <Example 1> Dehydration distillation of an aqueous solution of acrylic acid using toluene as an azeotropic agent was performed using a glass distillation apparatus. The distillation column was a glass cylinder having a diameter of 50 mm and packed with a Raschig ring of 3 mm to a height of 90 cm (the number of theoretical plates was 1).
5 steps). A 1-liter flask is connected to the bottom, and a water-cooled condenser is connected to the top. The outlet of the condenser was connected to a water ring vacuum pump to perform vacuum distillation.

The water-sealing liquid was withdrawn at a rate of 1 liter per hour, and at the same time, fresh water-sealing liquid was supplied so that the water-sealing liquid level of the vacuum pump was constant. This water sealing liquid was cooled at 8 ° C. by a refrigerator (ethylene glycol / water = 10% / 9).
(0%), the distillate condensed in the overhead condenser maintained at 18 ° C. is separated by standing in a decanter (gas-liquid separator), the entire azeotropic agent layer is refluxed to the distillation column, and the aqueous layer is withdrawn. Was. The distillation column was heated by heating the flask using an oil bath equipped with an oil temperature controller. As a raw material liquid for distillation, 55% by weight of acrylic acid, 1.5% by weight of acetic acid, 0.3% by weight of formaldehyde and a small amount of formic acid,
An aqueous solution of acrylic acid containing acetaldehyde, formaldehyde, and acrolein was used and supplied to the middle stage of the distillation column at a rate of 280 g / h together with 14 ml / h of toluene (azeotropic agent).

The operating pressure of the distillation column was controlled at 180 torr, and hydroquinone and phenothiazine were supplied as polymerization inhibitors from the top of the column, and air was supplied to the bottom (flask) of 15 ml / h. The bottom liquid was withdrawn by a pump so as to keep the liquid level in the flask constant. The supply amounts of these were adjusted so that the concentration of the polymerization inhibitor in the bottoms became 800 ppm for hydroquinone and 500 ppm for phenothiazine. At this time, the top temperature was 49 ° C., and the bottom temperature (bottoms) was 86 ° C. The reflux rate of the azeotropic agent at the top of the column was 750 ml / h. When the composition of the exhaust gas from the vacuum pump was confirmed by gas chromatography, the concentration of toluene as an azeotropic agent was 2%, which was in the explosion range. Driving while adjusting to become. After the distillation column was stabilized, distillation was performed continuously for 7 hours. After the distillation was completed, the vacuum pump was checked, but no formation or adhesion of the polymer was observed.

<Comparative Example 1> Acrylic acid aqueous solution was subjected to azeotropic dehydration distillation in the same manner as in Example 1 except that an oil seal type rotary vacuum pump was used as a vacuum pump. During the distillation operation (four hours after the start of the stable operation), the degree of vacuum could not be maintained, and the operation was stopped.

Example 2 A 20% ethylene glycol aqueous solution was used as a water seal liquid of a water seal vacuum pump, and the temperature of the water seal liquid was maintained at -3 ° C. in the same manner as in Example 1. A distillation operation was performed. The concentration of toluene in the exhaust gas of the vacuum pump was 0.8%, which was out of the explosion range.

Example 3 Acrylic acid aqueous solution was subjected to azeotropic distillation in the same manner as in Example 1 except that methyl isobutyl ketone was used instead of toluene as an azeotropic agent.
However, the entire amount of the azeotropic agent was not refluxed, the top liquid was continuously withdrawn, and 180 g of methyl isobutyl ketone was supplied per hour as a reflux liquid from the top of the column. After the distillation column was stabilized, distillation was performed continuously for 7 hours. After the distillation was completed, the vacuum pump was checked, but no formation or adhesion of the polymer was observed.

Example 4 Ethyl acrylate containing 0.05% of ethyl acetate, 0.2% of acrylic acid, and hydroquinone as a polymerization inhibitor was used as a raw material liquid at a rate of 30% per hour.
Ethyl acrylate was purified in the same manner as in Example 1 except that 0 g was supplied and ethyl acrylate containing methoxyquinone was supplied from the top of the column together with the reflux liquid. When the pressure at the top was controlled at 150 torr and the distillation ratio was operated at 2.0, ethyl acrylate containing 0.05% ethyl acetate was obtained from the top of the column. The overhead temperature was 60 ° C. After continuous operation for 7 hours in the same manner as in Example 1, the vacuum pump was checked, but no formation or adhesion of the polymer was observed.

Example 5 Purification of ethyl acrylate was carried out in the same manner as in Example 4 except that the temperature of the water-sealing liquid of the water-sealing vacuum pump was controlled at 40 ° C., and the water-sealing liquid was not withdrawn. Was done. After the operation for 7 hours, the vacuum pump was inspected. As a result, no formation or adhesion of the polymer was observed, but the viscosity of the water sealing liquid was increased.

Example 6 A reactive distillation apparatus made of glass (reactor capacity at the bottom of the tower was 1 liter) was used to carry out esterification reactive distillation of acrylic acid and butanol. 150 ml of strongly acidic ion exchange resin (PK-216: manufactured by Mitsubishi Chemical) as a catalyst, at a temperature of 80 ° C. and a pressure of 150 torr.
While stirring the reaction solution under a reduced pressure of r, 144 g / h of acrylic acid and 148 g / h of butanol were supplied as raw materials to the reactor, respectively. 288 m / h of slurry-like reaction liquid
The reactor was continuously withdrawn at a rate of 1 l. Since the reaction solution in the form of slurry contained 20% by volume of the ion exchange resin, the ion exchange resin was separated and continuously returned to the reactor together with the feedstock.

After the top liquid of the reactive distillation column was phase-separated into an oil layer and an aqueous layer, the aqueous layer was extracted and the oil layer was returned to the top of the column. The aqueous layer was distilled to recover butanol, which was recycled to the reactive distillation column. The condenser outlet at the top is connected to a water-sealed vacuum pump. The water-sealed liquid of the pump is maintained at 18 ° C. and fresh water is supplied at a rate of 1 liter / hour so that the level of the water-sealed pump is constant. Replaced with sealed liquid. After the distillation column was stabilized, distillation was performed continuously for 7 hours. After the distillation was completed, the vacuum pump was checked.
No polymer formation or adhesion was observed.

<Example 7> Distillation was carried out in the same manner as in Example 1 except that water separated into liquid and liquid from toluene was recovered and used at the top of the tower as a water seal liquid to be supplied to a water ring vacuum pump. Carried out. After continuous operation for 7 hours, the vacuum pump was checked, but no formation or adhesion of polymer was observed.

Example 8 As a water seal liquid to be supplied to a water ring vacuum pump, except that water obtained by distilling and recovering butanol from a distillate at the top of the column and again removing butanol by distilling the aqueous layer was used. Was subjected to reactive distillation in the same manner as in Example 6.
After the distillation column was stabilized, distillation was continuously performed for 7 hours. After the distillation was completed, the vacuum pump was checked, but no formation or adhesion of a polymer was observed.

[0027]

By using the purification method of the present invention,
In vacuum distillation of an easily polymerizable compound, it is possible to solve the problem of troubles such as blockage of vacuum equipment due to formation and adhesion of a polymer. Further, by using process wastewater generated by a reaction or the like as a water seal liquid, the amount of wastewater can be reduced, and the industrial value is high.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a liquid circulation line of a water ring vacuum pump according to the present invention.

[Explanation of symbols]

 1: Water-sealed vacuum pump 2: Gas-liquid separator 3: Heat exchanger 4: Vacuum line (suction) 5: Water-sealed liquid supply line 6: Exhaust 7: Drain 8: Inert gas 9: Cooling water

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yukihiro Hasegawa 1 Tohocho, Yokkaichi-shi, Mie F-term in Yokkaichi Office of Mitsubishi Chemical Corporation (Reference) 4D076 AA07 AA16 AA16 AA22 BB04 BB08 CC12 CD22 DA10 DA21 DA22 EA02Y EA02Z EA03Z EA04Z EA06Z EA12Y EA14Y EA16Y EA17Y EA20Z GA01 GA03 GA05 HA03 4H006 AA02 AD11 BC52 BS10

Claims (7)

[Claims] 1. A method for purifying an easily polymerizable compound, wherein a water ring vacuum pump is used as a depressurizing device when distilling a liquid containing the easily polymerizable compound under reduced pressure. 2. The method for purifying an easily polymerizable compound according to claim 1, wherein the easily polymerizable compound is (meth) acrylic acid and / or (meth) acrylate. 3. The temperature of the water seal liquid of the water ring vacuum pump is set to 30.
The method for purifying an easily polymerizable compound according to claim 1, wherein the temperature is maintained at a temperature of not more than ℃. 4. The method for purifying an easily polymerizable compound according to claim 1, wherein process wastewater is used as a water sealing liquid. 5. The method for purifying an easily polymerizable compound according to claim 1, wherein the water sealing liquid is cooled by a circulation line having a cooling device. 6. A water sealing liquid is continuously or periodically withdrawn.
The method for purifying an easily polymerizable compound according to any one of claims 1 to 5, wherein the organic component is recovered from the extracted water sealing liquid. 7. The method for purifying an easily polymerizable compound according to claim 1, wherein an inert gas is supplied to the exhaust of the water ring vacuum pump.