JP2000080052A - Production of alkylene glycol - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an alkylene glycol by efficiently hydrolyzing an alkylene carbonate at a low temperature for a short time. SOLUTION: In continuously producing an alkylene glycol by hydrolyzing an alkylene carbonate, the reaction process is divided to a plurality of processes and a reaction pressure in each reaction process following the second stage is kept below a pressure of its preceding reaction stage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an alkylene glycol from an alkylene carbonate, and more particularly to a method for efficiently producing an alkylene glycol at a low temperature in a short time. Alkylene glycols, especially ethylene glycol, are used in raw materials for synthetic fibers and resins, antifreezes, and the like, and are industrially important compounds.

[0002]

2. Description of the Related Art As a method for producing an alkylene glycol, a method for hydrolyzing an alkylene carbonate is well known. This reaction is generally performed in the presence of a catalyst. In order to increase the reaction rate, for example, an alkali metal carbonate (US Pat. No. 4,117,250),
Molybdenum compounds (JP-B-55-154927), tungsten compounds (JP-B-55-154927)
And the like. The use of these catalysts accelerates the reaction, but the degree is not sufficient, and if the reaction is carried out at a high temperature to achieve an industrially satisfactory reaction rate, the quality of the product deteriorates. There was a problem that it would.

On the other hand, if the reaction is carried out at a low temperature for the purpose of ensuring quality, the reaction rate is reduced, and an excessive reactor capacity is required in order to obtain a desired production amount, or unreacted products are not contained in the product. Or an alkylene carbonate remained. However, during the production of ethylene glycol, which is the most important industrially, if ethylene carbonate remains, there is a problem that an azeotropic mixture with ethylene glycol is formed and separation / purification becomes difficult. Furthermore, if a large amount of water for hydrolysis is charged in order to improve the reaction rate, there arises a problem that a large amount of heat energy is required for heating during the reaction and for separating water in the purification system. That is, a method for producing an alkylene glycol by efficiently performing a hydrolysis reaction of an alkylene carbonate at a low temperature in a short time has not been found yet.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for efficiently producing an alkylene glycol at a low temperature in a short time by hydrolyzing an alkylene carbonate.

[0005]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have intensively studied a hydrolysis reaction method for alkylene carbonate, and as a result, divided the reaction step into a plurality of steps and reduced the operating pressure of the reaction step. The inventors have found that the reaction rate can be maintained at a high level by decreasing the rate as the process proceeds, and arrived at the present invention. That is, the gist of the present invention is that, when an alkylene glycol is continuously produced by hydrolyzing an alkylene carbonate, the reaction step is divided into a plurality of steps, and the reaction pressure in each of the second and subsequent reaction steps is reduced to the pressure in the preceding step. A method for producing an alkylene glycol, wherein the reaction is performed at a pressure equal to or lower than the pressure of the reaction step, and the reaction pressure of at least one reaction step of the second and subsequent reaction steps is lower than the pressure of the preceding step. Exist.

[0006] The gist of the present invention is the production method and the reaction pressure described above, wherein the reaction pressure of at least one of the second and subsequent reaction steps is 20 to 90% of the pressure of the preceding reaction step. Is 0.1 to 5 MPa, the above-mentioned production method wherein the reaction temperature is 50 to 200 ° C.,
And the alkylene carbonate is ethylene carbonate or propylene carbonate.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The reaction between the alkylene carbonate and water is represented by the following formula (1).

[0008]

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In the present invention, the reaction step is divided into a plurality of steps, the reaction pressure of the second and subsequent reaction steps is set to be lower than the reaction pressure of the preceding step, and at least one reaction step of the second and subsequent reaction steps is performed. The reaction is carried out at a pressure lower than that of the preceding stage. In particular, in making the reaction pressure in the second and subsequent stages lower than the reaction pressure in the preceding stage, it is preferable that the pressure be 20 to 90% of the pressure in the preceding stage.
If the pressure in a certain reaction step is rapidly reduced so as to be less than 20% of the pressure in the preceding step, the reaction solution tends to boil,
On the other hand, when it exceeds 90%, the effect of lowering the pressure is reduced, and the reaction rate may be reduced.

In the present invention, the reaction pressure in each of the divided reaction steps is preferably equal to or higher than the vapor pressure of the reaction solution in that step. When the reaction pressure is lower than the vapor pressure, the reaction liquid boils, the concentration of water in the liquid phase decreases, and the rate of the hydrolysis reaction decreases, and the amount of heat for heating is consumed as heat of vaporization and energy is consumed. Is also disadvantageous. The vapor pressure of the reaction solution refers to a saturated vapor pressure calculated from the composition of the reaction solution excluding carbon dioxide and the temperature of the reaction step.

The reaction pressure in the present invention is 0.1
-5 MPa, preferably 0.2-3 MPa. If the reaction pressure is lower than 0.1 MPa, the reaction liquid tends to boil as described above, while if the reaction pressure is higher than 5 MPa, equipment costs increase due to pressure resistance and the like, which is not economical. The reaction temperature to which the method of the present invention is applied is desirably in the range of 50 to 200 ° C. If the reaction temperature is lower than 50 ° C., the reaction rate is too low to be practical. On the other hand, when the reaction is performed at a high temperature exceeding 200 ° C.,
The quality of the product, alkylene glycol, is often poor. A reaction temperature with a better balance between reaction rate and product quality is in the range of 80-180C.

Since this reaction is an endothermic reaction, it is necessary to heat the system in order to proceed the reaction while maintaining the above reaction temperature. Commonly used heating methods include indirect heating through a jacket or coil with a high-pressure steam or a heat source such as an electric heater, or blowing steam (steam) with a vapor pressure higher than the reaction pressure into the reaction system. For example, a method of directly heating. In the method of the present invention, the number of reaction steps is desirably 2 to 8 steps.
If the number of steps is more than eight, there is a problem in that the construction cost of the equipment increases and the control of the reaction process becomes complicated. As a method of dividing a reaction step into a plurality of steps, it is general to provide a number of reactors corresponding to the number of steps. For example, one reactor is divided into a plurality of portions by partition walls and used. You may.

The molar ratio of water to alkylene carbonate in the reaction raw materials used in the present invention is preferably in the range of 1 to 5. A more preferred molar ratio is 1.3 to 5. If the molar ratio is less than 1, the water concentration in the reaction solution decreases as the hydrolysis of the alkylene carbonate progresses, so that it takes a long time to complete the reaction or the amount of impurities generated increases. On the other hand, if the molar ratio is higher than 5, high energy is required for heating the reaction system and removing excess water,
Not economic. Examples of the reactor that can be used in the method of the present invention include a tank reactor, a multi-stage reactor, and a reactive distillation column. In any case, it is necessary to efficiently separate carbon dioxide (carbon dioxide) generated by hydrolysis from the reaction system.

Although the hydrolysis reaction of the alkylene carbonate proceeds without a catalyst, it is more preferably carried out in the presence of a catalyst. Examples of suitable catalysts for use in the method of the present invention include sodium hydroxide, alkali metal hydroxides such as potassium hydroxide, sodium bicarbonate, alkali metal bicarbonates such as potassium bicarbonate, sodium carbonate, Examples thereof include carbonates of alkali metals such as potassium carbonate, ammonium salts such as tetrabutylammonium hydroxide and tributylmethylammonium iodide, and phosphonium salts such as tetrabutylphosphonium hydroxide and tributylmethylphosphonium iodide.

As a method for producing an alkylene glycol, a method of reacting an alkylene oxide with water in the presence of carbon dioxide is also known. Since this reaction is also via an alkylene carbonate as an intermediate,
By applying the present invention at the stage of completing the reaction for obtaining the alkylene glycol, the hydrolysis of the alkylene carbonate can be performed efficiently. The alkylene carbonate targeted by the method of the present invention is preferably an alkylene group having 2 to 30 carbon atoms,
Among them, ethylene carbonate and propylene carbonate, which are industrially important, are suitable. Particularly, when applied to ethylene carbonate having an azeotropic property with water, the effect is great. The alkylene group may have 1 carbon atom as a substituent.
It may have one or more than about 12 alkyl groups.

[0016]

EXAMPLES Hereinafter, the embodiments of the present invention will be described more specifically with reference to Examples, but the present invention is not limited to the Examples unless it exceeds the gist thereof. <Example> A reactor in which two tank-type reactors are connected in series (a first-stage reactor volume of 20 L and a second-stage reactor volume of 20 L)
L) was mixed with 5.6 of a mixture of ethylene carbonate, water and potassium carbonate (molar ratio = 1.0: 4.0: 0.005).
It was continuously supplied at a flow rate of kg / hr. The reaction temperature was set at 150 ° C. for both stages, and heating was performed with an electric heater to maintain this temperature. The reaction pressure was 0.65 in the first stage.
MPa, and the second stage was 0.30 MPa. The composition of the reaction solution at the outlet of each reaction stage was measured by gas chromatography, and the consistent conversion of ethylene carbonate and the conversion at each reaction stage were calculated. The results are summarized in the table.

<Comparative Example 1> A hydrolysis reaction of ethylene carbonate was carried out in the same manner as in the above Example, except that the pressure in the second-stage reactor was 0.65 MPa, which was the same as that in the first-stage reactor. The conversion of ethylene carbonate at the outlet of each reaction stage was measured in the same manner as in the above example. The results are shown in the table.

<Comparative Example 2> A hydrolysis reaction of ethylene carbonate was carried out in the same manner as in Comparative Example 1 except that the pressure in the first and second stage reactors was changed to 0.30 MPa.
The conversion of ethylene carbonate was measured similarly. The results are shown in the table. Note that, under this condition, the reaction solution boiled in the first stage.
Is lower than.

[0019]

[Table 1] Conversion rate about 100%: detection limit (10 ppm) or less by gas chromatography

<Evaluation of Results> In the same reactor and the same residence time (the same charge rate), the final conversion of ethylene carbonate was about 100% in the examples, 99.1% in Comparative Example 1, and Better than 99.2% of Example 2.
In particular, the conversion in the second stage to which the method of the present invention was applied was about 100% in the example, whereas the comparative example in which the method was not applied was 86.3% in comparative example 1 and 91.63 in comparative example 2. There is a remarkable difference of 1%.

[0021]

By using the method of the present invention, the alkylene carbonate can be rapidly hydrolyzed, so that an alkylene glycol can be efficiently produced with a smaller reactor and a shorter residence time. .

Claims (5)

[Claims] When continuously producing an alkylene glycol by hydrolyzing an alkylene carbonate, the reaction step is divided into a plurality of steps, and the reaction pressure of each of the second and subsequent reaction steps is reduced by the reaction pressure of the preceding reaction step. A method for producing an alkylene glycol, wherein the reaction is carried out at a pressure equal to or lower than the pressure and at least one of the reaction steps in the second and subsequent reaction steps is lower than the pressure in the preceding step. 2. The method for producing an alkylene glycol according to claim 1, wherein the reaction pressure of at least one of the second and subsequent reaction steps is 20 to 90% of the pressure of the preceding reaction step. 3. The method for producing an alkylene glycol according to claim 1, wherein the reaction pressure is 0.1 to 5 MPa. 4. The method for producing an alkylene glycol according to claim 1, wherein the reaction temperature is 50 to 200 ° C. 5. The method according to claim 1, wherein the alkylene carbonate is ethylene carbonate or propylene carbonate.
5. The method for producing an alkylene glycol according to any one of items 4 to 4.