JPH03223267A - Preparation of epichlorohydrin - Google Patents

Abstract

PURPOSE:To prepare epichlorohydrin in high conversion and yield by preliminarily reacting dichloropropanol with an alkali, feeding the preliminary reaction product into a reaction distillation tower and subsequently subjecting the product to the remaining dehydrochlorination reaction in the tower. CONSTITUTION:2,3-Dichloro-1-propanol and/or 1,3-dichloro-2-propanol is preliminarily treated with an aqueous solution or suspension containing 0.05-0.4 molar equivalent of an alkali (e.g. CaOH) at 10-40 deg.C. The preliminarily treated product is continuously fed into a reaction distillation tower together with 1.15-0.7mol equivalent of an alkali for the remaining dehydrochlorination reaction to provide the objective compound. The epichlorohydrin is useful as a raw material for epoxy resins or synthetic rubbers, as a stabilizer for chlorinated rubbers, or as an intermediate or starting substance for glycidyl ethers, amine adducts or others.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention dehydrochlorinates 2,3-dichloro-1-propanol and/or 1,3-dichloro-2-propanol using an alkali to produce epichlorohydrin. It relates to a manufacturing method.

[Conventional technology]

Epichlorohydrin is a raw material for epoxy resins and synthetic rubber.
It is used in large quantities as a stabilizer for chlorinated rubber, glycidyl ethers, glycidyl esters, glycerin and its derivatives, amine adducts, and other intermediates or starting materials.

Epichlorohydrin is a mixture of 2,3-dichloro-1-propanol and 1,3-dichloro-2-propanol, which is conventionally obtained by the reaction of allyl chloride with chlorine water, and a low concentration aqueous solution of about 3 to 5% by weight, which is obtained by reacting allyl chloride with chlorine water. It is used industrially by mixing a suspension of an alkali such as calcium oxide, feeding it to a plated reactive distillation column, dehydrochlorinating it and stripping it with steam, and extracting the epichlorohydrin produced from the top of the column. Manufactured. Since the dichloropropanol obtained by this method is obtained as a low-concentration aqueous solution as described above, it is maintained within a sufficient solubility range in the liquid phase in the column, and no decrease in the reaction rate is observed. On the other hand, a large amount of steam is required for stripping the product.

In order to improve the water vapor consumption rate, a method has been proposed in which dichloropropanol is used at a high concentration of 10 to 50% by weight based on the total weight of the liquid fed to the reactive distillation column (Japanese Patent Laid-Open No. 60-258172). issue). However, it has been found that using dichloropropanol at such a high concentration lowers the apparent reaction rate compared to when using a dilute solution as described above. In other words, high concentrations of dichloropropanol in the feed solution excluding alkaline content, such as 50 to 80% by weight, have recently become available, but the solubility of dichloropropanol in water is 20% at 60°C in an aqueous solution. Below, it is 30% or less at 80°C, and further decreases due to the salting out effect due to the salt generated during the reaction. Further, the distribution ratio of dichloropropanol to the product epichlorohydrin and water is approximately 10:1. Therefore, it is presumed that the dichloropropanol concentration in alkaline water becomes low and the apparent rate of dehydrochlorination decreases.

As the reaction rate decreases, dichloropropanol in the overhead distillate increases. If the residence time in the column is increased, the conversion rate of dichloropropanol increases, but the selectivity of epichlorohydrin decreases due to consumption by sequential reactions. It is possible to separate the distilled dichloropropanol by distillation and recycle it, but if there is a large amount to be recycled, the amount to be processed in the distillation column will increase, which will increase both equipment costs and energy costs, and the amount of loss will also increase. I don't like it because it causes harmful effects.

As a method to solve these problems, a method has been proposed in which a portion of the alkaline component is supplied above the dichloropropanol supply position (Japanese Patent Application Laid-open No. 17874/1983).
In this method, the produced epichlorohydrin has an increased chance of coming into contact with alkaline components again during the process of being stripped by steam, so stripping while preventing the ring-opening reaction of epichlorohydrin is important from both the column design and stable operating conditions. involves great difficulty.

The applicant previously discovered that when producing epichlorohydrin by supplying dichloropropanol and an aqueous alkali solution or suspension to a plated reactive distillation column, dichloropropanol was produced as an overhead distillate using a partial condenser. We proposed a method that allows epichlorohydrin to be obtained in high yield with a high conversion rate of dichloropropanol, even when the concentration of dichloropropanol in the feed solution is high, by condensing the part enriched with dichloropropanol and refluxing it to a distillation column. (Tokuganhira [281
419). However, as described above, a decrease in the apparent reaction rate due to the high concentration of dichloropropanol is unavoidable, and it is not necessarily easy to compensate for this by controlling the operation of the partial condenser alone.

[Problem to be solved by the invention]

An object of the present invention is to provide a method for increasing both the conversion rate of dichloropropanol and the selectivity of epichlorohydrin when high-concentration dichloropropanol is supplied to a reactive distillation column together with an aqueous alkali solution or suspension.

[Means and effects for solving the problem] The present inventors,
2.3-dichloro-1-propanol and/or 1.3
- When dichloropropanol consisting of dichloro-2-propanol is supplied to the reactive distillation column, the concentration of dichloropropanol in the mixture is increased by pre-treating it with an alkali component in an amount that does not reach the molar equivalent of the dichloropropanol and at a low temperature. The present invention was accomplished by discovering a method for obtaining epichlorohydrin at a high yield with a high conversion rate of dichloropropanol by reducing the apparent reaction rate that occurs when a highly concentrated dichloropropanol solution is used.

That is, the present invention provides 1 of 2,3-dichloro-1-propanol and/or 1,3-dichloro-2-propanol.
When producing epichlorohydrin by a dehydrochlorination reaction using an alkaline aqueous solution or suspension containing an alkaline component of 1 to 1.2 molar equivalents, 0.05 to 0.4 molar equivalents of dichloropropanol are added in advance to the above dichloropropanol. of alkali components are mixed at 10 to 40°C to partially dehydrochlorinate the mixture, and then continuously fed to a reactive distillation column together with 1.15 to 0.7 molar equivalents of alkali components to dehydrochlorinate the remainder. This is a method for producing epichlorohydrin characterized by stripping the produced epichlorohydrin with steam and extracting it from the top of the column.

The dichloropropanol used in the present invention may be 2,3-dichloro-1-propanol as described above, or 1
, 3-dichloro-2-propanol, or a mixture thereof.

The alkaline compounds used in the dehydrochlorination reaction are alkali metal or alkaline earth metal hydroxides, oxides, or salts with weak acids, such as sodium hydroxide, calcium hydroxide, potassium hydroxide, sodium carbonate, and carbonic acid. Potassium, calcium oxide, barium oxide, etc. are used as an aqueous solution or suspension. The amount used is 1.0 to 1.2 of the theoretical amount required for the dehydrochlorination reaction of dichloropropanol.
It's double. The concentration of the alkaline aqueous solution or suspension used here is suitably 3 to 15% by weight in view of ease of handling and solubility of dichloropropanol.

Before supplying dichloropropanol to the reactive distillation column, 0.0.
A preliminary reaction is performed at 10 to 40° C. with an alkaline aqueous solution or an alkaline suspension containing an alkali content of 0.5 to 0.3 molar equivalents to partially dehydrochlorinate the mixture.

As dichloropropanol, the crude product derived from the previous step can be directly dehydrochlorinated by the method of the present invention without being purified. Crude products often contain hydrogen chloride, so alkali is required for neutralization. In this case, the total amount of the above alkaline content and the alkaline content required for neutralization may be supplied during the preliminary reaction. Even when dichloropropanol containing hydrogen chloride is used in this way, if the preliminary reaction according to the present invention is carried out, the hydrogen chloride concentration can be reduced to substantially zero in the raw material feedlot of the reactive distillation column. It is effective in preventing unsteady neutralization reactions and dehydrochlorination reactions, and in preventing column corrosion due to the presence of acids.

The pre-reacted dichloropropanol is supplied to the reactive distillation column at a predetermined flow rate. The remaining alkali content used in the pre-reaction may be mixed with the dichloropropanol mentioned above just before the feed-drop to the tower and supplied from one feed-drop; however, the conversion rate of dichloro-propanol in the pre-reaction must be strictly controlled. In order to keep the composition of the mixture constant and to quickly stabilize the reaction in the reactive distillation column and maintain a steady state, it is desirable to feed from another feeder provided at the same stage of the column. Alternatively, this alkaline content may be supplied mixed with the condensate of the dephlegmator. When the epichlorohydrin produced in the pre-reaction is supplied to the column, it easily transfers to the gas phase, and the concentration of dichloropropanol in the liquid phase is lower than when the pre-reaction was not performed, so the solubility decreases accordingly. The resulting apparent decrease in reaction rate is suppressed.

Furthermore, by increasing the conversion rate of dichloropropanol in advance through a preliminary reaction, the residence time in the column can be shortened, and the number of plates in the column can also be reduced.

Coupled with the fact that the alkali concentration within the column can be reduced accordingly, the formation of by-products can be reduced and the selectivity of epichlorohydrin can be increased. Furthermore, in industrial production, the height of the tower can be reduced, which is effective in reducing plant costs including the frame and other incidental equipment. In order to obtain such an effect, the molar equivalent ratio of dichloropropanol and alkali component and the temperature are important in the preliminary reaction. When the alkali content is less than 0.05 molar equivalent per molar equivalent of dichloropropanol, almost no improvement effect is obtained, and this is equivalent to the case where the alkali content is immediately supplied to the column and reacted without performing a preliminary reaction. Also, the alkaline content is 0.
If the amount exceeds 3 molar equivalents, the conversion rate of dichloropropanol will increase and the amount of by-products will increase, resulting in a decrease in the selectivity of epichlorohydrin and a loss of epichlorohydrin that cannot be ignored, making it impossible to obtain the effect of the pre-reaction and causing no effect. It is the meaning. If the temperature of the pre-reaction exceeds 40° C., consumption of the produced epichlorohydrin by hydrolysis and addition reaction with the produced salt is promoted, resulting in a decrease in the selectivity of epichlorohydrin after the completion of the entire reaction.

If the temperature of the preliminary reaction is less than 10°C, the reaction rate will decrease,
Due to the decrease in the solubility of dichloropropanol in alkaline water, it is difficult to complete the preliminary reaction in a practical time, and in some cases, disadvantages such as instability of the feed composition to the column occur, which is not preferable.

The apparatus for the preliminary reaction used in the method of the present invention includes a stirred tank reactor and a tube reactor. In the latter case, part of the reactor may be annular to allow circulation of the reaction mixture, and a pump may be used to circulate the liquid to enhance the mixing effect. A static mixer can also be inserted into the circulation path to further increase the mixing effect. Further, the preliminary reaction may be performed in a continuous manner or in a batch manner.

The reactive distillation column used in the method of the present invention includes a packed column,
Examples include perforated plate towers, perforated plate towers with downcomers, etc.
Among these, a perforated plate column with a downcomer is most suitable. For example, at the top of the column there is a reflux liquid feedlot, 4 to 6 liters from the top.
In the lower stage there is a feedlot for raw materials di) chloropropanol and alkali,
A device with a steam blowing nozzle installed under the lowest stage is used.

When it is desired to obtain both the conversion rate of dichloropropanol and the selectivity of epichlorohydrin of 90% or more, the number of theoretical plates is usually 13 to 17 when the preliminary reaction of the present invention is not performed, but according to the method of the present invention, the number of theoretical plates is usually 13 to 17. 10 to 11 stages is sufficient.

〔Example〕

The method for producing epichlorohydrin of the present invention will be explained in more detail below using Examples. In addition, all composition percentages in the examples are weight units and conversion rates.

The reactive distillation column was constructed so that it could be easily disassembled and assembled for experiments. The tower body consists of a set of two perforated plates with a downcomer (porosity 13%) of 15 mm in depth, and a steel cylinder with an inner diameter of 100 mm with flanges on both ends as one unit, and the number of units can be increased or decreased according to the required number of stages. The stage interval after assembly is 150mm. A feeder for raw materials and alkali was provided in the fifth stage from the top, and a steam blowing nozzle was provided below the bottom stage. The top outlet of the column is connected to a sleeve-type total condenser with a heat transfer area of 0.3m2 via a sleeve-type dephlegmator with a heat transfer area of 0.3m2.The condensate of the fractionator is connected to the raw material feedro. On the same stage, the condensate from the total condenser is piped to enter the separation tank.The upper layer (aqueous layer) of the separation tank is piped to flow back to the upper base stage, and the lower layer (oil layer) ) enters the distillate receiving tank.The liquid is drawn out from the bottom of the tower while keeping the liquid level constant using a liquid level controller, and is piped to enter the bottoms liquid receiving tank. The condensed product outlet and the upper part of the liquid separation tank were connected to a vacuum pump so that the operating pressure of the column could be changed.

Example 1 Preliminary reaction: 5.9 kg of water and 18.3 kg of a suspension containing 5% calcium hydroxide were preheated to about 40°C and placed in a jacketed iron stirring tank with a capacity of 5 ON. After preliminarily reacting the mixture at 40°C for 25 minutes, it was immediately cooled and maintained at a temperature not exceeding 10°C. The preliminary reaction rate was 23%.

Reaction vaporization: The liquid after the preliminary reaction was extracted from the bottom outlet of the stirring tank at a rate of 2.54 kg/hr while stirring, and an alkali suspension with the same concentration as above was obtained at 4.86 kg/hr.
It was supplied to the above-mentioned reactive distillation column together with r. This reactive distillation column has 24 stages, and 1.5 liters of water smoke is emitted from the steam injection nozzle.
Blow 7 kg/hr, top pressure 500mm
Hg, tower top temperature 86°C, tower bottom temperature 99°C 2 dephlegmator temperature 8
The column was stabilized by running for 8 hours at 2°C. The fractionation rate was 40% based on the overhead distillate.

After the column was stabilized, the oil layer fractionated from the condensate of the total condenser was sampled and analyzed by gas chromatography.The conversion rate of 2.3-dichloro-1-propanol was 98.0%, and the conversion rate of epichlorohydrin was 98.0%. selection rate of 98.5%
The content of 2,3-dichloro-1-propanol in the oil layer was 3.9%.

Example 2 Preliminary reaction: 2.3-Dichloro-1-propanol 58.5%.

1.3-dichloro-2-propanol 4.4%, water 26%
．． 9%, hydrogen chloride 1O92% mixture 17.6 kg
and 10% calcium hydroxide suspension 31.0k
Preliminary reaction was carried out for 60 minutes in the same manner as in Example 1 using g. The preliminary reaction rate was 40%.

Reactive distillation: Liquid 4, 86 subjected to preliminary reaction in the same manner as in Example 1
kg/hr and an alkaline suspension with the same concentration as above2.
54 kg/hr was fed to the same reactive distillation column as used in Example 1, and 1.7 kg of water vapor was supplied from the steam injection nozzle.
Top pressure of 500 mmHg while blowing g/hr.
, tower top temperature 85°C, tower bottom temperature 99°C, 1 condenser temperature 80°C
The tower was stabilized after eight hours of operation. The fractionation rate was 50% based on the overhead distillate.

After the column was stabilized, the product was analyzed in the same manner as in Example 1, and it was found that 2,3-dichloro-1-propanol and 1,
The conversion rate of 3-dichloro-2-propanol is 99.2% in total, and the selectivity of epichlorohydrin is 98.3%.
, 2,3-dichloro-1-propanol and 1 in the oil layer
．． The content of 3-dichloro-2-propanol was 1.1% and 0.1%, respectively.

Comparative Example In Example 1, 2,3 dichloro-1-propanol, water and calcium hydroxide suspension were directly fed to the above reactive distillation column without performing the preliminary reaction, and desalination was carried out in the same manner as in Example 1. A hydrogen reaction was performed.

2. The conversion rate of 3-dichloro-1-propanol was 96.
1%, the selectivity of epichlorohydrin is 97.5%, and the content of 2,3-dichloro-1-propanol in the oil layer is 4
．． It was 3%.

From the above Examples and Comparative Examples, it is clear that the conversion rate of dichloropropanol and especially the selectivity of epichlorohydrin are improved by performing the preliminary reaction.

〔Effect of the invention〕

Unnecessary side reactions can be minimized by preliminarily reacting dichloropropanol with a small amount of alkali at a low temperature according to the method of the present invention and then supplying the reactant to the reactive distillation column. Correspondingly, the alkali content to be supplied to the column can be reduced, the alkali concentration in the column can be lowered as a whole, and hydrolysis of epichlorohydrin can be reduced. All of these are effective in increasing the conversion rate of dichloropropanol and improving the selectivity of epichlorohydrin. The method of the present invention is effective as a method of compensating for the decrease in the apparent reaction rate of 2,3-dichloro-1-propanol, especially when a high concentration of dichloropropanol is used.

In addition, when using a mixture of 2,3-dichloro-1-propanol and 1,3-dichloro-2-propanol, the reaction rate of the latter is higher, so by performing a preliminary reaction, the latter is consumed first. Since the content of the former is relatively large when it is supplied to the column, operating conditions that are optimal or close to the optimum for the former can be selected within the column, making reaction control easier.

Furthermore, the number of plates in the column can be reduced by the amount of reaction that has progressed, and by-products can be reduced compared to when the reaction is carried out in the entire column, making it possible to reduce the content of organic matter in the bottoms. Useful.

Claims (1)

[Claims] 2,3-dichloro-1-propanol and/or 1,3
-1 molar equivalent of dichloro-2-propanol and 1 to 1.
When producing epichlorohydrin by dehydrochlorination reaction using an alkaline aqueous solution or alkaline suspension containing 2 molar equivalents of alkaline content, 0.05 to 0.4 molar equivalents of alkali content is added to the dichloropropanol in advance.
After partial dehydrochlorination by mixing at 0-40°C, 1.1
Production of epichlorohydrin, characterized in that it is continuously fed to a reactive distillation column together with 5 to 0.7 molar equivalents of alkali, the remainder is dehydrochlorinated, and the produced epichlorohydrin is stripped with steam and extracted from the top of the column. Method.