JPS6237021B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention dehydrates α-phenylethyl alcohol (hereinafter referred to as α-PEA) in the liquid phase using a dehydration catalyst to produce styrene at a temperature of 180 to 220°C.
This invention relates to a method for producing high-purity styrene with a small amount of impurities in a high yield by using an organic sulfonic acid as a dehydration catalyst and maintaining a specific concentration of α-PEA in the reaction liquid phase in a temperature range of It is something. Styrene monomer is generally produced by dehydrogenating ethylbenzene, but α-
The method of producing styrene by dehydrating PEA has recently been reconsidered industrially. α−
Various methods have been proposed for producing styrene by dehydrating PEA in the presence of a catalyst, including a gas phase method and a liquid phase method. A method for dehydrating α-PEA in the liquid phase in the presence of a catalyst is described in U.S. Patent No. 3,526,674. The dehydration process is carried out in the presence of an acid, a carboxylic acid, an arylsulfonic acid, or a solid catalyst having a surface area of 15 m ² /g or more, and it is stated that alumina is particularly suitable as the dehydration catalyst. In the process of producing styrene by dehydrating α-PEA, it is very important industrially to obtain high-purity styrene in good yield. The industrial value of the styrene production process is greatly reduced. In other words, styrene is widely used as a monomer for producing polystyrene and other polymers, but if by-products produced in the process of dehydrating α-PEA are mixed into the styrene product, the polymerization behavior during polymer production may be affected. This may cause a change in the quality of the polymer obtained by polymerization or may cause problems with the quality of the polymer obtained by polymerization, so it is necessary to suppress the contamination of such impurities as much as possible. The content of non-polymerizable impurities such as ethylbenzene and cumene in the styrene product is also strictly limited, and ethylbenzene, for example, is usually kept below about 500 ppm (0.05%). However, since ethylbenzene and styrene have similar boiling points, it is extremely difficult to separate them by distillation. Therefore, separating and removing ethylbenzene from styrene usually requires a large amount of distillation cost, and even after such rectification, several hundred ppm of ethylbenzene cannot be avoided. Furthermore, α-methylstyrene is one of the by-products that is relatively difficult to separate from styrene, and its removal requires considerable distillation costs. Ethylbenzene and α-methylstyrene are the main light-boiling byproducts produced in the process of producing styrene by dehydration of α-PEA, but other products are also produced by reactions with impurities contained in the raw material α-PEA. Various light boiling compounds may be formed. The mechanism by which ethylbenzene and α-methylstyrene are produced in the dehydration reaction of α-PEA is not clear, and no method for suppressing the production of these by-products has been known so far. The present inventors have conducted studies on a method for dehydrating α-PEA that produces fewer byproducts such as ethylbenzene, and as a result, they have arrived at the method of the present invention. That is, the present inventors dehydrated α-PEA in the liquid phase to produce styrene.
Using an organic sulfonic acid as a catalyst and α-
It has been found that by keeping the concentration of PEA below the value expressed by the following formula, the production ratio of by-products including ethylbenzene can be kept extremely low. α-PEA concentration (wt%)=2×10 ⁻³ ×(260−t) ² where t represents the reaction temperature (° C.). The catalyst used in the process of the invention is an organic sulfonic acid. Organic sulfonic acids include aliphatic sulfonic acids and aromatic sulfonic acids. Examples of aliphatic sulfonic acids include methanesulfonic acid, ethanesulfonic acid, 1-propanesulfonic acid, and 1-propanesulfonic acid.
Butanesulfonic acid, β-hydroxyethanesulfonic acid, 1,4-butanedisulfonic acid, 1,5-pentanedisulfonic acid, higher alkanesulfonic acid, etc. are used. Examples of aromatic sulfonic acids include benzenesulfonic acid, p-toluenesulfonic acid, ethylbenzenesulfonic acid, o-,
m- and p-xylenesulfonic acid, mesitylenesulfonic acid, p-phenolsulfonic acid, o-cresolsulfonic acid, p-chlorobenzenesulfonic acid, sulfanilic acid, metanilic acid, sulfosalicylic acid, dodecylbenzenesulfonic acid, benzene-m- Disulfonic acid, 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, 1-naphthol-4-sulfonic acid, 1-naphthol-2-sulfonic acid, 1-naphthylamine-4-sulfonic acid, 1
-Naphthylamine-8-sulfonic acid, 2-naphthol-3,6-disulfonic acid, 2-naphthol-
6,8-disulfonic acid, 1-naphthol-8-amino-3,6-disulfonic acid, 8-hydroxyquinoline-5-sulfonic acid, 1-naphthol-6-
Amino-3-sulfonic acid or diaminostilbendisulfonic acid is used. Furthermore, derivatives of these organic sulfonic acids that liberate sulfonic acid in the reaction system are also considered to be organic sulfonic acids in the present invention. The above catalysts may be used alone or in combination. Further, various compounds may be used in combination with these catalysts. For example, diphenylamine, ε-caprolactam, 4,4′-
Thio-bis-(6-t-butyl-3-methylphenol), N-methylpyrrolidone, phenyl-α
-naphthylamine, N・N'-diphenyl-p-
By coexisting phenylene diamine, hexamethylene phosphotriamide, quinoline, ammonia, alkali metal salts, and other compounds with these organic sulfonic acids, high-boiling byproducts can be reduced and the yield of styrene can be improved. . The amount of the catalyst used in the method of the present invention is not particularly limited, but it is usually present in the reaction medium in an amount of 0.02 to 5.0% by weight, more preferably 0.1 to 5.0% by weight in the reaction medium. It is used in the presence of 2.0% by weight. Regarding the method of adding the catalyst, it may be added directly to the reaction system, but it can also be supplied after being dissolved in an appropriate solvent. As such a solvent, water or raw material α-PEA is particularly preferably used. In the method of the present invention, it is important to carry out the reaction in a temperature range of 180 to 220°C. i.e.
If a reaction temperature higher than 220° C. is employed, as mentioned above, the production rate of undesirable by-products such as ethylbenzene and α-methylstyrene increases, and there is also the problem that sulfur compounds are mixed into the styrene. Furthermore, at temperatures below 180°C, a sufficient reaction rate cannot be obtained for industrial implementation, and the heavy by-product α-PEA dehydrated dimer (hereinafter referred to as DPE) cannot be obtained.
(referred to as ) increases in the by-product ratio. As for the reaction pressure, the purpose of the present invention can be achieved with almost no generation of light boiling by-products even if the operation is carried out under normal pressure conditions or reduced pressure conditions, but the reaction must be carried out at an absolute pressure of 650 mmHg or less. As a result, the production of heavy by-products can be suppressed without substantially reducing the conversion rate of α-PEA, and the yield of styrene can be further improved. The lower limit of the reaction pressure is not particularly limited, but even if the reaction pressure is lowered to 100 mmHg or less, the effect of reducing the amount of high-boiling byproducts produced is not so great, and the increase in manufacturing cost and operating cost of the reactor is taken into consideration. Then,
It is preferable to operate at an absolute pressure of 100 mmHg or higher.
Also, instead of lowering the reaction pressure, the same effect as reducing pressure can be obtained by adding steam or an inert gas such as nitrogen or carbon dioxide. I can't help it. In this case, the amount of inert gas introduced into the reaction system is preferably 0.5 or more in molar ratio to the supplied α-PEA. When carrying out the method of the present invention, a suitable solvent can be used as the reaction medium. As such a solvent, one having a boiling point of 200°C or higher is generally preferred. Examples of suitable solvents include acetophenone, tetrahydronaphthalene (tetralin), diphenylmethane, 1,2-diphenylethane, higher alkylbenzenes, alkylnaphthalenes, diphenyl ether, 1-methyl-3-phenylindane, 1,3-diphenylbutene, 1,1 -Diphenylethane, etc. However, it is most preferred as an industrial embodiment to use high-boiling by-products, mainly styrene oligomers, produced under the reaction conditions as the reaction medium. Styrene is a substance that polymerizes extremely easily, and it is preferable to remove it from the system as soon as possible after it is produced in the reaction medium. A useful method for making this possible is the so-called reactive distillation method, in which styrene is removed from the system by distillation at the same time as the reaction. The method of the present invention uses α-PEA using a reactive distillation method.
It is also conveniently applied to the dehydration reaction of In the method of the present invention, α in the reaction liquid phase is
- It is important to keep the concentration of PEA below the value calculated by the following formula depending on the reaction temperature. α-PEA concentration (wt%)=2×10 ⁻³ ×(260−t) ² where t represents the reaction temperature (° C.). The calculated values of the above equation at typical temperatures are as follows. Temperature (°C) α-PEA concentration (wt%) 180 12.8 190 9.8 200 7.2 210 5.0 220 3.2 230 1.8 240 0.8 According to the present invention, the concentration of α-PEA in the reaction liquid phase is set to the above value at each reaction temperature. By maintaining the following, the production ratio of ethylbenzene to styrene can be suppressed to about 0.1% by weight or less.
On the other hand, when the concentration of α-PEA exceeds the above value, the production ratio of ethylbenzene increases, requiring a large amount of cost for separation from styrene.
More preferably, the concentration of α-PEA is kept at half or less of the value calculated from the above formula. This not only eliminates the need to separate and remove ethylbenzene anew, but also allows the production ratio of ethylbenzene to be lowered to a level lower than the concentration of ethylbenzene contained in commonly available styrene products. As mentioned above, this means that there is no need for the expense of separating ethylbenzene, and it is possible to produce high-quality styrene with a low ethylbenzene content, and its industrial value is extremely high. It is. The concentration of α-PEA in the reaction liquid phase is determined by a combination of various factors. These factors include the type and concentration of the catalyst, the composition of the raw materials, the type of reaction medium, temperature, pressure, reaction type, and in the case of reactive distillation, the average residence time, number of plates in the distillation column, and reflux. There are ratios etc. According to the method of the present invention, regardless of the combination of these factors, the desired reaction results can be achieved by keeping the concentration of α-PEA in the reaction liquid phase below the above-mentioned value. These factors cause α− in the reaction liquid phase.
The effect on PEA concentration, all other things being the same, is generally as follows: In other words, the higher the catalyst concentration, the lower the α-PEA concentration in the raw material, the higher the temperature, the lower the pressure, the longer the average residence time, the fewer the number of plates in the distillation column, and the lower the reflux ratio, respectively. The α-PEA concentration in the reaction liquid phase decreases. On the other hand, these factors are also related to the reaction rate of α-PEA, the production ratio of heavy byproducts, catalyst cost, operating cost, or equipment cost, so it is necessary to combine the factors to satisfy these points as well. be. By appropriately combining these, high purity styrene can be produced with high reaction rate and high selectivity. α- of the raw material used in the method of the present invention
PEA does not necessarily have to be pure and may be a composition containing other ingredients. For example, when ethylbenzene is used as a precursor for α-PEA, a composition containing acetophenone is usually obtained. There are no particular restrictions on the content of these compounds in the raw material α-PEA;
Does not require purification of PEA. After the reaction according to the invention has ended, styrene is isolated from the reaction product by distillation. In this case, the production ratio of by-products such as ethylbenzene and α-methylstyrene, whose boiling points are close to that of styrene, is extremely small, so styrene with higher purity than conventional styrene can be produced easily and in high yield through extremely simple rectification. The great effect of the method of the present invention is that it can be obtained easily. Next, the method of the present invention will be explained with reference to Examples.
The scope of the present invention is not limited thereby. Example 1 In a 300 c.c. flask equipped with a reflux device, 200 c.c. of tetralin as a solvent and 0.02 g of p-toluenesulfonic acid as a catalyst were placed and heated to reflux.
Then, while continuing to reflux, the concentration of the predetermined amount, i.e. 10
%, 24%, 38%, and 53% of α-PEA at a rate of 100 g/hour, simultaneously produced water and styrene and unreacted α-PEA were fed at a rate of 100 g/hour.
100% of distillate containing PEA and tetralin per hour
The reaction was carried out by withdrawing the reaction mixture from the system at a rate of 1.5 g.
The reaction liquid phase and distillate were analyzed by gas chromatography to track the reaction. The reaction reached steady state in about 3 hours, and the reaction temperature at this time was about 205°C. α- in the reaction liquid phase determined from the average of analysis values from 3rd hour to 6th hour
The relationship between the PEA concentration and the production rate of styrene and ethylbenzene is shown in FIG. 1 for each of the above α-PEA solutions. Examples 2 to 11 A heavy fraction mainly composed of styrene oligomers and p-toluenesulfonic acid are charged in predetermined amounts into a 500 c.c. round bottom flask equipped with a rectification tube having approximately 5 theoretical plates. After heating to a predetermined temperature using a mantle heater, a mixture of α-PEA and acetophenone is supplied at a predetermined rate. The reaction is carried out while maintaining the temperature and pressure of the reaction liquid phase at predetermined values, and at the same time distillation is carried out through a rectifying tube to obtain a distillate mainly consisting of styrene, α-PEA, acetophenone, and water. Further, during this distillation, pure water is supplied to the upper part of the rectification tube at a predetermined rate. The heavy components produced by the reaction were taken out from the flask at appropriate times to keep the amount of reaction liquid in the flask constant. At this time, a considerable amount of the catalyst extracted along with the catalyst is supplied to the flask. The organic layer of the distillate was separated and quantified by gas chromatography to determine the α-PEA reaction rate, styrene selectivity, and ethylbenzene selectivity. In addition, the reaction liquid phase extracted from the flask was analyzed by gas chromatography, and the α-
The PEA concentration was determined. The results thus obtained are shown in Table 1. The detailed reaction conditions in each of these Examples are shown in Table 2. The symbols used in each table below have the meanings shown below. Raw material purity: Proportion of α-PEA in the mixture of α-PEA and acetophenone (wt%) Reaction temperature: Temperature of the reaction liquid phase (°C) Reaction pressure: Pressure inside the flask (mmHg) Catalyst concentration: wt% SV: Value obtained by dividing the raw material supply rate by the weight of the reaction liquid phase (hr ^-1 ) Reflux ratio: Value obtained by dividing the pure water supply rate by the raw material supply rate [PEA]: α-PEA concentration in the reaction liquid phase (wt%) Reaction Rate: Reaction rate of α-PEA (%) SM: Ratio of produced styrene to reacted α-PEA (mol%) EB: Ratio of produced ethylbenzene to reacted α-PEA (mol%) HB: Reacted α-PEA The ratio of heavy components produced to the total weight (mol%). However, the heavy content is calculated in terms of styrene.

【table】

[Table] Comparative Examples 1 to 9 In order to compare with Examples 2 to 11, reactions were carried out in cases where the concentration of α-PEA in the reaction liquid phase or the reaction temperature was outside the range of the present invention. . The results are shown in Table 3, and detailed reaction conditions are shown in Table 4. The same operations as in Examples 2 to 11 were performed except for the conditions shown in the table.

【table】

[Table] Examples 12 to 18 Table 5 shows the results of the same operation as Example 11 except that various sulfonic acids or esters thereof were used instead of α-toluenesulfonic acid as a catalyst.
Shown below.

[Table] Comparative Examples 10 and 11 Instead of sulfonic acids as a catalyst, aluminum isopropoxide was hydrolyzed and then 6
Experiments were conducted using alumina prepared by time-calcining. The results are shown in Table 6. Conditions other than those listed in Table 6 are raw material purity 99.5%, catalyst concentration 10%,
SV1, reflux ratio 0.2.

【table】 [Brief explanation of the drawing]

FIG. 1 shows the relationship between the production rate of styrene and ethylbenzene and the concentration of α-phenylethyl alcohol in the reaction liquid phase in Example 1 of the method of the present invention.

Claims (1)

[Claims] 1. In producing styrene by dehydrating α-phenylethyl alcohol in a liquid phase in the presence of a catalyst, the catalyst is an organic sulfonic acid and the reaction temperature is
180 to 220℃, α-
A method for producing styrene, characterized in that the concentration of phenylethyl alcohol is maintained below a value expressed by the following formula. Concentration (wt%) = 2 x 10 ^-3 x (260 - t) ² (where t represents reaction temperature (°C)) 2 Claim No. 2 characterized in that the reaction pressure is 650 mmHg or less absolute pressure. The method described in Section 1.