JPH0254836B2 - - Google Patents

Description

[Detailed description of the invention]

In the present invention, 4,4-dimethyl-1,
Atmospheric pressure as a by-product when manufacturing 3-dioxane
The present invention relates to a method for treating a fraction containing tertiary-butyl alcohol having a boiling point of 75 to 95°C (hereinafter sometimes referred to as crude tertiary-butyl alcohol). The method of reacting isobutene and formaldehyde in an aqueous sulfuric acid solution to synthesize 4,4-dimethyl-1,3-dioxane and then decomposing the dioxane to produce isoprene is well known (for example, as described in
It is also well known that tertiary butyl alcohol is produced as a by-product during this process (see Japanese Patent Publication No. 44-20343). Tertiary-butyl alcohol obtained by this method usually contains formaldehyde, trioxane, tertiary-butyl methyl formal, methylal,
Dimethylene glycol dimethyl ether, 4,4
- Contains formals such as dimethyl-1,3-dioxane (formaldehyde, trioxane, and formals are collectively referred to as formaldehyde-based compounds in this specification). The tertiary-butyl alcohol is generally decomposed in the presence of an acidic catalyst after removing formaldehyde-based compounds by separation operations such as extraction and fractional distillation, and converted to isobutene to produce 4,4-dimethyl-1,3
- Reused as a raw material in the production of dioxane. However, the tertiary-butyl alcohol obtained by the above separation operation has low purity and still contains the formaldehyde-based compounds, so when the tertiary-butyl alcohol is decomposed into isobutene in the presence of an acidic catalyst, A tar substance is produced as a by-product, resulting in undesirable results such as a decrease in yield and deterioration of the catalyst. The present inventors have conducted intensive studies to develop a method that can advantageously utilize tertiary butyl alcohol containing such formaldehyde-based compounds, and as a result, they have arrived at the present invention. That is, according to the present invention, isobutene and formaldehyde are reacted in a strongly acidic aqueous solution to produce 4,4-dimethyl-1,3-dioxane. Crude tertiary butyl alcohol containing formaldehyde-based compounds was heated at 150 to 210℃.
By continuously or intermittently supplying the acidic aqueous solution with a pH of 0.5 to 2.5 and decomposing it at a temperature of Not only can the crude tertiary butyl alcohol be treated stably over a long period of time, but also isoprene and isoprene can be obtained in good yields along with isobutene. According to the present invention, not only isobutene is produced by the decomposition of crude tertiary-butyl alcohol, but also isoprene is produced from the formaldehyde-based compound and isobutene contained in the crude tertiary-butyl alcohol. Since the amount of by-products of tar-like substances derived from 4,4-
It is possible to omit the frequent catalyst activation operations conventionally required when circulating the dimethyl-1,3-dioxane production process, and it becomes possible to treat crude tert-butyl alcohol over a long period of time. In other words, according to the present invention, the separation operation of formaldehyde-based compounds in crude tertiary-butyl alcohol is eased, and at the same time, it is possible to ease the separation operation of formaldehyde-based compounds in crude tertiary-butyl alcohol, which has conventionally been an inhibiting factor for stable treatment of the crude tertiary-butyl alcohol over a long period of time. The advantage is that the formaldehyde-based compounds that were previously stored are effectively utilized to produce isoprene, which enables stable processing over a long period of time. Conventionally, methods for decomposing tertiary alcohols to obtain the corresponding olefins include liquid phase reactions using strong acidic substances such as sulfuric acid, phosphoric acid, hydrochloric acid, iodine, oxalic acid, and sulfonic acids as catalysts, as well as silica, silica alumina, Gas phase reactions using solid acids such as activated alumina, thorium oxide, kaolinite, and solid phosphoric acid as catalysts are widely known. However, when the crude tertiary-butyl alcohol used in the method of the present invention is decomposed according to these known methods, due to the formaldehyde-based compounds contained in the crude tertiary-butyl alcohol, In a liquid phase reaction using a reaction operation method, the yield of isobutene decreases, and in a gas phase reaction, carbonaceous substances are deposited on the catalyst, resulting in a decrease in catalytic activity within a short period of time. On the other hand, it is known that conjugated dienes are produced when isobutene and formaldehyde are reacted in an aqueous solution of sulfuric acid, phosphoric acid, or other inorganic or organic strong acid substances (U.S. Patent No. 2,350,485). The yields of the products described in the examples are significantly lower. However, according to the method of the present invention, the crude tertiary butyl alcohol is decomposed by continuously or intermittently supplying the crude tertiary butyl alcohol to an acidic aqueous solution and treating the product while distilling it out from the acidic aqueous solution together with water. The reaction and the decomposition reaction of formaldehyde-based compounds, the Prins reaction between the reaction products isobutene and formaldehyde, and the decomposition reaction of the products occur simultaneously, and the products are quickly removed from the reaction zone, resulting in high boiling point substances. The production of isoprene is suppressed, and in addition to isobutene, isoprene can be obtained in good yield. The crude tertiary-butyl alcohol used in the method of the present invention has a boiling point at atmospheric pressure that is produced as a by-product when producing 4,4-dimethyl-1,3-dioxane by reacting isobutene and formaldehyde in a strongly acidic aqueous solution. It is a mixture having a temperature of 75 to 90°C and containing tertiary butyl alcohol and a formaldehyde compound, and usually contains tertiary butyl alcohol in a proportion of 65 to 85% by weight. The composition of formaldehyde compounds contained in crude tert-butyl alcohol is 4,4-
Although it varies depending on the reaction conditions when assembling dimethyl-1,3-dioxane and the separation conditions from the reaction mixture, generally 5 to 15% by weight (formaldehyde-based compounds are mixed with formaldehyde in crude tert-butyl alcohol). (corresponding to 3 to 8% by weight). An example of the composition of crude tertiary butyl alcohol is as follows. Tertiary butyl alcohol 70.52% by weight Tertiary butyl methyl formal 2.36 Methyral 2.14 Dimethylene glycol dimethyl ether
1.10 trioxane 0.41 4,4-dimethyl-1,3-dioxane
0.30 Formaldehyde 5.59 Methyl tert-butyl ether 2.02 Methanol 7.88 4-Methyl-5,6-dihydro-2H-pyran
0.32 Water 4.87 The concentration of the acidic aqueous solution used in the method of the present invention is selected such that the pH of the acidic aqueous solution is 0.5 to 2.5. If the pH of the acidic aqueous solution exceeds 2.5, not only will a practical reaction rate not be obtained, but the yield of isoprene will decrease and the amount of high-boiling substances produced will increase. On the other hand, if the pH of the acidic aqueous solution is less than 0.5, successive side reactions of the produced isobutene and isoprene increase, resulting in not only a decrease in their yield but also significant corrosion of the equipment. A suitable concentration of the acidic aqueous solution is selected depending on the reaction temperature, the feed rate of crude tert-butyl alcohol, the feed rate of water, etc. Generally, a high concentration is selected when the reaction temperature is low and the crude tert-butyl alcohol feed rate and water feed rate are high, and when the reaction temperature is high and the crude tertiary-butyl alcohol feed rate and water feed rate are low A low concentration is selected. As the acidic aqueous solution, an aqueous solution of an acidic substance having low volatility or non-volatility under the reaction conditions is used. Specific examples of the acidic substances include inorganic acids such as phosphoric acid, sulfuric acid, and boric acid, heteropolyacids such as phosphotungstic acid, and organic acids such as p-toluenesulfonic acid, benzelsulfonic acid, trifluoromethanesulfonic acid, and oxalic acid. and acid salts such as sodium hydrogen sulfate. From the viewpoint of low corrosion resistance, boric acid, phosphoric acid, or tungstic silicoic acid is preferred, and boric acid or phosphoric acid is particularly preferred. The treatment of crude tertiary butyl alcohol according to the process of the invention can generally be carried out at temperatures within the range of 150 DEG to 210 DEG C. If the temperature does not reach 150°C, not only a practical reaction rate cannot be obtained, but also the yield of the target product decreases. The temperature is 210℃
If it exceeds 20%, side reactions will increase and there will be disadvantages in terms of the pressure and heat source of the reaction system. A suitable temperature is selected depending on the pH of the acidic aqueous solution. Usually, a low temperature is selected when the pH of the acidic aqueous solution is low, and a high temperature is selected when the pH of the acidic aqueous solution is high. Since the treatment of crude tertiary butyl alcohol needs to be carried out in an acidic aqueous solution maintained at the above-mentioned temperature, it is usually carried out under pressure in order to keep the reaction zone in a liquid phase. Specifically, it is preferable to apply a pressure to the extent that the liquid phase boils under the treatment conditions, and generally, the pressure of the reaction mixture which is in a boiling state at the treatment temperature may be applied. In the method of the present invention, the feed rate of crude tert-butyl alcohol to the acidic aqueous solution maintained under the treatment conditions depends on the pH and concentration of the acidic aqueous solution, for example, if the pH of the acidic aqueous solution is high and the treatment temperature When the pH of the acidic aqueous solution is low, a low feed rate is selected, and conversely, when the pH of the acidic aqueous solution is low and the treatment temperature is high, a high feed rate is selected. Specifically, the feed rate of crude tertiary butyl alcohol is preferably selected from the range of 30 to 700 g per hour per 1 kg of the acidic aqueous solution depending on the processing conditions. If the feed rate exceeds the above upper limit, the amount of crude tert-butyl alcohol distilled out without being decomposed increases, and if the feed rate falls below the lower limit, isobutene and isoprene are sequentially reduced. This is not preferable because the reaction increases and the amount of high-boiling substances produced increases. The treatment of crude tertiary-butyl alcohol according to the method of the present invention can be carried out while supplying water and/or steam to the reaction zone in addition to the crude tertiary-butyl alcohol. can be quickly taken out of the reaction zone, and the amount of by-products of high-boiling substances can be reduced. Preferably, the amount of water and/or steam fed to the acidic aqueous solution together with the crude tertiary-butyl alcohol is at least 0.1, in particular at least 0.3, in weight ratio to the crude tertiary-butyl alcohol. There is no upper limit in the strict sense of the amount of water and/or steam supplied, but if this amount is extremely large, the decomposition rate of the supplied crude tertiary butyl alcohol will decrease and the energy consumed will increase, so it is less than 2. , particularly preferably 1 or less. Furthermore, the process of the present invention can be carried out while supplying isobutene to the reaction zone in addition to crude tertiary butyl alcohol and water and/or steam, thereby increasing the amount of isoprene produced in the reaction during the process. At the same time, the amount of high-boiling substances can be further reduced. The amount of isobutene supplied is preferably 2 or less in weight ratio to the crude tertiary butyl alcohol. Even if this amount exceeds 2, the increase in the effect of adding isobutene is small, which is rather disadvantageous in terms of energy. The method of the invention is advantageously carried out in continuous mode. An example of a preferred continuous operation is to continuously charge crude tert-butyl alcohol to an aqueous acidic solution maintained at a predetermined concentration, temperature, and pressure while stirring and react, while simultaneously distilling the product together with water. This is a method in which a portion of the aqueous phase of the condensate is circulated to the reaction system after the distillate is condensed.
When raw materials are mixed with a certain proportion of water and supplied,
In order to keep the amount of acidic aqueous solution in the reaction zone constant,
It is necessary to continuously take out the supplied water and the water produced by the reaction together with the products out of the reaction zone. The undecomposed crude tertiary butyl alcohol distilled out together with the product is separated and recovered and recycled. When crude tertiary butyl alcohol is processed for a long period of time, a small amount of high-boiling substances, especially tar substances, which are produced as by-products during the processing period, accumulate in the acidic aqueous solution; It can be easily separated and removed by continuously or intermittently taking out a portion of the aqueous solution from the reaction zone and decanting it or by performing a usual separation operation during extraction. The acidic aqueous solution after separation of high-boiling substances can be recycled to the reaction zone. Therefore, in the method of the present invention, the acidic aqueous solution, which is both the catalyst and the solvent for carrying out the treatment operation in the liquid phase, can be used repeatedly over a long period of time without undergoing any special regeneration or purification steps. This is industrially important and is a major feature of the method of the present invention, along with the ability to stably recover isoprene together with isobutene from crude tertiary butyl alcohol in good yields. High purity isobutene and isoprene can be obtained from the distillate obtained by treating crude tertiary butyl alcohol by distillation or other operations. Isobutene is useful as a raw material for the synthesis of synthetic rubber, methyl methacrylate, alkylphenol, isoprene, etc., and can also be recycled to the reaction zone if desired. Isoprene is also extremely useful as a synthetic raw material for synthetic rubber and terpene compounds. EXAMPLES The present invention will be specifically explained below using Examples, but the present invention is not limited in any way by these Examples. Example 1 A magnetic stirring type 500 was equipped with a crude tertiary butyl alcohol inlet pipe, a thermometer, and a condensing pipe connected to a distillate receiver, and was able to purge the gas phase through a dry ice acetone trap.
ml reactor was charged with two Batsuful sheets of width 8 mm x length 60 mm, and 180 g of orthoboric acid and 120 g of water were charged.
The mixture was heated and dissolved while stirring and maintained at 170°C. The pH of this boric acid aqueous solution was 0.6 (155°C). Next, 59% by weight of crude tertiary butyl alcohol consisting of the ingredients shown in Table 1 was added to the boric acid aqueous solution maintained in this state.
An aqueous solution is introduced into the crude tertiary butyl alcohol inlet tube at a rate of 204 g/hour using a pressure-resistant metering pump, and at the same time, a gaseous mixture mainly composed of product and water is introduced into the condensation tube in order to keep the liquid level constant. The treatment was carried out for 2 hours while being guided. The pressure during treatment was 5.6 Kg/cm ² ·G. The organic phase and aqueous phase of the distillate collected in the receiver by condensation were separated and each was analyzed by gas chromatography. The liquid collected in the dry ice/acetone trap was also analyzed using gas chromatography. The results are shown in Table 2. The results were calculated according to the following formula. Conversion rate of tertiary-butyl alcohol (%) = Number of moles of tertiary-butyl alcohol consumed/number of moles of tertiary-butyl alcohol in the supplied crude tertiary-butyl alcohol x 100 Selection of isobutene based on tertiary-butyl alcohol Rate (%) = Number of moles of isobutene produced/Number of moles of tertiary butyl alcohol consumed x 100 Conversion rate (%) of formaldehyde-based compounds = Total number of moles of (++ x 2+ x 3++) consumed/Supplied Total number of moles of (++×2+×3++) in the crude tertiary butyl alcohol x 100 Selectivity of isoprene based on formaldehyde compounds (
%) = Number of moles of isoprene produced/consumed (+
+×2+×3++) total number of moles×100 (However, the numbers ~ in the above formula represent the components with corresponding numbers in the raw materials shown in Table 1.)

【table】

[Table] Example 2 Using the same apparatus as in Example 1, the same procedure as in Example 1 was carried out except that the feed rate of the crude tertiary butyl alcohol aqueous solution was changed to 255 g/hour, and the results shown in Table 3 were obtained.

[Table] Example 3 Using the same equipment as in Example 1, the same procedure as in Example 1 was performed except that the feed rate of the raw material aqueous solution was 335 g/hour, and the results shown in Table 4 were obtained.

[Table] Examples 4 to 6 Using the same equipment as in Example 1 except that Batsuful was not used, a 50% by weight aqueous solution of crude tertiary butyl alcohol containing the components shown in Table 5 was heated to 360% by weight.
The results shown in Table 6 were obtained by processing in the same manner as in Example 1, except that the conditions shown in Table 6 were used.

【table】

【table】

[Table] Examples 7 to 9 Using the same equipment as in Example 1 except that Batsuful was not used, a 50% by weight aqueous solution of crude tertiary butyl alcohol containing the components shown in Table 7 was heated to 360% by weight.
The process was as in Example 1, except that the conditions shown in Table 8 were used. The results are shown in Table 8.

【table】

【table】

[Table] Example 10 Using the same equipment as in Example 1, the same process as in Example 1 was carried out except that a 70% by weight aqueous solution of crude tertiary butyl alcohol containing the components shown in Table 7 was supplied at a rate of 257 g/hour. . The results are shown in Table 9.

[Table] Example 11 Crude tertiary butyl alcohol inlet pipe, thermometer, electromagnetic stirrer, condenser, and two distillates connected by a three-way kettle so that the gas phase could be purged through a dry ice-acetone trap. 60 g of orthoboric acid and 40 g of water were charged into a 300 ml pressure-resistant glass reactor equipped with a receiver, and heated and dissolved while stirring. The pH of this boric acid aqueous solution is 0.6
It was hot (155℃). Next, while maintaining this aqueous solution at 190°C and stirring, add a 50% by weight aqueous solution of crude tertiary butyl alcohol containing the ingredients shown in Table 10.
The treatment was continued for 70 hours while being introduced into the reactor at a rate of 105 g/h. During that time, the distillate for 3 hours was collected and analyzed in the same manner as in Example 1.
The results shown in 11 were obtained. However, the results in the table were calculated based on the tertiary-butyl alcohol in the crude tertiary-butyl alcohol introduced.

【table】

[Table] * Tertiary butyl alcohol standard Note that the tarry substances that remained in the reactor at the end of the treatment phase separated within 1 minute when stirring was stopped at the reaction temperature, and the amount was 0.18% of the supplied raw material. It was 6.5% by weight based on the boric acid aqueous solution in the reactor. Example 12 150 g of orthoboric acid and 150 g of water were charged in the same equipment as in Example 1, and at 180°C, 59% by weight of crude tertiary butyl alcohol consisting of the components shown in Table 12 was prepared.
The results shown in Table 13 were obtained in the same manner as in Example 1 except that the aqueous solution was fed at a rate of 254 g/hour. The pH of the boric acid aqueous solution used for the treatment was 0.8 (155°C).

【table】

[Table] Example 13 Using the same equipment as in Example 1, Table 14 was added to 300 g of a 1.0% by weight phosphoric acid aqueous solution (PH = 1.6, 25°C) at 180°C.
The results shown in Table 15 were obtained in the same manner as in Example 1, except that the raw materials shown in Table 1 were fed at a rate of 14 g/hour, water at a rate of 28 g/hour, and isobutene at a rate of 6.5 g/hour. Obtained.

【table】

【table】

【table】

Claims (1)

[Claims] 1. 75-95 at atmospheric pressure, which is produced as a by-product when producing 4,4-dimethyl-1,3-dioxane by reacting isobutene and formaldehyde in a strongly acidic aqueous solution.
Crude tert-butyl alcohol having a boiling point of 150 °C and containing formaldehyde-based compounds is
Continuously or intermittently supplied to an acidic aqueous solution with a pH of 0.5 to 2.5 maintained at a temperature of 210°C and decomposed, simultaneously producing isobutene and isoprene and low boiling point components to distill out of the reaction zone together with water. A method for treating crude tertiary butyl alcohol, characterized by: 2. The method according to claim 1, wherein isobutene and isoprene are each separated from the distillate by distillation. 3. According to claim 1, a part of the acidic aqueous solution is continuously or intermittently taken out from the reaction zone, and after removing high-boiling substances contained in the acidic aqueous solution, the acidic aqueous solution is recycled to the reaction zone. the method of. 4. The method according to claim 2, wherein a part of the separated isobutene is recycled to the reaction zone.