JPS6243974B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a process for producing isoprene by the reaction of isobutene and/or tertiary butanol (sometimes referred to as _C4 ) and formaldehyde (sometimes referred to as FA). Attempts have been made for a long time to synthesize isoprene in one step by reacting isobutene or its precursor with formaldehyde, and various methods have been proposed. For example, Japanese Patent Publication No. 46-6936 discloses a gas phase reaction method using a phosphoric acid-calcium oxide-chromium oxide catalyst. However, this method has an extremely short catalyst life and is not practical. JP 48-28884, JP 49-10926, JP 52-30483 and JP 57-
Publication No. 130928 discloses a liquid phase reaction method using various acid aqueous solutions as catalysts. but,
When the present inventors conducted additional tests based on these patent publications, no results were obtained that were industrially satisfactory in terms of reaction results, reaction methods, and other aspects (see Reference Examples below). JP-A-52-91807 discloses that isoprene was produced in a yield of over 70% by a batch or piston flow reaction using a sulfanilic acid derivative as a catalyst. After further testing, the main product was 4,4-dimethyl-
1,3-dioxane, and only a very small amount of isoprene was produced (see Reference Example 5 below).
Furthermore, in the method described in the patent publication mentioned above,
The reaction is carried out in a closed system in the presence of a large excess of isobutene and at a temperature above the critical temperature of isobutene, but this reaction method has the disadvantage of requiring high pressure and increasing equipment costs. As mentioned above, there are many problems that need to be solved in the one-step method for producing isoprene from isobutene and/or tertiary butanol and formaldehyde, and this is due to the fact that 4,4-dimethyl This is a major reason why the so-called two-step process using -1,3-dioxane has been adopted. The present inventors have previously studied from various angles these methods for producing isoprene in one stage in a liquid phase, and found that C ₄ and FA are continuously or intermittently supplied together with water into an acidic aqueous solution, and the reaction system is Isoprene can be produced in a good yield by carrying out the reaction while maintaining the ratio of the partial pressure of organic matter and the partial pressure of water within a specific range and at the same time distilling the produced isoprene and unreacted raw materials out of the reaction zone together with water. (Japanese Unexamined Patent Publication No. 70623/1983). However, the reaction for obtaining isoprene from isobutene and FA in one step essentially requires a large isobutene/FA ratio in the reaction zone, resulting in the disadvantage that the reaction operation consumes a large amount of energy. i.e.
Using an excess of C ₄ relative to FA results in a large amount of energy being consumed in the evaporation, condensation and circulation of CC ₄ . In accordance with the method previously discovered by the present inventors, when the reaction is carried out while maintaining the ratio of the partial pressure of organic matter in the reaction system to the partial pressure of water within a specific range,
A corresponding increase in C ₄ requires an increase in the amount of water to be evaporated, which leads to a further increase in the energy consumed. According to the present invention, the above-mentioned drawbacks are solved in a method for producing isoprene by reacting isobutene and/or tertiary-butanol with formaldehyde in an acidic aqueous solution. (b) continuously or intermittently supplying isobutene and/or tertiary butanol to the first reaction zone and continuously or intermittently supplying a formaldehyde source and water to each reaction zone; c) Distilling isoprene, low-boiling by-products and unreacted raw materials from each reaction zone together with water and feeding this to the next reaction zone; (d) Recovering isoprene from the distillate obtained from the final reaction zone. It was found that this can be improved by That is, according to the method of the present invention, the total volume of the reaction zone and the ratio of C ₄ to FA used throughout the entire reaction zone (hereinafter the ratio of C ₄ to FA used throughout the entire reaction zone is referred to as C ₄ /FA) are changed. It is possible to increase the ratio of C ₄ to FA in each reaction zone (hereinafter the ratio of C ₄ to FA in each reaction zone will be referred to as C/F) without causing any problems, thereby realizing more favorable conditions for the production of isoprene. can. In addition to the FA supply rate, the water supply rate, reaction pressure, reaction temperature, acid strength of the acidic aqueous solution, and reaction zone volume can be appropriately selected for each reaction zone, allowing the sequential reaction of the produced isoprene. The increase in isoprene yield by increasing the C/F value can be greater than the loss due to As a result, the method of the present invention can increase the yield of isoprene at the same C ₄ /FA value compared to the case where the reaction is carried out in a single reaction zone. In other words, according to the method of the present invention, _the value of C ₄ /FA required to achieve the same isoprene yield can be reduced compared to when the reaction is carried out in a single reaction zone. Isoprene can be produced in an energetically advantageous manner, reducing the amount of water used and the amount of water to be evaporated. The effect produced by the present invention is more pronounced as C ₄ /FA is smaller, but in consideration of the yield of isoprene, C ₄ /FA is preferably at least 2. Although there is no upper limit on C ₄ /FA in a strict sense, increasing it unnecessarily not only reduces the effect of increasing the number of connected reaction zones, but also becomes disadvantageous in terms of energy. Therefore, C ₄ /FA should not exceed 15. In the present invention, as mentioned above, C ₄ is used in excess with respect to FA, so the C ₄ supplied to the reaction zone is
Most of the unreacted water is distilled out as unreacted, but since the distillate has a composition close to the equilibrium composition of isobutene and tertiary butanol under the reaction conditions, most of the unreacted
As long as C ₄ is recycled to the reaction, even if either isobutene or tertiary butanol is charged as a starting material to the first reaction zone, a mixture of isobutene and tertiary butanol will ultimately be used as the reaction raw material. It turns out. The number of reaction zones connected in the method of the present invention is preferably as large as possible in order to maintain a constant C ₄ /FA and obtain a high yield of isoprene. It is largest when the number increases from 1 to 2, and decreases as the number increases from 2 to 3 and from 3 to 4. Usually, the number of reaction zones is selected within the range of 2 to 4 in consideration of C ₄ /FA and the complexity of the reaction operation. Although it is preferable to feed the entire amount of raw C ₄ to the first reaction zone, a portion thereof can also be fed to the second and subsequent reaction zones. but,
It usually does not provide any special benefits. FA, which is the other raw material, is supplied separately to each reaction zone.The division ratio of FA is determined appropriately taking into account the amount of acidic aqueous solution and acid strength in each reaction zone, but the C ₄ in each reaction zone is It is preferable to divide it so that the ratio of FA and FA is 4 to 30. The amount of water supplied to each reaction zone is determined in accordance with the amount of water distilled from the reaction system so that the amount of acidic aqueous solution in the reaction zone is kept constant. On the other hand, the amount of water evaporated from each reaction zone is the pressure of the reaction system (P)
It changes depending on. Therefore, in the method of the present invention in which the reaction is carried out while quickly distilling the product together with water from the reaction zone, the pressure of each reaction system (with the exception of low-boiling compounds that are inactive under the reaction conditions) Water is supplied so that the amount of the acidic aqueous solution does not change substantially while maintaining the pressure (subtracting the partial pressure of the raw material) at 1.1 to 2.5 times the vapor pressure (Pw) at the reaction temperature of the acidic aqueous solution. is preferable. This is because the value of P/Pw has a close relationship with the distillation of the product from the reaction zone. Note that Pw is a physical constant that is uniquely determined by the type, concentration, and temperature of the acidic substance contained in the acidic aqueous solution, and P is dependent on the amount of raw materials and products present in the reaction system in addition to Pw. . P/
When Pw approaches 2.5, the yield of isoprene decreases significantly. When P/Pw is less than 1.1, there is no noticeable decrease in the yield of isoprene, but the conversion rate of formaldehyde decreases, and the ratio of water to isoprene in the distillate increases, resulting in a reduction in the reaction zone. The amount of heat consumed increases. In the method of the present invention, a first reaction zone is supplied with C ₄ , an FA source and water, and the other reaction zones are supplied with the distillate obtained from the previous reaction zone together with a fresh FA source and water. Therefore, the amount of water newly supplied to the second and subsequent reaction zones should be adjusted so that the relationship 1.1≦P/Pw≦2.5 is satisfied, taking into consideration the amount of water supplied from the previous reaction zone. It is better to do so. The distilled aqueous gaseous mixture may be completely condensed or partially condensed before being supplied to the next reaction zone, but it is more energetically advantageous to supply it as a gas to the next reaction zone. . In this case, in order to ensure smooth flow of the distillate, it is preferable to lower the pressure of the reaction system toward the later reaction zones. Therefore, the amount of water supplied to each reaction zone should preferably be such that P/Pw satisfies the above relationship from the viewpoint of reaction results and smooth reaction implementation, and the pressure of the reaction system is lower in the later reaction zones. be selected as appropriate. In the method of the present invention, it is possible to carry out the reaction while supplying a low-boiling compound that is inactive under the reaction conditions in addition to the reaction raw materials in the acidic aqueous solution, but this does not bring any special benefits. do not have. A low-boiling compound that is inert under the reaction conditions that can be used is a compound that does not substantially change before and after the reaction, and specifically, n-propane, n-butane, n-butane, etc.
Examples include hydrocarbons having 1 to 10 carbon atoms such as hexane and cyclohexane, and inert gases such as nitrogen gas. Reaction temperature is 150~
It is best to choose a temperature within the range of 220℃. The reaction temperature may be changed for each reaction zone, or the reaction temperature may be the same for each reaction zone. The reaction temperature is selected appropriately depending on the acid strength of the acidic aqueous solution in each reaction zone; for example, a lower temperature is used for higher acid strength.
Higher temperatures are chosen for lower acid strengths. If the reaction temperature is lower than 150°C, the yield of isoprene will decrease even if the acid strength of the acidic aqueous solution is increased in order to maintain the reaction rate at a constant level. The reaction temperature is
Even if the temperature exceeds 220°C, the isoprene selectivity does not decrease significantly, but the FA conversion rate under conditions that give the optimum selectivity decreases. If reaction conditions are selected such that the conversion rate of FA is high at a reaction temperature exceeding 220°C, the sequential reactions from isoprene will increase, resulting in a decrease in the selectivity of isoprene. The preferred rate of supply of the FA source to the acidic aqueous solution is determined by taking into account the reaction temperature, the acid strength of the acidic aqueous solution, and the reaction pressure, and the FA source is uniformly or unevenly supplied to each reaction zone. To increase the supply rate of the FA source, increase the acid concentration of the acidic aqueous solution, or
Alternatively, it is necessary to raise the reaction temperature, and in this case there is a concern about corrosion of the reactor. Therefore, the feed rate of the FA source is usually preferably 3 mol or less per hour per 1 kg of the acidic aqueous solution when calculated as the FA source. Although there is no lower limit in the strict sense of the FA supply rate, if the supply rate is unnecessarily reduced, the volumetric efficiency of the reaction zone will decrease and this will be disadvantageous in terms of equipment, so the supply rate of the FA source should be When converted to FA, it is preferably 0.2 mol or more per hour per 1 kg of acidic aqueous solution. The catalyst used in the method of the present invention is an inorganic acid,
Acidic substances such as organic acids and their salts, which are used in the reaction zone in the form of aqueous solutions. The acid strength of the acidic aqueous solution in the reaction zone varies depending on the type of acidic substance, the reaction temperature, the supply rate of the FA source, etc., but is usually selected from the pH range of 0.5 to 2.5. If the pH of the acidic aqueous solution exceeds 2.5, the yield of isoprene will decrease significantly, and if the pH is less than 0.5, not only will the yield of isoprene decrease, but also significant corrosion of the reaction equipment will occur. The acidic substance is preferably one that is low volatile or non-volatile under the reaction conditions, and specifically includes inorganic acids such as phosphoric acid, sulfuric acid, and boric acid, heteropolyacids such as silicotungstic acid and phosphotungstic acid, and p-toluene. Mention may be made of organic acids such as sulfonic acid, benzenesulfonic acid, trifluoromethanesulfonic acid, oxalic acid, and acid salts such as sodium hydrogensulfate. These catalysts may be used alone or in combination of two or more. Further, the same catalyst may be used in each reaction zone, or a different catalyst may be used in each reaction zone. Formaldehyde sources used in the method of the present invention include formaldehyde aqueous solutions, formaldehyde gas, etc. In addition, trioxane, which decomposes under the reaction conditions to give formaldehyde,
Paraformaldehyde and the like can also be used. Methyral and other formals can also be used. However, in the present invention, it is essential to supply water to the reaction zone, and since formaldehyde takes the form of an aqueous solution in the reaction zone, it is advantageous in terms of reaction operation to use a formaldehyde aqueous solution as the formaldehyde source. The isobutene and tertiary butanol used in the process of the invention may contain other hydrocarbons, 3-methyl-1,3-butanediol, 3-methyl-2-
Buten-1-ol, 3-methyl-3-butene-
1-ol, 3-methyl-1-buten-3-ol, methyl isopropyl ketone, 2-methylbutanal, methyl tert-butyl formal, 4.4
-dimethyl-1,3-dioxane, 4-methyl-
5,6-dihydro-2H-pyran and the like may be included. It is also possible to use alkyl tertiary butyl ethers, such as methyl tertiary butyl ether, which gives isobutene and tertiary butanol under the reaction conditions. Isobutene has a critical temperature of 144.7℃,
Since it exists in a gaseous state under the reaction conditions, it is necessary to efficiently dissolve gaseous isobutene in an acidic aqueous solution during the reaction. For this purpose, the acidic aqueous solution may be vigorously stirred, and if necessary, a baffle plate or the like may be inserted to ensure efficient gas-liquid contact. If the reaction is carried out over a long period of time, a small amount of high-boiling by-products, especially tar-like substances, generated during the reaction will accumulate in the acidic aqueous solution. A portion of the acidic aqueous solution is taken continuously or intermittently from each reaction zone and then introduced into a decanter or an extraction column to remove high-boiling byproducts from the acidic aqueous solution. The acidic aqueous solution after removing high-boiling byproducts can be recycled to each reaction zone and reused. In the method of the present invention, isoprene can be obtained by separating the distillate obtained in the final reaction zone into an aqueous phase and an organic phase, and fractionating the organic phase.
The isoprene obtained by the present invention has high purity;
It is extremely useful as a starting material for polyisoprene and terpene compounds. The present invention will be specifically explained below with reference to Examples, but the present invention is not limited thereto. Example 1 A pressure-resistant unit with an internal volume of 750 ml equipped with an isobutene inlet tube (in the case of the second reactor, the distillate gas inlet tube from the first reactor), a formaldehyde aqueous solution inlet tube, a baffle plate, a thermometer, and an electromagnetic stirrer. A reaction apparatus was used in which two glass reactors were connected by a heat-insulated steam pipe. The aqueous reaction gas from the first reactor is introduced into the second reactor through the steam pipe without being condensed, and the aqueous reaction gas distilled from the second reactor is condensed and then introduced into the second reactor. The waste was collected in a tank. The same amount of formaldehyde was introduced into the first and second reactors. The above two reactors were charged with 187.5 g of water and 112.5 g of orthoboric acid, and the amount of water was 15.5 g/cm ² in the first reactor and 14.7 g/cm 2 in the second reactor.
A 37.5% by weight boric acid aqueous solution was prepared by heating to 180° C. under a pressure of Kg/cm ² . The above pressure was maintained by introducing nitrogen gas and inserting a valve between the two reactors. The vapor pressure of a 37.5% by weight aqueous solution of orthoboric acid at 180℃ is 8.4Kg/cm ²
The pH was 1.2. The first reactor was charged with 257.6 g/hr. (4.60 mol/hr.) and 6.93% by weight formaldehyde aqueous solution, respectively.
It was fed at a rate of 99.6 g/hr. (0.23 mol/hr.). After confirming that the aqueous reaction gas from the first reactor is introduced into the second reactor, 23.5% of the 29.4% by weight formaldehyde aqueous solution is added to the second reactor.
g/hr. (0.23 mol/hr.), and the reaction was carried out for 2.5 hours under the above-mentioned pressures and temperatures with stirring at 1000 revolutions per minute. The aqueous reaction gas distilled from the second reactor was condensed in a condenser and collected in a distillation tank. The pressure was finely adjusted and kept constant by purging the system with nitrogen gas. Furthermore, the level of the acidic aqueous solution in the reactor was kept almost constant during the reaction. The distillate collected in the distillation tank from 1.5 hours after the start of the reaction to the end of the reaction and the substances entrained in the nitrogen gas purged during this period (introduced into a trap cooled with dry ice-acetone and absorbed into n-butyl ether) ) was analyzed to determine the reaction results. The distillate was separated into an aqueous phase and an organic phase, and the aqueous phase was analyzed by gas chromatography (internal standard method) and the sodium sulfite method to quantify unreacted FA. The components in the organic phase and the trap were analyzed by gas chromatography (internal standard method). The results are shown in Table 1. Comparative Example 1 Pressure-resistant glass with an internal volume of 750 ml equipped with two raw material introduction pipes for isobutene and formaldehyde aqueous solutions, a baffle plate, a thermometer, an electromagnetic stirrer, and a receiver for collecting distillate connected to a condenser. Put 300g of 37.5% by weight orthoboric acid aqueous solution into the reactor, and add 14.8Kg/
Heated to 180 °C under a pressure of cm ² . The above pressure was maintained by introducing nitrogen gas. Isobutene and 11.36% by weight aqueous formaldehyde solution were each added at 128.8 g/hr. (2.30 mol/hr.) into the above reactor.
) and 60.72 g/hr. (0.23 mol/hr.), and the reaction was carried out for 2.5 hours under the above-mentioned pressure and temperature with stirring at 1000 revolutions per minute. The aqueous reaction gas distilled from the reactor was condensed in a condenser and collected in a receiver for collecting distillate. The pressure was finely adjusted and kept constant by purging the system with nitrogen gas. Furthermore, the level of the acidic aqueous solution in the reactor was kept almost constant during the reaction. Reaction results were determined by the same method as in Example 1. The results are shown in Table 1. Example 2-3 Using the same apparatus as in Example 1, a reaction was carried out under the same reaction method and operating conditions as in Example 1, except that the supply isobutene/supply FA and the amount of water supplied were changed accordingly. . The results are shown in Table 1. Comparative Example 2 Using the same apparatus as in Comparative Example 1, a reaction was carried out using the same reaction method and operating method as in Comparative Example 1, except that the supplied isobutene/supplied FA and the amount of supplied water were changed accordingly. The results are shown in Table 1.

[Table] Example 4-6 A 3.0% by weight phosphoric acid aqueous solution was used instead of an orthoboric acid aqueous solution, the reaction temperature was 178°C, and the reaction pressure, raw material and water supply amounts were changed as shown in Table 2. The reaction was carried out using the same reaction method and operating conditions as in Example 1, except for the following. The vapor pressure of a 3.0% by weight phosphoric acid aqueous solution at 178°C is 9.6.
Kg/cm ² and pH was 1.3. The results are shown in Table 2. Comparative Example 3-5 Comparison was made using the same equipment as in Comparative Example 1 and adjusting the reaction conditions so that the supplied isobutene/supplied FA in Comparative Examples 3, 4 and 5 was the same as that in Examples 4, 5 and 6. The reaction was carried out according to the method and operating conditions of Example 1.

【table】

[Table] Example 7 Isobutene introduction tube (distillate gas introduction tube from the first and second reactors in the second and third reactors, respectively), formaldehyde aqueous solution introduction tube, baffle plate, thermometer, electromagnetic type Internal volume with stirrer installed
A reaction apparatus was used in which three 750 ml pressure-resistant glass reactors were connected by a heat-insulated steam pipe. 1st
The aqueous reaction gases from the reactor and the second reactor are respectively introduced into the second reactor and the third reactor through the steam pipes without condensation, and are also distilled from the third reactor. The aqueous reaction gas was condensed and then collected in a distillation tank. The same amount of formaldehyde was introduced into each of the first, second and third reactors. Each of the above three reactors was charged with 300 g of a 3.0% by weight phosphoric acid aqueous solution, and in the first reactor,
16.5Kg/cm ² , 16.0Kg/cm 2 in the second reactor
cm ² and heated to 178° C. under a pressure of 15.5 Kg/cm ² in the third reactor. The above pressure was maintained by introducing nitrogen gas and inserting a valve between each reactor. In addition, 3.0% by weight of phosphoric acid aqueous solution
The vapor pressure at 178°C is 9.6Kg/cm ² . The first reactor was charged with 231.8 g/hr of isobutene and 6.65% by weight formaldehyde aqueous solution, respectively.
(4.14 mol/hr.) and 103.7 g/hr. (0.23 mol/hr.). After confirming that the aqueous reaction gas from the first reactor was introduced into the second reactor, a 48.1% by weight formaldehyde aqueous solution was added to the second reactor at 14.35 g/hr (0.23 mol/hr).
hr). Similarly, after confirming that the aqueous reaction gas from the second reactor was introduced into the third reactor, a 48.1% by weight formaldehyde aqueous solution was added to the third reactor at 14.35 g/hr (0.23 mol/hr).
hr), and the reaction was carried out for 2.5 hours under the above-mentioned pressures and temperatures with stirring at 1000 revolutions per minute. The aqueous reaction gas distilled from the third reactor was condensed in a condenser and collected in a distillation tank. The pressure was finely adjusted and kept constant by purging the system with nitrogen gas. Furthermore, the level of the acidic aqueous solution in the reactor was kept almost constant during the reaction.
Reaction results were determined by the same method as in Example 1.
The results are shown in Table 3. Example 8 Using the same apparatus as in Example 7, a reaction was carried out under the same reaction method and operating conditions as in Example 7, except that the supply isobutene/supply FA and the amount of water supplied were changed accordingly. The results are shown in Table 3.

【table】

[Table] Example 9 Using the same equipment as in Example 1, FA was introduced into the first reactor and the second reactor at a ratio of 2:1, and the FA supply rate and water supply amount were The reaction was carried out according to the reaction method and operating conditions of Example 4, except for some changes. The results are shown in Table 4. Example 10 A reaction was carried out according to the reaction method and operating conditions of Example 9. However, the first reactor was replaced with a pressure-resistant glass reactor with an internal volume of 1000ml, and
400g of 3.0% by weight phosphoric acid aqueous solution was charged, and the second
Pour 200g of phosphoric acid aqueous solution of the same concentration into the reactor,
The reaction was carried out so that the volumes of the acidic aqueous solutions in the first reactor and the second reactor were 2:1. The results are shown in Table 4. Example 11 Using the same apparatus as in Example 1, FA was introduced into the first reactor and the second reactor at a ratio of 1:2, and the FA supply rate and water supply amount were varied. The reaction was carried out in accordance with the reaction method and operating conditions of Example 4 except for this. The results are shown in Table 4. Example 12 A reaction was carried out according to the reaction method and operating conditions of Example 11. However, the second reactor was replaced with a pressure-resistant glass reactor with an internal volume of 1000 ml, and
Prepare 400g of 3.0% by weight phosphoric acid aqueous solution, and
Pour 200g of phosphoric acid aqueous solution of the same concentration into the reactor,
The reaction was carried out so that the volumes in the first reactor and the second reactor were 1:2. The results are shown in Table 4.

【table】

[Table] Example 13 Isobutene introduction pipe (in the second, third and fourth reactors, distillate gas introduction pipe from the previous reaction), formaldehyde aqueous solution introduction pipe, baffle plate, thermometer,
A reaction apparatus was used in which four pressure-resistant glass reactors each having an internal volume of 750 ml and equipped with an electromagnetic stirrer were connected by a heat-insulated steam pipe. The aqueous reaction gases from the first, second and third reactors are respectively introduced into the second, third and fourth reactors without condensation through the steam pipes and from the fourth reactor into the distillate. The emitted aqueous reaction gas was condensed and then collected in a distillation tank. The same amount of formaldehyde was introduced into each of the first, second, third and fourth reactors. Each of the above four reactors was charged with 300 g of a 3.0% by weight phosphoric acid aqueous solution, and in the first reactor,
16.5Kg/cm ² , 16.0Kg/cm 2 in the second reactor
178 cm ² under a pressure of 15.5 Kg/cm ² in the third reactor and 15.0 Kg/cm ² in the fourth reactor.
heated to ℃. The above pressure was maintained by introducing nitrogen gas and inserting a valve between each reactor. The vapor pressure of a 3.0% by weight aqueous phosphoric acid solution at 178°C is 9.6Kg/cm ² . The first reactor was charged with 309.1 g/hr of isobutene and 5.15% by weight formaldehyde aqueous solution, respectively.
(5.52 mol/hr.) and 134.0 g/hr. (0.23 mol/hr.). After confirming that the aqueous reaction gas from the first reactor was introduced into the second reactor, an 84.1% by weight formaldehyde aqueous solution was added to the second reactor at 14.35 g/hr. (0.23 mol/hr.).
hr.). Similarly, after confirming that the aqueous reaction gas from the second reactor was introduced into the third reactor, a 48.1% by weight formaldehyde aqueous solution was added to the third reactor at 14.35 g/hr. (0.23 mol). /hr.). Furthermore, after confirming that the aqueous reaction gas from the third reactor was introduced into the fourth reactor, a 48.1% by weight formaldehyde aqueous solution was added to the fourth reactor at a rate of 14.35 g/hr.
(0.23 mol/hr.), and the reaction was carried out for 2.5 hours under the above-mentioned pressures and temperatures with stirring at 1000 revolutions per minute. The aqueous reaction gas distilled from the fourth reactor was condensed in a condenser and collected in a distillation tank. The pressure was finely adjusted and kept constant by purging the system with nitrogen gas. Furthermore, the level of the acidic aqueous solution in the reactor was kept almost constant during the reaction. Reaction results were determined by the same method as in Example 1. The results are shown in Table 5.

【table】

[Table] Reference example 1 Example 5 described in Japanese Patent Publication No. 49-10926
The reaction was carried out according to the reaction method. However, as for the reactor, there is a statement that a titanium reactor is the best in JP-A-48-502, which is filed by the same applicant as this patent and whose inventor overlaps, so a titanium-lined autoclave is used. was used. Titanium-lined autoclave with stirrer
10 g of a 37% formaldehyde aqueous solution and 68 g of tertiary butanol were charged, as well as 2.4 g of ferrous chloride and 26 g of water, which were sealed in a glass sealed tube and placed in an autoclave. After heating the autoclave and the temperature inside the autoclave reaches 160℃,
Stirring was started, the glass sealed tube was broken, and the reaction was carried out at 160°C for 18 minutes. After the reaction, the reaction solution was pumped into ice-cooled dilute alkaline water and rapidly cooled to stop the reaction. (using a pressure-feeding method). The separated oil and water layers were analyzed by gas chromatography to determine the amount of isoprene produced. The amount of isoprene produced was 3.52 g, and the yield was 42% based on the formaldehyde charged. In addition, an attempt was made to quantify unreacted formaldehyde in the aqueous layer using the sodium sulfite method, but the amount was below the detection limit. Reference Example 2 Example 2 described in Japanese Patent Publication No. 52-30483
The reaction was carried out according to the reaction method. However, a titanium-lined autoclave was used as the reactor. A titanium-lined autoclave with a stirrer was charged with 11.5 g of 26% formaldehyde aqueous solution, 11.1 g of water, and 59.2 g of tertiary butanol, and then potassium alum was added.
A glass sealed tube containing 1.13 g and 3 g of water was placed in an autoclave. After attaching the top lid, 33.6 g of isobutene was introduced into the autoclave.
After the autoclave was heated and the internal temperature reached 160°C, stirring was started, the glass sealed tube was broken, and the reaction was carried out at 160°C for 1 hour. After the reaction was completed, the reaction solution was pumped into dilute alkaline water that had been ice-cooled in advance to stop the reaction. The amount of isoprene produced was determined in the same manner as in Reference Example 1, and was found to be 2.34 g. This corresponds to a yield of 34.5% based on the formaldehyde charged. Further, unreacted formaldehyde was not detected. Reference Example 3 A reaction was carried out according to the reaction method of Example 1 described in JP-A-48-502. A titanium-lined autoclave with a stirrer was charged with 9.2 g of a 26% formaldehyde aqueous solution, 8.5 g of water, and 47.4 g of tertiary butanol, and then a glass sealed tube containing 0.86 g of aluminum chloride hexahydrate and 2.0 g of water was placed inside the autoclave. I put it in. After installing the top lid, 27 g of isobutene was introduced into the autoclave. The reaction was carried out at 160° C. for 30 minutes in the same manner as in Reference Example 1, followed by the same post-treatment and analysis. The amount of isoprene produced was 2.55g,
The yield based on the formaldehyde charged was 47%. Further, unreacted formaldehyde could not be detected. Reference Example 4 Example 8 described in JP-A-57-130928
The reaction was carried out according to the method. Tertiary butanol in a stainless steel (SUS-316) autoclave with an internal volume of 1 and equipped with a stirrer.
100g, 12.12% formaldehyde aqueous solution 38.0g
(4.6g formaldehyde), tungstic silicoic acid
Add 0.09g and 142.3g of water and heat to 210℃ while stirring.
As soon as the temperature rose, stirring was stopped and the mixture was rapidly cooled. The time required to reach 210°C from room temperature was 1 hour. After cooling to room temperature, the reaction solution was taken out into a 500 ml glass pressure pin and separated into an organic phase and an aqueous phase.
The organic phase and the neutralized aqueous phase were analyzed by gas chromatography to determine the amount of isoprene produced. The amount of unreacted formaldehyde in the neutralized aqueous phase was further determined by the sodium sulfite method. The conversion rate of formaldehyde is 98.2%, the selectivity of isoprene based on formaldehyde is 50.2%, and the yield of isoprene based on charged formaldehyde is 49.3.
It was %. Reference Example 5 Example 1 described in JP-A-52-91807
The reaction was carried out according to the reaction method. 16.6 g of a 36% formaldehyde aqueous solution containing 6% methanol in a stainless steel (SUS-316) autoclave with an internal volume of 300 ml equipped with a stirrer,
50.4 g of an 88% aqueous tertiary butanol solution and 0.1 g of sulfanilic acid were charged. Then isobutene
33.6g was introduced, heated to 130°C, and reacted for 20 minutes. During this time, it took 45 minutes to raise the temperature. Next, the reaction temperature was raised to 180°C and the reaction was carried out for 40 minutes. The time required to raise the temperature during this period was 32 minutes.
After the reaction was completed, the reaction mixture was rapidly cooled and purged into a trap cooled with dry ice-acetone until the pressure reached normal pressure.
The contents of the autoclave were separated, and the oil layer, water layer, and trap contents were analyzed by gas chromatography. Furthermore, the aqueous layer was analyzed for formaldehyde using the sodium sulfite method. As a result, the conversion rate of formaldehyde was 85%, and the selectivity of isoprene based on formaldehyde was 0.8%.
The main product was 4,4-dimethyl-1,3-dioxane.

Claims (1)

[Scope of Claims] 1. A method for producing isoprene by reacting isobutene and/or tertiary butanol with formaldehyde in an acidic aqueous solution, comprising: (a) having an acidic aqueous solution present in a plurality of reaction zones connected in series; (b) continuously or intermittently supplying isobutene and/or tertiary butanol to the first reaction zone and continuously or intermittently supplying a formaldehyde source and water to each reaction zone; (c) supplying each reaction zone continuously or intermittently; (d) isoprene is recovered from the distillate obtained from the final reaction zone; and (d) isoprene is recovered from the distillate obtained from the final reaction zone. A method for producing isoprene. 2 Isobutene and/or supplied to the first reaction zone
Or, the ratio of the number of moles of tertiary butanol to the total number of formaldehyde sources supplied to each reaction zone in terms of formaldehyde is at least 2, and the pressure of each reaction system is the vapor pressure at the reaction temperature of the acidic aqueous solution. 1. The method according to claim 1, wherein the amount is 1.1 to 2.5 times. 3. The method according to claim 1, wherein the formaldehyde source is supplied to each reaction zone at a rate of 3 mol or less per hour per 1 kg of acidic aqueous solution when the formaldehyde source is converted to formaldehyde. 4. The method according to claim 1, wherein the acidic aqueous solution has a pH of 0.5 to 2.5. 5. The method according to claim 1, wherein the number of connected reaction zones is 2.3 or 4. 6. Claim 1, in which a portion of the acidic aqueous solution is continuously or intermittently withdrawn from each reaction zone, and after removing high-boiling by-products dispersed in the acidic aqueous solution, the acidic aqueous solution is recycled to the reaction zone. The method described in section.