JPS6315249B2 - - 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. Special Publication No. 48-28884, Publication No. 10926-1972, Publication No. 30483-1972, and Publication No. 30483-1972
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 performance 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 at a temperature above the critical temperature of isobutene.
Although the reaction is carried out in a closed system, 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 these problems arise when producing isoprene using 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 investigated from various angles these methods for producing isoprene in one stage in a liquid phase, and have continuously or intermittently supplied C ₄ and FA together with water into an acid aqueous solution. At the same time, the ratio of C ₄ to FA is greatly exceeded, and the ratio of the partial pressure of organic matter and water in the gas phase of the reaction system is maintained within a specific range. It was discovered that isoprene can be produced in good yield by carrying out the reaction while distilling the reaction raw materials out of the reaction zone together with water.However, as a result of further research on the acid aqueous solution used as a catalyst, The present invention was completed based on the discovery that a mixed acid aqueous solution containing 0.5 to 5% by weight of boric acid and 0.5 to 5% by weight of phosphoric acid has extremely excellent performance in terms of volatility, stability, corrosion resistance, catalyst life, etc. I came to the conclusion. That is, according to the present invention, in a method for producing isoprene by reacting isobutene and/or tertiary butanol with formaldehyde in an acid aqueous solution, 15 to 30% by weight of boric acid and 0.5 to 5% by weight of boric acid are used as the acid aqueous solution. Using a mixed acid aqueous solution containing phosphoric acid and continuously or intermittently supplying isobutene and/or tertiary butanol, a formaldehyde source, and water to the acid aqueous solution, the produced isoprene, low-boiling byproducts, and unreacted raw materials are removed. Provided is a method for producing isoprene, characterized in that the reaction is carried out while distilling the aqueous gaseous mixture. The above mixed acid aqueous solution has excellent properties such as extremely low corrosiveness, non-volatility, high stability and does not change under reaction conditions, and extremely long catalyst life. According to this method, isoprene is produced in a good yield, and isoprene can be produced industrially advantageously. 15-30% by weight in the reaction according to the method of the invention
An aqueous mixed acid solution containing 0.5 to 5% by weight of boric acid and 0.5 to 5% by weight of phosphoric acid is used as a catalyst. Boric acid has a dissociation constant [for example, orthoboric acid has a dissociation constant of only 5.8×10 ^-10 at 25°C -LANGE'S HAND-
BOOK OF CHEMISTRY, 1209 pages, McGraw
-Hill Book Co., (1967)], it is an extremely weak acid, and its corrosivity to equipment is extremely low. However, when boric acid is used alone, it must be used at concentrations greater than 30% by weight to achieve practical reaction rates and isoprene yields. When boric acid is used at such a high concentration, the amount of isobutene, which exists in gaseous form at the reaction temperature, dissolved in the boric acid aqueous solution is reduced. Therefore, the ratio of C ₄ to FA (C ₄ /FA) required to achieve the same isoprene yield must be increased compared to when a strong acidic substance such as sulfuric acid or phosphoric acid is used as a catalyst. However, it is disadvantageous in terms of energy. On the other hand, phosphoric acid is highly corrosive, and its use alone poses problems in terms of equipment corrosion. In the method of the present invention, which uses a mixed acid aqueous solution containing 15 to 30% by weight of boric acid and 0.5 to 5% by weight of phosphoric acid as a catalyst, corrosivity is significantly reduced compared to the case where the same concentration of phosphoric acid is used. Furthermore, by suppressing the boric acid concentration to a low level, the solubility of isobutene in the acid aqueous solution is improved, and as a result, the yield of isoprene can be improved. Corrosivity increases when the boric acid concentration is less than 15% by weight. When the boric acid concentration exceeds 30% by weight, the improvement effect in terms of isoprene yield and operability becomes small. When the phosphoric acid concentration is less than 0.5% by weight, it is necessary to increase the concentration of boric acid mixed with phosphoric acid to 30% by weight or more in order to obtain a practical reaction rate, which improves isoprene yield and operability. effect becomes smaller. When the phosphoric acid concentration exceeds 5.0% by weight, although corrosion is suppressed to some extent compared to when phosphoric acid of the same concentration is used alone, the corrosion rate is high, and the problem of equipment corrosion still remains. Next, the results of a corrosion test of stainless steel in an aqueous phosphoric acid solution or a mixed acid aqueous solution of phosphoric acid and boric acid are shown in Table 1 below. The test was conducted using the following method. 600 g of an acid aqueous solution having the composition shown in Table 1 was charged into a pressure-resistant glass container having an internal volume of 1000 ml and equipped with a thermometer, a pressure gauge, and an electromagnetic stirrer. For the purpose of bringing the atmosphere in the system closer to the reaction conditions actually used, formaldehyde was added in an amount such that the concentration in the acid aqueous solution was 3000 ppm. Next, a SUS316 stainless steel test piece (5 cm x 1 cm x 0.3 cm) was polished with #240 sandpaper and then with #1000 sandpaper, and then the test piece was polished using water, methyl alcohol, and ethyl ether in this order. It was washed and fixed to a thermometer using Teflon. After purging the inside of the system with nitrogen gas, it was maintained at 178°C for 24 hours while stirring at 300 revolutions per minute. After the container was cooled to room temperature, the test piece was removed, washed with water, methyl alcohol, and ethyl ether in that order, and dried. The surface area, weight loss before and after the test, and corrosion rate of the test pieces were investigated. For reference, Table 1 shows corrosion tests conducted in a similar manner when phosphoric acid was replaced with sulfuric acid (experiment number 6,
The results of 7) are also listed; in this case, the corrosion rate was higher in the mixed system, and the results corresponded to an increase in acid concentration.

[Table] In the reaction according to the method of the present invention, the ratio of the number of moles of C ₄ supplied and the number of moles of the FA source supplied converted to FA (hereinafter referred to as C ₄ /FA) is at least 3. preferable. When C ₄ /FA is less than 3, the yield of isoprene decreases. From the viewpoint of reaction yield, the larger the C ₄ /FA is, the better it is, and there is no upper limit in the strict sense of this value, but even if it is increased unnecessarily, the effect of improving the isoprene yield is small, and on the contrary, C ₄ /FA should normally not exceed 20, since the amount of heat used increases and becomes economically disadvantageous. When C ₄ /FA is the same, the larger the composition of tertiary butanol in C ₄ is, the better the yield of isoprene can be obtained. In this reaction, C ₄ is used in excess with respect to FA, so most of the C ₄ supplied to the reaction zone distills out unreacted, but the distillate is separated from isobutene and tertiary under the reaction conditions. Since it has a composition close to the equilibrium composition of tertiary butanol, as long as unreacted C ₄ is recycled to the reaction, even if either isobutene or tertiary butanol is introduced into the reaction solution as a starting material, isobutene will eventually be produced. and tertiary butanol will be used as a reaction raw material. 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 acid 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, carbonaceous compounds represented by n-propane, n-butane, n-hexane, cyclohexane, etc. Number 1
~10 hydrocarbons and inert gases such as nitrogen gas can be exemplified. When adopting a reaction method in which isoprene, low-boiling point byproducts, and unreacted raw materials are distilled out of the reaction zone together with water while supplying C ₄ , FA source, and water in an acid aqueous solution, the reaction zone can be adjusted by adjusting the reaction pressure. The ratio of each component evaporated from water to water can be regulated; if the reaction pressure is high, the proportion of water to the total of components other than water in the distillate decreases, and if the reaction pressure is low, the amount of acid aqueous solution decreases. In order to keep the amount constant, the amount of water supplied increases, and the opposite phenomenon occurs. In order to obtain isoprene in a good yield, the reaction pressure (however, if a low-boiling compound that is inactive under the reaction conditions is supplied with the raw material, the pressure after subtracting its partial pressure) is preferably the same as the vapor pressure at the reaction temperature of the acid aqueous solution. 1.1~
It is best to keep it within the range of 2.5 times. The vapor pressure of the acid aqueous solution at the reaction temperature (hereinafter referred to as Pw)
is a physical constant uniquely determined by the type and concentration of acid contained in the acid aqueous solution. The reaction pressure is Pw
When the amount exceeds 2.5 times, the yield of isoprene decreases significantly. When the reaction pressure is less than 1.1 times Pw, no significant decrease in isoprene is observed, but FA
The conversion of isoprene decreases, and the ratio of water to isoprene in the distillate increases, increasing the amount of heat consumed in the reaction. The amount of water fed to the reaction zone is usually adjusted so that the amount of acidic aqueous solution in the reaction zone is kept constant. That is, this amount is determined by the amount of water distilled from the reaction zone and the amount of water gained or lost by the reaction. The ratio of the number of moles of water distilled from the reaction zone to the number of moles of raw materials and products distilled is determined by the reaction pressure. Since the number of moles of raw materials and products to be distilled is approximately equal to the number of moles of _C4 supplied,
The ratio of distilled water and supplied C ₄ will be determined by the reaction pressure. Therefore, the amount of water to be supplied may be determined by taking into account the reaction pressure, the amount of C ₄ supplied, and the increase or decrease of water due to the reaction. In the method of the present invention, the reaction temperature is preferably 150
Selected from the range of ~220℃. The reaction temperature is appropriately selected depending on the acid strength of the acid aqueous solution; for example, a lower temperature is selected for higher acid strength, and a higher temperature is selected for lower acid strength. When the reaction temperature is lower than 150°C, it is not only difficult to maintain the reaction rate at a constant level, but also leads to a decrease in the yield of isoprene. Even if the reaction temperature exceeds 220°C, the yield of isoprene does not decrease significantly, but because the vapor-liquid equilibrium between FA and water changes, the conversion rate of FA under conditions that give the optimum selectivity decreases. If the reaction conditions are selected such that the conversion rate of FA is high at a reaction temperature exceeding 220°C, the sequential reaction from isoprene will increase.
This causes a decrease in isoprene selectivity. A preferable supply rate of the FA source to the acid aqueous solution is determined by taking into account the reaction temperature, the acid strength of the acid aqueous solution, and the reaction pressure. In order to increase the supply rate of the FA source, it is generally necessary to increase the acid concentration of the acid aqueous solution or to increase the reaction temperature, and in this case, there is a concern about corrosion of the reactor. 15-30% by weight as acid aqueous solution
In the method of the present invention using a mixed acid aqueous solution containing 0.5 to 5% by weight of boric acid and 0.5 to 5% by weight of phosphoric acid, the feed rate of the FA source is usually 1 kg of the acidic aqueous solution when the FA source is converted to FA. The amount is preferably 3 mol or less per hour. 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 FA source supply rate should be lower than the FA source. per hour per 1 kg of acid aqueous solution when converted to FA
The amount is preferably 0.2 mole or more. 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. Since water is supplied to the reactor and formaldehyde takes the form of an aqueous solution in the reaction zone, it is advantageous in terms of reaction operation to use an aqueous formaldehyde solution as the formaldehyde source. In addition to other hydrocarbons, the isobutene and tertiary butanol used in the method of the present invention include
-Methyl-1,3-butanediol, 3-methyl-2-buten-1-ol, 3-methyl-3-buten-1-ol, 3-methyl-1-butene-3
-ol, methyl isopropyl ketone, 2-methylbutanal, methyl tertiary butyl formal,
4,4-dimethyl-1,3-dioxane, 4-methyl-5,6-dihydro-2H-pyran, etc. may be included. Alkyl tertiary butyl ethers such as methyl tertiary butyl ether which give isobutene and tertiary butanol under the reaction conditions can also be used as _C4 source compounds. 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 acid aqueous solution during the reaction. For this purpose, the acid aqueous solution may be stirred vigorously, and if necessary, a grinding 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 byproducts, especially tar substances, generated during the reaction will accumulate in the acid aqueous solution. A portion of the aqueous acid solution can be continuously or intermittently withdrawn from the reaction zone and led to a decanter or extraction column to remove high-boiling byproducts from the aqueous acid solution. The produced isoprene can be obtained by fractional distillation from the organic layer distilled out by the reaction. The isoprene obtained by the present invention has high purity and is extremely useful as a starting material for polyisoprene, terpene compounds, and the like. EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited thereto. Example 1 A stainless steel (SUS316) test piece (5 cm x 1
A reaction apparatus consisting of a pressure-resistant glass reactor with an internal volume of 750 ml and equipped with a magnetic stirrer and a gas distillation tube was used. The gas distillate pipe is connected to a distillate receiver (two types, one for preliminary reaction and one for quantitative determination) via a condenser.
were connected. 60g of orthoboric acid, 3.0g of phosphoric acid in the reactor
237g of water and 180g under a pressure of 15.6Kg/ ^cm2 .
Heat to °C, 20% by weight boric acid and 1.0% by weight phosphoric acid
A mixed acid aqueous solution was prepared. The pressure was kept constant by finely adjusting the pressure by introducing nitrogen gas before supplying the raw materials and by purging the nitrogen gas during the reaction. In addition, 178 of the above mixed acid aqueous solution
The vapor pressure at °C is 9.3Kg/ ^cm2 . While supplying isopten to the reactor at a rate of 129 g/hr. and a 12.2% by weight aqueous formaldehyde solution to the reactor at a rate of 56.6 g/hr., the contents were stirred at a speed of 1000 revolutions per minute at the above-mentioned temperature and pressure. The aqueous reaction gas distilled from the reactor was condensed in a condenser and collected in a pre-reaction distillation tank. After 3 hours of reaction, the distillate collection was switched to the quantitative distillation tank 2
Time sampling was performed. The reaction pressure was controlled by degassing, and during sampling, the sample was introduced into a trap cooled with dry ice-acetone and absorbed into n-butyl ether. During this time, the pressure, temperature and liquid level in the reactor remained constant. The distillate in the quantitative distillation tank was separated, and the aqueous phase and organic phase were each analyzed. The amount of formaldehyde contained in the aqueous phase was determined by the sodium sulfite method.
The amount of tertiary butanol was determined by gas chromatography (internal standard method). In addition, isobutene, tertiary butanol, isoprene, and byproducts contained in the organic phase were determined by gas chromatography (internal standard method). Isobutene and isoprene were also determined in the liquid collected in the trap by gas chromatography (internal standard method). The specimens were washed with water, methyl alcohol and ethyl ether in this order, dried and examined for weight loss before and after the reaction. The results are shown in Table 2. Examples 2-4 Using the same reaction apparatus as in Example 1, a reaction was carried out in the same manner as in Example 1, except that the acid concentrations of phosphoric acid and boric acid were changed. The results are also listed in Table 2. Comparative Example 1 Using the same reaction apparatus as in Example 1, a reaction was carried out in the same manner as in Example 1, except that boric acid was not added as a catalyst and only an aqueous phosphoric acid solution was charged into the reactor. The results are also listed in Table 2. Comparative Example 2 Using the same reaction apparatus as in Example 1, a reaction was carried out in the same manner as in Example 1 except that phosphoric acid was not used as a catalyst and only an aqueous boric acid solution was charged into the reactor. The results are also listed in Table 2.

[Table] Example 5 Using the same reaction apparatus and reaction conditions as Example 1
Continuous reaction was carried out for 1000 hours. During the reaction, high-boiling byproducts that gradually accumulated in the reaction zone were separated from the reaction zone by extraction with methyl isopropyl ketone. In addition, phosphoric acid and boric acid dissolved in the separated high-boiling by-products are recovered by washing with water and fed to the reactor. The feed amount was adjusted so that it was the same. The results are shown below.

【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. 100 g of tertiary butanol and 12.12% formaldehyde aqueous solution 38.0 g in a stainless steel (SUS-316) autoclave with an internal volume of 1 and equipped with a stirrer.
(4.6 g of formaldehyde), 0.09 g of silicotungstic acid, and 142.3 g of water, and heated to 210 g with stirring.
The temperature was raised to ℃, stirring was immediately 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 bottle 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 the charged formaldehyde is
It was 49.3%. 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 and 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, it 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)

[Claims] 1. A method for producing isoprene by reacting isobutene and/or tertiary butanol with formaldehyde in an acid aqueous solution, in which 15 to 30% by weight of boric acid and 0.5 to 5% by weight of phosphoric acid are used as the acid aqueous solution. isobutene and/or tertiary butanol, a formaldehyde source, and water are continuously or intermittently supplied to the acid aqueous solution, and the generated isoprene, low-boiling byproducts, and unreacted raw materials are aqueous. A method for producing isoprene, characterized in that the reaction is carried out while distilling it as a gaseous mixture of isoprene. 2. The method according to claim 1, wherein the reaction temperature is 150 to 220°C. 3. The method according to claim 1, wherein the ratio of the number of moles of the isobutene and/or tertiary butanol supplied to the number of moles of the formaldehyde source supplied in terms of formaldehyde is at least 3. 4. The method according to claim 1, wherein the pressure of the reaction system is 1.1 to 2.5 times the vapor pressure of the acid aqueous solution at the reaction temperature. 5. The method according to claim 1, wherein the formaldehyde source is supplied at a rate of 3 mol or less per hour per 1 kg of acid aqueous solution when the formaldehyde source is converted into formaldehyde. 6. The method according to claim 1, wherein the aqueous acid solution is continuously or intermittently withdrawn from the reaction zone, high-boiling byproducts dispersed in the aqueous acid solution are removed, and then the aqueous acid solution is recycled to the reaction zone. .