JPS6245211B2 - - 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. 46-6963 discloses a gas phase reaction method using a calcium phosphate-chromium oxide catalyst. However, this method has a 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. For example, in Japanese Patent Publication No. 49-10926, Example 5
When the reaction was carried out at 160℃ for 18 minutes using FeCl ₂ as a catalyst, the reaction rate was 82% based on formaldehyde.
% yield of isoprene was produced. However, when the present inventors tried Example 5 of Japanese Patent Publication No. 49-10926, Example 2 of Japanese Patent Publication No. 52-30483, and Example 8 of Japanese Patent Publication No. 57-130928, we found that As shown in the example, the yield of isoprene was around 50% or less. Even when other examples than those mentioned above were tested, similar low yields of isoprene were obtained. 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).
In the method described in the above-mentioned patent publication, the reaction is carried out in a closed system at a temperature above the critical temperature of isobutene, but such a reaction method requires high pressure and has the drawback of increasing equipment costs. Further, US Pat. No. 2,350,485 describes a method for producing a conjugated diene by reacting an olefin with an aldehyde, and describes that the reaction can be carried out using various reaction formats.
Only one example is described which shows an example of the reaction between butene and formaldehyde in a closed system, and what is more, the 2,3-dimethyl-
The yield of 1,3-butadiene is as low as 23%. When the present inventors reacted isobutene and formaldehyde under the same reaction conditions as in this example, the yield of isoprene was also approximately the same as the yield of 2,3-dimethyl-1,3-butadiene. Ta. As mentioned above, the one-step method for producing isoprene from isobutene and/or tertiary-butanol and formaldehyde includes problems that need to be solved, and the process for producing isoprene from 4,4-dimethyl- This is a major reason why the so-called two-step process using 1,3-dioxane has been adopted. The inventors of the present invention have conducted intensive studies to solve the drawbacks of these conventionally known techniques regarding a one-step method for producing isoprene in a liquid phase, and as a result, have arrived at the present invention. That is, according to the present invention, in a method for producing isoprene by reacting isobutene and/or tertiary butanol with formaldehyde in a reactor containing an acidic aqueous solution, the formaldehyde aqueous solution is liquid and the isobutene and/or are reacted.
Alternatively, tertiary butanol and water (excluding the water contained in the formaldehyde aqueous solution) are continuously or intermittently supplied as a gas to the reactor, and a portion of the acidic aqueous solution is taken out from the reactor, heated, and then added to the reactor. Isoprene can be produced in good yield by carrying out the reaction while circulating and distilling isoprene, water, and other low-boiling components produced out of the reaction zone. The method of the present invention has many advantages, such as excellent operational stability, long catalyst life, and the ability to carry out the reaction at relatively low temperatures and pressures, thereby keeping equipment costs low. As mentioned above, the method of the present invention involves continuously or intermittently supplying an FA aqueous solution as a liquid and _C4 and water as a gas to a reactor containing an acidic aqueous solution, while producing isoprene, water and other low boiling point substances. The main idea is to distill the components out of the reaction zone, and at the same time take out a portion of the acidic aqueous solution from the reactor, heat it, and then circulate it back into the reactor. It is essentially important to carry out the reaction while distilling the produced isoprene out of the reaction zone in order to obtain isoprene in a good yield. Also,
The reactor to provide the necessary heat for the reaction and distillation of isoprene, water and other low-boiling components by feeding _C4 and water (excluding water contained in the FA aqueous solution) to the reactor in gaseous state. This reduces the amount of heat that must be given to the acid aqueous solution taken out, heated, and returned to the reactor (hereinafter sometimes referred to as the reaction solution), thereby reducing the consumption of isoprene due to side reactions during heating, and increasing the isoprene yield. It was found that the rate could be further improved. If all raw materials are supplied to the reactor in a gaseous state, the amount of heat that should be given to the reaction liquid will be minimal, but according to the inventors' experiments,
When the FA aqueous solution is vaporized and introduced into the reactor, it is preferable because the decrease in the isoprene yield based on FA due to the consumption of FA during the vaporization exceeds the increase in the isoprene yield due to the increase in the amount of heat that should be given to the reaction solution. do not have. For the reasons stated above, in the method of the present invention, the FA aqueous solution is supplied to the reactor in the form of a liquid, and the C ₄ and water are supplied in the form of a gas. When carrying out the method of the present invention, it is preferable that the ratio of the number of moles of C ₄ supplied to the number of moles of formaldehyde supplied (hereinafter referred to as C ₄ /FA) is at least 3. When C ₄ /FA is less than 3, the yield of isoprene decreases. From the viewpoint of reaction yield, the larger C ₄ /FA is, the better, 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 will be small, and it may be used instead. Generally, C ₄ /FA should not exceed 20, since the amount of heat increases and becomes economically disadvantageous. In the present invention, in this way _{, C4} for FA
was used in excess, so it was supplied into an acidic aqueous solution.
Most of the C ₄ is distilled off unreacted, but this can be reused after being separated from other components. Since unreacted C ₄ has a composition close to the equilibrium composition of isobutene and tertiary butanol under the reaction conditions, as long as unreacted C ₄ is recycled to the reaction, either isobutene or tertiary butanol can be used as a starting material. Even if one of them is added to the reaction solution, a mixture of isobutene and tertiary butanol will ultimately be used as the reaction raw material. When adopting a reaction method in which isoprene and low-boiling components are distilled out of the reaction zone together with water while supplying C ₄ , FA source, and water into a reactor containing an acidic aqueous solution, the pressure inside the reactor must be adjusted. The ratio of each component to water that evaporates from the reaction zone can be determined by the method; when the pressure is high, the proportion of water to the total of components other than water in the distillate decreases, and when the pressure is low, the proportion of water to the total of components other than water decreases. The opposite phenomenon occurs. In order to obtain isoprene in a good yield, the pressure inside the reactor (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 adjusted to the reaction temperature of the acidic aqueous solution. of vapor pressure at
It is preferable that it be within the range of 1.1 to 2.5 times. Note that the vapor pressure of the acidic aqueous solution at the reaction temperature (hereinafter referred to as Pw
) is a physical constant uniquely included depending on the type and concentration of the acidic substance contained in the acidic aqueous solution. When the pressure inside the reactor exceeds 2.5 times Pw, the yield of isoprene decreases significantly. When the pressure inside the reactor is less than 1.1 times Pw, there is no significant decrease in isoprene, but the conversion rate of FA decreases and the ratio of water to isoprene in the distillate increases. The amount of heat consumed in the reaction increases. In the method of the present invention, it is possible to carry out the reaction while supplying, in addition to the reaction raw materials, a low-boiling compound that is inactive under the reaction conditions into the reactor, if desired. The low-boiling compounds that are inert under the reaction conditions that can be used here are compounds that do not substantially change immediately after the reaction, and are specifically represented by n-propane, n-butane, n-hexane, cyclohexane, etc. Examples include hydrocarbons having 1 to 10 carbon atoms, and inert gases such as nitrogen. The reaction temperature suitable for the method of the present invention is determined by considering the acid strength of the acidic aqueous solution, and is usually 150 to 220°C.
Selected from the range of °C. If the reaction temperature is less than 150°C, the yield of isoprene will decrease even if the concentration of the acidic aqueous solution is increased to maintain the reaction rate at a constant level. Even if the reaction 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 that increase the conversion rate of FA, the sequential reactions from isoprene will increase, resulting in a decrease in the selectivity of isoprene. The preferred rate of supply of FA to the reactor is determined by taking into account the acid strength of the acidic aqueous solution, the reaction temperature, and the reaction pressure. In order to increase the feed rate of FA, it is necessary to increase the acid strength of the acidic aqueous solution or to increase the reaction temperature, and in this case, the problem of corrosion of the reactor arises. Therefore, the feed rate of FA is preferably 3 mol or less per hour per 1 kg of acidic aqueous solution. Although there is no lower limit in the strict sense of the feed rate of FA, if the feed rate is unnecessarily reduced, the reactor will become larger and disadvantageous in terms of equipment, so the feed rate of FA should be 0.2 mol per hour per 1 kg of acidic aqueous solution. It is better that it is above. 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 an aqueous solution. The acid strength of these acidic aqueous solutions varies depending on the type of acidic substance, reaction temperature, FA supply rate, etc., but is usually selected from the pH range of 0.5 to 2.5. 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.
- Organic acids such as toluenesulfonic acid, benzenesulfonic acid, trifluoromethanesulfonic acid, oxalic acid, and acid salts such as sodium hydrogensulfate may be mentioned. The concentration of the formaldehyde aqueous solution used in the method of the present invention is preferably higher in order to reduce the load on the heat exchanger due to entrained water. However, if the concentration is too high, paraformaldehyde will precipitate, resulting in operational inconvenience. From these points, the concentration of the formaldehyde aqueous solution is usually 20 to 70% by weight, preferably 25 to 70% by weight.
Selected from a range of 60% by weight. 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. The amount of water fed to the reactor is usually adjusted so that the amount of acidic aqueous solution in the reactor 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 off is determined by the pressure within the reactor. Since the number of moles of raw material and product to be distilled is approximately equal to the number of moles of C ₄ supplied, the ratio of water distilled to C ₄ supplied is determined by the pressure inside the reactor. Become. Therefore, the amount of water fed depends on the pressure inside the reactor,
The amount may be determined by taking into account the amount of C ₄ supplied and the increase and decrease of water due to the reaction. Hereinafter, the present invention will be specifically explained with reference to Examples. Example 1 Raw material inlet, distillation pipe, distillate condenser, stirrer,
Internal volume: 120mm equipped with thermometer, pressure gauge, catalyst water outlet, catalyst water circulation line, heat exchanger, and distillate receiver tank.
A reactor made of Hastelloy G-3 was used. The total volume of the catalyst water circulation line and heat exchanger was 25. Put 89 kg of 3% phosphoric acid water into the reactor, circulation line and heat exchanger, heat it with the heat exchanger while stirring, and bring the internal temperature of the reactor under a pressure of 16.0 kg/ ^cm2 .
The temperature was 178℃. Isobutene was then fed to an isobutene evaporator at a rate of 31 Kg/hr for vaporization, and was then fed to the reactor through a water evaporator. Water was supplied to the water evaporator at a rate of 8.6 Kg/hr, vaporized together with isobutene, and supplied to the reactor. then
A 27.67% formaldehyde aqueous solution was supplied to the reactor at a rate of 7.3 Kg/hr to start the reaction. The gas distilled from the reactor was condensed in a condenser and sent to a distillate receiving tank. After reacting for 6 hours, the collection of the condensate was switched to a quantitative distillate receiving tank, and the reaction was continued for an additional 3 hours. During this time, the pressure was maintained at 16.0 Kg/cm ² and the internal temperature of the reactor was maintained at 178°C. The vapor pressure of a 3.0% phosphoric acid aqueous solution at 178°C is 9.6 Kg/cm ² . The separated aqueous phase of the distillate in the quantitative distillation tank was extracted, and the weight of the aqueous phase was measured. The weight of the organic phase was determined by extracting a portion into a pressure bottle, measuring the specific gravity, and multiplying this by the volume. Regarding the aqueous phase, the amount of formaldehyde contained therein was determined by the sodium sulfite method, and the amount of tertiary butanol was determined by gas chromatography (internal standard method). Also, isoprene contained in the organic phase,
Isobutene, tertiary butanol and by-products were determined by gas chromatography (internal standard method). The reaction product was as follows. Supplied isobutene 1646 mol Supplied formaldehyde 200.4 mol C ₄ /FA (mol/mol) 8.2 Supplied water (including water in formaldehyde aqueous solution) 2331 mol Formaldehyde distilled 4.0 mol Distilled isoprene 140.9 mol Distilled water 2420 mol distilled water/Feed C ₄ (mol/mol) 1.47 Formaldehyde feed rate per 1 kg of catalyst water
0.75 mol/hr Formaldehyde conversion rate 98.0% Isoprene yield (based on consumed formaldehyde) 71.7% Comparative example 1 Formaldehyde aqueous solution was vaporized together with isobutene and water in a water evaporator and supplied to the reactor, and reaction initiation 24 The reaction was carried out in the same manner as in Example 1, except that after a certain period of time, the tank was switched to a quantitative distillate receiving tank. The reaction results were as follows. Formaldehyde conversion rate: 98.2% Isoprene yield (based on consumed formaldehyde): 62.4% Comparative Example 2 In place of the heat exchanger used in Example 1, a shell-and-tube heat exchanger with a total volume of 115 mm including the circulation line was used. use,
The reaction was carried out by supplying water directly to the reactor without passing through the evaporator. The amount of 3% phosphoric acid water supplied is 150 kg,
The feed rate of raw materials and water was 52Kg/hr of isobutene, so that the feed rate per 1Kg of phosphoric acid water was the same.
The amount of water was 13Kg/hr, and the amount of 27.67% formaldehyde aqueous solution was 12.6Kg/hr. The reaction temperature, reaction time, and pressure were the same as in Example 1. The reaction results were as follows. Formaldehyde conversion rate 98.0% Isoprene yield (based on consumed formaldehyde) 61.5% Example 2 The concentration of the formaldehyde aqueous solution was 45.20%, the feed rate was 4.6 Kg/hr, and the water feed rate was
The reaction was carried out in the same manner as in Example 1 except that the reaction rate was 11.5 Kg/hr. The reaction results were as follows. Supplied isobutene 1650 mol Supplied formaldehyde 204.5 mol C ₄ /FA (mol/mol) 8.1 Supplied water (including water in formaldehyde aqueous solution) 2350 mol Formaldehyde distilled 4.8 mol Distilled isoprene 144.0 mol Distilled water 2443 mol distilled water/Feed C ₄ (mol/mol) 1.48 Formaldehyde feed rate per 1 kg of catalyst water
0.77 mol/hr Formaldehyde conversion rate 97.7% Isoprene yield (based on consumed formaldehyde) 72.1% Examples 3 to 7 The following reactions were carried out in the same manner as in Example 1.
The results are summarized in Table 1. All conditions other than those listed in Table 1 are the same as in Example 1.

[Table] When tertiary butanol was supplied instead of isobutene, the tertiary butanol was vaporized together with water in a water evaporator and supplied. 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 layer was 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 38.0 (formaldehyde 4.6g), silicotungstic acid
Add 0.09g and 142.3g of water and heat to 210℃ while stirring.
Immediately, 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 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 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)

[Claims] 1. A method for producing isoprene by reacting isobutene and/or tertiary butanol with formaldehyde in a reactor containing an acidic aqueous solution, wherein the formaldehyde aqueous solution is in a liquid form and isobutene and/or tertiary butanol is reacted with formaldehyde in a reactor containing an acidic aqueous solution. Butanol and water (excluding the water contained in the formaldehyde aqueous solution) are continuously or intermittently supplied to the reactor as a gas, and a portion of the acidic aqueous solution is taken out from the reactor, heated, and then circulated to the reactor to generate the product. A method for producing isoprene, characterized in that the reaction is carried out while distilling isoprene, water and other low-boiling components out of the reaction zone. 2. The method according to claim 1, wherein the ratio of the number of moles of isobutene and/or tertiary butanol supplied to the number of moles of formaldehyde supplied is at least 3. 3. The method according to claim 1, wherein the pressure inside the reactor is 1.1 to 2.5 times the vapor pressure of the acidic aqueous solution at the reaction temperature.