JPS6245212B2 - - 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 trials based on these patent publications, no results were obtained that were industrially satisfactory in terms of reaction formation 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 type 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 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 an acid aqueous solution, a boric acid aqueous solution having a boric acid concentration of 30 to 60% by weight is used as the acid aqueous solution; The following general formula () for boric acid aqueous solution (In the formula, R ¹ represents a hydrogen atom or a methyl group,
R ² and R ³ represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, where one of R ¹ , R ² and R ³ represents an alkyl group, and n is 2 to 4.
is an integer of 15. However, the total number of carbon atoms included in the formula shall be at least 8. ), and adding isobutene and/or tertiary butanol, a formaldehyde source, and water continuously or intermittently to the mixture of boric acid aqueous solution and glycol ether. By carrying out the reaction while distilling isoprene, low-boiling by-products, and unreacted raw materials produced together as an aqueous gaseous mixture, isoprene can not only be produced in a good yield, but also corrosion of the equipment can be significantly reduced. Can be done. 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, in the method of the present invention, 30 to 60% by weight
A specific amount of glycol ether represented by the general formula () is added to an aqueous solution of boric acid, and isoprene is added to the mixture of boric acid and glycol ether while continuously or intermittently supplying C ₄ , an FA source, and water. The main idea is to carry out the reaction while distilling off low-boiling byproducts and unreacted raw materials. 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. In the reaction according to the method of the present invention, the boric acid aqueous solution is
Used at a concentration of ~60% by weight. When the concentration is less than 30% by weight, not only a sufficient reaction rate cannot be obtained, but also the yield of isoprene decreases. On the other hand, if the concentration exceeds 60% by weight, the solubility of isobutene in the boric acid aqueous solution decreases, and the yield of isoprene decreases. In the method of the present invention, a boric acid aqueous solution is thus used as a catalyst, and the boric acid aqueous solution has a dissociation constant [for example, an aqueous solution of orthoboric acid has a dissociation constant of 25
The dissociation constant at °C is only 5.8 × 10 ^-10 −
LANGE'S HANDBOOK OF CHEMI STRY,
1209, McGraw-Hill Book Co., (1967)], as it is an extremely weak acid, corrosion of the equipment is significantly suppressed, and according to the inventors' study, SUS304 stainless steel and SUS316 stainless steel When steel was immersed in a 45% by weight boric acid aqueous solution maintained at 170°C for 71 hours with stirring, the corrosion rate was less than 0.1 mm/year in all cases. In the method of the present invention in which 5 to 15% by weight of glycol ether represented by the general formula () is added to an aqueous boric acid solution, isobutene is not added to the aqueous boric acid solution even though the concentration of the aqueous boric acid solution is 30% by weight or more. As a result of the increased dissolution amount, the yield of isoprene at the same C ₄ /FA value is significantly increased compared to the case without the addition of the glycol ether. The reason why the solubility of isobutene in an aqueous boric acid solution is improved by adding the glycol ether represented by the general formula () to an aqueous boric acid solution is that the glycol ether is excellent in both isobutene and an aqueous boric acid solution. This is thought to be due to their affinity. In the general formula (), examples of the alkyl group having 1 to 4 carbon atoms represented by R ² and R ³ include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, and an n-butyl group.
Any one of R ¹ , R ² and R ³ must be an alkyl group. If R ¹ , R ² and R ³ are hydrogen atoms at the same time, the affinity of glycol ether for isobutene decreases and no effect of adding glycol ether can be expected. It is necessary that n in the general formula () is an integer of 2 to 15. When n is 1, R ¹ , R ² and
As in the case where R ³ is also a hydrogen atom, no effect of adding glycol ether can be expected, and glycol ether is distilled out during the reaction, which is not preferable. When n exceeds 15, the affinity of the glycol ether for boric acid aqueous solution decreases, which is not preferable. The total number of carbon atoms contained in the general formula () must be at least 8, and R ¹ , R ²
The type of and R ³ and the value of n are determined so that this requirement is satisfied. If the total number of carbon atoms is less than 8, the affinity of the glycol ether for isobutene decreases, which not only reduces the effect of adding the glycol ether, but also undesirably distills the glycol ether during the reaction. Examples of suitable glycol ethers include polypropylene glycol with an average molecular weight of 700, tripropylene glycol monomethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol monobutyl ether, and the like. Glycol ether is 5% for boric acid aqueous solution.
It is added at a rate of ~15% by weight. If the amount of glycol ether added is less than 5% by weight, the effect of adding glycol ether will be small, and if the amount of glycol ether added exceeds 15% by weight, the catalytic activity of the boric acid aqueous solution will decrease and the yield of isoprene will decrease. do. In the reaction according to the method of the present invention, the ratio of the number of moles of C ₄ supplied to the number of moles of the FA source supplied in terms of FA (hereinafter referred to as C ₄ /FA) is preferably at least 3. 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. A mixture of boric acid aqueous solution and glycol ether
Isoprene, while supplying C ₄ , FA source and water
In the method of the present invention in which low-boiling point by-products and unreacted raw materials are distilled out together with water, the ratio of each component evaporated from the reaction zone to water can be determined by adjusting the reaction pressure. When the reaction pressure is high, the ratio of water to the total of components other than water in the distillate decreases, and when the reaction pressure is low, the amount of water supplied increases to keep the amount of the mixture of boric acid aqueous solution and glycol ether constant. However, the opposite phenomenon occurs.
In order to obtain isoprene in a good yield, the reaction pressure must be adjusted to the boric acid aqueous solution before adding the glycol ether (hereinafter, unless otherwise specified, boric acid aqueous solution means one that does not contain glycol ether, and the boric acid aqueous solution to which glycol ether is added) (sometimes simply referred to as a mixed liquid) is the vapor pressure at the reaction temperature of
It is preferable that it be within the range of 1.1 to 2.5 times. The vapor pressure of boric acid aqueous solution at the reaction temperature (hereinafter referred to as Pw)
) is a physical constant uniquely determined by the concentration of the boric acid aqueous solution. When the reaction pressure exceeds 2.5 times Pw, the yield of isoprene decreases significantly. When the reaction pressure 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 and is consumed in the reaction. The amount of heat generated increases. The amount of water supplied to the reaction zone is usually adjusted so that the amount of mixed liquid in the reaction zone remains 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 C ₄ supplied, the ratio of water to be distilled and C ₄ supplied 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 concentration of the boric acid aqueous solution; for example, a lower temperature is selected for a higher concentration, and a higher temperature is selected for a lower concentration. 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 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, resulting in a decrease in the selectivity of isoprene. The preferred rate of supply of the FA source to the mixed solution of boric acid aqueous solution and glycol ether is determined in consideration of the reaction temperature, the concentration of the boric acid aqueous solution, and the reaction pressure. In order to increase the supply rate of the FA source, it is necessary to increase the concentration of the boric acid aqueous solution or to increase the reaction temperature. The feed rate of the FA source is usually preferably 3 mol or less per hour per 1 kg of the mixed liquid when the FA source is converted to FA. 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. When converted to FA, it is preferably 0.2 mol or more per hour per 1 kg of mixed liquid. Examples of the formaldehyde source used in the method of the present invention include a formaldehyde aqueous solution and formaldehyde gas. In addition, trioxane, paraformaldehyde, and the like, which decompose under reaction conditions to give formaldehyde, 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-buten-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. If the reaction is carried out over a long period of time, a small amount of high-boiling by-products, especially tar substances, generated during the reaction will accumulate in the reaction zone. Remove intermittently,
High-boiling by-products can be removed by passing to a decanter or extraction column. 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 extraction 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. 120g of orthoboric acid and 150g of water in the reactor
and polypropylene glycol [manufactured by NOF Corporation,
An average molecular weight of 700 and a vapor pressure of 0.01 mmHg or less at 20°C] were charged and heated to 170°C under a pressure of 9.7 kg/cm ² . 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. The vapor pressure of the above boric acid aqueous solution at 170℃ is
It is 6.2Kg/ ^cm2 . While supplying isobutene to the reactor at a rate of 122 g/hr. and a 11.36% by weight aqueous formaldehyde solution to the reactor at a rate of 57.7 g/hr., the contents were stirred at a speed of 1000 revolutions per minute at the above 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 the reaction was carried out for 3 hours, the collection of the distillate was switched to a quantitative distillation tank, and sampling was carried out for 2 hours. 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). In addition, stainless steel specimens for corrosion tests were washed with water, acetone, methyl alcohol, and ethyl ether in this order, dried, and the weight loss before and after the reaction was examined. The results are shown in Table 1. Example 2 Diethylene glycol monobutyl ether (20℃
Using the vapor pressure of 0.01mmHg), calculate the amount added.
30g, and isobutene and
The reaction was carried out in the same manner as in Example 1, except that the feeding rate of the 11.36% by weight formaldehyde aqueous solution was 129 g/hr. and 60.7 g/hr., respectively. The results are also listed in Table 1. Comparative Example 1 No polypropylene glycol was added, and the feed rate of isobutene and 11.36 wt% formaldehyde aqueous solution was 116 g/1, respectively.
The reaction was carried out in the same manner as in Example 1, except that the reaction rate was 54.7 g/hr. The results are also listed in Table 1. Comparative Example 2 The amount of water charged was 180 g without adding polypropylene glycol (the amount of water was increased by an amount equivalent to the amount of propylene glycol added), and the feeding rate of isobutene and 11.36% by weight formaldehyde aqueous solution 129g each/
The reaction was carried out in the same manner as in Example 1 except that the reaction rate was 60.7 g/hr. The results are also listed in Table 1.

【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.
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. In a stainless steel (SUS-316) autoclave with an internal volume of 300 ml equipped with a stirrer, 16.6 g of a 36% formaldehyde aqueous solution containing 6% methanol,
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 acid aqueous solution, in which a boric acid aqueous solution having a boric acid concentration of 30 to 60% by weight is used as the acid aqueous solution, and The following general formula () for boric acid aqueous solution (In the formula, R ¹ represents a hydrogen atom or a methyl group,
R ² and R ³ represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, where one of R ¹ , R ² and R ³ represents an alkyl group, and n is 2 to 4.
is an integer of 15. However, the total number of carbon atoms included in the formula shall be at least 8. ), and adding isobutene and/or tertiary glycol ether to the mixture of boric acid aqueous solution and glycol ether.
This method is characterized in that the reaction is carried out while continuously or intermittently supplying butanol, a formaldehyde source, and water while distilling the produced isoprene, low-boiling byproducts, and unreacted raw materials as an aqueous gaseous mixture. Manufacturing method. 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 reaction pressure is 1.1 to 2.5 times the vapor pressure of the boric acid aqueous solution at the reaction temperature. 5 The supply rate of the formaldehyde source is 1 kg of a mixed solution of boric acid aqueous solution and glycol ether when the formaldehyde source is converted to formaldehyde.
2. The method according to claim 1, wherein the amount is 3 mol or less per hour.