JPS59184136A - Production of isoprene - Google Patents

Abstract

PURPOSE:To obtain isoprene in high yield in the liquid phase by the one-stage method, by reacting an isobutylene source with a formaldehyde source in the liquid phase in the presence of water and an acidic catalyst at a low temperature, and reacting the reaction mixture in a gas liquid mixture system under a specific pressure or below at a high temperature. CONSTITUTION:One or more isobutylene sources selected from isobutylene, tert- butanol and alkyl tert-butyl ether are reacted with a formaldehyde source in the presence of water and an acidic catalyst in the complete liquid phase in a low-temperature reaction zone at 145 deg.C or below, preferably 60-140 deg.C to synthesize an isoprene precursor. The resultant effluent liquid is then fed to a high- temperature reaction zone at 150 deg.C or above, preferably 150-230 deg.C and reacted in the state of a gas liquid mixture under 40 atm or below, preferably 4-35 atm to decompose the above-mentioned isoprene precursor into isoprene. The isoprene can be produced in a simplified process continuously in high yield by this method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing isoprene by a liquid phase one-step process,
More specifically, the isobutylene source and the formaldehyde source are subjected to a liquid phase reaction in the presence of water and an acidic catalyst in a low temperature reaction zone, and then subsequently reacted in a high temperature reaction zone at low pressure and under a gas-liquid mixed state. This invention relates to a method for producing inobrene in high yield.

Isobutylene, tertiary butanol (hereinafter abbreviated as TEA), methyl tert-butyl ether (hereinafter M
TB1! ! isobutylene sources such as
A method for producing imprene from a formaldehyde source such as formaldehyde, paraformaldehyde, etc. by a one-step liquid phase reaction in the presence of an acidic catalyst has been known (for example, Japanese Patent Publication Nos. 48-28884 and 49-10).
No. 926, No. 50-10285, etc.).

This one-step method basically has fewer reaction steps compared to the so-called two-step method, which synthesizes isoprene from isobutylene and formaldehyde via 4,4-dimethyl-1,3-dioxane, which has already been industrialized. Although it has advantages, on the other hand, it has the disadvantage that the selectivity is still insufficient and a large amount of by-products, which are difficult to handle, are produced.

Furthermore, as a specific example of such a one-stage method, a method in which the reaction is carried out in two stages, one at a low temperature and one at a high temperature, is also known. For example, Tokuko Sho 55-2
No. 415 discloses that an inbutylene source and formaldehyde are catalyzed by a specific amino group-containing sulfonic acid such as sulfanilic acid or orthanylic acid in the presence of a small amount of water.
A two-step reaction process of ~13Qc and 160-200C is described.

This method is primarily intended to prevent clogging of the equipment due to formaldehyde polymerization, but the inventors' additional tests of this method revealed that a large amount of by-products were present in the product and that the catalyst was not clogged. It was confirmed that formaldehyde reacts and lowers the basic unit.

Therefore, the inventors of the present invention conducted intensive studies to improve these shortcomings seen in the prior art, and found that after performing a liquid phase reaction at a low temperature, a high temperature reaction is performed in a gas-liquid mixture system below a certain pressure. It was also found that imprene could be obtained in high yield.

According to the present invention, at least one source of imbutylene selected from isobutylene, tertiary phthanol, and alkyl tert-butyl ether and a source of formaldehyde are continuously subjected to a liquid phase reaction in the presence of water and an acidic catalyst. When producing isoprene, an isoprene precursor is synthesized by reacting an inbutylene source and a formaldehyde source in a complete liquid phase in a low-temperature reaction zone in the presence of water and an acidic catalyst, and then the liquid derived from the zone is heated to a high temperature. 40
A method for producing isoprene by a one-step liquid phase method is provided, which is characterized in that an imprene precursor is decomposed into isoprene at a temperature below atmospheric pressure and under a gas-liquid mixed state.

The inbutylene source used as a reaction raw material in the present invention is inbutylene, TEA'j or an alkyl tertiary-butyl ether, and a specific example of the alkyl tertiary-butyl ether is MTBlli. Although these imbutylene sources may be used alone, they can also be used in the form of a mixture of two or more types, and it is particularly preferable to use imbutylene and other imbutylene sources in combination.

On the other hand, the formaldehyde source used may be any source that can generate formaldehyde in the reaction system, and specific examples thereof include formaldehyde aqueous solution,
Examples include formaldehyde polymers (eg, paraformaldehyde, trioxane), formaldehyde precursors (eg, methylal, 4,4-dimethyl-1,3-diochitin), and the like. Further, a formaldehyde aqueous solution in which rose formaldehyde is dissolved to increase the formaldehyde concentration, or a formaldehyde aqueous solution containing methanol as a stabilizer can be similarly used.

Among these, formaldehyde aqueous solutions are prized because of their ease of handling, availability, and the need for water in the reaction system.

The ratio of the isobutylene source and formaldehyde source to be used is appropriately selected depending on the reaction conditions, but usually the theoretical amount of inbutylene 2 generated from the diisobutylene source is calculated based on 1 mole of formaldehyde generated from the formaldehyde source.
When the amount of inbutylene source used is too small, preferably 3 moles or more, the conversion rate of formaldehyde tends to decrease and the production of by-products tends to increase. On the other hand, if the amount of isobutylene source used becomes excessively large, the cost required to recover the unreacted isobutylene source will increase.
In the present invention, when the isobutylene source and the formaldehyde source are reacted, a two-step reaction at low and high temperatures is carried out, and the high temperature reaction is performed under a pressure of 40 atmospheres or less. It is essential to carry out the reaction under a gas-liquid mixed state.

The first requirement is to carry out the reaction in advance at a temperature of 145c or less, preferably 60-140t:' (hereinafter referred to as low temperature reaction), then 1500c or more, preferably 150-2
It is necessary to carry out the reaction at a temperature of 30C (hereinafter referred to as high temperature reaction).In the process of the low temperature reaction carried out in advance, 4,4-dimethyl-1,5-dioxane and 3-methyl-1 are reacted with isobutylene and formaldehyde. , 3-pumenediol, 3-methyl-3-buten-1-ol, etc., are synthesized. At this time, it is important to keep the reaction temperature below 145C; if this temperature is exceeded, the amount of final product isoprene produced increases at this stage, so formaldehyde or 4.4- Due to the reaction between formaldehyde generated by the decomposition of dimethyl-1,3-dioxane and isoprene, the by-product of oran species increases due to the difficulty of processing.On the other hand, if the reaction temperature becomes too low, the reactivity decreases, making it impractical. . Furthermore, the reaction temperature in the low-temperature reaction does not necessarily need to be kept constant, and as long as it is within a range of 145C or less, it may be raised sequentially or may be raised stepwise by dividing it into two or more stages.

The reaction strength of such a low-temperature reaction zone may be appropriately selected so that a gas phase does not exist, and is usually 1 to 80 ky/m. This is not preferable because it causes a decrease in the reaction rate if it is precipitated.

On the other hand, in the process of high-temperature reaction, inglene is produced by decomposition of the isoprene precursor produced by low-temperature reaction. At this time, if the reaction temperature is less than 150C, the decomposition rate of the imprene precursor is slow, and if it is too high, on the other hand, isoprene polymers and carbon-like or tar-like by-products tend to increase.

The high temperature reaction in the present invention is 40 atmospheres or less, preferably 40 atmospheres or less.
It is carried out in a gas-liquid mixture under conditions of ~35 atm. As the reaction pressure increases, energy efficiency and yield become inferior, and equipment costs also increase. On the other hand, the lower limit of the pressure is not particularly limited as long as the gas-liquid mixed state can be maintained, and the lower the pressure, the greater the effect.
Note that the pressure referred to in the present invention should be understood as a key gauge pressure without particular limitation.

Furthermore, the high temperature reaction needs to be carried out in a gas-liquid mixed state, thereby making it possible to greatly reduce by-products and improve the yield of isoprene compared to when the reaction is carried out in a completely liquid phase.

Incidentally, as a means of converting the reaction system into a gas-liquid mixed system, in addition to pressure control, it is also possible to mix in an inert gas (e.g. nitrogen, carbon dioxide, hydrocarbon gas), but in this case, the large size of the equipment In addition, the effect of improving the yield of imprene cannot be said to be so remarkable. In the present invention, an acidic catalyst is used in the reaction between the inbutylene source and the formaldehyde source.

The acidic catalyst may be any substance that exhibits acidity under reaction conditions in the presence of water; specific examples include hydrochloric acid,
Inorganic acids such as m-acid, nitric acid, phosphoric acid, hypophosphorous acid, phosphorous acid, tungstic acid, molybdic acid, telluric acid, hydrobromic acid, chlorosulfonic acid, silicotungsten acid, stannic acid, hypochlorous acid, etc. Acid, formic acid, sulfuric acid, cono-phosphoric acid, citric acid, phthalic acid, halatoluenesulfonic acid, )'J fluoromethanesulfonic acid, sulfonic acid ion exchange am
Organic acids such as, potassium salts, chromium salts, ammonium sulfate, ammonium phosphate, etc.
Examples include strong nonmetallic inorganic acid salts such as antimony chloride, metal salts such as ferric sulfate, nickel sulfate, tin chloride, cupric pyrophosphate, neurium phosphate, zirconium phosphate, and the like.

Among these, phosphorus compounds such as phosphoric acid and phosphates, heteropolyacids, organic acids, and their salts are prized from the standpoint of preventing corrosion of equipment. These acidic catalysts are usually used alone, but if necessary Two or more types of catalysts can be used in combination as appropriate.The amount of catalyst used is not necessarily constant depending on conditions such as the type of catalyst, reaction temperature, and reaction time, but it can be determined by conducting simple preliminary experiments. It can be determined as appropriate.

In addition, the reaction time may be selected appropriately; in low-temperature reactions, the residence time is usually 5 minutes to 5 hours, preferably 10 minutes to 2 hours.
On the other hand, in high-temperature reactions, it is usually 2
The time period is from minutes to 2 hours, preferably from 4 minutes to 1 hour.

The amount of water used in the reaction can be selected as appropriate, but usually 9 parts by weight of formaldehyde generated from the formaldehyde source.
The amount is 1 part by weight or more, preferably 2 to 100 parts by weight. Further, if necessary, polar solvents such as alcohols and ketones, fatty acids, aromatic hydrocarbon solvents, and the like can be allowed to coexist.

The reactor used may be of any structure as long as it can mix the reaction liquid well, and specific examples include a stirrer reactor, a perforated plate column, and a packed column. As reactors for high-temperature reactions, base reactors such as empty columns, perforated plate columns, and packed columns are preferred because of their ease of handling and simple structure.

Although the pressure conditions for the low-temperature reaction and the high-temperature reaction may be the same, it is preferable to provide independent pressure control mechanisms for each reaction in order to facilitate reaction control and ensure optimum conditions for each.

Thus, according to the present invention, isoprene can be produced in high yield through a simplified process without isoprene precursor isolation, and the production of by-products that are difficult to process can be significantly suppressed. can. Further, since most of the formaldehyde is consumed by the reaction, there is no need to recover it from the reaction solution, and furthermore, a basic reactor with a simple structure and easy handling can be used as a reactor in high-temperature reactions.

Next, the present invention will be explained in more detail with reference to Examples.

In addition, parts and percentages in the examples are based on weight unless otherwise specified.

Example 1 A serpentine stainless steel pipe with an internal diameter of 6 mm and a length of 7 m is used as a low-temperature reactor, and its outlet is connected to an internal pressure regulating valve, and the outlet pipe from the valve is connected to a high-temperature reactor. A serpentine stainless steel pipe with an inner diameter of 6 mm and a length of 2 m is used as a high temperature reactor, and the outlet pipe from the reactor is connected to an internal pressure regulating valve via a cooling pipe. The liquid discharged from the valve was collected in a pressure-resistant glass container, and the isoprene contained in the organic layer and the unreacted formaldehyde remaining in the aqueous layer were analyzed by gas chromatography. The reactors for low temperature and high temperature reactions are immersed in an oil bath and maintained at 120C and 165C, respectively. Then formaldehyde 5 was added to this low temperature reactor.
, 3%, water 45.7%, TEA 39.1%, phosphoric acid 9.
670 each of an aqueous solution consisting of 9% and imbutylene.
77 o'clock and 4001 it - 7 o'clock flow rate is supplied by pump, low temperature reactor is 60 9/♂, high temperature reactor is 20 k
The pressure was maintained at lI/♂ and the reaction was carried out continuously. As a result, the formaldehyde conversion rate was 100%, and the isoprene yield was 7 times 4% based on formaldehyde (the same applies hereinafter).

Furthermore, by measuring the amount of heat used to heat the reactants in the high-temperature reactor, it was found that inbutylene in the reactor was vaporized, indicating that the reaction was proceeding in a gas-liquid mixed system.

Example 2 A reaction was carried out in accordance with Example 1 except that the pressure of the high temperature reactor was maintained at 10#/cnl''.

As a result, the conversion rate of formaldehyde was 100%, and the yield of imprene was 81.3 mol%.

Comparative Example 1 The reaction was carried out in the same manner as in Example 1, except that a new device for supplying nitrogen gas to the high temperature reactor was installed and nitrogen gas was pumped in an amount equivalent to 15NJAl.◇As a result, formaldehyde The conversion rate was 999%, and the isoprene yield was 68.0 mol%.

Comparative Example 2 A reaction was carried out in the same manner as in Example 1, except that the total pressure in the high temperature reactor was maintained at 58 kg/m.

As a result, the formaldehyde conversion rate was 100% and p
1 isoprene yield was 55.8 mol%.

Furthermore, from the measurement of the amount of heat used to heat the reactants in the high-temperature reactor, no vaporization of isobutylene in the reactor was observed.

Comparative Example 3 A reaction was carried out in accordance with Example 2, except that the pressure in the low temperature reactor was maintained at 1°, 5 #/♂. As a result, the formaldehyde conversion rate was 98.0 mol, and the isoprene yield was 48.1 mol. It was observed that vaporization was occurring, and the reaction was progressing in a gas-liquid mixed system.

Comparative Example 4 The reaction was carried out in the same manner as in Example 1, except that the low-temperature reactor in Example 1 was not used and the reaction was carried out only in the high-temperature reactor.As a result, the conversion rate of formaldehyde was 93.7%. C,
The isoprene yield was 48.2 mol.

Patent applicant: Zeon Corporation

Claims (1)

[Claims] (t) At least one isobutylene source selected from inbutylene, tertiary-butanol, and alkyl tertiary-butyl ether and a formaldehyde source are continuously reacted in a liquid phase in the presence of water and an acidic catalyst to produce inprene. In the production of isoprene, an isoprene precursor is synthesized by reacting an inbutylene source and a formaldehyde source in a complete liquid phase in a low-temperature reaction zone in the presence of water and an acidic catalyst, and then the liquid derived from the zone is transferred to a high-temperature reaction zone. 1. A method for producing isoprene, which comprises decomposing an isoprene precursor into inprene at a pressure of 40 atmospheres or less under a gas-liquid mixed state. 2. The production method according to claim 1, in which the pressure restriction in the high temperature reaction zone is carried out independently of the low temperature reaction zone◇