JPS5925337A - Preparation of isoprene - Google Patents

Abstract

PURPOSE:To obtain the titled substance in high selectivity in high yield, by carrying out a reaction of an isobutylene source and a formaldehyde source in a low-temperature reaction zone charged with a cation exchange resin first, followed by doing it in a high-temperature reaction zone wherein the reaction solution is treated at high temperature. CONSTITUTION:At least one isobutylene source selected from isobutylene, tertiary butanol and an alkyl tertiary butyl ether and a formaldehyde source together with water and a water-soluble acidic catalyst are fed to a low-temperature reaction zone packed with a cation exchange resin catalyst and reacted at 30-115 deg.C, preferably at 50-110 deg.C, to synthesize an isoprene precursor. The reaction solution introduced from the low-temperature zone, containing a water-soluble acidic catalyst, is fed to a high-temperature zone, subjected to the latter stage reaction at >=120 deg.C, preferably 130-210 deg.C, so that the precursor is decomposed to give isoprene. The amount of isobutylene is preferably <=20mol based on 1mol formaldehyde.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing isoprene by a liquid phase method, and more particularly, the present invention relates to a method for producing isoprene by a liquid phase method, and more particularly, the present invention relates to a method for producing isoprene by a liquid phase method, and more specifically, the production of isoprene using a water-soluble acidic catalyst as a source of inbutylene and a source of formaldehyde in a low temperature reaction zone filled with a cation exchange resin catalyst. The present invention relates to a method for producing -f noprene in high yield by carrying out a liquid phase reaction in the presence of the present invention and then supplying the reaction solution to a high temperature reaction zone to continue the liquid phase reaction.

Inbutylene, tertiary butanol (hereinafter referred to as TB), methyl tert-butyl ether (hereinafter referred to as M
Isobuty I/ such as 'l' B E)
A method of producing isoprene from 771R and a formaldehyde source such as formaldehyde, varabomaldehyde, etc. by a liquid phase one-step reaction in the presence of an acidic catalyst is conventionally known (for example, Japanese Patent Publication Nos. 48-28884 and 49-10926). issue.

No. 50-10283, etc.).

The basic principle of this method is that there are fewer reaction steps compared to the so-called two-step method, which synthesizes isoprene from imbutylene, porno, and aldehyde via 4,4-dimethyl-L3-dioxane, which has already been industrialized. However, 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.

In addition, the isobutylene source and formaldehyde d+, convert to the enemy phase reaction of 1 to exchange cations 1!4111'r'! ;j
For example, a method for synthesizing 44-dimethyl-1,3-dioxane from isobutylene and formaldehyde using an isoprene precursor (Japanese Patent Publication No. 39-2
No. 489, No. 44-4766, No. 49-46628), a method for synthesizing isoprene from inbutylene and formaldehyde (Japanese Patent Publication No. 52-3048.2, Japanese Patent Publication No. 47-39008-Yumi), etc. are known. ing. However, the former method isolates and purifies the isoprene intermediate from the reaction solution and synthesizes isoprene after the step (a). The reactor has the disadvantage of being inferior in efficiency.

Therefore, the present inventors have worked diligently to improve these shortcomings and characteristics found in the prior art, and as a result, we have developed a reaction in a low-temperature reaction zone filled with a cation-exchange resin, and 4U of isoprene can be produced with high selectivity and high yield by subjecting the reaction solution derived from 1211 to high temperature and then combining the reactions in a high temperature reaction zone.

This discovery led to the completion of the present invention.

Thus, according to the present invention, at least one isobutylene source selected from isobutylene, tertiary-butanol, and alkyl tert-butyl ether and a formaldehyde source are subjected to a continuous liquid phase reaction in the presence of an acidic catalyst and water to produce isoprene. When producing isoprene precursor, an isoprene precursor is synthesized by supplying an isobutylene source, a formaldehyde source, water, and a water-soluble acidic catalyst to a low-temperature reaction zone filled with a cation-exchange resin catalyst, and then the reaction solution discharged from the zone is heated to a high temperature. A method for producing isoprene is provided, the method comprising feeding an isoprene precursor to a reaction zone to decompose an isoprene precursor into isoprene.

In the present invention, when performing a reaction between an isobutylene source and a water-formaldehyde source, the isobutylene source, formaldehyde source, water, and a water-soluble acidic catalyst are first fed to a low-temperature reaction zone filled with a cation exchange resin catalyst, and the reaction takes place at a low temperature. (hereinafter referred to as the first stage reaction), and then the reaction solution containing the water-soluble acidic catalyst derived from the zone is supplied to the high temperature reaction zone and reacted at high temperature (hereinafter referred to as the second stage reaction).
This is an essential requirement.

In the first stage reaction, an isobutylene source, a formaldehyde source, water, and a water-soluble acidic catalyst are continuously fed into a reactor filled with a cation exchange resin, and the isoprene precursor is synthesized by reacting at a relatively low temperature. Ru.

The cation exchange resin used here is preferably a sulfonic acid type strongly acidic one, and specific examples include a sulfonic acid type resin having a core of styrene/divinylbenzene copolymer, and a core having a phenol-formaldehyde condensate. Examples include sulfonic acid type resins, which are sulfonic acid type resins, and perfluorosulfonic acid type resins, which are copolymers of sulfonated fluorinated vinyl ether and fluorocarbon, and may be of gel type, porous type, or carrier-supported type.

The reactor used may be of any structure as long as it can be filled with the cation exchange resin; specific examples include one reactor with a stirrer when used in a suspension state, and a reactor with a stirrer when used in a fixed bed state. A packed column is exemplified.

Specific examples of water-soluble acidic catalysts that can be used include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, chlorosulfo/acid, silicotungstic acid, formic acid, acetic acid, propionic acid, oxalic acid, succinic acid, and citric acid. , organic acids such as halatoluenesulfonic acid, trifluoromethanesulfonic acid, etc., double salts such as potash brightpan, chromium brightpan, etc., metal salts such as ferric sulfate, nickel sulfate, tin chloride, cupric pyrolate, etc. 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 substances are usually used alone, but two or more types of catalysts may be used in combination if necessary, while the reactor used in the subsequent reaction should be of a structure that allows for good mixing of the reaction liquid. Any type may be used, and specific examples include a reactor with a stirrer, a perforated plate column, and a packed column.

The amount of catalyst to be used is not necessarily constant depending on conditions such as the type of catalyst, reaction temperature, and reaction time, but can be appropriately determined by conducting a simple preliminary experiment. Further, the amount of catalyst used in the first-stage reaction and the second-stage reaction can be determined independently depending on the respective reaction temperatures and reaction times.

In the preliminary reaction process, isoprene such as 4,4-dimethyl-L3-dioxane, 3-methyl-1,3-butanediol, 3-methyl-3-buten-1-ol, etc. is produced by the reaction of inbutylene and formaldehyde. A precursor is synthesized. At this time, the 5 reaction source degree is 30 to 115.
It is appropriate to maintain C1 preferably between 50 and 110°C; if this temperature is exceeded, the amount of final product isoprene produced increases at this stage, so formaldehyde or 44- The reaction between formaldehyde generated by the decomposition of dimethyl-L3-dioxane and isoprene increases the by-product of bilanes, which are difficult to treat, and also makes it difficult to maintain the performance of the cation exchange resin catalyst over a long period of time.On the contrary, the reaction temperature If it becomes too low, the reactivity decreases and the practicality becomes poor.This first-stage reaction usually consumes 90% or more of the raw material polyaldehyde source.

The reaction solution containing the water-soluble acidic catalyst derived from the low-temperature reaction zone is then supplied to the high-temperature reaction zone, where it is subjected to a subsequent reaction to decompose the isoprene precursor and produce isoprene. At this time, the reaction temperature was set at 1'20°C or higher.
Preferably, it is appropriate to set the temperature at 130 to 210°C; if it is lower than that, the decomposition rate of the inbrene precursor will be slow, and if it is too high, the isoprene polymer and carbon-like or tar-like byproducts will be produced. There is a tendency to increase.

The reaction temperature in the first and second stage reactions does not necessarily need to be kept constant, and may be raised sequentially or divided into two or more stages and raised stepwise (1° The isobutylene source used is isobutylene, TBA or an alkyl tert-butyl ether, and a specific example of the alkyl tert-butyl ether is MTBE.These in-butylene sources may be used alone, but two Preferably, they are used in the form of a mixture of more than one species.

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 a gas containing a formaldehyde source obtained by oxidizing methanol, pornography, an aqueous aldehyde solution, and a formaldehyde source obtained by oxidizing methanol. Polymers (e.g.)
<laformaldehyde, triochira/), precursors of formaldehyde (e.g. methylal, 44-dimethyl-L
3-dioxane, glycol formal), etc. An aqueous solution of formaldehyde in which formaldehyde is dissolved in an aqueous L-formaldehyde solution to increase the formaldehyde concentration, or an aqueous solution of formaldehyde containing methanol as a stabilizer can be similarly used.

Among these, ease of handling, ease of acquisition, and the use of water/water in the reaction system.
From the standpoint of necessity, the ratio of the isobutylene source containing formaldehyde and the formaldehyde source is selected as appropriate depending on the reaction conditions, but usually, per mol of theoretical formaldehyde generated from the formaldehyde source, the amount generated from the inbutylene source is The theoretical amount of isobutylene is 1 mol or more, preferably 2 mol or more, and when the amount of inbutylene source used is small, 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 isobuty-1-non source used becomes too large, the cost required to recover the unreacted isobutylene source will increase.
From this point of view, it would be appropriate to use 20 mol or less of isobutylene per 1 mol of formaldehyde.The ratio used does not need to be the same in the first and second reactions, and can be added as appropriate.

The amount of water used in the reaction can be selected as appropriate, but it is usually 1 part by weight per 1 part by weight of formaldehyde produced from the formaldehyde source; preferably 2 to 100 parts by weight, and if necessary, alcohol. , polar solvents such as ketones, fatty acids, aromatic hydrocarbon solvents, etc. can coexist.

In addition, the reaction time may be selected appropriately; in the first stage reaction, the residence time is usually 5 minutes to 5 hours, preferably 10 minutes to 2 hours.
On the other hand, in the latter stage reaction, it is usually 2 minutes to 2 hours, preferably 4 minutes to 1 hour. In the first stage reaction, the coexistence of a water-soluble acidic catalyst and a cation-exchange resin catalyst as catalysts can significantly shorten the reaction time, increase the reactivity of formaldehyde, and further increase the yield of the isoprene precursor. Can be done.

Further, the reaction pressure may be appropriately selected, and is usually 1 to 25 kg/c+4 in the first stage reaction, while it is usually 5 to 100 kg/cnl in the second stage reaction.

In the present invention, the water-soluble acidic catalyst used in the first-stage reaction can be reused as an aqueous solution derived from the second-stage reaction as it is, or after appropriately performing necessary treatment.

Specific examples of such treatments include removal of small amounts of organic matter contained, concentration adjustment by concentration, and the like. Moreover, a new catalyst can be replenished as needed.

According to the present invention, isoprene can be produced in high yield through a simplified process without isoprene precursor isolation. In addition, since most of the formaldehyde is consumed during the reaction, there is no need to recover it from the reaction solution.
In addition, the production of by-products that are difficult to process can be suppressed to a large extent by +1vgK. Furthermore, since the water-soluble acidic catalyst can be reused, loss of the catalyst is small, and since the reaction temperature can be lowered, the amount of thermal energy consumed can be suppressed.

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

In addition, parts and sections in Examples and Comparative Examples are based on weight unless otherwise specified. A stainless steel tube with an inner diameter of 20 mm and a length of 700 mm was used as the reactor for the first stage reaction of the examples, and sulfone was contained in it. Fill with acid type cation exchange resin (trade name: DOWEX 50W, 50-300 mesh). On the other hand, an empty stainless steel tube with an inner diameter of 4 mm and a length of 8000 mm is used as a reactor for the subsequent reaction. Each reactor is controlled to a predetermined temperature.

Next, 2.1 g of formaldehyde was added to this pre-stage reactor.
Water SO, 6 oz, TBA 12.5 q and phosphoric acid 5.4 q
Aqueous solution consisting of 6 (raw material B) and isobutylene (raw material B
) are each supplied at a predetermined flow rate, and the reaction liquid flowing out from the front reactor is supplied as it is to the rear reactor.
The reaction is carried out continuously under a pressure of α, and the reaction solution emitted is cooled, collected, and analyzed. In the analysis method, an organic layer is extracted from the collected reaction solution using carbon tetrachloride, and isoprene contained in this organic layer and unreacted formaldehyde remaining in the aqueous layer are analyzed using gas chromatography.

Table 1 shows the results of experiments conducted by changing the reaction temperature and raw material supply amount.

Example 2 Formalin aqueous solution 15 consisting of 20% formaldehyde and 80% water was used as a raw material aqueous solution to be supplied to the first stage reactor.
．． 3 Ji'/hr and water obtained by separating the oil layer from the reaction liquid flowing out from the latter reactor and separating water as appropriate.8
Aqueous solution 1 consisting of 0%, 4% TBAI and 6% phosphoric acid
The reaction was carried out according to experiment number (]-1) of Example 1 except for using 30.09/hr in combination. the result,
The formaldehyde conversion was on the order of 100 moles, and the isoprene yield was over 83.6 moles.

Example 3 The first stage reactor was filled with a sulfonic acid type cation exchange resin (trade name DOWEX Msc-1, macroporous type, converted to H type), and formaldehyde 2.1 as an aqueous solution of the feed material, Water 76.4%, TBAI
The reaction was carried out according to Experiment No. (1-1) in the Examples except that an aqueous solution consisting of 2.5% and 9.0% citric acid was used. As a result, the conversion rate of formaldehyde was 1
The isoprene yield was over 77.2 mol.

Example 4 Aqueous solution of feedstock: 2.0% formaldehyde, 49.9% water, 44% TBA. The reaction was carried out according to Experiment No. (1-1) in Example 1, except that an aqueous solution consisting of O and 4.1% phosphoric acid was used at a rate of 200 i /br and the supply of isobutylene was stopped. As a result,
The conversion of pornoaldehyde was 100 mol, and the isoprene yield was 76.9 mol.

Comparative Example] The reaction was carried out in accordance with the experiment number (+-1) of Example 1, except that the subsequent reaction was not performed. As a result, the formaldehyde conversion rate was over 95.9 mol, and the isoprene yield was over 25.9 mol. At this time,
It was observed that a large amount of imprene precursors such as 44-dimethyl-1,3-dioxane, 3-methyl-3-buten-I-ol, and 3-methyl-1,3-butanediol were produced.

Comparative Example 2 The reaction was carried out in accordance with Experiment No. (1-1) of Example 1Ill I, except that the first stage reaction was not carried out.

As a result, the formaldehyde conversion rate was 100 mol, and the isoprene yield was 73.8%.

Patent applicant: Zeon Corporation

Claims (1)

[Claims] L Isoprene is produced by continuously reacting a formaldehyde source with at least one imbutylene source selected from isobutyne/, tertiary butanol, and alkyl tert-butyl ether in a liquid phase in the presence of an acidic catalyst and water. In this process, an inbutylene source, a formaldehyde source, water, and a water-soluble acidic catalyst are fed into a low-temperature reaction zone filled with a cation exchange resin catalyst to synthesize an inprene precursor, and then the inprene precursor is synthesized. A method for producing isoprene, which comprises supplying a liquid derived from the jF region to a high temperature reaction zone to decompose an isoprene precursor into isoprene.