JPS60226834A - Preparation of isoprene - Google Patents

Abstract

PURPOSE:To obtain isoprene in high yield, by reacting an isobutylene source with a formaldehyde source initially at a low temperature under conditions of reduced amount of water in the presence of an acid catalyst, treating the reaction product at a high temperature, and circulating an aqueous layer separated from a solution withdrawn therefrom through a reaction zone in the latter stage. CONSTITUTION:An isobutylene source, formaldehyde source and water containing an acid catalyst are fed to a reaction zone and kept at 30-140 deg.C, preferably 50-135 deg.C to synthesize an isoprene precursor, and a reaction mixture withdrawn from the above-mentioned reaction zone is treated at a high temperature, preferably >=145 deg.C, particularly 145-230 deg.C to decompose the isoprene precursor into isoprene. In the process, the solution withdrawn from the reaction in the latter stage is separated into an oil layer and aqueous layer. At least part of the aqueous solution containing the acid is directly circulated or subjected to suitable required treatment and circulated through the reaction in the later stage for use. EFFECT:Catalyst cost can be reduced, and the amount of the water to be used in the reaction in the former stage can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing imprene by a liquid phase method, and more particularly, to a method for producing isoprene in good yield from an isobutylene source and a formaldehyde source in an efficient process.

Isobutylene, tertiary butanol (hereinafter abbreviated as TBA), methyl tert-butyl ether (hereinafter referred to as M
A method for producing isoprene from an inbutylene source such as TBE (abbreviated as TBE) and a formaldehyde source such as formaldehyde, paraformaldehyde, etc. by a liquid phase one-step reaction in the presence of an acidic catalyst has been known for a long time. An improved method has been developed in which the reaction is carried out in two stages: low temperature and high temperature. For example, JP-A-58-11
No. 6428 describes a method of reacting an inbutylene source and a formaldehyde source in the presence of water and an acidic catalyst in two steps at a reaction temperature of 145° C. or lower and 150° C. or higher. According to this method, the yield of isoprene can be increased compared to the conventional method, but it is necessary to coexist a large amount of water in the reaction, which increases the size of the reaction equipment and the energy cost required for heating. There were problems such as these, and improvements were desired.

Therefore, the present inventor conducted intensive studies to improve these drawbacks seen in the prior art, and as a result, discovered that in low-temperature reactions, even if the amount of water is reduced, there is no significant effect on the reaction.
Based on this knowledge, we have completed the present invention.

In the present invention, when performing a reaction between an isobutylene source and a formaldehyde source, first, an inbutylene source, a formaldehyde source, and water containing an acidic catalyst are supplied to a low-temperature reaction zone to synthesize an isoprene precursor (hereinafter referred to as the first stage reaction). Then, the reaction mixture discharged from the zone is treated at high temperature to decompose the isoprene precursor into isoprene (hereinafter referred to as post-stage reaction).

In the preliminary reaction process, 44-dimethyl-L3-dioxane, 3-methyl-L3-butanediol, 3-methyl-
Isoprene precursors such as 3-buty/-1-ol are synthesized. At this time, it is appropriate to maintain the reaction temperature at 30 to 140°C, preferably 50 to 135°C,
If this temperature is exceeded, the amount of isoprene, the final product, increases at this stage, so the treatment is carried out due to the reaction between isoprene and formaldehyde generated by the decomposition of formaldehyde or 44-dimethyl-L3-dioxane present in the system. The number of by-products of difficult biran species increases.

On the other hand, if the reaction temperature is too low, the reactivity will decrease, making it less practical.

The reaction mixture derived from the first stage reaction zone is then supplied to the high temperature reaction zone together with water containing an acidic catalyst which is circulated from the second stage reaction zone which will be described later, and the decomposition reaction of the isoprene precursor to isoprene is carried out.

At this time, one reaction temperature is 145°C or higher, preferably 145°C or higher.
It is appropriate to set the temperature at 230°C; if it is lower than that, the decomposition rate of the isoprene precursor is slow (on the contrary, if it is too high, there is a tendency for isoprene polymers and carbon-like or tar-like by-products to increase. be.

The reaction temperatures in the first and second stage reactions do not necessarily need to be kept constant, and may be raised sequentially.

Alternatively, it may be divided into two or more stages and raised in stages.

In the present invention, it is essential to carry out derivation from the post-stage reaction and then circulate it to the post-stage reaction for use. The method of oil/water separation may be according to a conventional method, and generally a decantation method is adopted. Further, specific examples of processing the circulating aqueous solution include removal of small amounts of organic matter contained therein, concentration adjustment by concentration, and the like. Moreover, a new catalyst can be replenished as needed.

The aqueous solution containing the catalyst other than that to be recycled to the latter stage can be recycled to the first stage reaction as necessary, thereby reducing the catalyst cost.

The aqueous solution to be supplied to the first stage reaction is preferably one whose concentration has been adjusted by concentration, while the aqueous solution to be supplied to the second stage reaction is preferably the aqueous solution derived from the second stage reaction and introduced at a high temperature.

The acidic catalyst used in the reaction may be any substance that exhibits acidity under reaction conditions in the presence of water.5Specific examples include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hypophosphorous acid, phosphorous acid, and tungstic acid. , molybdic acid, telluric acid, hydrobromic acid, chlorosulfonic acid, silicotungstic acid, stannic acid,
Inorganic acids such as hypochlorous acid, formic acid, oxalic acid, succinic acid, citric acid, phthalic acid, halatoluenesulfonic acid,
Organic acids such as trifluoromethanesulfonic acid, salt double salts such as potash and chromium salts, strong nonmetallic inorganic acid salts such as ammonium sulfate, ammonium phosphate, and nitimony, ferric sulfate, nickel sulfate, Tin chloride, cupric pyrophosphate.

Examples include metal salts such as boron phosphate, zirconium phosphate, and sodium phosphate. Among them, υ) acids, phosphorus compounds such as 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 two or more types of catalysts can be used in combination as necessary.

The concentration of the catalyst used in the first-stage reaction and the second-stage reaction varies depending on the reaction temperature and reaction time, but can be appropriately determined by a simple preliminary experiment.

In the present invention, the amount of water used in the first stage reaction can be significantly smaller than the amount of water used in the second stage reaction. The amount is usually 1 part by weight or more, preferably 2 to 5 parts by weight per 1 part by weight of formaldehyde generated from the formaldehyde source.
It is 0 parts by weight. On the other hand, the amount of water used in the subsequent reaction is 5
Usually, the amount is 6 parts by weight or more, preferably 10 to 100 parts by weight, per 1 part by weight of formaldehyde generated from the formaldehyde source supplied to the first stage reaction.

The reaction time and reaction pressure may be selected appropriately, and in the first stage reaction, the reaction time is usually 5 minutes to 5 hours, preferably 10 minutes to 2 hours, and the reaction pressure is 1 to son/cIl.
It is. On the other hand, in the latter stage reaction, the reaction time is usually 2 minutes to 2 hours, preferably 4 minutes to 1 hour, and the reaction pressure is 5 to 150 kl? /d. Further, during the reaction, polar solvents such as alcohols and chthons, fatty acids, aromatic hydrocarbon solvents, and the like can be allowed to coexist, if necessary.

The reactor used may be of any structure as long as it can mix the reaction liquid well, and specific examples thereof include a reactor with a stirrer, a perforated plate column, a packed column, and the like. In particular, 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 ease of construction.

Further, the pressure conditions for the first-stage reaction and the second-stage reaction may be the same, but in order to facilitate reaction control and ensure optimum conditions for each, it is preferable to provide a pressure control mechanism for each K independently.

The isobutylene source used as a reaction raw material in the present invention is isobutylev, TBA, or purkyl tert-butyl ether, and MTBE is a specific example of the alkyl tert-butyl ether. Although these isobutylene sources may be used alone, they are preferably used in the form of a mixture of two or more.

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-containing formaldehyde obtained by oxidation of methanol, formaldehyde aqueous solution, formaldehyde polymers (e.g. , paraformaldehyde, trioxane), formaldehyde precursors (e.g. methylal, 44-dimethyl-1,3-
dioxane, glycol formal), etc. Further, an aqueous formaldehyde solution in which paraformaldehyde is dissolved to increase the formaldehyde concentration, or an aqueous formaldehyde 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 inbutylene source and formaldehyde source to be used is appropriately selected depending on the reaction conditions, but usually, the theoretical amount of inbutylene generated from the isobutylene source is preferably 1 mol or more per 1 mol of the theoretical amount of formaldehyde generated from the formaldehyde source. When there is a small amount of Mashi/I+Riko n, To1L Soryutoh Melia 3-handed Len eyebrows Koda number, the conversion rate of formaldehyde tends to decrease and the production of by-products also tends to increase.

On the other hand, if the amount of isobutylene source used becomes too large, the cost required to recover the unreacted isobutylene source will increase, so from this point of view, 2
It is appropriate that the amount is 0 mol or less, preferably 10 mol or less. The usage ratio does not need to be the same in the first reaction zone and the second reaction zone (.

It can also be added as appropriate.

According to the present invention, the yield can be improved compared to the conventional method, and the amount of water used in the front reaction zone can be reduced, so the reactor can be made smaller, and the reaction from the front reaction zone can be reduced. The amount of heating when supplying the mixed liquid to the subsequent reaction zone can be reduced.

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

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

Example 1 A multistage blade tank type reactor consisting of 10 stirring chambers of 0.91 mm was used as the reactor for the first stage reaction, and a supply pipe of water containing an acidic catalyst was connected to an outlet pipe of the reactor. A pipe for introducing a mixture of the liquid discharged from the first stage reactor and water containing an acidic catalyst is connected to the second stage reactor. A packed tower with an inner diameter of 28 mm and a length of 1.5 m filled with a porcelain lacquer pilling is used as a subsequent reactor, and the outlet pipe from the reactor is connected to an oil-water separator.

The oil layer outlet pipe from the separator is connected to a sampling vessel. The liquid derived from the oil layer is collected in a container, and then analyzed for isoprene by gas chromatography. A portion of the aqueous layer derived from the oil-water separator is returned to the rear reactor as it is, and a portion is returned to the front reactor after passing through an acid concentration step using a water evaporator.

The reactors for the first and second reactions are maintained at 120°C and 160°C, respectively, by electric heaters. Then, 18% formaldehyde and 60 TBA were added to this first stage reactor.
%, the remainder is 165 parts/hour of an aqueous solution consisting of water, 400 parts/hour of inbutifluoride, 19% of phosphoric acid obtained from the acid concentration step, 2.5% of lithium phosphate, and the remainder 4 of an aqueous solution consisting of water.
Supply 00 parts/hour. Furthermore, between the first reactor and the second reactor, TBA79, which is the aqueous layer derived liquid from the oil-water separator, is used.
The reaction was carried out continuously by supplying an aqueous solution of 16% phosphoric acid, 2.1 g phosphoric acid, 2.1 g lithium phosphate, and water at a flow rate of 700 parts/hour. Reaction pressure is 5 for the first stage reaction.
sktt/cd, the downstream pressure was maintained at 20 to 9/d.

No formaldehyde was detected in the aqueous layer discharged from the oil-water separator throughout the period from 10 hours after the start of the reaction to 100 hours, and it was found that the conversion rate of formaldehyde was 100%. Moreover, the yield of isoprene was 81.6 molti on average.

Comparative Example A reaction was carried out in the same manner as in Example 1, except that the aqueous solution containing the acidic catalyst was not supplied between the first reactor and the second reactor. As a result, the formaldehyde conversion rate was 100 mol, but the isoprene yield was 67.5 mol.

Patent applicant: Zeon Corporation

Claims (1)

[Claims] 1. A first stage reaction zone (A) in which an isoprene precursor is synthesized by reacting an isobutylene source and a formaldehyde source in the presence of an acidic catalyst and water at a low temperature, and the liquid derived from this zone is treated at a high temperature to produce an isoprene precursor. In a method for producing isoprene via a second reaction zone (B) where it is decomposed into isoprene, the liquid derived from the second reaction zone (B) is separated into an oil layer and an aqueous layer, and at least a part of the aqueous layer is transferred to the second reaction zone (B). A method for producing isoprene characterized by recycling.