JPS60252432A - Production of isoprene - Google Patents

Abstract

PURPOSE:To produce isoprene, by reacting an isobutylene source with a formaldehyde source in a low-temperature reaction zone in a completely liquid phase to obtain an isoprene precursor, carrying out the heat-exchange of the obtained reaction liquid with the liquid discharged from the high-temperature reaction zone, and decomposing the reaction liquid to isoprene in the high-temperature reaction zone. CONSTITUTION:An isobutylene source (e.g. isobutylene, t-butanol, alkyl t-butyl ether, etc.) is made to react with a formaldehyde source in the presence of water and an acidic catalyst in a low-temperature reaction zone in a completely liquid phase at 60-140 deg.C to obtain the isoprene precursor. The obtained reaction liquid is subjected to the heat-exchange with the liquid discharged from the high- temperature reaction zone, and is decomposed to isoprene at 150-230 deg.C and <=40atm in the mixed stage of gas and liquid in the high-temperature reaction zone. EFFECT:The objective compound can be produced easily in high yield without separating the isoprene precursor. The high-temperature reaction can be stabilized, and the energy cost can be remarkably saved.

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, it relates to a method for producing imprene in a high yield in an efficient process from an inbutylene source and a formaldehyde source. A method for producing isoprene by a one-step liquid phase reaction in the presence of an acidic catalyst from an inbutylene source such as in butylene (abbreviated as MTBK) and a formaldehyde source such as formaldehyde, rose formaldehyde, etc. is conventionally known (for example, Publication No. 48-28884,
49-10926, 50-10283, etc.).

In this one-step method, imprene is synthesized from imbutylene and formaldehyde, which have already been commercialized, via 44-dimethyl-1,3-dioxa/. It has the basic advantage of fewer reaction steps compared to the so-called two-step process, but on the other hand.

This has the disadvantage that the selectivity is still insufficient and a large amount of by-products that are difficult to handle are produced.

Therefore, the present inventors conducted studies to improve the shortcomings of such a one-step method, and as a result, they first introduced an inbutylene source and a formaldehyde source into a low-temperature reaction zone and reacted in a complete liquid phase to synthesize an isoprene precursor. Later, he proposed a method of decomposing the isoprene precursor into isoprene by supplying the derived liquid to a high-temperature reaction zone at a pressure of 40 atmospheres or less and under a mixed gas-liquid state (Japanese Patent Application No. 58-56700).

According to this method, isoprene can be obtained in higher yield than conventional methods. However, on the other hand, it is necessary to supply a large amount of heat in the process of transitioning from low-temperature reaction to high-temperature reaction, which makes it difficult to control the temperature in the high-temperature reaction zone, and the reactor in the high-temperature reaction zone becomes complicated and large. Furthermore, when considering the amount of heat to be supplied, there was a disadvantage in that it was disadvantageous in terms of cost.

Therefore, the inventor of the present invention conducted intensive studies to improve this point, and found that installing a heat exchanger between the low-temperature reaction zone and the high-temperature reaction zone makes it easier to control the reaction, makes the reactor simpler and smaller, and allows It has been found that this method is extremely advantageous in terms of cost as well as the cost of replacement.

Thus, according to the present invention, at least one source of imbutylene selected from isobutylene, tertiary-butanol, and alkyl tert-butyl ether and a source of formaldehyde are subjected to a continuous liquid phase reaction in the presence of water and an acidic catalyst to produce isoprene. In producing isoprene precursor, an isoprene precursor is synthesized by reacting an isobutylene 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. Production of isoprene by a liquid phase one-step process characterized by exchanging heat with the derived liquid and then supplying the isoprene precursor to a high temperature reaction zone to decompose the isoprene precursor into imprene at a pressure of 40 atmospheres or less and under a gas-liquid mixed state. law is provided.

The isobutylene source used as a reaction raw material in the present invention is isobutylene, TBA, or alkyl tert-butyl ether, and specific examples of the alkyl tert-butyl ether include:

MTBE is exemplified. These inbutylene sources may be used alone or in the form of a mixture of two or more types, and it is particularly preferable to use inbutylene and another isobutylene source 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,
Formaldehyde polymers (e.g. paraformaldehyde, trioxane), formaldehyde precursors (e.g. methylable, be-4-dimethyl-L3-dioxane)
Examples include. 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 preferred from the viewpoints of 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.

Usually, the theoretical amount of isobutylene generated from the isobutylene source is 2 moles or more, preferably 3 moles or more per mole of formaldehyde generated from the formaldehyde source, and if the amount of isobutylene source used is small, the conversion rate of formaldehyde will decrease. , the production of by-products also tends to increase. On the other hand, if the amount of inbutylene source used becomes too large, the cost required to recover the unreacted isobutylene source will increase, so from this point of view, it is appropriate to use 20 moles or less of isobutylene per 1 mole of formaldehyde.

In the present invention, when carrying out the reaction between the isobutylene source and the formaldehyde source, a two-step reaction is carried out at low and high temperatures, and the high temperature reaction is carried out under a pressure condition of 40 atmospheres or less,
In addition, it is essential to carry out the reaction under a gas-liquid mixed state, and to exchange heat between the liquid derived from the low temperature reaction and the liquid derived from the high temperature reaction between the low temperature reaction and the high temperature reaction.

The reaction in the present invention is carried out in advance at a temperature of 145°C or lower, preferably 60 to 140°C (hereinafter referred to as low temperature reaction), and then 150°C or higher, preferably 150 to 23°C.
It is carried out at a temperature of 0° C. (hereinafter referred to as high temperature reaction).

In the preliminary low-temperature reaction process, isoprene precursors such as 44-dimethyl-L3-dioxane, 3-methyl-1,3-butanediol, and 3-methyl-3-buten-1-ol are produced by the reaction of isobutylene and formaldehyde. be synthesized. At this time, it is important to keep the 0-reactivity level below 145°C; if this temperature is exceeded, the amount of isogrene, the final product, will increase at this stage.
Due to the reaction between formaldehyde and isoprene generated by the decomposition of formaldehyde or 44-dimethyl-L3-dioxane present in the system, by-products of orchids, such as processing difficulties, increase. On the other hand, if the reaction temperature is too low, the reactivity decreases, which is not practical. Also, low temperature reaction (
(The reaction temperature at 1 does not necessarily need to be kept constant;
If the temperature is within the range of 45°C or less, the reaction pressure may be raised sequentially or divided into two or more stages and raised stepwise.The reaction pressure in the low-temperature reaction zone may be appropriately selected so that no gas phase exists. If a gas phase exists in this zone, formaldehyde polymers will precipitate in the gas phase portion of the reactor and the reaction rate will decrease.

Undesirable.

On the other hand, in the process of high-temperature reaction, isoprene is produced by decomposition of the isogrene precursor produced by low-temperature reaction. At this time, if the degree of one reaction source is less than 150°C, the rate of decomposition of the isoprene precursor is slow.

On the other hand, if it becomes too high, polymerized products of inbrene 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 is maintained (the lower the pressure, the greater the effect).

In addition.

The pressure referred to in the present invention should be understood as gauge pressure unless otherwise specified.

Furthermore, the high-temperature reaction needs to be carried out in a gas-liquid mixed state, thereby making it possible to significantly 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 the present invention, heat exchange is performed between the low temperature reaction and the high temperature reaction. Any structure that allows the high-temperature reaction liquid to come into thermal contact and exchange heat well may be used. Specific examples include multi-tube cylindrical heat exchangers, double-tube heat exchangers, and single-tube heat exchangers. This heat exchanger, for example a heat exchanger or a special heat exchanger such as a plate heat exchanger, moderately heats the liquid extracted from the low temperature reaction zone, making it easier to control the temperature in the high temperature reaction zone. In addition, the liquid extracted from the high-temperature reaction zone is a gas-liquid mixture system, so the latent heat of vaporization can be effectively used, and it is not a simple liquid phase system. Thermal efficiency is extremely high compared to heat exchange.

In the present invention, an acidic catalyst is used in the reaction between the isobutylene 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 salting,
Sulfuric acid, nitric acid, phosphoric acid, hypophosphorous acid.

Snous acid, tungstic acid, molybdic acid, telluric acid,
Hydrobromic acid, chlorosulfonic acid, tungstic silicoic acid,
Inorganic acids such as stannic acid, hypochlorous acid, organic acids such as formic acid, oxalic acid, succinic acid, citric acid, phthalic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, sulfonic acid-based ion exchange resins, potassium Throat double salts such as alum bread and chromium alum, strong nonmetallic inorganic salts such as ammonium sulfate, ammonium phosphate, and antimonochloride, ferric sulfate, nickel sulfate, tin chloride, cupric birophosphate, boron phosphate, Examples include metal salts such as zirconium phosphate and sodium phosphate. Among these, phosphorus compounds such as phosphoric acid and phosphates, heteropolyacids, organic acids, and their salts are prized for their ability to prevent corrosion of equipment.

Although these acidic catalysts are usually used alone.

Two or more types of catalysts can be used in combination as appropriate depending on the required trap. The amount of catalyst used depends on the type of catalyst and reaction temperature.

Although it is not necessarily constant depending on conditions such as reaction time,
It can be determined appropriately by conducting a simple preliminary experiment.

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 minutes to 2 hours, preferably 4 minutes to 1 hour.

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

Any reactor may be used as long as it has a structure that allows the reaction solution to be mixed well, and specific examples thereof include a reactor equipped with a stirrer, a perforated plate column, and a packed column. 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 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 control of one reaction and to ensure optimal conditions for each.

Thus, according to the present invention, inprene can be produced in high yield through a simplified process without isolating the inglene precursor, and the high temperature reaction can be stabilized and energy costs can be significantly reduced. .

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 multi-stage blade tank type reactor consisting of stirring chambers with a volume of 0.97.10 was used as a low-temperature reactor, its outlet was connected to an internal pressure control valve, and the outlet pipe from the valve was a single pipe. The tube is connected to the outer tube of a type heat exchanger, and the outlet tube from the heat exchanger is further connected to a high temperature reactor. As a high-temperature reactor, a packed column with an inner diameter of 28 m and a length of 1.5 m filled with a porcelain lacquer pilling was used.
The outlet pipe from the reactor is connected to the inner pipe of the single-tube heat exchanger via an internal pressure regulating valve. The derived liquid 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 heated to 120℃ and 16℃ by electric heaters, respectively.
Maintained at 0°C.

Next, 5.5 g of formaldehyde was added to the low temperature reactor.
Water 53. iq6. An aqueous solution consisting of 30% TBA, xO phosphoric acid, 0.9% sq6° lithium phosphate and isobutylene were supplied by pump at flow rates of 980g/hour and 580.9/hour, respectively, and the low temperature reactor was heated at 35kg/ctl.
The high temperature reactor was maintained at a pressure of 20 Yu/d.

The reaction was carried out continuously. As a result, the conversion rate of formaldehyde was 100 molar, and the yield of imprene was 78°2 molar based on formaldehyde (the same applies hereinafter).

In addition, from the measurement of the heat t for heating the reactants in the high-temperature reactor, it was confirmed that vaporization of inbutylene in the reactor occurred, and the reaction was proceeding in a gas-liquid mixed system.

Also from measuring the amount of heat for heating in the high temperature reaction zone.

It has been found that the amount of heat required for heating in the high-temperature reactor is reduced to 1/3 compared to the case where no heat exchanger is installed.

Patent applicant: Zeon Corporation

Claims (1)

[Claims] 1. Isoprene is produced by a continuous liquid phase reaction of at least one isobutylene source selected from isobutylene, tertiary butanol, and alkyl tertiary butyl ether and a formaldehyde source in the presence of water and an acidic catalyst. During production, 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. A method for producing isoprene, which comprises decomposing an isoprene precursor into isoprene at a temperature of 40 atmospheres or less and under a gas-liquid mixed state by exchanging heat with a liquid derived from the above, and then supplying the isoprene precursor to a high-temperature reaction zone. 2. The production method according to claim 1, wherein the pressure restriction in the high temperature reaction zone is carried out independently of the low temperature reaction zone,