JPS5931507B2 - Method for producing maleic anhydride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing maleic anhydride.

Specifically, the present invention relates to an improvement in a method for producing maleic anhydride by continuously concentrating and dehydrating an aqueous maleic acid solution. Maleic anhydride is usually produced by heating, concentrating, and dehydrating an aqueous maleic acid solution. This concentration and dehydration is carried out by various methods, but since maleic acid isomerizes and rearranges to fumaric acid when an aqueous solution is heated, it is important to prevent the formation of fumaric acid during concentration and dehydration. In recent years, thin film evaporators have come into use as a concentration and dehydration device that meets these requirements.

There are two types of thin film evaporators: vertical and horizontal.
In both cases, a blade that rotates at high speed is installed inside a cylinder that is heated from the outside, and the maleic acid aqueous solution supplied from one end of the cylinder forms a uniform thin film on the inner wall of the cylinder by the rotation of the blade, rapidly concentrating, It is dehydrated and becomes a mixed vapor of water vapor and maleic anhydride vapor, which flows out from the evaporator. This method has the advantage that rearrangement from maleic acid to fumaric acid is small because the heating time is short. However, the maleic acid aqueous solution supplied to the thin-film evaporator generally contains high-boiling by-products derived from the maleic acid production reaction process, and the maleic acid aqueous solution is also supplied to the thin-film evaporator. It is inevitable that some rearrangement of maleic acid to fumaric acid will occur during the concentration process to a concentration suitable for . Furthermore, some rearrangement from maleic acid to fumaric acid, etc. occurs inside the thin film evaporator. These high-boiling substances are discharged from the evaporator in liquid form, but as the reaction from an aqueous maleic acid solution to maleic anhydride progresses, these high-boiling substances are gradually concentrated and crystals of fumaric acid precipitate, resulting in a viscous solution. This creates a slurry that can clog the evaporator and piping during long-term operation. The inventors of the present invention have conducted intensive research to overcome the deficiencies of these conventional methods and establish an industrially advantageous method for producing maleic anhydride. It has been found that by concentrating and dehydrating an aqueous maleic acid solution, the production of fumaric acid is extremely small, and even if the yield of maleic anhydride is increased, clogging of equipment, piping, etc. can be prevented.

The present invention has been achieved based on this knowledge, and its purpose is to provide an industrially advantageous method for producing maleic anhydride from an aqueous maleic acid solution. When reacting to produce maleic anhydride, an aqueous maleic acid solution having a concentration of 80% or more and maintained at a temperature of 100°C or more and 1
A heating medium maintained at a temperature of 20° C. or higher is supplied to a spray tower, and the two are brought into spray contact in the spray tower to concentrate and dehydrate the maleic acid aqueous solution, and the maleic anhydride and water vapor produced are distilled. This can be easily achieved by heating the bottom effluent containing the heating medium to 120° C. or higher and then circulating it to the spray tower.

The present invention will be explained in detail below.

The maleic acid aqueous solution supplied to the spray tower in the method of the present invention is prepared by absorbing a maleic anhydride-containing gas obtained, for example, by partial oxidation of unsaturated hydrocarbons with water in a conventional manner.
It is easily prepared by preparing a 0-60% maleic acid aqueous solution and then treating it with a conventional evaporator or concentrator.

Therefore, the maleic acid aqueous solution was heated to 80% by the evaporator.
% or more, preferably 90% or more, especially 90 to 95%, and then fed to the spray tower. The maleic acid aqueous solution supplied to the spray tower is maintained at a temperature of 100°C or higher, preferably 120-150°C. In the spray tower, the maleic acid aqueous solution comes into direct contact with a high-temperature heating medium in a spray state, and is concentrated and dehydrated in a short time to produce water vapor and maleic anhydride. As the heating medium, one that has a boiling point higher than that of maleic anhydride, preferably 250°C or higher, has low reactivity with maleic acid or maleic anhydride, and does not adversely affect the quality of the maleic anhydride produced is used. used. Furthermore, it is desirable that the composition has an appropriate viscosity under the operating conditions of the spray tower, has low solubility in water, maleic acid, and maleic anhydride, and is capable of suspending fumaric acid crystals. In addition, since it is recycled as a heat source for the spray tower, it does not change or deteriorate.
That is, it needs to be thermally stable. There are no particular restrictions on the type of heat medium as long as it satisfies these requirements. Examples of the heat medium include silicone oil and saturated aliphatic hydrocarbons. Of course, the invention is not limited to only the illustrated heating medium. The saturated aliphatic hydrocarbon has 15 or more carbon atoms, preferably 20 to 50 carbon atoms.
More preferably, saturated aliphatic hydrocarbons having 25 to 40 carbon atoms are used alone or as a mixture of two or more. The temperature of the heating medium supplied to the spray tower is appropriately selected from a wide range depending on the amount of heating medium supplied, the concentration of maleic acid supplied, the supply rate, the desired dehydration rate, the operating pressure inside the spray tower, and the like. Since the dehydration reaction of maleic acid in the spray tower used in the method of the present invention is rate-limiting, it is possible to significantly increase the dehydration rate by increasing the temperature of the heating medium. However, if the temperature is too high, maleic acid This is not advantageous since the isomerization from to fumaric acid and the halzation reaction cannot be ignored either. The temperature of the heating medium can be significantly lowered by increasing the amount of heating medium supplied in order to improve the contact efficiency between the maleic acid aqueous solution and the heating medium, or by sufficiently reducing the operating pressure inside the spray tower. Usually, the temperature of the heating medium is 120°C or higher, preferably 150-250°C, more preferably 180-250°C.
Selected from a temperature range of 30°C. The amount of heating medium supplied to the spray tower varies appropriately depending on the temperature of the heating medium, but is usually at least 2 times the weight of the maleic acid aqueous solution, preferably 2 times the weight of the maleic acid aqueous solution.
A feed rate of ~20 times by weight, particularly preferably 4 to 10 times by weight, is used. The operating pressure of the spray tower is normal pressure or reduced pressure.
Preferably 400 mmHg or less, particularly preferably 40 to
Selected from a range of 200 mmHg.

The temperature of the heating medium, the temperature of the maleic acid aqueous solution, and the heating medium are adjusted so that the contact time between the maleic acid aqueous solution and the heating medium in the spray tower is usually 20 seconds or less, preferably 1 to 10 seconds, and particularly preferably 2 to 5 seconds. It is desirable to adjust the ratio by adjusting the ratio of /maleic acid aqueous solution and the size of the droplets of the sprayed maleic acid aqueous solution.

If the droplets of the sprayed maleic acid aqueous solution are too small, they may not come into sufficient contact with the heating medium, and may also be distilled out from the top of the column along with the maleic anhydride vapor and water vapor; on the other hand, if the droplets are too large, The height of the spray tower is required to ensure sufficient contact with the heating medium, which is not advantageous from an industrial implementation point of view. The size of spray droplets of maleic acid aqueous solution is usually 10~
5000 microns, preferably from 50 to 500 microns. In addition, the size of the sprayed droplets of the heating medium is related to the ratio of heating medium/aqueous maleic acid solution, and there is no particular restriction as long as the size allows sufficient contact with the droplets of the aqueous maleic acid solution. Usually, the size of the droplet is about the same as or larger than that of the maleic acid aqueous solution droplet. When bringing the maleic acid aqueous solution and the heating medium into contact with each other by spraying, the two are mixed before being supplied to the spray tower and then sprayed from a nozzle in the spray tower, or both are separately supplied to the spray tower and then They are brought into contact with each other by spraying from nozzles within the chamber. In this case, both may be brought into contact with each other in countercurrent or cocurrently. Various types of spray towers are used, such as empty towers, packed towers, and those with perforated plates, but empty towers are usually used in consideration of accumulation of by-products, hartz, etc.

The heating medium sprayed into the spray tower is used as a heating medium for concentrating and dehydrating the maleic acid aqueous solution, and then removes high-boiling substances and hartz contained in the maleic acid aqueous solution, fumaric acid and high-boiling acids generated in the tower. The suspended substance is extracted from the bottom of the spray tower.

The bottom effluent containing the heating medium is introduced into a heater, where it is heated and recycled to the spray tower. Impurities such as fumaric acid, hartz, and high-boiling substances, which are by-produced in the tower, accumulate in the heat medium that is circulated, so if necessary, a part of the liquid extracted from the bottom of the tower is transferred to the heat medium recovery system. The extracted liquid is then sent to a process to remove the impurities contained in the extracted liquid. As a treatment method, water is added to the bottom extraction liquid containing a heating medium to dissolve and suspend the impurities, and this is separated into oil and water, and fumaric acid, Harz, etc. suspended in the extraction liquid are A method of over-separating the solid matter and, if a sap is required, separating it by standing, and removing heat medium-insoluble substances such as water and high-boiling substances, is adopted. The bottom extraction liquid from which impurities and the like have been removed is heated to a temperature of 120° C. or higher and recycled as a spray tower heating medium. The gas mixture containing maleic anhydride vapor and water vapor obtained according to the process of the invention is then introduced into a maleic anhydride separation system and, if necessary, further into a maleic anhydride purification system. Next, one example of an embodiment of the method of the present invention will be described based on the drawings.

In Fig. 1, A is a thin film evaporator, B is a cyclone, and C is a thin film evaporator.
indicates a spray tower, D indicates a heater, E indicates a circulation pump, F indicates a heat medium recovery system, and G indicates a circulation pump.

A maleic acid aqueous solution with an appropriate concentration is supplied from conduit 1 to thin film evaporator A.
The aqueous maleic acid solution is concentrated in the evaporator to a concentration of 80% or more, maintained at a temperature of 100° C. or more, and introduced into cyclone B via conduit 2. The water vapor entrained in the concentrated maleic acid aqueous solution is discharged from the upper part of cyclone B via conduit 3. Since this water vapor also contains a part of maleic acid and maleic anhydride, it is preferable to recover it by an appropriate method. From the lower part of the cyclone B, a maleic acid aqueous solution concentrated to a concentration of 80% or more is introduced into the spray tower C through a conduit 4. While flowing through the conduit 4, the maleic acid aqueous solution is heated at 100°C.
It is necessary to maintain the above value. On the other hand, the heating medium is heated to 120° C. or higher by heater D, and introduced into spray tower C via conduit 5. (In one embodiment, the heating medium may be line-mixed with the maleic acid aqueous solution in the conduit 4 before being introduced into the spray tower.) The maleic acid aqueous solution and the heating medium are mixed into atomized form through a nozzle in the spray tower C. In this case, for example, various spray types shown in FIG. 2 are employed. Maleic anhydride vapor and water vapor generated by contact with the heating medium are distilled off from the top of the spray tower C via conduit 6. This mixed vapor is then sent to a maleic anhydride separation system (not shown) and, if necessary, to a maleic anhydride purification system (not shown).
will be introduced in In addition, from the bottom of the spray tower C, a heat medium, undehydrated maleic acid, fumaric acid which is a thermal rearrangement product of maleic acid, and high boiling point components such as Harz contained in the introduced maleic acid aqueous solution are collected. is discharged from conduit 7,
Most of the mixture is heated to 120° C. or higher in a heater D by a circulation pump E, and then recirculated to a spray tower C. On the other hand, spray tower C
Fumaric acid and high-boiling substances, which are by-products from the dehydration reaction of maleic acid, accumulate and increase in the bottom effluent containing the heating medium that is circulated to the bottom of the tower. A part of the liquid extracted from the bottom of the circulation tower is extracted and sent to the heat medium recovery system F.
In the heating medium recovery system F, fumaric acid and high-boiling substances are removed from the bottom effluent by a specific method and then recycled as a heating medium for the spray tower C. In the method of the present invention, the maleic acid aqueous solution and the heating medium are in direct contact, so the thermal efficiency is good and the heat transfer area can be large, and the heat transfer area can be adjusted appropriately by changing the ratio (heating medium/maleic acid aqueous solution). It has the advantage of being possible.

Therefore, the maleic acid aqueous solution supplied into the spray tower comes into contact with the heating medium and is concentrated and dehydrated instantly or within a few seconds.
Produces water vapor and maleic anhydride vapor. Therefore, the residence time of the maleic acid aqueous solution in the spray tower (which approximately corresponds to the contact time between the maleic acid aqueous solution and the heating medium) is significantly shortened, and the generation of fumaric acid due to the isomerization of maleic acid is reduced. Significantly suppressed. Further, the supplied maleic acid aqueous solution is usually 95% or more, preferably about 100% dehydrated, and distilled from the spray tower as a gas mixture of maleic anhydride vapor and water vapor. In conventional thin-film evaporators, it is difficult to shorten the residence time of the maleic acid aqueous solution beyond a certain level (for example, 60 seconds or less), and fumaric acid is generated by isomerization of maleic acid. However, it has not been possible to increase the dehydration rate from maleic acid to maleic anhydride very high due to clogging of equipment and piping due to the precipitation of crystals.

(Usually, the dehydration rate of maleic acid is 90% or less) As explained above in detail, according to the method of the present invention, (1) the residence time of the maleic acid aqueous solution is reduced to 1/10 or less compared to the conventional thin film evaporator; Therefore, the formation of fumaric acid due to the isomerization of maleic acid can be significantly reduced.

(2) Since the maleic acid aqueous solution and the heating medium are brought into direct spray contact in the spray tower, the thermal efficiency is higher than that of conventional indirect contact, and the heat transfer area can be increased and the equipment can be simplified.

(3) By using a heat medium, it is possible to prevent clogging of equipment and piping due to precipitation of fumaric acid crystals, etc., and continuous operation for a long time is possible.

(4) Since the dehydration rate from maleic acid to maleic anhydride can be almost 100%, compared to conventional methods,
The yield of maleic anhydride can be increased.

This eliminates the need for the conventional process of recovering maleic acid from high-boiling substances. Benefits include:

Next, the present invention will be explained in more detail by giving examples.
The present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1 A C4 hydrocarbon fraction obtained by naphtha decomposition was oxidized with air in the presence of a phosphorus-palladium catalyst, and the oxidation product gas was absorbed with water according to a conventional method. A 5% maleic acid aqueous solution (320k9/hr) was heated and concentrated in a double tube evaporator (external jacket: 170°C), and then introduced into a cyclone to separate most of the water vapor.

When the steam coming out from the top of the cyclone is cooled, 1
A 0% maleic acid aqueous solution was obtained at 170k9/Hr.
On the other hand, from the lower end of the cyclone, a 90% maleic acid aqueous solution having a temperature of 140°C was obtained at 150k9/Hr.
This is then sprayed upward into droplets of 100 microns from a nozzle installed in the tower 100 (7!L) below the top of the spray tower, which has an inner diameter of 100 cTn and a height of 500 cTrL and is empty inside. In addition, 200°C water was extracted from the bottom of the spray tower (heated with a heater) and circulated to the spray tower.
A heating medium of the following composition heated to Circulating heat transfer liquid 885k consisting of Hr
g/Hr was sprayed downward into droplets of 100 microns from a nozzle installed in the tower 70 cm below the top of the spray tower, and brought into spray contact with the maleic acid aqueous solution in a countercurrent manner. The interior of the spray tower was maintained at a reduced pressure of 60 mmHg. The contact time between the maleic acid aqueous solution and the heating medium in the spray tower was about 2 seconds. 80% maleic anhydride from the top of the spray tower
A gas mixture of water vapor and water vapor was distilled off at 140k9/Hr.

On the other hand, if the concentration of the heating medium in the liquid drawn from the bottom of the spray tower becomes too low, the concentration of reaction by-products will increase, and some of the reaction by-products will crystallize. In order to maintain the heating medium concentration inside at 70% or higher, a portion of it was extracted and washed with water. That is, a part of the liquid drawn out from the bottom of the spray tower is extracted at 200k9/11r, led to a separation tank and washed with water, and then the heat medium liquid layer 190k9/Hr separated by standing is recycled to the heat medium line of the spray tower. It circulated. The amount of fumaric acid removed in the separation tank was 0.7k9/Hr, and the production rate of fumaric acid from maleic acid in the spray tower was 0.5%.

Even if this spray tower continued to operate for a long time, it was possible to operate safely without causing any blockage of the equipment or conduits.Heating medium*.Saturated aliphatic hydrocarbon composition distribution. As in Example 1, a maleic acid aqueous solution was heated and concentrated in a double tube evaporator, then introduced into a cyclone, and the 94% maleic acid aqueous solution having a temperature of 140°C obtained from the lower end of the cyclone was evaporated horizontally at 9607/Hr. Continuously fed to the conductor end of the thin film evaporator.

The evaporator has a cylindrical shape with an inner diameter of 90 mm and a heating section length of 300 mm.In the center of the evaporator is a rotor blade having a gap of approximately 5 mm between the heating surface and the rotor blade, which rotates at 450 rpm. is circulated, and the inside of the evaporator is 30
The vacuum was maintained at 0 mmHg. The residence time of the aqueous maleic acid solution in the evaporator was about 100 seconds. A gas mixture of 85% maleic anhydride and water vapor was distilled out from the gas outlet at the discharge end of the evaporator at 730 y/hr. On the other hand, a mixture of maleic anhydride and maleic acid containing 14.2% of fumaric acid and 18.2% of Harz was obtained from the liquid outlet at the discharge end of the evaporator at 2307/Hr. The production rate of fumaric acid from maleic acid in the evaporator was 3.6%.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing one embodiment of the method of the present invention. FIG. 2 is a schematic diagram showing an example of the type of spray tower used in carrying out the present invention. A... Thin film evaporator, B...
...Cyclone, C... Spray tower, D...
... Heater, F ... Heat medium recovery system.

Claims (1)

[Scope of Claims] 1. When producing maleic anhydride by dehydrating an aqueous maleic acid solution, the solution has a concentration of 80% or more, and 1.
A maleic acid aqueous solution maintained at a temperature of 00°C or higher and 12
Supplying a heating medium maintained at a temperature of 0° C. or higher to a spray tower,
The maleic acid aqueous solution is concentrated and dehydrated by spray contacting them in the spray tower, the maleic anhydride and steam produced are distilled out, and the bottom effluent containing the heating medium is heated to 120° C. or higher. A method for producing maleic anhydride, which comprises heating and then circulating it to the spray tower. 2. The method for producing maleic anhydride according to claim 1, wherein the heating medium is silicone oil. 3. The method for producing maleic anhydride according to claim 1, wherein the heating medium is a saturated aliphatic hydrocarbon having 15 or more carbon atoms. 4. The method for producing maleic anhydride according to claim 1, wherein the heating medium is a saturated aliphatic hydrocarbon having 20 to 50 carbon atoms. 5. The method for producing maleic anhydride according to any one of claims 1 to 4, wherein the temperature of the maleic acid aqueous solution is 120 to 150°C. 6. The method for producing maleic anhydride according to any one of claims 1 to 5, wherein the temperature of the heating medium is in the range of 150 to 250°C. 7. Maleic anhydride according to any one of claims 1 to 6, wherein the amount of the heating medium supplied to the spray tower is 2 to 20 times the weight of the maleic acid aqueous solution. manufacturing method. 8. The method for producing maleic anhydride according to any one of claims 1 to 7, characterized in that the maleic acid aqueous solution and the heating medium are mixed in advance and then brought into spray contact in a spray tower. 9. The method for producing maleic anhydride according to any one of claims 1 to 7, characterized in that the maleic acid aqueous solution and the heating medium are brought into countercurrent spray contact in a spray tower. 10 Adding water to a part of the bottom extraction liquid containing the heating medium,
Anhydrous according to any one of claims 1 to 9, characterized in that the heat medium layer from which the water layer containing impurities has been separated is heated to a temperature of 120° C. or higher and circulated to the spray tower. Method for producing maleic acid.