JPH0219370A - Production of maleic anhydride - Google Patents

Abstract

PURPOSE:To advantageously obtain the title compound from >= 4C aliphatic hydrocarbon using a specific fluid bed catalyst by returning the catalyst recovered in a cyclone to a reoxidation zone provided in the lower region of a thick fluid layer and simultaneously controlling inlet temperature of the cyclone. CONSTITUTION:When >= 4C aliphatic hydrocarbon is subjected to catalytic vapor phase oxidation by an oxygen-containing gas fed from the lower part of a gas dispersing plate 2 in a fluid bed reactor 1 providing the gas dispersing plate 2 at the bottom, forming a thick fluid layer 1 consisting of an oxidation catalyst using a V-P based complex oxide as an active catalyst above the plate 2 and providing cyclones 12 and 13 for recovering a scattering catalyst at the top to provide the title compound, the above-mentioned raw material is fed to the position 7 separated apart from the above of the dispersing plate 2 in the lower region of the fluid layer 5 and simultaneously substantial part of the recovered catalyst is returned to the lower region of a flow stream layer 5. Further, a heat exchanger 11 is installed in a dilute fluid layer 10 above the fluid layer 5 and the inlet temperature of the cyclones 12 and 13 is controlled to 330-450 deg.C to suppress non-catalyst oxidation, secure the safeness and simultaneously reduce the loss of product.

Description

[Detailed description of the invention] [Industrial application field] 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 gas phase oxidation using an aliphatic hydrocarbon having at least a carbon number, such as butane, butenes, butadiene, etc., as a raw material.

[Conventional technology]

Maleic anhydride is usually produced by gas phase oxidation of benzene or aliphatic hydrocarbons having 9 or more carbon atoms such as butane, butenes, butadiene. Maleic anhydride is also recovered as a by-product in the phthalic anhydride production process by gas-phase oxidation of ortho-xylene and naphthalene.

An industrially advantageous production method is to produce maleic anhydride using an aliphatic hydrocarbon having a carbon number of 2 as a raw material.
Many efforts have been made to develop catalysts and processes for this purpose.

A point to be noted in all the reactions involved is that the product, maleic anhydride, has high reactivity.

That is, maleic anhydride is susceptible to non-catalytic oxidation in an oxygen-containing gas atmosphere such as high-temperature air, and consideration must be given to yield and safety. Further, when butane or a mixture of hydrocarbons having 9 carbon atoms containing butane is used as a raw material, unreacted butane is contained in a substantial concentration in the reaction product gas leaving the catalyst layer. In this case, since butane is susceptible to non-catalytic oxidation at high temperatures in an oxygen-containing gas atmosphere such as air, safety considerations must be taken.

In industrial processes, the above-mentioned oxidation has conventionally been carried out mainly in a fixed bed type catalyst bed in which a heat exchanger-type multitubular reactor is filled with catalyst particles of a diameter bed.

In this case, the reaction product gas is maintained at a high temperature close to the reaction temperature for several seconds to several tens of seconds after leaving the catalyst bed until entering the cooling heat exchanger, but the influence of the vessel walls is small. The space from the catalyst layer to the outlet of the reactor is mainly susceptible to non-catalytic oxidation, and the reality is that the reaction product gas is maintained at a high temperature in this space for several seconds. Therefore, depending on the composition of the reaction product gas, there is a high risk of spontaneous combustion and explosion induced by non-catalytic oxidation, and to a lesser extent, there is a high possibility of loss of products and increase in by-products. . As a countermeasure to this problem, methods have been proposed in which the temperature is lowered by mixing a non-aqueous cooling gas with the gas discharged from the catalyst layer in the reactor, or by indirectly exchanging heat with the cooling fluid (Japanese Unexamined Patent Application Publication No. 1983-1982). No. 1 and 773, U.S. Patent No. 4t, 0 (14 Kai No. 27).

On the other hand, in the gas phase oxidation process using a fluidized bed catalyst, which has recently attracted attention, hydrocarbons are oxidized in the gas phase in a dense fluidized bed in which a large amount of oxidation catalyst is kept in a fluidized state by an upward flow of gas.

More specifically, gaseous hydrocarbon raw materials are mixed in advance with an oxygen-containing gas such as air and introduced into a dense fluidized bed, or gaseous carbonization is carried out in a dense fluidized bed in a fluidized state with an oxygen-containing gas such as air. A hydrogen raw material is introduced and a catalytic reaction is carried out.

The oxidation catalyst used here has a composite oxide containing vanadium and phosphorus as main constituent elements (hereinafter referred to as "vanadium-phosphorus composite oxide") as an active ingredient.
It can be manufactured by various conventionally known methods. Examples of these include U.S. Patent Nos. 4t and 5J! ? /issue,
The same No. θ3 request 0'13, the same No. II! ;j, '131
No. 1, same No. J / 7.771, same No. J / 0
．． ．． 2 j No. 1, Patent No. 670, European Patent No. 2↓Q6, U.S. Patent No. 41,3 No. 75
No. 6, No. 5, 0. /Core issue, No. 11. (174
! In the case of these fluidized bed reactions, the catalyst is carried upwards from the dense fluidized bed in accordance with the kinetic energy of the catalyst particles, accompanied by the reaction product gas.

The height reached is generally called the transport exit height (TDH) (for example, the "Fluidization method" by Okura Kunii (1966 i)
First published on October 2S, published by Nikkan Kogyo Shimbun), etc.). The catalyst entrained in the gas is circulated through this to the dense fluidized bed and reused.

Therefore, in a fluidized bed reactor, a dilute fluidized bed with a low catalyst density, which is several times the volume of the dense fluidized bed, exists above the dense fluidized bed where most of the catalyst is present. Since the catalyst density is low in this region, the risk of non-catalytic oxidation of feedstock hydrocarbons and products is much greater than in fixed bed reactions.

It is generally known that in order to suppress non-catalytic oxidation, it is better to lower the temperature of the reaction product gas to a moderate level. For example, in the above-mentioned Japanese Patent Application Laid-Open No. 53-1983, the gas exiting the catalyst layer in a fixed bed reactor is heated to 675°F (
ssy °C) or less, preferably 625 °F (,7 kota °C)
Hereinafter, it is described that the temperature is more preferably cooled to 5 gθ'F (3011°C) or less. However, even if this method of simply lowering the temperature of the reaction product gas as much as possible is applied to a fluidized bed reactor,
It is virtually impossible for fluidized bed reactions to proceed smoothly;
Not practical. This is because excessive cooling will excessively lower the temperature of the catalyst particles that are collected by the cyclone and circulated to the dense fluidized bed, increasing the risk of reaction termination and catalyst deterioration. This is because the installed excessively large heat exchanger tube for heat removal causes an excessive reduction in the equivalent diameter, which increases the linear gas velocity and affects the TDHO value itself. In addition, a fluidized bed type gas phase oxidation reactor has been proposed in which a gas such as water vapor, air, or nitrogen is blown into the diluted fluidized bed to cool it during an abnormal reaction, but in this case, a cyclone is also used. The load for catalyst collection increases excessively, often resulting in loss of fluidized bed catalyst. Furthermore, since a catalyst containing a vanadium-phosphorus complex oxide is usually used in the reaction for producing maleic anhydride, there is a high risk of the catalyst absorbing moisture and solidifying, deteriorating fluidity, etc. in the case of steam injection.

As mentioned above, in the conventional technology for producing maleic anhydride by gas phase oxidation of aliphatic hydrocarbons having 9 or more carbon atoms such as butane using a fluidized bed reaction method, the reaction in a concentrated fluidized bed is stabilized. It is difficult to prevent the loss of unreacted hydrocarbons such as butane and the product maleic anhydride due to non-catalytic oxidation in the dilute fluidized bed at the top of the reactor, and to ensure safety, or There were problems such as catalyst loss due to the introduction of a large amount of cooling gas into the diluted fluidized bed when an abnormal reaction occurred in the diluted fluidized bed.

[Means to solve the problem]

Based on the knowledge of the behavior of catalyst particles in a fluidized bed reactor and the characteristics of a fluidized bed reactor, the present inventors suppressed non-catalytic oxidation in a diluted fluidized bed to ensure safety and produce As a result of extensive research into ways to reduce property loss as much as possible, we have arrived at the present invention.

That is, the gist of the present invention is to provide a fluidized bed reactor containing an oxidation catalyst containing a vanadium-phosphorus composite oxide as an active ingredient.
Oxygen-containing gas is supplied from below the gas dispersion plate at the bottom to fluidize the catalyst to form a dense fluidized bed of the catalyst above the gas dispersion plate. Maleic anhydride is produced by a gas phase oxidation reaction by supplying a group hydrocarbon, which flows out of the rich fluidized bed while entraining a small amount of the catalyst and forms a dilute fluidized bed of the catalyst above the rich fluidized bed. The reaction product gases rising while forming are withdrawn from the fluidized bed reactor via a cyclone at the top, and then a feed of the withdrawn hydrocarbons is directed upwardly from the gas dispersion in the lower region of the dense fluidized bed. returning a substantial portion of the catalyst recovered in the cyclone at a distance to the lower region of the dense fluidized bed;
A method for producing maleic anhydride, comprising: cooling the gas to a temperature in the range of 0-(730°C) using an indirect heat exchanger installed in the dilute fluidized bed.

The present invention will be explained in detail below.

In the method of the present invention, p-maleic anhydride is produced by a gas phase oxidation reaction by bringing a raw material hydrocarbon into contact with an oxygen-containing gas in a fluidized bed reactor containing an oxidation catalyst in a fluidized state.

As the catalyst, an oxidation catalyst containing a vanadium-phosphorus composite oxide as an active ingredient is used. The catalyst can be produced by various known methods as described above.

As the raw material hydrocarbon, aliphatic hydrocarbons having at least several carbon atoms are used. Suitable raw material hydrocarbons are aliphatic hydrocarbons having several grams of carbon, such as butane (n-butane), butenes (/-butene, copeten), butadiene (l,3-butadiene), and more preferably butane. It is.

Air is usually used as the oxygen-containing gas, but air diluted with an inert gas, air enriched by adding oxygen, etc. can also be used.

The fluidized bed reactor used in the method of the present invention has a gas distribution plate at the bottom defining the lower end of the catalyst fluidized bed, and a cyclone at the top for recovering the scattered catalyst from the reaction product gas and returning it to the catalyst fluidized bed. The feedstock hydrocarbon feed port may be provided in the lower region of the dense fluidized bed at a position upwardly away from the gas distribution plate, and the feedstock hydrocarbon feed port is provided in the lower region of the dense fluidized bed, for example, at a position apart from the gas distribution plate and the above. An indirect heat exchange device for heat removal from the reaction product gas, such as a heat removal coil, must be provided at a location between or near the hydrocarbon supply port where a circulating bed is to be formed in the cyclone. There is.

FIG. 1 is a schematic diagram showing an example of the internal configuration of a fluidized bed reactor used in the method of the present invention. It is blown into the reactor from the feed log below the fluidized distribution plate. The oxidation catalyst on the gas distribution plate is fluidized by the oxygen-containing gas, forming a dense fluidized bed 5 above the gas distribution plate. 6 is a heat removal coil installed in the dense fluidized bed to control the reaction temperature. The raw material hydrocarbon is blown into the dense fluidized bed from g via the supply pipe 7. The feed port g opens downward to promote mixing of the raw material hydrocarbon and the oxygen-containing gas, but may open in other directions as long as sufficient mixing is ensured. In the dense fluidized bed, maleic anhydride is produced by the gas phase oxidation reaction of the raw material hydrocarbon.In addition to the target product maleic anhydride, unreacted oxygen and the raw material hydrocarbon, as well as by-products carbon dioxide, water and - The reaction product gas containing various concentrations of carbon oxide and the like flows out from the upper surface 9 of the dense fluidized bed, accompanied by a relatively small amount of the catalyst, forming a lean fluidized bed io of the catalyst thereabove. As mentioned above, the volume of the lean fluidized bed is usually several times that of the dense fluidized bed. /l is a heat removal coil installed in the dilute fluidized bed, which removes heat from the reaction product gas to a controlled extent as described below. The reaction product gas is then passed through cyclones /2 and /3 installed at the top of the reactor.
The desired product, maleic anhydride, is recovered from the produced gas. This method of recovering maleic anhydride is well known;
A variety of methods are known, but mainly consist of absorption with aqueous or organic media, concentration of the absorption liquid, and purification by distillation.

In the fluidized bed reactor 1 in FIG. 1, the cyclone is a single-stage type with a first-stage cyclone/co and a first-stage cyclone 13, but a three-stage or more multi-stage configuration can be used if necessary. The lower end 16 of the date preg 15 of the first stage cyclone/co is connected to the gas distribution plate g and the feedstock hydrocarbon supply port g.
and is configured such that a substantial portion of the catalyst recovered in the cyclone is returned to the region. Note that it is also possible to provide the lower end 16 of the date preg at a position slightly above the supply port g, as will be described later. The lower end tg of the date preg 17 of the second stage cyclone 13 opens at a higher position within the dense fluidized bed, so that the residual portion of the catalyst is returned to the dense fluidized bed.

When performing a gas phase oxidation reaction of feedstock hydrocarbons in a fluidized bed reactor with the above configuration, the inside of the reactor is an extremely complex system that includes reactions and material flows (including some circulation). Since each zone in the reactor influences each other, it is necessary to take this interdependence into account when setting the conditions for each zone.

For example, the reaction product gas that flows out of the dense fluidized bed and rises in the diluted fluidized bed contains residual unreacted raw material hydrocarbons, such as butane and maleic anhydride, which is a reaction product, as well as carbon monoxide, which is a by-product of the reaction. Contains combustible materials. Further, at least a portion of the oxygen supplied to the reactor as an oxygen-containing gas such as air remains unreacted in the reaction product gas. Therefore, the composition of the reaction product gas may fall within the explosive range in some cases, so in industrial processes, the concentration and composition of flammable substances, oxygen concentration, etc. are monitored and the gas is supplied to the reactor to ensure that it does not fall within the explosive range. It is necessary to determine the concentration of the raw material hydrocarbon in the dense fluidized bed, and to determine the reaction conditions of the dense fluidized bed, taking this into consideration as the explosion range has considerable dependence on temperature and pressure. There is.

However, as for the reaction temperature, it largely depends on the performance and characteristics of the catalyst, the contact time, etc. Therefore, the reaction temperature of the dense fluidized bed is determined primarily from this point of view. In particular, in the case of a catalyst containing a vanadium-phosphorus complex oxide as an active component, if the reaction temperature is too low, the reoxidation rate of the catalyst will be low and the catalyst will be strongly reduced, giving rise to concerns about changes in reactivity and deactivation. For this reason, the reaction in a dense fluidized bed is usually 310~
zoooC, preferably (Io.

It is carried out in a temperature range of about 10 to 10°C.

However, if the reaction temperature in the dense fluidized bed is in the above temperature range, especially in the higher temperature range, the reaction product gas flowing out of the dense fluidized bed will have a high temperature, so the reaction will not occur in the lean fluidized bed. Non-catalytic oxidation of the product gas will proceed at a significant rate.

In the method of the present invention, in order to suppress the above-mentioned non-catalytic oxidation, the reaction product gas is cooled by an indirect heat exchanger installed in the dilute fluidized bed.

In this case, while suppressing non-catalytic oxidation (also called auto-oxidation) in the lean fluidized bed as much as possible, the temperature of the catalyst particles refluxed to the rich fluidized bed via the cyclone should be controlled to reduce the temperature of the catalyst particles in the rich fluidized bed. In order to maintain the temperature within a range that does not affect the reaction, care must be taken in setting the temperature range for cooling. io to sufficiently reduce the rate of non-catalytic oxidation.

The temperature cannot be lowered below ℃. This is because the temperature of the catalyst particles collected by the cyclone and circulated to the dense fluidized bed is too low, making it impossible to maintain the temperature necessary for normal catalytic reaction in the dense fluidized bed, which destabilizes the system. It is from. In particular, if the temperature of the catalyst particles is low, there is a risk of causing excessive reduction, deposition of carbonaceous deposits, etc., a decrease in activity, and deterioration of fluidity.

Therefore, in the present invention, cooling in the dilute fluidized bed is performed so that the temperature of the reaction product gas at the cyclone inlet is in the range of 330-'IrO°C. The temperature range is preferably 330-'700°C, more preferably 3!
0-IIo 0'C.

In the fluidized bed reaction according to the present invention, the concentration (molar concentration) of the feedstock hydrocarbon relative to the supplied air or other oxygen-containing gas is determined so that the composition of the reactor outlet gas is in the explosive range under the temperature and pressure conditions. It should be set to avoid this. When the feedstock hydrocarbon is butane, the concentration is usually less than 1% or 3%, depending on the performance of the catalyst.
It is 5 inches or more. Even if the above concentration is 3.34 or more, if the concentration is too high, oxygen will be insufficient and the effective conversion rate in one pass will decrease, which is not advantageous.

Usually, the upper limit of the hydrocarbon concentration is less than 0, preferably less than 3, preferably less than 3, considering economic efficiency. A concentration range of approximately 6 g to 6 g is selected. In addition, when the raw material hydrocarbon is butenes, butadiene, or other aliphatic hydrocarbons having several carbon atoms, the concentration range to be selected is approximately the same.

Further, in the method of the present invention, the feedstock hydrocarbon is supplied in the lower region of the dense fluidized bed at a position spaced upward from the gas distribution plate. In this case, there is a region in the lower part of the dense fluidized bed where no raw material hydrocarbon is supplied and the catalyst is treated substantially only with oxygen-containing gas such as air. In this region, the catalyst used in the oxidation reaction of hydrocarbons and transferred to the reduction side is oxidized. Therefore, this region will be called the reoxidation zone. The height of the reoxidation zone, that is, the distance between the gas distribution plate and the hydrocarbon supply position, should be set appropriately considering the properties of the catalyst, especially the reoxidation rate, oxygen concentration, etc., but is usually 0. .3-377B, preferably 0.1-/, j
It is about m.

In the method of the present invention, as described above, the reduced catalyst is reoxidized by providing a reoxidation zone in the lower region of the dense fluidized bed and returning a substantial portion of the catalyst recovered by the cyclone to this reoxidation zone. Facilitate. The most reliable way to return a substantial portion of the recovered catalyst to the reoxidation zone is to open the lower end of the date preg in the cyclone into the reoxidation zone, but the lower end of the date preg should be slightly above the reoxidation zone. Similar results can be obtained even if the opening is open, since most of the recovered catalyst falls into the reoxidation zone.

As mentioned above, returning the cyclone recovered catalyst to the lower region of the dense fluidized bed is a fairly common method in gas phase oxidation using a fluidized bed, but the problem is The reoxidation rate of the catalyst is generally rather low, and the temperature needs to be above a certain level to promote sufficient reoxidation.

Since there is convective circulation of the catalyst in the dense fluidized bed, when the catalyst that has been collected in the cyclone and transferred to the reduction side is circulated to the reoxidation zone, it must be at a temperature lower than the reaction temperature of the dense fluidized bed. Although this can be done to some extent, there is a limit to this, and if the temperature of the circulating catalyst is on the low side, the above-mentioned disadvantages will occur. In the method of the present invention, the temperature of the circulating catalyst can be maintained within an appropriate range since a controlled degree of cooling is performed in the dilute fluidized bed as described above.

[For production]

In the method of the present invention, the reoxidation of particularly highly reduced recovered catalyst is promoted by forming a reoxidation zone in the lower region of the dense fluidized bed and returning thereto a substantial portion of the recovered catalyst from the cyclone. There is. In addition, by performing a controlled degree of heat removal in the lean fluidized bed, it is possible to effectively suppress non-catalytic oxidation of the reaction product gas and to avoid the disadvantages caused by the low temperature of the recovered catalyst returned from the cyclone to the rich fluidized bed. It's evasive.

The effects of cooling in a diluted fluidized bed on the reaction product gas and catalyst will be shown below using reference examples.

Tokukai Show 3? - Example 9!933 - using an inch vertical tube reactor, tIoo-tith.

Hydrocarbons are oxidized in the gas phase at ℃, the catalyst in the outlet gas is separated using a catalyst filter, the gas is extracted from the system, and the temperature of the gas exiting the renamer, which is introduced into a preheated explosion container with a volume of 1. SO~3sθ°C). In this explosive container/!
Ignition was made with a KV alternating current spark (0.07 seconds), and the presence or absence of an explosion was determined based on the pressure rise inside each vessel. The composition and conditions of the outlet gas were changed by changing the reaction, temperature, concentration of raw materials and inlet oxygen (adjusted by completely mixing air and nitrogen), contact time, pressure, etc.

Gas-phase oxidation of shibutane (99% purity) was carried out using the apparatus with the above configuration, and the critical oxygen concentration (=
The lower limit of oxygen concentration at which an explosion occurs) was measured. The butane concentration during the reaction was about 100 ml, the butane conversion rate was gO to qtr%, and the maleic anhydride yield was &g-j4%. Explosive container temperature J! ; 0-4j The critical oxygen concentration values in the range of 0°C were as shown in Table 1 below.

Table 7 This is due to the oxidation of combustible substances in the phase. Although there is no direct correlation with the explosion test using forced ignition using this device, this test shows that the reaction temperature for oxidation without a catalyst is −q
It is clear that lowering the temperature of the reaction product gas to a temperature below eoo°C with respect to t and o°C is advantageous with respect to non-catalytic oxidation in the gas phase and the explosion induced thereby.

Reference Example-1 (Influence on Catalyst) A small-sized fluidized bed reactor with forced circulation of catalyst with a diameter of /,j inch with a structure in which catalyst overflow from a dense fluidized bed is returned to the bottom of the reactor using an external piping with an inner diameter of 1 inch. A gas-phase oxidation reaction of butane was carried out using a gas-phase oxidation system, while varying the temperature at which it was returned to the bottom of the dense fluidized bed.

Nitrogen was flowed into the circulation pipe at a flow rate of 34/f1r.

The same catalyst as in Reference Example-/ was filled with sky, and a daciptan/air mixed gas was used at a reaction temperature of 20° C., normal pressure, and LvlO/S. The reoxidation zone is 3! ran, and butane was supplied downward from this position and mixed with air in the dense fluidized bed.

The temperature of the reoxidation zone is 4! There was not much difference in the reaction results when changing the temperature to 0°C, 360°C, and 300°C at the initial stage, but after the time had elapsed, the activity showed a tendency to decrease as the temperature decreased, as shown in Table 1 below. .

〔Effect of the invention〕

By carrying out the fluidized bed reaction according to the method of the present invention, it is possible to effectively suppress non-catalytic oxidation in a diluted fluidized bed! Since suitable reaction conditions within the dense fluidized bed can be maintained, maleic anhydride can be produced safely and economically.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of the internal configuration of a fluidized bed reactor used in the method of the present invention. / Fluidized bed reactor λ Gas distribution plate 3 Oxygen-containing gas supply pipe! , Dense fluidized bed 6 Dense fluidized bed heat removal coil 7 Raw material hydrocarbon supply pipe IO Lean fluidized bed// Lean fluidized bed heat removal coil/Co, 13: Cyclone/q: Reaction product gas extraction pipe is, /7: Dip leg Figure 1

Claims (1)

[Claims] (1) Oxygen-containing gas is supplied from below the gas distribution plate at the bottom to a fluidized bed reactor containing an oxidation catalyst containing a vanadium-phosphorus composite oxide as an active ingredient, and the catalyst is fluidized to disperse the gas. forming a dense fluidized bed of the catalyst above the plate;
An aliphatic hydrocarbon having a carbon number of 4 or more is fed into the dense fluidized bed, maleic anhydride is produced by a gas phase oxidation reaction, and it flows out of the dense fluidized bed while accompanying a small amount of the catalyst to form the dense fluidized bed. extracting the rising reaction product gas from the fluidized bed reactor through a cyclone at the top while forming a dilute fluidized bed of the catalyst above the bed, and then recovering maleic anhydride from the withdrawn reaction product gas. The method includes: supplying the hydrocarbons in a lower region of the dense fluidized bed at a location upwardly spaced from the gas distribution plate; and supplying a substantial portion of the catalyst recovered by the cyclone to the dense fluidized bed. and the temperature of the reaction product gas at the cyclone inlet is 33°C.
A method for producing maleic anhydride, comprising: cooling the gas using an indirect heat exchanger installed in the dilute fluidized bed so that the temperature ranges from 0 to 450°C.