JPH0678251B2 - Method for producing methacrylic acid and / or methacrolein - Google Patents

Description

TECHNICAL FIELD The present invention provides a novel method for producing methacrylic acid and / or methacrolein. More specifically, it relates to a method for oxidizing methacrylic acid and / or methacrolein in a single step by oxidizing isobutane in the gas phase in the presence of a catalyst.

(Prior Art) Conventionally, many methods for producing menthacrylic acid and / or methacrolein are known, for example, a method of synthesizing from isobutylene via methacrolein by two-step oxidation (see, for example, JP-A-54-54). No. 3008), and a method for synthesizing methacrylic acid and / or methacrolein using isobutylene as a raw material (see, for example, JP-A-52-122317).
And a method for dehydrogenating isolacic acid (eg,
JP-A-50-41812).

However, saturated hydrocarbons such as isobutane are conventionally considered to be an inert gas, and it is described that they are used as a diluent for a reaction gas when oxidizing olefins and aldehydes. On the other hand, although isobutane is extremely poor in reactivity as described above, in British Patent No. 1340891, in the gas phase, antimony and molybdenum oxides are coexistent in the presence of oxygen. It has been shown that methacrylic acid is produced with a very low selectivity of 2% when used as a catalyst.

Further, JP-A-55-62041 discloses a method for producing methacrylic acid by oxidizing isobutane in the presence of molecular oxygen using a catalyst composed of antimony, molybdenum, phosphorus and oxygen. However, also in this method, when the isobutane concentration is 10%, the conversion is 10%, and the selectivity of methacrylic acid is only 50%. Therefore, the concentration of methacrylic acid in the produced reaction gas is 0.5%, which is extremely dilute and the production efficiency is low. Also, when isobutane concentration was increased to 28% to improve productivity, the conversion rate was 9% and the selectivity of methacrylic acid was 46%, which lowered the reaction results and increased the isobutane concentration to increase the production efficiency. However, even if an attempt was made to improve the yield, the reaction yield was lowered, and it was inevitable as an industrial production method.

Further, when these methods are carried out industrially, the conversion rate of isobutane is low, and recycling of unreacted isobutane is economically essential. However, the reaction gas contains a diluting gas together with oxygen gas, and particularly contains a large amount of nitrogen if air, which is an inexpensive supply source of oxygen, is used. Therefore, these cannot be recycled to the reactor as they are, and a step of separating isobutane and diluent gas is required. However, the separation operation is very expensive, which increases the cost and loses the advantage of using isobutane. In order to avoid such separation from isobutane, there is a method of using pure oxygen, but pure oxygen itself is expensive and is not advantageous. Therefore, the isobutane method, which is considered to be an excellent method in principle, has not been an advantageous method from the industrial viewpoint as compared with the conventional isobutylene oxidation method.

(Problems to be Solved by the Invention) Accordingly, it is an object of the present invention to provide a method for producing methacrylic acid and / or methacrolein with high productivity by one-step oxidation of isobutane.

(Means for Solving the Problems) The inventors of the present invention have conducted extensive studies to achieve such an object, and as a result, have found that isobutane can be added to a catalyst containing a heteropolyacid containing P and As as a central element and Mo. It is quite unexpectedly possible to contact methacrylic acid and / or methacrylic acid and irrespective of the isobutane gas concentration by contacting isobutane and molecular oxygen at the same time.
Or, it has been found that methacrolein is formed with high selectivity.

The present invention relates to a method for producing methacrylic acid and / or methacrolein based on a new concept characterized by carrying out an oxidation reaction in the absence of substantially isobutane and oxygen at the same time using a catalyst containing a specific heteropolyacid. Is. In such a method, methacrylic acid and / or methacrolein is rapidly produced even when a high concentration of isobutane is used, and for example, it reaches a concentration of about 5% in the reaction gas, which is industrially feasible. We were able to reach such high productivity.

The reason for this effect is currently under investigation, but the following effects are considered. In the catalyst of the present invention, when isobutane and molecular oxygen are brought into contact with the catalyst without being present at the same time, first, methacrylic acid and / or
Alternatively, it is considered that methacrylic acid and / or methacrolein can be efficiently produced because active oxygen effective for producing methacrolein is produced on the catalyst in a sufficient amount and can be subsequently contacted with isobutane to react. On the other hand, when isobutane and molecular oxygen coexist, it is considered that due to competitive adsorption of the two with respect to the catalyst, adsorption of isobutane is inhibited and active oxygen on the catalyst becomes insufficient, resulting in a decrease in isobutane oxidation activity.

It is also a great feature that the selectivity of methacrylic acid and / or methacrolein has been improved in the absence of molecular oxygen. When molecular oxygen is present in the oxidation process of isobutane, it is presumed that the sequential oxidation of methacrylic acid and methacrolein or the excessive oxidation of the isobutane intermediate oxidation product occur together, resulting in a decrease in the selectivity of methacrylic acid and methacrolein.

Further, the alternating use of isobutane and oxygen makes it possible to select the optimum reaction conditions for the reduction process with isobutane and the oxidation process with oxygen. It is considered that this is an important point that more active oxygen that does not cause a side reaction is generated and methacrylic acid and / or methacrolein can be produced with high selectivity.

Further, according to the method of the present invention, since oxygen gas and isobutane are not mixed, a high concentration of isobutane gas can be used without being restricted by the explosion range. Moreover, since methacrylic acid and / or methacrolein can be produced with a high selectivity even at a high concentration of isobutane gas, methacrylic acid and / or methacrolein can be economically produced with high production efficiency even at a low conversion rate.

Further, since isobutane and oxygen are supplied without being mixed, titanium and isobutane do not mix even if inexpensive air is used as an oxygen source, and a step of separating them is not necessary. Therefore, it has epoch-making significance from the viewpoint of industrially producing methacrylic acid and / or methacrolein from isobutane.

It is important that the catalyst used in the present invention contains a heteropolyacid containing P or As as a central element and Mo. Heteropolyacids containing P or As as a central element and Mo are phosphomolybdic acid and arsenic molybdic acid, and various structures are known (Chemical region Vol 29, No. 12, P853, Sasaki,
Matsumoto). A typical example is 12-molybdophosphoric acid having a Keggin structure. Further, a structure in which a part of Mo constituting phosphomolybdic acid or arsenic molybdic acid is replaced with vanadium or tungsten is also effective as the catalyst of the present invention.

On the other hand, heteropolyacids have various crystal structures, for example, 12-molybdophosphoric acid changes to cubic, triclinic, and tetragonal with the decrease of coordinated water, and has a structure corresponding to the amount of coordinated water. Exists in.

It is known that these heteropolyacids take various reducing states, and it is preferable to use them in the reducing state of the heteropolyacid.

Furthermore, various salts of these heteropolyacids can be used as the catalyst.

Effective salts include ammonium salts, salts with amines such as pyridine and quinoline. This may be one that partially forms a salt with ammonium ions, or one in which ammonium ions have been partially or wholly removed by firing from the ammonium salt.

In addition, Bi, Te, U, As, Ti, Zr, Co, Cu, Sb, Tl, Ag, Nb, Ta, Se, In,
Ga, Al, alkali metal, alkaline earth metal, rare earth metal,
It may be a salt of another metal or a mixture containing these metals. Also, a mixture thereof is effective as a catalyst. Mixtures with ammonium salts can also be used.

A carrier may be used for these catalysts. Examples of the carrier include silica, alumina, silicon carbide, titania, zirconia, and diatomite.

These heteropolyacids can be prepared by known methods [for example, G.A.Tsudidinos, Industrial and Engineering Chemistry, Products Research.
And Development (GATsigdinos, Ind.Eng.Ch
em., Prod.Res.Dev.,) Vol.13, P267, 1974 and Gee
A. Tsudidinos, Inorganic Chemistry Vol.7, No.3,19
68 years].

The ammonium salt can be synthesized from a heteropoly acid. In this case, aqueous ammonium salts such as ammonia water, ammonium chloride and ammonium nitrate can be used as the ammonium ion source. In addition, organic amines can be similarly used and are useful. These ammonium salts are
Use after baking at 300-600 ℃. Baking in an inert gas is more preferable.

Other metal salts or composites can be synthesized by mixing salts of metal carbonates, nitrates, chlorides and the like with heteropolyacids, drying and firing, and using them as catalysts.

In carrying out the present invention, the type of reactor used may be a fluidized bed, a fixed bed, or any other type of reactor.

Further, a method of alternately contacting isobutane and oxygen with the catalyst is not particularly specified. For example, isobutane gas and oxygen-containing gas may be temporally switched and circulated in the same reactor. In this case, only the isobutane reaction gas needs to be separately collected at the outlet of the reactor. When a fluidized bed type reactor is used, two reactors are used, the reactor supplying isobutane gas and the reactor supplying oxygen-containing gas are connected, and the catalyst is moved between them to continuously The reaction can be carried out. An example is shown in the drawing, in which 1 is a raw material supply port, 2 is an oxygen-containing gas supply port, 3
Is a reaction gas outlet, 4 is an oxygen gas outlet, 5 is a fluidized bed for isobutane reaction, 6 is a fluidized bed for oxygen catalyst, and 7 and 8 are catalyst transport pipes. Isobutane is a raw material supply port 1
From the reaction gas extraction port 3 together with the reactants. The catalyst is from the fluidized bed 5 for isobutane reaction to the catalyst oil feed pipe 8
Through the fluidized bed 6 for oxygen contact, and contact with oxygen,
Then, it returns to the isobutane reaction fluidized bed 5 through the catalyst transport pipe 7. According to this method, a mixed gas of the product substantially free of molecular oxygen and unreacted isobutane can be obtained from the reactor supplying isobutane.
Further, the temperature of each reactor can be set separately, and the temperature can be set to the optimum temperature for the catalyst. Similarly, a moving bed reactor can be used.

Although isobutane gas is used as the raw material gas to be supplied to the reaction, the mixing of other hydrocarbons is not limited as long as it does not affect the reaction. An inert gas is used as a diluent for the oxidation reaction using a normal oxygen mixed gas, for the purpose of limiting the explosion range and maintaining high reaction results. However, no special dilution is necessary in carrying out the reaction of the present invention, and 100% isobutane gas can be used if desired. However, it is advantageous to supply water vapor in an amount of about 5 to 40% because the target product can be obtained with a high selectivity. Of course, if desired, it may be diluted with a gas such as nitrogen, argon, helium or carbon dioxide. A trace amount of oxygen may be mixed in as long as it does not substantially affect the reaction results. Further, it is more economical to use unreacted isobutane recovered from the reaction gas for isobutane, but at that time, a small amount of carbon monoxide,
Carbon dioxide and other reaction products may be mixed. Further, the methacrolein produced at the same time can be recovered and added to a part of the raw material gas.

The gas used in the operation of bringing the catalyst into contact with oxygen must contain molecular oxygen. The concentration of molecular oxygen in the gas is not particularly specified, but a concentration of 0.1% or more is advantageous because the time required for regeneration can be shortened. Pure oxygen can be used, but even if the concentration is too high, the effect of shortening the regeneration time is small. Preferably 0.5-30 mol
% Concentration. Steam and inert gases such as nitrogen, helium, carbon dioxide, argon can be used to dilute to the desired concentration. Addition of water vapor has the effect of increasing the selectivity of the product during the reaction. Further, the oxygen gas may be recovered after being brought into contact with the catalyst and used again as an oxygen source.

In the operation according to the invention, the catalyst is reduced on contact with isobutane, the extent of which is important. If the catalyst is excessively reduced, it takes a long time to regenerate it, and in an extreme case, it becomes difficult to regenerate it, and continuous use becomes impossible.

An important point during regeneration is to re-oxidize the reduced catalyst to a certain degree of reduction with each regeneration. However, it is preferable to always use the catalyst in a slightly reduced state, and it is better not to re-oxidize it until the completely oxidized state.

The contact time between the source gas and the catalyst (catalyst capacity divided by the amount of the source gas supplied per second at the reaction temperature) was 0.
A range of 05-50 seconds is appropriate. More preferably 0.1 to 2
It is in the range of 0 seconds.

The reaction pressure can be widely set from reduced pressure to increased pressure, but atmospheric pressure to 2 atm is industrially advantageous.

The reaction temperature can vary widely. However, if the temperature is too low, the reaction rate is low, and if the temperature is high, the catalyst is decomposed and the selectivity is lowered. The temperature is preferably 250 to 600 ° C, more preferably 270 to 450 ° C.

The temperature required for regeneration is 250 to 600 ° C, preferably 270 to 450 ° C. This temperature does not have to be the same as the reaction temperature, and the optimum temperature for the catalyst can be arbitrarily set within the above range depending on the conditions such as the reactor.

The produced methacrylic acid and methacrolein can be separated and purified by a known appropriate method such as cooling, absorption, distillation or the like to obtain their respective products. Unreacted isobutane is
It can be recovered and used again as a raw material. Further, after recovering methacrylic acid from the reaction gas by a known method such as cooling condensation, absorption, adsorption, etc., a part or all of the recovered gas containing methacrolein is supplied again to the reactor as a part or all of the raw material. be able to.

(Example) Example 1 Powdered ammonium phosphonate ammonium budnate (manufactured by Nippon Inorganic Chemical Co., Ltd.) was molded into pellets at a pressure of about 100 kg / cm ³ and crushed to select particles of 10 to 20 mesh. This was weighed at 5 g and baked at 450 ° C. for 3 hours in a nitrogen stream.

2.5 g of this catalyst was filled in a U-shaped tube made of Pyrex with an inner diameter of 6 mm and set in a constant temperature bath. The temperature of the thermostat is set to 350 ° C., a) a mixed gas of 62 mol% isoptan and 38 mol% steam at 40 ml / mm for 5 seconds, and b) 20 mol% oxygen, 42 mol% helium, 38 mol% steam. Contact time with mixed gas
The operation of circulating for 10 seconds at 1.5 seconds was continuously performed alternately using a valve linked with a timer. When the reaction gas was analyzed by gas chromatography after 3 hours, 8% of isobutane was converted and the selectivity of methacrylic acid was 54%.
The selectivity of methacrolein was 17%.

Comparative Example 1 2.5 g of the catalyst prepared in the same manner as in Example 1 was charged in the same reactor. Keep the temperature at 350 ℃, isobutane 60 mol%, oxygen 2
A mixed gas of 0 mol% and steam of 20 mol% was supplied at a contact time of 1.5 seconds. When the reaction gas was analyzed after 3 hours, the conversion of isobutane was 3% and the selectivity of methacrolein was 44%.
Therefore, methacrylic acid was not detected.

Example 2 Phosphomolybdic acid (Nippon Inorganic Chemicals Co., Ltd.) was passed through a glass tube with an inner diameter of 25 mm at a temperature of 300 ° C. for 3 hours while flowing hydrogen at 30 ml / mm.
Burned for hours.

When this was used for the reaction under the same conditions as in Example 1, the conversion of isobutane was 7% and the selectivity of methacrylic acid was 25%.
%, The selectivity of methachlorelin was 10%.

Example 3 Disodium hydrogen phosphate _{(Na 2 HPO 4 · 12H 2} O) 17.9g 100
Dissolved in ml water. This was mixed with 22.4 g of sodium metavanadate (NaVO ₃ ) dissolved in 100 ml of hot water, and after cooling, 5 ml of concentrated sulfuric acid was added. Separately, 121 g of sodium molybdate (Na ₂ MoO ₄ .2H ₂ O) was dissolved in 200 ml of water to prepare a solution, which was mixed with the above solution. Concentrated sulfuric acid in this solution
85 ml was added. Next, after adding 500 ml of ethyl ether and stirring with a separating funnel, the mixture was allowed to stand, the intermediate layer was taken out and air-dried to obtain 10-molybdo-2-vanadric acid.

Take 10 g of this and add 4.0 g of ammonium nitrate (NH ₄ NO ₃ ) to 100
It was added to a solution dissolved in ml of water.

After further adding 1.0 g of ethylene glycol, it was dried at 60 ° C. by a rotary evaporator. This is 100 ℃
After being calcined for 1 hour at 450 ° C. for 3 hours in a nitrogen stream, a catalyst was obtained. Table 1 shows the results of the reaction carried out under the same conditions as in Example 1.

Example 4 21 g of phosphomolybdic acid (Nippon Inorganic Chemistry) and 2.9 g of phosphotagustonic acid (Nippon Inorganic Chemistry) were dissolved in 100 ml of water, and the temperature was 60 ° C.
It was stirred for 2 hours. Then, it dried with a 60 degreeC rotary evaporator. The obtained crystals are mainly H ₃ PMo ₁₁ Wo
_{It was 40} · nH ₂ O.

10 g of this was taken and a catalyst was prepared in the same manner as in Example 3. The results obtained by carrying out the reaction under the same conditions as in Example 1 are shown in Table 1.
Shown in.

Example 5 200 ml of 121 g of sodium molybdate (Na ₂ MoO ₄ .2H ₂ O)
20% of a 30% arsenic acid solution was added to the solution dissolved in water of.
After adding 80 ml of concentrated sulfuric acid to this solution, 300m of ethyl ether
l was added. The lower layer separated into three layers was taken out and air-dried to obtain arsenic molybdic acid.

Using this instead of the phosphomolybdic acid of Example 5, a catalyst was prepared in the same manner as in Example 5.

Table 1 shows the results of the reaction carried out under the same conditions as in Example 1.

Example 6 ammonium nitrate 10g of bismuth nitrate in water 600ml was dissolved the _{[Bi (NO 3) 3 · 5H} 2 O ] 9.72g addition, after stirring well, was added phosphomolybdic acid 47 g. This solution was stirred at 60 ° C. for 1 hour, 5 g of ethylene glycol was added, and the mixture was dried with a rotary evaporator.

This was dried at 150 ° C for 1 hour and then in nitrogen for 3 hours 440
Baked at ° C.

The results of the reaction performed under the same conditions as in Example 1 are shown in Table 2.

Examples 7 to 12 In Example 6, various metal salts were used instead of bismuth nitrate to prepare catalysts and carry out the reaction. The results are shown in Table 2.

Comparative Example 2 Using the same catalyst as in Example 6, the reaction was performed under the same reaction conditions as in Comparative Example 2.

The reaction results were an isobutane conversion of 2.5%, methacrylic acid selectivity of 0%, and methacrolein selectivity of 51%.

Example 13 2.5 g of the catalyst prepared in Example 6 was tested using the same reactor as in Example 1. However, the gas used is 1)
Mixed gas of 10 mol% isobutane, 20 mol% steam, 70 mol% helium and 2) 13 mol% oxygen, 20 mol% steam,
It was a mixed gas of 67 mol% helium. 5) gas of 1)
The gas of 2) was then alternately supplied to the reactor for 10 seconds. The contact time was 1.2 seconds. The reaction results at 3 hours after the start of the reaction were an isobutane conversion of 7%, methacrylic acid selectivity of 65%, and methacrolein selectivity of 15%.

Example 14 3.2 g of antimony pentachloride (SbCl ₃ ) was added dropwise to a solution of 2.04 g of nitric acid in 250 ml of water. Next, phosphomolybdic acid 23.
4g and 20.2g of finely divided silica (Aerosil TT600) were added and stirred for 1 hour. Then, 6 g of ethylene glycol was added and dried by a rotary evaporator.

The solid obtained is calcined at 200 ° C for 1 hour and then 420 ° C in a nitrogen stream.
It was baked in.

Using this catalyst, the reaction was carried out under the same reaction conditions as in Example 1, and as a result, the conversion of isobutane was 11% and the selectivity of methacrylic acid was 46%.
%, The methacrolein selectivity was 18%.

Example 15 The same operation as in Example 14 was performed except that 10 g of silicon carbide and 5.5 ml of ammonia water (25% by weight) were added instead of the finely divided silica.

The reaction results were an isobutane conversion of 9%, methacrylic acid selectivity of 50%, and methacrolein selectivity of 15%.

Example 16 The reaction was carried out using two micro fluidized bed reactors each having an inner volume of 50 ml and equipped with a catalyst outlet and a catalyst inlet. The catalyst is
The catalyst of Example 3 supported on 10% by weight of silica was used.

The first reactor was charged with 20 g of the catalyst, and a gas containing 60 mol% of isobutane and 40 mol% of steam was supplied at a contact time of 2.0 seconds.

The second reactor was charged with 30 g of catalyst and air was supplied with a contact time of 2.5 seconds. In addition, the catalyst was extracted from each of the two reactors at 1 g / sec and introduced into the other reactor.

As a result of analyzing the gas produced from the first reactor, the conversion of isobutane was 7%, the selectivity of methacrylic acid was 51%, and the selectivity of methacrolein was 16%.

(Effects of the Invention) As is apparent from the above-mentioned examples, according to the present invention, methacrylic acid and / or methacrolein can be produced at a high selectivity even with a high concentration of isobutane gas by one-step oxidation of isobutane. You can

[Brief description of drawings]

The drawing is an explanatory view showing an example in the case of using a fluidized bed type reactor. 1 ... Raw material supply port, 2 ... Oxygen gas supply port, 3 ... Reaction gas outlet port, 4 ... Oxygen gas outlet port, 5 ... Isobutane reaction fluidized bed, 6 ... Oxygen contact fluidized bed, 7 , 8
...... Catalysis theory pipe

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location B01J 27/19 Z 9342-4G

Claims (1)

[Claims] 1. A method for producing methacrylic acid and / or methacrolein, which comprises alternately contacting isobutane and oxygen with a catalyst containing a heteropolyacid containing P or As as a central element and Mo.