JP2003306464A - Method for regenerating catalyst for producing methacrylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for obtaining a highly active regenerated catalyst by sufficiently restoring the activity of a heteropoly acid-based catalyst containing phosphorus, molybdenum and vanadium and used in a vapor phase catalytic oxidation reaction of methacrolein. <P>SOLUTION: The method comprises carrying out a heat treatment of the heteropoly acid-based catalyst at 290-400°C under the stream of a gas containing ≥3 vol.% of molecular oxygen and ≥3 vol.% of water vapor. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for regenerating a heteropolyacid catalyst used for producing methacrylic acid by subjecting methacrolein to a gas phase catalytic oxidation reaction.

[0002]

2. Description of the Related Art Conventional method 1 for producing methacrylic acid
As one of the methods, a method is known in which methacrolein is subjected to a gas phase catalytic oxidation reaction using a heteropolyacid catalyst. In this reaction, the activity of the catalyst usually decreases gradually with the elapse of the reaction time. Therefore, in order to extend the useful life of the catalyst, it is considered to recover the activity of the catalyst by a regeneration treatment. For example, in JP-A-58-156351, a catalyst composed of free phosphomolybdic acid or phosphovanadomolybdic acid whose activity has been lowered in the above reaction is used under the flow of a gas containing at least 10% by volume of steam. 70 to 2
A method of heat treatment at 40 ° C has been proposed. Further, in JP-A-6-7685, a catalyst containing phosphorus, molybdenum and vanadium, which has been used in the above reaction and whose activity has been reduced, is used under the flow of a gas containing at least 0.1% by volume of molecular oxygen. A method of heat treatment at 300 to 410 ° C has been proposed.

[0003]

However, in these conventional methods, the effect of recovering the catalytic activity is not always sufficient, and a regenerated catalyst having a desired activity may not be obtained. Therefore, it is an object of the present invention to provide a method for regenerating a catalyst for producing methacrylic acid, which is superior in activity of the regenerated catalyst to these conventional methods.

[0004]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the catalyst used in the above reaction is carried out at a specific temperature under the flow of a gas containing molecular oxygen and water vapor at a specific concentration or higher. It was found that the above object can be achieved by heat treatment within the range, and the present invention has been completed. That is, the present invention provides a heteropolyacid catalyst containing phosphorus, molybdenum and vanadium used for a gas phase catalytic oxidation reaction of methacrolein under the flow of a gas containing at least 3% by volume of molecular oxygen and at least 3% by volume of steam. By heat treatment at 290 to 400 ° C,
The present invention relates to a method for regenerating a catalyst for producing methacrylic acid.

The present invention will be described in detail below. The catalyst to be regenerated by the present invention is a heteropolyacid catalyst containing phosphorus, molybdenum and vanadium as an essential component, which is used when methacrylic acid is produced by a gas phase catalytic oxidation reaction of methacrolein. The catalyst may be composed of a free heteropoly acid or a salt of a heteropoly acid. With respect to such a heteropolyacid catalyst for producing methacrylic acid, many reports have been made so far regarding its composition, physical properties, preparation method, etc. (for example, JP-A-59-12758 and JP-A-SHO). 60
-239439, JP-A-5-96172,
JP-A-8-10621 and JP-A-11-22641
No. 1, etc.).

The gas phase catalytic oxidation reaction of methacrolein using this heteropolyacid catalyst is usually carried out by supplying methacrolein together with molecular oxygen and water vapor to a fixed bed reactor filled with a catalyst, Industrially, a multi-tube type reactor is used as the reactor. The composition of the raw material gas is usually 1 to 10% by volume of methacrolein, 3 to 20% by volume of molecular oxygen, and 5 to 30% by volume of water vapor.
The balance is an inert gas such as nitrogen or carbon dioxide.
Air is usually used as the molecular oxygen source, and steam is usually used as the water vapor source. Regarding the reaction conditions, the feed rate of the raw material gas is usually 500 to 5000 h ⁻¹ as a space velocity (standard state standard. The same applies hereinafter), that is, a feed rate per 1 L of catalyst (L / h).
The reaction temperature is 250 to 350 ° C. The reaction product gas containing the obtained methacrylic acid is usually condensed or absorbed by water and then subjected to a separation and purification operation, and the recovered unreacted methacrolein can be recycled as a raw material,
Further, the exhaust gas can be recycled as the above-mentioned inert gas source after being burned if necessary.

The above-mentioned raw material methacrolein can be suitably produced by subjecting isobutylene or t-butyl alcohol to a gas phase catalytic oxidation reaction using an oxide catalyst containing molybdenum, bismuth and iron.
Usually, this gas-phase catalytic oxidation reaction is used as a first-stage reaction, and the methacrolein obtained is used as a raw material, and the above-mentioned gas-phase catalytic oxidation reaction is used as a second-stage reaction. Manufactured. The first-stage reaction is usually carried out by supplying isobutylene or t-butyl alcohol together with molecular oxygen to a fixed bed reactor filled with a catalyst, and the reactor is industrially of a multitubular type. Is used. The composition of the raw material gas for this first stage reaction is usually
Isobutylene or t-butyl alcohol is 2 to 10% by volume, molecular oxygen is 3 to 20% by volume, and water vapor is 0 to 30.
The content is% by volume, and the balance is an inert gas such as nitrogen or carbon dioxide. Air is usually used as the molecular oxygen source, and steam is usually used as the water vapor source.
Further, as the inert gas source, the exhaust gas of the second stage reaction may be used after being burned if necessary. Regarding the conditions of the first-stage reaction, the feed rate of the raw material gas is usually 500 to 5000 h ⁻¹ as space velocity and the reaction temperature is 300 to 400 ° C. The methacrolein obtained by the first-stage reaction may be subjected to the second-stage reaction by subjecting the first-stage reaction product gas to a separation operation to obtain methacrolein of relatively high purity, which is used in the second-stage reaction. The separation method attached to
There are roughly two types, namely, a direct coupling system in which the first-stage reaction product gas containing methacrolein is directly subjected to the second-stage reaction without being subjected to a separation operation [for example, “Petrochemical Process” (Petroleum Institute of Japan). Ed., Kodansha Scientific Co., Ltd., published in 2001, pp. 174-175].

When methacrolein is subjected to a gas phase catalytic oxidation reaction in the presence of a heteropolyacid catalyst as described above,
Usually, as the reaction time elapses, by-products are strongly adsorbed to the catalyst, the catalyst is thermally deteriorated, etc.
The activity of the catalyst gradually decreases. Therefore, in the present invention, the catalyst used in the above reaction is subjected to a heat treatment within a specific temperature range under the flow of a gas containing molecular oxygen and water vapor at a specific concentration or higher, whereby the catalyst is regenerated.

In the above gas, the molecular oxygen concentration must be at least 3% by volume, and preferably 10% by volume or more. If the molecular oxygen concentration is too low, the activity of the regenerated catalyst will be insufficient. The upper limit of the molecular oxygen concentration is not particularly limited, but it is usually up to about 20% by volume because it is easy to use air as the molecular oxygen source.

In the above gas, the water vapor concentration needs to be at least 3% by volume, preferably 8% by volume or more. If the water vapor concentration is too low, the activity of the regenerated catalyst will not be sufficient. On the other hand, the higher the water vapor concentration, the higher the activity of the regenerated catalyst tends to be, but when it exceeds 30% by volume, it tends to almost reach the upper limit. Therefore, the upper limit of this water vapor concentration is usually about 30% by volume. is there. Steam is usually used as the water vapor source.

The flow velocity of the gas is usually 10 to 2000 h ^-1 as space velocity, preferably 100 to 10
00h ^-1 . An inert gas such as nitrogen or carbon dioxide is usually used as a component other than molecular oxygen and water vapor in the gas. In addition, this regeneration treatment gas is used in a form not containing methacrolein.

The temperature of the heat treatment must be 290 ° C. or higher, preferably 320 ° C. or higher, and 40
It is necessary to set the temperature to 0 ° C or lower, preferably 370 ° C or lower. If the temperature is too low or too high, the activity of the regenerated catalyst is not sufficient. In addition, the time for the heat treatment depends on other conditions, but is generally 0.5 to 20 hours.

Regeneration of the catalyst may be carried out by extracting the catalyst from the reactor and placing it in a separately prepared container for regeneration treatment, or may be carried out without removing the catalyst from the reactor. However, from the viewpoint of operability of switching between reaction / catalyst regeneration, it is desirable to carry out in the reactor like the latter.

Among the above-mentioned heteropolyacid catalysts, the target of the regeneration method of the present invention is more preferably a catalyst composed of a salt of heteropolyacid, and a catalyst composed of an acid salt of heteropolyacid (partially neutralized salt). More preferable.

The regeneration method of the present invention comprises the first step of the gas phase catalytic oxidation reaction of isobutylene or t-butyl alcohol described above.
In a two-step gas phase catalytic oxidation reaction in which the gas phase catalytic oxidation reaction of the obtained methacrolein is a second step reaction,
It can be suitably adopted as a method for regenerating the second-stage reaction catalyst. As described above, the two-stage gas-phase catalytic oxidation reaction includes a separation system in which methacrolein of relatively high purity separated from the first-stage reaction product gas is subjected to the second-stage reaction,
There is a direct coupling system in which the first-stage reaction product gas containing methacrolein is subjected to the second-stage reaction without being subjected to a separation operation, and the regeneration method of the present invention is applicable to the catalyst for the second-stage reaction in any system. However, particularly in the latter direct connection system, substantially the entire amount of unreacted raw materials and by-products in the first-stage reaction product gas is introduced into the second-stage reactor, and the activity of the second-stage reaction catalyst is increased. Since it is likely to decrease, the regeneration method of the present invention, which is excellent in the effect of recovering the catalytic activity, is preferably adopted.

In the above two-stage gas phase catalytic oxidation reaction,
Not only the catalyst for the second-step reaction but also the catalyst for the first-step reaction usually has a gradual decrease in catalytic activity with the passage of reaction time.
When the regeneration treatment of the second-stage reaction catalyst is performed, it is desirable that the regeneration treatment of the first-stage reaction catalyst is also performed. This regeneration treatment of the catalyst for the first stage reaction is carried out at 360 to 450 ° C., more preferably 360 to 40 ° C. under the flow of a gas containing at least 3% by volume, preferably 10 to 20% by volume of molecular oxygen.
It can be suitably performed by heat treatment at 0 ° C. Note that this gas may contain water vapor, but unlike the gas used for regeneration of the second-stage reaction catalyst,
Not required. Further, as a component other than molecular oxygen and water vapor in this gas, an inert gas such as nitrogen or carbon dioxide is usually used.

The regeneration treatment of the first-stage reaction catalyst may be carried out by extracting the catalyst from the reactor and putting it in a separately prepared regeneration treatment container, as in the case of the second-stage reaction catalyst. You can go without removing it, but
From the viewpoint of operability of switching between reaction / catalyst regeneration, it is desirable to carry out in the reactor like the latter.

In the direct coupling type two-stage gas-phase catalytic oxidation reaction, it is easy to pass the gas in series to the first-stage reactor and the second-stage reactor in this order, so it is necessary to put the catalyst in the reactor. Up to this point, it is possible to perform the regeneration treatment of the first-stage reaction catalyst and the regeneration treatment of the second-stage reaction catalyst together with good operability. Specifically, a gas containing a predetermined concentration of molecular oxygen and water vapor may be circulated in series in the first-stage reactor and the second-stage reactor to keep the catalyst layer of each reactor at a predetermined temperature. ,
A gas containing a predetermined concentration of molecular oxygen is supplied to the first stage reactor, the second stage
A gas containing a predetermined concentration of water vapor may be added at the inlet of the second-stage reactor to a place where the catalyst layer of each reactor is maintained at a predetermined temperature while being circulated in series with the two-stage reactor. In this way, the gas containing molecular oxygen is circulated through the first-stage reactor and the second-stage reactor in series to perform the catalyst regeneration treatment, so that the outlet of the first-stage reactor enters the inlet of the second-stage reactor. It is also possible to remove solid substances such as carbonaceous substances that may be deposited in the flow channels up to.

When the direct-coupling two-stage gas-phase catalytic oxidation reaction is carried out by supplying isobutylene or t-butyl alcohol together with molecular oxygen and water vapor to the first-stage reactor, a certain period of time is required. After the reaction, the supply of isobutylene or t-butyl alcohol is stopped, and if necessary, the concentrations of molecular oxygen and water vapor in the supplied gas are adjusted, and the temperature of the catalyst layer of each reactor is adjusted. If is adjusted, it is possible to smoothly switch the catalyst regeneration from the reaction.

In the direct coupling type two-stage gas-phase catalytic oxidation reaction, the temperatures of the first-stage reaction and the second-stage reaction are usually adjusted so that the first-stage reaction and the second-stage reaction maintain a predetermined conversion rate, respectively. Specifically, it is carried out by gradually increasing the temperature of the heat medium in the first-stage reactor and the second-stage reactor as the catalyst activity decreases as the reaction time elapses. Therefore, when the temperature of the heat medium of the first-stage reactor is 360 ° C. or higher and the temperature of the heat medium of the second-stage reactor is 290 ° C. or higher, that is, when the temperature is required for the regeneration treatment of both catalysts, If the supply of isobutylene or t-butyl alcohol is stopped, the catalyst regeneration can be switched from the reaction very smoothly. It should be noted that the catalyst regeneration operation is usually from half a year to
It is desirable to do it once a year on a regular basis.

[0021]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited thereto.

Reference Example 1 (a) Preparation of catalyst In 224 kg of ion-exchanged water heated to 40 ° C., 38.2 kg of cesium nitrate [CsNO ₃ ] and copper nitrate trihydrate [C
_{u (NO 3) 2 · 3H} 2 O] 10.2kg, 85 wt% orthophosphoric acid 24.2Kg, and 70 wt% nitric acid 25.2
kg was dissolved, and this was designated as solution A. Meanwhile, ion exchange water 330kg heated to 40 ° C., ammonium molybdate tetrahydrate _{[(NH 4) 6 Mo 7} O 24 · 4H 2 O] 297k
g of ammonium metavanadate [NH ₄
VO ₃ ] 8.19 kg was suspended, and this was designated as solution B.
Solution A was added dropwise to solution B with stirring, and then 10.2 kg of antimony trioxide [Sb ₂ O ₃ ] was added.
The mixture was stirred in a sealed container at 120 ° C for 17 hours. The obtained slurry was dried using a spray dryer to obtain a catalyst precursor powder. For 100 parts by weight of this powder, a ceramic fiber [manufactured by Toshiba Monoflux Co., Ltd., FI
BERFRAX RFC400SL] 4 parts by weight, ammonium nitrate 8 parts by weight, and ion-exchanged water 10 parts by weight were added and kneaded, and extrusion-molded into a cylindrical shape having a diameter of 5 mm and a height of 5 mm. This molded product was heated at 90 ° C and humidity of 35% RH.
After drying for 3 hours at 220 ° C in an air stream at 22
The catalyst was obtained by calcination in the order of 250 ° C. for 1 hour in an air stream, 435 ° C. for 3 hours in a nitrogen stream, and then 390 ° C. for 3 hours in an air stream. This catalyst is phosphorus,
It consisted of an acid salt of a heteropolyacid containing molybdenum, vanadium, antimony, copper and cesium in atomic ratios of 1.5, 12, 0.5, 0.5, 0.3 and 1.4, respectively.

(B) Activity test of prepared catalyst 4 g of methacrolein prepared by charging 9 g of this catalyst in a glass microreactor having an inner diameter of 15 mm and mixing methacrolein, air, steam and nitrogen therein A raw material gas having a composition of 12% by volume of molecular oxygen and 17% by volume of water vapor was supplied at a space velocity of 670 h ⁻¹ , and the furnace temperature (the temperature of the furnace for heating the microreactor. The same applies hereinafter) to 280 ° C. The activity test was performed. 1 from the start of the reaction
The conversion of methacrolein over time was 96%, and the methacrylic acid selectivity was 78%.

Reference Example 2 (a) Acquisition of deteriorated catalyst Molded catalyst made of oxide containing molybdenum, bismuth, iron, cobalt and cesium in atomic ratios of 12, 1, 2.5, 7.5 and 0.6, respectively. 1300 ml was filled in a steel reaction tube having an inner diameter of 25 mm, which was used as a first stage reactor. 1800 ml of the catalyst prepared in Reference Example 1 (a) was filled in a steel reaction tube having an inner diameter of 30 mm, which was used as a second stage reactor. Isobutylene 5% by volume, molecular oxygen 12 prepared by mixing isobutylene, air, steam and nitrogen
The raw material gas having a composition of volume% and steam 7.5 volume% is
3.2 volume% of methacrolein, 8.5 volume% of molecular oxygen, and steam prepared by mixing the obtained first-stage reaction product gas with air and nitrogen by supplying it to a single-stage reactor at a space velocity of 1200 h ^−1. A gas having a composition of 11% by volume was supplied to the second-stage reactor at a space velocity of 1000 h ⁻¹ to carry out a second-stage vapor-phase catalytic oxidation reaction. During this period, the conversion of isobutylene in the first-step reaction was about 99%, and the conversion of methacrolein in the second-step reaction was 7%.
The heat medium temperature of the first-stage reactor and the heat medium temperature of the second-stage reactor were adjusted so as to be 2% or more. For this reason, at the start of the reaction, the temperature of the heat medium in the second stage reactor should be 275 ° C.
The temperature of the heat medium in the second stage reactor was set to 293 ° C. after 3000 hours had passed from the start of the reaction. At this time, the reaction was stopped, the catalyst was taken out from the second-stage reactor, and the catalyst charged in about 1/3 portion from the reactor inlet was sampled. This was used as a deterioration catalyst in the following examples.

(B) Activity test of deteriorated catalyst As a result of conducting the activity test of this deteriorated catalyst in the same manner as in Reference Example 1 (b), the conversion of methacrolein was 21%. The total carbon content of this deteriorated catalyst was 0.6% by weight.
The total carbon content of the catalyst prepared in Reference Example 1 (a) was 0.
It is 0%.

Example 1 After conducting the activity test of the deteriorated catalyst in Reference Example 2 (b), air was added to the microreactor filled with the deteriorated catalyst.
A gas containing 12% by volume of molecular oxygen and 18% by volume of steam prepared by mixing steam and nitrogen was supplied at a space velocity of 500 h ^-1 and the furnace temperature was 350 ° C. for 15 hours.
Heat treatment was performed. Then, the activity test of the catalyst after this heat treatment was performed in the same manner as in Reference Example 1 (b), and as a result, the methacrolein conversion rate was 91%. The total carbon content of the catalyst after this heat treatment was 0.0%.

Examples 2 to 14, Comparative Examples 1 to 4 The deteriorated catalyst obtained in Reference Example 2 (a) was filled in a glass microreactor having an inner diameter of 15 mm, and air, steam and nitrogen were mixed therein. A gas containing the molecular oxygen and water vapor prepared as described above at a concentration shown in Table 1 was supplied at a space velocity of 500 h ⁻¹ and heat-treated at the furnace temperature shown in Table 1 for the time shown in Table 1. Then, the activity test of the catalyst after this heat treatment was performed in the same manner as in Reference Example 1 (b). The results (methacrolein conversion rate) are shown in Table 1.

[0028]

[Table 1]

Example 15 In the same manner as in Reference Example 2 (a), the two-step vapor phase catalytic oxidation reaction was performed again. After 72 hours from the start of the reaction, the temperature of the heat medium of the first-stage reactor was 348 ° C., the temperature of the heat medium of the second-stage reactor was 275 ° C., and the temperature of the heat medium of the first-stage reactor was 6000 hours after the start of the reaction. Was 362 ° C., and the heat medium temperature of the second-stage reactor was 294 ° C. At this point, the conversion of isobutylene in the first-step reaction was 99.0%, and the conversion of methacrolein in the second-step reaction was 73.2%.

At this point, the reaction was temporarily stopped, and the first-stage reaction catalyst and the second-stage reaction catalyst were regenerated. That is, a gas containing 14% by volume of molecular oxygen and 18% by volume of water vapor prepared by mixing air, steam and nitrogen, and having a space velocity of 690 h ⁻¹ in the first stage reactor,
In the second-stage reactor, the first stage reactor and the second-stage reactor were circulated in series so that the space velocity was 500 h ⁻¹ . Then, the heating medium temperature of the first-stage reactor was slowly raised to 370 ° C. and the heating medium temperature of the second-stage reactor was raised to 350 ° C. and kept for 10 hours.

Thereafter, the heat medium temperature of the first stage reactor is set to 350.
C., the heat medium temperature of the second stage reactor was 288.degree. C., and Reference Example 2
The two-stage gas-phase catalytic oxidation reaction was restarted under the same conditions as above. After 2200 hours had elapsed from the restart of the reaction, the heat medium temperature of the first-stage reactor was 354 ° C and the heat medium temperature of the second-stage reactor was 289 ° C. At this point, the conversion rate of isobutylene in the first stage reaction was 9
9.2%, the methacrolein conversion rate of the second stage reaction was 80.
It was 3%.

Example 16 After carrying out the two-stage gas-phase catalytic oxidation reaction in Reference Example 2 (a), the catalyst in the first-stage reactor was left as it was, and the second-stage reactor was prepared in Reference Example 1 (a). The above-mentioned new catalyst was replaced, and the two-step gas phase catalytic oxidation reaction was performed again under the same conditions as in Reference Example 2. When 4000 hours had elapsed from the restart of the reaction, the heat medium temperature of the first-stage reactor was 363 ° C and the heat medium temperature of the second-stage reactor was 292 ° C. At this point, the conversion of isobutylene in the first stage reaction was 98.9%, and the conversion of methacrolein in the second stage reaction was 7%.
It was 2.6%.

At this point, only the supply of isobutylene was stopped, and the temperature of the heat medium in the first-stage reactor was 363 ° C. and the temperature of the heat medium in the second-stage reactor was 292 ° C. and was maintained for 2 hours.

Then, the supply of isobutylene was restarted,
The reaction was restarted. The conversion of isobutylene in the first-stage reaction was 99.7% and the conversion of methacrolein in the second-stage reaction was 85.8% after 20 hours had elapsed from the restart of the reaction.

[0035]

EFFECTS OF THE INVENTION According to the present invention, the activity of the heteropolyacid catalyst containing phosphorus, molybdenum and vanadium used in the gas phase catalytic oxidation of methacrolein can be sufficiently restored and the regeneration having excellent activity can be achieved. A catalyst can be obtained.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Junya Yoshizawa             Sumitomo Chemical 5-1, Soukai-cho, Niihama-shi, Ehime             Industry Co., Ltd. (72) Inventor Hiroyuki Ando             Sumitomo Chemical 5-1, Soukai-cho, Niihama-shi, Ehime             Industry Co., Ltd. F-term (reference) 4G069 AA02 AA03 AA10 BB06B                       BC06B BC26B BC31B BC54B                       BC59B BD07B CB17 FB63                       FC01                 4H006 AA02 AC46 BA12 BA13 BA14                       BA35 BA75 BA81 BA84 BC10                       BC11 BC18 BC30 BE30 BS10                 4H039 CA65 CC30

Claims (3)

[Claims] 1. A heteropolyacid-based catalyst containing phosphorus, molybdenum and vanadium used for a gas phase catalytic oxidation reaction of methacrolein under a gas flow containing at least 3% by volume of molecular oxygen and at least 3% by volume of steam. To 2
A method for regenerating a catalyst for producing methacrylic acid, which comprises heat treatment at 90 to 400 ° C. 2. A first-stage reaction in which isobutylene or t-butyl alcohol is subjected to a gas phase catalytic oxidation reaction in the presence of an oxide catalyst containing molybdenum, bismuth and iron, and
The reaction product gas containing methacrolein obtained by the step reaction is subjected to a gas phase catalytic oxidation reaction in the presence of a heteropolyacid catalyst containing phosphorus, molybdenum and vanadium.
The second step in the two-step gas phase catalytic oxidation reaction consisting of
The regeneration method according to claim 1, which is carried out on the catalyst used in the stage reaction. 3. The catalyst used in the first-stage reaction is mixed with a gas containing at least 3% by volume of molecular oxygen at 360 to 360 ° C.
The regeneration method according to claim 2, wherein heat treatment at 450 ° C. is also performed.