JPH081005A - Method for producing catalyst for methacrylic acid production - Google Patents

Abstract

PURPOSE:To obtain a catalyst having high reactivity, strength and long life as a catalyst by removing ammonia from ammonium salt of Keggin type heteropoly acid at low temp. in a gas atmosphere containing nitrogen oxide. CONSTITUTION:The catalyst to produce methacrylic acid is obtd. from a partially neutralized salt of heteropoly acid expressed by the formula. In the formula, X is at least one element selected from among arsenic, antimony, boron and the like, Y is at least one element selected from vanadium, tungsten, and the like, Z is at least one element selected from alkali metals, alkaline earth metals, and thallium, (a) to (f) are atomic ratios of these elements, and when b=12, (a), (c), (d), (e) satisfy 0<a<=3, 0<=c, d, e<=3, and (f) is not 0 and is determined according to the oxidation state and atomic ratio of each element. This catalyst is produced by mixing an aq. soln. or water suspension of the source material in the presence of ammonia groups, concentrating, drying, and treating in a gas containing nitrogen oxides at 150-400 deg.C to release ammonia.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a heteropolyacid catalyst used for the production of methacrylic acid by vapor phase catalytic oxidation. Specifically, it relates to improvement of a heteropolyacid catalyst used for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein, isobutane, isobutyric acid, isobutyraldehyde and the like with molecular oxygen.

[0002]

Many catalysts for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein have been proposed (for example, JP-A-50-101316, JP-A-50-142510,
Japanese Unexamined Patent Publication No. 59-4445), a part of which is already used for industrial scale production. Further, catalysts for producing methacrylic acid by oxidative dehydrogenation of isobutyric acid (JP-A-57-72935 and the like) and oxidation of isobutyraldehyde (JP-A-57-144238 and the like) are also well known. Further, a catalyst for producing methacrylic acid or methacrolein by oxidizing isobutane or tertiary butanol (JP-A-55-127328).
No.), and a catalyst for directly oxidizing isobutane to obtain methacrylic acid and methacrolein (JP-A-2-42032).

The catalyst used in these reactions is
Both have a structure of a heteropolyacid containing molybdenum and phosphorus as main components and / or a salt thereof, and regarding the composition, partial replacement of molybdenum with vanadium,
Improvements such as the addition of co-catalyst components such as copper, antimony and arsenic have been proposed. Further, as a method for preparing these catalysts, in JP-A-57-165040, a heteropolyacid salt containing an ammonium root and an alkali metal is prepared and then calcined in an inert gas at 400 to 550 ° C. It is disclosed that a catalyst active at low temperature can be obtained by deammonification by.

If the catalyst raw material contains nitrate radicals, the nitrate radicals are decomposed to produce nitrogen oxides when the catalyst is calcined. When preparing a molybdenum-bismuth-based catalyst used for the synthesis of methacrolein by baking, 1% by volume or more of nitrogen oxides such as nitrogen dioxide produced by decomposition of nitrate radicals and oxygen in a baking atmosphere. 0.5% by volume
A method of holding the above is known (Japanese Patent Laid-Open No. 5-2373).
No. 88). Further, a method of reactivating a deteriorated catalyst using a nitrogen-containing compound (mainly nitric oxide) (Japanese Patent Laid-Open No. 56-91846)
No.) is also known.

[0005]

However, in the production of methacrylic acid which has already been put into practical use, a problem with the known catalyst is that both the reaction yield (activity and selectivity) and the catalyst life are satisfied. That is not always enough. Compared with, for example, a catalyst that produces acrylic acid from acrolein, not only the selectivity of the reaction is low, but also the reaction activity and life are poor. Therefore, a large amount of catalyst is required, and the burden of facility cost and catalyst cost is large. . One of the main reasons that the performance of the catalyst is not sufficient is that the method using isobutane or isobutyric acid as a raw material has not been industrialized yet.

The present inventors previously prepared a Dawson type heteropolyacid salt (a part is an ammonium salt of a heteropolyacid) as a catalyst precursor, and calcined the Keggin-type heteropolyacid salt (a part is an ammonium salt of the heteropolyacid). We proposed a method for producing a catalyst which is prepared by deammonification by calcination in an inert gas at a temperature of 400 to 500 ° C. after a crystal transition to a salt) (JP-A-4-63139). An object of the present invention is to further improve this catalyst to provide a catalyst having higher reaction activity, selectivity, catalyst strength and long catalyst life.

[0007]

Means for Solving the Problems In order to achieve the above object, the inventors of the present invention have made earnest studies on improvement of a heteropolyacid catalyst, and as a result, when deammonifying an ammonium salt of a Keggin-type heteropolyacid, It has been found that the active gas alone requires a high temperature of at least 400 ° C. or higher, which leads to a decrease in the surface area and pore volume of the catalyst and further a decrease in the catalyst activity. Therefore, in this catalyst calcination step, ammonium salt of Keggin-type heteropoly acid can be deammonified at a low temperature in a nitrogen oxide-containing gas to suppress reduction of the surface area and pore volume of the catalyst, and a highly active catalyst can be obtained. The inventors have found that they can be obtained and completed the present invention.

That is, the present invention relates to the general formula Pa Mob Xc.
YdZeOf (in the formula, P, Mo, and O are phosphorus, molybdenum, and oxygen, respectively, and X is arsenic, antimony, boron,
Copper, germanium, bismuth, zirconium, selenium,
At least one element selected from the group consisting of cerium, iron, chromium, nickel, manganese, cobalt, tin, silver, zinc, palladium, rhodium and tellurium is added to Y.
Is at least one element selected from the group consisting of vanadium, tungsten and niobium, Z is at least one element selected from the group consisting of alkali metal, alkaline earth metal and thallium, and subscripts a, b,
c, d, e and f represent the atomic ratio of each element, and b = 12
And a is a value of 3 or less that does not include 0 (zero),
c, d and e take a value of 3 or less including 0 (zero),
f is a value determined by the oxidation state of each element other than O and the atomic ratio), in the method for producing a catalyst for producing methacrylic acid, which comprises a partially neutralized salt of a heteropolyacid represented by the following formula: Methacryl which is characterized in that ammonia is desorbed by treating a solid obtained by mixing an aqueous solution or a water suspension of raw materials and concentrating and drying it in a gas containing nitrogen oxide at a temperature of 150 to 400 ° C. It is a method for producing a catalyst for acid production.

The basic structure of the catalyst of the present invention is a conventionally well-known partially neutralized salt of phosphomolybdic acid with alkali metal, alkaline earth metal or thallium. Other components such as arsenic and antimony are effective for improving the selectivity of methacrylic acid and are recommended to be added. Although it is already known that a catalyst containing these elements is effective, its effectiveness is further improved by combining it with the specific catalyst preparation conditions of the present invention.

In the catalyst of the present invention, it is essential that ammonium radicals are present at the stages of mixing, precipitation and heat aging treatments described later. Ammonium molybdate is suitable as a raw material for molybdenum and ammonium, but molybdenum oxide, phosphomolybdic acid and the like may be used in combination with ammonia or an ammonium salt. Phosphoric acid is generally used as phosphorus, but it may be used in the form of a salt of another essential element such as ammonium phosphate. As the other components, any of nitrates, sulfates, carbonates, chlorides, hydroxides, oxides and phosphates may be used. Further, a nitrate group-containing compound such as nitric acid or ammonium nitrate may be added.

The above raw materials are at least two kinds of aqueous solutions or suspension solutions, and the solutions are mixed to precipitate a precipitate.
After mixing, the resulting slurry may be heat aged at 100 to 200 ° C. for 1 hour or more. Heat aging treatment time is 1
It is not particularly limited as long as it is longer than the time, but usually 1 to 4
2 hours. Even if it is processed for a longer time, there is no corresponding effect.

The slurry that has been subjected to the heat aging treatment is concentrated and dried by a known method, that is, a box dryer, a drum dryer, a spray dryer, a band dryer, an infrared dryer, an airflow dryer and the like. Catalyst raw material to be used, precipitation temperature, pH,
The crystal system varies depending on the subsequent aging treatment, heat treatment, etc., but the catalyst used in the present invention generally has a structure of a Dawson type heteropolyacid salt, a Keggin type heteropolyacid salt, or a mixture of both. It has become.

When the Dawson type heteropolyacid salt is heated at about 150 to 350 ° C., it is transformed into a Keggin type heteropolyacid salt, and coexisting neutralized products such as ammonium nitrate are removed. This heating step is carried out by a known apparatus, but in order to avoid the adverse effect on the catalytic activity and strength due to the rapid decomposition of ammonium nitrate, it is possible to heat the heteropoly acid in a shape divided into about 10 mm or less for several hours. desirable. The Keggin-type heteropolyacid salt thus obtained is a mixed salt of a salt of a heteropolyacid such as an alkali metal and an ammonium salt of a heteropolyacid. It is necessary to desorb ammonium roots.

In order to desorb ammonium roots in an atmosphere of an inert gas such as nitrogen, firing should be carried out at a temperature of about 400 to 500 ° C, preferably about 420 to 450 ° C. At a temperature of 400 ° C. or lower, desorption of ammonium root is insufficient and high activity cannot be expressed. When fired in air, decomposition of heteropolyacid occurs above 400 ° C.
Sintering occurs and the activity becomes low. However, when treated with a gas containing nitrogen oxides, particularly a mixed gas of nitric oxide and an inert gas such as nitrogen, 150 to 400 ° C.
More preferably, the ammonium root is easily desorbed by treating at a low temperature of 250 to 350 ° C. The concentration of nitric oxide in the gas containing nitrogen oxides is about 1 to 100% by volume, preferably about 2 to 20% by volume, and the treatment time is about 0.5 to 10 hours.

When nitrogen oxides are used, the mechanism of action as to why ammonium roots are desorbed at low temperatures is not clear, but the denitration reaction of ammonia and nitrogen oxides (NO + N
It is thought that H ₃ → N ₂ ) is involved.

When nitrate is contained in the catalyst raw material,
Nitrogen oxides are generated by the thermal decomposition thereof, but it is not sufficient in quantity to remove the ammonium root of the heteropolyacid ammonium salt at low temperature as in the present invention,
Nitrogen oxides must be positively added.

The state of desorption of ammonium root can be confirmed by an activity test in the oxidation reaction of methacrolein, but it is 1 in the infrared absorption spectrum of the catalyst (Keggin-type heteropolyacid salt).
This can be confirmed by the disappearance of the absorption of ammonium ions near 400 cm ^-1 . Also, in thermal analysis, the Keggin-type heteropolyacid salt in a nitrogen gas stream had a weight loss unless a temperature of 400 ° C. or higher was observed and no exothermic peak was observed. It can be confirmed that the weight decreased and the exothermic peak occurred at around 200 ° C.

Even when the Dawson-type heteropolyacid salt is directly treated with a nitrogen oxide-containing gas at 150 to 400 ° C., the transition from the Dawson-type heteropolyacid salt to the Keggin-type heteropolyacid salt and the neutralization products of ammonium nitrate and the like are obtained. Removal and desorption of ammonium radicals proceed, and the calcination of the catalyst is completed.

The catalyst of the present invention is obtained by desorbing ammonium roots with a nitrogen oxide-containing gas, and then about 4 in air.
There is no problem in firing at 00 ° C or lower.

Since the catalyst prepared by the method of the present invention has a low desorption temperature of ammonia, it becomes a catalyst having a high surface area, and is highly active.

The catalyst of the present invention is used for the production of methacrylic acid by oxidation of various raw materials including the oxidation of methacrolein. In use, the catalyst is used alone or as a low surface area carrier such as α-alumina, silica, silicon carbide and the like. It is used in the form of being supported or diluted and mixed, and in the case of a fixed bed, it is used after being formed into a columnar shape, a spherical shape, a ring shape, a clover shape, a gear shape, a block shape or the like. As a method for molding into these shapes, known molding methods such as tablet molding, tumbling granulation, extrusion molding, fluidized granulation and spray granulation are used. Various additives such as graphite, stearic acid, and glass fiber may be added at the time of molding in order to improve the moldability or the activity and strength of the molded product. A reaction type such as a fluidized bed or a moving bed can also be used.

The physical properties of the catalyst obtained in the present invention differ depending on the catalyst composition and preparation method, but usually the surface area is 1 to 2.
0 m ² / g, pore volume after molding is 0.1 to 0.4 cm ³
/ G, pore radius is 500-10000Å, crush strength is 1
It is more than kg. With the catalyst prepared under the same conditions, the surface area and pore volume of the catalyst are increased by deammonifying in a nitrogen oxide-containing gas at low temperature.

When methacrolein is catalytically oxidized in the gas phase to produce methacrylic acid using the catalyst of the present invention, the raw material used does not necessarily have to be pure methacrolein, but isobutylene or tertiary butanol. A methacrolein-containing gas obtained by vapor-phase catalytic oxidation of methacrolein or a vaporized methacrolein obtained by a liquid phase method may be used.

The oxygen source may be pure oxygen, but industrially air is used. As the other diluent gas, nitrogen, carbon dioxide, steam or the like can be used. The concentration of methacrolein in the reaction material gas is about 1 to 10%, and the ratio of oxygen to methacrolein is about 1 to 5. The space velocity of the raw material gas is preferably in the range of about 500 to 5000 h ⁻¹ , and the reaction temperature is preferably about 260 to 340 ° C. The reaction pressure is usually around normal pressure or slightly elevated pressure.

When isobutane is directly oxidized using the catalyst of the present invention to produce methacrylic acid or methacrolein, the isobutane concentration in the raw material gas is preferably as high as about 15% or more. Pure oxygen, oxygen-enriched air, air or the like is used as the oxygen source. A suitable ratio of oxygen to isobutane is about 0.2 to 2.

It is desirable that the reaction gas contains water vapor in the range of about 3 to 30%. The raw material gas may contain a diluting gas such as nitrogen, carbon dioxide or carbon monoxide. The conversion cannot be so high in this reaction, so unreacted isobutane and optionally oxygen are recovered and recycled. By-product methacrolein is recycled or introduced into another reactor and oxidized to methacrylic acid. Space velocity is about 300-3
000h ^-1, the reaction temperature is about two hundred and seventy to three hundred and forty ° C. are preferred. The reaction pressure may be atmospheric pressure or increased pressure.

The catalyst of the present invention is oxidative dehydrogenation of isobutyric acid,
It can also be used for the production of methacrylic acid by the oxidation of isobutyraldehyde. It can also be used when producing methacrylic acid from isobutylene in a single step.
In these reactions, the reaction conditions similar to the oxidation of methacrolein can be adopted.

[0028]

The catalyst produced by the method of the present invention has a higher reaction activity in the production of methacrylic acid than conventional catalysts.
It has selectivity, good strength and long catalyst life. Its industrial significance is particularly high because of its high reaction activity and selectivity.

[0029]

The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The definitions of conversion rate and selectivity are as follows. (Methacrolein oxidation reaction) Methacrolein conversion rate = (reacted methacrolein mole number / supplied methacrolein
Number of moles) x 100 Methacrylic acid selectivity = (Number of moles of methacrylic acid formed / Reacted methacrolein
Mol number) × 100 (isobutane oxidation reaction) isobutane conversion rate = (mol number of reacted isobutane / mol number of fed isobutane) × 100 methacrolein selectivity = (mol number of methacrolein formed / reacted isobutane)
Number of moles) x 100 Methacrylic acid selectivity = (number of moles of methacrylic acid formed / reacted isobutane
Number of moles) x 100

Example 1 To 4800 g of ion-exchanged water, 450 g of 85% phosphoric acid, 130 g of copper phosphate Cu ₃ (PO ₄ ) ₂ .3H ₂ O, 819 g of cesium nitrate and 284 g of 60% arsenic acid aqueous solution were added, and the mixture was heated to 40 ° C.
The solution was stirred and dissolved by maintaining the solution in the form of a homogeneous aqueous solution. (Solution A) 6990 kg of ion-exchanged water was charged into a reactor made of stainless steel and having a 20 L jacket, and the temperature was kept at 40 ° C. Ammonium molybdate (NH ₄ ) ₆ Mo ₇ O ₃₂
・ 4H ₂ O 6356 g was added and dissolved by stirring.
(Liquid B)

The whole amount of the liquid A was injected into the reactor containing the liquid B to form a precipitate, which was made into a slurry, 137 g of vanadium pentoxide was added, and steam was flown through the jacket to prepare 1
After heating to 25 ° C. and aging treatment for 38 hours, water was evaporated at 120 ° C. in a dryer. The dried product at this stage had a so-called Dawson type heteropolyacid salt structure by X-ray diffraction. 30 parts of water and 4 parts of glass fiber were added to 100 parts of the dried solid crushed in a mortar, and after kneading, extrusion molding was carried out using a mold to obtain a molded catalyst raw material having a diameter of 5 mm and a length of about 7 mm. After drying this at 120 ℃, 320 in an air stream
Calcination was carried out for 2 hours. The catalyst at this stage had a Keggin-type heteropolyacid salt structure by X-ray diffraction and infrared absorption analysis.

40 g of the catalyst at this stage was filled in a glass tube having an inner diameter of 25 mm, and nitrogen monoxide at 60 cc / min and nitrogen 54
Under a mixed gas flow of 0 cc / min, the catalyst was obtained by treating at 350 ° C. for 3 hours. This catalyst has a specific surface area of 13.9 m ²
/ G, and the peak attributed to the ammonium root at 1400 cm ^-1 disappeared in infrared absorption analysis.

9 ml of this catalyst was filled in a glass reaction tube having an inner diameter of 15 mm, and a raw material gas having a composition consisting of 4 mol% of methacrolein, 12 mol% of oxygen, 16 mol% of water vapor and the balance of nitrogen was a space velocity (STP standard). The activity test of the methacrolein oxidation reaction was conducted at 270 ° C. through the reaction tube at 670 h ⁻¹ . As a result, the conversion of methacrolein was 7
The selectivity was 8.0% and the methacrylic acid selectivity was 84.2%. The conditions of the methacrolein oxidation activity test were the same in the following examples.

Example 2 In Example 1, the catalyst 40 of Keggin type heteropolyacid salt was used.
g in a glass tube with an inner diameter of 25 mm and nitric oxide 12
A catalyst was prepared in the same manner as in Example 1 except that the catalyst was obtained by treatment at 250 ° C. for 3 hours under a mixed gas flow of 0 cc / min and 540 cc / min of nitrogen. As a result of the activity test, the conversion of methacrolein was 80.4% and the selectivity of methacrylic acid was 84.
5%.

Example 3 In Example 1, the catalyst 40 of the Keggin type heteropolyacid salt was used.
g in a glass tube with an inner diameter of 25 mm, and
Example 1 except that a catalyst was obtained by treatment at 250 ° C. for 3 hours under a mixed gas flow of cc / min and 570 cc / min of nitrogen.
A catalyst was prepared and an activity test was conducted in the same manner as in. As a result of the activity test, the conversion of methacrolein was 78.4% and the selectivity of methacrylic acid was 84.2%.

Comparative Example 1 In Example 1, the catalyst of the Keggin-type heteropolyacid salt was
A catalyst was prepared and an activity test was conducted in the same manner as in Example 1 except that the catalyst was obtained by calcining in nitrogen at 435 ° C. for 3 hours and in air at 380 ° C. for 3 hours. This catalyst has a specific surface area of 6.5 m
A ² / g, the results of the activity test, the methacrolein conversion rate 68.0%, were selectivity of methacrylic acid 84.6%.

Example 4 An isobutane oxidation reaction was carried out using the catalyst prepared in Example 1. 6 ml of a catalyst was filled in a glass reaction tube having an inner diameter of 15 mm, and a raw material gas having a composition of 25 mol% isobutane, 12 mol% oxygen, 15 mol% steam and the balance nitrogen was reacted at a space velocity (STP standard) of 1000 h ^-1 . The reaction was carried out at a reaction temperature of 310 ° C. through a tube. As a result, the isobutane conversion was 7.9% and the methacrolein selectivity was 9.4.
%, And the selectivity for methacrylic acid was 59.6%. The conditions of the isobutane oxidation reaction activity test are the same in the following examples.

COMPARATIVE EXAMPLE 2 In Example 1, the Keggin-type heteropolyacid salt catalyst 40 was used.
g in a glass tube with an inner diameter of 25 mm and nitrogen 600 cc
A catalyst was prepared in the same manner as in Example 1 except that the catalyst was obtained by treating at 350 ° C. for 3 hours under a flow rate of / min. In the infrared absorption analysis of this catalyst, a peak attributed to an ammonium root at 1400 cm ^-1 remained. As a result of the isobutane oxidation reaction activity test, the isobutane conversion rate was 2.2%, the methacrolein selectivity was 22.1%, and the methacrylic acid selectivity was 48.2.
%Met.

Comparative Example 3 The catalyst 40 of the Keggin-type heteropolyacid salt in Example 1 was used.
g in a glass tube with an inner diameter of 25 mm and nitrogen 600 cc
A catalyst was prepared in the same manner as in Example 1 except that the catalyst was obtained by treating at 435 ° C. for 3 hours under a flow rate of / min. In the infrared absorption analysis of this catalyst, the peak attributed to the ammonium root at 1400 cm ^-1 disappeared, but the specific surface area was 1
It was 0.1 m ² / g. As a result of an isobutane oxidation reaction activity test, the isobutane conversion was 6.4%, the methacrolein selectivity was 8.7%, and the methacrylic acid selectivity was 54.3%.

Claims (2)

[Claims] 1. A general formula Pa Mob XcYdZeOf (wherein P, Mo and O are phosphorus, molybdenum and oxygen, respectively, and X is arsenic, antimony, boron, copper, germanium, bismuth, zirconium, selenium, cerium, iron,
At least one element selected from the group consisting of chromium, nickel, manganese, cobalt, tin, silver, zinc, palladium, rhodium and tellurium, and Y is at least one element selected from the group consisting of vanadium, tungsten and niobium. Z represents at least one element selected from the group consisting of alkali metals, alkaline earth metals and thallium, and has the subscripts a, b, c, d, e and f.
Indicates the atomic ratio of each element, and when b = 12, a is 0
Values less than or equal to 3 that do not include (zero) are 0 for c, d, and e
A catalyst for the production of methacrylic acid comprising a partially neutralized salt of a heteropolyacid represented by a value of 3 or less, including (zero), and f being a value determined by the oxidation state and atomic ratio of each element other than O). In the production method of 1, the aqueous solution or water suspension of the catalyst raw material is mixed in the presence of ammonium root, and the solid obtained by concentrating and drying is treated at a temperature of 150 to 400 ° C. in a gas containing nitrogen oxides. A method for producing a catalyst for producing methacrylic acid, characterized in that ammonia is desorbed by means of desorption. 2. The method according to claim 1, wherein the concentration of nitric oxide in the gas containing nitrogen oxide is 1 to 100% by volume.