JPH0463139A - Catalyst for production of methacrylic acid - Google Patents

Abstract

PURPOSE:To obtain a catalyst having higher reactivity, selectivity and long life by calcining a solid of partially neutralized salt of specified heteropoly acid at 400-500 deg.C in an inert gas. CONSTITUTION:Vanadium pentoxide (V2O5) is used as the vanadium source. The partial neutral salt of heteropoly acid is prepared as a dissolved or suspended state of the catalyst source in water in the presence of ammonium group and is heated at >=80 deg.C for one hour or longer. Then the material is concentrated and drive to obtain the solid, which is then calcined at 400-500 deg.C in an inert gas. Thus, the catalyst for the production of methacrylic acid is obtained. This catalyst can be used for the production of methacrylic acid by oxidation of methacrolein or various source materials. The catalyst is used in a signal form, or is deposited on a carrier as alumina, silica, silicon carbide, or diluted or mixed for use.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improvements in heteropolyacid catalysts used in the production of methacrylic acid by gas phase catalytic oxidation. More specifically, the present invention relates to improvements in heteropolyacid catalysts used to produce methacrylic acid by gas-phase catalytic oxidation of methacrolein, isobutane, etc. with molecular oxygen.

[Prior Art] Many catalysts have been proposed for producing methacrylic acid by vapor phase catalytic oxidation of methacrolein (for example, Japanese Patent Application Laid-open Nos. 101316-1982, 142510-1980,
JP-A No. 59-4445, etc.), some of which have already been used in industrial scale production. Furthermore, the production of methacrylic acid by oxidative dehydrogenation of isobutyric acid (JP-A-57-72936, etc.) and oxidation of isobutyraldehyde (JP-A-57-144238, etc.) is also well known. Furthermore, a catalyst for producing methacrylic acid and methacrolein by oxidizing isobutylene or tertiary butanol (JP-A-55-1
27328), and recently, catalysts for directly oxidizing isobutane to obtain methacrylic acid and methacrolein (Japanese Patent Application Laid-Open No. 2-42032, etc.) have also been proposed.

It is known that catalysts used in these reactions have a structure of a heteropolyacid and/or a salt thereof whose main components are molybdenum and phosphorus, and the composition is such that a portion of molybdenum is formed by vanadium. Substitution, addition of promoter components such as copper, antimony, arsenic,
Various improvements have been made regarding the preparation method, such as the use of cyclic amines.

[Problems to be Solved by the Invention] However, the problems with these known catalyst systems are that even in the oxidation of methacrolein, which has already been put into practical use, both the reaction yield (activity and selectivity) and the catalyst life are affected. However, it is not necessarily sufficient to satisfy the following. For example, compared to a catalyst for producing acrylic acid from acrolein, it not only has poor reaction selectivity but also poor reaction activity and lifespan, and as a result, a large amount of catalyst is required, resulting in large equipment costs and catalyst costs. One of the main reasons why even when using isobutane, isobutyric acid, etc. as raw materials has not yet been commercialized is that the performance of the catalyst is not sufficient. The object of the present invention is to improve current catalysts and provide a catalyst that has higher reaction activity, higher selectivity, and longer catalyst life.

[Means for Solving the Problems] In order to achieve the above-mentioned problems, the present inventors have conducted intensive studies on improving heteropolyacid-based catalysts, and have developed a method that has a specific catalyst composition and includes a special preparation process. The present invention was achieved by discovering that the prepared catalyst achieves the above object.

That is, the present invention is based on the general formula % (wherein, P, Mo, V, As, Cu, O
represent phosphorus, molybdenum, vanadium, arsenic, copper and oxygen, respectively; X represents at least one element selected from the group consisting of rubidium, cesium and thallium;
Also, subscripts a, b, c, d, e, f
and g indicates the atomic ratio of each element, and when b = 12,
Partially neutralized salt of a heteropolyacid represented by a, c%dSeS f each takes a value of 3 or less without O (zero), and g indicates a value determined by the valence and atomic ratio of other elements) Using vanadium pentoxide (V 20 s ) as the vanadium raw material, and with the catalyst raw material dissolved or suspended in water in the presence of ammonium radicals, 80
It is characterized by being prepared by a method including a step of heat treatment at a temperature of 1 hour or more at a temperature of 100° C. or higher, and a step of calcining the solid obtained after concentration and drying in an inert gas at a temperature of 400 to 500° C. This is a catalyst for producing methacrylic acid.

The basic structure of the catalyst of the present invention is a well-known partially neutralized salt of phosphomolybdic acid with rubidium, cesium, and thallium, but it also contains vanadium, arsenic, and copper as essential components. Although it is already known that these elements are effective, as a result of various studies on the relationship between the combination of these compositions and the preparation method, the following was found regarding the composition.

First, catalysts that do not contain vanadium but contain arsenic have high reaction selectivity regardless of the preparation method, but they have the disadvantage that the reaction rate tends to decrease when used for a long time, and are not suitable for industrial use. On the other hand, a catalyst that does not contain arsenic but contains vanadium can have a certain degree of reaction selectivity and lifetime using conventional preparation methods, but both are insufficient. If a preparation method using the vanadium pentoxide of the present invention as a raw material and including a heating step is used, a catalyst is obtained in which the reaction rate is less likely to decrease, but the reaction selectivity is not improved. Although arsenic is required to increase reaction selectivity and vanadium is required for longevity, catalysts containing both have shorter lifetimes than those containing only vanadium using conventional preparation methods. In order to have a combination of reaction selectivity, activity, and lifetime, it is necessary to contain both vanadium and arsenic, and to make it using the special preparation method of the present invention. Copper is also an essential component for improving reaction activity and selectivity.

In addition, antimony, silver, iron, cobalt, lanthanum, cerium, etc. may be included as optional components.

The catalysts of this invention are prepared using specific raw materials and methods. Vanadium pentoxide is used as the raw material for vanadium,
Further, it is necessary that the suspension contains ammonium radicals at the stage of heat treatment of the suspension, which will be described later. I don't really understand why it is better to use vanadium pentoxide, but using raw materials that are highly soluble in water such as ammonium metavanadate, vanadyl oxalate, and molybdovanadophosphate instead of vanadium pentoxide improves both reaction activity and lifespan. not enough. Ammonium molybdate is suitable as a raw material for molybdenum and ammonium, but a combination of molybdenum oxide, phosphomolybdic acid, etc., and ammonia or an ammonium salt may be used. For phosphorus and arsenic, phosphoric acid and arsenic acid are generally used, but they may also be used in the form of salts with other essential components such as ammonium phosphate and copper phosphate. Ingredients such as copper and rubidium are nitrates, chlorides,
Carbonates, hydroxides, phosphates, etc. can be used.

Dissolve or suspend the above raw materials in water and add about 80%
It is necessary to carry out a heat treatment process at a temperature of 0.degree. C. or higher for about 1 hour or more. If the heat treatment temperature is about 80° C. or lower, or if the reaction time is about 1 hour or less even if it is about 80° C. or higher, the reaction will not proceed sufficiently, resulting in a catalyst with poor methacrylic acid selectivity.

This process is carried out using an autoclave at a temperature of 100°C or more.
Although it can be carried out at about 100 to 150°C, it is usually carried out under boiling (100°C) and reflux at normal pressure. The treatment time is not particularly limited as long as it is about 1 hour or more, but it is usually carried out for about 1 to 24 hours. Even if you do it for a longer time, there will be no effect.

Water-soluble raw materials may be used by separately dissolving them in water, but
There is no problem even if it is prepared as a powder. Vanadium pentoxide must be prepared in powder form. In this process, a heterogeneous reaction involving solids clearly occurs, and in the solid obtained by evaporating this slurry to dryness, no vanadium pentoxide crystals were observed by X-ray diffraction, and P :Mo ratio is 1:
It is a salt of a so-called Dawn-type heteropolyacid of No. 9. When this is heated to about 250℃, P:Mo becomes 1:1.
The structure changes to the so-called Keggin-type heteropolyacid salt of No. 2. Since it is prepared containing an ammonium radical, the solid at this stage is a mixed salt of the X component of the heteropolyacid (such as rubidium) and ammonium. As it is, it does not have the properties of a solid acid and has low activity, so it must be activated by firing.

Approximately 400~50f)℃ in an inert gas atmosphere such as nitrogen,
Preferably it is fired at a temperature of about 420-450°C. As a result, almost all of the ammonium components are eliminated and become protonic acids, exhibiting high activity. When fired in air, the heteropolyacid decomposes and sinters at temperatures above about 400°C, resulting in low activity, and below about 400°C, many ammonium roots remain, so activity is thought to be low as well. . After firing in an inert gas, it may be fired in air at a temperature of about 400'l or less.

The catalyst of the present invention can be used to produce methacrylic acid by oxidizing various raw materials, including the oxidation of methachloride, but it can be used as a single catalyst, supported on a carrier such as alumina, silica, or phosphoric acid carbide, or in the form of a diluted mixture. In the case of a fixed bed, it is used after being shaped into a cylinder, sphere, ring, etc. Reaction formats such as fluidized bed and moving bed may also be used.

When producing methacrylic acid by catalytically oxidizing methacrolein in the gas phase using the catalyst of the present invention, the raw material used does not necessarily have to be pure methacrolein, but imbutylene or tertiary-butanol. A methacrolein-containing gas obtained by phase contact oxidation or a gas obtained by vaporizing methacrolein obtained by a liquid phase method may be used. The oxygen source may be pure oxygen, but air is used industrially. Other diluent gases include nitrogen, carbon dioxide,
- Carbon oxide, water vapor, etc. can be used. The concentration of methacrolein in the reaction raw material gas is approximately 1 to 10%, and the ratio of oxygen to methacrolein is approximately 1 to 5.

The space velocity of the raw material gas is preferably in the range of about 500 to 5000 h-', and the reaction temperature is preferably about 260 to 340°C. The reaction pressure is usually around normal pressure or under slightly increased pressure. .

Further, when isobutane is directly oxidized to produce methacrylic acid and methacrolein using the catalyst of the present invention, the isobutane concentration in the raw material gas is preferably as high as about 15% or more. As the oxygen source, pure oxygen, oxygen-enriched air, air, etc. are used. The ratio of oxygen to isobutane is approximately 0.
Approximately 2 to 2 is appropriate. Approximately 3% water vapor is contained in the reaction gas.
It is desirable to contain it in a range of 30%. The raw material gas may contain nitrogen, carbon dioxide, carbon oxide, etc. as a diluent gas. Since conversion rates cannot be very high in this reaction, unreacted isobutane and optionally oxygen are recovered and recycled.

By-product methacrolein is recycled or led to another reactor where it is oxidized to methacrylic acid. Space velocity is about 300-300
0 h-' and the reaction temperature is preferably about 270 to 340°C. The reaction pressure is normal pressure or increased pressure.

The catalyst of the present invention can also be used for the production of methacrylic acid by oxidative dehydrogenation of isobutyric acid and oxidation of isobutyraldehyde. It can also be used to produce methacrylic acid from inbutylene in one step. In these reactions, reaction conditions similar to those for the oxidation of methacrolein can be employed.

[Effects of the Invention] The catalyst of the present invention has higher reaction activity, higher selectivity, and longer catalyst life than conventional catalysts in the production of methacrylic acid.

[Example] The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples.

The definitions of conversion rate and selectivity are as follows. Example 1 Ammonium molybdate (
(NH4)sMOloaa” 4H20) 105.9
g1 Vanadium pentoxide 1.82g, copper phosphate (Cu.

Suspend 2.17 g of (PO,)2.3H20), and further add 7.49 g of 85% phosphoric acid and 4.7 g of 60% arsenic acid aqueous solution.
3 g of cesium nitrate and 17.5 g of cesium nitrate were dissolved in ion-exchanged water to make 180 ml, and the resulting slurry was stirred and heated at about 100° C. for 15 hours while being refluxed. Place this in a stainless steel vat and put it in an electric furnace for 15 minutes.
Water was evaporated at 0°C.

The dry matter at this stage has a 2θ (CuKα) of 9 in X-ray diffraction.
, 6°, 11.1°, 12.4°, 15.5°, 19°1', 20.7°, 22.7°, 25.9°, 27.6
It has a peak at 960.925.890.650.53Qcrrr in the laser Raman spectrum.
' It was found that it has a structure of a so-called Dawson-type heteropolyacid salt. This is further fired at 250°C.

This one was determined by X-ray diffraction as IO, 5°, 18.4°, 23
It was found that it was a so-called Keggin-type heteropolyacid salt having peaks at 8 degrees, 26.1 degrees, 30.2 degrees, etc. The product calcined at 435° C. for 5 hours in a nitrogen stream still has the structure of a Keggin-type heteropolyacid salt.

2% graphite was added to this powder and the mixture was compressed into a cylindrical tablet having a diameter of 5 mm and a height of 5 mm to obtain a catalyst. The composition of this catalyst excluding oxygen, hydrogen, and nitrogen is MO+zP+, 5AS
o, <Vo, aCuo, *CS+, e.

A glass reaction tube with an inner diameter of 15 mm was filled with 9 ml of this catalyst, and a raw material gas having a composition of 4 mol% methacrolein, 12 mol% oxygen, 16 mol% water vapor, and the balance nitrogen was heated at a space velocity (STP standard) of 670 h. -1 through the reaction tube,
The activity test was conducted at a reaction temperature of 280°C. As a result, methacrolein conversion rate was 87.5%, methacrylic acid selection ¥=
It was 88.6%.

In addition, as an accelerated life test, 3 ml of this catalyst was tested with an inner diameter of 15 m.
A glass reaction tube of 300 m was filled with a gas having the same composition as above, passed through the reaction tube at a space velocity of 2000 h-', and the reaction temperature was 3.
It was operated continuously at 20°C. As a result, after the start of the reaction, 15
The reaction results at the 1st hour were methacrolein conversion rate of 65.3%;
The methacrylic acid selectivity was 86.5%, and the results after 2000 hours were 59.8% and 87.0%, respectively.

Comparative Example 1 A catalyst was prepared in the same manner as in Example 1 except that 4.56 g of vanadium pentoxide was used instead of arsenic.

Its composition is Mo+zP+, sV+, oCuo, C5r-
It is e. In the same activity test as Example 1, the conversion rate was 78.8.
%, the selectivity was 79.3%, and the selectivity was not particularly sufficient.

Comparative Example 2 105.9 g of ammonium paramolybdate was dissolved in 40 Q, m 1 of ion-exchanged water, and separately 7.72 g of 85% phosphoric acid, 7.10 g of 60% arsenic acid aqueous solution, and 1.20 g of copper nitrate. A solution of 17.5 g of cesium nitrate dissolved in 300 ml of ion-exchanged water was added, and the mixture was evaporated to dryness using a rotary evaporator. This was calcined at 435° C. for 5 hours in a nitrogen stream, and then formed into tablets in the same manner as in the example. Its catalyst composition is MO++P+,zASo,6
Cu0. +C3+, e.

The results of the same activity test as in Example 1 were that the conversion rate was 82.8%;
Although the selectivity was 90.0%, which was a good result, the results of the accelerated life test showed that the conversion rate was 60.2% and the selectivity was 87.0% in 15 hours.
9%, at 2000 hours the conversion rate was 29.4% and the selectivity was 88.0%, which was a particularly significant decrease in the conversion rate.

Comparative Example 3 105.9 g of ammonium paramolybdate and 2.34 g of ammonium metavanadate (NH, VO,) were dissolved in 400 ml of ion exchange water, and 8.65 g of 85% phosphoric acid and 4.73 g of 60% arsenic acid aqueous solution were added separately. , copper nitrate3.
62g, 17.5g of cesium nitrate and 30g of ion exchange water
A catalyst having the same composition as in Example 1 was prepared by the same method as in Example 1.

The results of the activity test were 68.5% conversion, selection, $88.
5%, which is insufficient especially in terms of activity. Furthermore, the results of an accelerated life test showed a conversion rate of 51.3% and a selectivity of 85% in 15 hours.
．． The conversion rate was 6%, but after 2000 hours, the conversion rate was 31.5%.
, the selectivity was 85.8%.

Comparative Example 4 12 Molybdophosphoric acid (H=PMo, □0..・30H2
0) Dissolve 118.2 g and 4.73 g of 60% arsenic acid in 500 ml of ion-exchanged water, add 2.28 g of vanadium pentoxide, and heat at boiling temperature for 15 hours in the absence of ammonium ions. did.

As a result, the vanadium pentoxide is dissolved, and a clear orange-red liquid containing free molybdovanadophosphoric acid is obtained. This includes 17.5 g of cesium nitrate and 4.8 g of ammonium nitrate.
A solution of 1.20 g of copper nitrate dissolved in 300 ml of ion-exchanged water was added, and the mixture was directly concentrated and dried using a rotary evaporator. Thereafter, the catalyst was prepared in the same manner as in Example 1. Its composition is MO12P +A Sa, <V
a, sCuo-+CS+, a.

The results of the activity test were a conversion rate of 55.0% and a selectivity of 88.2.
%, which is insufficient especially in terms of activity.

Comparative Example 5 A slurry obtained using the same raw materials and the same method as in Example 1 was concentrated and dried while stirring without any particularly long heating process. Thereafter, the same procedure as in Example 1 was carried out to obtain a catalyst having the same composition as in Example 1.

The results of the activity test were a conversion rate of 83.5% and a selectivity of 80.6.
%, which is not sufficient especially in terms of selectivity.

Comparative Example 6 A catalyst having the same composition as in Example 1 was obtained in the same manner as in Example 1, except that instead of being calcined in a nitrogen stream, it was calcined in air at 370° C. for 5 hours.

The results of the activity test were a conversion rate of 68.5% and a selectivity of 89.2.
%, which is not sufficient especially in terms of reaction activity.

Example 2 M O+zP+, sA SD, 4V0.25Cuo, s
A catalyst having a composition of c s2.0 was obtained.

The results of the activity test were a conversion rate of 84.5% and a selectivity of 89.2.
%Met. Furthermore, the results of the accelerated life test showed that the conversion rate was 68.3% and the selectivity was 85.7% in 15 hours;
After 00 hours, the conversion rate was 61.6% and the selectivity was 86.3%.

Example 3 The amount of vanadium pentoxide was 1.14 g, the amount of 60% arsenic acid aqueous solution was 7.10 g, and the amount of cesium nitrate was 15°59 g.
The process was carried out in the same manner as in Example 1 except that Mo+aP+-
A catalyst having a composition of 5Aso, sVo, asCuo, +cS+-s was obtained.

The results of the activity test were a conversion rate of 86.2% and a selectivity of 89.6.
%Met. Furthermore, the results of the accelerated life test showed that the conversion rate was 70.2% and the selectivity was 86.1% in 15 hours;
After 00 hours, the conversion rate was 60.8% and the selectivity was 86.8%.

Example 4 M o +
zP +, sA S++, 4V0.5Cun-sCS+
A catalyst with the following composition was obtained.

The results of the activity test were a conversion rate of 94.2% and a selectivity of 84.1.
%Met.

Example 5 An example was carried out in the same manner as in Example 3, except that 86.3 g of molybdenum trioxide (MoO3) and 30 g of 28% ammonia water were used instead of ammonium molybdate, and the heating and stirring time was changed to 24 hours. A catalyst having the same composition as in Example 3 was prepared.

The results of the activity test were a conversion rate of 832% and a selectivity of 89.9%.
Met.

Example 6 Cesium carbonate (CszC03) instead of cesium nitrate
A catalyst having the same composition as in Example 3 was prepared in the same manner as in Example 3, except that 13.0 g was used.

The results of the activity test were that the conversion rate was 84.2%, and the selection rate was 88.
It was 9%.

Example 7 Rubidium nitrate (RbN○,) instead of cesium nitrate
M
O12P1.5A So, 6V0.25Cuo, 3Rb
A catalyst having a composition of 1-6 was prepared.

The results of the activity test showed that the conversion rate was 85.3%, and the selection rate was 85.3%.
It was 7.5%.

Example 8 Thallium nitrate (T I N03) was used instead of cesium nitrate.
) MO12P+, 5ASO, 1lV0.25Cuo, 3T
A catalyst having a composition l+,s was prepared.

The results of the activity test were a conversion rate of 83.8% and a selectivity of 87.9.
%Met.

Example 9 Using the catalyst of Example 1, an oxidation reaction of isobutane was carried out.

A glass reaction tube with an inner diameter of 15 mm was filled with 9 g of catalyst, and a raw material gas consisting of 42 mol % of isobutane, 33 mol % of oxygen, 12 mol % of water vapor, and the balance nitrogen was supplied at a space velocity (STP standard) of 600 h-'.

The reaction pressure was 1.5 atm. When the reaction temperature was set to 310° C. and analysis was performed 15 hours after the start of the reaction, the inbutane conversion rate was 9.2%, the methacrylic acid selectivity was 50.2%, and the methacrolein selectivity was 13.5%. The reaction continued as it was, and the results after 2000 hours were a conversion rate of 8.4%, a methacrylic acid selectivity of 49.5%, and a methacrolein selectivity of 16.8.
%Met.

Example 10 Using the same catalyst as in Example 4, the same reaction test as in Example 9 was conducted. The reaction temperature was 300°C, and after 15 hours, the isobutane conversion rate was 8.9% and the methacrylic acid selectivity was 51.3%.
, the methacrolein selectivity was 14.3%. 2 more
The results after 000 hours were a conversion rate of 8.2%, a methacrylic acid selectivity of 50.0%, and a methacrolein selectivity of 17.5%.

Comparative Example 7 Using the same catalyst as in Comparative Example 3, the same reaction test as in Example 9 was conducted. The results after 15 hours of operation at a reaction temperature of 320°C were: isobutane conversion rate of 10.5%, methacrylic acid selectivity of 45.2%, and methacrolein selectivity of 13.3%. Furthermore, the results after 1000 hours were: conversion rate 5.2%, methacrylic acid selectivity 44.0%, methacrolein selectivity 1.
The conversion rate was 9.8%, which was a significant decrease in the conversion rate.

Example 11 Using the same catalyst as in Example 1, an oxidative dehydrogenation reaction of isobutyric acid was carried out.

A glass reaction tube with an inner diameter of 15 mm was filled with 9 g of catalyst, and a raw material gas containing 5 mol % of isobutyric acid, 60 mol % of air, and 35 mol % of water vapor was supplied at a space velocity (STP standard) of 670 h-'. Isobutyric acid conversion rate 98.2% at reaction temperature 300℃
, the methacrylic acid selectivity was 81.8%.

Claims (1)

[Claims] 1. General formula P_aMo_bV_cAs_dCu_eX_fO_g(
In the formula, P, Mo, V, As, Cu, and O are each phosphorus,
Molybdenum, vanadium, arsenic, copper and oxygen, X
indicates at least one element selected from the group consisting of rubidium, cesium, and thallium, and the subscripts a, b,
c, d, e, f and g indicate the atomic ratio of each element, b = 1
2, a, c, d, e, and f each take a value of 3 or less that does not include 0 (zero), and g indicates a value determined by the valence and atomic ratio of other elements). It is a partially neutralized salt of a heteropolyacid that uses vanadium pentoxide (V_2O_5) as a vanadium raw material, and the catalyst raw material is dissolved or suspended in water in the presence of an ammonium group at a temperature of 80°C or higher. For the production of methacrylic acid, which is prepared by a method comprising a step of heat treatment for 1 hour or more, and a step of calcining the solid obtained after concentration and drying in an inert gas at a temperature of 400 to 500 ° C. catalyst.