JP3287066B2 - Method for producing acrylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing acrylic acid. More specifically, the present invention relates to an improvement in a method for producing acrylic acid by gas phase catalytic oxidation of acrolein and molecular oxygen.

[0002]

2. Description of the Related Art A large number of composite oxide catalysts containing molybdenum and vanadium as essential components have been proposed as catalysts for producing acrylic acid by gas phase catalytic oxidation of acrolein.

For example, Japanese Patent Publication No. 41-1775 discloses M
A catalyst supporting o-V on a carrier is disclosed in
No. 1371 is a Mo-V-Cu-Cr / W-based material having a carrier surface area of 2 m ² / g or less and a porosity of 30 to 65 as physical properties.
%, A catalyst using a carrier having a pore size of 50 to 1500 μm of 90% or more is disclosed in JP-B-59-8178.
A catalyst in which a catalytically active substance comprising VW-Cu / Fe / Mn / Cr- (Sn) is coated on a carrier by a specific method has been reported. As a catalyst for synthesizing acrylic acid by subjecting acrolein to gas-phase catalytic oxidation, a so-called coating catalyst in which an active substance mainly composed of Mo-V is supported on an inert carrier is often used, and the reaction yield is high. 95%
Has become a high-performance thing.

[0004]

However, when acrylic acid is industrially produced using this catalyst, it is desired to further improve the productivity of acrylic acid per unit volume of the catalyst and the catalyst life. Increasing the flow rate of the raw material acrolein to increase the productivity of acrylic acid increases the heat of reaction and increases the temperature peak due to heat storage in the catalyst layer, only accelerating the reduction in yield due to excessive oxidation and the deterioration of the catalyst due to heat load. Instead, it can cause a runaway reaction.

In this reaction, the reaction product gas is usually
After quenching with water to form an aqueous acrylic acid solution, the acrylic acid is separated and purified through processes such as extraction and distillation.If the reaction gas contains a large amount of unreacted acrolein, wastewater treatment and complicated measures for product quality are required Thus, it is desirable to make the reaction rate of acrolein as high as possible. For this reason, the acrolein reaction rate is usually 99% or more, preferably 99.5% or more, but this is not a simple matter.

In order to keep the temperature peak low, it is common to reduce the diameter of the reaction tube to improve heat removal.
There is a limit in industry, and the reactor becomes large in order to obtain the same catalyst capacity, which is not economical.

Another method for keeping the temperature peak low is to gradually increase the activity of the catalyst from the inlet side of the raw material gas toward the outlet side, as disclosed in JP-B-53-3068.
No. 8 discloses an example in which the catalyst layer on the inlet side is diluted with an inert substance. Japanese Patent Publication No. 63-38331 discloses a molybdenum-bismuth-iron composite oxide catalyst used for synthesizing acrolein by oxidizing propylene in the gas phase by changing the types or amounts of alkali metals and thallium. And a method of arranging a more active catalyst from the raw material gas inlet side toward the outlet side.

As for the method for producing acrylic acid by subjecting acrolein to gas phase catalytic oxidation, a method of arranging the catalyst so as to increase the activity of the catalyst from the inlet side of the raw material gas toward the outlet side thereof is as follows. Only the method of dilution with is known.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing acrylic acid by subjecting acrolein to gas-phase catalytic oxidation, thereby preventing excess heat storage in the catalyst layer and improving the yield and productivity of acrylic acid by a simpler method than before. And a means for extending the life of the catalyst.

[0010]

Means for Solving the Problems As a result of intensive studies on the means for solving the above problems, the present inventors have prepared catalyst layers having different loading rates, and have higher catalyst layers from the inlet side of the raw material gas toward the outlet side. It has been found that the object can be achieved by filling and reacting a catalyst having a supported ratio, and the present invention has been accomplished.

That is, the present invention provides a gas phase contact of acrolein with molecular oxygen using a fixed-bed multitubular reactor packed with a catalyst in which a catalytically active substance containing at least molybdenum and vanadium is supported on an inert carrier. A method for producing acrylic acid by oxidizing, characterized in that a catalyst having a larger loading ratio of a catalytically active substance is sequentially charged and reacted from a raw material gas inlet side to an outlet side of a reaction tube, and the reaction is performed. Is the way.

The catalyst used in the present invention is a catalyst in which a catalytically active substance containing at least molybdenum and vanadium is supported on an inert porous carrier. This catalytically active substance is a composite oxide containing molybdenum and vanadium, but may contain other components in addition to this. In this case, as other components, for example, copper, cobalt, iron,
Examples include bismuth, nickel, chromium, manganese, magnesium, tungsten, antimony, and niobium. Further, it may contain a component such as silica, alumina and titania as a catalytically active component.

The composition of the catalytically active substance of the present invention is represented by the following general formula. Moa Vb Cuc Ad Be Cf Ox (where Mo is molybdenum, V is vanadium, Cu is copper, A is tungsten and / or niobium, B is cobalt, iron, nickel, manganese, bismuth, chromium, antimony, magnesium, arsenic , Tin, strontium and calcium, at least one element selected from the group consisting of silicon, aluminum, titanium, zirconium and cerium; O represents oxygen; a, b , C, d, e, f, and x represent the number of atoms of Mo, V, Cu, A, B, C, and O, respectively, and when a = 12, b = 1 to 6, c = 0 to
5, d = 0 to 6, e = 0 to 5, f = 0 to 10, and x take values determined by the oxidation state of each element. )

The raw materials for the catalytically active component are not particularly limited, but are generally used ammonium salts,
Nitrate, sulfate and the like are used.

The carrier used in the present invention may be any carrier as long as it is inert to the present reaction, and generally has an outer diameter of 2 to 1 made of fused alumina, silicon carbide, silica-alumina, porcelain or the like.
A molded article having a shape of about 0 mm, such as a sphere, a column, or a cylinder, is used. The molded body preferably has a large porosity having a macropore of 10 μm or more.

The method for preparing the catalyst is not particularly limited, but a method in which a slurry obtained by mixing the compound solution of the active ingredient is impregnated in a carrier, and the mixture is tumbled and evaporated to dryness. There is a method of coating the carrier with a precursor of an active substance which has been evaporated to dryness in advance and is calcined or further calcined. As a method for coating the powder, there is a method in which the powder is suspended in water and impregnated in the carrier, or a method in which the powder is attached to the carrier that has absorbed water using a dish-type granulator, a marmellaizer, or the like.

Usually, the catalytically active component is calcined at 300 to 430 ° C. before or after molding. By employing a so-called steaming method as the calcining method, the catalytic performance is further improved.

A feature of the present invention is that a catalyst having a different loading ratio of the catalytically active substance is prepared, a catalyst having a lower loading ratio is filled at the inlet side of the raw material gas, and a catalyst having a higher loading ratio is gradually increased toward the outlet side. Is to fill. The loading ratio (weight ratio of active substance per catalyst) can be selected in the range of 10 to 50%. The method of changing the loading rate may simply change the ratio between the catalytically active substance and the carrier in the loading molding step.

Since the activity of the catalyst used in the present invention depends on the amount of the catalytically active substance, the activity of the catalyst is substantially proportional to the loading rate. Therefore, by filling the catalyst with a higher loading rate toward the outlet side, a catalyst having a low activity at the inlet side and a high activity toward the outlet side is distributed. The supported catalyst used in the present invention has a higher reaction selectivity for the target product than a tablet-shaped or cylindrical shaped catalyst comprising only the active substance, and the lower the supported ratio, the higher the selectivity.

Since acrolein largely reacts in the first half of the catalyst layer, the temperature peak is suppressed to a low level by arranging a supported catalyst having a low loading and a high selectivity at the inlet side as in the present invention. Combined with the effect, the overall acrylic acid yield is improved over the conventional method.

Although it is ideal that the catalysts with different loading ratios of the catalytically active substance are filled in a large number of types and then packed in succession, two to three types of catalysts are practically sufficient. For example, the loading rate is about 10 to 3 from about 1/3 to 2/3 from the inlet side of the reaction tube.
0% of the catalyst is charged from the outlet side to about 1/3 to 2/3 with a catalyst having a loading of about 20 to 40%.

The raw material acrolein in the present invention is
Using a molybdenum-bismuth-based composite oxide catalyst.
Catalyst obtained by catalytic oxidation of propylene with dendritic oxygen.
Lorain can be used as it is. In the source gas
The concentration of acrolein is selected in the range of 3 to 8%.
According to Ming, problems such as runaway of reaction even at high concentration of 5% or more
Driving is possible without. One source of molecular oxygen
In general, air is advantageously used, but the so-called exhaust gas circulation
Use pure oxygen or oxygen-enriched air when using the formula
You can also. Oxygen concentration is considered as explosion range.
It is selected from the range of 0.5 to 1.5 times the in. Also raw materials
5% or less in gas including water produced by propylene oxidation reaction
Desirably, the upper water is present. The space velocity of this reaction is
500-3000h^-1(Standard conversion)
However, according to the invention, in particular 1200 h ^-1High load conditions above
But you can react without any problem. The reaction pressure is from normal pressure to several atmospheres,
The reaction temperature is about 220 to 320 ° C.

[0023]

According to the present invention, compared with the conventional method of diluting a catalyst with an inert substance, heat storage in the catalyst layer can be easily prevented, and high productivity of acrylic acid can be obtained without fear of runaway reaction. Not only can a higher conversion of acrolein and a higher yield of acrylic acid be obtained than with conventional methods.

[0024]

EXAMPLES Hereinafter, the present invention will be described with reference to examples.
The present invention is not limited to this. Acrolein conversion (%) and acrylic acid yield (%) are defined as follows. It is assumed that acrylic acid in the source gas does not react. Acrolein is Acr, acrylic acid is AA
Abbreviated. Acr conversion (%) = (mol of reacted Acr / feed A)
cr mole number) × 100 AA yield (%) = (molar number of AA acid produced / mol number of supplied Acr) × 100

[0025] Example 1 Water 160 l copper sulfate _{(CuSO 4 · 5H 2 O)} 8
0.8kg and cobalt sulfate (CoSO ₄ · 7H
To dissolve the ₂ O) _30.4kg. Separately, add 650 liters of hot water to ammonium metavanadate (NH ₄ VO ₃ ) 3
7.9 kg, monoethanolamine (H ₂ NCH ₂ CH
₂ OH) 8.8 kg and ammonium molybdate _{((NH 4) 6 Mo 7} O 24 · 4H 2 O) 228.4kg
Dissolve. The two are mixed, and 32.4 kg of 20% silica sol (SiO ₂ ) is added, followed by concentration with stirring.

The mixed concentrate is taken out in the form of a slurry, dried at 200 ° C. for 14 hours under a stream of air, and subsequently dried at 250 ° C.
For 3 hours. The powder obtained by crushing this solid is
Using a dish-type granulator, coating granulation was performed while adhering to a porous α-alumina carrier (average particle size: 5 mmφ) containing water. At this time, three types of powder and carrier having different ratios of loading and carrier were prepared. After drying each molded product, about 13 kg per container (a rectangular parallelepiped with a lid of 500 mm x 350 mm x 120 mm with a hole of 3 mmφ)
At the same rate. Put into a firing furnace and raise the temperature to 380 ° C.
It was kept for a time and fired. After being taken out of the container, it was transferred to an open-type container and calcined at 300 ° C. for 6 hours in an air flow to obtain a catalyst.

The composition of this catalyst excluding the oxygen as an active substance is as follows:
Mo ₁₂ V ₃ Cu ₃ Co ₁ Si ₁ . The catalyst having a loading of 23% is referred to as catalyst A, the catalyst having a loading of 27% is referred to as catalyst B, and the catalyst having a loading of 31% is referred to as catalyst C.

A stainless steel reaction tube having an inner diameter of 30 mm was charged with 1000 ml of catalyst A on the inlet side of the raw material gas and 1000 ml of catalyst C on the outlet side, and propylene was subjected to gas phase catalytic oxidation in the presence of a molybdenum-bismuth composite oxide catalyst. Using a mixed gas of an acrolein-containing gas and additional air obtained as a raw material, a reaction was performed at a space velocity of 1800 h ^-1 (converted to a standard state). Acrolein in the raw material gas is 5.8% by volume,
Oxygen 6.5% by volume and steam 28% by volume. The remainder was unreacted propylene, acrylic acid and other pre-reaction by-products with nitrogen.

The reaction can be started without any problem such as runaway of the reaction temperature, and the temperature of the heating medium for heating the reaction tube after 3 days is 262.
° C, the temperature peak of the catalyst layer is in the portion of catalyst A,
° C. The reaction result at this time was an Acr reaction rate of 99.8.
% And the AA yield was 96.1%. The reaction was continued as it was. After 250 days, the temperature of the heating medium was 265 ° C., and the peak temperature was 30.
6 ° C., the reaction result was 99.9% for Acr conversion, and AA
The yield was 96.2%.

Comparative Example 1 20 parts of catalyst C alone were placed in a stainless steel reaction tube having an inner diameter of 30 mm.
When the reaction was started under the same conditions as in Example 1, the peak temperature of the catalyst layer was about 360 ° C at a heating medium temperature of 256 ° C. At this time, the Acr reaction rate was 98.
The AA yield was 43.5% and the AA yield was 93.5%. An attempt was made to raise the reaction rate by further raising the temperature of the heating medium, but the peak temperature was 38
The temperature exceeded 0 ° C., and the reaction was stopped because the temperature tended to increase further.

Comparative Example 2 20 parts of catalyst B alone were placed in a stainless steel reaction tube having an inner diameter of 30 mm.
The reaction was carried out under the same conditions as in Example 1 with a filling of 00 ml.
At the start of the reaction, the temperature of the heat medium rises, and a steady state is reached on the fifth day by slowly increasing the flow rate of acrolein. At a heat medium temperature of 265 ° C, the peak temperature of the catalyst layer becomes 348 ° C.
Acr conversion 99.2%, AA yield 94.6%
Met. The reaction was continued as it was. After 250 days, the temperature of the heating medium was 270 ° C and the peak temperature was 326 ° C.
The cr reaction rate was 99.1%, and the AA yield was 94.5%.

Comparative Example 3 A mixture of 600 ml of catalyst C and 400 ml of carrier at the gas inlet side of a stainless steel reaction tube having an inner diameter of 30 mm and 1000 ml of catalyst C alone at the outlet side were reacted under the same conditions as in Example 1. Was done. The reaction can be started without any problem, the peak temperature of the catalyst layer is 310 ° C. at a heating medium temperature of 268 ° C. after 3 days, the Acr conversion is 99.8%, and the AA yield is 9
It was 4.8%. The reaction was continued as it was. After 250 days, the heating medium temperature was 275 ° C., the peak temperature was 308 ° C., and the reaction results were Acr conversion rate of 99.5% and AA yield of 94.6%.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI // C07B 61/00 300 C07B 61/00 300 (56) References JP-A-3-294239 (JP, A) JP-A Sho 59 -8178 (JP, A) JP-B 63-38331 (JP, B1) JP-B 53-30688 (JP, B1) JP-B 49-11371 (JP, B1) JP-B 41-1775 (JP, B1) (58) Fields investigated (Int.Cl. ⁷ , DB name) C07C 57/055 B01J 23/28 B01J 23/88 B01J 35/02 C07C 51/235 C07B 61/00 300

Claims (4)

(57) [Claims] 1. A gaseous catalytic oxidation of acrolein with molecular oxygen using a fixed-bed multitubular reactor filled with a catalyst in which a catalytically active substance containing at least molybdenum and vanadium is supported on an inert carrier. A method for producing acrylic acid, characterized by sequentially filling and reacting a catalyst having a higher loading rate of a catalytically active substance from a raw material gas inlet side to an outlet side of a reaction tube. 2. The composition of a catalytically active substance containing at least molybdenum and vanadium has a general formula Moa Vb C
uc Ad Be Cf Ox (where Mo is molybdenum, V is vanadium, Cu is copper, A is tungsten and / or niobium, B is cobalt, iron, nickel, manganese, bismuth, chromium, antimony, magnesium, arsenic, tin ,
At least one element selected from the group consisting of strontium and calcium, C is at least one element selected from the group consisting of silicon, aluminum, titanium, zirconium and cerium, O represents oxygen, a, b,
c, d, e, f and x are Mo, V, Cu, A,
Represents the number of atoms of B, C and O, and when a = 12, b
= 1-6, c = 0-5, d = 0-6, e = 0-5, f =
0 to 10 and x take values determined by the oxidation state of each element. 2. The method for producing acrylic acid according to claim 1, wherein 3. The loading rate of the catalytically active substance is 1 at the inlet side catalyst.
2. The composition according to claim 1, wherein the content of the catalyst is 0 to 30% and the content of the catalyst at the outlet side is 20 to 40%.
The method for producing acrylic acid according to the above. 4. A catalyst having a catalyst active substance loading of 10 to 30% in 1/3 to 2/3 from the inlet side of the reaction tube, and a catalyst loading of 20 to 30% in 1/3 to 2/3 from the outlet side. The method for producing acrylic acid according to claim 1, wherein the method is carried out by filling the catalyst with 40% of the catalyst.