KR101534355B1 - Process for producing methacrylic acid - Google Patents

Abstract

An object of the present invention is to provide a method which enables the catalyst to be used for a long time in the production of methacrylic acid by gas-phase catalytic oxidation of methacrolein with molecular oxygen. In the present invention, in the production of methacrylic acid by gas-phase catalytic oxidation of methacrolein, which is a raw material, with molecular oxygen in the presence of a catalyst comprising molybdenum and phosphorus-containing complex oxides, Pressure control for changing the reaction pressure stepwise or continuously so that the reaction rate of the raw material is constant in the temperature range and at the same time or independently controlling the molar ratio of the molecular oxygen / Or continuously changing the molar ratio.

Description

PROCESS FOR PRODUCING METHACRYLIC ACID < RTI ID = 0.0 >

The present invention relates to a method for producing methacrylic acid, more specifically, to a method for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen in the presence of a catalyst.

Patent Document 1 discloses a method for continuously producing an object by using a catalyst, in which the reaction temperature is gradually increased to the limit allowed in the process as the catalytic activity is lowered to maintain the reaction rate. In the prior art, a method of producing methacrylic acid by catalytic gas phase oxidation of methacrolein over a catalyst comprising a composite oxide containing molybdenum and phosphorus is well known and is also known to be used industrially. In this case, methacrylic acid is often produced at a reaction temperature of 250 to 400 ° C. by using the catalyst as a stationary phase. Although the catalyst used in this gas-phase catalytic oxidation reaction is used for a relatively long period of time, The cause of deterioration of the catalyst is the reduction of the catalyst component, the sublimation and scattering of the catalyst component, and the change of the crystal phase in the catalyst structure.

Various proposals have been made for a method of regenerating such deteriorated catalyst. For example, Patent Document 2 discloses a method of treating a deteriorated catalyst at a temperature of 70 to 240 캜 in an air stream having a steam partial pressure of 10% by volume or more. Patent Document 3 discloses a method of performing heat treatment at a temperature of 300 to 410 캜 for 0.5 to 50 hours under an oxidizing gas flow containing 0.1% by volume or more of molecular oxygen.

However, when considering from the industrial standpoint, it is very cumbersome to carry out the regeneration treatment every time the catalyst is deteriorated. Further, since the production of methacrylic acid must be temporarily stopped every time the catalyst is used, . That is, as a technical point of view, a method of producing methacrylic acid while suppressing deterioration of the catalyst as much as possible is desired rather than a method of regenerating the deteriorated catalyst.

For example, Patent Document 4 proposes to suppress catalyst deterioration by controlling the raw material gas composition and the space velocity of the raw material gas relative to the catalyst. Patent Document 5 proposes to increase the working pressure in the gas phase during the operation time for the purpose of dealing with inactivation of the catalyst.

Patent Document 1: Japanese Patent Application Laid-Open No. 2000-191582

Patent Document 2: JP-A-1983-156351

Patent Document 3: JP-A-1994-7685

Patent Document 4: JP-A-2002-193871

Patent Document 5: International Publication No. 2005/113127 pamphlet

DISCLOSURE OF INVENTION

Problems to be solved by the invention

However, the degree of catalyst deterioration inhibition is not necessarily sufficient in industrial practice, and further technical innovation is demanded.

An object of the present invention is to provide a method capable of long-term use of a catalyst in the production of methacrylic acid by gas-phase catalytic oxidation of methacrolein with molecular oxygen.

Means for solving the problem

The present invention relates to a method for producing methacrylic acid by vapor phase catalytic oxidation of methacrolein as a raw material with molecular oxygen in the presence of a catalyst composed of a composite oxide containing molybdenum and phosphorus, Pressure control for changing the reaction pressure stepwise or continuously so that the reaction rate of the raw material is constant in the temperature range and at the same time or independently controlling the molar ratio of the molecular oxygen / Or continuously changing the molar ratio of the methacrylic acid.

Effects of the Invention

According to the method for producing methacrylic acid of the present invention, the catalyst can be used for a substantially long period of time.

1 is a view showing a control method of a second reaction in Example 1. Fig.

2 is a diagram showing a control method of the second reaction in Comparative Example 1. Fig.

3 is a view showing a control method of the second reaction in Comparative Example 2. Fig.

BEST MODE FOR CARRYING OUT THE INVENTION

The catalyst used in the present invention is not particularly limited as long as it is a complex oxide containing molybdenum and phosphorus, but a complex oxide having a composition represented by the following formula (1) is preferable.

Mo _a P _b Cu _c V _d X _e Y _f O _g

Wherein X represents at least one element selected from the group consisting of iron, cobalt, nickel, zinc, magnesium, calcium, strontium, barium, titanium, chromium, tungsten, At least one element selected from the group consisting of manganese, silver, boron, silicon, tin, lead, arsenic, antimony, bismuth, niobium, tantalum, zirconium, indium, sulfur, selenium, tellurium, lanthanum, A, b, c, d, e, f and g represent atomic ratios of the respective elements, and when a = 12, 0.1? 3, 0.01? c? 3, 0.01? d? 3, 0? e? 10 and 0.01? f? 3, and g is an atomic ratio of oxygen required to satisfy the valence of each component.

In the present invention, the method for preparing the composite oxide catalyst containing molybdenum and phosphor is not limited to a specific method, and various methods such as coprecipitation, evaporation, Method can be used. Specifically, the raw material containing the constituent elements of the composite oxide is used to dissolve or suspend the required amount in a solvent such as water, and the obtained mixed solution or aqueous slurry is evaporated to dryness, and further, Followed by shaping, followed by heat treatment. The heat treatment is preferably carried out at 200 to 500 DEG C for 1 to 30 hours under oxygen flow, under air flow or nitrogen flow.

In the present invention, the raw material used for preparing the catalyst is not particularly limited, and a nitrate, carbonate, acetate, ammonium salt, oxide, or halide of each element can be used in combination. As the molybdenum raw material, for example, ammonium paramolybdate, molybdenum trioxide, molybdic acid, molybdenum chloride and the like can be used. As the phosphorus raw materials, there can be used polyphosphoric acid, metaphosphoric acid, hydrogen peroxide, pyrophosphoric acid, ammonium phosphate and the like.

The catalyst to be used in the present invention may be a catalyst for forming an uncarrier, but may be carried on an inert carrier such as silica, alumina, silica-alumina, or silicon carbide, or may be used by diluting them.

In the present invention, methacrolein, which is a starting material, is subjected to gas-phase catalytic oxidation with molecular oxygen in the presence of the above catalyst to produce methacrylic acid. For example, gas-phase catalytic oxidation can be performed by passing a reaction gas containing a raw material and molecular oxygen through a reaction tube filled with the catalyst.

Although it is economical to use air as a molecular oxygen source, if necessary, air enriched with pure oxygen can be used. The molar ratio of the molecular oxygen to the raw material in the reaction gas is preferably in the range of 0.5 to 3: 1. It is preferable that the reactive gas contains an inert gas for dilution. The reaction gas may contain steam. The concentration of the raw material in the reaction gas is preferably 1 to 10% by volume.

The reaction pressure is preferably 20 to 300 kPa (gauge pressure; hereinafter, pressure notation is all gauge pressure) as an average pressure of the reaction gas inlet / outlet pressure of the reactor. The reaction temperature is preferably in the range of 230 to 400 ° C, particularly 250 to 350 ° C.

However, the catalyst used for such gas-phase catalytic oxidation is degraded with time. Causes of the decrease in activity include decomposition of the catalyst structure due to temperature (sublimation and scattering of the catalyst component, change of the crystal phase in the catalyst structure), reduction of the catalyst component by the reactant (methacrolein) Reduction of the catalyst component by temperature, and the like. As a result of intensive studies, the inventors of the present invention have found that, in the present catalyst system, decomposition of a catalyst structure due to temperature or reduction of a catalyst component due to a reactant (methacrolein) and temperature is dominant as a cause of deterioration, will be.

That is, in the present invention, the pressure control is performed so as to change the reaction pressure stepwise or continuously in a reaction temperature range of 285 DEG C to 305 DEG C so as to maintain the reaction rate of the raw material without raising the reaction temperature as much as possible And at the same time, the molar ratio control is performed to change the molar ratio (O / R) of the molecular oxygen in the reaction gas or the raw material (O / R) in the reaction gas stepwise or continuously. By performing these two kinds of control, decomposition by the temperature of the catalyst structure and reduction of the catalyst component due to the reactants and the temperature are suppressed, and compared with the case of controlling only the conventional reaction temperature, the use period (catalyst life) Is dramatically improved.

The change of the reaction pressure and / or the change of the molar ratio of the molecular oxygen / raw material in the reaction gas is performed so that the reaction rate of the raw material becomes constant. Here, "the reaction rate of the raw material is constant" means that it is within the range of ± 2.5% from the operation management reaction rate in the normal operation. The operation response rate is the target response rate during normal operation. For example, the reaction pressure is changed so that the reaction rate of the raw material does not exceed (the operation management reaction rate + 2.5%) at the point when the reaction rate of the raw material decreases until the reaction rate of the raw material falls below (the operation management reaction rate -2) The mole ratio of the molecular oxygen in the raw material to the molar ratio of the raw material may be changed.

As such an operation method, for example, when the activity is lowered and the reaction rate is lowered, the reaction rate and the molar ratio (O / R) of the molecular oxygen / raw material in the reaction gas are increased to keep the reaction rate almost constant And the like. While the activity of the catalyst temporarily increases during the continuation of the reaction, the activity of the catalyst becomes lower in the long run than in the initiation. When the activity temporarily increases, the reaction method may be performed by lowering one or both of the reaction pressure and the molar ratio (O / R) of the molecular oxygen / raw material in the reaction gas.

It is effective to perform the control so as to raise the reaction pressure with the progress of the reaction. The pressure at the start of the reaction is preferably 90 to 130 kPa, more preferably 100 to 120 kPa. The pressure at the end of the reaction is preferably 100 to 140 kPa, more preferably 110 to 130 kPa. Although the reaction pressure may be continuously increased, it is preferable to raise the reaction pressure stepwise from the viewpoint of control easiness. When raising the reaction pressure stepwise, it is preferable to raise the reaction pressure by two or more times. For example, the initial reaction pressure is set to 100 to 110 kPa, the reaction pressure once to 110 to 120 kPa in the course of the reaction, and finally the reaction pressure is set to 120 to 130 kPa. On the other hand, the reaction pressure referred to herein is an average pressure of the inlet pressure and the outlet pressure of the reactor.

The method of raising the pressure is not particularly limited, and for example, a method of changing the control valve set value at the outlet of the reaction gas to increase the inlet pressure and the outlet pressure together.

It is effective to control the molar ratio (O / R) of the molecular oxygen in the reaction gas to the raw material in accordance with the progress of the reaction. The molar ratio (O / R) at the start of the reaction is preferably 1.4 to 1.9, more preferably 1.5 to 1.6. The molar ratio (O / R) at the end of the reaction is preferably 1.6 to 1.9, more preferably 1.7 to 1.8. Although the molar ratio (O / R) may be continuously increased, it is preferable to raise the molar ratio (O / R) stepwise from the viewpoint of control easiness. When raising the temperature stepwise, it is preferable to raise the temperature by two or more times. (O / R) of 1.5 to 1.6 and a molar ratio (O / R) of 1.6 to 1.7 once in the course of the reaction, and finally the molar ratio (O / R) 1.8. As a method for changing the molar ratio (O / R), for example, either the concentration of the molecular oxygen in the raw material gas and the concentration of the raw material may be changed or both may be varied, but the production amount of methacrylic acid It is preferable to change only the concentration of the molecular oxygen without changing the concentration of the raw material. In the case of changing only the concentration of molecular oxygen, it is preferable to adjust the concentration of the inert gas such as nitrogen so that the space velocity of the raw material gas does not change.

The reaction pressure and the molar ratio (O / R) of the molecular oxygen / raw material in the reaction gas can be independently changed, and can be changed simultaneously or alternately. As described above, a great effect is obtained by performing control in which the change of the reaction pressure and the change of the molar ratio of the molecular oxygen in the reaction gas / the raw material in the reaction gas are combined.

Depending on the change in the reaction pressure and / or the change in the molar ratio (O / R) of the molecular oxygen / raw material in the reaction gas, the conditions may be reversed depending on the degree of change in the activity of the catalyst.

In addition to the change of the reaction pressure and the change of the molar ratio (O / R) of the molecular oxygen / raw material in the reaction gas, a higher effect can be obtained by controlling the temperature by changing the reaction temperature. For example, the reaction temperature may be changed so that the reaction rate of the raw material does not exceed (the operation management reaction rate + 2.5%) at the point when the reaction rate of the raw material is lowered below the (management reaction reaction rate -2)%. The reaction temperature can be changed independently of the reaction pressure and / or the molar ratio (O / R), and can be changed at the same time.

The catalyst after the reaction under this control can be further used for ordinary gas-phase catalytic oxidation, and the period of use (catalyst life) of the catalyst at that time is also improved.

Hereinafter, the present invention will be described more specifically by way of examples. In the examples and comparative examples, " part " means the mass part. The analysis of the raw material gas and the reaction product gas was carried out by gas chromatography.

In the following examples, the vapor phase catalytic oxidation reaction of the raw material, methacrolein, is carried out. The reaction rates of methacrolein, the selectivity and yield of methacrylic acid produced are respectively defined as follows.

Reaction rate (%) of methacrolein = (B / A) x 100

Selectivity (%) of methacrylic acid = (C / B) x 100

Yield (%) of methacrylic acid = (C / A) x 100

Where A is the number of moles of metacrolein supplied, B is the number of moles of methacrolein reacted, and C is the number of moles of methacrylic acid produced.

[Reference Example]

(Preparation of catalyst)

100 parts of ammonium paramolybdate, 2.8 parts of ammonium metavanadate and 9.2 parts of cesium nitrate were dissolved in 300 parts of pure water. While stirring this, a solution prepared by dissolving 7.7 parts of an 85 mass% aqueous phosphoric acid solution in 10 parts of pure water and 1.1 parts of tellurium acid in 10 parts of pure water was added and the temperature was raised to 95 캜 with stirring. Subsequently, a solution prepared by dissolving 2.3 parts of copper nitrate, 7.6 parts of ferric nitrate, 1.4 parts of zinc nitrate and 1.8 parts of magnesium nitrate in 80 parts of pure water was added. Further, this mixed solution was stirred at 100 DEG C for 15 minutes, and the obtained slurry was dried by using a spray dryer.

To 100 parts of the obtained dried product, 2 parts of graphite was added and mixed and molded into a ring shape having an outer diameter of 5 mm, an inner diameter of 2 mm and a length of 5 mm by a tableting molding machine. The resultant molded product was calcined at 380 캜 for 5 hours under air circulation to obtain a catalyst. The composition of the catalyst is an atomic ratio excluding oxygen,

Mo ₁₂ P _1.4 Cu _0.2 V _0.5 Fe _0.4 Te _0.1 Mg _0.15 Zn _0.1 Cs ₁ .

[Example 1]

(First reaction)

3000 g of the catalyst obtained in Reference Example was charged into a stainless steel reaction tube having an outer diameter of 27.5 mm and a height of 6 m and having a heat transfer bath on the outside. Subsequently, the reaction was carried out at a temperature of 285 占 폚 (hereinafter referred to as a reaction bath temperature) and a reaction consisting of 6% by volume of methacrolein, 9.9% by volume of oxygen, 10% by volume of water vapor and 74.1% by volume of nitrogen Gas catalytic oxidation of methacrolein was carried out under the condition that the gas was passed through the catalyst layer at a space velocity of 1000 hr < ^{-1 &} gt ;. The initial reaction products were analyzed to find that the methacrolein reaction rate was 75.3%, the selectivity of methacrylic acid was 80.7%, and the yield of methacrylic acid was 60.8%. The temperature of the heat bath at this stage is 285 ° C, the reaction pressure is 110 kPa, and the mole ratio of molecular oxygen / raw material in the reaction gas is 1.65.

(Second reaction)

Subsequent to the first reaction, control was performed at an operation management reaction rate of 75%. Specifically, as shown in Fig. 1, the temperature of the heat bath, the reaction pressure, and the mole ratio of the molecular oxygen / raw material in the reaction gas were changed, and the methacrolein reaction rate was maintained at 75 ± 2.5%. 1, T is the temperature of the heat bath, P is the reaction pressure, M is the mole ratio of the molecular oxygen / raw material in the reaction gas, R is the methacrolein reaction rate, and t is the continuous operation time . The duration of the continuous operation of the second reaction was 2880 hours. Analysis of the reaction product at this stage showed that the reaction rate of methacrolein was 75.4%, the selectivity of methacrylic acid was 82.3%, and the yield of methacrylic acid was 62.1%. The temperature of the heat bath at this stage is 305 ° C, the reaction pressure is 130 kPa, and the mole ratio of molecular oxygen / raw material in the reaction gas is 1.85. On the other hand, when increasing the molecular oxygen / raw material molar ratio, the space velocity was also constant since the concentration of the raw material was made constant, the concentration of molecular oxygen was increased only, and the concentration of nitrogen was decreased by that portion.

(Third reaction)

After the second reaction, the reaction was continued until the temperature of the heat bath reached 320 캜 while controlling the temperature of the heat bath so that the operation management reaction rate of the methacrolein was constant at about 75%. The period of continuous operation until the end of the third reaction was 4704 hours in total. The reaction products of this stage were analyzed to find that the methacrolein reaction rate was 75.2%, the selectivity of methacrylic acid was 81.2%, and the yield of methacrylic acid was 61.1%.

[Comparative Example 1]

(First reaction)

The first reaction was carried out as in Example 1. [

(Second reaction)

As in Example 1, except that the temperature of the heat bath and the reaction pressure were changed and the methacrolein reaction rate was maintained at 75 ± 2.5% as shown in FIG. 2, the second reaction . The duration of the continuous operation of the second reaction was 2616 hours. Analysis of the reaction products at this stage revealed that the methacrolein reaction rate was 75.1%, the selectivity of methacrylic acid was 82.5%, and the yield of methacrylic acid was 62.0%. At this stage, the temperature of the heating bath is 305 ° C, the reaction pressure is 130 kPa, and the molar ratio of molecular oxygen / raw material in the reaction gas is 1.65.

(Third reaction)

After the second reaction, the third reaction was carried out as in Example 1. The period of continuous operation until the end of the third reaction was 4464 hours in total. Analysis of the reaction products at this stage revealed that the methacrolein reaction rate was 75.2%, the selectivity of methacrylic acid was 81.0%, and the yield of methacrylic acid was 60.9%.

[Comparative Example 2]

(First reaction)

The first reaction was carried out as in Example 1. [

(Second reaction)

As shown in Fig. 3, the second reaction was carried out in the same manner as in Example 1, except that the temperature of the heat bath was changed and the methacrolein reaction rate was maintained at 75 ± 2.5%. The duration of the continuous operation of the second reaction was 2160 hours. Analysis of the reaction products at this stage revealed that the methacrolein reaction rate was 75.2%, the selectivity of methacrylic acid was 82.5%, and the yield of methacrylic acid was 62.0%. The temperature of the heat bath at this stage is 305 ° C, the reaction pressure is 110 kPa, and the molar ratio of molecular oxygen / raw material in the reaction gas is 1.65.

(Third reaction)

After the second reaction, the third reaction was carried out as in Example 1. The period of continuous operation until the end of the third reaction was 3792 hours in total. The reaction product of this stage was analyzed to find that the methacrolein reaction rate was 75.1%, the selectivity of methacrylic acid was 81.2%, and the yield of methacrylic acid was 61.0%.

As described above, the catalyst can be used for a long period of time by controlling the reaction pressure and / or changing the mole ratio of the molecular oxygen / raw material in the reaction gas so that the reaction rate of the raw material, methacrolein, becomes constant.

Claims (3)

A process for producing methacrylic acid by vapor phase catalytic oxidation of methacrolein as a raw material with molecular oxygen in the presence of a catalyst containing a complex oxide containing molybdenum and phosphorus, The pressure control for changing the reaction pressure stepwise or continuously in the range of 90 kPa to 140 kPa is performed so that the reaction rate of the raw material is within the range of ± 2.5% from the management reaction rate during normal operation, Wherein the mole ratio of the molecular oxygen / raw material in the reaction gas is changed stepwise or continuously in the range of 1.4 to 1.9. The method according to claim 1, Wherein the pressure is controlled so that the reaction pressure is changed stepwise or continuously in the range of 110 kPa to 130 kPa. 3. The method according to claim 1 or 2, Wherein the mole ratio of the molecular oxygen / raw material in the reaction gas is changed stepwise or continuously in the range of 1.65 to 1.85.

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