JP4553440B2 - Method for producing methacrylic acid - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for stably producing methacrylic acid at a high yield by gas phase oxidation of methacrolein.
[0002]
[Prior art]
When producing methacrylic acid by gas phase oxidation of methacrolein using a phosphorus-molybdenum multi-component metal oxidation catalyst, the catalyst used is charged into a heat exchange type multi-tubular reactor, and the raw material methacrolein is charged with molecular oxygen. It is well known to introduce it together with it to carry out a catalytic gas phase oxidation reaction.
[0003]
The reaction temperature of gas phase oxidation of methacrolein using a phosphorus-molybdenum multi-component metal oxidation catalyst is generally 200 to 400 ° C. In this reaction, since a reaction rate of 100% of methacrolein cannot be obtained, unreacted methacrolein is recovered and circulated and supplied to the reactor. Accordingly, unreacted methacrolein is contained in the catalyst layer outlet gas of the reactor, and methacrolein is easily post-oxidized, which causes a problem of yield reduction.
[0004]
As a solution to this problem, Japanese Patent Application Laid-Open No. 64-29339 discloses that a hot reaction gas of 300 to 340 ° C. coming out of an oxidation reactor is cooled to 220 to 260 ° C., particularly 230 to 250 ° C. using a heat exchanger. In this case, it is described that the post-oxidation of the methacrolein-containing reaction gas is prevented. As the heat exchanger at that time, a tubular heat exchanger can be used, and the heat exchange specific surface area is preferably 200 m ² / m ^3. It is described.
[0005]
Thus, in order to prevent post-oxidation of methacrolein, it is important how quickly the catalyst layer outlet gas of the reactor is rapidly cooled. However, the temperature range of 220 to 260 ° C. is the dew point region of the reaction gas (catalyst layer outlet gas), and when cooled below the dew point, condensation of the reaction gas occurs, and the heat exchanger and piping are contaminated or blocked. Energy is wasted due to an increase in power loss due to an increase in pressure loss and an accompanying increase in power for the air compressor and the like. In some cases, continuous operation becomes impossible due to heat exchanger blockage.
[0006]
On the other hand, in Japanese Patent Publication No. 7-119187, as a method for suppressing the production of acetonylacetone, which is an impurity, there is a method in which a cooling zone is provided in an extended portion of a reaction tube to rapidly cool a gas after reaction (catalyst layer outlet gas). Are listed. However, this publication does not describe the improvement in the yield of methacrylic acid. In fact, the study by the present inventors is not satisfactory in terms of preventing the post-oxidation of methacrolein and improving the yield of methacrylic acid. there were.
[0007]
[Problems to be solved by the invention]
The present invention has been made in order to solve the conventional problems. In the process of producing methacrylic acid by vapor phase oxidation of methacrolein, the post-oxidation of methacrolein is prevented, and a high yield of methacrylic acid is stabilized. It aims at providing the method of manufacturing to.
[0008]
[Means for solving problems]
As a result of extensive research, the present inventor used as conditions for preventing post-oxidation of methacrolein for the time required for rapid cooling, the gas temperature at the outlet of the catalyst layer of the reactor that requires rapid cooling, the gas temperature after rapid cooling, and rapid cooling The present inventors have found the conditions to be satisfied by the heat exchanger and have arrived at the present invention.
[0009]
In other words, methacrylic acid that gas-phase catalytically oxidizes methacrolein by introducing a raw material gas containing at least methacrolein and molecular oxygen into a heat exchange type multi-tubular reactor filled with a phosphorus-molybdenum multi-metal oxide catalyst. In the production method, the catalyst layer outlet gas of the reactor is led to a cooling device satisfying the following formula (I), and when the temperature of the outlet gas exceeds 300 ° C., the outlet gas leaves the catalyst layer. The present invention relates to a method for producing methacrylic acid, characterized by quenching a gas to 300 ° C. or less within a time of 0 seconds or less.
[0010]
40 ≦ S / V ≦ 100 [m ² / m ³ ] (I)
However, V represents the volume of the space in which the outlet gas is cooled in the cooling device (hereinafter referred to as cooling space), and S represents the cooling heat transfer area in the cooling space.
[0011]
At this time, the temperature at which the outlet gas is cooled in the cooling device is preferably not less than the dew point of the outlet gas and not more than 300 ° C.
[0012]
As the cooling device, a tubular heat exchanger with fins is preferable, and as the cooling heat transfer area S, a metal surface area that is forcibly cooled by a refrigerant in a cooling space can be used.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The catalyst used in the gas phase oxidation reaction of methacrolein in the present invention is not particularly limited as long as it is one or two or more oxide catalysts containing phosphorus and molybdenum as main components. Molybdenum-based heteropolyacids or metal salts thereof are preferred, and those represented by the following general formula are particularly preferred.
[0014]
Mo _a P _{b Ac} B _d C _e D _f O _x
Here, in the formula, Mo represents molybdenum, P represents phosphorus, A represents at least one element selected from the group consisting of arsenic, antimony, germanium, bismuth, zirconium, boron, silicon, and selenium, B is at least one element selected from the group consisting of copper, iron, chromium, nickel, manganese, cobalt, tin, silver, zinc, palladium, rhodium, titanium, tantalum, iridium, sulfur, lanthanum, cerium and tellurium. C represents at least one element selected from the group consisting of vanadium, tungsten and niobium, D represents at least one element selected from the group consisting of alkali metal, alkaline earth metal and thallium, O represents oxygen. A, b, c, d, e, f and x represent the atomic ratio of Mo, P, A, B, C, D and O, respectively, and when a = 12, 0.1 ≦ b ≦ 3, 0 ≦ c ≦ 3, 0 ≦ d ≦ 3, 0 ≦ e ≦ 3, 0.01 ≦ f ≦ 3, and x is an atomic ratio of oxygen necessary to satisfy the valence of each component. .
[0015]
Further, the shape of the catalyst is not particularly limited, and may be any shape such as a spherical shape, a cylindrical shape, or a hollow shape. Further, it can be supported on an inert carrier such as silica, alumina, silica / alumina, or silicon carbide, or diluted with this.
[0016]
As a reactor used for the reaction in the present invention, for example, a heat exchange type multi-tube reactor in which reaction tubes having an inner diameter of about 20 to 30 mm are bundled is generally used. The reaction tube is filled with a catalyst, and the shell side is heated. By circulating the medium, the heat generated by the oxidation reaction is removed and the reaction temperature is controlled. As for the diameter of the reaction tube, if the inner diameter is too small, the pressure loss in the catalyst packed bed increases, resulting in a decrease in yield. Conversely, if the inner diameter is too large, the heat generated by the oxidation reaction is removed. This may make it difficult to form hot spots on the catalyst layer and lower the yield. Therefore, in consideration of these, the diameter of the reaction tube can be appropriately set.
[0017]
In the present invention, when the temperature of the exit gas exceeds 300 ° C., it is essential to rapidly cool the gas to 300 ° C. or less within a time of 3.0 seconds or less after the exit gas leaves the catalyst layer. If the time exceeding 3.0 seconds is required, it is insufficient to prevent the post-oxidation of methacrolein, and the post-oxidation of methacrolein when the temperature of the catalyst layer outlet gas of the reactor is 300 ° C. or lower. Hardly happens.
[0018]
The cooling device used in the present invention has the formula (I)
40 ≦ S / V ≦ 100 [m ² / m ³ ] (I)
(However, V represents the volume of the space in which the outlet gas is cooled in the cooling device (hereinafter referred to as cooling space), and S represents the cooling heat transfer area in the cooling space.)
And when the gas is attached to the outlet side of the reactor, any gas can be used as long as the gas can be rapidly cooled to 300 ° C. or lower within 3.0 seconds after the outlet gas leaves the catalyst layer.
[0019]
As the most preferable cooling device, a finned tube heat exchanger can be mentioned. And it is preferable to guide the outlet gas to the shell side and to flow the refrigerant to the tube side. When this apparatus is used, the cooling space volume V is a shell-side volume, and the cooling heat transfer area S is a metal surface area including tubes and fins. By using such a finned tube heat exchanger, the relationship between the cooling space volume V and the cooling heat transfer area S is 40 m ² / m ³ ≦ S / V ≦ 100 m ² / m ^3.
Meet easily. Furthermore, since the pressure loss is small, the yield reduction can be reduced.
[0020]
In the present invention, the cooling temperature of the catalyst layer outlet gas is preferably equal to or higher than the dew point of the outlet gas. For example, if the dew point of the outlet gas is about 240 ° C., the cooling temperature of the catalyst layer outlet gas is preferably 250 ° C. or higher. When cooled below the dew point, some of the outlet gas may condense and block the piping or heat exchanger. In particular, when a cooling device is installed and installed directly connected to the reaction tube, it becomes a big problem.
[0021]
Incidentally, the method of providing a gas quenching zone directly connected to the outlet of a reaction tube filled with a catalyst as described in Japanese Patent Publication No. 7-119187 as a cooling device has the following problems. That is, when a reaction tube having an inner diameter of about 20 to 30 mm is used and a gas quenching zone is provided directly connected to a reaction tube filled with a catalyst, the specific surface area in the quenching zone is naturally 200 to 140 m ² / m ^3. . In other words, when the gas quenching zone is provided directly connected to the reaction tube filled with the catalyst, the specific surface area in the quenching zone becomes a value that cannot be uniformly operated once the reaction tube inner diameter is determined. In addition to the heat medium unit that controls the reaction temperature, another heat medium unit must be provided to cool the reaction gas, resulting in excessive facilities. Furthermore, since the pressure of the reaction tube catalyst layer increases as the reaction tube becomes longer, the yield is reduced, which is not preferable.
[0022]
Even when a multi-tubular heat exchanger is separately provided on the outlet side, when the process gas is flowed to the tube side and the refrigerant is flowed to the shell side, the pressure of the reaction tube catalyst layer increases and the yield decreases. It is easy to invite.
[0023]
In the raw material gas used in the present invention, molecular oxygen is required together with methacrolein, and it is economically advantageous to use air as the oxygen source. However, if necessary, air enriched with pure oxygen is used. May be. The amount of oxygen in the raw material gas is preferably in the range of 0.3 to 4 times mol, particularly 0.4 to 2.5 times mol of methacrolein. The source gas may contain an inert gas such as nitrogen, water vapor, or carbon dioxide.
[0024]
【Example】
Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In the description, the reaction rate of methacrolein, the methacrylic acid produced, and the selectivity of side reaction products are defined as follows.
[0025]
Reaction rate of methacrolein (%) = (B / A) × 100
Selectivity of methacrylic acid or by-products (%) = (C / B) × 100
Here, A is the number of moles of methacrolein supplied, B is the number of moles of reacted methacrolein, and C is the number of moles of produced methacrylic acid or by-products.
[0026]
Further, “parts” in the following description represents parts by weight, and analysis of the raw material gas and the product gas was performed by gas chromatography. Moreover, the catalyst composition was calculated | required from the raw material preparation amount.
[0027]
[Example 1]
The composition of elements other than oxygen is
Mo ₁₂ P _1.5 Cu _0.3 Fe _0.4 V _0.5 Cs ₁
Was prepared and molded into a ring shape having an outer diameter of 5 mm, an inner diameter of 2 mm, and a length of 3 mm.
[0028]
Next, as schematically shown in FIG. 1, a reactor 2 (inner diameter) is provided with seven stainless steel reaction tubes having an inner diameter of 25.4 mm and a length of 3200 mm, and the shell side is capable of heat exchange by circulating molten salt. 208.3 mm) is prepared, and a mixture of 370 ml of catalyst and 130 ml of alumina spheres having an outer diameter of 5 mm is filled on the raw material gas inlet side of the reaction tube, and 1000 ml of catalyst is filled on the outlet side. It was set to 3000 mm. And the temperature of molten salt was set to 290 degreeC, molten salt was introduce | transduced from the heat-medium inlet line 5, was discharged | emitted from the heat-medium outlet line 6, and was circulated.
[0029]
Next, a finned tubular heat exchanger 3 (heat transfer area 0.152 m ² ) is installed directly to the reaction tube outlet, and the outlet gas from the catalyst layer is supplied to the shell side of the finned tubular heat exchanger. On the other hand, air preheated to 140 ° C. as a refrigerant on the tube side was introduced from the refrigerant supply line 7, discharged from the refrigerant outlet line 8 and circulated. The S / V on the shell side of this device is 50 m ² / m ³ .
[0030]
Next, methacrolein 5.0 vol%, oxygen 10.0 vol%, water vapor 9.0 vol%, and the remaining mixed gas consisting of nitrogen gas into the reaction tube at a space velocity (SV) of 1200 h- ¹ (standard temperature / standard pressure conversion). The raw material gas supply line 1 supplied.
[0031]
As a result of the reaction under such conditions, the temperature between the outlet of the reaction tube and the finned tubular heat exchanger was 310 ° C. The temperature of the gas cooled by the finned tubular heat exchanger was 275 ° C. Moreover, the time from the exit gas leaving the catalyst layer to the exit of the finned tubular heat exchanger was 2.6 seconds.
[0032]
When the reaction gas after cooling was condensed and collected from the reaction gas outlet line 4 and the composition analysis was performed, the conversion rate of the raw material methacrolein was 85%, the selectivity to methacrylic acid was 84.5%, and to COx. The selectivity was 12% and the other 3.5%.
[0033]
[Comparative Example 1]
In Example 1, air preheated to 200 ° C. was supplied as a refrigerant to the tube side of the finned tubular heat exchanger, and the reaction was performed in the same manner as in Example 1 except that.
[0034]
The temperature between the reaction tube outlet and the finned tube heat exchanger was 310 ° C. as in Example 1, but the temperature of the gas cooled by the finned tube heat exchanger was 305 ° C.
[0035]
At this time, the conversion rate of the raw material methacrolein was 85%, the selectivity to methacrylic acid was 81%, the selectivity to COx was 14%, and the other was 5%.
[0036]
[Comparative Example 2]
As shown in FIG. 2, the reaction tube outlet portion of the reactor 2 and the finned tubular heat exchanger 3 were connected by using a pipe 9 having an inner diameter of 52.7 mm and a length of 1 m, and a heat insulating material was wound around the pipe surface. The reaction was carried out in the same manner as in Example 1 except that. S / V was 94 m ² / m ³ (note that the space in the pipe is not included in the cooling space). In the apparatus shown in FIG. 2, portions other than the pipe 9 are the same as those in the apparatus shown in FIG.
[0037]
As a result, the temperature of the pipe immediately after the reaction tube outlet was 310 ° C. The temperature at the heat exchanger inlet was 308 ° C. The temperature of the gas cooled by the finned tubular heat exchanger was 275 ° C. The time from the exit gas leaving the catalyst layer to the exit of the finned tubular heat exchanger was 6 seconds.
[0038]
At this time, the conversion rate of the raw material methacrolein was 85%, the selectivity to methacrylic acid was 80%, the selectivity to COx was 15%, and the other was 5%.
[0039]
[Comparative Example 3]
As shown in FIG. 3, a reactor directly connected to a reaction tube and provided with a gas cooling unit 13 having a length of 1000 mm is divided into two parts, a catalyst charging unit 12 and a gas cooling unit 13 having a length of 1000 mm by a shielding plate. The heat medium can be circulated independently, and the heat medium temperature of the gas cooling part is adjusted so that the gas temperature coming out of the gas cooling part becomes 275 ° C. More heating medium was supplied, and the heating medium was discharged from the heating medium outlet line 11 and circulated. The gas cooling part was filled with alumina spheres having an outer diameter of 5 mm. S / V was 147 m ² / m ³ .
[0040]
As a result, the conversion rate of the raw material methacrolein was 85%, the selectivity to methacrylic acid was 82%, the selectivity to COx was 14%, and the others were 4%.
[0041]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the process of preventing the post-oxidation of methacrolein in the process of producing methacrylic acid by gas phase oxidation of methacrolein and stably producing methacrylic acid with high yield can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a process shown in Example 1. FIG.
FIG. 2 is a diagram showing a process shown in Comparative Example 1;
FIG. 3 is a diagram showing a process shown in Comparative Example 3;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Raw material gas supply line 2 Reactor 3 Finned tube heat exchanger 4 Reaction gas outlet line 5 Heat medium inlet line 6 Heat medium outlet line 7 Refrigerant supply line 8 Refrigerant outlet line 9 Pipe 10 Heat medium inlet line 11 Heat medium outlet Line 12 Catalyst filling part 13 Gas cooling part

Claims (3)

Production of methacrylic acid for gas-phase catalytic oxidation of methacrolein by introducing a raw material gas containing at least methacrolein and molecular oxygen into a heat exchange type multi-tubular reactor filled with a phosphorus-molybdenum multi-component metal oxide catalyst In the method
The catalyst layer outlet gas of the reactor is led to a cooling device satisfying the following formula (I), and when the temperature of the outlet gas exceeds 300 ° C., the time within 3.0 seconds after the outlet gas leaves the catalyst layer A method for producing methacrylic acid, wherein the gas is rapidly cooled to 300 ° C. or less.
40 ≦ S / V ≦ 100 [m ² / m ³ ] (I)
(However, V represents the volume of the space in which the outlet gas is cooled in the cooling device (hereinafter referred to as cooling space), and S represents the cooling heat transfer area in the cooling space.) The method for producing methacrylic acid according to claim 1, wherein a temperature at which the outlet gas is cooled in the cooling device is not less than a dew point of the outlet gas and not more than 300 ° C. The cooling device is a finned tube heat exchanger, and the cooling heat transfer area is a metal surface area that is forcibly cooled by a refrigerant in a cooling space. The manufacturing method of methacrylic acid of description.

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