JP2004026799A - Method for catalytic gas phase oxidation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for a catalytic gas phase oxidation preventing a violent reaction or early deterioration of a catalyst and enabling the production stably in a high yield for a long period in producing (meth)acrylic acid, or the like, from propylene or isobutylene by the method for a catalytic gas phase oxidation using a multi-tubular reactor. <P>SOLUTION: This method for oxidation by introducing a raw material gas into reaction tubes of the multi-tubular reactor equipped with a plurality of reaction tubes (1a, 1b, 1c) filled with the catalyst in a shell (2) of the multi-tubular reactor and a plurality of baffles (6a, 6b) in the inside of the reactor comprises measuring a temperature of the catalyst filled in the reaction tube not connected with at least one baffle. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention prevents a runaway reaction or early deterioration of a catalyst when producing (meth) acrylic acid or the like from propylene or isobutylene by a catalytic gas-phase acid oxidation method using a multitubular reactor, and is stable over a long period of time. The present invention relates to a catalytic gas-phase acid oxidation method capable of producing a high yield with high efficiency.
[0002]
[Prior art and its problems]
An ordinary multitubular reactor has a plurality of reaction tubes filled with a catalyst and a plurality of obstructions having openings for distributing a heat medium introduced into the shell throughout the shell in a shell of the reactor. It has a structure in which a board and a board are installed.
In general, the temperature of the heat medium flowing in the shell is detected, and the operation control of the multitubular reactor is generally performed based on the detection result while uniformly controlling the temperature of the heat medium in the cell. Was.
[0003]
Most of the reaction tubes contained in the shell are connected to the baffle plate, however, some reaction tubes passing through the openings provided in the baffle plate are not connected to the baffle plate.
In the catalyst layer inside the reaction tube that is not connected to the baffle plate, local heat accumulation points (hot spots) due to reaction heat of the catalyst are likely to occur.
When a hot spot occurs, a part of the catalyst is deteriorated due to excessive heat generation and the life is shortened.
Also, in order to prevent the generation of hot spots and optimize the life performance of the catalyst, the concentration of the raw material gas introduced into the reaction tube must be reduced, or the supply amount must be limited, and stable over a long period of time. In some cases, (meth) acrylic acid or the like cannot be produced with high yield.
[0004]
[Means to solve the problem]
The present invention provides a catalytic gas-phase acid oxidation method using a multitubular reactor which has solved the above-mentioned problems, and the gist thereof is as follows.
(1) A multi-tube reactor in which a plurality of reaction tubes filled with a catalyst and a plurality of baffles for changing a flow direction of a heat medium introduced into the shell are provided inside a shell of the multi-tube reactor. In a catalytic gas phase oxidation method in which a raw material gas is introduced into a reaction tube of a reactor and oxidized, a temperature of a catalyst filled in a reaction tube not connected to at least one baffle plate is measured. Is a catalytic gas phase oxidation method.
(2) A multi-tube reactor in which a shell of a multi-tube reactor is provided with a plurality of reaction tubes filled with a catalyst and a plurality of baffles for changing a flow direction of a heat medium introduced into the shell. In a catalytic gas phase oxidation method in which a raw material gas is introduced into a reaction tube of a reactor and oxidized, the temperature of a catalyst filled in a reaction tube not connected to at least one baffle plate and the temperature of a catalyst filled in the reaction tube are connected to all baffle plates. And measuring the temperature of the catalyst filled in the reaction tube.
(3) The method of any of the above (1) and (2), wherein the temperature or the flow rate of the heat medium introduced into the shell is controlled based on the measured temperature of the catalyst. .
(4) The method according to any one of the above (1) to (3), wherein the temperature of the catalyst is measured at 2 to 20 points in the axial direction of the reaction tube.
(5) The method of any of the above (1) to (4), wherein the catalyst temperature is measured using a multipoint thermocouple.
(6) The method according to any one of the above (1) to (5), wherein the flow direction of the raw material gas flowing in the reaction tube and the macroscopic flow direction of the heat medium flowing in the shell are the same. .
(7) The method of any one of the above (1) to (6), wherein the reaction tube is filled with a plurality of catalyst layers having different activities.
(8) The method according to any one of the above (1) to (7), wherein the raw material gas contains propylene, isobutylene, or (meth) acrolein as a substance to be oxidized.
[0005]
BEST MODE FOR CARRYING OUT THE INVENTION
The catalytic vapor phase oxidation method of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a sectional view of one embodiment of a multitubular reactor used in a catalytic gas phase oxidation method.
FIG. 2 is a perspective view of one embodiment of the baffle plate provided in the multitubular reactor.
FIG. 3 is a perspective view of another embodiment of the baffle plate provided in the multitubular reactor.
FIG. 4 is a view of the multitubular reactor of FIG. 1 as viewed from above.
FIG. 5 is a sectional view of another embodiment of the multitubular reactor used in the catalytic gas phase oxidation method.
FIG. 6 is a partial cross-sectional view of the intermediate tube plate and the heat shield plate provided in the multi-tube reactor of FIG.
[0006]
The outline of the catalytic gas phase oxidation method of the present invention and the multitubular reactor used in the catalytic gas phase oxidation method will be described with reference to FIG.
Reference numeral 2 denotes a shell of a multitubular reactor in which reaction tubes 1a, 1b, and 1c filled with a catalyst are fixed and installed by both a lower tube sheet 5b and an upper tube sheet 5a. I have.
The upper and lower ends of the shell 2 are provided with inlets / outlets 4a and 4b for a source gas Rg for reaction, and the source gas Rg flows through the reaction tubes 1a, 1b, and 1c in the upward or downward flow direction. The flow direction is not particularly limited, but an upward flow is more preferable.
[0007]
An annular conduit 3a for introducing the heat medium Hm is provided on the outer periphery of the shell 2, and the heat medium Hm pressurized by the circulation pump 7 is introduced into the shell 2 from the annular conduit 3a.
The heat medium Hm introduced into the shell 2 rises while changing the flow direction as indicated by arrows by the baffle plates 6a, 6b, 6a provided inside the shell 2, and during this time, the heat medium Hm is After contacting the outer surfaces of the shells 1b and 1c to remove the reaction heat, the shell 2 returns to the circulation pump 7 through an annular conduit 3b provided on the outer periphery of the shell 2.
A part of the heat medium Hm that has absorbed the reaction heat is cooled by a heat exchanger (not shown) from a discharge pipe 8b provided at the upper part of the circulation pump 7, and then returned to the circulation pump 7 from the heat medium supply pipe 8a. It is sucked and introduced into the shell 2.
The temperature of the heat medium Hm introduced into the shell 2 is adjusted by adjusting the temperature or the flow rate of the heat medium flowing from the heat medium supply pipe 8a. The temperature of the heat medium Hm is measured by a thermometer 14 inserted on the inlet side of the annular conduit 3a.
[0008]
A rectifying plate (not shown) is provided on the body plate portion inside the annular conduits 3a and 3b to minimize the circumferential distribution of the heat medium flow velocity. As the rectifying plate, a perforated plate or a plate having a slit is used, and the opening area of the perforated plate or the slit interval is changed so that the heat medium Hm having the same flow rate and the same flow rate from the entire circumference is introduced into the shell 2. It is rectified.
The temperature inside the annular conduit (3a, preferably 3b) can be monitored by arranging a plurality of thermometers 15 at equal intervals around the circumference as shown in FIG.
[0009]
Generally, at least three baffles (6a, 6b, 6a) are provided inside the shell 2. Due to the presence of the baffle plate, the flow of the heat medium Hm in the shell 2 first gathers from the outer peripheral portion of the shell 2 to the central portion. Then, the direction is changed while moving up the opening of the baffle plate 6a, and reaches the inner wall of the shell 2 toward the outer peripheral portion.
Next, the heating medium Hm changes its direction again while rising along the gap between the inner wall of the shell 2 and the outer periphery of the baffle plate 6b, and gathers at the center. Finally, the baffle plate 6a rises up the opening and is introduced into the annular conduit 3b toward the outer periphery along the lower surface of the upper tube plate 5a of the shell 2 and then sucked by the circulation pump 7 and circulated again in the shell 2. You.
[0010]
The specific structure of the baffle plate used in the present invention may be either a segmented baffle plate of the segment type shown in FIG. 2 or a disc-shaped baffle plate shown in FIG.
In both types of baffle plates, the relationship between the flow direction of the heat medium and the axis of the reaction tube does not change.
The baffle plate 6a has an outer periphery coinciding with the inner wall of the shell 2 and has an opening near the center thereof. Further, since the outer periphery of the baffle plate 6b has a smaller diameter than the inner wall of the shell 2, a gap is formed between the outer periphery of the baffle plate 6b and the inner wall of the shell 2.
At each of the openings and gaps, the heat medium rises, changes the direction of the flow, and changes the flow velocity.
[0011]
A thermometer 11 is inserted into the reaction tubes 1a, 1b, and 1c provided inside the shell 2, and a signal is transmitted to the outside of the shell 2 so that the axis of the reaction tube of the catalyst layer filled in the reaction tube is formed. The temperature distribution in the direction is measured.
A multipoint thermometer or a thermometer 11 that moves in a sheath and can measure a plurality of points is inserted into the reaction tubes 1a, 1b, and 1c to measure temperatures at 2 to 20 points in the tube axis direction.
[0012]
The reaction tubes 1a, 1b, 1c provided inside the shell 2 are divided and arranged by three baffles 6a, 6b, 6a, and are divided into three types in relation to the flow direction of the heating medium Hm.
That is, since the reaction tube 1a is connected to the baffle plate 6b, the flow direction of the heat medium Hm is restricted only by the baffle plate 6b and penetrates through the openings of the other two baffle plates 6a. It is not restricted by the baffle plate 6a.
The heat medium Hm introduced into the shell 2 from the annular conduit 3a is changed in direction at the center of the shell 2 as indicated by an arrow in FIG. Since the reaction tube 1a is located at the position where the direction is changed, the heat medium Hm flowing on the outer periphery of the reaction tube 1a mainly flows parallel to the tube axis of the reaction tube 1a.
[0013]
Since the reaction tube 1b is connected to the three baffles 6a, 6b, 6a, the flow direction of the heat medium Hm is restricted by each of the baffles. Then, the flow of the heat medium Hm flowing around the outer periphery of the reaction tube 1b flows at right angles to the tube axis of the reaction tube 1b at almost all positions of the reaction tube 1b. Most of the reaction tubes provided inside the shell 2 are arranged at the positions of the reaction tubes 1b.
Further, since the reaction tube 1c is not connected to the baffle plate 6b but penetrates the gap between the outer periphery of the baffle plate 6b and the inner wall of the shell 2, the flow of the heat medium Hm at this position is restricted by the baffle plate 6b. But flows parallel to the tube axis of the reaction tube 1c.
[0014]
FIG. 4 shows the positional relationship between the reaction tubes 1a, 1b, 1c and the baffles 6a, 6b, 6a and the mutual relationship between the flows of the heat medium Hm.
At the opening of the baffle plate 6a (the innermost dotted circle), the flow of the heat medium Hm is not only parallel to the reaction tube 1a at the gathering position of the heat medium Hm, that is, at the center of the shell 2, but especially at the baffle plate 6a. At the midpoint of the opening, the heat medium Hm hardly flows and the flow velocity is close to zero, so that the heat transfer efficiency is very poor. Therefore, the reaction tube 1a may not be disposed at this position.
[0015]
FIG. 5 shows another embodiment of the present invention in which the inside of the shell 2 of the reactor is divided by the intermediate tube sheet 9.
Separate heat medium Hm is provided in the space in the divided shell 2. ₁ And Hm ₂ Are circulated and separately temperature controlled.
The upper part and the lower part in the reaction tubes 1a, 1b and 1c are separated by an inert material layer not involved in the reaction, and each is filled with a different catalyst, and each is controlled to an optimum temperature for the catalyst. The reaction takes place. The position where the inert substance is interposed is a portion corresponding to the position where the outer circumferences of the reaction tubes 1a, 1b and 1c are connected to the intermediate tube plate 9.
The raw material gas Rg is introduced into the shell 2 from the raw material gas inlet 4a, and sequentially reacts as it passes through the reaction tubes 1a, 1b, and 1c to form a product.
For example, propylene or isobutylene is introduced as a mixed gas with a molecular oxygen-containing gas, and becomes (meth) acrolein in the lower part, and then oxidized to (meth) acrylic acid in the upper part.
[0016]
In FIG. 6, reference numeral 9 denotes an intermediate tube sheet, and three heat shield plates 10 are fixed to the lower surface of the intermediate tube sheet 9 by spacer rods 13.
As shown in this figure, by attaching two or three heat shield plates 10 at a position below or above 100 mm below or above the intermediate tube sheet 9, the heat medium Hm ₁ Or Hm ₂ However, it is preferable to form a stagnation space 12 with no flow, thereby providing a heat insulating effect.
The reason for attaching the heat shield plate 10 to the intermediate tube sheet 9 is as follows. That is, in FIG. 5, the heat medium Hm introduced into the lower portion of the shell 2 ₁ And Hm introduced in the upper part ₂ When the control temperature difference from the temperature exceeds 100 ° C., the heat transfer from the high-temperature medium to the low-temperature medium cannot be ignored, and the accuracy of controlling the reaction temperature of the low-temperature catalyst deteriorates. In such a case, heat insulation that hinders heat transfer above and / or below the intermediate tube sheet 9 is required.
[0017]
A gas in which propylene or isobutylene and / or (meth) acrolein is mixed with a molecular oxygen-containing gas or water vapor is introduced into the multitubular reactor used for the catalytic gas phase oxidation as a raw material gas Rg for the reaction.
The concentration of propylene or isobutylene is 3 to 10% by volume, oxygen is 1.5 to 2.5 (molar ratio) to propylene or isobutylene, and steam is 0.8 to 2 (molar ratio).
The introduced source gas Rg is divided into reaction tubes 1a, 1b, 1c, etc., passes through the reaction tubes and is reacted by the contained oxidation catalyst, and the distribution of the source gas Rg to each reaction tube is determined by the reaction tubes. It is affected by the amount of catalyst filled into the catalyst, the packing density, and the like. Since the amount of the catalyst and the density of the cascade are determined at the time of the operation of charging the catalyst into the reaction tubes, it is very important to uniformly fill the reaction tubes with the catalyst.
To achieve this uniform filling, a method is used in which the weight of the catalyst to be filled in each reaction tube is made uniform and the catalyst filling time is adjusted to make the packing density constant.
[0018]
The raw material gas Rg passing through each of the reaction tubes 1a, 1b, and 1c is initially heated while passing through the inert agent layer filled in the inlet portion, and reaches the reaction start temperature.
The raw material (propylene or isobutylene) is oxidized by the catalyst contained as the next layer in the reaction tube, and the temperature is further increased by the heat of reaction.
The amount of reaction is the largest at the inlet of the catalyst layer, and if it is larger than the amount of heat removed by the heating medium Hm, the generated reaction heat acts as a rise in the temperature of the raw material gas Rg, and hot spots may be formed. The hot spot is often formed at a position of 300 to 1,000 mm at the entrance of the reaction tubes 1a, 1b, 1c.
[0019]
Therefore, the heat removal effect by the flow of the heating medium Hm is most important within 1,000 mm of the inlet of the reaction tubes 1a, 1b, 1c. When the amount of reaction heat generated here exceeds the heat removal capability of the heat medium Hm from the outer periphery of the reaction tube, the temperature of the raw material gas Rg further increases, and the amount of reaction heat generated further increases. A runaway reaction may occur, exceeding the allowable maximum temperature of the catalyst, causing a qualitative change in the catalyst and causing deterioration or destruction.
Taking as an example a pre-stage reactor for producing acrolein by an oxidation reaction of propylene with a molecular oxygen-containing gas, the temperature of the heating medium Hm is 250 to 350 ° C, and the maximum allowable temperature of the hot spot is 400 to 500 ° C. It is.
Further, the temperature of the heat medium Hm in the latter reactor for oxidizing acrolein with a molecular oxygen-containing gas to obtain acrylic acid is 200 to 300 ° C, and the allowable maximum temperature of the hot spot is 300 to 400 ° C.
[0020]
As the heat medium Hm flowing in the shell 2 which is the outer periphery of the reaction tubes 1a, 1b and 1c, a nitrate, which is a mixture of nitrates, is often used, but an organic liquid-based phenyl ether-based heat medium may also be used.
Heat is removed from the outer periphery of the reaction tubes 1a, 1b, and 1c by the flow of the heat medium Hm. The heat medium Hm introduced into the shell 2 from the annular conduit 3a for introducing the heat medium is more centrally located than the outer periphery of the shell 2. There was a position where the flow direction was reversed, and a position where the flow direction was reversed at the center, and it was found that the heat removal effect was extremely different at each position.
When the flow direction of the heat medium Hm is perpendicular to the tube axis of the reaction tube, the heat transfer coefficient is 1,000 to 2,000 W / m. ² ° C, but at a non-perpendicular flow, it depends on the flow velocity, upward flow, or downward flow, but 100 to 300 W / m when a night game is used as a heating medium. ² In most cases, it can only be in ° C.
[0021]
On the other hand, the heat transfer coefficient of the catalyst layer in the reaction tubes 1a, 1b, and 1c depends on the flow rate of the raw material gas Rg. ² Since the temperature is on the order of degrees Celsius, it is natural that the rate of heat transfer is determined by the gas phase in the tube.
Specifically, when the flow of the heat medium Hm is perpendicular to the tube axes of the reaction tubes 1a, 1b, and 1c, the heat transfer resistance of the outer periphery of the tube is 1/10 to 1/20 of the gas Rg in the tube. Even if the flow velocity on the side changes, the effect on the overall heat transfer resistance is small.
However, since the heat transfer coefficient inside and outside the reaction tubes 1a, 1b, and 1c is almost the same when the night flow is parallel to the tube axis, the heat removal efficiency is greatly affected by the flow state around the tube. That is, the heat transfer resistance of the outer periphery of the tube is 100 W / m. ² At ° C., the overall heat transfer coefficient is half that, and half of the change in the heat transfer resistance on the outer periphery of the tube affects the overall heat transfer coefficient.
[0022]
When actually performing the reaction, it is necessary to sufficiently monitor the difference in the heat transfer coefficient.
The reaction tube 1b, which has a large overall heat transfer coefficient and a low maximum temperature due to the temperature distribution in the tube axis direction of the catalyst layer in the reaction tube, and is considered to be an average as a whole in the shell 2, has all the baffles (usually three plates). ).
The reaction tubes arranged at positions where the heat medium Hm changes direction are a reaction tube 1c that is not restricted by one baffle plate and a reaction tube 1a that is not restricted by two baffle plates.
[0023]
When the supply amount of the raw material gas Rg to the reaction tubes 1a, 1b, and 1c is increased, or when it is desired to maintain a high reaction temperature and obtain a high conversion, the maximum temperature of the reaction tubes rises to form a hot spot, thereby deteriorating the catalyst. And the likelihood of runaway reactions increases.
In such a case, it is necessary to strictly control the temperature of the heating medium Hm. A plurality of thermometers 11 are inserted into the plurality of reaction tubes 1a or 1c, and the temperature of the heat medium Hm is controlled while monitoring the hot spot temperature of each reaction tube, and the temperature of the heat medium Hm is strictly controlled to an appropriate temperature. Thereby, a desired reaction result can be obtained, and deterioration of the catalyst can be prevented, so that long-term continuous operation can be performed.
[0024]
When the maximum temperature of the reaction tube 1a is close to the limit temperature, the temperature of the heat medium Hm is lowered, but the temperature of the reaction tube 1c downstream of the position showing the maximum temperature may increase, so that monitoring cannot be neglected. .
When the reaction conversion is lower than an appropriate value, the temperature of the heating medium Hm needs to be increased. In this case, too, the maximum temperature of the reaction tube is monitored so as not to exceed the limit temperature. The maximum temperature of the reaction tube or the position indicating the maximum temperature of the reaction tube also changes when the supply amount of the raw material gas, which is a mixed gas of propylene or isobutylene and a molecular oxygen-containing gas, into the shell 2 is increased or decreased. Sometimes.
[0025]
Further, it is more preferable to insert the thermometer 11 also into the plurality of reaction tubes 1b and adjust the temperature of the heating medium Hm while monitoring the catalyst layer temperature of the reaction tubes.
By measuring the maximum temperature of the reaction tube 1b occupying the majority and comparing it with the maximum temperature of the reaction tube 1a or 1c in another region, it is possible to further optimize the reaction results. It is preferable that the difference between the maximum average temperatures of the reaction tubes (average values of the maximum values of the temperatures of the reaction tubes) in the respective regions be within 30 ° C., particularly 20 ° C., more preferably 15 ° C. If this difference is too large, the reaction yield tends to decrease, which is not preferable.
[0026]
The number of the reaction tubes 1a, 1b, and 1c in each region where the thermometer 11 is inserted is one or more, and preferably three to five. When the number of insertions is small, even when the temperature of the heat medium Hm introduced into the annular conduit 3a of the shell 2 is uneven, an abnormality in the maximum temperature of the reaction tube may not be detected.
Note that the above-mentioned region refers to an aggregate of reaction tubes that are connected to and supported by the same baffle plate via openings or gaps of the same baffle plate.
[0027]
There is no limitation on the type of baffle for the purpose of changing the flow direction of the heat medium Hm flowing in the shell 2 or preventing the bypass flow of the heat medium Hm, but the segment baffle and the disc-shaped baffle shown in FIGS. It seems that a disk-shaped baffle is used in particular.
The area of the central opening of the baffle plate 6a is 5 to 50%, preferably 10 to 30%, of the inner cross-sectional area of the shell 2.
The gap area formed by the outer periphery of the baffle plate 6b and the inner wall of the shell 2 is 5 to 50% of the inner cross-sectional area of the shell 2, and preferably 10 to 30%.
If the opening ratio and gap ratio of the baffles 6a and 6b are too small, the flow path of the heat medium Hm becomes long, the pressure loss between the annular conduits 3a and 3b increases, and the power of the circulation pump 7 increases. If it is too large, the number of the reaction tubes 1a and 1c will increase.
[0028]
The installation gap between the baffle plates (the space between the baffle plates 6a and 6b and the space between the baffle plate 6a and the upper tube plate 5a, the lower portion 5b) is often equal, but is determined by the heat of oxidation reaction generated in the reaction tube. If the required flow rate of the heating medium Hm is ensured and the pressure loss of the heating medium is set to be low, the intervals need not necessarily be equal.
It is necessary to avoid that the highest temperature position of the temperature distribution in the reaction tubes 1a, 1b, 1c and the position of the baffle plates 6a, 6b, 6a are the same. Since the flow rate of the heat medium near the surface of each baffle plate is reduced, the heat transfer coefficient is low, and the possibility of forming hot spots increases when the highest temperature positions of the reaction tubes overlap.
[0029]
Since the inside of the reaction tubes 1a, 1b and 1c containing the oxidation catalyst in the shell 2 is in the gas phase, and the maximum linear velocity of the raw material gas is limited by the catalyst, the heat transfer coefficient in the tube of each reaction tube is It is a small, heat transfer rate-limiting process. Therefore, the inner diameter of the reaction tube is very important.
The inner diameter of the reaction tubes 1a, 1b, 1c is affected by the amount of reaction heat in the tubes and the particle size of the catalyst. Preferably, the diameter is 20 to 30 mm. If the inner diameter of each reaction tube is too small, the weight of the catalyst to be filled decreases, and the number of reaction tubes increases with respect to the required amount of catalyst, and the shell 2 becomes large.
On the other hand, if the inside diameter of the reaction tube is too large, the contact between the catalyst and the surface of the reaction tube becomes small with respect to the required heat removal amount, and the heat transfer efficiency for heat removal of the reaction heat decreases.
[0030]
The thermometer 11 inserted into the reaction tube is usually a column having a plurality of thermocouples, resistance temperature detectors and the like covered with an outer tube (thermowell) as an outer wall, or one thermometer. Use a thermocouple that can move inside the sheath.
The thermometer 11 needs to be installed at the tube axis position at the center of the reaction tube, and by providing a projection or the like on the outer tube surface, the distance between the thermometer 11 and the inner wall of the reaction tube is limited so as to overlap the tube axis position. You.
The tube axis of the reaction tube and the central axis of the thermometer 11 preferably coincide with each other, and the protrusions provided on the thermometer 11 are preferably disposed before and after the position where the catalyst layer has the highest temperature.
The diameter of the outer tube (thermowell) of the thermometer 11 is 15 mmφ or less. Due to the relationship with the inner diameter of the reaction tube, the distance from the inner wall of the reaction tube needs to be at least twice the particle diameter of the catalyst particles. If the catalyst particle diameter is 5 mm and the inner diameter of the reaction tube is 30 mmφ, the outer tube diameter of the thermometer 11 needs to be 10 mmφ or less.
If the packing density of the catalyst is different between the reaction tube in which the thermometer 11 is inserted and the other reaction tube, the accurate temperature cannot be measured. Therefore, the outer diameter of the thermometer 11 is preferably 6 mmφ or less, more preferably 2 to 4 mmφ. .
[0031]
In each part of the cross section of the shell 2, the flow rate and the heat transfer coefficient of the heat medium Hm are analyzed, and attention is paid to the fact that there is a part where the heat transfer coefficient is low. Regarding the reaction tube, particularly the reaction tube 1a and its vicinity, disposed in the portion having a low heat transfer coefficient, the baffle plate opening near the center of the cross section of the shell 2 (the central circular portion in the case of a disk-shaped baffle) is extremely small. There is a part with a low heat transfer coefficient.
This portion is near the center of the opening of the baffle plate 6a, and it is recommended not to install a reaction tube in a portion having a shell cross-sectional area ratio of 0.5 to 5% of this portion. If this portion is smaller than 0.5%, it is required to set the flow rate of the heat medium Hm to be twice or more in order to make the heat transfer coefficient equal to or more than the minimum limit of the required value, thereby increasing the power of the circulation pump 7. .
However, if the portion where the reaction tube is not provided exceeds 5%, the body diameter of the shell 2 becomes large in order to install the required number of reaction tubes.
The reaction tube 1a that is not supported by the baffle plate 6a has an opening width of the baffle plate 6a (in the case of the segment baffle plate in FIG. 2) or 30 to 80% of the opening diameter (in the case of the disk-shaped baffle plate in FIG. 3). It is preferable not to install.
[0032]
1 to 5, the flow direction of the heat medium Hm in the shell 2 is indicated by an arrow as an ascending flow, but the present invention is also applicable to a flow in the opposite direction.
In determining the direction of the circulating flow of the heating medium Hm, it is necessary to avoid a phenomenon in which a gas that may be present at the upper end of the shell 2 and the circulating pump 7, particularly an inert gas such as nitrogen, is entrained in the heating medium flow. .
In the case where the heat medium Hm has an upward flow as shown in FIG. 1, if gas is entrained in the upper part of the circulation pump 7, a cavitation phenomenon is observed in the circulation pump and the pump may be damaged in the worst case.
[0033]
In the opposite case, a gas entrainment phenomenon also occurs in the upper part of the shell 2, and a gaseous stagnation part is formed in the upper part of the shell 2, and the upper part of the reaction tube corresponding to the gas stagnation part is not cooled by the heating medium Hm.
In order to prevent gas accumulation, it is essential to install a gas vent line and replace the gas in the gas layer with the heating medium Hm. For this purpose, the heating medium pressure of the heating medium supply pipe 8a is increased, and the heating medium discharge pipe is used. The pressure rise in the shell 2 is measured by placing 8b as high as possible. The heat medium discharge pipe 8b is provided at least above the upper tube sheet 5a.
[0034]
The flow direction of the raw material gas Rg can be either upward flow or downward flow in the reaction tubes 1a, 1b, and 1c. However, in terms of the relative relationship with the heating medium flow, a parallel flow is preferable.
The amount of heat generated in the reaction tubes 1a, 1b, and 1c is the largest at the entrance, and the hot spot is often located at a position on the axis of the reaction tube 300 to 1,000 mm from the entrance.
The position of the hot spot in relation to the baffle plate is often in the range between the upper tube plate 5a or the lower tube plate 5b and the baffle plate 6a, and the heating medium Hm at a controlled temperature is directly supplied to the reaction tube. By supplying to the tube axis position of the reaction tubes 1a, 1b, 1c corresponding to the highest temperature, it becomes easy to control the generation of hot spots. Therefore, it is preferable that the macroscopic direction of the heating medium Hm and the flow direction of the raw material gas Rg be the same direction, that is, the cocurrent.
[0035]
The amount of heat transfer, that is, the amount of reaction heat, is calculated by heat transfer coefficient × heat transfer area × (catalyst layer temperature−heat medium temperature). To lower the maximum temperature of the reaction tube, the surface area of the reaction tube (heat transfer area) A method of reducing the reaction heat per unit is effective.
In order to equalize the calorific value of the reaction heat, two or more catalyst layers having different activities are filled in the same reaction tube. It is preferable to fill a plurality of catalyst layers into the reaction tube so that the catalyst layer having lower activity is on the inlet side and the catalyst layer is switched to the catalyst layer having higher activity after the peak of the temperature distribution.
[0036]
As a method for adjusting the activity of the catalyst layer, for example, a method of using a catalyst having a different activity by adjusting the composition of the catalyst, or adjusting the activity by mixing the catalyst particles with the inert particles and diluting the catalyst. There is a method of doing.
A catalyst layer having a high ratio of inert particles (the ratio of catalyst particles in the mixed particles: dilution ratio) is provided at the inlet of the reaction tubes 1a, 1b, and 1c, and the dilution ratio is low or not diluted downstream of the reaction tubes. Fill the catalyst layer. Although the dilution ratio varies depending on the catalyst, a dilution ratio of 0.3 to 0.7 in the former stage is often used.
The latter stage dilution ratio is suitably used in the range of 0.5 to 1.0. For the change or dilution of the activity of the catalyst, two to three stages are usually employed.
[0037]
The dilution ratio of the catalyst charged in the reaction tubes 1a, 1b, 1c does not need to be the same for all. For example, since the reaction tube 1a has a high maximum temperature in the reaction tube, the possibility of catalyst deterioration is high. To avoid this, it is possible to decrease the dilution ratio of the former stage and increase the dilution ratio of the latter stage.
If the reaction conversion rate of each reaction tube is different, the average conversion rate and yield in the entire reactor are affected. Therefore, it is preferable to set so that the same conversion rate is obtained in each reaction tube even if the dilution rate is changed. .
The present invention is suitable for a multitubular reactor for oxidizing propylene or isobutylene with a molecular oxygen-containing gas or a multitubular reactor for oxidizing (meth) acrolein with a molecular oxygen-containing gas to obtain (meth) acrylic acid. Applied. The catalyst used for the oxidation of propylene is preferably a Mo-Bi-based multi-component composite metal oxide, and the catalyst for oxidizing acrolein to produce acrylic acid is preferably a Mo-V-based composite oxide. .
Since propylene or isobutylene is oxidized in two stages, it is possible to use two multitubular reactors, each of which can be filled with a different catalyst for the reaction. However, as shown in FIG. The present invention can also be applied to a case where the shell side is divided into two or more chambers by a middle tube plate, each is filled with another catalyst, and (meth) acrylic acid is obtained in one reactor.
[0038]
【Example】
Example 1
In carrying out the oxidation reaction of propylene, as the catalyst (A), Mo = 12, Bi = 5, Ni = 3, Co = 2, Fe = 0.4, Na = 0.2, B = 0.4, K = 0.1, Si = 24, O = x (atomic ratio) (oxygen composition x is a value determined by the oxidation state of each metal, the same applies hereinafter) as catalyst (B) A catalyst having a composition (atomic ratio) of Mo = 35, V = 7, Sb = 100, Ni = 43, Nb = 3, Cu = 9, Si = 20, and O = x was produced according to a conventional method to obtain a catalyst powder. Was.
Each of the catalyst powders was molded to produce and use a ring-shaped catalyst having an outer diameter of 5 mmφ, an inner diameter of 2 mmφ, and a height of 4 mm.
The reactor shown in FIG. 1 has a shell length of 3,500 mm, an inner diameter of 24 mmφ, and an outer diameter of 28 mmφ. Using. The reaction tube is not arranged in a circular part having a diameter of 500 mm at the center of the shell.
[0039]
The baffles are arranged at equal intervals in the order of 6a-6b-6a in the order of 6a-6b-6a, and the aperture ratio of each baffle is 18%. The diameter of the opening of the baffle plate 6a is 1,480 mmφ, and the outer diameter of the baffle plate 6b is 3,170 mmφ.
In FIG. 1, 1,534 reaction tubes 1a, 1,740 reaction tubes 1c, and a reaction tube 1b are provided inside the shell.
[0040]
A molten salt nitrate of a nitrate mixture was used as the heating medium Hm, and supplied from the lower side surface of the shell 2.
As the reaction temperature, the temperature of the night game supplied to the shell 2 measured by the thermometer 14 in FIG. 1 is used. The flow rate of the night game was adjusted so that the temperature difference between the outlet and the inlet of the shell 2 was 4 ° C.
Each reaction tube was charged with 1.5 L of the catalyst (A), and a raw material gas Rg having a propylene concentration of 9% by volume at a gauge pressure of 75 kPa was supplied from a lower portion of the reactor.
A thermometer 11 having 10 measurement points in the tube axis direction was inserted into the reaction tubes 1a, 1b, and 1c to measure the temperature distribution. Six thermometers were inserted in each of the two regions in the region of the reaction tube 1a, the region of 1b, and the region of 1c.
In order to accurately detect the maximum temperature of each reaction tube, the measurement points of the thermometer 11 were arranged at intervals of 250 mm from the inlet of the reaction tube to 1,500 mm, and at intervals of 400 mm thereafter. Using the thermometer 11, the maximum temperature of the reaction tube was recorded.
[0041]
When the temperature of the heating medium Hm was set to 331 ° C., the average value of the maximum temperature of each reaction tube was 410 ° C. for the reaction tube 1a, 390 ° C. for the reaction tube 1b, and 390 ° C. for the reaction tube 1c. And in this case, the propylene conversion was 97% and the yield was 92%.
[0042]
Example 2
Using the same reactor as in Example 1, acrylic acid was produced by supplying a molecular oxygen-containing gas (oxygen concentration: 15% by volume) to the outlet gas of the reactor of Example 1 at a rate of 35% by volume to cause a reaction. .
Each reaction tube was filled with 1.2 L of the catalyst (B). The reaction was performed under the same conditions as in Example 1 except that the temperature of the heating medium Hm was adjusted to 275 ° C.
The average value of the maximum temperature of each reaction tube was 330 ° C. for the reaction tube 1a, 300 ° C. for the reaction tube 1b, and 300 ° C. for the reaction tube 1c. And in this case, the conversion of the reaction was 99%, and the yield was 90.5% calculated on the basis of propylene.
[0043]
Example 3
Using the same reactor as in Example 1, the catalyst (A) and a ring-shaped inert molded with an inert substance (alumina) were mixed at a ratio of 1: 1 and filled at a position of 1,500 mm from the inlet of the reaction tube. The remaining 1,800 mm reaction tube was filled with only the catalyst (A), and the remaining 200 mm was filled with aluminum balls having no activity in the reaction.
The reaction was carried out under the same conditions as in Example 1 except that the temperature of the heating medium Hm was adjusted to 335 ° C.
[0044]
The measurement point of the thermometer used for the measurement of the catalyst layer in the reaction tube was 15 points, and the measurement was performed at an interval of 200 mm.
When the temperature distribution of each catalyst layer was measured, the catalyst layer had two maximum temperatures.
When the first maximum temperature and the second maximum temperature are shown from the inlet of the reaction tube, the average value of the first maximum temperature is 393 ° C. and the second maximum temperature is 345 ° C. in the reaction tube 1a, respectively. The first maximum temperature was 370 ° C. and the second maximum temperature was 350 ° C. on average. Further, in the reaction tube 1c, the first maximum temperature was 365 ° C. and the second maximum temperature was 380 ° C. on average.
The temperature of the heating medium Hm was 4 ° C higher than when the catalyst was not diluted, but the maximum temperature of each of the catalyst layers was 10-20 ° C lower than that of the higher one, prolonging the catalyst life and stabilizing it. Driving was expected.
The total yield of acrolein and acrylic acid obtained from propylene was 92.5%.
[0045]
Comparative Example 1
Example 2 except that no thermometer was inserted into the reaction tubes 1a and 1c, and the same thermometer as that of Example 1 was inserted only into the reaction tube 1b connected to all the baffles and having good heat removal efficiency. The reaction was performed in the same manner as described above.
When the inlet temperature of the heating medium Hm was changed from 275 ° C. to 280 ° C. in order to make the conversion of acrolein from 99% to 99.5%, the maximum value of the temperature distribution of the catalyst layer in the reaction tube 1b was 310 ° C. became.
The reaction product gas was analyzed and the conversion of acrolein was measured. The conversion was found to be 97.9%. After that, when the operation was continued, the conversion rate gradually decreased. Therefore, when the inlet temperature of the heating medium Hm was further increased by 2 ° C. to 282 ° C., the conversion rate of acrolein was further decreased.
When the conversion of acrolein dropped to 95%, the reaction was stopped and the catalyst in the reaction tubes was inspected. No abnormality was found in the catalysts in the reaction tubes 1b and 1c. However, among the reaction tubes 1a, particularly, the catalyst in about 350 reaction tubes 1a disposed near the center of the reactor was remarkably deteriorated and deformed, and the catalytic activity was lost. It is believed that the catalyst was exposed to high temperatures of 400 ° C. or higher.
[0046]
【The invention's effect】
The present invention relates to a catalytic gas-phase acid oxidation method using a multitubular reactor.In the present invention, the internal temperature of a reaction tube filled with a catalyst contained in a shell of the reactor is measured. By controlling the temperature and flow rate of the heat medium introduced into the shell based on the temperature, when producing (meth) acrylic acid or the like from propylene or isobutylene, it is possible to prevent runaway reaction or early deterioration of the catalyst, For a high yield.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of one embodiment of a multitubular reactor used in a catalytic gas phase oxidation method.
FIG. 2 is a perspective view of one embodiment of a baffle provided inside a multitubular reactor.
FIG. 3 is a perspective view of another embodiment of a baffle plate provided in a multitubular reactor.
FIG. 4 is a view of the multitubular reactor of FIG. 1 as viewed from above.
FIG. 5 is a cross-sectional view of another embodiment of the multitubular reactor used in the catalytic gas phase oxidation method.
FIG. 6 is a partial cross-sectional view of an intermediate tube plate and a heat shield plate provided in the multi-tube reactor of FIG.
[Explanation of symbols]
1a, 1b, 1c ... reaction tubes,
2. Shell of multitubular reactor
5a, 5b ... tube sheet,
6a, 6b ... baffles,
9 ... intermediate tube sheet,
11: catalyst thermometer,
14, 15 ... thermometer of heat medium,
Hm: heat medium,
Rg: raw material gas,

Claims (8)

In a shell of a multitubular reactor, a multitubular reactor having a plurality of reaction tubes filled with a catalyst and a plurality of baffles for changing the flow direction of the heat medium introduced into the shell is provided. In a catalytic gas phase oxidation method in which a raw material gas is introduced into a reaction tube and oxidized, the temperature of a catalyst filled in a reaction tube not connected to at least one baffle plate is measured. Phase oxidation method. In a shell of a multitubular reactor, a multitubular reactor having a plurality of reaction tubes filled with a catalyst and a plurality of baffles for changing the flow direction of the heat medium introduced into the shell is provided. In a catalytic gas phase oxidation method in which a raw material gas is introduced into a reaction tube and oxidized, the temperature of a catalyst filled in a reaction tube not connected to at least one baffle plate and the reaction connected to all baffle plates A catalytic gas phase oxidation method comprising measuring a temperature of a catalyst filled in a tube. The catalytic vapor phase oxidation method according to any one of claims 1 to 2, wherein the temperature or the flow rate of the heating medium introduced into the shell is controlled based on the measured temperature of the catalyst. The catalytic gas phase oxidation method according to any one of claims 1 to 3, wherein the temperature of the catalyst is measured at 2 to 20 points in the axial direction of the reaction tube. The catalytic vapor phase oxidation method according to any one of claims 1 to 4, wherein the temperature of the catalyst is measured using a multipoint thermocouple. The catalytic vapor phase oxidation method according to any one of claims 1 to 5, wherein a flow direction of the raw material gas flowing in the reaction tube and a macroscopic flow direction of the heat medium flowing in the shell are the same. The catalytic vapor phase oxidation method according to any one of claims 1 to 6, wherein a plurality of catalyst layers having different activities are filled in the reaction tube. 8. The catalytic gas phase oxidation method according to claim 1, wherein the raw material gas contains propylene, isobutylene, or (meth) acrolein as a substance to be oxidized.

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