JPS6029290B2 - Catalytic vapor phase oxidation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a catalytic gas phase oxidation reaction carried out using a fixed bed multi-tubular heat exchange reactor.

To be more specific, the present invention provides a method for maintaining a catalyst used in an exothermic catalytic gas phase oxidation reaction under its optimum reaction conditions and suppressing the occurrence of hot spots (abnormally high temperatures locally in the catalyst layer). The structure of a tubular heat exchange reactor and its use are provided. <Subsequent technology> Since catalytic gas phase oxidation reactions are generally very exothermic, it is extremely important to control the reaction temperature within a certain range and to prevent hot spots from occurring within the reaction zone. This is said to be the area that requires the most effort from engineers in this technical field.

In particular, when naphthalene or ortho-xylene is oxidized to produce phthalic anhydride, when benzene, butylene or butadiene is oxidized to produce maleic anhydride, when propylene is oxidized to produce acrolein or acrylic acid, or when propylene is oxidized to produce acrolein or acrylic acid, When the oxidation reaction must be converted into the target product through sequential reactions, as in the case of producing acrylonitrile by ammoxidation of Circulation alone is never sufficient, and eventually hot spots develop, causing excessive oxidation reactions to occur in some areas.
As a result, undesirable combustion reactions increase, leading to a decrease in the yield of the desired product. Additionally, the catalyst is constantly exposed to high temperatures due to the presence of hot spots;
The life of the catalyst will be shortened, resulting in disadvantages. In order to prevent these disadvantages, various measures have been taken in such gas phase oxidation. The most common method is to reduce the diameter of the catalyst-filled tube in order to increase the amount of heat removed per unit catalyst. However, if this method is used to carry out the reaction, the number of tubes to be filled will be excessively large, the cost of manufacturing the reactor will increase, and the time and effort required to fill and extract the catalyst will be disadvantageous. Other effective methods include diluting the catalyst layer with an inert substance, and
As described in the specification of Japanese Patent No. 5485, in all or part of the length of the reaction tube filled with a catalyst, a sealed hollow material is placed in the center of the cross section of the tube so that no catalyst is present. , and a space through which the reaction mixture does not pass is provided to suppress hot spots.

These methods have the disadvantage that they are expensive due to the inclusion of substantially inert substances.

At the same time, there is also the drawback that it takes time and effort to recover effective metal components from the catalyst that has been extracted after the activity of the catalyst has deteriorated. Another effective method is
There is a method of suppressing hot spot temperatures from increasing by gradually increasing the activity of the catalyst from the inlet to the outlet of the reactant gas. However, this method not only requires the production of at least two types of catalysts with different activities, it is not possible to select the optimal reaction temperature for the catalyst packed in each layer, and furthermore, the activity changes over time. When the degree of each change is different, it becomes more difficult to maintain optimal reaction temperature control.
The overall yield of the target substance is undeniably reduced.

On the other hand, reactors with various improvements have been proposed.

For example, in the specification of JP-A-48-80473,
A technique has been described in which a regulator is provided in the hot soot circulation mechanism to change the reaction temperature setting according to the reaction process to obtain a high yield, but in the reactor disclosed herein, It is almost impossible to obtain more than two temperature ranges. Further, in US Pat. No. 3,147,084 and West German Published Patent Application No. 2,513,405, the shell side of a multi-tubular heat exchange reactor is completely separated by a shielding plate.
A method for catalytic oxidation of hydrocarbons is disclosed using a reactor which is divided into two spaces and hot soot at different temperatures is circulated through each space.

In this reactor, each reaction tube and shielding plate are completely fixed by welding, so they are strongly affected by distortion due to thermal expansion, and depending on the usage conditions, the reaction tube or shielding plate may deform or come off. There are concerns. Furthermore, the flow of heat medium may cause vibration and corrosion, potentially causing serious damage. Furthermore, this reactor is expensive to manufacture and has difficult manufacturing techniques. That is,
In a catalytic gas phase oxidation reaction, the amount of heat removed is taken into consideration and the diameter of each reaction tube cannot be made large, so a single reactor often contains several thousand reaction tubes. This is because each reaction tube and shielding plate must be fixed by welding, or if welding is not used, it is necessary to make a hole in the shielding plate with a diameter equivalent to the outer diameter of the reaction tube. However, this is considered to be technically difficult. <Problems to be Solved by the Invention> Therefore, the present invention provides a method for maintaining a catalyst used in an exothermic catalytic gas phase oxidation reaction under its optimum reaction conditions, thereby suppressing the occurrence of hot spots. Provided is a structure of a multi-tubular heat exchange reactor that not only has a simple structure, can simplify the manufacturing process, and has the advantage of low manufacturing cost, but also has a configuration in which almost no thermal distortion occurs, and its usage. The purpose is to

<Means for Solving the Problems> In order to achieve the above object, the present inventors have completed various studies and have completed the present invention.

That is, the present inventors have discovered that when carrying out an exothermic catalytic gas phase oxidation reaction using a fixed bed multi-tubular heat exchange reactor, the reactor is equipped with one or more shielding plates on the shell side. divided into two or more spaces in the length direction of the reaction tube,
Hot soot is filled in each section, and if desired, each section is provided with a heat medium circulation mechanism, respectively, and each reaction tube passing through the shielding plate does not come into direct contact with the shielding plate. A reaction tube is used in which the distance between the outer wall of the reaction tube and the shielding plate is maintained at 0.2 to 5 ribs, the inside of the reaction tube is filled with one or more oxidation catalysts, and We have discovered a catalytic vapor phase oxidation method characterized in that the temperature of hot soot in sections separated by shielding plates is adjusted so that the temperature difference is within the range of 0 to 10 degrees Celsius. did. Furthermore, the present inventors have discovered that when performing a soot-attached gas phase oxidation reaction accompanied by heat generation using a fixed bed multi-tubular heat exchange reactor, the reactor is equipped with one or more shielding plates on the shell side. The reaction tube is divided into two or more in the length direction, and if desired, each divided section is filled with a heating medium and each section is provided with a heating medium circulation mechanism. Each reaction tube that penetrates the shielding plate does not come into direct contact with the shielding plate, and the reaction tube is provided with a donut-shaped fin having an outer diameter large enough to cover the gap between the reaction tube and the shielding plate that the reaction tube penetrates. The distance between the fins and the shielding plate is maintained at 0.2 to 5 cm, and the reactor reaction tube is filled with one or more oxidation catalysts. We have discovered a catalytic vapor phase oxidation method characterized in that the temperature of hot soot in sections separated by shielding plates is adjusted so that the temperature difference between the sections is within the range of 0 to 100 degrees Celsius. It is.

Hereinafter, the reactor used to carry out the present invention will be explained with reference to the drawings.

FIG. 1 is an example of a reactor according to the present invention, and shows a longitudinal sectional view of a reactor 1 having two temperature regions A and B. FIG.

The container is loaded with a bundle of reaction tubes 4, each of which is fixed at its upper and lower ends to tube plates 7 and 7' by tube expansion, welding, or the like. The reaction tube may be filled with a catalyst depending on the purpose of the reaction, and when the catalyst is filled, a wire mesh or a receiver 14 is installed at the bottom of the reaction tube to prevent it from falling. The reaction raw material passes through the introduction tube 2, enters the front cap 3, enters the reaction tube east 4, is subjected to reaction and is converted into the target product, passes through the rear cap 5 to the outlet 6, and is collected, purified, and recovered. sent to the process. In addition, in this reaction step, the reaction raw materials may be introduced from 6 and transported out through 1. East outside of the reaction tube of the reactor (shell side) 13
A heat exchange medium is supplied to keep the reaction temperature in the reaction tube constant during the reaction process.
1 and 11' through known annular conduits 9A and 9B, respectively, and subjected to heat exchange action and discharged from 12 and 12' through known annular conduits 9A' and 9B'. , and are cooled (or heated) by heat exchangers 15 and 15' (or heating devices 15 and 15') and provided for circulation. Of course, the method of circulating the heat medium is not limited to the method described above.

For example, if the temperature difference between A and B is very large, the heat medium should be circulated, for example, if it is introduced from 11 in area A, it is introduced from 12' in area B, and the heat medium is introduced from 12' in area B, By making the flow in the same direction, it becomes easier to maintain and control the reaction temperature. In addition, in order to more easily control the temperature in the temperature range, it is also possible to provide a flow rate adjustment mechanism for each circulation mechanism, and to adjust the amount of heat generated in both areas A and B and the heat between A and B in advance. the amount of movement of the medium, and 16
, 16' if the amount of heat medium circulated in the heat medium circulation device is known, the hot soot cooling (or heating) of 15 or 15'
It is also possible to promote or omit either one of the mechanisms. or,
If temperature control in both areas A and B is to be performed more strictly, it is also possible to use one or more shielding plates.

In addition, if the reactor has a large diameter or is equipped with a large number of reaction tubes, change the flow path of hot soot from the direction change plate 1.
It is recommended to further enhance the heat exchange effect.

Reference numeral 8 in FIG. 1 is a shield plate for separating two reaction temperature regions.

This shielding plate 8 is shown in FIG. 2 to show it in more detail.
FIG. 2 represents a section of the reactor in cross section at the location of the shielding plate. 4 is a reaction tube, 8 is a shielding plate, and 4 and 8 are
A distance of 0.2 to 5 fences is maintained to allow the movement of hot soot.

This spacing is important, and if there is no such spacing and the reaction tube 4 and the shielding plate 8 are close to each other or stuck together, there will be a temperature difference between areas A and B, and heating and cooling will occur frequently in the reactor. In such a case, thermal distortion may occur in the reaction tube or the shielding plate, or the reaction tube and the shielding plate may come into contact with each other, causing wear.

Moreover, manufacturing the reactor requires time and expense, which is not a good idea. On the other hand, if the interval is too large, the amount of hot soot transferred between A and B increases, making temperature control difficult. According to the findings of the present inventors, in order to achieve satisfactory temperature control with almost no movement of hot soot, the distance between the reaction tube wall and the shielding plate should be 0.2 to 5, preferably 0. .3-1. It is necessary to take revenge.

FIG. 3 shows a portion of a longitudinal cross-sectional view of the reactor at the position of the shielding plate in the case where the movement of hot soot is almost prevented by fins fixed to the reaction tube.

4 is a reaction tube, 8 is a shielding plate, and the distance between 4 and 8 is designed to maintain a distance of 0.2 to 15 to allow movement of hot soot.

The existence of this gap is important, and without this gap the reaction tube 4
If the and shielding plate 8 are close to each other or stuck together, A,
If there is a temperature difference in region B or if heating and cooling are frequently performed in the reactor, thermal distortion may occur in the reaction tube or shielding plate, or contact between the reaction tube and the shielding plate may cause wear. do not have.

Moreover, it takes time and effort to manufacture the reactor, which is not a good idea. However, it is unnecessary and not advisable to make this interval particularly large. Since the distance between the reaction tubes is 6 to 3 meters in a normal multi-tube reactor, the distance between the shielding plate and the reaction tubes is naturally limited. As clearly shown in FIG. 3, the fins extend over the space and are fixed to the reaction tube.

The distance between the fin and the shielding plate is 0.2 to 5, preferably 0.
．． The temperature is adjusted to 3 to 1 soot, so that almost no movement occurs during the hot soot circulation, and the temperature in each reaction temperature range can be satisfactorily controlled. The fins may be installed parallel to the shielding plate, or may be installed so that the green tips of the fins are at close distance to the shielding plate, as shown in FIG. Of course, the fins may be attached to either the upper or lower sides of the shielding plate, or they may be attached alternately to the upper and lower sides as shown in FIG. Of course, the spacing of 0.2 to 5 bars, preferably 0.3 to 5 bars, as described above will be influenced to some extent by the hot soot used.

When using a highly viscous molten salt (mainly a mixture of potassium nitrate and sodium nitrite),
The reaction temperature is high, and even if the spacing is somewhat wide, the amount of heat transfer medium that moves between them can be small. However, when using a phenyl ether type (such as "Dowsome") hot wire, it is preferable to keep the spacing somewhat narrower than in molten salts, even for low-temperature reactions. In addition to the above two types, examples of the heat medium that can be used in the present invention include steam, hot oil, naphthalene derivatives (SK oil), mercury, and the like.

Thus, catalytic gas phase oxidation reactions can be carried out very easily using the reactor defined by the present invention.

As already mentioned, the reactor specified in the present invention is
Most suitable for carrying out sequential oxidation reactions,
According to the findings of the present inventors, the hot soot temperature in each section is at most 1
It has been found that it is possible to create a temperature difference of 00 qo. Therefore, the reactions to which the reactor of the present invention is applied and the specific implementation thereof will be explained below. First, when producing phthalic anhydride from ortho-xylene or naphthalene, for example, if two reaction temperature zones A and B as shown in Figure 1 are used, the first stage
00 to 4000C, 350 to 45000C in the latter stage, and 30 to 600C if the catalyst has a single composition.
A temperature difference of . Also, when producing maleic anhydride,
When two reaction temperature zones A and B are adopted, 3 in the first stage
A temperature of 20 to 400° C. is employed in the latter stage, and a temperature of 350 to 450° C. is employed in the latter stage, and good results are obtained by maintaining the temperature difference between 20 and 50° C., which can also be easily satisfied. Of course, the method of the present invention can also be carried out with good results using two or more catalysts of different compositions.

Furthermore, it is possible to carry out the reaction at a reaction temperature that meets the performance of each catalyst. And what is even more distinctive is that
It has been found that the method of the present invention can also perform catalytic gas phase oxidation reactions in which the reaction temperatures in each reaction zone differ by 50 to 100°C, such as acrolein from propylene and acrylic acid by further oxidizing acrolein. .

Next, the method of the present invention will be explained in more detail based on Examples. Example 1 Since the length is 4, the inner diameter is 25.0 and the outer diameter is 29.0. In a vertical multitubular reactor with 24 reaction tubes made of mountain steel, the shielding plate is located at the middle height, and the distance between the reaction tubes penetrating the shielding plate and the shielding plate is approximately 0.6. Phthalic anhydride was synthesized by catalytic gas phase oxidation of ortho-xylene with air using a regulated reactor as shown in FIG.

The catalyst used for this oxidation was prepared according to Example 1 described in Japanese Patent Publication No. 49-41271, and the composition ratio of the catalyst components was V24:Ti02 = 2.1:97.9 weight ratio. P2050 for the total of V2Q, Ti02.
49% by weight, K200.146% by weight, Nb2050.
It contained 244% by weight and 2030.04% by weight of Gd.

When the pore distribution of this catalyst was measured using a mercury intrusion porosimeter, it was found that the pore volume occupied by 0.05 to 0.45 pores was 88% of the total pore volume of 10 or less. Each reaction tube was filled with 1500 cc of the catalyst thus obtained, so that the layer length was 3.

Then, one part of the total length of the packed layer is in the temperature range of the previous stage A.
The enemy was made to be in the temperature range of the second stage B. At the initial stage of the reaction, the temperature range of A and B of the molten salt temperature on the reactor shell side were kept at 355G0 and 37500, respectively, and the space velocity (S.V) was set at a concentration of 20 hours - air/orthoxylene at a space velocity (S.V) of 4000 hours. -1 (NTP) to start the reaction. Thereafter, the reaction was continued for one year while controlling the temperature in both temperature ranges A and B so as to obtain the optimum phthalic anhydride yield. The results are shown in Table-1. The yield of phthalic anhydride in the table is the weight percent based on the supplied ortho-xylene. Gas concentration (G.C) represents Z-air-terortho-xylene. Table 1 Comparative Example 1 The same catalyst as used in Example 1 was used, no shielding plate was installed, and the temperature range was one.
Using a reactor of the same scale as in Example 1, the reaction was continued for 12 months under the reaction conditions shown in Table 2.

The results are shown in Table-2. Table 2 Example 2 Using the same catalyst and reactor as used in Example 1, the reaction was carried out for 12 months under the reaction conditions shown in Table 3, with the gas concentration raised to 16 minutes - air/t-ortho-xylene. went.

The results are shown in Table-3. Table 13 Comparative Example 2 In Comparative Example 1, the gas concentration was increased to 16 minutes - air/t-ortho-xylene, and the reaction was continued for 3 months under the reaction conditions shown in Table 4.

The results are shown in Table 4. Table 4 Example 3 Phthalic anhydride was produced according to the method of Example 1 using two types of catalysts.

The catalyst was Example 1 described in JP-A-51-43732.
Prepared according to. That is, the composition ratio of the catalytically active material as the front catalyst is V2Q:Tj02:Nb203:P2
05:K20:Na20=2:Group:0.25:1.02
:0.15:0.1 (weight ratio) was obtained.

When this catalyst was subjected to a mercury intrusion porosimeter to measure the pore distribution, it was found that the volume of pores with 0.15 to 0.45 pores was 88% of the total pore volume with 10 or less pores.
Below, this means that 88% of the pongee hole volume is between 0.15 and 0.45 mm.
This is abbreviated as ``.This is the first-stage catalyst.Next, as the second-stage catalyst, the composition ratio of the catalytically active material is V2Q:Tj02:
Nb24:P205:K20:Na20=2:Satoshi:0.
25:1.3:0.15:0.1 (weight ratio), 0
．． A catalyst having a pongee hole volume of 87% between 15 and 0.45 French was obtained.

The thus obtained catalyst was placed in a reaction tube of a reactor similar to that used in Example 1, with 1.5 liters of the latter stage catalyst in the temperature region B, and then 1.5 liters of the former stage catalyst in the temperature region A. 5 skin was filled and a reaction was performed.

The reaction conditions and reaction results are shown in Table-5. Table 5 Example 4 Maleic anhydride was synthesized from benzene using the same reactor as in Example 1.

The catalyst used in this oxidation was prepared according to Example 1 of JP-A-51-64487. The catalyst material composition ratio of the completed catalyst obtained is V2Q:Moo3:P20
5:Na20=1:0.40:0.015:0.06(
The total apparent porosity was %, the surface area was approximately 0.05 molar ratio, and 95% of the pore volume occupied by pores with a diameter of 100 or less was composed of string pores with a diameter of 10 or more. .

The thus obtained catalyst was used at a rate of 1,500 ml per reaction tube.
cc filling, and the layer length was set to 3. At the beginning of the reaction, the temperature range of A is 5℃, and the temperature range of B is 37℃.
Benzene was added to S.C. at a concentration of 22 soybean/terbenzene, each maintained at 0.degree. V. A 250-dish r-1 (NTP) reaction was initiated. After that, the temperature in both zones A and B is controlled to obtain the optimum yield of maleic acid.
The reaction continued for several months. The results are shown in Table-6. Table 6 Comparative Example 3 Using the same catalyst as used in Example 4, using a reactor of the same scale as Example 4, without a shielding plate, with a single temperature range. The reaction was then continued under the reaction conditions shown in Table 7.

The results are shown in Table-7. Table 7 Example 5 In the same reactor as in Example 1 except that the length of one reaction tube was 6.

Acrylic acid was synthesized by oxidation of pyrene. The catalysts used for this oxidation were the catalyst of Example 1 of Japanese Patent Publication No. 47-42813 (first stage catalyst) as a catalyst for mainly producing acrolein from propylene, and the catalyst for producing acrylic acid by oxidizing acrolein. The catalyst (second stage catalyst) of Example 1 of Hakamako Sho 49-11371 was prepared. That is, as for the first-stage catalyst, the composition of the catalyst excluding oxygen is C in atomic ratio. 4FeIBiIW2M
.

10Sil. 35 pretend 6F.

The oxidation catalyst is the core B, and as the latter stage catalyst, the metal composition of the catalyst is M.

12V4.6C ratio. Both 2Cr and 6W2.4 oxidation catalysts were used, respectively.

Among these catalysts, first, the latter stage catalyst was used per reaction tube,
1250 cc was filled in a temperature range of B, and the bed height was set to 2.5.

On top of it, 250 cc of spherical alundum with five legs was filled for cooling the reaction gas so that its upper end was on the same plane as the shielding plate. Furthermore, on top of that, 1000c of catalyst for the front stage
c was filled so that the length of the full trunk layer was 2 skins. Reaction composition gas: propylene 6.0% by volume, oxygen 12%
．． Cough volume %, as water vapor 10. A mixed gas having a composition of % cough volume and an inert gas with the remainder being mainly nitrogen is supplied to the pre-catalyst by S.I. V. Provided by 160 other r-1 (NTP)
In the early stage of the reaction, the temperature range of A is 310 pm,
The reaction was started while keeping the temperature range of B at 240:00. Thereafter, the reaction was continued for 12 months while controlling the temperatures in both temperature ranges A and B so as to obtain the optimum yield of acrylic acid. The results are shown in Table-8. Table 8 Example 6 In Example 5, the reactor was configured such that the distance between the outer wall of the reaction tube and the shielding plate was adjusted to approximately 0.6 cm, but the heat medium temperature in area A at this time was 310 qo. Yes, the heating medium temperature in area B at a distance of 250 willows below the shielding plate 8 is 240
Met.

However, when the distance between the outer wall of the reaction tube and the shielding plate is adjusted to 6 degrees, the distance at which the hot soot temperature in area B reaches 240°C under the same conditions is 100 degrees, and the hot soot temperature in areas A and B is It was difficult to control.

<Effects> As is clear from the above explanation, the reactor provided by the method of the present invention as described above not only has the advantage that the foundation is easy to construct, the manufacturing process can be simplified, and the manufacturing cost is low. It has the characteristics that the temperature of hot soot can be easily controlled and that almost no thermal distortion occurs.

By using this reactor, it is possible to carry out the catalytic gas phase oxidation reaction by adjusting the hot soot temperature in the catalyst layer part where the most heat is generated to be lower than the hot soot temperature in other parts, and hot spots. This makes it possible to control the reaction temperature so that the conversion of the raw material to be oxidized in the next step reaches substantially 100%, and the catalyst can be used most effectively. In particular, when using the above reactor for saddle-colored gas phase reactions in which reactions proceed sequentially, wasteful combustion due to over-propagating reactions at hot spots can be suppressed and the yield of the desired product can be increased. Not only has it become possible, but it has also become possible to increase the concentration of the raw material compared to conventional catalytic gas phase oxidation.

In addition, when the reaction proceeds sequentially, at each stage,
Reactions that conventionally required two reactors due to different catalysts and different reaction temperatures can now be carried out in one reactor using the method of the present invention.

A further advantage of the present invention is that it has become possible to surprisingly extend the life of the catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a longitudinal section through a reactor for carrying out the reaction of the invention.

FIG. 2 shows a section of a cross-sectional view of the reactor in the plane of the shield. Figure 3 is a longitudinal sectional view of a reaction tube with fins attached at the position of the shielding plate, Figure 4 is a longitudinal sectional view showing another example of a reaction tube with fins attached, and Figure 5 is a longitudinal sectional view of a reaction tube with fins attached at the top and bottom of the reaction tube. An example is shown in which they are attached alternately. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. When carrying out an exothermic catalytic gas phase oxidation reaction using a fixed bed multi-tubular heat exchange reactor, the reactor includes:
The shell side is divided into two or more spaces in the length direction of the reaction tube by one or more shielding plates, each section is filled with a heating medium, and if desired, a heating medium circulation mechanism is installed in each section. Each reaction tube passing through the shielding plate does not come into direct contact with the shielding plate, and the distance between the outer wall of the reaction tube and the shielding plate is 0.2 to 0.2.
5 mm, the reactor reaction tube is filled with one or more oxidation catalysts, and the heating medium temperature in the sections separated by shielding plates is
A catalytic gas phase oxidation method characterized in that the temperature difference is adjusted to be within the range of 0 to 100°C. 2. When carrying out an exothermic catalytic gas phase oxidation reaction using a fixed bed multi-tubular heat exchange reactor, the shell side of the reactor is covered with one or more shielding plates in the length direction of the reaction tube. The reaction tube is divided into two or more sections, each section is filled with a heating medium as desired, and each section is provided with a heating medium circulation mechanism, and each reaction tube passing through the shielding plate is shielded. A donut-shaped fin is fixed to the reaction tube and has an outer diameter large enough to cover the gap between the reaction tube and the shielding plate through which the reaction tube passes without directly contacting the plate, and the fin and the shielding plate are fixed to each other. The reactor reaction tube is filled with one or more oxidation catalysts and separated by a shielding plate. A catalytic gas phase oxidation method characterized in that the temperature of the heating medium in each section is adjusted so that the temperature difference is within the range of 0 to 100°C.