JPH0699336B2 - Method for producing methacrolein and / or methacrylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention uses t-butanol as a starting material to obtain methacrolein and / or methacrylic acid by gas phase catalytic oxidation in the presence of a catalyst. The present invention relates to a method for obtaining methacrylic acid by vapor-phase catalytic oxidation.

(Prior Art) A method of producing methacrolein or the like by a fixed bed catalytic oxidation reaction using isobutene or t-butanol as a raw material is already well known, and many excellent catalysts therefor have been proposed.

For example, JP-A-56-12331, JP-A-56-46832, and JP-A-60-16383.
0, 58-59934, 55-36000, and JP-B-59-35897.

The reaction of producing methacrolein from isobutene or the like is an exothermic reaction, and by-products such as carbon monoxide and carbon dioxide are produced to some extent even when the above catalyst is used.

Especially the heat of reaction of carbon monoxide and carbon dioxide is very large,
The overall oxidation reaction process involves a large amount of heat generation, and if this reaction heat is not effectively removed, the temperature of the catalyst bed will rise excessively (less than the normal optimum reaction temperature).
(10 to 100 ° C. or higher) leads to a decrease in the yield of methacrolein, which is the target product, and when the reaction temperature rises in this way, the amount of carbon monoxide and carbon dioxide by-products increases,
The reaction temperature rises more and more and the runaway reaction state is finally reached. Or even if it does not become a runaway reaction state,
If you operate at a higher temperature than the normal reaction temperature,
It will accelerate the deterioration of the catalyst and make it impossible to maintain a sufficient catalyst life. Therefore, in the catalytic oxidation reaction with large heat generation as described above, a multi-tube heat exchanger type reactor is adopted, the contact is filled in the tube, and the refrigerant body having a temperature lower than the reaction temperature is provided outside the reaction tube. It is widely practiced to effectively remove the heat of reaction by flowing.

The control of the oxidation reaction is usually performed by mainly controlling the temperature of the refrigerant body in this way, and the heat of reaction removed by the refrigerant body has a heat exchanger installed separately. Generally, it is effectively recovered and used by generating steam using this heat exchanger.

(Problems to be Solved by the Invention) According to the conventional method, the catalyst used in the oxidation reaction step can be used for both t-butanol and isobutene, and there is almost no difference in the reaction results such as conversion or selectivity. There is no. Also, some catalysts targeting only t-butanol have been reported, for example, JP-B-59-10332.

However, the catalysts targeted for t-butanol have low conversion or no description of reaction time data on catalyst life according to their reports. Therefore, there are many examples in which a catalyst that can be used as a raw material for the production of itacrolein is isobutene or t-butanol. However, most of the raw materials reported for these are isobutene and t-butanol. There are few reports about.

Comparing the case of using t-butanol as a raw material and the case of using isobutene as a raw material in the oxidation reaction step of methacrolein production, the supply methods are almost the same, and the fact that t-butanol is at room temperature and atmospheric pressure is specially considered. Since the state is a liquid state, when t-butanol is used as a raw material, it is only that a vaporizer for vaporizing is installed before supplying it to the oxidation reactor.

The t-butanol thus vaporized is mixed with oxygen or a gas containing oxygen and supplied to the oxidation reactor without any distinction from isobutene. Normally, even if the above-mentioned catalysts are used, the reaction raw material gas is heated to an appropriate temperature (the maximum temperature of the refrigerant body) in order to exert its performance at 250 ° C or higher, and most at 300 ° C or higher. A preheating layer for raising the temperature is provided in front of the catalyst bed of the reaction tube.

As the packing used in this preheating layer, normally, an inactive granular material is selected, and the charging length is changed to heat and raise the temperature of the raw material gas to an appropriate temperature (the preheating layer is heated). The length is determined by operating conditions such as the target temperature for raising the raw material gas, the space velocity with respect to the catalyst bed, and other pressures).

The inventors of the present invention have conducted research using t-butanol as a raw material. However, as in the case of using isobutene as a raw material, a particle pair (specific surface area) composed of, for example, α-alumina 96% -4% silica is used. (0.01 m ² / g or less) was filled in the preheating layer to study the oxidation reaction.

However, when comparing the case where t-butanol is used as the feedstock and the case where isobutene is used as the feedstock, in both cases, the same catalysts used in terms of performance prepared at the same time are used, and the feedstock gas is used under the same operating conditions. Although it was heated to the same temperature in the preheating layer and contacted with the catalyst bed, it was found that there is a difference in the catalyst life between the two.

(Means for Solving the Problems) The inventors of the present invention have conducted extensive studies as to which of the differences in the catalyst lifespan is caused, and as a result, t-butanol undergoes catalytic dehydration decomposition to give isobutene and water. We have found that the phenomenon of decomposition into a large amount is greatly related to the life of the catalyst. That is, if t-butanol is dehydrated and decomposed into isobutene and water in advance and supplied to the oxidation reactor, the yield of methacrolein and the like and the life of the catalyst are exactly the same as when isobutene is used as a raw material. When butanol was supplied to the oxidation reactor without being decomposed, a change in the catalytic activity with time was clearly observed, and it was found that the decrease in the activity was extremely fast. That is, it has been found that the catalyst life is longer when t-butanol is dehydrated and decomposed into isobutene and water and is supplied to the oxidation reaction catalyst than when t-butanol is supplied to the oxidation reaction catalyst without being decomposed. Has been completed.

That is, the present invention uses a fixed bed multitubular reactor to produce methacrolein and / or methacrylic acid by catalytically reacting t-butanol with oxygen or a gas containing oxygen in the presence of a catalyst. Before the t-butanol or the raw material mixed gas containing t-butanol to be introduced into the catalyst is brought into contact with the catalyst bed, t-butanol is dehydrated and decomposed into isobutene and water and then fed, and / or methacrolein and / or The present invention relates to a method for producing methacrylic acid.

Generally, the catalytic dehydration decomposition property of t-butanol is well known and becomes an endothermic reaction. However, in the production of methacrolein and the like, what influence of the endothermic decomposition property of t-butanol on the catalyst is affected. It is not well known whether to give methacrolein, etc.
-There are many reports that it is the same when using butanol as a raw material and isobutene as a raw material. However, there is no report on the life of catalysts.

That is, the present invention uses t-butanol as a starting material in a shell-and-tube heat exchanger type reactor to oxidize a gas containing oxygen in the presence of a catalyst to produce methacrolein, and mix the raw materials to be introduced into a catalyst bed. The present invention relates to a method for producing methacrolein or the like in which at least 50% or more of t-butanol in a gas is previously decomposed into isobutene and water and supplied.
The catalyst used in the present invention is not particularly limited, and the effect of the present invention can be expected with any catalyst,
The present invention is a Mo-Bi-Fe system, Mo-
It can be applied to Bi-Fe-Co / Ni-alkali metal system and Mo-P.-alkali metal system.

The t-butanol used in the reaction does not have to be highly pure, and may be one that is commercially available in general, and may contain a large amount of water.

The raw material mixed gas may contain a diluent gas in addition to t-butanol and oxygen, and nitrogen, carbon dioxide, water or the like is preferably used as the diluent gas. The temperature on the refrigerant side varies depending on the catalyst used, the space velocity, the raw material mixed gas composition, the reaction pressure, etc., but it varies depending on the raw material mixed gas composition, the reaction pressure, etc., but is usually 250 to 500 ° C.

In order to achieve the object of the present invention, t in the raw material mixed gas is
By the time the butanol is brought into contact with the catalyst bed, at least 50% or more thereof should be decomposed into isobutene and water and supplied, and the effect of the present invention is not affected by the method of dehydrating and decomposing t-butanol. Therefore, the method of dehydrating and decomposing t-butanol is not particularly limited, and it can be carried out by a liquid phase method, a gas phase method or the like without catalyst or in the presence of a catalyst having a dehydrating activity. An industrially preferable method is a method using a dehydration catalyst, and examples of the dehydration catalyst include, for example, Catalyst Society, Volume 8, Catalyst Course, Industrial Catalyst Reaction I (published by Kodansha 1985).
As shown on page 275 onwards, sulfuric acid, phosphoric acid, polyphosphoric acid, boric acid, sulfonic acid, silica, alumina, silica-
A large number of catalysts such as alumina, solid phosphoric acid, heteropolyacid, ion exchange resins, activated carbon and the like are known.

Further, the present inventors have found that the dehydration reaction proceeds well if the reaction conditions are selected even on silicon carbide, which is generally considered to be inactive, and some α-alumina, as shown in the Examples below. It is also possible to use these.

Also, there is no particular designation as to the location where t-butanol is decomposed (1) inside the oxidation reactor, a preheating layer until the raw material mixed gas comes into contact with the catalyst bed of the reaction tube, or (2) separately from the oxidation reactor. The t-butanol may be decomposed in the decomposer (tank) installed at.

The following are industrially possible examples: (1) Silica-alumina or silicon carbide is filled in the preheating layer, and 50% or more, preferably 70% or more, of t-butanol is dehydrated and decomposed in the preheating layer to oxidize and react. Method of supplying raw material mixed gas to the. (2) A t-butanol decomposer (tank) is installed separately from the oxidation reactor,
Using highly active granules (eg activated alumina), contact them at a relatively low temperature (100-250 ° C), dehydrate and decompose 50% or more, preferably 70% or more, and supply the raw material mixed gas to the oxidation reactor. Method. However, when the contact temperature is high, carbon monoxide, carbon dioxide, etc. are slightly generated, so it is preferable to select an appropriate decomposition temperature.

In this case, since t-butanol can be decomposed at a relatively low temperature, the thermal energy in the high temperature range of 250 ° C. or higher in the oxidation reactor is not consumed by the endothermic energy due to the decomposition of t-butanol, but is caused by the oxidation. Almost all exothermic energy can be the target of heat recovery, and it is possible to more effectively use high-temperature heat energy with high utilization from the oxidation reactor. (3) Furthermore, the mixed gas obtained by combining (1) and (2) and using t-butanol as a raw material is first decomposed to some extent in the t-butanol decomposer (tank) of (2), for example, 30% to 80%. %, Preferably 50 to 80% is decomposed in a t-butanol decomposer (tank) and supplied to the oxidation reactor, and undecomposed t-butanol is further preheated to reach the catalyst bed in the oxidation reactor. 70% or more, preferably 90% or more of dehydration decomposition and contact with the catalyst bed can be proposed.

(Example) Next, an example is given and it demonstrates concretely.

Example 1 and Comparative Example 1 Operation was carried out by the steps shown in FIG. Inner diameter 21 mm, length
A 2 m stainless steel reactor was filled with 360 ml of catalyst (composition Mo ₁₂ Bi ₁ Fe ₁ Co ₆ Cs _0.14 ) prepared according to JP-A-58-59934 (filling length 1.0 m), and a molten salt circumscribing the reaction tube. The bath was heated with a throw-in heater while stirring with a stirrer, and the temperature was controlled. The preheating layer in the reaction tube has a length of 80 cm and is made of inert alumina (α-alumina 96%, diameter 4 mmφ, reference example 1).
(See reference), and the temperature of the raw material mixed gas was sufficiently raised to the same temperature as the temperature of the molten salt bath.

On the other hand, as a raw material, 85.0 g / Hr of t-butanol (containing 12 wt% water) was passed through a vaporizer to be vaporized, and then air 246 Nl / Hr and nitrogen 116 Nl /
It was mixed with Hr and fed to the oxidation reactor. The pressure inside the reactor was adjusted by a valve so that the pressure was 0.5 kg / cm ² · G at the reaction gas outlet.

In Example 1, a granular material (diameter 4 mmφ, see Reference Example 7) consisting of 90% γ-alumina and 10% silica was placed in the mixer shown in FIG.
It was filled with 70 ml and controlled by an electric heater so as to keep it at 180 ° C.

Table 1 shows the reaction data from the start of operation to 700 hours, and Fig. 2 shows the temperature distribution of the catalyst bed. Further, as Comparative Example 1, a stainless steel Raschig ring (6 mm
170 ml of φ diameter × 6 mmL, refer to Reference Example 8) was filled and kept at 180 ° C. as in Example 1.

On the other hand, as the catalyst, the same catalyst as used in Example 1 was filled in the same 360 ml reaction tube, and the operation was performed under the same conditions as in Example 1 except for the above. Table 1 shows the reaction data from the start of operation to 700 hours, and Fig. 3 shows the temperature distribution of the catalyst bed. Second
Comparing FIG. 3 and FIG. 3, it can be seen that the maximum temperature of the catalyst bed tends to decrease with the reaction time, but the position of the catalyst bed showing the maximum temperature has moved backward in Comparative Example 1. . That is, it is considered that the maximum temperature position of Comparative Example 1 moved to the rear because the activity of the raw material gas inlet portion of the catalyst bed became low. Also, comparing the reaction data, it can be seen that the conversion of isobutene in Comparative Example 1 decreased with the reaction time under the same conditions, but no such tendency was observed in Example 1. .

Example 2, Comparative Example 2 Under the conditions of Comparative Example 1 described above, Table 2 shows reaction data after 2700 hours have passed from the start of operation, and FIG. 4 shows a temperature distribution diagram of the catalyst bed, and Comparative Example Set to 2. That is, the experiment of Comparative Example 2 is an experiment in which the experiment of Comparative Example 1 was further continued until the elapsed time of 2700 hours.

As compared with Comparative Example 1, it can be seen that the catalytic activity is further reduced, and the conversion of isobutene is low even though the bath temperature is high.

The reactor which had been operating in such a state was temporarily stopped, the stainless Raschig ring in the mixer in FIG. 1 was extracted, and the same γ-alumina 90 as used in Example 1 was used.
% And silica 10% (4 mmφ diameter, Reference Example 7
It is Example 2 in which 170 ml of the reference) was charged and the operation was further continued while maintaining the temperature at 180 ° C. Just before entering the reaction tube, a part of the raw material mixed gas was sampled and analyzed. As a result, t-butanol was dehydrated and decomposed into 98% isobutene. The reaction data and the temperature distribution diagram of the catalyst bed are the same as those in Comparative Example 2
The table is shown in FIG. As shown in Table 2, the conversion rate of isobutene was clearly increased and the catalytic activity was exhibited as if the catalytic activity had been activated, even though the reaction time from Comparative Example 2 to Example 2 had elapsed. Further, looking at the temperature distribution map of the catalyst bed, the maximum temperature position of the catalyst bed returned to the same position as in Example 1.

Reference Examples 1 to 8 Table 3 shows the results of experiments conducted on the decomposability of t-butanol by the granules used for the preheating layer for the reaction tube and the packing in the mixer in Examples and Comparative Examples.

In this experiment, the decomposition rate of t-butanol was determined by using the same apparatus as in FIG. 1 except that the length of the reaction tube was shortened to 80 cm and the composition of the raw material gas was made exactly the same as that of the example.

Granules composed of 90% γ-alumina and 10% silica used in Examples 1 and 2 (diameter 4 mmφ, specific surface area 650 m ²
/ g, Reference Examples 6 and 7) was confirmed to efficiently decompose t-butanol into isobutene under the conditions of Example 1 and Example 2. On the other hand, reference example α-alumina (purity 96%, diameter
4 mmφ, specific surface area 0.01 m ² / g) was used for the reaction tube heat layer portion of Comparative Examples 1 and 2 and Example 2, but only about 20% decomposes t-butanol, and t-butanol It was confirmed that the degradability was low.

(Effects of the Invention) Some of the above have been described, but the summary is as follows.

(1) Since t-butanol is dehydrated and decomposed in advance and brought into contact with an oxidation catalyst, the catalyst bed does not act on the dehydration decomposition of t-butanol, and all parts of the catalyst bed are involved in the original oxidation reaction for obtaining methacrolein and the like. Will be donated. Therefore, the same catalyst life and activity as when isobutene is used as a raw material can be obtained.

(2) Compared with the case where t-butanol is not decomposed and is contacted with the catalyst bed, the portion that is donated to the oxidation reaction is substantially longer, so that the apparent space velocity is the same,
When t-butanol is decomposed in advance, the substantial space velocity becomes smaller, which is a preferable reaction condition for the catalyst.

Generally, when the space velocity becomes large, it is necessary to raise the reaction temperature in order to obtain the same conversion rate, which in turn accelerates the deterioration of the catalyst and shortens its life.

(3) The energy required for the dehydration decomposition of t-butanol is the same regardless of where t-butanol is decomposed.
If a highly active granular material such as γ-alumina is used, it can be decomposed at a relatively low temperature (150 to 250 ° C) and does not require a high temperature (250 to 500 ° C) like the refrigerant body of a reactor. .
Therefore, by decomposing outside the oxidation reactor, t-
The energy source required for the decomposition of butanol can be relatively easily obtained, for example, steam of about 10 kg / cm ² G can be used as the heat source. And the heat of the oxidation reaction can be effectively recovered without offsetting the energy of high temperature (250 to 500 ° C), which is highly utilized in the oxidation reactor, by the decomposition energy of t-butanol, and the effective use of the heat energy can be achieved. You can

[Brief description of drawings]

FIG. 1 is a flow sheet showing an example of an embodiment of the present invention. 2 ... Raw material gas mixer 3 ... Reaction tube FIGS. 2 and 3 show the temperature distribution of the catalyst bed in Example 1 and Comparative Example 1. FIG. 4 shows the temperature distribution of the catalyst bed in Example 2 and Comparative Example 2.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display area C07C 57/05

Claims (1)

[Claims] 1. A catalyst bed for producing methacrolein and / or methacrylic acid by catalytically reacting t-butanol with oxygen or a gas containing oxygen in the presence of a catalyst using a fixed bed multitubular reactor. Methacrolein and / or methacryl- yl, which is characterized in that, before the t-butanol or the raw material mixed gas containing t-butanol to be introduced is brought into contact with the catalyst bed, t-butanol is dehydrated and decomposed into isobutene and water in advance. Method for producing acid.