JPH0757741B2 - Method for producing methacrylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing methacrylic acid by catalytically oxidizing in the gas phase using isobutylene and / or tertiary butanol as a raw material. Especially with pre-stage oxidation to obtain methacrolein,
The present invention relates to a method for producing methacrylic acid through a two-step oxidation consisting of a latter-stage oxidation for obtaining methacrylic acid from methacrolein.

[Conventional technology and problems]

When isobutylene and / or tertiary butanol or the like is used as a raw material to produce methacrylic acid by catalytic oxidation in the gas phase,
There is a method of converting methacrylic acid at once by one-step oxidation, and a two-step oxidation method of once converting methacrolein to methacrylic acid. Among them, the one-step oxidation is difficult in terms of reaction results, and the two-step oxidation is industrially adopted at present. (Chemical engineering VOL47, NO.6,1983, PETROTECH VOL6, NO.9,1983) As a method of this oxidation, there are a two-step direct coupling reaction method and a single reaction method. The former directly supplies the former-stage product gas to the latter-stage reactor for reaction, and the latter separates and recovers methacrolein from the former-stage product gas, and supplies this methacrolein as a new raw material gas for the latter-stage reaction. Methacrylic acid is used, and two-step reactions are performed independently.

There are some drawbacks to such a two-stage oxidation method.

(A) The differential pressure of the reactor is increased, which hinders long-term continuous operation.

(B) An increase in differential pressure causes an increase in power consumption of the compressor.

(C) The increase in pressure promotes the decomposition reaction in the catalyst layer.

(D) If the retention area between the first and second stages is large, the methacrolein produced is autoxidized and decomposed.

The present invention provides a method for producing methacrylic acid which can solve the above problems, namely, increase in power of a compressor due to increase in differential pressure, promotion of decomposition reaction in a catalyst layer, and further decrease in working efficiency. To do.

[Means for solving problems]

As a result of various studies on the flow direction of the supply gas in the two-stage oxidation reaction system, the inventors have found that the above-mentioned obstacle is caused by the flow of the raw material, and the former stage is from the upper side to the lower stage, and the latter stage is the lower stage. The present invention has been completed by finding that the obstacle can be avoided by flowing a gas involved in the reaction from the lower side to the upper side.

That is, in the present invention, by reacting molecular oxygen with isobutylene and / or tertiary butanol in the presence of an inert gas and a catalyst, pre-stage oxidation to obtain methacrolein and the methacrolein in the presence of a catalyst are obtained. In the method for producing methacrylic acid from isobutylene and / or tertiary butanol, which is subjected to a two-stage oxidation consisting of a latter-stage oxidation to react with a gas containing oxygen to obtain methacrylic acid, the former-stage oxidation is performed from the upper side to the lower side of the reactor catalyst layer. After passing through the reaction, the post-reaction supplement gas is mixed as a cooling gas with the pre-reactor catalyst layer outlet gas just after the pre-reactor catalyst layer outlet, and the mixed post-reacting raw material gas is passed through from below the post-reactor catalyst layer to above. It is a method for producing methacrylic acid, which is characterized in that

According to the present invention, in addition to the increase in the differential pressure in the former stage and the defects associated therewith, it is possible to prevent disadvantages such as a decrease in work efficiency in the latter stage.

In the two-stage oxidation method, in order to control the flow direction of the gas to be supplied, in addition to the present invention, (1) a method in which both the upstream and downstream stages flow from the upper side to the lower side. (2) A method of flowing from the lower side to the upper side in both the front and rear stages is known. As an example of (1), JP-A-53-5361
3, JP-A-56-92831, JP-A-57-144237 and JP-A-59-11873. As an example of (2), PERP REPORT No.86-1,1987, CHE
There is M SYSTEMS INC. In the former case, the carbide of the polymerization inhibitor added to maintain the stability of methacrolein supplied in the latter stage gradually accumulates in the upper part of the catalyst layer, and / or the high boiling point substance or polymer generated in the first stage Deposition causes the above-mentioned defects (a), (b), and (c), which is not preferable. In the latter case, since the connecting pipe from the former stage to the latter stage is inevitably long, the above-mentioned defect (d) occurs. In order to avoid this, there is also a method of directly connecting a heat exchanger to the outlet of the reaction zone and quenching the produced gas, but this causes an obstacle at the time of filling the catalyst and significantly lowers the work efficiency. There is also a method of removing this, but in the case of a large-scale facility, the work is difficult, which is not preferable. On the other hand, the method of flowing the raw material gas from the lower side of the front stage and from the upper side of the rear stage can shorten the connecting pipe, but is not preferable for the same reason as in the example of (2).

The isobutylene and / or the tertiary butanol involved in the pre-stage oxidation of the present invention includes molecular oxygen, and usually other than nitrogen, carbon dioxide, etc., and the exhaust gas after separating the condensed components from the post-stage oxidation product is sufficiently preliminarily sufficient. After being mixed, this mixed gas state is supplied to the oxidation reactor at the preceding stage from above. In this case, the molar ratio of molecular oxygen to isobutylene and / or tertiary butanol is preferably in the range of 0.5 to 20, particularly preferably in the range of 1 to 10. The feed gas is mixed with an inert gas such as carbon dioxide or nitrogen for dilution in order to avoid an explosion range or suppress an abnormal rise in the catalyst layer temperature. The molar ratio with respect to the grade butanol is preferably in the range of 10 to 30. Further, in order to make the reaction proceed smoothly, it is preferable to add water in the form of water vapor in the form of water vapor in the range of 1 to 20 with respect to isobutylene and / or tertiary butanol.

The reaction temperature in the first stage is preferably 250 to 400 ° C. The amount of raw material gas supplied is 100 to 6000 / hr based on NTP with respect to space velocity (SV)
Is preferable, and more preferably 400 to 3000 / hr. or,
The reaction pressure is not particularly limited, but a pressure around atmospheric pressure is generally suitable.

The methacrolein involved in the subsequent post-stage oxidation is molecular oxygen,
The recovered methacrolein and the inert gas for dilution (these are referred to as the supplementary gas for the post-reaction) are mixed as a gas for cooling the pre-produced gas and supplied to the post-reactor from the lower part thereof. In this case, molecular oxygen is preferably used in a molar ratio of 0.5 to 20 with respect to methacrolein, and particularly preferably in a range of 1 to 10. The inert gas preferably has a molar ratio of 10 to 30 with respect to methacrolein.
Furthermore, water in the form of steam is used in a molar ratio of 1 to methacrolein.
It is preferable to add in the range of -20.

The reaction temperature in the latter stage is preferably 200 to 400 ° C. The raw material gas supply rate is preferably 100 to 5000 / hr, and more preferably 400 to 3000 / hr based on NTP in terms of space velocity (SV). The reaction pressure may be increased or decreased, but a pressure around atmospheric pressure is generally suitable.

〔The invention's effect〕

As described above, in the two-stage oxidation reaction, the raw gas is made to flow from the upper side to the lower side, so that the outlet of the produced gas is naturally the lower side of the catalyst packed bed, and therefore the heat exchanger for quenching and / or the quenching is performed. Even if the gas dispersion nozzle is installed, it does not hinder the work of filling the catalyst. Particularly in the case of the present invention,
Since the supplementary gas for the second-stage reaction is mixed as the quenching gas without previously cooling the first-stage generation, the connecting flange between the reactor and the heat exchanger is not required, and the manufacturing cost of the reactor is low. In the industrial equipment for carrying out the present invention, the size of the reactor is as large as 5 to 6 m in diameter due to its economic scale, so that the economical effect is large. Furthermore, after the product gas that has come out from the lower part of the first-stage reactor is rapidly cooled and then supplied to the second-stage reactor from below, the gas pipe becomes the shortest and the decomposition of methacrolein before entering the latter-stage reactor is minimized. Also, unlike the case of supplying from above, the deposition of high-boiling substances and carbides on the catalyst layer is eliminated, and stable operation can be carried out without increasing the differential pressure even during long-term operation.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1 The present invention was carried out as follows by the apparatus schematically shown in FIG.

The pre-stage reactor 6 is a multi-tubular reactor consisting of three steel pipe reaction tubes having an inner diameter of 25 mm and a length of 5 m.
-V system) 6 l, and a raw material gas having a composition of isobutylene: oxygen: nitrogen: steam = 1: 3: 18: 4 from the tube 1 is SV =
It was passed through the first-stage reactor 6 so as to be 1500 / hr (NTP standard) and heated to 360 ° C. with a molten salt. The latter-stage reactor 7 is a multi-tubular reactor composed of six steel pipe reaction tubes each having an inner diameter of 25 mm and a length of 5 m.
This was filled with 12 liters of the latter stage oxidation catalyst (heteropolyacid type). The raw material gas supplemented with methacrolein, air, nitrogen and steam from the pipe 3 was added to the product gas from the pipe 2 so that the methacrolein: oxygen: nitrogen: steam = 1: 2.5: 14: 7 molar ratio was obtained. From 4 to SV = 1200 / hr (NTP standard), it was passed through a reaction tube, heated to 310 ° C. with molten salt, and reacted for 300 days. During this time, the inlet pressure of the front-stage reactor 6 was 1.0 kg / cm ² g.
There was almost no increase in pressure. Also, after the end of operation,
After inspecting the lower part of the latter stage reactor 7 and the inlet pipe,
Only a small amount of black deposit was found in the pipe bend, and no abnormality was found in the catalyst layer. In addition, the reaction results during this period are the first and second stages, and the isobutylene conversion rate is 100.
%, Methacrolein yield 6.9%, methacrylic acid yield 6
At 4.5%, the active ingredient selectivity was 71.4%.

Comparative Example 1 The same reaction as in Example 1 was performed except that the same reactor as in Example 1 was used and the flow path was changed as shown in FIG. The pressure gradually started to increase from around 60 days, and at the 100th day, the inlet pressure of the front-stage reactor increased from 1.0 kg / cm ² g at the start of operation to 1.2 kg / cm ² g. Since there was a tendency for the pressure to increase further,
The operation was stopped and the top and bottom of each reactor were inspected for openness. As a result, a large amount of black deposits were seen at the top of the second reactor,
Similar deposits were also found in the inner layer above the catalyst layer. The reaction results during this period were as follows: the conversion of isobutylene was 100%, the yield of methacrolein was 6.1%, the yield of methacrylic acid was 62.1%, and the selectivity of the active ingredient was 68.2%.

Comparative Example 2 Continuous operation was performed in the same manner as in Example 1 except that the flow path was changed as shown in FIG. Similar to Comparative Example 2, the pressure gradually started to increase from about 60 days, and the inlet pressure of the front-stage reactor increased from 1.0 kg / cm ² g at the start of operation to 1.2 kg / cm ² g on the 100th day. After that, the tendency of further increase in pressure was observed, so the operation was stopped and the upper and lower sides of each reactor were inspected for open inspection. As a result, a large amount of black deposits was observed at the upper part of the second reactor, and similar deposits were also found at the inner layer part above the catalyst layer. In addition, the reaction results during this period were passed through the first and second stages, and the isobutylene conversion rate was 100.
%, Methacrolein yield 6.7%, methacrylic acid yield 6
At 2.5%, the active ingredient selectivity was 69.2%.

Comparative Example 3 Continuous operation was performed in the same manner as in Example 1 except that the flow path was changed as shown in FIG. Even after continuous operation for 100 days, the inlet pressure of the front-stage reactor was 1.0 kg / cm ² g, and almost no increase in pressure was observed. When the lower part of the second reactor and the inlet pipe were inspected after the completion of the operation, only a small amount of black deposit was found in the bend part of the pipe, and no abnormality was found in the catalyst layer. However, the reaction results during this period went through the first and second stages, with an isobutylene conversion rate of 100% and a methacrolein yield of 6.2.
%, The yield of methacrylic acid is 62.5%, and the selectivity of the active ingredient is 6
It was 8.7%.

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus used in the examples of the present invention, and FIGS. 2 to 4 are schematic views of apparatuses used in comparative examples. 1 ... Pipe for supplying raw material gas for first-stage oxidation reaction 2 ... Pipe for feeding produced gas for first-stage 3 ... Pipe for supplying supplemental gas for second-stage oxidation reaction 4 ... Pipe for feeding raw-material gas for second-stage oxidation reaction 5 ... Pipe for transporting the second-stage product gas 6 ... Front-stage oxidation reactor 7 ... Rear-stage oxidation reactor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirozo Segawa 2-1 Kyowa-cho, Nakajo-cho, Kitakanbara-gun, Niigata Prefecture (72) Inventor Katsuji Yoguchi 4-7-411 Kamo, Takaishi-shi, Osaka

Claims (1)

[Claims] 1. Pre-stage oxidation to obtain methacrolein by reacting molecular oxygen with isobutylene and / or tertiary butanol in the presence of an inert gas and a catalyst,
In the method for producing methacrylic acid from isobutylene and / or tertiary butanol, which undergoes two-step oxidation, which comprises the latter-stage oxidation in which the methacrolein is reacted with a gas containing molecular oxygen in the presence of a catalyst to obtain methacrylic acid, In the first-stage oxidation, the raw material gas is allowed to pass through the reactor from above to below,
Immediately after the exit of the catalyst layer of the front reactor, after mixing the replenishment gas for the second reaction as a cooling gas to the gas produced in the front stage, the mixed raw material gas is allowed to pass through from the lower side to the upper side of the catalyst layer of the rear reactor to react. A method for producing methacrylic acid.