DE2842092A1 - PROCESS FOR SEPARATING METHACROLEIN AND / OR METHACRYLIC ACID FROM METHACRYLIC ACID-CONTAINING GASEOUS REACTION MIXTURES - Google Patents

Description

UZ: M 879
Case: 56 427

SUMITOMO CHEMICAL COMPANY, LIMITED
Osaka, Japan
10

¹¹ Process for separating methacrolein "and / or methacrylic acid from methacrylic acid-containing gaseous reaction mixtures"
-15

The invention relates to a method for separating methacrolein and / or methacrylic acid from their aqueous solutions, in particular, an effective method for separating and recovering methacrylic acid and methacrolein in the Production of methacrylic acid, in the case of methacrolein and / or a compound under the reaction conditions Methacrolein gives, and molecular oxygen subjected to gas phase oxidation in the presence of a catalyst will.

Examples of compounds that form methacrolein under the reaction conditions (hereinafter: precursors (of Methacrolein) ") are isobutene and tert-butanol.

During the oxidation of methacrolein or its precursor in the gas phase together with water vapor and molecular oxygen (usually air) in the presence of an oxidation catalyst, a gaseous reaction mixture is obtained which in addition to methacrylic acid, acetic acid, carbon monoxide, carbon dioxide, unreacted methacrolein or its precursor,

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■ j contains oxygen, nitrogen and the like. It is therefore required to effectively separate not only methacrylic acid but also methacrolein from the reaction mixture .

There are various commercially available catalysts for the oxidation of methacrolein or its precursor to methacrylic acid known, which, however, are not fully satisfactory in technical operation.

■ ΙΟ Most currently known catalysts allow under reaction conditions in which the methacrolein conversion is low, a high selectivity for methacrylic acid, while under reaction conditions in which the conversion is high, they have a considerably lowered selectivity

• J5 result. In the case of a relatively low methacrolein conversion is therefore the development of effective methods for the separation of unreacted methacrolein from the aqueous Methacrylic acid solution and the return of the methacrolein to the oxidation reactor is an important factor that affects the Economics of the production of methacrylic acid by gas phase oxidation of methacrolein or its precursor certainly.

In JA-OS 111 017/1975, for example, there is a method for separating of methacrolein described from the gaseous reaction mixture, which consists essentially in that the methacrolein-containing gas mixture is absorbed in 50 to 500 mol of water, based on 1 mol of methacrolein, and the obtained aqueous solution containing the separated methacrolein, then distilled or stripped to the methacrolein to win. In order to separate the methacrolein from the gaseous reaction mixture by this process, the absorption must be carried out of methacrolein under high pressure or at low temperature or with a large amount of water or be carried out in an absorption tower with an extraordinarily large number of floors. Because methacrolein is in water only

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• Ι is very sparingly soluble (6.1 percent by weight at 25 ° C) the absorption of methacrolein in water is extremely difficult. If a large amount of water is used as an absorption solvent for the methacrolein, not only the Methacrolein absorption tower, but also the distillation and stripping tower following the absorption tower are enlarged. To contribute to the absorption of methacrolein high pressure must be the operating pressure of all equipment, including the reactor, the methacrolein absorption tower are connected upstream, are also increased with the increase in the operating pressure of the absorption tower. However, this is with great difficulty in terms of pressure resistance and safety of the equipment as well linked to profitability. Also the absorption of methacrolein at low temperatures or with absorption towers, which have a large number of floors is economically disadvantageous. For these reasons, the use solvents in which methacrolein is sparingly soluble, e.g. water, are unfavorable.

In view of the low solubility of methacrolein in water, the use of alcohols is disclosed in JA-OS 92 007/1974 suggested instead of water as a solvent for methacrolein absorption. Alcohols are suitable for this purpose; When the methacrolein is returned to the oxidation system, these organic solvents are even if only in traces, together with the separated methacrolein 'introduced into the oxidation system, where they various difficulties, e.g. poisoning of the catalyst or oxidation inhibition, as well as undesirable reactions, e.g. cause explosions by contaminating the vapor with the organic solvent. It is therefore not always beneficial to use organic solvents as solvents for methacrolein absorption, even if they absorb methacrolein very well.

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When looking for solvents for the absorption of methacrolein that absorb methacrolein very well and no difficulties even when returning to the oxidation system together with the separated methacrolein, e.g. do not cause catalyst poisoning, it has now been found that an aqueous methacrylic acid solution is far better Possesses solubility for methacrolein than water itself; see Fig. 1.

The object of the invention is to provide a method with the methacrolein can be completely separated from methacrylic acid, the concentration of the acid in aqueous solution is kept as high as possible.

The invention relates to a process for separating methacrolein and methacrylic acid from gaseous reaction mixtures which are formed in the catalytic gas phase oxidation of methacrolein, which is characterized in that the gas mixture from the oxidation reactor in which the catalytic gas phase oxidation is carried out is introduced into a condenser In which the gas mixture is brought ^{into direct countercurrent contact at 100 °} C. or less with part of the condensed liquid which has previously been obtained in the condenser, with mainly the water contained in the gas mixture and the methacrylic acid condensing. When this condensation is carried out in one step, the operating temperature is 100 ° C or less, preferably 30 to 80 ° C. When the condensation is performed in two stages, the operating temperature is in the first stage 100 ⁰ C or less, preferably 30 to 80 ° C, and in the second stage 10 to 50 ⁰ C. In this case, the temperature in the second stage preferably not higher than in the first stage. Operating temperatures above 100 ^° C. are not preferred, since they can lead to a polymerization of methacrolein and methacrylic acid.

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■ j The way in which the gas mixture is in direct countercurrent contact is brought with the condensed liquid is not particularly limited, and any conventional apparatus, e.g. Sieve tray, bell tray or spray towers can be used.

The methacrolein-containing gas from the upper end of the condenser is then introduced at the lower end of a methacrolein absorption tower, which is at a temperature of 30 ⁰ C or

• jO less, preferably 0 to 15 ⁰ C is operated. In the tower, the gas is brought into direct counter-flow contact with an aqueous solution containing 5 percent by weight or more, preferably 10 weight percent or more of methacrylic acid and _r is fed at the upper end of the tower, WO

• J5 when the methacrolein contained in the gas is absorbed in the solution. A gas almost free of methacrolein is therefore obtained at the upper end, while an aqueous methacrylic acid solution containing absorbed methacrolein is obtained at the lower end. Operating temperatures of the methacrolein absorption tower of 30 ^° C. or more are not preferred because they impair the methacrolein absorption. In addition, methacrylic acid concentrations of 5% by weight or less are not preferred because the solubility of methacrolein decreases and the absorption performance is deteriorated.

The type of methacrolein absorption tower is not particularly limited, and any conventional one may be used Towers are used, e.g. filler bodies sieve bottom, bell bottom or spray towers.

The aqueous methacrylic acid solution is used for methacrolein absorption used in an amount that the molar ratio of the solution to that entering the absorption tower or less, preferably 1 to 5.

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-j The absorbed methacrolein-containing aqueous methacrylic acid solution is withdrawn from the bottom of the absorption tower and a methacrolein-stripping tower introduced at the upper end, which is operated at 30 to 100 ⁰ C, preferably 50 to 80 ° C. The condensed liquid obtained in the condenser is introduced into the central part or the upper end of the stripping tower. An inert gas, for example nitrogen, air, carbon dioxide, exhaust gas that arises from the oxidation of methacrolein or its precursor, exhaust gas that arises from the combustion of the first-mentioned exhaust gas, or

a mixture of these inert gases is introduced at the lower end of the tower, the amount of gas being adjusted so that the molar ratio of the total liquid introduced into the tower to the gas is 3 to 30, preferably 5 to 20, being. • J5 wearing. The methacrolein contained in the aqueous solution and the condensed liquid is separated therefrom and withdrawn at the top of the tower in the form of a gas mixture, while that of methacrolein practically freed aqueous methacrylic acid solution is discharged at the lower end.

When the operating temperature of the methacrolein stripping tower is 30 ° C or less, the methacrolein vapor pressure is low, so that the stripping effect is impaired. Polymerization can occur at temperatures of 100 ° C or more come from methacrolein and methacrylic acid.

There is no particular limitation on the type of the stripping tower, and any conventional tower can be used which enable gas-liquid contact, e.g. packing elements; Sieve bottom, bell bottom or Spray towers.

The operating temperature of the absorption tower and the stripping tower can be set in different ways, depending on the type of tower. For example, you can use the tower

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provided with a jacket, or supply a heating medium through the jacket or a coil.

The aqueous solution containing 5 weight percent or more methacrylic acid contains ,, and as an absorption solvent for methacrolein at the top of the methacrolein absorption tower is supplied, an aqueous methacrylic acid solution can be obtained independently of the process according to the invention or part of the bottom liquid of the methacrolein stripping tower be. In the last-mentioned Palll, the bottom liquid is cooled and returned to the absorption tower .

The methacrolein-containing inert gas mixture from the upper end of the stripping tower can be used for the production of methacrolein or for other purposes or can be recycled together with an inert gas to the reactor for the catalytic gas phase oxidation of methacrolein or its precursor.
20th

The invention is explained in more detail in the drawing: FIG. 2 is a flow diagram of an embodiment of the separation of methacrolein and methacrylic acid, in which the condensation of the gas mixture from the reactor is carried out in two stages.

The gas mixture from the reactor 3 for the catalytic gas phase oxidation of methacrolein and / or its precursor is via line 4 to the lower end of a first condenser 5 supplied. The gas is then brought into direct countercurrent contact with a liquid containing methacrylic acid, which is circulated via the line 6, the cooler 8 and the line 9, the contained in the gas mixture Methacrylic acid and the water vapor condense. The methacrylic acid containing liquid is from the bottom of the first condenser 5 via line 7, the heat exhaust

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■ j exchanger 24 and the heater 25 the middle part of the methacrolein stripping tower 31 supplied. The head gas of the first capacitor 5 is fed via line 10 to the lower end of the second capacitor 11, the lower end Temperature than the first condenser 5 is operated. The gas is then in direct countercurrent contact with a methacry! acidic liquid that through line 12, cooler 14 and line 15 in the Cycle, with large parts of the head

-J ₀ gas from the first condenser remaining methacrylic acid or water vapor are condensed. The methacrylic acid-containing liquid from the lower end of the second condenser 11 is then fed to the middle part of the stripping tower 31 via the line 13 and the heat exchanger 23.

The line 7 for withdrawing the first condensed liquid and the line 13 for withdrawing the second condensed liquid Liquids can (as shown in FIG. 2) be connected separately to the stripping tower 31 or brought together and connected to the stripping tower 31.

The overhead gas from the second condenser 11, from the large one Fractions of methacrylic acid and water vapor have been removed in the first condenser 5 and second condenser 11 then via line 16 to the bottom of the methacrolein absorption tower 17 supplied. At the upper end of the absorption tower 17 is via line 26 an aqueous Methacrylic acid solution as a solvent for methacrolein absorption initiated. The solution is brought into countercurrent contact with the rising methacrolein-containing gas, so that it absorbs methacrolein. The methacrolein-free Overhead gas from the absorption tower 17 is on line 20 withdrawn and via an exhaust gas treatment zone in blown off the atmosphere. The aqueous methacrylic acid solution containing absorbed methacrolein is passed through the line 19 peeled off and the upper end of the stripping tower 31 over the heat exchanger 21 and the heater 22 are supplied.

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• j Preferably one operates (preferably, for example, 30 ⁰ C or less, 0 to 15 ⁰ C) to increase the Äbsorptionsturm T 7 at the lowest possible temperature to the amount of absorbed methacrolein. For this purpose, the temperature must be controlled by providing the tower with a jacket and / or a cooling coil inside and circulating a cooling medium. The aqueous methacrylic acid solution fed in through line 26 can be part of the circulating bottom liquid from the stripping tower 31 or an aqueous methacrylic acid solution which was obtained independently of the process according to the invention.

An inert gas is fed into the stripping tower 31 via line 32 introduced, e.g. air, nitrogen, carbon dioxide, exhaust gas, .15 that in the oxidation of methacrolein and / or its Precursor was obtained, or exhaust gas that arises from the combustion of the first-mentioned exhaust gas. Methacrolein will therefore stripped from the fluids supplied through lines 19, 13 and 7, while at the top one Methacrolein-containing gas mixture is withdrawn via line 27.

This gas mixture can be used for the production of methacrolein or for other purposes or via the heating device 28 and the gas supply line 1 are returned to the reactor 3 will. The bottom liquid from the stripping tower 31 is passed through line 29 into the heat exchangers 23 and 24 cooled and withdrawn via line 30 as a practically methacrolein-free aqueous methacrylic acid solution. The solution is sent to a methacrylic acid purification stage or other stages. Part of the bottom liquid from the stripping tower 31, the absorption tower 17 can be used as a solvent for methacrolein absorption the heat exchanger 21, the line 26 and the cooler 18 are fed.

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■ j In the methacrolein stripping tower 31, the operating temperature drops, as a large part of the methacrolein and some water evaporate. In order to keep the operating temperature within the To keep the required area, the tower must be provided with a jacket or a heating coil through which a Heating medium circulates. The arrangement of the heat exchangers 21, 23 and 24, the heating devices 22 and 25 and the cooler in the jacket system or the heating coil system of the absorption tower and the stripping tower does not necessarily have to be the flow -IO correspond to image of Fig. 2 if the operating temperatures of the absorption tower and the stripping tower are kept within the required areas. These devices can optionally be omitted or used in addition.

.15

If the condensation of the gas mixture does not occur at two temperature levels as shown in the figure, but only at one temperature level is carried out, this is done with the omission of the second capacitor 11, the lines 12, 13, 15 and 16, of the cooler 14 and the heat exchanger 23, in which the first condenser 5 is connected directly via the top gas line 10 the absorption tower 17 connects.

The operating temperature of the condenser is preferably chosen so that ordinary cooling water as the cooling medium in the Coolers 8 and 14 connected to the condenser can be used. Furthermore, for economic reasons the lowest possible operating temperature is preferred, since in this way the polymerization of methacrylic acid in of the condensed liquid can be prevented, the amount of water vapor that is in the head gas from the second (or first) condenser which is fed to the methacrolein absorption tower 17 via line 16 (or 10) is, decreases and thus the cooling capacity of the absorption tower 17 and the cooler 18 can be reduced. However, operating temperatures that are too low are disadvantageous,

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because if the average temperature difference between the operating temperature and the cooling medium is too low, an extremely large heat transfer surface in the coolers 8 and 14 is required. When using the first capacitor alone, an operating temperature of 30 to 80 ^° C. is therefore preferred. When using two capacitors, the operating temperature of the first capacitor is preferably 30 to 80 ^° C., while that of the second capacitor is 10 to 50 ^° C. below the temperature range of the first capacitor. The choice of a single-capacitor system, two-capacitor system or multi-capacitor system is therefore based on the following factors:

Required heat transfer area of coolers 8 and 14, .15 connected to the respective condensers, and cooling performance of the absorption tower and the cooler The respective advantages of the two systems cannot therefore be specified in advance.

The operating pressure of capacitors 5 and 11, the methacrolein absorption tower 17 and the methacrolein stripping tower 31 is depending on the operating pressure of the Reactor 3 chosen for the catalytic gas phase oxidation of methacrolein or its precursor. Preferably However, one chooses operating pressures that can be achieved without the line 16 or 27 to increase the pressure must be provided with a compressor; usually 0 to 7 atu, preferably 0.5 to 4 atu.

Fig. 1 shows the Henry coefficients of methacrolein in water and aqueous methacrylic acid solution. Fig. 2 shows an embodiment of the separation of methacrolein and methacrylic acid according to the invention Procedure.

The examples illustrate the invention. In the examples

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The reference numerals mentioned relate to FIG. 2.

example 1

A 310 ° C gas mixture containing 1.62 percent by volume methacrolein, 1.57 percent by volume methacrylic acid, 0.52 percent by volume acetic acid, 42.75 percent by volume steam and 53.53 percent by volume non-condensable gases such as oxygen, nitrogen, carbon monoxide and carbon dioxide , is used in an amount of 4528 Nl / hour. a porcelain tower filled with Raschig rings as the first capacitor. In the first condenser 1,698 g / h. obtain a condensate, whose temperature is 45 to 50 ⁰ C. The concentrations of methacrylic acid, methacrolein and acetic acid in the liquid amount to 15.24 weight percent overall • ^15, 0.18 weight percent and 3.37 weight percent.

The gas withdrawn at the upper end of the first condenser 5 contains 2.65 percent by volume methacrolein, 0.13 percent by volume

^ cent methacrylic acid and 8.08 volume percent steam and is used in an amount of 2 723 Nl / h. (Total volume) fed to a porcelain tower filled with Raschig rings as a second capacitor 11. In the second condenser, 94.66 g / hour. obtained a condensate, the temperature of which is 32 to 35 ° C. The concentrations of methacrylic acid, methacrolein and acetic acid in the liquid are 10.19 percent by weight, 0.74 percent by weight and 4.567 percent by weight, respectively. The gas withdrawn at the upper end of the second condenser 11 contains 2.75 percent by volume methacrolein, 0.04 percent by volume methacrylic acid and 4.62 percent by volume steam and is in an amount of 2,619 Nl / h (total volume) the lower end of a stainless steel tower filled with Raschig rings fed as a methacrolein absorption tower 17. As a solvent for methacrolein absorption, part of the bottom liquid from the methacrolein stripping tower 31 (the 15.1 percent by weight

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■ j methacrylic acid, 3.46 percent by weight acetic acid and 0.20 percent by weight methacrolein) to 8 to 10 ⁰ C and feeds it in an amount of 6,378 g / hour. at the top of the absorption tower 17.

; At the lower end of the absorption tower 17, 6689 g / h.

a methacrolein-containing liquid obtained, the 3.55 percent by weight Contains methacrolein, 14.46 percent by weight methacrylic acid and 3.40 percent by weight acetic acid. At the upper end of the absorption tower 17 are 2451 Nl / h.

withdrawn from a gas containing 60 ppm methacrolein. The methacrolein absorption tower (diameter 55 mm; height of the packing area 6 m) is provided with a jacket and is operated at 5 to 15 ^° C. Both the first and that

The second condensate is introduced into the middle part of the methacrolein stripping tower 31, while the obtained liquid containing absorbed methacrolein is fed to the upper end. At the lower end of the stripping tower 31, 692 Nl / hour. Introduced nitrogen. At the upper end of the stripping tower, 847 Nl / h. of a gas containing 8.48 percent by volume stripped methacrolein and 10.0 percent by volume steam. This gas is ^{heated to 280 °} C. and returned to the oxidation reactor 3. At the lower end of the methacrolein stripping tower 31, 8183 g / hour are obtained.

a bottom liquid containing 15.1 percent by weight methacrylic acid, 3.46 percent by weight acetic acid and 0.20 percent by weight methacrolein. Part of the bottom liquid (6378 g / h) is recycled as a solvent for methacrolein absorption, while the remainder (1805 g / h) is withdrawn as product. The stripping tower (diameter 55 mm, height of the Füllkörperbereichs 3 m) is filled with Raschig rings of stainless steel tower which is equipped with a jacket and is operated at 60 to 70 ⁰ C.

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- | Example 2

The process is carried out as in Example 1, except that the second condenser 11 is omitted and the overhead gas is passed of the first capacitor 5 directly to the lower end of the methacrolein absorption tower 17, which has a height of

Has a packing area of 6.5 m - At the top of the Absorption tower 17 receives a gas containing 65 ppm methacrolein while at the bottom of the tower 6778 g / h a liquid that contains 3.52 percent by weight - | Q percent absorbed methacrolein, 14.41 percent by weight Contains methacrylic acid and 3.34 percent by weight acetic acid. The compositions and flow rates in the others Ranges essentially correspond to those of Example 1 -

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Claims (4)

VOSSIUS · VOSSIUS · HILTL. · TAUCHNER - HEUNEMANN ΡΑΤΕΓJT TO WALTE SIEBERTSTRASSE A ■ 80O0 MÖNCHEN 86. PHONE: (O89) 4-74O75 CABLE: B EN ZOLPATENT MÖNCHEN · TELEX 5-29 4-33 VOPAT D u.z .: M 879 September 27, 1978 Case: 56 427 SUMITOMO CHEMICAL COMPANY, LIMITED
Osaka, Japan ¹¹ Process for separating methacrolein and / or methacrylic acid from gaseous reaction mixtures containing methacrylic acid " Priority: September 28, 1977, Japan No. 117 040/77 Claims Process for the separation of methacrolein and / or methacrylic acid from methacry! Acid-containing gaseous reaction mixtures, which in the gas phase reaction of methacrolein and / or a compound which gives methacrolein under the reaction conditions, and molecular oxygen at increased Temperature have been obtained in the presence of an oxidation catalyst, characterized in that the gaseous Introducing reaction mixture from the reactor in which the gas phase reaction was carried out into a condenser, in which the reaction mixture is in direct countercurrent contact with a. Part of the condensed liquid is brought to the has been previously obtained in the condenser at a temperature not higher than 100 ° C, so that the methacrylic acid and the water vapor condenses in the reaction mixture and the greater part of the methacrolein and non-condensable gas L_ 909814/1 000 _j ORIGINAL INSPECTED ■ j se are separated from the reaction mixture, the gas obtained is introduced at the lower end of a methacrolein absorption tower, which is operated at a temperature of not more than 30 ⁰ C, the methacrolein contained in the gas at a liquid / gas molar ratio of 8 or less is absorbed in an aqueous solution containing not less than 5% by weight of methacrylic acid and fed to the top of the absorption tower, and the obtained methacrolein-containing aqueous methacrylic acid solution is withdrawn at the bottom of the tower and fed to the top of a methacrolein stripping tower, the is operated at a temperature of 30 to 100 ° C, while at the same time the condensed liquid obtained by condensation of the gaseous reaction mixture in the middle part or at the top .15 of the stripping tower is introduced ■ and an inert gas such as nitrogen, air, carbon dioxide, exhaust gas or mixtures thereof, in a liquid / gas molar ratio v on 3 to 30 is fed at the lower end of the tower, methacrolein being separated from the methacrolein-containing aqueous methacrylic acid solution or the fed condensed liquid and drawn off at the upper end, while the aqueous methacrylic acid solution is drawn off at the lower end. 2. The method according to claim 1, characterized in that the direct countercurrent contact between the gaseous reaction mixture and part of the condensed liquid previously obtained in the condenser is carried out at 100 ⁰ C or less in one stage or in several stages. 3. The method according to claim 1, characterized in that part of the aqueous methacrylic acid solution from the lower end of the methacrolein stripping tower as an absorption solvent used for the methacrolein absorption tower. 9098U / 1000 -J- 28A2092 ¹ 1 4. The method according to claim 1, characterized in that one the methacrolein-containing gaseous mixture from the top of the methacrolein stripping tower in the circuit to the inlet of the Oxidation reactor recirculates. ^L 90981 A / 1000