JPS5913746A - Preparation of acrylic acid - Google Patents

Abstract

PURPOSE:To prepare the titled compound economically, without environmental pollution, by concentrating the process waste water of the catalytic vapor- phase propylene-oxidation process using a double effect evaporator, and reusing the obtained condensed liquid as the absorbent water for collecting acrylic acid. CONSTITUTION:Acrylic acid is prepared by the catalytic vapor-phase oxidation of propylene using steam and an O2-containing gas. In the above process, acrylic acid produced by the reactors 101 and 102 is cooled and absorbed in water in the collector 103 to obtain an aqueous solution. A part of the waste gas left after the collection is recycled to the oxidation reaction process through the pipe 10, and the aqueous solution of acrylic acid is sent to the acrylic acid separation steps 104-107. The waste water discharged from the separation step is concentrated by a double effect evaporator. That is, the waste water is introduced through the pipe 24 to the first evaporator 109, the vapor generated therefrom is recycled to the reactor 101, and the vapor generated from the second evaporator 110 is used as the heat source of the evaporator 109. The obtained condensed water is recycled through the pipe 9 and reused as the absorbent water for collecting acrylic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for effectively utilizing and detoxifying wastewater generated in a process for producing acrylic acid by catalytic gas phase oxidation of propylene. Specifically, the present invention is a process for producing acrylic acid by catalytic gas phase oxidation of propylene using water vapor and molecular oxygen-containing residue, and collecting acrylic acid produced in the oxidation reaction as an aqueous solution. A part of the waste gas after this is recycled for the oxidation reaction, and the collected acrylic acid aqueous solution is led to the acrylic acid separation stage, and the resulting waste water is concentrated using a double-effect tank. The waste water vapor obtained in the first stage concentrator is recycled for the oxidation reaction, and the waste water vapor obtained in the second stage concentrator is used as a heat source for the first stage concentrator. A closed/stem system for producing acrylic acid, which is characterized in that the acrylic acid is circulated and used for collecting the produced acrylic acid, and the concentrated wastewater obtained in the second stage concentrator is completely oxidized together with the remainder of the supernatant gas. The present invention relates to a manufacturing method.

The inventors of the present invention have already disclosed a method for producing acrylic acid by propionic acid-catalyzed gas phase oxidation (see Japanese Patent Application No. 51-256 fl 2 (see Japanese Patent Application Laid-open No. 52-10 R917)) in which propylene is used in the first and second stages of reaction. A process in which the resulting reaction product gas is separated into an acrylic acid aqueous solution and waste gas by an acrylic acid collection device, and a portion of the waste gas is recycled for use in the previous reaction. provided. Its characteristics are 1l-J: [When using waste gas in the first stage reaction, the concentration of acrylic acid in the raw material gas for reaction, which includes a part of the waste gas, should not exceed 0.5 volume. Therefore, the extraction temperature of the waste gas from the acrylic acid collection device should be maintained in the range of 35 to 80°C, and the 15 to 85 parts of the waste gas should be circulated to the first stage reactor.
And so. By this method, it is possible to obtain acrylic acid from 1-propylene in a high yield over a long period of time as a highly concentrated aqueous solution. A highly industrially viable process was proposed, which reduced the amount of wastewater and increased the yield of acrylic acid.

Therefore, the inventors of the present invention have carefully examined the method of the manual invention to further improve it on an industrial scale. In other words, we focused on the reaction method and the method of using 1 [) 1 1 [) 1 [] 1 [1] produced from the process, and developed the method of the present invention which has been converted into a clost process. This is what we have come to complete.

The process of producing acrylic acid by catalytic gas phase oxidation of propylene generates a large amount of waste water.

That is, a considerable amount of water vapor is mixed with the raw material gas involved in the oxidation reaction and is sent to the reaction product collection device together with by-product water produced by the reaction. In the collection device, water vapor is condensed and collected together with the main product, acrylic acid. In this case, the common method is to bring it into direct contact with absorbed water and cool and condense it. A 70% by weight aqueous acrylic acid solution is recovered. A large amount of waste water is extracted from this aqueous solution when acrylic acid is separated in the next extraction or azeotropic distillation step. This wastewater contains unrecovered acrylic acid, by-product acetic acid and propionic acid, as well as small amounts of organic acids such as maleic acid, as well as organic acids such as acrolein, formaldehyde, acetaldehyde, and other compounds. Various derivatives from , organic solvents for extraction and azeotropic distillation, polymerization inhibitors, etc. are contained in an amount of about 0.5 to 5% by weight.

Because wastewater containing a considerable amount of organic matter cannot be directly discharged into rivers, it must be detoxified using activated sludge methods or concentrated combustion methods. but,
The above-mentioned activated sludge method requires not a small amount of equipment and expenses, and it is difficult to achieve complete pollution-free treatment.On the other hand, the concentrated combustion method also requires equipment costs to process all of this wastewater. This inevitably becomes an expensive process.

Therefore, how to efficiently purify process wastewater, which is likely to be a source of pollution, is an extremely urgent and major issue in industry.

On the other hand, as mentioned above, in the process of producing ac II/acid, water is used as water vapor or cooling absorption water.
This is partly because there is a large amount of 11fO, and there is a strong demand for process development to return this wastewater to the 11fO manufacturing process.

The inventor discovered a method for returning the wastewater to the process. When wastewater is used as absorption water for collection of acrylic acid without separation, organic acids and other various impurities will be concentrated and accumulated in the system of absorption water - acrylic acid aqueous solution - wastewater. It was discovered that after reaching a certain equilibrium concentration, it was extracted together with acrylic acid and mixed into the final product, acrylic acid, resulting in a decrease in quality and weight.7 To make matters worse, in the waste gas recycling process where a part of the waste gas from the acrylic acid collection tower is used as part of the raw material gas for the oxidation reaction, the absorption water for acrylic acid collection has a high acid concentration. It has been found that when wastewater is reused, the extraction rate of acrylic acid not only decreases, but also the activity of the catalyst in the oxidation reaction gradually decreases and is inhibited, leading to a decrease in the yield of acrylic acid. That is, as the acid content of the wastewater as absorbed water increases, the efficiency of collecting acrylic acid in the acrylic acid collecting device also decreases, and the acrylic acid is entrained in the cycled waste gas. Therefore, it has become clear that it is inconvenient to reuse the wastewater without treatment.

In order to solve these problems, the present inventors concentrated wastewater using a double-effect can, utilized the condensed water obtained by evaporation from the wastewater, and examined the detoxification treatment of the concentrated wastewater. 8"
However, the steam from the wastewater obtained from the first stage of condensation was directly applied to the oxidation ring, and the steam from the wastewater obtained from the second stage of condensation was used for the first stage of condensation. It is advantageous to use it as a heat source and use the resulting condensate as absorption water, and to completely oxidize the concentrated wastewater that leaks out in the second stage of concentration together with the remainder of the waste gas after collecting acrylic acid. This discovery led to the completion of the present invention.

In other words, there is no use of the first-stage condensate, which may be concentrated FTi in the second stage, as absorption water for collecting acrylic acid.
There is no accumulation of boiled food (light θ1 with acrolein, pormaldehyde, and acetolytate) like that associated with the above, and the collection of acrylic acid can also be maintained at a high level. On the other hand, the water vapor IJ of the wastewater obtained from the first stage of condensation is accompanied by the light boiling point substances of T-chlorein, porium chloride, acetaldehyde, and acrylic acid in the evening. Always contain 0.5% by volume of acid in the raw material gas used for catalytic gas phase oxidation reaction.
Hereinafter, it was discovered that the scales should be used while adjusting the volume to 3 volume or less.

In the present invention, the water vapor required for the reaction is substantially 1
The temperature at the top of the absorption tower to which the absorbed water is supplied by the acrylic acid collector can be set arbitrarily, since it is supplied by the vapor of the waste water from the condensation stage, and by setting it as low as possible - rCrylic acid and water vapor are substantially condensed and absorbed, and the acid content that is entrained in the waste gas and released is operated so that almost all of it becomes cellulose.Industrial use generally uses cold water tower water, which can be done manually at low cost. The tower top temperature is set to 40°C or less, preferably 25 to 10°C. By setting the top temperature of the absorption tower as low as possible,
It can facilitate the collection of acrylic acid in the absorption tower. In addition, the condensed water of the wastewater is recycled as absorption water to collect acrylic acid, and the height of the absorption tower can be lowered, and the acrylic acid that was conventionally discarded from the wastewater can be transferred to the wastewater. Acrylic acid can be recovered by using condensed water as absorption water. Furthermore, since the temperature of the recycled waste gas is low, the amount of gas to be recycled is reduced, and the recycling blower can be made smaller.

It is preferable that the condensed water of the waste water used as absorption water is from the steam of the second stage of condensation.

This is because the steam from the first stage of condensation contains light-boiling substances such as chlorolein, formaldehyde, and cetaldehyde, so if it is recycled and reused as absorbed water, the absorbed water becomes
Acrylic acid water solution - Concentrates and accumulates in the wastewater system and is extracted together with acrylic acid, resulting in problems with polymerization in the culm during purification of acrylic acid and the final product acrylic acid ( This is because the quality deteriorates due to the contamination of the waste water.Therefore, as the absorption water, the condensed water of the waste water from the second stage of concentration, which has removed the light-boiling substances 1-j contained in the waste water, is used. .

Water vapor in the first stage of condensation that contains light boiling point substances such as chlorolein, pormaldehyde, and chloride.
It is recycled and used as reaction steam in the reactor. Since light boiling point substances are oxidized and burned in the reactor, they do not concentrate and accumulate in the system.

This steam is added and mixed so that the steam concentration in the gas phase 11 of the catalytic gas phase oxidation reactor is 3 to 30 volume, immediately 1 to 15 volume, It is easy to control the acrylic acid concentration so as not to exceed 0.5 volume M%, especially 0.3 volume M%. The concentrated waste liquid obtained from the second stage of concentration contains various solids and tar-like substances, and if necessary, after passing through an r-filter, the waste gas from the collection device is collected. Of this, the remaining gas, excluding the circulating portion, is completely oxidized and treated to make it non-polluting.

The complete oxidation treatment equipment can adopt either a catalytic combustion method or a direct combustion method in which it is mixed with P and is combusted, or advantageously a catalytic combustion method can be adopted. It is best to use a complete oxidation reactor filled with a monolithic catalyst supported with a noble metal such as palladium. This is because this monolith ad1 can advantageously completely oxidize (-7) high-boiling substances that tend to deposit a lot of tar and carbon.

Thus, by adopting the method of the present invention, it has become possible to create an industrially advantageous process that is pollution-free, with virtually no wastewater volume, and is extremely economical in terms of equipment and utilities. .

Hereinafter, the present invention will be explained in more detail with reference to the attached FIG. 1.

Reaction feed gas, i.e. air from line 1, line 2
propylene from line 3, first stage concentrate can]
0! The raw material gas, which is a mixture of steam from line 1 and waste gas from line i, passes through line 5, enters the reactor 101, and then enters the second reactor 102 via line i, where the reaction product Jj 114 from line 7. Acrylic acid containing reaction/-1' group sludge enters the lower part of line 7, and acrylic acid is collected by cooling and absorption. The aqueous acrylic acid solution is exchanged from line 9 to the soil part of the collection tower.The circulating water originating from the second stage condensation 110 is supplied from line 9 as absorbed water containing a stabilizer, and the acrylic acid is is absorbed and collected by cooling.

A part of the waste gas coming out from line 10 at the top of the column 103 is transferred to the raw material for reaction from line 1.
The remaining gas is reused as 1 gas, and the remaining gas is passed through line 11 and sent to an exhaust gas combustion device 112 where it is combusted and rendered harmless together with the concentrated wastewater from line 2.
released into the atmosphere.

The aqueous acrylic acid solution coming from line 8 is supplied to a light boiling point stripping tower (not shown) as necessary, and the light boiling points from the top of the tower are recycled to the acrylic acid collection tower 103. The aqueous solution is supplied to extraction column 104. The methiacrylic acid supplied in the extraction column 104 is passed through line 1 at the bottom of the column.
The organic solvent is extracted with the organic solvent supplied from 4, and is supplied to the solvent stripping tower 105 through line 15, and the solvent is recovered from the top of the tower and passed through line 16 and 14 to be reused in the extraction tower 04.
The acrylic acid liquid coming out from the bottom of the column enters the acetic acid separation column 106 via line 17, and acetic acid is separated and taken out from line 8 at the top of the column. The crude acrylic acid discharged from the bottom of the tower is supplied to the rectification tower 107 through line 19, the product acrylic acid is taken out from the top of the tower through line 20, and the heavy substances are taken out from the bottom of the tower through line 21, which are useful components. Certain acrylic acid and polymerization inhibitors are recovered (not shown), and the remaining liquid is pumped out of the system and used as fuel. The raffinate discharged from the bottom of the extraction column 104 is sent to line 2.・Solvent recovery tower 1 from 2
( ) 8 and recovers the solvent from the top of the column, line 23.
14 and then recycled to the extraction column 104. Then, the bottom liquid of the solvent recovery column 108 undergoes heat exchange with the feed liquid (not shown), and then is concentrated at the first stage of the line (24 l).
9 and concentrated. The vapor obtained from the condensation stage 1] is supplied to the first reactor 101 via a line.

Second stage condensation] The water obtained from 10 is used as a heat source for the first stage condensation 1 () 9, and after being condensed, it passes through line 9 to the absorbed water of acrylic acid collector jM+o:>. reused as Indeed, the wastewater from line 24 may be mixed with other wastewaters from the acrylic acid manufacturing process, such as esector steam condensate and cooling water.

The proportion of waste gas from the acrylic acid collection device that is recycled to the reactor is determined by the propylene concentration and oxygen concentration of the reaction conditions, but is usually 15 to 85 times the amount of waste gas.
Preferably it is between 20 and 80 centimeters. If this ratio is too high, the concentration of gaseous impurities that accumulate in the system will increase, causing process problems, and failures due to lack of oxygen in the system will likely occur. Furthermore, if this ratio is small, there will be an excess of oxygen in the system, resulting in the drawback that the propylene concentration cannot be increased due to the combustion range.

A method of recycling and utilizing reaction waste gas as an inert diluent gas has been widely used. For example, JP-A-4'
In the specification of No. 7-10614, when propylene is reacted in two stages to produce acrylic acid, the reaction waste gas is recycled as an inert diluent gas for the reaction in step E. Most of the gas capable of condensation is removed and used as an inert diluent gas in place of some or all of the water vapor. However, this method does not mention in detail the conditions of V) in which the reaction waste residue is reused as an inert diluent gas.

As a result of various studies on methods for reusing reaction waste gas in the reaction as an inert diluent gas, the present inventors found that the conditions for obtaining the waste gas and the conditions for reusing it as described above (
After discovering that the circulation rate (recirculation ratio) is very important, we conducted extensive research on these conditions, and found that the top temperature of the acrylic acid collection device for collecting waste gas was set at 25-40°C, the circulation ratio was set at 15-85°C, It has been found that acrylic acid can be industrially advantageously obtained in high yield over a long period of time only when waste gas is reused within a range of 20 to 80%, leading to the present invention. Previous, small Japanese Patent Publication No. 47--l 06]
According to the method of Publication No. 4, for example, in Example 13,
The reason why the conversion rate of propylene is low at 70% and the yield of acrylic acid is low at 50% is that the conditions of the entire process of converting waste gas to no-cycle, including the reaction conditions, deviate from the conditions of the method of the present invention. It is presumed that this was done by Irukokichi.

As such, the reasons why the temperature conditions in which the waste waste is collected and the recycling rate for its reuse are important in the present invention are still not fully understood, but it may be due to unidentified impurities generated in the oxidation reaction or to these conditions. If this happens, the waste gas may be accumulated and concentrated in the recycle system, or acrylic acid and by-product acetic acid, etc., may not be sufficiently collected. The present inventors estimate that this inhibits the reaction. This is because, according to the findings of the present inventors, if an acidic substance such as acrylic acid is mixed into the front catalyst layer, the conversion rate of propylene decreases, and the reaction temperature is increased in an attempt to further increase the decreased conversion rate. This is because there is a clear tendency for selectivity to decrease as the temperature increases. Furthermore, it was found that if the concentration of uncollected and circulated acrylic acid in the raw material gas supplied to the reactor was limited to less than (2), by volume, deterioration of the catalytic reaction over time could be prevented. be.

Best of all, the method of the present invention uses the entrained waste gas as an inert diluent gas to bring the reactant gas composition out of the combustible range and to reduce the amount of oxygen necessary to maintain long-term activity of the catalyst. The object of the present invention is to provide a method for safely and economically producing acrylic acid in a high yield based on a completely new technical idea in which the oxidized acrylic acid is replenished with fresh oxygen-containing gas such as air.

The oxygen concentration in the first stage specified by the present invention is 1.6 to 4.0% higher than the propylene concentration. The reason why the amount is limited to ( ) times by mole, preferably from 1.7 to 3.0 times by mole, is that this is the range necessary for converting propylene to acrylic acid in one pass in the present invention. If the molar ratio does not reach 1.6, even if the conversion of propylene is increased by the reaction between the AiJ stage and the subsequent stage, the acrylic acid flow rate decreases. Also,
If the amount exceeds 4.0 moles, it will inevitably fall into the explosion or combustible range due to the relationship with the amount of water vapor and propylene concentration, or it will be unavoidable to carry out processes with extremely low industrial productivity, so this is not desirable. It's not right.

Catalysts suitable for the present invention are, for example, as pre-catalysts! Special Publication No. 47-42241, Special Publication No. 42242, Special Publication No. 428]3, Special Publication No. 47-27441
C1, Special Publication No. 47-4 ] 329, Special Publication No. 48-47
No. 62, Special Publication No. 1976-476: No. U, Special Publication No. 1977-17
(i No. 4, JP-A-48-5710, JP-A-48-
4765, JP 50-+3: (08, JP 50-479] 7, JP 49-3 (1308, JP 47-298F!I, JP 47-3205)
No. 0, Special Publication No. 47-32051, Special Publication No. 47-320
No. 52, Special Publication No. 47-301 (i No. 3, Japanese Patent Publication No. 1973
-1771.1, Japanese Patent Publication No. 47-21081, Japanese Patent Publication No. 19-92006, etc., any catalyst can be used as long as it can satisfy the high reaction conditions as mentioned above. Can be done. That is, for the first stage reaction, the temperature is 250 to 450°C, preferably 270 to 37°C (1°C).
at a reaction temperature of 3 to 9 volume parts of bu-a-pyrene, preferably 4
~7 capacity range, oxygen 3~18 capacity range, preferably 6~]6
Volume ratio, water vapor volume ratio: 2 to 30, preferably 4 to 25 volume ratio, concentration molar ratio of oxygen and propylene: 1.6 to 4. O1
Preferably 1.7~;3. Contact time 1 for gases in the range of O
．． 0 to 7.2 seconds, preferably 1.8 to 3.6 seconds to achieve a propylene conversion rate of 80 moles or more, preferably 90
More than molar ratio, a calculation of acrolein and acrylic acid -
It is a catalyst that can achieve a flow yield of 70 molar or more, preferably 80 molar or more, and as a catalyst in the latter stage, for example, Japanese Patent Publication No. 119-11371, Japanese Patent Publication No. 11371-1973, No. 47276, JP-A-49-76810,
JP-A-49-133317, JP-A-50-25520
No., JP-A No. 51i1-413918, JP-A No. 50-9
No. 768, JP-A-50-1987, JP-A-50-83
No. 280, JP-A-50-97592, JP-A-47-3
Those described in each specification such as No. 9018 can be used. That is, 180 to 350°C for the subsequent reaction.
, preferably at a reaction temperature of 200-300°C and a contact time of 1
．． The reaction time is 0 to 7.2 seconds, preferably 1.6 to 3.0 seconds, and the midstream yield from propylene to acrylic acid is 70 moles or more from the Ai 7-stage reaction, with a suitable size system of 75 moles. (LJ is good.Acrylic acid by-produced in the first-stage reaction can be supplied as is to the raw material gas used for the second-stage reaction. It provides the same desirable results as the presence of water vapor, and has the effect of substantially reducing the load on the downstream catalyst.

The present invention has been described above, but the present invention will be explained more specifically by showing Examples and Comparative Examples below.

Example 1 Ammonium molybdate 10 was heated while preparing water 15) for the first stage catalyst.
．． 62Kg, ammonium paratungstate 3.24
9 was added to the solution and stirred vigorously (this is referred to as Solution A).

Separately, cobal nitrate +-7,00kg was added to 2t of water, ferric nitrate 2.43kg was added to 2t of water, and hismuth nitrate was added to 2.92kg of water.
9 was acidified by adding 0.6 t of concentrated nitric acid and dissolved in 3 t of cold water, and a mixture of these three types of nitrate solutions was added dropwise to the above solution A. Then, in terms of silicon dioxide, it is 2 ()
2.44 Kq of Noriyoku sol and 20.2 S' of potassium hydroxide containing 2.44 Kq of wt% were dissolved in 1.5 t of water, and the resulting suspension was heated and evaporated, followed by molding. A catalyst was prepared by calcining for 6 hours at 1"/150°C with air flow.The composition of the catalyst other than oxygen was Co4FeIB11w2M010 in atomic ratio.
Sl Yu, 35 Koo, 06.

While heating and stirring 6 tons of prepared water, 1.254 kg of paratungstic acid, 1.254 kg of metavanazine, 0:3 kg of ammonium molybdate, and 4.06 kg of ammonium molybdate were added. Then, mix and dissolve ammonium dichromate Ij, 14 and 9, and separately add nitric acid button II.
An aqueous solution was prepared by dissolving 03Kg in 1,72t of water, and both solutions were mixed. The material is made of α-alumina, has a surface area of 1 m2/?, a porosity of 42 mm, and a fine (with a diameter of 75 to 250 microns).
(The volume occupied by the total pore volume is the diameter of 12 times the total pore volume; 12 tons of granular carrier with 3 to 5 particles is added, evaporated to dryness with stirring, coated on the carrier, and then heated at 400°C. A catalyst was prepared by firing for 5 hours.The composition of this catalyst except for the carrier and other elements in atomic ratio was: Mo 12 V4.6 Cu 2.2 Cr O, 6W
It was 2.4.

"Reaction and acrylic acid collection method" 1st generation early stage catalyst + 2. (1t has an inner diameter of 25 grinds, a length of 3,
A multi-tubular reactor consisting of 10 steel reaction tubes of +100° C. was evenly packed into a multitubular reactor capable of heat exchange by circulating molten salt on the 7th L side, and heated to 1,325°C.

Separately, the second stage catalyst 9. Ot has an inner diameter of 25rn1 and a length of 3.
00 (consisting of 10 1 mm steel reaction tubes), the reactor was evenly packed into a multitubular reactor in which heat exchange could be performed by circulating molten salt on the inner side, and heated to 260°C.

The two reactors were connected by a conduit equipped with a heat exchanger so that the reaction product gas exiting from the reactor containing the first stage catalyst was introduced into the reactor containing the second stage catalyst.

The reaction product gas coming out of the reactor containing the latter stage catalyst has an inner diameter of 20
The tower is made of +1 mm stainless steel and is equipped with a 20-tier bubble rack with a steam jacket on the outer wall, and a multi-tubular cooler at the bottom. The condensed water of the waste water in the tiered concentrator is 1.0/H.
By letting it flow down, acrylic acid is collected as an acrylic acid aqueous solution, and furthermore, the water vapor of the wastewater from the first stage concentrator! , 2 Nm''/Hr was reacted and used as l-11 water vapor.

After removing light boilers from the obtained acrylic acid aqueous solution, acrylic acid was extracted from the acrylic acid aqueous solution using 1.5 times the weight of inpropyl acetate.

The extract contained 0.17 wt % acrolein, formaldehyde, acetaldehyde, etc. in terms of acrolein, and was then subjected to the following steps: solvent separation, light boiling point separation, and finally rectification to obtain the product acrylic acid.

- After removing the solvent from the raffinate, the extracted wastewater (2,41 (9,/Hr) is supplied to the first stage multi-tube concentrator, and then the second stage concentrates. Using the steam generated in the can as a heating source, the steam was heated to 1.2 Nm”/Hr (1,019/Hr).
I■r) was generated and used as reaction steam. The waste water concentrated in the first stage] and 4 to 7/Hr are supplied to the multi-tube concentrator in the second stage, and the waste water is concentrated using the water vapor introduced from the outside as a heating source, and the water vapor is concentrated. OKp/) was generated, and this steam was used as a heating source for the first stage concentrator. The condensed water obtained here was used as absorption water in an acrylic acid absorption tower. The wastewater is concentrated 1.7 times in the first stage concentrator and 4.7 times in the second stage /ζ. The pressure of the steam in the second stage heating source is 6 to 9/n, 2G, and the operating pressures of the second and first stages are 3/c, respectively. t: ”
G and IKri/l:m Set to 2G. Wastewater supplied to concentration 1, steam obtained in the 1st stage, 2nd stage +f+
The analytical values of the resulting condensed water and concentrated water were as shown in Table 1.

Table (Enthronement weight %) Acrylic acid Acetic acid Maleic acid Other organic matter supply water 0.5] 0.56 0.75 0.4:3 The gas discharged from the acrylic acid collection device is partially purged. The rest was returned to the reactor population containing the front-stage catalyst by a blower, and propylene, air, and steam from the first-stage concentrator were added to this, mixed, and introduced into the reactor containing the front-stage catalyst. . To the front reactor, propylene 5.5 volume, water vapor + (1.0 volume, oxygen 12.5 volume,
Mixed gas consisting of a small amount of other reaction products and nitrogen +6
．． It was introduced at a rate of 2 m3/h (in terms of NT and P). At that time, the top temperature of the acrylic acid collector (d35°C) and the waste gas circulation rate were 42.5%.

Thus the conversion of propylene 4'! +5, -+mol regret,
The yield of acrylic acid was 84.0 mol%, and stable operation was possible. In addition, the effluent from the tower Iη of the acrylic acid collection device is ], OKg/Hr, -rcri/l'l'lt
The collection rate was between 8 and 90. At this time, the acid concentration in the raw material gas was 0.07 volume as acrylic acid.

The purity and polymerization performance of the acrylic acid obtained by separating and purifying this acrylic acid aqueous solution using the culm are extremely satisfactory, and the equipment remains stable even after three months of continuous operation. He didn't notice any problems.

Comparative Example 1 The same equipment used in Example 1 was used, with the process modified as described below. In other words, the waste water vapor obtained from the first-stage concentrator is used as a heat source for the second-stage concentrator, and the condensed water is supplied as absorption water to the acrylic acid collection process, and the waste water vapor obtained from the second-stage concentrator is The water vapor produced by it
It was supplied as steam for the first after-treatment. Other reaction conditions and operating conditions were the same as in Example 1, and the concentration of acid circulated into the raw t1 gas was 0.0% as acrylic acid. It has a tl-9 capacity ratio and a propylene conversion rate of 91.
1 mole, and the acrylic acid yield was 83.7 moles, so there was no problem with the reaction, but aldehyde components such as acrolein, formaldehyde, and acetaldehyde in the acrylic acid aqueous solution accumulated, and the extraction process was difficult. The amount of ruthehyde in the liquid becomes +1.93 weight as acrolein,
In a solvent separation column? After continuous operation for a week, the polymer blockage occurred and operation became impossible. A problem occurred in that the acrylic acid that had been deposited also became colored.

Example 2 The following procedure was carried out using the same equipment and process used in Example 1. That is, the raw material gas composition introduced into the Fang 1 reactor as reaction conditions is 6 volumes of propylene, 15 volumes of water vapor, 13.7 volumes of oxygen,
The remainder is reacted with inert gases such as nitrogen and carbon dioxide, and trace amounts of organic compounds mixed in with water vapor, and the temperature at the top of the acrylic acid collection device is reduced to 1()℃, υ
The circulation rate of the 1-output waste was set at a range of 2.1.9. Conversion rate of propylene is 95.1 mol, yield of acrylic acid is 8:L8
Stable operation was carried out by the mole staff. Absorbed water obtained by condensing the 16 water vapor from the second stage of condensation through the first stage of condensation is sent to the acrylic acid collection device.
2.6 Ny+=3/1-1r (], 7 K9/H
r) was supplied to the reactor for oxidation reaction.

The collection rate of acrylic acid was 96 to 97%, and the acid content in the raw material gas was in the ratio of 5 as acrylic acid. The wastewater was concentrated 1.8 times in the first stage of the shredder, and 8.8 times in the second stage. The analytical values of the wastewater supplied to the concentrator (8 K9/Hr), the steam obtained in the first stage, the condensed water of the steam obtained in the second stage, and the bottom liquid concentrated in the second stage are as follows. It was as shown in Table 2.

E 2 Table (Unit: Heavy duty range) Acrylic acid Acetic acid Maleic acid Other organic substances (supply and wastewater (1, 4 (10,420, 6:
351 stage 1] Water vapor 0. :U3 0.37
0. +1・1 F+, iU02nd stage condensed water
II, 38 0-42 +), 01
i fl, II 2nd stage concentrated water tl, 7f
i O,605,(101,12

[Brief explanation of drawings]

FIG. 1 shows one flow sheet for implementing the invention.

Claims (1)

[Claims] (1) In the process of producing acrylic i by catalytic vapor phase oxidation of propylene using water vapor and molecular oxygen-containing gas, part of the waste gas after acrylic acid produced in the oxidation reaction is collected as an aqueous solution. is recycled for the oxidation reaction, while the collected acrylic acid aqueous solution is led to the acrylic acid separation process, and the wastewater discharged there is concentrated using a double-effect can, and the first concentration can The resulting wastewater vapor is recycled for the oxidation reaction, the concentrated liquid is supplied to the second-stage concentrator, and the wastewater vapor obtained in the second-stage concentrator is used as the heat source for the first-stage concentrator. The resulting condensed water was recycled to collect the acrylic acid produced.
A method for producing acrylic acid, which comprises completely oxidizing concentrated wastewater obtained in a third-stage concentrator together with the remainder of the waste gas.