JPS6038341A - Purification of acrylic acid - Google Patents

Abstract

PURPOSE:To obtain acrylic acid together with acetic acid from the bottom of a distillation column economically, preventing the distilling-out of acrylic acid from the column top, by distilling an aqueous solution of acrylic acid containing acetic acid and obtained by the catalytic vapor-phase oxidation of propylene and/or acrolein with a specific distillation column using an azeotropic agnet. CONSTITUTION:Acrylic acid is produced by the catalytic vapor-phase oxidation of propylene and/or acrolein. In the above process, an aqueous solution containing 50-80wt% acrylic acid and 2-8wt% acetic acid and obtained from the above reaction gas is supplied to a distillation column having a recovery zone with a theoretical plate number of >=10, and distilled in the presence of an azeotropic agent having a boiling point of preferably 110-130 deg.C at normal pressure. The azeotropic mixture of the azeotropic agnet and water and essentially free from acrylic acid and acetic acid is distilled out from the top of the column, and a mixture of acrylic acid and acetic acid free from the azeotropic agent and water is obtained from the bottom of the column. The distillate from the column top is pollution-free, and can be reused as the absorbing water for collecting acrylic acid after recovering the azeotropic agnet therefrom.

Description

[Detailed description of the invention] The present invention relates to a method for purifying acrylic acid.

Specifically, the present invention involves catalytic gas phase oxidation of propylene and/or acrine to obtain a reaction gas containing acrylic acid, which is rapidly cooled, condensed and collected, and further absorbed and collected by cooling water. An aqueous acrylic acid solution containing mainly acrylic acid, acetic acid, and water is distilled using an azeotrope to remove acrylic acid and acetic acid and substantially water and the azeotrope. This invention relates to a method for purifying acrylic acid, characterized in that a mixture of acrylic acid and acetic acid is mainly obtained from the bottom liquid, and acrylic acid is separated and purified from the bottom liquid.

Conventionally, methods for producing acrylic acid include the steps of extracting and purifying acrylic acid by extracting an aqueous acrylic acid solution obtained by catalytic gas phase oxidation of propylene and/or acrolein with an organic solvent. In other words, it is common to use an extraction operation as a step for separating water from an aqueous solution (for example,
See specification of Publication No. 30493. ).

However, the water discharged from this extraction T culm contains unrecovered acrylic acid, by-product organic acids such as m-acid, propionic acid, maleic acid, aldehydes such as acrolein and acetaldehyde, and polymerization of these compounds. The wastewater contains high boiling point substances and tar-like substances such as 2@acrylic acid, condensates, etc., and even if it is to be disposed of, it must be detoxified by an activated sludge method or a concentrated combustion method, and equipment for this purpose is required. and utilities, etc., must be extremely costly. On the other hand, even if it is used as absorbed water for acrylic acid collection in the process, the acrylic acid collection efficiency of the acrylic acid collection device will decrease due to the increase in acid content in the process due to the acid content in the wastewater. However, if the exhaust gas from this equipment is reused as an inert gas source for the raw material gas, the acid content in the raw material gas will increase and the oxidation reaction (J It also causes accelerated deterioration of the catalyst activity v1.

In addition, with recent improvements in coordination oxidation reactions and collection technology,
The concentration of the acrylic acid aqueous solution obtained is 50~
J: The sea urchin is becoming more and more 80% by weight.

Therefore, the present invention uses this aqueous acrylic acid solution with a J: height of 11 degrees, and without performing an extraction operation as in the past.
This method was completed by adopting an azeotropic distillation method as a direct dehydration operation, and further investigating a method to suppress the distillation of acrylic acid and acetic acid to the top of the column to only a trace.

That is, the present invention is specified as follows.

[1] When producing acrylic acid by catalytic gas phase oxidation of propylene and/or acrolein, an aqueous acrylic acid solution containing acetic acid obtained from the reaction gas is
The recovery section is supplied to a distillation column with a theoretical plate number of at least 10, and is distilled from the top in the presence of an entrainer. Azeotrope-4- A method for purifying acrylic acid, characterized in that a composition is distilled out and a mixture of mainly acrylic acid and acetic acid, which is free of water and an azeotropic agent, is obtained at the bottom of the column.

[2) The temperature of the azeotropic agent used is 110 to 130°C at normal pressure.
The method described in [1] above, wherein the boiling point is in the range of .

0) The above [1) or (2), wherein the acrylic acid aqueous solution supplied to the distillation column contains acrylic acid in a range of 50 to 80% by weight and acetic acid in a range of 2 to 8% by weight.
Method described.

The present invention will be explained in more detail below, and the purpose of the present invention will become clearer thereby.

Catalytic gas phase oxidation of propylene and/or acrolein using molybdenum-based multi-component catalysts to produce acrylic acid is currently practiced industrially. Recently, oxidation reaction and acrylic acid collection technology have shown great progress.-5-It has become possible to increase the concentration of acrylic acid aqueous solution to 50 to 80% by weight. This means that it is convenient to directly separate water from this aqueous solution by distillation, compared to the conventional method of separating acrylic acid and acetic acid from water by extraction of an aqueous acrylic acid solution.

Moreover, if only water can be efficiently separated from an aqueous acrylic acid solution and essentially acrylic acid and acetic acid can be obtained as a mixture, it is convenient for application to conventional processes. The present invention was developed to meet this objective.

The azeotropic agent used in the present invention is a compound that has a high water transport ability, that is, a compound that increases the proportion of water in the azeotropic composition, has a high boiling point, and has a high boiling point under normal pressure.
A temperature range of 10 to 130°C is preferred. in particular,
Examples include n-butyl acetate, isobutyl acetate, 5ea-butyl acetate, methyl isobutyl ketone, and the like.

Of course, these entrainers have boiling points close to that of acetic acid, and if they were simply subjected to distillation, acetic acid-6-acid would also be distilled out along with water (for example, See the specification of Japanese Patent Publication No. 18967/1983.

). 1- That is, the composition of the distillate becomes an azeotropic agent-foracetic acid composition, which results in the need for a similar separation operation again.

However, the present inventors have discovered that the distillation of acrylic acid can be suppressed by determining the reflux amount so that the vapor at the top of the distillation column has an azeotropic composition at the operating pressure. It was discovered that if the number of theoretical plates in the recovery section was set to at least 10, there would be traces of acetic acid on the distillate side. They discovered that it was possible to extract the bottom liquid.

In the distillation operation, the present inventors have discovered that the concentration peak of acetic acid and the concentration peak ρ of water exist separately. This is considered to be effective in suppressing the distillation of acetic acid. Furthermore, when the amount of acetic acid in the feed liquid increases, the stage where acetic acid is concentrated spreads out, approaches and overlaps the stage where water is concentrated, and some of the acetic acid is distilled out. Therefore, as the acetic acid concentration increases, the number of theoretical plates in the recovery section also increases to 10.
It will be necessary to exceed this level and raise it to about 15 steps. This is because 1 degree of acetic acid II in an acrylic acid aqueous solution is 2 to 8% by weight, which is extremely high.

By the method of the present invention, a distillation method that does not distill out not only acrylic acid but also acetic acid while using an entrainer with a large water carrying capacity has been established. Whereas pollution-free treatment was required through separation and recovery operations, the distillate can now be reused as absorption water for collecting acrylic acid after collecting the entrainer, and the Systemization pr + t? It has become extremely useful for

Example below. 1. The present invention will be explained in more detail by showing comparative examples and comparative examples.

Example 1 A two-stage oxidation reaction was carried out using a molybdenum-based multi-component catalyst to give 66.8% by weight of acrylic acid, 2.1% by weight of M resistance, and 28.8% by weight of water. , -8- What's left? + - An aqueous solution of acrylic acid consisting of aldehyde, acrolein, maleic acid, etc. was added to a distillation column with 48 forced perforated plates (19 theoretical plates) of 100 mm diameter.
It was supplied to each stage at a rate of 11 KLJ/Hr. Methyl isobutyl ketone (MIBK) was used as an entrainer at an overhead operating pressure of 110
It was supplied to the top of the column so that the azeotropic composition at the top of the column at n+m1-1<1 (absolute pressure) and a temperature of 46° C. was 21% by weight (the remainder was mainly water). In addition, hydroquinone was supplied from the top of the tower as a polymerization inhibitor at a concentration of 0.1% by weight based on acrylic acid.
: Air was supplied from the bottom of the column at a rate of 10 (1/l-1r). When the distillation reached a nearly steady state, the 81 degree distribution of each component in the column was measured, and the results were as shown in Table 1. Ta.

The bottom liquid was 7.7 to 9/Hr, but the vinegar M was 3.1%.

Acrylic acid was 96.2% by weight, and M I B K and water were not detectable. The distillate contained trace amounts of acetic acid and acrylic acid.

Comparative Example 1 In the operation in Example 1, the acrylic acid aqueous solution was supplied from the 31st stage, and the rest was carried out in the same manner as = 9 -. Trace amounts of acrylic acid were contained. The distillation rate of acetic acid reached 3210t1%. In addition, there is M in the bottom liquid.
Traces of r B K iJ'3 and water were present. The concentration distribution of each component in the column when the distillation reached a steady state was as shown in Table 1.

Table 1 10- Example 2 The same acrylic acid aqueous solution used in Example 1 was fed to the 21st stage of the same distillation column as used in Example 1, and n-butyl acetate was used as an entrainer.It 130 mlHg (absolute pressure) and temperature 50°C, azeotropic composition 28% by weight (remaining water)
The mixture was charged from the top of the column so that

The bottom liquid contained 3.0% by weight of acetic acid, 96.2% by weight of acrylic acid, n-butyl acetate and water with traces of Pi! A composition of i was obtained. In addition, acetic acid, J: and acrylic acid in the distillate were contained in a total amount of 0.07% by weight.

Example 3 To the same distillation column as used in Example 1, the same aqueous acrylic acid solution as used in Example 1 was fed to the 23rd stage, and isobutyl acetate was added as an entrainer at an operating pressure of 130+no+Ha (absolute pressure) and a temperature of 47%. C. and the azeotropic composition was 19.2% by weight (residual water) from the top of the column, and the rest was distilled in the same manner as in Example 1.

As a bottom liquid, 31% by weight of acetic acid, 96.1% by weight of acrylic acid, and only traces of isobutyl acetate and water were obtained. In addition, trace amounts of acetic acid and acrylic acid were contained in the distillate.

Comparative Example 2 The same procedure as in Example 3 was carried out except that the acrylic acid aqueous solution was supplied to the 33rd stage, and 2.5% by weight of acetic acid was used as the bottom liquid.
, Acrylic I! A composition containing 196.8% by weight, 11) isobutyl acid and trace amounts of water was obtained.

In addition, acetic acid in the distillate was 1.2% by weight, and acrylic acid was 0.2% by weight.
The distillation rate of acetic acid was 18% by weight. , Patent applicant Kusumoto Shokubai Kagaku Kogyo Co., Ltd. -12- Procedural amendment (voluntary) November 2, 1980 Manabu Shiga, Commissioner of the Patent Office1, Indication of case Patent application No. 145645 of 19812, Invention Name of acrylic acid purification method 3, Person making the amendment Patent applicant: 5-1 Koraibashi, Higashi-ku, Osaka, Osaka Prefecture (462) Nippon Shokubai Chemical Co., Ltd. Representative Director: Mibeki Toshikawa 03-502-1651 5. Amendment Section 6 of the detailed description of the invention of the subject application of Meishin 1 Tatami, self-answer of the amendment (1) In the 4th line of page 9 of the specification, it says "In the 23rd step of the tower..." Correct that to "23rd step from the top of the tower..."

(2) On page 9, lines 7-8 of the same page, the statement ``...Azeotropic composition at the top of the column: 21 qb (residual residue is mainly water)...'' has been replaced with [... ...Top azeotrope composition (2111L1i1% water, 79% by weight MIBK)..." is corrected.

(3) In the first line from the bottom of No. 9, the phrase "...supply to the 31st stage..." has been changed to "...supply to the 31st stage..."・・・・・・
” he corrected.

(4) On page 11, lines 5 and 6, “...Azeotropic composition 28% by weight (Zanshoshasui)...”
``...'' means [...Azeotropic composition (Water 28 weight section, Vinegar @! n
-Butyl 72 weight-it%)...'' is corrected.

(5) In lines 5 and 4 from the 11th Teicho, “...
...Azeotropic composition 19.2% by weight (residual water)..."
The statement has been corrected to "...Azeotropic composition (19.21i of water, 80.8% by weight of isobutyl acetate)...".

3- 289-

Claims (1)

[Scope of Claims] [1] When producing acrylic acid by catalytic gas phase oxidation of propylene and/or acrolein, an aqueous acrylic acid solution containing acetic acid obtained from the reaction gas is 10, and distilled in the coexistence of an azeotropic agent, distilling an azeotropic composition substantially consisting of an azeotropic agent and water and not containing acrylic acid and acetic acid from the top of the column; A method for purifying acrylic acid, characterized in that a mixture of mainly acrylic acid and acetic acid is obtained from the bottom of the column without containing water or an entrainer. [2) The temperature of the azeotropic agent used is 110 to 130°C at normal pressure.
The method according to claim (1), characterized in that the aqueous solution of acrylic acid supplied to the distillation column has a boiling point in the range of 50 to 80% by weight of -1- acrylic acid. The method according to claim 0 or [2], characterized in that acetic acid is contained in an amount of 2 to 8% by weight.