JPH10168024A - Purification of acetic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently obtain acetic acid useful in petrochemical industry and organic chemical industry by a simple method by introducing ozone into a distillation column and distilling acetic acid containing impurities while bringing ozone into contact with the acetic acid. SOLUTION: In the method for purifying acetic acid containing organic halides (n-butyl iodide, etc.) obtained by a carbonylation reaction of one or more selected from among methanol, methyl acetate and methyl ether and carbon monoxide in the presence of a catalyst containing a metal of the group VIII (e.g. rhodium catalyst in 200-1,000ppm in a reaction solution), 5-20wt.% of methyl iodide in the reaction solution and water at 150-250 deg.C under 2-30a atmospheric pressure, >= about 1ppm of ozone based on the weight of the acetic acid to be treated is introduced into a distillation column and the acetic acid is distilled while bringing ozone into contact with the acetic acid containing impurities in an ordinary retention time to give high-purity acetic acid useful as a fundamental chemical.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for purifying acetic acid. The present invention particularly relates to a method for purifying acetic acid containing, as an impurity, an organic halide obtained by a catalytic carbonylation reaction of methanol with a rhodium catalyst.

[0002]

BACKGROUND ART Acetic acid is used in petrochemical industry, organic chemical industry,
It is one of the basic chemicals used in large quantities in the pharmaceutical and agrochemical manufacturing industries, the polymer chemical industry, and the like.

Acetaldehyde oxidation, naphtha oxidation and the like have long been used as industrial methods for producing acetic acid, but the simplest method is a method involving the carbonylation of methanol (US Pat. No. 3,769,329). is there. In this method, during the carbonylation of methanol,
Rhodium is used as the metal catalyst and organic halide is used as the cocatalyst.The former is dissolved or dispersed in the reaction solution or supported by an insoluble solid, and the latter is an organic iodide, especially methyl iodide. Is used. Also, most typically and generally, the reaction is carried out using a catalyst dissolved in a liquid reaction medium in which carbon monoxide gas is constantly bubbled.

[0004] Although the above-mentioned production method is widely used as a method in which generation of impurities is small, acetic acid such as an unsaturated organic compound, a reducing organic compound, and an organic halide produced by a side reaction is mixed therein. Must be sufficiently removed from The acetic acid quality test includes a test called a permanganate reducing substance test (permanganate thyme) that uses a quantitative method based on the reduction action on permanganate, and the product acetic acid must pass this test. However, impurities causing this deterioration include carbonyl compounds, organic halides, etc., and these impurities deactivate the catalyst especially for certain uses, for example, conversion of acetic acid to vinyl acetate. It must be removed from the product acetic acid. Usually, these impurities are removed by distillation, but the boiling point of the organic halide contained as impurities is often a value close to the boiling point of acetic acid, and carbonyl compounds such as acetaldehyde are the boiling points of methyl iodide. In many cases, it is extremely difficult to completely remove these by a physical method called distillation.

Various techniques have been proposed to solve the above problems. For example, a method of removing an amino compound by reacting a carbonyl compound as an impurity is disclosed in
-74634 and JP-A-4-266684. Further, a method of removing a carbonyl compound by utilizing azeotrope is disclosed in JP-B-3-51696 and JP-B2-394.
No. 90. However, these methods can reduce carbonyl compounds, but cannot sufficiently remove organic halides. Recently, various methods using an ion exchange resin have been disclosed as a method for removing alkyl iodides (Japanese Patent Publication No. 5-21031).
JP-A-5-246935, JP-A-4-28233
9, JP-A-6-40999, JP-A-5-12501
No. 1, JP-A-5-301839). However, a large amount of equipment is required for the ion exchange resin treatment. Further, the wet product stream taken out from near the bottom of the methyl iodide-acetic acid splitter column is dried by distillation. No. 46924 discloses an azeotropic method with methyl acetate in JP-B-61-8811. In the above-mentioned method, it is possible to improve the separation efficiency of alkyl iodide by increasing the reflux ratio, but even if both are used, it cannot be sufficiently removed to a satisfactory level.

A method for removing organic iodides, unsaturated compounds and carbonyl compounds using ozone is disclosed in
No. 211548. This method involves contacting ozone with the product after distillation of the wet product stream removed from near the bottom of the methyl iodide-acetic acid splitter column, but after treating with ozone, further adding a saturated aldehyde. Purification, such as treatment with activated carbon, is required to remove the species.

Further, a method of treating a fraction of a splitter column in which a reducing compound (unsaturated compound) causing deterioration of permanganate time is concentrated with ozone is disclosed in Japanese Patent Application Laid-Open No.
No. 133249. However, even if the fraction is subjected to ozone treatment, the reducing substance generated in the reactor is continuously supplied to the distillation column, so that the reducing substance always exists in the column and prevents the product from being mixed into acetic acid. It is not possible. Further, it is impossible to reduce the ppb-order alkyl iodide mixed in the acetic acid product.

[0008]

DISCLOSURE OF THE INVENTION The present invention provides a method for efficiently producing high-purity acetic acid by a simple method without using a large amount of equipment, that is, containing an organic halide as an impurity. It is an object to provide a method for purifying acetic acid.

[0009]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, by blowing ozone into a distillation column in a process for producing acetic acid, it is possible to simultaneously decompose impurities while decomposing products. Was found to be able to be removed, and high-purity acetic acid could be efficiently produced, and the present invention was completed.

[0010] That is, the present invention provides a method for purifying acetic acid containing an organic halide as an impurity, wherein ozone is blown into a distillation column and distilled while contacting with the acetic acid containing the impurity.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The acetic acid production process according to the present invention will be described.

The group VIII metal-containing catalyst used in the present invention is rhodium, iridium, ruthenium, osmium,
Examples include compounds such as cobalt and nickel. The catalyst can be used in any suitable form that can be dissolved or converted to a soluble form under the reaction conditions. The form of the rhodium catalyst may be any as long as it can form a rhodium carbonyl complex species in the reaction system, and non-limiting examples include RhX ₃ (wherein
X represents Cl, Br or _{I), RhX 3 · 3H 2} O
(Wherein X represents Cl, Br or I), Rh ₂ (C
O) ₁₆ , Rh (CO) X [(C ₆ H ₅ ) ₃ M] ₂ (where X represents Cl, Br or I, M represents P, As or Sb), Rh (CO) ₂ X [(C ₆ H ₅ ) ₃ M] (where X represents Cl, Br or I, M represents P, As or Sb), HRh (CO) [(C ₆ H ₅ ) ₃ P] ₃ , [R
h (C ₂ H ₄ ) Cl] ₂ , K ₄ Rh ₂ X ₂ (SnX ₃ )
₄ (wherein, X represents Cl, Br or I) and a rhodium component described in JP-B-47-3334. The concentration of rhodium in the reaction solution is 200-1,000.
0 ppm, preferably 300 to 600 ppm.

[0013] Non-limiting examples of the use form of the iridium catalyst include IrX ₃ (where X represents Cl, Br or I), [Ir (CO) ₂ X ₂ ] (where X is C
l, Br or I), [Ir (CO) ₂ X ₂ ]
^- (wherein, X represents Cl, Br or I), [Ir (C
_{H 3) X 3 (CO)} 2] - ( wherein, X is Cl, represents Br or _{I), Ir 4 (CO)} 12 IrX 3 · 4H 2 O
(Wherein, X represents Cl, Br or I), _IrX 3 · 4
H ₂ O (where X represents Cl, Br or I), Ir ₃
(CO) ₁₂ , iridium metal, Ir ₂ O ₃ , Ir
O ₂ , Ir (acac) (CO) ₂ , Ir (acac)
(CO) ₃ , iridium acetate [Ir ₃ O (OAc)
₆ (H ₂ O) ₃ ] [OAc], [H ₂ IrX ₆ ] (wherein X represents Cl, Br or I), and preferably, for example, acetate, oxalate and acetoacetate And halogen-free complexes of iridium. The concentration of iridium in the reaction solution is 500 to 4,000 pp
m, preferably from 2,000 to 3,000 ppm.

As a non-limiting example of the mode of use of the ruthenium catalyst, RuX ₃ (where X is Cl, Br or I
The _{represented), RuX 3 · 3H 2 O} ( wherein, X is Cl, Br
Or I), ruthenium chloride, ruthenium oxide, ruthenium (III) formate, [Ru (CO) ₃ X ₃ ] ⁻ H ⁺
(Wherein X represents Cl, Br or I), tetra (aceto) chlororuthenium (II, III), ruthenium acetate (II
I), ruthenium (III) propionate, ruthenium (III) butyrate, ruthenium pentacarbonyl, triruthenium dodecacarbonyl and mixed ruthenium halocarbonyls such as dichlorotricarbonyl (II) dimer, dibromotricarbonylruthenium (II) dimer, and Other organic ruthenium complexes, such as tetrachlorobis (4-cymene) diruthenium (II), tetrachlorobis (benzene) ziruthenium (II), dichloro (cycloocta-1,5-diene) ruthenium (II) polymer and tris (Acetylacetonate) ruthenium (III) and the like.

The use form of the osmium catalyst includes, but is not limited to, OsX ₃ (where X is Cl, Br or I
), OsX ₃ .3H ₂ O (where X is Cl, Br
Or I), osmium metal, osmium tetroxide,
Triosmium dodecacarbonyl, pentachloro-μ-
Nitrodiosmium, as well as mixed osmium halocarbonyls such as tricarbonyldichloroosmium (I
I) Includes dimers and other organic osmium complexes. The concentration of osmium in the reaction solution is 500 to 4,000.
0 ppm, preferably 2,000 to 3,000 ppm.

These catalysts can be used alone or in combination of two or more.

Hereinafter, a case where a rhodium catalyst is used will be described as an example.

In the present invention, an iodide salt is added particularly as a stabilizing agent for the rhodium catalyst under a low water content and as a promoter.
This iodide salt may be any as long as it generates iodide ions in the reaction solution. If example, LiI, NaI, KI, RbI , alkali metal iodide salts such as _{CsI, BeI 2, MgI 2,} CaI
Alkaline earth metal iodide salts such as ₂ , BI ₃ , AlI ₃
And other aluminum group metal iodide salts. Organic iodide salts other than metal iodides may be used. For example, quaternary phosphonium iodides (eg, methyl iodide adducts such as tributylphosphine and triphenylphosphine or hydrogen iodide adducts), and quaternary ammonium iodide salts (E.g., methyl iodide adducts or hydrogen iodide adducts such as tertiary amines, pyridines, imidazoles, and imides). Particularly, an alkali metal iodide salt such as LiI is preferable. The amount of the iodide salt used is 0.07 to 2.5 mol / l as iodide ion in the reaction solution, and preferably 0.25 to 1.5 mol / l.

In the present invention, methyl iodide is used as a catalyst promoter and is present in the reaction solution in an amount of 5 to 20% by weight, preferably 12 to 16% by weight. The water concentration in the reaction solution in the present invention is 15% by weight or less, preferably 10% by weight or less, more preferably 1 to 5% by weight. Further, 0.1 to 30% by weight of methyl acetate, preferably 0.1 to 30% by weight.
It is present in an amount of 5 to 5% by weight, and the remaining main component in the reaction solution is acetic acid, which is a product and also a reaction solvent. When dimethyl ether and methyl acetate are used as raw materials, they react with carbon monoxide to form acetic anhydride, and then quickly react with water to form acetic acid.

The typical reaction temperature of the carbonylation in the present invention is about 150-250 ° C, and about 180-220 ° C.
A temperature range of ° C. is preferred. The carbon monoxide in the reactor can vary widely, but is typically about 2-30 atmospheres, preferably 4-15 atmospheres. The total reactor pressure is about 15-40, due to the partial pressure of the by-products and the vapor pressure of the liquid involved.
Within atmospheric pressure.

The reaction of methanol to acetic acid-the acetic acid recovery system includes a carbonylation reactor, a flasher and a methyl iodide-acetic acid splitter column. In carbonylation reactors, the reaction liquid contents are usually automatically maintained at a constant level. Fresh methanol and sufficient water are continuously introduced into the reactor as needed to maintain at least a measurable water concentration in the reaction medium.

The crude reaction liquid obtained by the carbonylation reaction in the presence of a catalyst, a cocatalyst, a catalyst stabilizer and a reaction accelerator is withdrawn from the reactor and introduced into a flasher. The flasher is preferably at a pressure below the carbonylation reaction pressure,
Typically, a pressure of 1 to 6 atmospheres is maintained. The flasher is maintained at a temperature of 100-200 ° C. with or without heating or cooling.

The catalyst circulating liquid containing a catalyst component which does not evaporate in the flasher is circulated to the carbonylation reactor as it is, or if necessary, treated with hydrogen or carbon monoxide.

The vapor fraction vaporized by the flasher is supplied as vapor and / or liquid to a methyl iodide-acetic acid splitter column. The methyl iodide-acetic acid splitter column can preferably be operated at about the same pressure as the flasher, but can also be operated at higher or lower pressures. The operating temperature of the methyl iodide-acetic acid splitter column depends on the supplied component composition, the operating pressure, the number of stages, and the amount of reflux.

From the top of the methyl iodide-acetic acid splitter column, a low-boiling-point circulating stream consisting mainly of methyl iodide is withdrawn and recycled to the carbonylation reactor. Also,
From the bottom or sidestream near the bottom, a wet product stream consisting mainly of acetic acid is withdrawn, introduced into the next distillation column and dried. The dried acetic acid stream may be used as it is or may be subjected to further processing as necessary to produce acetic acid.

In the present invention, in such an acetic acid production process, impurities such as organic halides are decomposed in a distillation column such as a methyl iodide-acetic acid splitter column or a distillation column for drying a wet product stream. A sufficient amount, that is, about 1 ppm or more of ozone based on the weight of acetic acid is blown in, and the decomposition product is removed by distillation while being brought into contact with the acetic acid containing the above impurities and decomposing. Further, after the ozonolysis treatment of acetic acid containing the above impurities, a method of separating the decomposed product from acetic acid using a subsequent step such as distillation or adsorption or treatment with an ion exchange resin is also possible. However, performing ozone decomposition treatment using the existing distillation column under the operating conditions of the distillation column not only eliminates the need for new equipment, but also enables continuous multi-stage gas-liquid contact reactions and significantly increases ozone treatment efficiency. ,preferable.

The ozone generator is not particularly limited as long as it can be used for experiments or industrially.

The main impurities to be treated are alkyl halides, n-butyl iodide, i-butyl iodide, ethyl iodide, propyl iodide, pentyl iodide, hexyl iodide, heptyl iodide. And octyl iodide, such as alkyl iodides having up to about 10 carbon atoms in the alkyl group, and mixtures thereof. In addition, by implementing the present invention, impurities such as unsaturated compounds and carbonyl compounds can be reduced at the same time.

The maximum concentration of ozone in the processing solution is determined by the explosion range at the above-mentioned composition and temperature of the acetic acid-ozone mixture. In particular, care must be taken that the off-gas of the condenser at the top of the distillation column does not enter the explosion range. There is. If necessary, an appropriate amount of an inert gas such as nitrogen may be charged. In addition, the ozone reaction generally passes through the ozone adduct ozonide and peroxide (peroxide), which are decomposed and completed. If an excessive amount of ozone is used, a very unstable ozonide may be explosively decomposed. Therefore, care must be taken, for example, in the presence of a reducing agent.

Although ozone may be blown into any part of the distillation column, it is preferable to blow ozone so as to disperse entirely in the liquid phase at the bottom of the distillation column in order to increase the residence time. The contact time between ozone and the treatment liquid is determined by the residence time in the distillation column, and the treatment can be repeated. However, the residence time in ordinary distillation can provide a sufficiently good result.

The amount of ozone is about 1 ppm or more, preferably about 1 ppm to 50 ppm, based on the weight of the acetic acid to be treated.

It is preferable that the amount of the ozone-containing gas blown be 0.6% by weight or less based on the liquid or gas supplied to the distillation column so as not to affect the gas-liquid contact efficiency of the distillation column. The temperature and pressure of the ozone treatment may be determined according to the distillation operation conditions selected for the purpose of the distillation column. The pressurizing condition and the depressurizing condition are appropriately selected. If the pressurizing condition is selected, the operating temperature inevitably increases due to the rise in boiling point, and as a result, the decomposition reaction rate by ozone and the ozone treatment efficiency increase remarkably. Can be done.

[0033]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

In the following examples, the test equipment for the production of acetic acid was prepared by using a reaction liquid composition of 14% by weight of methyl iodide and 8 parts of water.
Weight%, methyl acetate 1.6 weight% acetic acid 70.9 weight%,
A liquid (wet product stream) drawn from near the bottom of the methyl iodide-acetic acid splitter column was obtained during operation with lithium iodide 5 wt% and rhodium 400 ppm to remove organic halide impurities. The analysis of the organic halide was performed by gas chromatography equipped with an ECD (Electron Capture Detector).

[0035]

Comparative Example 1 Assuming a distillation column for drying a wet product stream, an experiment was conducted under normal pressure at a reflux ratio of 2.2 using a 40φ Older Show (50 stages).

The bottom liquid was acetic acid, and the bottom rate was 79% by weight of the charged amount. The bottom temperature was 121 ° C and the tower top temperature was 98 ° C. The charged liquid was introduced from the 33rd stage from the bottom. The analysis results of the hexyl iodide concentration are as follows.

[0037]

[Table 1]

[0038]

Comparative Example 2 The bottom of the distillation column obtained in Comparative Example 1 was charged into a stirring tank, and ozone produced from air (ozone concentration in air: 0.5 vol%) was blown at 0.072 NL / min.
Batch processing was performed. Operating conditions were normal pressure and 35 ° C. The analysis results of the hexyl iodide concentration are as follows.

[0039]

[Table 2]

[0040]

Comparative Example 3 In the distillation column of Comparative Example 1, methanol was introduced into the 43rd column from the bottom in an amount of 3% of the weight of the charged liquid.
This methanol reacts with acetic acid in the column to form methyl acetate and water, which azeotropes with the organic halide. The amount of heated steam and the amount of distilling were increased by an amount equivalent to 3%. The analysis results of the hexyl iodide concentration are as follows.

[0041]

[Table 3] In order to reduce the hexyl iodide concentration to the same level as in Example 1 without ozone treatment, the heating steam and the rising steam in the distillation column must be increased by 3%, which is uneconomical. I have.

[0042]

Example 1 0.056 NL of ozone produced from air (ozone concentration in air: 0.5 vol%) was placed on the bottom of a distillation column.
The same operation as in Comparative Example 1 was performed except that the air was blown at a rate of / min.
Nitrogen gas at 0.2 NL / min was introduced into the overhead condenser. The analysis results of the hexyl iodide concentration are as follows. In addition, no peroxide was detected.

[0043]

[Table 4]

[0044]

Example 2 The same operation as in Example 1 was carried out except that the blowing amount of ozone produced from air was changed to 0.205 NL / min. Although 0.5 NL / min of nitrogen gas was introduced into the overhead condenser, the effect on the condenser capacity was negligible.

After decomposition of hexyl iodide, an increase in methyl iodide and hydrogen iodide was observed in the distillate, but it was confirmed that there was no remarkable increase in the concentration of these decomposed components in the bottom acetic acid. .

[0046]

[Table 5] The permanganate time of the bottoms was 240 minutes or more.

It is also possible to further increase the removal efficiency of organic halides by increasing the operating pressure by conducting distillation at an increased operating pressure.

[0048]

According to the present invention, acetic acid containing an organic halide as an impurity can be efficiently purified by a simple method without using a large amount of equipment.

Claims (4)

[Claims] 1. A method for purifying acetic acid containing an organic halide as an impurity, wherein ozone is blown into a distillation column to perform distillation while contacting the acetic acid containing the impurity. 2. A reaction mixture of carbon monoxide with one or more selected from methanol, methyl acetate and dimethyl ether in the presence of a Group VIII metal-containing catalyst, methyl iodide and water, and the reaction crude from a carbonylation reactor. Withdraw the liquid,
The catalyst circulating liquid containing a catalyst component which is introduced into the flasher and does not evaporate in the flasher is circulated to the carbonylation reactor, and the steam fraction evaporated in the flasher is separated into steam and / or steam.
Alternatively, in a method of purifying acetic acid containing an organic halide as a liquid to a methyl iodide-acetic acid splitter column and purifying the acetic acid containing an organic halide with the methyl iodide-acetic acid splitter column and / or a subsequent distillation column, A method for purifying acetic acid, characterized in that the acetic acid is blown into the inside and distilled while being brought into contact with the acetic acid containing the impurity. 3. The method according to claim 1, wherein the amount of ozone contacted is about 1 ppm or more based on the weight of acetic acid to be treated.
The method for purifying acetic acid according to the above. 4. The organic halide is n-butyl iodide,
The method for purifying acetic acid according to claim 1 or 2, which is i-butyl iodide, sec-butyl iodide, pentyl iodide, hexyl iodide, heptyl iodide, or octyl iodide.