JPH0232264B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to the carbonylation products obtained when dimethyl ether and/or methyl acetate and/or methanol are carbonylated in the presence of an iodine-containing catalyst, acetic acid and/or anhydride. The present invention relates to a method for separating iodine and its compounds from acetic acid and/or ethylidene acetate.

PRIOR ART According to DE 28 36 084, for example, the reaction mixtures resulting from carbonylation reactions of this type are usually worked up by distillation. In this case, the non-volatile catalyst components are first separated from the volatile components of the reaction mixture in a first separation step. Next, low-boiling components such as methyl iodide, unreacted methyl acetate and dimethyl ether, and in some cases methanol are distilled off from the top of the column in a low-boiling distillation column. Thereafter, in each subsequent column first the acetic acid and then the acetic anhydride and in the last column optionally ethylidene acetate are isolated overhead.

The carbonylation products obtained in this way contain, as impurities, iodine compounds in the ppm range, which are extremely difficult to identify due to their small concentrations, and are therefore not suitable for initial production in industrial processes using noble metal catalysts. As a product, it can only be used in a very limited manner.

West German Patent Application No. 2104828 describes potassium permanganate, potassium permanganate, obtained from acetic acid by reacting an alcohol or olefin with carbon monoxide in the presence of a catalyst system consisting of a noble metal component and a halogen component. sodium permanganate,
A trace amount of halogen can be removed by treatment with potassium dichromate, sodium dichromate, chromium trioxide, chromium potassium oxalate, potassium chlorochromate, potassium chlorate and/or potassium chromate at 16 to 200°C. A method for removing compound impurities is described. In this case, the acetic acid containing less than 500 ppb of halides, in particular iodides, is added to the acetic acid in an amount of 1.0% by weight relative to the acetic acid before or during the distillation.
contact with the metal compound in an amount up to . In this case the separation of halide compounds reaches 90-98%. This method is not very effective for purifying carbonylation products containing acetic anhydride, since the oxidizing agent reacts with the acetic anhydride and the iodide can no longer be bound.

German Patent Application No. 2 256 510 relates to a process for removing trace amounts of iodine from acetic acid, in which iodine-containing compounds are distilled into oxides in a system of two distillation columns. , hydroxides, carbonates, bicarbonates and salts of weak organic acids of alkali and alkaline earth metals;
Alternatively, depending on the iodine content present in each case, up to a final content of <40 ppb to <5 ppb can be removed from the acetic acid used by adding a mixture of alkaline earth metal compounds and hypophosphorous acid. In this process, the alkali and alkaline earth metal salts and the hypophosphorous acid are used in the form of an aqueous solution. This means that the purification method described above is not suitable for removing impure iodine compounds from acetic anhydride, since in this case the anhydride is saponified.

German Patent Application No. 2901359 describes a process for removing iodine from organic compounds, in particular from mixtures obtained when olefins are oxidatively acylated with iodine-containing catalysts, such as carboxylic acid esters of ethylene or propylene glycol. is described, and in this case, the iodine-containing organic compound is heated at 50 to 200℃.
with an oxidizing agent and the reaction mixture is simultaneously or subsequently contacted with an adsorbent for iodine. The oxidizing agent used is preferably oxygen or hydrogen peroxide, and the adsorbent used is preferably activated carbon. In the examples hydrogen peroxide (20%) is used as the oxidizing agent. Iodine removal reaches 92.4-99.5%,
The iodine content is only reduced to 40 ppm, which does not quite satisfy the required purity. This case too has the disadvantage that water is introduced into the system due to the use of hydrogen peroxide.

German Patent Application No. 3107731 describes a method for separating organic iodine compounds from carbonylation products of methanol, methyl acetate and dimethyl ether by liquid phase extraction using non-aromatic hydrocarbons. . In this case, according to the embodiment, the iodine content is only reduced to a maximum of 100 ppb iodine. Even ignoring that the iodine value is too high, this process is prohibitively expensive due to the additional distillation of the extractant.

According to DE 2940751 A1, iodine compounds present as impurities are removed from the carbonylation product of methyl acetate by treatment with cesium, potassium and/or sodium acetate. , the corresponding alkali metal iodide is obtained. Methyl iodide reduction amount
2 ppm does not meet the requirements of purified carbonylation products and further processing. Furthermore, gas chromatographic analysis of methyl iodide does not allow a complete understanding of the total iodine content in the carbonylation product, and therefore it is difficult to report on the effectiveness of iodine separation.

Problem to be Solved by the Invention The problem of the present invention is not to limit the removal of iodine-containing substances to alkyl- and aryl iodides or other easily distillable iodine-containing compounds, but to The object of the present invention is to obtain a process by which all aspects of iodine can be separated almost quantitatively from the input product to be purified. Examples of removable iodine compounds include butyl iodide, ascent iodide, acetyl iodide,
Mention may be made of hydrogen iodide and optionally substituted ammonium and phosphonium iodides.

Means for Solving the Problem This problem is solved according to the method of the present invention in order to reduce the amount of total iodine that impures the carbonylation product to an iodine content of 20 ppb or less.
The solution is to treat with peracetic acid, diacetyl peroxide or compounds which give rise to these substances under reaction conditions at temperatures of ~200°C and to separate them by distillation.

Furthermore, the process according to the invention advantageously and selectively comprises: a) using a carbonylation product with a total iodine content of less than 100 ppm; b) carrying out the treatment of the carbonylation product at a temperature of 100 to 140° C. for 0.5 to 120 minutes. c Characterized by fractional distillation of carbonylation products treated with peracetic acid, diacetyl peroxide or compounds that give rise to these substances under the reaction conditions.

According to the invention, iodine compounds or elemental iodine, which are extremely difficult to separate by distillation methods and which are still present as impurities in the carbonylation product from which the catalyst and low boilers have already been removed, can be distilled off by treatment with peracetic acid. It was unexpected that the iodine compound could be converted into an iodine compound that could be easily separated by the process and that an iodine-free carbonylation product could actually be obtained after the rectification process without the use of an adsorbent.

A special advantage of the treatment with peracetic acid is that, in the presence of acetic anhydride, this becomes acetic acid when reacted with iodine compounds, and the concentration of acetic acid present in any case in the mixture of carbonylation products increases only slightly. It is to be.

peracetic acid is used in at least a stoichiometric amount relative to the total iodine content in the carbonylation product;
As a result, the mixture of carbonylation products to be further worked up by distillation no longer contains unreacted peracetic acid.

Examples Example 1 To 1000 g of a carbonylation product mixture containing 80% by weight of acetic anhydride, 20% by weight of acetic acid and 800 ppb of iodine in the form of little known iodine compounds, 30 g of a 10% solution of peracetic anhydride in glacial acetic acid are added, Heat at 120°C for 60 minutes. A subsequent fractional distillation yields pure acetic acid and pure acetic anhydride with an iodine content of <10 ppb.

Example 2 (comparative example) Example 1 is repeated, but without adding the peracetic acid solution. The acetic acid obtained by fractional distillation contains 2800 ppb of iodine, and the acetic anhydride obtained contains 300 ppb of iodine.

Example 3 To 1000 g of a carbonylation product mixture containing 90% by weight of acetic anhydride, 10% by weight of acetic acid and 1200 ppb of iodine in the form of little known iodine compounds, 20 g of a 10% solution of peracetic anhydride in glacial acetic acid are added and heated to 132°C. Heat for 15 minutes. A subsequent fractional distillation yields pure acetic acid and pure acetic anhydride with an iodine content of <10 ppb.

Example 4 (Comparative Example) Example 3 is repeated, but without adding the peracetic acid solution. The acetic acid obtained by fractional distillation contains 7000 ppb of iodine, and the acetic anhydride obtained contains 400 ppb of iodine.

Example 5 To 1000 g of a carbonylation product mixture containing 80% by weight of acetic anhydride, 20% by weight of acetic acid and 1100 ppb of iodine in the form of little known iodine compounds, 20 g of a 10% solution of peracetic anhydride in glacial acetic acid are added at 132 °C. 15 at temperature
Add continuously over a period of minutes. Fractional distillation then produces acetic acid and acetic anhydride with an iodine content <10 ppb.

Example 6 In a continuously operating laboratory apparatus for the production of acetic anhydride by carbonylation of dimethyl ether and methyl acetate, after separation of the noble metal catalyst and the low boilers methyl iodide and unreacted methyl acetate. 100 parts of the resulting product stream consisting of 80% by weight of acetic anhydride and 20% by weight of acetic acid and having an iodine content of 600 ppb are continuously fed in such a way that the average residence time at 138° C. in the reaction tube is 30 minutes. and add 3 parts of a 10% anhydrous solution of peracetic acid in glacial acetic acid. Fractional distillation then produces acetic acid and acetic anhydride with an iodine content <10 ppb.

Example 7 Example 6 is repeated, but the peracetic acid solution is metered directly into the bottom of the low-boiling distillation column at a temperature of 138°C. In this column, methyl iodide and unreacted methyl acetate are quantitatively separated from the top of the column. In this case, the average residence time is 20 minutes. In the next fractional distillation of the bottom product, the iodine content <
10 ppb of acetic acid and acetic anhydride are obtained.

Example 8 (Comparative Example) Example 7 is repeated without adding peracetic acid solution to the bottom of the low-boiling distillation column. The acetic acid obtained after fractional distillation is iodine
Contains 2400ppb, and the obtained acetic anhydride contains iodine
Contains 150ppb.

Example 9 75% by weight of acetic acid and H ₂ O ₂ (60% by weight) 7.5 to a product stream consisting of 25% by weight of acetic anhydride and an iodine content of 800 ppb
% by weight and 3 parts of acetic acid containing 30% by weight of acetic anhydride. Under the conditions that will now exist, the well-known peracetic acid is formed (Findley, Swern, Sceanlan, Journal of the American Chemical Society (J.Amer.Chem Soc.), 67
(1945), p. 413; Hopff, Hoffmann paper,
"Belvetica Chimica Acta" (Helv.Chim.
Acta), 40 (1957), pp. 1585, 1590). The temperature inside the reaction tube was 123°C, and the average residence time was 30 minutes. In the next fractional distillation, the iodine content <
10 ppb of acetic acid and acetic anhydride are produced.

Example 10 (comparative example) 0.8 g of potassium permanganate is added to 1000 g of a carbonylation mixture containing 75% by weight of acetic acid and 25% by weight of acetic anhydride and 800 ppb of iodine in the form of an unknown iodine compound.
Add. The mixture was then heated under reflux for 60 minutes at 120 °C.
Heat at ℃. After distilling off the added oxidizing agent, this process determines the iodine value in the product mixture.
It was only reduced to 200ppb.

Claims (1)

[Claims] 1. A method for separating iodine and its compounds from acetic acid, acetic anhydride or ethylidene acetate, which are carbonylation products obtained when dimethyl ether, methyl acetate or methanol is carbonylated in the presence of an iodine-containing catalyst. To reduce the amount of total iodine contaminating the carbonylation product to a content below 20 ppb iodine, the carbonylation product was treated with peracetic acid, diacetyl peroxide or these substances under the reaction conditions at a temperature of 20 to 200 °C. A method for separating iodine and its compounds from a carbonylation product obtained during carbonylation of dimethyl ether, methyl acetate or methanol, which comprises treating with a compound that produces iodine and separating it by distillation. 2. The process according to claim 1, wherein a carbonylation product having a total iodine content of less than 100 ppm is used. 3. The treatment of the carbonylation product is carried out at a temperature of 100-140°C for 0.5-120 minutes.
or the method described in paragraph 2. 4 Fractional distillation of carbonylation products treated with peracetic acid, diacetyl peroxide or compounds that give rise to these substances under the reaction conditions, claim 1
The method described in any one of paragraphs to paragraphs 3 to 3.