JPS60222439A - Purification of crude acetic anhydride - Google Patents

Abstract

PURPOSE:To produce the titled compound economically in an industrial scale, without necessitating the distillation process, etc., nor causing the problems such as the formation of a resin by thermal degradation and the post-treatment, by treating a crude acetic anhydride with an ozone-containing gas under normal temperature and pressure. CONSTITUTION:Crude acetic anhydride produced by decomposing acetic acid and absorbing the resultant ketene in acetic acid, is purified by treating with an ozone-containing gas. The ozone-containing gas may be air or oxygen ozonized with a commercially available ozonizer, and the concentration of ozone is usually 10-20g/m<3> in the case of using air as the raw material. The consumption of the ozone is 300-1,000g-O3/T, preferably 300-600g-O3/T. The reaction can be carried out at normal temperature. The contact of the reaction liquid with the reaction gas can be carried out in a tank or tower, and if necessary, the system may be furnished with a cooling apparatus.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for purifying crude acetic anhydride obtained by the ketene method.

[Conventional technology]

Industrial methods for producing acetic anhydride include the Wacker method (ketene method), in which acetic acid is thermally decomposed to obtain ketene, and the ketene is absorbed and reacted with acetic acid to obtain acetic anhydride, and methyl acetate is reacted with carbon monoxide. Although the so-called Halcon method and the like are known to obtain at least acetic anhydride, the Varaka method, which involves thermal decomposition of acetic acid, is more common.

Crude acetic anhydride obtained by absorbing and reacting ketene obtained by thermally decomposing acetic acid with acetic acid contains a considerable number of various impurities, and these impurities are separated by distillation.

[Problem that the invention seeks to solve]

Acetic anhydride used in the cellulose acetate production process is often made from acetic acid that has been concentrated and recovered from the acetic acid aqueous solution discharged from the cellulose acetate production process, and this concentrated acetic acid contains impurities from the cellulose system. are contained without being completely removed, so the produced acetic anhydride is also subject to the disadvantages of these.

Since the crude acetic anhydride thus obtained contains various low-boiling and high-boiling compounds generated during the thermal decomposition reaction of acetic acid and the absorption reaction of ketene and acetic acid, it is removed by distillation to remove low and high boiling points. Acetic acid decomposes into acetic acid and ketene in equilibrium at high temperatures, and ketene reacts with each other to form diketene and its high-boiling compounds, resulting in a decrease in yield and an increase in thermal energy used for purification. This increases consumption (this is clear from the fact that the colorless and transparent acetic anhydride made from the steamer becomes more colored when heated under normal pressure, and the degree of coloration increases over time).

In addition, the high-boiling compounds produced by-product at this time are further converted into resin-like chars and adhere to the inside of the tower and the walls of heat exchangers, etc., resulting in a decrease in operating efficiency and troubles.

Although the identity of the impurities contained in acetic anhydride has not yet been fully elucidated, the potassium permanganate test (hereinafter referred to as the Chameleon test) and the sulfuric acid coloring test (hereinafter referred to as the Chameleon test) are commonly used as practical measures to evaluate the quality of acetic anhydride. , and tear adhesion test) (chameleon test) Acetic anhydride with a long retention time and a low APHA value, which indicates the state of coloration in the tear adhesion test, is considered to be of good quality.

The Chameleon test was conducted with J-Ko S K-8886, and the Sulfur Test Company sample! Add 0.5- sulfuric acid to +01 and 25℃
After 5 minutes have elapsed, the colored state is expressed using APHA. Since impurities in acetic anhydride cannot be easily removed by distillation alone, chemical addition methods are used as a quality improvement measure. However, with these addition methods, post-processing (especially waste pollution problems) is troublesome.

[Means for solving problems]

As a result of long-term research into a method for obtaining high-quality acetic anhydride, the inventors of the present invention have developed a purification method that is completely different from conventional methods and does not have these disadvantages. Discovered a method to obtain acetic anhydride of a high quality equivalent to or better than that of distilled purified products (chameleon test: long retention time, breakage test: pale APHA) without performing distillation operations. The invention has been completed.

The purification method of the present invention requires a good puncture test for distilled products, and the acetic anhydride is used for treating cellulose, which contains a large amount of reducing substances and has a secondary problem of coloration. Particularly valuable if. In other words, the single process 11 of contact treatment with ozone-containing gas does not require υ1 thermal energy, and the chameleon test and fracture test can be improved without reducing the yield of acetic anhydride by increasing the temperature. acetic anhydride can be obtained.

[Effect]

The raw material crude acetic anhydride used in the present invention can be applied to any concentration of crude acetic anhydride during the ketene method acetic anhydride production process, as well as those with a chameleon test of 0 minutes and a sulfurization test of PHA 500 or higher. However, as the amount of impurities in the crude acetic anhydride obtained from the reaction process increases, the amount of ozone-containing gas injected increases. For this reason, it is more effective to produce crude acetic anhydride by selecting reaction conditions that reduce the amount of double bond components such as diketene contained in the crude acetic anhydride.

Furthermore, by leaving an appropriate amount of ozone in the treated acetic anhydride, it is advantageous in that its oxidizing power can be utilized when the acetic anhydride is used in the cellulose acetate production process in the subsequent process. .

The ozone-containing gas used in the present invention may be ozonized by using a commercially available ozone generator and supplying air or oxygen. Usually, when air is used as a raw material, the ozone concentration is 10 to 20 f. /m5. The amount of ozone-containing gas injected is sufficient to match the content of impurities that are considered to have an adverse effect on the chameleon test, breakage test, etc. in the acetic anhydride to be treated, but in practical terms It is necessary to determine it appropriately by experiment, taking into account contact efficiency, purification rate, etc., and the ozone consumption is usually 50θ~1000 t-0,/
T, preferably 600 to 600 t −0,/
Process with T.

In most cases, the reaction temperature in the method of the present invention is room temperature, which is sufficient to achieve the purpose. Contact between reaction liquid and reaction gas is by tank type.
Any method such as an informal method may be used, and a cooling device may be installed as necessary.

〔Effect of the invention〕

The effects of the present invention are as follows.

b) It is carried out at room temperature and pressure and does not involve distillation, so thermal energy can be saved.

b) Since it is not exposed to high temperatures, it prevents the decomposition of acetic anhydride, improves the yield υ, and converts it into a resin due to thermal changes.

It can prevent troubles caused by carbide.

c) Since ozone itself has no residue, no post-treatment is necessary. Therefore, since there is no addition of drugs, agents, or oxidizing agents, there is no need for post-treatment of additives, and there are no problems such as pollution caused at that time.

2) Ozone-containing gas is directly produced on-site and used immediately, so it does not require storage and is easy to continuously and automatically manage.

Thus, according to the invention, b) by bubbling the crude acetic anhydride with an ozone-containing gas.

The effects of (1), (3), and (2) are exhibited, and high-quality acetic anhydride with a chameleon test; a long retention time, and a tear test; and a pale color of APHA can be obtained.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example-1 Inner diameter 651111. Height 180III+ (inner capacity 600
WLt1 effective capacity 500d) glass container (air washing bottle)
K crude acetic anhydride! (Chameleon test tank; holding time 1 minute or less; tearing test; mu PHA 500 or more) 400 tons of ozone-containing air (ozone concentration?
271r't/NJ) was supplied at 50 Ml/11 to bring about gas-liquid contact. The quality of acetic anhydride after one-pass aeration for 30 minutes was analyzed and found to be chameleon test; retention time 100 minutes; tear test i APHA 25.

Examples 2 and 3, Comparative Example 1 Except that the ozone-containing air ventilation time was changed to 30 minutes, and the supply amount was increased or decreased by changing the ventilation time for one type of ozone.

Table 1 shows the results of the same treatment as in Example-1. Further, as Comparative Example-1, the same treatment as in Example-1 was performed except that air containing no ozone was used, and the results are shown in Table-1. The amount of treated crude acetic anhydride was 400 tons each.

Examples 4 to 7 Three glass containers (reactors) used in Examples 1 to 3 were connected in series, and each was charged with 40 of crude acetic anhydride.
The table below shows the results of ventilation of ozone-containing air from the one-pass method in Examples 1 to 3 to triple ventilation using exhaust gas.
Shown in 2.

Claims (1)

[Claims] A method for purifying crude acetic anhydride, characterized by treating crude acetic anhydride with an ozone-containing scalpel.