JPS6058214B2 - Acetic acid recovery method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for efficiently and stably recovering acetic acid from an aqueous acetic acid solution discharged from a cellulose acetate manufacturing process.

In particular, it relates to improvements in the process of extracting acetic acid from an aqueous acetic acid solution using an organic extractant. Cellulose acetate is produced by acetylating cellulose with acetic anhydride, precipitating it with water, washing it, and drying it.

The acetic acid aqueous solution discharged from the precipitation and washing process contains 20 to 40 wt% of acetic acid, depending on the precipitation and washing method, as well as dissolved water-insoluble cellulose acetate and low polymerization depending on the acetic acid concentration. It contains a small amount of water-soluble cellulose acetate with a degree of acetation. Efficient and stable recovery of acetic acid from such an aqueous solution containing acetic acid and cellulose acetate is extremely important for increasing the utilization rate of valuable materials and preserving the environment. An extraction method using an organic solvent is known as a method for recovering acetic acid from an aqueous solution, and can also be applied to an aqueous solution discharged from the fibrillar acetate process.

In extraction methods using ethyl acetate, benzene, isopropyl ether, methyl ethyl ketone, etc. alone or in combination as organic extractants, most of the cellulose acetate dissolved in the aqueous solution is extracted as acetic acid is extracted. It is dissolved in the liquid and discharged from the extractor, but a part of the water-insoluble acetic acid cotton forms a film on the surface of the droplet and precipitates.

For this reason, the rate of transfer of acetic acid to the organic solvent is slower than when there is no precipitate, and the rate of liquid separation in a decanter is also slow, making it difficult to handle a large amount. In addition, after liquid separation, precipitates accumulate near the oil-water interface and adhere to interface control sensors such as floats and electrical conductivity meters, making stable control impossible. There is a problem in that a great deal of effort and time is expended. Furthermore, because of this precipitate, a centrifugal type or perforated plate column extractor with good extraction efficiency cannot be used, but instead a ring-out plate column extractor or a spray column extractor with a simple structure is used. The present inventors have previously proposed an extraction method using a tertiary amine and an organic diluent as extractants, which have extremely high extraction efficiency (see Japanese Patent Application Laid-Open No. 10131/1983). Since the moving speed is slow, it is preferable to use a mixer-settler type extractor. In this case, since the extracted acetic acid reacts with the tertiary amine to form a salt, almost all of the water-insoluble acetic acid fiber in the aqueous solution is precipitated in the extractor. . On the other hand, water-soluble cellulose acetate remains dissolved in the aqueous phase of the extract. It was also found that since the above-mentioned precipitates form a film on the surface of the droplets, the liquid separation speed in the settler becomes slow and a large throughput cannot be obtained. Further, after liquid separation, a large amount of precipitate accumulates near the oil-water interface in the settler, so that continuous discharge from the settler is impossible and stable interface control is also impossible. The present invention solves these difficulties and makes it possible to efficiently and stably extract acetic acid from the aqueous acetic acid solution discharged from the cellulose acetate manufacturing process.

According to the findings of the present inventors, there is no water-insoluble cellulose acetate in the aqueous acetic acid solution (generally 20 to 40 Wt% concentration) discharged from the cellulose acetate production process, although it varies depending on the acetic acid concentration. .1-10yIe dissolved.

On the other hand, water-soluble acetic acid cotton was also dissolved to the same extent. In the method of extracting acetic acid from this aqueous acetic acid solution using the organic solvent as described above, water-soluble cellulose acetate does not have any effect on the extraction, but the precipitated water-insoluble cellulose acetate is extracted. It was found that it had a negative effect on Therefore, the present inventors believed that changing water-insoluble cellulose acetate to water-soluble cellulose acetate would prevent the precipitation of acetic acid cotton in the extractor and enable stable extraction operations. As a result of studying how to make cellulose acetate water-soluble, we discovered that when heated at a high temperature of 100°C or higher, it easily undergoes hydrolysis and depolymerization, turning into water-soluble cellulose acetate. Ivy.
That is, the present invention is a method for extracting acetic acid from an acetic acid aqueous solution discharged from a cellulose acetate manufacturing process using an organic extractant and recovering acetic acid from the extract, in which the acetic acid aqueous solution is heated to 100°C or higher as a pretreatment. Acetic acid characterized by extraction after heat treatment at high temperature. There are some related to the collection method.

The heat treatment conditions, that is, the heat treatment temperature and time required, vary depending on the amount of water-insoluble cellulose acetate dissolved, but as an example, 28Wt containing 1.4yIe of water-insoluble cellulose acetate is used.
% acetic acid aqueous solution is shown in FIG. 1. The relationship between heating temperature and treatment time is shown in FIG.

In Figure 1, A is 100℃, B is 140℃, and C is 17℃.
The amount of water-insoluble cellulose acetate versus treatment time at 5°C is not shown. The amount of water-insoluble cellulose acetate was determined by replacing acetic acid with water by simple distillation under vacuum, and then quantifying the precipitated solid content. As shown in Figure 1, the reaction rate of hydrolysis and depolymerization is slow at a temperature of about 100°C, requiring a long treatment time, but the higher the temperature, the faster the reaction rate. It can be made water-soluble in a short time. It is also possible to accelerate the reaction rate by adding a mineral acid such as sulfuric acid or an oxidizing agent such as hydrogen peroxide. In FIG. 1, D is the case when 1% sulfuric acid was added at 100°C. The heat treatment temperature is preferably 100 to 200°C, and it is desirable to reduce the concentration of water-insoluble cellulose acetate to, for example, 0.1f11' or less by the heat treatment, but of course this concentration is not critical, and the present invention It may be heated for an appropriate time to a concentration that provides the desired effect of the invention. For example, it is heated at 175° C. for about one hour, but the heating time can be extended or shortened as appropriate depending on the concentration of residual sulfuric acid. According to the present invention, the following advantages (1) to (4) can be obtained.

- (1) Since a film of precipitates is not formed on the surface of the droplet, the moving speed and liquid separation speed are fast, and a large throughput can be achieved.

(2) Stable interface control is possible because no precipitates are deposited at the oil-water interface.

(3) It is possible to save labor and time for removing precipitates.

(4) It is possible to use an extractor with good extraction efficiency.

Furthermore, high-temperature heat treatment requires a heat medium such as steam, but energy consumption can be reduced if energy is used effectively by exchanging heat between the final treatment liquid and the treatment liquid.

In the present invention, any known organic extractant may be used, but a combination of a tertiary amine and an oxygen-containing organic solvent may be used as an organic extractant as disclosed in JP-A No. 56-10131. The most preferred method is to perform extraction using Examples of the present invention will be shown below.

Example 1 1.3yIe of water-insoluble cellulose acetate and 0.4yIe of water-insoluble cellulose acetate were extracted using a 40φ glass ring-and-plate tower extractor with 4 plates.
A 28wt% acetic acid aqueous solution containing 7 fIe of water-soluble cellulose acetate was heat-treated at 155°C for 3 hours, cooled to 40°C, fed from the top of the extractor at a rate of 13k91Hr, and ethyl acetate-benzene was added from the bottom of the extractor. 20kg of mixed solvent
Countercurrent contact was achieved by supplying at a rate of 1 hour.

At this time, 25 kg of an extract containing 7.9 wt% water and 14.3 wt% acetic acid was obtained for 1 hour. This extract contains O.9
The water-soluble cellulose acetate of y1' was dissolved. Note that no precipitates were observed in the extractor or near the oil-water interface in the decanter. Comparative Example 1 Using the same apparatus as in Example 1, the same acetic acid aqueous solution was supplied at 40° C. without heat treatment at a rate of 6.5 kg IHr, and the same mixed solvent was supplied at a rate of 10 k91 Hr.

At this time, the extract was discharged at a rate of 12 kg for 1 hour, but the precipitates were not discharged immediately after the start of operation and were deposited near the oil-water interface in the decanter. After 4 hours of operation, the acetic acid aqueous solution as the feed liquid was increased to 8k91Hr, and the mixed solvent was increased to 12.5k91Hr.
Where it increased, it flattened.

Example 2 Using a glass mixer-settler type extractor with 5 stages of countercurrent flow, 4 mL of the same heat-treated acetic acid aqueous solution as in Example 1 was added.
The first tank was charged at a rate of 400yIHr at 0°C, and a mixed solvent of tri-n-octylamine 3,3·5-trimethylcyclohexanone in a ratio of 50:50V'01 was charged in countercurrent from the fifth tank at a rate of 410f1Hr.

At this time, an extract containing 5.0 wt% water and 20.7 wt% acetic acid was discharged at 530 yIHr, and no cellulose acetate was detected. On the other hand, the extraction waste liquid was discharged in 260y1Hr and contained 3.1y1e of cellulose acetate. No precipitates were observed near the oil-water interface of each stage of the settler.
Note that acetic acid can be recovered from the extract obtained according to the present invention by a known method such as distillation.

[Brief explanation of the drawing]

FIG. 1 is a graph showing an example of the relationship between heat treatment temperature and time of an acetic acid aqueous solution containing water-insoluble cellulose acetate.

Claims (1)

[Claims] 1. In the method of extracting acetic acid from an acetic acid aqueous solution discharged from the cellulose acetate manufacturing process using an organic extractant and recovering acetic acid from the extract, a 100% acetic acid aqueous solution is used as a pretreatment.
A method for recovering acetic acid, which is characterized by performing extraction after heat treatment at a high temperature of ℃ or higher.