JPH0713036B2 - Purified solvent recovery method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for recovering a recovery solvent containing an acetate ester collected by an activated carbon adsorption method in a purified state.

[Conventional technology]

The technology for recovering hydrocarbon solvent in exhaust gas using the activated carbon adsorption method has already been generalized and almost solved, but many problems still remain for ester and ketone hydrocarbons. As one of them, when acetic acid ester is adsorbed and collected by activated carbon and steam desorption is performed, the acetic acid ester is partially hydrolyzed into acetic acid and alcohol by the catalytic action of activated carbon.

For example, a very small part of ethyl acetate is decomposed as shown in the following formula (1), and the acetic acid produced lowers the pH of the recovered ethyl acetate and makes it difficult to reuse the recovered solvent.

Therefore, the recovered acetic acid ester must be deoxidized by some method and then reused as a neutral solvent.

FIG. 2 is a flow chart showing a conventional acetate recovery process.

First, the raw gas containing acetic acid ester is sent through a pretreatment device 1 such as a filter to a adsorption tank 3 filled with activated carbon 3-1 via a blower 2 to adsorb and collect a solvent, and then introduced from a vapor line E. It is desorbed by the generated steam and condensed and liquefied by the condenser 4.

The liquefied acetate ester and water are separated by the separator 5,
The aqueous phase recovers the solvent content in the waste water distillation column 6 to which the condenser 7 is connected and returns it to the separator 5. The solvent phase is dehydrated by a dehydration vapor deposition tower 8 to which a condenser 9 is connected, and then sent to a product recovery tank 10.

[Problems to be solved by the invention]

However, the ethyl acetate recovered by the conventional method as shown in Fig. 2 contains 100 to 1000 ppm of acetic acid, and since it shows acidity, it causes problems in product quality during reuse, equipment corrosion, and work due to acetic acid odor. The environment deteriorates. Especially in the application fields of magnetic tape, synthetic film paper, etc., it is necessary to use the acetic acid content of about 10 ppm or less, and it is impossible to reuse it without deoxidation treatment.

Usually, as a measure against this type of organic acid, it is difficult to suppress decomposition of the acetic acid ester at the time of adsorption, and deoxidation treatment after recovery is required.

Generally, the deoxidizing method includes (1) a method of neutralizing by adding an alkaline solvent such as ethanolamine (2) a method of deoxidizing with an inorganic alkaline substance such as caustic soda (3) a method of distilling and refining As is known, the method (1) reduces the purity,
The method (2) reduces the efficiency of acetic ester recovery by promoting the decomposition of acetic acid ester, and the method (3) reduces the acetic acid concentration to 10 pp.
It is difficult to purify to m or less, and when other solvents are included, a very complicated distillation operation is required, which is not practical.

Thus, a method for effectively deoxidizing or separating the organic acid contained in the acetate ester has not been found, and the utility value of the recovery solvent is small as it is, and the recovery device functions only to prevent atmospheric pollution. Therefore, the original intention of reuse is halved.

The present invention is intended to solve these problems, in a solvent gas treatment method containing acetic acid ester, to efficiently remove the organic acid from the collected solvent phase, to provide an excellent acetic acid ester recovery method. The present invention is applicable to the purification of a recovered solvent in a solvent recovery device containing acetic ester.

[Means for solving problems]

Therefore, the acetic ester recovery method of the present invention, the raw gas containing acetic ester is sent to the adsorption tank, after collecting the solvent, desorption by the desorption means, the condensation means, and the solvent phase and the aqueous phase by the separation means. After separation, the solvent phase on the downstream side of the separation means is brought into contact with an aqueous solution of potassium carbonate (or an aqueous solution of sodium carbonate) for deoxidation, and then purified by a dehydration means and a purification means to recover the purified acetate ester. It has a feature.

The mechanism of deoxidizing acetic acid from acetic acid ester which is the recovery solvent of the present invention is based on the following reaction formulas (2) and (3).

The upper limit concentration of the aqueous potassium carbonate solution used is 25 wt% and sodium carbonate is 6 wt%. This is because the upper limit of the concentration of the former rapidly increases when the decomposition rate of ethyl acetate becomes 25 wt% or more, and the upper limit of the concentration of the latter is determined by the solubility in water. The lower limit concentration is determined by the concentration of acetic acid in the recovery solvent, but is usually about 1 wt%.

For example, the decomposition rate of ethyl acetate changes depending on the potassium carbonate aqueous solution concentration, and increases as the concentration increases, but when using a potassium carbonate concentration 5 wt% aqueous solution, ethyl acetate is about 0.02%.
Decompose to some extent. At such a decomposition rate, since the original ethyl acetate contains a considerable amount of ethyl alcohol, even if the decomposition rate is increased to such an extent, its effect is extremely small.

〔Example〕

An embodiment of the present invention will be described below based on the flow chart of the process example shown in FIG.

In the figure, 101 is a pretreatment device, 102 is a blower, 103 is an adsorption tank, 103-1 is an activated carbon layer, 104 is a condenser, 105 is a separator, 106 is a drainage distillation tower (hereinafter, drainage tower), 107 is a condenser, and 108. Is a dehydration distillation column (hereinafter, dehydration column), 109 is a condenser, 110 is a product recovery tank, 111 is a catalytic deoxidization column (hereinafter, deoxidation column), 112 is a pump, 113 is an intermediate tank, 114 is a purification column, 115 Is a condenser, 116 is a drain tank, and 117 is a tank.

The raw gas containing acetic acid ester is sent to a adsorption tank 103 having an activated carbon layer 103-1 through a pretreatment device 101 such as a filter and a blower 102. In the adsorption tank 103, the activated carbon layer 103-1
The solvent is collected by the exhaust gas, and the cleaned exhaust gas is discharged from the exhaust port F to the atmosphere.

On the other hand, the collected solvent is desorbed by the steam introduced from the vapor line E, and the distillate is condensed and liquefied by the condenser 104 and sent to the separator 105.

In the separator 105, the condensate is separated into a solvent and water, and in the water phase, a drainage tower 106 connected to the condenser 107 collects the solvent component contained in the water phase and returns it to the separator 105 again.

On the other hand, the solvent phase separated by the separator 105 is the deoxidizing tower 111.
Is counter-currently contacted with an aqueous solution of potassium carbonate (or an aqueous solution of sodium carbonate, hereinafter only potassium carbonate will be described), deoxidized and stored in the intermediate tank 113.

The aqueous solution of potassium carbonate supplied to the deoxidizing tower 111 is supplied by the pump 1
It is supplied through a circulation line J including 12 and the circulation line J is replenished with the high-concentration potassium carbonate aqueous solution in the tank 117 by pH control. Further, due to the countercurrent contact, a part of the circulating liquid containing a large amount of potassium acetate is discharged from line G as waste liquid.

The deoxidized solvent stored in the intermediate tank 113 is the condenser 1
It is dehydrated in a dehydration tower 108 connected to 09, and then sent to a purification tower 114 connected to a condenser 115 to remove potassium salt (or sodium salt) and sent to a product recovery tank 110.

The potassium salts such as potassium carbonate and potassium acetate contained in the deoxidizing solvent in a small amount and removed in the refining tower 114 are again sent to the bottom of the dehydration tower 108, condensed at the bottom of the tower, and extracted into the drain tank 116. .

As described above, in the method of the present invention, deoxidation is carried out by bringing the solvent phase into contact with an aqueous solution of potassium carbonate, and then the acetic acid ester is recovered by performing purification, but potassium carbonate deoxidizes the acetic acid ester containing acetic acid. The reason for this is that the dissociation constant is relatively small compared to caustic soda and the alkali strength is moderately weak. If the alkaline strength is too strong, not only the neutralization of acetic acid but also the decomposition of acetic acid ester will be promoted, leading to a decrease in the recovery rate.

Next, the test results when ethyl acetate containing acetic acid is brought into contact with the aqueous solution of potassium carbonate by stirring by the batch method under the following conditions are shown below.

Test results Condition Potassium carbonate aqueous solution 5 wt% Mixing ratio 1: 1 Contact temperature 25 ℃ As shown in the above test results, the acetic acid removal rate was 99.9% or more. The decomposition rate of ethyl acetate during hydrolysis is about 0.02.
It was in%. After the ethyl acetate phase separation, the decomposition rate was 0.01% when left standing in another storage tank for 48 hours. This proves that potassium carbonate is suitable for deoxidation of acetic acid-containing acetate. Further, the pH of the recovered solvent was not problematic by distillation, and no increase in the decomposition product ethanol by the distillation operation was observed.

〔effect〕

As described above in detail, according to the acetic acid ester recovery method of the present invention, after the solvent component of the raw gas containing acetic acid ester is collected by the activated carbon adsorption method, it is desorbed by the desorption means, and the condensation means and the separation means. To separate it into an aqueous phase and a solvent phase, and to deoxidize the solvent phase by bringing the solvent phase into contact with an aqueous solution of potassium carbonate on the downstream side of the separation means, and then to recover the purified acetic acid ester through dehydration and purification means. Therefore, the acetic acid ester can be effectively and efficiently recovered, which eliminates the conventionally required deoxidation treatment after solvent recovery and improves the reuse value of the recovered solvent, as well as the deterioration of the working environment and the equipment Corrosion can be prevented.

[Brief description of drawings]

FIG. 1 is a flow chart showing an embodiment of the present invention, and FIG. 2 is a flow chart of a conventional method.

Claims (1)

[Claims] 1. A solvent phase is contacted with a potassium carbonate aqueous solution or a sodium carbonate aqueous solution on the downstream side of a separating means for separating an aqueous phase and a solvent phase in a solvent recovery method for recovering an acetate from a raw gas containing an acetate. A method for recovering a purified solvent, characterized in that the purified acetic acid ester is recovered by means of dehydration and purification, followed by dehydration and purification.