JPH05269338A - Method for recovering solvent - Google Patents

Abstract

PURPOSE:To eliminate wastewater itself and to save excessive installation cost and running cost by extracting and regenerating active carbon adsorbing impurities with solvent having melting action on the impurities before physically separating the solvent and the impurities. CONSTITUTION:Active carbon 15-2 or 15-1 in adsorber 14-2 or 14-1 adsorbing impurities, such as phenol is extracted by solvent, such as methanol having dissolving action on the impurities and the extract is stored in a cushion tank 19. Next, the liquid is fed to a methanol regenerator 21 by a solvent pump 20 and distilled to discharge water content and the impurities from the bottom. This waste liquid is fed to an incinerator 22 and incinerated. And purified methanol is recovered from the top and reused for extracting the active carbon 15-2 or 15-1 in the phenol adsorber 14-2 or 14-1 again.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a solvent recovery method.

[0002]

2. Description of the Related Art As shown in FIG. 4, a conventional activated carbon adsorption steam desorption type solvent recovery apparatus sends a raw gas 1 by a gas blower 2 to an adsorption tank 3-1 or 3-2 to activate carbon 4-1 or 4
-2 to adsorb and remove the solvent, desorb the solvent adsorbed on the activated carbon 4-1 or 4-2 with water vapor 5, and allow the desorbed solvent and water vapor to flow through the condenser 6 to condense and cool, and the condensed and cooled solvent and water. Is subjected to specific gravity separation with a separator 7, and the solvent is recovered and reused as it is, or is subjected to purification treatment as necessary. On the other hand, the waste water flows into the waste water tank 8, is heated by the feed pump 9 via the preheater 10, and is then sent to the waste water distillation column 11.
The low boiling point impurities (from water) dissolved in the waste water are extracted from the tops of the waste water distillation towers. Although the low-boiling point impurities can be removed in the waste water distillation tower 11, the high-boiling point (from water) cannot be removed. Therefore, after cooling with the cooler 12, the high-boiling point in the waste water by the waste water treatment facility 13 such as activated sludge treatment is used. After reducing impurities, etc., it is discharged to the outside of the system.

[0003]

In recent years, the regulation of wastewater has become strict, and conventionally, in order to reduce the BOD in wastewater, equipment such as activated sludge treatment is required, and the equipment cost and operating cost are large. In addition, recently, the number of cases where the drainage itself cannot be discharged is increasing.

In view of the above-mentioned state of the art, the present invention intends to provide a method of eliminating solvent itself, saving extra equipment cost and operating cost, and also carrying out solvent recovery even in an area where water cannot be discharged. It is a thing.

[0005]

Means for Solving the Problems The present invention provides (1) a method for recovering a solvent from solvent-containing air containing impurities by an activated carbon adsorption steam desorption type solvent recovery device,
After desorbing the solvent adsorbed on the activated carbon, the condensed waste water of the steam used for desorption in the desorption process is separated from the solvent, and then sent to an adsorption tower with a built-in activated carbon to adsorb and remove the impurities dissolved in the waste water. A low-temperature, low-pressure steam is obtained by indirectly exchanging heat with steam, and the steam is reused as steam to be used in the desorption step, and the activated carbon in the adsorption column that adsorbed impurities is used as a solvent having a dissolving effect on impurities. Extraction and regeneration, the solvent in which impurities are dissolved is physically separated into impurities and solvent, and the obtained solvent is used for extraction and regeneration of the activated carbon in the adsorption column that adsorbed impurities, and the rest is incinerated. Characteristic solvent recovery method.

(2) In the method of recovering a solvent from the solvent-containing air containing impurities by an activated carbon adsorption steam desorption solvent recovery device, the condensed waste water of the steam used for desorption in the desorption step of desorbing the solvent adsorbed on the activated carbon is used. After separating from the solvent, the resulting wastewater is blown so that the concentration of impurities in the wastewater does not exceed the allowable concentration, the blowwater is incinerated, and the rest of the wastewater is subjected to indirect heat exchange with high-pressure steam at a low temperature, A method for recovering a solvent, characterized in that low-pressure steam is used and the steam is reused as steam used in the desorption process. Is.

[0007]

In the first aspect of the present invention, the solvent used for regenerating the activated carbon having adsorbed impurities may be any solvent having a dissolving action for impurities,
Of course, the recovery solvent itself can also be used.

In the second aspect of the present invention, it is preferable that the amount of blow water to be incinerated is detected and controlled so that the concentration of impurities in the wastewater does not exceed a concentration ratio above the allowable concentration.

[0009]

【Example】

(Example 1) An example of the present invention will be described with reference to FIG. This example shows the case of recovering methanol from methanol-containing air (hereinafter referred to as raw gas) containing phenol as an impurity.

The raw gas 1 is sent to the adsorption tank 3-1 or 3-2 by the blower 2, and the raw gas 1 is supplied to the activated carbon 4-1 or 4-2.
The methanol and phenol contained therein are adsorbed.

Methanol and phenol adsorbed on the activated carbon 4-1 or 4-2 are desorbed by the desorbed steam 5, flown into the condenser 6 together with the desorbed steam, are condensed and cooled, and flow into the intermediate tank 7. In the intermediate tank 7, both methanol and phenol are water-soluble, so that they are in a mixed aqueous solution state.

This mixed aqueous solution is heated by a feed pump 8 through a preheater 9 to about 70 ° C., and then sent to a waste water distillation column 10. In the waste water distillation tower 10, methanol is recovered from the top of the tower by distillation, and the waste water containing phenol is extracted from the bottom of the tower. This drainage flows to the drainage cooler 12,
After being cooled to about 40 ° C., it is sent to the phenol adsorption column 14-1 or 14-2 by the drainage pump 13.

In the phenol adsorption column 14-1 or 14-2, the phenol in the waste water is adsorbed and removed by the activated carbon 15-1 or 15-2. The wastewater from which the phenol has been removed flows to the wastewater heater 16, is heated to 70 to 80 ° C., and then flows to the steam separator 17, where the reboiler 18 indirectly exchanges heat with the high-temperature (158 ° C.) steam from the reboiler and evaporates. Then, it becomes a low temperature (102 ° C.) steam and is reused as the desorbed steam 5.

On the other hand, activated carbon 15-2 or 15- in the phenol adsorption column 14-2 or 14-1 which adsorbs phenol
1 is extracted with methanol, cushion tank 19
Accumulated in. The liquid stored in the cushion tank 19 is a mixed solution of phenol, water and methanol adsorbed and attached to the activated carbon 15-2 or 15-1, and this liquid is sent to the methanol regeneration tower 21 by the solvent pump 20. Water and phenol are discharged from the bottom of the column by being distilled. This waste liquid is sent to the incinerator 22 for incineration. Purified methanol is recovered from the top of the methanol regeneration tower 21 and reused again for extracting the activated carbon 15-2 or 15-1 of 14-1 or 14-2 of the phenol adsorption tower.

The following is an example of the operation results of this embodiment. Raw gas air flow rate; 20000 Nm ³ / H Methanol concentration in raw gas; 6000 ppm Phenol concentration in raw gas; 10 ppm Phenol adsorption tower inlet wastewater amount / temperature; 1100 kg / H, 40 ° C. Phenol adsorption tower inlet wastewater concentration; 700 ppm Phenol adsorption tower outlet Phenol concentration in waste water: 20 ppm Methanol regeneration tower outlet waste liquid amount (incineration disposal); 18 kg / H Methanol regeneration tower outlet waste liquid composition; Water 95.2% Phenol 4.7% Methanol 0.1%

When the conventional method is used, 1100 kg / H of waste water containing 700 ppm of phenol is discharged, and this treatment facility is required.

The operation cycle of the phenol adsorption tower in this example is shown below.

[Table 1] 1. Adsorption process: Adsorbs phenol contained in wastewater. 2. Regeneration step: a step of desorbing phenol from activated carbon to prepare for the next adsorption, which consists of the following detailed steps. 1) Drainage process ...- Drain the water in the adsorption cylinder. 2) Extraction process: Extract the phenol adsorbed on the activated carbon with methanol. 3) Waste solvent process ... Pull out the extraction methanol in the adsorption column. 4) Desorption process: Methanol adhering to and adsorbing on activated carbon is desorbed by steam.

Example 2 FIG. 2 shows an example 2 of the solvent recovery process according to the present invention. Toluene is recovered from toluene-containing air (hereinafter referred to as raw gas) containing IPA (isopropyl alcohol) and ethyl acetate as impurities. The raw gas 1 is adsorbed by the blower 2 to the adsorption tank 3-1 or 3-2.
Toluene and impurities in the raw gas are adsorbed on the activated carbon 4-1 or 4-2.

Toluene and impurities adsorbed on the activated carbon 4-1 or 4-2 are desorbed by the desorbed steam 5, flown together with the desorbed steam to the condenser 6, condensed and cooled, and then flowed to the separator 7 to separate the solvent and the waste water into a specific gravity. .. The separated solvent contains some impurities such as IPA and ethyl acetate, and is purified and distilled before reuse.

On the other hand, after the drainage is stored in the drainage tank 8,
After being fed to the preheater 10 by the feed pump 9 and heated to about 70 ° C., it is sent to the drainage distillation column 11. In the waste water distillation tower 11, IPA having a boiling point lower than that of water dissolved in the waste water,
Ethyl acetate and some ethanol produced by hydrolysis of ethyl acetate are removed.

The wastewater from which low-boiling-point impurities have been removed is withdrawn from the bottom of the wastewater distillation tower, flows into the steam separator 13, and is reheated by the reboiler 14 by indirect heat exchange with the high-temperature (158 ° C) steam from the boiler. , Becomes a low temperature (102 ° C.) steam and is reused as the desorbed steam 5.

Here, in the waste water in the steam separator 13, a small amount of acetic acid produced by hydrolysis of ethyl acetate is produced. Since acetic acid has a higher boiling point than water, reusing the waste water as it is will condense the acetic acid and cause problems such as corrosion and bad odor of the equipment. Therefore, blow it to the extent that it does not hinder the concentration. This blow water is sent to the incinerator 15 for incineration.

The following is an example of the operation results in this embodiment. Raw gas air flow rate; 41100 Nm ³ / H Raw gas toluene concentration; 1100 ppm Raw gas IPA concentration; 45 ppm Raw gas ethyl acetate concentration; 45 ppm Drainage circulation amount; 1100 kg / H Drainage blow amount; 110 kg / H (1
0% blow) Circulation drainage properties; Acetic acid content 1000p
pm

When the conventional method is used, 1100 kg / H of waste water containing 100 ppm of acetic acid is discharged, and this treatment facility is required.

FIG. 3 shows a modification of FIG. This is used in the steam separator 13 of the solvent recovery process example 2 in FIG.
An organic matter concentration meter such as a C meter 16 is installed to detect organic matter in the waste water and control the amount of blow water.

[0026]

According to the present invention, the following curing is achieved. The operating cost for eliminating drainage is about 1/10 of the cost for operating conventional wastewater treatment.

Solvent recovery can be performed even in areas where the solvent recovery method could not be implemented due to wastewater discharge regulations.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a second embodiment of the present invention.

FIG. 3 is an explanatory view of a modification of the second embodiment of the present invention.

FIG. 4 is an explanatory diagram of a conventional solvent recovery process.

Claims (2)

[Claims] 1. A method for recovering a solvent from air containing a solvent containing impurities in an activated carbon adsorption steam desorption solvent recovery device, wherein condensed water of steam used for desorption in a desorption step of desorbing a solvent adsorbed on activated carbon is used as a solvent. After separating it into an adsorption tower containing activated carbon, the impurities dissolved in the waste water are adsorbed and removed, and then indirectly heat-exchanged with high-pressure steam to form low-temperature, low-pressure steam, and the steam is desorbed in the desorption step. While reusing as water vapor to be used, the activated carbon in the adsorption column that has adsorbed impurities is extracted and regenerated with a solvent that has a dissolving effect on impurities, and the solvent in which impurities are dissolved is physically separated into impurities and solvent, The solvent recovery method is characterized in that the obtained solvent is used for extraction and regeneration of the activated carbon in the adsorption column that has adsorbed impurities, and the rest is incinerated. 2. A method for recovering a solvent from air containing a solvent containing impurities by an activated carbon adsorption steam desorption solvent recovery device, wherein the condensed waste water of steam used for desorption in the desorption step of desorbing the solvent adsorbed on the activated carbon is the solvent. After the separation, the resulting wastewater is blown so that the concentration of impurities in the wastewater does not exceed the allowable concentration, and the blown water is incinerated, and the remaining wastewater is indirectly heat-exchanged with high-pressure steam at a low temperature,
A method for recovering a solvent, characterized in that low-pressure steam is used and the steam is reused as steam used in the desorption process.