JP3631073B2 - Organic solvent recovery method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for recovering an organic solvent in an organic solvent-containing gas using activated carbon, and more specifically, relates to a method for recovering an organic solvent by a pressure swing method using water vapor.
[0002]
[Prior art]
Organic solvents are used in large quantities in industries such as various chemical industries, semiconductor industries, electronic component and machine manufacturing industries, and dry cleaning industries. In these industries, when an organic solvent is used, a gas containing the organic solvent is generated. Since these generated gases are harmful, complete recovery is required.
[0003]
As a method for recovering the organic solvent in the gas containing the organic solvent, a method using activated carbon is generally used. In this method, a gas containing an organic solvent is passed through an adsorption tower packed with activated carbon, and the organic solvent is adsorbed onto the activated carbon, whereby the organic solvent in the organic solvent-containing gas is collected by the activated carbon. Yes.
[0004]
In this method, as a method for desorbing the solvent collected by the activated carbon, there is a conventional steam desorption method in which water vapor is continuously supplied to the adsorption tower. In the case of this method, a large amount of water vapor is used for desorption of the solvent, so that the amount of drainage inevitably increases. Since a solvent is mixed in this waste water, a large-scale treatment facility is required. Further, since high-temperature steam is used, the solvent may be chemically changed during desorption, and this tendency is strong particularly when a chlorine-based solvent such as trichlene is desorbed. For this reason, the quality of the recovered solvent may be deteriorated.
[0005]
Attempts have also been made to reduce the amount of water vapor used. In JP-A-5-84417, for the purpose of reducing the amount of water vapor used, first, the inside of the adsorption tower is depressurized in the desorption process, and then the water vapor is supplied to the adsorption tower and then the water vapor supply is stopped. A method of evacuating is disclosed.
[0006]
Similarly, JP-A-2-126919 and JP-A-10-337438 disclose a pressure swing method in which an organic solvent is desorbed through water vapor into an adsorption tower under reduced pressure. However, in these methods, there is a problem that the structure and operation become complicated in order to reduce the amount of water vapor. In any of the above methods, the supply pressure of water vapor is within the normal pressure range necessary for supplying water vapor to the adsorption tower. Not done.
[0007]
In addition, a method of evacuating the inside of the adsorption tower while heating the activated carbon with a heater is disclosed so that no water vapor is used (Japanese Patent Laid-Open No. 51-32481). However, this method has a problem that the desorption efficiency is low as compared with the desorption method using water vapor.
[0008]
[Problems to be solved by the invention]
While various studies were made to solve the above problems, the present inventors supplied water vapor to the adsorption tower in a pressurized state unlike a normal method, and then condensed the water vapor so that the inside of the adsorption tower was moderate. It has been found that the organic solvent can be efficiently desorbed from the activated carbon by performing a pressure swing in a reduced pressure state. According to this method, the amount of water vapor used can be small, and since the contact time between the water vapor and the solvent is short, it has been found that there are advantages such that the recovered solvent is unlikely to deteriorate.
[0009]
The present invention has been completed on the basis of the above knowledge, and its object is to provide a method for recovering an organic solvent that solves the above-mentioned conventional problems.
[0010]
[Means for Solving the Problems]
In order to solve the above problem, the present invention provides:
[1] An adsorption process in which an organic solvent-containing gas is supplied to an adsorption tower packed with activated carbon to adsorb the organic solvent in the gas to the activated carbon, and desorption by desorbing and recovering the organic solvent from the activated carbon adsorbing the organic solvent In the method for recovering an organic solvent in an organic solvent-containing gas, the desorption step includes a first step of supplying water vapor to the adsorption tower and substituting the air in the adsorption tower with water vapor; The second step of making the pressurized state in step 2 and the organic solvent adsorbed on the activated carbon by condensing the water vapor put in the pressurized state in the second step together with the organic solvent vapor in a condenser to bring the inside of the adsorption tower into a reduced pressure state. And a third step of desorbing and collecting. A method for recovering an organic solvent in an organic solvent-containing gas.
[0011]
The above-mentioned recovery method is [2] The pressure state of the second step is 0.5 to ⁵ kgf / cm ² ,
[3] The reduced pressure state in the third step is 150 to 400 torr,
[4] It includes that the activated carbon is a fibrous activated carbon.
[0012]
Hereinafter, the present invention will be described in detail with reference to the drawings.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a flow diagram showing an example of an organic solvent recovery device in an organic solvent-containing gas used in the practice of the present invention.
[0014]
In FIG. 1, reference numeral 2 denotes an adsorption tower, which is a cylindrical pressure-resistant vessel whose both ends are closed. The adsorption tower 2 is filled with activated carbon (not shown).
[0015]
The activated carbon is not particularly limited, and any activated carbon such as granular activated carbon, molded activated carbon, powdered activated carbon, fibrous activated carbon, fibrous activated carbon formed into a felt shape, woven fabric shape, roving shape, paper shape, mat shape, etc. Can be employed. In particular, fibrous activated carbon made from acrylonitrile, phenol, rayon, pitch or the like is preferred for applications requiring high-speed adsorption / desorption. In particular, fibrous activated carbon is excellent in adsorption ability and adsorption rate of organic solvents in a low concentration region because the pore distribution is mainly composed of micropores. Reference numeral 4 denotes an organic solvent-containing gas introduction pipe connected to the vicinity of the bottom 6 of the adsorption tower 2, and a valve 8 is interposed in the introduction pipe 4. A gas containing an organic solvent, which is a gas to be treated, is introduced into the adsorption tower 2 from the tower bottom 6 through the introduction pipe 4.
[0016]
Reference numeral 10 denotes an adsorption-treated gas outlet pipe connected to the vicinity of the tower top 12 of the adsorption tower 2. Reference numeral 14 denotes a valve interposed in the outlet pipe 10.
[0017]
The organic solvent-containing gas introduced into the adsorption tower 2 from the vicinity of the tower bottom 6 comes into contact with the activated carbon filled in the adsorption tower 2 and adsorbs and removes the organic solvent to the activated carbon. It moves and is discharged to the outside through the outlet pipe 10.
[0018]
Reference numeral 16 denotes a water vapor supply pipe connected to the tower top 12, and a valve 18 is interposed therein. Steam is supplied into the adsorption tower 2 from the top 12 through the steam supply pipe 16.
[0019]
20 is a water vapor suction pipe in which a valve 22 is interposed, one end of which is connected to the bottom 6 of the adsorption tower 2 and the other end is connected to a condenser 24, and the valve 22 is opened. Thus, the inside of the adsorption tower 2 and the inside of the condenser 24 are kept in communication.
[0020]
26 is a vent gas pipe in which a valve 28 is interposed, and is connected to the condenser 24, and the gas in the adsorption tower 2 is discharged through the vent gas pipe 26 as necessary.
[0021]
A cooling water supply pipe 30 is connected to the condenser 24, and a valve 32 is interposed therein. Cooling water is supplied to the condenser 24 through the cooling water supply pipe 30, whereby the inside of the condenser 24 is cooled. Reference numeral 34 denotes a cooling water outlet pipe.
[0022]
A condensate take-out pipe 36 is connected to the condenser 24 so that the take-out pipe 36 and the suction pipe 20 are kept in communication with each other. Reference numeral 38 denotes a condensate tank, and 40 a valve, which are interposed in the take-out pipe 36, respectively.
[0023]
Next, the case where the organic solvent in the organic solvent-containing gas is recovered using the recovery device will be described.
[0024]
(Adsorption process)
First, with the valves 18, 22, 40 closed and the valves 8, 14 opened, an organic solvent-containing gas (treated gas) is introduced into the adsorption tower 2 through the introduction pipe 4. The organic solvent-containing gas makes gas-solid contact with the activated carbon filled in the adsorption tower 2, and the organic solvent is sequentially moved upward in the tower while being adsorbed and removed by the activated carbon. The adsorption-treated gas obtained by removing the organic solvent is discharged to the outside through the outlet pipe 10 from the top of the tower.
[0025]
After the organic solvent is sufficiently adsorbed by the activated carbon, the supply of the organic solvent-containing gas is stopped and the valves 8 and 14 are closed.
[0026]
(Desorption process)
First step (water vapor replacement)
First, the valves 18, 22, 28, and 32 are opened, whereby pressurized steam is supplied into the adsorption tower 2 through the steam supply pipe 16, and cooling water is supplied to the condenser 24. The temperature of the supplied water vapor is preferably 110 ° C. or higher, and particularly preferably 110 to 140 ° C. in terms of economy and practical use.
[0027]
Although cooling water temperature changes with boiling points of the organic solvent collect | recovered, it is preferable that it is normally 32 degrees C or less and exceeds 0 degreeC, and 7-20 degreeC is especially preferable.
[0028]
The water in the adsorption tower is replaced with water vapor supplied into the adsorption tower 2, whereby the air is discharged to the outside via the suction pipe 20, the condenser 24 and the vent gas pipe 26.
[0029]
Second step (pressurization)
With the valve 18 still open, the valves 22, 32, 28, 40 are closed. Thereby, the inside of the adsorption tower 2 is heated and pressurized with heated steam. It is preferable that the temperature in the adsorption tower 2 is normally raised to about 110-140 degreeC. Moreover, it is preferable that the pressure in the adsorption tower 2 is normally raised to about 0.5-5 kgf / cm < ² > (gauge pressure). By setting such temperature and pressure, a preferable moderate degree of decompression is achieved in the third step described later.
[0030]
The temperature of saturated steam is determined by its pressure. Further, the pressure (= temperature) of the desorption vapor is related to the boiling point of the solvent to be recovered. For example, when the solvent boiling point is about 130 ° C. or lower, the desorption water vapor pressure is preferably 0.5 to ¹ kgf / cm ² . Further, when the solvent boiling point is about 130 to 200 ° C., the desorption water vapor pressure is preferably 3 kgf / cm ² .
[0031]
The water vapor temperature need not necessarily exceed the boiling point of the solvent. Of course, the higher one is preferable, but there is a relation with the water vapor volume as described later. That is, even when the temperature is lower than the boiling point of the solvent, there is a desorption amount of the solvent corresponding to the vapor pressure at that temperature. In addition, when exposed to vacuum in the next step, the solvent is almost completely desorbed even if the water vapor temperature does not exceed the boiling point of the solvent.
[0032]
Regarding the vapor specific volume and the degree of vacuum in the next step, it is preferable to keep the water vapor pressure as low as possible in order to increase the degree of vacuum in the next step. That is, the specific volume (m ³ / kg) increases as the water vapor pressure is lowered. When the same volume is filled with low-pressure steam and with high-pressure steam, the low-pressure steam has a smaller volume after condensation. This is because the volume change increases the degree of vacuum.
[0033]
For example, in the case of 0.5 kgf / cm ² of water vapor, it becomes 1.18 m ³ / kg. On the other hand, in the case of 3 kgf / cm ² of water vapor, it becomes 0.47 m ³ / kg.
[0034]
Third step (condensation, decompression)
Valve 18 is closed and valves 22, 32 are opened. As a result, the inside of the adsorption tower 2, the condenser 24, and the condensate tank 38 are brought into communication. Then, the water vapor confined in the adsorption tower 2 in a pressurized state and the organic solvent vapor desorbed by the water vapor flow into the condenser 24 together with the water vapor, where they are cooled and condensed, and enter the condensate tank 38. Stored. In the condenser 24, since the condensation is constantly progressing, the internal pressure of the adsorption tower 2 rapidly decreases with time, and finally becomes a moderate degree of decompression. Specifically, it is preferably 150 to 400 torr, and about 200 to 300 torr is convenient for operation.
[0035]
In this way, the organic solvent adsorbed on the activated carbon is exposed to the heat received from the water vapor and the reduced pressure state, and is almost completely desorbed from the activated carbon, and is collected in the coagulating liquid tank 38.
[0036]
The amount of water contained in the activated carbon is also much less than that under normal pressure by being exposed to a moderately reduced pressure in this third step.
[0037]
In this way, the organic solvent is recovered and the activated carbon is regenerated, thereby completing one cycle of recovering the organic solvent, and the same cycle is repeated thereafter.
[0038]
Normally, the solvent recovery device needs to continuously treat the exhaust gas. As shown in FIG. 2, a plurality of adsorption towers (two adsorption towers 2 and 2 ′ in FIG. 2) are provided, and adsorption and desorption are sequentially performed. It has come to repeat.
[0039]
In this case, the vent gas is sent to the adsorption tower 2 or 2 ′ through the vent gas pipe 26, and the adsorption process is performed again. This dramatically increases the solvent recovery rate. On the other hand, when only one tower is used, a small amount of remaining solvent is discharged to the outside. In FIG. 2, reference numerals are the same as those in FIG. 1, and therefore, only major reference numerals are given and description thereof is omitted.
[0040]
Hereinafter, the present invention will be described more specifically with reference to examples.
[0041]
【Example】
The solvent was recovered using the organic solvent recovery device having the configuration shown in FIG.
[0042]
The adsorption tower 2 has an internal volume of 310 L, and 7 kg of fibrous activated carbon (trade name Fineguard manufactured by Toho Rayon) was packed therein. After supplying 16Nm ^{3 of} air containing 5000 ppm of isopropyl alcohol as an organic solvent, 119 ° C. water vapor was supplied to the adsorption tower at almost atmospheric pressure with the valves 8, 14 closed and the valves 18, 22, 28 opened. Then, the air in the adsorption tower 2 was replaced with water vapor.
[0043]
Thereafter, the valves 22, 28 and 40 were closed, the inside of the adsorption tower ² was pressurized to 1 kgf / cm ² , and then the valve 18 was closed.
[0044]
When the valve 22 was opened, the organic solvent and water vapor in the adsorption tower 2 were transferred to the condenser 24, and condensation of these began. As the condensation progressed, the pressure in the adsorption tower 2 quickly decreased and finally decreased to 210 torr.
[0045]
In the aggregating liquid tank 38, a mixed liquid of water and an organic solvent was recovered. The recovery rate of isopropyl alcohol was 93%. In this apparatus, most of the remaining 7% was discharged into the atmosphere from the vent gas pipe 26 during the column replacement.
[0046]
The temperature of the cooling water was 16 ° C. The time required for one cycle was 8 minutes.
[0047]
In this example, since the fibrous activated carbon was used, the adsorption / desorption rate was fast, and it could be recovered even with an organic solvent in a low concentration region. The recovered isopropyl alcohol concentration was about 35% by volume (isopropyl alcohol 330 ml, water 600 ml). The concentration of the recovered liquid is about 3.5 times higher than that of the conventional method in which steam is continuously flowed.
For this reason, one cycle could be made a short time.
[0048]
【The invention's effect】
In the present invention, in the recovery of the solvent, the pressure in the adsorption tower is reduced by condensing and removing the water vapor after pressurizing the water vapor in the adsorption tower, so that the solvent recovery efficiency is high. Furthermore, since the water vapor used is substantially the same volume as the adsorption tower volume, the thermal energy efficiency is good. Furthermore, since the organic solvent is not exposed to hot water vapor for a long time in the desorption process, the recovered organic solvent hardly changes.
[0049]
In addition, since the amount of water vapor used is small, the amount of condensate discharged is small, so the problem of wastewater treatment is reduced, and if the solvent to be recovered is water-soluble, a high concentration condensate can be obtained. Subsequent solvent recovery processing is facilitated. Further, when fibrous activated carbon is used as the activated carbon, the adsorption / desorption rate is higher than that of normal granular activated carbon, so that the organic solvent-containing gas can be processed at a high speed and at a low concentration.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an example of a solvent recovery apparatus used in the organic solvent recovery method of the present invention.
FIG. 2 is a flowchart showing another example of a solvent recovery apparatus used in the organic solvent recovery method of the present invention.
[Explanation of symbols]
2, 2 ′ Adsorption tower 4 Introduction pipe 6 Bottoms 8, 8 ′, 14, 18, 18 ′, 22, 28, 32 Valve 10 Outlet pipe 12 Tower top 16 Steam supply pipe 20 Suction pipe 24 Condenser 26 Vent gas pipe 30 Cooling Water 34 Outlet pipe 36 Condensate outlet pipe 38 Condensate tank

Claims (4)

An adsorption step of supplying an organic solvent-containing gas to an adsorption tower packed with activated carbon to adsorb the organic solvent in the gas to the activated carbon, and a desorption step of desorbing and recovering the organic solvent from the activated carbon adsorbing the organic solvent. In the method for recovering an organic solvent in an organic solvent-containing gas, the desorption step includes a first step of supplying water vapor to the adsorption tower and replacing the air in the adsorption tower with water vapor, and pressurizing the inside of the adsorption tower with water vapor. a second step of the state, desorption to recover an organic solvent having adsorbed the adsorption tower is condensed in the condenser together with the second step in the pressurized state in steam of organic solvent vapors into the active carbon by the reduced pressure And a third step of recovering the organic solvent in the organic solvent-containing gas. The method for recovering an organic solvent according to claim 1, wherein the pressurized state in the second step is 0.5 to ⁵ kgf / cm ² . The method for recovering an organic solvent according to claim 1 or 2, wherein the reduced pressure state in the third step is 150 to 400 torr. The method for recovering an organic solvent according to any one of claims 1 to 3, wherein the activated carbon is fibrous activated carbon.

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