JPH11114364A - Treatment of gas containing low boiling point solvent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treating method in which effective treatment of gas containing low boiling point solvent can be made by an adsorptive and desorptive mechanism which is suitable for adsorbing low boiling point solvent fluctuating largely in the concentration and is not excessively large in the equipment. SOLUTION: This treating method is as follows: (1) gas containing low boiling point solvent (gas to be treated 1) fluctuating in the concentration discharged from a gas source is once adsorbed on an adsorptive dam mechanism (adsorption unit 3) having adsorbed selected from particulate active carbon and particulate zeolite, (2) the gas containing low boiling point solvent adsorbed on the adsorptive dam mechanism is gradually released and desorbed and at the same time, the concentration of the low boiling point solvent in the gas desorbed at the gradual release and desorption is leveled, and (3) the gas containing the low boiling point solvent of the leveled concentration is fed to an adsorptive and desorptive mechanism for catching and adsorbing it. In order to level the gas concentration, the concentration of the solvent-containing gas after passing through the adsorptive dam mechanism is detected by a gas concentration detecting mechanism 5, and the detected results give feedback to a temperature adjusting mechanism 2 of the gas to be treated 1 to heat or cool the solvent-containing gas fed to the adsorptive dam mechanism.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the capture and adsorption of low-boiling solvent-containing gases such as low-boiling halogenated hydrocarbon gases such as methylene chloride and tricrene.

More specifically, in capturing and adsorbing the above-mentioned gas containing a low-boiling-point solvent, the gas containing a low-boiling-point solvent whose concentration temporarily fluctuates greatly from an apparatus serving as a source of a gas containing a low-boiling-point solvent is leveled and absorbed. The present invention relates to a treatment method for efficiently capturing and adsorbing a low-boiling-point solvent-containing gas supplied to a desorption mechanism.

[0003]

2. Description of the Related Art Conventionally, low boiling organic solvents, methylene chloride,
Low boiling solvents such as low boiling halogenated hydrocarbons such as trichlene are widely used as solvents for dissolving resins, for reaction processes, for dry cleaning, for cleaning various precision equipment parts, and for coating. Exhaust gas (hereinafter referred to as low-boiling-point solvent-containing gas) discharged from processing equipment in these various industrial fields causes environmental pollution when released into the atmosphere. Therefore, it is trapped and adsorbed by an adsorbent and further desorbed. Desorption from an adsorbent by treatment is widely performed. On the other hand, the adsorbent that has undergone the desorption treatment is again subjected to the adsorption treatment and is repeatedly used.

As an adsorbent for capturing, adsorbing, and desorbing a gas containing a solvent having a low boiling point, an adsorbent such as activated carbon or zeolite is used. Such activated carbon includes granular activated carbon, powdered activated carbon, and fibrous activated carbon.

[0005] Fibrous activated carbon (namely, activated carbon fiber, abbreviation: ACF) is 35 to 70 times as expensive as granular activated carbon and powdered activated carbon, and therefore its cost as an adsorbent is relatively high. On the other hand, on the other hand, since the adsorption speed is higher than that of the granular activated carbon and the powdered activated carbon, the adsorption / desorption efficiency is excellent. For this reason, the absorption / desorption treatment cycle can be shortened, and the layer height of the adsorbent using fibrous activated carbon as the adsorbent can be reduced to one tenth or less than that of granular activated carbon or powdered activated carbon. ,
There is an advantage that the suction / removal mechanism can be designed to be small. In addition, even if the bed height of the adsorbent is reduced, it can be applied to the absorption and desorption of low-concentration low-boiling-point solvent-containing gas, making it particularly effective as an adsorbent for treating low-concentration low-boiling-point solvent-containing gas. is there.

On the other hand, granular activated carbon has a lower adsorption rate than fibrous activated carbon. Therefore, in order to increase the adsorption efficiency, the adsorption / desorption mechanism usually requires a large amount (higher layer thickness and thicker layer). ) Is filled. Therefore, granular activated carbon is eventually suitable for adsorbing large volumes of gas.However, in applications where the adsorption / desorption cycle is repeated, the adsorption rate is lower than that of fibrous activated carbon, so it is absolutely necessary to absorb particulate activated carbon. -There is a problem that the desorption efficiency is poor. Due to the characteristics of such granular activated carbon, it is necessary to use a longer absorption / desorption cycle.

[0007]

The concentration of the low-boiling solvent-containing gas discharged from various processing apparatuses is different from the concentration when the gas is discharged at a low concentration in a steady operation state, the initial stage of drying, the initial stage of reaction, the transfer of liquid, or There are two types of characteristic concentration states when the liquid is temporarily discharged at a high concentration such as when the filter is replaced. For example, in a steady operation state, even when the gas concentration is as low as about 200 ppm, the gas may be temporarily exhausted at a high concentration of about tens of thousands ppm at the time of liquid transfer or filter replacement. .

FIG. 1 is a model chart showing a change in concentration of such a gas containing a low boiling point solvent having a large concentration fluctuation with respect to the discharge time. As a specific example, the ethanol concentration of the exhaust gas from a batch type batch dryer is shown. It is a thing. According to FIG. 1, the gas discharged from the tablet batch dryer has a temporary ethanol concentration of 20 at the beginning of drying.
The gas is discharged as a high concentration gas of 00 ppm, and thereafter is discharged as a low concentration gas of about 100 ppm on average.

In designing an absorption / desorption mechanism used for capturing and adsorbing a low-boiling-point solvent-containing gas having such a concentration fluctuation, a low-boiling-point solvent-containing gas is captured and adsorbed in response to the concentration fluctuation. In order to do so, the following countermeasures can be considered.

[0010] When high concentration gas is discharged from a device that is a source of a low boiling solvent-containing gas, the low boiling solvent-containing gas is prevented from leaking from an adsorption / desorption mechanism for trapping and adsorbing to cause air pollution. Therefore, the absorption / desorption mechanism is designed in accordance with the maximum value of the concentration of the high concentration gas.

An adsorption / desorption mechanism in which a plurality of adsorption units are installed in parallel is used, and adsorption and desorption are performed while switching alternately during steady operation, and a plurality of units are simultaneously used during temporary high concentration gas discharge.

In the above-mentioned countermeasures, in the case of the absorption / desorption mechanism using granular activated carbon as an adsorbent, the granular activated carbon has a higher bulk density than the fibrous activated carbon. Since the filling weight can be increased, it is suitable for temporary high concentration gas capture / adsorption treatment. However, as described above, the granular activated carbon has a lower adsorption speed than the fibrous activated body, so that the adsorbent is not adsorbed during steady operation.
There is a problem that the desorption efficiency is poor.

In the above countermeasures, the absorption / desorption mechanism using a structure in which fibrous activated carbon is laminated or a paper honeycomb structure in which fibrous activated carbon or powdered zeolite is carried as an adsorbent is used. The tolerance that can respond to gas concentration fluctuations is small. The reason for this is that these adsorbents are expensive and the adsorption / desorption speed is high, so that the design is such that the amount of the adsorbent is reduced. In addition, since fibrous activated carbon has a lower bulk density than granular activated carbon, if the apparatus is designed to cope with concentration fluctuations that temporarily generate high-concentration gas, the scale of the apparatus becomes excessive and almost all the time Of low concentration gas occupying
At the time of the adsorption process, most of the devices do not function and are in an idle state, so that there is a problem that the cost increases and the device design is not preferable.

[0014] In the above-mentioned countermeasures, the same problems as in the above countermeasures when using granular activated carbon,
Alternatively, there is a problem in using fibrous activated carbon or powdered zeolite.

Conventionally, an apparatus for arranging a combination of fibrous activated carbon and granular activated carbon and adsorbing harmful components contained in exhaust gas has been proposed in British Patent No. 1,456,231. The method for treating harmful components using the apparatus is as follows:
This is a method in which a gas containing harmful components is passed through an adsorbent obtained by simply stacking granular activated carbon and woven activated carbon (that is, fibrous activated carbon) in series in a layered manner to perform an adsorption treatment.

However, the above-mentioned British Patent No. 1,45
In the method of No. 6,231, the woven activated carbon and the granular activated carbon are laminated and integrated, and both adsorbents simultaneously perform the trapping / adsorbing treatment or the desorption treatment. In such a method in which both adsorbents function at the same time, the advantage of excellent absorption and desorption efficiency of the fibrous activated carbon is not fully utilized, and at the same time,
The advantages of granular activated carbon suitable for high concentration gas adsorption have not been fully exploited.

Accordingly, the present invention solves the problems of these existing methods and provides a processing method suitable for adsorbing a gas containing a low boiling point solvent having a large concentration fluctuation. It is an object of the present invention to provide a processing method capable of efficiently processing a low-boiling-point-solvent-containing gas by an absorption / desorption mechanism that does not make the gas excessive.

[0018]

In order to solve the above-mentioned problems, a method for treating a gas containing a low-boiling solvent according to the present invention comprises:
(1) adsorbing a low-boiling-point solvent-containing gas of varying concentration discharged from a low-boiling-point solvent-containing gas generation source to an adsorption dam mechanism having an adsorbent selected from granular activated carbon and granular zeolite; The low-boiling solvent-containing gas adsorbed to the adsorption dam mechanism is slowly released and desorbed, and at the same time, the concentration of the low-boiling solvent-containing gas desorbed at the time of the slow releasing and desorbing is leveled. (3) The low-boiling solvent containing the leveled concentration The gas is supplied to a suction / desorption mechanism that captures / adsorbs the gas.

The method for treating a low-boiling solvent-containing gas according to the present invention is characterized in that the low-boiling solvent-containing gas having a maximum peak concentration is discharged from the low-boiling solvent-containing gas generating source when the low-boiling solvent-containing gas has a maximum peak concentration. Put the low-boiling solvent-containing gas in the `` temporary deposit '' state in an adsorption dam mechanism that contains granular activated carbon or granular zeolite that can absorb gas as an adsorbent, and then steady-state low-concentration gas from the low-boiling solvent-containing gas source. The gas containing the low-boiling-point solvent is gradually released and desorbed sequentially from the "temporary deposit" state at the time of discharge, thereby leveling the concentration of the gas supplied to the absorption / desorption mechanism.

The adsorption dam mechanism using the granular activated carbon or the granular zeolite as an adsorbent used in the method for treating a gas containing a low boiling point solvent according to the present invention is supplied to an adsorption / desorption mechanism disposed downstream of the adsorption dam mechanism. It functions as a "release control dam" for leveling and adjusting the concentration of the low-boiling solvent-containing gas.

The method for treating a gas containing a low-boiling-point solvent according to the present invention has the effect of reducing fluctuations in the concentration of the gas to be treated supplied to the absorption / desorption mechanism, and achieving a reduction in the size of the absorption / desorption mechanism. According to the present invention, it is not necessary to design the absorption / desorption mechanism in accordance with the peak of the concentration of the exhaust gas from the device serving as the low-boiling-point solvent-containing gas generation source.

In the method for treating a low-boiling solvent-containing gas according to the present invention, the method of leveling the concentration of the gas desorbed from the adsorption dam mechanism comprises: It can be done by adjusting.

In the method for treating a low-boiling-point solvent-containing gas of the present invention, the method of leveling the concentration of the gas desorbed from the adsorption dam mechanism includes detecting the concentration of the low-boiling-point solvent-containing gas after passing through the adsorption dam mechanism. The detection result can be fed back to the gas temperature control mechanism disposed upstream of the adsorption dam mechanism to heat or cool the low-boiling solvent-containing gas supplied to the granular activated carbon or the granular zeolite.

The method for treating a gas containing a low-boiling solvent according to the present invention is characterized in that the suction dam mechanism and the absorption / desorption mechanism do not simultaneously exhibit the absorption / desorption functions, but individually exert the functions.

The absorption / desorption mechanism used in the method for treating a gas containing a low-boiling solvent according to the present invention is a mechanism for adsorbing and recovering a solvent from a gas containing a low-boiling solvent having a leveled concentration. The material of the adsorbent used is preferably selected from high-performance adsorbents such as fibrous activated carbon, powdered zeolite, and powdered activated carbon in order to efficiently process a gas containing a low boiling point solvent.

The suction / detachment mechanism is located upstream of the suction / detachment mechanism.
It is distinguished from an adsorption dam mechanism that uses granular activated carbon or granular zeolite as an adsorbent and can adsorb a low-boiling-point solvent-containing gas to a peak concentration from a low-boiling-point solvent-containing gas source. The structure of the absorption / desorption mechanism is preferably a laminated structure of fibrous activated carbon, or a paper honeycomb structure supporting an adsorbent composed of powdered zeolite or powdered activated carbon, in order to efficiently process a gas containing a low boiling point solvent. . Such a structure of the adsorbent is suitable for performing adsorption and desorption of a solvent efficiently by alternately repeating adsorption and desorption.

The fibrous activated carbon used for the absorption / desorption mechanism is derived from acrylonitrile-based fibers, phenol-based fibers, pitch-based fibers, rayon-based fibers, and the like.
Substantially carbon fibers having an adsorption capacity of specific surface area of 800 to 2000 m ² / g can be suitably used.

As the powdery zeolite used for the adsorption dam mechanism or the adsorption / desorption mechanism, powdery zeolite synthesized by various methods can be used.
Crushed charcoal, granulated charcoal, and beaded charcoal can be used as the granular activated carbon.

In the method for treating a low-boiling solvent-containing gas according to the present invention, preferred examples of the low-boiling solvent-containing gas to be treated include ketones such as methylene chloride, tricrene, perchrene, acetone, methyl ethyl ketone, and methanol. A gas containing a low-boiling solvent having a boiling point of about 150 ° C. or less, such as alcohols such as ethanol.

Examples of such a device serving as a gas source containing a low-boiling solvent include a dryer, a reaction can, a cleaning device,
Precision equipment cleaning equipment, automatic coating equipment and the like.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for treating a gas containing a low boiling point solvent according to the present invention will be described with reference to a flow sheet of the treatment process in FIG. 2 as an example.

In FIG. 2, reference numeral 1 denotes a gas to be treated supplied from a gas source containing a low boiling point solvent, and 2 denotes a gas to be treated disposed between an apparatus serving as a gas source containing a low boiling point solvent and an adsorption unit 3. 1 shows a temperature control mechanism, and the type of the temperature control mechanism 2 for the gas to be treated 1 is not particularly limited.
Reference numeral 3 denotes an adsorption unit (adsorption dam mechanism) in which granular activated carbon or granular zeolite is packed in layers, and is a fixed bed type packed bed. Reference numeral 4 denotes the gas leveled by the adsorption unit 3. Reference numeral 5 denotes a gas concentration detection mechanism disposed downstream of the adsorption unit 3 and upstream of a suction / desorption mechanism (not shown).

The gas to be treated 1 supplied from the low-boiling-point solvent-containing gas generating source is first supplied to the adsorption unit 3 before being supplied to the adsorption / desorption mechanism. Then, it is supplied to the suction / desorption mechanism. The gas concentration detecting mechanism 5 and the temperature adjusting mechanism 2 cooperate with each other. When the gas concentration is detected by the gas concentration detecting mechanism 5 and the gas concentration falls below a predetermined level, the gas concentration is fed back to the temperature adjusting mechanism 2 and the adsorption unit is operated. 3 works in such a manner that the temperature of the low-boiling-point solvent-containing gas supplied to 3 increases. Further, when the gas concentration rises to a predetermined gas concentration or more, it works in cooperation to lower the temperature. By the cooperation of the gas concentration detection mechanism 5 and the temperature adjustment mechanism 2 as described above, the gas concentration of the gas 4 gradually released from the adsorption unit 3 is always leveled.

The temperature control mechanism 2 for gradually releasing the low-boiling-point solvent-containing gas adsorbed on the adsorption unit 3 operates in cooperation with the above-mentioned gas-concentration detecting mechanism 5 and the concentration of the low-boiling-point solvent-containing gas. If the fluctuation of the gas 4 is known in advance, the adsorption / slow release is adjusted by heating or cooling by setting a timer or the like, and the concentration of the gas 4 supplied to the adsorption / desorption mechanism is leveled. You can also.
The leveled gas 4 is then supplied to a suction / desorption mechanism.

The capacity of the absorption / desorption mechanism depends on the total concentration of the peak concentration and the normal concentration of the gas containing the solvent having a low boiling point, and the total amount of the adsorption unit.
Is determined in consideration of the adsorption capacity and the like. In this case, the optimum conditions can be selected, and the capacity of the absorption / desorption mechanism is much smaller than the case of directly adsorbing a low-boiling-point solvent-containing gas having a peak concentration from a low-boiling-point solvent-containing gas source.

[0036]

EXAMPLES Exhaust gas containing the following methylene chloride (boiling point: 40.4 ° C.) whose concentration fluctuates in a 160-minute cycle (gas to be treated, exhaust gas amount: 9 m ² / min, superficial linear velocity: 23.4)
cm / s) by the method shown in the flow sheet of FIG. To control the temperature of the exhaust gas, 24
° C and the minimum concentration were adjusted to 28 ° C. The adsorbent to be filled in the adsorption unit is a granulated activated carbon layer as a crushed carbon (specific surface area: about 1000 m ² / g, trade name: Kuraray Coal GG)
18 kg (4/8, manufactured by Kuraray Co., Ltd.) was used at a layer height of 600 mm. As a result, the peak concentration of methylene chloride contained in the exhaust gas was 6,900 ppm, and the minimum concentration was 150 p.
pm, the gas concentration fluctuation after leveling by the processing of the present embodiment is 650 pp at the peak concentration.
m, the minimum concentration is adjusted to 150 ppm.
It was constant even after 0 cycles.

FIG. 3 shows data on the gas concentration on the inlet side, the gas concentration on the outlet side, and the temperature of exhaust gas of the adsorption unit when operated using the adsorption unit filled with new activated carbon. It is a graph which plotted the gas concentration and the elapsed time on the horizontal axis. As can be understood from the graph of FIG. 3, as a result of the leveling of the concentration of the gas to be treated, the design of the absorption / desorption mechanism can be designed according to the peak concentration after the leveling.

Comparative Example A treatment was carried out in the same manner as in the above example, except that the same granular activated carbon layer and exhaust gas as in the above example were used, and only the temperature of the exhaust gas was fixed at 24 ° C. As a result, the minimum concentration was about 100 ppm, and there was no sustained release effect. The peak concentration was 650 in the first cycle.
ppm, but the second cycle: 3,000 ppm,
Third cycle: Desorption gradually became difficult at 5,500 ppm, and no leveling effect was obtained. FIG. 4 is a graph showing data on the gas concentration on the inlet side, the gas concentration on the outlet side, and the temperature of the exhaust gas of the adsorption unit of the comparative example as a graph with the gas concentration on the vertical axis and the elapsed time on the horizontal axis.

[0039]

According to the method for treating a low-boiling-point solvent-containing gas of the present invention, even if a high-concentration low-boiling-point solvent-containing gas (gas to be treated) is temporarily discharged from a low-boiling-point solvent-containing gas source, Once adsorbed by the adsorption dam mechanism (granular activated carbon or granular zeolite) and then the gas concentration decreases, the target gas is heated to gradually release the components adsorbed on the adsorption dam mechanism, Since the gas is supplied to the suction / desorption mechanism, the concentration of the gas to be processed to be supplied to the suction / desorption mechanism can be equalized, and the processing apparatus can be designed efficiently.

[Brief description of the drawings]

FIG. 1 shows the relationship between the concentration of ethanol in exhaust gas discharged from a tablet dryer and time.

FIG. 2 is a flow sheet showing the processing steps of the method for treating a gas containing a low boiling point solvent according to the present invention.

FIG. 3 is a graph showing data on the gas concentration on the inlet side, the gas concentration on the outlet side, and the temperature of the exhaust gas of the adsorption unit in the embodiment, with the vertical axis representing the gas concentration and the horizontal axis representing the elapsed time.

FIG. 4 is a graph showing data on the gas concentration on the inlet side, the gas concentration on the outlet side, and the temperature of the exhaust gas of the adsorption unit in the comparative example when the gas temperature is kept constant. Is shown as a graph.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas to be processed 2 Temperature control mechanism 3 Adsorption unit 4 Gas 5 Gas concentration detection mechanism

Claims (5)

[Claims] (1) A low-boiling-point solvent-containing gas having a variable concentration discharged from a low-boiling-point solvent-containing gas generating source is once adsorbed to an adsorption dam mechanism having an adsorbent selected from granular activated carbon and granular zeolite. (2) the low-boiling-point solvent-containing gas adsorbed on the adsorption dam mechanism is gradually released and desorbed, and at the same time, the concentration of the low-boiling-point solvent-containing gas desorbed at the time of the slow-release desorption is leveled; (3) the leveled concentration A low-boiling-point solvent-containing gas, which is supplied to an absorption / desorption mechanism for capturing and adsorbing the low-boiling-point solvent-containing gas. 2. The method of leveling the concentration of the low-boiling solvent-containing gas desorbed during the slow release desorption is performed by adjusting the temperature of the low-boiling solvent-containing gas before being supplied to the adsorption dam mechanism. Item 6. The method for treating a gas containing a low boiling point solvent according to Item 1. 3. The method of leveling the concentration of a low-boiling-point solvent-containing gas desorbed during the slow-release desorption comprises detecting the concentration of the low-boiling-point solvent-containing gas after passing through an adsorption dam mechanism, and adsorbing the detection result. 3. The method for treating a low-boiling-point solvent-containing gas according to claim 1 or 2, wherein the gas is supplied to the granular activated carbon or the granular zeolite by heating or cooling by feeding back to a gas temperature regulating mechanism disposed upstream of the dam mechanism. . 4. The method for treating a low-boiling-point solvent-containing gas according to claim 1, wherein the structure of the absorption / desorption mechanism is a laminated structure of fibrous activated carbon or a paper honeycomb structure supporting an adsorbent. 5. The method according to claim 4, wherein the adsorbent carried on the paper honeycomb structure is selected from fibrous activated carbon, powdered zeolite, and powdered activated carbon.