Organic solvent recovery system and organic solvent recovery method

Abstract

An organic solvent recovery system according to the present invention includes three or more treatment tanks that accommodate an adsorbent capable of adsorbing and desorbing an organic solvent, and that alternately perform adsorption of the organic solvent contained in a supplied treatment target gas and desorption of the organic solvent by means of supplied heated steam, the organic solvent recovery system comprising: a heated steam supply unit that supplies the heated steam to one treatment tank selected from the plurality of treatment tanks; a treatment target gas supply unit that connects the remaining plurality of treatment tanks in parallel and supplies the treatment target gas to at least one of the plurality of treatment tanks connected in parallel; a recovery unit that recovers the organic solvent from the desorbed gas discharged from the treatment tank when the heated steam is supplied; and a heating unit that heats the treatment target gas supplied from the treatment target gas supply unit.

Description

Organic Solvent Recovery System and Organic Solvent Recovery Method

[0001] The present invention relates to an organic solvent recovery system and an organic solvent recovery method.

[0002] In recent years, emission concentration regulations for hazardous air pollutants have been tightened, and it has been desired to reduce the concentration of exhaust gas discharged from gas treatment devices. Conventionally, there are treatment devices that recover and reuse organic solvent-containing gas discharged from factories and the like, and prevent organic solvents from being discharged into the atmosphere. Such a treatment device has two or more treatment tanks filled with an adsorbent, and each treatment tank alternately performs an adsorption step of adsorbing the organic solvent-containing gas to be treated and a desorption step of desorbing the organic solvent adsorbed on the adsorbent with water vapor, thereby continuously performing treatment. A gas treatment device that performs such processing is known (see, for example, Patent Document 1).

[0003] Examples of adsorbents for gas treatment devices include Activated Carbon Fiber (hereinafter referred to as ACF). ACF has an excellent function of adsorbing low-concentration organic solvent-containing gas, and has been used as an adsorbent for a long time. For example, there has been proposed a gas treatment device in which ACF is fixed to a support or formed into a cylindrical shape by self-supporting and vertically arranged in a core material (see, for example, Patent Documents 2, 3, 4, and 5).

[0004] In granular activated carbon, the pores involved in adsorption are macropores, whereas in ACF, they are micropores. Therefore, ACF has a faster adsorption and desorption rate for organic solvents, and desorption is completed in a shorter time, so the quality of the recovered solvent is better.

[0005] Furthermore, when water vapor is used to desorb the organic solvent from the adsorbent, the adsorbent becomes wet once. Therefore, in order to maintain adsorption performance during long-term operation, it is necessary to dry the adsorbent before the next desorption. If this drying is insufficient, the wetted portion of the adsorbent expands as operation progresses, significantly reducing adsorption performance. Since ACF dries much faster than granular activated carbon, it is common for the adsorption step to also serve as drying.

[0006] Japanese Patent Publication No. 2001-347126, Japanese Patent Publication No. 51-38278, Japanese Utility Model Publication No. 7-2028, Japanese Utility Model Publication No. 7-2029, Japanese Utility Model Publication No. 7-2030

[0007] However, as the concentration of organic solvents in the gas being treated increases, the weight of the adsorbent per unit volume of treated air increases, making it difficult to combine drying with the adsorption process in some cases.

[0008] In such cases, one possible strategy is to raise the temperature of the gas to be treated before adsorption in order to improve the drying capacity during adsorption. However, raising the temperature leads to a decrease in the amount of organic solvent adsorbed by the adsorbent, which in turn results in a larger device size.

[0009] Another possible approach is to reduce the humidity of the gas to be treated before adsorption. However, this would require adding a dehumidification mechanism to the upstream side of the device, which would increase the size of the device and raise running costs.

[0010] Another approach would be to add a drying tank in addition to the treatment tanks used for adsorption and desorption, and to perform a separate drying process. However, this would require adding a separate gas line for drying, in addition to the gas line being treated, thus complicating the piping.

[0011] Especially when processing airflow is high, it becomes necessary to arrange large-diameter gas ducts in a complex manner, and furthermore, dampers must be installed in each processing tank to switch between introducing two lines: the gas to be processed and the gas for drying. This raises concerns about the need to increase the size and cost of the equipment.

[0012] Therefore, the present invention has been made in view of the above problems, and its objective is to provide an organic solvent recovery system, etc., that prevents the adsorption capacity from decreasing due to the adsorbent becoming wet with water vapor, and that is more compact and has lower running costs than conventional systems.

[0013] As a result of diligent research by the inventors, it was discovered that by adopting the following configuration, an organic solvent recovery system can be obtained that suppresses the decrease in adsorption capacity due to water vapor, is more compact than conventional systems, and has lower running costs, thus leading to the present invention. In other words, the present invention is as follows.

[0014] The organic solvent recovery system of the present invention comprises three or more processing tanks that contain an adsorbent capable of adsorbing and desorbing organic solvents, and alternately perform adsorption of organic solvents contained in a supplied gas to be treated and desorption of the organic solvents by supplied heated steam; a heated steam supply unit that supplies the heated steam to one of the processing tanks selected from the plurality of processing tanks; a gas to be treated supply unit that connects the remaining plurality of processing tanks in parallel and supplies the gas to be treated to at least one of the plurality of processing tanks connected in parallel; a recovery unit that recovers the organic solvent from the desorbed gas discharged from the processing tank when the heated steam is supplied; and a heating unit that heats the gas to be treated supplied from the gas to be treated supply unit.

[0015] In the organic solvent recovery system of the present invention, in addition to the above configuration, the adsorption in the treatment tank may be performed in the order described above, consisting of thermal adsorption by supplying the gas to be treated heated by the heating unit, and normal adsorption by supplying the gas to be treated that has not been heated.

[0016] In addition to the above configuration, the organic solvent recovery system of the present invention may also use activated carbon fibers or granular activated carbon as the adsorbent.

[0017] The present invention provides an organic solvent recovery method that, in addition to the above configuration, has an organic solvent recovery system comprising three or more treatment tanks containing adsorbents capable of adsorbing and desorbing organic solvents contained in a gas to be treated. Each treatment tank sequentially performs a heated adsorption step in which heated gas to be treated is supplied to the adsorbent, a normal adsorption step in which unheated gas to be treated is supplied to the adsorbent, and a desorption step in which heated vapor is supplied to desorb the organic solvent adsorbed on the adsorbent.

[0018] The organic solvent recovery system and method of the present invention suppress the reduction in adsorption capacity due to water vapor, reduce running costs compared to conventional methods, and enable highly efficient and continuous treatment of the gas to be treated. Furthermore, the organic solvent recovery system can be configured compactly.

[0019] This figure shows the configuration of the organic solvent recovery system in this embodiment and the first step of the organic solvent recovery method using this organic solvent recovery system. This figure shows the configuration of the organic solvent recovery system in this embodiment and the second step of the organic solvent recovery method using this organic solvent recovery system. This figure shows the configuration of the organic solvent recovery system in this embodiment and the third step of the organic solvent recovery method using this organic solvent recovery system. This figure shows the configuration of the organic solvent recovery system of Comparative Example 1. This figure shows the configuration of the organic solvent recovery system of Comparative Example 2. This figure shows the measurement results obtained by recovering organic solvents using the systems of the examples and comparative examples.

[0020] Embodiments of the present invention will be described in detail below with reference to the drawings. In the embodiments described below, the same or corresponding parts will be denoted by the same reference numerals in the drawings, and their descriptions may not be repeated. Also, in the embodiments described below, when the number, quantity, etc. are mentioned, the scope of the present invention is not necessarily limited to the number, quantity, etc., unless otherwise specified.

[0021] The organic solvents used in this invention are methylene chloride, chloroform, carbon tetrachloride, ethylene chloride, trichloroethylene, tetrachloroethylene, o-dichlorobenzene, m-dichlorobenzene, Freon-112, Freon-113, HCFC, HFC, PFAS, propyl bromide, butyl iodide, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, vinyl acetate, methyl propionate, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, diethyl carbonate, ethyl formate, diethyl ether, dipropyl ether, tetrahydrofuran, dibutyl ether, anisole, methanol, ethanol, isopropanol, n-butanol, 2-butanol, isobutanol, t-butanol, and This refers to lyl alcohol, pentanol, heptanol, ethylene glycol, diethylene glycol, phenol, o-cresol, m-cresol, p-cresol, xylenol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, holone, acrylonitrile, n-hexane, isohexane, cyclohexane, methylcyclohexane, n-heptane, n-octane, n-nonane, isononane, decane, dodecane, undecane, tetradecane, decalin, benzene, toluene, m-xylene, p-xylene, o-xylene, ethylbenzene, 1,3,5-trimethylbenzene, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, and dimethyl sulfoxide, etc.

[0022] Referring to Figure 1, the configuration of the organic solvent recovery system 100 in this embodiment will be described. Figure 1 is a diagram showing the configuration of the organic solvent recovery system 100 in this embodiment. This organic solvent recovery system 100 is configured to realize a parallel adsorption method and includes a first treatment tank 2, a second treatment tank 3, and a third treatment tank 4.

[0023] The first treatment tank 2 contains a cylindrical first adsorbent 5A, the second treatment tank 3 contains a cylindrical second adsorbent 5B, and the third treatment tank 4 contains a cylindrical third adsorbent 5C. The first adsorbent 5A, the second adsorbent 5B, and the third adsorbent 5C undergo an adsorption process when the gas to be treated passes from the outside to the inside, and a desorption process when heated steam passes from the inside to the outside. ACF is used for the first adsorbent 5A, the second adsorbent 5B, and the third adsorbent 5C.

[0024] The gas to be treated line 30 (the gas to be treated supply section) is connected to the raw gas fan 1 and is connected to the inlet side of the raw gas fan 1. The gas to be treated introduction line 31 is connected to the raw gas fan 1 and is connected to the outlet side of the raw gas fan 1. The gas to be treated introduction line 31 is connected to the first treatment tank 2 via the first treatment gas introduction valve 21 at the first treatment gas branch line 31A, to the second treatment tank 3 via the second treatment gas introduction valve 22 at the second treatment gas branch line 31B, and to the third treatment tank 4 via the third treatment gas introduction valve 23 at the third treatment gas branch line 31C.

[0025] A gas heater 51 (heating unit) is provided in the heat treatment gas introduction line 41, which branches off from the gas to be treated introduction line 31. Each of these is connected to the first treatment tank 2 via the first heat treatment gas introduction on / off valve 25 at the first heat treatment gas branch line 41A, to the second treatment tank 3 via the second heat treatment gas introduction on / off valve 26 at the second heat treatment gas branch line 41B, and to the third treatment tank 4 via the third heat treatment gas introduction on / off valve 27 at the third heat treatment gas branch line 41C.

[0026] The first treatment tank 2 receives the gas to be treated from the first treatment gas branch line 31A. As the gas passes through the first adsorbent 5A, organic solvents in the gas are adsorbed and removed, resulting in a clean gas which is then released into the outside air through the exhaust port 31D of the first treatment tank. (Normal adsorption process)

[0027] In the second treatment tank 3, the heated gas to be treated, heated by the gas heater 51, is introduced via the second heat treatment gas branch line 41B. As it passes through the second adsorbent 5B, organic solvents in the heat treatment gas are adsorbed and removed, resulting in a clean gas which is then released into the outside air via the exhaust port 31E of the second treatment tank. (Heat adsorption process)

[0028] In the third treatment tank 4, heated steam is introduced from the heated steam supply device 60 (heated steam supply section) via the third heated steam line 61C, desorbing the organic solvent adsorbed on the third adsorbent 5C. The desorbed gas containing water vapor is cooled and liquefied in the condenser 72 via the desorption gas line 71 and recovered in the separator 73 (recovery section). The uncondensed gas contained in the condenser 72 and separator 73 is sent via the return gas line 74 to the treated gas line 30 upstream of the raw gas fan 1. (Desorption process)

[0029] Here, Figure 2 shows the case when the first treatment tank 2 is in the (desorption process), the second treatment tank 3 is in the (normal adsorption process), and the third treatment tank 4 is in the (heated adsorption process), and Figure 3 shows the case when the first treatment tank 2 is in the (heated adsorption process), the second treatment tank 3 is in the (desorption process), and the third treatment tank 4 is in the (normal adsorption process), and the flow of the gas to be treated, the heated gas to be treated, and the heated steam is the same as in Figure 1 described above.

[0030] In each processing tank, the processes are switched in the following order: (heat adsorption process) → (normal adsorption process) → (desorption process). Switching in any other order may result in a significant decrease in performance.

[0031] Furthermore, in the organic solvent recovery system 100 of this embodiment, a temperature control and / or humidity control mechanism may be installed in the gas line 30 to be treated. Doing so will increase the ability to treat the organic solvent in the gas to be treated with the adsorbent and allow the device to be made more compact.

[0032] Furthermore, in the organic solvent recovery system 100 of this embodiment, a gas heater 51 is provided in the heat treatment gas introduction line 41 to improve the drying capacity of the adsorbent. Compared to the independent drying method shown in Figure 5, the amount of processing air applied to the gas heater can be reduced, which in turn reduces the utility used for the gas heater and thus lowers running costs.

[0033] In this embodiment, the adsorbent used in the organic solvent recovery system 100 may be ACF or granular activated carbon. Here, ACF refers to a specific surface area of ​​300 to 3000 m² obtained by processing raw material fibers such as acrylonitrile (PAN) fibers, rayon fibers, coal pitch fibers, phenolic resin fibers, petroleum pitch fibers, and plant-derived fibers using existing methods. ２ The ideal values ​​are: per g, fiber diameter of approximately 2 μm to 30 μm, fiber length of approximately 0.5 mm to 100 mm, and average pore diameter of approximately 4 Å to 30 Å.

[0034] The organic solvent recovery system 100 in this embodiment will be described in more detail below with reference to examples.

[0035] (Example) The organic solvent recovery system shown in Figures 1 to 3 described above was used. 3.4 kg / tank of ACF "K-FILTER" manufactured by Toyobo MC Co., Ltd. was used as the adsorbent.

[0036] A gas to be treated at 25°C containing 20,000 ppm of methylene chloride is subjected to an airflow of 2.4 m³. ３ The raw gas is sent to fan 1 at / min, and the normal adsorption process uses an airflow of 1.2 m³. ３ The gas to be treated at a rate of / min was introduced into the first treatment tank 2 and treated with the first adsorbent 5A. This treated gas was then released to the outside as clean gas from the exhaust port 31D of the first treatment tank. In addition, a heating adsorption process was performed with an airflow of 1.2 m³. ３ The gas to be treated at / min was heated to 50°C using a gas heater 51 and introduced into the second treatment tank 3, where it was treated with the second adsorbent 5B. This treated gas was then released to the outside as clean gas through the exhaust port 31E of the second treatment tank.

[0037] While the first treatment tank 2 and the second treatment tank 3 were processing the gas to be treated and the heated gas to be treated, heated steam was introduced into the third treatment tank 4 from the heated steam supply device 60 and discharged as a desorption gas. The desorption gas was liquefied and cooled in the condenser 72 through the desorption gas line 71, and separated into methylene chloride and water in the separator 73 and recovered.

[0038] After a certain period of time has elapsed, each step is switched, wherein the first treatment tank 2 is set to a step of introducing heated steam for desorption (desorption step), the second treatment tank 3 is set to a step of introducing the gas to be treated (normal adsorption step), and the third treatment tank is set to a step of introducing heated gas to be treated (heated adsorption step).

[0039] The above step switching was sequentially repeated for 8 cycles, and the dichloromethane concentration in the clean gas discharged from the first treatment tank and the second treatment tank was measured using a total hydrocarbon meter (HCM-1B: manufactured by Shimadzu Corporation).

[0040] (Comparative Example 1) The organic solvent recovery system of Comparative Example 1 shown in FIG. 4 was used. As the adsorbent, 3.4 kg / tank of ACF "K-FILTER" manufactured by Toyobo MC Co., Ltd. was used. A gas to be treated at 25° C containing 20,000 ppm of methylene chloride was supplied at an air volume of 2.4 m ３ / min into the first treatment tank 2 by the raw gas fan 1, and treated with the first adsorbent. This treated gas was discharged to the outside as clean gas from the exhaust port 31D of the first treatment tank. On the other hand, heated steam was introduced into the second treatment tank 3 from a heated steam supply device 60, and discharged as desorption gas. The desorption gas passed through a desorption gas line 71, was liquefied and cooled in a condenser 72, and separated into methylene chloride and water in a separator 73, which were then recovered.

[0041] After performing the step of adsorbing the gas to be treated in the first treatment tank 2 for a certain period of time, each step is switched, wherein the first treatment tank 2 is set to the step of introducing heated steam for desorption (desorption step), and the second treatment tank 3 is set to introduce the gas to be treated (adsorption step).

[0042] The above step switching was repeated for 8 cycles, and the dichloromethane concentration in the clean gas discharged from the first treatment tank was measured using a total hydrocarbon meter (HCM-1B: manufactured by Shimadzu Corporation).

[0043] (Comparative Example 2) The organic solvent recovery system of Comparative Example 2 shown in FIG. 2 was used. As the adsorbent, 3.4 kg / tank of ACF "K-FILTER" manufactured by Toyobo MC Co., Ltd. was used. A gas to be treated at 25° C containing 20,000 ppm of methylene chloride was supplied at an air volume of 2.4 m ３ / min to the raw gas fan 1, and as the first adsorption step, at an air volume of 1.2 m ３ / min of the gas to be treated was introduced into the first treatment tank 2 and treated with the first adsorbent. This treated gas was discharged to the outside as clean gas from the exhaust port 31D of the first treatment tank. Also, as the second adsorption step, the air volume was 1.2 m ３ / min of the gas to be treated was introduced into the second treatment tank 3 and treated with the second adsorbent 5B. This treated gas was discharged to the outside as clean gas from the exhaust port 31E of the second treatment tank.

[0044] After a certain period of time, each step was switched. The first treatment tank 2 was set to the step of introducing heated steam for desorption (desorption step), the second treatment tank 3 was set to the step of introducing the gas to be treated (first adsorption step), and the third treatment tank was set to the step of introducing the gas to be treated (second adsorption step).

[0045] The above step switching was repeated for 8 cycles, and the dichloromethane concentration in the clean gas discharged from the first treatment tank was measured by a total hydrocarbon meter (HCM-1B: manufactured by Shimadzu Corporation).

[0046] Figure 6 shows the measurement results of the example and comparative examples. As can be seen from Figure 6, it was confirmed that according to the organic solvent recovery system and the organic solvent recovery method of the example, the exhaust methylene chloride concentration and the removal rate were higher than those of Comparative Example 1 and Comparative Example 2.

[0047] The reason for the difference in exhaust methylene chloride concentration and removal rate between the example disclosed herein and Comparative Examples 1 and 2 is considered to be that in the example, a part of the gas to be treated was heated and introduced into each treatment tank, so continuous operation was possible without the adsorbent getting wet.

[0048] The embodiments and examples disclosed herein are illustrative in all aspects and are not restrictive. The technical scope of the present invention is defined by the claims, and includes all modifications within the meaning and scope equivalent to the description of the claims.

[0049] The organic solvent recovery system of the present invention prevents the adsorption capacity from decreasing, is more compact than conventional systems and has lower running costs, thus greatly contributing to the treatment of gas to be treated.

[0050] 1 Raw gas fan, 2 First treatment tank, 3 Second treatment tank, 4 Third treatment tank, 5A First adsorbent, 5B Second adsorbent, 5C Third adsorbent, 6 First automatic upper damper, 7 Second automatic upper damper, 8 Third automatic upper damper, 9 First automatic lower damper, 10 Second automatic lower damper, 11 Third automatic lower damper, 12 Drying fan, 21 First treatment gas introduction valve, 22 Second treatment gas introduction valve, 23 Third treatment gas introduction valve, 25 First heat treatment gas introduction valve, 26 Second heat treatment gas introduction valve, 27 Third heat treatment gas introduction valve, 30 Treatment gas line (treatment gas supply section), 31 Treatment gas introduction line, 31A First treatment gas branch line, 31B Second treatment gas branch line, 31C Third treatment gas branch line, 31D First treatment tank exhaust port, 31E Second treatment tank exhaust port, 31F Third treatment tank exhaust port, 41 Heat treatment gas introduction line, 41A First heat treatment gas branch line, 41B Second heat treatment gas branch line, 41C Third heat treatment gas branch line, 51 Gas heater (heating section), 60 Heating steam supply device (heating steam supply section), 61 Heating steam introduction line, 61A First heating steam line, 61B Second heating steam line, 61C Third heating steam line, 62 First heating steam introduction on / off valve, 63 Second heating steam introduction on / off valve, 64 Third heating steam introduction on / off valve, 71 Desorption gas line, 72 Condenser, 73 Separator (recovery section), 74 Return gas line, 80 Air introduction line, 81 Drying air introduction line, 81A First drying air branch line, 81B Second drying air branch line, 81C Third drying air branch line, 82 First drying air introduction on / off valve, 83 Second drying air introduction on / off valve, 84 Third drying air introduction on / off valve, 100 organic solvent recovery system.

Claims

1. An organic solvent recovery system having three or more treatment tanks that contain an adsorbent capable of adsorbing and desorbing organic solvents, and alternately perform adsorption of organic solvents contained in a supplied gas to be treated and desorption of the organic solvents using supplied heated steam, characterized in that the system comprises: a heated steam supply unit that supplies the heated steam to one of the treatment tanks selected from the plurality of treatment tanks; a gas to be treated supply unit that supplies the remaining plurality of treatment tanks in parallel and supplies the gas to be treated to at least one of the plurality of treatment tanks connected in parallel; a recovery unit that recovers the organic solvent from the desorbed gas discharged from the treatment tank when the heated steam is supplied; and a heating unit that heats the gas to be treated supplied from the gas to be treated supply unit.

2. The organic solvent recovery system according to claim 1, wherein the adsorption in the treatment tank is performed in the order described above: thermal adsorption by supplying the gas to be treated heated by the heating unit, and normal adsorption by supplying the gas to be treated that has not been heated.

3. The organic solvent recovery system according to claim 1 or 2, wherein the adsorbent is activated carbon fiber or granular activated carbon.

4. An organic solvent recovery method in an organic solvent recovery system having three or more treatment tanks containing adsorbents capable of adsorbing and desorbing organic solvents contained in a gas to be treated, wherein each treatment tank sequentially performs a heated adsorption step in which heated gas to be treated is supplied to the adsorbent, a normal adsorption step in which unheated gas to be treated is supplied to the adsorbent, and a desorption step in which heated vapor is supplied to desorb the organic solvent adsorbed on the adsorbent.

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