JP2024064550A - Apparatus and method for recovering volatile organic compounds - Google Patents

Abstract

To provide means which may recover a volatile organic compound by a method that can achieve miniaturization while reducing energy loss.SOLUTION: A recovery device makes a vapor of a volatile organic compound adsorbed by a porous carbon material that adsorbs the vapor of the volatile organic compound by releasing and applying stress and desorbs the vapor or a liquefied material thereof, applies the stress to the porous carbon material that adsorbs the vapor, makes the vapor or the liquefied material thereof desorbed from the porous carbon material, and recovers the vapor or the liquefied material thereof desorbed from the porous carbon material.SELECTED DRAWING: Figure 8

Description

The present invention relates to a recovery device and recovery method for volatile organic compounds.

Regulations on fine particulate matter contained in the air environment are in place on a global scale, and in Japan, the Air Pollution Control Act and other relevant laws and regulations regulate the release of fine particulate matter into the atmosphere.

Fine particulate matter refers to small particles suspended in the air with a particle diameter of 2.5 μm or less. Its components include carbon components, nitrates, sulfates, ammonium salts, and inorganic elements such as silicon, sodium, and aluminum. It contains particles of various particle sizes, and its composition varies depending on the region, season, and weather conditions. This fine particulate matter is broadly divided into those directly emitted by burning materials (primary particles) and those generated by chemical reactions in the ambient air (secondary particles). Of these, secondary particles are generated when gaseous substances such as volatile organic compounds (VOCs) emitted during the use of solvents and paints, evaporation from oil handling facilities, and forests react with light and ozone in the atmosphere. In particular, emissions of volatile organic compounds from paints, cleaning agents, adhesives, and inks account for approximately 75% of the total, and even when viewed by industry, emissions from industries that handle a lot of paints, etc. account for the majority.

For example, a typical paint factory has several painting booths and drying lines, paint mixing and supply areas, as well as equipment for transporting and removing dust from materials to be painted, and polishing equipment. The exhaust air passes through pre-filters installed at multiple exhaust ports to remove large particles of mist and dust, and passes through a dedicated exhaust duct before being absorbed and treated in an external recovery system filled with activated carbon or zeolite before being released into the atmosphere. Methods for treating volatile organic compounds can be broadly divided into combustion methods, adsorption methods, and other methods. Of these, the adsorption method is a method of physically and chemically adsorbing and recovering volatile organic compounds, and is a method in which the adsorption and desorption of volatile organic compounds is repeated while regenerating the adsorbent.

As a conventional means for recovering volatile organic compounds using an adsorption method, Patent Document 1 discloses an organic solvent-containing gas treatment system in which a gas to be treated containing an organic solvent is introduced into an organic solvent adsorption/desorption device equipped with an adsorption tank filled with an adsorbent, the organic solvent is adsorbed in the adsorption tank, and treated gas with a reduced organic solvent concentration is discharged. After the adsorption process in the adsorption tank is completed, steam is introduced into the organic solvent adsorption/desorption device to desorb the organic solvent from the adsorbent, thereby regenerating the adsorbent. Examples of adsorbents that can desorb organic solvents by the introduction of steam include granular activated carbon, activated carbon fiber, zeolite, and silica gel.

JP 2009-273975 A

In conventional organic solvent-containing gas treatment systems such as that disclosed in Patent Document 1, the solvent vapor is desorbed by supplying heated gas (steam, etc.) to an adsorbent that has adsorbed volatile organic compounds (organic solvents), which results in energy loss and low efficiency, as well as a large number of piping and a large volume.

Therefore, the present invention aims to provide a means for recovering volatile organic compounds using a method that reduces energy loss and allows for miniaturization.

The present inventors have conducted intensive research to solve the above problems. As a result, they have found that the above problems can be solved by a method in which a volatile organic compound vapor is adsorbed onto a porous carbon material that adsorbs the vapor of a volatile organic compound and desorbs the vapor or a liquefied product thereof by releasing and applying stress, a stress is applied to the porous carbon material that has adsorbed the vapor to desorb the vapor or a liquefied product thereof, and the vapor or a liquefied product thereof that has been desorbed from the porous carbon material is recovered, and the present invention has been completed.

That is, one aspect of the present invention is a volatile organic compound recovery device that adsorbs the vapor of a volatile organic compound onto an adsorbent and then desorbs and recovers the vapor or its liquefied product, and includes an adsorption/desorption section including a porous carbon material that adsorbs the vapor and desorbs the vapor or its liquefied product by releasing and applying stress, a stress application section that releases and applies the stress to the porous carbon material, and a recovery section that recovers the vapor or its liquefied product desorbed from the porous carbon material.

Another aspect of the present invention is a method for recovering a volatile organic compound, comprising: adsorbing a vapor of a volatile organic compound to a porous carbon material that adsorbs the vapor of the volatile organic compound and desorbs the vapor or a liquefied product thereof by releasing and applying stress; applying stress to the porous carbon material that has adsorbed the vapor, thereby desorbing the vapor or a liquefied product thereof from the porous carbon material; and recovering the vapor or a liquefied product thereof desorbed from the porous carbon material.

According to the present invention, it is possible to recover volatile organic compounds using a method that reduces energy loss and allows for miniaturization.

1 is a schematic cross-sectional view showing the configuration of a volatile organic compound recovery system according to one embodiment of the present invention. FIG. 1 is a diagram showing a state in which a porous carbon material is contracted by applying stress to the material, thereby desorbing volatile organic compounds. FIG. 1 shows XRD spectra of GMS and CMS. FIG. 2 is a diagram for explaining the meaning of Equation A using a saturated vapor pressure curve of methanol. The graph shows adsorption isotherms obtained when GMS was used as an adsorbent and methanol was used as an adsorbate (volatile organic compound), with no stress being applied to GMS (no stress applied) and when a stress of 100 MPa was applied to GMS. The graph shows adsorption isotherms obtained when GMS was used as an adsorbent and diethyl ether was used as an adsorbate (volatile organic compound) and when no stress was applied to GMS (no stress applied) and when a stress of 100 MPa was applied to GMS. 1 is a graph comparing the energy required to desorb methanol adsorbed on an adsorbent for a prior art method (desorption by heating from activated carbon) and the method of the present invention (desorption by applying stress from GMS). 1 is a photograph showing the state of a pressing machine taken with a thermo camera before and after a pressing process was performed using a pressing machine after methanol was adsorbed into the GMS powder. FIG. 2 is an explanatory diagram and photographs showing the state of a pressing machine before and after a pressing process is carried out using a pressing machine after diethyl ether is adsorbed on GMS powder in the presence of air.

Below, an embodiment of the present invention will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the claims, and is not limited to the following form. Note that the dimensional ratios in the drawings are exaggerated for the convenience of explanation, and may differ from the actual ratios.

<Volatile organic compound recovery system>
FIG. 1 is a schematic cross-sectional view showing the configuration of a volatile organic compound recovery system (hereinafter, also simply referred to as a "VOC recovery system") according to one embodiment of the present invention.

The VOC recovery system 10 is composed of a volatile organic compound recovery device (hereinafter also simply referred to as "VOC recovery device") 100, a paint booth 200 which is a source of volatile organic compounds, and a control unit 150 which controls the operation of the system. The VOC recovery system 10 can be used to recover volatile organic compounds emitted from the painting process of industrial products such as automobiles, and refrigerants such as alternative fluorocarbons emitted when air conditioners for automobiles are disposed of.

As shown in FIG. 1, the VOC recovery device 100 includes an adsorption/desorption section 110 consisting of a sealable cell 114 in which a graphene meso sponge (GMS) 112 (porous carbon material) capable of adsorbing volatile organic compound vapor is disposed, a piston 120 that releases and applies stress to the graphene meso sponge (GMS) 112 in the cell 114, and a recovery chamber 130 that recovers the vapor of the volatile organic compound or its liquefied product desorbed from the graphene meso sponge (GMS) 112. The VOC recovery device 100 also includes a pipe 142 that communicates between the cell 114 and the recovery chamber 130 so that the vapor of the volatile organic compound or its liquefied product can move between the cell 114 and the recovery chamber 130, and a valve 144 that switches the pipe 142 between a connected state and a blocked state. When the valve 144 is opened, the pipe 142 is in a connected state, and when the valve 144 is closed, the pipe 142 is in a blocked state. The control unit 150 controls the operation of the VOC recovery device 100 by changing the magnitude of the stress applied by the piston 120 and by switching the valve 144 between open and closed.

As shown in FIG. 1, the cell 114 of the VOC recovery device 100 is connected to the paint booth 200 via a pipe 212. This pipe 212 communicates between the cell 114 and the paint booth 200 so that vapors of volatile organic compounds can move between them. In addition, a valve 214 is installed in the pipe 212 to switch the pipe 212 between an open state and a closed state, as described above. The control unit 150 of the VOC recovery device 100 controls the operation of the VOC recovery system 10 by switching the valve 214 installed in the pipe 212 between open and closed. Each component of the VOC recovery system 10 will be described below.

[Adsorption/Desorption Part]
1, the adsorption/desorption unit 110 has a sealable cell 114 in which a graphene meso sponge (GMS) 112 (a porous carbon material) capable of adsorbing vapor of a volatile organic compound is disposed. In this embodiment, the GMS 112 is used as an example of a porous carbon material.

(Porous carbon materials)
The porous carbon material is a porous material containing carbon as a main component, preferably consisting of only carbon, has elasticity, and is capable of contracting to desorb volatile organic compounds when stress is applied, and of expanding to adsorb volatile organic compounds when stress is released. Thus, the porous carbon material contracts to desorb volatile organic compounds when stress is applied from the piston 120 functioning as a stress application section, and freely expands to adsorb volatile organic compounds when the stress is released.

The term "elasticity" refers to the property of being able to reversibly deform significantly and recover to nearly its original shape when stress is released, even if it is contracted by applying external stress by the piston 120 (stress application section). The elastic limit of the porous carbon material is preferably designed to be greater than the stress required to desorb volatile organic compounds. The elastic limit of the porous carbon material is preferably designed appropriately according to the scale of application of the VOC recovery device 100, etc.

"Porous" also means having multiple (preferably nano-level) pores. Nano-level pores are preferably micropores or mesopores with a diameter of 0.5 to 100 nm, more preferably 0.7 to 50 nm, and even more preferably 0.7 to 6 nm. The International Union of Pure and Applied Chemistry (IUPAC) defines pores with a diameter of 2 nm or less as micropores, pores with a diameter of 2 to 50 nm as mesopores, and pores with a diameter of 50 nm or more as macropores.

In general, the surface of a solid has a high potential energy due to van der Waals forces, and acts to condense the molecules of a volatile organic compound. In particular, in this embodiment, the volatile organic compound adsorbed to the porous carbon material is surrounded by small pore walls at the nano level, so the potential energy due to van der Waals forces (physical adsorption forces) of the solid surface is extremely high. At this time, the volatile organic compound in a gaseous state is adsorbed to the pore walls of the porous carbon material at the density of a liquid. In other words, adsorption to a porous carbon material is a phenomenon of the same nature as a phase change from gas to liquid, and the heat of adsorption is approximately equal to the latent heat of condensation. In the following explanation, it is assumed that a volatile organic compound changes phase from gas to liquid when adsorbed to a porous carbon material, and changes phase from liquid to gas when desorbed. It is also assumed that the heat of adsorption is equal to the latent heat of condensation.

Volatile organic compounds with liquid density inside the pores of the porous carbon material that are adsorbed on the pore walls are in equilibrium with vapor at a pressure below the saturated vapor pressure. In other words, the gas adsorbed on the pore walls of the porous carbon material becomes liquid at a pressure below the saturated vapor pressure.

When stress is applied to the porous carbon material, the pores of the porous carbon material 20 shrink as shown in FIG. 2 (A) before the application of stress and (B) under the application of stress, and the volatile organic compounds 30 adsorbed on the pore walls are desorbed. At this time, the volatile organic compounds 30 adsorbed at the density of a liquid are released again as a gas to the outside of the porous carbon material 20. By recovering the desorbed volatile organic compounds 30 in this way, the VOC recovery device 100 is able to recover volatile organic compounds using a method that reduces energy loss and allows for miniaturization.

On the other hand, when the stress is released in the porous carbon material 20, the porous carbon material 20 expands freely, the pores return to their original size, and the volatile organic compound 30 can be adsorbed again. As described above, the volatile organic compound 30 is adsorbed on the pore walls of the porous carbon material 20 at the density of a liquid. That is, when the volatile organic compound 30 is adsorbed into the porous carbon material 20, it undergoes a phase change from gas to liquid, generating latent heat of condensation.

The specific type of porous carbon material is not particularly limited as long as it is a material that has elasticity, can contract to release volatile organic compounds 30, and can expand to adsorb volatile organic compounds 30.

The BET specific surface area of the porous carbon material is not particularly limited, but is, for example, in the range of 800 to 4200 m ² /g, and preferably in the range of 800 to 2600 m ² /g. By using a porous carbon material with a large BET specific surface area within these ranges, the amount of adsorbate adsorbed can be increased. The pore volume of the porous carbon material is also not particularly limited, but is, for example, preferably 1.0 to 6.0 mL/g, more preferably 1.8 mL/g or more, and particularly preferably 2.0 mL/g or more. If the pore volume of the porous carbon material is 1.0 mL/g or more, the amount of adsorbate adsorbed and desorbed does not become too small even in a vapor pressure region with a relatively high relative pressure, so this is preferable. If the pore volume is 6.0 mL/g or less, the pore diameter becomes sufficiently small, and the amount of adsorption becomes high, so this is preferable.

Such materials include carbon materials that include a single-layer graphene skeleton and have the porosity and elasticity required for desorption and adsorption of volatile organic compounds 30. Specific examples of such carbon materials include zeolite template carbon (ZTC), graphene meso sponge (GMS), carbon meso sponge (CMS), and the like. Zeolite template carbon (ZTC), graphene meso sponge (GMS), and carbon meso sponge (CMS) are all made of a single-layer graphene skeleton and have the porosity and elasticity required for desorption and adsorption of volatile organic compounds 30.

ZTC is composed of a single-layer graphene sheet. It is known that uniform pores (diameter about 1.2 nm) are three-dimensionally ordered and interconnected, and that it has an extremely high BET specific surface area and pore volume (maximum BET specific surface area of 4100 m ² /g and pore volume of 1.8 mL/g). The ordered structure of ZTC was analyzed using an X-ray diffraction device (MiniFlex600, CuK, manufactured by Rigaku Corporation). The BET specific surface area of ZTC was analyzed using liquid nitrogen adsorption (77 K) (Microtrac BEL, BELSORB-max).

The method for producing ZTC is described in Nishihara, H. et al., Chemistry-European Journal 15, 5355 (2009), etc. Specifically, first, a porous material (e.g., zeolite, etc.) having pores inside the structure and a structure in which the pores are connected in a network form is prepared as a template. Then, an organic compound (e.g., acetylene, ethylene, etc.) is introduced into the surface and inside the pores of this porous material under heating conditions, and the organic compound is carbonized by heating, and carbon is deposited on the porous material. Here, the carbonization of the organic compound and the deposition of carbon can be performed, for example, by a chemical vapor deposition (CVD) method. Then, the porous material serving as the template is removed. This method makes it possible to easily produce a carbon material (i.e., ZTC) that reflects the three-dimensional structure of the template. The ZTC produced by the above method has excellent flexibility and elasticity, and can reversibly deform from a pore diameter of approximately 1.2 nm to approximately 0.7 nm.

GMS is also a sponge-like mesoporous material with micropores of about 6 nm in size, with most of the pore walls being composed of single-layer graphene. Like ZTC, it has an extremely high BET specific surface area (about 2000 m ² /g) comparable to that of activated carbon. On the other hand, unlike activated carbon and carbon black, it contains almost no graphene ends that cause corrosion, so it also has excellent corrosion resistance (oxidation resistance). In addition, due to the properties of graphene, which is flexible and tough, GMS has excellent flexibility and elasticity, and can reversibly elastically deform from about 5.8 nm to about 0.7 nm in pore diameter.

The manufacturing method of GMS is described in Nishihara, H. et al., Advanced Functional Materials, Vol. 26, 2016, 6418-6427. Specifically, first, metal oxide nanoparticles made of alumina or the like (for example, gamma alumina such as SBa-200 (trade name)) are prepared as nano-sized spherical substrates. This material has high catalytic activity against carbon coating by the CVD method described below and excellent sintering resistance.

Next, the surface of the spherical substrate (metal oxide nanoparticles) prepared above is coated with carbon by a CVD method using an organic compound as a carbon source. This carbon coating using the CVD method makes it possible to form a uniform carbon layer on the entire surface of the spherical substrate (metal oxide nanoparticles). In addition, examples of organic compounds used in this case include methane, acetylene, ethylene, propylene, and benzene, but it is preferable to use methane as the carbon source from the viewpoint that a coating with a graphene sheet with particularly few defects can be achieved. In addition, in the CVD process, the organic compound may be introduced in a state where a spacer such as quartz sand (silica sand) is mixed with the spherical substrate (metal oxide nanoparticles) in order to improve the flow of the gas flow. In addition, an inert gas such as nitrogen may be used as a carrier gas for introducing the organic compound, and the concentration of the carbon source in the mixed gas of the carrier gas and the carbon source (organic compound) is preferably about 10 to 30% by volume.

As the CVD process progresses, the color of the sample changes to black, while the reaction vessel (e.g., quartz tube) containing the sample remains transparent, so that it can be confirmed that carbon deposition occurs only on the surface of the spherical substrate (metal oxide nanoparticles). Here, since the spherical substrate (metal oxide nanoparticles) is not sintered even after the CVD process, the shape of the carbon-coated spherical substrate hardly changes from before carbon coating. The (average) number of layers of the carbon layer coated on the surface of the spherical substrate (metal oxide nanoparticles) in this way can be controlled based on the amount of carbon source (organic compound) input in the CVD process as well as the processing temperature and processing time during CVD, and corresponds to the (average) number of layers of the graphene layers in the finally obtained GMS. The value of this (average) number of layers is not particularly limited, but from the viewpoint of exhibiting excellent desorption/adsorption properties for volatile organic compounds 30, it is preferably 0.90 to 3.0, more preferably 0.95 to 2.0, even more preferably 0.98 to 1.5, and particularly preferably 1.0 to 1.1. There are no particular limitations on the processing temperature and processing time in the CVD process, but the processing temperature is preferably 800 to 1000°C, and more preferably 850 to 950°C. The processing time is preferably 1 to 10 hours, and more preferably 2 to 6 hours.

Then, the spherical substrate (metal oxide nanoparticles) used as the template is removed by chemical etching, leaving only the carbon layer coated on the surface of the spherical substrate. In this case, an aqueous solution of a strong acid or strong base may be used for the chemical etching. For example, hydrofluoric acid (HF) is an example of a strong acid (etching can be performed at room temperature in this case). For example, sodium hydroxide (NaOH) is an example of a strong base (heating to about 200 to 300°C is preferable in this case). When the spherical substrate (metal oxide nanoparticles) is removed by chemical etching, a carbon mesosponge (CMS) with spherical mesopores is obtained as a precursor of GMS.

Finally, the CMS thus obtained is washed with water as necessary, and then heat-treated for about 30 minutes to 2 hours at a temperature of about 1500 to 2000°C (preferably 1600 to 1800°C) under reduced pressure or normal pressure conditions. The atmosphere is not particularly limited, but in consideration of mass production, it is preferable to adopt an inert gas atmosphere such as nitrogen or argon. This advances the crystallization of the carbon layer into graphene, and GMS is obtained. Here, the spherical mesopores of CMS are very stable even at high temperatures during the above-mentioned heat treatment, so that the GMS thus obtained also retains mesopores similar to those of CMS. Since GMS has such mesopores, it can be flexibly and elastically deformed like a sponge. Therefore, it can contract to desorb volatile organic compounds 30, and expand to adsorb volatile organic compounds 30, and can be suitably used as the porous carbon material 20 in the VOC recovery device 100.

In the X-ray diffraction spectrum of the porous carbon material using Cu-Kα radiation, a peak derived from the (10) plane of carbon is preferably observed near 2θ=44°, and the half-width is preferably 1.2 to 3.2°. Examples of such porous carbon materials include GMS and CMS. When the inventors measured the X-ray diffraction spectra of GMS and CMS, as shown in Figure 3, a peak derived from the (10) plane of carbon was observed near 2θ=44° in these X-ray diffraction spectra, and the half-width was 2.2°. The X-ray diffraction measurement was performed by placing a sample on a silicon non-reflective plate and using an X-ray diffractometer XRD-6100 manufactured by Shimadzu Corporation. The radiation source was Cu-Kα, the voltage was 40 kV, and the current was 30 mA.

The porous carbon material according to this embodiment may be used in the form of a molded body bound by a binder.

(cell)
In the embodiment shown in FIG. 1, the cell 114 is a container constituting the adsorption/desorption unit 110, and the specific configuration is not particularly limited as long as the GMS 112 (porous carbon material) can be placed inside and can be sealed. A through hole is provided in a part of the wall of the cell 114 for passing the piston 120 (stress application unit) so that the piston 120 (stress application unit) can apply and release stress to the porous carbon material. The inside of the cell 114 is kept at a vacuum or a low pressure close to a vacuum. Therefore, the volatile organic compound introduced into the inside of the cell 114 can change phase from liquid to gas at a relatively low temperature.

[Stress application part]
In the embodiment shown in Fig. 1, the piston 120 functions as a stress application part that applies and releases stress to the GMS 112 (porous carbon material) included in the adsorption/desorption part 110. More specifically, the piston 120 (stress application part) applies stress to the porous carbon material to cause it to contract, and releases the applied stress to cause the porous carbon material to freely expand. This allows the stress application part to control the pore size of the porous carbon material by external stress.

The specific configuration of the stress application unit is not particularly limited, as long as it can reciprocate in a direction approaching and receding from the porous carbon material to apply and release stress to the porous carbon material. For example, a mechanical press using the rotational motion of a motor or a hydraulic press using fluid pressure such as hydraulic pressure can be used as the stress application unit.

[Collection chamber 130]
In the embodiment shown in FIG. 1, the recovery chamber 130 functions as a recovery section for recovering the vapor of the volatile organic compound or its liquefied product desorbed from the porous carbon material to which stress has been applied. As described above, the recovery chamber 130 is connected to the cell 114 via the pipe 142. When recovering the vapor of the volatile organic compound or its liquefied product adsorbed on the porous carbon material in the cell 114 into the recovery chamber 130, a valve 144 on the pipe 142 is opened in a state in which the porous carbon material is contracted by applying stress to the porous carbon material. The recovery chamber 130 may further be provided with an outlet (not shown) for discharging the recovered volatile organic compound or its liquefied product from the recovery chamber when the recovered volatile organic compound or its liquefied product is further recovered outside the VOC recovery system 10.

[Control unit 150]
The control unit 150 is composed of, for example, a CPU (Central Processing Unit), a RAM (Random Access Memory), and a computer-readable recording medium (not shown). In the embodiment shown in FIG. 1, the control unit 150 controls the operation of the piston 120 (stress application unit) and a valve 144 installed in the pipe 142. In this embodiment, the control unit 150 also controls the operation of a valve 214 installed in a pipe 212 that communicates between a coating booth 200 (described later) and the cell 114. Specifically, the control unit 150 switches the operation mode of the adsorption/desorption unit 110 between a desorption mode in which the volatile organic compound 30 is desorbed from the porous carbon material 20 and an adsorption mode in which the volatile organic compound 30 is adsorbed to the porous carbon material 20.

[Painting booth 200]
In this embodiment, the paint booth 200 is cited as an example of a source of organic solvent vapor among volatile organic compounds that are the target of recovery in the VOC recovery system 10. The specific configuration of the paint booth is not particularly limited as long as it generates volatile organic compound vapor, and it can be an environment in which any conventionally known painting process is performed. An example of the paint booth is, for example, a painting process, which is one of the manufacturing processes of automobiles. Examples of organic solvents as volatile organic compounds include acetone, methanol, ethanol, isopropyl alcohol, isobutyl alcohol, propylene glycol monoethyl ether, ethyl acetate, methyl ethyl ketone, benzene, toluene, xylene, and N,N-dimethylformamide. Mineral spirits and the like may also be used. The source of these organic solvents is not particularly limited to the paint booth, and may of course be an industrial process such as various cleaning processes and coating processes.

The volatile organic compounds to be recovered in the VOC recovery system 10 may be refrigerants such as alternative fluorocarbons, in addition to organic solvents. For example, in typical vapor compression heat exchange devices, HFC-134a, a fluorocarbon alternative fluorocarbon, is widely used as a volatile organic compound (refrigerant). The VOC recovery system 10 according to this embodiment may recover refrigerants such as alternative fluorocarbons used in the fields of air conditioning and refrigeration/freezing as volatile organic compounds.

<Operation of the volatile organic compound recovery system>
Next, the operation of the VOC recovery system 10 (VOC recovery device 100) according to this embodiment will be described.

The VOC recovery system 10 (VOC recovery device 100) according to this embodiment adsorbs the vapor of a volatile organic compound onto an adsorbent made of a porous carbon material, and then applies stress to the adsorbent (adsorption/desorption section) to desorb and recover the vapor or its liquefied form.

[Adsorption mode]
The adsorption mode is a mode in which the volatile organic compounds (organic solvents, refrigerants, etc.) to be recovered are adsorbed into the porous carbon material 112 of the adsorption/desorption section 110 .

In the adsorption mode, as shown in FIG. 1A, the control unit 150 controls the valve 144 to close and the valve 214 to open, and further controls the piston 120 to release the stress applied to the porous carbon material 112. As a result, the volatile organic compounds generated in the paint booth 200 are introduced into the cell 114 of the adsorption/desorption unit 110 and adsorbed into the porous carbon material 112 (arrow shown in FIG. 1A). At this time, it is preferable that the volatile organic compounds discharged from the paint booth 200 are generated through various filters, purification devices, etc. In addition, if necessary, a device such as a pump (not shown) may be used to promote the introduction of the volatile organic compounds from the paint booth 200. When a desired amount of volatile organic compounds is adsorbed into the porous carbon material 112 in the adsorption mode, the control unit 150 controls the valve 214 to close.

The amount of the volatile organic compound introduced into the cell 114 in the adsorption mode is not particularly limited, and may be an amount that allows at least a part of the volatile organic compound to be adsorbed by the porous carbon material 112. Here, as described above, when the volatile organic compound is adsorbed by the porous carbon material 112, it becomes a liquid state, but the vapor of the volatile organic compound may or may not be present in the space S in the cell 114 where the volatile organic compound may be present. In addition, when the vapor of the volatile organic compound is present in the space S, it may be present in an amount less than the saturated vapor amount, or may be present in the saturated vapor amount (when the volatile organic compound is introduced in an amount greater than the saturated vapor amount, the liquid-state volatile organic compound is present in the space S in the cell 114 even in the adsorption mode). Whether or not the vapor of the volatile organic compound is present in the space S in the adsorption mode and how much vapor is present are determined by the adsorption equilibrium of the volatile organic compound to the porous carbon material 112. Therefore, the conditions for adsorbing a desired amount of the volatile organic compound to the porous carbon material 112 in the adsorption mode can be obtained in advance by a preliminary experiment using the porous carbon material 112 used in the VOC recovery device 100 and the volatile organic compound that is the recovery target. The vapor pressure P in the cell 114 in the adsorption mode is not particularly limited, but is preferably equal to or lower than the saturated vapor pressure _Pe of the volatile organic compound at the temperature T of the porous carbon material described below (in other words, the relative pressure P/ _Pe = 1 or lower).

[Desorption mode]
The desorption mode is a mode in which the volatile organic compounds adsorbed in the porous carbon material 112 of the adsorption/desorption section 110 in the adsorption mode are desorbed.

In the desorption mode, as shown in FIG. 1B, the control unit 150 controls the valve 144 to open and the piston 120 (stress application unit) to apply stress to the porous carbon material 112. As a result, at least a portion of the volatile organic compounds adsorbed to the porous carbon material 112 in the adsorption mode is desorbed from the porous carbon material 112 in a gaseous or liquid state, and is recovered in the recovery chamber 130 through the pipe 142. In this way, the vapor of the volatile organic compounds generated in the coating booth 200 can be recovered as vapor or its liquefied form.

Here, it was previously believed that volatile organic compounds are desorbed exclusively in a gas phase state between porous carbon materials such as GMS by applying and releasing stress. In other words, the fact that there may be high stress application conditions that allow adsorption as vapor and recovery as liquid was not recognized at all. However, the present invention was completed by newly discovering conditions under which at least a portion of volatile organic compounds are desorbed as liquid. Therefore, even if the adsorbent of an existing volatile organic compound recovery device is changed to a porous carbon material such as GMS, as long as the stress application conditions that were thought to be adoptable within the framework of conventional recognition are adopted, a process of condensing the volatile organic compound vapor after desorption is required, which causes a problem of requiring extra energy. In contrast, in the present invention, by newly discovering conditions under which volatile organic compounds flow out as liquid, it is possible to recover volatile organic compounds as liquid by applying stress without the need for a condensation process of the desorbed vapor, thereby achieving high efficiency.

The magnitude of the stress applied to the porous carbon material 112 in the desorption mode is not particularly limited, and it is sufficient that at least a portion of the volatile organic compounds are desorbed from the porous carbon material 112 in a gaseous or liquid state. When this condition is met, the applied stress P is large enough to satisfy the following formula A. Note that the right side of the following formula A corresponds to the vapor pressure inside the cell in the desorption mode.

Here, in the formula A, T is the temperature [K] of the porous carbon material, R is the gas constant (8.31 [J/(K·mol)]), and P _e is the saturated vapor pressure of the volatile organic compound at the temperature T [K]. V is the volume [m ³ ] of the space S in which the vapor of the volatile organic compound can exist in the cell, and can be calculated by subtracting the actual volume of the porous carbon material (mass/true density of the porous carbon material) from the internal volume of the cell. Furthermore, n ₂ is the amount of substance [mol] of the volatile organic compound desorbed from the porous carbon material by the application of the stress, and can be calculated from the difference in the amount of adsorption before and after pressing in the adsorption isotherm (see FIG. 5 ) of the volatile organic compound to be recovered (for this reason, by obtaining in advance a relationship diagram between the system pressure (partial pressure of the vapor of the volatile organic compound) and the amount of adsorption, with the applied stress as a parameter, n ₂ can be calculated from the value of the applied stress). Further, _n1 is the amount of substance [mol] of the vapor of the volatile organic compound present in the space S within the cell before the application of the stress, and can be calculated as _n1 = PV/RT using the vapor pressure P within the cell before the application of the stress.

As shown in FIG. 4 along with the saturated vapor pressure curve of methanol, the above formula A means that the pressure calculated from the sum of the substance amount _n1 and the substance amount _n2 of the volatile organic compound exceeds the saturated vapor pressure at the temperature.

In addition, in a preferred embodiment of the above-mentioned desorption mode, when no vapor of a volatile organic compound is present in the space S in the cell 114, the stress application unit satisfies the following formula 1:

In the formula, T is the temperature [K] of the porous carbon material, R is the gas constant (8.31 [J/(K·mol)]), P _e is the saturated vapor pressure of the volatile organic compound at the temperature T [K], V is the volume [m ³ ] of the space in the chamber in which the vapor can exist, and n ₂ is the amount of substance [mol] of the volatile organic compound desorbed from the porous carbon material by the application of the stress.
It is preferable to apply stress to the porous carbon material under the condition that satisfies the following:

The above formula 1 means that if no vapor of the volatile organic compound is present in the space S at the time of the application of stress by the stress application unit, more than 20% of the vapor of the volatile organic compound desorbed from the porous carbon material 112 by the application of stress is recovered as a liquefied product. Here, as described in the examples below, if approximately 14% or more of the desorbed volatile organic compound can be recovered as a liquefied product, it can be said that a high energy efficiency has been achieved compared to conventional technology. Therefore, in this case, the recovery of more than 20% of the vapor of the desorbed volatile organic compound as a liquefied product is set as an indicator of a preferred embodiment.

Next, in another preferred embodiment of the desorption mode described above, when the amount of vapor of the volatile organic compound present in the space S in the cell 114 is less than the saturated vapor amount at the temperature of the porous carbon material, the stress application unit satisfies the following formula 2:

In the formula, T is the temperature [K] of the porous carbon material, R is the gas constant (8.31 [J/(K·mol)]), P _e is the saturated vapor pressure of the volatile organic compound at the temperature T [K], V is the volume [m ³ ] of the space in the chamber in which the vapor can exist, n ₂ is the amount of substance [mol] of the volatile organic compound desorbed from the porous carbon material due to the application of the stress, and n ₁ is the amount of substance [mol] of the vapor of the volatile organic compound present in the space in the chamber before the application of the stress.
It is preferable to apply stress to the porous carbon material under the condition that satisfies the following:

The above formula 2 means that when the amount of vapor of a volatile organic compound present in the space S at the time of application of stress by the stress application section is less than the saturated vapor amount (n ₁ ), more than 20% of the vapor of the volatile organic compound desorbed from the porous carbon material 112 by the application of stress is recovered as a liquefied product.

In yet another preferred embodiment of the above-mentioned desorption mode, when the vapor of the volatile organic compound is present in the space S in the cell 114 at the saturated vapor amount at the temperature of the porous carbon material, the stress application unit satisfies the following formula 3:

In the formula, T is the temperature [K] of the porous carbon material, R is the gas constant (8.31 [J/(K·mol)]), P _e is the saturated vapor pressure of the volatile organic compound at the temperature T [K], V is the volume [m ³ ] of the space in the chamber in which the vapor can exist, and n ₁ is the amount of substance [mol] of the vapor of the volatile organic compound present in the space in the chamber before the stress is applied.
It is preferable to apply stress to the porous carbon material under the condition that satisfies the following:

The above formula 3 means that when the vapor of the volatile organic compound is present in the space S at a saturated vapor amount ( _n1 = n _e ) at the time of stress application by the stress application unit, the entire amount of the vapor of the volatile organic compound desorbed from the porous carbon material 112 by the application of stress is recovered as a liquefied product. Thus, according to this embodiment, since the entire amount of the volatile organic compound desorbed by the application of stress is recovered as a liquefied product, it can be said that in the adsorption mode, it is preferable to introduce the vapor of the volatile organic compound so that the vapor of the volatile organic compound is present in the space S at a saturated vapor amount ( _n1 = n _e ).

The following embodiments are also within the scope of the present invention: the recovery device according to claim 1 having the features of claim 2; the recovery device according to claim 2 having the features of claim 3; the recovery device according to claim 2 having the features of claim 4; the recovery device according to claim 2 having the features of claim 5; the recovery device according to any one of claims 1 to 5 having the features of claim 6; the recovery device according to any one of claims 1 to 6 having the features of claim 7; the recovery device according to any one of claims 1 to 7 having the features of claim 8; the recovery device according to any one of claims 1 to 8 having the features of claim 9.

The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples.

[Experimental Example 1]
As a porous carbon material, GMS (derived from SBa-200, BET specific surface area 1692 m ² /g) was prepared. For this GMS, methanol was used as an adsorbate (volatile organic compound), and an adsorption isotherm was obtained under a saturated vapor pressure P ₀ = 16.9 [kPa] and a temperature T = 25 [°C]. In this case, the adsorption isotherm was obtained for each of the cases where no stress was applied to GMS (no stress application) and where a stress of 100 [MPa] was applied. The results are shown in FIG. 5. As shown in FIG. 5, it can be seen that the difference in the amount of methanol adsorbed between no stress application and stress application when compared at the same relative pressure increases as the partial pressure of methanol increases. From this, it can be said that a porous carbon material showing an adsorption isotherm similar to that of GMS is suitable as a constituent material of the adsorption/desorption part of the VOC recovery device according to one embodiment of the present invention.

In addition, when an adsorption isotherm was similarly obtained using diethyl ether as a volatile organic compound under a saturated vapor pressure P ₀ =71.6 [kPa] and a temperature T =25 [°C], it showed the same behavior as in the case of methanol, as shown in Figure 6.

[Experimental Example 2]
In the case of the conventional technology, when the amount of adsorbed methanol is adsorbed on activated carbon as an adsorbent and the adsorbed methanol is desorbed by heating, the amount of adsorbed methanol is set to 1 kg, and the energy required to desorb the methanol is calculated. As shown in "Power when activated carbon is used" in FIG. 7, the result is that the energy required increases in proportion to the amount of desorbed methanol. This is thought to be because the heat capacity increases as the amount of desorbed methanol increases. In contrast, in the case of the VOC recovery device according to one embodiment of the present invention, when methanol is desorbed by applying stress rather than heating, the energy required is about 40 kJ regardless of the amount of desorbed methanol. Here, as shown in FIG. 7, the two graphs intersect when the amount of desorbed methanol is about 14%. From this, it can be seen that if about 14% or more of the adsorbed methanol is to be desorbed, the method of desorbing methanol by applying stress rather than heating is more energy efficient than the heating method. The value of "about 14%" above was almost the same even when the adsorbent was changed to ethanol or diethyl ether.

[Experimental Example 3]
The GMS powder was placed in a resin mesh pack, and after the methanol was adsorbed, a pressing process was performed using a pressing machine. The state of the pressing device before and after the pressing process was photographed using a thermo camera, and the results are shown in FIG. 8. As shown in FIG. 8, it can be seen that methanol in a liquid state flows out of the pack after the pressing process. This also shows that a porous carbon material such as GMS is suitable as a constituent material of the adsorption/desorption part of a VOC recovery device according to one embodiment of the present invention, and that volatile organic compounds, which are adsorbates, can be desorbed by performing an appropriate pressing process.

[Experimental Example 4]
The cell containing the GMS powder and 35.0 kPa of atmospheric air was filled with sufficient diethyl ether vapor and allowed to stand for 12 hours to adsorb the diethyl ether to the GMS. At this time, the pressure inside the cell was 96.2 kPa [air: 35.0 kPa, diethyl ether (DEE): 61.2 kPa], and the temperature around the cell was 24.2°C (saturated vapor pressure: 69.5 kPa).

In this state, the GMS was pressed at 100 MPa for 30 seconds, and the diethyl ether was observed to flow out as a liquid (Figure 9). This shows that it is not necessary to maintain a vacuum state in the space inside the cell when the recovery device according to the present invention is in operation.

From the above, it can be seen that the present invention makes it possible to recover volatile organic compounds using a method that reduces energy loss while enabling miniaturization.

10 VOC recovery system,
20 Porous carbon materials,
30 Volatile organic compounds,
100 VOC recovery device,
110 Adsorption/Desorption Unit,
112 Graphene meso sponge (GMS) (porous carbon material),
114 cells,
120 Piston (stress application part),
130 recovery chamber,
142 Piping,
144 valve,
150 control unit,
200 paint booths,
212 Piping,
214 Valve.

Claims (10)

A volatile organic compound recovery device that adsorbs vapor of a volatile organic compound into an adsorbent and then desorbs and recovers the vapor or a liquefied product thereof,
an adsorption/desorption section including a porous carbon material that adsorbs the vapor and desorbs the vapor or a liquefied product thereof by applying and releasing a stress;
a stress application unit that applies and releases the stress to the porous carbon material;
a recovery section for recovering the vapor or a liquefied product thereof desorbed from the porous carbon material;
A volatile organic compound recovery device comprising: The volatile organic compound recovery device according to claim 1, wherein the adsorption/desorption unit includes a sealable cell and the porous carbon material disposed inside the cell. The stress application unit satisfies the following formula 1 when the vapor is not present in the space within the cell:

In the formula, T is the temperature [K] of the porous carbon material, R is the gas constant (8.31 [J/(K·mol)]), P _e is the saturated vapor pressure of the volatile organic compound at the temperature T [K], V is the volume [m ³ ] of the space in the cell in which the vapor can exist, and n ₂ is the amount of substance [mol] of the volatile organic compound desorbed from the porous carbon material by the application of the stress.
3. The device for recovering a volatile organic compound according to claim 2, wherein the stress is applied to the porous carbon material under a condition satisfying the following: and the recovery section recovers at least a part of the vapor of the volatile organic compound as the liquefied product. When the steam is present in the space within the cell in an amount less than the saturated steam amount at the temperature of the porous carbon material, the stress application unit satisfies the following formula 2:

In the formula, T is the temperature [K] of the porous carbon material, R is the gas constant (8.31 [J/(K·mol)]), P _e is the saturated vapor pressure of the volatile organic compound at the temperature T [K], V is the volume [m ³ ] of the space in the cell in which the vapor can exist, n ₂ is the amount of substance [mol] of the volatile organic compound desorbed from the porous carbon material due to the application of the stress, and n ₁ is the amount of substance [mol] of the vapor of the volatile organic compound present in the space in the cell before the application of the stress.
3. The device for recovering a volatile organic compound according to claim 2, wherein the stress is applied to the porous carbon material under a condition satisfying the following: and the recovery section recovers at least a part of the vapor of the volatile organic compound as the liquefied product. When the steam is present in the space within the cell in an amount of saturated steam at the temperature of the porous carbon material, the stress application unit satisfies the following formula 3:

In the formula, T is the temperature [K] of the porous carbon material, R is the gas constant (8.31 [J/(K·mol)]), P _e is the saturated vapor pressure of the volatile organic compound at the temperature T [K], V is the volume [m ³ ] of the space in the cell in which the vapor can exist, and n ₁ is the amount of substance [mol] of the vapor of the volatile organic compound present in the space in the cell before the stress is applied.
3. The device for recovering a volatile organic compound according to claim 2, wherein the stress is applied to the porous carbon material under a condition satisfying the following: and the recovery section recovers at least a part of the vapor of the volatile organic compound as the liquefied product. The volatile organic compound recovery device according to claim 1 or 2, wherein the half-width of the peak derived from the (10) plane of carbon in the X-ray diffraction spectrum of the porous carbon material using Cu-Kα radiation is within the range of 1.2 to 3.2°. 3. The device for recovering volatile organic compounds according to claim 1, wherein the porous carbon material has a BET specific surface area of 800 to 2600 m ² /g. The volatile organic compound recovery device according to claim 1 or 2, wherein the pore volume of the porous carbon material is 2.0 mL/g or more. The volatile organic compound recovery device according to claim 1 or 2, wherein the porous carbon material comprises zeolite template carbon (ZTC), graphene meso sponge (GMS) or carbon meso sponge (CMS). adsorbing a vapor of a volatile organic compound onto a porous carbon material that adsorbs the vapor of a volatile organic compound and desorbs the vapor or a liquefied product thereof by releasing and applying a stress;
applying a stress to the porous carbon material having adsorbed the vapor, thereby desorbing the vapor or a liquefied product thereof from the porous carbon material;
recovering the vapor or a liquefied product thereof desorbed from the porous carbon material;
A method for recovering volatile organic compounds, comprising: