HK1115345B - Photocatalyst protection - Google Patents

Description

Photocatalyst protection

Technical Field

The present invention relates to air treatment modules, and more particularly to protecting a photocatalyst in an air treatment module using a corona discharge device to remove contaminants from an air conditioning air stream.

Background

Air treatment modules are commonly used in automotive, commercial, and residential heating, ventilation, and air conditioning (HVAC) systems to move and purify air. Typically, the air stream flowing through the air treatment module includes trace contaminants such as biological species (biospecies), dust, particulates, odors, carbon monoxide, ozone, semi-volatile organic compounds (SVOC), Volatile Organic Compounds (VOCs) such as formaldehyde, acetaldehyde, toluene, propanol, butene, and silicon-containing VOCs.

Typically, filters and photocatalysts are used to purify air streams by removing and/or destroying contaminants. Typical filters include a filter media that physically separates contaminants from an air stream. Typical photocatalysts include monoliths (monoliths) coated with titanium dioxide, such as honeycombs, and uv light sources. Titanium dioxide operates as a photocatalyst to destroy contaminants when irradiated by ultraviolet light. Photons of the ultraviolet light are absorbed by the titanium dioxide and excite electrons from the valence band to the conduction band, thus generating holes in the valence band and adding electrons in the conduction band. The excited electron reacts with oxygen, while the hole remaining in the valence band reacts with water to form a reactive hydroxyl (hydroxyl) group. As contaminants in the air stream flow through the honeycomb and adsorb onto the titanium dioxide coating, the hydroxyl radicals attack and oxidize the contaminants to water, carbon dioxide, and other substances. The ultraviolet light may also kill biological species in the radiated gas stream.

Disadvantageously, typical air treatment module filters have a limited contaminant capacity. Once the contaminant capacity is reached, the filter does not physically separate additional contaminants from the air stream. Then, contaminants in the air stream flow through the filter and are oxidized by the photocatalyst. This is particularly troublesome when the photocatalyst oxidizes silicon-containing VOCs or SVOCs to form a silicon-based glass on the photocatalyst surface. The silicon-based glass may isolate the titanium dioxide from the passing air stream, thereby passivating the titanium dioxide. In severe cases, most of the catalytic activity of the photocatalyst disappears within two weeks of reaching the contaminant capacity of the filter. To prevent the photocatalyst from deactivating, the filter may be replaced before the contaminant capacity is reached or an additional filter may be used to physically separate a larger amount of contaminants, however the maintenance required to replace the filter in a short time interval and to continuously monitor the filter is costly and inconvenient.

Thus, there is a need for an air treatment module that more effectively protects the photocatalyst from passivating contaminants.

Disclosure of Invention

In general terms, the present invention is a system and method for protecting a photocatalyst in an air treatment system from passivation caused by oxidation of a particular contaminant.

The present invention provides a gas treatment system for treating a gas stream containing contaminants, comprising: a filter disposed in the airflow path; a photocatalyst in fluid communication with the filter, the photocatalyst operable between an open state and a closed state; and a plasma device in fluid communication with the photocatalyst, the plasma device positioned to treat contaminants in the gas flow path; wherein the filter retains at least a portion of the contaminants in the gas stream when the photocatalyst is in an open state in a first mode and then selectively releases the contaminants when the photocatalyst is in a closed state in a second mode, and the plasma device is positioned adjacent to the filter to chemically convert the contaminants released by the filter, the gas treatment system further comprising a controller for switching to the second mode and regenerating the filter.

In one embodiment, the plasma device is positioned upstream of the photocatalyst.

In one embodiment, the plasma device is positioned downstream of the filter.

In one embodiment, the filter includes a heater, and the heater heats the filter to selectively release the contaminants.

In one embodiment, an ozone-destroying material in fluid communication with the plasma device is included that receives ozone from at least the plasma device.

In one embodiment, the filter includes at least activated carbon that adsorbs the contaminants from the gas stream so as to retain the contaminants when the gas stream contacts the activated carbon.

In one embodiment, the plasma device is one of a plurality of plasma devices in fluid communication with the photocatalyst.

The present invention also provides a method of preventing a gas processing component in a gas processing system as described above from receiving selected contaminants in a gas flow path, comprising the steps of: (a) maintaining the contaminants in the gas flow path when the gas treatment member is in the first mode; (b) releasing the contaminant to the gas flow path when the gas treatment component is in the second mode; and (c) chemically converting the contaminant into a different chemically converted contaminant, wherein the gas treatment member comprises the photocatalyst and an associated light source to activate or deactivate the photocatalyst when the associated light source is turned on or off, respectively, and the first mode comprises the light source being turned on and the second mode comprises the light source being turned off.

In one embodiment, step (b) includes releasing the contaminant when the airflow in the airflow path is about zero, and step (c) includes chemically converting the contaminant when the airflow in the airflow path is about zero.

In one embodiment, step (a) comprises adsorbing the contaminant onto an adsorbent media.

In one embodiment, step (b) comprises heating the adsorbent media.

In one embodiment, said step (c) comprises generating a plasma and subjecting said contaminants to said plasma so as to produce said chemically converted contaminants.

In one embodiment, step (c) includes depositing the chemically converted contaminants in a receiving portion of a plasma apparatus.

In one example, the air treatment module includes a filter and heating element, a plasma device, and a photocatalyst and UV light that cooperate to purify the air stream flowing through the air treatment module. The air treatment module operates in two different modes. In the first mode, the air treatment module primarily draws air from and returns air to the space, and the heating element and plasma device are turned off. In a second mode, the air treatment module regenerates the filter and releases adsorbed contaminants using the heating element to heat the filter. The plasma device is selectively turned on and chemically converts the released contaminants into solid contaminant products that are deposited on a bias electrode of the plasma device. The UV light is turned off to ensure that the photocatalyst is not functional during the release and conversion of the contaminants. Once deposited, the substantially stable and inert solid contaminant product is unlikely to damage the photocatalyst.

One example method includes maintaining the contaminant in the gas flow path when the photocatalyst is in an open state, releasing the contaminant into the gas flow path when the photocatalyst is in a closed state, and chemically converting the contaminant into a different chemically converted contaminant.

The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the presently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.

Drawings

FIG. 1 is an HVAC system including an air treatment module.

FIG. 2 is a perspective view of an example air treatment module.

FIG. 3 is a schematic diagram of an example filter, plasma device, and photocatalyst.

Fig. 4 is a schematic view of another example of the filter of fig. 3.

FIG. 5 is a schematic view of an example air treatment module including an ozone-destroying material.

Fig. 6 is a schematic view of another air treatment module configuration including a second plasma device.

Detailed Description

Fig. 1 shows a residential, commercial, automotive or other structure 10 including an interior space 12 (e.g., a room, office or cabin). The HVAC system 14 heats or cools the interior space 12. Air within the interior space 12 is drawn into the HVAC system 14 via an inlet path 16. The HVAC system 14 changes temperature and purifies the drawn air using the air treatment module 18. The purified temperature altered air is then returned to the interior space 12 via the outlet path 20.

FIG. 2 shows a perspective view of an example air treatment module 18. The air treatment module 18 includes a compressor 30 for extracting and returning air. Air drawn from the interior space 12 flows within the airflow 32 into the filter chamber 34, which forms an air flow path through the air treatment module 18. The filter chamber 34 encloses a filter 36, a plasma device 38, and a photocatalyst 40 that cooperate to purify the air stream 32. The air flow 32 continues through the filter chamber to the coil 42. The coil 42 heats or cools the air flow 32 depending on the desired temperature of the interior space 12. After heating or cooling, the compressor 30 returns a flow of air 32 to the interior space 12 via the outlet path 20. It is to be understood that the illustrated air treatment module 18 is merely an example and the present invention is not limited to this configuration.

FIG. 3 shows a schematic of an example filter 36, plasma device 38, and photocatalyst 40. The filter 36 receives the air stream 32 and adsorbs contaminants from the air stream 32. The filter 36 comprises a known activated carbon filter media sandwiched between layers 44 of fibrous mesh. In one example, known activated carbons are modified, impregnated, or pore controlled. As is well known, a modifier such as potassium permanganate or other modifier may be impregnated within the activated carbon to modify the adsorptive properties of the activated carbon. The pore volume of the activated carbon can also be controlled within a desired range to modify the adsorption affinity. These features may provide the advantage of designing the filter 36 to preferentially absorb certain contaminants, such as formaldehyde, acetaldehyde, toluene, propanol, butene, silicon-containing VOCs, or other VOCs.

In another example, the filter 36 may additionally utilize zeolite and/or other types of filter media mixed with activated carbon between the layers of fibrous mesh 44 to obtain preferential absorption of certain contaminants. Alternatively, the activated carbon filter media may be integrated with the fiber mesh 44 by coating activated carbon onto the fibers making up the fiber mesh 44.

As shown in fig. 4, in another example, activated carbon filter media is provided in a first layer 46 and zeolite media and/or other filter media may be provided in an adjacent second layer 48.

A heating element 50, discussed in more detail below, surrounds the filter 36 and is selectively operable between an on and off state.

In one example, the plasma device 40 is generally located downstream of the filter 36 and is selectively operable between an open and closed state. The plasma device 38 is preferably a corona discharge device that generates a plasma glow discharge. More preferably, the plasma device 38 includes a bias electrode 54, such as a wire cathode.

In one example, the photocatalyst 40 is located downstream of the plasma device 38. The photocatalyst 40 is preferably a titania-coated monolith, such as a honeycomb, that operates as a photocatalyst to destroy contaminants when irradiated by Ultraviolet (UV) light 56. It is understood that photocatalyst materials other than titanium dioxide may be employed as well as structures other than those shown (e.g., integrating the photocatalyst 40 with the filter 36 in a single unitary fiber or honeycomb structure).

The UV light 56 may be selectively operated between an on state in which the photocatalyst 40 operates to destroy contaminants and an off state in which the photocatalyst 40 is inactive. In one example, the UV light 56 illuminates the photocatalyst 40 with wavelengths in the UV-C range, however other UV wavelength ranges may be employed depending on the type of photocatalyst and/or air purification needs of the air treatment module 18.

Operatively, the exemplary air treatment module 18 functions in two different modes. In the first mode, the air treatment module 18 serves the primary function of moving and returning air from the interior space 12 and purifying the air. In the first mode, the heating element 50 is selectively turned off, the plasma device 38 is selectively turned off, and the UV light 56 is selectively turned on. Thus, the filter 36 captures, confines, and absorbs certain contaminants, such as VOCs and SVOCs, from the air stream 32, and the photocatalyst 40 operates to destroy other contaminants passing through the filter 36. The heating element 50 and plasma device 38 are not functional in the first mode, however in other examples it may be advantageous to operate the heating element 50 and plasma device 38 simultaneously with the functions of filtering and moving air.

In the second mode, the air treatment module 18 functions primarily to regenerate the filter 36. That is, the activated carbon or other absorbent filter media is conditioned to desorb previously absorbed contaminants. The air flow 32 is turned off so that there is substantially zero air flow in the filter chamber 34. The heating element 50 is selectively turned on and heats the filter 36 to about 100 c, although other heating temperatures or heating profiles may be used. The filter 36 desorbs and releases the previously adsorbed contaminants. The plasma device 38 is selectively turned on and generates plasma, while the UV light 56 is preferably turned off to prevent the photocatalyst 40 from oxidizing the released contaminants.

The filter chamber 34 holds the released contaminants and essentially acts as a reaction vessel for the plasma device 38. The released contaminants, such as VOCs, SVOCs or other contaminants that the filter 36 is designed to absorb/release, come into contact with the plasma generated by the plasma device 38. The plasma chemically converts the contaminants into solid contaminant products and deposits the solid contaminant products on the receiving portion (bias electrode 54). Once deposited, the substantially stable and inert solid contaminant product is unlikely to damage the photocatalyst 40. In one example, the plasma deposits solid contaminant products onto the wire cathode. After a predetermined number of deposition cycles, the wire cathode is removed from the plasma device 38 and discarded or cleaned.

In the second mode, the heating element 50 and the plasma device 38 are operated for a selected predetermined amount of time. Preferably, this time is sufficient to i) release the majority of the contaminants from the filter 36, and thus regenerate the filter 36, and ii) convert the contaminants into a solid contaminant product. The time required will vary with the temperature, the size and type of filter media, the size of the filter chamber 34, and the size and type of plasma device 38 used.

Preferably, the UV light 56 remains off when switching from the second mode to the first mode in order to protect the photocatalyst 40 from any remaining contaminants that are not converted to solid contaminant products. The air flow 32 flows through the filter chamber 34 for a predetermined amount of time to purge the remaining released contaminants before turning on the UV light 56 to operate the photocatalyst 40.

In another example, the contaminant product includes organosilicon compounds, such as silicon-containing VOCs and silicon-containing SVOCs. The filter 36 releases the organosilicon compound upon heating, and the plasma generated by the plasma device 38 chemically converts the organosilicon compound to silica or other silicon-based glass. The plasma deposits silicon dioxide or other silicon-based glass on the bias electrode 54.

In another example, the filter 36 includes a single pleated layer having a pleating factor (pleating factor) of about 8 and having about 100 grams of activated carbon filter media. The filter 36 adsorbs approximately 90% of the organosilicon compounds in the incoming air stream 32 and takes approximately twelve hours to reach full capacity in the first mode of operation. For approximately twelve hours, the air treatment module 18 employs, for example, a controller to actively switch to the second mode and regenerate the filter 36. Alternatively or additionally to the controller, the operator may control the switching between the modes.

In another example shown in fig. 5, an ozone-destroying material 58, such as a known metal oxide catalyst, is included between the plasma device 38 and the photocatalyst 40. The ozone-destroying material 58 may, for example, be disposed on the honeycomb structure 60 and receive ozone from the plasma device 38 before the UV light 56 is turned on. The ozone-destroying material 58 adsorbs ozone onto the surface and decomposes the ozone. This feature may provide the advantage of exposing the photocatalyst 40 to less ozone, which may contribute to the passivation of the photocatalyst 40. It is to be understood that the ozone-destroying material 58 could alternatively be positioned in other locations within the filter chamber 34 than shown.

Fig. 6 shows a schematic view of another air treatment module 18 configuration, which includes a second plasma device 138 surrounding the filter 36. The second plasma device 138 includes a biased electrode 154 and operates similarly to and in conjunction with the plasma device 38 to chemically convert the released contaminants into solid contaminant products. The benefit of using the second plasma device 138 is a shorter time to completely chemically convert the contaminants released from the filter 36 or a greater efficiency of converting the released contaminants. Also, a plurality of additional plasma devices may be used.

Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Claims (1)

1. A gas treatment system for treating a gas stream containing contaminants, comprising:

a filter disposed in the airflow path;

a photocatalyst in fluid communication with the filter, the photocatalyst operable between an open state and a closed state; and

a plasma device in fluid communication with the photocatalyst, the plasma device positioned to treat contaminants in the gas flow path;

wherein the filter retains at least a portion of the contaminants in the gas stream when the photocatalyst is in an open state in a first mode and then selectively releases the contaminants when the photocatalyst is in a closed state in a second mode, and the plasma device is positioned adjacent the filter to chemically convert the contaminants released by the filter,

the gas treatment system also includes a controller for switching to the second mode and regenerating the filter.

2. The system of claim 1, wherein: the plasma device is positioned upstream of the photocatalyst.

3. The system of claim 1, wherein: the plasma device is positioned downstream of the filter.

4. The system of claim 1, wherein: the filter includes a heater, and the heater heats the filter to selectively release the contaminants.

5. The system of claim 1, wherein: comprising an ozone-destroying material in fluid communication with the plasma device, the ozone-destroying material at least receiving ozone from the plasma device.

6. The system of claim 1, wherein: the filter includes at least activated carbon that adsorbs the contaminants from the gas stream so as to retain the contaminants when the gas stream contacts the activated carbon.

7. The system of claim 1, wherein: the plasma device is one of a plurality of plasma devices in fluid communication with the photocatalyst.

8. A method of preventing a gas processing component in a gas processing system from receiving a selected contaminant in a gas flow path using the gas processing system of claim 1, comprising the steps of:

(a) maintaining the contaminants in the gas flow path when the gas treatment member is in the first mode;

(b) releasing the contaminant to the gas flow path when the gas treatment component is in the second mode; and

(c) chemically converting the contaminant into a different chemically converted contaminant,

wherein the gas treatment member comprises the photocatalyst and an associated light source to activate or deactivate the photocatalyst when the associated light source is turned on or off, respectively, and the first mode comprises the light source being turned on and the second mode comprises the light source being turned off.

9. The method of claim 8, wherein: the step (b) includes releasing the contaminant when the airflow in the airflow path is approximately zero, and the step (c) includes chemically converting the contaminant when the airflow in the airflow path is approximately zero.

10. The method of claim 8, wherein: said step (a) comprises adsorbing said contaminant onto an adsorbent media.

11. The method of claim 10, wherein: said step (b) comprises heating said adsorbent media.

12. The method of claim 8, wherein: said step (c) comprises generating a plasma and subjecting said contaminant to said plasma so as to produce said chemically converted contaminant.

13. The method of claim 12, wherein: said step (c) comprises depositing said chemically converted contaminants in a receiving portion of a plasma apparatus.