Patent Application
20220296765
The present disclosure relates to airborne odor, infestation, and microbial control devices, and more particularly, to an industrial scale photocatalytic odor control system that reduces or destroys odors, kills microbes and insect infestations, and decomposes volatile organic compounds present in the air.
BACKGROUND
Photocatalytic Oxidation (PCO) is a technology used for elimination or reduction of the level of contaminants in a fluid, such as air or water, using the chemical action of light. When ultraviolet (UV) light is used to energize a photocatalyst, the technology is more specifically termed Ultraviolet Photocatalytic Oxidation (UV-PCO).
The photocatalytic odor control device 100 described herein uses a novel thin film composition of a semiconductor material, such as titanium dioxide, deposited or otherwise coated in a specific and novel way on a substrate that may comprise a ceramic or a metal (such as aluminum and stainless steel).
Located within the photocatalytic chamber 112 is a plurality of photocatalytic plates 114 arranged in a predetermined pattern to provide maximum exposure to airflow. In the embodiment shown in
The photocatalytic chamber 112 is preferably shielded by one or more louvers 122 that provides an optical screen that prevents UV light from escaping the photocatalytic chamber 112. At least one coarse filter 123 is further provided at the exit. Exiting the photocatalytic chamber 112, the processed airflow enters a second and optional air treatment chamber 124 where a manganese-based (MnO2) catalyst is positioned. The manganese-based catalyst may be in any suitable form, such as pellets, and it is capable of neutralizing any remaining ozone (O3) that remains in the airflow. After leaving the second chamber 124, the treated air exits the housing 102.
As shown in
The photocatalytic reaction employed by the odor control device 100 involves photocatalytic plates 114 made of semiconductors with a sufficiently wide band gap energetic enough to activate water or surface hydroxyl ions thus creating .OH radicals that eliminate organic contaminants. These semiconductor materials include, but are not limited to, titanium dioxide
(TiO2), zirconium dioxide (ZrO2), zinc oxide (ZnO), calcium titanate (CaTiO3), tin (stannic) dioxide (SnO2), molybdenum trioxide (MoO3), and the like. Of this group, titanium dioxide (TiO2) is the preferred photocatalyst because of its chemical stability, relatively low cost, and electronic band gap that is suitable for photoactivation by UV light. The novel semiconductor composition/matrix used in this application provides a very specific bandgap, allowing more efficient formation of the reactive oxygen species.
There are two important types of titanium dioxide (TiO2)—rutile titanium dioxide and anatase titanium dioxide. The key difference among them is in their appearance. Anatase titanium dioxide is colorless, whereas rutile titanium dioxide is usually found in a dark red appearance. Rutile titanium dioxide is optically positive, whereas anatase titanium dioxide is optically negative. Rutile titanium dioxide has highly stable and is the most common type of titanium dioxide usually found in metamorphic and igneous rocks. Rutile titanium dioxide has a crystalline structure with a tetragonal unit cell having oxygen anions and titanium cations. The coordination number of titanium cations (Ti+4) is 6, while the coordination number of oxygen anion (O2−) is 3. Some vital properties of rutile titanium dioxide nanoparticles include greater dispersion, higher birefringence, and greater refractive index (RI) at visible wavelengths.
Rutile titanium dioxide has many useful applications including the manufacturing of metallic titanium and titanium dioxide pigments. It is also used for manufacturing plastics, papers, and paints. The finely pulverized form of titanium dioxide is white in color. Furthermore, the nanoparticles of rutile titanium dioxide have the ability to absorb UV rays and are transparent to visible light. That is the reason that they are used in the manufacturing of cosmetics.
The application described herein involves a suspension layer, or agglomerate of semiconductor nanoparticles, is irradiated with UV light that causes excitation of an electron from the valence band to the conduction band. This results in the formation of an oxidizing site (hole) in the valence band and a reducing site (electron) in the conduction band. Thus, organic compounds, cell walls, and molecules in general, are oxidatively degraded into harmless reaction products. Direct use of solely semiconductors like titanium dioxide is generally limited by its weak light absorption properties, large bandgap, and low oxidation efficiency. Therefore, photocatalytic oxidation procedures involving nanoparticles of TiO2 has been modified in many ways to improve its adsorption ability and efficiency. For example, surface-fluorinated TiO2 and ZnO/TiO2 nanocomposite films have been applied as photocatalysts. Further, adding an electron scavenger like Ce4+ also improves the efficiency of holes. Various other modifications have been proposed like use of molecular sieve 4A-TiO2-K2Cr2O7 system as a sensor and in-situ surface modification of TiO2 with 5-sulfosalicylic acid and KMnO4 catalysts in COD analysis.
The photocatalytic odor control technology is especially adapted to neutralize organic molecules present in the air that contribute to nuisance odors that result from certain agricultural, industrial, and commercial processes and activities such as food processing, waste processing, wastewater treatment, landfills, composting, animal feed manufacturing, breweries, distilleries, spice production, and cannabis operations. Further, photocatalytic air purification may be used in high occupancy or even residential applications to address volatile organic compounds (VOCs) that are potentially harmful gases emitted by a wide array of common household products. They are a primary cause of indoor air quality problems in the home. Young children, the elderly and people with respiratory problems may be more affected by VOC exposure than others. According to the U.S. Environmental Protection Agency (EPA), concentrations of many VOCs are up to ten times higher indoors than outdoors—regardless of whether the home is located in a rural or highly industrialized area. Other sources of odor include bacteria, virus, mold, mildew, yeast, microbes, smoke, allergens (e.g., dust, perfumes, pet dander, and pollen), and pest infestations (e.g., pheromones and waste).
The biggest advantage that photocatalytic odor control systems have over other air-cleaning technologies is that instead of simply trapping pollutants in a filtration material that still needs to be replaced and disposed of, the photocatalytic process employed by the odor control device 100 completely transform the harmful and odorous chemical molecules in the air and effectively destroys them.
As stated above, the photocatalytic odor control device 100 includes one or more plates 114 that has a substrate with a thin layer of semiconductor material (e.g., titanium dioxide) coating. In an exemplary embodiment, an elevated temperature coating process is used to deposit the titanium dioxide onto the substrate.
Referring to
The doped semiconductor powder can be fed into flame spray torch by a carrier gas or by gravity. Gravity-fed devices may use powder canisters or bottles mounted directly to, and on top of, the torch. Powder feed rate is controlled by a pinch valve that meters the powder into the body of the torch, where it is aspirated by the gases flowing through the torch. Carrier-gas-fed units use externally mounted powder feeders. External powder feeders use a carrier gas (typically nitrogen, air is also used) stream to transport the powder from the feeder through a hose to the spray torch. Wire- and rod-fed devices use air turbines built into the torch that power the drive rolls, which pull feedstock from the source and push it through the nozzle.
In this thermal coating process, the feedstock materials are utilized in the molten state at specific temperatures based on total composition. The carrier gas composition as well as the cooling and annealing rate of the post-deposition substrate surface are also novel elements of this application. The feedstock materials are molten by the spray torch and the particles/droplets accelerate toward the substrate surface by the expanding gas flow and in some cases also by air jets.
In the deposition processes, the fuel/oxygen ratio and total gas flow rates can be adjusted to produce the desired thermal output needed to melt the specific feedstock material. Optional air jets, downstream of the combustion zone, may also further adjust the thermal profile of the flame. In flame spray processes, the fuel/oxygen ratio and total gas flow rates are adjusted to produce the desired thermal output needed to melt the specific feedstock material. Optional air jets, downstream of the combustion zone, may also further adjust the thermal profile of the flame. Spray gas speeds typically are below 100 m s−1, generating particle speeds up to approximately 80 m s−1 before impact.
Forming a coating with a post-heat treatment by sintering/fusing can be carried out to obtain dense coatings with metallurgical bonding (diffusion bonds). This process consists of two separate stages, spraying and post-fusion, and is clearly different from other conventional processes, which are one-step processes and in which the coating adherence to the substrate material is mainly of the type of mechanical anchoring and bonding to the substrate surface asperities created by grit blasting of the surface prior to thermal coating. These types of coatings are homogeneous with good bonding and adhesion strength, 350-500 MPa. Because of the high fusing temperature (approximately 1050° C.), there is a risk of deformation.
Titania (TiO2) is a white oxide ceramic and comes in three crystalline forms: rutile with a tetragonal structure, anatase also with a tetragonal structure, and brookite with an orthorhombic structure. The preferred crystalline structure is a modified anatase, which can be modified by adding certain dopants or impurities. Doping of TiO2 with various elements increases its photocatalytic activity due to the formation of new energy levels near the conduction band. Photocatalysis involving titanium dioxide is a heterogeneous process in which the surface of the catalyst plays an important role. The structural properties of TiO2 are influenced by the spraying conditions, the doping concentration, and the dopants. The incorporation of dopants leads to the distortion of the TiO2 crystal lattice, thus changing its surface characteristics, and a decrease in the energy band gap. For example, the introduction of aluminum (Al) and copper (Cu) increases the photocatalytic activity by as much as 50% while doping with Molybdenum (Mo) and Tungsten (W) increases the activity by 75%. The dopant concentration can be in the range of 100 ppm and 500,000 ppm.
Upon doping with copper, clusters of copper oxide are formed on the surface of TiO2, which can also take part in the photocatalysis. The use of Cu is a more affordable and cheaper alternative to elements such as silver and gold, as well as platinum group metals. There also has been increasing interest in the use of trivalent metals (Al, Niobium—Nb) as doping materials as they improve the electrical, optical, and structural characteristics of titanium dioxide. Doping of
Al, Cu, Mo, or W leads to a narrowing of the band gap of TiO2, which increases its photocatalytic activity upon irradiation with visible light.
The introduction of Al3+ into the crystal lattice of titanium dioxide leads to the appearance of oxygen vacancies, which increases the photocatalytic activity. In the cases of transition metals of molybdenum and tungsten, not only Mo6+ and W6+ ions but also Mo4+, Mo5+, W4+, W5+, as well as Ti3+ ions, which also take part in photocatalytic processes, can be present on the powder surface.
XRF (X-ray fluorescence) is a non-destructive analytical technique used to determine the elemental composition of materials. XRF analyzers determine the chemistry of a sample by measuring the fluorescent (or secondary) X-ray emitted from a sample when it is excited by a primary X-ray source. Each of the elements present in a sample produces a set of characteristic fluorescent X-rays (“a fingerprint”) that is unique for that specific element, which is why XRF spectroscopy is an excellent technology for qualitative and quantitative analysis of material composition.
Photocatalytic activity of TiO2 increases as the particle size of TiO2 is decreased, especially when the particle size is less than 30 nm. The half-life (t0.5) of the photocatalytic degradation of MB also decreased as the particle sizes of TiO2 decreased. The preferred titanium dioxide particles sizes include: 1 μm, 5 μm, 50 μm, 100 μm, 200 μm, and 500 μm.
One potential output from conventional photocatalytic odor control systems is ozone. The U.S. Occupational Safety and Health Administration (OSHA) requires that the indoor “threshold limit value” (TLV) of an eight-hour exposure be limited to 0.1 part per million (ppm). The photocatalytic odor control system described herein prevents the direct formation of ozone by using the precise frequency of the UV light that activates the TiO2 to destroy ozone.
The crystalline structure (Anatase)—particle size (˜1 micron)—and dopants are selected to create the band gap in the TiO2 of 3.2 eV or greater, which corresponds to a wavelength of 388 nm or lower. The larger the band gap eV value, the greater the energy, and the lower the wavelength. Any wavelength less than 388 nm will activate the TiO2. UV light having a wavelength between 240 nm and 388 nm will break down ozone molecules to form oxygen. As long as UV light with a wavelength above 240 nm is used for the photocatalytic process, the dual functions of activating the TiO2 and neutralizing the ozone are achieved. In an exemplary embodiment, UV light having a wavelength of between 240 nm and 388 nm is used to activate the titanium dioxide and also destroy the resultant ozone. In an exemplary embodiment, the method includes irradiating the photocatalyst with an ultraviolet light having a wavelength between 240 nm and 388 nm at an intensity of greater than 1 W/cm2.
In the event ozone is formed due to catalyst breakdown, fouling, etc., an optional secondary process can be used to treat the air before it exits the photocatalytic odor control device 100. Manganese dioxide-based catalysts may be used for ozone destruction since it is highly effective in destroying ozone at ambient room temperature. These catalysts show very high ozone destruction efficiencies even in high humidity applications. Manganese dioxide catalysts require only a 0.36 second residence time, which means relatively small catalyst volumes are needed, making the catalytic system with a manganese dioxide-based catalyst very cost-effective. The inlet concentration of ozone does not affect the amount of catalyst required or the design of the system. Ozone concentrations ranging from a few ppm to well over 100K ppm can be effectively controlled by the use of this catalyst in the second treatment chamber 124.
Rutile is a direct bandgap semiconductor, meaning that under UV excitation (E>3.0 eV) electrons can easily be promoted from the rutile valence band (+2.3 V vs NHE) to the conduction band (−0.7 V vs NHE). However, fast electron-hole pair recombination also occurs. The net result is that there are few charge carriers available for photoreactions at the surface of rutile.
Anatase is an indirect bandgap semiconductor (VB +2.7 V vs NHE, CB −0.5 V versus NHE) meaning that both the charge separation and recombination under UV excitation (E>3.2 eV) are slower in anatase than in rutile. The slower recombination rate allows more electrons and holes generated in the bulk to reach to the anatase surface and participate in photoreactions. Accordingly, anatase will generally be a better photocatalyst than rutile due to the increased number of charge carriers (electrons and holes) reaching the surface of anatase.
This discussion neglects surface area effects, which are also important when comparing the relative activities of anatase and rutile. It is important to normalize reaction rates against exposed surface area when comparing anatase and rutile photocatalysts.
The effect of 5 MeV Cu++ ions irradiation on structural and optical properties of Anatase TiO2 nanoparticles (TiO2-NPs) is investigated. For this purpose, TiO2-NPs are irradiated with different Cu++ ions fluences, ranging from 1×1015 to 1×1016 ions/cm2 at room temperature. XRD results confirm the Ti3O7 phase appear at the dose of 5×1015 ions/cm2 and peak intensity of Ti3O7 phase gradually increases with an increase of Cu++ ions irradiation dose. At the dose of 1×1016 ions/cm2 TiO2 anatase phase are transformed to rutile phase. Same observations are confirmed from Raman spectroscopy. High resolution transmission electron microscopy (HRTEM) reveals that morphology converted into wavy shape and crystal structure doped with increased Cu ion irradiation dose to form vacancy loops and interstitial loops. Scanning electron microscopy (SEM) shows that TiO2-NPs have been fused to form a cluster of nanoparticles at high Cu ion beam dose, while bandgap of TiO2-NPs reduces from 3.19 eV to 2.96 eV as a function of Cu++ irradiation fluence. These phase transformations and crystal damage are the responsible for optical bandgap reduction. The mechanism for the currently observed phase transformation of TiO2 and coalescence of TiO2-NPs are discussed in term of thermal spikes model.
Rutile is a direct bandgap semiconductor, meaning that under UV excitation (E>3.0 eV) electrons can easily be promoted from the rutile valence band (+2.3 V vs NHE) to the conduction band (−0.7 V vs NHE). However, fast electron-hole pair recombination also occurs. The net result is that there are few charge carriers available for photoreactions at the surface of rutile.
Anatase is an indirect bandgap semiconductor (VB +2.7 V vs NHE, CB −0.5 V versus NHE) meaning that both the charge separation and recombination under UV excitation (E>3.2 eV) are slower in anatase than in rutile. The slower recombination rate allows more electrons and holes generated in the bulk to reach to the anatase surface and participate in photoreactions. Accordingly, anatase will generally be a better photocatalyst than rutile due to the increased number of charge carriers (electrons and holes) reaching the surface of anatase. This discussion neglects surface area effects, which are also important when comparing the relative activities of anatase and rutile. It is important to normalize reaction rates against exposed surface area when comparing anatase and rutile photocatalysts.
The effect of 5 MeV Cu++ ions irradiation on structural and optical properties of Anatase TiO2 nanoparticles (TiO2-NPs) is investigated. For this purpose, TiO2-NPs are irradiated with different Cu++ ions fluences, ranging from 1×1015 to 1×1016 ions/cm2 at room temperature. XRD results confirm the Ti3O7 phase appear at the dose of 5×1015 ions/cm2 and peak intensity of Ti3O7 phase gradually increases with an increase of Cu++ ions irradiation dose. At the dose of 1×1616 ions/cm2 TiO2 Anatase phase were transformed to Rutile phase. Same observations are confirmed from Raman spectroscopy. High resolution transmission electron microscopy (HRTEM) reveals that morphology converted into wavy shape and crystal structure doped with increase Cu ion irradiation dose to form vacancy loops and interstitial loops. Scanning electron microscopy (SEM) shows that TiO2-NPs have been fused to form a cluster of nanoparticles at high Cu ion beam dose, while bandgap of TiO2-NPs reduces from 3.19 eV to 2.96 eV as a function of Cu++ irradiation fluence. These phase transformations and crystal damage are the responsible for optical bandgap reduction. The mechanism for the currently observed phase transformation of TiO2 and coalescence of TiO2-NPs are discussed in term of thermal spikes model.
It is contemplated that in addition to a stand-alone air purification system equipped with fans and other devices that circulate air, the UV light and titanium dioxide-coated plates may be designed and packaged as an air purification module that can be retrofitted or installed to work with conventional air handlers, air conditions, and other systems through which air passes in a facility or building.
The features of the present invention which are believed to be novel are set forth below with particularity in the appended claims. However, modifications, variations, and changes to the exemplary embodiments described above will be apparent to those skilled in the art, and the photocatalytic odor control system described herein thus encompasses such modifications, variations, and changes and are not limited to the specific embodiments described herein.
This application claims priority to U.S. Provisional Application No. 63/163,710 filed Mar. 19, 2021.
| Number | Date | Country | |
|---|---|---|---|
| 63163710 | Mar 2021 | US |
