Patent Application
20230277967
Particulate matter (PM) pollution in air affects people's living quality tremendously, and it poses a serious health threat to the public as well as influencing visibility, direct and indirect radiative forcing, climate, and ecosystems. PM is a complex mixture of extremely small particles and liquid droplets. Based on the particle size, PM is categorized by PM2.5 and PM10 which refer to particle sizes below 2.5 μm and 10 μm, respectively. PM2.5 pollution is particularly harmful since it can penetrate human bronchi and lungs due to its small size. Hence, long term exposure to PM2.5 increases morbidity and mortality. Recently there have been serious PM pollution problems in developing countries with a large manufacturing industry such as China.
Measures taken by the public during hazy days are mostly focused on outdoor individual protection, such as using mask filters, which are often bulky and resistant to air flow. In indoor spaces, protection is available in modern commercial buildings through filtering in ventilation systems or central air conditioning; residential housing seldom have filtration protection from PM. Moreover, all these active air exchange by mechanical ventilation consumes enormous energy due to massive use of pumping systems. If staying indoors without sufficient air exchange, the indoor air quality is also of great concern. It would be ideal if passive air exchange, i.e., natural ventilation, by the wind through windows could be used for indoor air filtration. Owing to the large area of window, air exchange is very efficient. Protection at windows requires the air filters to not only possess a high PM capture ability but also a high optical transparency for natural lighting from sun and sight-viewing at the same time.
The PM2.5 pollution particles in air have complicated compositions including inorganic matter (such as SiO2, SiO42− and NO3−) and organic matter (such as organic carbon and elemental carbon) from diverse sources including soil dust, vehicular emission, coal combustion, secondary aerosols, industrial emission, and biomass burning. The behavior of PM particles are different due to their chemical compositions, morphologies and mechanical properties. Some rigid inorganic PM particles are mainly captured by interception and impaction on a filter surface. Some soft PM containing a lot of carbon compounds or water such as those from combustion exhaust would deform on filter surfaces and require stronger binding during the process of attaching to the filter. However, in existing air filter technology, not much work has been done to study the filter material properties. There are two types of air filters in common use. One is a porous membrane filter, which is similar to a water filtration filter (see
In order to eliminate or reduce the emission of PM into the air, PM often needs to be removed from sources associated with high temperature. This calls for technology capable of high temperature air filtration. Further, high temperature dust removal from exhaust gas is desirable in industries and has recently attracted more attention. However, existing technology could not meet the requirement of high-efficiency PM2.5 removal at high temperature. As shown in
As existing technology would not meet the requirements of high efficiency PM2.5 filters, there is a need for improvement.
Disclosed here is an improved polymer nanofiber filter technology, which has attractive attributes of high filtering efficiency, low resistance to air flow and light weight as shown in
One aspect of some embodiments of the invention described herein relates to an air filter comprising a substrate and a network of polymeric nanofibers deposited on the substrate, wherein the air filter has a light transmittance of at least 50% and a removal efficiency for PM2.5 of at least 70%.
In some embodiments, the polymeric nanofibers comprise a polymer comprising a repeating unit having a dipole moment of at least 0.5 Debye (D) or at least 1 D. In some embodiments, the polymeric nanofibers comprise a polymer comprising a repeating unit having a dipole moment of at least 2 D. In some embodiments, the polymeric nanofibers comprise a polymer comprising a repeating unit having a dipole moment of at least 3 D. In some embodiments, the polymeric nanofibers comprise a polymer comprising a repeating unit having a dipole moment of at least 3.5 D, at least 4 D, or at least 5 D, and up to 10 D, up to 12 D, or more. Examples of suitable repeating units include repeating units including polar groups, such as substituted alkyl groups (e.g., substituted with 1, 2, 3, or more halo groups or other polar groups listed below), substituted alkenyl groups (e.g., substituted with 1, 2, 3, or more halo groups or other polar groups listed below), substituted alkynyl groups (e.g., substituted with 1, 2, 3, or more halo groups or other polar groups listed below), substituted aryl groups (e.g., substituted with 1, 2, 3, or more halo groups or other polar groups listed below), hydroxyl groups, ketone groups, sulfone groups, aldehyde groups, ether groups, thio groups, cyano groups (or nitrile groups), nitro groups, amino groups, N-substituted amino groups, ammonium groups, N-substituted ammonium groups, amide groups, N-substituted amide groups, carboxy groups, alkylcarbonyloxy groups, alkenylcarbonyloxy groups, alkynylcarbonyloxy groups, arylcarbonyloxy groups, alkylcarbonylamino groups, N-substituted alkylcarbonylamino groups, alkenylcarbonylamino groups, N-substituted alkenylcarbonylamino groups, alkynylcarbonylamino groups, N-substituted alkynylcarbonylamino groups, arylcarbonylamino groups, N-substituted arylcarbonylamino groups, urea groups, epoxy groups, oxazolidone groups, and charged or hetero forms thereof. In some embodiments, the polymeric nanofibers comprise a polymer comprising a repeating unit having a ketone group and/or a sulfone group.
In some embodiments, the polymeric nanofibers comprise a polymer comprising a repeating unit which comprises a nitrile group. In some embodiments, the polymeric nanofibers comprise polyacrylonitrile (PAN). In some embodiments, the polymeric nanofibers comprise a polymer comprising a repeating unit which comprises polar functional groups (e.g., —CN, —OH, —CO—, —C—O—, —NO2, —NH—, —NH2, etc.). The higher dipole moment of the repeating unit of the polymer, the better adhesiveness of polymer to PM particles.
In some embodiments, the polymeric nanofibers have an average diameter of less than 1 micron. In some embodiments, the polymeric nanofibers have an average diameter of 10-900 nm. In some embodiments, the polymeric nanofibers have an average diameter of 20-800 nm. In some embodiments, the polymeric nanofibers have an average diameter of 30-700 nm. In some embodiments, the polymeric nanofibers have an average diameter of 50-500 nm. In some embodiments, the polymeric nanofibers have an average diameter of 100-300 nm.
In some embodiments, the polymeric nanofibers are electrospun onto the substrate.
In some embodiments, the polymeric nanofibers carry electric charges. In some embodiments, the polymeric nanofibers carry positive charges. In some embodiments, the polymeric nanofibers carry negative charges.
In some embodiments, the air filter has a light transmittance of at least 60%. In some embodiments, the air filter has a light transmittance of at least 70%. In some embodiments, the air filter has a light transmittance of at least 75%. In some embodiments, the air filter has a light transmittance of at least 80%. In some embodiments, the air filter has a light transmittance of at least 85%. In some embodiments, the air filter has a light transmittance of at least 90%. Transmittance values can be expressed by weighting the AM1.5 solar spectrum from 400 to 800 nm to obtain an average transmittance value. Transmittance values also can be expressed in terms of human vision or photometric-weighted transmittance, transmittance at a given wavelength or range of wavelengths in the visible range, such as 550 nm, or other wavelength or range of wavelengths.
In some embodiments, the air filter are used for applications which do not have optical transparency requirements. The air filter has a light transmittance less than 60%, or 30%, or 10% or 5%.
In some embodiments, the air filter has a removal efficiency for PM2.5 of at least 80%. In some embodiments, the air filter has a removal efficiency for PM2.5 of at least 90%. In some embodiments, the air filter has a removal efficiency for PM2.5 of at least 95%. In some embodiments, the air filter has a removal efficiency for PM2.5 of at least 98%. In some embodiments, the air filter has a removal efficiency for PM2.5 of at least 99%.
In some embodiments, multiple layers of the air filter might be used to achieve a removal efficiency of at least 80%. In some embodiments, multiple layers of the air filter has a removal efficiency for PM2.5 of at least 90%. In some embodiments, multiple layers of the air filter has a removal efficiency for PM2.5 of at least 95%. In some embodiments, multiple layers of the air filter has a removal efficiency for PM2.5 of at least 98%. In some embodiments, multiple layers of the air filter has a removal efficiency for PM2.5 of at least 99%.
In some embodiments, the air filter has a removal efficiency for PM10-2.5 of at least 80%. In some embodiments, the air filter has a removal efficiency for PM10-2.5 of at least 90%. In some embodiments, the air filter has a removal efficiency for PM10-2.5 of at least 95%. In some embodiments, the air filter has a removal efficiency for PM10-2.5 of at least 98%. In some embodiments, the air filter has a removal efficiency for PM10-2.5 of at least 99%.
In some embodiments, the air filter maintains its filtering efficiency under humid conditions. In some embodiments, the air filter has a removal efficiency for PM2.5 of at least 90% at a relative humidity of 60% at 25° C. In some embodiments, the air filter has a removal efficiency for PM2.5 of at least 90% at a relative humidity of 70% at 25° C. In some embodiments, the air filter has a removal efficiency for PM2.5 of at least 90% at a relative humidity of 80% at 25° C. In some embodiments, the air filter has a removal efficiency for PM2.5 of at least 90% at a relative humidity of 90% at 25° C.
In some embodiments, the air filter maintains its filtering efficiency after long-term exposure to PM2.5. In some embodiments, the air filter has a removal efficiency for PM2.5 of at least 90% after 50 hours of exposure to air having an average PM2.5 index of 300 and an average wind speed of 1 mile/hour. In some embodiments, the air filter has a removal efficiency for PM2.5 of at least 90% after 100 hours of exposure to air having an average PM2.5 index of 300 and an average wind speed of 1 mile/hour. In some embodiments, the air filter has a removal efficiency for PM2.5 of at least 90% after 200 hours of exposure to air having an average PM2.5 index of 300 and an average wind speed of 1 mile/hour.
In some embodiments, the air filter further comprises another or more materials. In some embodiments, the air filter further comprises a catalyst (e.g., TiO2, MoS2) adapted for degrading the PM absorbed on the polymeric nanofibers. In some embodiments, the air filter further comprises an anti-biopathogen material (e.g., Ag) adapted for killing bacteria and virus absorbed on the polymeric nanofibers. In some embodiments, the air filter further comprises materials adapted for absorbing and/or degrading other air pollutant (e.g., aldehyde, NOx and SOx).
Another aspect of some embodiments of the invention described herein relates to an air filtering device comprising the air filter described herein. In some embodiments, the air filter is a removable, detachable, and/or replaceable.
In some embodiments, the air filtering device is a passive air filtering device. In some embodiments, the air filtering device is a window screen. In some embodiments, the air filtering device is a wearable mask. In some embodiments, the air filtering device is a helmet. In some embodiments, the air filtering device is a nose filter. In some embodiments, the air filtering device is building air handling system. In some embodiments, the air filtering device is car air conditioning system. In some embodiments, the air filtering device is industrial exhaust filtration system. In some embodiments, the air filtering device is clean room filtration system. In some embodiments, the air filtering device is hospital air cleaning system. In some embodiments, the air filtering device is a net for outdoor filtering. In some embodiments, the air filtering device is a cigarette filter.
A further aspect of some embodiments of the invention described herein relates to a method for making the air filter described herein, comprising electrospinning the polymeric nanofibers onto the substrate from a polymer solution. In some embodiments, the polymer solution comprises 1-20 wt. % of the polymer. In some embodiments, the polymer solution comprises 3-15 wt. % of the polymer. In some embodiments, the polymer solution comprises 5-10 wt. % of the polymer.
A further aspect of some embodiments of the invention described herein relates to a method for making an air filtering device, comprising incorporating the air filter described herein into a window screen. A further aspect of some embodiments of the invention described herein relates to a method for making an air filtering device, comprising incorporating the air filter described herein into a wearable mask. A further aspect of some embodiments of the invention described herein relates to a method for improving indoor air quality, comprising installing the window screen described herein in a window frame.
Also disclosed here is an electric/conducting air filter. Accordingly, one aspect of some embodiments of the invention described herein relates to an electric air filter comprising a first layer adapted to receive a first electric voltage, wherein the first layer comprises an organic fiber coated with a conductive material.
In some embodiments, the first layer comprises a microfiber having at least one lateral dimension of 1000 micron or less. In some embodiments, the first layer comprises a nanofiber having at least one lateral dimension of 1 micron or less. In some embodiments, the microfiber or nanofiber comprise a polymer comprising a repeating unit which comprises polar functional groups (e.g., —CN, —OH, —CO—, —C—O—C—, —SO2—, —NO2, —NH—, —NH2). The higher dipole moment of the repeating unit of the polymer, the better adhesiveness of polymer to PM particles. In some embodiments, the microfiber or nanofiber comprise a polymer selected from nylon, polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), polystyrene (PS), or polyethylene (PE).
In some embodiment, the conductive material comprises metal. In some embodiment, the conductive material comprises elemental metal such as Cu. In some embodiment, the conductive material comprises conducting carbon, carbon nanotubes, graphene, graphene oxide or graphite. In some embodiment, the conductive material comprises metal oxide. In some embodiment, the conductive material comprises metal nitride. In some embodiment, the conductive material comprises a conductive polymer. In some embodiment, the conductive material is adapted to maintain a high conductivity for months or even years in air.
In some embodiment, the organic fiber is partially coated with the conductive material. In some embodiments, the organic fiber comprises a coated side and an uncoated side.
In some embodiment, the organic fiber is fully coated with the conductive material, wherein the outer surface of the conductive coating is further functionalized. In some embodiments, the outer surface of conductive coating is functionlized with a polar group to increase affinity for PM particles.
In some embodiment, the electrical air filter further comprises a second layer adapted to receive a second electric voltage, wherein the second layer is identical to or different from the first layer. In some embodiments, the first layer and the second layer are disposed parallel to each other in the electric air filter. In some embodiments, a positive voltage is applied on the first layer and a negative or neutral voltage is applied on the second layer. In some embodiments, a negative voltage is applied on the first layer and a positive or neutral voltage is applied on the second layer. In some embodiments, the air flow passes through the first layer before contacting the second layer. In some embodiments, the air flow passes through the second layer before contacting the first layer.
In some embodiment, the electrical air filter has a removal efficiency for PM2.5 of at least 80%. In some embodiments, the electrical air filter has a removal efficiency for PM2.5 of at least 90%. In some embodiments, the electrical air filter has a removal efficiency for PM2.5 of at least 95%. In some embodiments, the electrical air filter has a removal efficiency for PM2.5 of at least 98%. In some embodiments, the electrical air filter has a removal efficiency for PM2.5 of at least 99%.
In some embodiment, the electrical air filter has a removal efficiency for PM10-2.5 of at least 80%. In some embodiments, the electrical air filter has a removal efficiency for PM10-2.5 of at least 90%. In some embodiments, the electrical air filter has a removal efficiency for PM10-2.5 of at least 95%. In some embodiments, the electrical air filter has a removal efficiency for PM10-2.5 of at least 98%. In some embodiments, the electrical air filter has a removal efficiency for PM10-2.5 of at least 99%.
Another aspect of some embodiments of the invention described herein relates to an air filtering device comprising the electric air filter described herein. In some embodiments, the air filtering device is a ventilation system. In some embodiments, the air filtering device is an air-conditioning system. In some embodiments, the air filtering device is an automotive cabin air filter. In some embodiments, the air filtering device is a window screen.
A further aspect of some embodiments of the invention described herein relates to a method for making the electric air filter. In some embodiments, the method comprises sputter coating a metal or metal oxide onto a microfiber or nanofiber. In some embodiments, the microfiber or nanofiber is partially coated with the metal or metal oxide by directional sputter coating. In some embodiments, the microfiber or nanofiber is fully coated with the metal or metal oxide.
In some embodiments, the method comprises comprising treating the outer surface of the metal or metal oxide coating to generate a reactive group, and reacting said reactive group with an organic compound to functionalize the outer surface of the metal or metal oxide coating to increase affinity for PM particles. In some embodiments, the outer surface of the metal or metal oxide coating is treated with air plasma to generate —OH group. In some embodiments, the —OH group is reacted with a silane derivative (e.g., 3-cyanopropyltrichlorosilane) to functionalize the outer surface of the metal or metal oxide coating. Other suitable functional groups include those having high polarity and high dipole moment (e.g., —CN, —OH, —CO—, —NO2, —NH—, —NH2). The higher dipole moment, the better adhesiveness to PM particles.
A further aspect of some embodiments of the invention described herein relates to a method for filtering PM particles using the electric air filter, comprising applying an electric voltage on the first layer of the electric air filter. In some embodiments where the organic fiber in the first layer comprises a coated side and an uncoated side, the method can comprise placing the electric air filter in a manner to allow the uncoated side to face the direction of air flow.
In some embodiments, a positive electric voltage is applied on the first layer. In some embodiments, a negative electric voltage is applied on the first layer. In some embodiments, a positive voltage is applied on the first layer and a negative or neutral voltage is applied on the second layer. In some embodiments, a negative voltage is applied on the first layer and a positive or neutral voltage is applied on the second layer.
Another aspect of some embodiments of the invention described herein relates to an air filter for high temperature filtration, comprising a substrate and a network of polymeric nanofibers deposited on the substrate, wherein the air filter has a removal efficiency for PM2.5 of at least 70% at an operating temperature at least 70° C.
In some embodiments, the polymeric nanofibers comprise a polymer comprising a repeating unit having a dipole moment of at least 1 D, at least 2 D, or at least 3 D, or at least 4 D, or at least 5 D, or at least 6 D, and up to 10 D, up to 12 D, or more. Examples of suitable repeating units include repeating units including polar groups, such as substituted alkyl groups (e.g., substituted with 1, 2, 3, or more halo groups or other polar groups listed below), substituted alkenyl groups (e.g., substituted with 1, 2, 3, or more halo groups or other polar groups listed below), substituted alkynyl groups (e.g., substituted with 1, 2, 3, or more halo groups or other polar groups listed below), substituted aryl groups (e.g., substituted with 1, 2, 3, or more halo groups or other polar groups listed below), hydroxyl groups, ketone groups, sulfone groups, aldehyde groups, ether groups, thio groups, cyano groups (or nitrile groups), nitro groups, amino groups, N-substituted amino groups, ammonium groups, N-substituted ammonium groups, amide groups, N-substituted amide groups, carboxy groups, alkylcarbonyloxy groups, alkenylcarbonyloxy groups, alkynylcarbonyloxy groups, arylcarbonyloxy groups, alkylcarbonylamino groups, N-substituted alkylcarbonylamino groups, alkenylcarbonylamino groups, N-substituted alkenylcarbonylamino groups, alkynylcarbonylamino groups, N-substituted alkynylcarbonylamino groups, arylcarbonylamino groups, N-substituted arylcarbonylamino groups, urea groups, epoxy groups, oxazolidone groups, and charged or hetero forms thereof In some embodiments, the polymeric nanofibers comprise a polymer comprising a repeating unit having a ketone group and/or a sulfone group.
In some embodiments, the polymeric nanofibers comprise a polymer comprising a repeating unit which comprises an imide group. In some embodiments, the polymeric nanofibers comprise polyimide (PI). In some embodiments, the polymeric nanofibers comprise a polymer comprising a repeating unit which comprises a nitrile group. In some embodiments, the polymeric nanofibers comprise polyacrylonitrile (PAN). In some embodiments, the polymeric nanofibers comprise poly(p-phenylene sulfide). In some embodiments, the polymeric nanofibers comprise poly-p-phenylene terephthalamide. In some embodiments, the polymeric nanofibers comprise polytetrafluoroethylene. In some embodiments, the polymeric nanofibers comprise a polymer comprising a repeating unit which comprises polar functional groups (e.g., —CN, —OH, —CO—, —NO2, —NH—, —NH2, etc.). The higher dipole moment of the repeating unit of the polymer, the better adhesiveness of polymer to PM particles.
In some embodiments, the polymeric nanofibers have an average diameter of less than 1 micron. In some embodiments, the polymeric nanofibers have an average diameter of 10-900 nm. In some embodiments, the polymeric nanofibers have an average diameter of 20-800 nm. In some embodiments, the polymeric nanofibers have an average diameter of 30-700 nm. In some embodiments, the polymeric nanofibers have an average diameter of 50-500 nm. In some embodiments, the polymeric nanofibers have an average diameter of 100-300 nm.
In some embodiments, the polymeric nanofibers are electrospun onto the substrate.
In some embodiments, the polymeric nanofibers carry electric charges. In some embodiments, the polymeric nanofibers carry positive charges. In some embodiments, the polymeric nanofibers carry negative charges.
In some embodiments, the air filter has a light transmittance of at least 30%, or at least 40%, or at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90%. Transmittance values can be expressed by weighting the AM1.5 solar spectrum from 400 to 800 nm to obtain an average transmittance value. Transmittance values also can be expressed in terms of human vision or photometric-weighted transmittance, transmittance at a given wavelength or range of wavelengths in the visible range, such as 550 nm, or other wavelength or range of wavelengths.
In some embodiments, the air filter are used for applications which do not have optical transparency requirements. The air filter has a light transmittance less than 60%, or 30%, or 10% or 5%.
In some embodiments, at an operating temperature of 70° C. the air filter has a removal efficiency for PM2.5 of at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%. In some embodiments, at an operating temperature of 150° C. the air filter has a removal efficiency for PM2.5 of at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%. In some embodiments, at an operating temperature of 200° C. the air filter has a removal efficiency for PM2.5 of at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%. In some embodiments, at an operating temperature of 250° C. the air filter has a removal efficiency for PM2.5 of at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%. In some embodiments, at an operating temperature of 300° C. the air filter has a removal efficiency for PM2.5 of at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%. In some embodiments, at an operating temperature of 350° C. the air filter has a removal efficiency for PM2.5 of at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%.
In some embodiments, at an operating temperature of 70° C. the air filter has a removal efficiency for PM10-2.5 of at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%. In some embodiments, at an operating temperature of 150° C. the air filter has a removal efficiency for PM10-2.5 of at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%. In some embodiments, at an operating temperature of 200° C. the air filter has a removal efficiency for PM10-2.5 of at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%. In some embodiments, at an operating temperature of 250° C. the air filter has a removal efficiency for PM10-2.5 of at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%. In some embodiments, at an operating temperature of 300° C. the air filter has a removal efficiency for PM10-2.5 of at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%. In some embodiments, at an operating temperature of 350° C. the air filter has a removal efficiency for PM10-2.5 of at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%.
In some embodiments, the air filter has a pressure drop of 500 Pa or less, 300 Pa or less, or 200 Pa or less, or 100 Pa or less, or 50 Pa or less, at a gas velocity of 0.2 m/s. In some embodiments, the air filter has a pressure drop of 500 Pa or less, or 300 Pa or less, or 200 Pa or less, or 100 Pa or less, or 50 Pa or less, at a gas velocity of 0.4 m/s. In some embodiments, the air filter has a pressure drop of 700 Pa or less, or 500 Pa or less, or 300 Pa or less, or 200 Pa or less, or 100 Pa or less, at a gas velocity of 0.6 m/s. In some embodiments, the air filter has a pressure drop of 700 Pa or less, or 500 Pa or less, or 300 Pa or less, or 200 Pa or less, or 100 Pa or less, at a gas velocity of 0.8 m/s. In some embodiments, the air filter has a pressure drop of 1000 Pa or less, or 700 Pa or less, or 500 Pa or less, or 300 Pa or less, or 200 Pa or less, or 100 Pa or less, at a gas velocity of 1.0 m/s.
In some embodiments, the air filter maintains its filtering efficiency after long-term exposure to PM2.5 at high temperature. In some embodiments, the air filter has a removal efficiency for PM2.5 of at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%, after 50 hours of exposure to air having an average PM2.5 index of 300 and an average wind speed of 0.2 m/s at an operating temperature of 200° C. In some embodiments, the air filter has a removal efficiency for PM2.5 of at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%, after 100 hours of exposure to air having an average PM2.5 index of 300 and an average wind speed of 0.2 m/s at an operating temperature of 200° C. In some embodiments, the air filter has a removal efficiency for PM2.5 of at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%, after 200 hours of exposure to air having an average PM2.5 index of 300 and an average wind speed of 0.2 m/s at an operating temperature of 200° C.
In some embodiments, the air filter has a removal efficiency of at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%, for removing PM2.5 particles from car exhaust gas having a temperature of 50˜80° C. and a gas velocity of 2˜3 m/s. In some embodiments, the air filter has a removal efficiency of at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%, for removing PM10-2.5 particles from car exhaust gas having a temperature of 50˜80° C. and a gas velocity of 2˜3 m/s.
Another aspect of some embodiments of the invention described herein relates to an air filtering device for removing high temperature PM2.5 particles from pollution sources comprising the air filter described herein. In some embodiments, the air filter is a removable, detachable, and/or replaceable.
In some embodiments, the air filtering device for removing high temperature PM2.5 particles from pollution sources is an exhaust air filter. In some embodiments, the air filtering device is a vehicle exhaust filter. In some embodiments, the air filtering device is an industrial exhaust filter. In some embodiments, the air filtering device is a power plant exhaust filter.
A further aspect of some embodiments of the invention described herein relates to a method for making the air filter configured for high temperature filtration, comprising electrospinning the polymeric nanofibers onto the substrate from a polymer solution. In some embodiments, the polymer solution comprises 1-30 wt. % of the polymer. In some embodiments, the polymer solution comprises 2-20 wt. % of the polymer. In some embodiments, the polymer solution comprises 3-15 wt. % of the polymer. In some embodiments, the polymer solution comprises 5-10 wt. % of the polymer.
A further aspect of some embodiments of the invention described herein relates to a method for making a high-temperature air filtering device, comprising incorporating the air filter described herein into a vehicle exhaust filter. A further aspect of some embodiments of the invention described herein relates to a method for making a high-temperature air filtering device, comprising incorporating the air filter described herein into an industrial exhaust filter. A further aspect of some embodiments of the invention described herein relates to a method for making a high-temperature air filtering device, comprising incorporating the air filter described herein into a power plant exhaust filter.
These and other features, together with the organization and manner of operation thereof, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings.
Introduction. Described here a highly effective air filter with low air flow resistance for removal of PM pollution. Commercial air filters are bulky and have low air flow, which are not compatible with the requirements for a transparent air filter having optical transparency and high air flow. It is demonstrated here that by controlling the surface chemistry of nanofibers to allow strong adhesion between PM and the air filter, by injecting electric charge into nanofibers and also by controlling the microstructure of the air filters to increase the capture possibilities, transparent, high air flow and highly effective air filters can be achieved, which can have ˜90% transparency with >95% removal, ˜60% transparency with >99% removal, and ˜30% transparency with >99.97% removal of PM2.5 under extreme hazardous air quality conditions (PM2.5 index >300 or PM2.5 mass concentration >250 μg/m3). Such a nanofiber filter is not limited to any particular field of use. Its optical transparency is for showing that very thin layer of nanofiber filter can have high efficiency of PM removal. A field test in Beijing showed that an exemplary polyacrylonitrile (PAN) transparent air filter had excellent performance, demonstrating high PM2.5 removal efficiencies (98.69%, 99.42%, and 99.88%) at high transmittance (˜77%, ˜54% and ˜40%, respectively). The transparent air filter described herein can be used to solve the serious air pollution issues through indoor air filtration, outdoor personal protection and industrial exhaust filtration.
Air filter surface screening. To find effective materials for air filters, different polymers and polymers with other coatings was investigated for PM capture. Electrospinning was used to make polymer nanofibrous air filters (see
For testing the transparent air filter descried herein, the PM is generated by burning incense. The burning incense contains PM above 45 mg/g burned, and the exhaust smoke contains a variety of pollutant gases, including CO, CO2, NO2, SO2 and also volatile organic compounds, such as benzene, toluene, xylenes, aldehydes and polycyclic aromatic hydrocarbons (PAHs). This complex air exhaust is a model system containing many of the components present in polluted air during hazy days. A scanning electron microscope (SEM) was first used to characterize different fibrous filters before and after filtration. The images are shown in FIGS. 2C, 2D. The as-made nanofiber filters of different polymers had similar morphology with fiber sizes ˜200 nm and similar packing density. Since PP fibers cannot be made by electrospinning, they were peeled off from commercial mask to a transmittance of 70%. The PP thus has a different morphology, with fibers of much larger diameter as compared to the electrospun nanofibers. The SEM images of different filters after the filtration test show that the number and size of PM particles coated on the PAN filter were both larger than that of other polymers. The smoke PM formed a coating layer strongly wrapped around each nanofiber instead of only attaching to the surface of the nanofibers as in the case of inorganic PM (see
The quantified PM2.5 and PM10-2.5 removal by different fibrous filters is shown in
Evaluation of the PM removal efficiency, optical transparency and air flow of transparent air filters. Besides capture efficiency, the other two parameters for a transparent air filter, light transmittance and air flow, were then evaluated.
Besides capture efficiency, keeping a high air flow is another parameter to assess the performance of an air filter. All air flow tests were based on PAN air filter. In
In-situ time evolution study of PM capture by PAN transparent filter. The PM capture process and mechanism was studied by in-situ optical microscope (OM) and SEM using a PAN nanofibrous filter with a fiber diameter of ˜200 nm. The PAN nanofibrous filter was placed under the OM. Continuous flow with high concentration of smoke PM was fed to the fibrous filter.
SEM was used to characterize the detailed interaction between PM particles and PAN nanofibers and the images are shown in
PM chemical composition analysis. To further explain the performance difference of different fibrous filters in capturing smoke PM, the composition and surface chemistry of smoke PM was investigated.
PAN transparent air filter long term performance. The long term performance of the transparent filter was evaluated using a PAN filter with a transmittance of ˜75% under the condition of hazardous level equivalent to PM2.5 index >300 and a mild wind condition (<1 miles per hour). The performance is shown in
Performance of the transparent air filters in a field test (Beijing, China). In order to study the efficacy of the filters in a real polluted air environment, a field test was carried out on Jul. 3, 2014 in Beijing, China. The PM2.5 was at a hazardous level equivalent to a PM2.5 index >300. The results are shown in
Performance of PAN transparent air filter under different humidity and wind force conditions. Based on the real weather situation, wind force and humidity were also taken into consideration and the results are shown in
In conclusion, it was demonstrated that electrospun PAN nanofibers can be highly effective transparent PM filters because of its small fiber diameter and surface chemistry. Such nanofibrous filters can shut off PM from entering the indoor environment, maintain natural ventilation and preserving the optical transparency when installed on windows. An electrospun PAN transparent air filter with a transmittance of ˜75% can be used under hazardous PM2.5 level for as long as 100 hours with efficiency maintained at 95-100%. This high particle removal efficiency has also been proven by a field test in Beijing, showing the practical applicability of the transparent filters. It is believed that the transparent air filter described herein can be used as a stand-alone device or incorporated with existing masks or HEPA filters to achieve a healthier indoor living environment.
Nanofibrous Air Filters with High Temperature Stability for Efficient PM2.5 Removal from Pollution Sources. Particulate matter (PM) pollution has recently become a serious environmental problem in many countries. The direct removal of PM, especially PM2.5, from its sources is of great significance for the reduction of PM pollution. However, most of the PM sources are of high temperature up to 300° C. in the exhaust, which causes challenges for PM2.5 removal with existing technologies. Described here are high-efficiency air filters for the high temperature PM2.5 removal. The air filters are made of polyimide (PI) nanofibers by electrospinning. For a PI filter with 50% light transparency (only 30˜60 μm thick), >99.50% PM2.5 removal efficiency was achieved. The PI nanofibrous air filters exhibited high thermal stability and the PM2.5 removal efficiency kept almost unchanged for temperature ranging from 25° C. to 370° C. In addition, the PI filters had high air flux with very low pressure drop. Long-term test showed that the PI nanofibrous air filter could continuously work for more than 120 hours with high PM2.5 removal efficiency under extreme hazardous air-quality conditions (PM2.5 index>300). A field test showed that the polyimide air filters could effectively remove >99.5% of PM particles across all sizes from car exhaust at high temperature.
High-efficiency PI air filter fabrication. PI was chosen as the exemplary high temperature air filter material because of its excellent thermal stability at high temperatures. PI is a polymer of imide monomers and is known for thermal stability, good chemical resistance, as well as excellent mechanical properties. However, it is not yet known about their capability to remove PM in the air at high temperature. It is believed that polar functional groups are suitable to bind with PM and that PI has the right polar group for this purpose. There are various types of PIs in terms of molecular structures. A general molecular structure of PI is shown in
PI nanofibrous air filters were fabricated using electrospinning of PI-dimethylformamide solution. Electrospinning is a versatile processing technique of preparing uniform nanofibrous filters from diverse polymer solutions with controllable dimensions (
The PM particles used in this study were generated by burning incenses, which is a good model system for the air filtration as it contains a wide size distribution of particles and many of the components present in polluted air during hazy days, such as CO, CO2, NO2, SO2 and also volatile organic compounds such as benzene, toluene, xylenes, aldehydes, polycyclic aromatic hydrocarbons, etc. As shown in
The PM capture process and mechanism of the PI nanofibers were also studied by in situ OM imaging. As shown in
High temperature PM removal performance of PI air filters. The thermal stability of air filters affects their filtration performance at high temperature. Before testing the high temperature performance of PI nanofibrous air filters, their thermal stability was checked first. The PI nanofibers were placed in a box furnace set with different temperature. Each sample was kept for one hour at each temperature. As shown by
To test the PM removal performance of the as-made PI air filters at high temperature, a special testing device was designed shown as
The PM removal efficiency of PI filters was systematically studied with different optical transparency at different temperatures. As shown in
To obtain a better comparison, air filters made of other polymers were also tested, such as polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP) and three kinds of commercial air filters. The PAN and PVP also had diameters of ca. 200 nm. As shown by
Pressure drop of PI filters compared with commercial filters. In addition to the PM removal efficiency, another desirable parameter is the air flux with low pressure drop. It was reported that energy consumption is directly proportional to the pressure drop over the filters and normally accounts for 70% of the total life cycle cost of air filters. In the average commercial building, 50% of the energy bill is for the HVAC (Heating, Ventilation and Air Conditioning) system and 30% of that is directly related to the air filtration. Therefore, the low pressure drop of filters would save a lot of energy and cost during their applications.
There is usually a conflict between the two desirable filtration parameters: removal efficiency and high air flux with low pressure drop. A good filter is expected to show both a high filtration efficiency and a low pressure drop. Optical transmittance is a direct observation of the thickness of filters, correlated with the air flux. As shown in
Long-term and field-test performance of PI nanofibrous air filters. The long-term and field-test performance is desirable for the practical application of PI air filters in real environments. The long-term performance of the PI nanofibrous air filters was evaluated by using a PI filter with optical transmittance of 55% with temperature of 200° C. under the condition of hazardous level equivalent to the PM2.5 index >300 and mild wind condition (the wind speed is about 0.2 m/s). The long-term PM particle removal performance of PI filters is shown in
From the above demonstrations and comparisons, it is evident that PI nanofibrous air filters show excellent performance for high temperature filtration with high efficiency and low air pressure drop. As mentioned above, the polar chemical functional groups in PI molecules result in the strong binding affinity with PM2.5. The dipole moment for the repeating units of PI (6.16 D) is much higher than that of PAN (3.6 D) and PVP (2.3 D), rendering PI with high PM2.5 removal efficiency. The PI nanofibers have a high thermal stability and can work in a wide range of temperature. The PI air filters have a high PM2.5 removal efficiency at both room and high temperature. Although the other filters made of different polymers such as PAN and PVP as well as some commercial air filters also have high PM removal efficiency, they are unstable and do not work at high temperatures. Besides, the commercial air filters have high pressure drop, thus will consume more energy when removing PM particles. In comparison, the PI filters have both of high removal efficiency and very low pressure drop. This will allow a high air flow through the filters and save a lot of energy when removing PM particles.
The reason for the PI nanofibrous air filters having such low pressure drop lies at least in the following three aspects. First, the nanofiber diameter is small and the PI air filters have a low thickness. The thickness of PI filters is in the range of 0.01˜0.1 mm compared to traditional fibers with thickness of 2˜30 mm. There is a lot of empty space between nanofibers. Second, nanofibers have a much higher available specific surface areas than microfibers, which provides more contact between the PM and the fibers. Third, when the diameter of the nanofibers is comparable to the mean free path of the air molecules (66 nm under normal conditions), the gas velocity is non-zero at the fiber surface due to “slip” effect. Because of the “slip” effect, the drag force from the nanofibers onto the air flow is greatly reduced, thus greatly reduces the pressure drop.
The long-term performance test shows that the PI air filters have a high PM particle removal efficiency and a long lifetime. The PI filters can effectively removal almost all the PM particles from the car exhaust at high temperature. The above performance proves that the PI nanofibrous air filters can be used as very effective high-efficiency air filters for high temperature PM2 5 particles removal. For the industrial application of PI air filters, they can work both independently and work together with the industrial dust collectors at both room and high temperature.
Example 1.1—Electrospinning. The solution system for the polymers is 6 wt % polyacrylonitrile (PAN, MW=1.5×105g/mol, Sigma-Aldrich) in dimethylformamide (DMF, EMD Millipore), 7 wt % polyvinylpyrrolidone (PVP, MW=1.3×106 g/mol, Acros) in ethanol (Fisher Scientific), 10 wt % polyvinyl alcohol (PVA, MW=9.5×104 g/mol, Sigma-Aldrich) in distilled water, and 6 wt % polystyrene (PS, MW=2.8×105g/mol, Sigma-Aldrich) in DMF together with 0.1 wt % of myristyltrimethylammonium bromide (MTAB, Acros). The polymer solution was loaded in a 1-mL syringe with a 22-gauge needle tip which is connected to a voltage supply (ES30P-5W, Gamma High Voltage Research). The solution was pumped out of the needle tip using a syringe pump (KD Scientific). Fiber glass wire mesh (New York Wire) was sputter-coated (AJA International) with ˜150 nm of copper on both sides and was grounded to collect the electrospun nanofibers. The wire diameter was 0.011 inch, and the mesh size was 18×16. The electrospun nanofibers would lie across the mesh hole to form the air filter, similar to previous reports. The applied potential, the pump rate, the electrospinning duration, and the needle-collector distance were carefully adjusted to control the nanofiber diameter and the packing density.
Example 1.2—Optical transmittance measurement. The transmittance measurement used a xenon lamp (69911, Newport) as the light source, coupled with a monochromator (74125, Newport) to control the wavelength. An iris was used to trim the beam size to about 5 mm×5 mm before entering an integrating sphere (Newport) for transmittance measurement. A photodetector (70356, Newport) was inserted into one of the ports of integrating sphere. The photodiode is connected to lock-in radiometry system (70100 Merlin™, Newport) for photocurrent measurement. The samples were placed in front of the integrating sphere; therefore, both specular transmittance and diffuse transmittance were included. For air filters coated on copper wire mesh, a clean copper wire mesh with the same geometry was used as a reference. For self-standing filters, ambient air was used for reference. The transmittance spectrum was then weighted by AM1.5 solar spectrum from 400 to 800 nm to obtain the average transmittance.
Example 1.3—PM generation and efficiency measurement. For all performance tests unless mentioned otherwise, model PM particles were generated from incense smoke by burning. The smoke PM particles has a wide size distribution from <300 nm to >10 μm with the majority particles <1 μm. The inflow concentration was controlled by diluting the smoke PM by air to a hazardous pollution level equivalent to PM2.5 index >300. PM particle number concentration was detected with and without filters by a particle counter (CEM) and the removal efficiency was calculated by comparing the number concentration before and after filtration. In the rigid PM capture test, dust PM particles were fabricated by grinding soil particles using a ball mill to submicron sizes. The pressure drop was measured by a differential pressure gauge (EM201B, UEi test instrument).
Example 1.4—Characterization. The SEM images and EDX was done by FEI XL30 Sirion SEM with acceleration voltage of 5 kV for imaging and 15 kV for EDX collection. The TEM images and EELS data were collected by FEI Titan TEM with acceleration voltage of 300 kV. The XPS spectrum was collected by PHI VersaProbe Scanning XPS Microprobe with Al Kα source. The FTIR spectrum was measured by Bruker Vertex 70 FTIR spectrometer.
Example 2—Electric Air Filter.
Example 2.1—Material synthesis procedure for Cu-sputtered microfiber/nanofiber. The microfibers were produced by peeling off the commercial polypropylene (PP) to 200-500 μm. Nanofibers were made by electrospinning process. The polymer solution was loaded in a 1-mL syringe with a 22-gauge needle tip which is connected to a voltage supply (ES30P-5W, Gamma High Voltage Research). The solution was pumped out of the needle tip using a syringe pump (KD Scientific). The microfibers or nanofibers were sputter-coated (AJA International) with 50-300 nm of copper. See
Example 2.2—Material synthesis procedure for functionalized Cu-coated nanofiber. Core polymer nanofibers were synthesis by electrospinning process same as above. 50-300 nm of copper was coated by sputter. Then the nanofibers were air plasma treated to generate —OH group and linked with 3-cyanopropyltrichlorosilane through vapor surface modification. Other functional coating can be made through dip-coating from dilute polymer solutions. See
Example 2.3—PM generation and efficiency measurement. For all performance tests unless mentioned otherwise, model PM particles were generated from incense smoke by burning. The smoke PM particles has a wide size distribution from <300 nm to >10 μm with the majority particles <1 μm. The inflow concentration was controlled by diluting the smoke PM by air to a hazardous pollution level equivalent to PM2.5 index >300. PM particle number concentration was detected with and without filters by a particle counter (CEM) and the removal efficiency was calculated by comparing the number concentration before and after filtration. In the rigid PM capture test, dust PM particles were fabricated by grinding soil particles using a ball mill to submicron sizes. The pressure drop was measured by a differential pressure gauge (EM201B, UEi test instrument). Unless mentioned, the wind velocity used in the efficiency test was 0.21 m/s and the humidity was 30%.
Example 2.4—Filtration experiment. Two identical conducting air filter electrodes were put parallel to each other. Inflow air carried high concentration of PM pollutant (>250 μg/m3). The wind velocity was 0.21 m/s. During filtration, voltages from 0-15 kV was added to the two conducting air filters. The removal efficiency was calculated by comparing the PM concentration in the inflow and outflow which was detected by a particle counter.
Example 2.5—Results. As show in
Example 3.1—Electrospinning. The solution system for the polymers used in this study was 15 wt % PI resin (CAS #62929-02-6, Alfa Aesar) in dimethylformamide (EMD Millipore), 6 wt % PAN (MW=1.5×105 g/mol, Sigma-Aldrich) in dimethylformamide (EMD Millipore), 7 wt % polyvinypyrrolidone (MW=1.3×106 g/mol, Across) in ethanol (Fisher Scientific). A 1-mL syringe with a 22-gauge needle tip was used to load the polymer solution and connected to a voltage supply (ES30P-5W, Gamma High Voltage Research). A syringe pump (KD Scientific) was used to pump the solution out of the needle tip using. The electrospun nanofibers were collected by a grounded copper mesh. The wire diameter of the copper mesh was 0.011 inch, and the mesh size was 18×16. During electrospinning, the nanofibers would lie across the mesh hole to form the air filter.
Example 3.2—PM generation and efficiency measurement. The PM particles used in this work was generated by burning incense. The incense smoke PM particles had a wide size distribution from <300 nm to >10 μm, with the majority of particles being <1 μm. By diluting the smoke PM by air, the inflow concentration was controlled to a hazardous pollution level equivalent to the PM2.5 index >300. A particle counter (CEM) was used to detect the PM particle number concentration before and after filtration. The removal efficiency was calculated by comparing the number concentration before and after filtration.
Example 3.3—High temperature filtration measurement. The high temperature filtration measurement was conducted on an electrical tube furnace (Lindberg/Blue). First, a PI filter was coated by copper tape on the edge. Then the filter was placed between two stainless steel pipe flanges and fixed firmly with screws. Then the pipe flanges were connected into the filtration measurement system and placed inside the tube furnace. A PM particle counter (CEM) was used to measure the particle number concentration. For each temperature, the filter was kept for 20 min to be stabilized.
Example 3.4—Optical transmittance measurement. The optical transmittance measurement was conducted as follows. A xenon lamp (69911, Newport) was used as the light source, coupled with a monochromator (74125, Newport) to control the wavelength. The beam size was trimmed by an iris to ˜5 mm×5 mm before entering an integrating sphere (Newport) for transmittance measurement. A photodiode was connected to lock-in radiometry system (70100 Merlin, Newport) for photocurrent measurement. A photodector (70356, Newport) was inserted into one of the ports of integrating sphere. The filter samples were placed in front of the integrating sphere. Both specular transmittance and diffuse transmittance were included. For air filters collected on copper mesh, a clean copper mesh with the same geometry was used as a reference. For self-standing filters, ambient air was used for reference. The transmittance spectrum was weighted by AM1.5 solar spectrum from 400 to 800 nm to obtain the average transmittance.
Example 3.5—Pressure drop measurement. The pressure drop was measured by a differential pressure gauge (EM201B, UEi test instrument).
Example 3.6—Characterization. The SEM images were taken by FEI XL30 Sirion SEM with an acceleration voltage of 5 kV for imaging.
Embodiment 1: An air filter comprising a substrate and a network of polymeric nanofibers deposited on the substrate, wherein the air filter has a light transmittance of at least 50% and a removal efficiency for PM2.5 of at least 70%.
Embodiment 2: The air filter of Embodiment 1, wherein the polymeric nanofibers comprise a polymer comprising a repeating unit having a dipole moment of at least 2 D.
Embodiment 3: The air filter of Embodiment 1, wherein the polymeric nanofibers comprise a polymer comprising a repeating unit having a dipole moment of at least 3 D.
Embodiment 4: The air filter of any of Embodiments 1-3, wherein the polymeric nanofibers comprise a polymer comprising a repeating unit which comprises a nitrile group.
Embodiment 5: The air filter of any of Embodiments 1-4, wherein the polymeric nanofibers comprise polyacrylonitrile.
Embodiment 6: The air filter of any of Embodiments 1-5, wherein the polymeric nanofibers have an average diameter of 10-900 nm.
Embodiment 7: The air filter of any of Embodiments 1-6, wherein the polymeric nanofibers have an average diameter of 50-500 nm.
Embodiment 8: The air filter of any of Embodiments 1-7, wherein the polymeric nanofibers are electrospun onto the substrate.
Embodiment 9: The air filter of any of Embodiments 1-8, wherein the air filter has a light transmittance of at least 70%.
Embodiment 10: The air filter of any of Embodiments 1-9, wherein the air filter has a removal efficiency for PM2.5 of at least 90%.
Embodiment 11: The air filter of any of Embodiments 1-10, wherein the air filter has a removal efficiency for PM10-2.5 of at least 90%.
Embodiment 12: The air filter of any of Embodiments 1-11, wherein the air filter has a removal efficiency for PM2.5 of at least 90% at a relative humidity of 70%.
Embodiment 13: The air filter of any of Embodiments 1-12, wherein the air filter has a removal efficiency for PM2.5 of at least 90% after 100 hours of exposure to air having an average PM2.5 index of 300 and an average wind speed of 1 mile/hour.
Embodiment 14: A passive air filtering device comprising the air filter of any of Embodiments 1-13.
Embodiment 15: A window screen comprising the air filter of any of Embodiments 1-13.
Embodiment 16: A wearable mask comprising the air filter of any of Embodiments 1-13.
Embodiment 17: A method for making the air filter of any of Embodiments 1-13, comprising electrospinning the polymeric nanofibers onto the substrate from a polymer solution.
Embodiment 18: The method of Embodiment 17, wherein the polymer solution comprises 1-20 wt. % of the polymer.
Embodiment 19: A method for making an air filtering device, comprising incorporating the air filter of any of Embodiments 1-13 into a window screen.
Embodiment 20: A method for making an air filtering device, comprising incorporating the air filter of any of Embodiments 1-13 into a wearable mask.
Embodiment 21: An electric air filter comprising a first layer adapted to receive a first electric voltage, wherein the first layer comprises an organic fiber coated with a conductive material.
Embodiment 22: The electric air filter of Embodiment 21, wherein the organic fiber is partially coated with the conductive material.
Embodiment 23: The electric air filter of Embodiment 22, wherein the organic fiber is a microfiber or nanofiber, and wherein the conductive material is selected from metal, metal oxide, and conductive polymer.
Embodiment 24: The electric air filter of Embodiment 22, wherein the organic fiber comprises a coated side and a uncoated side, and wherein the uncoated side faces direction of air flow.
Embodiment 25: The electric air filter of Embodiment 21, wherein the organic fiber is coated with the conductive material, and wherein the conductive material is surface functionalized.
Embodiment 26: The electric air filter of Embodiment 25, wherein the organic fiber is a microfiber or nanofiber, wherein the conductive material is selected from metal, metal oxide, and conductive polymer, and wherein the conductive material is surface functionlized with a polar group to increase affinity for PM2.5.
Embodiment 27: The electric air filter of any of Embodiments 21-26, further comprising a second layer adapted to receive a second electric voltage.
Embodiment 28: A ventilation system comprising the electric air filter of any of Embodiments 21-27.
Embodiment 29: An air-conditioning system comprising the electric air filter of any of Embodiments 21-27.
Embodiment 30: An automotive cabin air filter comprising the electric air filter of any of Embodiments 21-27.
Embodiment 31: A window screen comprising the electric air filter of any of Embodiments 21-27.
Embodiment 32: A method for making the electric air filter of any of Embodiments 21-27, comprising sputter coating a metal or metal oxide onto a microfiber or nanofiber.
Embodiment 33: The method of Embodiment 32, wherein the sputter coating is directional, and wherein the microfiber or nanofiber is partially coated with the metal or metal oxide.
Embodiment 34: A method for making the electric air filter any of Embodiments 21-27, comprising treating a microfiber or nanofiber coated with a metal or metal oxide to generate a reactive group, and reacting said reactive group with an organic compound to functionalize surface of the metal or metal oxide coating to increase affinity for PM2.5.
Embodiment 35: The method of Embodiment 34, wherein the microfiber or nanofiber coated with the metal or metal oxide is treated with air plasma to generate —OH group, and wherein the —OH group is reacted with a silane derivative.
Embodiment 36: A method for filtering PM2.5 using the electric air filter of any of Embodiments 21-27, comprising applying an electric voltage on the first layer of the electric air filter.
Embodiment 37: The method of Embodiment 36, wherein the first electric voltage is a positive voltage.
Embodiment 38: The method of Embodiment 36, wherein the first electric voltage is a negative voltage.
Embodiment 39: A method for filtering PM2.5 using the electric air filter of Embodiment 24, comprising applying an electric voltage on the first layer of the electric air filter, and placing the electric air filter to allow the uncoated side to face the direction of air flow.
Embodiment 40: A method for filtering PM2.5 using the electric air filter of Embodiment 27, comprising applying a first electric voltage on the first layer, and applying a second electric voltage on the second layer, wherein the first electric voltage and the second electric voltage have opposite polarity.
Embodiment 41: An air filter for high temperature filtration, comprising a substrate and a network of polymeric nanofibers deposited on the substrate, wherein the air filter has a removal efficiency for PM2.5 of at least 70% at an operating temperature of 200° C.
Embodiment 42: The air filter of Embodiment 41, wherein the polymeric nanofibers comprise a polymer comprising a repeating unit having a dipole moment of at least 3 D.
Embodiment 43: The air filter of Embodiment 41, wherein the polymeric nanofibers comprise a polymer comprising a repeating unit having a dipole moment of at least 6 D.
Embodiment 44: The air filter of any of Embodiments 41-43, wherein the polymeric nanofibers comprise a polymer selected from polyimide, poly(p-phenylene sulfide), polyacrylonitrile, poly-p-phenylene terephthalamide, polytetrafluoroethylene, and derivatives thereof.
Embodiment 45: The air filter of any of Embodiments 41-44, wherein the polymeric nanofibers comprise polyimide.
Embodiment 46: The air filter of any of Embodiments 41-45, wherein the polymeric nanofibers have an average diameter of 10-900 nm.
Embodiment 47: The air filter of any of Embodiments 41-46, wherein the polymeric nanofibers have an average diameter of 50-500 nm.
Embodiment 48: The air filter of any of Embodiments 41-47, wherein the polymeric nanofibers are electrospun onto the substrate.
Embodiment 49: The air filter of any of Embodiments 41-48, wherein the air filter has a light transmittance of at least 30%.
Embodiment 50: The air filter of any of Embodiments 41-49, wherein the air filter has a removal efficiency for PM2.5 of at least 80% at an operating temperature of 200° C.
Embodiment 51: The air filter of any of Embodiments 41-50, wherein the air filter has a removal efficiency for PM10-2.5 of at least 80% at an operating temperature of 200° C.
Embodiment 52: The air filter of any of Embodiments 41-51, wherein the air filter has a pressure drop of 100 Pa or less at a gas velocity of 0.2 m/s.
Embodiment 53: The air filter of any of Embodiments 41-52, wherein the air filter has a removal efficiency for PM2.5 of at least 80% after 100 hours of exposure to air an average PM2.5 index of 300 and an average wind speed of 0.2 m/s at an operating temperature of 200° C.
Embodiment 54: An air filtering device for removing high temperature PM2.5 particles from pollution sources comprising the air filter of any of Embodiments 41-53.
Embodiment 55: A vehicle exhaust filter comprising the air filter of any of Embodiments 41-53.
Embodiment 56: An industrial exhaust filter or a powder plant exhaust filter comprising the air filter of any of Embodiments 41-53.
Embodiment 57: A method for making the air filter of any of Embodiments 41-53, comprising electrospinning the polymeric nanofibers onto the substrate from a polymer solution.
Embodiment 58: The method of Embodiment 57, wherein the polymer solution comprises 1-30 wt. % of the polymer.
Embodiment 59: A method for making an air filtering device, comprising incorporating the air filter of any of Embodiments 41-53 into a vehicle exhaust filter.
Embodiment 60: A method for making an air filtering device, comprising incorporating the air filter of any of Embodiments 41-53 into an industrial exhaust filter or a power plant exhaust filter.
As used herein, the singular terms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a molecule can include multiple molecules unless the context clearly dictates otherwise.
As used herein, the terms “substantially,” “substantial,” and “about” are used to describe and account for small variations. When used in conjunction with an event or circumstance, the terms can refer to instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation. For example, the terms can refer to less than or equal to ±10%, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.
Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity and should be understood flexibly to include numerical values explicitly specified as limits of a range, but also to include all individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly specified. For example, a ratio in the range of about 1 to about 200 should be understood to include the explicitly recited limits of about 1 and about 200, but also to include individual ratios such as about 2, about 3, and about 4, and sub-ranges such as about 10 to about 50, about 20 to about 100, and so forth.
In the foregoing description, it will be readily apparent to one skilled in the art that varying substitutions and modifications may be made to the invention disclosed herein without departing from the scope and spirit of the invention. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations, which is not specifically disclosed herein. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention. Thus, it should be understood that although the present invention has been illustrated by specific embodiments and optional features, modification and/or variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scopes of this invention.
This application is a continuation application of U.S. patent application Ser. No. 14/968,654, filed Dec. 14, 2015, which claims the benefit of U.S. Provisional Patent Application No. 62/091,041, filed Dec. 12, 2014, the content of each of which are incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62091041 | Dec 2014 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14968654 | Dec 2015 | US |
| Child | 18069126 | US |
