Gas separation: processes – Electric or electrostatic field
Reexamination Certificate
2002-07-11
2004-05-04
Chiesa, Richard L. (Department: 1724)
Gas separation: processes
Electric or electrostatic field
C095S058000, C096S016000, C096S224000, C422S004000, C422S022000, C422S024000, C422S121000
Reexamination Certificate
active
06730141
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device and a method for selectively removing gaseous pollutants from the ambient air, in particular in vehicle passenger compartments, aircraft passenger compartments, etc.
BACKGROUND INFORMATION
Air pollutants in interior spaces where people stay, such as in airplanes, passenger cars, offices, etc., represent a considerable problem for health and well-being. Air pollutants are emitted by pieces of equipment, surface coatings, etc., as well as during activities such as cooking, roasting and frying, and also by people in the room. In addition, substances other than air may also enter interior spaces from outside (e.g. emissions from traffic and/or industry). In order to prevent effects detrimental to the human organism, extensive filtering measures are necessary for treating and purifying the ambient air.
Devices based on non-regenerative adsorption processes are used to purify air. In this connection, filters having activated carbon, modified activated carbon, or zeolites are used. For example, German Published Patent Application Nos. 198 23 611 and 197 30 291 describes devices for removing pollutants, odorous substances, and toxic gases from air streams, the latter describing two adsorbers that may be alternately switched to adsorption mode and desorption mode (regenerative process). However, the efficiency of conventional adsorbents is limited, especially in the range of low concentration, i.e. in the emissions range in which concentrations typically lie in the ppb range (also referred to below as indoor air), since the loading linearly decreases with the pollutant concentration (Henry's Law). In order to retain a good filtering efficiency, the adsorber filters must be replaced or regenerated after a certain period of time. In addition, the efficacy and efficiency of the air purification is strongly dependent on environmental influences, in particular temperature and moisture. Additionally, microbial growth or an accumulation of fungi, bacteria, and pollen can cause the filter to become a health risk that should not be neglected. In addition, devices having such filter systems normally occupy a large volume that is particularly unavailable in automobiles and aircraft.
Devices and methods for purifying air may also ionize the entire volume of air. As described in German Published Patent Application No. 197 36 293, the ionization can be achieved using corona discharge. However, other air ionizers include ionization chambers and electrostatic filter systems (as illustrated in German Published Patent No. 298 08 126). The need to ionize all of the air results in a high power requirement, since the ionization routes used here must be supplied with appropriately high voltage. At the same time, the efficiency is usually disappointing. Many such systems are not effective enough to fulfill increasingly strict legal conditions. Another disadvantage attributed to ionizing oxygen molecules and nitrogen molecules is the formation of reactive ozone and nitrogen oxides.
The situation is similar with plasma-oxidation air-purification processes and photochemical air-purification processes, which attempt to completely break down the pollutants. In this case, one may also not rule out the formation of unwanted by-products, since not only the desired components but, in principle, all of the components of the air are ionized. In this context, ozone may again be formed, which further reacts to form free radicals, so that unwanted substances are formed. In order to induce as complete a decomposition as possible, both high electron energy/photon energies and free-radical concentrations are necessary, which in turn requires a large amount of power. In addition, the power consumption is inefficient since untroublesome components of the room air are also ionized. Furthermore, these devices also have the disadvantage of occupying a large amount of space, having a considerable weight, and being very expensive to maintain.
Devices are also used to remove dust particles and other microscopic particles from a gas stream. U.S. Pat. No. 4,543,484 describes an example of such a system, which either atomizes or electrically charges the particles to be removed, using a high-energy laser beam. The charged particles are then removed under the influence of an electric field. In this instance, the large amount of electrical power required and the large dimensions are also disadvantageous.
SUMMARY
An object of the present invention is to provide a method for removing gaseous pollutants from the ambient air, as well as a device for implementing the method, through which it is possible to selectively and completely remove undesirable emissions in the ambient air, using relatively simple equipment and relatively little energy.
The method of the present invention for removing gaseous pollutants from the ambient air, which may be used in aircraft cabins and motor-vehicle passenger compartments, distinguishes itself in that the air to be purified is first directed into a purification chamber and then irradiated with optical radiation, so that the pollutants contained in the air to be purified are ionized, using single-photon excitation or multiple-photon excitation. The ionized pollutants are then drawn off by applying an electric field, and are thereby removed from the air to be purified. The single-photon excitation and/or multiple-photon excitation is performed in a resonant and/or non-resonant manner.
The method provides that only the pollutants contained in the air to be purified are ionized and not, for example, components of the air, such as oxygen, nitrogen, carbon dioxide, argon, etc. That is, only the pollutant molecules contained in the air to be purified are selectively ionized, using photoionization, and removed from the air stream by an electric field. The energy of the radiated photons (or light quanta) is not sufficient for ionizing components of air, so that ionized pollutant molecules and non-ionized air molecules may be separated in a simple manner, using an electric field. This type of ionization also does not produce any undesirable or harmful by-products, as is the case with other ionization methods or oxidation methods.
The selective photoionization may be achieved in that the energy of the optical radiation acting on the air to be purified is less than the energy difference between-the ground state and the ionization limit of the air molecules, but the energy is high enough to ionize the pollutant molecules contained in the air to be purified.
Since the ionization energy of the main constituents of air, oxygen, nitrogen, carbon dioxide, argon, etc., is typically greater than 12.5 eV, where this value corresponds to the ionization energy of oxygen, an energy less than 12.5 eV may be used. The wavelength of the utilized optical radiation typically lies in the UV range, and the multiple-photon processes may be used.
In this context, photons having the same energy or wavelength or photons having different wavelengths may be used. In a multiple-photon process, one or more intermediate levels may be excited to resonance by suitably selecting the excitation wavelengths, for the effective excitation cross-sections are particularly large. In this instance, it may be necessary to select the wavelengths in such a manner, that the energy of the radiated photons corresponds to the energy of the first intermediate level, or that the sum of the energies of the radiated photons corresponds to the energy of the at least one intermediate level or the energies of several intermediate levels. The closer the photon energies are to the energy levels, the greater the probability of excitation.
By changing the wavelength of the radiation as a function of time, it is also possible to ionize different pollutant molecules one after another, since different pollutant molecules generally have different ionization energies. In this instance, the wavelength of the optical radiation may be varied between 200 nm and 330 nm as a function of time. The ionization of diffe
Goebel Johann
Oberpriller Helmut
Peuser Peter
Chiesa Richard L.
EADS Deutschland GmbH
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