Patent Application
20230400199
The invention relates to an insert device for an air conditioning installation which air conditioning installation comprises an air handling unit guiding air flowing in a given flow direction, wherein the air handling unit has a casing with a predetermined cross section in which at least a filter is housed. Furthermore, the invention relates to an air conditioning installation having an insert device.
Air conditioning installations are used in closed rooms where a number of humans or animals are present for living, working and/or meeting. In order to avoid an accumulation of dust the air conditioning installation serves for removing air from the room and for replacing it after filtering. In many cases at least some of the air removed from the room is replaced by fresh air drawn from the outside of the room for replacing accumulated CO2 by O2. If necessary, the fresh air may be heated or cooled.
Most of the air conditioning installations are suitable for removing particles from the air within the room so that at least a certain amount of the air within the room may be recirculated. However, most of that installations are designed to trap particles and chemical pollutants by further units which have to be replaced in time to avoid their ineffectiveness due to overload or fouling.
In this specification air conditioning installations are meant to include fixed installations where the air handling unit is connected to an air guiding tubing as well as installations where the air handling unit comprises a cabinet which may be positioned deliberately. Said cabinet may be used as a mobile air conditioning installation having input and output openings which may be in direct connection to the ambient air or, as an alternative, having at least one opening connected to a tube for sucking air to be cleaned from a room or for distributing cleaned air.
Air conditioning installations are known which are able to not only absorb but also destroy chemical and even microbiological pollutants. They use cabinets of a pretty large size as an air handling unit to which the air guiding tubing is connected. In times where there is an acute threat due to bacteria, viruses, and fungi the usual air conditioning installations can reasonably not be used if they only recirculate the air within a room. As a remedy, at least the insufficient air handling unit has to be replaced by an air handling unit suited for destroying chemical and especially microbiological contaminants. Said replacement works may be complicated since in many cases the new air handling unit will be much more voluminous compared with the used insufficient air handling unit. Therefore, in many cases insufficient air handling units themselves or insufficient mechanical filters in air handling units are not replaced with the result of risks for the health of the humans or animals within the room. The term “room” is used here including rooms within private houses, meeting rooms, business sites, conference centers or similar, factory halls, stables and so on.
Air handling units which are suitable for destroying airborne contaminants often include Advanced Oxidation Process (AOP), such as catalysts, and are used in air conditioning systems or air purifying systems for cleaning ambient air in hospitals, quarantine stations or public places like restaurants and the like. It is also known to use a combination of more than one catalyst, mainly a catalyst having an activity initiated by electromagnetic radiation, especially UV radiation, and a further catalyst which may be effective already at ambient temperature. The combination of both catalysts is found effective to destroy microbiological pollutions by the catalyst activated by means of electromagnetic radiation and to completely mineralize the reaction products of the first catalyst by means of the second catalyst. Examples of respective catalysts are described in CN 106582265 A and JP H11-137656 A. As an electromagnetic radiation source UV lamps are used and have to be arranged near the respective catalyst.
From JPH11-137656 for example a catalytic composition is known, consisting of a manganese oxide, titanium dioxide and an adsorbent. These are bound to a solid support via a binder. The binder partly covers the catalysts and therefore only a reduced amount can be reached by activating UV radiation and the molecules to be cracked. According to another embodiment, a suspension of the components is impregnated into a porous body or a fabric. These however provide a high flow resistance to a gas to be depolluted. Therefore it is not possible to efficiently clean large amounts of gases per time unit. In the implementation of this document, the ratio second catalyst may not exceed an amount of 22% of the titanium dioxide in order not to deteriorate the activity of the titanium dioxide.
It is an object of the present invention to allow the depollution of air within closed rooms in combination with present air conditioning installations.
According to the present invention an insert device as mentioned above has a frame casing with an outer closed periphery shaped to be mounted within the predetermined cross section of the casing of the air handling unit and having end faces open for the air flow, an air permeable catalytic grid structure comprising a carrier grid and a coating with a catalytic material is held at each of the end faces, the catalytic material is a mixture comprising an adsorbent, a first catalyst activatable by electromagnetic radiation and a second catalyst being activated at low temperature, and the frame casing in addition holds an electromagnetic radiation source device between the grid structures at its end faces.
The present invention is based on the idea to provide the air handling necessary for the destruction of chemical and biological contaminants within a compact insert device which can be inserted into commercially available air handling units of air conditioning installations in place of or in addition to a filter of said air handling unit. Consequently, the present invention allows an easy upgrade of customary air conditioning installations so that they become effective to destroy chemical and biological contaminants without severe reconstructions of the air conditioning installation. The second catalyst is already activated at low temperature which is especially the ambient temperature so that the second catalyst can be effective at ambient temperature even without a specific activator. Low temperature is meant to be below 70° C., especially below 50° C.
For many purposes it is advantageous to include a fan causing the air flow in the air handling unit. In some embodiments the air handling unit is a part of a fixed installation and connected to an air guiding tubing. As used herein, the term “air guiding tubing” is also known as “air duct” and the terms are used interchangeably herein. In other embodiments the air handling unit is a stand-alone unit or a cabinet connected to at least a tubing for sucking air to be purified and/or for distributing decontaminated air to desired place(s).
The insert device of the present invention may be designed to fit within a frame construction of the air handling unit designed for holding one or more filter units. That means that according to the present invention a frame construction as known for customary filters can be used for holding the insert device comprising the complete arrangement for destroying chemical and biological contaminants.
According to an aspect of the present invention an air conditioning installation comprising an air handling unit guiding air flowing in a given flow direction wherein the air handling unit has a casing with a predetermined cross section in which at least a filter is housed, the filter being held by a support frame having a peripheral shape adapted to the free cross section of the air handling unit is characterized in that the insert device is sealingly inserted into the support frame. Within the air handling unit the insert device with the catalysts may establish a filter unit which can be arranged and used in place of a previous filter unit or in addition to one or more other further units which may be usual filter units like absorbents. “sealingly inserted” means that there is no considerable bypass for the air flowing in the air handling unit so that essentially all of the air will pass through the insert device. A perfect seal is not required. In a specific embodiment the air handling unit also includes a fan for causing the air flow.
Since the customary filter units are arranged so as to be easily removable from the air handling unit for cleaning and/or replacement purposes the insert device according to the present invention can be easily inserted into the air handling unit. Accordingly, the insert device of the present invention allows an easy upgrade of customary air conditioning installations without using additional space or additional cabinets or similar.
In an embodiment of the insert device of the present invention the first catalyst is activatable by UV radiation and the electromagnetic radiation source emits UV radiation. For this purpose at least one UV source may be arranged as the electromagnetic radiation source device between the grid structures. The UV source may be at least a conventional UV lamp as well as an arrangement of UV LEDs. In another embodiment the electromagnetic radiation source device may be a plasma generator which generates UV radiation due to the radiation of a plasma which is preferably a cold plasma. In this embodiment the effect of the catalysts may be enhanced by means of the plasma wherein highly reactive species are formed which are able to destroy chemical as well as biological contaminants.
When both catalysts as well as the absorber are each mixed in a pulverulent condition a very fine distribution of the respective particles can be obtained when the grid carrier is coated with a slurry of said pulverulent materials.
In an embodiment of the present invention the catalytic grid structure is strongly resistant to the oxido-reduction process. It may have a honeycomb structure which provides a sufficient stability and a large surface for the catalytic effect combined with a low resistance for the flow of the air through the grid structure.
If necessary, the catalytic grid structure may be completely covered by a layer of an air permeable flexible filter material on the respective outer side of the insert device. That optional filter material may be especially designed to withhold UV radiation within the insert device so that no UV radiation will reach the outside region of the insert device and possibly harm a person working near the air handling unit. That layer may have a thickness of about 1 mm and can consist of a non-woven, e.g. from fiber glass. In another embodiment said layer may be in metallic grid having a mesh width in the order of some μm so as to withhold UV radiation on one hand and cause a low pressure drop for the flowing air on the other hand. For this purpose very fine walls of the metallic grid are necessary leading to a high flexibility of said layers at the input and the output side of the insert device establishing the catalytic reactor. For a mechanical stabilization the layers may be held by a support grid with a comparatively lower flexibility but with a mesh width of some millimeters so as to not increase the pressure drop for the flowing air.
The invention will be described in more detail with reference to embodiments illustrated in the accompanying drawings.
Within the air handling unit 1 a fan 3 is positioned which serves for moving the air within the air handling unit 1 and the air guiding tubing 2 (air duct) in a predetermined flow direction 4 indicated by an arrow in
The air handling unit 1 has conical ends for establishing the transition from the smaller diameter of the air guiding tubing 2 to the larger dimensions of the air handling unit 1. The air flowing into the air handling unit 1 passes a pre-filter 5 which regularly is a coarse filter for withholding larger particles of the air stream. Thereafter the air is accelerated by the fan 3 and then passes an insert device 6 according to the present invention. It can be seen from
After passing the insert device 6 the air flow may furthermore pass through a filter unit 7 which can optionally be arranged at the downstream end of the air handling unit 1. The filter unit 7 may consist of or comprise a HEPA (high efficiency particulate air) filter which is customary for air conditioning installations.
The shape of the frame casing 8 as well as the catalytic grid structures 12 depend on the dimensions of the free section of the air handling unit 1 of the air conditioning installation.
An embodiment of the catalytic grid structure 12 is illustrated in
In an embodiment, the carrier grid 17 is composed basically of aluminum or aluminum alloys. Aluminum has a high electrical conductivity. This allows to improve the separation of electrical charges formed by the catalyst during the oxydo-reduction process namely, a better separation of charges improve the efficiency of the reaction as their recombination is lower and they thereby participate more to catalytic reactions for airborne contaminants removal. In addition, the high thermal conductivity of aluminum allows to promote a better transfer of calories from ambient air which is typically in the field of 20 to 23° C. and from the heat emitted by UV-lamps to the second catalyst being activated at low temperature, like the manganese oxide (MnO) catalyst. The low temperature catalyst is typically activated in a range of 20 to 80° C. with good activity in the field of 40 to 55° C. like 45 to 50° C.
In addition, aluminum has also a low elastic limit, thus, avoiding also continuous deformations of the support and then to make catalytic coating fragile. In an embodiment, the catalyst as defined herein is coated without any binder, thus, deformations of the support could create many cracks at the catalyst surface and consequently make it fragile resulting in loss of the coating.
Also aluminum is an inert material, that cannot react or to be destroyed by the catalyst during the oxydo-reduction reaction as may be the case with organic materials, such as polymers. Moreover, aluminum is light, thus, easy removal of the insert device according to the present invention is possible without remarkable deformation. Thus, high class rate e.g. according to EN 1806 is possible.
In addition, the honeycomb shaped structure, which is a preferred structure of the carrier grid according to an embodiment of the present invention is favorable compared to other tridimensional structures. The material has very opened cells, thus, pressure drop is reduced. That means, there is no resistance to the air flow. Further, high irradiation is achieved allowing high activation of the first catalyst.
The material may be present in many different dimensions thickness and numbers of cells per cm2. Further, to consider many kinds of light sources, even small sources like LEDs that could be directly implemented inside the cells of the honeycomb to improve catalyst irradiation. The honeycomb structure allows to provide a rigid material, therefore, the catalyst coated, in particular embodiments of catalyst (without the presence of binder) inside the cells is well protected from handling and cracking. A hexagonal shape of aluminum honeycomb cells is an embodiment which best compromise between metallic surface, rigidity of the support and weight of metal.
The carrier grid 17 is coated with catalytic material. The compact structure of the insert device 6, 6′ is achieved due to the highly efficient catalytic material consisting of a first catalyst, a second catalyst and in adsorbent, said components are produced separately and are mixed in pulverulent condition each. The mixture is put in a suitable liquid e. g. a mixture of water and alcohol, to form a slurry which can then be coated on the whole surface of the carrier grid 17. The coating preferably takes place in several steps with thin layers each which together form the uniform coating of the desired thickness which may be between 1 μm and 250 μm. The coating may be performed by various methods including dip coating or spray coating. After each coating step the thin layer is allowed to dry before the next layer is applied. Thereby a binder-free coating can be achieved enhancing the efficiency of the catalyst.
The through holes or channels of the carrier grid 17 are designed so as to only little reduce the free cross section of the air handling unit 1 when the insert device 6 is mounted in the air handling unit 1. The area of the through hole may account for at least 80% preferably at least 90% of the area of the free cross section of the air handling unit 1. In order to provide a sufficient catalytic effect the length of the through holes should be at least 5 mm, in other embodiments at least 10 mm, 15 mm or 20 mm, up to 50 mm and more. The ratio of the length of the through holes and their distance between limiting walls (“diameter”) is preferably larger than 2, in other embodiments larger than 5, larger than 10 and in these cases not larger than 50, in other embodiments not larger than 30 or not larger than 20. The distance of the limiting walls of the through holes (for round through holes the diameter) is at least 2 mm, in other embodiments at least 5 mm or at least 7 mm. An upper limit is 50 mm, in other embodiments 20 mm or 10 mm. A straight channel formed by the through holes is preferred in view of a minimum pressure drop caused by the grid structure.
The carrier can for example be formed from a metal, such as aluminum or steel, a plastic material or a composite material. It can for example be formed as a grid, a plate or an expanded metal. In a preferred embodiment, the carrier is shaped from a corrugated and/or folded sheet forming a plurality of through holes, preferably in a honeycomb manner. Advantages of a honeycomb panel compared to a plane material are a larger surface to be coated and a lower pressure drop. Also the irradiance within the cells is better. The carrier is then often simply referred to as a honeycomb or honeycomb panel. Preferably the through holes have a hexagonal cross section.
In a preferred embodiment the through holes account for at least 80% of the volume of the carrier, more preferably for at least 85%, most preferably for at least 90%, especially of at least 95% of the volume of the carrier. This helps to ensure a sufficient gas flow through the carrier in use. Therefore the supporting structure of the carrier is provided thinly, for example in the form of thin metal, preferably aluminum, or another inert material i.e. basically no reaction with the catalyst. Aluminum provides the advantage of being lightweight and sufficiently inert, so that the catalysts are not attacking the carrier itself in a critical manner.
The through holes preferably have a length, along which the gas can flow through the carrier, of at least 1 cm, more preferably at least 2 cm. Preferably, the length does not exceed 20 cm, more preferably 10 cm. The length of the holes, which usually equals the thickness of the grid-like carrier, has great influence on the efficiency of the depollution. If the length is too short, the catalytically active surface provided is low and therefore the depollution is not efficient. If the length is too high, the UV radiation will not or not sufficiently reach the photocatalyst in the center of the holes, so that a part of the provided photocatalyst is not activated. Furthermore it is difficult to satisfactorily coat the center parts of long through holes. Therefore also the ratio between length and diameter of the holes can be important. The ratio is preferably larger than 2, more preferably larger than 5, especially larger than 10 and preferably not larger than 50, more preferably not larger than 30, especially not larger than 20. If the cross section of a through hole is not circular, the diameter of an approximated circumscribed circle or a circle approximated via the least squares method may be used to determine the diameter for calculation of the ratio. The diameter of the holes preferably is at least 2 mm, more preferably at least 5 mm, especially at least 7 mm. Preferably the diameter of the holes does not exceed 50 mm, more preferably 20 mm, especially 10 mm.
The through holes preferably run straight and are not curved or angled along their length.
The ratio between the diameter of the through holes and the thickness of the bars or sheets of the carrier separating neighboring through holes is preferably larger than 10, more preferably larger than 20, especially larger than 40.
In a preferred embodiment, the slurry is binder-free. This means that no additional inorganic or organic binder is added, to enhance the adherence of the first catalyst, the second catalyst and the adsorbent on the carrier. Binders for example are cellulose and its derivatives, certain proteins or polymers and inorganic binders such as silica or alumina. Residual amounts of the suspension liquid, for example capillary bound, are not considered a binder. Also water, for example deriving from atmospheric humidity, is not considered a binder. Preferably a slurry is still considered binder-free, as long as it does not exceed an amount of binder of 2% in relation to the total mass of the adsorbent, the first catalyst and the second catalyst. Especially there is no matrix of binder molecules formed around the catalysts and the adsorbent on the carrier after evaporating the suspension liquid.
The slurry can be applied to the carrier by various methods, including dipping. In a preferred embodiment the slurry is applied via spray coating. Spray coating resulted in a very durable and consisting coating, especially without the need for providing a separate binder to the slurry. The coating preferably resists an air pressure of up to 4 bars, especially without using a binder. The slurry is preferably applied with a spray gun. Preferably a manual spray gun is used, which especially is a low-medium pressure spray gun, for example with a maximum pressure Pmax of 8 bar. It preferably has a gravitational suction cup. The spray coating is preferably performed vertically. In one preferred embodiment, the inlet pressure is 3.5 bar and the liquid flow is 2.5-3.0 liters per minute. The distance between the carrier and the spray gun preferably lies between 10 and 30 cm, preferably at about 15 cm. With the above mentioned exemplary parameters, good coating properties were achieved.
Specifically the coating adhered satisfactorily to the carrier, which preferably is an aluminum honeycomb.
Since the further layer 18 may be very thin and flexible, a stabilization by a wire grid 19 is advisable. The wire grid is for stabilization purposes only and therefore may have a large mesh width, e. g. between 5 and 15 mm with a wire diameter between 0.2 and 1.0 mm.
The sandwich arrangement of carrier grid 17, further layer 18 and wire grid 19 can preferably be mounted in a holding frame 20 so that the catalytic grid structure 12 can easily be handled as a unit, even if a further layer 18 and a wire grid 19 is used. However, it should be noted, that the further layer 18 and the wire grid 19 are optional and may be omitted in some applications. The completely mounted catalytic grid structure 12 according to
The compact structure of the insert device 6 is especially possible with a special coating material for the carrier grid 17.
The coating preferably has a total thickness of at least 50 μm, preferably at least 75 μm, especially at least 100 μm. A coating of such thickness especially provides a satisfactory amount of catalyst for gas depollution. Preferably the thickness does not exceed 500 μm, more preferably does not exceed 350 μm, and especially does not exceed 250 μm. A preferred range lies between 100 μm and 250 μm. If the coating is too thick, it is possible that lower layers are not sufficiently irradiated and/or not sufficiently reached by contaminants to be depolluted. It can therefore lead to a waste of catalytic material.
The first catalyst can for example consist of tungsten oxide and/or zinc oxide. It is preferred but not necessarily the case that only one type of first catalyst is used. It is also possible to use more than one catalyst having photocatalytic activity.
In a preferred embodiment the first catalyst is titanium dioxide TiO2. Titanium dioxide is very well known for its photocatalytic properties. It is a semiconductor and can be activated by irradiation with UV and/or visible radiation of a wavelength from 100 nm to 400 nm. Preferably the UV radiation used for activating the first catalyst, especially titanium dioxide, has a wavelength of 365 nm or less, more preferable in the UV-C range between 100 nm and 280 nm, most preferably of 254 nm. The use of UV radiation in the UV-C range has the advantage of additionally using the direct disinfecting properties of the UV-C radiation. UV-C radiation therefore acts directly biocidal due to its high energy and indirectly biocidal as well as on non-biological contaminants by activating the first catalyst. The titanium dioxide can be already photo-activated.
For the activation of the first catalyst, preferably any kind of UV radiation emitting sources or light sources can be used, for example artificial lamps emitting UV radiation or light emitting diodes or fluorescent tubes emitting UV radiation or UV radiation formed by cold plasma-type electrodes.
Titanium dioxide has the advantage of being cost-efficient and having the ability to at least partly regenerate itself. It is highly active against different contaminants, including chemical and biological contaminants.
It is known that titanium dioxide in the crystalline form of anatase has the highest catalytic activity. Therefore it is one embodiment of the invention that the titanium dioxide completely is of the anatase type.
Explorations of the applicant on the other hand have shown that a certain proportion of titanium dioxide of the rutile type, against the prevailing opinion, is enhancing the overall depolluting capacities of the catalytic device. The separation of the electric charges on the surface of the catalyst is augmented and so is its efficiency.
It is a preferred embodiment of the invention that the first catalyst is titanium dioxide TiO2 in the form of a mixture of anatase and rutile with an anatase/rutile ratio between 60/40 and 99/1. Preferably the ratio is at least 60/40, more preferably at least 70/30 and especially at least 80/20. The ratio is preferably not exceeding 99/1, more preferably not exceeding 95/5, and especially not exceeding 90/10. In a further preferred embodiment the ratio is between 77/23 and 83/17, especially 80/20. In a preferred embodiment the first catalyst, especially titanium dioxide, is doped, especially with silver ions or platinum ions. Doping of the first catalyst increases the biocidal effect on biological contaminants and on the destruction of possibly harmful byproducts of the destroyed contaminants. The presence of the doping ions increases the number of possible oxidation and reduction reactions.
The titanium dioxide preferably has an elementary particle size of 10-50 nm, more preferably of 15-35 nm, especially around 25 nm. These elementary particles tend to aggregate. The average particle size of these aggregates preferably ranges between 200 and 600 nm, more preferably, between 300 and 500 nm, especially around 420 nm. This, however, does not exclude that some aggregates have a particle size of 1 micron or more.
In a preferred embodiment the second catalyst is a low-temperature catalyst. A low temperature catalyst preferably is a catalyst being already catalytically active at temperature lower than 100° C., more preferably at temperatures lower than 50° C., most preferably already at room temperature of 20° C. This does however not imply, that it must be inactive at higher temperatures. Preferably the catalytic activity is increased with increasing temperature at least over a certain temperature interval, preferably 20° C. to 100° C. or 50° C. to 100° C.
That is, the second catalyst is a low-temperature catalyst. Low-temperature catalysts are activated by calorific energy. The term low-temperature catalyst is thereby used to differentiate this type of catalysts, which are activated at relatively low temperatures, from thermal catalysts, which are activated at relatively high temperatures of usually between 500° C. and 1200° C. A low-temperature catalyst according to the invention therefore is not only catalytically active at a relatively low-temperature but it is activated by the calorific energy at this relatively low temperature. In other words, a photocatalyst which is capable of being photo-activated at ambient temperature is no low-temperature catalyst, because it is not activated by the calorific energy at ambient temperature but by the irradiation. A low temperature catalyst preferably is a catalyst being already catalytically activated and, thus, active, at temperature lower than 100° C., more preferably at temperatures lower than 50° C., most preferably already at room temperature of 20° C. This does however not imply, that it must be inactive at higher temperatures. Preferably the catalytic activity is increased with increasing temperature at least over a certain temperature interval, preferably 20° C. to 100° C. or 50° C. to 100° C.
Low-temperature catalysts are for example metal oxides like nickel oxide or cerium oxide. In a preferred embodiment of the invention the second catalyst is manganese monoxide MnO, which is an efficient low-temperature catalyst. Explorations of the applicants have shown that manganese monoxide is significantly more efficient than the well-known manganese dioxide MnO2, whose catalytic activity is insufficient. Therefore preferably the manganese monoxide used in this embodiment is not or substantially not contaminated with manganese dioxide. In a preferred embodiment, the amount of manganese dioxide is lower than 5%, more preferably lower than 1%, most preferably lower than 0.1% of the total mass of the manganese monoxide used as second catalyst. Optimally, no manganese dioxide is present as an impurity of the manganese monoxide second catalyst.
Manganese monoxide, especially in crystalline form, allows the generation of highly reactive radical species when in contact with oxygen, for example from the air. Preferably the temperature is higher than 35° C., especially between 35° C. and 55° C., more preferably between 45 and 50° C. Preferably the relative humidity of the gas to be depolluted, especially air, is between 30-80%, more preferably 50%. Under these circumstances a very efficient generation of the radical species is possible. The radical species are able to react also with very small contaminants in the nano or micro scale, such as aldehydes like formaldehyde, which are usually hard to crack. This is, inter alia, because such small molecules are hard to be trapped. Hydrophilic catalysts are usually quickly saturated with water or other polar small molecules so that hardly any sites are available for small contaminants to be trapped and then oxidized. Manganese monoxide offers the specific advantage that it is only poorly reacting with water and trapping water molecules on its surface so that more sites are available for contaminants. Furthermore, the pores within the manganese monoxide are preferably smaller than those of the titanium dioxide so that larger molecules are trapped less and, again, more sites remain available for small contaminants. The radical species also react with biological contaminants.
A disadvantage of manganese monoxide is that it is unstable compared to manganese dioxide. Therefore, when synthesizing manganese monoxide, special care needs to be taken on the reaction parameters, when the formation of manganese dioxide is to be avoided, as preferred. One important reaction parameter is the temperature. When using a calcination temperature higher than 300° C., a substantial amount or solely manganese dioxide is formed.
Since the formation of titanium dioxide from precursors usually requires temperatures of more than 300° C., for example 300° C.-600° C., a simultaneous calcination of manganese monoxide precursors and titanium dioxide precursors to form manganese monoxide on the one hand and titanium dioxide on the other hand, is impossible. A calcination temperature of higher than 600° C. during the formation of the titanium dioxide may lead to an excessive formation of rutile, which is undesired. On the other hand, a certain amount of rutile, as described above, enhances the efficiency of the catalyst.
Therefore, when the first catalyst is titanium dioxide and the second catalyst is manganese monoxide, preferably no simultaneous calcination takes place.
It is preferred but not necessarily the case, that the synthesis of the first catalyst, the second catalyst and/or the adsorbent is part of the manufacturing method of the catalytic device. Preferred embodiments of the synthesis will be explained in detail below. If at least the synthesis of titanium dioxide as first catalyst and manganese monoxide as second catalyst is part of the manufacturing method, no simultaneous calcination of their precursors preferably takes place. They are preferably synthesized apart from each other.
One advantage of using a low-temperature catalyst, especially manganese monoxide, is that the necessarily accruing waste heat of the UV radiation source can be used to warm the low-temperature catalyst thereby increasing its catalytic efficiency. Hence, a synergy can be achieved when combining a photocatalyst and a low-temperature catalyst in one stage and preferably arrange them spatially close to the UV radiation source in order to use the waste heat efficiently. Preferably a temperature of up to 40° C., up to 50° C. or up to 90° C. can be achieved on the surface of the catalytic device.
The adsorbent is preferably a compound having a large specific surface area, preferably of at least 300 m2/g, more preferably of at least 500 m2/g, most preferably of at least 1000 m2/g, especially more than 2000 m2/g. The adsorbent can for example be activated carbon or activated coke.
In a preferred embodiment the adsorbent is a zeolite. Zeolites are microporous aluminosilicate minerals which can be naturally occurring or artificial. Zeolites can be synthetic.
Preferably a hydrophilic zeolite is used, as explorations of the applicant show that biological contaminants tend to be better adsorbed by a hydrophilic than a hydrophobic zeolite. Preferably a zeolite of type A or ZSM-5 is used. The zeolite is preferably a synthetic zeolite, especially a synthetic zeolite of type A or ZSM-5.
Synthetic zeolite has the advantage of being pure and having a homogenous structure due to the fact that is synthesized.
In a preferred embodiment of the invention, the first catalyst is titanium dioxide, the second catalyst is manganese monoxide and/or the adsorbent is a zeolite. The zeolite is preferably a synthetic hydrophilic zeolite of type A. These configurations are preferred for all applicable embodiments described herein.
In a preferred embodiment of the invention, the first catalyst is titanium dioxide, the second catalyst is manganese monoxide and/or the adsorbent is a zeolite. The zeolite is preferably a synthetic hydrophilic zeolite of type A. These configurations are preferred for all applicable embodiments described herein.
The applicants have found, that certain ratios of the single components are advantageous, for efficient elimination of contaminants. Preferably the ratio between the zeolite of type A and titanium dioxide ranges between 3:1 and 1:1, especially is around 2:1. The ratio of the zeolite of type A and manganese monoxide preferably ranges between 5:1 and 3:1, especially is around 4:1. The ratio of titanium dioxide and manganese oxide preferably ranges between §:1 and 1:1, especially is around 2:1. These preferred ratios also apply for first catalysts, second catalysts and adsorbents other than titanium dioxide, manganese monoxide and/or the zeolite of type A.
Hydrophilic zeolite of type A has a high affinity to chemical and biological contaminants and no natural equivalent. It has an affinity to the cellular membranes of microorganisms. These adsorb to the surface of the zeolite for electrostatic reasons. Additionally, the hydrophilic zeolite of type A has a direct antimicrobial effect, which makes its use even more synergistic. Hydrophilic zeolite of type A has a crystal structure formed from an anionic aluminosilicate structure, neutralized by alkaline or alkaline earth metal cations.
Preferably the zeolite, especially the zeolite of type A comprises a sodalite crystal structure.
The structure of the zeolite links multiple elementary sodalite cages. A sodalite cage consists of multiple polyhedrons with eight hexagonal faces and six square-shaped faces. The sodalite cages forming the zeolite are interconnected via the square-shaped faces. The specific structure of the sodalite cages gives the zeolite an open 3D structure, whereby especially 47% of the total volume is formed by interstices. Therefore the zeolite provides a large surface for adsorption of biological and chemical contaminants within a small volume. Additionally the open 3D structure allows for a high water absorption and retention capacity. Since water can be used to form highly reactive radical species like the hydroxyl radical on the surface of the catalysts, this can be advantageous. Furthermore the water retention capacity may, depending on the circumstances, ensure that no water film is formed on the catalysts, thereby degrading their efficiency. On the other hand a very high amount of adsorbent, especially zeolite, may provide for a water excess, thereby degrading the efficiency of the catalysts. Preferably the amount of adsorbent therefore does not exceed 80%, especially does not exceed 70% of the total mass of first catalyst, second catalyst and adsorbent. On the other hand, if the amount of adsorbent is very low, the water retention capacity might not be sufficient. Therefore the amount of adsorbent preferably is not lower than 40% especially not lower than 30% of the total mass of first catalyst, second catalyst and adsorbent.
The inventors have explored that the combination of two different catalysts and an adsorbent is synergistically effective for depolluting a gas. The contaminants are adsorbed onto the adsorbent. By way of the mass transfer phenomenon, they migrate to the catalyst particles. The generation of reactive species on the surface of the catalysts then leads to destruction of the contaminants, preferably to complete mineralization of the contaminant. Also byproducts during the destruction of the contaminants are preferably destroyed further so that no possibly harmful byproducts are released into the depolluted gas or are released but destroyed within one of the next depolluting cycles. The adsorbent can thereby also form a reservoir for pollutants to be destroyed, for example during a peak load of the gas with contaminants. An amount of contaminants that would exceed the catalytic capacity of the catalysts per time unit can therefore preferably be held back by the adsorbent and then be guided to the catalysts with a time delay. This makes it possible to also treat peak loads that would, without adsorbent, exceed the capacity of the catalysts per se. In order to provide good adsorbing properties, the amount of the adsorbent is preferably higher than the amount of each catalyst and/or the cumulated amount of the catalysts, with respect of the total mass of the first catalyst, the second catalyst and the adsorbent.
The adsorbent is holding back contaminants which are then transferred to the catalysts via mass transfer. On the other side, by this phenomenon, the adsorbent is constantly regenerated and its adsorbing capacity restored. This demonstrates a real synergy of providing these compounds within one mixture. In order to optimally achieve this effect, the mingling of the catalysts and the adsorbent is preferably performed intensively, especially to provide a mixture as homogenous as possible. The amount of the first catalyst is preferably at least 10%, more preferably at least 20% and does preferably not exceed 30%, especially does not exceed 40% of the total mass of the first catalyst, the second catalyst and the adsorbent. The amount of the second catalyst is preferably at least 5%, more preferably at least 10%, especially at least 15% and does preferably not exceed 20%, especially does not exceed 30% of the total mass of the first catalyst, the second catalyst and the adsorbent.
In a preferred embodiment, the components are provided in the following ranges, in weight percent with regard to their total mass: Between 27% and 30% of the first catalyst, between 11% and 17% of the second catalyst and between 55% and 59% of the adsorbent.
A specific and preferred embodiment contains an amount of 29% of the first catalyst, 12% of the second catalyst and 59% of the adsorbent.
The explorations of the applicants showed that this ratio shows a good efficiency as well as satisfying water retention capacities and contaminant retention capacities. With these amounts an especially sustainable and long lasting composition is provided that also provides very good depolluting attributes. Additionally, the amount of UV/visible radiation needed to activate the first catalyst provides for a sufficient and useful amount of waste heat to increase the catalytic activity of the second catalyst in this amount, when the second catalyst is a low-temperature catalyst.
Additionally, this invention relates to an embodiment in which the amount of the first catalyst is lower than 27% and higher than 30%, the amount of the second catalyst is lower than 11% and higher than 17% and the amount of the adsorbent is lower than 55% and higher than 59%, each in weight percent and with regard to their total mass. All further preferred configurations and embodiments described herein apply to this specific embodiment.
As stated above it is preferred but not necessary, that the synthesis of the first catalyst, the second catalyst and/or the adsorbent is part of the manufacturing method of the catalytic device. The syntheses each are performed apart from another.
If the first catalyst, as preferred, is titanium dioxide, it is preferably synthesized by using a sol-gel process and precursors like titanium tetrachloride or butyl titanate, followed by a calcination at temperatures of 300-600° C. Also different methods for producing powdered titanium dioxide like thermal plasma technology, laser pyrolysis, hydrothermal or electrochemical synthesis are possible.
A preferred sol-gel process for synthesizing the titanium dioxide first catalyst in a powdered form is now described in detail:
The precursor titanium tetrachloride is mixed with absolute ethanol in a ratio between 0.5:10 and 3:10, preferably with a ratio of 1:10, for 4 h at room temperature. The formed sol is then placed in an ultrasonic bath for a time of 20 to 40 minutes, preferably 30 minutes. Consecutively the sol is dried at a temperature of 100° C. and 130° C., preferably 120° C. for a time between 1 h and 24 h, preferably 7 h in order to obtain a powder. This powder is then progressively calcined at a temperature between 530 and 570° C., preferably at 550° C., for 2 h to 3 h, preferably 2 h. Thereby the temperature is increased in steps of 10-12° C./minute. The obtained powdered titanium oxide is then cleansed with deionized water and consecutively dried at a temperature between 90 and 110° C., preferably 100° C.
If the second catalyst is, as preferred, manganese monoxide, it is preferably synthesized from precursors like manganese acetate, manganese nitrate and/or manganese sulfate followed by a calcination at temperatures below 300° C.
A preferred process for synthesizing the manganese monoxide second catalyst in a powdered form is now described in detail:
A precursor, preferably manganese acetate, is mixed with a solution of potassium permanganate in a ratio in mol/l of 1.8/1.2 for at least 24 h at room temperature between 21 and 25° C. Afterwards it is filtered and rinsed with deionized water. The obtained powder is calcined for several hours, preferably 72 h, with an increase in temperature of 6° C./min until a temperature between 280 and 300° C. is reached. The result is rinsed with deionized water and consecutively dried at 100° C. until the powdered manganese monoxide is obtained which can then be used. In order to obtain a well useable powder, the liquid is preferably fully evaporated. The low temperature below 300° C. is used to avoid the formation of the more stable but undesired manganese dioxide.
If the adsorbent is a synthetic hydrophilic zeolite of type A, it is preferably synthesized as follows:
Preferably, in step 7, the temperature is between 75 and 130° C., preferably 100° C. for 3 h to 4 h. It is the target to fully evaporate the water from mixture D. Preferably, in step 8, mixture D is cooled by lowering the temperature to a value lower than in step 7 but above room temperature. This cooling allows to avoid the forming crystals of solid E to stick to the bottom of the container in which mixture D is initially located. In one specific embodiment of step 8, the temperature is lowered to 30° C., considering that room temperature is between 20 and 25° C., so that it is easy to remove solid E without it sticking to the bottom.
In a usual manner the pH-value of the rinsing water in step 9 is measured with a pH meter or any other measuring device known by the person skilled in the art that allow a determination of the pH-value. By measuring the pH value of the rinsing water indirectly the surface pH-value of solid E, which will form the synthetic hydrophilic zeolite of type A is measured.
It is preferred that the surface of the zeolite is slightly alkaline, since this enhances the formation of van der Waals forces with the titanium dioxide and the manganese monoxide, which have a slightly acidic surface. This facilitates to generate a homogenous catalytic composition.
In step 10 the drying duration and temperature of solid E allow a gradual removal of the water molecules on the surface of the zeolite. Removing the water too rapidly would lead to the risk of crack formation in the surface of the zeolite. This cracks would weaken the important 3D structure. This is why a drying time between 8 and 15 h with a temperature of 100-120° C. is chosen, to progressively remove the water molecules without risking to weaken the structure of the zeolite.
In step 11 the synthetic hydrophilic zeolite of type A can be grinded using any grinding device.
In a particular embodiment, the adsorbent, especially the zeolite, is grinded to achieve a particle size between 0.5 and 2.5 μm. This particle size increases the affinity for certain microorganisms
A preferred method for mingling the first catalyst, the second catalyst and the adsorbent is to introduce the first catalyst, the second catalyst and the adsorbent, each in a powdered state and either already pre-mingled or separate, into a liquid to form a slurry. This slurry is then preferably vigorously mixed and the liquid is evaporated to form a dry powdered mixture of the first catalyst, the second catalyst and the adsorbent. This mixture can then be used per se or to form the slurry that is coated onto the carrier.
In a detailed and preferred embodiment, in a liquid preferably consisting of 20% alcohol and 80% deionized water, between 5 and 10% of titanium dioxide, between 2 and 6% of manganese monoxide and between 10 and 20% of the zeolite, each in regard to the total mass of the liquid, are mixed. Consecutively the mixture is heated to evaporate the liquid in order to obtain a powdered catalytic composition which can then be used. It is preferably heated to a temperature of 75° C.-130° C. for a period between 24 h and 120 h, preferably 72 h.
The invention also specifically relates to a slurry, formed from the first catalyst, the second catalyst, the adsorbent and deionized water.
According to another aspect, the invention relates to a catalytic device, obtainable via a manufacturing method as described herein.
According to another aspect, the invention relates to a catalytic composition, containing, in weight percent with regard to its total mass and each in a powdered state, between 27% and 30% of a first catalyst having photocatalytic activity, between 11% and 17% of a second catalyst and between 55% and 59% of an adsorbent.
All embodiments and configurations described herein regarding the catalytic device are also preferred configurations and embodiments of the catalytic composition.
If the second catalyst, as preferred, is a low-temperature catalyst, the catalytic composition can also be called a non-thermal or a thermal catalyst, since no high heating is necessary to activate the catalyst. Since the first catalyst, the second catalyst and the adsorbent are each provided in the powdered state, the catalytic composition can also be called a powdery non-thermal or a thermal catalyst. In one embodiment, the first catalyst having photocatalytic activity is yet photo-activated.
According to a specific and preferred embodiment of the catalytic composition, the first catalyst is titanium dioxide TiO2, the second catalyst is manganese monoxide MnO and the adsorbent is a zeolite. The zeolite preferably is a synthetic hydrophilic zeolite of type A.
Additionally, this invention relates to an embodiment of the catalytic composition, in which the amount of the first catalyst is lower than 27% and higher than 30%, the amount of the second catalyst is lower than 11% and higher than 17% and the amount of the adsorbent is lower than 55% and higher than 59%, each in weight percent and with regard to their total mass. All further preferred configurations and embodiments described herein apply to this specific embodiment.
The applicants used different catalytic compositions on multiple organic compounds. The following table shows the rate of elimination of the different compounds in mg of a carbon equivalent of each compound per hour [mgC/h], using different catalytic compositions. The use of the carbon equivalent serves to improve the comparability of the numbers and compensates for the fact that the different compounds have a different number of carbon atoms, which leads to a different amount of degradation reactions depending thereupon. Isopropyl alcohol is abbreviated as IPA and butanone as MEK. The relative amount of the components is displayed in weight percent with regard to the total mass of the composition. Titanium dioxide is abbreviated as T, Manganese monoxide as M and the hydrophilic synthetic zeolite of type A as ZA.
As can be taken from the table above, the different compositions showed different elimination rates with respect to the different compounds. It can be seen that, each, the sole titanium dioxide (composition F) and the sole manganese monoxide (composition E) were in general less effective than the combinations of two catalysts and an adsorbent. It can also be seen that the compositions H, B and C showed a greater or equal efficiency compared to compositions F and E as well as the combination of manganese monoxide and the zeolite (composition D). This is true with the exception of ethanol, which was eliminated with a higher efficiency at composition D.
Therefore, the combination of the two different catalysts and the adsorbent show a synergistic effect over the sole catalysts or the combination of manganese monoxide with a zeolite.
For the following investigations, composition C was used, since it showed an overall good elimination profile, but especially on the hydrophilic compounds IPA, ethanol and MEK. The efficient elimination of these hydrophilic compounds gives reason for the assumption that such a composition is also efficient on microbial contaminants, since the cell walls of most microbial contaminants are hydrophilic.
In order to demonstrate the efficiency, the following experiments were performed with biological contaminants, using
The experiments were performed in an isolator of class A with 0.8 m3 in which an apparatus having the sandwich design as described above was arranged. The carrier was made of aluminum in the honeycomb shape. The UV radiation source was a UV-C emitting lamp of 18 W.
An aerosol generator is used to provide the air flow within the isolator. Each time the air comprises only one of the mentioned contaminants. The contaminated air is then treated with the apparatus.
In order to demonstrate the efficiency of the treatment, a bio collector is used to collect samples from the air before and after the treatment, to provide a comparison.
The samples are used to prepare a culture in a medium corresponding to the contaminant used.
For Legionella pneumophila a BYCE medium obtained from Biomerieux is used, containing agar and L-cysteine.
For Bacillus subtilis an LB Luria Bertani medium is used.
For the T2-bacteriophages a medium comprising E. Coli BAM was used and the number of lysis plagues deriving from active virus was examined.
The results show a decrease of 2 log (99.45%) for Legionella pneumophila, 1 log (96.67%) for spores of Bacillus subtilis and 3 log for the bacteriophages T2 (99.98%) after the treatment compared to the air before treatment.
Furthermore additional similar experiments were performed using different biological and chemical contaminants. These were performed within a microbiological safety cabinet having a volume of 0.537 m3. The apparatus was running for 10 minutes. Afterwards and beforehand, the samples were collected for comparison. No outlet filter was used.
The reduction of human coronavirus strain 229E (H-CoV-229E) was >log 2.2 (>99.4%).
The reduction of Staphylococcus aureus CIP 4.83 after a running time of 15 minutes was log 1.3 (94.9%).
Another similar set of tests was performed using different biological contaminants.
These were performed with the apparatus having the sandwich design and a HEPA exit filter. The flow rate was 1000 or 1400 m3/h and the duration 6 minutes.
The efficiency for removing Staphylococcus epidermidis (ATCC 14 990) was >99.88% and for removing Aspergillus brasiliensis (ATCC 16 404) >99.75% at 1400 m3/h. The efficiency for removing Staphylococcus epidermidis (ATCC 14 990) was >99.91% and for removing Aspergillus brasiliensis (ATCC 16 404) >99.82% at 1000 m3/h.
The same tests were performed without the use of the HEPA filter: The efficiency for removing Staphylococcus epidermidis (ATCC 14 990) was 92.94% and for removing Aspergillus brasiliensis (ATCC 16 404) 93.59% at 1400 m3/h. The efficiency for removing Staphylococcus epidermidis (ATCC 14 990) was 96.32% and for removing Aspergillus brasiliensis (ATCC 16 404) approx. 90.00% at 1000 m3/h.
Additionally the removal of airborne cat allergens (Fel d 1) was examined using the HEPA filter and a flow rate of 1400 m3/h. The efficiency lay between >99.80% and >99.86%.
Also the reduction of VOC was examined, applying an air flow of 1000 m3/h using filters (A) and without using filters (B) and 1400 m3/h using filters (C) and without the use of filters (D).
The efficiency for removing acetaldehyde was 31.5%±20% (A), 39.4%±11.1% (B), 45.5%±11.0% (C) and 56.2%±8.2% (D).
The efficiency for removing acetone was 98.1%±1.7% (A), 94.5%±0.5% (B), 90.5±1.3% (C) and 100%±2.3% (D).
The efficiency for removing acidic acid was 99.7±0.1% (A), 99.3±0.2% (B), 99.5%±0.10% (C) and 99.4%±0.1% (D).
The efficiency for removing heptane was 98.0±0.2 (A) and toluene 98.4%±0.1% (A).
| Number | Date | Country | Kind |
|---|---|---|---|
| 20208188.1 | Nov 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/081923 | 11/17/2021 | WO |
