A process for treating a catalyst arranged for catalytic oxidation of at least one volatile organic compound (VOC), and a catalyst treatment system for use in said process

Abstract

The present invention relates to a process for treating a VOC- catalyst (3) arranged for catalytic oxidation of at least one volatile organic compound (VOC), said process comprises passing a gaseous fluid comprising ozone at a concentration of at least 0.2 ppm over / through the catalyst (3), and wherein said process is carried out at a temperature below 50 oC. The treatment process comprises two processes a regeneration process and a suppression process, and when the gaseous fluid comprising ozone is passed over the catalyst, any coke deposits on the VOC-catalyst will be at least partly removed, and further coke deposits are effectively prevented from being accumulated on / in the VOC-catalyst.

Description

[0001] A process for treating a catalyst arranged for catalytic oxidation of at least one volatile organic compound (VOC) , and a catalyst treatment system for use in said process .

[0002] The present invention relates to a process for treating a catalyst arranged for catalytic oxidation of volatile organic compounds (VOCs ) from a gas stream .

[0003] Organic compounds with a boiling point below 250 ° C and saturated vapour pressure equivalent to the atmospheric pressure ( 101 . 325 kPa) are identified as volatile organic compounds (VOCs ) . There exists a large number of VOCs include aromatics , aliphatic hydrocarbons , oxygenated VOCs , halogenated VOCs , sulphur- or nitrogen-containing VOCs , some of which originates from the nature , but the main problematic source of VOC emissions originates from industrial activities , e . g . the chemical industries , food processing, etc .

[0004] VOCs have a high volatility at ambient conditions and since some VOCs are very harmful to the respiratory system and central nervous system even at low concentrations , it is extremely important to reduce their emissions into the atmosphere / surrounding environment .

[0005] There exist a large number of techniques for elimination and / or reducing emissions of VOCs originating from the industry . The commonly used technique is terminal control , i . e . recovering or destroying the produced VOCs . Terminal control technologies include adsorption, absorption, condensation, membrane separation, plasma method, biological degradation, catalytic oxidation and direct combustion . Among them, catalytic oxidation technology has attracted wide attention for its advantages of low catalytic temperature , low toxicity, high efficiency, environmental friendliness , simple equipment , and no secondary pollution . Unfortunately, VOC-catalyst s , i . e . catalysts arranged for removal of VOCs tend to slowly deteriorate in performance when used repeatedly or in a continuous process for a prolonged period of time . The catalyst activity decreases with time to a point where continued use of the catalyst is no longer economically viable . Due to the relatively high cost of synthesi z ing this type of catalyst , regeneration of the used / deact ivated catalyst is greatly preferred over replacement .

[0006] Most spent / deactivated catalysts are regenerated of f-site , i . e . the catalysis reactors and processes have to stop for disassembling the deactivate catalysts and transport them to the regeneration factory . This way is inconvenient and delays the continuous operation of industrial processes . Accordingly an in-situ regeneration of a deactivated catalyst is more convenient and attractive .

[0007] Many intrinsic mechanisms are known to cause catalyst deactivation, e . g . poisoning due to the chemisorption of certain species on the active sites ; thermal sintering and carbonaceous deposits ( coke ) on the surface and / or in the pores of the catalytic material . Some of these mechanisms might lead to permanent deactivation, but catalyst deactivation due to coke deposition is usually reversible .

[0008] The most frequently used methods to regenerate coked catalysts are carried out by heating or injecting a hot steam, hydrogen, oxygen, and different oxidants , reductants , or organic solvents into / over the catalytic material / reactor .

[0009] In fact , in most industrial processes , coke is typically burned off with air ( oxidation with 02) at high temperatures (between 400°C and 700°C) to reactivate the spent catalyst . However, one of the challenges is the exothermicity of coke burning, which may cause hot spots , local high temperature gradients , and eventually cause irreversible damage to the catalyst . Thus , temperature reduction becomes critical in order to avoid thermal damage during coke regeneration . Furthermore , the use of high temperatures is energy consuming and accordingly expensive .

[0010] One way to promote the coke combustion rate and reduce the regeneration temperature is to modify the catalysts with metals ; however such strategies have known to potentially result in reduced catalyst stability and regenerability . Other ways is to adjust the O2concentration in the regeneration flow; adjust the flow rate ; temperature ; and / or use different oxidising agents .

[0011] One promising approach is to use the oxidant agent ozone (O3) that is known to have strong oxidi z ing properties . Such a system is e . g . known from CN210131538 that discloses an indoor air centrali zed purification device comprising a catalyst for removal of VOCs that can be regenerated using oz one . However, the document discloses that the regeneration process requires heating in order to obtain an effective removal of coke from the catalyst material .

[0012] Thus , it is one aspect of the present invention to provide a process for treating a VOC catalyst , using much les s energy for the regeneration process compared to the traditional regeneration systems and methods ,

[0013] It is a second aspect of the present invention to provide a process for regenerating a coke-contaminated catalyst without heating the catalyst and / or the gas that is passed over the catalyst ,

[0014] It is a third aspect of the present invention to provide a process for regenerating a coke-contaminated catalyst which does not require addition of expensive oxidi z ing agents thereby reducing both costs and space for storage facilities ,

[0015] It is a fourth aspect of the present invention to provide a process for regenerating a coke-contaminated catalyst that is simple and reliable to use , and which preferably provides a continuous regeneration of said catalyst , and

[0016] It is a fifth aspect of the present invention to provide a process for suppressing and / or preventing coke from being deposited on / in a catalyst , thereby eliminating the drawbacks that may result from a coke-contaminated catalyst .

[0017] The novel and unique features whereby these and further aspects are achieved according to the present invention is by providing a process for treating a catalyst arranged for catalytic oxidation of at least one volatile organic compound (VOC) , said process comprises passing a gaseous fluid comprising ozone at a concentration of at least 0 . 2 ppm through / over the catalyst , and wherein said process is carried out at a temperature below 50 °C .

[0018] The treatment process can either be a regeneration process , i . e . a process for regenerating an at least partly coke- contaminated catalyst and / or a suppression process i . e . a process suppressing and / or preventing accumulation of carbonaceous species ( coke ) on / in the catalytic material .

[0019] In principal the two processes i . e . the regeneration process and the suppression process are identical . A gaseous fluid comprising a relatively high concentration of ozone ( 0 . 2 ppm or more ) is passed over / through the catalyst i . e . the catalytic bed / material . The main difference is whether any carbonaceous species already has been deposited on the catalyst (whereby the catalyst is at least partly deactivated) or no such deposits has accumulated in / on said catalyst . In either case , when the gaseous fluid comprising ozone is passed over the catalyst , any coke deposits will be at least partly removed, and further coke deposits are effectively prevented from being accumulated on / in the VOC-catalyst .

[0020] Ozone has a high oxidation potential ( 2 . 07V) , and the inventors of the present invention has shown that by using relatively high concentrations of ozone ( 0 . 2 ppm or more ) it i s possible at low temperatures , i . e . below 50 °C to provide an efficient regeneration of a coke-contaminated catalyst and / or to prevent the catalyst from being coke-contaminated by preventing depositions of coke to accumulate on the surface and / or in the pores of the catalytic material . Furthermore , since the operating temperature of the process is below 50°C, the risk of hydrothermal degradation, and / or metal sintering of the catalyst during the treatment process are completely eliminated . It is further preferred that the proces s is carried out at a temperature above 20 °C, preferably between 25 °C and 40°C in order to obtain an efficient treatment process .

[0021] Within the context of the present invention the term "gaseous fluid"' refers to a gas-flow that comprises ozone and which is passed over the catalyst during the treatment process , i . e . the regeneration and / or the suppression process . The term " coke- contaminated catalyst" means a catalyst in which carbonaceous deposits ( coke ) is deposited on the surface and / or in the pores of the catalytic material whereby the activity of the catalyst is reduced, at least to some extend . The term "VOC-catalyst" refers to a catalyst arranged for catalytic oxidation of at least one volatile organic compound (VOC) , however the term " catalyst" and "VOC-catalyst" are used interchangeably .

[0022] The gaseous fluid comprises a concentration of ozone of at least 0 . 2 ppm . However, a faster and more efficient treatment process may be provided if the concentration of ozone in the gaseous fluid is higher . It is in this respect preferred that the concentration of ozone is least 0.5 ppm, or at least 1 ppm, or at least 1.5 ppm or even more preferred at least 2 ppm, and even more preferred at least 3 ppm, as the inventors of the present invention has found that such concentrations effectively can be used for both the regeneration process and the suppression process.

[0023] However, when the treatment process aims at regenerating a coke-contaminated catalyst VOC-catalyst , i.e. when the treatment process is a regeneration process, it is preferred that the concentration of ozone in the gaseous fluid is at least 0.5 ppm, preferably at least 1 ppm, whereas lower ozone concentrations i.e. around 0.2 - 0.5 ppm in the gaseous fluid is sufficient when the treatment process is a suppression process, i.e. when it aims at preventing any deposits from being accumulated on the catalyst, as the organic material in the suppression process continuously is removed from the exhaust gas .

[0024] In a preferred embodiment the ozone concentration is at least 0.2 ppm and less than 1 ppm, as said concentration has proven highly advantageously for both treatment processes according to the present invention, i.e. both the regenerating process and the suppression process.

[0025] The feed gas for the gaseous fluid may in one preferred and especially inexpensive embodiment be ambient air. However other feed gases can also be used in the process according to the invention, e.g. an exhaust gas to be treated in the VOC- catalyst, and wherein said exhaust gas comprises one or more VOCs; oxygen; oxygen enriched air or oxygen enriched exhaust gas (e.g. comprising more then 50 vol% oxygen) ; and / or air enriched with other oxidants etc. The only requirement being that the gaseous fluid that is passed over / through the catalyst comprises at least 0.2 ppm ozone, preferably at least 0.5 ppm ozone and even more preferred at least 1 ppm ozone in order to provide the gaseous fluid used in the treatment process according to the invention .

[0026] Due to the relatively high concentration of ozone , i . e . at least 0 . 2 ppm in the gaseous fluid, the inventors has found that it is not required to heat the gaseous fluid and / or the exhaust gas before it is passed over the catalyst , as the ozone effectively will decompose the carbonaceous deposit s on / in the catalyst . Thus , the relatively low temperature used in the process according to the invention reduces the required energy consumption and accordingly the environmental impact of the process .

[0027] Ozone may be produced in an ozone generator and added to the feed gas in the relevant concentration thereby providing the gaseous fluid .

[0028] It is however preferred that the ozone is generated by one or more first UV-lamps arranged for operating in an UV-spectrum which produces ozone .

[0029] The present invention also relates to a treatment system for a catalyst arranged for catalytic oxidation of at least one volatile organic compound (VOC) , said regeneration system comprises a

[0030] - a VOC-catalyst , optionally a coke-contaminated VOC- catalyst , and

[0031] - at least one ozone generating zone comprising at least one UV-lamp arranged for generating ozone from a feed gas in a concentration of at least 0 . 2 ppm, wherein said system is arranged for being operated at a temperature below 50 °C .

[0032] Said treatment system may be a regeneration system for regenerating a coke-contaminated VOC-catalyst , and / or a suppression system arranged for preventing coke from depositing on the VOC-catalyst Ozone generation from UV light typically happens below 240 nm, preferably between 170 nm and 190 nm, such as e.g. 172 nm and / or 185 nm, where the photons emitted from the UV-lamps splits oxygen molecules into two single oxygen atoms, which then combines with a naturally occurring oxygen molecule to form an ozone molecule. It is accordingly preferred that the feed gas comprising oxygen, e.g. air or oxygen-enriched air, and is passed into the ozone generating zone in order to generate a gaseous fluid comprising ozone at a concentration of at least 0.2 ppm. In this way ozone can be generated on site via the at least one UV-lamps, and since it is used immediately, no storage area is required for the ozone. The ozone generation zone is preferably placed upstream of the catalyst, i.e. before said catalyst seen in the flow direction gas flow though the catalyst treatment system.

[0033] In a preferred embodiment according to the present invention the exhaust gas to be treated is also passed through / over the ozone generation zone, i.e. said gas flow is allowed to pass over the at least one UV-lamp before it enters into the VOC- catalyst. In this way the feed gas for the gaseous fluid may comprise (consist of) the exhaust gas to be treated, e.g. in combination with ambient air and / or additional oxygen.

[0034] The VOCs (and potentially other organic contaminants) present in the exhaust gas will be decomposed by the ozone, thereby reducing the concentration of the VOCs. In addition to generating ozone, the generated radiation (emitted photons in the UV and VUV range) from the UV-lamps will both break down the VOCs through the process of photolysis, and generate hydroxyl radicals, i.e. additional oxidants, which also assist in oxidising / removing / decomposing the VOCs present in the exhaust gas. This will overall result in lower concentrations of VOCs in the exhaust gas before it enters the VOC-catalyst , where the remaining concentrations of VOCs are removed. Thus , the unique process according to the invention, will ensure that ozone is produced by the UV-lamps whereby not only carbonaceous deposits on / in the catalyst effectively is removed, but the photons / ozone will also assist in decomposition VOC in the exhaust gas before said exhaust gas enters the VOC-catalyst , and in this respect reduce the amount of carbonaceous species that can be deposited on the catalyst . Accordingly, a more effective oxidation process of the exhaust gas is provided, less or no coke is deposited on the VOC- catalyst , and said catalyst will accordingly have a longer lifetime .

[0035] In a preferred embodiment the feed gas and / or exhaust gas also passes over at least one second UV-lamp operating in an UV- spectrum specifically arranged for generating hydroxyl (OH) radicals in the presence of 02and H20, i . e . in an UV-spectrum below 305 nm . In addition to the strong oxidant : hydroxyl radical , additional oxidants , e . g . excited oxygen species , e . g . 'OH, 0^ , 03P to be generated from oxygen present in the feed gas , which may also assist in oxidise / remove / decompose VOCs present in the exhaust gas .

[0036] Said first and second UV-lamps may be the same or different UV- lamps , it is however preferred that the feed air and / or exhaust gas passes one or more first UV-lamps arranged for emitting a first wavelength, and one or more second UV-lamps arranged for emitting a second wavelength, and wherein the first and the second wavelength is different . This will ensure that feed gas passing though the system according to the invention will be exposed to photons having different wavelengths . For instance , if the first UV-lamp ( s ) emits a wavelength of 172 nm (generating ozone ) and the second UV-lamp ( s ) emits a wavelength of 185 nm (generates -OH) , the exhaust gas will in one embodiment , be subjected to both wavelengths providing a more effective treatment of the catalyst . I f the system according to the invention comprises at least one UV-lamps arranged for generating OH-radicals it is preferred that the catalyst treatment system comprises a water vapour delivery system arranged for increasing the relative humidity and / or absolute water content of the feed gas and / or exhaust gas to at least above 90% , in order to ensure that the radicals are generated at highest efficiency .

[0037] At least one or more further UV-lamps e . g . a third, forth and fifth etc . UV-lamp ( s ) may also be provided emitting, a third, forth and fifth, etc . wavelength respectively . Thus , in addition to having at least one first UV-lamp for generating the relevant concentrations of ozone , the system can in a preferred embodiment comprise at least one second, third etc . UV-lamp emitting a wavelength arranged for a different purpose , e . g . for decomposing one or more VOCs before the exhaust gas reaches the catalyst . For instance , an exhaust gas comprising formaldehyde may require use of a different wavelength than an exhaust gas comprising benzene . Further groups of UV-lamps may be added if the exhaust gas comprises several VOCs . In this respect , the UV-lamps may be individually arranged for removing or reducing the concentration of one or more relevant VOCs , and the process and system according to the invention may accordingly be constructed to meet different requirements depending on the pollutants / compounds in the exhaust gas to be treated .

[0038] The photons emitted from the UV-lamps may also assi st in the regeneration process , especially if the UV-lamps are placed in close proximity to the catalyst . In a preferred embodiment according to the invention, the UV-lamps is preferably arranged such that the entire outer surface of the catalyst in addition to being subjected to ozone also is subjected to photons emitted from the UV-lamps , i . e . the number, orientation and position of the UV-lamps relative to the catalyst (s) are selected in order to obtain said effect.

[0039] It is accordingly preferred that the outer surface of the catalyst is placed in close proximity to the one or more UV- lamps. For instance, when the UV-lamps emit a wavelength of 172 nm the UV-lamps may be placed relative close to the outer surface of the catalyst. As an example can be mentioned that the longitudinal axis of the elongated UV-lamps is placed in parallel with an outer plane surface of the catalyst, such that the shortest distance (taken in cross-section) between the surface of the UV-lamp(s) closest to the catalyst, and the outer surface of the catalyst is less than about 2 cm, and preferably lower, e.g. 1.5 cm or even more preferred 1.0 cm.

[0040] In one embodiment UV-lamps are placed on more than one side of the catalyst, e.g. both before and after the catalyst, seen in the flow direction of the exhaust gas, thereby ensuring that substantially the entire outer surface of the catalyst is subjected to the emitted photons, thereby effectively cleaning / treat ing the catalyst. It should be noted, that the distance between the surface of the catalyst and the UV-lamps depends on the wavelength emitted, and if the emitted wavelength is e.g. 254 nm the shortest distance between the UV- lamps and the outer surface of the catalyst may be longer, e.g. between meter and 1 meter.

[0041] It is preferred that some or all of the UV-lamps are excimer lamps. Excimer lamps are quasi-monochromat ic light sources available over a wide range of wavelengths in the ultraviolet (UV) and vacuum ultraviolet (VUV) spectral regions. The operation of excimer lamps is based on the formation of excited dimers (excimers) . These excimer formations are unstable and will disintegrate within nanoseconds, giving up their excitation (binding) energy in the form of photons (radiation) at a characteristic wavelength. In one advantageous embodiment , the excimer lamps emit a wavelength of about 172 nm . The inventors of the present invention have found that this wavelength in a very energy efficient way is capable of removing / decomposing a large number of VOC ' s by means of photolysis from the exhaust gas (thereby preventing coke-deposits on the catalyst ) , and at the same time produce ozone in the relevant concentrations to regenerate the catalyst , i . e . remove any deposits that might have accumulated on said catalyst .

[0042] In a preferred embodiment according to the present invention, the excimers are produced using the rare gases , i . e . He2, Ne2, Ar2, Kr2and Xe2, or the rare gas halides (e . g . ArF , KrF , XeCL and XeF ) . However, halogen and mercury halogen mixtures (e . g . HgCl , HgBr and Hgl ) are also contemplated within the scope of the present invention .

[0043] The excimers may be produced according to the present invention, by silent electrical discharge where the relevant gas for producing the excimers , e . g . xenon, are placed in a gap between two concentric quarts tubes . This technology is are well known and will not be discussed in further details in this application, however one preferred excimer lamp for use in the present invention may be a xenon lamp obtained from USHIO America Inc .

[0044] The wavelength of the emitted photons depends on the gas used to provide the excimer . This means that different wavelengths of the photons can be obtained by selecting an excimer lamp with the gas of interest . For instance , a xenon excimer lamp will generate radiation with a wavelength of 172 nm, whereas an argon excimer lamp will provide a wavelength of 129 nm and a krypton fluoride excimer lamp will provide a wavelength of 222 nm . A complete list of the relevant wavelength can be found in the literature . The use of excimer lamps offer a number of advantages , high intensity at a defined wavelength, no-self absorption, and flexibility in the construction of the air treatment system according to the present invention .

[0045] Since only a single gas is used in each excimer lamp, the radiation output by the excimer lamps is restricted to a narrow UV wavelength range . This allows a perfect match with the absorption spectrum of the carbonaceous compounds that are deposited on the catalyst material and shall be removed from said catalyst and / or from the exhaust gas . Furthermore , one or more of the excimer lamps may be selected in order to match the absorption spectrum of one or more specific compounds in the exhaust gas that are to be treated .

[0046] A further advantage of using excimer lamps is that they only generate little heat , making them highly suitable for use in a process for treating a catalyst that is carried out at a low temperature , i . e . below 50 °C . In addition, excimer lamps may have a long lifetime because the electrodes are not in direct contact with the discharge gases and will thus avoid any corrosion during the discharge process and no contamination of the excimer gas , as is often the situation in conventional UV- mercury lamps leading to a short operating lifetime . Finally, non-toxic materials are used in the excimer lamps and thus inherently, there is no environmental problem .

[0047] The catalyst treatment system according to the invention may in a preferred embodiment comprise a control unit arranged for controlling the operational mode of the catalytic treatment system and accordingly the process according to the invention . In this respect , a number of ozone sensors are preferably placed in the ozone generation zone , in an area between the ozone generation zone and the catalyst , and / or after the catalyst , such that the ozone concentration can be monitored and adjusted if necessary. For instance, if the ozone concentration is either to high or to low, the control unit may via conventional means be arranged for adjusting said concentration, e.g. by switching the one or more first UV-lamps on / off; by adjusting the oxygen concentration in the feed gas; by adjusting the flow rate of the feed gas, etc.

[0048] The control unit may also control other functions and parameters of the catalyst treatment system e.g. adjust the flow rate of the exhaust gas and / or the feed gas, control the speed of a fan arranged for drawing the gas-flows through the system, etc. The may in this respect comprise a number of additional sensors, e.g. temperature sensors, flow rate sensors, oxygen concentration sensors, humidity sensors etc. and which also sends information to the control unit such that said process parameters can be adjusted if relevant. A person skilled in the art will understand that the catalyst treatment system may comprise a number of units, e.g. ducts, valves, switches etc. in order to effect said parameter changes. Such units are well known in the art of process engineering and will not be discussed in further details in this application.

[0049] The control unit can in one embodiment deactivate the UV-lamps for a certain period of time, e.g. if the concentrations of ozone exceeds a certain limit, e.g. 5 ppm. Any coke that may accumulate on the catalyst during said period, can later be removed in the regeneration process with the UV-lamps are switched on again. It is however preferred that the UV-lamps are turned on all the time, in order to reduce accumulation of coke on the catalyst.

[0050] The control unit may e.g. be operative via a simple manual operation by an operator, but it is preferred that the control unit controls / monitors the system and process automatically based on information received by the sensors, such that an operator only needs to intervene in the process in exceptional cases , e . g . if a failure is detected .

[0051] A person skilled in the art will understand that if the exhaust gas comprises large concentrations of VOCs , VOCs that are not decomposed by the generated ozone and optionally radicals / photons , will be decomposed by the VOC-cat alyst , such that the treated gas only comprises VOCs in concentrations below the allowable threshold for the respective VOC . However, this may result in coke-deposits being accumulated on the catalytic material , even though is in a lower degree than if the exhaust gas was not subjected to the ozone treatment before it reaches the catalyst . In such a situation, the system according to the invention is arranged for regenerating the catalyst by e . g . cutting off the flow of exhaust gas to the ozone generating zone and instead directing a feed gas that is free from any VOC over the ozone generating zone (thereby providing a gaseous fluid without VOCs ) whereby an effective regeneration process of the VOC-catalyst can be performed .

[0052] The VOC-catalyst can be any kind of conventional catalyst as long as it can remove one or more VOCs . Catalysts used for the oxidation of VOCs can be classified into three maj or groups : noble metals catalysts , non-metal oxide catalysts , and mixed- metal catalysts .

[0053] In this respect supported precious metal catalysts in monolith, honeycomb, or pellet forms are well known oxidation catalysts having high act ivity and stability and are widely used for various gas phase VOC emission control needs . As an alternative , due to the high cost of precious metal s such as platinum and the catalyst sensitivity to some poisons such as sulphur and halogen-containing components have motivated the search for effective dispersions of noble metals and poisonresistant alternatives for such oxidation catalysts . Non-noble metal oxide catalysts , although generally less active than the noble metal catalysts, are also widely used for oxidation of VOCs because of their lower cost.

[0054] It is however preferred that the catalyst is a supported precious metal catalysts in either monolith, honeycomb, or pellet forms. Preferred catalysts comprise platinum (Pt) and / or palladium (Pd) as catalytically active components, e.g. supported on aluminium (e.g. A12O3) , activated carbon, cobalt (e.g. CO3O4) , a foam (organic or inorganic) or cardboard. Alternatively the catalyst can comprise mixed oxides of manganese and copper with different wt% of copper, or manganese based catalysts supported on Y_A1203. All of which the inventors has found have an especially high potential of being reactivated using ozone.

[0055] The catalyst is preferably arranged for removing one ore more of the following VOCs: propane, butane, methyl chloride, formaldehyde, vinyl chloride, carbon tetrachloride, toluene, acetone, isopropyl alcohol, hexanal, and carbon disulfide, all of which are considered toxic to humans in relatively low concentrations .

[0056] Due to the relatively high concentrations of ozone in the gaseous fluid (at least 0.2 ppm) , there may be an excess amount of ozone that is not used to regenerate the catalyst and / or to oxidize the organic substances in the exhausts gas.

[0057] Ozone is a hazarded gas and relatively low amounts of ozone can cause chest pain, coughing, shortness of breath, and throat irritation. Ozone may also worsen chronic respiratory diseases such as asthma and compromise the ability of the body to fight respiratory infections.

[0058] Several federal agencies have accordingly established health standards or recommendations to limit human exposure to ozone. As examples can be mentioned that the Food and Drug Administration (FDA) requires ozone output of indoor medical devices to be no more than 0.05 ppm, the Occupational Safety and Health Administration (OSHA) requires that workers not be exposed to an average concentration of more than 0.10 ppm for 8 hours and the National Institute of Occupational Safety and Health (NIOSH) recommends an upper limit of 0.10 ppm, not to be exceeded at any time.

[0059] The half-life of Ozone is approximately 7 to 20 minutes depending upon temperature, pH, humidity and the amount of contaminants in the air.

[0060] Thus, in order to ensure that only the allowed concentrations of ozone are let out into the atmosphere, the catalyst treatment system may comprise an ozone decomposing unit arranged after the catalyst (seen in the flow direction) and before the outlet of said system.

[0061] Said ozone decomposing unit may be any kind of unit arranged for decomposing ozone, e.g. one or more addition UV-lamps (e.g. excimer lamps) operating in a wavelength area which will decompose ozone, i.e. in an area around 254 nm.

[0062] Alternatively, or in addition, the VOC-catalyst may be arranged for both decomposing VOCs and ozone, or the system may comprise an additional catalyst arranged for decomposing ozone.

[0063] Catalysts arranged for decomposing ozone are known in the art, and may e.g. be a substrate with a catalyst material of a type known in the art for ozone decomposition, such as a catalyst including platinum and a base metal.

[0064] In any case the ozone decomposing unit is arranged for reducing the content of ozone in the treated air, e.g. by converting ozone into oxygen, thereby ensuring that the ozone concentration in the surroundings will stay well below the mentioned standards and recommendations for limiting human exposure to ozone .

[0065] Irrespectively of the individual arrangement of the catalyst , the inventors of the present invention has found that when the catalyst is operated at relatively low temperatures , i . e . between 20-50°C, preferably between 25 °C and 40°C a very effective regeneration of the catalyst is provided .

[0066] In comparison a standard regeneration process of a catalyst arranged for catalytic oxidation of VOCs operates at a temperature of between at least 400 °C and 700 °C, thus the treatment system according to the invention provides a very simple and effective means for reducing the energy needed to regenerate a catalyst arranged for removing VOCs from an exhaust gas .

[0067] Due to the relatively low operation temperature , below 50°C during regeneration, it is not required to heat the exhaust gas before said gas enters the catalytic, thereby reducing energy and cost for the regeneration process significantly .

[0068] The temperature of the exhaust gas will of course depend on the origin of said gas , however if said exhaust gas does not have a temperature in the optimal temperature range , e . g . between 20 °C - 50 °C, preferably between 25 °C and 40 °C it is preferred that said gas is heated and / or cooled before entering the ozone generating zone , by passing the said gas through a temperature conditioning zone placed before the catalytic zone . Said temperature conditioning zone i s arranged for providing a conditioned exhaust gas , i . e . an exhaust gas streams having a temperature between 20-50°C, preferably between 25 °C and 40°C . The heating and / or cooling of the exhaust gas can be achieved in any conventional way, e . g . by heat ing / cooling it in a heat exchanger . It is not preferred to heat the exhaust gas above 50 ° C, or cool it below 18 ° C as this may negatively influence the energy efficiency of the catalyst .

[0069] Even in situations where the exhaust gas to be treated has a temperature in the optimal temperature range , it may still be advantageously to pass the exhaust gas through a temperature conditioning zone , as this will ensure that the operation temperature in the catalytic zone is always optimal and that variations in the exhaust gas will not negatively influence the treatment process .

[0070] In a preferred embodiment the catalyst treatment system comprises a flow rate controlling means arranged for providing a turbulent flow of the gaseous fluid comprising 0 . 2 ppm ozone . Said flow rate controlling means may be the fan arranged for generate the flow though the system, and preferably has a speed that provide a flow rate of the gaseous fluid between 0 . 5 m / s and 2 m / s , as such a flow rate will provide the desired turbulent flow over the catalyst especially when the catalyst has a honeycomb structure / f orm . A turbulent flow wi ll increase mixing and react ion time of the compounds flowing through the catalyst , while minimi z ing the pressure drop of the flow streams across the honeycomb catalyst .

[0071] In order to provide the relevant flow through the regeneration system according to the invention, the system may be placed in an exhaust duct and may comprise at least one fan for providing the desired flow rate . In addition said system may comprise further units normally associated with an exhaust system e . g . filters placed before and / or after the catalyst ( s ) ; ducts and valve for sub-streams , e . g . for enriching the feed gas with oxygen, etc .

[0072] In a preferred embodiment according to the present invention the treatment system according to the invention is arranged for being retrofitted into an existing gas treating system at a relevant work stations in plants , factories and other sites that produces gas emissions comprising at least one VOC . This local treatment contributes to a highly improved working environment and reduces cost for expensive installation of new equipment .

[0073] The invention will be explained in greater detail below, describing only an exemplary embodiment of the catalyst treatment system and process of using said system with reference to the sole drawing, in which

[0074] Fig . 1 schematically shows a simplified embodiment of a catalyst treatment system 1 according to the invent ion,

[0075] Fig . 2 illustrates the ozone concentration before ( circles ) and after ( squares ) a VOC-catalyst in example 1 ,

[0076] Fig . 3 illustrates the adsorption of formaldehyde on the catalyst surface over time in example 2 , and

[0077] Fig . 4 illustrates the removal of formaldehyde over time in example 2 .

[0078] The catalyst treatment system 1 according to the invention comprises an ozone generating zone 2 , a VOC-catalyst 3 and a control unit .

[0079] The system comprises a housing (e . g . a duct in a gas exhaust system) 5 having an air inlet 6 and an air outlet 7 , and a fan 8 arranged for drawing the air through the system 1 . In the embodiment shown the fan 8 is arranged near the outlet 7 , but said fan could be placed anywhere in the housing 5 , the only requirement being that the fan is capable of drawing air through the system, and preferably also is capable of creating a turbulent flow over the catalyst , especially if the catalyst has a honeycomb structure . The ozone generating zone 2 comprises five UV lamps 9 that may be the same, e.g. arranged for producing ozone or they may be different i.e. arranged for emitting two or more wavelengths. In the embodiment shown in the figure four of the UV lamps 9 emits a wavelength of 172 nm, i.e. they will produce ozone, and one of the UV lamps 9' will emit a wavelength of 185 nm, i.e. it will increase the production of radicals in the feed gas. The number of UV-lamps may of course be higher or lower, be arranged in groups, in a matrix etc., the only requirement being that the UV-lamps are capable of producing a concentration of ozone in the feed gas of at least 0.2 ppm, thereby providing the gaseous fluid.

[0080] In the embodiment shown the feed gas is also the exhaust gas Apol, to be treated, i.e. an exhaust gas comprising one or more VOCs e.g. formaldehyde. However said feed gas could equally well be ambient air, oxygen enriched exhaust gas, etc. In addition to generating ozone the UV-lamps will also emit photons in the UV and VUV range that will assist in decomposing the VOCs in the exhaust gas through the process of photolysis and also generate further oxidants (radicals) that will assist in oxidising / removing / decomposing VOCs present in the exhaust gas. Thus, when VOCs in the exhaust gas, Apol, enters the ozone generating zone 2 said VOCs will be subjected to ozone, radicals and radiation by the UV-lamps, which overall will result in lower concentrations of VOCs in the gas flow before it enters the catalyst 2, where the remaining VOCs are removed.

[0081] Thus, the treatment process according to the invention, will ensure that ozone continuously is produced by the UV-lamps, whereby not only any carbonaceous deposits on / in the catalyst effectively is removed, but the photons / ozone will also assist in cleaning the exhaust gas to be treated, and in this respect reduce the amount of carbonaceous species that can be deposited on the catalyst. If the coke is deposited on the catalyst to such an extend that it reduces the effect of the catalyst , the system is arranged such that the flow of exhaust gas can be closed, and a feed gas without any VOCs can be used for the gaseous fluid in order to regenerate the VOC-catalyst . When the catalyst is regenerated, the exhaust gas can be used as feed gas again .

[0082] The UV-lamps 9 used in the present invention may be any UV-lamp capable of submitting photons ( radiation) with the desired wavelength ( s ) . However, in a preferred embodiment the UV lamps 9 are excimer lamps , which offer a number of advantages , high intensity at a defined wavelength, no-self absorption, and flexibility in the construction of the air treatment system according to the present invention . Furthermore , excimer lamps only generate little heat , making them highly suitable for use in domestic faci lities , as cooling is not required before the treated air may be submitted into the surroundings . The UV- lamps 9 in the system 1 may however also be LED-lamps and / or conventional mercury lamps , or combinations of excimer lamps , LED-lamps and mercury lamps .

[0083] Since ozone is hazardous to humans ( it causes injury on the respiratory system) even at low concentrations , the catalyst treatment system 1 may comprise a ozone decomposition unit (not shown) placed between the catalyst 3 and the outlet 7 , which unit is arranged to decompose any remaining ozone in the treated gas flow Atreatbefore it is submitted into the surroundings .

[0084] Said ozone decomposing unit may be any kind of unit arranged for decomposing ozone , e . g . one or more additional UV-lamps (e . g . excimer lamps ) operating in a wavelength area ( around 254 nm) which will decompose ozone , or the system may comprise an additional catalyst arranged for decomposing ozone . The speed of the fan 8 may be adjusted such that the air flow through the ozone generation zone 2 and / or the catalyst 3 can be adapted depending on the area / room to be treated . For instance , the flow rate of the gas to be treated and / or the gaseous fluid comprising ozone , is / are preferably between 0 . 5 m / s and 2 m / s , which will providing a turbulent flow over a catalyst with a honeycomb structure , thereby increasing mixing and reaction time of the compounds flowing through the catalyst .

[0085] The control unit 4 is arranged for controlling the operational mode of the catalyst treatment system 1 according to the invention . This may be by a simple manual operation , but it is preferred that the control unit is operated automat ically .

[0086] In the embodiment shown the air treatment system comprises an ozone sensor 10 arranged for measuring the ozone concentration in an area between the catalyst 3 and the ozone generating zone 2 , thereby ensuring that the gaseous fluid that flows over the catalyst 3 has an ozone concentration of at least 0 . 2 ppm .

[0087] The control unit 4 is also arranged for received information from the ozone sensor 10 and if the ozone concentration is different from the desired value of at least 0 . 2 ppm, takes precautions e . g . activating more or fewer UV-lamps in order to generate more or less ozone . In a similar way the catalyst treatment system may comprise further sensors e . g . temperature , humidity and flow rate sensors , and components e . g . fan, ducts and valves which can be operated and adjusted by the control unit in order to change different process parameters .

[0088] The catalyst treatment system may also comprise an operating unit 11 arranged for communicating with the control unit 4 , and preferably also for receiving and processing data / s ignals relating to the values measured by the sensor 10 , and for transmitting information to an operator . This will enable an operator to constantly monitor the condition of the catalyst treatment system 1, and be alerted centrally, e.g. if the ozone concentration is different from the desired value, etc.

[0089] Examples :

[0090] Example 1 :

[0091] An experiment was performed to investigate the following: i) the applicability of a xenon excimer lamp (X = 172nm - obtainable from Puresphere) for generating ozone in a feed gas in a concentration of at least 0.2 ppm, and i) the VOC-catalyst (Mn / Cu on cordierite, obtainable from Puresphere) capability to efficiently remove ozone at different exposure levels at ambient temperature.

[0092] These experiments were performed in the laboratory on a single pass test unit built to operate at 3000 m3 / h.

[0093] The ozone was produced in situ by four excimer UV lamps (n = 4, X = 172 nm) operating at increase duty cycles from 0.2 to 1.0.

[0094] The ozone concentration was measured with an ozone monitor (2B Tech, Model 211 Ozone Monitor) that was connected to a stream selector measuring before and after the VOC-catalyst.

[0095] Ten ozone levels were investigated. The results of the experiment are shown in Fig. 2. The ten levels were ranging from lowest to the highest possible ozone concentrations produced by the excimer UV-lamp based ozone generating zone.

[0096] The circles indicate the concentration before the VOC-catalyst and the squares shows the outlet ozone concentration after the VOC-catalyst . From the data it can be seen that the excimer UV-lamp based ozone generating zone efficiently achieved ozone inlet concentrations above the effective VOC-catalyst regeneration level combined with high ozone removal efficiency .

[0097] Example 2

[0098] An experiment was performed to investigate the long-term formaldehyde removal efficiency of a VOC-catalyst (Mn / Cu on cordierite , obtainable from Purespherei .

[0099] The test was performed on a laboratory test setup where the VOC- catalyst had a constant flow of ( 0 . 6-0 . 9 m3 / h) . The VOC-catalyst performance with respect to formaldehyde removal ef ficiency was evaluated by exposing the VOC-catalyst to air containing formaldehyde .

[0100] Fig . 3 show the result s from the experiment where the catalyst had been exposed to air containing formaldehyde for 60 hours . The left and right y-axi s shows the removal efficiency of formaldehyde and the concentration of formaldehyde in the test setup, respectively . The decreasing removal efficiency support s that formaldehyde i s adsorbed onto the catalyst surface over time . After the catalyst had been operating for more than 60 hours the experiment was stopped . At thi s point , the removal ef ficiency was reduced to below 15% (gray dot s ) supporting deterioration of the VOC-catalyst due to chemi sorption of formaldehyde on the active sites of the VOC- catalyst and / or carbonaceous deposit s ( coke ) on the surface and / or in the pores of the catalytic material .

[0101] A similar experiment was performed with an air flow containing formaldehyde and ozone . The result s are shown in Fig 4 . The removal efficiency of the catalyst with respect to formaldehyde remained stable above 95% and the experiment was ended after the catalyst had been operating for more than 90 hours supporting no deterioration of the VOC-catalyst due to the regenerative proces s of having ozone present during the catalytic oxidation of formaldehyde . Modifications and combinations of the above principles and designs are foreseen within the scope of the present invention .

Claims

Claims .

1. A process for treating a VOC-catalyst (3) arranged for catalytic oxidation of at least one volatile organic compound (VOC) , said process comprises passing a gaseous fluid comprising ozone at a concentration of at least 0.2 ppm over / through the catalyst (3) , and wherein said process is carried out at a temperature below 50 °C.

2. A process according to claim 1, wherein the process is carried out at a temperature above 20 °C, preferably at temperature between 25 °C and 40°C.

3. A process according to claim 1, wherein the concentration of ozone in the gaseous fluid is at least 0.2 ppm and less than 1 ppm.

4. A process according to claim 1 or 2, wherein the concentration of ozone in the gaseous fluid is at least 0.5 ppm, or at least 1 ppm, or at least 1.5 ppm or even more preferred at least 2 ppm, and even more preferred at least 3 ppm.

5. The process according to any of the preceding claims, wherein the treatment process is a regeneration process for regenerating an at least partly coke-contaminated VOC-catalyst (3) , and wherein the concentration of ozone in the gaseous fluid is at least 0.5 ppm.

6. The process according to any of claims 1, 2, or 3, wherein the treatment process is a suppression process arranged for suppressing / prevent ing accumulation of carbonaceous species (coke) on a VOC-catalyst (3) , and wherein the concentration of ozone in the gaseous fluid is between 0.2 and 0.5 ppm.

7. The process according to any of the preceding claims, wherein ozone is generated in a feed gas by at least one first UV-lamp (9) arranged for operating in an UV- spectrum which produces ozone, thereby providing the gaseous fluid comprising at least 0.2 ppm ozone.

8. The process according to claim 7, wherein said at least one first UV-lamp (9) is arranged for emitting a wavelength between 170 nm and 190 nm, preferably around 172 nm or around 185 nm.

9. The process according to claims 7 or 8, wherein said feed gas comprises or consists of, an exhaust gas comprising one or more VOCs .

10. The process according to claim 9, wherein the exhaust gas is passed over at least one second UV-lamp (9' ) operating in an UV-spectrum arranged for generating radicals, preferably in an UV-spectrum below 305 nm.

11. The process according to any of the claims 7 - 10, wherein at least one of the first and / or second UV-lamps (9, 9' ) are excimer lamps.

12. A catalyst treatment system (1) for a VOC-catalyst (3) arranged for catalytic oxidation of at least one volatile organic compound (VOC) , said catalyst treatment system (1) comprises a VOC-catalyst (3) , and at least one ozone generating zone (2) comprising at least one first UV-lamp (9) arranged for generating ozone from a feed gas in a concentration of at least 0.2 ppm, wherein said system (1) is arranged for being operated at a temperature below 50 °C.

13. The catalyst treatment system (1) according to claim 12, in which the VOC catalyst (3) is at least partly coke- contaminated .

14. The catalyst treatment system (1) according to claim 12 or 13, wherein the ozone generation zone (2) is placed upstream of the VOC-catalyst (3) seen in the flow direction of the exhaust gas.

15. The catalyst treatment system (1) according to any of the claims 12 - 14, wherein the system (1) comprises at least one ozone sensor (10) arranged for determining the ozone concentration in the ozone generation zone (2) .

16. The catalyst treatment system (1) according to any of the claims 12 - 15, wherein the system (1) further comprises one or more additional sensors selected from a temperature sensor, a flow rate sensor, an oxygen sensor and a humidity sensor.

17. The catalyst treatment system (1) according to any of the claims 12 - 16, wherein the system (1) comprises a control unit (4) arranged for controlling the operational mode of the catalytic treatment system (1) e.g. by adjusting the ozone concentration in the ozone generating zone (2) .

18. The catalyst treatment system (1) according to any of the claims 12 - 17, wherein the ozone is generated by the one or more first UV-lamps arranged for operating in an UV-spectrum which produces ozone, preferably in a UV- spectrum around 185 nm.

19. The catalyst treatment system (1) according to any of the claims 12 - 18, wherein the VOC-catalyst has a honeycomb form, and wherein said catalyst comprisesplatinum (Pt) and / or palladium (Pd) as catalytically active components, preferably supported on aluminium, activated carbon, or cobalt.

20. The catalyst treatment system (1) according to any of the claims 12 - 19, wherein the catalyst treatment system (1) comprise an ozone decomposing unit arranged after the VOC-catalyst (3) , seen in the flow direction, and wherein said ozone decomposing unit is a catalyst arranged for decomposing ozone or comprises at least one UV-lamp operating in a wavelength area which will decompose ozone.

21. The catalyst treatment system (1) according to any of the claims 12 - 20, wherein the system (1) comprises flow rate controlling means arranged for providing a turbulent flow of the gaseous fluid comprising 0.2 ppm ozone .

22. The catalyst treatment system (1) according to any of the claims 12 - 21, wherein the flow rate of the gaseous fluid is between 0.5 m / s and 2 m / s .

23. The catalyst treatment system (1) according to any of the claims 12 - 22, wherein the system (1) is arranged for being retrofitted into an existing gas treatment system at a relevant work station in plants, factories and other sites that produces gas emissions comprising VOCs .

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