EP2640510A1

EP2640510A1 - Ozone decomposition catalyst for use in a sterilisation and/or decontamination process

Info

Publication number: EP2640510A1
Application number: EP11808243.7A
Authority: EP
Inventors: James Robert Jennings
Original assignee: Steritrox Ltd
Current assignee: Dow Global Technologies LLC
Priority date: 2010-11-17
Filing date: 2011-11-17
Publication date: 2013-09-25
Also published as: GB2485546A; GB201019389D0; WO2012066295A1

Abstract

The use of a catalyst comprising at least one active metal or metal oxide supported on a mixed titanium/silicon oxide support in the conversion of ozone to oxygen at a temperature of less than 40°C in a humid atmosphere. The catalyst may be employed in a method of sterilisation, decontamination and/or sanitation of an enclosed environment, the method comprising producing a humidified enclosed environment; discharging ozone into the humidified environment; maintaining the ozone and water vapour pressure levels at a concentration that will achieve the required degree of decontamination and passing the substantially decontaminated, sterilised and/or sanitised environment through an ozone depletion catalyst comprising the at least one catalytically active metal or metal oxide supported on a mixed titanium/silicon oxide support to reduce the concentration of ozone to a predetermined level; Optionally, a hydrocarbon containing a carbon-carbon double bond may be introduced into the environment to aid removal of the ozone.

Description

OZONE DECOMPOSITION CATALYST FOR USE IN A STERILISATION AND/OR

DECONTAMINATION PROCESS

This invention relates to an improved catalyst for the conversion of ozone to oxygen in a humid atmosphere, and to the use of said catalyst in a sterilisation and/or decontamination process.

It is a requirement to sterilise and sanitise enclosed spaces, such as kitchen areas and hospital rooms, quickly and effectively in order to destroy potentially harmful micro-organisms, such as bacteria and viruses, contaminating the air and surfaces there within, in an acceptable timescale and to leave said enclosed spaces fit for immediate re-entry.

The biocidal activity of ozone is widely known and appreciated, and it is also known that the provision of ozone in a humid atmosphere increases the biocidal effectiveness .

However, problems associated with the use of ozone as a biocide have been the relatively lengthy post-treatment process to ensure that the environment is safe for returning occupants, the use of potentially environmentally damaging chemicals during the process, the overall lack of simplicity in quickly setting up and using the apparatus, and the relatively short life time of the catalyst systems that may be used for removal of the ozone. The applicant's previous application, GB0904262.3 (GB2468517A) describes a process whereby the beneficial effect of ozone in a humidified atmosphere is utilised with the residual atmosphere being freed from harmful ozone within a useful timescale. The method involves the steps of creating a humidified atmosphere, discharging ozone to provide a specific concentration range and maintaining this degree of humidity and ozone by injecting additional water and ozone when the concentrations fall below given levels for a time period sufficient to achieve the required degree of sterilisation. The ozone concentration is then depleted to a safe level, for example by the addition of a substance that will react with ozone, by passing the ozone-containing atmosphere over an ozone decomposition catalyst, or by exposing the ozone-containing atmosphere to ultraviolet radiation of a wavelength commensurate with ozone decomposition.

This procedure is effective in the depletion of ozone to a safe level, but problems associated with the process include reduced activity of the catalyst over time.

In another co-pending earlier application, GB 0904266.4 (GB2468519) the Applicant describes a similar process for the sterilisation of contaminated premises in which the ozone is decomposed by passing the atmosphere over a suitable ozone decomposition catalyst but, prior to this, the ozone-containing atmosphere is subjected to a conditioning treatment wherein it is dehumidified and heated by suitable means. The step of dehumidifi cation includes the incorporation of a trap containing an absorbent for water such as silica gel and/or a molecular sieve, and/or a conventional dehumidifier. This had the advantage of increasing the lifetime of the catalyst, thus resulting in less maintenance of the equipment and the cost of replacement catalyst units. A further improvement to the lifespan of the catalyst is described in the Applicant's copending unpublished application GB 1015296.5 which passes substantially dry air over the catalyst for a period of time at regular intervals. Nevertheless, it is desirable to increase the life of the catalyst still further.

The present invention seeks to provide a solution to these problems, in particular to provide a process that achieves a high degree of sterilisation and/or decontamination that enables a substantially sterilised area to be made safe of harmful products within an acceptable timescale and with an improved catalyst lifespan.

According to a first aspect of the present invention, there is provided a use of a catalyst for the conversion of ozone to oxygen at a temperature of less than 40°C in a humid atmosphere, the catalyst comprising at least one catalytically active metal or metal oxide supported on a mixed titanium/silicon oxide support.

According to a second aspect of the present invention, there is provided a method of sterilisation, decontamination and/or sanitation of an enclosed environment, the method comprising;

a) producing a humidified enclosed environment;

b) discharging ozone into the humidified environment;

c) maintaining the ozone and water vapour pressure levels

concentration that will achieve the required degree of contamination, sterilisation and/or sanitation of the humid environment; and d) passing the substantially decontaminated, sterilised and/or sanitised environment through an ozone depletion catalyst to reduce the concentration of ozone to a predetermined level, the catalyst comprising at least one catalytically active metal or metal oxide supported on a mixed titanium/silicon oxide support.

A third aspect of the present invention provides a sterilisation and

decontamination apparatus comprising a humidifier unit, an ozone discharge unit, an ozone depletion catalyst and a controller by which the humidifier unit and ozone discharge unit are controllable based on predetermined conditions, the ozone depletion catalyst comprising at least one catalytically active metal or metal oxide supported on a mixed titanium/silicon oxide support. Preferably, the catalyst used in the first, second and third aspects of the present invention comprises a titanium/silicon mixed oxide support impregnated with at least one metal selected from the group consisting of iron, cobalt, nickel, silver, copper, manganese, zinc and any platinum group metal or any oxide thereof. Preferably, the active metal comprises at least one platinum group metal, in particular platinum or palladium.

The mixed oxide support may have any appropriate amounts of SiCh and TiC . Preferably, at least 10 % by weight of the support comprises TiC . The conversion of ozone to oxygen according to the first and second aspects of the present invention preferably occurs at ambient temperature, preferably being in the range 10-30°C. The humidified environment should have a relative humidity in excess of 65 % , preferably at least 75 %, more preferably at least 85 %, especially being at least 90% at ambient temperature. In this respect, the humidified environment preferably has a partial pressure of water vapour of at least 5.00 torr but this will depend upon the temperature of the environment. For example, a cool environment having a temperature of around 6°C will preferably have a partial pressure of 6.00 torr and a warmer environment having a temperature of around 18°C will preferably have a partial pressure of around 13.9 torr. However, higher humidity levels do not always achieve optimum results and the level of humidity required will depend on the particular conditions and parameters of the process and enclosed environment.

Step (c) of the decontamination process according to the second aspect of the present invention may include replenishing the humidity and ozone levels to maintain effective levels for decontamination. Preferably, these levels are held for a predetermined period of time (the "dwell time").

In one embodiment of the process according to the second aspect of the present invention, a hydrocarbon containing a carbon-carbon double bond may be introduced into the environment to react preferentially with any residual ozone (step (e)). Preferably, the hydrocarbon comprises a secondary olefin, cis or trans, including cyclic olefins. The decontaminated and sterilised environment may be recycled through the catalyst until the concentration of the ozone, and any other harmful products that may be present, fall to a safe level.

The process according to the second aspect of the present invention may also include one or more additional steps for extending the working life of the catalyst. For example, the process may include a catalyst conditioning phase prior to the decontamination phase, the conditioning phase comprising passing a substantially dry inert gas, such as air, over or through the catalyst. This process may be repeated with the catalyst being flushed out with the substantially dry gas prior to each sterilisation phase.

In the context of this disclosure, "substantially dry" air means air containing a moisture level below that of the humidified environment. The substantially dry air contains any level of moisture below that of the humidified environment but the lower the water content of the substantially dry air the greater the beneficial effect of the conditioning treatment. Preferably, the dry air is passed through the catalyst for a time period sufficient for the catalyst to reach equilibrium with the dry air. This may be a number of hours, including overnight in some situations.

Alternatively or additionally, the ozone-rich atmosphere may be subjected to a dehumidification step prior to passing the atmosphere over the catalyst. Said dehumidification step may include, inter alia, passing the atmosphere through a water absorbent trap and/ or a dehumidifier and/or heating the atmosphere.

The invention will now be more specifically described, by way of example only, with reference to the following Example which describes the preparation of a catalyst for use in the invention and with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic side elevational view of one embodiment of sterilisation and decontamination apparatus for carrying out the process according to the second aspect of the invention; and

Figure 2 is a diagrammatic front view of the apparatus shown in Figure 1 ;

The sterilisation and decontamination process of the present invention uses ozone at high humidity levels (generally in excess of 90 % at ambient temperature) for the sterilisation and decontamination of an enclosed environment. However, the actual relative humidity will depend upon the temperature of the environment to be treated. The process and apparatus also includes an ozone depletion catalyst for reducing levels of the ozone and any unwanted by-products which may be present (such as hydrogen peroxide) to a safe level in minimal time, thereby reducing the time during which a room has to be kept unoccupied. However, it is unusual for catalysts to operate close to the dew point, particularly when water is not one of the reactants. This can result in the surface of the catalyst becoming covered by a film of water molecules, thus inhibiting the required reaction. The present invention alleviates this problem by providing an improved catalyst that is able to operate at high humidity levels but low (ambient) temperatures. The catalyst comprises at least one platinum group metal on a titanium/silicon oxide support. This type of catalyst has been shown to have an extended working life compared with catalysts prepared on a different type of support. Example: Preparation of Catalyst comprising a platinum group metal on a mixed titanium/silicon oxide support.

The catalyst for use in the present invention has been used previously for the combustion of methane (Chem Comm, 46(34), 6317, 2010) in the automotive industry. The catalyst may be prepared by the hydrolysis of a mixture of tetraethoxysilane and titanium isopropoxide, drying and subsequent impregnation with a platinum group metal, such as palladium. The catalyst is less prone to deactivation in the presence of sulphur compounds and water vapour in the conversion of methane to carbon dioxide at temperatures in excess of 300°C than an equivalent catalyst prepared using a conventional support.

It has surprisingly been found that the catalyst also may be used for low temperature conversion of ozone to oxygen in a humid environment. This was unexpected as temperatures in the range 10-30°C would not normally be considered to be sufficiently high to allow appreciable desorption of adsorbed species from the catalyst surface which is required to maintain catalytic activity.

The mixed titanium/silicon oxide support may be prepared by mixing an appropriate high surface area metal oxide but, more preferably, is prepared by co- precipitation from aqueous solution. Co-precipitation may be carried out, for example, by the addition of an alkaline compound, such as sodium silicate, to a soluble titanium compound in a suitable solvent system or by the hydrolysis of a mixture of titanium and silicon derivatives, such as chlorides. The precipitate is washed extensively to remove any anions or cations, such as chloride, sulphate and sodium, which would adversely affect the activity of the finished catalyst.

After filtration, drying and optional calcination, the mixed oxides are formed into a desired size and shape by conventional techniques used in the manufacture of catalysts, such as pelleting, granulation or extrusion. The formed support, following optional further calcination, is then impregnated with a platinum group metal that is active for the decomposition of ozone.

Impregnation may be carried out using standard techniques known in the art, using salts or colloids of the active metal component.

Without prejudice to the invention, it is believed that the new mixed oxide support offers preferential adsorption sites for water vapour in the humid environment. Therefore, the active metal component is available for a longer period of time before the catalyst becomes saturated with water vapour. The illustrated example uses a platinum group metal as the active metal but other known active metals for the conversion of ozone may be supported on the titania/silica carrier, such as oxides of manganese. In a preferred embodiment of the invention, the catalyst is subjected to a pre- or post-treatment drying period which enables full or substantially full activity of the catalyst to be recovered.

The accompanying drawings illustrate one embodiment of a sterilisation and decontamination apparatus 10 according to the third aspect of the invention for carrying out the second aspect of the present invention. In the illustrated embodiment the process utilises both an ozone depletion catalyst according to the present invention and a subsequent hydrocarbon quenching step for removal of the ozone after decontamination. However, it is to be appreciated that the process is not limited in this manner and in another embodiment (not illustrated) the process only uses the ozone depletion catalyst. The apparatus comprises a portable enclosure 12 which can be opened and which, in use, can generate a positive pressure within the interior to protect sensitive devices contained within the enclosure from the deleterious affects of the ozone. However, it is to be appreciated that alternative means could be provided to protect internal sensitive components from being damaged by the ozone. The enclosure 12 has wheels 14 and houses a humidifier unit 16 having a humidified air outlet 17, an ozone discharge unit 18 having an ozone discharge outlet 20, a vessel containing an ozone catalyst 70, an ozone catalyst fan 71 , a hydrocarbon discharge unit 22 having a hydrocarbon discharge outlet 24, and a control unit 26.

The humidifier unit 16 in the illustrated example includes a humidifier 28, a humidistat sensor 30, a temperature sensor 31 and a water reservoir 34. If an ultrasonic humidifier is used, a compressed air supply also needs to be provided, for example, in the form of a compressed air tank 32 or container housed within the enclosure 12. The compressed air tank is connected to the water reservoir 34 and the humidifier 28. Preferably, water droplets having a diameter of less than 5 microns, especially 2-3 microns, are introduced into the air to enhance the rate of evaporation of the water into the atmosphere. In this respect, the smaller the size of the droplet the faster the evaporation of the liquid water. Accordingly, small water droplets, defined by nozzle type and operating conditions, are preferred but it is to be appreciated that the use of larger droplet sizes may be appropriate in certain circumstances, for example to minimize cost.

The ozone discharge unit 18 includes an ozone generator 36, an ozone detector sensor 38, and an oxygen supply 56 for supplying oxygen to the ozone generator 36. Oxygen is preferred to air for the generation of ozone because this avoids the formation of toxic oxides of nitrogen, increases the rate at which the required concentration of ozone is achieved and also increases the yield of ozone. The ozone catalyst 70 comprises a platinum group metal supported on a mixed titanium/silicon support as described in the Example above. However, alternative active substances may be used, such as a mixture of platinum group metals or oxides of manganese. The hydrocarbon discharge unit 22 includes a hydrocarbon supply 42 in the form of a tank or container containing a volatile unsaturated hydrocarbon, such as butene. Preferably, the butene is butene-2. However, the hydrocarbon can be any suitable hydrocarbon having a carbon-carbon double bond, for reasons which will become apparent hereinafter. The selection of hydrocarbon is based on its speed of reaction with ozone and the toxicology of its decay products.

The control unit 26 controls the apparatus 10 and is preset with at least one sterilisation and decontamination routine. The control unit 26 includes a controller 46 and a user interface 48 by which a user can input commands to the apparatus 10.

The apparatus 10 may include an on-board battery 50 and/or may be connectable to a mains power supply. In the case of the on-board battery 50, the battery is preferably rechargeable. If a mains-operated apparatus is provided, this may have a battery back-up system to enable the machine to failsafe in the event of a mains power failure.

The apparatus 10 will also typically include other safety features, such as safety sensors, and software routines to prevent start-up or initiate shut-down in the event of a system failure.

In use, prior to activation of the humidifier 28 and ozone generator 36, substantially dry air is directed over the ozone catalyst 70 to remove any water molecules that are present on the surface of the catalyst. The step may occur whilst the apparatus 10 is located in the area to be decontaminated or in an area remote therefrom. The dry air is passed through the catalyst for approximately one hour or until the catalyst approximately reaches equilibrium with the dry air. It is to be appreciated that this "drying step" is only optional to enhance further the activity of the catalyst. The apparatus 10 is then located in the area which is to be sterilised and decontaminated, if not already there. The power to the apparatus 10 is switched on, and the control unit 26 undertakes an initial safety check. If the safety check is not passed, the apparatus 10 does not operate and outputs a suitable indication using warning lights 52. During the process, safety checks are made continuously, and in the event of a system failure, the system defaults to a safe mode.

The humidifier and ozone generator are switched on to raise their levels by the required degree to effect sterilisation and decontamination of the environment.

The controller 46 continues to monitor the ozone level, relative humidity through the hu idistat sensor 30 and ambient temperature through the thermocouple. If after a predetermined interval of time, for example 10 minutes, the calculated relative humidity level and/or the required ozone level has not been reached, the controller 46 aborts the sterilisation and decontamination routine and provides a suitable indication.

Oxygen is supplied to the ozone generator 36, and ozone is generated. The generated ozone is then fed into the discharging humidified airstream. The controller 46 provides a suitable indication that the ozone generator 36 is operating, and monitors the ambient ozone levels through the ozone detector sensor 38.

Both the ozone and water vapour concentrations to be detected can be altered. However a typical setting is 25 ppm v/v of ozone and a water vapour pressure of 13.6 torr., Once the preset ozone and water vapour levels have been detected within the allotted interval, the controller 46 enters a timing phase, known as the "dwell time".

The dwell time can also be altered, for example, to one hour, and will depend on the degree and type of decontamination / sterilisation to be provided. For instance, contamination by spores or moulds, such as Clostridium difficile, generally require a longer dwell time than contamination by bacteria, such as listeria and methicillin resistant staphyloccocus aureus (MRS A).

During the dwell time, the ozone concentration and relative humidity are continuously monitored. If the ozone level falls below a predetermined threshold, the ozone discharge unit 18 is reactivated to replenish the ozone levels. If relative humidity level falls below the calculated value, the humidifier unit 16 is reactivated to restore the water vapour level.

Again, during the reactivation period, should either the ozone concentration or the relative humidity fail to reach the above-mentioned predetermined minima within a set time interval, for example 10 minutes, the controller 46 aborts the sterilisation and decontamination routine and outputs a suitable indication.

After the dwell time has elapsed, the controller 46 closes the compressed air valve 54 and the oxygen supply valve 60, and the humidifier unit 16 and the ozone discharge unit 18 are switched off. A pump 71 then blows the atmosphere through the catalyst 70 to reduce the levels of ozone, the level of ozone being monitored continuously. When the concentration of the ozone has fallen to the required level, such as around 8 ppm v/v, an olefin is introduced by means of a hydrocarbon discharge valve 58 of the hydrocarbon discharge unit 22. The concentration of ozone is continuously monitored. The catalyst 70 may be continuously deployed until the concentration of ozone falls below its OEL.

When the ozone detector sensor 38 detects that the ozone concentration levels are less than a predetermined value, for example 0.2 ppm or less, the controller 46 closes the hydrocarbon discharge valve 58 and outputs an indication that the sterilisation and decontamination routine is complete. The ozone level of 0.2 ppm, depending on the size of the area being sterilised and decontaminated, is usually achieved within 3 to 4 minutes. If the ozone detector sensor 38 fails to indicate that the predetermined safe level of ozone has been reached within a predetermined time interval, for example within 10 minutes, the controller 46 outputs an indication warning of potentially hazardous ozone levels in the room. The controller may be programmed to allow a time interval to pass in excess of the standard half-life of ozone before announcing that the room may be re-occupied.

Optionally, drier air is then passed through the catalyst 70 by means of fan 71 to remove any water molecules on its surface. The dry air has a lower relative humidity than the processed air that has been humidified prior to introduction of the ozone and, preferably, is completely dry. Ideally, this air is passed through the catalyst for a time period sufficient for the catalyst to reach equilibrium with the dry air. It is preferable if this air has not been exposed to the decontamination process, i.e. , the unit 10 is removed from the enclosure to a clean, dry atmosphere prior to re- activation of the fan 71. The clean, dry atmosphere may comprise a remote storage area where the fan is left to run for a predetermined amount of time or may be a new area to be decontaminated, with the fan being run for a sufficient period of time prior to activation of the decontamination phase. Alternatively, a separate source of dry clean air may be provided to purge the catalyst. This drying step may be run between each decontamination phase or cycle or only after a number of decontamination cycles.

It is envisaged that the sterilisation and/or decontamination apparatus may be integrally formed as part of an area, or may be only partly portable. For example, the compressed air supply and/or oxygen supply could be integrally formed as part of the area to be regularly sterilised and decontaminated. Alternatively, components could be housed within the enclosure of the apparatus. In this case, the required supply could be linked to the apparatus via a detachable umbilical pipe. The machine may also consist of a main unit and a wirelessly connected remote controller wherein the required preset routine may be remotely initiated by a user from outside the area to be sterilised and/or decontaminated.

Although the oxygen supply is typically in the form of one or more oxygen tanks or cylinders, a commercially available oxygen concentrator can be used. The apparatus uses an electric fan 72 as a gas movement device to circulate the dry air, humidified air, ozone and hydrocarbon. However, depending on the particular application, an air mover may be used instead of an electric fan.

The above-described apparatus utilises a method of producing an artificially high level of non-condensing humidity, and generating in-situ a high concentration of ozone.

The materials of the apparatus are resistant to the corrosive effects of ozone and the solvent effects of the hydrocarbon.

The condition of all the valves are monitored using integrally incorporated sensors connected to the controller. The valves failsafe to an appropriate position, such as the closed position so that user safety is maintained at all times. The controller may also incorporate a tamper proof recording system to monitor use, time, date, operational success/failure and other parameters required to measure performance of the machine.

It is thus possible to provide a method for providing a degree of sterilisation and/or decontamination which is fast and effective and does not requirement frequent replacement of the ozone catalyst, due to the use of a catalyst that is able to convert ozone to oxygen at high humidity levels and low temperatures without poisoning the catalyst. Furthermore, the apparatus may be discrete and portable. The method can provide better than 99.99% effective sterilisation and decontamination of an area without an impact on the environment from harmful by-products. Rapid re-use of a contaminated area can thus be realised. The embodiments described above are given by way of examples only, and other modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined by the appended claims.

Claims

Use of a catalyst for the conversion of ozone to oxygen at a temperature of less than 40°C in a humid environment, the catalyst comprising at least one catalytically active metal or metal oxide supported on a mixed titanium/silicon oxide support.

Use of a catalyst as claimed in claim 1 wherein the at least one catalytically active metal is selected from the group consisting of iron, cobalt, nickel, silver, copper, manganese, zinc and any platinum group metal or any oxide thereof.

Use of a catalyst as claimed in claim 2 wherein the at least one catalytically active metal is a platinum group metal.

Use of a catalyst as claimed in claim 3 wherein the platinum group metal is palladium.

Use of a catalyst as claimed in any one of claims 1 to 4 wherein the temperature is in the range 10-30°C.

A method of sterilising, sanitising and/or decontaminating an enclosed environment, the method comprising the steps of:

a) producing a humidified enclosed environment;

b) discharging ozone into the humidified environment;

c) maintaining the ozone and water pressure levels at a concentration that will achieve the required degree of decontamination, sterilisation and/or sanitation of the humid environment; and

d) passing the substantially decontaminated, sterilised and/or sanitised environment through an ozone depletion catalyst to reduce the concentration of ozone to a predetermined level, the catalyst comprising at least one catalytically active metal or metal oxide supported on a mixed titanium/silicon oxide support.

7. A method according to claim 6 wherein the catalyst is a mixed titanium/silicon oxide support impregnated with an active metal selected from the group consisting of iron, cobalt, nickel, silver, copper, manganese, zinc and any platinum group metal or any oxide thereof.

8. A method according to claim 7 wherein the catalyst is a mixed titanium/silicon oxide support impregnated with at least one platinum group metal.

9. A method according to claim 8 wherein the catalyst is a mixed titanium/silicon oxide support impregnated with palladium.

10. A method according to any of claims 6 to 9 wherein the temperature is between 10 - 30°C.

11. A method according to any one of claims 6 to 10 further comprising replenishing the humidity and ozone levels in step (c) to maintain effective levels for decontamination.

12. A method according to any one of claims 6 to 11 further comprising step (e) introducing a hydrocarbon having a secondary olefinic carbon

carbon double bond into the enclosed environment to react preferentially with the discharged ozone.

A method according to any one of claims 6 to 12 further comprising passing a substantially dry inert gas through the ozone depletion catalyst prior to and/or after each decontamination process.

A method as claimed in claim 13 wherein the substantially dry gas is passed through the catalyst at intervals between a predetermined number of repeat decontamination processes.

A method as claimed in any one of claims 6 to 14 further comprising the step of dehumidifying the ozone rich atmosphere prior to its passage through the catalyst.

Sterilisation and decontamination apparatus comprising a humidifier unit, an ozone discharge unit, an ozone depletion catalyst and a controller by which the humidifier unit and ozone discharge unit are controllable based on predetermined conditions, the ozone depletion catalyst comprising at least one catalytically active metal or metal oxide supported on a mixed titanium/silicon oxide support.