GB2483652A

GB2483652A - Method of sterilisation

Info

Publication number: GB2483652A
Application number: GB1015296.5A
Authority: GB
Inventors: James Robert Jennings
Original assignee: Steritrox Ltd
Current assignee: Steritrox Ltd
Priority date: 2010-09-14
Filing date: 2010-09-14
Publication date: 2012-03-21
Anticipated expiration: 2030-09-14
Also published as: GB2483652B; GB201015296D0

Abstract

A method of sterilisation, sanitisation and/or decontamination comprising a catalyst conditioning phase and a subsequent decontamination phase, the catalyst conditioning phase comprising directing a substantially dry inert gas through an ozone depletion catalyst 70 and the subsequent decontamination phase comprising the steps of producing a humidified enclosed environment; discharging ozone into the humidified environment; maintaining the ozone and water pressure levels at a concentration that will achieve the required degree of decontamination and sterilisation of the humid environment; and passing the substantially decontaminated and sterilised environment through the catalyst 70 to reduce the concentration of ozone to a predetermined level. The inert gas may be air, and a hydrocarbon containing a carbon-carbon double bond may be introduced into the environment to aid removal of the ozone. A method for increasing the life of an ozone depletion catalyst is also disclosed.

Description

pprovements in and relating to sterilisation andlor decontamination This invention relates to a method of sterilisation and/or decontamination, including sanitation,of an enclosed environment. F. 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 returrnng occupants, the use of potentially environmentally damaging chemicals during the process, the general poor effectiveness of the process in sanitising the environment, the overall lack of simplicity in quickly setting up and using the F apparatus and the relatively short life time of the catalyst systems deployed.

The applicant's previous unpublished application, GB0904262 3, 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 F problems associated with the process include reduced activity of the catalyst over time.

In another co-pending unpublished application, GB 0904266.4 the Applicant F 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 dehumidification includes the incorporation of a trap containing an absorbent for water such as silica gel and/or a molecular sieve, and/or a conventional F: 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. However, it is desirable to provide alternative methods to increase the life of the catalyst 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 tirnescale and with an improved catalyst lifespan.

According to a first aspect of the present invention, there is provided a method for increasing the life of a catalyst, in particular, an ozone depletion catalyst, comprising the step of directing a substantially dry inert gas through the catalyst.

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 catalyst conditioning phase and a subsequent decontamination phase, the catalyst conditioning phase comprising directing a substantially dry inert gas through an ozone depletion catalyst and thc subsequent F decontamination phase comprising; a) producing a humidified enclosed environment; b) discharging ozone into the humidified environment; c) maintaining the ozone and water vapour pressure levels at a 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 the catalyst to reduce the concentration of ozone to a predetermined level.

Preferably, this cycle is repeated with the catalyst being flushed out with the substantially dry gas prior to each sterilisation phase.

Any suitable inert gas may be used for conditioning of the catalyst but preferably the gas is air. It is preferable for the conditioning phase to occur at ambient temperature. F: In the context of this disclosure, "substantially dry" air means air containing a moisture level below that of the humidified environment. The humidified environment should have a relative humidi in excess of 65 %, preferably at least 75 %, more preferably at least 85 %, especially being at least 90%. 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 It is to be appreciated that conditioning phase may be achieved using the air of the enclosed environment to be sanitised or, more preferably, a separate source of dry air This separate source of dry air may be the ambient air in a new location to be decontammated/stenlised prior to commencing the humidification step of the decontamination phase, or may he in a separate storage location between decontamination runs -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.

More preferably still, the catalyst is subjected to longer periods of dry air treatment at regular intervals. For example, dry air is passed through the catalyst for a period of several hours in each 24-hour period. It is preferable for this step to be carried out at an area remote from the decontamination site to avoid exposure of the catalyst to any organic residues that may be a by-product of certain embodiments of the decontamination process. For example, the conditioning phase may be carried out at a new location during step-up of the process or may be carried out at a storage location.

Optionally, the substantially dry air may be dehumidified prior to its passage through the catalyst to minimize the amount of water in the air, ideally to produce dry F air approaching 0% relative humidity.

As detailed above, the humidified environment produced in step (a) of the decontamination phase is preferably around 90 % v/v at ambient temperatures.

Preferably, the humidified environment has a partial pressure of water vapour of at least 5 00 torr but this will depend upon the tempet arnie 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 tort 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. Optionally, the humidity levels of the humid environment may be reduced prior to passage of the ozone-rich air through the catalyst.

Tn cetain embodiments of the present invention, a hydrocarbon containing a F 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 invention will now be more specifically described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 i.s a diagrammatic side elevational view of one embodiment of sterilisation and decontamination apparatus for carrying out the process of the invention; and Figure 2 is a diagrammatic front view of the apparatus shown in Figure 1; The 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 F 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 reactiorn The present invention alleviates this problem by flushing the catalyst with drier air prior to its humidification, preferably with substantially dry air, to rejuvenate the catalyst and thereby prolong its life.

In a preferred process of the invention, the catalyst is flushed with air before and after the sterilization cycle. It has been found that this leads to an increase in the average activity of the catalyst and its life. 1:.

Without prejudice to the invention, it is believed that at least part of the deactivation of the catalyst arises from an accumulation of a minute film of water molecules onto th.e surface of the catalyst. The actual thickness of this film wil.l be determined by the partial pressure of water vapour present, the ambient temperature and the surface characteristics of the catalyst. While the film of water is not a true F. poison of the catalyst surface, it nevertheless presents a physical barrier between the atmosphere and the catalyst surface and thus inhibits the catalytic reaction Since the actual surface is not poisoned in the true sense, removal of at least part of the said film results in a partial restoration of the original activity of the catalyst For these procedures to be effective, it is required that the humidity of the atmosphere during the restoration procedure be less than that of the process air after the completion of the decontamination, sterilisation and/or sanitisation process otherwise the equilibrium concentration of moisture on the catalyst surface does not alter.

The accompanying drawings illustrate one embodiment of a sterilisation and decontamination apparatus 10 for carrying out the method of the present invention. In the illustrated embodiment the process utilises both an ozone depletion catalyst and a subsequent hydrocarbon quenching step for removal of the ozone after F;, decontamination. However, it is to be appreciated that the process is not limited in 1: 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 interna] sensitive components from being damaged by the ozone. The P 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 F humidistat sensor 30, a temperature sensor 31 and a water reservoir 34. lf 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 he appreciated that the use of larger droplet sizes may be appropriate in certain circumstances, for example to minhiize 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 is any suitable catalyst that is able to remove ozone from the atmosphere. The catalyst may be selected from a range of proprietary substances that are known to be active in the catalytic decomposition of ozone. Such catalysts may optionally contain platmum group metals, oxides of manganese, and other substances which may have a promoting effect 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. 11 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 m 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.

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. Jf 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 bumidistat sensor 30 and ambient temperature through the thennocouple.

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 control]er 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 1.0 be detected can be altered.

However a typical setting is 25 ppm v/v of ozone and 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 ccdwell 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 clostridiuin difficile, generally require a longer dwell time than contamination by bacteria, such as listeria and inethicillin resistant staphyloccocus aureus (MRSA).

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 faHs 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 stelisation and decontamination routine and outputs a suitable indication.

After the dwell nme has elapsed the conti oiler 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 vlv, 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 deëoritamination 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.

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 decontamined, with the fan being nm 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.

The conditioning phase of the present invention may be run betwccn each decontamination phase or cycle or only after a number of decontamination cycles.

It is envisaged that the sterilisation andlor 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 sterihsed and decontammated 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 routme 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 F 10. ozone. F 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, k 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 stenlisation F and/or decontamination which is fast and effective and does not requirement fiequent i eplacement of the ozone catalyst due to the periodic rejuvenation of the catalyst by means of the conditioning phase. 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 a without departing from the scope of the invention as defined by the appended claims.

Claims

Claims 1. A method for increasing the life of a catalyst comprising the step of directing a substantially dry inert gas through or over the catalyst.
2. A method as claimed in claim 1 wherein the catalyst is an ozone depletion catalyst.
3. A method as claimed in claim 1 or claim 2 wherein the inert gas is air.
4. A method as claimed in claim 1, 2 or 3 wherein the inert gas is dehumidified prior to directing the gas through or over the catalyst.
5. A method of sterilising, sanitising and/or decontaminating an enclosed environment, the method comprising a catalyst conditioning phase and a subsequent decontamination phase, the catalyst conditioning phase comprising directing a substantially dry inert gas through or over an ozone depletion catalyst and the subsequent decontamination phase compdsing 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, stenlised and/ot sanmsed environment through the ozone depletion catalyst to reduce the concentration of ozone to a predetermined level.
6. A method as claimed in claim 5 wherein the substantially dry inert gas has a lower relative humidity than the humidified environment produced in step (a).
7. A method as claimed in claim 5 or claim 6 further comprising passing the substantially dry inert gas through the ozone depletion catalyst prior to each decontamination phase.
8. A method as claimed in claim 5 or claim 6 wherein the conditioning phase is carried out at intervals between a predetermined number of repeat decontamination phases.
9. A method as claimed in any one of claims 5 to 8 wherein the inert gas is air.
10. A method as claimed in claim 9 wherein the dry air is sourced from the enclosed environment.
11. A method as claimed in any one of claims 5 to 9 wherein the inert gas is sourced from outside the enclosed environment.
12 A method as claimed in any one of claims 5 to 11 further comprising the step of dehumidifying the inert gas prior to exposure to the catalyst.
13. A method. as claimed in any one of claims 5 to 12 wherein the dry inert gas is passed through the catalyst until the catalyst and the inert gas approach or reach equilibrium
14. A method as claimed in any one of claims 5 to 13 further comprising step (e) introducing a hydrocarbon having a secondary olefmic carbon carbon double bond into the enclosed environment to react preferentially with the discharged ozone.