WO2013021155A1

WO2013021155A1 - Process and device for sterilisation and decontamination of an environment

Info

Publication number: WO2013021155A1
Application number: PCT/GB2012/000643
Authority: WO
Inventors: James Robert Jennings
Original assignee: Steritrox Limited
Priority date: 2011-08-11
Filing date: 2012-08-08
Publication date: 2013-02-14
Also published as: GB2493549A; GB201113840D0

Abstract

A process for the removal of ozone from an environment comprising passing the ozone-containing environment over or through an inert support "carrying a reducing agent, the agent being selected from the group consisting of a transition group element or salt thereof, a main group element from group 4 to 6, and an anion capable of oxidation to a higher valence state, or mixtures thereof, for reaction with the ozone. The reducing agent and support may be incorporated into a cartridge for use in a device for the sterilisation, decontamination or sanitation of an enclosed environment.

Description

Process and Device for Sterilisation and Decontamination of an Environment

The present invention relates to an improved process for the removal of ozone from an environment, especially the removal of ozone in a humid environment, and to a process and device for the sterilisation, sanitisation and/or decontamination of an environment.

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

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, ozone is toxic or hazardous to higher organisms and must be removed from the treated environment prior to allowing access into the area. 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 general ineffectiveness of the process package in sanitising the environment, and the overall lack of simplicity in quickly setting up and using the apparatus.

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 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 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.

The processes mentioned above use a catalyst for the removal of ozone but the high humidity levels of the environment can quickly lead to catalyst deactivation. . This has been found to be the case for a range of catalysts tested under conditions used in the Applicant's decontamination process. Non-catalytic (i.e. stoichiometric) reagents for the _. removal of the residual ozone have therefore been investigated, such as butene-2 (European Patent No. 1500404B - Steritrox Limited). This is effective at the removal of ozone but suffers to some extent from volatile residual oxidation products from the reaction of ozone with butene-2. Thus, it is desirable to identify alternative ozone removal agents that may be used in the decontamination process which do not produce volatile oxidation products.

It is an aim of the present invention to provide alternative ways of removing ozone from an environment, especially a humid environment, particularly but not exclusively ozone generated during a sterilisation, sanitisation and/or decontamination process to provide cheaper resources for the process, provide a reduction in production of volatile oxidation products, increase the recyclability of the components used and/or to provide a more compact device for carrying out the process. According to a first aspect of the present invention, there is provided a process for the removal of ozone from an environment comprising passing the ozone-containing , environment over or through an inert support carrying a reducing agent, the agent being selected from the group consisting of a transition group element or salt thereof, a main group element from group 4 to 6 and an anion capable of oxidation to a higher valence state, or mixtures thereof, for reaction with the ozone.

Preferably, the ozone contaminated environment has a high humidity level, preferably 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.

The reducing agent may comprise a metal selected from the group consisting of iron, cobalt, chromium, vanadium, titanium, copper or manganese. A suitable anion is sulphite or nitrite. Phosphorus or sulphur are also suitable reducing agents. In a preferred embodiment of the present invention, moist elemental sulphur is used as the reducing agent.

A second aspect of the present invention provides a process for the sterilisation, decontamination and/or sanitation of an enclosed environment, the process comprising:

(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) stoichiometrically removing ozone from the enclosed environment by contacting the substantially decontaminated, sterilised and/or sanitized environment with a reducing agent selected from the group consisting of a transition group element or salt thereof, a main group element from group 4 to 6, and an anion capable of oxidation to a higher valence state, or mixtures thereof, for reaction with the ozone to reduce the concentration of the ozone to below a predetermined level.

Preferably, the reducing agent is provided on an inert support to increase the surface area of the agent for contact with the ozone in the environment. Preferably, the support has a honeycomb structure, more preferably having parallel channels to minimize backflow through the support. Preferably, the support comprises a ceramic material, such as silica, a clay mineral, alumina and/or titania.

Alternatively, the reducing agent may be coated on ceramic granules or particles. In a preferred embodiment of the present invention, the reducing agent comprises finely divided elemental sulphur which is mixed with water and a surfactant to provide an emulsion. The inert support may be sprayed with, or more preferably, dipped in the emulsion to provide a support coated with the agent. It is to be appreciated that the inert support must be stable to the reaction product, such as sulphuric acid.

The reaction of the ozone and water with the reducing agent preferably provides a nonvolatile product, such as an acid solution. More preferably, the acid forms a thin film of material on the inert support. The amount of reducing agent contained on the inert support will depend upon the amount of ozone to be removed. However, it is preferable for the amount to be such that all the sulphur is converted to acid during the process. Preferably, the acid support is washed in dilute water or alkali, such as sodium carbonate, after use to neutralise the acid formed.

The removal of ozone 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").

The decontaminated and sterilised environment may be recycled through the reducing agent until the concentration of the ozone, and any other harmful products that may be present, fall to a safe level.

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 process according to the second aspect of the invention may be carried using a static or portable air decontamination or sanitation device. To this end, a third aspect of the present invention provides a humidifier unit, an ozone discharge unit and an ozone reducing agent mounted on an inert support, and a controller by which the humidifier unit and ozone discharge unit are controllable based on predetermined conditions.

Preferably, the components are provided within a casing or enclosure with a discharge outlet extending from an intended upper surface of the casing. More preferably, the reducing agent carried on an inert support is mounted or contained within a removable cartridge which may be temporarily placed into the device and removed for recycling or replacement. It is to be appreciated that the casing or enclosure may contain additional components for optimization of the operation of the device, such as a hydrocarbon discharge unit, UV catalyst, appropriate sensors, an oxygen supply and/or a water reservoir or connector for attachment to a water source. If a connector is included for attachment to a water source, preferably a filter and/or other water purification means is included in the machine.

A framework may be provided for supporting the components within the enclosure. The components may be made of any suitable material that is inert to ozone.

One or more air movement devices, such as fans, may be provided within the housing to provide effective distribution of the ozone and humidity. Such devices may also aid cooling of the components and prevent the build up of hot spots within the housing. The ozone removal cartridge may be a stand-alone component for temporary placement in the sterilisation, decontamination and/or sanitation device. To this end, a fourth aspect of the present invention provides an ozone removal cartridge comprising a receptacle containing an inert support carrying a reducing agent, the agent being selected from the group consisting of a transition group element or salt thereof, a main group element from group 4 to 6, and an anion capable of oxidation to a higher valence state, or mixtures thereof, for reaction with the ozone. The invention will now be more specifically described, by way of example only, to the following examples in which Example 1 describes an ozone removal agent according to one embodiment of the present invention and Example 2 describes a sterilisation, decontamination and/or sanitation device incorporating the ozone removal agent of Example 1 , and with reference to the accompanying drawings, in which :

Figure 1 is a rear elevation external view of a sterilisation and decontamination device according to one embodiment of the present invention; Figure 2 is a side elevation external view of the device shown in Figure 1 ;

Figure 3 is a perspective external view of the device shown in Figure 1 , with the lectern detached from the main body; Figure 4 illustrates some of the internal components of the sterilisation and decontamination device shown in Figure 1 ;

Figure 5 illustrates an experimental setup which demonstrates the effectiveness of a sulphur reducing element used in one embodiment of the present invention; and

Figure 6 shows results carried out using the experimental setup of Figure 5.

Example 1 Reducing agent for ozone removal according to one embodiment of the present invention.

A preferred reducing agent for the present invention is moist elemental sulphur that reacts directly with the ozone to produce sulphuric acid, following the reaction shown below:

For the removal of 4g ozone, the molecular weight of which is 48, 0.083 moles of stoichiometric reagent are required, assuming a single electron transfer during oxidation. Thus, around 0.9g of sulphur should remove 4g ozone. This means that only a relatively small amount of reducing agent is required for the removal of relatively large quantities of ozone.

The elemental sulphur is mixed with water and an appropriate surfactant to provide a fine emulsion and then a ceramic honeycomb support, such as cordierite or other suitable alumina, silica and/or titania composite, is dipped in the emulsion, removed and dried gently to provide a support for the reducing agent which provides a high surface area for the agent and creates a low pressure drop for gases that pass through the support. ¹

The reducing agent supported on the inert support may be placed in a receptacle to provide a cartridge. Prior to use, the cartridge is sealed to prevent oxidation of the reducing agent.

Other types of reducing agents may be incorporated onto an inert support, such as sodium sulphite for oxidation to sodium sulphate and ferrous sulphate for oxidation to ferric sulphate. However, the handling properties of these substances are not ideal and moist elemental sulphur is the reducing agent of choice.

Figure 5 illustrates experimental apparatus used to demonstrate the effectiveness of a sulphur reducing element used in an embodiment of the present invention. The apparatus comprises a funnel 100 having an inlet 105 and an outlet 110. The inert support in this setup comprises a column of beads, with the beads being coated with a sulphur reducing elementf this is shown in Figure 5 as a sulphur-coated seed bed 115. Ozone enriched air is drawn into the inlet 105 of the funnel 100, passed through the sulphur-coated seed bed 1 15, and passed out through the outlet 110.

The overall mass of beads used for the seed bed 115, before being coated sulphur, was 80 grams, with the overall mass increasing to 124 grams after being coated with sulphur, so that the total mass of sulphur added was 44 grams. Of that amount, 17.6 grams (before coating) was used in the experimental seed bed 115, so that the resultant mass of sulphur used in testing was 9.68 grams. The air flow speed at the inlet 105 was 1.5 m/s. Measurements of ozone concentration (in parts per million or PPM) were taken at the inlet 105 and the outlet 1 10, and these concentrations are plotted respectively in Figure 6, along with a plot showing the percentage difference between inlet and outlet concentrations.

■ ί . . . ■

Example 2. Sterilisation, decontamination and/or sanitisation device

incorporating the reducing agent of Example 1.

Referring now to the accompanying drawings, there is shown an example of a sterilisation and decontamination device 1 for carrying out a process according to one embodiment of the present invention. The apparatus comprises a portable enclosure 1 having a main body 10 and a detachable control panel 12. In the embodiment shown, the control panel is in the preferred form of a detachable lectern but it is to be appreciated that the invention is not limited thereto and that the control panel may be provided elsewhere on the enclosure or remote thereto.

The main body 10 has wheels 14 and handles 15 and houses the components of the device (see, in particular, Figure 4) that are required for carrying out the decontamination process, in particular a humidifier unit and an ozone generator unit. The main body also includes one or more cartridges 40 comprising a removable receptacle containing a reducing agent and support such as that described in Example 1 above. A hydrocarbon generator unit (not included in the illustrated embodiment) may optionally be included for supplying a hydrocarbon containing a carbon-carbon double bond and/or for aiding removal of by-products. A discharge outlet assembly 16 extends from the top of the main body to discharge the required substances into the atmosphere and a microprocessor is provided within the unit for controlling discharge from the outlet assembly. The discharge outlet assembly comprises a pair of converging plates 72, 14 between which the air containing the ozone, is discharged. Water discharge nozzles 80 are attached to the upper surface of the top plate 74 to introduce filtered water to a specific formula providing the necessary sterilisation and conductivity to provide effectiveness of humidification application and minimal system maintenance to the atmosphere. One or more water reservoirs deliver water to a pump (not shown) which in turn delivers pressurized water to the discharge nozzles. A cover or cap 82 is fitted over the wafer discharge nozzles, the cover being contoured such as to direct any water to a drainage collection point and a mesh or gauze 78 is provided between the converging plates to prevent the ingress of any foreign objects. The ozone generator unit includes an ozone generator 60, an ozone detector sensor, and an oxygen supply (not shown), preferably being a standard oxygen cylinder, for supplying oxygen to the ozone generator. All these components are housed within or on the housing forming the main body 10. A suitable framework may be provided for supporting the various components.

If the decontamination device 1 is to include a hydrocarbon discharge unit this too is housed within the main body 0 of the machine and includes a hydrocarbon supply in the form of a tank or container containing the hydrocarbon having a carbon-carbon double bond, such as a secondary olefin, cis or trans, including cyclic olefins together with means to discharge the hydrocarbon through the discharge outlet. Access to the interior of the main body 10 of the machine is provided by a removable, preferably lockable, side panel or lid. The main body 10 also includes part of a control unit in the form of a microprocessor which controls the apparatus 1 and may be preset with at least one sterilisation and decontamination routine. The control unit includes a controller and a user interface which is located on the detachable lectern 12 by which a user can wirelessl input commands to the main body to remotely control operation of the device.

The apparatus 1 may include an on-board battery and/or may be connectable to a mains power supply. Preferably, the main body 10 may be connected to a mains supply and the lectern 12 is battery-operated, being charged by power from the main body when the lectern is docked therein.

The apparatus 1 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, the whole device 1 comprising the main body 10 connected to the lectern 12 is wheeled into an area which is to be sterilised and/or decontaminated. The unit is correctly positioned and then the lectern is detached from the main body by lifting and tilting the lectern onto its wheels. The lectern is then wheeled but of the room and positioned across a door or other opening that allows access to the area being decontaminated. This acts as a warning and bollard to prevent any person entering the area. Furthermore, the lectern enables operation of the components within the main body to be controlled remotely from outside of the room by means of the user interface connected wirelessly to the microprocessor controlling the main body within the room. During operation of the device, the display unit on the top part of the lectern may display a visible warning to inform personnel that the decontamination process is being carried out and that the area, should be left unoccupied. The lectern may also provide a visible or audio message when decontamination is complete, informing the user that

. ^' r .

the room may be re-occupied. Other appropriate data and information may be stored for access by the user.

During operation of the device, the area is sealed and the control unit located on the main body undertakes appropriate initial safety checks such as checking the relative humidity. If the safety check is not passed, the apparatus 1 does not operate and outputs a suitable indication using warning lights which may be on one or both of the main body and the lectern. During operation of the process, safety checks are made continuously, and in the event of a system failure, the system defaults to a safe mode.

The controller continues to monitor the conditions provided by the device and once a calculated relative humidity level is reached, the controller activates the ozone generator and ozone is generated. Alternatively, the ozone may be generated prior to or simultaneously with the production of the required relative humidity levels. The generated ozone is fed into the discharging humidified airstream that passes through the discharge outlet 16. The controller provides a suitable indication that the ozone generator is operating, and monitors the ambient ozone levels through the ozone detector sensor. ^■ s Both the ozone and water vapour concentrations to be detected can be altered by means of the user interface. 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 enters a timing phase, known as the "dwell time". The dwell time can also be altered using the remote user interface, for example, to one hour, and will depend on the degree and type of decontamination / sanitisation 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 staphylococcus 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 is reactivated to replenish the ozone levels. If the humidity falls below the calculated value, the humidifier unit 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 aborts "the sterilisation and decontamination routine and outputs a suitable indication.

After the dwell time has elapsed, the controller shuts down the various supply units and the treated environment is drawn through the cartridge so that the ozone stoichiometrically reacts with the reducing agent to form a thin layer of sulphuric acid on the inert support. Prior to this, no ozone-containing air is drawn through the reducing agent so minimal oxidation of the reducing agent takes place, being the result of diffusion only. If a hydrocarbon is to be supplied, a hydrocarbon discharge unit is activated to discharge the hydrocarbon into the ambient environment. The hydrocarbon preferentially reacts with the residual ozone to accelerate the breakdown of the ozone, thereby offering faster user re-entry to the treated area.

When an ozone detector sensor detects that the ozone concentration levels are less than a predetermined value, for example 0.2 ppm or less, the controller shuts off supply of the hydrocarbon and outputs an indication that the sterilisation and decontamination routine is complete. Again this is visible on the user display of the lectern and, optionally, the main body of the machine. The ozone level of 0.2 ppm, depending on the size of the area being sterilised and decontaminated, is usually achieved in less than 3 to 4 minutes.

If the ozone detector sensor fails to indicate that the predetermined safe level of ozone has been reached within a predetermined time interval following introduction of the hydrocarbon, for example within 10 minutes, the controller outputs an indication warning of potentially hazardous ozone levels in the room. The controller may be programmed to allow a time interval to elapse in excess of the standard half-life of ozone before announcing that the room may be re-occupied.

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 with a relatively cheap and re-chargeable means for removal of the generated ozone. Whilst acid is produced on the spent ozone removal cartridge, this can be neutralized with washing in alkali or dilute water: The cartridge may be returned to the manufacturer and re-filled with new reducing agent or may be disposed of and replaced with a new cartridge placed in the machine.

It is possible to provide one or multiple cartridges depending upon the dimensions of the environment to be treated. Ideally, activation of the one or more cartridges may be controlled automatically with reference to the dimensions of the environment to be treated which can be input into the controller by the user of the machine.

It is thus possible to provide a device for decontamination of an area which is fast and effective, discrete and portable. The method may provide better than 99.99% effective sterilisation and/or decontamination of an area without an impact on the environment from harmful by-products. Rapid re^fuse of a contaminated area can thus be realised. The above-described method has proven to be lethal to a wide variety of pathogens, including bacteria such as Methicillin Resistant Staphylococcus Aureus ( RSA).

The device according to the present invention is able to facilitate both atmospheric and surface decontamination of a hospital room within just one hour. The device is such that is can be wheeled into a vacated room and be activated from outside the room by janitorial staff with minimal training using, for example, a touch screen control pad. The entire process requires minimal supervision while the intelligent control system constantly monitors room conditions and alerts staff when decontamination is complete or a problem is encountered.

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

013/021155 17 CLAIMS

1. A process for the removal of ozbrie from an environment comprising passing the ozone-containing environment over or through an inert support carrying a reducing agent, the agent being selected from the group consisting of a transition group element or salt thereof, a main group element from group 4 to 6, and an anion capable of oxidation to a higher valence state, or mixtures thereof, for reaction with the ozone.

2. A process according to claim 1 wherein the reducing agent is a metal salt, the metal component being selected from the group consisting of iron, cobalt, chromium, vanadium, titanium, copper and manganese.

3. A process according to claim 1 wherein the reducing agent is the anion sulphite or nitrite.

4. A process according to claim 1 wherein the reducing agent is moist elemental sulphur;

5. A process according to any one of claims 1 to 4 wherein the inert support has a honeycomb structure.

6. A process according to any one of claims 1 to 5 wherein the inert support comprises a ceramic material selected from the group consisting of silica; alumina and/or titania.

7. Ά process according to any one of claims 1 to 4 wherein the inert support comprises ceramic granules or particles.

8. A process for the sterilisation, decontamination and/or sanitation of an enclosed environment, the process comprising:

(a) producing a humidified enclosed environment;

(b) discharging ozone into the humidified environment;

9. A process according to claim 8 further comprising replenishing the humidity and ozone levels in step (c) to maintain effective levels for decontamination.

10. A process according to claim 8 or claim 9 further comprising recycling of the decontaminated and sterilised environment through the reducing agent in step (d) until the concentration of the ozone falls to a safe level.

11. A process according to claim 8, 9 or 10 wherein the reducing agent is provided on an inert support to increase the surface area of the agent for contact with the ozone in the environment.

12. A process according to claim 11 wherein the support has a honeycomb structure.

13. A process according to claim 11 or claim 12 wherein the support comprises a ceramic material selected from silica, alumina and/or titania.

14. A process according to claim 11 wherein the inert support comprises ceramic granules or particles.

15. A process according to any one of claims 1 to 12 further comprising mixing elemental sulphur with water and a surfactant to provide an emulsion which is then applied to the inert support.

16. A process according to claim 15 wherein the reducing agent reacts ith ozone to form an acid on the support which is washed with dilute water or alkali after use to neutralise the acid formed.

17. A decontamination, sterilisation and/or sanitation device comprising a humidifier unit, an ozone discharge unit and an ozone reducing agent mounted on an inert support, and a controller by which the humidifier unit and ozone discharge unit are controllable based on predetermined conditions.

18. A device as claimed in claim 7 wherein the reducing agent carried on an inert support is mounted or contained within a removable cartridge.

19. An ozone removal cartridge comprising a receptacle containing an inert support carrying a reducing agent, the agent being selected from the group consisting of a transition group element or salt thereof, a main group element from group 4 to 6, and an anion capable of oxidation to a higher valence state, or mixtures thereof, for reaction with the ozone.