Halocarbon recycling methods and systems

Abstract

A method for capturing halocarbon from a gas, the method comprising processing gas containing halocarbon with material which is undamaged by exposure to supercritical fluid. A method for reclaiming halocarbon from a material, the method comprising exposing the material to a supercritical fluid. A module for processing a gas containing halocarbon, the module comprising material for capturing halocarbon from a gas, wherein the module is arranged to withstand supercritical fluid.

Claims

1. A method for recovering volatile anaesthetic agent from a filter, comprising subjecting the filter to a supercritical fluid, wherein the agent is dissolved in the supercritical fluid thereby forming a supercritical solution which carries the agent from the filter, wherein subsequently the volatile anaesthetic agent is separated from the supercritical solution.

2. The method as claimed in claim 1, in which the method further comprises removing contaminants from the supercritical solution.

3. A method as claimed in claim 1, in which the supercritical fluid is carbon dioxide or nitrous oxide.

4. The method as claimed in claim 1, in which the anaesthetic agent comprises a plurality of different volatile anaesthetic agents.

5. The method as claimed in claim 4, in which the method comprises separating the plurality of different volatile anaesthetic agents from each other.

6. The method as claimed in claim 1, further comprising one or more separations performed by chromatography, said one or more separations being one or more of: removing contaminants from the supercritical solution; and separating different volatile anaesthetic agents from each other.

7. The method as claimed in claim 6, in which the separation uses supercritical fluid as a separating agent or mobile phase.

8. The method as claimed in claim 1, further comprising one or more separations performed by fractionation, said separations being one or more of: removing contaminants from the supercritical solution; and separating different volatile anaesthetic agents from each other.

9. The method as claimed in claim 8, in which fractionation is driven by the supercritical fluid.

10. The method as claimed in claim 1, comprising one or more separations and monitoring product produced by a separation.

11. The method as claimed in claim 10, in which product is monitored by one or more of infrared spectroscopy, mass spectroscopy, UV detection, Raman spectroscopy, acoustic resonance spectroscopy, or piezoelectric crystal resonance.

12. The method as claimed in claim 1, in which the method comprises collecting one or more types of anaesthetic agent from the supercritical fluid.

13. The method as claimed claim 12, in which a cooled cyclonic collector is used to collect the, or each, agent.

14. The method as claimed in claim 1, in which the supercritical fluid is carbon dioxide and in which agent is separated from the supercritical carbon dioxide by depressurisation of the supercritical solution below the critical pressure of carbon dioxide at temperatures below the critical temperature of carbon dioxide to form carbon dioxide gas and to selectively condense one or more agent fractions from the gaseous carbon dioxide.

15. The method as claimed in claim 1, in which gas including the anaesthetic agent is passed through the filter so that agent binds thereto.

16. The method as darned in claim 15, in which the gas is from a medical environment and/or from an anaesthetic machine.

17. The method as claimed in claim 1, in which the filter comprises one or more of aerogel, silicon dioxide, zeolite, carbon, and activated carbon.

18. The method as claimed in claim 1, in which the supercritical fluid is at a pressure between 7 MPa and 50 MPa.

19. The method as claimed in claim 1, in which the supercritical fluid is at a temperature between 30 C. and 100 C.

20. The method as claimed in claim 1, in which the agent is separated from the supercritical solution by depressurisation of the supercritical solution below the critical pressure of the supercritical fluid at temperatures below the critical temperature of the supercritical fluid to form a gas phase of the supercritical fluid and to selectively condense one or more agent fractions from the gas phase of the supercritical fluid.

21. An apparatus for recovering anaesthetic agent from a gas, comprising a module housing filter material and into which gas can pass so that agent binds to the filter, the module being resistant to supercritical fluid and able to withstand supercritical pressure and temperature so as to enable captured agent to be reclaimed by exposure to supercritical fluid.

22. The apparatus of claim 21, in which the module is able to withstand a pressure between 7 MPa and 50 MPa.

23. The apparatus of claim 21, in which the module is able to withstand a temperature between 30 C. and 100 C.

24. The apparatus of claim 21, in which the module is able to withstand a pressure between 7 MPa and 50 MPa and a temperature between 30 C. and 100 C.

25. A method for recycling volatile anaesthetic agent from a gas derived from a patient in a medical environment, comprising the steps of: passing the gas through a filter so that anaesthetic agent becomes bound thereto; subjecting the filter material to a supercritical fluid, thereby forming a supercritical solution; removing contaminants from the supercritical solution; collecting the anaesthetic agent from the supercritical solution; and reintroducing the anaesthetic agent to a patient.

26. The method as claimed in claim 25, in which the supercritical fluid is at a pressure between 7 MPa and 50 MPa when the filter material is subjected to the supercritical fluid.

27. The method as claimed in claim 25, in which the supercritical fluid is at a temperature between 30 C. and 100 C. when the filter material is subjected to the supercritical fluid.

28. The method as claimed in claim 25, in which the anaesthetic agent is collected from the supercritical solution by depressurisation of the supercritical solution below the critical pressure of the supercritical fluid at temperatures below the critical temperature of the supercritical fluid to form a gas phase of the supercritical fluid and to selectively condense one or more agent fractions from the gas phase of the supercritical fluid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which like components are assigned like numerals, and in which:

(2) FIG. 1 is a schematic diagram of the breathing circuit of an anaesthetic machine according to the prior art;

(3) FIG. 2 is a schematic diagram illustrating a module for capturing anaesthetic agent from contaminated gas according to an embodiment of the invention;

(4) FIG. 3 is a schematic diagram illustrating an alternative module for capturing anaesthetic agent from contaminated gas from the anaesthetic machine and theatre environment according to an embodiment of the invention;

(5) FIG. 4 is a schematic diagram illustrating the invention in use in a medical environment which comprises multiple theatres and/or anaesthetic machines according to an embodiment of the invention;

(6) FIG. 5 is a schematic diagram illustrating apparatus for reclaiming anaesthetic agent captured in a canister according to an embodiment of the invention;

(7) FIG. 6 is a schematic diagram illustrating alternative apparatus for reclaiming and purifying anaesthetic agent captured in a canister according to an embodiment of the invention;

(8) FIG. 7 is a schematic diagram illustrating apparatus for separating anaesthetic agents according to an embodiment of the invention;

(9) FIG. 8 is a schematic diagram illustrating alternative apparatus for separating anaesthetic agents according to an embodiment of the invention;

(10) FIG. 9 is a schematic diagram illustrating apparatus for recycling anaesthetic agent for use in an anaesthetic machine according to an embodiment of the invention;

(11) FIG. 10 is a schematic diagram illustrating alternative apparatus for recycling anaesthetic agent for use in an anaesthetic machine according to an embodiment of the invention;

(12) FIG. 11 is a schematic diagram illustrating apparatus for capturing anaesthetic agent for delivery to a cardiac bypass machine according to an embodiment of the invention; and

(13) FIG. 12 is a schematic diagram illustrating the use of the invention for delivering anaesthetic agent to a breathing circuit in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

(14) A module 90 for processing halocarbon, in particular capturing anaesthetic agent from a gas is shown in FIG. 2. A pressure canister 100 comprises a housing 103 containing material for capturing halocarbon from a gas, which is held in the canister 100 by at least one mesh (not shown in FIG. 2). In the presently described embodiment of the invention the material is a filter material 102 which is an aerogel which is formed from silica (SiO.sub.2) and functionalised with halocarbon. In alternative embodiments of the invention the filter material may comprised from other materials described below. The module 90, and in particular, the canister 100, is able to withstand supercritical fluid to allow supercritical fluid to pass through the filter material 102.

(15) An aerogel is a synthetic porous ultra-light material derived from a gel, in which the liquid component of the gel has been replaced with gas. An aerogel is formed by first creating a gel. Once the gel is created, the liquid component of the gel is removed by solvent exchange. Finally, the material is subjected to supercritical CO.sub.2. Supercritical CO.sub.2 is a fluid state of CO.sub.2 in which CO.sub.2 is at a pressure and temperature at or above its critical temperature and pressure, which are 31.1 C. (304.25 K) and 7.39 MPa (72.9 atm) respectively. When it is in a supercritical state, CO.sub.2 has the properties of a gas and a fluid in that it will expand to fill its container like a gas but can dissolve materials like a liquid. In addition, supercritical CO.sub.2 does not have any surface tension. Therefore, when supercritical CO.sub.2 is allowed to vaporise it does not exert capillary hydrostatic pressures onto the aerogel material that would normally collapse it. The end result is that all the liquid is removed from the gel to arrive at an aerogel in which the gel structure remains intact.

(16) The most common type of aerogel is silica aerogel. However, other aerogels exist, such as aerogels manufactured from carbon or metal oxides, calcium carbonate and resorcinol formaldehyde. The produced aerogel may be doped with metal compounds, such as nickel, precious metals, fluorocarbons or metal oxides. Doping of the aerogel gives certain properties such as preventing water absorption, gas selectivity, catalysis or adsorbent characteristics, for example. The produced aerogel may also be functionalized by cellulose, carbonisation of the aerogel, carbon nanotubes and polymerisation of monomer after aerogel formation to improve mechanical strength.

(17) The canister 100 has an ingress conduit 104 which is removably connected to an ingress pipe 106 which receives waste gas 38 from the exhaust pipe 40 of an anaesthetic machine. As the patient breathes out, the pressure of their exhaled air pushes the waste gas 38 through the pressure release valve 32, which then flows through the canister 100. The canister 100 comprises an egress conduit 108 to which an egress pipe 110 is removably connected. Processed gas 122 exits the canister 100 through the egress pipe 110 into the atmosphere. The egress pipe 110 comprises a small activated charcoal filter 120 through which gas exiting the canister 100 passes to ensure that any residual volatile agent is absorbed and prevented from being released into the atmosphere.

(18) In use, waste gas 38 flows from the exhaust pipe 40 of the anaesthetic machine into the ingress pipe 106. The anaesthetic machine from which the canister 100 receives waste gas 38 may deliver several different types of agent. Accordingly, the canister 100 may process and collect a mixture of volatile anaesthetic agents.

(19) As mentioned above, the waste gas 38 contains non-metabolised volatile anaesthetic agent 12, which is a class of halocarbon. The anaesthetic agent 12 is captured from the waste gas 38 by processing the waste gas 38 containing the anaesthetic agent 12 with the filter material which, as described above, is undamaged by exposure to supercritical fluid. The waste gas 12 containing anaesthetic agent is passed through the filter material 102. The volatile anaesthetic agent 12 in the waste gas 38 binds to the filter material 102 as the waste gas 38 passes through the canister 100. The agent 12 binds to the filter material 102 mainly due to van der Waals and some very week hydrogen bonding. Once the waste gas 38 has passed through the filter material 102, the processed gas 122 exits the canister 100 via the egress pipe 110. Any residual agent 12 remaining in the processed gas 122 is absorbed by the activated charcoal filter 120 before the processed gas 122 exits into the atmosphere.

(20) When the filter material 102 in the canister 100 is saturated with agent 12, the feed of waste gas 38 to the ingress pipe 106 may be terminated and the canister 100 removed from the ingress pipe 106 and the egress pipe 110.

(21) An alternative module 90a according to an alternative embodiment of the invention is illustrated in FIG. 3. A canister 101 has an ingress conduit 104 which is removably connected to an ingress pipe 106 which receives waste gas 38 from the exhaust pipe 40 of an anaesthetic machine. In addition, canister 101 has a first duct 105a and a second duct 105b in the housing 103. The first and second ducts 105a, 105b allow gas from another source to pass through the canister 101. In the presently described embodiment, environmental air 107 from an operating theatre, which may contain small quantities of anaesthetic agent 12, is free to pass through the ducts 105a, 105b.

(22) Filter material 102 is held inside the housing 103 by an ingress mesh 109a and an egress mesh 109b. The meshes 109a, 109b are metal. The canister 101 comprises an egress conduit 108. The width of the canister 101 reduces to form a conical venturi chamber 111 which has an egress neck portion 113. The egress conduit 108 is mounted on the egress neck portion 113.

(23) A pump (not shown) is attached to the egress conduit 108 and arranged to suck the waste gas 38 and environmental air 107 from the ingress pipe 106 and ducts 105a, 105b respectively. The combination of waste gas 38 and environmental air 107 is sucked through the filter material 102. The anaesthetic agent 12 is captured from the combination of waste gas 38 and environmental air 107 as they pass through the filter material 102. The resultant processed gas 122 is then released into the atmosphere after passing through a further activated charcoal filter (not shown in FIG. 3) to capture any residual agent 12.

(24) When the filter material 102 in the canister 101 is saturated with agent 12, the feed of waste gas 38 and environmental air 107 to the canister 101 is terminated and the canister 101 is removed from the ingress pipe 106 and the egress pipe 110.

(25) One or more canisters 100 may be used to process gasses from a plurality of anaesthetic machines and/or operating theatres. FIG. 4 illustrates a processing system 150 for processing gas form a plurality of anaesthetic machines and/or operating theatres using a first canister 100a and a second canister 100b. The canisters 100a, 100b may be similar to the canister 100 described with reference to FIG. 2.

(26) In the system illustrated in FIG. 4, a first receiving pipe 152a receives waste gas 38 from a first anaesthetic machine; a second receiving pipe 152b receives waste gas 38 from a second anaesthetic machine; and a third receiving pipe 152c receives environmental air 107 from an operating theatre. For simplicity three receiving pipes 152a, 152b, 152c are shown in FIG. 4. However, the processing system 150 may comprise any number of receiving pipes. Each receiving pipe 152a, 152b, 152c may receive waste gas 38 from an anaesthetic machine or environmental air 107 from an operating theatre.

(27) The receiving pipes 152a, 152b, 152c converge into a main receiving pipe 154. The waste gas 38 and environmental air 107 flow towards a first directional valve 156a. The first directional valve 156a directs the flow of waste gas 38 and environmental air 107 to either a first ingress pipe 106a or a second ingress pipe 106b. FIG. 4 shows the first directional valve 156a directing the flow of waste gas 38 and environmental air 107 into the first ingress pipe 106a. The first canister 100a is connected between the first ingress pipe 106a and a first egress pipe 110a, so that the waste gas 38 and environmental air 107 flows through filter material 102 in the first canister 100a, which captures anaesthetic agent from the gas 38 and air 107. The second canister 100b is connected between the second ingress pipe 106b and a second egress pipe 110b, so that the waste gas 38 and environmental air 107 flows through filter material 102 in the second canister 100b when the first directional valve 156a directs the flow of gas 38 and air 107 through the second ingress pipe 106b.

(28) The first egress pipe 110a and second egress pipe 110b meet at a second directional valve 156b which directs processed gas 122 to a main egress pipe 110. The second directional valve 156b directs the flow of processed gas 122 from the first egress pipe 110a or the second egress pipe 110b to the main egress pipe 110.

(29) The directions of each of the first directional valve 156a and the second directional valve 156b are controlled by a valve controller 158. The valve controller 158 is operatively linked to a module for monitoring gas. In the present embodiment, infra-red spectroscopy, which in the presently described embodiment is a Fourier transform infrared spectroscopy (FT-IR) device 160, is used to analyse the gas flowing in each of the first and second egress pipes 110a, 110b. In alternative embodiments of the invention, a dispersive infra-red device may be used. The FT-IR device 160 is arranged to receive samples 161 from the gas flowing in each of the first and second egress pipes 110a, 110b. Alternative monitoring means or sensors and methods include mass spectroscopy, UV detection, Raman spectroscopy, Acoustic resonance spectroscopy and piezoelectric crystal resonance.

(30) In the configuration illustrated in FIG. 4, the FT-IR device 160 periodically tests processed gas 122 from the first egress pipe 110a. The FT-IR device 160 analyses each sample for anaesthetic agent 12. Detection of anaesthetic agent 12 above a predetermined concentration in the processed gas 122 indicates that the filter material 102 in the first canister 100a is saturated with anaesthetic agent 12. For example, once the filter material is saturated with agent 12, the concentration of agent 12 in the gas exiting the canister 100a will rise to the concentration of agent 12 entering the canister 100a. If the concentration of agent 12 in the gas exiting the canister 100a and flowing through the first egress pipe 100a, is detected by the FT-IR device 160 as rising above the predetermined threshold concentration, the FT-IR device 160 sends a saturation signal 162 to the valve controller 158.

(31) Alternatively, an increase in concentration of agent 12 exiting the canister 100a may trigger the sending of a saturation signal 162 to the valve controller. For example, while agent 12 is captured by the filter material 102, a constant concentration of agent 12, which may be a trace amount, may exit a canister 100a. Therefore, an indication of saturation of filter material 102 may be the increase in the concentration of agent 12 exiting the canister 100a.

(32) When anaesthetic agent 12 above the predetermined concentration is detected in the first egress pipe 110a by the FT-IR device 160, the FT-IR device 160 sends a saturation signal 162 to the valve controller 158. On receipt of the saturation signal 162 the valve controller 158 sends a switch signal 164 to each of the valve controllers 156a, 156b. On receipt of the switch signal 164 the first valve controller 156a switches the direction of flow of waste gas 38 and environmental air 107 to the second ingress pipe 106b, and the second directional valve 156b switches direction to allow processed gas 122 to flow from the second egress pipe 110b to the main egress pipe 110. Once the gas 38 and air 107 are flowing through the second canister 100b the first canister may be replaced. In turn, once the filter material of the second canister 100b has been saturated the directional valves will switch in the opposite direction to allow the replacement of the second canister 100b.

(33) Accordingly, the processing system 150 provides a system in which the output of more than one anaesthetic machine and/or the environmental air of more than one operating theatre can be passed through a bank of canisters. Further embodiments of the processing system may comprise more than two canisters connected in parallel via corresponding ingress and egress pipes. A processing system according to these further embodiments may be used to process the anaesthetic gas scavenging system (AGSS) of an entire hospital.

(34) The canister 100 shown in FIG. 5 has been used to absorb an anaesthetic agent 12 which is bonded to the filter material 102 in the canister 100. A method for reclaiming the anaesthetic agent 12 from the filter material 102 is described herein with reference to FIG. 5 which shows a reclamation system 200 for retrieving agent 12 from the canister 100 according to an embodiment of the invention.

(35) The reclamation system 200 exposes the filter material 102 to a supercritical fluid. In the current embodiment, supercritical CO.sub.2 203 is fed into the canister 100, wherein supercritical CO.sub.2 203 passes through the filter material 102. Liquid CO.sub.2 201 is fed into the system 200 from a liquid CO.sub.2 tank 202 and collects in a CO.sub.2 reservoir 204. A separation pump 206 pumps CO.sub.2201 from the reservoir 204 into a separation condenser or accumulator 208 which pressurises and raises the temperature of the CO.sub.2 201 above its critical temperature and pressure to form supercritical CO.sub.2 203. The separation pump 206 and the accumulator 208 control the conditions under which the supercritical CO.sub.2 203 enters the canister 100.

(36) The supercritical CO.sub.2 203 is fed into the egress conduit 108 of the canister 100 wherein it passes through the filter material 102. Volatile anaesthetic agent 12 bound to the filter material 102 will dissolve in the supercritical CO.sub.2 203, so that both the agent 12 and the supercritical CO.sub.2 203 form a supercritical solution 250. The supercritical CO.sub.2 203 acts to displace and dissolve the agent 12 from the filter material 102. The supercritical solution 250 exits the canister 100 through the ingress conduit 104.

(37) The supercritical CO.sub.2 203 acts as a mobile phase, drawing supercritical agent 12 within it through a chromatography column 210. Chromatography columns may separate supercritical agent 12 based on polarity, molecular size and weight as discussed below. The supercritical solution 250 is supplied to an injector 211 which injects the supercritical solution 250 in aliquots into the chromatography column 210.

(38) The pressure inside the canister 100 and the chromatography column 210 is maintained by a back-pressure regulator 205. After passing through the chromatography column 210, separated volatile anaesthetic agents 12 and CO.sub.2 are released from their supercritical state and the volatile anaesthetic agents 12 are collected by cyclonic collection into a collection vessel 212. The gaseous CO.sub.2 is subsequently re-compressed for re-use. The accumulator 208, canister 100 and chromatography column 210 are maintained at supercritical temperatures by one or more ovens (not shown). The cyclonic collector 212 may be maintained at cold temperatures to liquefy the anaesthetic agent 12 from the gaseous CO.sub.2 201.

(39) The chromatography column 210 may be based on polarity, molecular size and weight and/or other molecular physiochemical differences that lead to different rates of flow under the influence of a supercritical fluid mobile phase. For example, a chromatography column with molecular size filters may lead to different retention times within the column that can separate different types of anaesthetic agents 12 from each other. Alternatively, a polarity based chromatography column may separate contaminants from supercritical solution 250. In an alternative embodiment of the invention, after injection of an aliquot of supercritical solution 250 for separation, pure supercritical CO.sub.2 203 may be provided to the column as the mobile phase (not shown).

(40) In addition to capturing agent 12, the filter material 102 also captures contaminants, for example, water, urea, ammonia, formaldehyde, which may also be released into the supercritical solution 250. In the currently described embodiment, a polarity based chromatography column such as 2-PE (2-Ethyl Pyridine) is used to separate anaesthetic agents from contaminants.

(41) The reclamation system 200 allows contaminants to be removed from the supercritical solution 250 via the chromatography column 210 and by cyclonic collection into the collection vessel 212.

(42) It will be clear to those skilled in the art that more than one chromatography column 210 can be placed in series to perform different separations. If a plurality of anaesthetic agents 12 is absorbed by the filter material 102, a further chromatography column may be required after contaminants have been removed. In the preferred embodiment, a chromatography column 210 based on molecular size is used to separate anaesthetic agents. Monitoring of the product of one or more of the chromatography columns may be performed by infra-red monitoring equipment, such as those described herein. The flow of the product of one or more of the chromatography columns may be controlled by a controller, such as a computer to select volatile agents 12 and exclude contaminants where required.

(43) When the canister 100 has been used to capture a single type of agent 12 and the risk of the filter material capturing contaminants is minimal, there is no need to use a chromatography column 210. Either the mixture of supercritical CO.sub.2 and supercritical volatile anaesthetic agent 12 remains in a supercritical state for subsequent redelivery to the patient via the breathing circuit, or they are depressurised from supercritical conditions and the volatile anaesthetic agent 12 is collected by the cyclonic collector 212. The gaseous CO.sub.2 is subsequently re-compressed for re-use, as described in detail below.

(44) The gaseous CO.sub.2 207 flows into a recompression pump 214 which pumps the gaseous CO.sub.2 207 into a recompression condenser 216 which converts the gaseous CO.sub.2 207 into liquid CO.sub.2 201 which is stored in the CO.sub.2 reservoir 204, or any excess is stored in the liquid CO.sub.2 tank 202.

(45) FIG. 6 illustrates an alternative reclamation system 200a and method for extracting anaesthetic agent 12 from the filter material 102 of a canister 100 which comprises three chromatography columns: a first chromatography column 210a, a second chromatography column 210b and a third chromatography column 210c.

(46) Liquid CO.sub.2 201 is fed into the system 200a from a liquid CO.sub.2 tank 202. A pump 206 pumps CO.sub.2 201 from the liquid CO.sub.2 tank 202 into a temperature-controlled accumulator 208. This pressurises and raises the temperature of the CO.sub.2 201 above its critical temperature and pressure to form supercritical CO.sub.2 203 and provides a reservoir to supply a constant flow of supercritical CO.sub.2 203. The pump 206 and the temperature-controlled accumulator 208 control the conditions under which the supercritical CO.sub.2 203 enters the canister 100.

(47) The supercritical CO.sub.2 203 is fed into the egress conduit 108 of the canister 100 wherein it passes through the filter material 102 which has captured a plurality of volatile anaesthetic agents 12. Volatile anaesthetic agents 12 bound to the filter material 102 dissolve in the supercritical CO.sub.2 203, forming a supercritical solution 250. The supercritical solution 250 exits the canister 100 through the ingress conduit 104 and collects in a supercritical fluid collection vessel 213.

(48) The supercritical solution 250 is fed into a main injection pipe 209, which feeds a first injection pipe 209a, a second injection pipe 209b and a third injection pipe 209c. The first injection pipe 209a supplies supercritical CO.sub.2 203 and agent 12 solution 250 to a first injector 211a; the second injection pipe 209b supplies supercritical CO.sub.2 203 and agent 12 solution 250 to a second injector 211b; and the third injection pipe 209c supplies supercritical CO.sub.2 203 and agent 12 solution 250 to a third injector 211c.

(49) The first injector 211a, the second injector 211b and the third injector 211c are arranged to inject supercritical CO.sub.2 203 and agent 12 solution 250 aliquots into the first chromatography column 210a, the second chromatography column 210b and the third chromatography column 210c respectively.

(50) Each Injection of solution 250 into each chromatography column is followed by a flow of pure supercritical CO.sub.2 203, which is supplied from the accumulator 208 via a supercritical CO.sub.2 supply line 227. Supercritical CO.sub.2 203 acts as the mobile phase of the chromatography columns 210a, 210b, 210c which drives separation of anaesthetic agents 12 from contaminants. The chromatography columns aim to remove and separate hydrophilic contaminants such as methanol and formaldehyde and significantly different hydrophobic contaminants such as anaesthetic agent breakdown products from the supercritical solution 250; thereby maximising the purity of the agent 12 reclaimed by the invention.

(51) In the presently described embodiment, the chromatography columns separate agents 12 based on polarity. Anaesthetic agents 12 have very similar polarities and are therefore eluted together. However, in alternative embodiments of the invention chromatography columns may be used which separate agents based on other characteristics such as size exclusion. For example, a molecular size exclusion chromatography column that distinguishes between the molecular sizes of the anaesthetic agents 12 may be used to separate agents from each other for subsequent collection in cyclonic collectors. Alternatively, chromatography columns may be placed in series to perform different separations on the same aliquot of supercritical solution 250.

(52) The product produced by each chromatography column 210a, 210b, 210c is fed into a first chromatography egress pipe 217a, a second chromatography egress pipe 217b and a third chromatography egress pipe 217c respectively. Each chromatography egress pipe 217a, 217b, 217c is connected to a respective collection pipe 219a, 219b 219c and a respective waste pipe 221a, 221b, 221c. The first collection pipe 219a, the second collection pipe 219b and the third collection pipe 219c converge into a main collection pipe 219. The first waste pipe 221a, the second waste pipe 221b and the third waste pipe 221c converge into a main waste pipe 221 which leads to a waste vent 229. The flow of product through each chromatography egress pipe 217a, 217b, 217c is directed to either the respective collection pipe 219a, 219b 219c or the respective waste pipe 221a, 221b, 221c by a respective control valve 223a, 223b, 223c which are controlled by a valve controller 225.

(53) An FT-IR device 160 monitors the product produced by each chromatography column 210a, 210b, 210c. When the FT-IR device 160 detects that agent 12 is being produced by the one or more chromatography columns 210a, 210b, 210c, the valve controller 225 sets the respective control valve(s) 223a, 223b, 223c so that the agent-product 230 flows through the respective collection pipe(s) 219a, 219b, 219c. In addition to anaesthetic agent 12, the product 230 produced by the one or more chromatography columns 210a, 210b, 210c also contains CO.sub.2. The product 230 is in a supercritical state. The supercritical state is maintained by a back-pressure regulator 205, shown in FIGS. 7 and 8. All components including those downstream of the accumulator 208 are located in a temperature controlled environment (not shown) above the supercritical temperature of the fluid. In the preferred embodiment, the supercritical fluid is carbon dioxide and the temperature is 35 C., although other temperatures above the supercritical temperature of CO.sub.2 could be used.

(54) Alternatively, when the FT-IR device 160 detects that one or more chromatography columns 210a, 210b, 210c is no longer producing anaesthetic agent 12, the valve controller 225 sets the respective control valve(s) 223a, 223b, 223c so that the waste-product 231 flows through the respective waste pipe(s) 221a, 221b, 221c to the waste vent 229. The waste vent 229 allows the waste product 231 to change to the gas phase which is vented into the atmosphere.

(55) The reclamation systems described herein typically operate at 7.4 MPa to 50 MPa (or higher). A preferred pressure is 10 MPa; and at 31 C. to 100 C. (or higher). A preferred temperature is 35 C. The reclamation systems described here may equally be used to reclaim agent 12 from a canister 101 described with reference to FIG. 3.

(56) If a plurality of different anaesthetic agents 12 have been captured by the canister 100 shown in FIG. 6, the gas 230 produced by the one or more chromatography columns 210a, 210b, 210c will contain a plurality of anaesthetic agents 12. FIGS. 7 and 8 illustrate apparatus and methods for separating each agent 12 from a plurality of anaesthetic agents 12 contained in the gas 230.

(57) FIG. 7 shows an agent collection system 600 in which one or more substances are separated from a supercritical solution comprising halocarbon and supercritical fluid. In the presently described embodiment, the supercritical solution is agent-product 230 from which one or more halocarbons are separated. Agent-product 230 is supplied to a chromatography column ingress pipe 602. The agent-product 230 contains three anaesthetic agents 12: agent A 12a; agent B 12b; and agent C 12c. The agents 12a, 12b 12c are dissolved in supercritical CO.sub.2. Example agents include isoflurane, sevoflurane and desflurane.

(58) The chromatography column ingress pipe 602 supplies agent-product 230 to a chromatography column 210. A chromatography column egress pipe 604 directs the product of the chromatography column 210 to a back-pressure regulator 205 to which a directional valve 605 is connected. The back-pressure regulator 205 depressurises the product of the chromatography column 210, which causes the product of the chromatography column 210 to cool. To mitigate the effects of cooling, the back-pressure regulator 205 contains a heating module (not shown) that prevents icing following decompression which may lead to sticking of the valve 605. The directional valve 605 is controlled by a controller 607. A FT-IR device 160 monitors the product produced by the chromatography column 210 by firing light through an in-line IR flow cell (not shown) located in the chromatography column egress pipe 604, and sends corresponding signals 614 to the controller 607, which is described further below.

(59) The agent collection system 600 comprises a collection module 608, the interior of which is cooled by a temperature control system to liquefy the anaesthetic agent 12. The interior of the collection module 608 comprises three accumulators: a first heat accumulator 610a, a second heat accumulator 610b and a third heat accumulator 610c. Each heat accumulator 610a, 610b, 610c is connected to the directional valve 605 by a respective accumulator ingress pipe 612a, 612b, 612c.

(60) The FT-IR device 160 ensures that each heat accumulator 610a, 610b, 610c collects a different agent. For example, when the FT-IR device 160 detects that agent A 12a is being produced by the chromatography column 210, the FT-IR device 160 sends a signal 614 to the controller 607 which in turn sets the valve 605 so that agent A 12a flows into the first accumulator 610a. If the FT-IR device 160 detects that that agent B 12b is being produced by the chromatography column 210, the FT-IR device 160 sends a signal 614 to the controller 607 which in turn sets the valve 605 so that agent B 12b flows into in the second accumulator 610b. Similarly, if the FT-IR device 160 detects that that agent C 12c is being produced by the chromatography column 210, the FT-IR device 160 sends a signal 614 to the controller 607 which in turn sets the valve 605 so that agent C 12c flows into the third accumulator 610c. Each heat accumulator 610a, 610b, 610c is arranged to transfer heat away from the anaesthetic agent gas 12a, 12b, 12c which are cooled and liquefy entering it which collects in an associated cyclonic collector 616a, 616b, 616c. Gaseous CO.sub.2 is allowed to escape from each cyclonic collector 616a, 616b, 616c though an associated cyclonic vent 618a, 618b, 618c.

(61) Alternative embodiments may contain further chromatography columns. Chromatography columns may separate based on polarity, molecular size or weight.

(62) The preferred embodiment of the invention uses a size exclusion chromatography column with a pore size that differentiates between the different anaesthetic agents.

(63) Alternatively, supercritical fractionation can be used to separate individual anaesthetic agents. This process refers to use of staged depressurisation of CO.sub.2 and its use as a driving gas in cold fractionating columns to elute the different agents based on their volatility. Thus lower volatility fractions condense first during slow transit through the column. The more volatile fraction continues into the next column with CO.sub.2. In this column, further cooling of the column causes condensation of this fraction and its separation from CO.sub.2.

(64) FIG. 8 shows an alternative agent collection system 600a which uses fractionation to separate anaesthetic agent 12 from agent-product 230. As above, the agent-product 230 is in a supercritical state when it enters the system 600a. The agent-product 230 flows along a pipe 650 to a back pressure regulator 205. Agent-product 230 is depressurised below critical pressure and warmed to prevent icing by the back-pressure regulator 205. Agent-product 230 flows to a first fractionating column 652a along a first fractionating column ingress pipe 654a.

(65) A first fractionating column egress pipe 656a extends from the first fractionating column 652a to a first pressure reducing valve 205a. Pressure is further controlled by the downstream pressure-regulator valve 658a. A second fractionating column ingress pipe 654b extends from the first pressure reducing valve 658a to a second fractionating column 652b. A second fractionating column egress pipe 656b extends from the second fractionating column 652b to a second pressure reducing valve 205b. A vent pipe 659 extends from the second pressure reducing valve 205b to a vent 660.

(66) Each fractionating column 652a, 652b comprises non-absorbent beads 661a, 661b, and a cooling jacket 662a, 662b to allow temperature control of each fractionating column 652a, 652b. A first collection vessel 664a is associated with the first fractionating column 652a, and a second collection vessel 664b is associated with the second fractionating column 652b.

(67) The pressure of the solution 503 is lowered in stages by the pressure regulating valves 205a and 205b. Less volatile agent 12, for example Agent X 12x, is liquefied by the first fractionating column 652a and collects in the first collection vessel 664a. CO.sub.2 and anaesthetic agent with a higher volatility, for example Agent Y 12y, passes into the second fractionating column 652b, which may be further depressurised by the pressure regulating valve 205b. Due to the low temperatures in the fractionating column 661b, the remaining anaesthetic agent liquefies and collects in the second collection vessel. Gaseous CO.sub.2 is released via the vent 660. Alternatively, gaseous CO.sub.2 may be recompressed for future use (not shown).

(68) A plurality of fractionating columns may be arranged in parallel which enables selected agents to be recovered at a higher rate. Alternatively, a plurality of fractionating columns may be arranged in series, as shown in FIG. 8, to allow a greater range of agents to be collected.

(69) In alternative embodiments of the invention, in-line infra-red, preferably FT-IR sensor, devices may be used to detect the presence of anaesthetic agents and contaminants in liquidised agent 12x, 12y. Further separation steps, for example using chromatography or fractional distillation, may then be used to achieve the required purity of agent 12x, 12y

(70) According to a further embodiment of the invention, a recycling system 300 for reintroducing halocarbon is shown in FIG. 9. The recycling system 300 comprises halocarbon-binding material, filter material 102 in the presently described embodiment, for capturing halocarbon from a gas. The system 300 is arranged to expose the material to gas containing halocarbon to capture the halocarbon, and to supercritical fluid to dissolve the halocarbon in a supercritical solution. In the presently described embodiment, the halocarbon is volatile anaesthetic agent 12 that has been extracted from the waste gas 38 of an anaesthetic machine, and returned back into the same anaesthetic machine, as shown in FIG. 9.

(71) The recycling system 300 shown in FIG. 9 has a first module as described above, and the system 300 is arranged to supply fluid to the module so that the fluid passes through the filter material 102. The recycling system 300 offers the optimum in volatile anaesthetic agent 12 recycling to patients during long operations and in intensive care. The recycling system 300 is arranged to continually recycle a single volatile anaesthetic agent 12.

(72) The recycling system 300 comprises a first silica aerogel canister 100a and a second silica aerogel canister 100b. Each canister 100a, 100b has a waste gas ingress conduit 104a, 104b to allow waste gas 38 to enter each canister 100a, 100b and a gas egress conduit 108a, 108b to allow processed gas to exit each canister 100a, 100b. The first waste gas ingress conduit 104a and the second waste gas ingress conduit 104b are each connected to a respective first waste gas ingress pipe 106a and second waste gas ingress pipe 106b. Each ingress pipe 106a, 106b comprises an ingress valve 302a, 302b for controlling the flow of waste gas 38 into the respective canister 100a, 100b. The first processed gas egress conduit 108a and the second processed gas egress conduit 108b are each removably connected to a respective first egress pipe 110a and second egress pipe 110b. The first and second egress pipes 110a, 110b meet to form a single main egress pipe 110 which comprises a Fourier transform infrared spectroscopy (FT-IR) device 160 arranged to detect the presence of volatile anaesthetic agent 12 in the main egress pipe 108. A rise in the concentration of volatile anaesthetic agent 12 in the main egress pipe 108 indicates that the canister currently removing agent 12 from the waste gas 38 is saturated which will necessitate a switch in the operation of the canisters 100a, 100b. After the gas has passed through the Fourier transform infrared spectroscopy (FT-IR) device 160, it then passes through a small activated charcoal filter 120 which captures any residual agent 12.

(73) In addition to a waste gas ingress conduit 104a, 104b and processed gas egress conduit 108a, 108b each canister 100a, 100b has a supercritical CO.sub.2 ingress port 304a, 304b and a supercritical CO.sub.2 egress port 306a, 306b. Each CO.sub.2 ingress port 304a, 304b is connected to a CO.sub.2 ingress pipe 308a, 308b which supplies supercritical CO.sub.2 203 into each respective canister 100a, 100b. Each CO.sub.2 ingress pipe 308a, 308b comprises a CO.sub.2 valve 310a, 310b for controlling the flow of supercritical CO.sub.2 203 into each respective canister 100a, 100b. Each CO.sub.2 ingress pipe 308a, 308b is fed from a main CO.sub.2 ingress pipe 308. Each supercritical CO.sub.2 egress port 306a, 306b is connected to a respective CO.sub.2 egress pipe 312a, 312b. Each CO.sub.2 egress pipe 312a, 312b is connected to a main CO.sub.2 egress pipe 312 which carries supercritical CO.sub.2 203 from the first and second canisters 100a, 100b.

(74) The main CO.sub.2 egress pipe 312 leads to a back pressure regulator 320 that warms and decompresses the CO.sub.2 and dissolved agent 12. A cooled cyclonic separation chamber 322 liquefies and separates the volatile agent 12 from the gaseous CO.sub.2. The gaseous CO.sub.2 flows in a recovered CO.sub.2 pipe 324 to a CO.sub.2 reservoir 204. A CO.sub.2 tank 202 is connected to the recovered CO.sub.2 pipe 324 to top-up the CO.sub.2 in the recycling system 300. A separation pump 206 pumps CO.sub.2 from the reservoir 204 into a separation accumulator 208. The separation pump 206 increases the pressure of the CO.sub.2 above the critical pressure of CO.sub.2 (73 bar). The accumulator 208 and canisters 100a, 100b are housed in an oven (not shown) to maintain the temperature above the critical temperature of CO.sub.2 (31.1 C.). The accumulator 208 warms the CO.sub.2 and provides a buffer of supercritical CO.sub.2 to maintain the pressure in the circuit above critical pressure. Preferably the operating temperature is 35 C. and the pressure 100 bar (10 MPa). However, in alternative embodiments these values may be higher. The separation pump 206 and the accumulator 208 control the conditions under which the liquid CO.sub.2 enters the main CO.sub.2 ingress pipe 308.

(75) The delivery chamber 316 is warmed above the critical temperature of CO.sub.2 and stores agent 12 dissolved in supercritical CO.sub.2 for use in a breathing circuit 2 of an anaesthetic machine. The delivery chamber 316 may receive injected recycled anaesthetic agent 12 from the cyclonic separator 322 via the delivery pipe 314 or from a container 326 containing non-recycled agent 12 which may have been obtained from another source. The anaesthetic agent 12 in the delivery chamber 316 is dissolved in supercritical CO.sub.2. The concentration is measured by a Fourier transform infrared spectroscopy (FT-IR) device 160. Accordingly, the concentration of agent 12 in the supercritical CO.sub.2 may be adjusted to the correct level by adding more or less agent 12 from the cyclonic separator 322 or container 326 or by adding supercritical CO.sub.2 to the delivery chamber 316 from the separation pump 206 (connection not shown).

(76) An injection pipe 330 extends from the delivery chamber 316 to the breathing circuit 2 of an anaesthetic machine. The injection pipe 330 comprises a warmed injector 334 under the influence of a computer and clinician-controlled valve 332. The injector injects agent 12 dissolved in supercritical CO.sub.2 into the breathing circuit 2, preferably directly into the inspiration pipe 6. As the CO.sub.2 is decompressed and warmed it vaporises and disperses the anaesthetic agent 12 for delivery to the patient. The soda lime canister 34 of the breathing circuit 2 may be moved to the inspiratory limb 6 to absorb the small amounts of CO.sub.2 delivered by the injector 334.

(77) A method of recycling halocarbon is now described with reference to FIG. 9. A patient breathes in gas containing volatile anaesthetic agent 12 supplied by the inspiration tube 6 of a breathing circuit 2 modified as described above and shown in FIG. 9. The patient exhales unused agent 12 via an expiratory tube 8. Waste gas 38 released by a pressure-relief valve 32 (not shown in FIG. 9) flows through the exhaust pipe 40 which is connected to a main ingress pipe 106 which splits into the first ingress pipe 106a and the second ingress pipe 106b. The first ingress valve 302a is open to allow waste gas 38 into the first canister 100a and the second ingress valve 302b is closed to prevent waste gas 38 from entering the second canister 100b. The waste gas 38 containing agent 12 is processed by the halocarbon-binding material to bind halocarbon to the material. The flow through the first canister 100a is as described above with reference to FIG. 2 and exits the first canister 100a via its egress port 108a. The processed gas 122 is released into the atmosphere via an activated charcoal filter 120.

(78) The first CO.sub.2 valve 310a is closed to prevent supercritical CO.sub.2 entering the first canister 100a and the second CO.sub.2 valve 310b is open to allow supercritical CO.sub.2 to enter the second canister 100b. The material 102 is exposed to the supercritical CO.sub.2 entering the second canister 100b which flows through the filter material 102 to dissolve halocarbon, i.e. the agent 12, bound to the material 102 by dissolving the agent 12 in the supercritical CO.sub.2, as described above with reference to FIG. 5. The dissolved halocarbon and supercritical fluid to form a supercritical solution. The supercritical solution in which agent 12 is diluted exits the second canister 100b through the second supercritical CO.sub.2 egress port 306b.

(79) During processing of waste gas 38 by the current embodiment of the invention, the first ingress valve 302a and the first CO.sub.2 valve 310a are arranged so that when the first ingress valve 302a is open the first CO.sub.2 valve 310a is closed, and vice versa. Similarly, the second ingress valve 302b and the second CO.sub.2 valve 310b are arranged so that when the second ingress valve 302b is open the second CO.sub.2 valve 310b is closed, and vice versa. Accordingly, the valves 302a, 302b, 310a, 310b are arranged such that either of the first canister 100a or the second canister 100b cannot receive waste gas 38 and supercritical CO.sub.2 simultaneously. In addition, during processing of waste gas 38 by the current embodiment of the invention, the first ingress valve 302a and the second ingress valve 302b are arranged so that they cannot be in the same state, i.e. open or closed at the same time. Similarly, the first CO.sub.2 valve 310a and the second CO.sub.2 valve 310b are arranged so that they cannot be in the same state, i.e. open or closed at the same time.

(80) In an alternative embodiment, an ingress three-way valve located at the junction of the main ingress pipe 106, first ingress pipe 106a and second ingress pipe 106b may be substituted for each of the first and second ingress valves 302a, 302b. In addition, a three-way CO.sub.2 valve located at the junction of the main supercritical CO.sub.2 pipe 308, first supercritical CO.sub.2 pipe 308a and second supercritical CO.sub.2 pipe 308b may be substituted for the first and second supercritical CO.sub.2 valves 310a, 310b.

(81) The supply of waste gas 38 and supercritical CO.sub.2 302 entering the two canisters 100a, 100b of the recycling system 300 system is controlled by the valves 302a, 302b, 310a, 310b so that one canister 100a, 100b receives waste gas 38 while the other canister 100b, 100a receives supercritical CO.sub.2 203. Accordingly, one canister 100a, 100b captures agent 12 from the waste gas 38 while agent 12 is removed from the other canister 100b, 100a for re-use in the breathing circuit 2 of the anaesthetic machine.

(82) The states in which the valves 302a, 302b, 310a, 310b operate are swapped simultaneously at regular intervals. In the embodiment of the invention shown in FIG. 9, during a first swap the first ingress valve 302a is closed, the first CO.sub.2 valve 310a is opened, the second ingress valve 302b is opened and the second CO.sub.2 valve 310b is closed. At a later point the states of the valves 302a, 302b, 310a, 310b are swapped back to their previous states when the filter material 102 of the first canister 102a is saturated. It is envisaged that in other embodiments of the invention the swap may occur before saturation of the filter material 102. When the states of the valves 302a, 302b, 310a, 310b are first swapped, the first canister 100a no longer receives waste gas 38, but receives supercritical CO.sub.2 203 instead to release the agent 12 captured in the canister 100a. The second canister 100b no longer receives supercritical CO.sub.2 203, but receives waste gas 38 instead to capture agent 12.

(83) Swapping the states of the valves 302a, 302b, 310a, 310b and therefore the functions of the canisters 100a, 100b enables continuous operation of the agent recycling system 300. As mentioned above, the filter material 102 is able to withstand supercritical fluid. Therefore, the material and one or more modules according to an embodiment of the invention may be reused, i.e. be subject to many capture-reclamation cycles, without appreciable decay in their performance. However, in alternative embodiments of the invention, the filter material and/or one or more modules may require replacement after a number of capture-reclamation cycles. The agent 12 recovered by the recycling system 300 may be kept dissolved in supercritical CO.sub.2 203 which may be injected directly into the breathing circuit 2 of an anaesthetic machine as described above, or returned to a vaporiser (not shown).

(84) Anaesthetic machines allow anesthetists to deliver a specific oxygen fraction with an accurately diluted amount of volatile agent 12 to the patient. The invention enables agent 12 to be rapidly administered to the patient with the required concentration. Providing volatile anaesthetic agent 12 directly into the breathing circuit 2 of the anaesthetic machine enables fast induction of the agent 12. The invention also provides an anaesthetist with fine control of the dosage of agent 12. An infra-red absorption spectra machine 160 monitors the concentrations of agent 12 in the inspiratory tube 6 and expiratory tube 8 of the breathing circuit 2. The concentration of agent 12 in the inspiratory tube 6 is monitored to ensure that the correct concentration of agent is administered to the patient. The concentration of agent 12 in the expiratory tube 8 is monitored as an Indicator of the depth of anaesthesia. For example, the level of end-tidal agent concentration is a reliable indicator of the depth of anaesthesia. The infra-red absorption spectra machine 160 is linked to a control module (not shown) that controls the delivery of the agent 12 by influencing the function of the delivery valve 332 based on the readings obtained by the infra-red absorption spectra machine 160.

(85) The invention also enables the entire output from the patient to be scavenged for agent 12. Furthermore, the invention provides immediate clearance of agent 12 from the breathing circuit 2 and rapid wake-up of the patient.

(86) FIG. 10 illustrates an alternative recycling system 301 which has many features in common with the apparatus described above. The alternative recycling system 301 delivers anaesthetic agent 12 dissolved in supercritical CO.sub.2 203 and recycles captured waste gas 38 itself, and comprises a chromatography column 210 to separate anaesthetic agent 12 from contaminates. The alternative recycling system 301 is preferably used with a single anaesthetic agent, although further chromatography or fractional distillation methods could be used to allow the use of multiple anaesthetic agents.

(87) In the alternative recycling system 301 waste gas 38 from a breathing circuit 2 of an anaesthetic machine flows through a main ingress pipe 154 to the first and second canisters 100a, 100b via respective first and second ingress pipes 154a, 154b. In an alternative embodiment, the main ingress pipe 154 may also receive environmental air 107 from operating theatres.

(88) According to a method of using the alternative recycling system 301, the first ingress valve 302a is open to allow waste gas 38 into the first canister 100a and the second ingress valve 302b is closed to prevent gas 38 entering the second canister 100b. The gas 38 is processed by the first canister 100a as described above to capture the agent 12 and exits the first canister 100a via its egress port 108a. The processed gas 122 is released into the atmosphere.

(89) The first CO.sub.2 valve 310a is closed to prevent supercritical CO.sub.2 entering the first canister 100a and the second CO.sub.2 valve 310b is open to allow supercritical CO.sub.2 to enter the second canister 100b. Supercritical CO.sub.2 entering the second canister 100b flows through the filter material 102 to reclaim agent 12 bound to the filter material 102 by dissolving the agent 12 in the supercritical CO.sub.2 forming a supercritical solution 250. The supercritical solution 250 exits the second canister 100b through the second supercritical CO.sub.2 egress port 306b, the second CO.sub.2 egress pipe 312b and through the main CO.sub.2 egress pipe 312 into a supercritical solution reservoir 338.

(90) The supercritical solution reservoir 338 supplies supercritical solution 250 to a chromatography column injector 211 which injects aliquots of supercritical solution 250 into a chromatography column 210 via a chromatography column ingress pipe 340. A supply line 227 supplies pure supercritical CO.sub.2 203 to act as the mobile phase. A chromatography column egress pipe 341 allows fluids to leave the chromatography column 210. The chromatography column 210 separates contaminates from anaesthetic agent 12 and supercritical CO.sub.2, and a mixture of anaesthetic agent 12 and supercritical CO.sub.2 exits the chromatography column 210 via the chromatography column egress pipe 341.

(91) The agent 12 dissolved in supercritical CO.sub.2 flows along the chromatography column egress pipe 341 to a back-pressure regulator 345 which decompressed and warms the mixture. The decompressed mixture flows to a valve 342 which is controlled by a FT-IR device 160 which monitors the fluid in the chromatography column egress pipe 341. When the fluid in the chromatography column egress pipe 341 contains contaminates, the valve 342 releases any contaminants into the atmosphere via a chromatography column egress port 344. When the samples contain agent, the valve 342 directs the fluid flow to a heat accumulator 346 which transfers heat away from the fluid flow so that the anaesthetic agent 12 cools and liquefies for collection in a cyclonic separation chamber 320.

(92) A controllable agent injector 348 controls the injection of liquefied agent into a delivery chamber 316. The FT-IR device 160 monitors the concentration of agent in the delivery chamber 316. The concentration of agent in the delivery chamber 316 may be adjusted by adding more agent 12 by the controllable agent injector 348 or more supercritical CO.sub.2 203 by a controllable supercritical CO.sub.2 injector 349.

(93) The supercritical CO.sub.2 and agent at a controlled concentration are injected directly from the compression pipe 330 into the breathing circuit 2 by a warmed injector 504. An infra-red absorption spectra machine 160 monitors the concentrations of agent 12 in the inspiratory tube 6 and expiratory tube 8 of the breathing circuit 2. The infra-red absorption spectra machine 160 is linked to a controller 505 to ensure that the correct concentration of agent is administered to the patient. The controller 505 can also be influenced by the clinician. As the supercritical CO.sub.2 is depressurised by the injector 504, it is warmed to prevent icing. This disperses and vaporises the anaesthetic agent 12 into the breathing circuit 2. Only small amounts of CO.sub.2 are used and these are absorbed by the soda lime 36 in the breathing circuit 2.

(94) According to another embodiment, the invention may be used to deliver a supercritical solution of anaesthetic agent dissolved in a supercritical fluid to a medical device. FIG. 11 illustrates a cardiac bypass circuit 400 comprising a pulmonary gas exchange 402, which is also known in the art as an oxygenator, which removes waste gas 38 from venous blood 404 while simultaneously oxygenating blood. A pump 406, a suction line 408 and a venous line 410 are used to take venous blood 404 from a patient during an operation. The venous blood 404 taken from the patient is collected in a blood reservoir 412 before entering the pulmonary gas exchange 402.

(95) Oxygen and anaesthetic agent 12 are supplied to the pulmonary gas exchange 402 from an anaesthetic machine (not shown in FIG. 11) via an oxygen tube 414 and waste gas 38 exits the exchange 402 via an exhaust pipe 30. The waste gas 38 contains volatile anaesthetic agent 12 that has not been metabolised or absorbed by the patient. The exhaust pipe 30 is connected to an ingress pipe 106 which is removably connected to the ingress conduit 104 of a canister 100 as shown in FIG. 2 and described above. The canister 100 captures the agent 12 by binding the agent 12 to the filter material 102 as the waste gas 38 passed through the filter material, as described above with reference to FIG. 2. Waste gas 38 from which agent 12 has been removed by the canister 100 exits the canister 100 though the egress conduit 108 to which an egress pipe 110 is removably connected. The egress pipe 110 comprises a small activated charcoal filter 120 to capture any residual agent 12 in the processed gas 122 before the processed gas 122 is released from the egress pipe 110 into the atmosphere. Oxygenated blood from which the agent 12 has been removed exits the pulmonary gas exchange 402 via an exchange exit tube 416.

(96) A supercritical solution 418 comprising supercritical CO.sub.2 203 and volatile anaesthetic agent 12 is stored in a pressurised storage tank 420 which is mounted in a heated sleeve 421 to maintain the temperature above critical temperature. The storage tank 420 supplies a warmed electronically controlled injector valve 432 which is controlled by a controller 433. The supercritical solution 418 is injected directly into the patient's blood flowing through the exchange exit tube 416. The supercritical CO.sub.2 203 is depressurised by the injector valve 432 and is absorbed into blood with the dispersed and vaporised anaesthetic agent 12. The blood-agent dilution flows from the exchange exit tube 416 into a centrifugal pump 422 which is controlled by the controller 433, and propels the blood containing the agent dilution into an arterial line 424 which feeds the blood-agent dilution into an artery of the patient. The arterial line 424 comprises a bubble trap 426 to prevent gas bubbles from entering the patient's circulatory system.

(97) Samples of blood are taken from the arterial line 424 for analysis. The samples of blood are measured by an infra-red absorption spectra machine 160 to determine the concentration of agent 12 in the blood being returned to the patient. The concentration of agent 12 delivered into the exchange exit tube 416 may then be altered if necessary. The infra-red absorption spectra machine 160 also monitors the waste gas 38 from the pulmonary gas exchange 402 for volatile anaesthetic agent 12, which provides a means of measuring the depth of anaesthesia. In addition, the infra-red absorption spectra machine 160 monitors the processed gas 122 to indicate when the filter material 102 has been saturated with agent 12.

(98) In alternative embodiments of the invention, either of the recycling systems 300, 301 described above may be combined with the cardiac bypass circuit 400 to form a recycling system for reintroducing volatile anaesthetic agent that has been extracted from the blood of a patient by the cardiac bypass circuit 400. In further embodiments of the invention, a mixture of anaesthetic and supercritical CO.sub.2 may be injected into the gas feed to the oxygenator or the arterial line 424 of a cardiac bypass circuit 400. This invention may also be used in mini-bypass circuits that do not have a venous blood reservoir 412.

(99) In a further embodiment, the invention may be used in a portable anaesthetic machine 500, such as may be used by the military, disaster relief organisations or hospitals, as shown in FIG. 12. The portable anaesthetic machine 500 comprises a replaceable pressurised storage tank 502 containing a supercritical solution 503 of anaesthetic agent dissolved in supercritical CO.sub.2. The replaceable storage tank 502 is mounted in a warming sleeve 421 which ensures that the solution is maintained at a supercritical temperature. The warming sleeve is controlled by a warming sleeve controller 507.

(100) The storage tank 502 feeds an injector 504 controlled by an injector system controller 509 which injects solution 503 into a vaporisation chamber 21 which is incorporated into the breathing circuit 2 of the portable anaesthetic machine 500. The unidirectional valve 16 is connected to an inspiratory tube 6 which is arranged to supply gas containing an anaesthetic agent 12 for inhalation by a patient. The portable anaesthetic machine 500 comprises an expiratory tube 8 through which exhaled and unused gases and agent 12 are transported away from the patient via a unidirectional expiratory valve 26 to an expiratory pipe 24.

(101) A CO.sub.2 absorber canister 34 is connected to the expiratory pipe 24. The absorber canister 34 contains lime soda 36 to absorb carbon dioxide from the gas that flows through the canister 34. A ventilator or bag 506 links the CO.sub.2 absorber canister 34 to the vaporisation chamber to complete the breathing circuit 2 and provide a means of pressuring the breathing circuit 2 to deliver a breath to the patient.

(102) The portable anaesthetic machine 500 comprises an infra-red monitoring device. In the presently described embodiment a FT-IR device 160 is used which is arranged to monitor the level of agent 12 flowing in the inspiratory pipe 6 and the expiratory pipe 8. In alternative embodiments of the invention, the infra-red monitoring device may be a dispersive infra-red device to improve portability as dispersive infra-red devices are typically simpler and smaller than a FT-IR device. If the FT-IR device 160 detects that the level of agent in the flowing in each of the inspiratory pipe 6 and the expiratory pipe 8 requires adjustment, it sends a signal 508 to the controller 509 which instructs the injector 504 to increase or reduce the injection of solution 503, as necessary. The controller 509 also adjusts the ventilator to deliver the required pressure and rate for ventilation as decided by the clinician.

(103) A pressure release valve 32 directs waste gas 38 through an ingress pipe 106 to an ingress conduit 104. The waste gas 30 is processed by a canister 100 containing filter material 102 which captures agent 12. Processed gas 122 exits the canister 100 via an egress conduit 108, flows through an activated charcoal filter 120 and vented into the atmosphere.

(104) In alternative embodiments of the invention, a catalyst may be deposited onto a ceramic honeycomb structure at the ingress conduit 104 of the canister 100. In this position, the catalyst will act on d supercritical solution as it egresses the canister 100 during reclamation. In further embodiments, the catalyst is introduced as a dopant into an aerogel. It will be clear to those experienced in the art, that many different precious and non-precious metals might be used as a catalyst.

(105) Although particular embodiments of the invention have been disclosed herein in detail with reference to a medical environment, this by way of example only and for the purposes of illustration only. The invention may be used for the capture and reclamation of halocarbons in other industries in which halocarbon capture and/or reuse is desirable or required.

(106) In an alternative embodiment of the invention, exhaust gas from the production area of a factory which uses halocarbons is passed through a canister 100, 101 containing filter material. The halocarbons are captured by the filter material. Once the filter material has been saturated, it may be subjected to supercritical CO.sub.2, as described above, to dissolve the halocarbons in the supercritical CO.sub.2 to produce a supercritical solution. The halocarbons may be separated from the supercritical CO.sub.2 by chromatography and fractional distillation, as described above.

(107) Nitrous oxide (N.sub.2O) is an important gas in pediatric and maternal anaesthesia. However, N.sub.2O is unstable under supercritical conditions, but may be controlled when used with a reduction catalyst.

(108) In a further embodiment of the invention, the module 90 may comprise a reduction catalyst such as precious or semi-precious metals/metal oxides. In a preferred embodiment, the metal catalyst is platinum although others such as titanium oxide, tungsten oxide, vanadium oxide, molybdenum oxide, rhodium, palladium may be used. The reduction catalyst may be deposited onto the filter material 102, which may preferably be aerogel or any of the other filter materials described above. Alternatively, the filter material 102 may comprise the reduction catalyst. The reduction catalyst may be loaded with reactant, preferably urea before halocarbon capture or before halocarbon reclamation by supercritical CO.sub.2 extraction. In this way, as waste gas 38 containing agent 12 passes into the module, nitrous oxide may react with the urea (CO(NH.sub.2).sub.2) in the presence of the catalyst to form nitrogen (N.sub.2), water (H.sub.2O) and carbon dioxide (CO.sub.2).

(109) When the canister 100 is saturated with agent 12, it may be flushed with supercritical CO.sub.2 to elute the halocarbon agent 12 as described in FIGS. 5, 6, 9 and 10. In the present embodiment, due to the presence of nitrous oxide absorbed onto the filter material and the selective reduction catalysts, it will also reduce nitrous oxide. Carbon dioxide is pumped into the canister to achieve supercritical pressure, preferably at 10 MPa and 35 C. degrees, although higher pressures and temperatures may be required. When the circuit is pressurised, flow through the system when the back pressure regulator opens results in supercritical N.sub.2O diluted in supercritical CO.sub.2 passing through the filter material and catalyst in the presence of urea. Reaction rates are high at supercritical pressure and temperature and in the absence of oxygen. Nitrogen gas and other by-products may be extracted from the agent by chromatographic separation.

(110) It will clear to those skilled in the art that this invention may be used for the selective reduction catalysis of nitrous oxide intermediates (NO.sub.x) including nitrous oxide (N.sub.2O) in situations outside of the reclamation of anaesthetic agents, such as power or heat generation and in the automobile industry.

(111) In other embodiments of the invention other supercritical fluids such as supercritical nitrous oxide (N.sub.2O) may be used. N.sub.2O becomes supercritical at a similar temperature and pressure as CO.sub.2 and behaves in a similar manner to supercritical CO.sub.2. For example, in an alternative embodiment of the invention described above, supercritical N.sub.2O may be used to dissolve agent 12 bound to the filter material 102 in an alternative canister 100, 101 that has been saturated with agent 12. In these embodiments, it is envisaged that reduction catalysts as described above will be used to reduce N.sub.2O to nitrous and oxygen, and/or supercritical N.sub.2O may be diluted in supercritical CO.sub.2 to stabilise supercritical N.sub.2O.

(112) The aforementioned embodiments are not intended to be limiting with respect to the scope of the appended claims, which follow. Furthermore, features of one or more of the above embodiments may be readily combined with one or more features of another embodiment. It is also contemplated by the inventors that various substitutions, alterations, and modifications may be made to the invention without departing from the scope of the invention as defined by the claims.