GB2605909A - Improvements to separation and condensation of anaesthetic agents and description of a process of catalytic breakdown of nitrous oxide and its intermediates - Google Patents

Abstract

A method for separating one or more substances from an anaesthetic agent solution. The method comprises a polarity-based separation step to separate out contaminants from anaesthetic agent/s.

Description

IMPROVEMENTS TO SEPARATION AND CONDENSATION OF

ANAESTHETIC AGENTS AND DESCRIPTION OF A PROCESS OF

CATALYTIC BREAKDOWN OF NITROUS OXIDE AND ITS INTERMEDIATES

WITH THE CAPTURE AND REMANUFACTURE OF ENVIRONMENTAL

HALOCARBONS FROM THE ATMOSPHERE

Technical Field

The present invention relates to methods and systems for separating anaesthetic agents and halocarbons dissolved in supercritical fluids and to the capture of atmospheric pollutants with catalytic breakdown of nitrous oxide and its intermediates and the capture and re-manufacture of halocarbons.

Background

Volatile anaesthetic agents are typically halogenated fluorocarbons, examples of which include desflurane, isoflurane, sevoflurane enflurane and halothane. Volatile anaesthetic agents are liquid at room temperature but evaporate easily to produce a vapour for inhalation by a patient to induce anaesthesia. Anaesthetic agents are used extensively in modern healthcare and represent a significant cost. They are also potent greenhouse gases due to their ability to absorb infrared light and their upper atmospheric persistence. Isoflurane and Halothane also contain Chlorine and Bromine groups that contribute to ozone depletion.

The applicant's unpublished International Patent Application, hereinafter referred to as P34906VV0, details methods and systems for the capture and remanufacture of halocarbons and anaesthetic agents. In this method, halocarbons are captured onto a filter material, for example a halocarbon-modified cellulose aerogel, from the exhaust of the anaesthetic machine then eluted and purified by chromatography and fractional separation using supercritical fluids, preferably carbon dioxide.

Supercritical fluids dissolve and elute the anaesthetic agents but also purify them by supercritical chromatography and/or fractional separation, preferably but not exclusively in a single process. Fractional separation or 'supercritical fractionation' as referred to in P34906W0, refers to the separation of halocarbons based on their volatility by using subcritical pressures of carbon dioxide in fractionating columns at different temperatures to separate out individual agents and collect them for bottling. P34906W0 details two different collection systems.

The first collection system 600 shown in Figure 1 shows supercritical CO2 and a purified plurality of anaesthetic agents 230 introduced through an ingress pipe 602 into a chromatography column 210 based on molecular size exclusion. The separated anaesthetic agents exit the column through an egress pipe 604 and are detected by a detector, preferably a ultraviolet photodiode array, mass spectrometer, photoacoustic spectrometer, acoustic resonance spectrometer or most preferably an infrared spectrophotometer I 60 which sends a feed 614 to a controller 607. The controller 607 influences the valve 605 position. The separated anaesthetic agents dissolved in supercritical CO2 pass to the back-pressure regulator 205 and are depressurized. They pass to the valve 605 and under the influence of the controller 607, and are separated into their respective condensation pipes 612a, 612b, 6I2c which run in thermal store jackets 610a, 6I0b, 6I0c to cool and liquidize the anaesthetic agents in a temperature controlled environment 608. Liquid anaesthetic agent then passes into the respective collection chambers 61 6a, 61 6b, 61 6c and gaseous CO2 6I 8a, 6I 8b, 61 Sc is released from each chamber.

The second collection system is for separating the purified plurality of anaesthetic agents by the use of supercritical fractionation. This term refers to the sequential depressurization of carbon dioxide from supercritical pressures through fractionation columns in which temperature is used to select out the least volatile anaesthetic agent before condensing the more volatile anaesthetic agent in a second column. This allows for the separation of individual anaesthetic agents based on volatility but also allows for condensation at pressure. This is advantageous as even low flow rates of supercritical CO2 convert to very high gas flows when depressurized. To maintain effective temperature gradients and condense volatile agents in such a high gas flows is difficult. By pressurizing the condensation and separation stages, the flow rates are reduced and the temperatures that are required for efficient collection are increased, requiring less intensive cooling apparatus.

P34906VVO details a supercritical fractionation process 600a shown in Figure 2 in which a plurality of purified anaesthetic agents dissolved in supercritical CO2 230 are delivered to a back-pressure regulator 205 via a conduit 650. The supercritical solution is depressurized by the back-pressure regulator 205 but to a pressure maintained by a downstream pressure regulator 205a. The mixture of gaseous CO2 and anaesthetic agents passes through an ingress pipe 654a into a first fractionation column 652a which is temperature controlled in a thermal jacket 662a and contains inert beads 661a to increase thermal transfer to the gaseous mixture.

The pressure and temperature are such that the lowest volatility anaesthetic agent I 2x condenses and is collected in a collection chamber 664a that can be isolated from the pressurised collection column. Carbon dioxide and the more volatile agent remain gaseous, passing into an egress conduit 656a to through the pressure regulator 205a leading to further depressurization under the influence of a second downstream pressure regulator 205b. The gaseous mixture passes through an ingress pipe 654b to a second fractionation column 652b, contained in a temperature controlled thermal sleeve 6626 and containing inert beads 66Ib for thermal transfer. This column is held at such temperatures and pressures to ensure condensation of the more volatile anaesthetic agent but leaving CO2 in its gaseous state to pass through the second column 6526 into the egress pipe 65613 to the pressure regulator 205b. Gaseous CO2 depressurises to atmospheric pressure and passes into the atmosphere through egress pipe 659 and vent 660.

Summary of the invention

P34906W0 specifies the use of columns in series to separate agents. The first column separates out contaminants from halocarbon based on polarity (diffusivity, dipole and hydrogen bonding). The second column would be based on size-exclusion chromatography. According to an aspect of this invention, there is provided a method using a second polarity-based stationary phase, preferably a cyano column, for separation of anaesthetic agents rather than the size-exclusion column described in P34906W0.

An aspect of the present invention provides a method for separating one or more substances from a supercritical solution, the method comprising a polarity-based separation step to separate out contaminants and/or to separate out one or more different types of halocarbon.

A plurality of polarity-based separation steps may be used.

At least one separation step may be used to separate contaminants and the or at least one of the further steps may be used to separate out one or more different types of halocarbon.

One or more separating columns may be provided.

A plurality of columns arranged in series may be provided.

One or more size separation steps may also be included in the method.

In one embodiment, for example, a hydrophilic and a hydrophobic column may be used to separate out contaminants, then a third polarity-based separating column may be used to separate out one or more anaesthetic agents.

The separation system of aspects and embodiments of the present invention may be used before a chromatography step in addition to or instead of its use after chromatography.

According to another aspect of the invention, there is provided a method for the use of higher pressures than in P34906W0 that may require the fractionation columns to be warmed to selectively condense less volatile agents. Higher pressures, preferably 5-60MPa although other sub-critical pressures may be used, reduce the column flow rates to improve column thermal stability and gas transit time but require the first column to be heated to prevent the condensation of the second more volatile anaesthetic agent Figure 2 shows an agent collection system 600a which uses fractionation to separate anaesthetic agent 12 from agent-product 230.

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 depressurized 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.

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 2056.

A vent pipe 659 extends from the second pressure reducing valve 2056 to a vent 660. Each fractionating column 652a, 6526 comprises non-absorbent beads 661a, 661 b, and a cooling jacket 662a, 6626 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.

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. CO2 and anaesthetic agent with a higher volatility, for example Agent Y 12y, passes into the second fractionating column 6526, 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 CO2 is released via the vent 660. Alternatively, gaseous CO2 may be recompressed for future use (not shown).

A plurality of fractionating columns may be arranged in parallel which would enable selected agents to be recovered at at different, high pressures. Alternatively, a plurality of fractionating columns may be arranged in series, as shown in Figure 3 to enable rapid separation of anaesthetic agents.

In alternative embodiments of the invention, detectors, preferably a ultraviolet photodiode array, mass spectrometer, photoacoustic spectrometer, acoustic resonance spectrometer or most preferably an infrared spectrophotometer 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.

In an embodiment of this invention an expansion chamber is incorporated into the circuit 600a shown in Figure 2 to allow a continuous flow of CO2 to maintain fractionation column thermal performance and also the recirculation of CO2 This expansion chamber receives a feed of subcritical CO2 that has been depressurized by a variable pressure-reducing valve from the accumulator and also receives the charge of anaesthetic agent and CO2 from the chromatography back pressure regulator. The expansion vessel allows a continuous flow of sub-critical pressurised CO2 through the columns to develop and maintain thermal stability. Aliquots of anaesthetic agent dissolved in supercritical CO2 are delivered from multiple chromatography columns after selection by infrared spectroscopy and depressurized by a back-pressure regulator into the expansion chamber.

This delivery is intermittent, whereas the fractionation columns require a continuous flow of CO2 to maintain efficiency. The expansion vessel uses the direct feed of CO2 from the accumulator and its own volume to buffer the intermittent delivery of anaesthetic agent from the chromatography columns to generate a continuous flow for the fractionation columns.

Furthermore, it allows the re-use of pure CO2 that has had all anaesthetic condensed therefrom.

According to a further aspect of this invention a process is described whereby a recirculation system to separate individual anaesthetic agents by supercritical fractionation operates by using columns in parallel rather than in series as in process 600a in Figure 2. In this system, a plurality of purified anaesthetic agents dissolved in CO2 is delivered in bursts from the chromatography-based purification system as the anaesthetic agents are selected from contaminants under the infrared or other detection means. It is depressurized below critical pressure by the back-pressure regulator leading to a gaseous state but is maintained at pressure, preferably 5-60MPa although other sub-critical pressures may be used. This charge of gas passes into an expansion chamber in a temperature-controlled environment that mixes it with fresh and re-circulated CO2 and equilibrates temperature. The gaseous mixture passes into a fractionation column that due to the pressure of the mixture may require heating, preferably from 0 to 300 degrees Centigrade, to allow condensation of the less volatile agent but leave the CO2 and more volatile agent in a gaseous form to pass through the column. It is anticipated that this column will not be 100% efficient. It is intended to ensure that only a single agent is condensed, but this is at the expense that not the entire fraction of less volatile agent is collected on the first pass. Remaining gases are then recirculated to the expansion vessel and pass through the column again multiple times. In this way, the entire fraction of less volatile agent is condensed over several passes with the more volatile agent and CO2 remaining in a gaseous state. Once infra-red spectroscopy detects that only the more volatile agent remains, it signals to a controller to switch a valve and pass the gases from the expansion chamber into a different column which is held at higher pressures of 5-70MPa, although other sub-critical pressures may be used, and temperatures, preferably 0-300 degrees Centigrade) that ensure that CO2 remains gaseous but that the more volatile anaesthetic agent condenses for collection. Further re-circulation cycles ensure that the entire fraction of the more volatile agent is condensed and only pure CO2 remains before the process is stopped and the pure CO2 is stored for re-use.

The condensed anaesthetic agents are allowed to leave the pressurised fractionation columns by computer-controlled needle valves that pass the separated liquid anaesthetic agents into a temperature controlled expansion vessel. The vessel fills with liquid anaesthetic agent at or near atmospheric pressure but is sealed and its internal volume increases to maintain atmospheric pressure. Carbon dioxide will be dissolved into the anaesthetic agent at the partial pressure it was in the column. This CO2 will be released as a gas as the anaesthetic agent is depressurized, vapourising some anaesthetic agent. The expansion vessel will therefore be cooled to condense all the separated anaesthetic agent but leave the CO2 in its gaseous state. Carbon dioxide will then be released and the liquid anaesthetic agent removed, bottled and warmed to room temperature after passing through a quality control check using gas chromatography-mass spectrometry to ensure purity.

The method described in this invention is advantageous as the heating of the collection columns allows the use of higher pressures that reduces flow through the columns and enables better control of heat transfer and condensation conditions. Furthermore, the use of columns in parallel means that pressure does not need to be reduced to ensure flow through the columns in series. In P34906W0 this leads to the requirement of low temperatures in the second column to condense the more volatile anaesthetic agent at a lower pressure than the first column. This invention allows for higher pressures to condense the more volatile anaesthetic agent, reducing the flow rate through the column and also increasing the temperature, avoiding the need for intensive cooling apparatus to maintain column thermal gradient stability.

It will be clear to those skilled in the art and from P34906W0 that separation/condensation and chromatography could be used in any order and may be used multiple times in the same process. Futhermore, it will also be clear that the preferred fraction collection systems can be used to separate and collect any volatile halocarbon released by industry or present in the environment in addition to anaesthetic agents.

In a further aspect of the invention, the systems described in this application can be used to clean the atmosphere, either above areas of high pollution or in the upper atmosphere. Devices to achieve altitude, including but not exclusively limited to helium balloons or aeroplanes, are used to carry a halocarbon capture medium, for example a functionalised aerogel, to the desired altitude. High flow-rate fans pass large volumes of air through the capture medium, capturing halocarbons, nitrous oxide, nitrous intermediates (N0x) as well as other environmental pollutants. The systems described in this application can then be used to break down nitrous oxide and nitrous intermediates using high-pressure catalytic conversion with these potentially explosive nitrogen/oxygen compounds diluted in supercritical CO2 (supercritical fluids perfectly dissolve each other and nitrous oxide achieves a supercritical state at similar temperatures and pressures to CO2). Halocarbons are not broken down and continue to a pressurized condenser that liquefies them or they are re-bound to a capture medium as described at atmospheric pressure. They are returned to ground level and are subjected to the processes described, namely to use supercritical fluid, preferably carbon dioxide, to dissolve, purify, separate and condense halocarbons for re-sale.

This system has several important aspects. The capture medium may be an aerogel. This is the lightest solid with the largest surface area to volume ratio known. It is also fully recyclable if based on modified cellulose as described by one aspect of P34906W0. As a large surface area is required for the flow-rates required for meaningful cleaning, this is the ideal material to take into the atmosphere.

The concentration of nitrous oxide intermediates in the environment far exceeds that of halocarbons and nitrous oxide intermediates are not economical to re-process currently. It is therefore cost-effective to catalyse the breakdown of this compound, under controlled conditions to produce nitrogen and oxygen, at the site of capture. The halocarbon can then be extracted from the aerogel using the same supercritical fluid and stored for return to the ground, perhaps leaving the airborne apparatus still in the position required for extraction rather than returning to ground.

In a further aspect of the invention there is provided an atmosphere scrubbing device comprising a halocarbon capture medium.

A further aspect provides an atmosphere scrubbing device comprising a capture medium for capturing one or more types of environmental pollutant.

The device may be carried on or by, or forming part of: a building an aeroplane, a balloon.

The capture medium may be formed as a filter.

The material for the medium/filter may be or comprise aerogel. The most common aerogel is made of silicon dioxide (Si02), but aerogels according to the invention may be made from or comprise other materials, for example, resourcinol formaldehyde, carbon, calcium carbonate and zeolite (aluminosilicate). Zeolites are micro-porous alumina silicate minerals found naturally but may also be made artificially. Carbon may be exposed to high temperatures to expand its surface area for absorption. The filter material may be doped with a metal.

According to the invention, aerogel may be functionalised by the addition of one or more of halocarbon, metal oxide, cellulose, carbon nanotubes, or internally supported by polymers to improve their chemical or mechanical properties. These changes may improve the binding of halocarbons and/or the stability of the aerogel. For example, functionalisation with halocarbon improves the binding of halocarbon to the material. The material may comprise granular particles.

Furthermore, the material may comprise or be a metal or metal oxide which may be formed by forming metal-oxygen-metal bridges. Examples of preferable metals and metal oxides include nickel, molebdnum, alumina, titania, zirconia, iron, chromia, vandia. platinum, rhodium, palladium and tungsten. The material may comprise or be a precious metal. A metal and/or a metal oxide may be added by deposition to the material, for example by physical or chemical vapour phase deposition.

Supercritical N20 may be broken down or reduced by including a reduction catalyst. For example, a metal catalyst reduces nitrous oxide, often in the presence of urea or ammonia. In a preferred embodiment of the invention, the material comprises a reduction catalyst, which may be a metal catalyst which may be deposited on the material. A preferred metal catalyst is platinum, The catalyst may be loaded with reactant, preferably urea, before the halocarbon has been captured by the material or before the material is exposed to supercritical fluid. As gas is exposed to the material, nitrous oxide in the gas may react with the urea (CO(NH2)2) in the presence of the catalyst to form nitrogen (N2), water (H20) and carbon dioxide (CO2).

In a preferred embodiment of the invention, when the material has been exposed to halocarbon and nitrous oxide, the material may be flushed with supercritical CO2 to elute the halocarbon and remaining nitrous oxide (N20). Carbon dioxide may be supplied to the material and pressurised to achieve supercritical pressure, preferably around I OMPa although other pressures above the critical pressures of CO2 and N20 may be used, and heated to achieve supercritical temperature, preferably 35*-300.C. However, other supercritical temperatures and pressures may be used. When the supercritical CO2 flows through the material the N20 may be diluted in supercritical CO2 and may become supercritical N20. The supercritical N20 and supercritical CO2 mixture may pass through the catalyst absorbed onto a matrix and/or reactant in a subsequent chamber.

The breakdown of N20 of may occur at supercritical temperatures and pressures. At supercritical temperatures and pressures the reaction speed of the breakdown of N20 is significantly faster than at room temperature and pressure. The invention is advantageous in that the dilution of N20 in supercritical CO2 prevents a runaway reaction occurring, which may cause an explosion. Nitrogen gas, water and any other by-products may be separated by the separation steps detailed herein and in P34906W0.

The returned halocarbons are valuable as well as being potent greenhouse gases and ozone depleting agents. If we are able to return these compounds, separate and purify them for reuse then we can circularize the economy of their use. This will ensure the responsible use and life-cycle of an important class of chemical, namely halocarbons, that are under political pressure to be removed from use. For example, automobile air conditioning refrigerants can be purchased for a cost that includes their recapture and processing for re-use. With an efficient capture and remanufacture system, this may not be significantly more than the cost of their manufacture from raw materials. Halocarbons are inert, non-combustible and are not biologically active at environmental exposure doses. They are used in a range of industries as diverse as fire quenching systems to drug dispersion systems for inhalers. The possible circularization of this economy could have significant cost and environmental impact in the global economy.

Further aspect and embodiments may relate to nitrous oxide breakdown.

Carbon dioxide may be added to a filter material and N20 first, forming a dilute supercritical solution and then this is passed into a subsequent chamber containing a urea reactant and a catalyst for decomposition.

Different aspects and embodiments of the invention may be used separately or together.

Further particular and preferred aspects of the present invention are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with the features of the independent claims as appropriate, and in combination other than those explicitly set out in the claims.

Brief description of drawings

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: Figure I is a schematic diagram of a chromatography separation and condensation system for anaesthetic agents described in P34906W0; Figure 2 is a schematic diagram of a supercritical fractionation separation system for the separation and condensation of anaesthetic agents described in P34906W0; Figure 3 is a schematic diagram of a supercritical fractionation system using an in-series system with the addition of an expansion vessel for the separation and condensation of anaesthetic agents or halocarbons; and Figure 4 is a schematic diagram of a supercritical fractionation system using a parallel recirculation system for the separation and condensation of anaesthetic agents or halocarbons.

The example embodiments are described in sufficient detail to enable those of ordinary skill in the art to embody and implement the systems and processes herein described. It is important to understand that embodiments can be provided in many alternate forms and should not be construed as limited to the examples set forth herein Accordingly, while embodiment can be modified in various ways and take on various alternative forms, specific embodiments thereof are shown in the drawings and described in detail below as examples. There is no intent to limit to the particular forms disclosed. On the contrary, all modifications, equivalents, and alternatives falling within the scope of the appended claims should be included. Elements of the example embodiments are consistently denoted by the same reference numerals throughout the drawings and detailed description where appropriate.

Unless otherwise defined, all terms (including technical and scientific terms) used herein are to be interpreted as is customary in the art. It will be further understood that terms in common usage should also be interpreted as is customary in the relevant art and not in an idealized or overly formal sense unless expressly so defined herein.

All orientational terms are used in relation to the drawings and should not be interpreted as limiting on the invention.

Detailed description of drawings

The system 700 shown in Figure 3 shows an in-series fractional separation and condensation system, including an expansion chamber and CO2 recirculation, driven by the depressurization of supercritical CO2, referred to as supercritical fractionation in P34906W0.

Carbon dioxide 201 from a pressurised cylinder 202 is fed to a pump 206a, increasing pressure to a set point above the critical pressure of CO2 (7.29MPa). This fluid passes to an accumulator 208 in a temperature-controlled environment (not shown) above the critical temperature of CO2 (31.1 degrees C). The supercritical CO2 from the accumulator passes into elution and chromatography systems (not shown in detail).

The supercritical CO2 is used to elute anaesthetic agent from a capture filter material and then purify it by multiple column supercritical fluid chromatography. A detection system preferably a ultraviolet photodiode array, mass spectrometer, photoacoustic spectrometer, acoustic resonance spectrometer or most preferably an infrared spectrophotometer selects peaks corresponding to pure anaesthetic agent and these are delivered via a back pressure regulator to an expansion vessel 701. Another direct feed of CO2 from the accumulator 208 is delivered to the expansion vessel 701 passing through a variable pressure-reduction valve 702 and safety valve 703a that protects the downstream circuit from supercritical pressures.

Aliquots of a mixture of anaesthetic agents and gaseous CO2 are delivered to the expansion vessel 701 when peaks are selected by the detector. The volume of the expansion vessel 701 and the direct flow of CO2 from the accumulator 208 buffer this intermittent flow to produce a continuous flow of a mixture of anaesthetic agents carried in gaseous CO2 from the expansion vessel 701 via an egress pipe 704. This mixture passes to the first fractionating column 652a containing inert beads 661 to turbulate flow and improve heat transfer. The mixture is held a pressure determined by a downstream pressure-reducing valve 205a. The pressure slows the flow of gases through the column to improve heat transfer and condensation of the anaesthetic gases when compared to atmospheric pressure. As this column is intended to selectively condense the least volatile anaesthetic agent, it is heated to prevent the more volatile fraction from condensing. This is by thermal sleeve 662a and a temperature-controlled environment 705a. The column temperature is measured by thermocouples 706a, 7066 with readouts 707a and 7076 respectively. The least volatile fraction 12x condenses and is collected by the opening of a needle valve 708a under computer control (not shown). The liquid anaesthetic agent passes into an expansion chamber 709a which increases its volume to maintain atmospheric pressure. The chamber 709a is maintained in a cold sleeve 7I2a to keep the purified anaesthetic agent 12x in liquid form while dissolved CO2 is released for venting 710a. It is then checked for purity using gas chromatography-mass spectrometry (GC-MS) and bottled (not shown).

The more volatile anaesthetic agent and gaseous CO2 leave the column 652a via an egress pipe 711a to the pressure-reducing valve 205a and an detector 160, preferably a ultraviolet photodiode array, mass spectrometer, photoacoustic spectrometer, acoustic resonance spectrometer or most preferably an infrared spectrophotometer, to ensure the absence of the least volatile fraction. The mixture passes into the second fractionation column 6526 held at a lower pressure than the first fractionation column by a pressure reduction valve 205b. Because of the need to condense a more volatile fraction at a lower pressure, the second fractionation column is cooled by a temperature-controlled environment 705b and thermal sleeve 6626. Column intake and exit temperatures are measured by thermocouples 706c and 706d with respective readouts 707c and 707d. The condensed fraction 12y is collected at the bottom of the column and is transferred to an expansion chamber 709b by needle valve 708b under computer control (not shown). This chamber is cooled using a thermal sleeve 7126 to keep the anaesthetic agent liquid while the gaseous CO2 is vented 710b.

The pure CO2 leaves the fractionation column 652b via the pressure-reducing valve 205b and detector160b to pass back to the expansion chamber via a pump 206b to reduce the need for CO2 via the direct feed from the accumulator 208. Thereby the direct feed is replaced by the recirculated feed. If the pressure in the circuit rises above a set threshold, pure CO2 is vented to the environment 122 via a pressure safety valve 703b and vent 660.

The system 800 shown in Figure 4 details a parallel anaesthetic agent fraction collection system using the sequential depressurization of CO2, so-called supercritical fractionation in P34906VV0.

Carbon dioxide 201 stored in a pressurised cylinder 202 is fed to a pump 206a to raise the pressure to a set point above the critical pressure of CO2 (7.29MPa). This is then fed to an accumulator 208 in a temperature-controlled environment above the critical temperature of CO2 (31.1 degrees C). The supercritical CO2 from the accumulator passes into the elution and chromatography systems (not shown in detail). The supercritical CO2 is used to elute anaesthetic agent from a capture filter material and then purify it by multiple column supercritical fluid chromatography. Infra-red spectroscopy selects peaks corresponding to pure anaesthetic agent and these are delivered via a back pressure regulator to an expansion vessel 701. Another direct feed of CO2 from the accumulator 208 is delivered to the expansion vessel 701 passing through a variable pressure-reduction valve 702 and safety valve 703 that protects the downstream circuit from supercritical pressures. Aliquots of a mixture of anaesthetic agents and gaseous CO2 are delivered to the expansion vessel 701 when peaks are selected by a detector, preferably a ultraviolet photodiode array, mass spectrometer, photoacoustic spectrometer, acoustic resonance spectrometer or most preferably an infrared spectrophotometer. The volume of the expansion vessel 701 and the direct flow of CO2 from the accumulator 208 buffer this intermittent flow to produce a continuous flow of a mixture of anaesthetic agents carried in gaseous CO2 from the expansion vessel 701 via an egress pipe 704 to a computer controlled valve 71 3a. This directs the mixture into the first fractionation column 652a containing inert beads 661 under a pressure set by the pressure-reducing valve 205a. The pressure of the column slows the gas flow rate to improve column thermal stability and condensation of the less volatile anaesthetic agent. However, the pressure requires the heating of the column to prevent the condensation of the more volatile fraction of anaesthetic gas. This is achieved by the column being in a temperature-controlled environment (not shown) and being surrounded by a thermal sleeve 662a. Column temperature is measured by thermocouples 706a and 706b and read-outs 707a and 7076. The less volatile fraction I 2x condenses and is collected at the bottom of the fractionation column 652a. It is released into an expansion chamber 709a via a needle valve 708a under computer control (not shown). The expansion of the chamber volume ensures that pressure remains at atmospheric pressure. The anaesthetic agent is cooled by a thermal sleeve 71 2a to prevent the anaesthetic agent vapourising as the CO2 dissolved in the anaesthetic agent is vapourised. This CO2 is vented 7I0a.

The column is set up to ensure that none of the more volatile fraction is collected at the expense of the possibility that not all of the less volatile fraction is collected. Therefore, gas exiting the first fractionating column 652a is checked by a detector 160a, preferably a ultraviolet photodiode array, mass spectrometer, photoacoustic spectrometer, acoustic resonance spectrometer or most preferably an infrared spectrophotometer, and if some of the less volatile fraction remains, it is passed back to a pump 206b and delivered to the expansion chamber 701 to go back through the valve 7I3a and into the first fractionation column 652a again. By multiple passes through the first fractionation column, complete condensation of the less volatile anaesthetic agent should be achieved without contamination by the more volatile fraction.

When all of the less volatile fraction has been condensed, a controller (not shown) closes valve 71 3a and opens valve 71 3b, passing the CO2 and the more volatile fraction into the second fractionating column 652b. This is at a higher pressure controlled by the pressure-reducing valve 205b. The temperature of the column is controlled by a temperature-controlled environment (not shown) and thermal sleeve 662b and measured by thermocouples 706c, 706d and read-outs 707c and 707d respectively. The more volatile fraction 12y condenses, leaving gaseous pure CO2 to pass out of the column. The fraction 12y collects at the bottom of the column and passes into an expansion chamber 7091a via a needle valve 7081a under computer control (not shown). The expansion of the chamber volume ensures that pressure remains at atmospheric pressure. The anaesthetic agent is cooled by a thermal sleeve 7I2b to prevent the anaesthetic agent vapourising as the CO2 dissolved in the anaesthetic agent is vapourised. This CO2 is vented 7106. It may be that some anaesthetic agent remains with the gaseous CO2. This is detected by the detector 160b after passing through the pressure-reducing valve 205b. This signals to a controller (not shown) that recirculates the gases back to a pump 2066 and the expansion chamber 701 to pass through the column 5626 again and complete condensation over one or more cycles.

One advantage of system 800 over system 700 is that a pressure-reduction is not required between the first and second fractionation columns. This is problematic as the first column has high pressures requiring heating of the column to stop the more volatile anaesthetic agent condensing and then the second column has low pressures but needs to condense the more volatile fraction requiring low temperatures and long columns due to high flow rates. By using a parallel system, the pressure can be independently altered to condense the different agents at easily attainable temperatures and flow rates.

A further advantage of the preferred embodiment is that system 800 allows for incomplete condensation which is a likely occurrence. By using recirculation, system 800 is able to carefully and completely condense individual fractions of anaesthetic agent.

Further aspects and embodiments are provided in the following numbered paragraphs.

I. A method for separating one or more halocarbons from a supercritical solution, the method comprising a polarity-based separation step to separate out contaminants and/or to separate out one or more different types of halocarbon.

2. The method of paragraph 1, in which a plurality of polarity-based separation steps are used.

3. The method of paragraph 2, in which at least one separation step is used to separate contaminants and the or at least one of the further steps is used to separate out one or more different types of halocarbon.

4. The method of any preceding paragraph, in which one or more separating columns are provided.

5. The method of paragraph 4, in which a plurality of columns arranged in series are provided.

6. An anaesthetic agent collection system for fractionally separating one or more anaesthetic agents from agent-product in a supercritical state, the system comprising one or more chromatography columns which intermittently deliver anaesthetic agent dissolved in supercritical fluid to one or more fractionation columns, the system further comprising an expansion chamber for buffering the intermittent flow of agent from the chromatography columns whereby to generate a substantially continuous flow for the fractionation column/s.

7. A recirculation system for separating individual anaesthetic agents by supercritical fractionation, the system including a plurality of separating columns arranged in parallel.

8. An atmosphere scrubbing device comprising a halocarbon capture medium.

9. An atmosphere scrubbing device comprising a capture medium for capturing one or more types of environmental pollutant.

10. The method of paragraph 8 or paragraph 9 wherein the capture medium is an aerogel.

The method of paragraph 10 wherein the aerogel is based on cellulose and modified by a halocarbon.

12. The device of paragraph 8 or paragraph 9, carried on or by, or forming part of: a building; an aeroplane, a balloon.

13. A method for the safe breakdown of nitrous oxide and its intermediates by dilution in supercritical carbon dioxide at temperatures and pressures to create a mixture of supercritical fluids.

14. The method of paragraph 13 wherein the breakdown of supercritical nitrous oxide diluted in supercritical carbon dioxide is catalysed by a catalyst, preferably a precious metal such as platinum, rhodium, palladium or a transition metal oxide such as but not exclusively limited to chromia or aluminia.

15. The method of paragraph 14, wherein the reaction requires a further reactant, urea, ammonia or anhydrous ammonia.

16. The method of any of paragraphs 13 to 15 wherein the catalyst is bound to the filter material and reactant added to the capture chamber.

17. The method of any of paragraphs 13 to 15 wherein the catalyst is bound to a material, such as but not exclusively limited to a ceramic or aerogel, and is reacted with supercritical nitrous oxide diluted in supercritical carbon dioxide and urea or ammonia in a separate chamber subsequent to the capture chamber.

18. A method for separating one or more halocarbons from a plurality of halocarbons dissolved in a supercritical solution, the method comprising supercritical chromatography using a polarity-based column.

Claims (4)

1. CLAIMSI. A method for separating one or more substances from an anaesthetic agent solution, the method comprising a polarity-based separation step to separate out contaminants from anaesthetic agent's.
2. 2. A method as claimed in claim I, comprising a step of separating one or more different types of anaesthetic agent.
3. 3. A method as claimed in claim 2, in which the step to separate one or more different types of anaesthetic agent comprises a polarity-based separation step.
4. 4. A method as claimed in any preceding claim I, in which one or more separating columns are provided.S. A method as claimed in any preceding claim, in which a plurality of columns arranged in series are provided.