WO2009006586A2

WO2009006586A2 - Self-contained oxygen generating and breathing systems

Info

Publication number: WO2009006586A2
Application number: PCT/US2008/069187
Authority: WO
Inventors: Kevin Ward; Everett E. Carpenter; Gary Huvard
Original assignee: Virginia Commonwealth University
Priority date: 2007-07-03
Filing date: 2008-07-03
Publication date: 2009-01-08
Also published as: WO2009006586A3

Abstract

A portable, small footprint oxygen generating and rebreathing apparatus uses H2O2 and a catalyst to generate copious quantities of breathable oxygen, without producing toxic byproducts. In one embodiment, the present invention encompasses a portable oxygen supply device, with a hydrogen peroxide feedtank, decomposition chamber containing a metal oxide catalyst, and one or more supply lines to provide oxygen to the operator of the device. The rebreathing apparatus also provides for carbon dioxide removal from exhaled air.

Description

SELF-CONTAINED OXYGEN GENERATING AND BREATHING SYSTEMS

DESCRIPTION

BACKGROUND OF THE INVENTION

Field of the Invention The invention generally relates to a portable oxygen generating apparatus and methods. In particular, the invention provides an apparatus and methods in which H₂O₂ and a catalyst react to generate copious quantities of breathable oxygen, without producing toxic byproducts.

Background of the Invention Rapid onsite generation of oxygen remains problematic as does transport of traditional oxygen cylinders in emergency situations. For example, use of oxygen in the initial levels of combat care is not possible because transport of oxygen tanks are too cumbersome and dangerous. These same issues apply in civilian care when mass casualties are encountered. A prime example of this problem would be an influenza pandemic requiring thousands of victims to undergo mechanical ventilation using high concentrations of oxygen. Current hospital oxygen supplies would be easily overwhelmed and providing similar care in field hospitals would simply not be possible.

Many examples of chemical oxygen generating systems exist. The most widely known example of these exist in aircraft to provide passengers with oxygen in case of sudden cabin decompression and for miners trapped underground. Chemical generation of oxygen usually takes the form of using an oxygen precursor such as metal oxides. While these produce oxygen, they require an ignition source, produce significant heat, and frequently generate toxic substances such as chlorine, which must be somehow removed from the system. Furthermore, none of these generating schemes allow for the rebreathing and recycling of oxygen.

Salonia (US patent 5,665,316, September 9, 1997) teaches a portable oxygen generating system that employs liquid H₂O₂ (e.g. 35%) and lead strip catalysts. H₂O₂ is released from a feed tank to a reactor which contains the catalyst, and H₂O₂ is decomposed to form O₂ and H₂O, which pass through cooling coils and into a separator tank. Liquid H₂O settles in the bottom of the separator tank and can be removed from the tank via a draw off pipe. O₂ passes through a conduit to the user. A return pipe allows O₂ to be circulated back to the feed tank in order to equalize pressure in the system. However, this system lacks versatility in that it is restricted to the use of liquid H₂O₂, and does not include a means for rebreathing or recycling oxygen.

The prior art has thus far failed to provide a portable oxygen generator that produces copious quantities of breathable oxygen without generating toxic substances, and that includes a means for rebreathing or recycling oxygen.

0 SUMMARY OF THE INVENTION

The present invention is based on the development of a portable oxygen generation system that is capable of producing large quantities of breathable oxygen for prolonged periods of time, without producing toxic byproducts. The O₂ source used in the generator is concentrated H₂O₂ or H₂O₂ precursor in either a solid or liquid form. Advantages of using5 H₂O₂ include: the lack of production of noxious byproducts such as chlorine; the ability to generate very large quantities of O₂ from relatively small quantities of starting materials (e.g. H₂O₂ and catalyst); the production of oxygen without the use of electricity; and the possibility, in some embodiments, to provide warmed, humidified O₂ to the user as a side effect of the chemistry employed. Importantly, the apparatus may also include a mechanism O for recirculating exhaled air, thereby extending the period of time for which the generator can provide oxygen without replenishing the starting materials (e.g. H₂O₂ and catalyst). The mechanism includes means for receiving previously respired air, means for removing exhaled CO₂ from the previously respired air, and means for conducting CO₂-scrubbed O₂ back to the user of the apparatus.

5 BRIEF DESCRIPTION OF THE DRAWINGS

Figure IA-D. Schematic representations of packets for containing reactants. A, a mixture of dry reactants to which water is added from a source external to the packet; B, internal packet contains source of liquid; C, multiple compartments within a packet; D, reactant on an absorbent matrix. O Figure 2A-B. Schematic representations of compartments in an apparatus. A, two compartments; B, three compartments.

Figure 3: Schematic representation of a gas reservoir with a removable cap and a valve to control oxygen release.

Figure 4: Schematic representation of a two chamber oxygen generation and delivery system.

Figure 5 A-E. A, Schematic representation of a two chamber oxygen generation and delivery system within a housing; B, inflatable chamber; C, resuscitator bag with attached pouch; D, gas mask with internal packet or cartridge; E, gas mask with external compartment to receive a packet or cartridge. Figure 6A-B. Schematic representation of oxygen generating and rebreathing system. A, scrubbed respired air is recirculated into an oxygen storage/accumulation reservoir. B, scrubbed respired air is recirculated into a conduit.

Figure 7. Schematic depiction of a ventilator rebreathing circuit.

Figure 8. Schematic depiction of a personal flotation device (PFD)-like rebreathing circuit. Figure 9A-B. Number of breaths vs fractional inspired oxygen concentrations (FiO2). A, for

16 breaths; B, for 6000 breaths.

Figure 10A-B. A, closed loop system; B, closed loop system with mechanical ventilator.

Figure HA-D. Exemplary prototype A, schematic depiction; B, actual photograph; C, data showing generations of oxygen using the prototype: rate is shown by dashed line; amount is shown by solid line; D, second exemplary prototype.

Figure 12A-B. A, Pressure increased with time as oxygen was generated by the catalytic decomposition of hydrogen peroxide; B, number of moles of oxygen released closely approached the theoretical limit based on urea hydrogen peroxide.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The portable oxygen generating apparatus of the invention includes 1) a compartment for containing H₂O₂ and a compartment for containing a catalyst, both of which may be in either a solid or liquid form; or 2) a single compartment for containing both solid H₂O₂ and a solid catalyst. When oxygen generation is desired, the contents of the two compartments are combined in the presence OfH₂O, or a source of H₂O is added to the single compartment, and reaction ensues. In some embodiments of the invention, discussed in detail below, the compartment(s) is/are located within disposable packets, which, during oxygen generation, are placed within a housing capable of containing the reactant packet and the oxygen that is generated, and providing the oxygen to a user. In other embodiments of the invention, also described in detail below, the compartments are built into a housing, reactants are added to the compartments, and various mechanisms for combining the reactants, in the presence of water, are present, as are a means of capturing the oxygen that is generated, and of sending the oxygen to a user. As used herein, the terms "reactant" and "reactants" refer to a suitable form OfH₂O₂, or a suitable catalyst, or both. For all embodiments of the invention, the reactants for generating oxygen include at least one suitable form OfH₂O₂ and at least one suitable catalyst. The reaction preferably occurs in an aqueous environment in order for reaction to proceed. If both the H₂O₂ and catalyst are solids, they may be stored together as long as the mixture is not reactive. An external source of water may be added to promote reaction. However, in this case, both reactants must be scrupulously dried to prevent adventitious generation of oxygen during storage due to residual moisture. Those of skill in the art are knowledgeable concerning methods of dessicating such materials. Dessication may, for example, be carried out at elevated temperatures (but not so high as to damage the reactants), and/or under vacuum, by freeze drying, etc. Further, an inert desiccant (i.e. one that does not react with either H₂O₂ or the catalyst, and that does not interfere with oxygen generation) may be added to the mixture that is to be stored. Examples of suitable desiccants include but are not limited to, for example, magnesium sulfate, zeolites, various silicon gels, silica gel packs, and highly hydrophilic polymers such as carbomers and polyacrylamides, etc., the quantity of desiccant being limited so as not to interfere appreciably when the mixture is wetted to begin the oxygen generating reaction. In one embodiment, a paper filter-type material is impregnated with magnesium sulfate ("DryRite") and the paper is used as a separator between the reactants. Alternatively, reactant particles (a suitable solid form OfH₂O₂ and/or a catalyst) may be coated with one or more dry, non-reactive substances (e.g. cellulose, dextrans, etc.) to help maintain the reactants in a non-reactive state until water is added to the system. Water would dissolve the coatings and reaction would then take place.

Additionally, some catalysts will lend themselves to incorporation within the interstices of an absorbent carrier matrix. For example, the catalyst MnO₂ can be deposited on the fibers of and in the interstices of filter paper. A concentrated solution of potassium permanganate is absorbed into a paper filter and allowed to dry slowly in air. During the drying process, the permanganate is slowly reacted with moisture via well-known chemistry to produce solid particles OfMnO₂ throughout the filter paper. When this is dried, MnO₂-containing paper is contacted with an aqueous solution of hydrogen peroxide, the solution is rapidly absorbed into the filter paper and the MnO₂ immediately catalyzes the decomposition of hydrogen peroxide to water and oxygen. Alternatively, if the hydrogen peroxide is in the form of a solid, the MnO₂-containing paper and solid form OfH₂O₂ (which may be stored together or brought into proximity prior to the initiation of reaction) may both be contacted with water to initiate the reaction. In some embodiments, both the catalyst and the H₂O₂ are associated with an absorbent carrier matrix or substrate. Other suitable substrates include but are not limited to glass filter papers, fabrics of various types, fibrous ceramic materials, synthetic fibrous materials like nylons and polyesters etc. Many more suitable substrates for deposition of solid catalyst particles will occur to those skilled in the art. Additionally, other catalysts that are suitable for deposition on the surfaces of porous solids, fabrics, or filters will occur to those skilled in the art. The deposition may be by chemical reaction as in the permanganate example above or by absorption of a slurry of crystalline solids or nanoparticles of the catalyst followed by evaporation of the carrier liquid. Additionally, such catalytic solids may be deposited directly into a substrate using well-known vapor deposition methods or by using solutions in near- or supercritical fluids or as slurries in near- or supercritical fluids. Other methods for the deposition of solids on or into porous solids, fabrics, or filters will occur to those skilled in the art. This aspect of the invention is illustrated schematically in Figure ID, where absorbent matrix or support 50 is shown with impregnated reagent 51. hi other embodiments of the invention, H₂O₂ and catalyst are stored separately and come into contact with each other only immediately prior to oxygen generation, hi this case, both H₂O₂ and catalyst may be solids, or one or the other may be in liquid form. If both are solids, a mechanism of releasing the two from storage and mixing them in the presence of water is provided. If one or the other is in the form of an aqueous liquid, then additional water need not be added, hi this embodiment, the two are stored separately, and upon mixing, reaction ensues due to the inherent presence of water in the aqueous liquid. Reaction in Packets

In one embodiment of the invention, the reactants are provided in disposable packets, either separately or together, as discussed above, and the packets are designed so that the O₂ generating reaction takes place wholly within the packet. According to one embodiment, solid, desiccated reactants are mixed and sealed within a packet, e.g. with a "teabag" type design. The packet is formed from material that is impermeable to liquids and solids, but not to gases. In other words, the reactants are positioned or contained within a material that has these characteristics. The material that is used should be strong and difficult to tear but easily cut or punctured with a sharp object. Further, the material should be flexible or pliable so that it can be manipulated (e.g. by manual kneading) to mix the contents. In a preferred embodiment, Tyvek® is used, although other gas permeable but water impermeable materials may also be used. Such materials include but are not limited to papers and filters that are treated with hydrophobic coatings, composite fabrics (e.g., spunbonded-meltblown- spunbonded laminates or SMS fabrics), semipermeable polymer membranes with high oxygen permeabilities such as poly(glycolic acid) and poly( vinyl alcohol), and a variety of fabrics coated with polymeric materials (e.g. GoreTex® and polyurethane-coated fabrics) that make the fabrics suitable for use as protective garments, etc. hi order to begin the production of oxygen, the contents of the packet are contacted with water. This can be accomplished by any of several methods that may occur to those skilled in the art. For example, the packet wall may be punctured or breached e.g. by a hypodermic syringe or needle other similar device, and water can be injected from the device into the packet to start the reaction. Oxygen that is generated escapes through the gas- permeable walls of the packet and is captured, stored and/or sent to the user by any of several mechanisms discussed below. However, water, reactants and byproducts remain within the packet, which can be disposed of when the reaction is complete. This embodiment is illustrated schematically in Figure IA, where packet 10 containing mixed, dried reactants 20 and syringe 30, which is used to puncture the packet wall, is shown.

Alternatively, the source of water may be a second water-containing packet that is located within the reactant packet. This embodiment is illustrated schematically in Figure IB, which shows packet 10 containing dried reactants 20, and internal packet 40. Such an internal packet is formed from a material that is impermeable to water and is relatively sturdy, but which can be ruptured upon application of pressure (e.g. by squeezing or flexing the packet), thereby releasing the water contained therein into the solid reactants. Examples of suitable materials include but are not limited to aluminum foil, various packaging plastics, packets made of waxes or waxed papers, thin glass ampules, etc. hi yet other embodiments, a compartmentalized packet may be designed which has multiple internal chambers (e.g. two or more) for containing different components (e.g. water and dried mixed reagents) in an isolated fashion. The compartments are separated by barriers which can be ruptured to release and allow mixing of their contents upon the application of pressure. This embodiment is depicted schematically in Figure 1C, which shows packet 10 with internal chambers 11 and 12 (shown in phantom) and barrier 13 (also in phantom) interposed between the two chambers.

The embodiments illustrated in Figures IB and C may be employed when one or the other, or both, of the H₂O₂ and catalyst are in the form of an aqueous liquid. For example, solid H₂O₂ may be stored in the packet as described above, and a liquid catalyst may be stored in internal packet 40 as described above for water. Conversely, a solid catalyst may be stored in the outer packet and liquid H₂O₂ may be stored in internal packet 40. Generally, it is preferable for a liquid component to be stored in the smaller, internal packet, although this need not always be the case. But generally, it is easier to expel liquid contents from an internal packet into the outer packet, than to expel a solid component from an internal packet into the outer packet, given the propensity for liquids to flow readily, hi addition, when one or the other, or both, of the H₂O₂ and catalyst are in the form of an aqueous liquid, a compartmentalized packet as discussed above and illustrated in Figure 1C may be used, hi this case, the two liquid reactants, or the one liquid and one solid are stored separately, one within compartment 10 and the other within compartment 12, and are mixed upon rupture of barrier 13. hi each of these embodiments, rupture of an internal packet or of a barrier between compartments may be facilitated by engineering into the material from which the packet or barrier is formed, weakened sections that are predisposed to break in response to pressure, hi all embodiments of the invention in which packets are employed, once the reactants are combined, the packet may be briefly kneaded or shaken to ensure thorough mixing of the reactants.

Generation of Oxygen within Compartments of the Apparatus hi other embodiments of the invention, the reactants for generating O₂ are stored in chambers built into the apparatus of the invention, and are reacted within a decomposition chamber of the apparatus. For example, if liquid H₂O₂ and a solid catalyst are used, the liquid H₂O₂ is contained within a compartment of the apparatus that can store the liquid H₂O₂ in an unreacted form until it is used to generate oxygen. Such a compartment can typically be closed off from or isolated from the rest of the apparatus, for example, by the use of orifices that allow filling of the compartment and egress of the H₂O₂ when needed for reaction, and valves that control the movement of the liquid H₂O₂ into and out of the compartment. This embodiment is illustrated in Figure 2A, which shows apparatus housing 100 and internal compartments or chambers 101 and 102. When production of oxygen is initiated, metered quantities of liquid H₂O₂ are released from compartment 101 through conduit 103 into a second isolatable compartment 102 (e.g. a reaction or decomposition chamber) where the H₂O₂ will be reacted with solid catalyst to produce O₂ and water. However, those of skill in the art will recognize that, in some cases, all stored liquid H₂O₂ may be added to the decomposition chamber at once. The solid catalyst may be stored in the chamber, or may be introduced into the chamber from another storage compartment at the time of reaction.

On the other hand, if solid H₂O₂ and a liquid catalyst are used, the placement of these entities within the apparatus will generally be reversed. Generally, the liquid catalyst will be held or stored in isolated compartment 101 in an unreacted state, and will be allowed to flow into decomposition chamber 102 in a metered fashion (i.e. in a controlled manner that accords with the desired rate of reaction). However, those of skill in the art will recognize that, in some cases, all stored liquid catalyst may be added to the decomposition chamber at once. The solid H₂O₂ may be either introduced into the decomposition chamber at the time of reaction, or may be held or stored in the chamber in an unreacted state until contacted by the liquid catalyst. hi yet another embodiment of the invention the H₂O₂ and the catalyst are both solids, hi this embodiment, the two are either stored separately or together in the apparatus, (e.g. stored together within decomposition chamber 102). If stored together, storage conditions are such that they do not react until oxygen generation is desired. For example, the reactants are stored in a dry state, and the decomposition chamber may include one or more desiccants to scavenge residual water. Reaction can be initiated by addition of, for example, a catalytic amount of a third substance such as water or other aqueous liquid, which may be stored in

— ft — and introduced from compartment 101, or, alternatively, may be supplied from a water reservoir that is attached to the apparatus. The dry reactants (either loose, or in wettable packets, cartridges, etc.) are introduced into a chamber of the apparatus and stored there, or introduced immediately before use. The contents of the water reservoir is added to the chamber by any of several mechanisms to start the reactions. For example, if the water reservoir is built into the apparatus, a plunger device may be used to do so. If the water reservoir is separate and stored "on board", it may be sufficient to simply open the reservoir (fastened e.g. by a screw cap) and pour water into the chamber containing the reactants.

In alternative embodiments, a catalytic amount of water can be supplied by the breath of a user of the apparatus. In other words, to activate the oxygen generating capability of the apparatus, a user is instructed to breath into the apparatus, and the moisture in the user's exhaled breath (which has 100% humidity) is sufficient to start the reaction, which proceeds only when sufficient moisture is present. In extreme situations, especially when supplies are limited or difficult to access, the reactions described herein may be initiated by any available source of aqueous fluid, including but not limited to fluids that are otherwise intended primarily for drinking (water, juices, alcoholic beverages, soda, etc.), saline solutions, body fluids such as saliva or urine, water from natural sources such as lakes or puddles, etc. hi some embodiments of the invention, both the H₂O₂ and the catalyst are liquid. In this embodiment, shown schematically in Figure 2B, the two reactants are stored separately in isolated compartments 101 and 104 and come into contact with each other only when both are introduced into decomposition chamber 102. Alternatively, one liquid may be stored in one compartment (e.g. 101 of Figure 2A) and the other stored in another compartment (e.g. 102 of Figure 2A) and combined when the contents of one compartment is transferred to the other. In some further embodiments of the invention, it may be preferable that the H₂O₂ and the catalyst be available in a form that allows expended reactant to be readily discarded and replaced by fresh reactant. This feature of the invention can be implemented, for example, by packaging one or both of the reactants (either separately, or together in the case where both are solids) in the form of a cartridge, cannister, or other container that is designed to fit into a compartment of the apparatus. Those of skill in the art are familiar with various suitable packaging options (e.g. various cartridges, ampules, etc.) that are suitable for packaging discrete quantities of solids and liquids, and which provide a protective barrier that can be breached when required to allow release of the contents, or to allow other materials to enter and contact the contents. Such packaging may include disposable packets such as those discussed above. Such containers maybe disposable, or capable of being refilled. They may be designed with a shape and/or size that is specific for the contents, so that it would not be possible to, for example, insert a liquid catalyst container into a compartment of the apparatus intended to receive a container of solid H₂O_2, or to orient the container incorrectly within the apparatus, etc. Further designs for providing reactants for the apparatus will occur to those of skill in the art (e.g. screens or filters coated or impregnated with reactant which can be placed within a decomposition chamber, paper embedded with reactant, walls of a decomposition vessel coated or otherwise containing reactant, wire pads embedded with reactant, etc.). In some embodiments, the catalyst and H₂O₂ are packaged separately to take advantage of the reusable nature of the catalyst (a single catalyst cartridge may be used repeatedly), whereas the H₂O₂ source is generally not reusable and must be replaced. All such possible variations are intended to be encompassed by the present invention. Design of the apparatus

Regardless of the exact means of packaging and storing the reactants, and whether reaction occurs within a packet or within a chamber of the apparatus, according to the invention, H₂O₂ and catalyst are brought into contact with each other within a compartment or reservoir of the apparatus in a manner that allows the two to interact so that breakdown of the H₂O₂ into O₂ and H₂O occurs. The O₂ that is generated may be used immediately or may be stored for later use. Many different mechanical arrangements can be considered for use as a reservoir for the oxygen-generating reactions and/or temporary storage of oxygen, hi most cases, an oxygen reservoir will contain a means of egress for O₂ and a conduit through which the flow of O₂ can be directed. Generally, the conduit allows the O₂ to leave the chamber, usually via a valve that prevents unwanted substances (e.g. unreacted H₂O₂ and/or catalyst) from entering the conduit. For example, Figure 3 depicts schematically a single cylinder 200 with a cap 201, which contains O₂ generating reactants 20, a means of O₂ egress 202, and conduit 203. hi this embodiment, the apparatus also includes valve 204 to control oxygen release, and a means of monitoring the amount of oxygen remaining in reservoir 205 (e.g. a pressure gauge), both of which are disposed along conduit 203. This embodiment is particularly suited to the used of reactants in packets, since when the amount of oxygen in the reservoir falls below a desired level, the reservoir may be opened, the existing oxygen generating packet may be removed and discarded, and a new oxygen generating packet may be inserted. In another embodiment of the oxygen storage and delivery system, a standard gas regulator may be used to adjust and control the delivery pressure and/or flow rate of oxygen from reservoir 200. In other embodiments, the apparatus may include multiple chambers (reservoirs) for the oxygen storage and delivery system. Figure 4 depicts an apparatus comprising first reservoir 300, which is the site of decomposition and contains oxygen generating reactants 20. Oxygen from first reservoir 300 passes through one-way valve 301 (which is disposed along conduit 302) and is stored in and delivered from second reservoir 400. Second reservoir 400 includes valve 404 to control oxygen release, and a means of monitoring the amount of oxygen remaining in the reservoir 405 (e.g. a pressure gauge) disposed along conduit 403, through which O₂ flows to the user. By this arrangement, the oxygen generating reactants can be replaced without altering or affecting the delivery rate of oxygen from second reservoir 400. For example, cap 301 on first chamber 300 may be safely removed after the oxygen pressure is reduced by venting. Reactants 20 can then be safely removed and replenished. During the venting, opening, refilling, and recapping process, oxygen continues to flow from second reservoir 400 to the user.

Those of skill in the art will recognize that, while the embodiments illustrated in Figures 3 and 4 are depicted as "stand alone" units, this need not be the case. Rather, the illustrated chambers may be disposed within a housing. This embodiment of the invention is illustrated in Figure 5 A, which shows reservoirs 300 and 400 located within housing 500. Further, while chambers 300 and 400 are shown as side-by-side, this need not be the case. They may be arranged one over the other as well. In addition, chambers 300 and 400 may be separate cavities within an apparatus, but this need not be the case. For example, a single cavity that is divided, e.g. by a membrane such as a water impervious but gas permeable membrane (e.g. naflon). In some embodiments of the invention, the membrane is coated with a catalyst.

The chamber from which oxygen is discharged and sent to the user generally contains a means of egress for the oxygen and a conduit through which oxygen it sent to a user. This is also illustrated in Figure 5 A, where means of egress 406 and conduit or supply line 403 are shown. Typically, for a direct use apparatus, the conduit terminates in a manner that allows the user to directly and readily access the O₂ that has been produced, e.g. an "oxygen mask" that covers the nose and mouth or a nasal cannula allowing oxygen to be directed to the nose and thus nasal passages, etc. In this manner the device is used in a manner similar to conventional medical oxygen tanks. Furthermore, tubing or other conduit material can lead from the apparatus to devices such as mechanical ventilators or other devices such as manually operated bag-valve mask devices used to provide patients with volume ventilation and supplemental oxygen. The flow of oxygen into these devices can be titrated with gauges coming from the conduits allowing for the control of the concentration of oxygen received by the patient. Additional devices within the ventilator or separate from the ventilator but still a part of the device can be used to entrain room air in various amounts to vary the concentration of inspired oxygen. Various oxygen sensing meters and devices can be used to assist the user in producing the desired levels.

In some embodiment of the invention, a single end user may be the O₂ recipient. However, this need not be the case. The apparatus of the invention is capable of generating sufficient O₂ to supply more than one individual, and the device may be configured to do so. Further, the apparatus may be used to deliver O₂ in a non-individualized, non-direct manner, i.e. to release the O₂ from the conduit into a space such as a room, cabin of an airplane, compartment of an underwater or space vehicle, etc., to generally provide ambient O₂ to all individuals in the space.

In some embodiments of the invention, various valves and gauges are included in the apparatus to control the movement and rate of movement of reactants and/or oxygen. Those of skill in the art will recognize that many types of suitable valves exist that may be used in the practice of the invention. Generally, one-way valves are preferred, so that reactants are prevented from entering areas of the apparatus where they are not wanted, e.g. so that they do not come into contact with one another until it is desired for them to do so, and/or so that reactants and products are not mixed when delivered to the user, hi particular, it is especially desirable that H₂O₂ and/or catalyst do not enter the conduit that conducts O₂ to the person using the apparatus. As a fail safe measure, in case some unreacted H₂O₂ should enter the conduit, the conduit may possess a region that contains additional catalyst that will interact with and cause the residual H₂O₂ to decompose prior to reaching the user. Such a region may be in the form of a plug of material (e.g. steel wool) impregnated with catalyst, a screen that contains catalyst and is placed within the conduit in the path of O₂ flow; a coating of catalyst on one area of the conduit wall; a "bubbler" containing liquid catalyst through which the oxygen stream is bubbled; dry catalyst packed in e.g. a cartridge or sack or filter placed in the flow stream prior to or within the conduits (or both); etc. hi addition to the valves that control the movement of reactants and products within the apparatus, the apparatus may also include pressure sensitive relief valves to prevent over-pressurization of the apparatus. Gauges that are employed may be of any suitable type, many of which are known to those of skill in the art.

In some embodiments, the conduit that transports the oxygen to the user contains or is juxtaposed to or passes through a cooling mechanism (e.g. cooling fins). This causes condensation of any water vapor that is present to liquid water, with concomitant cooling of the O₂ stream. This embodiment is illustrated schematically in Figure 5 A, where cooling means 410 is depicted. Condensed water may be trapped in a reservoir (shown schematically as reservoir 411 in Figure 5A) which is in communication with cooling device 410 in a manner that allows collection of water condensed by cooling device 410, and may even be built into cooling device 410. Water is later emptied, or maybe continuously expelled from the apparatus during use, e.g. by expulsion route 413 (Figure 5A). The liquid water may be prevented from traveling to the user by, for example, the interposition of a water impermeable membrane, e.g. within or at the entrance of conduit 403 or between cooling device 410 and conduit 403, or at another suitable location. Further, those of skill in the art will recognize that it may not be necessary, or even desirable, to remove all water and heat from the stream of O₂. Retaining some moisture and warmth may be preferable in order to enhance the comfort of the O₂ recipient and to prevent dehydration. Therefore, the amount or degree of cooling may be adjusted in order to retain a certain desirable level of heat and moisture.

For an immediate use apparatus, the flow rate of oxygen to a user of the apparatus should be in the range of about 200 to about 10,000 cc/min. The rate of oxygen generation by reactants is generally in the range of about 1000-10,000 cc/min. The rate of oxygen generation can be varied based on the adjustment of one or more of several parameters, including but not limited to: the types of reactants, their concentrations, the speed at which they are mixed, the amount and form of catalyst, the presence of non-reactive fillers, etc. A filler is an inert substance, or a substance that at least does not react with H₂O₂ and catalyst in this system, that is added to effectively dilute the concentration OfH₂O₂ in order to slow down the rate of reaction, hi addition, temporary storage of excess oxygen in an onboard chamber (e.g. chamber or reservoir 400 in Figures 4-6). Further, control may be maintained by including, at various suitable positions in the apparatus, valves that control the ingress and egress of oxygen into and out of the various components of the apparatus. Gauges to monitor pressure within chambers and/or within delivery conduits or lines may also be included.

In yet another embodiment of the invention, the oxygen that is generated is passed through one or more filters to further dry or otherwise purify the oxygen before reaching the user. With reference to Figure 4, such a filter may, for example, be placed within, at the entrance of, or anywhere along conduit 303. Alternatively, such a filter may be placed at the entrance of, within or anywhere along conduit 403. In other embodiments, the oxygen receptacle may be a cylinder with a movable piston. The piston moves to allow the volume in the cylinder to expand as oxygen is generated, and can be depressed to maintain a desired pressure.

The apparatus of the invention may be of any design that is useful for the particular application that is being served. For example, for the apparatus may be designed in the form of a wearable tank with a mask that covers the nose and/or mouth of the user. Alternatively, the apparatus may be in any of several non-wearable forms that are readily portable, e.g. such that it can be stored in a case with a handle and carried, or wheeled, to the site of use. Alternatively, the apparatus may be installed or built into a structure e.g. into the wall, ceiling or floor of a building, refuge, vehicle, etc., where the ability to generate oxygen on site is desired. The invention could be particularly pertinent to the generation of oxygen in aircraft, in underwater vehicles, and in spacecraft.

While the apparatus of the invention, particularly "wearable" versions thereof, may be fashioned of solid materials, this need not be the case. Very light-weight and highly portable versions of the apparatus may be developed in which the portion of the device that houses the oxygen generating reactants is of a minimal size, and the receptacle that receives and optionally stores generated oxygen is made of a flexible, expandable, gas impermeable fabric such as an inflatable rubber, hi this case, the chamber that receives the oxygen (which may also be the decomposition chamber) expands or balloons as oxygen is generated, as is schematically illustrated in Figure 5B, where deflated chamber 800 contains an 02 generating packet or cartridge 801, which, when activated (represented by the arrow), inflates flexible chamber 800. Oxygen is transmitted from the expanded chamber to the user 69187

via conduit 802. Alternatively, resuscitator bags, such as shown in Figure 5C, and which are known in the art may be used. While these are generally used by emergency personnel by connecting to a traditional oxygen tank, in the practice of the invention, the design may be modified to receive oxygen generating components within pouch 810 of the resuscitator. A source of reactants (e.g. a packet or cartridge, etc.) may be activated (e.g. by adding water) and then placed in pouch 810, oxygen flows into resuscitator bag 811, is provided to the user in a manner similar to that which is employed when conventional oxygen tanks are used, hi addition, oxygen may be generated directly within an oxygen mask by adding an activated reactant packet or cartridge to the interior of the mask, or to a compartment that communicates directly with the interior of the mask and thus allows the direct flow of oxygen to the user. These embodiments are illustrated in Figure 5D and E, which schematically show oxygen mask 820 with an internal packet or cartridge 821, or an external compartment 822 for receiving a packet or cartridge. In this embodiment, the nature and amount of reactants are adjusted so that a suitable amount of oxygen is generated. This design may be especially useful for providing extra oxygen for relatively short periods of time. Rebreathing feature

An average individual has an oxygen consumption rate of about 250-300 cc/minute (at approximately 37 ⁰C and 1 atm pressure). The apparatus of the invention as described above, will generally be able to provide at least about 6 hours of breathable (e.g. 50-100%) oxygen, hi order to do this, a rebreathing feature may be introduced. In this embodiment, respired or exhaled air from the user of the apparatus is recirculated back into the apparatus, CO₂ is absorbed (scrubbed) from the respired air (for example, by a CO₂ absorbing substance such as soda lime, 1 kg of which can remove approximately 140 liters of CO₂ at approximately 37 ⁰C and 1 atm pressure), and the oxygen is recirculated back to the user.

This embodiment of the invention is illustrated in Figure 6A-B. With reference to Figure 6 A, the respired air is circulated from the user through conduit 600 and into chamber 601 where CO₂ is removed. The CO₂ removal agent may be provided, for example, in the form of a disposable or refillable cartridge, filter, etc., or any other suitable form, or may be added directly to a chamber in a loose form. The purified oxygen flows through conduit 602 to reservoir 400, where it is mixed with oxygen generated from H₂O₂. Similarly, with reference to Figure 6B, air exhaled by the user flows through conduit 700 into chamber 701 where CO₂ is absorbed, and the purified oxygen is then channeled into conduit 403, which provides oxygen to the user. Chamber 701 may be built into or attached to housing 500 (as shown), or may be within a separate housing (not shown, e.g. within a stand alone housing). By recirculating purified respired air, 1 kg of a solid form OfH₂O₂ (e.g. UHP, which is 30% H₂O₂ by weight) and provide e.g. 50 to 100% oxygen to a user for a minimum of about 6 hours, without replenishing reactants. If highly stabilized forms OfH₂O₂ are used (for example, a highly stabilized solution of 50% H₂O₂, which will produce more than 215 liters of oxygen in several minutes), that time can be extended to at least about 10 hours or longer. Further, designs of the apparatus in which reactants can be readily replaced (e.g. reactants are contained in disposable packets, and, optionally oxygen is temporarily stored within the apparatus), the time during which breathable oxygen can be generated and supplied to a user may be extended indefinitely, and will depend largely on the availability of replacement reagents and CO₂ scrubbing agents.

Exemplary rebreathing devices are depicted in Figures 7 and 8, which show a bedside oxygen generation and rebreathing system that includes a ventilator (Figure 7) and a individual direct use oxygen generation and rebreathing system that is designed in a manner similar to a personal flotation device (PFD), respectively.

Figure 8 shows a schematic depiction of a PFD-type or style of oxygen generating apparatus that includes O₂ generating element 60, O₂ accumulation chamber 61, means for a user to access O₂ 62 (e.g. an oxygen or breathing mask), means to remove/scrub CO₂ from air exhaled by the user 63, and means to remove H₂O 64. The flow of oxygen and/or scrubbed respired air proceeds through at least one conduit of the system in the direction indicated by arrows. Oxygen enters O₂ accumulation chamber 61 via conduit 66a and is subsequently sent to the user via conduit 66b. Means to directionally control the flow of gases 65 is/are also included. Preferably these are valves (e.g. one-way valves) which direct the flow of oxygen to the user and the flow of respired air away from the user e.g. via conduit 66c. hi this embodiment, scrubbed respired air is directed back to O₂ generator 60 via conduit 66d (or optionally, to O₂ accumulation chamber 61, not shown) and thus maybe added to the oxygen that is being generated from H₂O₂, thereby extending the length of time the apparatus can provide oxygen after a single loading of reactants. Those of skill in the art will recognize that various valves or switches may be interposed along the conduit. Nevertheless, the conduits generally form a continuous closed loop within the apparatus. The particulars of the design of reactant source, O₂ generator 60, O₂ accumulation chamber 61, means for user to access O₂ 62 (e.g. an oxygen or breathing mask), means to remove/scrub CO₂ from the system 63, and means to remove H₂O 64 are similar to those described elsewhere in the application. Various additions (as described for e.g. Figure 10) can be added to allow for closed loop feedback to further conserve and optimize oxygen usage.

Reactants and chemical reactions

According to the invention, O₂ is generated by the breakdown OfH₂O₂, in the presence of a suitable catalyst. The reaction, which also produces water, is illustrated in Formula 1 :

If a solid form OfH₂O₂ is used, a two step reaction is carried out. First, water catalyzes the production OfH₂O₂ from the solid, as illustrated by Formula 2, where "HP" represents the H₂O₂ component of the solid and "X" represents an additional component(s), e.g. urea in urea hydrogen peroxide: X - HP ^water ) X + HiOi

The H₂O₂ that is generated then reacts with a suitable catalyst according to Formula 1.

Those of skill in the art are familiar with liquid solutions OfH₂O₂ that may be used in the practice of the invention. Generally, such solutions will contain at least 30% H₂O₂ or greater. Solutions in the range of from about 30 to about 90 % H₂O₂ may be employed, with solutions ranging from about 40 to about 90%, or from about 50 to about 90% being preferred. However, solutions of about 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or even about 95% may be employed.

Likewise, those of skill in the art will recognize that many solid forms OfH₂O₂ exist which can be used in the practice of the invention. Examples include but are not limited to: various inorganic peroxides such as calcium peroxide, sodium peroxide, zinc peroxide, magnesium peroxide, etc.; various peroxide adducts (i.e. compounds which include hydrogen peroxide molecules), for example, sodium carbonate perhydrate (Na₂CO₃-I-SH₂O₂), urea hydrogen peroxide [UHP, (NH₂)₂CO^»H₂O₂)], histidine hydrogen peroxide, adenine hydrogen peroxide, alkaline peroxyhydrates such as sodium orthophosphorate, etc. In addition, a solid nanoparticulate peroxide may be formed by a method such as freeze drying, spray drying, homogenization, controlled precipitation, and the like, of hydrogen peroxide.

Usually water is used to release H₂O₂ from adducts such as urea hydrogen peroxide. However, some chemicals other than water are also known to do so. These include but are not limited to various organic chemicals with active hydrogens such as alcohols, diols, aldehydes, organic acids, organic diacids, organic polyols, and polyacids; as well as organic alcohols, carboxylic acids, aldehydes, and polymeric versions of the same; etc. Such chemicals may be used in the practice of the invention instead of water, when H₂O₂ adducts are employed. Suitable catalysts for causing the auto-oxidation/reduction OfH₂O₂ to O₂ and water include but are not limited to stable catalysts such as iron chloride, MnO₂, hydroxides of lead, silver, cobalt, manganese, osmium, copper, nickel, iron, chromium, selenium, platinum, mercury, etc. Enzyme catalysts such as catalase may also be employed. Some forms of carbon and graphite are known to catalyze the decomposition. Additional catalysts include but are not limited to MnO (manganous II oxide or manganous oxide), MnO₂

(manganese IV oxide or manganese dioxide), titanium dioxide (TiO₂), ferric oxide, and ferrous oxide. Compounds of other Mn oxidation states may also be used. Other compounds which may catalyze the reaction are discussed by Schumb et al. (W. C. Schumb, C. N. Satterfield, and R.L. Wentworth, 1995, Hydrogen Peroxide, Reinhold Publishers, New York, pp. 467-500). These catalysts may be combined with H₂O₂ in either a wet or dry form. For example, the catalysts may be provided in the form of aqueous slurries at concentrations from about 5 wt% solids to about 60 wt% solids, or as solid/water pastes at concentrations above 60 wt%. In other embodiments of the invention, the oxidation of hydrogen peroxide can be used in lieu of the auto-oxidation/reduction of hydrogen peroxide. Many strong oxidizers are known to oxidize hydrogen peroxide to water and oxygen, including but not limited to iodine, ferric iron compounds, mercury (IT) compounds, silver (I) compounds, inorganic nitrites, bromine, concentrated sulfuric acid, chlorine gas, chromate compounds, permanganate compounds, ozone, flourine, etc. hi some embodiments of the invention, a "solid" reactant is an essentially homogenous dry form of the reactant and is generally in the form of solid granules, powders, cakes, tablets, pellets, etc. However, a "solid" reactant may also be impregnated into and/or dried onto a support of some type, or coated onto the interior or a portion of the interior of the decomposition chamber itself. For example, fabric, paper or other absorbent material may be wetted with a reactant, dried, and stored in a packet as described above. Alternatively, a reactant may be coated onto a support in a liquid or partially liquid (e.g. slurry) form and allowed to dry on the form. Such a form may be, for example, specifically designed to fit snugly into a section of the apparatus. Alternatively, such forms may be disposed within a disposable packet. One or both of the dry reactants (dry form OfH₂O₂, dry catalyst) may be thus immobilized, either on separate supports, or on the same support. It may be advantageous to utilize one immobilized dry reactant or both immobilized dry reactants in order to discourage mixing and reaction during storage. Other means of isolating and contacting the ingredients used herein will occur to those skilled in the art, and all such are intended to be encompassed by the invention.

In addition, other compounds and materials may be added to the mixture in the packet in order to help contain the ingredients within the packet and further render the oxygen generating system spatially independent. For example, it may be advantageous to add compounds that form gels with water or materials that absorb and bind aqueous solutions.

By sequestering water generated by the reaction, the possibility of water entering the conduit that conducts oxygen to the user is minimized. Examples of such substances include but are not limited to various poly(carboxlic acids), polyacrylamides, papers and fabrics made from water absorbing fibers or films. In general, such fibers include, for example, natural fibers such as wool, cotton, cellulose, yak hair, ermine etc. Synthetic alternatives include absorbent nylons, polyesters, etc. and fibers or films made from, for example, lignosulfonic acids, various polyacrylamides and polyacrylic acids and salts thereof, poly(acryonitrile-co- butadiene-coacrylic acid), poly(acrylic acid-co-maleic acid), poly)allylamines, polyethylenes, polyiosbutylenes, polymethyl vinyl ethers, polypropylenes, poly(vinylpyridines), polyvinylpyrrolidones, and the like. The polyacrylamides in particular are important as many are "superabsorbers" used in diapers and such. Materials for construction of the apparatus

Those of skill in the art will recognize that many materials exist that are suitable for use in constructing the apparatus of the invention. If storage and decomposition of reactants is carried out directly within a chamber or compartment of the apparatus, then the materials must be of a type the does not react with reactants. Examples of suitable inert materials include but are not limited to aluminum, stainless steels and non-rusting alloys, other metals coated with epoxy or rubber, nylon, polypropylene, polydeethylene, Teflon, and other polymers that so not have active groups such as alcohol, aldehyde or acid; various non-reactive engineering plastics such as polycarbonates, PVC, CPVC, polysulfones, PEEK, etc. If reacting materials do not directly contact the apparatus (e.g. if they are disposed within a water-impermeable packet, then the choice of materials may be wider as corrosion due to reactants would be less likely. Alternatively, materials that are susceptible to corrosion may be used in portions of the apparatus that do not directly contact reagents, and/or portions of the apparatus that directly contact reagents may be coated or lined with inert materials, many of which are known to those of skill in the art. The rate at which oxygen is generated by the apparatus may be greater than the rate at which an individual user utilizes the oxygen, or the oxygen may be generated in anticipation of use. Therefore, at least one chamber of the apparatus must generally be capable of receiving oxygen and temporarily storing it as it is metered out slowly to the user. Thus, as will be understood by those of skill in the art, the design of the apparatus must also take into account safety considerations such as the sturdiness of materials used, ability to expand or lack thereof, resistance to explosion, etc.

While the apparatus of the invention, particularly "wearable" versions thereof, may be fashioned of solid materials, this need not be the case. Very light-weight and highly portable versions of the apparatus may be developed in which the portion of the device that houses the oxygen generating reactants is of a minimal size, and the receptacle that receives and optionally stores generated oxygen is made of a flexible, expandable, gas impermeable fabric such as an inflatable rubber. Uses of the invention

Those of skill in the art will recognize that the invention may be advantageously employed in a variety of situations, particularly those in which transport and storage of large quantities of oxygen by traditional methods are impractical or unsafe. These include but are not limited to emergency situations where on-site oxygen generation is desired, e.g. in order to provide oxygen until more standard medical care is available, or until the emergency situation is resolved. Also included are scenarios that are not necessarily emergencies, but in which the capability to generate oxygen on site would be advantageous. Examples of all such situations include but are not limited to combat; persons trapped underground e.g. in mines; elderly patients in need of home oxygen treatments; at crash sites for use by emergency medical personnel; in aircraft in case of depressurization; in hospitals, e.g. in times of natural disaster, mass casualty or pandemic situations when traditional systems are overwhelmed; during chemical spills; for firefighters; in underwater vehicles, diving suits, or abodes; in spacecraft, space suits, space stations, etc. outside the earth's atmosphere; as an adjunct to high altitude gear e.g. for use by mountain climbers or rescue teams; etc. Further, the apparatus and methods of the invention may be used in concert with traditional methods, e.g. to fill conventional oxygen tanks, or to replace or supplement conventional oxygen delivery systems. The methods and apparatus of the invention may be used in any situation where it is desired to quickly and safely generate breathable oxygen on-site. One of the overarching advantages of the proposed apparatus is that oxygen is produced only when actually needed thus eliminating the risk of carrying and storing traditional high pressure oxygen canisters which represent a constant threat of explosion if penetrated. This danger is present in transport and is a particular hazard in combat zones. Furthermore, traditional oxygen canisters are of no use once their contained oxygen is utilized since there are no current means to "recharge" them on the fly. The current disclosed invention allows "recharging" in all of its embodiments by allowing replacement of the chemical reactants which produce useable oxygen. Thus, large quantities of stored "pre-oxygen" reactants can be carried and used on an as-needed basis which reduces transport hazards. The invention is further illustrated by the following non-limiting examples.

EXAMPLES EXAMPLE 1. Chemically produced oxygen and rebreathing strategies

The devices and methods of the present invention provide for onsite production, use, and conservation of oxygen in low-weight small foot-print devices. A typical resting respiratory quotient or fractional inspired oxygen concentrations (FiO₂) for an individual is

0.8 The invention provides a combination of chemically produced oxygen and rebreathing- recirculating strategies which allow for up to 6 hours of oxygen utilization at fractional FiO₂ values of 0.5 to 1.0.

Oxygen is stored in several readily available compounds. Perhaps the best known is hydrogen peroxide. Although most commonly known in its liquid form, hydrogen peroxide exists in solid forms such as urea hydrogen peroxide (UHP). UHP is a 1:1 adduct of urea and H₂O₂ and is very stable, decomposing at a temperature of 75-85 ⁰C. It is 32% H₂O₂ by weight with a density of 1.4 g/cc. One gram of UHP (32% H₂O₂ by weight and equal to 1 cc), will produce approximately 130 cc oxygen. When the urea adduct is cleaved from the H₂O₂ , the H₂O₂ is then free to react with a catalyst to produce oxygen and water.1 kg of UHP will produce about 638 grams of urea, 191 grams of water and 170 grams of oxygen. At 1 atm and 23 ⁰C, 170 grams of oxygen will produce approximately 130 liters of O₂. The entire reaction can take place within minutes. The calculations below provide the stoichiometric basis for the amount of oxygen produced by 1 gm of UHP.

Ig UHP l mol UHP I mOl H₂O₂ l mol θ₂ . .. _{1 Λ}__{3 t} . _ — • • Z-±* 2_ = 5.43χiθ ³mols ofθ

92 g of UHP l mol UHP 2 mol H₂O₂ 2 PV = nRT

(latm)V = 4.7x1 (T³ (0.08206 ^{L a}"/^» _mol._κ)(297 K) V = 132 ml O₂ produced at 1 atm and 23⁰C(RT)

Rebreathing circuits including the capability to remove CO₂ are a common component of anesthesia equipment. The major innovation proposed herein for a ventilator rebreathing circuit includes a disposable oxygen generating cartridge containing UHP (or other hydrogen peroxide species), a separate cartridge containing reusable catalyst, and a component (e.g. cartridge) for the removal of CO₂ from respired air using, e.g. sodalime. Typically, 1 kg of sodalime will absorb approximately 140 liters CO₂. Since resting respiratory quotient is 0.8, 1 kg of sodalime will remove most of the CO₂ generated from the aerobic metabolism of 130 liters O₂.The device of the invention can be recharged using additional cartridges.

The rebreathing circuit for spontaneously breathing individuals may be patterned after an airline personal flotation device. These are envisioned for use on the field and in mass casualty environments where supplemental inhaled oxygen is desired but in which standard oxygen 'E' cylinders are unavailable or limited and where disposability or transportation are issues. On-site O₂ production is provided for spontaneously breathing subjects or subjects receiving assisted ventilation without a mechanical ventilator. Figures 9A-B graphically depict the number of breaths to achieve an FiO₂ of 1.0 and the expired fraction of oxygen (FeO₂), given the following assumptions: Oxygen generated by 1 kg of UHP = 130 liters; Oxygen consumption average = 250 cc/minute; Tidal Volume = 600 cc; Respiratory Rate = 10 breaths/minute; Inspiratory-Expiratory ration of 1 :2; total body N₂ of 10 liters. Note that it takes approximately 14 breaths or 90 seconds to achieve a mean FiO₂ of 0.9-1.0 (Figure 9A). This can be maintained for approximately 3,600 breaths before the FiO₂ begins to decrease to 0.8 after approximately 6 hours (Figure 9B). After 4,800 and 5,100 breaths respectively, FiO₂ decreases from 0.5 to 0.2. Thus, a minimum FiO₂ of 0.5 can be maintained for 4,800 breaths or 480 minutes or 8 hours, beyond which FiO₂ will decrease to room air values after 5,100 breaths or 8.5 hrs. At this time, all that remains is approximately 6.6 liters of residual N₂ from lungs plus an additional 3.4 liters of N₂ from body stores to total 10 liters N₂ and 2.5 liters of O₂. The addition of a gas mixer will of course allow for much longer duration of supplemental oxygen if an FiO₂ of less than 0.8 is sufficient. Such a mixing device will entrain room air (with an FiO₂ of 0.21) to allow decreasing the delivered FiO₂. Such mixing devices are usually accompanied by an oxygen concentration measuring device, hi such a manner, automated electronic feedback loops can be created allowing careful utilization of produced oxygen to help maintain the arterial hemoglobin oxygen saturation levels at desired levels (between 90-100%). Such closed feedback loops can include pulse oximetry measured hemoglobin oxygen saturation levels (SpO₂) which provide information to a metering gauge of the oxygen producing apparatus.

When SpO₂ levels fall, for example, from 99% to 94%, additional oxygen is metered into the breathing circuit from the reservoir where it is used to ventilate the patient (including rebreathing input) until SpO₂ levels increase again, at which time dosing from the reservoir may be halted. This aspect of the invention is illustrated schematically in Figure 1OA, which shows portable oxygen generating device 90 from which oxygen flows through conduit(s) 92 to a user. Arrows indicate direction of flow. The user accesses the oxygen via oxygen-providing means 91 (in this exemplary case, an oxygen mask). The level of hemoglobin O₂ saturation of the user is measured/monitored using measuring means 93, in this exemplary case, a pulse oximeter. Information concerning the level of oxygenation of the user feeds back to or is transmitted from measuring means 93 to means to adjust the oxygen flow 94 via circuit 98. Depending on the measured level of O₂ saturation of the user, means to adjust the oxygen flow 94 controls the amount or level of oxygen delivered from device 90 to the user. The amount of oxygen delivered to the user is automatically (or manually, if necessary) adjusted up or down (i.e. is increased or decreased) according to a predetermined acceptable value or range of values of user O₂ saturation measured as described above. The system may incorporate the rebreathing components described earlier for removal of CO₂. This is illustrated schematically in Figure 1OA, where conduit 95 leads from the user to CO₂ scrubbing chamber 97. Alternatively, CO₂ may be scrubbed by either of the two mechanisms illustrated in Figures 6A and B, or others which may occur to those of skill in the art. Scrubbed air circulates back into conduit 92 and is transmitted to the user. In addition or as an alternative to pulse oximetry, various O₂ monitoring means (e.g. an O₂ sensing meter such as 96 of Figure 10A) can be placed within the breathing circuit (especially if rebreathing is applied). Similar to the technique described above, manual or automatic means can be used to monitor and allow bleeding of additional oxygen into the circuit at predetermined levels since the oxygen utilization of the patient will begin to slowly deplete the oxygen within the rebreathing circuit/feed back loop. Again, this technique of closed loop oxygenation allows for further conservation of the chemically produced oxygen, hi a further embodiment illustrated schematically in Figure 1OB, mechanical ventilator 95 assists in or coordinates the provision of oxygen to the user, hi this embodiment, means to adjust the oxygen flow 94 may be separate as shown or may be part of ventilator system 95. Ventilator system 95 may also include means to entrain ambient room air 96, shown in phantom, which may be part of ventilator system 95 per se, or may be located outside ventilator system 95. Room air may be mixed with the oxygen that is delivered to "dilute" the oxygen, thereby conserving the supply of oxygen. Together, these components form a closed loop as illustrated in Figures 1OA and B, and variants thereof that will occur to those of skill in the art. The amount of oxygen provided to the user is thereby coordinated with the actual needs of the user, as evidenced by measurements of oxygen saturation. Thus, sufficient oxygen is delivered, but oxygen is not wasted.

EXAMPLE 2. Generation of oxygen from 50% H₂O₂ and FeCl_2/3 catalyst

Experiments were conducted in which oxygen was generated using 50% H₂O₂ and FeCl₂₇₃ as the catalyst, in order to text for the presence of toxic gases in the products. Briefly,

5 ml 50% H₂O₂ was added dropwise to solid FeCl_2/3 in an enclosed vacuum flow system, and the production of gases was monitored by Fourier transform Infrared (FTIR) and GC mass spectroscopy. The results showed that 1 liter of oxygen was generated (1 atm pressure and 25 ⁰C, i.e. 298 ⁰K) in less than 3 seconds with a ~4 ⁰C temperature gain. No Cl₂ or other toxic gases were evolved during the reaction. EXAMPLE 3. Development of prototypes A cylindrical vessel with a double walled aluminum casing is depicted schematically in Figure 1 IA and a photograph of the same is provided in Figure 1 IB. A plastic hydrogen peroxide container sits inside the top section of the vessel. A separate lower section contains a catalyst. A lever is operably connected to a needle below the hydrogen peroxide container in a manner so that when the lever is pressed, the needle punctures the container and H₂O₂ drips onto the catalyst. The water byproduct is pushed into the inner wall of the vessel. The reaction chamber is open to an oxygen dispensing tube, allowing oxygen to go directly out into the delivery tube.

Figure 11C shows a graph depicting the rate and total amount of oxygen generated using this prototype to react 150 ml of 32% H₂O₂ with a mixture OfFeCl₃ and CuCl₂ as a catalyst. The changing rate of production is a function of the changing rate of drops, which slows down as the bottle is emptied.

A second prototype is depicted schematically in Figure 1 ID. This prototype includes an upper H₂O₂ reservoir which is capped and isolated from a lower reaction or decomposition chamber. The lower decomposition chamber is the site of peroxide decomposition. It contains a catalyst, e.g. a mixture of ferrous and cuprous chlorides, or buffer and catalase. Oxygen generation rate is determined by the peroxide drip rate, and a thumbscrew is provided for adjusting the drip rate OfH₂O₂ from the reservoir into the decomposition chamber. Oxygen generated in the chamber passes through a check valve that prohibits liquid from being pushed out in the gas stream. The vessel is made of nylon and is completely reusable after e.g. rinsing and refilling with reactants.

EXAMPLE 4. Oxygen Delivery via Hydrogen Peroxide Generation and Decomposition within a disposable packet

Oxygen is produced from a two step chemical reaction sequence: 1) the decomposition of urea hydrogen peroxide adduct (UHP) by water to produce hydrogen peroxide and urea and, 2) the catalytic auto-oxidation/reduction of hydrogen peroxide by solid manganese (IV) dioxide (MnO₂) to produce liquid water and oxygen. UHP and MnO₂ are combined and placed in a "teabag" made from Tyvek® nonwoven protective garment material. All four edges of the teabag are heat sealed to completely contain the solids. A small amount of water is injected via syringe through the teabag and quickly mixed with the solid ingredients. The production of oxygen begins immediately and the teabag begins to inflate. Before appreciable oxygen can escape, the teabag is placed into an aluminum gas filter cartridge and capped with a screw-on lid attached to a gas manifold. A pressure gauge on the manifold is used to follow the increase in pressure as oxygen generation proceeds to completion.

Genetically, Tyvek® is a nonwoven fabric made from hydrophobic high density polyethylene fibers. The Tyvek® chosen for this example was a product that is lightly heat bonded on each surface and then embossed with a pin punch to "soften" the material. The microporous fabric has moderately high gas permeability but very poor wettability and, therefore, allows oxygen but not water or solids to pass through. Thus, the Tyvek® teabag keeps all of the reactants contained while allowing the oxygen to escape to a gas reservoir. Materials and Methods

Urea hydrogen peroxide (2.64 g) and manganese (IV) dioxide (MnO₂, 2.0 g) were mixed and added to a Tyvek® teabag that was constructed by heat sealing three edges of two 1.5" x 3.0" swatches. The top of the teabag was heat sealed after the addition of the solid mixture. A syringe was used to inject 2.5 mL of distilled water into the teabag. The water and solids were quickly kneaded and the teabag was placed inside a 1.5" i.d. (inner diameter) x 6" long aluminum gas filter cartridge. The cartridge was then quickly attached to a gas manifold and the pressure was recorded with time. The previously measured volume of the manifold was combined with the pressure data and room temperature to compute the total moles of oxygen released before the reaction was terminated. Results

The results are presented in Figures 12A and B. As can be seen in Figure 12 A, pressure within the cartridge increased with time as oxygen was generated by the catalytic decomposition of hydrogen peroxide. Figure 12B shows the release of oxygen with time. As can be seen, quantitative release of oxygen was observed, the number of moles of oxygen released closely approaching the theoretical limit based on urea hydrogen peroxide.

This example shows that, quantitative oxygen release is achieved by the practice of the invention. Further, the increase in pressure does not harm the catalyst during the lifetime of the reaction. Discussion

The reactants were chosen based on safety and environmental impact (benign disposal) considerations as well as efficacy. Tyvek® was used to make the device positionally independent (e.g. it still works if turned upside down) and to guarantee containment of and easy removal and disposal of the ingredients. Additionally, the rate of oxygen generation can be changed by varying the absolute and/or relative amounts of UHP, MnO₂, and water or by changing the type and amount of oxygen-carrying molecule and/or oxidant/catalyst. Without regard to preferences and constraints, other chemicals and materials might be used by one skilled in the art to generate oxygen in a similar way and for similar reasons.

While the invention has been described in terms of its preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims. Accordingly, the present invention should not be limited to the embodiments as described above, but should further include all modifications and equivalents thereof within the spirit and scope of the description provided herein.

Claims

CLAIMSWe claim:

1. A portable oxygen supplying device for use by a person comprising: a housing; one or more supply conduits extending from said housing for supplying oxygen to a person; a hydrogen peroxide feed tank associated with said housing, said hydrogen peroxide feed tank including or configured to receive a source of hydrogen peroxide; a decomposition chamber associated with said housing, said decomposition chamber including or configured to receive a catalyst for decomposing hydrogen peroxide to water and oxygen; a first valve for controlling the flow of the source of hydrogen peroxide into said decomposition chamber; and a second valve configured to allow oxygen egress from said decomposition chamber to said one or more supply conduits, and to prevent one or more of hydrogen peroxide or catalyst egress from said decomposition chamber.

2. The portable oxygen supplying device of claim 1 further comprising a means for removing water from said decomposition chamber.

3. The portable oxygen supplying device of claim 1 further comprising a means for removing carbon dioxide from said one or more supply lines.

4. The portable oxygen supplying device of claim 1 wherein said housing is made from nylon or aluminum.

5. The portable oxygen supplying device of claim 1 further comprising heat dissipating fins associated with said housing.

6. The portable oxygen supplying device of claim 1 wherein said source of hydrogen peroxide is a solid hydrogen peroxide adduct selected from the group consisting of urea hydrogen peroxide, sodium percarbonate, calcium peroxide, magnesium peroxide, sodium peroxide, sodium perborate, and anhydrous poly(vinyl pyrrolidone) hydrone peroxide complexes.

7. The portable oxygen supplying device of claim 6 wherein said source of hydrogen peroxide is contained in a cartridge configured to be insertable into said housing.

8. The portable oxygen supplying device of claim 1 wherein said catalyst is selected from metals, metal alloys, metal oxides, and metal salts.

9. The portable oxygen supplying device of claim 1 wherein said catalyst is an enzyme.

10. An apparatus for generating oxygen, comprising a cartridge for containing concentrated H₂O₂ in the form of an H₂O₂ adduct selected from the group consisting of urea hydrogen peroxide (UHP, carbamide peroxide), sodium percarbonate, calcium peroxide, magnesium peroxide, sodium peroxide, sodium perborate, and anhydrous ρoly( vinyl pyrrolidone)/hydrogen peroxide complexes, said H₂O₂ adduct having a H₂O₂ concentration of greater than 30%; a cartridge for containing a catalyst capable of catalyzing the production of oxygen from said concentrated H₂O₂; and a means for selectively combining metered amounts of H₂O₂ from said cartridge containing concentrated H₂O₂ with said catalyst from said cartridge containing said catalyst so as to generate breathable quantities of oxygen.

11. A portable oxygen generator comprising: a feed tank to contain H₂O₂, said feed tank comprising a metering valve to meter a flow rate OfH₂O₂ from said feed tank; a decomposition chamber for receiving, through said metering valve, H₂O₂ from said feed tank, said decomposition chamber containing a catalyst to catalyze decomposition of said H₂O₂ to oxygen and water; a supply line to allow egress of said oxygen from said decomposition chamber, wherein said supply line comprises an isolation valve to prevent egress of said H₂O₂ or said catalyst, or both, from said decomposition chamber.

12. The portable oxygen generator of claim 11 wherein said portable oxygen generator further comprises heat fins to dissipate heat produced by said decomposition of said H₂O₂.

13. The portable oxygen generator of claim 11 wherein elements of said portable oxygen generator are made of nylon or aluminum.

14. The portable oxygen generator of claim 11 wherein said H₂O₂ is 3-60% aqueous hydrogen peroxide.

15. The portable oxygen generator of claim 11 wherein said catalyst is a metal or metal alloy containing iron, copper, lead, platinum, or silver.

16. The portable oxygen generator of claim 15 wherein said catalyst is a metal oxide or metal salt.

17. The portable oxygen generator of claim 11 wherein said catalyst is an enzyme based catalyst.

18. The portable oxygen generator of claim 17 wherein said enzyme based catalyst is selected from catalase and buffer.

19. The portable oxygen generator of claim 11 wherein said metering valve provides positional independence between said feed tank and decomposition chamber.

20. The portable oxygen generator of claim 11 wherein said metering valve is a needle valve or an electronic metering pump.

21. The portable oxygen generator of claim 11 wherein said supply line further comprises a catalyst to decompose peroxide in said supply line.

22. The portable oxygen generator of claim 21 wherein said catalyst is a mesh catalyst.

23. The portable oxygen generator of claim 11 wherein said portable oxygen generator is configured as a re-breathing system comprising means for resorbing CO₂; and means for recirculating exhaled air to said means for resorbing CO₂.

24. The portable oxygen generator of claim 11 wherein said decomposition chamber and said feed tank are compartmentalized within a single cannister.

25. The portable oxygen generator of claim 11 wherein said decomposition chamber and said feed tank are housed in separate cannisters.

26. A portable oxygen generator comprising: a decomposition chamber to contain solid H₂O₂; a catalyst tank to contain a aqueous catalyst; a metering valve which allows said aqueous catalyst to be metered into said decomposition chamber; and a supply line to allow egress of oxygen generated by decomposition of said solid H₂O₂ in said decomposition chamber, wherein said supply line comprises an isolation valve to prevent egress of said solid H₂O₂ or said aqueous catalyst, or both, from said decomposition chamber.

27. The portable oxygen generator of claim 26 wherein said solid H₂O₂ is selected from the group consisting of metal peroxides and peroxide adducts.

28. The portable oxygen generator of claim 27 wherein said metal peroxide is a calcium peroxide, a magnesium peroxide, or a zinc peroxide.

29. The portable oxygen generator of claim 27 wherein said peroxide adduct is urea hydrogen peroxide.

30. The portable oxygen generator of claim 26 wherein said portable oxygen generator further comprises heat fins to dissipate heat produced in said decomposition.

31. The portable oxygen generator of claim 26 wherein elements of said portable oxygen generator are made of nylon or aluminum.

32. The portable oxygen generator of claim 26 wherein said catalyst is a metal or metal alloy containing iron, copper, lead, platinum, or silver.

33. The portable oxygen generator of claim 32 wherein said catalyst is a metal oxide or metal salt.

34. The portable oxygen generator of claim 26 wherein said catalyst is an enzyme based catalyst.

35. The portable oxygen generator of claim 34 wherein said enzyme based catalyst is selected from catalase and buffer.

36. The portable oxygen generator of claim 26 wherein said metering valve provides positional independence between said catalyst tank and said decomposition chamber.

37. The portable oxygen generator of claim 26 wherein said metering valve is a needle valve or an electronic metering pump.

38. The portable oxygen generator of claim 26 wherein said supply line further comprises a catalyst to decompose peroxide in said supply line.

39. The portable oxygen generator of claim 38, wherein catalyst is a mesh catalyst.

40. The portable oxygen generator of claim 26 wherein said portable oxygen generator is a rebreathing system comprising means for resorbing CO₂; and means for recirculating exhaled air to said means for resorbing CO₂.

41. The portable oxygen generator of claim 26 further comprising a compartment to contain water.

42. The portable oxygen generator of claim 26 wherein said decomposition chamber and said catalyst tank are housed in separate canisters.

43. The portable oxygen generator of claim 26 wherein said decomposition chamber and said catalyst tank are compartmentalized within a single cannister.

44. The portable oxygen generator of claim 43 wherein said decomposition chamber, said catalyst tank, and said compartment to contain water are housed in separate canisters.

45. An apparatus for generating oxygen, comprising a housing; desiccated solid H₂O₂ and desiccated solid catalyst positioned within a material that is permeable to gas but is not permeable water.

46. The apparatus of claim 45, wherein said desiccated solid H₂O₂ and said desiccated solid catalyst are present as a mixture.

47. The apparatus of claim 45, wherein said desiccated solid H₂O₂ and said desiccated solid catalyst are present in separate compartments within said material.

48. The apparatus of claim 45, wherein said desiccated solid H₂O₂ is selected from the group consisting of urea hydrogen peroxide, sodium percarbonate, calcium peroxide, magnesium peroxide, sodium peroxide, sodium perborate, and a anhydrous poly(vinyl pyrrolidone)/ hydrogen peroxide complex.

49. The apparatus of claim 45, wherein said desiccated solid catalyst is selected from the group consisting of a metal or metal alloy containing iron, copper, lead, platinum, or silver; a metal oxide or metal salt; and an enzyme based catalyst.

50. The apparatus of claim 45, wherein said material is Tyvek®.

51. The apparatus of claim 49, wherein said desiccated solid catalyst is MnO₂.

52. The apparatus of claim 45, wherein said housing is inflatable.

53. The apparatus of claim 45, wherein said housing is a wearable mask.

54. Desiccated solid H₂O₂ and desiccated solid catalyst positioned within a material that is permeable to gas but is not permeable to water.

55. The desiccated solid H₂O₂ and desiccated solid catalyst of claim 54, wherein said material is puncturable by a needle.

56. The desiccated solid H₂O₂ and desiccated solid catalyst of claim 54, wherein said material is pliable.

57. The desiccated solid H₂O₂ and desiccated solid catalyst of claim 54, wherein said material is Tyvek®.

58. The desiccated solid H₂O₂ and desiccated solid catalyst of claim 54, wherein said desiccated solid H₂O₂ is selected from the group consisting of urea hydrogen peroxide, sodium percarbonate, calcium peroxide, magnesium peroxide, sodium peroxide, sodium perborate, and a anhydrous poly(vinyl pyrrolidone)/hydrogen peroxide complex.

59. The desiccated solid H₂O₂ and desiccated solid catalyst of claim 54, wherein said desiccated solid catalyst is selected from the group consisting of a metal or metal alloy containing iron, copper, lead, platinum, or silver; a metal oxide or metal salt; and an enzyme based catalyst.

60. The desiccated solid H₂O₂ and desiccated solid catalyst of claim 57, wherein said desiccated solid catalyst is MnO₂.

61. The portable oxygen supplying device of claim 1, wherein said device is part of a closed feed back loop that further comprises means to measure a level of oxygen saturation in said person; and means to adjust an amount of oxygen provided to said person in response to said level.

62. The apparatus of claim 10, wherein said apparatus is part of a closed feed back loop that further comprises means to provide said oxygen to a user; means to measure a level of oxygen saturation in said user; and means to adjust an amount of oxygen provided to said user in response to said level.

63. The portable oxygen generator of claim 11 , wherein said portable oxygen generator is part of a closed feed back loop that further comprises means to provide said oxygen to a user; means to measure a level of oxygen saturation in said user; and means to adjust an amount of oxygen provided to said user in response to said level.

64. The portable oxygen generator of claim 26, wherein said portable oxygen generator is part of a closed feed back loop that further comprises means to provide said oxygen to a user; means to measure a level of oxygen saturation in said user; and means to adjust an amount of oxygen provided to said user in response to said level.

65. The apparatus of claim 45, wherein said apparatus is part of a closed feed back loop that further comprises means to provide said oxygen to a user; means to measure a level of oxygen saturation in said user; means to adjust an amount of oxygen provided to said user in response to said level; and, optionally, means to monitor oxygen concentration within said closed feed back loop.

66. The portable oxygen generator of claim 11, wherein said catalyst is associated with an absorbent carrier matrix.

67. The portable oxygen generator of claim 45, wherein said desiccated solid H₂O₂Or said desiccated solid catalyst or both said desiccated solid H₂O₂ and said desiccated solid catalyst are associated with an absorbent carrier matrix.

68. The desiccated solid H₂O₂ and desiccated solid catalyst of claim 54, wherein said desiccated solid H₂O₂ or said desiccated solid catalyst or both said desiccated solid H₂O₂ and said desiccated solid catalyst are associated with an absorbent carrier matrix.

69. The portable oxygen generator of claim 16, wherein said catalyst is MnO₂.

70. A portable closed loop oxygen generating and rebreathing apparatus, comprising an oxygen generating element, an oxygen accumulating chamber; means for a user to access oxygen generated by said oxygen generating element; means for removing CO₂ from air exhaled by said user; means for removing water from air exhaled by said user; at least one conduit; and means for directionally controlling a flow of said oxygen generated by said oxygen generating element and said air exhaled by said user through said at least one conduit.