Patent Application
20190009208
This invention relates generally to the product packaging and preservation and, more specifically, to an Electrochemical Nitrogen Generator System and Method.
Preservation of oxygen-sensitive items, such as food, medication, sera, artifacts, manuscripts, etc most times requires the absence of oxygen. The level of oxygen present should be as low as possible, particularly if these items have to be preserved over long durations. Historically, the options for reducing the oxygen concentration surrounding such items have been: flushing the container with nitrogen while the container is being filled with the contents (e.g. medicine into vials); oxygen removal via ab- or ad-sorbent materials after the container has been filed with the contents; via applying a vacuum to the container after filling with the contents; or by the extraction of oxygen (such as by electrolytic cell).
The industrial filling of vials while under nitrogen environment, conducted on a large scale at high filling rates, allows oxygen levels to be reduced to a concentration of about 2-3%, which may be adequate for some contents, but typically is not acceptable for prolonged durations of storage or highly sensitive contents.
Application of a vacuum would generally yield an oxygen concentration of 5%, while resulting in a vacuum level of 0.24 atmospheres (absolute), which may also result in the removal of chemicals distilling from the items to be protected (i.e. water and the like). However, rigid containers must be used in order to sustain the internal vacuum, and these containers are highly susceptible to leakage because they are constantly maintained at a pressure much lower than the surrounding environment.
Absorbents that either bind or react with the oxygen have limited removal capabilities in as much as large amounts of absorbents may be required to protect the items, making this approach cost-prohibitive.
In the cases of artifacts such as fabrics or manuscripts, libraries must install large storages of nitrogen, at the exterior of buildings and supply a stream of nitrogen to counteract any oxygen that may leak into the system. This approach is also cost-prohibitive for many circumstances.
One patent—U.S. Pat. No. 6,171,368 by Maget for “Gas Extraction from Closed Containers” (Maget 368) presents another option, namely electrochemical extraction of oxygen from medical vials, also described in an article1 specifically citing the protection of epinephrine (a compound extremely sensitive to oxidative degradation). This invention allows oxygen reduction to levels of 1,000 ppm (0.1%) or below, which is more than adequate for prevention of oxidation over long durations, at a vacuum that is never below 0.8 atmosphere. The problem with the Maget 368 design is that the limitations of the Electrolytic Cell and the associated power supply restricts its applicability to small containers (e.g. small vials). 1 International Journal of Pharmaceutical Compounding 1999 No. 6, pp 493-495
The drawbacks in each of these examples illustrates that there is a need for improved, low-cost techniques and systems for viably protecting items from degradation due to oxygen contamination.
In light of the aforementioned problems associated with the prior devices and methods, it is an object of the present invention to provide an Electrochemical Nitrogen Generator System and Method. The system and method should provide the ability to create a nitrogen-rich environment in containers of a variety of sizes. The system and method should be able to extract the oxygen from the air within the container without reducing the internal pressure substantially below atmospheric. A version of the method should be provided to reduce the oxygen content and replace it with nitrogen through a series of sequential fractional steps. In another form, the system and method should provide a “streaming” approach of bleeding off oxygen-containing contents of the container, while continuously replacing it with air until such time as the percentage of oxygen within the container is below the desired level. In yet another version, the system and method should operate under pressure, thereby injecting pressurized air, either in sequential fractional steps or via continuous flow, whereby at the end of the process, the internal contents of the container are in a pressurized nitrogen environment, and the oxygen expelled from the container during the process is also under pressure.
The objects and features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages, may best be understood by reference to the following description, taken in connection with the accompanying drawings, of which:
The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventor of carrying out his invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the generic principles of the present invention have been defined herein specifically to provide a/an Electrochemical Nitrogen Generator System and Method.
The present invention can best be understood by initial consideration of
In addition to the contents 14 is also a head volume 18. This volume 18 is that part of the internal sealed volume of the container 12 that is not filled with the contents 14—it includes the volume above the contents 14, as well as around the contents 14 (in the case of solid contents). Immediately after being sealed, the head volume 18 has an initial condition of air at atmospheric pressure—condition CI is, then: 1 atmosphere in pressure, approximately 78% nitrogen, 21% oxygen, and 1% of inert gases (mainly argon). For the purpose of this invention, the inert gases are incorporated in a nitrogen-equivalent of 79%.
The process for removing the O2 from the container 12 and replacing it with N2 is one of a series of O2 extraction steps, with each extraction step followed by the replacement of the extracted O2 with air. After the oxygen is removed from the head volume 18 (starting at CI), the first extraction condition is reached—condition CE1 is: 0.79 atmosphere pressure, approximately 100% nitrogen, and virtually 0% oxygen. This should be intuitively obvious, since the volume of the oxygen within the head volume 18 has been removed.
Next, after the head volume is re-filled to atmospheric pressure with air (replacing the O2 that has been removed), the interior of the container 12 will reach the first addition condition—CA1 is 1 atmosphere in pressure, approximately 95% nitrogen, and approximately 5% of oxygen. This reduction in O2 is simply because the pure O2 that was removed has been replaced by gas that only contains approximately 21% oxygen.
Assuming that 5% is still an unacceptably high O2 concentration, a second O2 extraction is performed until the container 12 reaches a second extraction condition—CE2 is approximately 0.96 atmosphere pressure, approximately 100% nitrogen, and virtually 0% oxygen.
Assuming that the slightly vacuum state of the head volume 18 is unacceptable, a second air addition step is performed so that the interior of the container reaches second addition condition—CA2 is 1 atmosphere in pressure, approximately 99 percent nitrogen content, and approximately 1 percent oxygen content.
While other versions of the method and system are a part of the present invention, even in this simplest form, it can be seen that this iterative step-down in oxygen concentration has a substantial benefit over the prior approaches because (a) it can be performed on a wide range of sizes of containers; (b) there is no restriction regarding the type of protected contents that can be N2-packed by this method; (c) it does not require the use of rigid containers; (d) there is no added risk of contamination inherent in vacuum-packed packages; and (e) it does not require costly chemical absorbents. Table I provides an example of the method with:
The last step to achieve a pressure of 1.00 atmosphere would be to add 9.26 cc of air, containing 7.32 cc of nitrogen and 1.94 cc of oxygen for a final volume of 1,000 cc and an oxygen concentration of 0.194% or 1940 ppm of oxygen.
Note that total amount of oxygen removed to create that purity level of nitrogen is 263.36 cc (210+44.1+9.26). Therefore, the efficiency of these steps is 210/263,36=79.7%. The concentration of oxygen CO=0.21n+1, where (n) represents the number of (extract/add) steps. For a targeted value of CO the number of steps can be calculated.
Note also that this illustration is not meant to imply that oxygen concentration levels of 0% are achievable by the extractor and that, in fact, oxygen concentrations of ca. 0.5-1% are acceptable and yet prevent oxidative degradation. We will consider such a more practical case in the following, albeit the same arguments are possible.
Furthermore, the addition of streams of air does not have to be conducted in individual discrete steps but can also be achieved in a continuous manner, i.e. with an air intake leak that would cease to operate as internal and external pressure become equal. Practically, if a concentration of oxygen of 5% is adequate for preservation of item in container, a concentration easily achievable with the electrochemical extractor, the following conditions are possible:
An initial extraction of 96% of the initial oxygen present would be adequate to achieve a 5% atmosphere of oxygen. Therefore, individual steps do not require deep oxygen removal.
Table III below provides a comparison to a conventional vacuum-evacuation system:
As can be seen, the 5% oxygen concentration level is achieved by the extractor at a benign pressure of 638 mmHg that does not affect the jar contents. However, at a level of 181 mmHg required by the vacuum pump, considerable water evaporation occurs as well as the possibility to extract low vapor pressure chemicals, if present. For a vacuum pump to achieve low oxygen levels (1000 ppm=0.1%) a near absolute vacuum is required, a task requiring expensive turbo mechanical pumps.
There is a conventional electrolytic cell 22 (EC 22), which is attached to a substrate 28 (such as a cap that threads onto the opening of the container [12]). The EC 22 is defined by an inlet port 24 (through which oxygen is drawn via electrolytic reaction), and outlet port 26 (from which the O2 is expelled). In cases where additional O2 removal capability is desired, it is possible to stack electrolytic cells 22 atop on another as depicted in
The process of O2 removal is further detailed in
If it is desired that the contents be packaged under pressure, then the container will be pressurized with compressed air 106—making the P(D) the elevated pressure.
The oxygen is then extracted from the container to the desired O2 state (typically to total removal of all O2) 108. Next, air is added to the container until the internal (head volume) pressure reaches P(D)—the pressurized air source 106 will be applied, if appropriate.
If the oxygen concentration has been reduced to the desired level 114, then the extractor device is removed from the container 116. If the removal of additional oxygen is desired 112, then steps 108 and 110 are repeated until the O2 level (and N2 level) in the head volume reaches the desired level 114.
After placing the contents into the container 100, the extractor/admitter device (cap or other structure) is attached to the container 103. As will be discussed below, the extractor/admitter device has a mechanism for admitting air into the container at a controlled rate in a continuous fashion, while also including an electrolytic cell [22] or stacked cells in operation to remove O2 from the air in the head volume [18].
Once sealed and pressurized with air 106, oxygen is extracted from the container while air is admitted into the container so as to maintain the internal pressure above P(MIN) 118. Presumably, both the O2 extraction rate and the air admission rate are controllable and adjustable. If the oxygen concentration is not at the desired level 120, then the extraction/addition process 118 continues. Once the desired O2 concentration is reached 122, oxygen extraction and air addition are both ceased 124, 126 (simultaneously or sequentially, depending on the structure). Subsequently, the extractor/admitter device is removed from the container 117.
The air intake leak defined as intake leakage rate, R, cc/hr=βΔP, where β is a coefficient cc/hr-atm and ΔP is the pressure difference between exterior vs interior of container namely (1−PT) since the exterior pressure is 1 atm and the container total pressure is PT≤1.
In this instance for a 1000 cc container, after the extractor has removed all oxygen, the air intake volume will be 210 cc of which 44.1 cc is oxygen for a final oxygen concentration of 4.41%.
Initially the ΔP=0.21 atm, the oxygen concentration is zero and the highest intake rate of air is achieved, namely (0.21β) and after some time, when the container pressure is at 1 atm, the intake rate vanishes to zero, the container is at atmospheric pressure and the oxygen content is 4.41%. No further gas flow takes place except for diffusional transfers, oxygen in, nitrogen out.
In essence, opening the container to air and immediately closing it would yield the same end result as a slow intake leak, except that atmospheric pressure would be created instantly, but it would not be possible to achieve oxygen levels below 4.41%, unless the sequence (extract/add) is repeated.
To achieve a pressure of 0.998 atm, i.e. practically atmospheric pressure, using a leak with a β value of 10 liters/hr-atm the vent needs to stay open for 28 minutes.
However, this process would not yield an environment with an oxygen concentration below 4.41%. This would be the practical case when the leak is opened and subsequently closed, and the process is repeated.
Instead of multiple stages, the process can be continuous with an extractor AND an air intake leak operating steadily until equilibrium is achieved and the container maintained at atmospheric pressure and low oxygen concentration. In that instance the total pressure remains at approximately 1 atm.
Since whenever a certain oxygen volume is removed from the container an equivalent volume of air is admitted into it. The volume of oxygen in the container becomes:
V
OX
=V
0
OX(e−kt)=0.21VT(e−kt) and the volume of nitrogen is VN2=VT(1−0.21e−kt), where:
k=0.79αIOPT/VT with α=0.23 liters/Ahr; IO=0.5 A/cm2-atm of oxygen; and PT=gas pressure of 1 atm.
For the continuous operation the only requirement is that the rate of air intake should not affect the extractor performance.
For an intake restrictor defined by the rate (R) of air intake such that:
R=β(Pambient−PT)=βΔP, where β in liters/hr-atmosphere
For a balance system operation βΔP=αIOPO
If a factor f=βΔP/αIOPO defines the ratio (rate of air input/rate of oxygen output), the system for f<1 will result in restrictor interference with the oxygen output, whereas if f=the system will operate essentially as a closed system, and if the system is open loop, operating unrestricted.
The basic requirement will be that at the time of the largest oxygen extraction rate (at time zero), 0.21βΔP>dVO/dt and this condition needs to be satisfied for small values of ΔP.
The container volume is 1 liter; the volume oxygen is 0.210 liter, the balance being inert gas volume of 0.790 liters. The extractor cell area is 16 cm2. The time-dependent nitrogen and oxygen volumes in the container for two different operating conditions are reported in the following table:
In this case the intake leak can be constant without affecting high quality of nitrogen or closed after completion of the 6 hours process.
The leak can be a short micro-bore tubing, or a Porex plug or any sized restrictor.
In order to fully expand on the potential versions of the system of the present invention,
Therefore, to obtain a nitrogen purity of 95+% only one extraction step will be required followed by an exposure to environmental air and nitrogen will be available at atmospheric pressure. For multiple steps resulting in more concentrated nitrogen at atmospheric pressure the only penalty is the need to extract the equivalent of oxygen of [0.21VT(1+0.21+0.212+0.213+ . . . 0.21n)]=rather than 0.21VT for a ratio of 1.266, i.e. penalty of 26%.
In a related embodiment, the power supply 20 required to operate extractor 16A/16B is optionally a constant voltage/variable current source supplying 1.6-1.65 volts (or 3 volts) to extractor 16A/16B, to achieve the maximum current (limiting current) possible, or a variable current source with a voltage limiter limiting the applied voltage to 1.6-1.65 volts.
For example,
a chamber of 1,000 liters (1 m3) has to be maintained at an inert gas concentration of at least 99% at atmospheric pressure and room temperature to preserve archival records kept under glass, and only infrequently taken out of the chamber. The limiting current density for the extractor operating initially on air, being about 0.15 amperes/cm2, the k-value of the nitrogen generation system becomes equal to 1.7×10−4 (hr-cm2)−1. Since the “pump down” duration in not critical, the total operating area of the extractor is selected to be 500 cm2 for a k-value of 0.085 hr−1. The resulting characteristics of the system are described in the following table.
The operating system requires an AC/DC converter as a power source located either internally or externally to the chamber, a nitrogen gas circulating fan and a small air intake aperture. Once the 99% nitrogen concentration is achieved, the generator can be either stopped or continue idling with a capability to further enrich the nitrogen or to act as maintenance equipment should an air intake leak occur at a rate not exceeding 5 liters/hr, or the equivalence of 0.5% of the container volume per hour. The dual functions of the generator are beneficial since the chamber can be maintained at a high nitrogen concentration without the need of “flushing” the system. After opening the chamber to the air environment, the generator will automatically resume oxygen extraction until the desired nitrogen concentration is achieved.
Stack 16B (for example) consists of 80 series-connected cells each 10 cm×10 cm in size, thus an area of 100 cm2 each. The stack voltage is about 120 volts DC operating at a maximum current of 100 amps. (At a pressure of 10 atm, or an initial oxygen pressure of 2.1 atm, the limiting current will be about 1 amps/cm2 or 1 max=100 amps, thus an equivalent of 8,000 amps equivalent (the product of Amps/cell times the number of cells) for the extraction of oxygen at a maximum rate of 0.23 Liters/Ahr×8,000=1,840 liters-atm/hr or 184 liters of oxygen at 10 atm.
With valves 36, 52 and 46 closed, the power supply 20 is activated, thereby extracting oxygen from container 12 to be released into tank 44 with a movable wall (piston) to maintain the oxygen under pressure. Since container 12 holds 205 liters of oxygen at 10 atm, (or 2050 liters @ 1 atm), and since the pump-down is targeted at 4% of oxygen, the total volume of oxygen to be removed will be 1,700 liters-atm requiring 7400 amps-hr equivalent. Since the average current per cell is approximately 51 amps, the duration to 4% will be about 1.8 hours, and the container pressure will be 8.3 atm. If the nitrogen quality is acceptable the gas in container 12 can be released to storage 50 through line 48 and open valve 52.
If a better grade of nitrogen is required, container 12 is re-supplied with compressed air from tank 42, before nitrogen is withdrawn. In that instance, the oxygen concentration will increase to 6.9%. Before re-activating the power supply, the container will hold 69.8 liters of oxygen at 10 atm. After extracting 375.5 liters˜atm of oxygen to reduce the oxygen content in nitrogen to about 3.4%, the process will require an additional 1624 A-hr delivered over a period of about 0.8 hours.
The effectiveness of the dual activation of the power source becomes (0.205−0.04)×1,000×10/2075.5=79.5%. The electric energy requirements for each operating cell are: 179 and 201.6 whr for the production, respectively, of 9600 and 9800 liter-atm of nitrogen.
At the end of step 2, 98% nitrogen can be released from container 12 by opening valve 52, and the cycle can be restarted.
A further modification of this fractionation process would consist in conducting the process in a continuous manner similarly to that [10A] illustrated in
Table V represents calculated values for the energy consumption related to the production of 96% and 98% nitrogen, namely 1.49 and 1.65 Kwh/m3N2 (STP). These values are based on operating the nitrogen generator at maximum (limiting) current, that is at a cell voltage of 1.6 volts. Since the specific energy consumption (Kwh/m3 of nitrogen) is proportional to the cell voltage energy gains can be achieved at lower cell voltages, that is at currents below limiting currents.
Note: The separation of oxygen from nitrogen starting from an air source is based currently on three principal process technologies: A) low temperature (−200° C.) distillation, an energy-intensive process, B) pressure swing adsorption, divided in TSA temperature swing adsorption, 2) PSA pressure, 3) VSA vacuum and 4) VPSA hybrid process. This technology has been developed mainly with production of medical oxygen as a product, and C) membrane separation.
Process A is mainly used in large industrial installation, whereas B and C are used for compact low volume generation equipment such as for medical uses or bench-top devices for applications that generally do not require large gas volumes and are frequently on stand-by.
While all illustrations have emphasized the production of concentrated nitrogen from air, the technology can also be applied to gas phase enrichment of other binary or multi-component mixtures such as N2/H2, NH3/H2, H2/O2, etc.
When operating in such a high-temperature condition, it is necessary that the incoming air stream is moisturized by a humidifier 62 (which may be a combined heater and humidifier as shown). The O2 is extracted from the gas steam by extractor 60, and then the moisture is removed from the N2 stream via condenser 64.
Since the O2 component of the gas at the first cell 22A is much higher than the O2 component of the gas at the fourth cell 22D, first cell 22A is operated at a much higher voltage than fourth cell 22D. The same applies to all four cells 22A-22D, and therefore the operating voltages V1-V4 will be different from cell 1 22A-cell 4 22D. Furthermore, the current density of the cells will also (typically) be different from one another (CD1-CD4 as shown here). Whereas the prior art series-arranged electrochemical cells has always been operated at a consistent voltage and current (and therefore extraction rate), in this embodiment 60, each cell 22A-22D is operated independent from one another in terms of voltage supply (PS1-PS4).
Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiment can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.
This application is filed within one year of, and claims priority to Provisional Application Ser. No. 62/530,005, filed Jul. 7, 2017.
| Number | Date | Country | |
|---|---|---|---|
| 62530005 | Jul 2017 | US |
