Abstract:
A gas storage and delivery system for replacing gas lost from a pressurized container or a carbonated beverage, or for introducing a gas such as oxygen into a beverage such as bottled water or a sports drink.

Description:
This application claims the benefit of U.S. provisional application Ser. No. 60/225,817, filed Aug. 16, 2000, entitled GAS STORAGE AND DELIVERY SYSTEM FOR PRESSURIZED CONTAINERS. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to pressurized containers, and more particularly, to a gas storage and delivery system for restoring and maintaining pressure as it is depleted from pressurized containers such as aerosol dispensers, bottles of carbonated beverage, and the like. 
     2. Prior Art 
     Pressurized containers are commonly used to dispense many products, including paint, lubricants, cleaning products, hair spray, and food items. These containers are typically aerosol dispensers in which the product is stored under pressure with a suitable propellant. Dispensing of the product occurs when a discharge nozzle is depressed, permitting the pressurized product to be forced out through the nozzle, usually as a spray, stream or foam. As product is depleted from the container, the pressure exerted by the propellant decreases, especially evident with compressed gases, and may become diminished to the extent that all of the product cannot be dispensed from the container, or desired characteristics are not achieved. 
     Many products, e.g., hair spray, require a carrier in addition to the propellant component, e.g., alcohol, that dries quickly upon discharge from the container. Volatile organic compounds (VOCs) such as propane, isobutane, dimethyl ether, and the like, are suitable as propellants for many products, but their use is limited due to environmental concerns. For instance, under some current regulations no more than 55% of the contents of the container can comprise a VOC. In an aerosol dispenser, as much as 25% of the VOC could be required for use as a propellant, leaving about 30% VOC in the product. This 25% reduction typically is made up with water, which does not dry as quickly as the VOC, resulting in a “wet” product when used. 
     Carbon dioxide (CO 2 ) is environmentally friendly, and is therefore useful as an aerosol propellant, but its use has been limited due to the drop off in pressure from start to finish as the product is used. For example, in a typical situation the starting pressure might be 100 psig and the finishing pressure only 30 psig. At this low finishing pressure all of the product may not be discharged, and/or proper aerosolization may not be obtained. 
     Carbonated beverages are also bottled under pressure, usually by a pressurized inert gas, such as CO 2 , placed in the bottle along with the beverage. Over time, the pressure of the gas may decrease, resulting in a “flat” drink. This is particularly true when plastic containers are used to bottle carbonated beverages. The shelf life of such products may be undesirably short. 
     Further, cans of pressurized gas are provided for cleaning dust and the like from sensitive equipment, such as computers, computer keyboards, etc., by blowing a pressurized stream of propellant onto the equipment. Currently available products for this purpose use a VOC (e.g., Dymel® by DuPont) as the propellant. These materials are relatively expensive for the intended use. 
     Accordingly, there is a need for a system to replenish and maintain a desired pressure in pressurized containers, such as aerosol dispensers and carbonated beverages, and particularly to such a system that is inexpensive and environmentally friendly. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system and method to replenish and maintain a desired pressure in pressurized containers, such as aerosol dispensers and carbonated beverages. 
     In accordance with the invention, a gas storage system is employed in pressurized containers to store and release gas to replenish pressurized gas depleted from the container. More particularly, the invention uses a material that is capable of adsorption and storage of a large quantity of gas, and then releasing it under predetermined conditions. Additionally, the material of the invention is a non-toxic material. 
     The storage body used in the invention is known as a pressure swing adsorption (PSA) system, wherein adsorption of gas into the body occurs at a high pressure, and desorption of gas from the body occurs at a low pressure. Such adsorption/desorption devices are capable of storing under pressure a volume of gas that is 18 to 20 times the volume of the body. 
     For example, the invention may use a storage body made from granular activated carbon, or a carbon fiber composite molecular sieve (CFCMS) material, to adsorb and store a quantity of a desired gas, such as nitrous oxide or carbon dioxide, for example. The storage body may be pre-charged with the desired gas and then placed in a pressurized container, or in communication with the interior of the container, or it may be placed in a container and a desired gas introduced under pressure into the container to charge the storage body, for subsequent release of the gas as the propellant or carbonization gas becomes depleted, thereby restoring the pressure in the container to a desired level. 
     A mass of granular activated carbon may be formed into a cohesive shape such as a ball or cube or the like which is simply placed in the container, or the mass of activated carbon may be encased in a film or cover. The cover may be something that functions only to contain the carbon and prevent its admixture and discharge with the product, or it may be a gas permeable membrane that is capable of passing the desired gas but prevents contact between the carbon and the liquid or other product in the container. One suitable source of granular activated carbon, for example, is a 10×50 mesh material available from Westvaco Corporation under number 1072-R-99. One suitable film may comprise a Tetratex® 1316 membrane film, for example, available from Tetratec PTFE Technologies. 
     For some applications, nitrous oxide may be used in lieu of or in combination with carbon dioxide. Nitrous oxide is more compatible with products having an oil component, for example. 
     An alternative storage body can comprise a carbon fiber composite molecular sieve (CFCMS) material, as disclosed in U.S. Pat. Nos. 5,912,424 and 6,030,698, which are incorporated in full herein. 
     During filling of an aerosol container, the storage body may be placed in the container and a suitable propellant gas introduced into the container to a pressure of 150 psig, for example, whereupon the body will adsorb 75 psig, for example. Product is then introduced into the container, increasing the pressure back up to 80 to 100 psig, for example. As product is expelled, gas is released from the body to restore the pressure in the container to a desired predetermined level. 
     The body may have any desired shape, such as spherical, tubular, cubic, etc., and may have any desired suitable size to store and release an appropriate amount of gas during use of the system. Further, the carbon material may be enclosed within a suitable membrane for one-way flow of the gas out of the material and through the membrane into the container, while precluding direct contact between the product and the carbon. Such membranes are employed in reverse osmosis water purification systems, for example. 
     The gas storage and release system of the invention may also be used to discharge oxygen or another gas into a beverage, such as bottled water or a sports drink, if desired. 
     In essence, the invention comprises the use of a gas adsorption material in a pressurized container as a reservoir for a gas such as carbon dioxide, nitrous oxide, and the like, and which releases the gas into the container as the pressure in the container decreases as product is dispensed, thus maintaining a desirable pressure in the container and obtaining a more uniform product discharge from beginning to end. 
     The use of activated carbon to adsorb additional gas in an aerosol container can increase the available gas to a level which results in the pressure remaining more uniform until the product is depleted. This, in turn, maintains a more consistent, uniform and acceptable spray pattern from beginning to end because the pressure at the end is very close to the starting pressure. 
     The carbon dioxide can be used alone or in combination with other gases, such as nitrous oxide, or the nitrous oxide can be used alone or in combination with other gases, and/or any one or all of these can be used in combination with liquified compressed gases such as propane, isobutane, dimethyl ether or Dymel® (trademark of DuPont), to produce desired spray patterns which would permit reduction in the quantity of volatile organic compounds used in the pressurized product. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing, as well as other objects and advantages of the invention, will become apparent from the following detailed description when considered in conjunction with the accompanying drawings, wherein like reference characters designate like parts throughout the several views, and wherein: 
     FIG. 1 is a somewhat schematic longitudinal sectional view of an aerosol dispenser employing a gas storage and release system according to the invention; 
     FIG. 2 is a somewhat schematic longitudinal sectional view of a beverage bottle containing a beverage, and having a gas storage and release system according to the invention incorporated into the cap; 
     FIG. 3 is an enlarged longitudinal sectional view of a bottle cap incorporating the gas storage and release system of the invention; 
     FIG. 4 is an end view of the cap of FIG. 3, looking in the direction of the arrow  4 , with portions broken away; 
     FIG. 5 is a perspective view of a body of gas-adsorbing material enclosed in a porous film or cover; and 
     FIG. 6 is a transverse sectional view of a body of gas-adsorbing material enclosed in a gas permeable membrane. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An aerosol dispenser is indicated generally at  10  in FIG.  1 . The dispenser includes a container  11  made of metal or other suitable material, having a bottom  12  and a top  13 . A discharge nozzle assembly  14  is mounted on the top and includes a nozzle  15  that may be manually depressed to open and permit product P to be dispensed from the container through the nozzle. A dip tube  16  extends from the bottom of the container to the discharge nozzle assembly. As seen in this figure, the level of product in the container does not occupy the entire volume of the container, and the space above the product level is filled with a pressurized propellant gas to exert pressure on the product and force it through the dip tube and nozzle when the nozzle is depressed. The foregoing structure and operation are conventional. 
     In accordance with the invention, a storage body  20  of a gas-adsorbing material such as granular activated carbon, or carbon fiber composite molecular sieve (CFCMS) material, is placed in the container with the product to adsorb and store a quantity of a desired gas, such as carbon dioxide, nitrous oxide, for example. The body is capable of storing, under pressure, a volume of gas that is many times greater than the volume of the body. For instance, the CFCMS material can hold 18 to 20 times the volume of the body. As disclosed herein, the storage body is known as a pressure swing adsorption (PSA) system, wherein adsorption of gas into the body occurs at a high pressure, and desorption of gas from the body occurs at a low pressure. Thus, as the pressure of the propellant gas in the container falls below a predetermined threshold value, gas is released from the body, restoring the pressure in the container. 
     The body  20  may be formed as a cohesive block of carbon material, e.g., granular activated carbon or carbon fiber composite molecular sieve (CFCMS) material, which is placed in the container in contact with the product. Gas, such as carbon dioxide, is stored in the carbon material and released to restore pressure in the container as product is dispensed. 
     A film or cover  21  may be placed around the body of carbon material to prevent dispersion of the carbon into the product, and/or to prevent direct contact between the carbon and product. That is, the film may comprise a porous member  21   a  (see FIG. 5) that simply contains the carbon material and permits free flow of gas and product, or it may comprise a membrane or film  21   b  (see FIG. 6) that permits flow of carbon dioxide outwardly through the film into the product, but prevents flow of product into the carbon material. For example, the film  21   b  may comprise a reverse osmosis membrane placed around the body of carbon fiber material to permit flow of gas from the body into the product, but to prevent flow of product through the membrane to the body. 
     Use of the invention to store and release gas into a beverage is shown generally at  30  in FIGS. 2-4. In this embodiment, a beverage bottle  31  has a quantity of beverage  32  therein, and a closure cap  33  placed on the end of the bottle. 
     In accordance with the invention, a storage body  34  of activated carbon, or carbon fiber composite molecular sieve (CFCMS) material, is placed in the cap. If desired, the body may be isolated from the interior of the bottle by a suitable film or cover, such as reverse osmosis membrane  35 . 
     If the beverage is a carbonated beverage, the body may store a quantity of CO 2 , which is released from the body into the container to restore pressure in the container, and CO 2  into the beverage, lost due to depletion of the beverage and the CO 2 , or permeation of the CO 2  through the container wall. 
     The beverage may also comprise water, or a sports drink, and the gas can comprise O 2 , to give a boost of energy to a person drinking from the bottle. 
     While particular embodiments of the invention have been illustrated and described in detail herein, it should be understood that various changes and modifications may be made to the invention without departing from the spirit and intent of the invention as defined by the scope of the appended claims.