This is a Continuation-In-Part Application of International Application PCT/GB2007/004158 filed Oct. 31, 2007 and claiming the priorities of GB application 061885.3 filed Nov. 2, 2006 and GB application 0717116.8 filed Sep. 4, 2007.
This invention relates to systems for dispensing substances from containers and more particularly, to systems employing a very simple but effective two phase solid/gas adsorption/desorption mode of operation.
A large number of products are on the general market packaged in canisters—some of which cause the product to be dispensed therefrom in the form of small or atomized particles and are therefore commonly referred to as “aerosols”. They can be dispensed from the canister by means of a gas (or vapor) pressure generated in situ in the canister, by acting as a dispensing or propellant gas. Such products include ones for personal care including hair sprays, shaving creams, deodorants and the like and ones for household use including cleaning substances, room fragrances, insect repellents or the like, and many more. In addition, many beverages, including beer and soft drinks and the like, are dispensed from canisters by means of gas pressure.
In some cases, such products are admixed with the pressurized gas in the canister. Operation typically of a push-down operating valve causes both the product and the gas to be dispensed from the pack by means of the gas pressure, for example via a ‘dip tube’ extending in to the product from a nozzle which is commonly associated with the release valve, all of which are contained in a dispense assembly or dispense block.
In other cases, the product and pressurized gas are separated from each other within the canister. Typically, some form of divider or membrane is present in the canister, for example, one in the form of a bag containing the product which is sealingly attached to the canister internal wall in the vicinity of the release valve. The gas is present between the divider and the internal walls of the pack, i.e. surrounding the bag and the gas pressure in turn exerts pressure on the product in the bag.
Alternatively, the divider may be a piston which slides within the canister with the product on one side and a gas on the other side and which acts to drive the product from the canister by the action of gas pressure.
Whichever type of pressure pack is adopted will depend on the nature of the product and the use to which it is to be put and on the nature and properties of the propellant gas, in particular whether the propellant gas might react with the product or whether, for example, it might be flammable or odorize the product.
The use of chlorofluorocarbons (CFCs) previously became very popular as propellant gases for such product dispense canisters in that they can be readily condensed and vaporized in a reversible manner responsive to the surrounding pressure. This was followed by the use of hydrofluorocarbons (HFCs) and also hydrochlorofluorocarbons (HCFCs) which were regarded as being somewhat more environmentally friendly.
However, more recently, such propellant gases have in general been phased out owing to their acknowledged environmentally harmful properties, in particular ozone depletion of the upper atmosphere.
Alternative propellant gases which have been commonly used are certain hydrocarbon gases including liquid petroleum gases (LPGs) such as propane and butane. Such gases, however, are by their nature extremely flammable are environmentally harmful in some respects and in addition can introduce an odor in to the product being dispensed.
It is known that numerous attempts have been made to replace LPG propellant gases with gases such as air, nitrogen, carbon dioxide and the like. These attempts have largely been effected simply by utilizing a pressurized gas within the canister.
In practice, the canister valve is depressed to propel the product from the canister in the general manner described above.
However, such attempts have been largely unsuccessful due to the large pressure changes in the canister during use, commonly leading to reduced dispense characteristics at low pressures and a loss of pressure before full product dispense which results in a slow dispense of the residual product from the canister.
In addition, it is known that there has been considerable effort to develop further alternative propellant systems for such product dispense. For example, there is disclosed in European Patent Application No. 385 773, the use of two-phase gas/solid or gas/liquid or three phase gas/liquid/solid propellant systems in which the solid is a polymer having molecular microvoids occupied by the gas or gas/liquid under pressure and the gas is released therefrom when the pressure of the system is reduced.
There is additionally disclosed in a further European Patent Application No. 502 678, the use of a three phase gas/liquid/solid propellant system in which the solid is a material such as a foam or a fibrous mass having open voids occupied by the gas/liquid under pressure and the gas is released therefrom when the pressure of the system is reduced.
It is known that efforts to develop such prior systems were based primarily on the preferred embodiments described in these European applications, namely the use of a gas/liquid/solid system in which carbon dioxide as the gas was dissolved in acetone as the liquid which itself occupied voids in a solid.
Acetone has been used as the liquid in such a system only in connection with canisters employing a membrane, for example, a bag containing the product, in order to separate the propellant system from the product to be dispensed. However, acetone is an aggressive chemical and it is also known that it was found that the use of acetone in such systems tended to cause problems associated with chemical attack of the membrane material and leakage of the acetone through and around the membrane resulting in the failure of the membrane.
A further prior attempt to produce a product dispense system utilizing gas pressure is disclosed in UK Patent Specification No. 1 542 322 in which a propellant gas, including propane/butane, certain CFCs and carbon dioxide, is adsorbed on to a solid with dispense gas pressure being produced in situ during use of the system by means of bringing the solid into contact with a propellant displacing agent—preferably, water—in order to release the adsorbed gas. As such, the system as a whole is necessarily very complex due in particular to the need to employ the propellant displacing agent during use and provide means to bring it in to contact with the solid.
It was also disclosed in our co-pending Application PCT/GB2005/000145 that the use of a new system not involving polymeric materials and not involving troublesome liquids or displacing agents and being more suitable for commercially viable assembly in to the aerosol canister can provide an efficient sorption/desorption propellant system for product dispense.
In accordance with the disclosures of this prior application, a dispensing system for dispensing a product from a canister is provided which comprises a solid-gas arrangement in which the gas is adsorbed on to the solid under pressure and desorbed therefrom when the pressure is released and in which the solid comprises activated carbon and the gas comprises one or more of nitrogen, oxygen (or mixtures thereof including air), carbon dioxide, nitrous oxide and argon, the container having valve means to allow the gas adsorbed on to the carbon to be desorbed and effect product dispense.
It is the object of the present invention to provide an efficient product dispensing system on the basis of a simple two-phase gas adsorption/desorption concept.
In a dispensing system for dispensing a product from a canister, which comprises a solid/gas arrangement with a gas adsorber for storing gas, the canister having valve means for dispensing the product while allowing the gas adsorbed by the carbon to be desorbed, the system incorporates a scavenger for the removal or neutralization of a substances which detrimentally affects the performance of the system.
The gas is preferably carbon dioxide in view of its generally superior adsorption characteristics in relation to activated carbon as an adsorbent.
The term ‘adsorbed gas’ used herein refers to the gas used in the system according to the invention.
It was found that such a system, despite its simplicity, can provide the basis for an efficient, safe, reliable and reproducible system for product dispense.
It has been found in particular that the new dispense system can provide for—by means of careful selection of the type of activated carbon employed, the amount of carbon, the initial pressure and therefore the amount of gas adsorbed on the carbon—a low pressure change during intermittent use between an initial product dispense and full product dispense from a canister.
The pressure change afforded by this system between a “full” and “empty” canister is such that the canister in which it is positioned can maintain an effective discharge of product with an effective and acceptable controlled spray pattern in terms in particular of its being uniform and/or homogeneous with a predetermined particle size and distribution.
Such systems have been shown to be particular suited to the dispensing of products from small, hand-held ‘aerosol’ canisters, for example, ones having a 200 or 300 ml capacity. The term ‘aerosol’ when used herein includes any handheld dispensing devices for the delivery of product whether or not the product is actually atomized or whether or not it incurs any other form of product breakup.
In accordance with the prior disclosures, the dispensing system is preferably incorporated in to a canister in which a product to be dispensed is held under gas pressure. In such embodiments, carbon dioxide desorbed from the carbon adsorbent pressurizes the canister and maintains the pressure therein generally and during actuation of the canister dispensing valve in particular.
Preferably, the product and the solid/gas arrangement are present in separate compartments in the canister. This is primarily to keep the product and the solid apart from each other in order to hold the solid in a predetermined part of the canister and/or to ensure in particular that the product, which may for example be in an aqueous or other type of solution, does not contaminate the solid and thereby detract from its efficiency of adsorption.
In some instances, the compartments may be separated by means of a wholly or substantially impermeable membrane. This membrane may take the form of a flexible bag which is sealingly attached either to the interior wall of the canister or to the canister operating valve or dispense block and which in use holds the product to be dispensed. The solid/gas arrangement is generally positioned within the canister outside the bag such that pressure is exerted on the exterior of the bag when pressure therein is released on actuation of the valve and product dispense effected via the valve through a nozzle. An elastic material may be employed to form the bag. Furthermore, the membrane whether of elastic or non-elastic material may be used and may be sealingly attached to any relevant part of the canister interior.
The substantially impermeable membrane may alternatively take the form of a piston slideably mounted in the canister interior with the gas/solid arrangement on one side of the piston and the product to be dispensed on the other side such that actuation of a dispense valve causes pressure from gas desorbed from the solid to move the piston and urge product to be dispensed from the canister via the valve.
In other instances, the compartments may be separated by means of a fixed partition. Such a partition may usefully be positioned in any expedient part of the canister, including the base thereof, to form the solid/gas arrangement compartment therein. It can, for example, be a concave-shaped disc in a ‘flat’ canister base or one of greater concavity than the (usually) concave-shaped canister base (as viewed from the exterior of the canister). It may advantageously be crimped to the canister between the canister wall(s) and its base to form an annular compartment between the disc and the base.
The solid compartment may also be in the form of a container or ‘widget’ that may be fixed to the canister (or part thereof) or allowed to be free within the canister interior.
In addition, the carbon container may be associated with the canister dip tube, for example, by being mounted around the dip tube for ease of assembly of the canister generally and the positioning of the container therein, and, separately to allow for a ready filling of the container with adsorbed gas via the dip tube and via a one-way valve therebetween.
Generally, the product and the solid/gas arrangement of the dispensing system are present in individual compartments in the canister, which are separated by a partition which may be fixed or displaceable. This keeps the product and the solid apart from each other in order to hold the solid in a predetermined part of the canister and/or to ensure in particular that the product, which may for example be in aqueous or other type of solution, does not contaminate the solid and thereby detract from its efficiency of adsorption.
With a fixed pattern, for example, the substantially rigid wall of the carbon container, it is generally required that the gas from the solid/gas compartment can flow in to the product compartment, but not vice versa and this can readily be effected by having a one-way in the partition.
Equally, there was a general need to provide means to allow the introduction of carbon dioxide in to the solid/gas compartment prior to use of and during use of the system. This can also be effected by a one-way valve to prevent back flow of the gas from the solid/gas compartment.
Each one-way valve should be designed such that it operates only under a certain applied pressure, for example, a small fraction of 1 bar; otherwise, the valve does not open.
With certain valve designs, it is possible for a single valve to operate separately as a pressure sensitive valve in either direction depending on the requirements of the system.
In such embodiments, the container for the carbon should have one-way valve means in order to allow the carbon dioxide to be desorbed from the solid and pass in to the product compartment when the pressure in the canister falls, i.e. on operation of the canister dispensing valve, and thereby maintain the canister pressure at a predetermined level for further use of the aerosol.
In all cases, the one-way valve means may be made from any material and be of any suitable form including ones incorporated integrally in to the body of the carbon container. One form which is particularly useful may comprise an upstanding valve body terminating in a parallel, double plate arrangement—preferably formed integrally with the wall of a product bag or fixed partition—such that the plates act as a closed valve in their usual position but which can move under their inherent resiliency to an open position by virtue of gas pressure effective thereon in a predetermined direction, i.e. from the interior of the carbon container. Such a valve is sometimes referred to as a ‘sphincter’ valve.
The one-way valve advantageously is formed integrally with the partition and is preferably made from a plastic material, for example, PET or silicone rubber.
With a displaceable partition, this will generally be impermeable to the gas and may take the form, for example, of a bag for holding the product or a piston slideable within the canister with the desorbed gas from the carbon deforming the bag or moving the piston within the canister under the increased gas pressure applied thereon during actuation of the dispensing valve.
In other embodiments, the dispensing system may be implemented with a product not held before its dispense under gas pressure. In such embodiments, the desorbed gas is not used to effect product dispense until it is required in use. These embodiments may be put in to effect by restraining the gas pressure in the solid/gas container and effecting its release therefrom via valve means only when required during product dispense.
In these embodiments, the desorbed gas may be used to effect product dispense by:
i) causing the desorbed gas pressure to act directly on a product to effect product dispense, for example, by urging the product through a dip tube inserted in to the product in the canister, or
ii) causing the desorbed gas pressure to act indirectly on the product to effect product dispense, for example, by its impingement on to a piston slideably mounted in a canister body or part thereof, or
iii) causing the desorbed gas to effect product dispense by fluid dynamic (fluidic) action through the formation of a vacuum into which a product is drawn, sucked or otherwise urged, for example, by causing desorbed gas to flow through a venture in which the gas flow is increased and the pressure is decreased in the ‘throat’ thereof, i.e. a partial vacuum is formed, and to which the product canister can be linked to effect product dispense.
In these separate embodiments, it was disclosed that it may be advantageous—especially in regard to paragraphs i) and ii) above—to provide valve means to release the pressure applied directly or indirectly to the product to effect its dispense when the canister is not being used.
Use of the separate embodiments with an unpressurized canister is particularly useful in the case of a product in which the propellant gas can dissolve.
In all embodiments, the carbon is advantageously held in a container which is preferably proximate to the dispensing block, for example, by being attached thereto or may be less firmly linked, for example, via a tube through which the carbon dioxide can be introduced in to the container.
In such preferred embodiments, the dispensing block itself advantageously incorporates a canister dispensing valve and passageways linking the interior of the canister with the exterior thereof via the valve. As such, the dispensing block, together with the carbon container, can readily and effectively be sealingly inserted into an aperture in the canister during canister assembly.
In particular, the linkage of the container to the dispensing block generally allows firstly for a ready operation of the pressure pack and secondly allows for a simple mode of manufacture and assembly of the aerosol canister by allowing for the dispensing block—incorporating the canister dispensing valve necessary passageways linking the interior of the canister with the exterior thereof, and also the carbon container linked thereto—to be inserted in to an aperture in the canister, ideally the top of the canister, advantageously in a single assembly step.
The invention therefore allows standard designs of canister to be employed without modification to the body thereof in order to suit implementation of the invention generally and to include canisters made of steel or aluminum or other material.
In preferred embodiments, the dispensing block and the carbon container are advantageously joined, for example by being made as an integrally formed unit, for example with the carbon container being situated beneath the dispensing block in a normal upright orientation of the canister. It is also advantageous for a dip tube to depend from the dispensing block, preferably being positioned centrally (axially) in the carbon container and, in use of the propellant system, extending in to the body of the canister within the product to be dispensed.
The container for the carbon can be, for example, be made of a flexible plastic/polymer material in the form of a bag or alternatively be cylindrical in shape and advantageously made from a more rigid material, again preferably from a plastic/polymer material. The container is preferably cylindrical in shape.
In general, it is preferred for the carbon to be placed in the container prior to the final assembly of the canister, i.e. prior to insertion of the dispensing block, and into the product itself to which the container is linked in to the canister aperture as described above.
The product to be dispensed by the system of the invention is commonly inserted in to the canister via a dip tube depending from the dispensing block and through which, in use of the aerosol, the product is dispensed via the dispensing valve in the reverse direction. The solid/gas container is advantageously linked to the dispensing block, for example, by being positioned co-axially about the dip tube and as such can be regarded as an integral part of the dispensing block. In such cases, the block as a whole can therefore readily be placed in a canister aperture simultaneously during canister assembly.
Means must also be provided for the introduction of the gas under pressure into the carbon container in order to cause it to be adsorbed onto the carbon and subsequently desorbed therefrom on operation of the dispensing valve. This can be effected, for example, by providing a suitable route via the dispensing block in to the container interior and including (as described above), a one-way valve to prevent back flow of the gas.
Overall, therefore the product dispensing system provides a simple and effective way of utilizing gas desorbed from the adsorbent per se in order to provide a sufficient gas volume to produce an initial gas pressure and thereafter to maintain gas volumes, and necessary gas pressures, to enable a complete product dispense to be effected.
In all embodiments, a pressure regulator may be used to regulate the gas pressure released from the adsorbent of the dispense system of the invention to a predetermined pressure level or within a predetermined range of pressure. For example, a 10 bar (a) pressure provided by desorbed gas may be regulated to produce propellant gas at 3 bar.
With regard to the gas, it should be introduced into the dispensing system under pressure and which will be adsorbed onto the carbon such that its molecules are much more closely packed together than in the usual gaseous form at the same temperature and pressure.
This means that, when the gas is introduced under pressure in to a “gas space” surrounding the carbon, considerably more gas will be adsorbed onto the carbon. Consequently, as the system is activated, typically by actuating the pressure release valve, there will in practice be only a relative and surprisingly small pressure reduction within the system which, in use of the system, therefore allows for the effective dispensing of all of the product.
In utilizing carbon dioxide gas in particular, it is preferably injected initially under pressure in liquid form, for example, down a dip tube depending from or integrally formed with the valve block.
Adding the carbon dioxide, in this way, will generally produce a mixture of carbon dioxide snow and cold carbon dioxide gas.
Using carbon dioxide in the form of a liquid or snow can in practice at least partially thermally balance the heat of adsorption of the carbon dioxide on to the carbon and maintain temperatures close to ambient.
A double valve arrangement may be employed for measuring exact quantities of liquid carbon dioxide present between two valves positioned in a delivery tube of constant cross-section so as to define the required volume of gas needed for each canister as they pass along a conveyor assembly line. This is preferably effected by closing the upstream valve once the required volume of carbon dioxide is present between the valves and allowing the volume to ‘vaporize’ and to urge the stream of snow/gas in to the canister.
The gas may also be charged in to the container in the form of a solid carbon dioxide which is easy to handle and affords the benefits described above for liquid carbon dioxide.
In general, it is beneficial to charge the gas in to the container by means other than a ‘bung hole’ in the base of the canister as the presence of a bung hole may lead to gas leakage during storage/use of the canister.
Activated carbons are well-known per se and have the advantage that they are relatively inexpensive; they are non-polymeric substances. In general, activated carbons are manufactured from a variety of carbonaceous materials including (1) animal material (blood, flesh, bones etc.), (2) Plant materials such as wood, coconut shell, corn cobs, kelp, coffee beans, rice hulls and the like and (3) peat, coal, tars, petroleum residues and carbon black.
Activation of the raw carbonaceous materials can be effected in a variety of known ways including calcining at high temperature (e.g. 500° C.-700° C.) in the absence of air/oxygen followed by activation with steam, carbon dioxide, potassium chloride or flue gas at, say, 850° C. to 900° C., followed by cooling and packaging.
Selected activated carbons are suitable for use in the systems of the invention, for example, ones having a density of from 0.2 g/cm3to 0.55 g/cm3, preferably 0.35 g/cm3to 0.55 g/cm3.
The quantity of carbon required in implementing the invention will vary depending on parameters including the gas employed, the initial and the final pressures during the dispense of product, the nature of the product and its physical characteristics and the desired properties of the dispensed product. As such, the carbon may advantageously occupy from 5 to 95% of the canister interior volume.
In the case of a standard size (300 ml) canister, it is preferred for many product types to have a carbon content of from 5 to 30% of carbon (by volume) which generally equates, for selected carbons, to the presence of 10 to 60 ml of carbon, more preferably 30 to 50 ml of carbon, for example, 40 ml of carbon.
With other product types, especially those of relatively high concentration of active ingredient(s), the carbon content may usefully be from 30 to 95%, preferably from 60 to 90%.
In the case of the higher concentration products in particular, but also generally, the product dispensed from the nozzle of a canister may advantageously be improved by causing a separate bleed of gas to be directed in to the dispensing valve or block and therein to mix with product being expelled therefrom in order to effect a greater dispersion of the dispensed product.
Such improvements are especially useful with more concentrated and/or more viscous products which might otherwise be difficult to dispense adequately for effective spray pattern or whatever.
For certain embodiments, the activated carbon is present in the form of one or more pellets or torroids, i.e. in a much larger size than the granules in which it is normally supplied, for example, of a size of at least 0.5 cm in length or greater. Such pellets or torroids may be fabricated by sintering or other binding processes and preferably will allow for a much larger surface area for the carbon dioxide and therefore a commensurately larger and more effective gas release on reduced pressure.
The pellets or torroids can advantageously be manufactured as sticks or tubes and/or with surface ribs or grooves or with apertures therethrough; all such forms can be capable of aiding adsorption/desorption of the gas.
In general, specific ways of treating and/or handling the carbone are important aspects of the invention and may be essential for the implementation of the dispensing systems.
In particular, it has been found that there may be a propensity for the required properties of the carbon to degrade after the carbon activation process. Such degradation may include adsorption sites on the carbon being blocked by a gas or gases present in the atmosphere present around the carbon and which cannot subsequently be displaced by the gas that is to be adsorbed as the working gas in the dispensing systems of the invention. Although the blocking process may be reversible in certain cases, displacement by the preferred gas may not be effected completely and therefore would detract from the subsequent adsorption of the gas. In some instances, desorption of the initially held gas may be aided by high temperature and/or vacuum.
Preferably, therefore, the activated carbon is held, advantageously from the time of its production, under a blanketing atmosphere; this atmosphere may comprise the adsorbed gas itself, or a gas or gases (including mixtures with the adsorbed gas) that do not prevent the adsorbed gas subsequently occupying the carbon adsorption sites, in particular by virtue of being held at the adsorption sites on the carbon less strongly than the adsorbed gas.
It should be noted that the activated carbons might occasionally require some additional treatment(s) including in particular heat treatments in order to reactivate and/or regenerate the full characteristics of the carbon. Such additional treatment(s) are included in the term ‘manufacture’ and/or ‘activation’ throughout this specification and the appended claims.
Certain gases, including water vapor, are more strongly held at the carbon adsorption sites than the adsorbed gas and carbon dioxide in particular and therefore should be rigorously excluded from the atmosphere around the carbon; subsequent attempts to dislodge the strongly held gases will not be successful.
Although some gases are less strongly held at the adsorption sites than carbon dioxide in particular and therefore should be rigorously excluded from the atmosphere around the carbon; subsequent attempts to dislodge the strongly held gases will not be successful.
Although some gases are less strongly held at the adsorption sites than carbon dioxide and other adsorbed gases, they may still interfere with the subsequent adsorption efficiency characteristics of the adsorbed gas and should be avoided as blanketing gases.
In the case of carbon dioxide as the adsorbed gas, the blanketing atmosphere preferably includes or comprises carbon dioxide itself. This can be especially advantageous in the implementation of dispensing systems when the carbon dioxide is preferably adsorbed on to the carbon at elevated temperatures. Other suitable gases include helium and hydrogen which are generally capable of being displaced from the adsorption sites by carbon dioxide. The potential use of other blanketing gases can be established by a skilled adsorption scientist on a theoretical or practical basis.
Adsorption is an exothermic process in which considerable amounts of heat may be generated. The adsorption of these preferred embodiments with a blanketing atmosphere that includes carbon dioxide itself is beneficial in that it allows an initial level of adsorption of carbon dioxide to occur—together with dissipation of the generated heat—prior to the use of the carbon in the dispensing systems. This can lead to significant advantages from the resultant lower amounts of heat generated when the remaining carbon dioxide is adsorbed under pressure in subsequent high speed production of canisters incorporating the dispensing systems.
With all adsorbed gases, the blanketing of the carbon is preferably effected from the time of cooling and is preferably maintained continuously up to the time of (final) assembly of the canisters in which the dispensing systems are employed. To achieve this, the use of non-permeable containers for holding the blanketed carbon is required in order to isolate the carbon from undesirable gases.
In any event, the carbon granules or pellets or torroids may advantageously be pre-saturated with carbon dioxide (or other adsorbed gas) prior to use in order to improve the adsorption parameters. The granules/pellets/toroids may be advantageously cooled in such pre-saturation processes by use of cooled carbon dioxide, for example, carbon dioxide solid or snow being in contact with the carbon.
Preferably, the carbon granules/pellets/torroids are usefully kept in contact with a source of carbon dioxide or other adsorbed gas, especially cold gas, liquid or snow, prior to placement in a canister and this may provide sufficient adsorbed gas for use in the system without the need to add further amounts of gas.
In the case of certain products, it has been found that it may be useful for optimum dispense characteristics to pre-treat the product with adsorbed gas prior to, or during, its introduction in to the canister. This can be especially useful in the case of highly soluble gases such as carbon dioxide, i.e. ‘pre-carbonation’. Such a process is more useful in the case of product to be admixed with the adsorbed gas in the canister; it may, however, also apply to product present in the canister separated from the adsorbed gas by a moveable partition including a bag whether or not the partition allows for a certain leakage of gas therethrough.
However, whatever form of carbon is employed in the product dispensing systems and whatever means, including blanketing, that may be used to protect the carbon, it has been found that problems can be encountered if the carbon comes into contact with substances which may detrimentally affect its performance prior to the carbon being placed in the aerosol canister, during manufacture/assembly of the canister and/or, most importantly, after manufacture/assembly during storage and/or use of the canister.
The invention provides means whereby such problems can be obviated or at least minimized.
In accordance with the invention, there is provided a dispensing system for dispensing a product from a canister, which comprises a solid/gas arrangement in which the gas is adsorbed on to the solid under pressure and desorbed therefrom when the pressure is released and in which the solid comprises activated carbon and the gas comprises one or more of nitrogen, oxygen (or mixtures thereof including air), carbon dioxide, nitrous oxide and argon, the container having valve means to allow the gas adsorbed on to the carbon to be desorbed and effect product dispense, wherein the system incorporates a scavenger for the removal or neutralization of a substance which detrimentally affects the performance of the system.
IT is accordingly another object of the invention to prevent any detrimental effect on the adsorption/desorption characteristics of the carbon and, additionally, to prevent any detrimental effects on the mode of operation of the system.
A main potential detrimental substance, as stated above, is water or water vapor. Other detrimental substances may be an alcohol or a liquid hydrocarbon, or mixtures thereof or with other substances including water.
Whether or not a blanketing atmosphere is present to protect the carbon or other means are employed for that purpose, it has been surprisingly found that a scavenging agent for any water (or aqueous mixtures) that might come into contact with the carbon may be useful in maintaining the necessary adsorption/desorption characteristics of the carbon.
It has been found that water vapor has the potential to permeate from a water-containing or water-based product through or around a product bag held within the canister during use and/or storage of the canister and into that part of the canister interior in which the adsorbent is held, so that the use of a desiccant is surprisingly beneficial. For example, the material from which the product bag is made maybe (or in use become) somewhat permeable to water, alternatively, the manner in which the bag is attached to the canister body or to a valve block present in the canister aperture may degrade and again become susceptible to permeation of water. Equally, the bag may be ruptured in situ in the canister by a variety of means and thereby allow an escape of product from the bag.
Suitable water scavenging agents, or desiccants, include silica gel, certain types of zeolyte, for example, Type X or Type Y, calcium chloride, calcium oxide and alumina.
Scavenging agents for other substances will be apparent to the skilled chemist.
The scavenging agents are preferably present in an amount of 0.1 to 10% by volume of the carbon adsorbent, more preferably from 1 to 5%.
In the case of the leakage of water (or aqueous mixtures) in particular from the product bag or, indeed, the ingress of water into the canister for whatever reason, the water may itself cause the adsorbed gas to be desorbed from the adsorbent with the effect not only of detrimentally affecting the adsorption/desorption characteristics of the dispensing system but also cause an increase in the internal gas pressure of the canister. Such an increase in pressure may be undesirable in terms of system performance and also, in certain circumstances, raise the internal pressure of the canister to values above that which is recommended or allowed in relation to canister pressure rating or other regulation.
Although such an increase in canister pressure may normally be accommodated within the canister rating, problems could arise in extreme cases, especially during the time of pressure testing a canister incorporating a dispensing system of the invention, for example, during a water bath pressure test at, say 50° C.
It has been surprisingly found that the use of calcium oxide as the scavenging agent for such water (or aqueous mixture) leaks also acts to obviate (or at least minimize) the potential increase in internal canister pressure caused by gas released from the adsorbent by the water impinging on the carbon. This is thought to be effected by a chemical reaction(s) between the released carbon dioxide gas to form calcium carbonate.
The exact sequence of the chemical reaction(s) is not fully understood but involves the formation of calcium hydroxide initially via the reaction of the calcium oxide with the water which subsequently reacts with the carbon dioxide present in the canister (including the released from the adsorbent) to form calcium carbonate.
The reaction balance can generally be regarded as an equilibrium condition and, in order to achieve the formation of calcium carbonate, it is generally advantageous to ensure that the aqueous solution is alkaline in order to avoid the formation of calcium bicarbonate. An alkaline solution may occur naturally in situ, especially in the presence of the carbon adsorbent. This, however, should be monitored experimentally and addition of an alkali, for example, sodium hydroxide or potassium hydroxide, may be made.
The use of calcium oxide in this manner will not generally affect the performance of the dispensing system in that calcium oxide is not reactive in the dry state at normal temperatures. The reactions described above will occur only in the case of ingress of water to alleviate the possibility of higher pressure exceeding safety limits.