GB2391186A

GB2391186A - Dosing device using osmosis to generate internal pressure to expel dosing product

Info

Publication number: GB2391186A
Application number: GB0312207A
Authority: GB
Inventors: John Baker
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-05-28
Filing date: 2003-05-28
Publication date: 2004-02-04
Anticipated expiration: 2023-05-28
Also published as: GB2391186B; GB0212305D0; GB0312207D0

Abstract

A dosing device comprises a secondary chamber 5 containing a dosing substance, bounded on one side by a secondary membrane 6, and on the other side by an impermeable member 4 which flexes or displaces. A first chamber 2 bounded on the other side of the flexible / displaceable member 4, contains an osmotic agent promoting the imbibing of liquid across a first membrane 3, generating pressure which transfers via member 4, into secondary chamber 5. Increased pressure in the secondary chamber 5 promoting increased diffusion of the dosing substance through the secondary membrane 6. In use the entire device is submerged in a carrier fluid, being the target of the dosing, and itself imbibed to generate the internal osmotic pressure in the device to intimate dosing. The action of the device can be seen in the transition from fig. 1 to fig.2. The impermeable member 4 may by an impermeable flexible membrane or a piston. The osmotic agent may be such as an inorganic salt in dry form or solution, a sugar, or a fluid imbibing hydrogel. The device has a wide range of applications may be particularly suited to the slow release of dosing substance.

Description

2391 1 86

Controlled dosing device for toilet flush water or other _.. _..

_eplications The invention relates to a controlled dosing device 5 designed to slowly release a chemical additive into toilet or urinal flush water or another body of water where a very low dose rate is required. In a preferred embodiment, the invention comprises a self propelling osmotic pumping device loaded with a chemical additive at 10 manufacture and capable of delivering a low level of the additive directly into the toilet flush water in order to maintain the toilet in a clean and fresh state.

Controlled dosing of low rates (i.e. mg/h, g/h or ng/h) 15 of undiluted additives or chemicals into bodies of water or aqueous solutions for the purposes of chemical conditioning is difficult to achieve using known mechanical dosing pumps. Currently available mechanical dosing pumps capable of delivering such low levels are 20 relatively expensive to fabricate, require an external power source and may suffer from blockages or other operational problems. There are many devices currently available on the market for releasing chemical additives into toilet or urinal flush waters, but these devices are 25 usually dispensers attached to the toilet pan, or based upon slow dissolving tablets or blocks placed into the toilet cistern.

There are many drawbacks with devices fixed to the toilet 30 pan, not least the fact that they can fall into the toilet bowl and cause blockages. Other drawbacks are that the chemical additive delivered by such devices is only mixed into a small portion of the flush water and that the dosage rate in use cannot be adequately controlled Lo 35 provide a long dosing life of the device.

Slow dissolving blocks placed in the cistern are an alternative but do not allow the use of liquid additive blends or perfumes. In addition the dissolution rate of 5 these blocks is not adequately controlled and they may be used up within a number of days.

An object of the current invention is to provide a cheap re-usable or disposable device designed to deliver a 10 liquid chemical additive, which is preferably a synergistic liquid blend of chemicals, directly to a body of toilet flush water so that it may act throughout the entire system. The device is suitable for dosing over a prolonged period with acceptable accuracy, security of 15 delivery and a defined dosing lifetime. Since the device of the present invention is self-propelling and does not rely upon a complex mechanical action to deliver the chemical it will be reliable in operation and cheap to fabricate using readily available materials. In addition, 20 many other potential applications for the device are outlined. The invention provides a device for the controlled dosing of a liquid chemical additive into toilet or urinal flush water or another receiving fluid comprising two adjacent chambers, the first chamber being 25 partially bounded by an osmosis membrane and containing an osmotically active agent, the second chamber being partially bounded by a secondary membrane and containing the liquid additive blend Lo be dosed, the two chambers being separated from each other by a member that is 30 substantially impermeable to both the osmotically active agent in the first chamber and the liquid additive blend in the second chamber and which is able to move or deform in order that an increase in hydrostatic pressure generated in the first chamber is at least partially 35 transferred to the second chamber where it may he used to

( l expel a quantity of the liquid additive blend through the secondary membrane and into a receiving fluid.

Preferably, the osmosis membrane of the first chamber is 5 a commercially available thin film composite membrane, advantageously possessing good wetting characteristics (i.e. low hydrophobicity) and a uniform high permeability to water.

10 Low relative hydrophobicity of thin film composite reverse osmosis membranes is imparted by an ultrathin barrier layer which is formed from a hydrophilic polymer such as cross linked aromatic polyamide. The relative surface hydrophobicity of such a membrane surface can be 15 measured by contact angle measurements as described in Gekas et al (1992) 'Contact Angles of Ultrafiltration Membranes and their possible correlation to membrane performance' Journal of Membrane Science 72: 293- 302.

One such technique for measuring contact angle is captive 20 (air) bubble contact angle measurement in which an air bubble is introduced into a liquid reservoir beneath a submerged membrane sample. The angle formed at contact between the hydrated sample surface and air bubble is calculated from the bubble's height and diameter at the; 25 interface, and is reported as a contact angle in degrees: the greater the contact angle, the greater the hydrophobicity of the polymer surface. The term "low hydrophobicity" is used herein to describe membranes having a contact angle of 70 degrees or lower when 30 measured by this technique.

High relative flux of thin film composite membranes is provided by the ultrathin semipermeable (barrier) layer.

"High permeability" as used herein means a pure water] 35 permeability equivalent to at least 1 l/m7.h per bar of

applied pressure (l/m2.h is a common way of expressing I membrane flux; others use m3/m2.h or even m/s).

Preferably the osmotic membrane has a pH operating range 5 of about pH2 to about pH12.

Preferably the osmotic membrane is substantially resistant to bacterial degradation.

10 Preferably the osmotic membrane is stable at temperatures up to about 40 degrees Celsius.

Preferably the osmotic membrane's performance is not significantly impaired if the osmotic membrane is allowed 15 to dry out.

Preferably, the chemical additive to be dosed from the device is for the conditioning of toilet or urinal flush water and includes a low molecular weight non-oxidising 20 biocide; a scale inhibitor based on phosphoric acid chemistry, a non-ionic or anionic surfactant, and a fragrance or perfume.

Alternatively, the biocide component of the chemical 25 additive blend may be based on a soluble transition metal I compound, in particular a copper or silver compound.

The impermeable member separating the two chambers may be i a slideable piston or a sheet of material that is folded 30 in a concertina or other fashion so as to be able to move into one of the chambers.

Preferably, the impermeable member separating the two i chambers is a flexible membrane, advantageously 35 manufactured from synthetic or natural rubber.

Preferably, the rate at which the chemical additive is I released into the receiving fluid is at least partly dependent on the rate at which the secondary membrane allows the chemical additive to pass through it.

Preferably, the secondary membrane is a commercially available ultrafiltration membrane based on polysulphone, polyvinylidene fluoride or polyolefinfluoro polymer chemistry with selective permeability and advantageously 10 possessing a high degree of uniformity of pore size with good chemical resistance to strong acids and alkalis, strong oxidising and reducing agents.

The secondary membrane may be selectively permeable on the basis of molecular weight cut off values.

The secondary membrane may be obtained by partial chemical degradation of an osmosis membrane, nanofiltration membrane or reverse osmosis membrane.

The secondary membrane may be derived by partial chemical degradation of a pre-used osmosis membrane, nanofiltration membrane or reverse osmosis membrane.

25 Preferably, the secondary membrane has nanofiltration, ultrafiltration or microfiltration properties.

Preferably, the device is arranged so that hydrostatic pressure in the first chamber increases in response to an 30 influx of the receiving fluid as a result of higher osmolarity in the first chamber than in the receiving fluid. Preferably, the receiving fluid is water contained within 35 a toilet or urinal cistern which is periodically discharged and refilled with fresh water.

Alternatively, the receiving fluid is a natural or artificial body of water, for example a reservoir, pond or lake, or a natural or artificial flow of water, for 5 example a river or piped flow of water.

Alternatively, receiving fluid may be part of a water supply, water treatment or sewage or effluent treatment system. Alternatively, the receiving fluid may be water in a heating or cooling circuit of domestic, commercial or industrial equipment.

15 Preferably the chemical additive which is to be dosed comprises a synergistic blend of chemicals for the chemical conditioning of toilet flush water including a surfactant, a scale inhibitor, a fragrance and a biocide.

This blend of chemicals, of which an example is 20 presented, is based largely on low molecular weight compounds or those that have been discovered to permeate the secondary membrane without causing any loss of flux or transmissivity of the membrane during the working lifetime of the device. Such a blend of chemicals is 25 known to permeate sufficiently rapidly under the applied pressure generated by the osmotic pump action of the osmotic cell.

Alternatively, the substance to be dosed may consist of a 30 chemical biocide.

Alternatively, the substance to be dosed may consist of a scale control or corrosion control chemical.

35 Alternatively, the substance to be dosed may comprise a reducing agent capable of preventing corrosion by oxygen

scavenging, or of chemically neutralizing oxidisinq agents present in the receiving fluid.

The dosing action may be initiated by immersing the 5 device into the receiving fluid or otherwise allowing fluid to access the osmosis membrane, for example, by diverting a portion of a flow into a side stream into which the device has been previously placed.

10 Optionally, the device may comprise a check valve limiting fluid access to the external surface of the osmosis membrane. Alternatively or additionally, a check valve may be provided to limit egress of the chemical additive from the device.

Optionally, the device may comprise a pressure regulating valve in the housing and able to communicate between the osmotic cell and the environment external to the device, or alternatively on the flexible member separating the 20 osmotic cell and the secondary cell. Such a pressure regulating valve is arranged to be closed unless the internal pressure of the osmotic cell rises above a predetermined threshold upon which occurrence the valve will open and allow fluid communication between the 25 osmotic cell and the environment external to the device, or the osmotic cell and the secondary cell. This communication will allow a portion of the contents of the osmotic cell to be vented to the environment external to the device or the secondary cell thereby reducing the 30 osmotic cell pressure. When the osmotic cell pressure falls below a predetermined threshold the pressure regulating valve will re-close. By such an arrangement the pressure in the osmotic cell can be regulated to a substantially constant value at least for a period of 35 time before the osmotic medium has lost its high osmolarity. By keeping control of the osmotic cell

pressure, the rate of release of substance to be dosed may be controlled. Additionally, a pressure release valve may be employed to prevent osmotic cell pressure from rising to a level where damage to a component of the 5 device is likely to occur. Pressure release valves are widely known; they include spring biased valves and weighted valves. The pressure threshold at which such a valve opens may be fixed or adjustable.

10 In applications other than toilet or urinal flush water conditioning, the preferred dosing rate will depend on the volume of receiving fluid to be dosed, the nature and concentration of the substance to be dosed and the application that the device is used in.

In some applications it may be preferable for the substance to be dosed to be released at rates of less than 1 mg per hour.

20 In other applications it may be preferable for the substance to be dosed to be released at rates of less than l fig per hour.

In other applications it may be preferable for the 25 substance to be dosed to be released at rates of less than 1 ng per hour.

In other applications it may be preferable for the substance to be dosed to be released at rates of less 30 than 0.1 ng per hour.

In other applications it may be preferable for the substance to be dosed to be released at rates of less than 0.01 ng per hour.

T

It will be apparent that more than one device may be used together in order to achieve a desired dose rate. For example, a 0.4 ng per hour dose rate could be achieved by the simultaneous use of two devices each providing a 5 0.2 ng per hour dose rate.

The substance to be dosed may be released at a substantially constant rate for a continuous period of more than l week.

Alternatively, the substance to be dosed may be released at a substantially constant rate for a continuous period of more than 1 month.

15 Alternatively, the substance to be dosed may be released at a substantially constant rate for a continuous period of more than 6 months.

Alternatively, the substance to be dosed may be released 20 at a substantially constant rate for a continuous period of more than l year.

The osmotically active material present in the first chamber may comprise one or more inorganic salts in dry 25 form or solution.

Alternatively, the osmotically active material present in the first chamber may comprise a viscous liquid such as glycerine. Alternatively, the osmotically active material present in the first chamber may comprise a fluid imbibing swellable hydrogel. 35 The osmosis membrane may be prewetted by a wetting agent in order that the time required for the membrane to be

( wetted by the receiving fluid, and to start functioning is reduced.

The secondary membrane may also be pre-wetted by a 5 wetting agent in order that the time required for the membrane to be wetted by the receiving fluid and/or the substance to be dosed, and to start functioning is reduced. 10 For user convenience the device may be packaged with a quantity of wetting agent.

The wetting agent may be packaged so as to be in contact with the osmosis membrane of the device. Alternatively 15 or additionally the wetting agent may be packaged so as to be in contact with the secondary membrane of the device. Such packaging could be achieved by a variety of means including, but not limited to, packing the device in a leak proof bag or box which contains wetting agent 20 and holding a portion of wetting agent in contact with a membrane by the use of peelable foil seals.

Alternatively, the wetting agent may be packaged in a form suitable for user application to the osmosis 25 membrane immediately before use of the device.

The wetting agent may comprise a detergent.

The wetting agent may comprise an alcohol for example 30 ethanol or isopropyl alcohol.

The wetting agent may be provided pre-soaked into a textile or paper wipe.

35 The invention also provides the use of a device as described herein.

The device may be used for the dosing of sanitary chemicals or other additives into a batch system such as a toilet or urinal cistern.

Alternatively, the device may be used for the dosing of biocide or scale control or corrosion control chemical into a circulating cooling or heating system.

10 Alternatively, the device may be used for the dosing of biocide or scale control or corrosion control chemical into a flow-through industrial water process.

The invention also provides a device substantially as 15 described herein with reference to and as illustrated by way of any of Figs. 1 to 6 or the examples herein.

The invention makes use of an osmotic pumping mechanism to force additive through a secondary membrane which is 20 selected for its ability to deliver chemical additive at a pre-determined rate. Osmotic pumps are used in the pharmaceutical industry to effect controlled release of pharmaceuticals subcutaneously. The present invention uses an osmotic pump coupled with a secondary membrane to 25 dose additive into a toilet or urinal cistern or other receiving fluid. The present invention does not rely upon movement of the additive through a port, valve or capillary. Such ports, valves or capillaries are prone to blockage by biological, organic or inorganic material, 30 the present invention mitigates this drawback.

Accordingly the dosing action may be initiated by placing the entire device in the toilet or urinal cistern or other receiving fluid to be treated with the additive.

35 This action initiates an osmotic flow, which in turn propels the substance to be dosed into the receiving

fluid. The dosing action can be stopped by simply removing the device from the receiving fluid or by closing an optionally provided valve to prevent flow of receiving fluid through the osmosis membrane.

In addition to the dosing of chemical additives and blends of chemical additives into toilet or urinal cisterns, other potential suggested uses for this invention include: 10 Dosing of biocides and scale/corrosion control chemicals and/or reducing agents into circulating cooling or heating systems.

Dosing of biocides into circulating cooling or heating systems for the purposes of Legionella control.

15 Dosing of biocides and scale/corrosion control chemicals and/or reducing agents as pre-treatment for flow through industrial water processes.

Dosing of plant nutrients into water, soil or other medium in which a plant may be growing.

20 Dosing a nutrient, food, fungicide or other additive into a fish tank or aquaria.

Dosing of disinfectant, fungicide or algaecide chemicals into swimming pool water Any other application where a low residual level of 25 chemical is required in the target fluid for a long period of time.

The device of the invention consists of a housing containing an osmotic cell which produces an osmotic 30 pumping mechanism and a secondary cell containing the additive to be dosed. The additive is released into the receiving fluid through a secondary membrane which serves to control the rate of flow to the receiving fluid.

An embodiment of the invention will now be described with reference to the accompanying figures.

Fig. 1 shows a cross section through the device before 5 use.

Fig. 2 shows a cross section through the device after use or in the latter stages of use.

10 Fig. 3 shows a further embodiment of the invention in which the device is fitted with a check valve for non-

continuous operation.

Fig. 4 shows a further embodiment of the invention in 15 which the device is fitted with a pressure regulation valve. Fig. 5 and Fig. 6 show experimental data derived from the examples given below.

Fig. 1 shows the device to consist of two separate cells, within a common housing (1).

The first cell is the primary or osmotic cell (2), which 25 contains a suitable osmotic agent appropriate to the application. The osmotic cell is bounded on one side by a semi-permeable osmosis membrane (3) and on the other by a non-permeable flexible membrane (4). Both of these membranes are fixed in position around the edge of the 30 housing, but the flexible membrane is able to stretch inside the housing of the device as the device operates.

The second cell is the secondary or reservoir cell (5) which contains the chemical additive to be dosed. The secondary cell is bounded on one side by the non 35 permeable flexible membrane (4) and on the other by the

( secondary membrane (6) through which the additive must pass into the receiving solution.

It will be understood that the term "semi-permeable S osmosis membrane" refers to a membrane that is permeable to the solvent of the receiving fluid, for example water, but which is substantially less permeable to the osmotic agent. 10 Fig. 2 shows the device following use with an enlarged osmotic cell (2) and a reduced secondary cell (5) from where substance to be dosed has been expelled during use.

The dosing action is initiated by placing the device into 15 the receiving fluid, for example aqueous solution or water body. Within a short period of time, water will penetrate the semi-permeable osmosis membrane (3) and a differential osmotic pressure will be set up across the membrane. The period of time taken for wetting of the 20 semi- permeable osmosis membrane and establishment of osmosis will be partly dependent on the membrane properties but may be reduced by application to the osmosis membrane of a suitable wetting agent such as alcohol solution.

The osmotic pressure differential is caused by the difference in osmotic potential between the external solution and that in the osmotic cell (2), which will have a higher osmotic potential attributable to the 30 presence of the osmotic agent. This will cause the diffusion of water from the outside environment into the osmotic cell. The rate of diffusion of water into the osmotic cell will be primarily dependent upon the magnitude of the osmolarity differential across the semi 35 permeable osmosis membrane, the active area of semi-

permeable osmosis membrane employed in the osmotic cell,

and the permeability of the osmosis membrane to water.

The diffusion into the osmotic cell will cause a build up -

of pressure in the osmotic cell. The non-permeable flexible membrane (4) will then deform outwards into the 5 secondary cell (5) as a result of the build up of pressure in the osmotic cell. This in turn will cause a -

build up of pressure in the secondary cell which will drive the permeation of substance to be dosed through the secondary membrane (6) into the receiving fluid. The lO flux, that is to say the rate of permeation, through the -

secondary membrane determines the rate of dosing of the additive into the host water or fluid body.

Loss of substance to be dosed into the receiving fluid by 15 simple diffusion not resulting from an increased pressure -

in the secondary cell may be minimised by using a secondary membrane that exhibits an increase in flux as a result of the application of pressure to it.: 20 The housing of the device (1) may be constructed of any material that is compatible with the osmotic agent, the -

additive to be dosed and the application. Suitable -

materials may be inert plastics or polymers such as polyp-: vinyl chloride, commercially available high or low 25 density polyethylene, polypropylene, or acrylonitrile butadiene-styrene. The housing may be of any shape, but: a cylindrical housing with a circular or oval cross -

section may be the most ideal shape in order to simplify construction. = 30 - The semi-permeable membrane (3) of the osmotic cell (2) may be any membrane which allows osmosis to take place, and which is compatible with the osmotic agent, the additive to be dosed and the application. This membrane 35 may be defined as one which is permeable to water, but is wholly or partially impermeable to the osmotic agent.

( Commercially available thin film composite reverse osmosis or nanofiltration membranes, manufactured for water treatment processes are the most suitable materials currently available and are supplied by a number of 5 manufacturers. Thin film composite membranes are preferred for this application because they offer excellent wetting characteristics and a high permeability to water with good rejection of dissolved salts. Thin film composite membrane consist of a ultrathin barrier 10 layer of approximate thickness of 0.2 - 1.0 micron which supports osmosis, which is formed in situ on a porous support layer during manufacture. Interfacial polymerization techniques used to form these types of membranes on a pre-existing support layer were first 15 disclosed in U.S. Patent 4,039,440 (1977) Cadotte J. E. Reverse Osmosis Membrane. Subsequent commercial development of these types of membranes followed during: the 1980's.

20 In order to facilitate rapid wetting of the membrane aiding the onset of osmotically driven flow into the osmotic cell it is important that the semi-permeable osmosis membrane is arranged in the device so that the ultrathin composite layer of membrane is facing the 25 external environment.

Other membrane materials which are available commercially or formed in situ are widely known to the art but are less suitable for the current invention because of 30 reduced wetting characteristics (i.e. a greater degree of hydrophobicity) and lower permeability to water. Such characteristics will mean that the time for the onset of osmosis will be unpredictable and subsequent dosing rate would be too small for use in a water treatment 35 application. Such membrane materials have been suggested in a number of osmotic pumping devices recently disclosed t

including EP0040457, EP0089598, WO 00/23663. These comprise membranes made from a variety of materials including but not restricted to cellulose acetate, cellulose triacetate, aromatic polyamide, crosslinked 5 aromatic polyamide, Aryl-alkyl polyamide/polyurea, polybenzimidazole, polyacrylonitrile, polypiperazineamide, sulphonated polysulphone, polyvinyl alcohol. 10 Further information on osmosis membranes may be obtained from Allegreza A. E. (1988) Commercial Reverse Osmosis Membranes and Modules. In Reverse Osmosis Technology Ed.

Parekh, B. S. Publ. Marcel-Dekker Inc. New York. 53-120.

15 As an alternative to using a commercial source of osmosis membrane, a membrane may be constructed in situ by techniques known as solvent casting or interracial polymerization as discussed above. Alternatively dynamically formed membranes capable of supporting 20 osmosis may also be used.

Solvent casting techniques for the formation of skinned asymmetric membranes are the subject of U.S. Patent 3,133,132 (1964) Loeb S. and Sourirajan S. High flow 25 porous membranes for separa ting wa ter from aqueous solutions. Dynamically formed membranes can be formed by depositing from a pressurized solution certain colloidal or 30 dissolved species such as colloidal zirconium oxide or-

polyacrylic acid onto the surface of a finely porous substrate. Such formation techniques are detailed ire Johnson, J. S. (1972) Polyelectrolytes in aqueous solutions - Filtration, hyperfiltration an dynamic 35 membranes, in Reverse Osmosis Membrane Research Eds.

f Lonsdale H. K. and eodall H. E. Publ. Plenum Press, New York, 379-403.

The osmosis membrane may require a support against 5 movement or stretching as the osmotic cell pressure increases in order that the generated osmotic cell pressure is transferred to the secondary cell. If such support is required, it may be provided by attaching a suitable mesh, grill, grid or similar structure to the 10 device in front of or attached to the osmosis membrane.

As stated above, recent development of thin film composite membranes offer low hydrophobicity characteristics which reduce the time for water or other 15 fluid to overcome surface tension effects, penetrate the membrane structure and initiate the osmotic flow across the membrane. Surface tension may also be reduced by the application of a wetting agent such as alcohol in a suitable strength solution. Ethanol or iso-propyl 20 alcohol are able to act as an effective wetting agents in 0.1% to 100% (v/v) solutions in water, 20% to 100% solutions being most suitable. Further details of chemical agents intended to reduce the hydrophobicity of an osmosis membrane and decrease wetting time may be 25 found in Kulkarni A. et al. (1996) Flux enhancement by hydrophilization of thin film composite reverse osmosis membranes J. Membrane Science 114:39.

Table l lists a number of types of commercial membrane 30 which make use of the materials previously listed and are suitable for use as the primary osmosis membrane. Table 1 serves to illustrate and not limit the present invention. Membrane type Primary manufacturer FT30, XLE Dow Chemical Company Inc.

TFC, TEC-ULP TFCS, Fluid Systems / Koch membrane TFCL systems Inc. CPA, IFC, ESPA, ESNA, Hydranautics / Nitto Denko LEC corporation Desal - 1, Desal - 2, Desalination Systems Inc. Desal - 3 SU membrane Toray Table 1: Suitable thin film composite primary osmosis 5 membranes The nonpermeable flexible membrane (4) may be constructed of any material which is compatible with the osmotic agent, the additive to be dosed and the 10 application. This membrane may be able to stretch because of elastic properties or it may be manufactured so as to incorporate folds in a concertina or other suitable fashion such that it is able to unfold into the secondary cell in response to pressure build up in the 15 osmotic cell. Materials which could be used for the non-

permeable flexible membrane include but are not restricted to polypropelene, plasticised poly vinyl chloride, neoprene rubber, latex rubber.

20 The semi-permeable and non-permeable membranes may be fixed to the housing by any adhesive or method which is compatible with the materials of construction, the osmotic agent, the additive to be dosed and the application. Suitable adhesives which could be used 25 include curable urethane or epoxy resin adhesives.

Alternatively the membranes may be bonded to the housing

using ultrasonic welding, an established technique bonding thermoplastics.

It may be necessary to provide support for the secondary 5 membrane against movement or stretching as the secondary cell pressure increases. If such support is required, it may be provided by attaching a suitable mesh, grid or similar structure to the device in front of or attached Lo the secondary membrane.

The use of a wetting agent as described above in relation to the osmosis membrane may also be beneficial to the performance of the secondary membrane when applied to the secondary membrane.

The osmotic agent, which is present in the osmotic cell may be any substance, which is compatible with the materials of construction and of sufficiently high osmolarity. The quantity of osmotic agent employed in 20 the device can be varied as a calculated function of the I osmolarity of the target fluid body in order to dose the required quantity of additive from the chemical reservoir (i.e. the secondary cell). An excess of the osmotic agent may be used to ensure a substantially constant 25 driving force during the working lifetime of the device.

There are various osmotic agents which could be employed in the device. For example, an inorganic salt in dry form or in solution may be used. Suitable salts include, but are not restricted to, sodium chloride, sodium 30 sulphate, magnesium chloride, potassium chloride or mixtures thereof. Alternatively a viscous liquid such as a commercial Glycerine preparation may be used. So-

called fluid imbibing swellable hydrogels may also be used either on their own or mixed with another osmotic 35 agent.

Ideally, the osmotic agent should be capable of delivering an osmotic pressure differential of 0.1 to 10 bar across the semi-permeable membrane.

5 Osmotic agents may be used in diluted form to reduce the dose rate. It is also possible to use a mixture of osmotic agents to combine specific attributes, for instance, the improved wetting characteristics of glycerine together with the higher osmotic potential of 10 sodium chloride. Table 2 lists a number of simple and readily available osmotic agents which could be used in the device. Table 2 serves to illustrate and not limit the present invention. In the event that the device described in this application is used in a food or 15 potable water application, non-toxic osmotic agents, for example sugars may be suitable osmotic agents because they represent a lower health risk in event of a leak or rupture of the device.

Osmotic agent Concentration in use (v/v in water) i Sodium chloride Dry salt or 5-25% Potassium chloride Dry salt or 5-25% Magnesium chloride-6 hydrate Dry salt Glycerine 10-100; Glucose 25-50% or dry powder Sucrose 25-50:; or dry powder Fructose 25-50% or dry powder 20 Table 2: Suggested osmotic agents The secondary membrane (6) may comprise any material which possesses nanofiltration, ultrafiltration or microfiltration properties, sufficient mechanical 25 strength for the application and which is compatible with

( the osmotic agent, the additive to be dosed and the application. In this context the term nanofiltration, implies any membrane with a nominal pore size less than about 0.001 m, the term ultrafiltration implies any 5 membrane with a nominal pore size of about 0.001 Am to about 0.02 m, and the term microfiltration implies any membrane with a nominal pore size of more than about 0.02 m. Alternatively, any membrane which could be deemed to have a molecular weight cut-off value of less than about 10 500 Daltons would be classed as a nanofiltration membrane. A cut off of about 500 to 200,000 Daltons would define a ultrafiltration membrane, and a cut off of more than about 200,000 Daltons would define a microfiltration membrane. The concept of classifying 15 membrane porosity by reference to the molecular weight cut-off valve is as proposed by Porter M.C. (1975) Chemical Engineering Progress 71:55. Converting molecular size to molecular weight may not be highly accurate if no account is taken of molecular shape.

20 Therefore the values given above should be taken to be approximate. It should be noted that most commercial membranes state a nominal pore size, though in practice there will be a range of pore sizes around this figure.

The width of the pore size range will to some extent be 25 influenced by the conditions under which the membrane is formed. The effective pore size in use may be partially dependent on the conditions (applied pressure etc) under which the membrane is used.

30 Commercial ultrafiltration membranes based on polysulphone or polyvinylidene fluoride chemistry are the preferred materials for deployment as the secondary membrane as these possess a uniformity of pore size and good chemical stability. Such membranes may be

fabricated with either an asymmetric or compost structure. Other suitable membranes include membranes made of 5 materials including but not restricted to cellulose acetate, cellulose triacetate, regereated cellulose acetate, aromatic polyamide, crosslinked aromatic polyamide, Aryl-alkyl polyamide/polyurea, polybenzimidazole, polyacrylonitrile, 10 polypiperazineamide, sulphonated polysulphone, chlorinated polyethylene or polyvinyl alcohol. Suitable membranes are available from a number of primary manufacturers at low cost. The pore size of such membranes are frequently defined by reference to 15 molecular weight cut-off value (MWCO), which indicates the size of molecule which will pass through the membrane. Since the range of pore sizes, molecular weight cut-off and flux rates of available membranes vary greatly the secondary membrane can be selected for its 20 ability to deliver a given rate of chemical additive.

Suitable secondary membranes may be fabricated by solvent casting, irradiation and chemical etching, or by stretching techniques. Such techniques for the formation of micro-filtration membranes are the subject of U. S. 25 Patent Nos: 3, 303, 085i 3,801,404; 3,953,566 and 3, 962,153.

Ultrafilters for deployment as the secondary membrane may also be fabricated using solvent casting and annealing 30 techniques. By manipulation of the membrane casting operation and annealing conditions, the molecular weight cut-off value of the membrane may be defined over a greater or lesser range of pore sizes. Such manipulations are discussed in Strathmann H. et al. 35 (1975) The formation mechanism of asymmetric membranes.

Desalination 16:179; and Strathmann ll. and Kock K. (1977)

( The formation mechanism of phase inversion membranes Desa 1 i na t i on 2 1: 2 4 1.

Alternatively, the secondary membrane may be ceramic or 5 composed of a sintered metal such as aluminium.

Alternatively, the secondary membrane may be constructed from an osmosis membrane of or similar to those mentioned in Table 1, after chemical treatment to destroy the 10 surface film which provides osmotic properties, thus exposing the support layer. This support layer may possess ultrafiltration or microfiltration properties according to the type of membrane and the extent of chemical treatment.

Suitable chemical treatment to produce a secondary membrane from a new or used primary (osmosis) membrane comprises soaking of the membrane in a suitable oxidising agent for a period determined to produce the desired 20 degree of degradation of the membrane surface.

Alternatively a strong acid or alkali may be used. By using this method of secondary membrane manufacture, it is possible to recycle used osmosis membranes, for example, used reverse osmosis membranes previously used 25 in water purification devices. Use of recycled membranes may bring cost and environmental benefits. Table 3 lists a number of chemical agents which could be used for this purpose. Table 3 serves to illustrate and not limit the present invention.

/ Suitable oxidising Concentration Time of treatment agent in use Sodium hypochlorite 0.1-12% 1-50 hours solution Hydrogen peroxide / 0.1 - 10%, pH<4 20-200 hours peracetic acid Hydrochloric acid 1-32% 20-200 hours Sodium hydroxide 1-50% 20-200 hours Table 3: Suggested chemical agents for degrading reverse 5 osmosis membranes In one embodiment of the device, illustrated in Fig. 3, there is the addition of a check valve (7), which may be used to stop the flow of receiving fluid into the primary 10 membrane, thus stopping the osmotic flow into the primary cell. In this manner, it is possible for the device to be used in intermittent operation, for greater economy.

Alternatively, the check valve may be attached to the outlet end of the device in order to stop the flow of 15 additive into the receiving fluid, provided that the device construction is able to accommodate the osmotic pressure build up in the osmotic cell.

In one embodiment of the device, illustrated in Fig. 9 there is an additional pressure regulation valve (8) in 20 the wall of the osmotic chamber. This valve may be used to regulate the pressure in the osmotic chamber by opening and releasing a quantity of material from the osmotic chamber if the pressure in the osmotic chamber rises above a threshold value. Alternatively, such a 25 valve may be placed in the flexible membrane separating the osmotic cell and secondary cell.

( The dosing life of the device is a function of the volume of the reservoir and the dose rate. The device may be scaled up to any size as is determined to be suitable and economic for each application. The dose rate is directly 5 proportional to the flow through the secondary membrane which is dependent upon the pore size of the secondary membrane and the driving force behind it.

When the controlled dosing device is deployed to treat 10 and condition toilet flush water, a chemical blend based upon the following chemicals has been proven to be discharged from the device at sufficient rates for a viable conditioning effect in a flush water volume of between 6-10 litres.

A low molecular weight non oxidising biocide compatible with the secondary membrane. Compounds proven to be applicable include quaternary ammonium compounds and isothiazolones. This component should constitute 20 between 25% and 50% by weight of the blend. In order that these compound exert a biostatic effect in the flush water, the in use concentration is required to be in the range of approximately 1-10 mg/l.

A low molecular weight scale inhibitor based on 25 phosphonate chemistry. In this category, there are a number of potential agents which have been shown to be compatible with the preferred secondary membrane material. Those include ninotri (methylene phosphoric acid)(ATMP) and its derivatives) 1, Hydroxyethylidene 30 1, 1 diphosphonic acid (HEDP) and its derivatives; Ethylenediaminetetra (methylene phosphoric acid) (EDTMP) and its derivatives) Hexamethylenediarninetetra (methylene phosphoric acid) (HMDTMP) and its derivatives; Diethylenetriaminepenta (methylene 35 phosphoric acid) DETPMP and its derivatives. This component should preferably constitute between 10-25r,

by weight of the blend. Such agents are able to prevent the formation of limescale when present at parts-per-million levels by so-called threshold action.

This retards the onset of precipitation of the hardness 5 salts whilst the flush water is in the toilet or urinal system. In order to exert a threshold effect to prevent the deposition of scale these agents will be required to be present at an in use concentration of at: least 1- 10 mg/l in the flush water.

10 A surfactant with molecular weight less than 2000 Daltons compatible with the secondary membrane. In this category the preferred agent is an anionic or non ionic surfactants such as a fatty alcohol ethoxylate or sodium dodecyl sulphate. The surfactant component 15 should constitute between 5 and 10% by weight of the blend or varied as necessary to solubilise the perfume component of the concentrate. Various in use concentrations of surfactant may be used. Preferably the in use concentration of surfactant is sufficient to 20 cause good wetting of surfaces that come into contact with the treated water and good foaming characteristics of the treated water.

A perfume compound constituting up to 25% by weight of the blend.

If necessary, the viscosity of the blend may be adjusted with alcohol or glycol in order to achieve the desired permeation rate through the secondary membrane.

:30 The blend of beneficial agents may be used undiluted as a concentrate in the controlled dosing device to obtain a long dosing lifetime for a small device or may be diluted with water as necessary. In some cases it may be beneficial to increase the size of the device so that it 35 can also act as a cistern volume adapter to reduce the

( flush volume of the toilet or urinal and therefore act as a water saving device.

In other applications, the device may be used over a wide 5 range of temperature, as determined by the materials of construction. The performance of the device will vary as a function of the temperature of the fluid into which it is placed. A temperature correction factor that can be applied with reasonable accuracy over a temperature range 10 of from 15 to 35 degrees Celsius is given in Ko and Guy (1988) Brackish and Seawater Desalting. In Reverse Osmosis Technology Ed. Parekh, B. S. Published by Marcel-

Dekker Inc. New York. 185.

15 The osmotic cell may be designed to rupture in a controlled fashion at the end of its working lifetime when the secondary cell has been depleted of additive.

controlled rupture of the osmotic cell would result from incorporation of a weak or bursting' point into the 20 structure of the osmotic membrane, the flexible membrane or any section of the housing bounding the osmotic cell.

This bursting point may be formed by providing a serration pattern into the flexible or osmotic membrane.

This bursting point may also be incorporated by providing 25 a small portion of ultrathin housing surrounding the osmotic cell. This point would be designed to rupture when the osmotic cell has reached its maximum design expansion and the cell pressure then continues to rise above a desired threshold due to the incorporation of 30 excess osmotic agent in the osmotic cell at the time of manufacture. The incorporation of excess osmotic agent in the osmotic cell will ensure a relatively constant dose rate from the device in operation.

35 In conjunction with the controlled rupture feature it may also be beneficial to mix a dye material with the osmotic

agent or to use an intrinsically coloured dye material.

The rupture of the osmotic cell at the end of the working lifetime of the device would then be accompanied by a release of coloured material into the receiving fluid 5 which would signal to the user that the device is exhausted and requires replacement.

Examples

The following examples demonstrate the feasibility of a 10 device for dosing a blend of chemicals for toilet or urinal flush water conditioning. The device of illustrated in the examples is designed such that it will provide an average dose rate of 3 ml per day of additive over a period of 60 days.

( Materials used in examples Component Type and manufacturer Size employed ln device Primary Commercial thin film Circular disc of osmosis composite reverse osmosis membrane of membrane membrane with approximate diameter 25.1 mm 96% sodium chloride rejection Secondary Commercial Circular disc of membrane ultrafiltration membrane membrane of with MWCO value of 20000 diameter 25.1 mm dalton Osmotic Various inorganic salts S ml volume medium in dry form Substance to Trial formulation be dosed comprising 8% propan-2 ol; 5% alkyl dimethyl benzyl ammonium chloride; 5% non-ionic surfactant and S% carnation fragrance compound.

Balance of trial formulation is deionized water Housing ABS plastic tube Length - 10Smm Luminal cross section diameter - 50mm To provide secondary cell volume of 186 ml, with additional volume for [osmotic agents and

- - |impermeable flexible I mfmhrn 1 '''a 1 _ 1 All membranes used were new.

In order to demonstrate the principles of the device the 5 action of each of the primary and secondary membranes of the device were demonstrated separately by mounting that membrane across the lumen of the housing arid applying the appropriate substances to an appropriate side of the membrane. Membranes were fixed to either end of the 10 housing by use of flanges, compression fittings and O-ring seals.

Example 1

This example demonstrates the properties of the osmosis 15 membrane, in particular the time required for the onset of osmosis and the build up of pressure in the osmotic cell. The osmosis membrane was fixed to one end of the housing which contained osmotic medium. In this simulation 5 ml volume of three separate osmotic mediums 20 were employed. These were granular sodium chloride -

purchased as table salt; potassium chloride purchased as general purpose reagent (BDH chemicals); magnesium chloride hexahydrate purchased as general purpose reagent (BDH chemicals). The other end of the housing was closed 25 to the external environment. Osmosis was initiated by immersing the apparatus into a tank of waLer. Pressure build up in the osmotic cell was recorded by use of a manometer tube sealed to the housing.

30 Results Pressure in the osmotic cell was measured over time and is illustrated by the graph of Fig. 5. Fig. 5 shows results from 3 experimental runs each made using different osmotic agent. All runs were conducted using

identical membranes from the same manufacturing batch.

It can be seen that osmotic cell pressure build up commenced only 24 hours following the commencement of the experiment. Use of a wetting agent would have resulted 5 in faster pressure build up.

Example 2

This experiment was carried out to simulate the performance of the secondary cell. Two simulated 10 secondary cells consisting of a housing with a secondary membrane fixed across the opening of one end and a vertical tube fixed to the other end were constructed.

The secondary cells were filled with additive solution.

A pressure of approximately 36 KPa was imposed across the 15 membrane by filling the vertical tube with an appropriate head of additive. The rate of transmission of the additive across the secondary membrane was then measured over a one month period. This data was then corrected to show the permeability of the membrane samples to the 20 additive over this period. This data is presented in Fig. 6, and can be seen to be substantially constant at I an average rate of approximately 1.7 l/m2.h. bar.

Discussion and Conclusions

25 The average permeability displayed by the membrane used in the example 2 indicates that this will be able to permeate approximately from 2 to 3 ml of the additive over a 24 hour period, with an applied pressure of 20 KPa (approximately 0.2 bar). Example 1 has shown that the 30 osmotic cell of the device of the invention has the capability to rapidly attain this value.

Therefore the examples detailed above serve to demonstrate that the device of the invention has 35 capability, in the embodiment shown, to dose an additive consistently in the range of O.Z mg/h over a period of at

( least 60 days, and that the dosing effect can be initiated and reach an acceptable level in a matter of days.

Claims

CLAIMS:

1. A device for the controlled dosing of a chemical additive into a receiving fluid comprising two 5 adjacent chambers, the first chamber being partially bounded by an osmosis membrane and containing an osmotically active agent, the second chamber being partially bounded by a secondary membrane and containing the chemical additive, the two chambers being separated 10 from each other by a member that is substantially impermeable to both the osmotically active agent in the first chamber and the chemical additive in the second chamber and which is able to move or deform in order that an increase in hydrostatic pressure generated in the 15 first chamber is at least partially transferred to the second chamber where it may be used to expel a quantity of the chemical additive through the secondary membrane and into a receiving fluid.

20

2. A device as claimed in claim 1, wherein the impermeable member separating the two chambers is a slideable piston or a sheet of material folded so as to be able to move into one chamber.

25

3. A device as claimed in claim l, wherein the impermeable member separating the two chambers is a flexible membrane.

4. A device as claimed in claim 3, wherein the 30 flexible membrane is manufactured from synthetic or natural rubber.

5. A device as claimed in any of the preceding claims, wherein, the rate at which the chemical additive 35 is released into the receiving fluid is at least partly

dependent on the rate at which the secondary membrane allows the chemical additive to pass through it.

6. A device as claimed in any of the preceding 5 claims, wherein the secondary membrane is selectively permeable.

7. A device as claimed in any of the preceding claims, wherein the secondary membrane is selectively 10 permeable on the basis of molecular weight cut off values

8. A device as claimed in any of the preceding claims, wherein the secondary membrane is obtained by partial chemical degradation of an osmosis membrane, 15 nanofiltration membrane or reverse osmosis membrane.

9. A device as claimed in claim 8, wherein the secondary membrane is derived from a pre-used osmosis membrane, nanofiltration membrane or reverse osmosis 20 membrane.

10. A device as claimed in any one of claims 6 to 9, wherein the secondary membrane has nanofiltration, ultrafiltration or microfiltration properties.

11. A device as claimed in claim 10, wherein the secondary membrane is an ultrafiltration membrane comprising a polysulphone polymer, polvinylidene fluoride or polyolefin.

12. A device as claimed in any of the preceding claims, wherein the secondary membrane has a high degree of uniformity of pore size and resistance to the chemical additive.

(

13. A device as claimed any of the preceding claims, wherein the device is arranged so that hydrostatic pressure in the first chamber increases in response to an influx of the receiving fluid as a result 5 of higher osmolarity in the first chamber than in the receiving fluid.

14. A device as claimed in any of the preceding claims, wherein the receiving fluid is water or an 10 aqueous solution.

15. A device as claimed in claim 12, wherein the receiving fluid is contained in a toilet or urinal cistern which may be periodically flushed.

16. A device as claimed in any one of the preceding claims, wherein the chemical additive comprises a sanitary chemical.

20

17. A device as claimed in any one of the preceding claims, wherein the chemical additive comprises a chemical biocide.

18. A device as claimed in any one of the preceding 25 claims, wherein the chemical additive comprises a scale control or corrosion control chemical.

19. A device as claimed in any one of the preceding claims, wherein the chemical additive comprises a 30 fragrance or perfume.

20. A device as claimed in any one of the preceding claims, wherein the chemical additive comprises a synergistic blend of chemicals for the chemical 35 conditioning of toilet flush water including a surfactant, a scale inhibitor, a fragrance and a biocide.

(

21. A device as claimed in any one of the preceding claims, wherein the dosing action is initiated by immersing the device into the receiving fluid.

22. A device as claimed in any one of claims 1 to 21, wherein the device comprises a check valve limiting fluid access to the external surface of the osmosis membrane or limiting egress of the chemical additive from 10 the device.

23. A device as claimed in any one of claims 1 to 22, wherein the device comprises a pressure regulation valve able to communicate between the osmotic cell and the environment external to the device or between the osmotic cell and the secondary cell.

24. A device as claimed in any of the preceding claims, wherein the chemical additive is released at 20 rates of less than 1 mg per hour.

25. A device as claimed in any of the preceding claims, wherein the chemical additive is released at: rates of less than 1 fig per hour.

26. A device as claimed in any of the preceding claims, wherein the chemical additive is released at rates of less than 1 ng per hour.

30

27. A device as claimed in any of the preceding claims, wherein the chemical additive is released at rates of less than 0.1 ng per hour.

28. A device as claimed in any of the preceding 35 claims, wherein the chemical additive is released at rates of less than 0.01 ng per hour.

(

29. A device as claimed in any of the preceding claims, wherein the chemical additive is released at a substantially constant rate for a continuous period of 5 more than 1 week.

30. A device as claimed in any of the preceding claims, wherein the chemical additive is released at a substantially constant rate for a continuous period of 10 more than 1 month.

31. A device as claimed in any of the preceding claims, wherein the chemical additive is released at a substantially constant rate for a continuous period of 15 more than 6 months.

32. A device as claimed in any of the preceding claims, wherein the chemical additive is released at a substantially constant rate for a continuous period of 20 more than 1 year.

33. A device as claimed in any of the preceding claims, wherein the osmotically active material present in the first chamber comprises one or more inorganic 25 salts in dry form or solution.

34. A device as claimed in any of the preceding claims, wherein the osmotically active material present in the first chamber comprises a viscous liquid such as 30 glycerine or a solution of one or more sugar.

35. A device as claimed in any of the preceding claims, wherein the osmotically active material present in the first chamber comprises a fluid imbibing swellable 35 hydrogel.

(

36. A device as claimed in anyone of the preceding claims, wherein the osmotic membrane is a commercially available thin film composite reverse osmosis membrane which exhibits low hydrophobicity and high pure water 5 permeability.

37. A device as claimed in any one of the preceding claims, wherein the osmosis membrane or the secondary membrane or both membranes are prewetted by a wetting 10 agent in order that the time required for the membrane to be wetted by a fluid and to start functioning is reduced.

38. A device as defined in any one of the preceding claims, packaged with a quantity of wetting agent.

39. A device as claimed in claim 38, wherein the wetting agent is packaged so as to be in contact with the osmosis membrane or the secondary membrane or both membranes.

40. A device as claimed in claim 38, wherein the wetting agent is packaged in a form suitable for user application to the osmosis membrane or the secondary membrane immediately before use of the device.

41. A device as claimed in any one of claims 37 to 40, wherein the wetting agent comprises a detergent.

42. A device as claimed in any one of claims 37 to 30 41, wherein the wetting agent comprises an alcohol for example ethanol or isopropanol.

43. A device as claimed in any one of claim 38 or 39 to 42, wherein the wetting agent is provided pre 35 soaked into a textile or paper wipe.

44. A device as claimed in any of the preceding claims, wherein the osmotic agent is selected for its intensive colouration or mixed with a dye to give its colouration, so that if the osmotic cell is ruptured, the 5 water into which the device is placed becomes coloured to an extent sufficient to alert the user to the rupture event.

45. A device as claimed in claim 44, wherein the 10 device incorporates a weak point in the structure of the osmotic membrane, the flexible membrane or a part of the housing bounding the osmotic cell, said weak point rupturing when the osmotic cell pressure reaches a predetermined threshold.

46. Use of a device as claimed in any of the preceding claims.

47. Use of a device as claimed in any of the 20 preceding claims for the dosing of sanitary chemicals or other additives into a batch system such as a toilet cistern.

48. Use of a device as claimed in any of claims 1 25 to 46 for the dosing of biocide or scale or corrosion control chemical into a circulating cooling or heating system.

49. Use of a device as claimed in any of claim 1 to 30 46 for the dosing of biocide or scale or corrosion control chemical into a flow-through industrial water process.

50. A device substantially as described herein with 35 reference to and as illustrated by way of any of Figs. 1 to 6 or the examples herein.