GB2442941A

GB2442941A - A method for the generation of water with reduced ionic solutes

Info

Publication number: GB2442941A
Application number: GB0620970A
Authority: GB
Inventors: Philip Peter Monro
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-10-21
Filing date: 2006-10-21
Publication date: 2008-04-23
Also published as: GB0620970D0

Abstract

A device comprising one or more proximal and distal chambers separated by a selectively permeable membrane which has a restricted but not absolute restriction of porosity with respect to dissolved solutes. This device is designed to generate a solution with a reduction in the concentration of these solutes distal to this membrane by the processes of forward and/or reverse osmosis. Such devices can further utilize those solutes initially present on the proximal side of the membrane but which have crossed the membrane themselves so that they then act as osmotic drivers and so facilitate the further movement of solutes across the membrane.

Description

TITLE: A novel method for the generation of water with reduced ionic

solutes.

Field of the invention

This invention relates to the use of membranes with reduced but not absolute exclusion of some or all of dissolved solutes to generate water of reduced solute concentration.

While not suggesting any restriction in application of such technology our preferred application is reduction in dissolved ionic solutes and gain with implied restriction by the process of forward osmosis.

Please note: In the majority of the following text reference is frequently made to changes in saline concentrations and saline masses present in water. It will be apparent to those skilled in the art, that with respect to naturally occurring solutions, and in particular those commonly called "sea water" the majority of solutes present are dissolved ionic salts of which sodium chloride is the most common. However, in all cases this reference should be considered as an extended case of "by way of example only" as the proposed novel technology can be applied to the reduction of any dissolved solute by the use of forward osmosis.

Existing technology There are a number of existing methods for reducing the salinity of water to generate, potable water, water for agricultural applications or for industrial use. These include reverse osmosis and forward osmosis. Current working systems incorporate membranes with the highest possible exclusion of dissolved solutes and to achieve this require high operating pressures and the associated pressure resisting engineering. As a consequence manufacturing and operating costs (mainly energy consumption) of such plants are high.

Note: It has been proposed by others that salt exclusion of saline solutions can be achieved in forward osmosis with a membrane with a pore size significantly larger than that of the ionic salts as the presence of sugars on the distal side of the membrane themselves prevent the passage of the dissolved salts. Our own unpublished observations suggest this claim is not valid The present invention The following invention describes unexpected observations and hence novel applications on how reverse and forward osmosis membranes can be used to generate water of reduced salinity in a manner that is predicted to use less energy than is currently the case.

While not being a limiting condition we suggest that in forward osmosis some of these advantages are enhanced by using a membrane that permits some of the dissolved salts to cross the membrane as the salts that have crossed the membrane can then themselves then act as osmotic drivers. That is a membrane that has restricted but not totally exclusion of the solute species to be reduced. In this case, as the dissolved salts that cross the membrane will themselves exert an osmotic pressure, the passage of some but not all of the dissolved ions may themselves act as osmotic drivers.

It must be stressed that there may be applications where our technology is used in conjunction with existing technologies to both reduce the salinity of the feed solution and/or removal of the solutes added to generate forward osmosis.

Independently the proposed new technology can be applied to the lower salt concentrations present in for example brackish water.

It will be appreciated, by those skilled in the art that "sea water" and "brackish water" is imprecise terms as their compositions varies considerably. Consequently, where there is any technical reference to the reduced salinity of sea water' or "brackish water" these are presented examples only. Similarly the technology can be applied to: 1. Aqueous solutions that are not potable.

2. Other organic or inorganic solute dissolved in the water.

3. Any non-dissolved material (including by way of example only) any prions, viral particles, bacteria or plant or animal species, or any part of any of these that are excluded due to their inability to cross the membrane.

Further, and purely for convenience and with out any claims to their absolute correctness, we have used information on sea water including osmotic pressures, as published in the CRC Handbook of Chemistry and Physics 59 Edition 1978-79 Ed by Weast R.C. and Astle M.J. Thus with respect for sea water' we will assume a concentration of 3.5%(%w/w) with a published osmolarity of 1.009 Osm/kg Similarly we will use other information from the same publication. For example, Tables 1 and 2 contain numerical data compiled (with some simplification) from the same publication.

Table I Concentration (as %w/w dissolved in water) which are approximately equal in osmolarity to sea water' i.e. an osmolarity of 1.009 Osmlkg Citric acid 16.0 Ethanol 4.5 Ethylene Glycol 6.0 Fructose 16.0 Glucose 15.0 Glycerol 6.5 Lactose N/A Maltose 16.0 Mannitol 15.0 Methanol 3.5 Sodium acetate 4.0 Sodium carbonate 6.0 Sodium citrate 10.0 Sucrose 24.5 Urea 6.0 Note: No figures are available for inverse sugar' which is an equimolar mixture of fructose and glucose obtained by hydrolyzing sucrose but it is reasonable to assume it will be approximately 15.5 % Table 2 Maximum published concentration (as % w/w dissolved) and equivalent osmolarity Concentration Osmolarity (Osmlkg) Citric acid 30.0 2.285 Ethanol 68.0 26.62 Ethanol 100.0 N/A Ethylene Glycol 60.0 27.54 Fructose 28.0 2.256 Fructose 70.0 N/A Glucose 30.0 2. 577 Glucose 60.0 N/A Glycerol 40.0 8.33 Glycerol 100 N/A Lactose 8.0 0.266 Lactose 18.0 N/A Maltose 44.0 2.877 Maltose 60.0 N/A

TABLE 2 CONTINUED

Mannitol 15.0 0.988 Methanol 68.0 51.8 Methanol 100 N/A Sodium acetate 9.0 2.455 Sodium acetate 30.0 N/A Sodium carbonate 6.0 1.142 Sodium carbonate 15.0 N/A Sodium citrate 20.0 2.362 Sodium citrate 36 N/A Sucrose 42.0 2.652 Sucrose 84.0 N/A Urea 44.0 9.47 Note: Where N/A is also given this is where there is published osmolarity for the different concentration of the substance.

Practical considerations for the design of products to a solution with a reduced salinity with respect to the initial saline solution.

The examples of solutes (and water soluble organic liquids) given in Table 1 represent a reasonable cross section of available osmotic drivers. These concentrations are the minimum possible concentrations (when used on their own) that can act as an osmotic driver. Table 2 indicated the maximum possible concentration it is possible to achieve with these substances. It will be apparent that the higher the difference in osmotic pressure between the saline solution and that of the osmotic driver the greater is the amount of water that the driver can generate. Further, as would be expected to those skilled in the art, that for sugars their usefulness is reduced as their molecular weight increases. For this reason we have not considered in depth, substances of even higher osmotic weight such as dextrans and dexrins for while these can be used, due to their low osmotic pressure per unit weight they will not generate a significant mass of water.

A possible example of an economical osmotic driver would be the use of glucose/fructose mixtures (inverse sugar) or one of the equivalent low cost mixtures generated by hydrolysis etc. as a practical osmotic driver. Further, it will be apparent that were they shown to be an acceptable osmotic drivers, industrial alcohols can be What may be a practical compromise will be a mixture of low and higher molecular weight drivers. Further, if they can be retained within this compartment the addition of glycerol, sodium acetate, citrate and carbonates would significantly increase the osmotic pressure of these osmotic drivers. However, it will be appreciated by those skilled in the art that the concentration of any substances used as an osmotic driver must be reduced to that concentration that is acceptable on safety, technical and regulatory grounds for the use of that water. t.

For certain solvents (of which methanol and ethanol are given as examples only) their osmotic pressures are, in comparison to dissolved solutes extremely high.

Consequently, for an appropriately designed configuration they can act as very efficient novel osmotic drivers and this is considered separately below.

The commercial objective is to generate water with reduced salinity by forward osmosis using an osmotic driver whose removal requires less energy (and hence is an economical alternative to) conventional reverse osmosis.

To achieve this objective conventional wisdom would propose a membrane with a total retention of the salts present in saline solutions. However, as seen in Table 1 to achieve an adequate osmotic pressure by the osmotic drivers will require high concentrations of all readily available sugars and is likely to require a high power generation and difficult and expensive engineering requirements.

Further it is likely it will not generate the same flow/flux rate that is possible with a membrane with a larger pore size. By way of example only increasing the pore size to retain molecules similar to or larger than the glucose molecule or even reduces the retention of sodium chloride from 99% to 90%.

However, by allowing some salt to cross the membrane, so long as osmotic driver cannot cross back into the feed water an osmotic gradient is maintained and so water will continue to flow across the membrane. Compared with the use at this stage of a conventional high salt retaining membrane there can advantages including: 1. The flux rate can be higher at both at or near atmospheric pressure and at elevated pressure.

2. There will be a significant reduction in the energy used as the process will consume less energy.

This can be achieved in a number of ways with the following by example only having a membrane with a pore size only slightly above that of the saline ions so that their movement is reduced relative to the flow of water and hence water is produced with reduced salinity with respect to the feed water. In our opinion such a design feature is novel and not obvious particularly when combined with a further step(s) that reduces either the "driver" or the residual salt or both.

There would be similar novelty, where a salt retaining membrane was used but the osmotic driver contained the ions present in the proximal chamber but at a lower concentration than they are in the distal chamber. Thus by way of example only, when sea water is present in the proximal chamber, if we have a a salt tight' primary membrane and a sea water' concentration of 3.0% in the distal chamber then the osmotic difference' is 0.14 Osm/kg. Consequently by way of example if this solution were to contain glucose the concentration of this glucose could be reduced compared to the situation where glucose was the sole osmotic driver. Consequently, we propose that in specific configurations of the invention the osmotic driver contains a lower but acceptable level of saline to lower the required concentration of any other osmotic drivers, yet still be able to exert an osmotic pressure and hence a driving force for water to cross the membrane.

In its most simple design the invention will use a single stage process and a single membrane to both reduce the level of salts to an acceptable level and to generate adequate volumes of water. However, it will be apparent to those skilled in the art that there may be applications where it is better to achieve the required reduction in saline concentrations is a number of stages. Here the various stages may be similar or dissimilar configurations and membrane types. For example, a number of stages with incremental reduction in saline concentrations or a continuous flow system with gradual reduction in salt concentrations. Alternatively (or used in conjunction with) membranes with different porosity's to different solutes to further influence and regulate the above effects.

As water is removed from the saline solution its concentration will increase. Thus in one particular configuration of the invention, we would minimise the effect by aiming for a maximum flow/volume of seawater flowing across the membrane. However, it will be apparent to those skilled in the art that the lower is this increase in seawater salt concentration the easier will the design be. Consequently, we suggest it could be better to build the plant by the sea as it is likely to be less difficult and expensive to pipe the water with reduced salinity to the end user than to deliver large volumes of feed water to the manufacturing plant.

Further, it will be apparent to those skilled in the art that in some definitions pure water' is not classed as a solvent' as a solvent should contain dissolved solutes. Hence for avoidance of doubt where appropriate the use of the word solvent' does apply to the use of pure water'.

As the resulting water produced will have varying uses so to can be its quality. For example low grade water for agricultural use as against water for generating potable water. Hence for different applications the grade' and hence cost of the osmotic drivers can be matched to meet their final requirements. Further, if (as is considered in stage 2) it may be possible to remove or as a minimum reduce they, they then it may be possible to use a lower grade of osmotic driver.

Specifically, it will be appreciated by those skilled in the art that the cost of osmotic drivers could be a critical factor in the economics of the industrial process.

Consequently, it could have significant advantages in the economics of the industrial process if the cost of osmotic drivers could be reduced by using sugars derived from food grade organic waste. One example of such material would be that which utilises the actual or related technology to that developed by Biorefining Inc. of 4979 Olson memorial Highway, Golden Valley 55422 USA and whose web-site is www.biorefining.com. This company uses their proprietary technology "The biorefining Process" to convert residual plant matter from virtually any crop-processing residue (such as distiller's grain, sugar beet pulp or citrus pulp) into value-added products, mainly specialty sugars.

Further by selection of the residual plant material and the details of its processing it may be possible to directly (or as a minimum reduce the stages involved) develop a balance of sugars optimised for all or at least one stage in the industrial process.

It will be apparent to those skilled in the art that a membrane that will prevent (or even reduce) the passage of low molecular weight ions will also act as a barrier to potentially harmful material present in that water in solution or carried in any other way. For example, as organic toxins, high molecular weight heavy metals' (by way of example only radioactive elements, tin, antinomy and lead) and infective agents including prions, viruses, protozoa and larger infective agents. Thus an additional benefit of the use of membranes to reduce the salinity of the sea water will be to produce water that is also lower in potentially dangerous (or industrially disadvantageous) substances.

It will be apparent to those skilled in the art that to increase/reduce hydrophobic) /hydrophilic nature of the membrane can be used to selectively affect the movement of water and or specific components. This by way of example only will influence the relative movement of polar and non-polar liquids.

It will be apparent that the proposed technology can be used in conjunction with other methods which may have the potential to reduce salinity and/or to increase the efficiency of forward osmosis. Specific examples are pressure including hydrostatic pressure and increase in temperature. These can vary (or be combined) for different stages of the process.

It will be appreciated by those skilled in the art that where multiple stages are used that there can be intermediate holding tanks to store these intermediate solutions. Further that the concentrations and/or the composition can be modified and/or monitored.

In certain configurations it may be advantageous to have indicators (e.g. specific dyes) to indicate the level of a specific component or its presence. Similarly to indicate if any substance is leaking across the membrane. One such dye could be coloured dextrans used to indicate solute molecular weights.

Independent of these considerations it will be apparent that there are applications (and hence configurations and designs considered in this patent) that specifically apply to water containing dissolved salts at a level that is lower than sea water. For example, further reduction in the levels of salts in brackish water or salt contaminated aquifers which are becoming of major concern where there is contamination of ground water by salt beds or seawater. By way of example only in the main grape producing regions of Australia.

Similatly, there are applications for this technology where the reduction in dissolved solutes (all or specific substances) is carried out to enable the processed water to be suitable for a particular industrial application which does not involve human or other animal contact or consumption. In these applications it is possible that the treated water may not have to meet regulatory requirements applicable for human or other animal contact or consumption.

It cannot be emphasized too highly, that the key novelty of this patent is focused on the process where there are advantages in using a "leaky" membrane with respect of the solute present in solution on the proximal side of the selectively permeable membrane and not on development of specific membrane types and membrane coatings designed to achieve theses objectives. Consequently, while we are aware of membranes manufactured to specific specifications of salt retention we would claim novelty where any current or new design of membrane and/or membrane coating is used to achieve the objectives of this patent.

Experimental programme/data Part I Using a reverse osmosis membrane These were conducted using a single sheet of FILMTEC (TM) SW3OHR-380 membrane manufactured by the Dow Chemical Company. This membrane (when used in its intended spiral wound element) is stated by the manufacturer's publications to be a "premium grade seawater reverse osmosis element featuring both high active area and high salt rejection to offer the best long-term economics for seawater desalination systems." Any unused sample of the membrane was stored in an air/light excluding tube. When a sample was being prepared this was carried out in minimum light conditions and this precaution was continued when conducting the experiments.

A fresh piece of membrane was used for each individual experiment.

Test rig All experiments were conducted using the same specially constructed test-rig. The rig had the following features: The rig, manufactured in Perspex, is rectilinear in shape where the area of membrane exposed is approximately 37 cm long by 15 cm wide. The rig consists of two chambers each 1.5 cm in depth with two ports at each end of each the chamber that can be connected to tubing. The membrane was held in place between the two chambers by a series of stainless steel bolts and made leak tight by means of a pair of continuous o" rings. This gave an approximate volume of 0.75-liter volume of liquid per chamber. Other ports are incorporated into the design for filling and emptying. In all cases both chambers were completely filled with liquids with great care being taken to ensure all air bubbles were excluded. The exposed membrane is sandwiched between perforated stainless steel plates which occlude approximately 20% of the exposed membranes.

Thus the approximate area of the exposed membrane is 400 sq cms.

It was observed that, while the plates did appear to hold the membrane rigidly in place, the application of either positive pressure (when solutions were "pushed" through the rig) or negative pressure (when solutions were "drawn" through the rig) generated some bowing of the membrane and hence expulsion or uptake of solution. However, so long as there was no change in the applied flow rate, this effect could be ignored so long as the readings obtained in the first fifteen minutes were ignored. Attempts were made to generate liquid flows in both chambers with liquids flowing in the same direction or as a counter flow system. However these experiments failed due to slight variations in flow rates producing cyclical positive and negative bowing of the membrane during the course of an experiment. Consequently, attempts to have solutions flowing in both chambers were abandoned.

In all cases the rig was used that the large flat surfaces were in a horizontal position by the use of spirit levels. In addition, in all experiments, the heights and positions of any tubing relative to the surface of the test-rig was minimised to ensure there was no significant positive or negative hydrostatic pressure and/or siphoning of the liquid contents. This was limited to not more than 25 cms. from the mid-line of the test rig.

Either or both chamber could be connected to a variable speed pump that enables solutions to be drawn or pushed over the membrane, where the solutions flow parallel to the long axis of the chamber. The pump configuration allowed for flow rates to be varied from 2 to 50 mIs per minutes per chamber.

Either or both chambers can be connected to tubing that are not connected to the pump but remain at atmospheric pressure.

However as noted above flowing solutions were restricted to the upper (proximal chamber) Flow experiments However, in the majority of experiments the following set up was used, where as stated above the rig was used in the horizontal position: Experiments were conducted such that the expected movement of solutions was from the upper (flowing) chamber to the lower (static) chamber and where any over flow solution from the lower chamber could be collected without any inward leakage of air bubbles.

The upper chamber was used with a flowing solution. Based on preliminary experiments the reservoir of additional solution was between 100 and 200 mIs of the same solution contained in the upper chamber.

The delivery and return solution tubing, of this upper chamber, was held in a clamp above the reservoir so that the tubing was not in contact with the reservoir pot.

However, the tubing delivering the solution to the rig was below the liquid level of the reservoir solution while the return solution was held above the liquid level. Thus as solution is pumped round liquid can be seen to "drip" into the reservoir.

Consequently, by placing the reservoir chamber on a suitable top-pan balance, the balance would gravimetrically allow any change in the volume of solutions in the upper chamber to be monitored and recorded. These were determined on a top-pan balance reading to 0.01 g.

Further, it will be appreciated that as the contents of the reservoir pot was being continually mixed with the solution in the upper chamber of the rig any changes in its composition in the reservoir pot will reflect any changes in the composition of solution in the upper chamber.

Consequently, and by way of example only, a conductivity measuring probe can be inserted in this open chamber to determine changes in conductivity of solutions in the upper chamber. In these experiments conductivity was determined using a Model 4310 multi-range Conductivity Meter made by Jenway Ltd (UK). The probe used is self-correcting with respect to temperature changes.

The accuracy of the instrument was checked using reference solutions prepared in analytical grade water (Fisher Scientific W/O100/24) using protocols supplied by Jenway Ltd. However, it should be noted that although the instrument can determine the conductivity of a wide range of solutions its accuracy of determining the conductivity of a particular solution is not greater that plus or minus 1% of the current full range. As discussed below this fact has resulted in a major limitation in the findings of this experimental study.

In addition, the approximate concentration of glucose present in any water or saline fractions was determined using proprietary glucose test tests intended for home urine analysis (glucose Medi-Test ref: MED 112 manufactured by Macherey-Nagel, Germany).

When the contents of the lower chamber are not being pumped to a recirculating reservoir the contents are continually mixed by means of a magnetic stirrer below the chamber with mixing taking place due to a PTFE sealed magnet being placed in the lower chamber.

In a typical experiment, the liquid in the lower chamber over flows into a collecting pot.

To ensure that liquid does not drainlsiphon into the collecting pot the tubing is raised 10 cm above the level of the test rig with the open end 5 cm above the test rig, It will be realised that even with mixing of the solution in the lower chamber the composition of the collected solution can differ from that of the lower chamber. Consequently, no chemical determinations were made on the solutions in the lower chamber except at the start and end of experiment. For the latter the contents of the lower chamber and the collecting pot were fully mixed before any sample was collected.

I

Solutions and chemicals used in part I of this study In all cases the stated percentage concentration of a solution was based on a weight to volume calculation. For example, a one-liter solution stated to be 30% sucrose was prepared by dissolving 300 grams of sucrose in 700 ml of water. These solutions were prepared using single glass distilled water.

Instead of seawater, salt solutions of similar osmolarity were prepared using sodium chloride (cat. no. 43,320-9) supplied by Aldrich Chemical Company.

For glucose "domestic" dextrose monohydrate was used (Thornton & Ross Ltd, UK) with the weights of the sugar and water used adjusted to take into account the water of crystallization present in the dextrose monohydrate.

For sucrose "domestic" sugar was used (British Sugar plc.) Combinations of experimental solutions investigated In all cases the first mentioned solution is that in the upper (flowing) chamber.

1. Water v 1.25% sodium chloride solution 2. Water v 3.5% sodium chloride solution 3. Water v 7.0% sodium chloride solution 4. Water v 30% glucose solution 5. Water v 30% sucrose solution 6. 3.5% sodium chloride solution v 30% glucose solution 7. 3.5% sodium chloride solution v 30% sucrose solution

Summary Protocols

In all of these experiments the following protocols were used: The rig was disassembled, washed and dried and reassembled using a piece of membrane that has recently been cut to size using a rectangular template. As mentioned above the handling of the membrane was carried out in minimum light conditions. Prior to inserting the membrane the magnetic stirring rod was placed in the lower chamber.

The membrane was placed so that the shiny (coated) surface was facing downwards.

I.e. in contact with the solution that had the solution of the highest osmotic pressure.

Both chambers were filled with their appropriate solution, taking steps to ensure there were no air bubbles present in either chamber. In all cases a suitable sized aliquot of these solutions were kept separately to provide a reference sample enable any changes in composition to be determined at intervals and at the end of the experiment.

Where appropriate the tubing was connected to the pump and/or placed either in or above the reservoir holding further solutions.

The variable speed peristaltic pump was switched on to generate the required flow rate.

The required flow rate was generated using a combination of pump speeds and various bore tubing connecting to the pump.

Changes in the volume in the upper (pumped) chamber were determined against time by recording the weight of solution in the reservoir on the balance. For precision measurements, where high concentrations of solutions are used, these apparent flow rates must be adjusted (obviously always increased) to take into account of the high density of the concentrated solutions.

At suitable time intervals (and at the end of the experiment) theconductivity and where appropriate, glucose concentration, were recorded. 1(3

Results TABLE 3 The flow of solution across an RO membrane with 3.5% sodium chloride solution on the proximal side and 25% glucose on the distal side TIME REF (mS) TEST (mS) VOLUME (ml) 9.15 --1.12 9.45 56.3 57. 0 4.85 10.00 57.6 57.2 6.06 10.30 57.4 57.0 9.07 11.00 57.0 56.8 12.55 11. 30 57.0 57.0 15.64 12.00 57.3 57.2 18.53 12.30 57.4 57.1 21.36 13.00 57.4 57.1 24.45 13.30 57.4 57.2 27.45 14.00 57.4 57.3 30.66 14.30 57.7 57.4 33.58 15.00 57.6 57.4 36.54 15.30 57.7 57.4 39.25 16.00 57.5 57.6 42.47 16.30 57.5 57.5 45.68 17.30 57.6 57.0 51.28 17.31 57.4 57.3 nla 17.32 57. 2 57.0 n/a Key: REF: Conductivity of fresh 3.5% sodium chloride solution TEST Conductivity of 25% sodium chloride solution in the proximal chamber VOL. Mass of 25% glucose solution expelled from distal chamber 141.1 Observations on the results of Table 3 Table 3 shows the results of a typical experiment. The table can be divided into regions where the initial extremely high flow rates are due to displacement of the membrane and not due to flow across the membrane.

However, in all cases, where there was a positive osmotic gradient between the two chambers there was a flow of solution across the membrane. This took place regardless of which combinations of solutions were used. Although there were variations, typical peak flow rates of approximately 3 mIs per hour are observed giving a flow of approximately 1.8 liters per square meter of membrane per 24 hours.

Table 3 confirms that forward osmosis can take place across a reverse osmosis membrane without additional hydrostatic pressure where the primary force moving the solute across the membrane is the pressure exerted by forward osmosis. Further that this can take place when the osmotic driver is 25% glucose and the primary solution is 3.5% sodium chloride solution. Consequently, there will be a dilution of the glucose solution with respect to glucose.

However, in this particular experiment, experimental error prevented us from conclusively demonstrating that this forward osmosis took place with retention of sodium chloride as the solute crossed the membrane. That is where the conductivity of the solution in the primary chamber would INCREASE, due to limitations in the analytical techniques used. However, such an effect was expected from the specification of the semi-permeable membrane used.

Measurements of glucose levels and sodium chloride values in the upper chamber, in those experiments where water was used, indicated that there was negligible back migration (dialysis) of both sugars and sodium chloride through the reverse osmosis membrane.

Discussion of the experimental data using conventional reverse osmosis membranes Table 3 shows that at times there appeared to be an INCREASE in concentration of the solution that does not cross the membrane. I.e. evidence that there is a REDUCTION in saline concentration of solutions crossing the membrane. However at other times the concentration does not change and at times even appears to DECREASE. In our view these variations in the conductivity (and hence concentration) of the feed solution are at least in part due to imprecision/limitations in the recording of the conductivity of the solutions involved. I.e. this test rig is unlikely to conclusively prove a reduction in the concentration salinity in liquid crossing the membrane.

However, these experiments confirmed that a significant mass of liquid can be drawn across a reverse osmosis membrane, due to forward osmosis when the feed solution is of an osmolarity equal to that present in sea water and hence can be applied to removing water from sea-water. Further, we think it is reasonable to speculate that, given the appropriate conditions, flow rates and area of membrane it would be possible to prove that forward osmosis with sugars as the osmotic driver can be used to both remove liquid from a sea-water solution using an osmotic driver of a higher initial concentration.

By way of example only, such a demonstration should be possible using the experimental test rigs produced by Aqulous -PCI Membranes (UK). By way of example only such experimental test rigs have a membrane area of up to 25.6 m squared.

Further it will be understood by those skilled in the art that we may have been unfortunate in the selection of the membrane we used to carry out our experimental programme. By way of example only, even using the test rig used in the present study the use of the AFC99 polyamide film membrane produced by Aquious membranes may have a tighter cut off than we were able to generate using the Dow Chemical Corporation membrane available to us.

Part 2 Using a membrane modified for the rehydration of sucrose by forward osmosis Materials and Methods Experiments were conducted using production grade solid vapour transmitting polyurethane film type Porelle P412 (PIL Membranes Ltd, King's Lynn, UK) of nominal thickness 12 microns. This membrane is stated to be "viral excluding". Samples of membrane were treated with a novel process which we have confirmed significantly increases the retention of dissolved sucrose. The following experiment was conducted to determine if this process also resulted in the ability of this treated membrane to totally or partially exclude sodium chloride in solution.

Experiments were conducted using specially constructed standard test chambers. The base of these consisted of a supported piece of treated membrane with a circular cross-sectional area of approximately 64 cm2 and an internal volume of 400 cm2. These enabled a standard area of treated membrane to be placed just below the surface of a known solution to determine by gravimetric and other methods changes in the volumes and compositions both internal and external to the test chambers.

In the cited experiment four similar test chambers were used. Each contained 100 grams of 25% (w/w) of "domestic' sugar (sucrose) solution and was placed separately in a square test chamber bath of slightly larger cross section containing 125 grams of 0.5% saline solution prepared using "Analar" grade sodium chloride solution. Both solutions were prepared using "domestic tap water". This ratio of solutions was selected as it was known to generate a positive osmotic gradient with respect to the sucrose solution and hence an uptake of solute by the sucrose solution.

The test chambers containing the sucrose solution were placed in contact with the saline solutions for four hours. Changes in masses were determined gravimetrically and changes in salinity of the outer solution were determined by conductivity using a Jenway (Dunmow, UK) model 4310 temperature compensated conductivity meter. /6

Results Pot Soin. uptake End ext. salinity Absolute salinity change Percent change 1 12.41 0.58% 0.08% 11.6% 2 11.76 0.58% 0.08% 11.6% 3 15.04 0.54% 0.04% 10.8% 4 13.99 0.54% 0.04% 10.8% This confirmed that this particular type of treated membrane would exclude a significant amount of saline during the process of forward osmosis.

General observations It must be stressed that both the cited groups of experiments represent data using materials supplied by one manufacturer in each case and with no attempt to optimize the base membrane or in the case of the Porvair membrane its treatment of for salt exclusion. Consequently it is to be expected that when the same experimental techniques are applied to materials specific selected and or developed for this intended process better results will be observed.

Further, as it is possible that at least some ionic salts will cross the membrane then the osmotic pressure exerted by these inorganic ions will add to the osmotic pressure of the sugars and hence continue to act as an osmotic driver as the concentration of the sugars is diluted.

It should be noted that, as far as possible, these experiments were conducted using solutions on both sides of the membrane that were equal and at atmospheric pressure.

We would propose that the mass of solution generated and/or any reduction in salinity may be enhanced by differences in hydrostatic pressure between the proximal and distal sides of the membrane. Further the increase in efficiency may be significant at pressures that are significantly lower than those normally used for generating solution of reduced salinity with conventional reverse osmosis plants. Hence we would suggest that significant energy savings could still result from the use of desalination by the use of forward osmosis if the system efficiency increased by the application of increased hydrostatic pressure.

Similarly no attempt was made to investigate if improved results would have been obtained by utilising those physico-chemical processes that those, skilled in the art know will favour such processes. By way of example only these include, temperature, improved flow rates, agitation, a reduced film of solution crossing the membrane and the use of counter-current and cross flow arrangements.

Independent of the options and variations considered else-where it will be known to those skilled in the art that reverse osmosis is used to produce water of reduced salinity where the salinity of the feed solution is significantly lower than that typically present in "sea-water". By way of example only, for the reduction in salinity of water classed as "brackish". We would think it reasonable that the techniques and processes considered for reducing the salinity of water (i.e. the application of forward osmosis) referred to as sea-water" can also be applied to waters where the salinity is less than typical sea-water. Again it will be apparent to those skilled in the art that such processes may be better carried out using membranes optimised for such salinities.

Again it will be apparent to those skilled in the art that it may not be possible to generate the required reduction in salinity by the use of a single module. Thus, again by way of example, it may be appropriate to use modules of similar and/or dissimilar design and membrane type to generate the required reduction in salinity.

Again it will be apparent to those skilled in the art that the use of forward osmosis to generate water of reduced salinity may involved solutions of increased viscosity compared with those seen in conventional reverse osmosis plants. For this reason and by way of example only it may be appropriate to use membranes/modules applicable for solutions of increases viscosity. By way of example only the BI parallel flow products manufactured by Aquious -PCI membranes stated to be suitable for "highly-viscous materials and low pressure drop.

Again it will be apparent to those skilled in the art that the solutions that have been generated using forward osmosis may contain solutes of a larger molecular weight that the inorganic ions present in seawater. With respect to subsequent processing and applications of such solutions those skilled in the art will realise that there are a number of options available depending on the end-user requirements. How in general terms how these are achieved are considered outside of the scope of the present invention However where the driving force for generating solute transfer totally or in part utilizes forward osmosis, it will be apparent to those skilled in the art that the optimum composition and concentration of the osmotic driver may vary at different stages of the industrial process. One consideration may be to have minimum viscosity compatible with the required osmotic gradient. By way of example only, when the required osmotic driving force is lower it may be advantageous to select as an osmotic driver a sugar concentration/composition, which may have a lower osmotic pressure but as a result a lower viscosity. The latter will generate cost advantages, as the energy required to pump the osmotic driver through the system will be lower. As discussed above one option for achieving this would be to incorporate in the osmotic driver solution ionic salts.

These would both increase the osmotic pressure and produce a lower viscosity than the exclusive use of sugars.

General conclusions

The above experimental data indicates that it is possible to reduce the salt concentration of a proximal solution using forward osmosis, at a much lower hydrostatic pressure than that used in conventional reverse osmosis.

These results were generated using both a conventional reverse osmosis membrane and a membrane specifically designed for forward osmosis of food substances at atmospheric pressure.

Consequently, we would suggest that the above system could be used for not only forward osmosis but reverse osmosis but at a lower hydrostatic pressure and hence lower manufacturing and operating costs.

While not being restricted to such a process we suggest there are applications where there are advantages in using a membrane that has some permeability to the solute present in the proximal solution which is ultimately required to be of a lower osmotic pressure.

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Claims

1. A device comprising one or more proximal and distal chambers separated by a selectively permeable membrane with a restricted but not total restriction in porosity with respect to dissolved solutes designed to generate a solution with a reduction in the concentration of these salutes distal to this membrane by

2. the process of forward osmosis that utilizes a high restriction in porosity on the movement of solutes present on the proximal side of the membrane resulting in predominately a simple dilution of the solution on the distal side of the with this dilution continuing until there is an inadequate osmotic difference between the two sides of the membrane,

3. the process of forward osmosis using a semi-permeable membrane/process that allows some movement of dissolved solutes across the membrane from the proximal to the distal side enabling that fraction that does cross the membrane to itself act as an osmotic driver and so facilitate the further movement of solutes across the membrane,

4. the process of reverse osmosis that utilizes a high restriction on the movement of salutes present on the proximal side of the membrane resulting in predominately a simple dilution of the solution on the distal side of the with this dilution continuing until there is an inadequate osmotic difference between the two sides of the membrane,

5. the process of reverse osmosis using a semi-permeable membrane/process that allows some movement of dissolved solutes across the membrane from the proximal to the distal side enabling that fraction that does cross the membrane to itself act as an osmotic driver and so facilitate the further movement of solutes across the membrane,

6. the use of any of the above cited processes to be used in any combination where solute of the required composition cannot be obtained in a single module to use multiple modules (of similar or dissimilar design) to obtain solute of the required composition and/or quality.

7. A water processing device according to claim 1 wherein the supply of water is a solution with the generic name "seawater".

8. A water processing device according to claim 1 wherein the supply of water is not seawater but from water containing some but lesser concentrations of dissolved ions, e.g. brackish water.

9. A water processing device according to claim 1 wherein, the potential osmotic drivers include, by way of example only, a single solute or in any combination the following solutes: glucose, sucrose, corn syrup. glycerol, trehalose, starches, dextrins and dextrans (for these last three examples they can be of any appropriate molecular weight which in turn can be closely defined or broad). w

10. A water processing device according to claim 1 wherein the potential osmotic drivers include, by way of example only, a single solute or in any combination on their own or with other substances organic liquids with high osmotic pressures, methanol, ethanol and glycerol.

11. A water processing device according to claim 1 wherein, the selected osmotic drivers can be manufactured to a standard and/or purity appropriate to the required end use and where by way of example only if the resulting water and/or solution is to be used for agricultural purposes only then quality/grade of the solutes used can be those allowed for this application.

12. A water processing device according to claim I wherein, the selected osmotic drivers can be manufactured to a standard and/or purity appropriate to the required end use and if the resulting water and/or solution is to be used for agricultural purposes only then quality/grade of the solutes used can be those allowed for this application.

13. A water processing device according to claim 1 wherein the selected osmotic drivers can be manufactured to a standard and/or purity lower than appropriate to the required end use, so long as there is a further purification stage which ensures that the water/solution when used does meet these requirements for its final use and where by way of example only if the resulting water and/or solution is to be used for human consumption, agricultural grade solutes can be used if there is down stream processing that results in the an appropriate improvement in quality required to meet the standards of its ultimate use.

14. A water processing device according to claim 1 wherein the selected osmotic drivers can be manufactured to a standard and/or purity lower than appropriate to the required end use, so long as there is a further purification stage which ensures that the water/solution when used does meet these requirements for its final use and by way of example only if the resulting water and/or solutton is to be used for human consumption, agricultural grade solutes can be used if there is down stream processing that results in the an appropriate improvement in quality required to meet the standards of its ultimate use.

15. A water processing device according to claim 1 wherein, for the avoidance of confusion where the term molecular exclusion' is used' this equally applies to molecular retention.

16. A water processing device according to claim 1 wherein, the membrane can be reinforced in any way appropriate to its final use.

17, A water processing device according to claim 1 wherein, the membrane can be manufactured to a shape/design that facilitates transfer between the compartments.

18. A water processing device according to claim I wherein, the membrane can be manufactured to a shape/design that facilitates transfer between the compartments and where by way of example only: spiral, fluted, hollow fiber, 2:, plate and frame, flat sheet, tubular cassette, cartridge pleated or folded membrane can be selected which has a molecular cutoff such that the main salts present in saline are retained.

19. A water processing device according to claim 1 wherein, the membrane can have a closely defined cutoff such that there is a sharp discrimination between those that go through and those retained, or partially retained.

20. A water processing device according to claim 1 wherein the membranes can be selected to retain one or more of the following: methanol, ethanol, glucose and sucrose.

21. A water processing device according to claim 1 wherein, membranes may be used in sequence with varying properties

22. A water processing device according to claim 1 wherein, configurations can be used to reduce, enhance, regulate the flow of solution/water through the membrane.

23. A water processing device according to claim 1 wherein, the design of the membranes can be those already in common use and these can include but are not restricted to those that are flat or spiral wound.

24. A water processing device according to claim 1 wherein, if the water is only required for applications where there is an acceptable but reduced salinity the processing can cease when water of reduced but acceptable salinity is obtained.

By way of examples only: plants with some salt tolerance, animal species of commercial importance, water required for human use but not consumption e.g. toilet facilities.

25. A water processing device according to claim 1 wherein, if the water is only required for applications where there is an acceptable but reduced salinity the processing can cease when water of reduced but acceptable salinity is obtained and where by way of examples only: plants with some salt tolerance, animal species of commercial importance, water required for human use but not consumption e.g. toilet facilities.

26. A water processing device according to claim 1 wherein the speed of flow of any of the solutions passing across the membrane can be independently varied with this flow being in the same or opposite directions.

27. A water processing device according to claim 1 wherein, the process can be used with any process or physical something that enhances, reduces or regulates the flow of material across the membrane and these include but are not restricted to pressure, or gravity feed and where these may be applied singly or in any combinations at different stages of the process.

26. A water processing device according to claim 1 wherein it may be applicable to use indicators to monitor as to the retention or passage of specific components and or leaks and defects in the manufacturing plant.

29. A water processing device according to claim 1 wherein, to reduce the concentration of osmotic drivers it may be advantageous to allow a proportion of the salts present on the proximal side of the membrane to cross that membrane and so generate an osmotic driver where the osmotic pressure is the combination solutes added to the distal chamber combined with some that have crossed the membrane from the proximal chamber.

30. A water processing device according to claim I wherein it may be advantageous to maintain a high difference in osmotic pressures to maximise the flow of water/solutes across the membrane.

31. A water processing device according to claim I wherein In certain configurations intermediate holding tanks (of any required size and dimension) can be introduced for the temporary storage of intermediate solutions.

32. A water processing device according to claim 1 wherein, the composition of any solution present in these intermediate storage tanks can be monitored and/or adjusted to meet specific industrial requirements.

33. A water processing device according to claim 1 wherein it may be advantageous to coating/treating membrane to influence flow rates.

34. A water processing device according to claim 1 wherein it may be advantageous to coating/treating membrane to reduce the process commonly called "membrane fouling".

35. A water processing device according to claim I wherein it may be advantageous to increase/reduce hydrophobic/hydrophilic nature of the membrane to selectively affect the movement of water and or specific components.

36. A water processing device according to claim 1 wherein it may be advantageous to increase the surface area of membrane (s) e.g. by fluting.

37. A water processing device according to claim 1 wherein In certain applications it may be advisable to allow solutes initially present on the proximal side of the membrane to cross to the distal side of the membrane, so long as the counter movement of the osmotic driver is reduced or ideally cannot cross back into the feed water and an osmotic gradient is maintained and so water will continue to flow across the membrane.

38. A water processing device according to claim 1 wherein In certain configurations and/or stages of the process it may be advantageous to incorporate some low molecular weight ionic substances to act as osmotic drivers.

39. A water processing device according to claim 1 wherein, there may be devices that provide multiple stages to the reduction in the level of saline present.

40. A water processing device according to claim 1 wherein In addition to and/or as an alternative to organic solvents, such as methanol and ethanol are used as osmotic drivers.

41. A water processing device according to claim 1 wherein In certain applications and at any stage, it may be advantageous to add a dry and/or concentrated osmotic driver into any part of the process.

42. A water processing device according to claim 1 wherein In certain applications and at any stage, it may be advantageous to add a dry and/or concentrated osmotic driver into any part of the process and where by way of example to initiate the process going at the start on say a new unit.

43. A water processing device according to claim 1 wherein In certain applications and at any stage, it may be advantageous to add a dry and/or concentrated osmotic driver into any part of the process and where by way of example the appropriate mass could be delivered to charge' the device with an additional Supply of osmotic drivers.

4.4. A water processing device according to claim I wherein, in addition to the general use of temperature to regulate a specific process it may in certain instances be an advantage to have differences in temperature between different stages and/or different sides of the membranes.

45. A water processing device according to claim 1 wherein, for certain applications it may be advantageous to use ionic organic substances which have relatively high osmotic pressures and where these include by way of example only sodium acetate.

46. A water processing device according to claim 1 wherein, for certain industrial processes it may be advantageous to use low cost bulk industrial products as osmotic drivers.

47. A water processing device according to claim 1 wherein, any of the above processes and/or methods can be used to remove/reduce the level of toxic material initially present in the water of which potentially toxic heavy metals are included as an example only.

48. A water processing device according to claim 1 incorporating singly or in any combination the above claims in which the feed solution is not all or partly saline but comprises all or in partly other dissolved substances.

END OF CLAIMS (1-48)