Solids from a Fluid

FIELD OF THE TECHNOLOGY

The technology relates to water purification and more particularly to the production and use of electret materials in water purification.

BACKGROUND OF THE TECHNOLOGY

The present technology relates to a manufacturing process for an electret fiber which retains a permanent monopolar electrostatic charge, and in particular relates to the manufacturing method and use of electret fibers in which fluid containing designated ions is then passed between and in contact with fibers such that at least a portion of the designated ions are

electrostatically bound to the charged material to produce a fluid effluent (output) having a reduced concentration of the designated ions.

OBJECTS AND SUMMARY OF THE TECHNOLOGY

The object of the present technology is to solve problems of the prior art and provide a new manufacturing method involving a charged head for forming novel electret fibres. Those fibres are then used in the removal of ions from a solution in novel devices.

Accordingly, in a first aspect, the present technology provides a method where small fibers of polymer, for example Linear Low Density Polyethylene (LLDPE) are heated until semi molten and at the correct moment subject to a high voltage field and allowed to cool, thus the fiber retains a permanent monopolar electrostatic charge.

In order to achieve this, the crystalline structure of the plastic needs to be aligned. In the presence of a high voltage electrostatic field the polar molecules of the plastic are rotated and aligned such that they remain in this position when the field is removed.

In a second aspect, the present technology provides a method of separating designated ions from a fluid containing the ions, the method comprising contacting the fluid with charged fibres such that at least a portion of the designated ions are electrostatically bound to the charged fibres, to produce a fluid effluent having a reduced concentration of the designated ions.

The present technology also provides a method of manufacturing an electret material and separating designated ions from a fluid containing the ions using this material, the method comprising:

(a) generating the charged fibres (b) by exposing the subject material to an electrostatic charge generated by electronic means such that the fiber retains a permanent monopolar electrostatic charge.

(b) contacting the fluid with charged fibres (a) for a time sufficient for at least some of the designated ions to be electrostatically bound to the charged material to produce an effluent have a reduced concentration of the designated ions;

Step (a) is preferably facilitated so that the charged material has a significantly high permanent monopolar electrostatic charge.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

In order that the technology be better understood, reference is now made to the following drawing figures in which:

Fig.i is a schematic view of the manufacturing process of an electret fibre processed product according to the present technology.

Fig.2 is a schematic diagram showing the high voltage charged injection head used in the alternate fibre manufacturing process.

Fig.2a is an alternate schematic diagram showing the high voltage charged injection head used in the alternate fibre manufacturing process.

Fig.3 is a schematic view showing the configuration of electret fibers in a parallel (straw or conduit) layout according to the present technology.

Fig is a schematic view showing alternate configurations of the electret fibers woven into mat form.

Fig.5 is a schematic view showing the mat rolled into a spiral form. Fig.6 is a schematic view showing an alternate device configuration using both positive and negative fibers in series.

Fig.7 is a process flow schematic (block diagram) showing the interconnected systems and measurement systems used in the present technology. BEST MODE AND OTHER EMBODIMENTS

Electrets are known in the art. Further description of electrets can be found in the publication "Electrets and Related Charge Storage Phenomena", Baxt, L. and Martin, P. (1968), by the Electrochemical Society, New York.

The electret material may be any material that it capable of retaining a charge. Examples of common electret material include, but are not limited to, polyvinylidenedifluoride (PVDF), polytetrafluoroethylene (PTFE),

polyethylene terephthalate (PET), polyethylene (PE) and polypropylene (PP).

The term "electret" or "charged material" as used herein in relation to the charged materials disclosed herein is intended to include materials of any shape including fibers or a collection or bundle of fibers, as well as woven and non-woven substrates made from electret fibres.

Conventionally the charged electret or charged material may be formed by existing methods known in the art. For example, in the case of electret beads formed from a polymer, the selected polymer material is melted in a container pressurized with an inert gas. The temperature and pressure of the container are closely controlled then, at the appropriate time, when the material is in an optimal state, a stream of the melted material is ejected from a nozzle and discharged as atomized droplets into a container. On discharge, the droplets, which form quickly into solid spheres of a predetermined dimension, have a high voltage source connected to the discharging nozzle, which cause the beads upon cooling to retain a permanent monopolar electrostatic charge. Fiber, sheet and rod-like electrets are processed similarly, but use an extruder to produce the material to be charged, which is then passed over high voltage combs whilst still in molten or semi molten form. Upon cooling, some 20 percent of the charge is lost and thereafter the charge remains stable.

Various existing techniques are available for the removal of dissolved ions from a liquid. These include distillation, reverse osmosis, Pervaporation, Electrodialysis, freezing and ion exchange.

Distillation is a process in which the liquid is evaporated, leaving the salt behind. The high energy cost of distillation can be reduced by using a vacuum to lower the boiling point or by using multiple stages. Reverse osmosis is a technique in which pressure, generated by a pump, forces the liquid through a semi permeable membrane against the osmotic pressure to produce pure liquid, leaving behind a more concentrated salt solution on the other side of the membrane.

Pervaporation is a process whereby a selective membrane is permeable to a given solute. The membrane has a vacuum maintained on the side opposite to the mixed material. The process is enhanced if the mixed material is maintained at the highest possible temperature consistent with not damaging the membrane.

Electrodialysis involves the use of ion-permeable membranes to filter out negatively and positively charges ions.

In the freezing technique, the salt containing liquid is frozen with the result that pure crystals of the liquid are formed and the dissolved salt is left in concentrated pockets of higher salinity.

In ion exchange, selected ions are stripped from fluids. The normal method for regeneration of the media is to introduce a counter-ion solution that effectively has a higher potential than the media. Hence, target ions are expelled with the counter-ion solution leaving behind a clean media for adsorption of the target ions in the next cycle. There are a number of disadvantages with this process:

a. The media is not usually highly charged even if it could be, because the stripping agent would not be able to overcome the higher potential. b. This low charge implies that the charge carrying capacity of the media is not as high as its maximum capability.

c. The size of the unit (and therefore the capital cost) is inversely

proportional to the potential of the media. A high potential results in a relatively smaller device and hence lower capital cost.

d. Chemical feedstock used in conventional processes provides an extra contaminant in the discharge, and if in a manual process leads to labour and additional cost, and servicing costs if automatic.

e. Stripping agents are extremely corrosive, necessitating ion exchange units to be built using costly exotic materials

f. Because of the low capacity of the ion exchange systems it has not been an economically viable method for desalination of seawater. It is usually used for brackish or mildly contaminated water where the salt load is significantly less than seawater.

g. Conventional ion exchange media contains material bulk that does not add to the ion exchange capacity resulting in increased size and cost for a given output.

The technology provides a new method of converting an existing commercially available fiber product into an electret material. It is possible to use this charged material to remove or strip ions from a liquid.

Accordingly, in a first aspect, the present technology provides a method where small fibers of (for example) existing Linear Low Density Polyethylene (LLDPE) may he heated until semi molten and at the correct moment subject to a high voltage field and allowed to cool, thus the fiber retains a permanent monopolar electrostatic charge.

In order to achieve this, the crystalline structure of the plastic needs to be aligned. In the presence of a high voltage electrostatic field the polar molecules of the plastic are rotated and aligned such that they remain in this position when the field is removed.

The rate of crystallization of a plastic is dependent on the temperature, of which there are two significant points.

A. Tg: The Glass transition temperature. Below Tg, there is virtually no molecular motion on a local scale.

B. Tm: The crystalline melting point. This is the temperature at which crystals melt and a crystalline structure polymer resembles an amorphous polymer, which has no short-range order. Tm generally increases as the degree of crystallinity increases. It is at this

temperature the plastic flows as a liquid.

At a certain temperature between Tg and Tm the polar molecules in the crystalline structure are free to align, whilst the plastic still retains the properties of a solid. It as this temperature we refer to the material being semi molten. Slight stretching of the fiber at this temperature is found to also assist in further aligning the structure. An alternative method is to pass a suitable polymer (for example) Linear Low Density Polyethylene (LLDPE) at a higher temperature (molten form) through openings in a charged, high voltage injector head at high pressure, subjecting it to a high voltage electric field and then rapidly cooling the fiber as it is drawn away from the head, thus the fiber retains a permanent monopolar electrostatic charge.

The amount and polarity of the charge depends on the voltage and the properties of the polymer material and the use to which the fibers are to be put. For example, when the method of the first aspect is used to strip the salt from seawater, the charge put on the charged material is a positive polarity.

Preferably, the diameter of the charged material fiber is in the order of 5-20 μπι. Fibers may be run parallel to each other and located lengthwise in a tube or conduit in such a way that fluid flow runs along the space between the fibers.

Accordingly, in a second aspect, the present technology provides a method of separating designated ions from a fluid containing the ions, the method comprising contacting the fluid with charged material such that at least a portion of the designated ions are electrostatically bound to the charged material, to produce a fluid effluent having a reduced concentration of the designated ions.

By designated ions we mean any selected ions that may be present in the liquid, for example, those ions of a salt dissolved in the liquid. The designated ions may be sodium ions and chloride ions, although it will be clear that the present technology has application to other ions.

The fluid may be a solution comprised primarily of sodium chloride

(Salt) and water. The fluid may be seawater.

Preferably, the fluid is contacted with the charged material by passing fluid through the charged material.

The charged material may be any permanently charged or polarized material, particularly a fibre or fiber product (strand, yarn, mat, woven substrate, non-woven substrate) carrying a charge or capable of inducing a charge in a non-charged particle. The charge may be negative or positive and is selected on the basis of the ions to be removed from the fluid. For example, sodium chloride dissolved in water has a net negative charge, in which case the charged material used will have a positive charge.

The technology will now be described with particular reference to the example of stripping or removal of salt from seawater, using charged fibers as the electret. However, the method of the present technology may be used to strip or remove other salts or ions from other fluids.

Salt ions in seawater have a net negative charge. A positive electrostatic charge on the charged material - preferably a charge many times higher than the ionic charge on the salt ion - easily captures the salt ion from the fluid. It is believed that the process continues with the charged fibers building up depositions beyond the rigid Stern's layer, and many times further than the normally diffuse Gouy-Chapman layer expected in a normal electrochemical processes encountered in flocculation. The region between these two layers is the plane of shear and the difference in potential at this plane with respect to the fluid is called the zeta potential, or the electro kinetic potential. The zeta potential for the charged ion can be many times greater than an

electrochemical zeta potential, even for the most electro-active molecules.

The current option in the method of the technology is to discard the charged material once there has been sufficient salt build-up thereon, leaving a substantially desalinated water.

Accordingly, the present technology provides a method of

manufacturing an electret material and separating designated ions from a fluid containing the ions using this material, the method comprising:

(a) generating the charged material used in (b) by exposing the subject material to an electrostatic charge generated by electronic means such that the fiber retains a permanent monopolar electrostatic charge.

(b) contacting the fluid with charged material (a) for a time sufficient for at least some of the designated ions to be electrostatically bound to the charged material to produce an effluent have a reduced concentration of the designated ions;

Step (a) is facilitated so that the charged material has a significantly high permanent monopolar electrostatic charge.

The electronic means may be of any suitable shape and/or

configuration. The electronic means may be one or more electrodes. The electrodes may be insulated by a dielectric material. The electrodes may be one or more flat or other plates with through openings, hollow tubes, made from a wire mesh or the like strategically located within the vessel containing the heated molten or semi molten material. The electronic means are preferably connected to a high voltage source so that strong electrostatic field(s) are generated. The electrostatic charge generated by any suitable means may be in the range of about 1 to 100 kV. From experience it has been found that a voltage in the order of 2okv is adequate.

Step (b) is facilitated so that the charged material is configured such that fluid may be bought into contact with the fibers. The fibers may be run parallel to each other and located lengthwise in a tube in such a way that fluid flow runs along the space between the fibers (40) and (42). The fibers may be woven, weaved, pressed or shaped in any suitable shape or configuration.

The fiber used in the technology may be any material that is capable of retaining a charge.

The preferred material is Low Density Polyethylene (LLDPE) and more preferably polytetrafluoroethylene (PTFE) but is not limited to this material and may either be single filament / strand or multi-filament / strand.

The preferred filament diameter is of the order of 5-20um.

As shown in Figures 1 and 7, LLDPE fiber feeds from a spool or other source (1) through a fiber guide via synchronized feed rollers (13) into a preheated chamber (2), containing air heated delivered by pre-heater (8), controlled by a thermocouple (Ti) and central controller (17), with the rate of air flow controlled by fan (7).

The temperature in the preheat chamber (2) is preferably in the range of 6o°C ±io°C.

The airflow entering the preheat chamber (2) is on the order of 0.08 - o.3m ³ /min, but may be varied outside this range depending on the thermal response of the temperature zones.

The fiber then passes through temperature controlled heating zones (3) controlled by a thermocouple (T2) and central controller (17), and then heating zone (4) controlled by a thermocouple (T3) and central controller (17), such that the fiber is in a semi molten state when it reaches the charge zone (5) where is exposed to a high voltage electrostatic charge. The temperature in zone (3) is preferably in the range of 75°C ±io°C. The temperature in the final zone (4) is critical to the production process and is determined by the melt temperature of the material fiber used in the production, for example for LLDPE preferably in the range of io6°C ±o.i°C.

Preferably the electrodes in the chamber (5) are run at a voltage in the range 1-iookV.

As the fiber passes along the charge zone (5) it is allowed to cool sufficiently for the fiber to retain the charge.

The length of the charge zone (5) must be sufficient for the semi molten fiber to acquire the charge and then cool sufficiently below the melting temperature while still in the charge area. Given the low thermal mass of the fiber a charge zone length of the order of 60 - 80 cm is sufficient.

The fiber then passes through cooling chamber (6),and is fed by synchronized feed rollers (12), passing an electrostatic charge detector (9) which measures the retained charge on the fiber before being collected (10).

The feed rollers (13) and (12) and collector (10) are synchronized by a variable speed stepper motor driver circuit located in the central controller

(17).

Slight differences in the roller diameter and/ or speed between feed rollers (13) and (12) ensure the fiber remains under tension and undergoes slight stretching.

Air in the cooling chamber (6) is returned with the airflow generated by fan or blower system (7) and then heated by a pre-heater system (8) before optionally being fed back into the preheated chamber (2), such that the system forms a closed loop.

A central control unit (17) monitors the temperature in each of the heating zones using thermocouple PID (Proportional-Integral-Differential) controllers to control power to the heating units to within the required tolerances. Airflow is controlled by the central control unit. The synchronized feed roller stepper motors are also driven by the central control unit, allowing for fiber feed rates to be varied and controlled accurately.

As shown in Figure 2 the alternate method of production the preferred material uses extruded Low Density Polyethylene (LLDPE) and more preferably polytetrafluoroethylene (PTFE) but the method is not limited to this.

For example, a mass of LLDPE 20 at a temperature near Tm is forced at high pressure through a charged steel injector plate 21 held within an opening in a fused Aluminium Oxide insulator block 22. The plate or head may have one or many through openings. The insulator block or fixture may incorporate a circumferential insulating shield 25 to better electrically isolate the charged plate 21 from the polymer injection machine that carries it. As shown in Figure 2a, the injector or extruder plate 23 may be formed from nickel plated nozzles 26 machined directly into the fused Aluminium Oxide insulator block 27. The plates 21, 23 may be retained by a steel ring 28 that is affixed to the spin head or extrusion or injection machine 29 by fasteners 30.

The steel injector plate or Nickel nozzles 21, 23 are connected to a high voltage power supply 31. The temperature of the LLDPE is critical to the production process and is determined by the melt temperature of the material used in the production, for example for LLDPE preferably in the range of i8o°C ±5°C. The working extrusion pressure is in the range of i6oopsi, but may be as high as 3500psi.

Preferably the electrodes 21, 23 are run at a voltage in the range 1- lookv.

As the material is forced through the injector plate it is exposed to a high electrostatic charge. The material then exits the plate 21, 23 still under the influence of the electrostatic charge in the form of thin filaments or fibers and is then rapidly cooled, thus the filaments/ fibers retain the charge.

Feed rollers 32 under head collect the filaments and provide tension on the filaments to ensure the filaments remain under tension and undergo slight stretching.

The preferred finished filament diameter is of the order of 5-20um. Charged fibers or filaments 40 are collected in one embodiment to form a bundle or array of generally parallel fibers within a tube, conduit or plenum 43 that forms a fluid flow path 42 as shown in Figure 3. The collected fibre bundle or array 40 may have a helical twist or weave within the tube 43. When within a tube or other enclosure 43 forming a fluid flow path 42, the tube may be of practically any diameter and shape. The ratio of fiber 40 to free space (by cross sectional area) in this form is referred to the packing density, the preferred ratio being about 50%.

The end of the tube may be closed off by porous end material 44 that holds the fibers in the tube lengthwise. The end material may be needle felt (pore size approximately 5 um), or other suitable material.

An alternate configuration is to have activated charcoal end pieces 44 in addition to further filter the fluid.

As shown in Figure 4, fibers, threads, strands etc. in accordance with the above teachings may be woven into an array, textile mat or sheet textile 50. Non-woven textile mats and bulk materials may also be formed from fibers, threads, strands etc. of the present technology.

As suggested by Figure 5, a textile sheet or array of the present technology may be wound into a roll 60. Fluids may flow along the length of the roll to be purified.

As suggested by Figure 6, a further alternate configuration is to also include a negatively charged fiber zone 61 before or after a positively charged fiber zone 62 in a flow path 63 having an enclosure 64, for example, to filter biological products.

Any description of prior art documents herein is not an admission that the documents form part of the common general knowledge of the relevant art in Australia or elsewhere.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the technology as shown in the specific embodiments without departing from the scope of the technology as broadly described.

The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Although the technology has been described with reference to specific examples, it will be appreciated by those skilled in the art that the technology may be embodied in many other forms.

As used herein, unless otherwise specified the use of the ordinal adjectives "first", "second", "third", etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.

Reference throughout this specification to "one embodiment" or "an embodiment" or "example" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present technology. Thus, appearances of the phrases "in one embodiment" or "in an example" in various places throughout this specification are not necessarily all referring to the same embodiment or example, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

Similarly it should be appreciated that in the above description of exemplary embodiments of the technology, various features of the technology are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed technology requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Any claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this technology.

Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as "processing," "computing," "calculating,"

"determining" or the like, refer to the action and/or processes of a

microprocessor, controller or computing system, or similar electronic computing or signal processing device, that manipulates and/or transforms data.

Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the technology, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

Thus, while there has been described what are believed to be the preferred embodiments of the technology, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the technology, and it is intended to claim all such changes and modifications as fall within the scope of the technology.

While the present technology has been disclosed with reference to particular details of construction, these should be understood as having been provided by way of example and not as limitations to the scope or spirit of the technology.