Patent Application
20200255299
The present invention claims priority to U.S. Ser. No. 62/383719, filed 6 Sep. 2016, the entire contents of which are herein incorporated by reference thereto.
Fluid transport that is driven by gradients of pressure, gravity, or electro-magnetic potential is well-known and studied in many fields. A subtler type of transport, called diffusiophoresis, occurs in a gradient of chemical concentration, either electrolyte or non-electrolyte. Diffusiophoresis has been defined as the migration of a particle in a solution or a suspension (i.e., colloidal suspension) in response to the macroscopic concentration gradient of a solute that interacts with the surface of the particle; depending upon the charge of particles the particle may move in a specified direction. Although the mechanism of diffusiophoresis is itself well-known, the diffusiophoresis mechanism is often considered to be an esoteric laboratory phenomenon, and has not been found to be particularly useful in larger scale separation processes which lend themselves to industrial applications.
The publication, “Boosting Migration of Large Particles by Solute Contrasts” by B. Abecassis, C. Cottin-Bizonne, C. Ybert, A. Ajdari and L. Bocquet, Nat. Mater., 7, (2008), pp. 785-789 describes particle diffusiophoresis, but does not disclose any other mechanisms for creating an ion gradient in a liquid by the use of a dissolved gas in the liquid to form such ion concentration gradients.
The present invention comprises several aspects, including those disclosed immediately hereinafter.
In one aspect the present invention is directed to a device effective in separating particles in a flowing suspension of the particles in a liquid which separation operates by dissolving gas into the liquid of the suspension to create an ion concentration gradient, and thereby imparting motion to the charged particles within the liquid and allowing for the creation of particle-rich and particle-depleted regions which may thereafter be separated. The device according to the preset aspect may be used by itself, or a plurality of individual devices may be operated in a parallel and/or serial fashion as described in more detail hereinafter.
In another aspect there is provided a method for separating charged particles in a flowing suspension which operates by dissolving gas into the suspension to form a concentration gradient of ions within the liquid, which concentration gradient causes the migration of the suspended particles due to diffusiophoresis to different regions within the flowing suspension which creates regions of high and low particle concentration, which are thereafter then separated from one another. The method may be practiced as a single separation process or multiple single separation processes may be practiced in parallel and/or serial fashion as described in more detail hereinafter.
The disclosed device and method may be used to supplement, complement, or as a replacement for existing filtration technologies.
The disclosed process offers at least several key advantages over conventional filtration techniques. First, the separated particles from the flowing suspension do not accumulate on a surface (i.e., a filter or filter substrate) over time, which causes a pressure drop across the surface, and consequently imposes that the filtration apparatus be taken offline in order to permit for the cleaning or replacement of the surface. Second, the device and method of the invention does not require the transport of the suspension through filter media, such as filters or membranes, causing clogging thereof and a consequent pressure drop across such filter media, which would reduce operating efficiency. Thirdly the separation of the particles is operable in a dynamic manner, that is to say does not rely upon the static storage of a quantity of the suspension to allow for flocculation to occur in order to cause separation of particles from a liquid carrier or liquid phase. Fourthly the devices of the invention require little or no maintenance, particularly as no filter media requires replacement. Other advantages will be understood from a further reading of this specification.
The disclosed device and method may be used to separate charged particles from within a carrier or bulk liquid within which the charged particles are entrained or are suspended, i.e. a colloid. The charged particles are responsive to an ion gradient present within the liquid within the disclosed device, such that wherein a region having an ion concentration gradient is present in the liquid, the particles will move in one direction within this gradient. While the disclosed device and method may be used in manner wherein the liquid is static and is not a flowing stream, in preferred embodiments the ion concentration gradient is present in the liquid and oriented in a direction which is angled with respect to or which is more preferably transverse to the direction of a flowing liquid comprising the charged particles, such that the movement of the charged particles occurs within this ion concentration gradient as a result of phoretic motion induced upon the particles, thus creating regions of high and low particle concentration within the liquid which may be subsequently separated from one another.
The disclosed device and method may be used to separate differently charged particles from within a carrier or bulk liquid within which the particles are entrained or are suspended, i.e. a colloid. For example particles having a positive charge may be separated from particles having a negative charge may be separated from each other using the disclosed device and method. The charged particles are responsive to an ion gradient present within the liquid within the disclosed device, such that wherein a region having an ion concentration gradient is present in the liquid, particles of various sizes and shapes, different charges (i.e., negative, or positive) and/or of differing magnitudes will move in different directions within this gradient. While the disclosed device and method may be used in manner wherein the liquid is static, in preferred embodiments the ion concentration gradient is present in the liquid is present in a direction which is angled with respect to or which is more preferably transverse to the direction of a flowing liquid comprising the charged particles, such that the movement of charged particles occurs within this ion concentration gradient as a result of phoretic motion induced upon the charged particles, creating regions of different particle concentrations which may be subsequently separated from one another.
The ion concentration gradient within the liquid is formed by first introducing a gas which is soluble in containing liquid which will generate ions within the liquid. By way of non-limiting example, wherein water is the carrier or bulk liquid one or more of the following gases may be advantageously used: H2S, CO2, HCN, HCl, HBr, HF, HI, Cl2, N2O4, NO2, SO2, SO3, and NH3, most of which form aqueous acidic species in water. Ammonia forms a basic solution but still forms ions within the liquid. Also useful are volatile organic acids whose vapour pressures and solubilities in water are sufficiently high at operating conditions of the process. Non-limiting examples of volatile organic acids include methanoic (formic) acid, which at 1 atmosphere has a boiling point of 100° C., ethanoic (acetic) acid, which at one atmosphere has a boiling point of 118° C. Others not particularly listed here may also be used as well.
In a preferred embodiment, the gas is CO2 which in water undergoes the following reversible reaction:
CO2+H2O<==>H++HCO3−
forming dissolved carbonic acid in water, and thus providing dissolved ions in the water. Other ionic species may be formed using one or more different gases, and a plurality of differing ionic species may be present in and useful in forming the ionic concentration gradient. Second, the gradient is established by exposing the charged particle containing liquid to a pressure gradient of the one or more gases spanning the liquid. Such may be effectuated by locating the liquid in a cavity having a volume (or plenum) which has at least a first portion or wall of a gas permeable material, and at least a second and separate second portion or wall of a gas permeable material which are both transmissive to the gas used and which effectively contains the charged particle containing liquid. The gas pressure present at the first portion or wall, is greater or lesser than the gas pressure at the second portion or wall such that the differential between these pressures ensures at the gas permeates a respective portion or wall and dissolves in the liquid, and in part forms a dissolved ionic species, the other portion or wall at a lower relative gas pressure ensures that the concentration of the gas does not reach a saturation level thereby ensuring that an ion concentration gradient is formed within the charged particle containing liquid between these portions or walls. In one embodiment the gas behind the first portion or wall and the second portion or wall are both at higher than atmospheric pressure, but at different relative pressures. In another embodiment the gas behind one of the portions or walls is at a pressure above atmospheric pressure while the other portion or wall is at atmospheric pressure and does not necessarily contain the gas, but may be open to the ambient atmosphere. In a further embodiment one of the portions or walls is exposed to a vacuum.
An ionic concentration gradient may be formed and existing between parts of a cavity (or plenum) between a first portion or wall of a gas permeable material and a second portion or wall of a gas permeable material.
The concentration of the dissolved ionic species present within the liquid can be controlled by establishing a desired pressure gradient of the soluble gas across the liquid, that is to say a desired pressure gradient is established to the first portion or wall and the second portion or wall. As the soluble gas may be used with or without other inert gases, i.e., in a mixture, the pressure of the soluble gas controls the concentration of the dissolved ion species present in the liquid as other inert gases, if present, may not necessarily pass into liquid or if present in the liquid may not form a dissolved ionic species within the liquid which would be useful in a separation process. The relative ratio of the gas pressure(s) behind the first portion or wall and the gas pressure behind second portion or wall is preferably 100:0, as the value of zero contemplates that the gas pressure behind the second portion or wall is actually a vacuum. Preferably however the relative ratio is in the range of between about 100:0.1; more preferably is between about: 100:1, 50:1; 40:1, 30:1, 25:1, 20:1, 15:1, 10:1, 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1 and 1.5:1. Optimal pressures of the device of the invention will of course vary by the nature of the liquid and the solubility of the gas within the liquid, and may be established by reference to known solubility parameters and/or via routine analytical methods by operating a device according to the invention as a desired flowrate of the liquid and with a desired gas, and varying the desired pressure gradient across the liquid in order to determine the resultant degree of solubility of the gas, and the ionic concentration gradient established within the liquid, which in turn will vary the degree of separation of the charged particles using the device.
The control of the temperature of the liquid containing the charged particles also influences the ionic concentration gradient as the liquid temperature directly influences the solubility of the dissolved ionic species. Thus, control of this temperature may be used in addition to the control via establishing a desired pressure gradient across the liquid as described herein. Optimal temperatures will of course vary by the nature of the liquid and the solubility of the gas within the liquid, and may be established by reference to known solubility parameters and/or via routine analytical methods by operating a device according to the invention as a desired flowrate of the liquid and with a desired gas, and varying the temperature in order to determine the resultant degree of solubility of the gas, and the ionic concentration gradient established within the liquid, which in turn will vary the degree of separation of the charged particles using the device.
The nature of the particles to be separated may vary widely and it is contemplated that they have a net positive or negative charge when present within the liquid when within the device of the invention, such that they may be moved by phoretic motion induced upon the particles by the presence of dissolved ionic species with the liquid, which ionic species is formed by a the in-situ reaction of gas entering the liquid and the liquid itself; preferably the dissolved ionic species is formed by a reversible in-situ reaction. Two or more different types of particles having different charges may be simultaneously separated from a liquid. Such may have different charges, i.e., positive, negative charges. The particles themselves may be biological or non-biological materials. Their size is non-limiting; it is only required that they be suspended or entrained within a liquid and be responsive to the phoretic motion induced by the dissolved ionic species in the liquid. In a certain embodiment, the charged particles are microbiological organisms such as bacterium and/or may be pathogens. In further embodiments, the particles are non-biological materials which have a net charge or a surface charge which may be either positive or negative.
Advantageously a first gas cavity is present behind the first portion or wall, and a second gas cavity is present behind the second portion or wall; in such embodiments the gas present in a respective cavity may migrate into the liquid in the cavity across the said first portion or wall and the second portion or wall. The first and the second gas cavities may be attached to a suitable source or pressurized gas, or may be open to the atmosphere, or may be attached to a suitable apparatus or source of vacuum. In one specific embodiment the second gas cavity is merely the exposed ambient atmosphere.
In a preferred embodiment the cavity is a channel having a non-circular cross-section or is a tube having a circular cross-section as described in more detail hereinafter and as depicted in one or more of the drawings.
The ratio of the length dimension is greater than the average transverse dimension is desirably selected in view of the nature of the particles to be separated, the bulk liquid and the operating liquid flow conditions of the particle containing liquid within the liquid containing cavity 20. Ideally the length is sufficient so to allow for a desired degree of particle separation from within the bulk liquid, at the operating conditions of the device of the invention.
The materials of construction of the device may be virtually any material which may be used to maintain a satisfactory pressure differential between the first and second cavities, and the second and third cavities so to allow for the devices and methods of the invention operate as described herein. Such materials are desirably sufficiently rigid, and are chemically resistant, or chemically inert to any of the liquids and/or gas is being used in a separation process. Coming to consideration are any of a number of synthetic polymers, metals, ceramic materials, and the like. As to the construction of the cavities and/or intermediate walls which may be present, naturally these also additionally must exhibit the ability to allow for the diffusion or transfer of the gas used in the device and/or method between adjacent cavities. This will of course in no small part depend upon the operating characteristics of the device, and in particular the liquid, the nature of the particulates contained within the liquid, and that the gas to be used. Again, synthetic polymers, metals, ceramic materials, and in particular microporous materials which allow for the selective transfer diffusion of gas, but yet which retain liquid such as membranes of various types contemplated to be particularly useful. Non-limiting examples of such materials include: synthetic polymers such as silicone polymers, i.e., poly(dimethyl siloxane), poly(methyl propyl siloxane), poly(methyl octyl siloxane), poly(trifluoropropyl methyl siloxane), and poly(phenyl methyl siloxane); polyacetylenes and substituted polyacetylenes, i.e., poly(1-trimethylsilyl-1-propyne) (PTMSP), poly(4-methyl-2-pentyne) (PMP); polyolefins, i.e., polypropylene, poly(4-methyl-1-pentene); poly(2,6-dimethyl-1,4-phenylene oxide) (PPO); polyamides, aromatic polyamides (polyaramids); polyimides, fluorinated polyimides, i.e, 6FDA-DAF, 6FDA-TMDA (2,3,5,6-tetramethyl-1,4-phenylenediamine); polysulfones; polycarbonates; as well as those based on celluloses, i.e., ethyl cellulose, cellulose acetate, and cellulose triacetate. Other materials include hydrogels; microporous polymers, e.g. microporous PTFE; coated carbon paper/woven fabric as commonly used as a gas diffusion layer in fuel cells; natural polymers and ceramics.
A material which is advantageously used are polysiloxane-based polymers such as polydimethylsiloxane same having a sufficiently high molecular weight such that it provides both effective barrier characteristics to the liquid but at same time allow for the perfusion of the gas, i.e., carbon dioxide. Thickness of these materials, and a particular the thickness of the cavities and/or intermediate walls to allow both effective barrier characteristics of liquids, and yet a sufficiently high rate of gas transfer across such materials may be established empirically, or by routine experimentation and will of course vary upon the configuration of a particular device to be fabricated, according to the present inventive teaching.
The configuration of the parts of a device are preferably arranged in such a manner that at least part of the first, second and third cavities are parallel with respect to one another with a region or part of the first and second cavities separated by a first permeable wall, and with a region or part of the first and second cavities separated by a second permeable wall. Nonlimiting parallel configurations are disclosed with respect to one or more of the drawings.
In one particularly preferred embodiment the first 10, second 20 and third cavities 30 are preferably tubes or channel shaped cavities each having an inlet and at least one outlet, respectively: a first cavity inlet 10a and a first cavity outlet 10b; a second cavity inlet 20a and a second cavity outlet 20b; and, a third cavity inlet 30a and a third cavity outlet 30b. The first, second and third cavities may be substantially straight, but may also be curved or contain both substantially straight sections and curved sections as well. The first and third cavities necessarily include an inlet and/or an outlet, but both are not usually essential, as, for example the first cavity may contain an inlet through which a quantity of a pressurized gas may be supplied, but no outlet would be required as the gas would be permeable through the permeable wall thereof and into the second cavity. Not dissimilarly the third cavity may contain an outlet, through which gas entering the third cavity via the second permeable wall may enter from the second cavity may be withdrawn such as by a vacuum, or may be allowed to vent to the ambient atmosphere. It is also foreseen that the third cavity may be connected to a vacuum source so to ensure that the pressure in the third cavity is reduced compared to the pressure extant in the first cavity. It is also foreseen that the third cavity 30 may be absent, as the permeable wall 14 may be in direct contact with the ambient atmosphere (and exposed to 1 atm pressure.)
As the pressures within the first cavity 10 and the third cavity 30 differ, the concentration of the ionic species formed by the dissolved gas present in the liquid 15 varies transversely between the walls 12, 14. The concentration of the ionic species may also be in part controlled or influenced by the temperature of the liquid 15. Such induces the migration of the suspended particles P due to diffusiophoresis to different regions within the flowing suspension which creates regions of high and low particle concentration, which thereafter may be separated from one another. Such is schematically shown in
The outlet of the second cavity 20 may include two or more outlets, with at least one (first) outlet containing and used to transport a quantity of the liquid containing a relatively reduced amount of the particulate, and at least one (second, or further) outlet containing a quantity of the liquid enriched in the particulate, both being relative to, or as compared to the liquid provided to the inlet 20a. In such a manner, the discrete concentration of the particles P within the different lamina of a liquid flowing through the second cavity 20 between its inlet and the outlet(s) may be controlled, and used as a separation process which does not require the use of a traditional filter medium through which the liquid must be allowed to, or forced to pass. Rather in the device and method of the present invention, the gas introduced in the first cavity migrates across the first permeable wall and into the particulate containing liquid flowing through the second cavity (or also referred to as the ‘liquid cavity’) wherein it becomes entrained, but preferably dissolved therein. The pressure differential across the second cavity, due to the relatively reduced pressure present in the third cavity induces gas transfer between the first and third cavity in a “net transverse direction”. A difference in the partial pressures of the soluble gas is required; whereas the total pressure may be constant. The direction of the gas flow transverse to the longitudinal flow direction of the particulate containing liquid ensures that a concentration gradient of the dissolved gas is present within the second cavity between the first and the third cavities, which in turn facilitates segregation of charged particles within the liquid.
The process and apparatus of the invention may also be used to concurrently separate two (or more) different types of species of charged particles as well.
With reference now to
Devices of the invention may be used singly (or a “unit device”, which may be identified hereinafter in a dotted line box labeled “A”), or a plurality of such devices may be operated concurrently. Two or more such devices may be operated in serial fashion, in a parallel fashion or in a combination of both.
While not shown in either of
In
The device 1 was constructed from a polydimethylsiloxane material (“Sylgard 184 Elastomer”) kit, ex. Dow Corning) using a conventional soft lithography technique. The monomer and cross-linker provided in the kit were mixed that it was ratio of 10:1. The second channels 20 has a width of 0.1 mm, a height of 0.02 mm and a length of 30 mm. The thickness of the polydimethylsiloxane material used to provide the gas permeable walls 12, 14 was 30 microns.
When operating the second channels had a flow rate of 2 μl/h; and the pressure drop across the channel was Δp≈0.2 kPa. The device was used to separate negatively charged particles present in a stream of deionized water, pumped through the apparatus using a syringe pump (“PhD Ultra”, ex Harvard Apparatus.)
The foregoing device was also used in the same manner to evaluate separation of positively charged particles as well. However, in order to avoid undesired adhesion of the positively charged particles to the walls of the second channels 20, first they were contacted by a 1% aqueous solution of 3-aminopropyltrimethoxysilane (ex. Sigma-Aldrich) was pumped through the second channels for 20 minutes, followed by rinsing with deionized water for 10 minutes. Thereafter, a liquid containing positively charged particles was provided to the device.
This behavior is illustrated in the following
The device and method of the invention may be used in any application which would benefit from such a separation technology, which as disclosed does not require the use of convention filtration media such as porous filters, such as fibrous, metal or ceramic filters or membrances, nor require establishing an electrical field such as may be required in electrolytic separation processes.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2017/049819 | 9/1/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62383719 | Sep 2016 | US |
