WO2013036111A1 - Solution comprising an osmotic agent and method of extracting water using said solution - Google Patents

Solution comprising an osmotic agent and method of extracting water using said solution Download PDF

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Publication number
WO2013036111A1
WO2013036111A1 PCT/NL2012/050612 NL2012050612W WO2013036111A1 WO 2013036111 A1 WO2013036111 A1 WO 2013036111A1 NL 2012050612 W NL2012050612 W NL 2012050612W WO 2013036111 A1 WO2013036111 A1 WO 2013036111A1
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Prior art keywords
group
membrane
osmotic
solution
water
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PCT/NL2012/050612
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French (fr)
Inventor
Emile Robin CORNELISSEN
Julius Bernardus VAN LIER
Kerusha LUTCHMIAH
Cornelis ROEST
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Kwr Water B.V.
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Publication of WO2013036111A1 publication Critical patent/WO2013036111A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/445—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by forward osmosis
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/002—Forward osmosis or direct osmosis
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/002—Forward osmosis or direct osmosis
    • B01D61/005—Osmotic agents; Draw solutions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/58—Multistep processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/10—Supported membranes; Membrane supports
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/10—Supported membranes; Membrane supports
    • B01D69/107—Organic support material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/08—Polysaccharides
    • B01D71/12—Cellulose derivatives
    • B01D71/14—Esters of organic acids
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/025—Reverse osmosis; Hyperfiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/027—Nanofiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/36—Pervaporation; Membrane distillation; Liquid permeation
    • B01D61/364—Membrane distillation

Definitions

  • Solution comprising an osmotic agent and method of extracting water using said solution
  • the present invention relates to a method of extracting water from an aqueous source by osmosis, a draw solution for use in the method and the use of osmotic agents in a draw solution.
  • Forward osmosis is a technologically applicable variant of osmosis, wherein water is naturally transported through a semi-permeable membrane driven by an osmotic pressure difference generated by the two solutions on both sides of the membrane.
  • water molecules migrate through the semi-permeable membrane from a low to high osmotic concentration corresponding to high to low chemical potential. This phenomenon will continue until an osmotic equilibrium is reached, generally until the same concentration is reached on both sides of the membrane.
  • microfiltration, ultrafiltration, nanofiltration and reverse osmosis are driven by hydraulic pressure. In terms of energy consumption, forward osmosis requires no additional energy supply .
  • forward osmosis mass transport is divided into: (i) a flux of water passing the membrane which dilutes the more
  • osmotic agents are known in the field, which include salts (e.g. NaCl, MgCl 2 , or KN0 3 ) , sugars (e.g. sucrose, glucose or fructose), or volatile solutes (e.g. SO 2 ) or certain mixtures thereof.
  • salts e.g. NaCl, MgCl 2 , or KN0 3
  • sugars e.g. sucrose, glucose or fructose
  • volatile solutes e.g. SO 2
  • this object is achieved by the provision of a method of extracting water from an aqueous source by osmosis, in particular forward osmosis, the method comprising the application of an osmotic pressure difference over a semi-permeable membrane by providing the aqueous source on one side of the membrane and a draw solution comprising an osmotic agent on the other side of the membrane, wherein the osmotic agent is an organic zwitterion and/or an organic compound comprising an onium group such as a quaternary ammonium group, sulfonium group or phosphonium group, or an organic compound
  • One advantage of the present invention is that the effectiveness of forward osmosis processes can now be enhanced, as the flux of water from the feed solution to the draw solution is improved. Furthermore, the reverse solute flux of the osmotic agent is minimized. Preferably though, the osmotic agent causes both an improvement in the flux of water from the feed solution to the draw solution, while the reverse solute flux of the osmotic agent is minimized.
  • the organic compound in an advantageous embodiment, is organic
  • zwitterion used as the osmotic agent is selected from the group consisting of a betaine comprising compound, a betaine and an amino acid.
  • a betaine is a neutral chemical compound with a positively charged cationic functional group which bears no hydrogen atom, in particular an onium group (such as ammonium, phosphonium, sulfonium group), and furthermore has a negatively charged functional group, such as a carboxylate group.
  • a zwitterion herein is a neutral molecule having a positive and a negative electrical charge, at different locations within the molecule. For sake of clarity, zwitterions herein are distinct from dipoles.
  • amino acid is a containing an amine group, a carboxylic acid group (also designated as “carboxylic group”) , and a side- chain that is specific to each amino acid.
  • carboxylic group also designated as “carboxylic group”
  • amino acid is to be understood as a natural or synthetic amino acid that
  • one or both of the organic zwitterion and/or the organic compound comprises an onium group.
  • quaternary ammonium group (NR.4 + , wherein R represents an alkyl rest, present four times in the quaternary ammonium group; the four alkyl rests of said ammonium can be
  • SR.3 + a sulfonium group (SR.3 + , wherein R represents an alkyl rest, present three times in the
  • the four alkyl rests of said sulphonium can be identical or different) , or a phosphonium group (PR + , wherein R represents an alkyl rest, present four times in the phosphonium group; the four alkyl rests of said
  • phosphonium can be identical, or different) .
  • the quaternary ammonium useful as osmotic agent in the present invention comprises the structure presented as Formula I:
  • R 1 , R 2 and R 3 are independently selected from a lower alkyl, branched or linear, preferably a C 1 -C6 alkyl, and wherein R 4 is selected from a carboxyl, an alcohol, hydroxyl or a lower alkyl comprising a carboxyl, an alcohol or hydroxyl .
  • R 1 , R 2 and R 3 are each selected from methyl, ethyl, propyl, butyl, pentyl and hexyl, linear or branched.
  • R 1 , R 2 and R 3 are methyl.
  • the osmotic agent used in the present invention is selected from the group consisting of glycine betaine, choline, valine, proline and glycine, or a combination thereof.
  • the osmotic agent according to the invention can be a natural osmolyte, meaning an organic compound produced by a cell which is used for osmotic purposes by the cell.
  • Such compounds include trimethylamine N-oxide,
  • inventions can be a synthetic osmolyte, such as EDTA, DTPA, BAPTA, or EGTA.
  • the organic compound comprising more than one carboxylic group comprises at least two carboxylic groups (-COOH) , at least three carboxylic groups, at least four carboxylic groups, at least five carboxylic groups.
  • the compound comprising more than one carboxylic group may be under the deprotonated form in solution, designated by -COO " , the carboxylate anion. All the
  • carboxylic groups may be deprotonated or the organic
  • the organic compound comprising more than one carboxylic group further comprises at least one tertiary amine group
  • NR' R' ' R' ' ' such as one, two, three or four tertiary amine groups.
  • a tertiary amine is an amine that comprises three hydrocarbon rests, such as alkyl rests that can be unsubstituted, or substituted by alkyls or organic functions such as hydroxyl (-OH) , thiols (-SH) , primary or secondary amines, an ether group (-0-) .
  • the organic compound comprising more than one carboxylic group, such as two, three, four, or five carboxylic groups further comprises at least one tertiary amine group, such as one, two, three, four or five tertiary amine groups.
  • Example of such compound are the ethylenediaminetetraacetic acid
  • EDTA, EGTA, BAPTA and DTPA can be (partially, or totally) deprotonated, or fully protonated (i.e. the carboxylic groups and one or more of the amine groups are protonated) in solution.
  • the osmotic agent is an organic compound comprising an onium group or an organic compound comprising more than one carboxylic group.
  • the method of the present invention relates to forward osmosis.
  • the osmotic agent according to the invention provides a high osmotic pressure difference in forward osmosis and is at least compatible with a forward osmosis membrane.
  • the term "forward osmosis" herein is meant to include direct osmosis, engineered osmosis, manipulated osmosis or pressure retarded osmosis. It is contemplated that, instead of using a forward osmosis membrane, it is also possible to use a reverse osmosis or a nanofiltration membrane in the method of the present invention.
  • the method of the present invention preferably takes place without applying hydraulic pressure. And, the forward osmosis process takes place under any suitable ambient pressure and temperature wherein water is or remains liquid.
  • the osmotic agents of the present invention are sufficiently water soluble, exhibit no or low solute leakage, have a suitably small molecular weight, i.e. with a molecular weight of preferably less than 600 g/mol, more preferably less than 500 g/mol, even more preferably less than 400 g/mol, most preferably 300 g/mol (without taking into account counter- ions if applicable) , are sufficiently repelled by forward osmosis membranes and provide a sufficient pull of water through these membranes.
  • the latter feature implies that the osmotic agent has considerable osmotic power, meaning it creates enough osmotic pressure difference or chemical potential difference.
  • the osmotic agent according to the present invention is present in such a concentration that an osmotic pressure of at least 0.5 bar is generated by the osmotic agent and/or by a combination of osmotic agents according to the present invention. In further embodiments, this osmotic pressure is at least 1 bar, at least 6 bar, at least 15 bar, at least 20 bar, or at least 24 bar
  • ⁇ iMRT.
  • M the molarity
  • R is the gas constant: 0.0821 L atm K -1 mol -1
  • T is the thermodynamic, absolute temperature (e.g.
  • the semi-permeable membrane is a membrane which is suitable for nanofiltration, reverse osmosis or preferably forward osmosis. Even though progress is made in the development of membranes for forward osmosis, the characteristics such membranes should have for them to be useful in forward osmosis processes are known by the skilled person. Typically, such membranes are
  • hydrophilic charged, either positively or negatively, and have a determined pore size and specific molecular weight cut-off value.
  • the osmotic agent is compatible with the semi-permeable membrane used in the process of the present invention.
  • the compatibility with the semi-permeable membrane may be tuned by adjusting e.g. the pH or a concentration of
  • the osmotic agent according to the present invention and the semi-permeable membrane as used are selected such that the osmotic agent is repelled by the membrane and/or excluded by size from passing the membrane. Such a selection can be based on charge differences between the membrane and osmotic agent, molecular weight or size of the agent versus the molecular weight cut-off value or pore size of the membrane as used and/or polarity differences exhibited by the agent and the membrane.
  • the osmotic process that takes place under the influence of the draw solution according to the present invention occurs under suitable conditions, meaning i.a. that the pH of the solution lies between pH 2 and 10, preferably between pH 3 and 8, most preferably between pH 4 and 6. Since the functionality of a charged compound is pH dependent, the pH of the draw solution is preferably
  • the osmotic agent is not of the same charge (or of opposite charge) as the semi-permeable
  • the osmotic agent comprises a charged group which is not of the same charge as the semi ⁇ permeable membrane as used.
  • the osmotic agent comprises a group which is of opposite charge of the semi ⁇ permeable membrane used.
  • the semi-permeable membrane has a molecular weight cut-off less than 1000 Da, preferably less than 200 Da, more preferably less than 100 Da.
  • Molecular weight cut-off (MWCO) herein is defined as refers to the lowest molecular weight solute (in Da) in which 95% of the solute is retained by the membrane.
  • the semi-permeable membrane used in the method of the invention has a pore size of between 0.001 and 0.0001 ⁇ , preferably between 0.0003 and 0.0005 ⁇ .
  • the semi-permeable membrane comprises an active layer and/or a support layer.
  • the semi-permeable membrane comprises a
  • hydrophilic, cellulose comprising active layer preferably comprising cellulose acetate, cellulose di-acetate,
  • the semi ⁇ permeable membrane comprises a support layer or a polyester mesh or a micro-porous support.
  • the semi-permeable membrane can furthermore include or be a Thin Film Composite membrane .
  • the forward osmosis membrane according to the invention can be used in two orientations, one wherein the draw solution faces the active layer and the feed solution faces the support layer, and vice versa.
  • the osmotic agents of the present invention provide an improvement over present day draw solutions in both orientations.
  • the active layer faces the draw side since that orientation provides some improvement over the reverse orientation.
  • the aqueous source i.e. feed solution or the aqueous target from which water is to be extracted
  • sewage Municipal wastewater, industrial (waste ) water, effluent, leachate, surface water, ground water, brackish water, sea water (or other sources for high quality water or drinking/process water) , bodily fluids, urine, blood and/or an aqueous solution for animal or human consumption.
  • industrially-derived wastewaters can be from any source.
  • the aqueous solutions for animal or human consumption are, in non-limiting examples, water for human consumption (e.g. recycled water used in space
  • An advantage of using forward osmosis according to the method of the present invention is that fruit juices, or other aqueous solutions for human consumption, can be processed without including a heating or cooling step which might impair the quality or affect the organoleptic properties of the aqueous solution for human or animal consumption.
  • the osmotic agent according to the invention is reused after being used as draw solution. Reuse of the osmotic agent is possible due its low solute leakage. Such reuse of the osmotic agent can be effectuated using the diluted draw solution as a starting point, using a reverse osmosis unit, a reconcentration unit, membrane distillation or nanofiltration .
  • the osmosis membrane used in the method of the present invention can be used in a flat configuration, such as flat sheets, in a spiral
  • Another aspect of the present invention relates to a draw solution for extraction of water by forward osmosis, comprising an organic zwitterion and/or an organic compound comprising an onium group, preferably a quaternary ammonium group, sulfonium group or phosphonium group as osmotic agent (s), or an organic compound more than one carboxylic group.
  • the draw solution preferably comprises any one of the more specifically defined osmotic agents as mentioned herein .
  • An advantage of the osmotic agents according to the present invention is that, when used in draw solutions, they provide an increased osmotic efficiency compared to small inorganic salts, such as NaCl .
  • Another benefit of the present invention is that when using the draw solution in forward osmosis, a lower internal concentration polarization is achieved, resulting in an increased forward osmosis efficiency (e.g. a lower reverse solute flux) .
  • the osmotic agents according to the present invention are not able, or at least to a lesser extent than existing agents (e.g.
  • the present invention thus provides a draw
  • organic zwitterions and/or organic compounds comprising an onium group, preferably a quaternary ammonium group, sulfonium group or phosphonium group, or an organic compound comprising more than one carboxylic group, as osmotic agents, with improved characteristics in
  • the draw solution of the present invention has a high osmotic pressure
  • the draw solution further comprises one or more biocides to reduce degradation of the osmotic agent.
  • the draw solution and installed setup may be sterile to reduce biodegradation of osmotic agents.
  • the installed setup may also comprise an UV installation to disinfect the draw solution to prevent degradation.
  • Yet another aspect of the present invention relates to the use of an organic zwitterion and/or an organic compound comprising a quaternary ammonium group as osmotic agent (s) in a solution, preferably in a draw
  • This use of the draw solution preferably comprises any one of the more specifically defined osmotic agents as mentioned herein.
  • inventions or draw solution comprising said agent, can be used in applications wherein the obtainment of bulk amounts of purified water is the main purpose, for example in the treatment of polluted sources such as in non-limiting examples, sewage, municipal wastewater, industrial
  • solutes can diffuse in two directions: from the feed solution into the draw solution (i.e. forward diffusion) and simultaneously from the draw solution into the feed solution (i.e. reverse diffusion) . Due to internal concentration polarization (i.e. the build-up of solutes within the osmosis membrane) , non ⁇ linear solute flux behaviour is observed (see Figure 1) .
  • C ⁇ s and C ⁇ A represent the draw solute concentrations on the support layer side and active layer side of the support layer-active layer interface, respectively.
  • A is the area of the active layer of the membrane and ⁇ ( cV) the total solute amount that crosses the membrane during the interval At.
  • This set-up also allows calculation of the water flux due to increase of the water volume in a measuring tube.
  • the volumetric flow rate of water can be calculated from the water volume and the time interval.
  • the flux of water in forward osmosis can be calculated experimentally using Equation II:
  • Jw is the water flux
  • A is the area of the active layer of the membrane
  • AV the total amount of water that crosses the membrane during the interval At.
  • Osmotic agents according to the appended claims have been found to exhibit both an improvement in the flux of water from the feed solution to the draw solution (as calculated by Equation II), while the reverse solute flux of the osmotic agent is minimized (as calculated by Equation I) .
  • the invention relates to a method of extracting water from an aqueous source by
  • osmosis comprising the application of an osmotic pressure difference over a semi-permeable membrane by providing the aqueous source on one side of the membrane and a draw solution comprising an osmotic agent on the other side of the membrane, wherein the osmotic agent is an organic zwitterion and/or an organic compound comprising a
  • positively charged group preferably a saturated positively charged group, such as an onium group preferably selected from a quaternary ammonium group, sulfonium group or
  • the invention also relates to a draw solution comprising an organic zwitterion and/or an organic compound comprising a
  • positively charged group preferably a saturated positively charged group, such as an onium group preferably selected from a quaternary ammonium group, sulfonium group or
  • the organic zwitterion in this broader respect is selected from the group consisting of a betaine, a betaine comprising compound and an amino acid.
  • the quaternary onium group in this broader respect, comprises the structure according to formula II:
  • R 5 is selected from N and P, preferably N " S + and P ,
  • R 1 , R 2 and R 3 are independently selected from H, a lower alkyl, branched or linear, preferably a C 1 -C6 alkyl, or aryl and
  • R 4 is selected from a carboxyl, an alcohol, hydroxyl, oxygen or a lower alkyl comprising a carboxyl, an alcohol, hydroxyl or oxygen.
  • FIG. 1 schematically depicts draw solute leakage into the feed solution using a forward osmosis membrane.
  • FS Feed Solution
  • AL Active Layer
  • SL Support Layer
  • DS Draw Solution
  • J w Water flux
  • J s Solute flux
  • C D C D
  • Ci s the draw solute concentration on the support layer side of the support layer-active layer interface
  • C ⁇ A the draw solute concentration on the active layer side of the support layer- active layer interface
  • C F Concentration of solute in feed solution
  • tA thickness of active layer
  • tS thickness of support layer.
  • FIGS. 2a and b show results obtained from experiments using various draw solutions comprising
  • FIG. 2a water flux and solute flux of glycine betaine (GB) is shown in comparison to NaCl, glucose and sucrose.
  • Membrane orientation feed solution facing the active layer (AL to FS) .
  • Figure 2b ratio of glycine betaine (GB) , NaCl, glucose and sucrose as measured during the experiment is shown (AL to FS) .
  • Figures 3a and b show results obtained from experiments using various draw solutions comprising
  • FIG. 3a water and solute flux of glycine betaine (GB) is shown and compared to NaCl, glucose and sucrose. Membrane orientation: draw solution facing the active layer (AL to DS) .
  • Figure 3b the ratio of glycine betaine (GB) , NaCl, glucose and sucrose as measured during the experiment is shown (AL to DS) .
  • Figure 4 shows the efficiency of amino acids and derivatives as forward osmosis draw solutions in water and solute fluxes.
  • Figure 5 shows the solute flux/water flux ration Js/Jw of amino acids and derivatives as forward osmosis draw solutions .
  • a standardized, laboratory-scale U-tube configuration was used to determine the forward osmosis behaviour of various draw solutions and selected feed solutions over a vertically-positioned forward osmosis membrane.
  • the U-tube configuration further comprised two pumps to allow continuous homogeneity of the draw and feed solutions and a measuring tube mounted on the draw side.
  • the forward osmosis membrane is hydrophilic with a thickness of less than 50 ⁇ . It comprises a dense,
  • active layer facing feed side (AL to FS) or active layer facing draw side (AL to DS) .
  • the membrane, with an active area of 0.011 m 2 was placed in a membrane holder.
  • a constant mixing rate of 5.5 L/min was applied to both the feed side and draw side to keep the solutions homogenous.
  • the water flux (J w ) was determined by the volume increase within the measuring tube on the draw side, using Equation III. There is a dilution of the draw solution over time due to an increase of water and also decrease of solutes (solute migration towards the feed side) .
  • the solute flux (J s ) moving towards the feed side was determined by means of a conductivity meter (feed solution was deionised water) , osmometer measurements or by using COD kit (Chemical Oxygen Demand) kits.
  • EXAMPLE 1 Active layer facing feed side (AL to FS) Deionised (DI) water was used as feed solution, either to assess the osmotic performance of various different solutes or for reference purposes in comparison to water extraction from sewage.
  • DI Deionised
  • Figure 2a shows the results wherein water and solute flux of an organic osmolyte, glycine betaine, is compared to different draw solutions of NaCl, glucose and sucrose.
  • Figure 2b demonstrates the relevant ratios for each draw solution.
  • Figure 2b shows that glycine betaine as draw solution gives the lowest ratio of 0.02 gram solute leakage per litre water extracted (g/1), while the highest ratio is observed with NaCl as draw solution, 0.8 g/1.
  • FIG. 3a shows the water and solute flux of glycine betaine with comparison to the different draw solutions NaCl, glucose and sucrose.
  • Figure 3b demonstrates the relevant ratios of each draw solution.
  • glycine betaine produced the highest water flux of 7.3 LMH. NaCl, glucose and sucrose solution all gave similar water fluxes of around 5.4 LMH. The solute leakage of glycine betaine has the lowest solute leakage 0.02 GMH (according to COD measurements), while NaCl, glucose, and sucrose gave 4.2 GMH, 2 GMH, and 1.7 GMH respectively. From Figure 3b, the glycine betaine as draw solution gives the lowest ratio 0.02 g/1, while the highest ratio is observed with NaCl as draw solution, 0.8 g/1.
  • NaCl or the other higher molecular weight substances glucose and sucrose are examples of NaCl or the other higher molecular weight substances glucose and sucrose.
  • EXAMPLE 3 Osmotic extraction of water from sewage Settled sewage was used as feed in combination with glycine betaine as draw solution in the experimental U-tube set-up.
  • the membrane orientation was such that the active layer faced the draw side.
  • the osmotic pressure generated by glycine betaine as used in the experiments was 24 bar. DI was used as reference feed solution.
  • UV spectroscopy is not suitable to measure the low
  • the titration can accurately measure low concentrations of EDTA in deionised water.
  • TOC measures the concentration of all amino acids and amino acid derivatives within the required concentration range. TOC analysis, was found to be the most reliable and accurate analysis method and was therefore used to measure all solute fluxes .

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Abstract

The present invention relates to a method of extracting water from an aqueous source by forward osmosis comprising the application of an osmotic pressure difference over a semi-permeable membrane by providing the aqueous source on one side of the membrane and a draw solution comprising an osmotic agent on the other side of the membrane, wherein the osmotic agent is an organic zwitterion and/or an organic compound comprising an onium group, or more than one carboxylic group.

Description

Solution comprising an osmotic agent and method of extracting water using said solution
The present invention relates to a method of extracting water from an aqueous source by osmosis, a draw solution for use in the method and the use of osmotic agents in a draw solution.
Forward osmosis is a technologically applicable variant of osmosis, wherein water is naturally transported through a semi-permeable membrane driven by an osmotic pressure difference generated by the two solutions on both sides of the membrane. In forward osmosis, water molecules migrate through the semi-permeable membrane from a low to high osmotic concentration corresponding to high to low chemical potential. This phenomenon will continue until an osmotic equilibrium is reached, generally until the same concentration is reached on both sides of the membrane.
Whereas forward osmosis is an osmotically-driven membrane process, other membrane processes, such as
microfiltration, ultrafiltration, nanofiltration and reverse osmosis are driven by hydraulic pressure. In terms of energy consumption, forward osmosis requires no additional energy supply .
In present day forward osmosis applications, forward osmosis mass transport is divided into: (i) a flux of water passing the membrane which dilutes the more
concentrated draw side, and (ii) a reverse solute flux which concentrates the feed solution at the feed side. Both fluxes contribute to a decrease of the osmotic pressure difference in this osmotic process. To increase the economic viability of the forward osmosis process, research goals are aimed at increasing the water flux towards the draw side and/or decreasing reverse flux of osmotic agents towards the feed side .
Several osmotic agents are known in the field, which include salts (e.g. NaCl, MgCl2, or KN03) , sugars (e.g. sucrose, glucose or fructose), or volatile solutes (e.g. SO2) or certain mixtures thereof. However, the efficiency of these osmotic agents in draw solutions is suboptimal as a consequence of various drawbacks. For example, although it is in general observed that inclusion of higher amounts of osmotic agents in the draw solution results in higher water fluxes, also an increased leakage of the osmotic agent is observed, i.e. draw solute leakage or reverse solute flux. Furthermore, there are difficulties in the recovery of the draw solute using a reconcentration system, fouling of the membranes occurs during forward osmosis (both on the feed solution side and the draw solution side of the membrane) and internal concentration polarisation phenomena are observed when using such osmotic agents.
There is thus a need in the field of forward osmosis for identifying osmotic agents that can provide a high osmotic pressure difference on the one hand and exhibit improved characteristics with respect to at least reduction of solute leakage on the other.
It is an object of the present invention to, inter alia, provide a solution to the above-mentioned
disadvantages.
This object, among others, is solved, completely or in part, by the invention according to the appended claims .
More in particular, this object, or other objects, is achieved by the provision of a method of extracting water from an aqueous source by osmosis, in particular forward osmosis, the method comprising the application of an osmotic pressure difference over a semi-permeable membrane by providing the aqueous source on one side of the membrane and a draw solution comprising an osmotic agent on the other side of the membrane, wherein the osmotic agent is an organic zwitterion and/or an organic compound comprising an onium group such as a quaternary ammonium group, sulfonium group or phosphonium group, or an organic compound
comprising more than one carboxylic group.
One advantage of the present invention is that the effectiveness of forward osmosis processes can now be enhanced, as the flux of water from the feed solution to the draw solution is improved. Furthermore, the reverse solute flux of the osmotic agent is minimized. Preferably though, the osmotic agent causes both an improvement in the flux of water from the feed solution to the draw solution, while the reverse solute flux of the osmotic agent is minimized.
In an advantageous embodiment, the organic
zwitterion used as the osmotic agent is selected from the group consisting of a betaine comprising compound, a betaine and an amino acid. Herein, a betaine is a neutral chemical compound with a positively charged cationic functional group which bears no hydrogen atom, in particular an onium group (such as ammonium, phosphonium, sulfonium group), and furthermore has a negatively charged functional group, such as a carboxylate group. A zwitterion herein is a neutral molecule having a positive and a negative electrical charge, at different locations within the molecule. For sake of clarity, zwitterions herein are distinct from dipoles. An amino acid is a containing an amine group, a carboxylic acid group (also designated as "carboxylic group") , and a side- chain that is specific to each amino acid. In the context of the present invention, the term the term amino acid is to be understood as a natural or synthetic amino acid that
comprises one or more amine group and one or more carboxylic group .
Advantageously, one or both of the organic zwitterion and/or the organic compound comprises an onium group. An onium group is a cation derived by the protonation of mononuclear parent hydrides of elements of the periodic table such as elements of the nitrogen group (Group 15) , chalcogens (Group 16), or halogens (Group 17), and similar cations derived by the substitution of hydrogen atoms in the former by other groups, such as organic radicals (also designated as alkyl radicals, such as tetramethylammonium, and further derivatives having polyvalent additions, such as iminium and nitrilium. Examples of onium groups area
quaternary ammonium group (NR.4+, wherein R represents an alkyl rest, present four times in the quaternary ammonium group; the four alkyl rests of said ammonium can be
identical or different) , a sulfonium group (SR.3+, wherein R represents an alkyl rest, present three times in the
sulphonium group; the four alkyl rests of said sulphonium can be identical or different) , or a phosphonium group (PR +, wherein R represents an alkyl rest, present four times in the phosphonium group; the four alkyl rests of said
phosphonium can be identical, or different) .
In a further advantageous embodiment, the quaternary ammonium useful as osmotic agent in the present invention comprises the structure presented as Formula I:
Figure imgf000006_0001
Formula I
wherein R1, R2 and R3 are independently selected from a lower alkyl, branched or linear, preferably a C1-C6 alkyl, and wherein R4 is selected from a carboxyl, an alcohol, hydroxyl or a lower alkyl comprising a carboxyl, an alcohol or hydroxyl .
Advantageously, R1, R2 and R3 are each selected from methyl, ethyl, propyl, butyl, pentyl and hexyl, linear or branched. Preferably, R1, R2 and R3 are methyl.
In an advantageous embodiment, the osmotic agent used in the present invention is selected from the group consisting of glycine betaine, choline, valine, proline and glycine, or a combination thereof.
The osmotic agent according to the invention can be a natural osmolyte, meaning an organic compound produced by a cell which is used for osmotic purposes by the cell. Such compounds include trimethylamine N-oxide,
dimethylsulfoniopropionate, trimethylglycine, sarcosine and the like. The osmotic agent according to the present
invention can be a synthetic osmolyte, such as EDTA, DTPA, BAPTA, or EGTA.
Advantageously, the organic compound comprising more than one carboxylic group, comprises at least two carboxylic groups (-COOH) , at least three carboxylic groups, at least four carboxylic groups, at least five carboxylic groups. The compound comprising more than one carboxylic group may be under the deprotonated form in solution, designated by -COO", the carboxylate anion. All the
carboxylic groups may be deprotonated or the organic
compound is only partially deprotonated (i.e. not every present carboxylic group is deprotonated) . Advantageously, the organic compound comprising more than one carboxylic group further comprises at least one tertiary amine group
(NR' R' ' R' ' ' ) , such as one, two, three or four tertiary amine groups. A tertiary amine is an amine that comprises three hydrocarbon rests, such as alkyl rests that can be unsubstituted, or substituted by alkyls or organic functions such as hydroxyl (-OH) , thiols (-SH) , primary or secondary amines, an ether group (-0-) . More advantageously, the organic compound comprising more than one carboxylic group, such as two, three, four, or five carboxylic groups, further comprises at least one tertiary amine group, such as one, two, three, four or five tertiary amine groups. Example of such compound are the ethylenediaminetetraacetic acid
(abbreviated EDTA, comprising four carboxylic groups and two tertiary amine groups), ethylene glycol tetraacetic acid
(abbreviated EGTA comprising four carboxylic groups and two tertiary amine groups), 1 , 2-bis (o-aminophenoxy) ethane- N, N, N ', N ' -tetraacetic acid) (abbreviated BAPTA, comprising four carboxylic groups and two tertiary amine groups), diethylene triamine pentaacetic acid (abbreviated DTPA comprising five carboxylic groups and three tertiary amine groups) . In the method according to the present invention, EDTA, EGTA, BAPTA and DTPA can be (partially, or totally) deprotonated, or fully protonated (i.e. the carboxylic groups and one or more of the amine groups are protonated) in solution.
In the context of the present invention, the expression "more than one" is to be understood as two, three, four, five, six, seven, eight.
In the context of the present invention, the osmotic agent is an organic compound comprising an onium group or an organic compound comprising more than one carboxylic group.
In an advantageous embodiment, the method of the present invention relates to forward osmosis. This means that, besides the herein described structural definitions, the osmotic agent according to the invention provides a high osmotic pressure difference in forward osmosis and is at least compatible with a forward osmosis membrane. The term "forward osmosis" herein is meant to include direct osmosis, engineered osmosis, manipulated osmosis or pressure retarded osmosis. It is contemplated that, instead of using a forward osmosis membrane, it is also possible to use a reverse osmosis or a nanofiltration membrane in the method of the present invention. Also, the method of the present invention preferably takes place without applying hydraulic pressure. And, the forward osmosis process takes place under any suitable ambient pressure and temperature wherein water is or remains liquid.
According to a preferred embodiment, the osmotic agents of the present invention are sufficiently water soluble, exhibit no or low solute leakage, have a suitably small molecular weight, i.e. with a molecular weight of preferably less than 600 g/mol, more preferably less than 500 g/mol, even more preferably less than 400 g/mol, most preferably 300 g/mol (without taking into account counter- ions if applicable) , are sufficiently repelled by forward osmosis membranes and provide a sufficient pull of water through these membranes. The latter feature implies that the osmotic agent has considerable osmotic power, meaning it creates enough osmotic pressure difference or chemical potential difference. The osmotic agent according to the present invention, either used in the method of extracting water according to the present invention, or comprised by the draw solution according to the invention, is present in such a concentration that an osmotic pressure of at least 0.5 bar is generated by the osmotic agent and/or by a combination of osmotic agents according to the present invention. In further embodiments, this osmotic pressure is at least 1 bar, at least 6 bar, at least 15 bar, at least 20 bar, or at least 24 bar These osmotic pressure values are derived from calculations based on the following Van t Hoff equation: Π = iMRT. Herein is i the Van 't Hoff factor, M is the molarity, R is the gas constant: 0.0821 L atm K-1 mol-1, and T is the thermodynamic, absolute temperature (e.g.
20°C) . It lies well within the capabilities of the skilled person to calculate such osmotic pressure differences for any osmotic agent operating in forward osmosis under the herein mentioned conditions.
In a preferred embodiment, the semi-permeable membrane is a membrane which is suitable for nanofiltration, reverse osmosis or preferably forward osmosis. Even though progress is made in the development of membranes for forward osmosis, the characteristics such membranes should have for them to be useful in forward osmosis processes are known by the skilled person. Typically, such membranes are
hydrophilic, charged, either positively or negatively, and have a determined pore size and specific molecular weight cut-off value.
Advantageously, the osmotic agent is compatible with the semi-permeable membrane used in the process of the present invention. In the context of the present invention, the compatibility with the semi-permeable membrane may be tuned by adjusting e.g. the pH or a concentration of
counter-ions in solution. Compatibility herein is to be construed as that the osmotic agent according to the present invention and the semi-permeable membrane as used are selected such that the osmotic agent is repelled by the membrane and/or excluded by size from passing the membrane. Such a selection can be based on charge differences between the membrane and osmotic agent, molecular weight or size of the agent versus the molecular weight cut-off value or pore size of the membrane as used and/or polarity differences exhibited by the agent and the membrane. The osmotic process that takes place under the influence of the draw solution according to the present invention occurs under suitable conditions, meaning i.a. that the pH of the solution lies between pH 2 and 10, preferably between pH 3 and 8, most preferably between pH 4 and 6. Since the functionality of a charged compound is pH dependent, the pH of the draw solution is preferably
selected such that the osmotic agent is not of the same charge (or of opposite charge) as the semi-permeable
membrane as used. Alternatively, the osmotic agent comprises a charged group which is not of the same charge as the semi¬ permeable membrane as used. Preferably, the osmotic agent comprises a group which is of opposite charge of the semi¬ permeable membrane used.
Preferably, the semi-permeable membrane has a molecular weight cut-off less than 1000 Da, preferably less than 200 Da, more preferably less than 100 Da. Molecular weight cut-off (MWCO) herein is defined as refers to the lowest molecular weight solute (in Da) in which 95% of the solute is retained by the membrane.
In a preferred embodiment, the semi-permeable membrane used in the method of the invention has a pore size of between 0.001 and 0.0001 μπι, preferably between 0.0003 and 0.0005 μπι. Furthermore, the semi-permeable membrane comprises an active layer and/or a support layer.
Preferably, the semi-permeable membrane comprises a
hydrophilic, cellulose comprising active layer, preferably comprising cellulose acetate, cellulose di-acetate,
cellulose tri-acetate, cellulose butyrate, cellulose acetate proprionate and/or mixtures thereof. Also, the semi¬ permeable membrane comprises a support layer or a polyester mesh or a micro-porous support. The semi-permeable membrane can furthermore include or be a Thin Film Composite membrane .
The forward osmosis membrane according to the invention can be used in two orientations, one wherein the draw solution faces the active layer and the feed solution faces the support layer, and vice versa. In the research that led to the invention, it was found that the osmotic agents of the present invention provide an improvement over present day draw solutions in both orientations. However, in a preferred embodiment, the active layer faces the draw side since that orientation provides some improvement over the reverse orientation.
For certain applications it is preferred though to operate in an active layer to feed side modus. This is in particular true for wastewater treatment since under those circumstances membrane fouling is expected to be less problematic .
The aqueous source, i.e. feed solution or the aqueous target from which water is to be extracted, herein is in non-limiting examples, sewage, municipal wastewater, industrial (waste ) water, effluent, leachate, surface water, ground water, brackish water, sea water (or other sources for high quality water or drinking/process water) , bodily fluids, urine, blood and/or an aqueous solution for animal or human consumption. These industrially-derived wastewaters can be from any source. The aqueous solutions for animal or human consumption are, in non-limiting examples, water for human consumption (e.g. recycled water used in space
travel), beverages, fruit juice. An advantage of using forward osmosis according to the method of the present invention is that fruit juices, or other aqueous solutions for human consumption, can be processed without including a heating or cooling step which might impair the quality or affect the organoleptic properties of the aqueous solution for human or animal consumption.
In an advantageous embodiment, the osmotic agent according to the invention is reused after being used as draw solution. Reuse of the osmotic agent is possible due its low solute leakage. Such reuse of the osmotic agent can be effectuated using the diluted draw solution as a starting point, using a reverse osmosis unit, a reconcentration unit, membrane distillation or nanofiltration .
In a non-limiting example, the osmosis membrane used in the method of the present invention can be used in a flat configuration, such as flat sheets, in a spiral
configuration, a hollow fibre membrane or any other suitable configuration .
Another aspect of the present invention relates to a draw solution for extraction of water by forward osmosis, comprising an organic zwitterion and/or an organic compound comprising an onium group, preferably a quaternary ammonium group, sulfonium group or phosphonium group as osmotic agent (s), or an organic compound more than one carboxylic group. The draw solution preferably comprises any one of the more specifically defined osmotic agents as mentioned herein .
An advantage of the osmotic agents according to the present invention is that, when used in draw solutions, they provide an increased osmotic efficiency compared to small inorganic salts, such as NaCl . Another benefit of the present invention is that when using the draw solution in forward osmosis, a lower internal concentration polarization is achieved, resulting in an increased forward osmosis efficiency (e.g. a lower reverse solute flux) . Without being bound by theory, it is currently believed that the osmotic agents according to the present invention are not able, or at least to a lesser extent than existing agents (e.g.
NaCl), to enter the semi-permeable membranes used in forward osmosis. In particular, it is believed that the support layer comprised by such membrane is less accessible to the osmotic agents of the invention.
The present invention thus provides a draw
solution, encompassing organic zwitterions and/or organic compounds comprising an onium group, preferably a quaternary ammonium group, sulfonium group or phosphonium group, or an organic compound comprising more than one carboxylic group, as osmotic agents, with improved characteristics in
comparison to solutions which rely in essence only on NaCl, glucose or sucrose for their osmolytic properties. The draw solution of the present invention has a high osmotic
efficiency, i.e. it is highly, or at least sufficiently, soluble in water and generates a high osmotic pressure at the conditions encountered in forward osmosis.
In another embodiment, the draw solution further comprises one or more biocides to reduce degradation of the osmotic agent. Also, the draw solution and installed setup may be sterile to reduce biodegradation of osmotic agents. The installed setup may also comprise an UV installation to disinfect the draw solution to prevent degradation.
Yet another aspect of the present invention relates to the use of an organic zwitterion and/or an organic compound comprising a quaternary ammonium group as osmotic agent (s) in a solution, preferably in a draw
solution .
This use of the draw solution preferably comprises any one of the more specifically defined osmotic agents as mentioned herein.
The osmotic agent according to the present
invention, or draw solution comprising said agent, can be used in applications wherein the obtainment of bulk amounts of purified water is the main purpose, for example in the treatment of polluted sources such as in non-limiting examples, sewage, municipal wastewater, industrial
(waste ) water, effluent, leachate, surface water, ground water, brackish water, sea water (or other sources for high quality water or drinking/process water) . Conversely, it can be used in applications wherein the obtainment of a more concentrated feed solution is the main purpose, i.e. to concentrate liquids. Such more concentrated liquids
comprise, in a non-limiting example, beverages for animal or human consumption. Also, concentrating sewage in the
production of biogas or any other aqueous solution
containing a product that needs to be recovered or reused, is encompassed by the present invention.
As stated above, in forward osmosis, solutes can diffuse in two directions: from the feed solution into the draw solution (i.e. forward diffusion) and simultaneously from the draw solution into the feed solution (i.e. reverse diffusion) . Due to internal concentration polarization (i.e. the build-up of solutes within the osmosis membrane) , non¬ linear solute flux behaviour is observed (see Figure 1) .
This internal concentration polarization results in a lower osmotic driving force.
In Figure 1, the higher concentration of solute in the draw solution, CD, creates a chemical potential gradient that drives both the forward water flux Jw, and the solute flux Js. For the draw solute to permeate across the
asymmetric membrane into the feed solution, where its concentration CF is negligible, it must be transported across the support layer of thickness tA. C±s and C±A represent the draw solute concentrations on the support layer side and active layer side of the support layer-active layer interface, respectively.
By using a U-tube set-up, such as described in the experimental section, it is possible to investigate and characterize fluxes of solutes and water in forward osmosis processes. Experimentally, the solute flux can be calculated using Equation I:
_ 1 A(cV)
(Equation I)
~ A At
Herein, A is the area of the active layer of the membrane and Δ ( cV) the total solute amount that crosses the membrane during the interval At.
This set-up also allows calculation of the water flux due to increase of the water volume in a measuring tube. The volumetric flow rate of water can be calculated from the water volume and the time interval. The flux of water in forward osmosis can be calculated experimentally using Equation II:
T 1 AV
JW = (Equation II)
Herein, Jw is the water flux, A is the area of the active layer of the membrane and AV the total amount of water that crosses the membrane during the interval At.
Both fluxes, Js and Jw, allow the study of the efficiency of the forward osmosis process: a high water flux is required while the solute leakage is to remain as low as possible.
Osmotic agents according to the appended claims have been found to exhibit both an improvement in the flux of water from the feed solution to the draw solution (as calculated by Equation II), while the reverse solute flux of the osmotic agent is minimized (as calculated by Equation I) .
In a broader respect, the invention relates to a method of extracting water from an aqueous source by
osmosis, comprising the application of an osmotic pressure difference over a semi-permeable membrane by providing the aqueous source on one side of the membrane and a draw solution comprising an osmotic agent on the other side of the membrane, wherein the osmotic agent is an organic zwitterion and/or an organic compound comprising a
positively charged group, preferably a saturated positively charged group, such as an onium group preferably selected from a quaternary ammonium group, sulfonium group or
phosphonium group. In this broader respect, the invention also relates to a draw solution comprising an organic zwitterion and/or an organic compound comprising a
positively charged group, preferably a saturated positively charged group, such as an onium group preferably selected from a quaternary ammonium group, sulfonium group or
phosphonium group.
The organic zwitterion in this broader respect, is selected from the group consisting of a betaine, a betaine comprising compound and an amino acid.
The quaternary onium group, in this broader respect, comprises the structure according to formula II:
Figure imgf000017_0001
wherein R5 is selected from N and P, preferably N" S + and P ,
R1, R2 and R3 are independently selected from H, a lower alkyl, branched or linear, preferably a C1-C6 alkyl, or aryl and
wherein R4 is selected from a carboxyl, an alcohol, hydroxyl, oxygen or a lower alkyl comprising a carboxyl, an alcohol, hydroxyl or oxygen.
Figures
Figure 1 schematically depicts draw solute leakage into the feed solution using a forward osmosis membrane. FS = Feed Solution, AL = Active Layer, SL = Support Layer, DS = Draw Solution, Jw = Water flux, Js = Solute flux, CD =
Concentration of solute in draw solution, Cis = the draw solute concentration on the support layer side of the support layer-active layer interface, C±A = the draw solute concentration on the active layer side of the support layer- active layer interface, CF = Concentration of solute in feed solution, tA = thickness of active layer, tS = thickness of support layer.
Figures 2a and b show results obtained from experiments using various draw solutions comprising
different osmotic agents. In Figure 2a, water flux and solute flux of glycine betaine (GB) is shown in comparison to NaCl, glucose and sucrose. Membrane orientation: feed solution facing the active layer (AL to FS) . In Figure 2b, ratio of glycine betaine (GB) , NaCl, glucose and sucrose as measured during the experiment is shown (AL to FS) .
Figures 3a and b show results obtained from experiments using various draw solutions comprising
different osmotic agents. In Figure 3a, water and solute flux of glycine betaine (GB) is shown and compared to NaCl, glucose and sucrose. Membrane orientation: draw solution facing the active layer (AL to DS) . In Figure 3b, the ratio of glycine betaine (GB) , NaCl, glucose and sucrose as measured during the experiment is shown (AL to DS) . Figure 4 shows the efficiency of amino acids and derivatives as forward osmosis draw solutions in water and solute fluxes.
Figure 5 shows the solute flux/water flux ration Js/Jw of amino acids and derivatives as forward osmosis draw solutions .
EXAMPLES
A standardized, laboratory-scale U-tube configuration was used to determine the forward osmosis behaviour of various draw solutions and selected feed solutions over a vertically-positioned forward osmosis membrane. The U-tube configuration further comprised two pumps to allow continuous homogeneity of the draw and feed solutions and a measuring tube mounted on the draw side.
An asymmetric cellulose triacetate based- (CTA) forward osmosis-type membrane was used [the Expedition-type or HydroWell-type, Hydration Technology Innovations, Albany, OR, USA] . The forward osmosis membrane is hydrophilic with a thickness of less than 50 μπι. It comprises a dense,
selective active layer and a porous support layer consisting of an embedded polyester mesh which provides mechanical support. Membranes were used in one of two different
orientations: active layer facing feed side (AL to FS) or active layer facing draw side (AL to DS) .
Forward osmosis experiments were carried out in the following experimental set-up.
The membrane, with an active area of 0.011 m2 was placed in a membrane holder. A constant mixing rate of 5.5 L/min was applied to both the feed side and draw side to keep the solutions homogenous. The water flux (Jw) was determined by the volume increase within the measuring tube on the draw side, using Equation III. There is a dilution of the draw solution over time due to an increase of water and also decrease of solutes (solute migration towards the feed side) . The solute flux (Js) moving towards the feed side was determined by means of a conductivity meter (feed solution was deionised water) , osmometer measurements or by using COD kit (Chemical Oxygen Demand) kits. All experiments were carried out for 7 h and the temperature, unless otherwise stated, was normalised to 20 °C. Measurements were taken from the feed solution at various time intervals. The water height in the measuring tube was recorded and a 5 ml or 25 ml sample (depending on the analysis) was collected from the feed side. For each time interval, measurements were
performed using an appropriate method. The solute flux was calculated using Equation II.
For each series of experiments, a new forward osmosis membrane was used after soaking it for 30 minutes in DI water. After installing the membrane with the selected orientation, both compartments of the U-tube were quickly filled (first 3L feed solution at the feed side and then 3L draw solution at the draw side) to prevent hydraulic
pressure differences over the membrane and drying of the membrane .
EXAMPLE 1 - Active layer facing feed side (AL to FS) Deionised (DI) water was used as feed solution, either to assess the osmotic performance of various different solutes or for reference purposes in comparison to water extraction from sewage. The fluxes of different draw
solutions were tested in the forward osmosis system using the following analytical grade solutes: NaCl, glycine betaine, sucrose and glucose. All solutions were prepared in DI water. For all experiments, unless otherwise stated, concentrations relating to an osmotic pressure of
approximately 24 bar were used. Figure 2a shows the results wherein water and solute flux of an organic osmolyte, glycine betaine, is compared to different draw solutions of NaCl, glucose and sucrose. Figure 2b demonstrates the relevant ratios for each draw solution.
From the results shown in Figure 2a, it can be concluded that with the forward osmosis membrane active layer facing the feed side, glycine betaine produced the highest water flux 4,5 LMH (Litre per square meter per hour, L/m2.h) by comparison with the electrolyte NaCl solution and as well the higher molecular weight substances: glucose and sucrose solution. The solute leakage of glycine betaine is 0.1 g/1 per hour (GMH, grams/m2.h) compared to NaCl, glucose and sucrose which give 3.7 GMH, 2.1 GMH, and 1.1 GMH
respectively. Figure 2b shows that glycine betaine as draw solution gives the lowest ratio of 0.02 gram solute leakage per litre water extracted (g/1), while the highest ratio is observed with NaCl as draw solution, 0.8 g/1.
These results indicate that with the forward osmosis membrane active layer facing the feed solution, glycine betaine exhibits the best performance among the other draw solutions studied with regards to its high water flux and low solute leakage.
EXAMPLE 2 - Active layer facing draw side (AL to DS) Figure 3a shows the water and solute flux of glycine betaine with comparison to the different draw solutions NaCl, glucose and sucrose. Figure 3b demonstrates the relevant ratios of each draw solution.
From the results shown in Figure 3a it was
concluded that with the forward osmosis membrane active layer facing draw side, glycine betaine produced the highest water flux of 7.3 LMH. NaCl, glucose and sucrose solution all gave similar water fluxes of around 5.4 LMH. The solute leakage of glycine betaine has the lowest solute leakage 0.02 GMH (according to COD measurements), while NaCl, glucose, and sucrose gave 4.2 GMH, 2 GMH, and 1.7 GMH respectively. From Figure 3b, the glycine betaine as draw solution gives the lowest ratio 0.02 g/1, while the highest ratio is observed with NaCl as draw solution, 0.8 g/1.
These results indicate that with the forward osmosis membrane active layer facing the draw side, glycine betaine has the best performance among the other draw solutions studied with regards to its high water flux and extremely low solute leakage.
From the series of experiments (Figure 2 and
Figure 3) it can be seen that glycine betaine has the highest water flux and lowest solute leakage for both membrane orientations in comparison to the ionic solution
NaCl or the other higher molecular weight substances glucose and sucrose.
EXAMPLE 3 - Osmotic extraction of water from sewage Settled sewage was used as feed in combination with glycine betaine as draw solution in the experimental U-tube set-up. The membrane orientation was such that the active layer faced the draw side. The osmotic pressure generated by glycine betaine as used in the experiments was 24 bar. DI was used as reference feed solution.
Again, samples were taken at regular intervals over a 7 hour time period.
The experiments revealed that glycine betaine as an osmotic agent in a draw solution behaved in a comparable manner with settled sewage as with deionised water. Results showed that water flux from sewage as feed is slightly lower (6.00 LMH) than DI water (7.30 LMH) . Solute flux, measured by COD for sewage as feed, is slightly higher than DI water (0.35 GMH vs. 0.14 GMH, respectively) . These results clearly demonstrate that extracting water from sewage is possible under the experimental conditions. It is contemplated that the slightly lower water fluxes and higher solute leakage is probably due to the more complex nature and higher osmotic pressure of sewage as feed solution compared to deionised water. This results in fouling or external concentration polarization of the membrane .
EXAMPLE 4 - measurements of solute flux of amino acids and derivaties thereof
Five analytical methods were used to measure the solute flux of the amino acids and amino acid derivatives to determine the most suitable method: 1) COD (chemical oxygen demand measurement) 2) measuring the osmotic pressure via an
Osmometer, 3) UV spectroscopy, 4) Titration, 5) TOC (total organic carbon measurement) .
Based on the results of both COD and the osmometer, the solute fluxes and therefore the ratios, were found to be very low. To check these results, calibration curves were made. The measured COD values were around 23 times lower than the theoretical values. Therefore the solute fluxes were underestimated. COD was found to be inaccurate in measuring the low variations of concentrations of the feed side . The measurement of osmotic pressure with an osmometer was found to be similar to the calibration curve, but not accurate enough.
UV spectroscopy is not suitable to measure the low
concentrations of the feed side accurately. Titration was used for EDTA and showed a strong correlation between the theoretical and experimental EDTA
concentrations. The titration can accurately measure low concentrations of EDTA in deionised water.
TOC measures the concentration of all amino acids and amino acid derivatives within the required concentration range. TOC analysis, was found to be the most reliable and accurate analysis method and was therefore used to measure all solute fluxes .
The flux overview is represented in figures 4 and 5.

Claims

Claims
1. Method of extracting water from an aqueous source by forward osmosis, comprising the application of an osmotic pressure difference over a semi-permeable membrane by providing the aqueous source on one side of the membrane and a draw solution comprising an osmotic agent on the other side of the membrane, wherein the osmotic agent is an organic zwitterion and/or an organic compound comprising an onium group, or more than one carboxylic group.
2. Method according to claim 1, wherein the organic zwitterion and/or the organic compound comprises an onium group selected from the group a quaternary ammonium group, a sulfonium group, a phosphonium group.
3. Method according to claim 1, wherein the organic zwitterion is selected from the group consisting of a betaine, a betaine comprising compound and an amino acid.
4. Method according to claim 1, wherein the onium group is a quaternary ammonium has a structure according to Formula I :
Figure imgf000025_0001
Formula I wherein R1, R2 and R3 are independently selected from a lower alkyl, branched or linear, preferably a C1-C6 alkyl, and wherein R4 is selected from a carboxyl, an alcohol, hydroxyl or a lower alkyl comprising a carboxyl, an alcohol or hydroxyl .
5. Method according to any of the claims 1-4, wherein the osmotic agent is selected from the group
consisting of betaine, glycine betaine, choline, valine, proline and glycine, or a combination thereof.
6. Method according to claim 1, wherein the organic compound comprising more than one carboxylic group further comprises at least one tertiary amine groups.
7. Method according to claim 1, wherein the osmotic agent is an organic compound comprising more than one carboxylic group and two tertiary amine groups.
8. Method according to any of the claims 1-7, wherein the semi-permeable membrane is suitable for forward osmosis, reverse osmosis, nanofiltration or ultrafiltration
9. Method according to any of the claims 1-8, wherein the osmotic agent is compatible with the semi¬ permeable membrane.
10. Method according to any of the claims 1-9, wherein the semi-permeable membrane has a molecular weight cut-off less than 1000 Da, preferably less than 200 Da, more preferably less than 100 Da.
11. Method according to any of the claims 1-10, wherein the semi-permeable membrane has a pore size of between 0.01 and 0.0001 μπι, preferably between 0.001 and 0.0001 μπι , more preferably between 0.0003 and 0.0005 μπι.
12. Method according to any of the claims 1-11, wherein the semi-permeable membrane comprises an active layer and/or a support layer.
13. Method according to any of the claims 1-12, wherein the semi-permeable membrane comprises a hydrophilic, cellulose comprising active layer, preferably comprising cellulose acetate, cellulose di-acetate, cellulose tri¬ acetate, cellulose butyrate, cellulose acetate proprionate and/or mixtures thereof.
14. Method according to any of the claims 1-13, wherein the semi-permeable membrane comprises a support layer or a polyester mesh or a micro-porous support.
15. Method according to any of the claims 1-14, wherein the osmotic agent is present in such a concentration that an osmotic pressure of at least 1 bar, at least 6 bar, at least 15 bar, preferably at least 20 bar, more preferably at least 24 bar is generated over the membrane.
16. Method according to any of the claims 1-15, wherein the aqueous source is sewage, wastewater, industrial water, effluent, and/or an aqueous solution for animal or human consumption.
17. Draw solution for forward osmotic extraction of water, comprising an organic zwitterion and/or an organic compound comprising a quaternary ammonium group, a sulfonium group, a phosphonium group, or more than one carboxylic group .
18. Use of an organic zwitterion and/or an organic compound comprising a a quaternary ammonium group, sulfonium group phosphonium group, or more than one carboxylic group, as an osmotic agent in a solution, preferably in a draw solution .
PCT/NL2012/050612 2011-09-05 2012-09-05 Solution comprising an osmotic agent and method of extracting water using said solution WO2013036111A1 (en)

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US11498853B2 (en) 2010-02-10 2022-11-15 Queen's University At Kingston Water with switchable ionic strength
US10377647B2 (en) 2010-12-15 2019-08-13 Queen's University at Kingson Systems and methods for use of water with switchable ionic strength
FR3004965A1 (en) * 2013-04-30 2014-10-31 Ederna DEVICE AND METHOD FOR EXTRACTING BY OSMOTIC EVAPORATION
WO2014177555A1 (en) * 2013-04-30 2014-11-06 Ederna Device and method for extraction by means of osmotic evaporation
US9399194B2 (en) 2014-07-16 2016-07-26 Battelle Energy Alliance, Llc Methods for treating a liquid using draw solutions
US10016725B2 (en) * 2016-08-30 2018-07-10 Industrial Technology Research Institute Ionic liquid for forward osmosis process and forward osmosis process
WO2018173330A1 (en) * 2017-03-23 2018-09-27 Kabushiki Kaisha Toshiba Drawing agent for forward osmosis and pressure retarded osmosis and a system using the same
JP2018158301A (en) * 2017-03-23 2018-10-11 株式会社東芝 Water treatment system and work medium
WO2018198918A1 (en) * 2017-04-28 2018-11-01 国立大学法人神戸大学 Draw solution, and power generating device and water treatment device using same
JPWO2020045525A1 (en) * 2018-08-31 2021-06-03 株式会社日本触媒 Draw solute and water treatment equipment
WO2020045525A1 (en) * 2018-08-31 2020-03-05 株式会社日本触媒 Draw solute and water treatment equipment
JP7162308B2 (en) 2018-08-31 2022-10-28 株式会社日本触媒 Draw solute and water treatment equipment
US11639299B2 (en) 2018-08-31 2023-05-02 Nippon Shokubai Co., Ltd. Draw solute and water treatment equipment
EP3978103A4 (en) * 2019-05-31 2022-07-20 Asahi Kasei Kabushiki Kaisha Raw material liquid concentration system
US11502322B1 (en) 2022-05-09 2022-11-15 Rahul S Nana Reverse electrodialysis cell with heat pump
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