WO2000029337A1

WO2000029337A1 - A system and a method for removing ions from aqueous liquid streams

Info

Publication number: WO2000029337A1
Application number: PCT/NL1999/000690
Authority: WO
Inventors: David Nicolaas Reinhoudt; Johannes Franciscus Joseph Engbersen; Frank Gerard Antoon Peters
Original assignee: PRIVA HORTIMATION BV
Current assignee: PRIVA HORTIMATION BV
Priority date: 1998-11-13
Filing date: 1999-11-11
Publication date: 2000-05-25
Anticipated expiration: 2001-05-13
Also published as: NL1010549C2; AU1190700A

Abstract

A system for selectively removing ions, especially metal ions, from aqueous liquid streams, said system comprising: an ionophore, which selectively binds to ions to be removed, being present in the liquid stream so as to yield an ion-ionophore complex, a hydrophobic solvent for said ionophore, said solvent being essentially immiscible with the aqueous liquid stream, wherein the ion-ionophore complex essentially is dissolvable in the hydrophobic solvent only.

Description

A system and a method for removing ions from aqueous liquid streams

The present invention relates to a system for removing selectively ions, both undesired and valuable, from aqueous liquid streams, especially for removing metal ions, for example alkali metal ions or other cations, for example sodium ions from sprinkling water, to a method for removing such ions from aqueous liquid streams, as well as to a system of apparatus for removing such ions from aqueous liquid streams . Water used in glasshouse horticulture for producing sprinkling water usually contains high amounts of sodium. Since the plants hardly take in any sodium, a lethal concentration of sodium will easily be obtained if drain water is recirculated. To this end, draining off water is necessary. The environment is polluted by large amounts of unused fertilizers being drained off simultaneously with the water. Recycling of drain water saves the environment (by discharging less fertilizers) and also means a saving for the gardener with respect to fertilizer costs. For, the gardener can rely on adding less fertilizer to the drain water, as it still contains non-used fertilizers. However, because of rising costs for water and in some parts of the world existing a shortage of water, there is an increasing interest with regard to excessive recycling of water, including the fer- tilizers contained therein.

To render said recycling possible and/or to minimize draining off water, Na⁺ should be removed selectively.

The object of the present invention is to provide a chemical system for removing valuable or undesired ions, for example in the form of undesired impurities, selectively from aqueous liquid streams.

According to a first aspect, the present invention provides a system according to claim 1.

Each year the Dutch glasshouse horticulture uses on an average 7500 cubic meters sprinkling water per hectare

(usually 2/3 rain water, 1/3 tap-water) . Since the total area of glasshouse horticulture in the Netherlands amounts to about 9600 hectare, this means a total annual water consumption of 72 million cubic meters . In the most important horticulture areas in the Netherlands, the tap-water contains about 1-3 mol sodium, Na⁺ per cubic meter. The alkali metal ion Na⁺ is no fertilizer and, in higher concentrations, it is detrimentous for the plants (phytotoxic) . Since the plants take in hardly any Na⁺, when using drain water a lethal amount of Na⁺ will soon be obtained. The maximum permissible concen- tration of Na⁺ in the root environment is about 5-8 mol per cubic meter, depending on the kind of plants. To this end, discharging drain water is necessary. By draining off said water, the environment is polluted with waste water being contaminated with phytotoxic Na⁺, fertilizers as well as resi- dues of plant protective agents . Recycling of drain water not only relieves the environment, but also provides savings with respect to consumption and costs of water and fertilizers (characteristic values: 30% water savings and 50% fertilizer savings) . When using the system according to the present invention, both undesired and valuable ions, especially sodium, can be removed selectively with respect to the valuable fertilizers being present in the sprinkling water as well. In addition, the aqueous liquid stream, the so-called water phase, does not need or needs hardly any pre-treatment or post-treatment, no high pressure is required, as, for example, in case of reverse osmosis, and consumption of energy and chemicals is low.

Further details and characteristics of the "iono- phore", also known as "carrier" or "extractant" are especially mentioned in claims 2-6.

The inventors have demonstrated that the present ionophores can bind very selectively to undesired or valuable ions, such that a complex comprising these ions, for example sodium ions, is obtained. By treatment with acid the complex metal ion is released (the binding is reversible) .

The solvent for the ionophore is preferably chosen from the group as mentioned in claim 12. The system preferably further comprises a stripper according to any of claims 14-17.

If, by incorporating a metal ion from the liquid, the complex is obtained, said complex diffuses to the other side of a liquid membrane containing the ionophore as well as the solvent. At this side another liquid phase being again immiscible and comprising a stripper, the so-called stripper phase, may be present. At this point the complex is broken up and the sodium ion is contained in the stripper phase . The ionophore, which again can bind to, for example, a sodium ion, diffuses back to the other side where the water to be treated is present. The ionophore in the liquid membrane phase therefore is essentially not used, but only serves as an ion carrier in this reversible process. When using the monoacid derivative of the calix(4)- tetra ester as an ionophore, one of the ester functions is transferred into the carbon acid. By deprotonating said carbon acid, a negatively charged carboxylate group is obtained, which compensates for the positive charge of the Na⁺-com- plexing. Co-transport of an anion is not necessary now if the sodium is extracted from the water phase. Therefore, the monoacid derivative of the calix(4) tetra ester is capable to complex the sodium (Na⁺) by exchanging with the proton (H⁺) , as shown in Figure 2. The sodium can be decomplexed by con- tacting it with an acid (H⁺) . If use is made of the calix(4)- tetra ester (i.e., without the monoacid) then at the same time co-transport of an ion should take place, because of the electroneutrality: (Na⁺:X^")°-ionophore) .

To assure that the liquid membrane phase (in which the ionophore is present) , the water phase as well as the stripper phase remain separated from each other, use can be made of a solid carrier material, for example a porous solid membrane, for example having the form of a hollow fibre membrane. In the pores of this, preferably hydrophobic, carrier material then the liquid membrane phase is absorbed. The carrier material has in this case the function of keeping the liquid membrane phase intact between the water phase and the stripper phase, but does not provide the chemical separation. Because of the direct contact of the organic phase with the aqueous phase, high losses of solvent can be obtained by known extraction techniques, like packed columns or mixer-settlers, because of direct losses of droplets into the organic phase. In horticulture this is not permissible.

According to a further aspect of the present invention, use is made of the system according to claim 21, for use in liquid membrane extraction or solvent extraction, for example : - bulk liquid membrane extraction, emulsion liquid membrane extraction, immobilized liquid membrane extraction, emulsion pertraction.

According to another aspect of the present invent- ion, a method is provided for removing undesired or valuable ions from aqueous liquid streams according to claim 22.

Figure 1 shows the principle of emulsion pertraction.

An emulsion consisting of the liquid membrane phase (M) with stripper phase droplets (S) flows at the inside of a hydrophobic hollow fibre membrane (HVM) containing pores (P) . At the outside of the fibres the water phase flows, from which sodium is to be removed. The pores of said hollow fibre membrane are filled with the organic membrane phase because the fibre membrane is hydrophobic. The hydrophobicity of the fibre membrane as well as the diameter of the pores assure that no stripper phase droplets will contact the aqueous phase .

Such a system is possible as well if the emulsion flows at the outside of the fibre and the water phase flows at the inside.

With the emulsion pertraction process according to the present invention the aqueous phase is separated from the emulsion phase by a hydrophobic hollow fibre membrane. In the emulsion the liquid membrane phase (organic extracting agent) is the continuous phase, and the stripper liquid is the disperse phase. The pores of the hydrophobic microporous membrane are filled with the liquid membrane phase. The component to be removed is bound from the water phase by the liquid membrane phase being present in the pores of the fibre membrane. At the other side of the fibre membrane, the liquid membrane phase is regenerated by the stripper phase dispersed in the liquid membrane phase. Concentration of, for example, sodium ions takes place in the stripper phase. The equilibrium of the extraction reaction is shifted directly by the stripper reaction.

With respect to the classical solvent extraction, the liquid membrane extraction, especially emulsion pertraction, according to the present invention presents the following advantages : - The water phase from which extraction is to take place as well as the organic phase are not mixed directly: there is in principle no formation of emulsion between these phases, there is in principle no secondary loss of extraction agent, there are no long settling times, no stir energy is necessary. The stripper phase containing contaminations that cannot be removed from the organic phase does not end up in the water phase, neither will the stripper phase be contaminated with water not being separated from the organic phase . - The mass flows of the water phase as well as the emulsion phase can be controlled independently: therefore, an additional freedom of movement with respect to the process is obtained, and an optimal contamination/concentration ratio can be obtained. - Extraction and stripping steps take place simultaneously. The extraction agent containing the contaminations is stripped directly.

Hollow fibre membrane modules have a high surface of exchange as well as a good substance exchange: this means that compact apparatus can be used.

Because of the modulary character of the process upscaling and downscaling is easily performed.

According to another aspect of the present invention, a system of apparatus according to claim 25 is provided. The invention will now be described by means of the theoretical background, the description and experiments hereafter, with reference to the drawings.

Theoretical background of the invention

A reproduction of the principle of liquid membrane extraction is shown in Figure 2.

Three phases are important in the chemical system: the supplying water phase (the water to be treated) - the liquid membrane phase (comprising the ionophore and its solvent) the stripper phase.

Water in which for example sodium (Na⁺) is present as well as fertilizers is contacted with the liquid membrane. These phases are immiscible with each other because the membrane phase is an organic (hydrophobic) liquid phase. In the liquid membrane phase the ionophore is dissolved, which ionophore selectively binds with, for example, only sodium ions so as to obtain a sodium-ionophore complex. The complex obtained is only soluble in the liquid membrane phase. Other ions (for example fertilizers) are not soluble in the liquid membrane phase.

If the complex is obtained on the interface between the supplying water phase and the membrame phase, said com- plex diffuses to the other side of the liquid membrane. At this side there is another, again immiscible, liquid phase, namely the stripper phase. By, for example, protonation of the ionophore the sodium ionophore-complex is broken up and the sodium ion disappears into the stripper phase. The iono- phore is again capable of binding another sodium ion and diffuses back to the other side where the water to be treated is present . The ionophore in the liquid membrane phase therefore is not consumed but only serves as a kind of carrier in this reversible process. To assure that the electroneutrality (as many positive (+) as negative (-) ions) is preserved, together with the transport of the Na⁺ a negatively charged ion should be co-transported or the Na⁺ should be exchanged with a positive ion (countertransport) . In Figure 2 the counter- transport mechanism is shown: the Na⁺ is exchanged with a proton (H⁺) . Countertransport of sodium ions with protons imparts the driving force to the extraction process.

Figure 3 shows schematically both co-transport and countertransport for Na⁺ by means of a calix (4) tetra ester and the monoacid derivative of the calix (4) tetra ester respectively as ionophores . In case the stripper phase has much more protons than the water phase (which means that it has a lower pH) then the driving force remains high and the sodium can be removed completely.

Since the water phase and the stripper phase are kept separated from each other by means of the liquid membrane, the sodium can be concentrated in the stripper phase. To assure that the liquid membrane phase is kept intact between the water phase and the stripper phase, use can be made of a porous solid carrier material. In the pores of this hydrophobic carrier material the liquid membrane phase is absorbed. The carrier material usually is a solid membrane. This solid membrane only takes care for keeping the liquid membrane phase between the water phase and the stripper phase intact.

Experiments

Organic solvents tested for the ionophores: calix (4) arene tetra ester and cali (4) arene-monoacid triester

The experiments comprised research for proper solvents for the ionophores. A summary of said solvents is shown in Table 1.

Table 1. Selection of the solvents tested

■ M-Hept = 5-methyl-5-heptanon • MIK = methyl-iβobutyl-keton

Some of these solvents are tested regarding their suitability to be used as a solvent in extraction experiments.

In first instance, 5-methyl-3-heptanon (M-hept) seemed to be a suitable solvent and also yielded good results during extraction experiments. Using a 0.05 M cali (4) tetra ester solution in M-hept, 83% sodium and 3% potassium were extracted from a 0.05 M sodium/potassium picrate solution. The selectivity was 22 (Na/K) . The solubility of M-hept in water, however, is about 2 percent by weight.

Extraction experiments were then performed with the solvents limonene, anisole (methoxy benzene) , mesitylene (1, 3 , 5-trimethyl benzene) and n-hexyl ether. The solubility of these solvents in water ranges between 108 and 13.8 milligrams per litre.

Solubility tests

A number of solvents were used in the solubility tests of the both ionophores. Generally, the solubility of the tetra ester was better than the solubility of the monoacid in the several solvents. The results are shown in Table 2.

Table 2. Solubility of carriers in solvents

Extraction and selection determinations The most important information regarding the extraction experiments are shown in Tables 3-5. Table 3 and 4 show the sodium and potassium extractions being measured as well as the selectivity calculated therefrom regarding the ionophores .

Performing methods of the experiments The experiments were performed as follows. Five millilitres of each chosen organic solvent, optionally with the carrier dissolved therein, were shaken intensively with 5 millilitres drain water for about 6 to 7 hours. In this drain water sodium and potassium ions were dissolved in equivalent amounts (0.05 M or 0.01 M) . As co-transport anions picrate, nitrate or perchlorate were used. Extraction experiments were performed as well by using real drain water.

After intensive shaking the layers were separated from each other and a small sample was drawm from the water layer. By means of atomic absorption spectroscopy (AAS) the sodium and potassium concentrations in said sample were determined. From this the selectivity was then calculated.

Tables 10-21 show a summary of all experiments, wherein: carrier = ionophore cone c = concentration ionophore in the solvent cone m = concentration metal ion in water phase added cone or mg = added additionally to the water phase (beside the salt mentioned in the table)

AAS-measurement and calculation

By means of the AAS technique the concentrations of sodium and potassium in the water layer were determined. The performance of the measurements and the calculation of the results are described herein below. Regarding the AAS measurement a standard calibration factor was used. This calibration factor was determined by measuring five solutions of which the metal concentrations were known. These concentrations were 0, 0.5, 1.5, 2.0 ppm metal (ppm = parts per million = milligrams per litre) . To prevent that other metals in the solutions to be examined would interfere during the measurement, all solutions to be examined contained 2000 ppm cesium chloride.

After plotting the measured values in a graph, a straight line was obtained, of which the interception with the axis as well as the coefficient of direction were determined. In cases where the concentration of the metal to be determined was between 0 and 2.0 ppm, the concentration can be calculated by means of the interception with the axis and the coefficient of direction.

The following formula was used for calculating the concentrations of the samples.

ext_saaple-interc . x deg. dil . co . dir.

Conc_sample [M] =

In said formula a number of variables are mentioned which will be briefly described hereafter. ^eχt_Sapi_e i^{s tne} measured value of the sample deg. dil. is the correction factor for the degree of dilution interc. is the interception with the axis co. dir. is the coefficent of direction M_metai i^{s tne} tnolar weight of the metal to be measured.

To obtain an impression of the degree of extraction, this is expressed in terms of percentage. This was calculated by means of the following formula:

( conc_blank - conc_sample)

% extraction = conc_blaΩ]c

The conc_blank is the concentration of the sodium and potassium respectively in a sample not extracted and used as a reference. The selectivity can now easily be calculated with the following formula:

N&blank ^X * H^aextractio__

^N^blaak ^Kblank

The AAS measurements were performed by using a spectral light suitable for measuring both sodium and potassium. The wavelengths which were used are 589.0 nanometers for sodium and 766.5 nanometers for potassium.

Extractions by using calix (4) tetra ester The results of the extractions when using calex(4) tetra ester as an ionophore in several organic solvents, wherein a ratio of 1:1 of sodium and potassium ions is present in the supplying phase, are shown in Table 3.

Table 3. Summary of the co-transport of the most important extraction data when using calex (4) tetra ester as an ionophore

Extractions when using calix (4) triester monoacid derivative

In this derivative one of the ester functions has been hydrolysed into the carbon acid. By deprotonating said acid the ionophore obtains a negative charge (calix (4) triester monocarboxylate) . To compensate for this negative charge the ionophore absorbs a sodium ion so as to obtain again a neutral charge (no charge) .

Table 4 shows the data of the extraction experiments performed when using 0.05 M calix (4) monocarboxylate as a carrier. Unless otherwise stated, N0₃ ^" was used as an anion in the supplying mixture .

From experiments it is shown that the deprotonation of the monoacid when using Ca(OH)₂ has a positive influence on the sodium extraction. The sodium extraction obtained is about 60%, whereas the amount of potassium extracted remains below 3%. This yields a good sodium selectivity for calix(4)- monocarboxylate . This it is remarkable that said monocarboxylate has a better extraction and selectivity, when extracting from a Na⁺/K⁺-supply mixture containing nitrate as an anion, in contrast with the calix (4) tetra ester.

Table 4. Summary of the extraction data for calix (4) triester monocarboxylate

² Extraction was performed after stripping

It is preferred that the calix (4) monoacid is deprotonated to obtain a good extraction. This aspect is surveyed somewhat further by performing a deprotonation of two bases. Firstly, several concentrations of NaOH were used to deprotonate the calix (4) monoacid. However, from experiments when using artificial drain water it is shown that this yielded a precipitate.

Secondly, Ca(OH)₂ was examined. From extraction experiments, during which an equivalent amount of OH^" with regard to the calix (4) monoacid was added, a sodium extraction of 75-80% could be determinated. The potassium extraction varies between 2 and 4%. Since a precipitate was generated, experiments comprising reduced concentrations of Ca(OH)₂ were performed as well. No precipitate was generated when adding 0.5 equivalents OH^" to artificial drain water. The sodium extractions and potassium extraction as measured during said experiments were 62-65% in the case of sodium and 1-3% in the case of potassium respectively. The selectivity α.(Na/K) as calculated varies between 21 and 39.

Extractions when using drain water The acidity (pH) of the drain water was about 11.5 before extraction and about 7 after extraction. A solution of 0.05 M calix (4) triester monoacid in limonene was used for performing the experiments. As a blank, drain water shaken with limonene would be used. Since, after shaking with limonene, a white turbidity was visible at the interface of the two phases, the starting concentration of the non-shaken drain water was determined as well . The reduction determined between the non-shaken and the shaken drain water respectively is, with respect to sodium, about 8% whereas, with respect to potassium reduction, it is about 10%. It is not probable that the reduction of sodium and potassium in the drain water is caused by absorption into the limonene phase, since this phase does not contain ionophore, but this reduction must be caused by the generation of precipitation. The values for the blank measurements shown in table 5 therefore should not be interpreted as the extraction results for a blank sample, but these values are used indeed for the correction of the percentage values of the extractions when using an ionophore.

Table 5. Summary of the extraction data when using drain water

From Table 5 it shows that the calix (4) triester monocarboxylate, when dissolved in limonene, also is a useful agent when using real drain water.

Stripping experiments

By means of a sulphuric acid solution it was possible to remove sodium from the calix (4) tetra ester monocarboxylate. To try this out, sulphuric acid solutions were prepared as follows: 0.1 M, 0.05 M as well as 0.01 M in demineralized water. Performance of these experiments was identical to the extraction experiments. The solution of cali (4) monocarboxylate used before during the extraction experiments was separated from the drain water. Then the monocarboxylate solution (about 4 millilitres) was shaken intensively with 5 millilitres sulphuric acid solution during 4 to 5 hours. After separation of the layers the concentration of sodium and potassium in the sulphuric acid layer was determined. Measuring data of the stripping experiments are shown in Table 6 below. Table 6. Measuring data of stripping experiments

100% stripping was obtained when using the monocarboxylate, with 0.1 M and 0.05 M H₂S0₄. When using a concentration of 0.01 M, sodium was almost completely washed out of the monocarboxylate, whereas no precipitate was obtained. The stripped monocarboxylate was used again for an extraction experiment to examine whether the monocarboxylate was resistent to washing with H₂S0₄. From AAS measurements (vide Table 4 hereafter) it shows that the stripped monocarboxylate was capable to extract sodium. The pH of the stripper phase was before stripping about 1, and after stripping about 2.

From the performed experiments it shows that the calix (4) tetra ester was suitable for selectively extracting sodium, with respect to potassium, from an aqueous phase, especially when a lipophile anion, such as picrate, is present being transported as well in the organic phase.

Cali (4) triester monoacid, as an ionophore, is suitable for selectively extracting sodium from an aqueous solution.

Emulsion pertraction

The preferred selection criteria regarding emulsion pertraction are mentioned hereafter.

Selection criteria regarding the ionophore: selectivity: high regarding sodium, especially compared to potassium reversible bonding: fast kinetics and a high concentration of sodium solubility in water: very low, as well depending on the costs. - availability: portions of l kg on short term solubility: > 50 mM in a suitable solvent stability: shelf life > 1 year

Selection criteria regarding the solvent: - solubility ionophore: > 50 mM solubility in water: < 0.01 g/1 toxicity: non-toxic or detrimentous resistance of membranes: no solvent for polypropylene/polyethylene - stability: chemically stable upon contact with acids and water, not biodegradable, shelf life > 1 year viscosity: < 50 cP flammability: explosion-safe apparatus not required availability: in portions of 100 litres

Selection critera stripper liquid kinetics : fast exchange with Na⁺ ions availability: bulk product composition: introducing no detrimentous ions into the sprinkling water

Selection criteria counterion (co-transport anion) for sodium in the ionophore phase (needed when using a non-charged carrier) : - solubility in solvent: identical as ionophore solubility in water: low, non-detrimentous for the plants availability: at least in portions of 1 kg Solvents: mesitylene, anisole and limonene Carrier: monoacid derivative of cali (4) tetra ester

(hereinafter referred to as monoacid)

Stripper acid: 0.01 M sulphuric acid Counterion: not necessary when using monoacid Durability test of a solid membrane material

By means of a punching test, polypropylene fibres were tested regarding chemical resistance as well as applicability in an emulsion pertraction process. The fibres being tested are of the type Q3/2, of Akzo Nobel.

When performing the punching tests, the fibres were contacted with drain water on the one hand and ionophore in solvent, on the other hand.

Three parallel tests were performed, wherein the ionophore was dissolved in the next three solvents : mesitylene anisole limonene

To perform the experiments, three modules were made, comprising in each module three fibres (potted) in a standard epoxy resin.

The modules were filled at the outside with drain water, and set to an excessive pressure of 0.25 bars. Thereafter, the inside of the fibres was filled with a solution of solvent and ionophore, and the pressure on the water phase was increased to 0.5 bar. Directly after filling the fibres with the solution of ionophore in the solvent, it was established that all three solvents incurred some swelling of the fibres, however this does not necessarily mean an obstruction with regard to the pertraction process. A direct penetration of water to the phase containing the ionophore as well as the solvent, was observed in the case of anisole. The two modules containing the other solvents did not cause any penetration after one week on an excessive pressure of 05 bar.

Said pressure was then increased to 1 bar. No direct penetration was perceivable. After one night, however, some penetration did occur.

Further inspection of the modules revealed that the epoxy potting was swollen (in the case of anisole heavily and in the case of mesitylene and limonene less heavily) as well as heavily weakened. This might have caused the leakage along the potting material. To counteract the swelling, three new modules were made containing another kind of chemically more resistant resin, namely Stycast .

In the same way as described above, these modules have been tested, with regard to penetration, with three solvents. After one week on an excessive pressure of 0.5 bar no penetration was perceivable. Indeed some penetration occurred when the pressure was increased to one bar, with all three solvents. No swelling or weakening of the Stycast potting material occurred.

It can be concluded from the above mentioned data that:

The polypropylene fibres do swell to some extent when using the combinations of solvent and ionophore tested: however, no direct problems will be obtained when performing the emulsion pertraction experiments.

When performing the emulsion pertraction process the pressure difference between the water phase and the ionophore phase is not allowed to be higher than 0.5 bar to prevent penetration of the membranes.

When producing the membrane modules a standard epoxy potting material will not be satisfactory because of the extreme swelling and weakening when using the combinations of solvents and ionophore tested. A Stycast potting will be satisfactory.

Emulsion pertraction system

An emulsion protraction system according to the present invention is shown in Figure 4. Said system comprises a supply l of water to be treated, a filter 2, a liquid membrane module 3, a discharge of treated water 4, an emulsion supply 5, a supply 6 of a fresh stripper phase, a discharge 7 of the stripper phase comprising the removed component 4, an apparatus 8 to split up the emulsion, as well as an apparatus 9 to obtain an emulsion of stripper phase in the membrane phase.

For dosage of the right amount of stripping acid, a control for the pH was provided, not shown in Figure 4. In use, by means of the filter 2, the solid coarse particles, if any, are stripped of the water comprising the dissolved undesired component, for example Na⁺. Thereafter the aqueous stream is adjusted to the correct pH with a basic solution. Now the aqueous stream is ready for extraction by means of the liquid membrane module 3. The aqueous stream comprising the decreased concentration of undesired component, is adjusted to the desired pH by means of an acid, and is ready for use. The undesired component is, in the module 3, taken up in the emulsion 5 being discharged from the apparatus for preparing emulsions 9. To maintain a suitable driving force in the direction of the stripper phase, it is desirable that the stripper phase is maintained at the right pH (for, protons are exchanged with sodium ions) . This is possible by supplying fresh stripper phase from a supply container 6 into the process. By means of a draining off stream 7 the stripper phase comprising the undesired component is discharged for recycling in another industrial process or it is drained off.

Experiments

To show the technical feasibility of pertraction, experiments were performed in a laboratory arrangement schematically shown in Figure 4. A little DAM module, type W222 comprising Stycast as potting material was installed in said arrangement as membrane module 3. The characteristics of the DAM module were as follows:

Type: DAM module W222 Serial number: D7J3514

Passage dimensions: 2*2 cm Passage depth: 2 cm fibres, 2 cm run out Number of fibres: 81 Membrane surface: 50,9 cm² (outer) Membranes: Akzo Nobel

Type of fibre: Q3/2 Membrane material : polypropylene Inner diameter: 600 μm Outer diameter: 1000 μm Effective pore diameter: 0,2 μm

Porosity: 75%

At the outside of the fibres the drain water was circulated and kept at some excessive pressure with regard to the ionophore phase circulated through the fibres. The ionophore phase comprised a solution of 0.05 M monoacid in limonene. Samples were drawn from the water phase, with certain time intervals so as to be analysed with regard to the concentration of sodium and potassium. From the progress of the concentration the film coefficient could be determined.

From this experiment the starting concentration of sodium amounted to 5 mmol per litre in a volume of 0.5 litre. The pH was adjusted to 11.7, by adding calcium hydroxide. The results and provisions of this experiments are shown in Table 7.

Table 7

Water phase Extractant phase Water phase

Time Flow Pressure pH Flow Pressure [Na+] [K+] [hh.mm] [1.min. -1] [bar] [-] [float] [bar] [ppm] [ppm]

08.03 0.87 0.28 11.70 117 n.b.

08.05 0.88 0.27 11.70 85 0.05

08.20 0.89 0.29 11.73 95 0.10

08.35 0.90 0.29 11.73 98 0.10 n.b.

09.05 0.91 0.29 11.71 100 0.10 114 n.b.

09.40 0.91 0.29 11.70 105 0.10 n.b.

10.05 0.92 0.31 11.71 145 0.14

10.35 0.93 0.32 11.71 145 0.14

11.05 0.93 0.32 11.71 148 0.14 107 n.b.

11.35 0.93 0.32 11.70 148 0.14

12.05 0.93 0.32 11.71 148 0.14 n.b.

13.05 0.93 0.32 11.71 148 0.14

14.05 0.93 0.32 11.70 149 0.14 n.b.

15.15 0.93 0.32 11,70 149 0.14

16.40 0.93 0.32 11,70 149 0.14 99 stripping acid 77 n.b. From the analysis results it shows that a decrease of the sodium concentration in the water phase is obtained.

From the supply phase 9 milligrams sodium is removed, in the stripping acid 7.7 milligrams is found. The decrease of the sodium concentration in the water phase has also been displayed graphically in Figure 5.

Economical evaluation

Location of the emulsion pertraction process

The emulsion pertraction process according to the present invention can practically be used for selectively removing sodium ions from drain water (2) as well as for removing said ions from tap-water (1) , vide Figure 6, wherein:

R = rain water V - evaporation

A = additional water D_d = drain water

M = supply of fertilizer S = discharge of drain water

G = sprinkling water D_r = recycling of drain water The location of the emulsion pertraction process in the present process may be prescribed by process technological reasons, but also by practical wishes. Two options for scale up calculations, as mentioned hereafter, have been investigated for reasons of economical evaluation. Case 1 relates to the treatment of drinking water, case 2 relates to the treatment of drain water.

Table 8 : Cases for scale up calculations

Case 1 Case 2

Volume flow (m³/year) 513 2820

Volume flow (m³/hour) 1 2

Operation time a year (hours) 2000 4000

[Na⁺]_before (mmol/1) 1,5 3,0

[Na⁺]_after (mmol/1) 0,5 2,9 pH (average) 7,5 5,5 Scale up calculations

Pertraction experiments were performed batchwise. For a practical application, usually a continuous operation is desirable. Therefore, the scale up calculations have been performed for a single pass emulsion pertraction installation. The calculations are based on the experimentally determined filling coefficient.

In a single pass emulsion pertraction installation sufficient membrane modules were coupled to obtain the desired removing degree.

The system in which the two cases before were performed is shown in Figure 4.

From a preparation container, for preparing the emulsion, continuously an emulsion of ionophore phase as well as stripper liquid was passed through the membrane module.

Continuously a new stripper liquid was added to the emulsion container as well.

In the case of Case 1 (tap-water) the surface necessary for the membrane was calculated to be 325 m² (calculated) and in the case of Case 2 (drain water) it was calculated to be 20 m². The difference between Case 1 and Case 2 was caused because in the case of Case 2 only a slight decrease of concentration needed to be realized, compared to the case of Case 1 (0.1 mmol.l^"1 and 1.0 mmol.l^"1 respect- ively) , whereas at the same time a higher concentration level could be maintained which meant that the driving force for transport of the ions to be removed was higher.

Table 9 shows a summary of the consumption as estimated for the cases 1 and 2. To determine the electric necessary power, a pump efficiency of 70%, a motor efficiency of 90% and a stirring power of 200 Watt for Case 1 and 100 Watt for Case 2, were used as a starting point. Table 9. Specification of consumption of Case l and Case 2

The invention is not restricted to the description as given above; the scope of protection is determined by the appending claims .

Table 10 : Extraction

Date Exp . Nr . Carrier Cone. Solvent Salt Cone . M Added U/ [M] [M] Cone. or mg

14-7-97 EX-01 Ester CHC13 Na-Pic 2.5 E-4 0.1 M NaCl

EX-02 Monoacid 2.5 E-4 CHC13 Na-Pic 2.5 E-4 0.1 M NaCl

15-7-97 EX-03 Ester 2.5 E-4 CHC13 K-Pic 2.5 E-4 0.1 M KC1

EX-04 Monoacid 2.5 E-4 CHC13 K-Pic 2.5 E-4 0.1 M KC1

EX-05 CHC13 K-Pic 2.5 E-4 0.1 M KC1

EX-06 CHC13 Na-Pic 2.5 E-4 0.1 M NaCl

EX-07 Toluene K-Pic 2.5 E-4 0.1 M KC1

EX-08 Toluene Na-Pic 2.5 E-4 0.1 M NaCl

EX-09 Ester 2.5 E-4 Toluene K-Pic 2.5 E-4 0.1 M KC1

EX-10 Ester 2.5 E-4 Toluene Na-Pic 2.5 E-4 0.1 M NaCl

16-7-97 EX-11 Monoacid 2.5 E-4 CHC13 NaOH 2.5 E-4 0.1 M NaCl

EX- 12 Monoacid 2.5 E-4 CHC13 Na-Pic 2.5 E-4 0.1 M NaCl

18-7-97 EX-13 Ester 2.5 E-4 Hexyl acetate Na-Pic 2.5 E-4 0.1 M NaCl

EX-14 Ester 2.5 E-4 Hexyl acetate K-Pic 2.5 E-4 0.1 M KC1

21-7-97 EX-15 Ester 2.5 E-4 Hexyl acetate Na-Pic 2.5 E-4 0.1 M NaCl U

EX-16 Ester 2.5 E-4 Hexyl acetate K-Pic 2.5 E-4 0.1 M KC1 U

Table 11: Extraction

EX-17 Hexyl acetate Na-Pic 2.5 E-4 0.1 M NaCl U EX-18 Hexyl acetate K-Pic 2.5 E-4 0.1 M KC1 u EX-19 Ester 2.5 E-4 Ethyl acetate Na-Pic 2.5 E-4 0.1 M NaCl u EX-20 Ester 2.5 E-4 Ethyl acetate K-Pic 2.5 E-4 0.1 M KC1 u EX-21 Ethyl acetate Na-Pic 2.5 E-4 0.1 M NaCl u EX-22 Ethyl acetate K-Pic 2.5 E-4 0.1 M KC1 u

22-7-97 EX-23 Hexyl acetate Na-Pic 2.5 E-4 0.1 M NaCl u EX-24 Ester 2.5 E-4 Hexyl acetate Na-Pic 2.5 E-4 0.1 M NaCl u EX-25 CHC13 Na-Pic 2.5 E-4 0.1 M NaCl u EX-26 Ester 2.5 E-4 CHC13 Na-Pic 2.5 E-4 0.1 M NaCl u EX-27 Hexyl acetate K-Pic 2.5 E-4 0.1 M KC1 u EX-28 Ester 2.5 E-4 Hexyl acetate K-Pic 2.5 E-4 0.1 M KC1 u EX-29 CHC13 K-Pic 2.5 E-4 0.1 M KC1 u EX-30 Ester 2.5 E-4 CHC13 K-Pic 2.5 E-4 0.1 M KC1 u

23-7-97 EX-31 MIK Na-Pic 2.5 E-4 0.1 M NaCl u EX-32 Ester 2.5 E-4 MIK Na-Pic 2.5 E-4 0.1 M NaCl u

Table 12 : Extraction

Date Exp . Nr . Carrier Cone. Solvent Salt Cone . M Added U/ [M] [M] Cone . or mg

EX-33 1-octanol Na-Pic 2.5 E-4 0.1 M NaCl U

EX-34 Ester 2.5 E-4 1-octanol Na-Pic 2.5 E-4 0.1 M NaCl U

EX-35 MIK K-Pic 2.5 E-4 0.1 M KC1 U

EX-36 Ester 2.5 E-4 MIK K-Pic 2.5 E-4 0.1 M KC1 U

EX-37 1-octanol K-Pic 2.5 E-4 0.1 M KC1 u

EX-38 Ester 2.5 E-4 1-octanol K-Pic 2.5 E-4 0.1 M KC1 u

25-7-97 EX-39 MIK Na/K (N03) 0.01 A

EX-40 Ester 0.05 MIK Na/K (N03) 0.01 A

EX-41 CHC13 Na/K (N03) 0.01 A

EX-42 Ester 0.05 CHC13 Na/K (N03) 0.01 A

28-7-97 EX-43 CHCL3 blank A

EX-44 Ester 0.05 CHCL3 blank A

EX-45 CHC13 Na-Pic 0 . 01 A

EX-46 Ester 0.05 CHC13 Na-Pic 0 . 01 A

EX-47 CHC13 NaCl04 0 . 01 A

EX-48 Ester 0.05 CHC13 NaC104 0 . 01 A

Table 13 : Extraction

Table 14 : Extraction

Date Exp . Nr. Carrier Cone. Solvent Salt Cone . M Added U/ [M] [M] Cone . or mg

EX-63 CHC13 Na/K (N03) 0.01 14.41 mg Na-Dodecyl sulphate

EX-64 Ester 0.05 CHC13 Na/K (N03) 0.01 14.41 mg Na-Dodecyl sulphate A

11-8-97 EX-65 CHC13 Na/K (N03) 0.01 A EX-66 Ester 0.25 CHC13 Na/K (N03) 0.01 A EX-67 M-HEPT Na/K (N03) 0.01 A EX-68 Ester 0.25 M-HEPT Na/K (N03) 0.01 A EX-69 CHC13 Na/K (Pic) 0.01 A EX-70 Ester 0.25 CHCL3 Na/K (Pic) 0.01 A EX-71 M-HEPT Na/K (Pic) 0.01 A EX-72 Ester 0.25 M-HEPT Na/K (Pic) 0.01 A

19-8-97 EX-73 M-HEPT Na/K (N03) 0.01 A EX-74 Ester 0.05 M-HEPT Na/K (N03) 0.01 A EX-75 M-HEPT Na/K (N03) 0.01 0.01 M Li-Dodecyl sulphate

EX-76 Ester 0.05 M-HEPT Na/K (N03) 0.01 0.01 M Li-Dodecyl sulphate

Table 15 : Extraction

Table 16: Extraction

Date Exp . Nr. Carrier Cone. Solvent Salt Cone . M Added U/A [M] [M] Cone, or mg

EX-91 Mesitylene Na/K (N03 0.01 A

EX-92 Ester 0.05 Mesitylene Na/K (N03 0.01 A

29-9-97 EX-93 Limonene Na/K (Pic 0.01 A

EX-94 Ester 0.05 Limonene Na/K (Pic 0.01 A

20-8-97 EX- 95 Limonene Na/K (N03 0.01 A

EX-96 Ester 0.05 Limonene Na/K (N03 0.01 A

EX-97 Mesitylene Na/K (N03 0.01 A

EX-98 Ester 0.05 Mesitylene Na/K (N03 0.01 A

1-10-97 EX-99 Mesitylene Na/K (Pic 0.01 A

EX-100 Ester 0.05 Mesitylene Na/K (Pic 0.01 A

EX-101 Mesitylene Na/K (N03 0.01 A

EX-102 Ester 0.05 Mesitylene Na/K (N03 0.01 A

EX-103 Anisole Na/K (Pic 0.01 A

EX-104 Ester 0.05 Anisole Na/K (Pic 0.01 A

EX-105 n-hexyl ether Na/K (Pic 0.01 A

EX-106 Ester 0.05 n-hexyl ether Na/K (Pic 0.01 A

Table 17: Extraction

Table 18 : Extraction

Table 19: Extraction

Table 20: Extraction

Table 21: Extraction

Claims

1. A system for selectively removing ions, especially metal ions, from aqueous liquid streams, said system comprising: an ionophore, which selectively binds to ions to be removed being present in the liquid stream, so as to obtain an ion-ionophore complex, - a hydrophobic solvent for said ionophore, said solvent being essentially immiscible with the aqueous liquid stream, wherein said ion-ionophore complex essentially is soluble in said hydrophobic solvent only.

2. A system according to claim 1, wherein said iono- phore comprises two or more, mutually connected arene compounds .

3. A system according to claim l or 2, wherein said ionophore is a cyclic molecule.

4. A system according to claim 3, wherein said iono- phore is a calixarene molecule, which preferably is function- alized.

5. A system according to claim 4, wherein said calixarene is a calix (4) arene, which preferably is chosen from the group essentially consisting of calix (4) arene compounds comprising structures 1) , 2) or 3) :

wherein R_1# R₂, R₃ and R₄ is H or: CH₂-C (X) -X-R' , CH₂-C(X)- NR'R'', CH₂-P(X) -X-R' , CH₂-P (X) -NR' R' ' , CH₂-0-S0₂-OR' , CH₂-0- S0₂-NR'R'', wherein X=0, S and R, R' , R' ' is H, alkyl, aryl, especially the compound wherein R₁=R₂=R₃=CH₂-C00R'R' ' and R₄=CH₂-C00H, also called the monoacid derivative of the calix (4) tetra ester.

6. A system according to any of the preceding claims, the ionophore being capable of, in use, forming an anion and/or further comprising a co-transport anion.

7. A system according to claim 6, wherein the co-transport anion is chosen from the group consisting of essentially picrate, perchlorate (C10₄ ^") , nitrate (NO ₃ ^") , or an anion of a (lipophilic) organic acid.

8. A system according to any of the preceding claims, further comprising a deprotonating agent for deprotonating the calix(4) carboxylate (s) .

9. A system according to claim 6, said deprotonating agent comprising a base, preferably a hydroxy, and most preferably NaOH and/or CaOH₂.

10. A system according to any of the preceding claims, wherein the ionophore has a selectivity towards sodium with respect to potassium of at least about 5 tot 1, for example about 10 to 1, preferably about 15 to 1, and most preferably about 25 to 1.

11. A system according to any of the preceding claims, wherein the solvent has a solubility in water of less than about 0,01 grams per litre.

12. A system according to any of the preceding claims, wherein the solvent is an organic solvent, for example chosen from the group essentially consisting of: 1- nonanol, 1-octanol, anisole (methoxybenzene) , CH₂C1₂, cyclo- hexane, di-amylether, di-isobutylketon, ethyl acetate, limonene (dipentene) , 5-methyl-3-heptanon (M-Hept) , mesitylene, methyl, salicylate, methylbenzoate, methyl- isobutyl-keton (MIK) , m-xylene, n-hexylether, nonanoic acid, nonylfenol, nitrophenyloctylether (NPOE) , o-nitrotoluene, o-xylene, paraffinic oil, toluene, hexyl acetate, CHC1₃, preferably chosen from the group essentially consisting of: hexylacetate, ethylacetate, 5-methyl 3-heptanon, methyl iso- butyl keton, CHC1₃, limonene, mesitylene, anisole, n-hexyl ether, and most preferably a terpene such as limonene or a saturated derivative thereof when the ionophore is the monoacid derivative of calix (4) tetra ester.

13. A system according to claim 12, wherein the solubility of the ionophore in the solvent is at least about 10 mM; and preferably > about 50 mM.

14. A system according to any of the preceding claims, further comprising a stripper for stripping the ions from the ionophore, wherein the stripper comprises a certain ion which is exchangeable with the ions in the ion-ionophore complex.

15. A system according to claim 14, wherein a proton present in the stripper is exchangeable.

16. A system according to claims 14 or 15, wherein the stripper comprises sulphuric acid.

17. A system according to claim 16, wherein the sulphuric acid is present in a concentration of less than about 0.5 M, preferably about less than 0.1 M and most preferably in a concentration of about 0.01 M.

18. A system according to any of the preceding claims, further comprising a solid carrier for maintaining the liquid membrane comprising the ionophore and its solvent between the aqueous liquid stream and the stripper.

19. A system according to claim 18, wherein the solid carrier comprises hydrophobic polypropylene membrane fibres.

20. A system according to any of the preceding claims for removing metal ions, especially sodium from water, especially from sprinkling water.

21. A system according to any of the preceding claims for use in liquid membrane extraction or solvent extraction, especially with: - bulk liquid membrane extraction, emulsion liquid membrane extraction, immobilized liquid membrane extraction, emulsion pertraction.

22. A method for removing ions, especially metal ions from aqueous liquid streams, comprising the steps of contacting the liquid streams, containing said ions to be removed, with an ionophore as mentioned in claims 1 to 6, so as to essentially yield a non-soluble ionophore-ion complex precipitating from the aqueous stream.

23. A method according to claim 22, wherein the ionophore is dissolved in a solvent as mentioned in any of the claims 11 to 13.

24. A method according to claim 22 or 23 comprising the further step of contacting the ionophore-ion complex formed with a stripper as mentioned in any of the claims 14 to 17.

25. A system of apparatus for removing valuable or undesired ions from an aqueous liquid stream, comprising a module in which is present a system according to any of claims 1 to 20.

26. A system of apparatus according to claim 25 for performing a method according to any of claims 22 to 24.

27. Use of an ionophore according to any of claims 1 to 6, for removing undesired ions, especially metal ions, from a liquid stream.

28. Use of a system of apparatus according to claim 25, for performing a method according to any of the claims 22 to 24.

29. Use of a system according to any of claims 1 to

21, in a method according to claims 22 to 24.

AMENDED CLAIMS

[received by the International Bureau on 28 April 2000 (28.04.00) ; original claims 1-29 replaced by amended claims 1-25 (3 pages)]

1. A system for selectively removing ions, especially metal ions, from aqueous liquid streams, said system comprising: an ionophore. which selectively binds to ions to be removed being present in the liquid stream, so as to obtain an ion-ionophore complex, said ionophore being a calixarene molecule, which, preferably is functionalized, a hydrophobic solvent for said ionophore, said solvent being essentially immiscible with the aqueous liquid stream, wherein said ion-ionophore complex essentially is soluble in said hydrophobic solvent only, wherein the ionophore is capable of, in use, forming an anion and/or further comprising a co-transport anion.

2. A system according to claim 1, wherein said calixarene is a calix(4)arene, which preferably is chosen from the group essentially consisting of calix(4)arene compounds comprising structures 1 ),

i ) _{2 )} 3 ) wherein R,. R₂, R₃ and R, is H or: CH₂ - C (X) - X-R' . CH₂ - C (X) - NR^'R^{* *} , CH: - P (X) - X-R^* . CH₂ - P (X) - NR'R" , CH_: - O - SO_: - OR^* , CH₂ -O - SO: - NR^* R^" . wherein X=O. S and R, R\ R^" is H, alkyl. aryl. especially the compound wherein R|_R R_.;,-CH; - COOR^'R^" and

- COOH. also called the monoacid derivative of the calix (4)tetra ester.

3. A system according to claim 1 , wherein the co-transport anion is chosen from the group consisting of essentially picrate, perchlorate (C I O ₃ ^" ). nitrate (NO ^" ), or an anion of a ( lipophilic) organic acid.

4. A system according to any of the preceding claims, further comprising a deprotonating agent for deprotonating the calix(4)carboxylate(s)

5. A system according to claim 1 , said deprotonating agent comprising a base, preferably a hydroxy, and most preferably NaOH and/or CaOH:. 6 . A system according to any of the preceding claims, wherein the ionophore has a selectivity towards sodium with respect to potassium of at least about 5 to 1 , for example about 10 to 1. preferably about 15 to 1, and most preferably about 25 to 1.

7. A system according to any of the preceding claims, wherein the solvent has a solubility in water of less than about 0,01 grams per litre. 8. A system according to any of the preceding claims, wherein the solvent is an organic solvent, for example chosen from the group essentially consisting of: 1 -nonanol. 1 -octanol. anisole (methoxybenzene), CH₂C I₂. cyclohexane, di-amylether, di- isobutylketon. ethyl acetate, limonene (dipentene). 5-methyl-3-heptanon (M-Hept), mesitylene. methyl salicylate, methylbenzoate, methyl-isobutyl-keton (MIK), m-xylene. n-hexylether, nonanoic acid, nonvlfenol, nitrophenvloctvlether, (NPOE), o-nitrotoluene. o-xylene. paraffinic oil, toluene, hexyl acetate, CHCI₃, preferably chosen from the group essentially consisting of; he.xvlacetate, ethylacetate. 5-methyl 3-heptanon, methyl isobutyl keton. CHC 1 . limonene, mesitylene, anisole. n-hexyl ether, and most preferably a terpene such as limonene or a saturated derivative thereof when the ionophore is the monoacid derivative of calix( 4) tetra ester.

9. A system according to claim 8. wherein the solubility of the ionophore in the solvent is at least about 10 mM; and preferably > about 50mM.

10. A system according to any of the preceding claims, further comprising a stripper for stripping the ions from the ionophore. wherein the stripper comprises a certain ion which is exchangeable with the ions in the ion-ionophore complex.

1 1. A system according to claim 10. wherein a proton present in the stripper is exchangeable.

12. A system according to claims 10 or 1 1. wherein the stripper comprises sulphuric acid. 13. A system according to claim 12. wherein the sulphuric acid is present in a concentration of less than about 0.5 M. preferably about less than 0.1 M and most prelcr bh in a concentration of about 0.01 M.

AMENDED SHEET (ARTICLE 19

14. A system according to any of the preceding claims, further comprising a solid carrier for maintaining the liquid membrane comprising the ionophore and its solvent between the aqueous liquid stream and the stripper.

15. A system according to claim 14, wherein the solid carrier comprises hydrophobic polypropylene membrane fibres.

16. A system according to any of the preceding claims for removing metal ions, especially sodium from water, especially from sprinkling water.

17. A system according to any of the preceding claims for use in liquid membrane extraction or solvent extraction, especially with: - bulk liquid membrane extraction, emulsion liquid membrane extraction, immobilized liquid membrane extraction, emulsion pertraction.

18. A method for removing ions, especially metal ions from aqueous liquid streams, comprising the steps of contacting the liquid streams, containing said ions to be removed, with an ionophore as mentioned in claims 1 or 2, so as to essentially yield a non-soluble ionophore-ion complex precipitating from the aqueous stream.

19. A method according to claim 18, wherein the ionophore is dissolved in a solvent as mentioned in any of the claims 7 to 9. 20. A method according to claim 18 or 19 comprising the further step of contacting the ionophore-ion complex formed with a stripper as mentioned in any of the claims 10 to 13.

21. A system of apparatus for removing valuable or undesired ions from an aqueous liquid stream, comprising a module in which is present a system according to any of claims 1 to 16.

22. A system of apparatus according to claim 21 for performing a method according to any of claims 18 to 20.

23. L^'se of an ionophore according to any of claims 1 or 2. for removing undesired ions, especially metal ions, from a liquid stream. 24. Use of a system of apparatus according to claim 21 , for performing a method according to any of the claims 18 to 20.

25. l 'se of a system according to any of claims 1 to 17. in a method according to claims 1 to 20.