METHOD FOR EXTRACTING A COMPOUND CONTAINED IN A LIQUID SOLUTION BY FORWARD OSMOSIS

Abstract

A method for extracting a determined compound contained in a liquid solution, referred to as the feed solution, by forward osmosis. The feed solution is circulated in contact with a first face of a membrane configured to selectively allow the transfer of the compound by osmosis. A second liquid solution containing potassium lactate, referred to as the extraction solution, is circulated in contact with a second opposing face of the membrane opposite the first face.

Claims

1-9. (canceled)

10. A method for extracting a given compound contained in a liquid solution by forward osmosis, the liquid solution being referred to as a feed solution, comprising steps of circulating the feed solution circulated in contact with a first face of a membrane configured to selectively allow a transfer of the given compound by the forward osmosis; and circulating a second liquid solution, referred to as an extraction solution, in contact with a second face of the membrane opposite to the first face of the membrane, wherein the extraction solution contains potassium lactate.

11. The method according to claim 10, wherein the extraction solution is an aqueous solution containing potassium lactate.

12. The method according to claim 10, wherein a concentration of potassium lactate in the extraction solution is between 5 and 9.4 mol/l.

13. The method according to claim 10, further comprising a final step of regenerating the extraction solution, by eliminating the given compound contained in the extraction solution, by evaporation of the given compound.

14. The method according to claim 10, wherein the membrane comprises an active layer at the first face and a support layer at the second face, the active layer being denser than the support layer.

15. A method for extracting a given compound contained in a liquid solution by forward osmosis, comprising a step of using potassium lactate.

Description

[0034] The features and advantages of the invention will emerge more clearly in the light of the example embodiments below, provided simply by way of illustration and in no way limitative of the invention, with the help of FIGS. 1 to 3, wherein:

[0035] FIG. 1 depicts a graph showing the specific salt flow (Jw/Js) according to the initial salt concentration of the extraction solution, at the end of a method for the extraction of water by forward osmosis from a feed solution consisting solely of water, for extraction solutions comprising respectively potassium lactate (KL), sodium lactate (NaL), potassium chloride (KCl) and sodium chloride (NaCl);

[0036] FIG. 2 depicts a graph showing the sucrose concentration of the feed solution as a function of time, during the implementation of a method for the extraction of water by forward osmosis from a feed solution consisting of sucrose in an aqueous vehicle, for extraction solutions comprising respectively potassium lactate (KL), sodium lactate (NaL), potassium chloride (KCl) and sodium chloride (NaCl); and

[0037] FIG. 3 depicts a graph showing the retrodiffusion flow of the salt (Js) through the membrane as a function of the sucrose concentration in the feed solution, during the implementation of a method for the extraction of water by forward osmosis from a feed solution consisting of sucrose in an aqueous vehicle, for extraction solutions comprising respectively potassium lactate (KL), sodium lactate (NaL), potassium chloride (KCl) and sodium chloride (NaCl).

A) FORWARD OSMOSIS DEVICE AND METHOD

[0038] For the following experiments, use is made of a forward osmosis device that is conventional per se, consisting of a cell (CF042A, Sterlitech) comprising a semi-permeable membrane and two closed circuits, in which there circulate respectively, in contact with the membrane, on the one hand the feed solution containing the compound to be extracted, and on the other hand the extraction solution.

[0039] The membrane used is a commercially-available membrane formed from cellulose triacetate (CTA) (Hydration Technology Innovations) having an active surface area of 42 cm.sup.2. The active layer of the membrane is placed in contact with the circuit for circulation of the feed solution, and the support layer of the membrane is placed in contact with the circuit for circulation of the extraction solution.

[0040] Each solution is driven in the associated circuit by a peristaltic pump at a rate of 40 litres/hour.

B) EXPERIMENTS

[0041] In the following experiments, various extraction solutions were tested, comprising respectively, in solution in water: [0042] potassium lactate in accordance with the present invention; [0043] by way of comparison, various compounds proposed by the prior art: sodium lactate, potassium chloride or sodium chloride.

[0044] In particular, sodium chloride is used as a reference osmotic agent since it is abundantly studied in the prior art.

[0045] For each of these salts, various concentrations are tested.

B.1) Series of Experiments 1

[0046] In a first series of experiments, the performances of the forward osmosis system obtained with the above four extraction solutions are compared under ideal conditions of use, in which pure water is used as the feed solution, the compound to be extracted therefrom being water.

[0047] The initial ranges of concentrations of salt in the extraction solution tested range from 0.3 M (for the minimum concentration) to the saturation or maximum acceptable viscosity concentration of each osmotic agent: 4.7 M for potassium chloride (KCl), 5.4 M for sodium chloride (NaCl), 9.4 M for potassium lactate (KL) and 8.5 M for sodium lactate (NaL).

[0048] Each test lasts for 30 minutes.

[0049] The initial and final volumes of feed solution and extraction solution, as well as the initial and final conductivities of the feed solution, are recorded.

[0050] These conductivities make it possible to calculate the concentrations of salts in the solutions. The flows of water extracted (Jw in l/(m.sup.2.Math.h) or LMH) and the retrodiffusion flow of the salt (Js in g/(m.sup.2.Math.h) or gMH) through the membrane are then calculated, as well as the specific salt flow (Jw/Js in l/g), representing the volume of water extracted per gram of salt that has diffused in the feed solution. A high value of this index indicates better performance of the osmotic agent.

[0051] The results obtained for each salt tested, in terms of specific salt flow (Jw/Js) as a function of the initial salt concentration in the extraction solution are shown in FIG. 1.

[0052] It is seen therein that the specific salt flow obtained for the method according to the present invention, using potassium lactate, is much higher than that obtained for potassium chloride and for sodium chloride, at all the concentrations tested. It is also higher than that obtained for sodium lactate at the highest concentrations, greater than or equal to approximately 5 M.

B.2) Series of Experiments 2

[0053] In a second series of experiments, the performances of the forward osmosis system obtained with the four extraction solutions described above are compared for the concentration of an aqueous solution of sucrose of 30 B to 60 B, the compound to be extracted therefrom being water.

[0054] The initial salt concentrations in the extraction solution tested are: 4.7 M for potassium chloride (KCl), 5.4 M for sodium chloride (NaCl), 9.4 M for potassium lactate (KL) and 8.5 M for sodium lactate (NaL).

[0055] 50 ml of a sucrose solution (feed solution) and 1 litre of extraction solution are introduced into the forward osmosis system.

[0056] Flow measurements and takings of samples for the determination of the salt concentrations are carried out at each 20 ml of water extracted from the feed solution. The concentrations of lactate that has retrodiffused in the feed solution are analysed with enzymatic kits. A volume of 20 ml of feed solution with a sucrose concentration at 30 B is then added to the system. In this way, the volume of feed solution always varies between 70 ml and 50 ml (the dead volume of the system being 50 ml).

[0057] The flows of water extracted (Jw in l/(m.sup.2.Math.h)) and the flows of retrodiffusion of salt (Js in g/(m.sup.2.Math.h)) are then calculated.

[0058] The results obtained, in terms of sucrose concentration in the feed solution as a function of time, are shown in FIG. 2. It can be seen therein that the concentration of the model sucrose solution up to 60 B takes place more quickly when the extraction solution contains potassium lactate or sodium lactate.

[0059] The change in the retrodiffusion flow of the salt (Js) through the membrane, according to the sucrose concentration in the feed solution, is shown in FIG. 3. During the concentration of the feed solution, it is observed that the flow of retrodiffused salt decreases when the sucrose concentration of the feed solution increases, whatever the salt used. This is easily explained by the fact that, during the concentration of the feed solution, the osmotic pressure of the latter increases and therefore the difference in osmotic pressure between the feed solution and the extraction solution decreases.

[0060] It is further observed that potassium lactate is associated with a lower retrodiffusion flow than the other salts studied. These results are consistent with those obtained with pure water as feed solution.

[0061] The flow of sucrose through the membrane was also calculated for each salt tested. It reaches a value of 0.10 gMH, with a variation of 0.07 gMH, whatever the salt used. The use in accordance with the present invention of an extraction solution based on potassium lactate therefore does not have a negative impact on the passage of sugar through the membrane, compared with the other salts tested.