Device for Producing Energy by Salinity Gradient Through a Membrane Based on Crosslinked Cellulose Fibres

Abstract

The present invention concerns a device for producing electrical energy, comprising: a) a first reservoir A for receiving an electrolyte solution having a concentration CA of a solute and comprising an electrode (30A) in contact with the electrolyte solution having concentration CA; b) a second reservoir B for receiving an electrolyte solution having a concentration CB of one and the same solute, CB being lower than CA, and comprising an electrode in contact with the electrolyte solution having concentration CB; c) a membrane separating the two reservoirs, said membrane comprising pores allowing the electrolytes to diffuse from reservoir A to reservoir B through said pore or pores; and d) a device capable of supplying the electrical energy generated by the potential difference existing between the two electrodes, characterized in that the membrane comprises at least one layer formed of a cellulosic material comprising a network of crosslinked cellulose nanofibres and/or microfibres.

Claims

1. A device for producing electrical energy comprising: a) a first reservoir A intended to receive an electrolytic solution having a concentration C.sub.A of a solute and comprising an electrode in contact with the electrolytic solution having a concentration C.sub.A; b) a second reservoir B intended to receive an electrolytic solution having a concentration C.sub.B of the same solute, C.sub.B being lower than C.sub.A, and comprising an electrode in contact with the electrolytic solution having a concentration C.sub.B; c) a membrane separating the two reservoirs, said membrane comprising pores allowing the electrolytes to diffuse from reservoir A to reservoir B through said pore or pores; and d) a device allowing to supply the electrical energy generated by the potential differential existing between the two electrodes, characterized in that the membrane comprises at least one layer formed of a cellulosic material comprising a network of crosslinked cellulose nanofibers and/or microfibers.

2. The device according to claim 1, wherein the thickness of the membrane is between 2 μm and 100 μm.

3. The device according to claim 1, wherein the membrane comprises from 10 to 20 g of cellulosic material per m.sup.2 of membrane.

4. The device according to claim 1, wherein the nanofibers and/or the crosslinked cellulose microfibers are functionalized by negatively charged groups and/or groups which become negatively charged in the presence of water.

5. The device according to claim 1, wherein the nanofibers and/or the crosslinked cellulose microfibers are functionalized by positively charged groups and/or groups which become positively charged in the presence of water.

6. The device according to claim 1, wherein the membrane comprises a single layer formed of a cellulosic material comprising a network of crosslinked cellulose nanofibers and/or microfibers.

7. The device according to claim 1 wherein the membrane is a composite membrane comprising two outer layers each formed of a cellulosic material comprising a network of crosslinked cellulose nanofibers and/or microfibers, between which is disposed an inner layer formed of a second material comprising nanoparticles functionalized by charged groups and/or groups which become charged in the presence of water.

8. The device according to claim 7, wherein the thickness of each of the outer layers is between 2 μm and 25 μm, and the thickness of the inner layer is between 10 nm and 2 μm.

9. The device according to claim 7, wherein the nanoparticles are lamellar nanoparticles.

10. A method for producing electrical energy using a device as described in claim 1, comprising the following steps: i) supplying an electrolytic solution having a solute concentration C.sub.A in reservoir A, so that the electrode with which it is equipped is in contact with said solution, ii) supplying an electrolytic solution having a concentration C.sub.B of the same solute, C.sub.B being lower than C.sub.A, in the reservoir B, so that the electrode with which it is equipped is in contact with said solution, iii) allowing the electrolytes to diffuse from reservoir A to reservoir B through the membrane, iv) capturing the electrical energy generated by the potential differential existing between the two electrodes, using the device.

11. The method according to claim 10, wherein said electrolytic solutions are aqueous solutions comprising a solute selected from the group consisting of alkali halides and alkaline earth halides.

12. The method according to claim 10, wherein the concentration ratio C.sub.A/C.sub.B is greater than 1 and less than or equal to 10.sup.9.

13. The device according to claim 2, wherein the thickness of the membrane is between 2 μm and 75 μm.

14. The device according to claim 3, wherein the membrane comprises from 15 to 20 g of cellulosic material per m.sup.2 of membrane.

15. The device according to claim 4, wherein the nanofibers and/or the crosslinked cellulose microfibers are functionalized by groups selected from the group consisting of the sulfonate group —SO.sub.3.sup.−, the carboxylate group —CO.sub.2.sup.−, the aminodiacetate group —N(CH.sub.2CO.sub.2.sup.−).sub.2, the phosphonate group PO.sub.2.sup.3−; the amidoxine group —C(═NH.sub.2)(NOH), the aminophosphonate group —CH.sub.2—NH—CH.sub.2—PO.sub.3.sup.2−, the thiol group —SH, and mixtures thereof.

16. The device according to claim 5, wherein the nanofibers and/or the crosslinked cellulose microfibers are functionalized by groups selected from the group consisting of the quaternary ammonium group —N(R).sub.3.sup.+ with R being a C1-C4 alkyl, the tertiary ammonium group —N(H)R).sub.2.sup.+ with R being a C1-C4 alkyl, dimethylhydroxyethylammonium group —N(C.sub.2H.sub.4OH)CH.sub.3).sub.2.sup.+, and mixtures thereof.

17. The device according to claim 16, wherein the tertiary ammonium group is —N(H)R).sub.2.sup.+ with R being a C1 alkyl.

18. The device according to claim 9, wherein the lamellar nanoparticles are lamellar nanoparticles of a metal oxide, of a dichalcogenide of a transition metal, carbon, or a mixture thereof.

19. The device according to claim 18, wherein the lamellar nanoparticles are lamellar nanoparticles of graphene oxide functionalized at the surface by negatively charged groups or groups which become negatively charged in the presence of water.

20. The device according to claim 18, wherein the lamellar nanoparticles of the dichalcogenide of a transition metal are lamellar nanoparticles of molybdenum disulfide.

21. The method according to claim 11, wherein said electrolytic solutions are aqueous solutions comprising a solute selected from the group consisting of NaCl, KCl, CaCl.sub.2 and MgCl.sub.2.

22. The method according to claim 12, wherein the concentration ratio C.sub.A/C.sub.B is greater than 1 and less than or equal to 10.sup.5.

Description

DESCRIPTION OF THE FIGURES

[0172] FIG. 1 schematically shows an example of an electrical energy production device according to the present invention, comprising two reservoirs 20A and 20B, respectively reservoir A and reservoir B, separated by a membrane 10. Each of the two reservoirs contains an electrolytic solution 22A and 22B having a respective concentration C.sub.A and C.sub.B of the same solute, in which an electrode 30A and 30B is soaked. The two electrodes 30A and 30B are connected to a device allowing to capture and then supply the electrical energy generated. Each reservoir A and B can be any device or natural environment, open or closed, capable of containing a liquid. In order to generate an ion flux through the membrane, the concentrations C.sub.A and C.sub.B of the same solute of the electrolyte solutions 22A and 22B are necessarily different. In the context of the present invention, it is arbitrarily considered that C.sub.B is lower than C.sub.A, which causes circulation of the ions of the solute from reservoir A to reservoir B. The membrane 10, separating the two reservoirs A and B comprises pores allowing the electrolytes to diffuse from reservoir A to reservoir B through the pores. The diffusion will take place from reservoir A to reservoir B. The pores have an average cross-section allowing both water molecules and solute ions to circulate. The electrodes 30A and 30B can be partially or entirely immersed in the solutions 22A and 22B. It is also possible to provide that the electrodes are in the form of at least part of a wall of the reservoirs. The device (32) allows to capture then supply the electrical energy spontaneously generated by the potential differential existing between the two electrodes 30A and 30B. It can consist of simple cables connecting a battery, a bulb or any other form of electrical consumer.

[0173] FIG. 2 schematically shows in section an example of membrane (10) according to the invention including a single layer (101) formed of a cellulosic material comprising nanofibers and/or crosslinked cellulose microfibers.

[0174] FIG. 3 schematically shows in section an example of membrane (10) according to the invention, in which the membrane is a composite membrane comprising two outer layers (101,103) each formed of a cellulosic material comprising crosslinked cellulose nanofibers and/or microfibers, between which is disposed an inner layer (102) formed of a material comprising nanoparticles functionalized at the surface by charged groups and/or groups which become charged in the presence of water.

EXAMPLES

[0175] The present invention will be better understood upon reading the following examples which illustrate the invention without limitation.

Example 1: Preparation and Measurement of the Membrane Power of a Monolayer Membrane

Equipment and Raw Materials

[0176] The material used is listed below:

[0177] A Buchner filter

[0178] A 1 bar vacuum pump

[0179] 0.1 μm PVDF filter paper

[0180] A proofing oven

The raw materials used in this example are listed below:

[0181] Cellulose nanofibers negatively charged by carboxymethylation or TEMPO oxidation;

[0182] Citric acid, 99% by volume.

Preparation of Monolayer Membranes

[0183] The preparation method used is as follows: [0184] 3.5 ml of nanocellulose solution are filtered on the buchner filter with a PVDF filter. The vacuum pump is set to 1 bar vacuum; [0185] Once all the solution has been filtered, 10 ml of citric acid solution is filtered thereon (which acts as a crosslinking agent between the nanofibers); [0186] Once all the filtered citric acid solution stops the pump, the Buchner device is opened and the filter paper with its filtrate is removed.
The filtrate filter paper assembly is then placed in a study oven at 85° C. for 15 minutes (drying and crosslinking reaction).
Finally, the membrane is detached from its filtration medium, to make things easier, it may possibly be soaked beforehand in an isopropanol solution.
The membranes thus obtained are composed of 17.5 g/m.sup.2 of nanocellulose.
These membranes have an inner layer of graphene oxide having a thickness of about 100 nm, and outer layers of cellulose each having a thickness of about 10 μm.

Membrane Power of the Monolayer Membrane

[0187] The tests were carried out with a device made up of two independent reservoirs each containing a solution of sodium chloride (NaCl) dissolved at 1M for the concentrated solution, then 0.1 M, 0.01 M and 0.001 M in dilute solution allowing to set the Rc gradient of 10, 100 and 1000 between the two reservoirs.
The two reservoirs are separated by a composite membrane in accordance with the invention obtained as detailed in Example 1.
Silver grid Ag/AgCl electrodes are immersed in each of the reservoirs on either side of the membrane to measure the electric current produced through the membranes.
The results are presented in Table 1.

TABLE-US-00001 TABLE 1 Cellulose NFC membrane Concentration gradient 1 000 100 10 U (mV) 220 150 95 R (Ohm .Math. cm.sup.2) 0.08 0.08 0.0725 I (mA) 2750 1 875 1 310 Pmax W/m.sup.2 1513 703 311 U Nernst (mV) 140 90 45 U Osmo (mV) 80 60 150 I Nernst (mA) 1 750 1 125 621 I Osmo (mA) 1 000 750 690 P Osmo Max (W/m.sup.2) 200 113 86

With:

[0188] U Osmo the potential linked to the membrane from which the Nernst potential of the electrodes is deduced (U Nernst)

[0189] I Osmo the current linked to the membrane, calculated by measuring the electrical resistance of the membrane according to Ohm's law I=U/R

[0190] P Osmo Max is calculated by the formula Pmax=(U×I)/4

The membrane powers are expressed in W/m.sup.2 by multiplying by 10 000 the values obtained on 1 cm.sup.2 of membrane.

Example 2: Preparation and Measurement of the Membrane Power of a Composite Membrane

Equipment and Raw Materials

[0191] The material used is the same as that detailed in Example 1.
The raw materials used in this example are listed below:

[0192] Cellulose nanofibers negatively charged by carboxymethylation or TEMPO oxidation;

[0193] Citric acid, 99% by volume;

[0194] Graphene oxide marketed by the company Sigma Aldrich under the reference no 777676.

Preparation of the Composite Membrane

[0195] The preparation method implemented in this example is detailed below: [0196] 1.75 ml of nanocellulose solution is filtered on the buchner filter with a PVD filter. The vacuum pump is set to 1 bar vacuum; [0197] Once all the solution has been filtered, 5 ml of citric acid solution is refiltered thereon (which will act as a crosslinking agent between the nanofibers); [0198] Once the citric acid has been filtered, 7 ml of graphene oxide solution is filtered [0199] Once the graphene oxide solution has been filtered, 1.75 ml of nanocellulose solution is refiltered; [0200] Once all the solution has been filtered, 5 ml of citric acid solution is refiltered thereon (which will act as a crosslinking agent between the nanofibers); [0201] Once all the filtered citric acid solution stops the pump, the Buchner device is opened and the filter paper with its filtrate is removed.
The filter paper/filtrate combination is then placed in a study oven at 85° C. for 15 minutes (drying and crosslinking reaction).
Finally, the membrane is detached from its filtration medium, to make things easier, it may possibly be soaked beforehand in an isopropanol solution.
The membranes thus obtained are composed of 17.5 g/m.sup.2 of nanocellulose and 0.34 g/m.sup.2 of graphene oxide (2% by mass).
The nanocellulose contents and the mass contents of graphene oxide were varied. Nanocellulose contents below 10 mg/m.sup.2 do not allow to obtain membranes with sufficient mechanical strength.
For reasons of mechanical strength and ionic resistance, these values of 17 g/m.sup.2 of cellulose and 4% by weight of graphene oxide seem optimal.

Membrane Power of the Composite Membrane

[0202] The tests were carried out with a device made up of two independent reservoirs each containing a solution of sodium chloride (NaCl) dissolved at 1 M for the concentrated solution, then 0.1 M, 0.01 M and 0.001 M in dilute solution allowing to set the Rc gradient of 10, 100 and 1000 between the two reservoirs.
The two reservoirs are separated by a composite membrane in accordance with the invention obtained as detailed in Example 1.
Silver grid Ag/AgCl electrodes are immersed in each of the reservoirs on either side of the membrane to measure the electric current produced through the membranes.
The results of these measurements are shown in Table 2.

TABLE-US-00002 TABLE 2 Cellulose NFC membrane + 2% graphene oxide Concentration gradient 1 000 100 10 U (mV) 330 250 151 R (Ohm .Math. cm.sup.2) 0.16 0.16 0.145 I (mA) 2063 1 563 1 041 Pmax W/m.sup.2 1702 977 393 U Nernst (mV) 140 90 45 U Osmo (mV) 190 160 106 I Nernst (mA) 875 563 310 I Osmo (mA) 1 188 1 000 731 P Osmo Max(W/m.sup.2) 564 400 194

With:

[0203] U Osmo the membrane potential from which the Nernst potential of the electrodes is deduced (U Nernst)

[0204] I Osmo the current linked to the membrane, calculated by measuring the electrical resistance of the membrane according to Ohm's law I=U/R

[0205] P Osmo Max is calculated by the formula Pmax=(U×I)/4

The membrane powers are expressed in W/m.sup.2 by multiplying by 10 000 the values obtained on 1 cm.sup.2 of membrane.
It has also been observed that by applying a pressure of 3 to 4 bars to the membrane between two metal plates during heating at 85° C., the mechanical stability of the membrane is improved by 10 to 20%.