GB2614704A

GB2614704A - Renewable energy source using Osmosis

Info

Publication number: GB2614704A
Application number: GB2119106.9A
Authority: GB
Inventors: Liberman Boris; Efrat Tomer
Original assignee: Ide Water Technologies Ltd
Current assignee: Ide Water Technologies Ltd
Priority date: 2021-12-29
Filing date: 2021-12-29
Publication date: 2023-07-19
Also published as: GB202119106D0

Abstract

The generation of hydrogen 11 from water 8 produced during osmotic processes, such as pressure retarded osmosis or forward osmosis is detailed. The low salinity water produced in a semi-permeable membrane 3 during these processes is subjected to electrolysis; splitting the water to produce hydrogen. A semi-permeable membrane 3 is defined with a salt rejection layer 4 and a support layer 5, which incorporates electrodes 9, 10 within the membrane to allow splitting of the water via electrolysis. The electrode(s) 9, 10 may comprise graphene and the membrane may further comprise a reference electrode. During the osmotic process, energy may be produced where the draw solution is provided by dissolving rock salt in salt domes.

Description

Renewable Energy Source using Osmosis

Field of the Invention.

The present invention relates generally to the production of a renewal energy source, in particular hydrogen, using osmosis, particularly but not exclusively forward osmosis or pressure retarded osmosis.

Background

The development of renewal energy sources is becoming increasingly important to address global warming and other environmental issues. Hydrogen is a good energy carrier for energy storage and hydrogen burns to produce water, with zero CO2 emissions. Thus, the efficient production and storage of hydrogen for energy generation is a very attractive proposition.

Water electrolysis technologies are known for producing hydrogen from water. Water is the reactant, which is dissociated to hydrogen and oxygen using a direct current.

Anode: H20 -11- IA 02+ 2H+ + 2e-Cathode: 2H+ + 2e H2 Overall: H20 H2 ± %02 A number of different types of water electrolysis processes have been investigated for hydrogen production including alkaline water electrolysis, proton exchange membrane water electrolysis, solid oxide water electrolysis and alkaline anion exchange membrane water electrolysis.

The satisfactory scale up of hydrogen generation may be hindered by a lack of a suitable source of water, a renewable energy source and/or a convenient location for storage of the hydrogen produced.

It is the aim of the present invention to provide an improved devices, processes and systems for hydrogen generation that address some or all of these issues.

Summary of the Invention

According to a first aspect of the present invention there is provided a semipermeable membrane comprising a salt rejection layer and a support layer, the membrane including at least one anode electrode and at least one cathode electrode, the electrodes comprising the salt rejection layer and/or being provided in, on or between one or both the salt rejection and support layers.

The semi-permeable membrane according to the first aspect of the present invention may be incorporated into osmotic processes and systems to enable electrolysis of water passing through the membrane to generate hydrogen and oxygen. Suitable membranes include but are not limited to reverse osmosis, nanofiltration, forward osmosis and pressure retarded osmosis membranes.

The electrodes may be incorporated into the semi-permeable membrane in many different configurations. For example, the at least two electrodes may be provided between the salt rejection and the support layers. Alternatively, at least one electrode may be positioned between the salt rejection layer and the support layer and at least one electrode may be provided on an external surface of the salt rejection layer. In another embodiment, the at least two electrodes may both be provided on an external surface of the salt rejection layer. The electrodes may be provided in the form of a grid or parallel spaced apart strips.

The salt rejection layer may be formed of a material that may serve as one of the electrodes.

The at least one electrode may be formed from graphene or an alternative conductive material. Thus, the salt rejection layer may be formed from graphene and comprise one of the electrodes. The support layer is preferably comprised of a porous material, preferably being a ceramic material.

The semi-permeable membrane may further comprise a reference electrode. Optionally, at least one dielectric material may be provided between the at least two electrodes.

According to a second aspect of the present invention, there is provided an osmotic process for the production of hydrogen and oxygen comprising delivering first and second solutions of different osmotic and gauge pressures to opposing sides of a semi-permeable membrane to create a low salinity solution across the membrane; the semi-permeable membrane including at least two electrodes; applying a current across the electrodes of the semi-permeable membrane to split the low salinity solution into hydrogen and oxygen; and collecting the hydrogen and oxygen.

Generally, the first solution is known as the draw solution and the second solution is known as the feed solution. For example, the feed solution may comprise sea water, brackish water, waste water or fresh water.

It is to be appreciated that the process of the second aspect of the invention preferably incorporates a semi-permeable membrane according to the first aspect of the present invention.

The osmotic process is preferably selected from pressure retarded osmosis and forward osmosis.

Preferably, the osmotic process further comprises: an enclosure comprising the semipermeable membrane having a first side and a second side opposite the first side; a first saline solution comprising the draw solution having an osmotic pressure POr and a gauge pressure PGr for entering the first side of the membrane; a second saline solution comprising the feed solution having an osmotic pressure POp and a gauge pressure PGp for entering the second side of the membrane; at least part of the feed solution from the second side of the membrane penetrating to the first side according to a net driving pressure defined by the balance of pressures PGr, POr, POp and PGp; wherein the draw solution and the penetrated part of the feed solution exit as a residual brine stream from the first side of the membrane via a residual brine outlet; a remainder of the feed solution at least periodically exits as a residual fluid stream from the second side of the membrane via an outlet and wherein at least part of a low salinity solution stream passes from the second side to the first side for splitting into hydrogen and oxygen as it passes across the semi-permeable membrane.

Preferably, the energy for operation of the process is produced efficiently. For example, the electricity for operation of the electrodes of the membrane may be provided using pressure retarded osmosis wherein the draw solution is provided by dissolving rock salt in salt domes. The dissolution of rock salt may be carried out under pressure, equal or near to PGr. Alternatively, dissolution may take place under atmospheric pressure. It is to be appreciated that the salt domes may also be used to store the hydrogen generated by the process.

A third aspect of the present invention provides a system for the production of hydrogen and oxygen from water comprising an enclosure having at least one semi permeable membrane having at least two electrodes comprising a cathode and an anode, the membrane having a first side and a second side opposite the first side; an inlet for delivering a first saline solution comprising the draw solution having an osmotic pressure POr and a gauge pressure PGr for entering the first side of the membrane; a second inlet for delivering a second saline solution comprising the feed solution having an osmotic pressure POp and a gauge pressure POp for entering the second side of the membrane; at least part of the feed solution from the second side of the membrane penetrating to the first side according to a net driving pressure defined by the balance of pressures PGr, POr, POp and PGp; wherein the draw solution and the penetrated part of the feed solution exit as a residual brine stream from the first side of the membrane via a residual brine outlet; a remainder of the feed solution at least periodically exits as a residual fluid stream from the second side of the membrane via an outlet and wherein a low salinity solution stream forms and passes from the second side to the first side; wherein the electrodes of the membrane serve to split the low salinity solution stream into hydrogen and oxygen as it passes across the semi-permeable membrane.

It is to be appreciated that a suitable power source should be provided for applying an electrical current to the electrodes. Suitable means should be provided for collection and storage of the hydrogen and optionally the oxygen.

The system according to the third aspect of the present invention preferably incorporates at least one semi-permeable membrane according to the first aspect of the present invention.

Brief Description of the Drawings

For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made by way of example only to the accompanying drawings in which: Figure 1A is a schematic top view of a section through FO or PRO semi-permeable membrane incorporating an electrode according to one embodiment of the present invention; Figure 1B is a three-dimensional view of the semi-permeable membrane shown in Figure 1A, shown with salt rejection layer 4 and feed 7 removed; Figure 2 is a three-dimensional view of a semi-permeable membrane incorporating an electrode according to an alternative embodiment of the present invention; Figure 3 is a three-dimensional view of a semi-permeable membrane incorporating an electrode according to another embodiment of the present invention; Figure 4 is a three-dimensional view of a semi-permeable membrane incorporating an electrode according to an yet another embodiment of the present invention; and Figure 5 is schematic diagram illustrating one embodiment of a system of the present invention for hydrogen generation and storage.

Detailed Description

The present invention relates to the generation of hydrogen from water produced during osmotic processes, such as pressure retarded osmosis or forward osmosis. The very low salinity water produced in the semi-permeable membrane during these processes is subjected to electrolysis thereby splitting the water to produce hydrogen. This is achieved by the provision of novel semi-permeable membranes that incorporate electrodes within the membrane to allow splitting of the water via electrolysis, as explained in further detail below.

Pressure retarded osmosis (PRO) is an osmotically driven membrane process that uses energy harnessed from the mixing between high and low salinity streams to produce mechanical energy (utilization of Gibbs free energy of mixing). Water permeates through semi-permeable membranes from a low concentration feed stream into a high concentration, partially pressurized, brine stream ("draw solution"). The hydraulic pressure is less than its osmotic pressure resulting in a net osmotic driving force for transport of water (permeate stream) from the feed stream to the brine stream. The permeate stream becomes pressurised and dilutes the brine stream and the energy in the pressurised permeate stream can be converted into mechanical or electrical energy via a turbine generator.

Forward osmosis is an alternative osmotically driven membrane process that uses the membrane to treat two liquid feed streams. One side of the membrane is a feed solution (FS) with a low osmotic pressure and the other side of the membrane is the draw solution (DS) with a higher osmotic pressure. The difference in osmotic pressure causes water to pass through the membrane from the FS side to the DS side, simultaneously diluting the DS and concentrating the FS. The membranes consist of an active layer (or salt rejection layer) and a porous support layer, with the FS side generally facing the active layer.

Both these processes generate a very low salinity water stream across the membrane. The present invention utilizes this water stream for the production of hydrogen. However, the invention is not limited to these types of membrane and could also be implemented in other types, such as reverse osmosis membranes and nanofiltrafion membranes.

Figures 1A and 1B of the accompanying drawings illustrate one embodiment of a novel semi-permeable membrane 3 according to the present invention which may be incorporated into a PRO or FO process as described above. The membrane is provided with electrodes 9, 10 which enable it to be used for hydrogen generation in addition to its conventional use.

Referring to Figure 1A, a feed stream (saline solution, FS) 7 is delivered to a feed side 2 of the semipermeable membrane 3. The membrane 3 consists of a salt rejection layer 4 and support layer 5 with a series of parallel electrodes 9, 10 positioned to the front of the feed side 2. During forward osmosis (FO) or pressure retarded osmosis (PRO), part of the feed stream 7 (saline solution) moves from the feed side 2 of semipermeable membrane though the salt rejection layer 4 (omitted from Figure 1B for sake of simplicity) and support layer 5 to the opposite side 1 (draw side) as permeate 8. This permeate stream 8 has a very low salinity (around 2%) and thus has an osmotic pressure lower than the feed stream 7 (POO and lower than the draw solution stream 6 (POO.

Movement of stream 8 (permeate) takes place under balance of osmotic and gauge pressures POr; P0f; PGr; PGf. This stream 8 (permeate), exists only as a moving stream during active FO or PRO process. It cannot be extracted as liquid but due to its very low salinity it can be electrochemically split during transit through the body of semipermeable membrane 3. This is achieved by electrodes 9, 10 incorporated into the membrane 3 which allow a direct current to be applied to the permeate stream 8 causing the water to dissociate into hydrogen 11 and oxygen 12 which may then be collected for later use.

Figures 2, 3 and 4 of the accompanying drawings illustrate alternative embodiments of semi-permeable membranes 3 according to the present invention, the membranes 3 being provided with electrodes 9, 10 in different positions within the membrane. Identical features already discussed in relation to Figures 1A and 1B are given the same reference numerals.

Figure 2 shows the membrane 3 with both electrodes 9, 10 (anode and cathode) positioned externally on the surface of the salt rejection layer 4. In contrast, Figure 3 shows membrane 3 with both electrodes 9, 10 positioned between the support layer 5 and the salt rejection layer 4. In Figure 4, one electrode 10 is positioned between the support layer 5 and the salt rejection layer 4 with the other electrode 9 positioned on an external surface of the salt rejection layer 4.

Thus, it is to be appreciated that any type, number and arrangement of electrodes may be provided within the semi-permeable membrane to allow water splitting to be carried out. Two or multiple electrodes may be installed between salt rejection and support layers, the electrodes can be installed in the support layer only, in rejection layer only or the electrodes can be installed in both layers.

The electrodes must have the necessary conductivity and one of the electrodes may comprise the active or salt rejection layer 4. A preferred embodiment of the semipermeable membrane has a salt rejection layer that also forms one of the electrodes. One preferred material for the electrode, which may also comprise the active or salt rejection layer 4, is graphene. Dielectric layers may also be incorporated into the membranes between the electrodes. The layers may be interconnected and may be produced by techniques such as casting or printing, gluing or growing.

The present application is equally suitable for two, three or more electrode systems, such as cathode, anode and reference electrodes, or other. Additional non salt rejection layers (membranes) can be installed near to the electrodes.

The method of water split carried out within the membrane can be conducted using any one of the conventional techniques for water electrolysis, such as PEM Electrolysis, Microbial Electrolysis, Solid Oxide Electrolysis, Alkaline Electrolysis, or any otherway of water split. Thus, the invention is not limited to one particular process of water split.

Different types of hydrogen and oxygen evacuation systems (not shown on drawings) may be applied to remove the gases from the membrane system.

The present invention utilizes a permeate stream produced during PRO or FO. This stream cannot be directly measured because it cannot be extracted from the membrane and is extremely thin. However, the inventors have recognized for the first time that this stream may be used for hydrogen production due to its extremely low salinity. In this respect, it is not readily known that at the contact surface between the salt rejection layer and the support layer of FO and/or PRO membranes there is continuous movement of low salinity water which has salinity about 1000 times less than feed solution (seawater) moving on one side (FS) of the FO/PRO membrane and about 10,000 less salinity than the draw solution (DS) on the other side. The present innovation positions electrodes in this extremely thin low salinity stream for the purpose of water split for hydrogen and oxygen production. Thus, the present invention provides novel permeable membranes for enabling water split and furthermore, provides a novel method and system for generating hydrogen and oxygen from water.

Figure 5 of the accompanying drawings illustrate one scheme which may incorporate the system for generating hydrogen as hereinbefore described. In particular, the scheme allows for production of green energy using osmotic power generation from salt domes, the energy then being utilised for water split as hereinbefore described followed by storage of the hydrogen in empty salt caverns. In this manner, the invention provides an extremely energy efficient manner for the production of green energy in the form of hydrogen.

The scheme involves 3 cycles; cycle 100 involving efficient energy generation by PRO using the different salt concentrations between sea water 2 and dissolved salt water from salt domes 26; cycle 200 involving hydrogen generation from water electrolysis using the electricity produced in cycle 100 and cycle 300 which evacuates the hydrogen produced in cycle 200 and delivers it for storage in salt dome caverns 35 formed during salt extraction for the PRO in cycle 100.

In further detail, cycle 100 creates electricity using Pressure Retarded Osmosis process (PRO). The PRO is driven by the difference in salinity between highly concentrated salt 10-25% (draw solution DS) dissolved from salt domes 26 and seawater 3.6-4.5% (the feed solution FS). The dissolution of salt rock in salt caverns 26 as an option can take place under high gas pressure PGr which can be of about 200 bar and forms the draw solution. Alternatively, the dissolution can take place under atmospheric pressure. This draw solution is delivered to a first PRO module 100 by means of pump 25 via pipe line 23 and enters the first side of the module 100 via inlet 22 the first side. The feed stream (FS) enters the second side of the PRO module 100 via inlet 20. Part of the feed stream penetrates from the second side to the first side of the membrane 3 as low salinity permeate and mixes with the draw solution. A mix of the draw solution and permeate then exit module 100 via outlet 23. Part of this mix is directed to turbine 27 for electricity generation.

The residual amount of the feed stream is discharged from module 100 via outlet 21 to environment (for example, the sea as shown in Figure 5) The electricity generated in turbine 27 or similar device from the output from module 100 is then directed to a Forward Osmosis (FO) module 200 as energy source for electrochemical water split into hydrogen and oxygen, with the low salinity water for water split coming from FO process and the water split being achieved by the incorporation of a membrane according to the invention into the module that has electrodes for effecting electrolysis. Sea water 2 may be used for the feed solution 30.

Module 200 FO from construction point of view is similar to PRO module 100. Movement of permeate stream from the feed side of membrane to the draw side also takes place under balance of osmotic and gauge pressures POr; P0f; PGr; PGf. However, the difference between modules 100 and 200 is in the gauge pressures PGr; PGf. On module 200 the PGr and PGf are low and permeate movement from the FS side to the DS side takes place mostly under the difference in osmotic pressures POr' and POf'. The membrane has electrodes (i.e. 9,10 in Figures 1A to 4) and optionally an additional reference electrode (not shown in drawings). These electrodes, together with the electricity from module 100, allow splitting of the low salinity permeate stream to take place producing hydrogen and oxygen. Any residual water 33 may be returned to the sea 2.

It is to be appreciated that the semi-permeable membranes incorporating electrodes according to the present invention may be installed in module 100 and module 200, thus allowing water split to take place on module 100 and module 200 at the same time. Alternatively, the electrodes can be installed in module 100 only or in module 200 only.

Following production of hydrogen in cycle 200, the hydrogen is then stored in salt dome caverns 35 produced during salt extraction for PRO process 100.

It is to be appreciated that modifications to the aforementioned membrane, process and system may be made without departing from the principles embodied in the examples described and illustrated herein.

Claims

Claims: 1 A semi-permeable membrane comprising a salt rejection layer and a support layer, the membrane including at least one anode electrode and at least one cathode electrode, the electrodes comprising the salt rejection layer and/or being provided in, on or between one or both the salt rejection and support layers.
2 The semi-permeable membrane as claimed in claim 1, wherein the at least two electrodes are provided between the salt rejection and the support layers.
3 The semi-permeable membrane as claimed in claim 1, wherein at least one electrode is positioned between the salt rejection layer and the support layer and at least one electrode is provided on an external surface of the salt rejection layer.
4 The semi-permeable membrane as claimed in claim 1, wherein the at least two electrodes are provided on an external surface of the salt rejection layer.
The semi-permeable membrane as claimed in claim 1 wherein the salt rejection layer comprises one of the electrodes.
6 The semi-permeable membrane as claimed in any one of the preceding claims wherein at least one electrode is formed from graphene.
7 The semi-permeable membrane as claimed in any one of the preceding claims further comprising a reference electrode.
8 The semi-permeable membrane as claimed in any one of the preceding claims further comprising at least one dielectric material provided between the at least two electrodes.
9 An osmotic process for the production of hydrogen and oxygen comprising delivering feed and draw solutions of different osmotic and gauge pressures to opposing sides of a semi-permeable membrane including at least two electrodes; applying a current across the electrodes of the semi-permeable membrane to split the low salinity solution into hydrogen and oxygen; and collecting the hydrogen and oxygen.
The osmotic process according to claim 9 wherein the process is pressure retarded osmosis.
11 The osmotic process according to claim 9 wherein the process is forward osmosis.
12 The osmotic process according to any one of claim 9 to 11 further comprising: an enclosure comprising the semi-permeable membrane having a first side and a second side opposite the first side; a first saline solution comprising the draw solution having an osmotic pressure POr and a gauge pressure PGr for entering the first side of the membrane; a second saline solution comprising the feed solution having an osmotic pressure POp and a gauge pressure PGp for entering the second side of the membrane; at least part of the feed solution from the second side of the membrane penetrating to the first side according to a net driving pressure defined by the balance of pressures PGr, POr, Pop and PGp; wherein the draw solution and the penetrated part of the feed solution exit as a residual brine stream from the first side of the membrane via a residual brine outlet; a remainder of the feed solution at least periodically exits as a residual fluid steam from the second side of the membrane via an outlet; and wherein at least part of a low salinity solution stream passes from the second side to the first side for splitting into hydrogen and oxygen as it passes across the semi-permeable membrane.
13. The osmotic process according to any one of claims 9 to 12 further comprising generating electricity using pressure retarded osmosis wherein the draw solution is provided by dissolving rock salt in salt domes.
14. The osmotic process according to claim 13 wherein dissolution of rock salt is carried out under pressure equal or near to PGr.
15. The osmosfic process according to claim 13 or claim 14 further comprising storing the generated hydrogen in the salt domes.
16 The osmotic process according to any one of claims 9 to 15 wherein the semipermeable membrane is as claimed in any one of claims 1 to 8.
17. A system for the production of hydrogen and oxygen from water comprising an enclosure having at least one semi permeable membrane having at least two electrodes comprising a cathode and an anode, the membrane having a first side and a second side opposite the first side; an inlet for delivering a first saline solution comprising the draw solution having an osmotic pressure POr and a gauge pressure PGr for entering the first side of the membrane; a second inlet for delivering a second saline solution comprising the feed solution having an osmotic pressure POp and a gauge pressure PGp for entering the second side of the membrane; at least part of the feed solution from the second side of the membrane penetrating to the first side according to a net driving pressure defined by the balance of pressures PGr, POr, POp and PGp; wherein the draw solution and the penetrated part of the feed solution exit as a residual brine stream from the first side of the membrane via a residual brine outlet; a remainder of the feed solution at least periodically exits as a residual fluid stream from the second side of the membrane via an outlet and wherein a low salinity solution stream forms and passes from the second side to the first side; wherein the electrodes of the membrane serve to split the low salinity solution stream into hydrogen and oxygen as it passes across the semi-permeable membrane.
18 The system as claimed in claim 17 wherein the at least one semi permeable membrane of the enclosure is as claimed in any one of claims 1 to 8.The