NL2003106C2

NL2003106C2 - Membrane, stack of membranes for use in an electrode-membrane process, and device and method therefore.

Info

Publication number: NL2003106C2
Application number: NL2003106A
Authority: NL
Inventors: Sybrandus Jacob Metz; Joost Veerman
Original assignee: Stichting Wetsus Ct Excellence Sustainable Water Technology
Priority date: 2009-06-30
Filing date: 2009-06-30
Publication date: 2011-01-04
Also published as: WO2011002288A1

Description

Membrane, stack of membranes for use in an electrodemembrane process, and device and method therefore 5 The present invention relates to membranes for use in an electrode-membrane process. These processes include electro-dialysis (ED) , reverse electro-dialysis (RED), membrane capacitive-deionisation (CDI), fuel cells, microbial fuel cells (MFC) and redox flow batteries.

10 Existing electro-membrane processes are provided with ion exchange membranes capable to transport cations or anions from one side of the membrane to the other. On both sides of the membrane in the electro-membrane processes there are provided fluids comprising ions that are subjected 15 to a driving force to transfer through the membrane. For example, in an RED stack with cells comprising an anion exchange membrane (AEM), a seawater compartment, a cation exchange membrane (CEM) and a river water compartment, wherein the water compartments comprise spacers giving 20 stability and acting as a turbulence promoter, the ions in the seawater tend to diffuse through the membranes towards the river water. In fact, the Na+ ions diffuse through the CEM and Cl“ ions diffuse through the AEM. In a RED process this ionic current is converted to an electrical current on 25 the electrodes thereby generating energy.

Electro-membrane processes suffer from resistances. These resistances include resistances caused by the membranes, and the fluid compartment. The resistances in the compartment include electrical resistances as well as 30 hydrodynamic resistances.

The object of the present invention is to improve the membranes for use in an electro-membrane process, thereby improving the overall efficiency of such process.

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This object is achieved with the membrane according to the invention, the membrane comprising: - membrane material; - one or more fluid supply channels provided in or on at 5 least one side of the membrane material; - one or more fluid outlet channels provided in or on at least one side of the membrane material, wherein the fluid supply channels are connected to the fluid outlet channels through passage ways.

10 By providing supply and outlet channels for the fluids on one hand and passage ways on the other hand, the functions of fluid supply and diffusion of ions is largely separated. In existing configurations these different functions are combined in the space between the membranes 15 that is defined by the spacer. According to the invention, the supply and outlet channels form the fluid supply part, while the passage ways define the reactor part. This enables providing relatively short fluid paths thereby minimising the hydrodynamic resistances associated with the fluid flow. 20 This improves the overall efficiency of the electro-membrane process, and especially the RED process.

The membrane material comprises an anion exchanging membrane material or a cation exchanging membrane material. The channels and/or passageways can be provided on 25 one side of the membrane material. This enables the provision of these channels and passageways in the compartment exhibiting the highest resistances and thereby the lowest efficiency. For example, in RED processes, this would typically be the river water compartment.

30 Alternatively, the channels and/or passageways are provided on both sides of the membrane. By providing the channels and/or passageways on both sides, the efficiency of the compartments on both sides of the membrane can be improved.

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As an additional advantage of providing supply channels and passageways in the membrane material the use of separate spacers is no longer required. This improves the assemblage of a stack of membranes according to the present 5 invention. Furthermore, investment costs are minimised as less parts are required. In addition, as no spacers are required the number of gaskets can also be reduced, and, preferably, no gaskets are required at all. This further improves the assemblage of a membrane stack and further 10 reduces investment costs. As a further advantage of reducing the number of parts, the possibilities for recycling material is improved as separating a stack of membranes, comprising only CEM and AEM, into different compounds is simplified significantly, for example.

15 A further additional advantage of the membrane according to the present invention is that up scaling of the electro-membrane process comprising the membranes according to the present invention is possible without requiring a complete redesign of the process and/or without a 20 significant efficiency loss. This advantage is mainly achieved by separating the functions of the supply part and the reactor part.

In a preferred embodiment according to the present invention, the passageways are constructed such that the 25 passageways are the main exchange positions for exchange of ions from one side of the membrane to the other.

By constructing the passageways such that the exchange of ions from one side of the membrane to the other is concentrated in or around these passageways it is 30 possible to separate the functions of the supply part and the reactor part, with the reactor part being the passageways. In a presently preferred configuration of these passageways the passageways have a depth of the passage, in 4 the direction substantially perpendicular to the membrane surface, significantly smaller as compared to the depth of the supply and outlet channels. This results in the electrical resistance in the fluid compartments being 5 reduced at the locations of the passageways. Therefore, the fusion of ions through the membranes is concentrated in or around the passageways. The overall effect of this concentration is an increased transfer of ions through the membrane thereby improving the overall efficiency of the 10 electro-membrane process, like a RED process. In a further preferred configuration of the passageways these passageways have a larger width, in a direction substantially parallel to the membrane surface, as compared to the supply and outlet channels. This increases the area of the membrane 15 with the concentrated diffusion of ions. This further increases the overall efficiency of the electro-membrane process .

In a further preferred embodiment according to the present invention the membrane material further comprises 20 one or more distribution channels between the supply and/or outlet channels and the passageways.

By providing a distribution channel between the supply channel and the passageway and/or a distribution channel between the passageway and the outlet channel a 25 (higher order) distribution network is achieved in the membrane according to the present invention. The provision of distribution channels results in a type of flexible network of channels, comparable to human lunges, for example. Also in this network the functions of supply and 30 reaction are separated. This improves the possibilities for up scaling the electro-membrane process using the membrane according to the present invention. These distribution 5 channels can be provided on one or both sides of the membrane material.

The present invention also relates to a stack of membranes for use in an electro-membrane process, the stack 5 comprising a number of membranes as described above, wherein between two adjacent membranes a first type of fluid compartment is provided that forms a fluid couple with a second type of fluid compartment such that ions are subjected to a driving force to move through the membrane 10 material from one compartment to the other.

Such stack of membranes provides the same effects and advantages as those stated with reference to the membrane .

In addition, in a preferred embodiment according 15 to the present invention the channels are provided in the fluid compartments having the lowest ion concentration. For example, in a RED process, the river water compartment has the lowest ion concentration and thereby the highest electrical resistance.

20 By providing the channels according to the present invention, the functions of supply and diffusion are separated resulting in an improved overall efficiency of the process as mentioned above.

Furthermore, in a preferred embodiment according 25 to the present invention alternately a membrane is provided having channels on both sides of the membrane and a membrane without having channels at all. This results in each compartment having on one side thereof the channels according to the invention and on the other side a more 30 conventional type of membrane. By providing such hybrid configuration of stack of membranes the benefits of the membrane according to the present invention can be achieved, 6 while investment costs associated with the membranes are kept to a minimum.

In a further preferred embodiment according to the present invention the stack of membranes further comprises 5 loosening means for enabling cleaning of the stack.

By providing loosening means it is possible to clean the membranes without dismantling the entire stack. By loosening the stack of membranes, the compartments can be flushed and thereby cleaned in an effective and easy way.

10 After cleaning, the loosening means are returned to their original position that enables an optimal processing of the electrode-membrane process. Optionally, cleaning includes the use of a back flush, i.e. providing a flow in the other direction. Especially in case the passageways have a smaller 15 depth as compared to the supply channels, contamination and the like will concentrate at the entrance of the passageways. The use of a back flush will flush these contaminations and the like away from the membrane.

An additional advantage of the loosening means is 20 the possibility to maintain the operation of the electromembrane process while cleaning. During cleaning the efficiency will be reduced, however, the process may continue producing output, while in existing processes the stack of membranes must be completely dismantled thereby 25 introducing a significant standstill of the process. This improves the overall performance of the electro-membrane process even further.

In a further preferred embodiment according to the present invention the adjacent membranes are fixedly 30 connected.

By connecting the membranes, for example by gluing the outer edges together, a stable and robust stack of membranes is achieved. This configuration does not reguire 7 the use of spacers and gaskets. Furthermore, by combining this configuration of stack of membranes with the loosening means mentioned above it is possible to clean this configuration in an efficient and effective way.

5 In a further preferred embodiment according to the present invention, the membranes are spiral-wounded.

Spiral-wounded membranes result in a relatively compact configuration of the stack of membranes according to the present invention. This improves the process output as 10 function of the process volume.

The present invention further also relates to a device and a method for performing an electro-membrane process. The method comprises the steps of: - providing a stack of membranes as described above; and 15 - operating the process.

Such device and method provide the same effects and advantages as those stated with reference to the membrane and the stack of membranes.

Further advantages, features and details of the 20 invention are elucidated on basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings wherein: - figure 1 shows a simplified RED membrane stack; - figure 2 shows membranes according to the present 25 invention; - figure 3 shows a side view of the membranes of figure 2; - figures 4A-D show embodiments of the membranes according to the invention.

A system 2 (figure 1) for a RED process, comprises 30 a number of CEMs 4 and AEMs 6. Membranes 4, 6 are placed between anode 8 and cathode 10. Between the AEM 6 and CEM 4 electrolyte compartments 12 are formed. In the illustrated system 2 alternately sea water 14 and river water 16 flows 8 through compartments 12. Due to the concentration differences of the electrolyte in the sea water 14 and the river water 16 electrolyte in the sea water 14 will be inclined to move to the river water 16 to level the 5 concentrations. In the simplified system 2 only sodium and chlorine ions are presented as positive and negative ions, respectively.

As the AEM 6 only allows anions to pass and the CEM 4 only allows cations to pass transport of anions and 10 cations will proceed in opposite directions. The anions (Cl-) will move in the direction of cathode 10. In order to maintain electric equality in the compartments 11 where anode 8 is placed, an oxidation reaction takes place. In the compartments 13 wherein cathode 10 is placed, a reduction 15 reaction takes place. This results in the generation of a flow of electrons in the electric circuit 18. In this circuit 18 electric work is performed by a load 20.

In the illustrated embodiment of system 2 use is made of the Fe(II)/Fe(III) redox couple for transfer of 20 electrons from and to the anode and cathode. To regenerate these components, the catholyte is transferred to the anode with flow 22 and the anolyte is transferred to the cathode with flow 24. This transfer can be arranged in a way known to the skilled person.

25 An AEM 26 and a CEM 28 (figure 2) are provided with channels according to the present invention. In the illustrated embodiments of membranes 26, 28, the channels are provided on one side of the membrane only. Membranes 26, 28 together form one RED cell, for example.

30 To illustrate the operation of membranes 26, 28 the example of a RED process will be used. Other electromembrane processes and/or other flows are also possible. A flow of sea water 30, flows through opening 32 in membrane 9 28 and enters the supply channel 34. On the other side of membrane 28 the flow 30 leaves membrane 28 through outlet channels 36 and finally opening 38. This results in an exiting sea water flow 40. Between supply channels 34 and 5 outlet channels 36 there are provided passageways 42 that in the illustrated embodiment are provided with a depth of the passageway significantly smaller than the depth of the supply channel 34 and outlet channel 36. The flow of sea water 30 passes through an opening 44 in membrane 26 without 10 entering membrane 26 and moves on to the next CEM. A flow of river water 46 passes membrane 28 through opening 48 and enters membrane 26 through opening 50. From opening 50 the river water enters supply channels 52. Via passageways 54 the flow enters outlet channels 56. The liguid leaves 15 membrane 26 through opening 58 passes membrane 28 through opening 60 as a flow 62.

A stack of membranes 64 (figure 3) comprising AEMs 26 and CEMs 28 are, in the illustrated embodiment, on one side of the membrane provided with supply channels. The 20 membranes 26, 28 comprise supply channels 66 and outlet channels 68 that are connected by passageways 70. Fluid flows from supply channel 66 to outlet channels 68 via passageways 70 indicated with flow 72. The current density 74 (II) is relatively small due to the long path of the 25 current through the supply channel 66. At the location of the passageways 70 the ionic current 76 (12) is relatively large especially due to the small paths for this current in the river water compartment. Also the current 78 (13) by the outlet channels 68 is relatively small. In this 30 configuration the hydrodynamic resistances in the supply channel 66 and outlet channel 68 are minimised.

By operating system 2 using membranes 26, 28 by providing the reguired flows to the electro-membrane 10 process, in the illustrated embodiment a RED process, the process is operated efficiently.

In an embodiment of membrane 78 according to the invention (figure 4A) fluid enters membrane 78 via opening 5 80 and reaches supply channel 82. Supply channel 82 distributes the fluid towards the passageways 84. The fluid passes passageways 84 and enters outlet channel 86 that transports the fluid to the exit opening 88. Openings 90, 92 are used to transport fluid to the adjacent membrane.

10 Openings 80, 88, 90, 92 have a depth equal to the thickness of membrane 78. Supply channel 82 and outlet channel 86 are provided with a relatively large depth as compared to the depth of the reactor part or passageways 84.

A higher order membrane design results in an 15 alternative membrane 94 (figure 4B) that comprises a fluid supply opening 96, supply channels 98, passageways 100, outlet channels 102 and exit openings 104. Also in this embodiment openings 106 and 108 enable transport of fluid to an adjacent membrane. In the illustrated embodiment the 20 supply channels 98 and outlet channels 102 are branched to achieve a network of channels and passageways. The depth of the supply and outlet channels 98, 102 is about 80% of the thickness of membrane 94, while the depth of passageway 100 is about 20% of this thickness. For a thickness of membrane 25 94 of about 0.5 mm this would mean a channel depth for the passageway 100 of about 0.1 mm and for the other channels of about 0.4 mm. The width of the channels in the illustrated embodiment is about 8 mm and for the passageways about 2 mm with the passageways 100 spaced 1 mm from each other. The 30 length of passageways 100 is about 15.6 mm and the diameter of openings 96, 104, 106, 108 is about 8 mm. The total length of membrane 94 is 150 mm. Membrane 109 is placed alternately with membrane 94 in a stack of membranes.

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Membrane 109 is provided with fluid through opening 108 and the fluid leaves membrane 109 through exit opening 106.

Especially when up scaling the membrane 94 to a larger membrane 110 (figure 4C) additional distribution 5 channels 112 are provided in membrane 110. Membrane 110 comprises openings 114, 116, 118, 120, supply channels 122 with distribution channels 112, and outlet channels 124 with distribution channels 126. Distribution channels 112, 126 are connected to passageways 128. This results in a branched 10 network of channels in membrane 110. The use of such higher order network with distribution channels 112, 126 enables an efficient up scaling of the membrane.

In an alternative embodiment, membrane 130 (figure 4D) is similar to membrane 110 with the exception of the 15 provision of additional inlet and outlet openings 114, 116. This embodiment of membrane 130 is especially appropriate with increasing membrane dimensions such that the supply and outlet of the fluids can be effectuated more efficiently using the additional openings 114, 116.

20 Depending on the dimensions of the membranes used in the electro-membrane process the number of distribution channels and further branches thereof can be designed.

The present invention is by no means limited to the above described embodiments thereof. The rights sought 25 are defined by the following claims, within the scope of which many modifications can be envisaged. Although the invention is illustrated for a RED process, it can also be applied to other electro-membrane processes including ED. In an ED process the desalinated water conducts electricity 30 very inefficiently. Therefore, the membranes according to the present invention can also be applied in an effective and efficient way to ED processes.

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CLAUSES

1. Membrane for use in an electro-membrane process, the 5 membrane comprising: - membrane material; - one or more fluid supply channels provided in or on at least one side of the membrane material; - one or more fluid outlet channels provided in or on at 10 least one side of the membrane material, wherein the fluid supply channels are connected to the fluid outlet channels through passage ways.

2. Membrane according to claim 1, wherein the membrane 15 material comprises an anion exchanging membrane material or a cation exchanging membrane material.

3. Membrane according to clause 1 or 2, wherein the channels are provided on both sides of the membrane.

20 4. Membrane according to clause 1, 2 or 3, wherein the passage ways are constructed such that the passage ways are the main exchange positions for exchange of ions from one side of the membrane to the other.

25 5. Membrane according to one or more of clauses 1-4, wherein the membrane material further comprises one or more distribution channels between the supply and/or outlet channels and the passage ways.

30 13 6. Stack of membranes for use in an electro-membrane process, the stack comprising a number of membranes according to one or more of clauses 1-5, wherein between two adjacent membranes a first type of fluid compartment is 5 provided that forms a fluid couple with a second type of fluid compartment such that ions are subjected to a driving force to move through membrane material from one compartment to the other.

10 7. Stack of membranes according to clause 6, wherein the channels are provided in the type of fluid compartments having the lowest ion concentration.

8. Stack of membranes according to clause 6 or 7, 15 wherein alternately a membrane is provided having channels on both sides of the membrane, and a membrane without having channels .

9. Stack of membranes according to clauses 6, 7 or 8, 20 further comprising loosening means for enabling cleaning the stack .

10. Stack of membranes according to one or more of clauses 6-9, wherein the adjacent membranes are fixedly 25 connected.

11. Stack of membranes according to one or more of clauses 6-10, wherein the membranes are spiral-wound.

30 12. Device for performing an electro-membrane process, comprising a stack of membranes according to any of clauses 6-11.

14 13. Method for performing an electro-membrane process, comprising the steps of: - providing a stack of membranes according to any of clauses 6-11; and 5 - operating the process.

Claims

A membrane for use in an electro-membrane process, the membrane comprising: 5. membrane material; - one or more fluid supply channels provided in or near at least one side of the membrane material; - one or more fluid outlet channels provided in or near at least one side of the membrane material, wherein the fluid supply channels are connected to the fluid outlet channels by passages.

2. Membrane according to claim 1, wherein the membrane material comprises anion exchange membrane material or cation exchange membrane material.

A membrane according to claim 1 or 2, wherein the channels are provided on both sides of the membrane. 20

4. A membrane according to claim 1, 2 or 3, wherein the passages are constructed such that the passages are the most important exchange positions for exchanging ions from one side of the membrane 25 to the other side.

5. Membrane as claimed in one or more of the claims 1-4, wherein the membrane material further comprising one or more distribution channels between the supply and / or outlet channels and the passages.

A membrane stack for use in an electro-membrane process, the stack comprising a number of membranes according to one or more of the claims 1-5, wherein between two adjacent membranes a first type of fluid compartment is provided that forms a fluid couple with a second type of fluid compartment such that ions are exposed to a driving force to move through the membrane material from one compartment to the other.

Membrane stack according to claim 6, wherein the channels are provided in a type of fluid compartment with the lowest ion concentration. 15

A membrane stack according to claim 6 or 7, wherein alternately a membrane is provided with channels on both sides of the membrane, and a membrane without channels. 20

A membrane stack according to claim 6, 7 or 8, further comprising releasing means for facilitating cleaning of the stack.

The membrane stack according to one or more of claims 6-9, wherein the adjacent membranes are fixedly connected.

11. Membrane stack according to one or more of the claims 6-10, wherein the membranes are spiral wound.

Device for performing an electro-membrane process, comprising a membrane stack according to one or more of the claims 6-11.

A method for performing an electro-membrane process, comprising the steps of: providing a stack of membranes according to one or more of claims 6-11; and - conducting a process.