A METHOD AND AN ARRANGEMENT FOR EXTRACTING CARBON DIOXIDE FROM AIR

FIELD OF THE INVENTION

The present invention relates to a method and an arrangement for extracting carbon dioxide from air.

BACKGROUND OF THE INVENTION Carbon dioxide (CO ₂ ) is a compound that is often regarded as undesirable. For example, carbon dioxide is generally regarded as a pollutant of the earth's atmosphere. In many technical or industrial processes, carbon dioxide is generated as a by-product, for example during combustion of oil or gasoline. Various proposals have been presented for removing carbon dioxide from air. For example, it has been suggested in US patent No. 6946288 that a ventilation system for a building can be provided with catalysing means for catalysing hydration of carbon dioxide contained in air into a solution of carbonate ions and hydrogen ions, and thereby remove carbon dioxide from the air.

Carbon dioxide is not always just an undesirable pollutant, it can also be used for different purposes. For example, it has been suggested in DE 196 44 684 Al that carbon dioxide can be used as a raw material in a process where methanol is manufactured. It is known that methanol can be used as a source of energy. For example, methanol can be used in a fuel cell in a process where electricity is generated. Methanol can also be used to produce energy by combustion.

Another possible use for carbon dioxide is disclosed in for example US patent No.

7008985 where it is suggested that carbon dioxide can be used as a propellant in aerosol spray containers.

It is an object of the present invention to provide a method and an arrangement for removing carbon dioxide from air, either to obtain carbon dioxide that will subsequently be put to use for other purposes or simply for reducing the content of carbon dioxide in the air.

DISCLOSURE OF THE INVENTION

The inventive method comprises the steps of providing a wall having a surface on which a carbonic anhydrase is arranged, exposing the wall to a stream of air, and using

the carbonic anhydrase to remove carbon dioxide from the stream of air. Optionally, the carbon dioxide so obtained may subsequently be used for some other purpose, for example to produce methanol. The carbonic anhydrase may be immobilized on the surface of the wall.

If the carbon dioxide is used to manufacture methanol, this can be done by a chemical reaction where electrical energy is used to transform water and carbon dioxide to methanol.

According to the invention, the wall is formed by a rotor blade, in particular a rotor blade of a wind power plant. Electrical energy from the wind power plant may optionally be used to transform water and carbon dioxide into methanol. Of course, even if the wall is formed by a rotor blade of a wind power plant, electrical energy used to produce methanol may also come from another source than the wind power plant.

The rotor blade may be divided into a plurality of cells separated from each other in the radial direction of the rotor blade. Each cell may then have a wall on which carbonic anhydrase is arranged, e.g. immobilized, such that each cell can extract carbon dioxide.

In case the carbon dioxide is used to produce methanol, the methanol so obtained may subsequently be used to produce electrical energy in for example a fuel cell.

The invention also relates to an arrangement for extracting/removing carbon dioxide from air. The arrangement comprises a wall having a surface upon which carbonic anhydrase is arranged/immobilized such that carbon dioxide can be extracted from a gas, in particular air. The wall is formed by a rotor blade, in particular the rotor blade of a wind power plant.

The arrangement may optionally also comprise a fuel cell connected to the wall and a source of electrical energy connected to the fuel cell.

In some embodiments, the rotor blade can be divided into a plurality of cells separated from each other in the radial direction of the rotor blade. At least some of the cells and possibly each cell has a wall on which carbonic anhydrase is placed, e.g. immobilized, such that some cells (or each cell) can extract carbon dioxide.

DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic representation of how carbon dioxide may be extracted in a cell designed for that purpose.

Figure 2 shows an embodiment of the invention where cells like the cell shown in Fig. 1 are placed in a rotor blade.

Figure 3 shows schematically how the invention may be applied to a wind power plant. Figure 4 is a cross-sectional schematic representation similar to Fig. 1 but showing more clearly the path of evacuation of carbon dioxide. Figure 5 is a side view of the cell shown in Fig. 4. Figure 6 shows schematically a process in a fuel cell.

Figure 7 is a schematic representation of a process run in reverse in relation to the process of Fig. 6.

DETAILED DESCRIPTION OF THE INVENTION With reference to Fig. 1, the inventive method for extracting carbon dioxide from air comprises providing a wall 1 having a surface 2 on which a carbonic anhydrase 3 is immobilized. Carbonic anhydrase is an enzyme that has the capacity to remove carbon dioxide from a stream of gas (for example a stream of air). A process where carbon dioxide is removed from air is disclosed in, for example, US patent No. 6143556 and reference is made to that document for further detail about carbonic anhydrase and the process by which carbonic anhydrase removes carbon dioxide from air. In the method according to the present invention, the surface 2 of the wall 1 is exposed to a stream of gas such as air. The carbonic anhydrase 3 is thereby put to use to remove carbon dioxide from the stream of gas. Optionally, the carbon dioxide so obtained may subsequently be used for some other purpose, for example as a propellant in aerosol spray containers or to manufacture methanol.

As indicated in Fig. 1, the wall 1 on the surface of which the carbonic anhydrase 3 is placed constitutes an outer surface of a cell 8 having an extraction chamber 19 for extraction of carbon dioxide. The chamber 19 may be divided into a front compartment 20 and a rear compartment 21 and where the front compartment 20 serves as an extraction compartment. The chamber 19 is filled with liquid. The liquid in the chamber 19 can be pumped around by a pump 22 that keeps the liquid circulating between the front compartment 20 and the rear compartment 21. The liquid pressure in the rear compartment should preferably be higher than the pressure in the front compartment 20. For this purpose, a flow restriction 23 may be formed between the rear and front compartment 20, 21. To enter the front compartment, the liquid must pass the flow

restriction 23. The liquid in the chamber 19 is an aqueous phosphate buffer system, i.e. it is based on water. The liquid may contain an anti-freezing agent. A rear wall 4 of the cell 8 is in contact with a primary evacuation conduit 24.

With reference to Fig. 2, the wall 1 is formed by a rotor blade 5 and is a part of the rotor blade 5. The rotor blade 5 is rotatably journalled such that the rotor blade may rotate. As indicated schematically in Fig. 3, the rotor blade 5 may in particular be the rotor blade 5 of a wind power plant 6.

The function of the arrangement is as follows. The rotor blade 5 rotates in the air. As the rotor blade 5 rotates in the air, it will contact large quantities of air that moves relative to the surface of the rotor blade 5. This is especially the case if the rotor blade 5 is the rotor blade 5 of a wind power plant and the rotation of the rotor blade 5 is caused by the wind. As a consequence, the carbonic anhydrase on the rotor blade 5 will contact much more air than if the carbonic anhydrase had been placed on a stationary wall. Carbon dioxide is absorbed by the carbonic anhydrase and passes through the wall 1 into the liquid in the front compartment 20 of the cell 8. The part of the wall 1 where the carbonic anhydrase 3 is placed is formed by a permeable or semipermeable membrane, for example a semipermeable plastic membrane or a lipid membrane. The membrane may be doped with ionophores to provide ion conducting channels. The liquid is circulated by pump 22 into the rear compartment 21. From the rear compartment 21, carbon dioxide passes through the rear wall 4 into the primary evacuation conduit 24. The rear wall 4 is also formed by a permeable or semipermeable membrane, for example a lipid membrane. During this process, the atmospheric pressure Pi is larger than the pressure P ₂ in the front compartment 20, i.e. Pi > P ₂ . The pressure P ₃ in the rear compartment 21 is also higher than the pressure P ₂ in the front compartment 20, i.e. P ₃ > P ₂ . The pressure P ₃ in the rear compartment 21 is also higher than the pressure P ₄ in the primary evacuation conduit 24.

Per second, 1 gram carbonic anhydrase can process 10 moles of carbon dioxide which equals 440 grams of carbon dioxide. In normal air, there is about 340 ml carbon dioxide per m ³ which equals 0.61 grams of carbon dioxide per m ³ . Consequently, 1 gram of carbonic anhydrase can process the carbon dioxide in 70 m ³ air per second.

The pH in the front compartment 20 should preferably exceed 7.0. A suitable pH level for the front compartment 20 may be, for example, 7.4. When pH is above 7, the carbon dioxide is more easily solved in the water phase in the front compartment 20 (the

extraction compartment). The carbonic anhydrase here works to transform the carbon dioxide into hydrocarbonate that is immediately solved in the liquid.

With reference to Fig. 2, the rotor blade 5 is preferably divided into a plurality of cells 8 separated from each other in the radial direction of the rotor blade 5, each cell 8 has a wall 1 on which carbonic anhydrase is arranged, e.g. immobilized, such that each cell 8 can extract carbon dioxide. If necessary, steps may be taken to reduce pressure in the cells.

In Fig, 3, the rotor blade is shown as being part of a wind power plant 6 and mounted on a hub 27. The hub is rotatably journalled in a housing 30 that is supported by a pillar 29.

As indicated in Fig. 4 and Fig. 5, the primary evacuation conduit 24 leads to a main evacuation conduit 25 that may be common to several cells 8 for extraction of carbon dioxide. With reference once again to Fig. 2, the main evacuation conduit 25 extends along the rotor blade 5 from an outer part of the blade 5 and up through the hub 27 of the rotor blade 5. The main evacuation conduit 25 can be connected to a source 26 of underpressure/vacuum that can be located inside the structure of the wind power plant 6. The source 26 of underpressure may be, for example, a pump or a fan. From the source 26 of underpressure, the carbon dioxide may optionally be sent through a further conduit 28 (see Fig. 3) to a further destination, for example to a storage tank for carbon dioxide or to a unit 9 where the carbon dioxide is used in a process for producing a further product. The unit 9 may be, for example, a fuel cell where carbon dioxide is used in a process to manufacture methanol. The unit 9 (for example a fuel cell 9) is thus connected to the wall 1 of the rotor blade 5 in such a way that carbon dioxide extracted from the air through the wall 1 can be transported from the wall 1 to the unit 9. In the above disclosed embodiment, the wall 1 is connected to the unit 9 through the conduits 24, 25 and 28 and the source of underpressure 26. However, it should be understood that the connection or communication line from the wall 1 to the unit 9 could be designed in other ways than that which has been disclosed above. For example, if a source of underpressure 26 is used, the source of underpressure 26 does not necessarily have to be located inside the structure of the wind power plant 6.

As mentioned above, the carbon dioxide extracted from air may optionally be used to produce methanol in a chemical reaction where electrical energy is used to transform water and carbon dioxide to methanol, i.e. electrical current + CO ₂ +H ₂ O → CH ₃ OH (the process is here indicated in a simplified form, in practice the process may include

the formation of intermediate compounds such as O ₂ ). When the rotor blade 5 is the rotor blade 5 of a wind power plant 6, electrical energy obtained from the wind power plant 6 can be used in a process where water and carbon dioxide is transformed into methanol. Alternatively, electrical energy for such a process may come from another source than the wind power plant 6. For example, it could come from the power-mains.

In order to produce methanol, a fuel cell 9 may be used. In a process to produce methanol, the fuel cell 9 will be run in reverse compared to its normal mode of operation where methanol would be used as fuel in a process where electricity is generated.

A possible process for producing methanol will now be explained with reference to Fig. 6. In Fig.6, it can be seen that the fuel cell 9 is shown as has an anode 15 and a cathode 16. The anode 15 and the cathode 16 are separated by a membrane 17. An electric circuit is indicated by the numeral 18. To produce methanol, carbon dioxide and water are fed into a fuel cell 9 through the opening 11 in the fuel cell 9. An electric current is added at the electric circuit 18. On the cathode side, water is added through opening 13 while O ₂ exits through opening 14 (it should be understood that Fig. 6 is a schematic representation). In Fig. 5, methanol (CH ₃ OH) leaves the fuel cell through opening 12.

It should be understood that the process can also be run in the opposite direction as indicated in Fig. 7. In Fig. 7, it is indicated how methanol is supplied to the fuel cell 9 through opening 12. In the resulting reaction, an electrical current is generated in the circuit 18.

It should be understood that the invention can also be described in terms of an arrangement for removing carbon dioxide from air. The arrangement comprises a wall 1 having a surface 2 upon which carbonic anhydrase 3 is immobilized such that carbon dioxide can be extracted from the air.

The function of the arrangement is as follows. When the wind is blowing, the rotor 5 of a wind power plant 6 is exposed to a stream of air. At the same time as electrical energy is generated by the wind power plant, carbon dioxide is extracted along the rotor blade 5.

From the rotor blade 5, a conduit may lead to a fuel cell 9 where the carbon dioxide can be transformed into methanol. A part of the electricity generated by the wind power

plant 6 is used for a reaction where the extracted carbon dioxide is used to produce methanol which can then be stored.

In some embodiments of the invention, the need for electrical energy may be monitored. For example, one or several indicators may be monitored in order to determine whether electrical energy is needed somewhere else. One such indicator may be, for example, the price of electricity. An increase in the price of electricity may indicate that the need for electricity has increased. At times when a high need for electricity is indicated, stored methanol may be used to produce electricity such that electricity can be produced when the need for electricity is large.

Instead of being a part of a wind power plant 6, the rotor blade 5 with carbonic anhydrase could be placed in an exhaust chimney where large amounts of gas containing carbon dioxide are discharged and it is desirable to reduce the level of carbon dioxide before the gas is discharged into the atmosphere. A rotor blade with carbonic anhydrase could also be used in a building to reduce the level of carbon dioxide.

With reference to Fig. 2, an embodiment is indicated where the rotor blade 5 is divided into a plurality of cells 8 that are separated from each other in the radial direction of the rotor blade 5. Each cell 8 has a wall 1 on which carbonic anhydrase 3 is immobilized such that each cell 8 can extract carbon dioxide. Since the cells 8 contain liquid, the liquid pressure could become undesirably high if one single cell extended along the entire rotor blade - the column of liquid would be high and the centrifugal forces would make the problem even more serious. If a plurality of cells 8 is used, the liquid in each cell can be separated from the liquid in the other cells. In this way, liquid pressure can be kept lower. Preferably, each cell should have an extension along the rotor blade (height) of no more than 20 mm even though dimensions larger than 20 mm could be considered. If the height of a cell is no more than 20 mm, this reduces the risk of excessively high pressure in the cell.

One aspect of the invention shall now be explained with reference to Fig. 4. In Fig. 4, the circulation of the liquid in chamber 19 is indicated as going in an anti-clockwise direction. In the front chamber adjacent the atmosphere, the liquid will then move in the direction of arrow C. The rotor blade 5 is preferably arranged such that, as the rotor blade 5 moves through the air, the air moves relative to the rotor blade in the direction of arrow A such that the wind assists in pressing the fluid in chamber 19 in the correct direction. In, for example, a wind power plant, the relative direction of movement of the

wind in relation to the rotor blade can be determined in advance and the cells 8 oriented such that the wind will assist in the circulation of liquid inside each cell 8.

With reference to Fig. 1, the arrangement according to the invention may optionally also include a fuel cell 9 where methanol can be may be manufactured. The fuel cell 9 is in communication with the wall 1 that is provided with carbonic anhydrase. A tank 10 may be connected to the fuel cell 9 such that methanol produced in the fuel cell 9 can be subsequently stored in the storage tank 10.

By placing the carbonic anhydrase 3 on a rotor blade 5 that rotates in the air, large amounts of air can come into contact with the carbonic anhydrase which means that larger quantities of carbon dioxide can be extracted. The invention can be used purely to reduce the content of carbon dioxide in air, for example in a building where humans live or work. For such purposes, the rotor blade could be a component of, for example, a fan and driven by a motor, for example an electric motor. The invention could also be put to use for such purposes where the objective is to obtain carbon dioxide. For such purposes, the rotor blade could be the rotor blade 5 of a wind power plant or some other device where a blowing wind causes the rotor blade to rotate.

The rotor blade provided with carbonic anhydrase could also be placed in an exhaust conduit where there is a flow of gas containing carbon dioxide. The rotatably journalled rotor blade 5 could then remove carbon dioxide from the gas and at the same time generate electrical energy.

While the invention has been described in terms of a method and an arrangement, it should be understood that these categories only reflect different aspects of one and the same invention. The method may thus comprise such steps that would be the inevitable result of using the inventive arrangement, regardless of whether such steps have been explicitly mentioned or not. In the same way, features of the arrangement have been explained with reference to the inventive method.