A multi-layered filter comprising chitosan-doped activated carbon fiber and production method thereof

Abstract

The invention relates to a multi-layered filter functioning according to the carbon dioxide capture by adsorption technique, which is one of the implementations of post-combustion carbon dioxide capture, and to the production method of said filter.

Description

[0001] DESCRIPTION

[0002] A MULTI-LAYERED FILTER COMPRISING CHITOSAN-DOPED ACTIVATED CARBON FIBER AND PRODUCTION METHOD THEREOF

[0003] Technical Field

[0004] The invention relates to a multi-layered filter functioning according to the carbon dioxide capture by adsorption technique, which is one of the implementations of post-combustion carbon dioxide capture, and to the production method of said filter.

[0005] State of the Art

[0006] As a result of the increasing release of greenhouse gases into the atmosphere, global warming has become an alarming threat to the environment and human life. Although many greenhouse gases such as carbon dioxide (CO2), methane (CH4), N2O, SOX, etc. are released into the atmosphere, the largest share of these gases belongs to carbon dioxide. Therefore, in the fight against global warming, it is crucial to develop and utilize CO2capture and storage (CCS) technologies to address the demand to reduce CO2 emissions. Carbon dioxide capture is the first step of CCS, and there are generally three types of carbon dioxide capture routes. These are; pre-combustion, oxy-fuel combustion, and post-combustion capture. In recent years, postcombustion CO2 capture has received more attention, as various materials and methods (such as absorption, adsorption, membrane separation and cooling techniques) can be used for CO2 separation and capture in this technique. However, said methods and materials are not fully successful in CO2separation and capture processes.

[0007] Today, large international companies and brands have started to use some indices to measure the environmental performance of their products for the purpose of sustainable production. In doing so, the suppliers in the entire production chain are inspected and these suppliers are required to fulfill some environmental criteria. One of these criteria is achieving low-emission production. In the near future, manufacturers that do not meet these criteria risk not finding customers. Since the countries to which Turkey exports the most are mostly European Union countries, Turkish companies are currently inspected in terms of these criteria and may face sanctions. These inspections and sanctions have been increasing in recent years in the textile and ready-to-wear sector, which is Turkey's largest sector with an export surplus. Therefore, from an economic point of view, the development of methods and materials to reduce carbon emissions and the accumulation of technological readiness and know-how to enable the domestic production of these materials have become indispensable for the country in the short and long term.

[0008] Due to the depletion of natural resources and the increase in waste disposal costs, recycling of textile wastes is becoming increasingly important all over the world. On the other hand, the reuse or recycling of consumed products is still at very low levels. In Turkey, there is a textile recycling industry concentrated especially in U§ak and its surrounding areas. Recycling companies break down woven or knitted waste textile materials into fibers and produce new products such as carpets, felts, and filling materials from these fibers. However, the recycled textile products obtained are mostly in the market as low quality and low value-added products. As an alternative, it is necessary to develop functional materials with high added value from waste textile materials.

[0009] In the state of the art, although activated carbon fabrics and felts are commercially produced for the implementations of carbon dioxide capture, there is no textile-based filter specifically produced for especially carbon dioxide capture. In general, it is possible to use substances such as powdered activated carbons, granular activated carbons, zeolites. However, since said materials are in powder or granular form, they need additional carrier equipment. The powdery nature of these materials, their brittle structure and the problem of clogging of the system during implementation are disadvantages for practical use.

[0010] In the present art, activated carbon fibers used for adsorption are produced using acrylic fibers (PAC), regenerated cellulose fibers (especially rayon), pitch-based fibers and phenolformaldehyde fibers. Therefore, an additional fiber production stage is required. In addition, the mechanical strength of activated carbon fibers is very low and they are easily torn and shredded.

[0011] The literature search conducted by taking into account the carbon dioxide adsorption methods and conditions (1 bar, 298 K) in the state of the art is given in Table 1 below.

[0012] Table 1 . Comparison of carbon dioxide adsorption values of activated carbon fibers produced with various fibers in the literature

[0013] As can be seen from the table given above, there are studies examining the chemical activation of acrylic fibers with KOH and the carbon dioxide adsorbing performance of the activated carbon fibers obtained. However, there is no use of waste fiber and chitosan application in the said studies. Further, the results given in the table show that the carbon dioxide adsorbing performance is quite low. Further, other documents in the state of the art are given in detail below in the form of Table 2. Table 2. Documents in the state of the art and their comparison

[0014] As can be understood from the table given above, waste textile fibers are not recycled and used in these documents. This leads to disadvantages such as the necessity of an additional fiber production step and therefore the difficulty of sustainable material production.

[0015] There is a need to provide new developments in order to eliminate said disadvantages stated above and in the state of the art.

[0016] Summary of the Invention

[0017] The present invention relates to a multi-layered filter functioning according to the carbon dioxide capture by adsorption technique, which is one of the implementations of post-combustion carbon dioxide capture, and to the production method of said filter, in order to eliminate the aforementioned disadvantages and to provide new advantages to the related technical field.

[0018] In the invention, there are activated carbon fibers in felt form in the middle layer and a carrier carbon fabric in the top layer. Between the carrier carbon fabric and the activated carbon fibers, there is a thermoplastic non-woven interlayer to hold these two structures together. Thanks to this multi-layered structure, the durability of the filter is increased, and also tearing and shredding are prevented. Further, the activated carbon fibers in the form of felt are protected from shredding, thus achieving an increase in the stability of the product.

[0019] The filter off the invention can be used as a carbon dioxide capturer in all kinds of implementations where carbon dioxide is released after combustion. Thus, it can be easily used in sectors such as the energy sector, which causes carbon dioxide emissions, all industrial sectors where fossil fuels are used, and the automotive sector.

[0020] The activated carbons contained in the invention provide high adsorption capacity, low cost, moisture resistance due to high hydrophobicity, and low energy requirement for regeneration.

[0021] The invention reduces carbon dioxide emission by capturing carbon dioxide released postcombustion. Thus, it reduces the global warming potential for each application where fossil fuels are used.

[0022] The filter of the invention is obtained by using waste textile fibers (acrylic, cotton, or wool). With the use and recycling of said waste products, a solution to the waste problem is provided. In addition, solutions are provided to the problems of transforming the textile recycling sector so that it can produce high value-added products, sustainable use of limited natural resources, and increasing the competitiveness of domestic producers.

[0023] In the invention, chitosan, a low-cost and environmentally friendly compound, is applied to the raw materials used in the production of activated carbon fiber. Thanks to the activated carbon fiber produced from chitosan-reinforced recycled fibers, higher carbon dioxide capture performance is provided compared to activated carbon fibers obtained from untreated fibers. In this way, the carbon dioxide capture performance of activated carbon fibers produced from waste textile fibers is brought to a competitive level with the performance of other commercial activated carbon fiber / fabric products.

[0024] The filter of the invention is very easy to use and has high strength due to its textile form and multi-layered structure. Since activated carbon fibers are produced using acrylic fibers, regenerated cellulose fibers (especially rayon), pitch-based fibers, and phenol-formaldehyde fibers, these fibers need to be produced for activated carbon fiber. In the invention, acrylic, cotton, or wool fibers obtained from textile wastes are used as raw materials in the production of activated carbon fibers. Thus, no additional fiber is produced to create raw materials, and both environmentally friendly and cheaper production is provided by using waste.

[0025] The invention provides the development of a functional material with high added value, which has the ability to adsorb carbon dioxide from recycled textile materials in felt form.

[0026] Description of the Drawings

[0027] The embodiments of the invention, briefly summarized above and discussed in more detail below, can be understood with reference to the example embodiments of the invention described in the accompanying drawings. It should be noted, however, that the accompanying drawings only illustrate typical embodiments of this invention and are not to be considered as limiting to its scope. Fig. 1. A representative view of the graph of carbon dioxide adsorption isotherms of PAC- based activated carbon felts with and without chitosan application (where "untreated" indicates activated carbon fibers produced without chitosan application)

[0028] Fig. 2. A representative view of the graph of carbon dioxide adsorption isotherms of CO-based activated carbon felts with and without chitosan application (where "untreated" indicates activated carbon fibers produced without chitosan application)

[0029] Fig. 3. A representative view of the graph of carbon dioxide adsorption isotherms of WO-based activated carbon felts with and without chitosan application (where "untreated" indicates activated carbon fibers produced without chitosan application)

[0030] Fig. 4. Representative views of PAC-based felt and activated carbon fiber SEM images.

[0031] Fig. 5. Representative views of CO-based felt and activated carbon fiber SEM images.

[0032] Fig. 6. A representative view of the layers contained in the filter of the invention.

[0033] Description of the References in the Drawings

[0034] For a better understanding of the invention, the description of the numbers in the figures is given below:

[0035] A. Middle Layer

[0036] B. Interlayer

[0037] C. Outer Layer

[0038] Detailed Description of the Invention

[0039] The example embodiments are described in more detail below with reference to the accompanying descriptions. Furthermore, the embodiments can be established in different forms and should not be interpreted as being limited to the embodiments specified herein. Rather, these example embodiments are provided so that this description will be thorough, and will fully convey the scope to those skilled in the art.

[0040] The terminology used in this description is intended to be used only to describe specific example embodiments and is not intended to be limiting. As used herein, the context of the forms “one”, “at least”, “preferably” and “and / or” comprise the plural forms unless clearly stated otherwise. The invention relates to a filter made of 5 layers, functioning according to the capture by adsorption technique, which is one of the implementations of post-combustion carbon dioxide capture. Said layers consist of activated carbon fiber, thermoplastic fabric, and carrier carbon fabric. In an embodiment of the invention, there is at least one activated carbon fiber, at least two layers of thermoplastic fabric, and at least two layers of carrier carbon fabric. In an embodiment of the invention, the middle layer (A) comprises activated carbon fiber in felt form, the interlayers (B) above and below the middle layer (A) comprise thermoplastic fabric, and the top and bottom layers comprise carrier carbon fabric, but the embodiment is not limited thereto. A representative view of said layers is shown in Figure 6.

[0041] In the invention, the middle layer (A) comprises activated carbon fiber, which is in felt form obtained from recycled textile fibers. In the invention, the interlayer (B) comprises commercial thermoplastic fabric that is made adhesive by heat treatment to ensure that the carbon fabric and the activated carbon fibers are bonded together. In the invention, the outer layer (C) comprises fabric woven from commercial carbon fibers as a carrier, which ensures increased strength of the activated carbon fibers.

[0042] The activated carbon fiber used in the invention is obtained by thermochemical processing of recycled felts of acrylic (PAG), cotton (CO), or wool (WO). Said production stages consist of stabilization of the structure by oxidation in the air environment, carbonization at high temperature (700-1000°C) in an inert gas environment, and chemical activation.

[0043] The carrier carbon fabric used in the invention is woven or knitted fabrics produced from commercial carbon fibers, but the embodiment is not limited thereto. The stability of the filter is ensured by using said fabrics as the outer layer (C).

[0044] The thermoplastic fabric used in the invention is commercial non-woven fabrics made of thermoplastic polymers that can become adhesive by heat treatment, but the embodiment is not limited thereto.

[0045] The production method steps of the multilayer filter of the invention are given below;

[0046] - Obtaining activated carbon fibers by subjecting felts of acrylic (PAG), cotton (CO), or wool (WO) mechanically recycled from textile wastes to chitosan application, stabilization, carbonization, and activation processes, respectively,

[0047] - Washing the obtained activated carbon fibers under condenser with 10-15% HCI solution at 90-100 °C for 45-60 minutes and with hot water at 80-100 °C for 8-10 minutes, respectively,

[0048] Drying at 100-110 °C for 20-25 hours after washing,

[0049] - stacking the carrier carbon fabric, thermoplastic fabric, dried activated carbon fiber, thermoplastic fabric, and carbon fabric on top of each other from bottom to top respectively, and holding at 120-180 °C under 0.1-0.3 MPa pressure for an average of 4-10 minutes,

[0050] - the thermoplastic fabrics soften or melt and the activated carbon fibers in felt form adhere between the carbon fabrics.

[0051] The method steps of the invention are performed in the order stated above. In summary, with the application of chitosan, the nitrogenous compound is first added to the structure, followed by stabilization to ensure that the fabric does not shred in heat treatments. Then, carbon fabric is obtained by carbonization and then pores are formed on the fibers by activation. The last steps are the process steps for the production of activated carbon fiber. With said steps, a multi-layered filter comprising chitosan-doped activated carbon fiber is obtained.

[0052] The steps in the chitosan application to acrylic (PAC), cotton (CO), or wool (WO) felts recycled from textile wastes in the first method step of the invention are given below.

[0053] Dip coating the felts of acrylic (PAC), cotton (CO), or wool (WO) in an aqueous solution of 0.5-1 .5% chitosan for 5 minutes,

[0054] - After dip coating, squeezing them through foulard cylinders such that the liquor ratio achieved / solution transferred to the fabric is 80-90% by weight,

[0055] Drying the felts at 85 °C for 3 hours and subjecting them to heat treatment at 180 °C for 30 minutes.

[0056] The felts are heat treated at 180 °C for 30 minutes to provide physical stabilization of chitosan.

[0057] In the invention, a 0.5-1 .5 chitosan solution having a molecular weight of 50,000 - 375,000 Da comprises an aqueous solution containing 2-5% acid. Said acids are preferably acetic acid, phosphoric acid, but the embodiment is not limited thereto. With said chitosan solution, the impregnation process is provided for raw materials such as acrylic (PAC), cotton (CO), or wool (WO).

[0058] The stabilization process applied after chitosan application to felts of acrylic (PAC), cotton (CO), or wool (WO) recycled from textile wastes in the first method step of the invention is

[0059] - subjecting the felts of acrylic (PAC), cotton (CO), or wool (WO) to oxidation in an air environment at 230-300 °C for 1-5 hours. In an embodiment of the invention, acrylic (PAG) and cotton (CO) felts are subjected to oxidation at 230 °C for 5 hours at a heating rate of 1 °C / min. Wool (WO) felts, on the other hand, are subjected to oxidation at 300 °C at a heating rate of 1 °C / min for 2 hours, but the embodiments are not limited thereto.

[0060] With the stabilization process stage included in the invention, it is ensured that the fiber form remains intact during and after the carbonization and activation processes that take place after stabilization.

[0061] The carbonization process is applied to the felts of acrylic (PAG), cotton (CO) or wool (WO) recycled from textile waste in the first method step under a nitrogen gas stream at 600 - 900 °C for 0.5-2 hours. In a preferred embodiment of the invention, the carbonization process is performed at 800 °C for 1 hour with a heating rate of 2 °C / min.

[0062] Chemical activation method with KOH (potassium hydroxide), ZnCh (zinc chloride), H3PO4 (phosphoric acid) or K2CO3 (potassium carbonate) is used in the activation process of felts of acrylic (PAC), cotton (CO), or wool (WO) recycled from textile wastes in the first method step of the invention. Said application steps are given below; impregnating carbonized felts with activating chemical solution prepared such that the ratio of felt: KOH by weight is 1 :0.5 - 1 :3,

[0063] Holding it at 105 °C for 24 hours after impregnation,

[0064] Under nitrogen gas flow, holding it at 500-800 °C for 0.5-1 hour with a heating rate of 5-10 °C / min in the pyrolysis reactor after holding.

[0065] In an embodiment of the invention, it is held under nitrogen gas flow at 700 °C for 1 hour with a heating rate of 10 °C / min in the pyrolysis reactor after holding, but the embodiment is not limited thereto.

[0066] Carbon-rich fibers (carbon fibers) are obtained by the carbonization process, and pore formation (mostly micro- and mesopores) is provided in the fibers with the activation process. In addition, the pores formed provide adsorption ability to the structure.

[0067] In the second method step of the invention, the activated carbon fibers obtained after chemical activation processes are washed under the condenser with boiling HCI solution and hot water, respectively. Said washing process with the water is continued until the pH is approximately 7. In the third method step of the invention, the drying process after washing takes place at 105 °C for 24 hours, but the embodiment is not limited thereto.

[0068] The activated carbon felts obtained by the invention are about 0.2-0.5 cm in thickness. Depending on the application, the thickness of the raw material felt can be adjusted, and it can be produced thinner or thicker.

[0069] In the last step of the invention, said carrier carbon fabric, adhesive intermediate layer, activated carbon fiber in felt form, adhesive interlayer, and carbon fabric are stacked on top of each other from bottom to top respectively, and kept under pressure at 150-180 °C for 5 minutes. Thus, the thermoplastic fabric in the adhesive interlayer softens or melts, allowing the activated carbon fibers in felt form to be trapped between the carbon fabrics.

[0070] The carbon ratios of the activated carbon fiber samples obtained by the invention are 68-70% for PAC (acrylic), 76-83% for CO (cotton), and 75% for WO (wool). Experimental studies show that the carbon content of activated carbon fibers produced from natural fibers increases with chitosan application. Similarly, the addition of chitosan increases the nitrogen content in the structure. The nitrogen content of PAC, CO and WO activated carbon fibers without chitosan was 1.9%, 0.52% and 0.53%, respectively, while it was 3.55%, 0.5-0.8% and 1.77%, respectively, in the samples with chitosan application. The experimental study for the invention containing said elemental analysis data is given in Table 3.

[0071] Table 3. Elemental analysis results for activated carbon fibers obtained from chitosan-applied and non-applied felts, (%) BET and carbon dioxide adsorption analysis of chitosan-applied and non-applied activated carbon felts for the filter of the invention were performed and the relevant results are given in Table 4. The BET surface area of the activated carbon fibers produced after chitosan addition (according to nitrogen gas adsorption technique in liquid nitrogen environment at 77 K by Brunauer, Emmet and Teller (BET) method) is 1373-1472, 1061 -1072, and 1575 m2 / g for PAC, CO and WO, respectively. Chitosan application reduces the surface area slightly. (1578, 1177, and 1807 m2 / g for PAC, CO and WO, respectively, for chitosan-free samples). On the other hand, it is determined that microporosity is much more dominant with the addition of chitosan in natural fiber-based (CO and WO) activated carbon fibers. With the invention, a crucial advantage is provided in terms of microporosity in carbon dioxide adsorption.

[0072] Table 4. BET and carbon dioxide adsorption analysis results of chitosan-applied and nonapplied activated carbon felts

[0073] Brunauer, Emmet and Teller (BET) method is used for carbon dioxide adsorption tests. According to said method, the adsorption capacity in carbon dioxide medium at 298 K is measured in mmol / g depending on the pressure. With the addition of chitosan, it is observed that the carbon dioxide adsorption capacity of activated carbon fibers, especially those produced from natural fibers, is greatly increased.

[0074] In addition, the carbon dioxide adsorption capacities (CO2 adsorption capacities at p / po=1 at 298 K) of activated carbon fibers produced from chitosan-applied PAC, CO and WO fibers are found to be 3.8-3.9 mmol / g, 4.0-4.1 mmol / g, and 4.3 mmol / g, respectively. It is observed that the fibrous structure of the material obtained at the end of activated carbon fiber production processes is preserved.

[0075] As can be seen from Figure 1 , higher carbon dioxide adsorption capacity is obtained in fabrics containing PAN fibers with the invention in which activated carbon fiber is produced after fabrics consisting of recycled fibers are impregnated with chitosan solution at the start.

[0076] As can be seen from Figure 2, a much higher carbon dioxide adsorption capacity is obtained in fabrics containing CO fibers with the invention in which activated carbon fiber is produced after fabrics consisting of recycled fibers are impregnated with chitosan solution at the start.

[0077] As can be seen from Figure 3, higher carbon dioxide adsorption capacity is obtained in fabrics containing WO fibers with the invention in which activated carbon fiber is produced after fabrics consisting of recycled fibers are impregnated with chitosan solution at the start.

[0078] Any features described in this description (including appended claims, summary and figures) may be replaced by other alternative features that may have equivalent or similar purposes, unless otherwise stated explicitly. That is, unless otherwise stated explicitly, each feature is only one example of a set of equivalent or similar features.

[0079] The above embodiments are intended only to describe the technical concept and features of the present invention, and the purpose of the present invention is to ensure that those skilled in the art understand the content of the present invention and practice the present invention, and the scope of the present invention is not limited thereto. Equivalent changes or modifications made in accordance with the spirit of the invention are intended to be included in the scope of the invention.

[0080] Industrial Applicability of the Invention

[0081] The invention relates to a multi-layered filter functioning according to the carbon dioxide capture by adsorption technique, which is one of the implementations of post-combustion carbon dioxide capture and to the production method of said filter, and is industrially applicable

[0082] The invention is not limited to the example embodiments above, and the person skilled in the art can readily present other different embodiments of the invention. These should be considered within the protection scope of the invention claimed by the claims.

Claims

CLAIMS1 . A method for producing a multi-layered filter functioning according to the carbon dioxide capture by adsorption technique, which is one of the implementations of post-combustion carbon dioxide capture, characterized by the steps of;- obtaining activated carbon fibers by subjecting felts of acrylic (PAC), cotton (CO), or wool (WO) mechanically recycled from textile wastes to chitosan application, stabilization, carbonization, and activation processes, respectively,- washing the obtained activated carbon fibers under condenser with 10-15% HCI solution at 90-100 °C for 45-60 minutes and with hot water at 80-100 °C for 8-10 minutes, respectively,- drying at 100-110 °C for 20-25 hours after washing,- stacking the carrier carbon fabric, thermoplastic fabric, dried activated carbon fiber, thermoplastic fabric, and carbon fabric on top of each other from bottom to top respectively, and holding at 120-180 °C under 0.1-0.3 MPa pressure for an average of 4-10 minutes,- the thermoplastic fabrics soften or melt and the activated carbon fibers in felt form adhere between the carbon fabrics.

2. A method according to Claim 1 , characterized by the steps below in order to enable chitosan application of the felts of acrylic (PAC), cotton (CO), or wool (WO) recycled from textile wastes in the first method step; holding the felts of acrylic (PAC), cotton (CO), or wool (WO) in an aqueous solution of 0.5-1 .5% chitosan for 5 minutes,- After holding, squeezing them through foulard cylinders such that the liquor ratio achieved / solution transferred to the fabric is 80-90% by weight,Drying the felts at 85 °C for 3 hours and subjecting them to heat treatment at 180 °C for 30 minutes.

3. A method according to Claim 2, characterized in that the 0.5-1 .5 chitosan solution having a molecular weight of 50,000 - 375,000 Da comprises an aqueous solution containing 2- 5% acid.

4. A method according to claim 3, characterized in that the acids used in the aqueous solution are acetic acid, phosphoric acid.

5. A method according to Claim 1 , characterized by, in order to enable stabilization processapplied after the chitosan application to the felts of acrylic (FAC), cotton (CO), or wool (WO) recycled from textile wastes in the first method step,- subjecting the felts of acrylic (FAC), cotton (CO), or wool (WO) to oxidation in an air environment at 230-300 °C for 1 -5 hours.

6. A method according to Claim 5, characterized in that the acrylic (PAC) and cotton (CO) felts are subjected to oxidation at 230 °C for 5 hours at a heating rate of 1°C / min.

7. A method according to Claim 5, characterized in that the wool (WO) felts are subjected to oxidation at 300 °C for 2 hours at a heating rate of 1 °C / min.

8. A method according to Claim 1 , characterized in that the felts of acrylic (PAC), cotton (CO) or wool (WO) recycled from textile waste in the first method step are subjected to a carbonization process under a nitrogen gas stream at 600 - 900 °C for 0.5-2 hours.

9. A method according to Claim 8, characterized in that the carbonization process is carried out at 800 °C for 1 hour at a heating rate of 2 °C / min.

10. A method according to Claim 1 , characterized by, in order to enable chemical activation process of felts of acrylic (PAC), cotton (CO), or wool (WO) recycled from textile waste in the first method step;- impregnating carbonized felts with activating chemical solution prepared such that the ratio of felt: KOH by weight is 1 :0.5 - 1 :3,Holding it at 105 °C for 24 hours after impregnation,Under nitrogen gas flow, holding it at 500-800 °C for 0.5-1 hour with a heating rate of 5-10 °C / min in the pyrolysis reactor after holding.

11. A method according to claim 10, characterized in that KOH (potassium hydroxide), ZnCk (zinc chloride), H3PO4 (phosphoric acid) or K2CO3 (potassium carbonate) is used in the chemical activation process.

12. A method according to claim 10, characterized in that it is held under a nitrogen gas flow at 700 °C for 1 hour with at a heating rate of 10 °C / min in the pyrolysis reactor after holding.

13. A method according to claim 1 , characterized in that in the third method step, the drying process is carried at 105 °C for 24 hours after washing.

14. A method according to claim 1 , characterized in that in the last method step, the carrier carbon fabric, the adhesive intermediate layer, the activated carbon fiber in felt form, the adhesive interlayer, and the carbon fabric are stacked on top of each other from bottom to top respectively, and kept under pressure at 150-180 °C for 5 minutes.

15. A filter obtained by a method according to any one of claims 1 -14.

16. A filter according to claim 15, characterized in that it comprises layers of at least one activated carbon fiber, at least two thermoplastic fabrics, and at least two carrier carbon fabric.

17. A filter according to claim 16, characterized in that the middle layer (A) comprises activated carbon fiber in felt form, the interlayers (B) above and below the middle layer (A) comprise thermoplastic fabric, and the top and bottom layers comprise carrier carbon fabric.

Images