In-Situ High Temperature Filtration for Gas-Solid Separation in the Production of Carbide-Derived Carbon

Abstract

To improve the efficiency of the CDC production process, the present invention proposes a reaction apparatus (10) for producing carbide-derived carbon by reacting a halogen gas with a metal carbide material. The reaction apparatus (10) comprises a reaction chamber (12) and a filter device (18) configured to discharge gas and having at least one filter element (22) for performing gas-solid separation. The reaction apparatus (10) is characterized in that, during operation of the reaction apparatus (10), the reaction chamber (12) has a reaction zone (30) at a temperature above 600 °C and the filter element (22) is configured to perform gas-solid separation within the reaction zone (30).

Description

Technical Field

[0001] The present invention relates to an advanced production process of microporous carbon. The apparatuses and methods described herein relate to in-situ high-temperature filtration for gas-solid separation within the heating zone of a reactor and to the production of porous carbon and metal halides from metal carbides. More specifically, the apparatuses and methods described herein relate to processes and equipment for batch, semi-batch, or continuous gas-solid separation processes within the heating zone of a reactor, which are carried out by direct filtration as a result of the formation of porous carbon and metal halides by halogenation of metal carbides.

Background Art

[0002] Porous carbon materials have been found to be used in applications ranging from energy storage to filtration and adsorption processes. Particularly in energy storage and filtration applications, the high specific surface area of this type of material has attracted attention. Carbon derived from carbides (CDCs) is a type of microporous carbon with a narrow pore size distribution and a high surface area to volume ratio. Usually, CDCs are produced by chemically removing metal or metalloid carbides from metal or metalloid inclusions by a halogenation reaction at high temperatures (e.g., in the range of 200°C to 1200°C as the temperature of the reaction zone). Thereby, metal or metalloid chlorides and microporous carbon remain as products.

[0003] CDCs can be synthesized from many different precursors such as the following carbides. Binary carbides (TiC, SiC, Al4C3, Mo2C, SiC, B4C, ZrC, NbC, etc.), or similar compounds with oxygen (oxycarbides, MC x O y ), or similar compounds with nitrogen (carbonitrides, MC x N y ), or ternary carbides (M1 x M2 yC), and mixtures thereof. Usually, the precursor is in the form of a powder with a different particle size distribution, but aggregates, pellets, and carbide films can also be used. From the perspective of structural order, the precursor carbide can be a single crystal, polycrystal, porous biomorphic carbide, or other forms.

[0004] There are several methods for extracting atoms other than carbon from carbides, but the most widespread one is chemical extraction using a halogen gas (X2) at high temperature (Equation (1)): MC x +y / 2X2→MX y +xC (1)

[0005] Gas-solid reactors such as fixed-bed, rotary kiln, and fluidized-bed reactors can be used to react the raw materials (reactants), carbides, and halogen gas. The mixture of reactants and products is present in the heated reaction zone. In principle, the solid (fixed bed, fluidized bed) remains in the reaction zone (or reactor), the gas stream (halogen) flows in as a reactant, and the mixture of metal halides and halogen exits the reactor.

[0006] U.S. Patent Application Publication No. 2012 / 219488 discloses a typical fixed-bed reactor for the continuous production of porous carbon materials by halogenation of carbides.

[0007] In a typical type of reaction, chlorine gas (Cl2) is used. According to the mass balance of the chlorination reaction (see Equation (1)), the theoretical yield of carbon derived from carbide (CDC) obtained from different carbides ranges from about 6 wt% in the case of molybdenum carbide to almost 30 wt% in the case of silicon carbide. In practice, the main products of the chlorination reaction of carbides are chlorides of the respective carbide-forming metals or metalloids (MCl y ). Therefore, a reactor suitable for the efficient production of porous carbon by halogenation of metal carbides at high temperature needs to be designed to keep the temperature conditions in the heating reaction zone uniform and to separate both CDC and metal chlorides to the maximum extent.

[0008]

Table 1

[0009] The CDC recovery rate is related to the overall yield of the process. On the other hand, it is necessary to remove all solid components (in this case, CDC and / or partially reacted carbides and / or pure carbides) from the metal halide group and the gas stream of halogens exiting the reactor. If solids are contained in the gas stream, it will cause problems in downstream units (such as condensers, filters, pumps, etc.) and also hinder further processes of the metal halide group and halogens. Also, it is important to keep the conditions of the solids uniform. That is, if there are changes or fluctuations in the temperature of the solids, usually the properties of the produced CDC will not be uniform. This should be avoided. Furthermore, the solids (partially or fully converted CDC) should not come into contact with surfaces or materials that can be a source of contamination or surfaces or substances that may act as a catalyst to promote the graphitization of CDC.

[0010] Gas-solid reactors usually include gas-solid separation units such as cyclones and / or filters. Cyclones are effective as gas-solid separation devices in the particle size range of more than 20 μm, but the efficiency decreases as the particle size becomes smaller. The US Environmental Protection Agency (USEPA) reports the following efficiencies in the document (EPA-452 / F-03-005).

[0011]

Table 2

[0012] Therefore, particles in the range of 10 μm or less are likely not to be separated.

[0013] U.S. Patent No. 6,673,133 shows the difficulty of separating particles less than 50 μm in the FCC unit. As a result, the FCC catalyst concentration is 200 - 1000 mg / Nm 3 and becomes.

[0014] Even if it is possible to measure the PSD (particle size distribution) of carbides of metals or metalloids, which are raw materials used in CDC production, it should be noted that since the particles are affected by abrasion, the resulting CDC does not necessarily have exactly the same PSD as the raw material. This is caused by mechanical stress due to collisions between particles and collisions between the solid layer and the wall surface. As a result, the particles gradually deteriorate (abrade).

[0015] The exothermic nature of the reaction in CDC production is also a factor, causing thermal stress. This thermal stress occurs intermittently and may locally cause cracks (fragmentation) in the structure.

[0016] Using gas-solid separation methods such as cyclones and / or filters that require changes in flow characteristics (such as temperature) at different stages of CDC production is inefficient and exposes the material to different conditions, affecting its properties and ultimately the performance of the CDC. When materials leave the reaction zone or the reactor itself and come into contact with other unit operations or other structural materials, the fully or partially reacted CDC is exposed to contaminants, which will affect the performance of the material when it is returned to the reactor and recovered as a product. In addition, low gas-solid separation efficiency brings risks such as accumulation, formation of sludge due to condensation of metal halides, and blockage of unit operations, equipment, and pipes, which may have a serious impact on safety.

[0017] The gas flow associated with the production of CDC is composed of metal halides (e.g., metal chlorides) and halogen gases (e.g., chlorine) or their hydrogen derivatives (e.g., hydrogen chloride).

[0018] Due to the production reaction conditions of CDC, the gas is discharged from the reactor at a high temperature exceeding 600°C. Metal chlorides are known to accelerate the corrosion rate of metal alloys, so special materials are required for the structural materials of the condenser. Corrosion of the metal alloy results in the mixing of undesirable contaminants into the gas stream. Even with special materials, contaminants may mix in at high temperatures. That is, if any partially or fully reacted CDC comes into contact with different structural materials outside the reactor and is returned to the reactor or the heating zone, contaminants may be formed due to the high temperature and corrosivity of metal halides and halogens. These contaminants can affect the purity and properties of the produced CDC and ultimately its performance.

[0019] 316L stainless steel, a typical structural material that can be used in cyclones, has a recommended upper operating temperature of 343°C as described in a publication by Special Metals Corporation (SMC-026) when in contact with dry chlorine.

Summary of the Invention

[0020] The present invention aims to improve the efficiency of the CDC production process.

[0021] This object is achieved by the subject matter of the independent claims. Preferred embodiments are the subject matter of the dependent claims.

[0022] The present invention provides a reactor for reacting a halogen gas with a metal carbide material to produce carbon derived from the carbide. The reactor comprises a reaction chamber and a filter device having at least one filter element configured to discharge the gas and perform gas-solid separation. During operation, the reaction chamber has a reaction zone having a temperature exceeding 600°C, and the filter element is configured to enable gas-solid separation within the reaction zone.

[0023] Preferably, the reactor is configured as a fluidized bed reactor and includes a plenum and a gas distribution plate that separates the reaction chamber from the plenum. During operation, the reaction zone is formed adjacent to the gas distribution plate.

[0024] Preferably, the reaction chamber has an upper part of the reaction chamber. During operation, a non-reaction zone with a temperature of less than 600 °C is formed adjacent to the reaction zone, and the filtration element extends from the upper part of the reaction chamber through the non-reaction zone towards the reaction zone.

[0025] Preferably, the filtration element extends to the reaction zone. Preferably, during operation, the filtration element extends such that the filtration element extends into the fluidized material.

[0026] Preferably, the filtration element has a filtration wall that defines a gas channel, and the gas channel is separated from the reaction chamber by the filtration wall.

[0027] Preferably, the filtration element is made of a macroporous material, preferably a macroporous ceramic carbon material, and has a pore size configured to reduce the amount of carbon derived from partially or completely converted carbides leaking from the reaction chamber.

[0028] Preferably, the filter device includes a first filtration element and a second filtration element, and the first filtration element and the second filtration element are fluidly connected so as to combine the gas flows from each of the first filtration element and the second filtration element into a single exhaust gas flow.

[0029] The present invention provides a method for producing carbon derived from carbide having a temperature of more than 600 °C, which has a reactor, preferably a reaction chamber, in which a halogen gas and a metal carbide material are reacted in the reactor according to any one of the preceding claims, and during the reaction of the halogen gas and the carbide material, gas-solid separation is performed by a filtering element of a filtering device in a reaction zone of the reaction chamber.

[0030] Preferably, the reactor is configured as a fluidized bed reactor and includes a plenum and a gas distribution plate that separates the reaction chamber from the plenum, and during operation, the reaction zone is formed adjacent to the gas distribution plate.

[0031] Preferably, the reaction chamber has an upper part of the reaction chamber, and during operation, a non-reaction zone having a temperature of less than 600 °C is formed adjacent to the reaction zone, and the filtering element performs gas-solid separation in the non-reaction zone and the reaction zone.

[0032] Preferably, during operation, the filtering element contacts a material fluidized by a gas flowing from the plenum to the reaction chamber.

[0033] Preferably, the filtering element performs gas-solid separation with a filtering wall and discharges the gas filtered through the gas channel.

[0034] Preferably, the filtering device includes a plurality of filtering elements, and the filtering device combines the gas flows from each of the filtering elements into a single exhaust gas flow.

[0035] The present invention provides the use of a filtering element made of a porous material, which is brought into contact with a reaction zone at a temperature of at least 600 °C and optionally into contact with a corrosive environment such as a halogen gas to perform gas-solid separation.

[0036] The present invention provides an in-situ high-temperature filtration method for gas-solid separation in the heating zone of a fluidized bed reactor for producing carbon from a metal or metal-like carbide, or a mixture of such carbides, by reacting a carbide at a high temperature with a halogen-containing gas to extract non-carbon atoms from the metal or metal-like carbide.

[0037] The method described herein includes in-situ gas-solid separation in the heating zone of the reactor so that the gas stream exiting the reactor is free of solid particles. This reduces the impact of any parameter variations on the partially or fully converted CDC and reduces exposure to surfaces and structural materials that could introduce impurities into the solid bed.

[0038] This enables an increase in the flow rate of the gas stream, contributing to a reduction in the overall required time for an ongoing batch. This is possible because a different separation method for gas-solid separation is used compared to other methods such as cyclones.

[0039] Filter functions such as thermal shock, material compatibility, low pressure loss requirements, and the formation and support of a permeable filter cake are considered. Any material in contact with the solid (partially or fully converted CDC) is made of a material that does not introduce contaminants upon contact with the solid and does not act as a graphitizing catalyst. Also, the material selection is based on the ability to withstand the process conditions without degradation or with minimal degradation.

[0040] Preferably, a method for producing carbon derived from a carbide by reacting a metal or metalloid carbide with a halogen gas includes a reaction chamber having an inlet for the reaction gas stream, a filter device in the hot zone, and an outlet for the effluent gas stream. Preferably, high-efficiency gas-solid separation is incorporated within the reaction chamber at a high temperature above 600 °C and in a corrosive environment.

[0041] Preferably, the halogen gas is chlorine and the temperature of the reaction unit is in the range of 600 to 1200 °C.

[0042] Desirably, by gas-solid separation, the loss of carbon from the carbide that has been partially or completely converted from the reactor is reduced or minimized, and the overall yield of CDC is improved.

[0043] Preferably, the contact between the partially and / or completely converted CDC and the contaminated surface is reduced or eliminated.

[0044] Desirably, for the partially and / or completely converted CDC, the application of a uniform parameter profile such as temperature is maintained.

[0045] Preferably, the solid component is reduced or removed in the effluent gas stream.

[0046] Preferably, by gas-solid separation, through an increase in the flow rate of the halogen gas to the reactor, the overall batch cycle and / or the conversion time are shortened.

[0047] Preferably, the fluidized bed reactor comprises a reaction chamber and an inlet for the reaction gas and / or the inert gas. Preferably, at least two filter elements are arranged in the reactor zone at a temperature above 600 °C. Preferably, the filter element has an outlet for the filtered gas stream, and the filtered gas stream from the first filter element merges with the filtered gas stream from the second filter element and then proceeds to the downflow unit.

[0048] Preferably, the filter element is arranged at least partially within the heating zone at any location and / or at any height within the zone and may be immersed in the solid bed.

[0049] In one example, silicon carbide (SiC) is used for the synthesis of CDC according to the general reaction shown in Table 1, and the reaction occurs at about 900 - 1200 °C depending on the claims, the heating profile of the reactor, and the length of the heating zone. In the case of the chlorination of SiC, the composition of the gas stream is mainly silicon tetrachloride (SiCl4, STC) and unreacted chlorine gas (Cl2). In addition to these main components, it should be noted that due to the moisture contained in the flow of chlorine gas (purity 99.8%), an unknown amount of hydrochloric acid (HCl) may be contained in this gas stream. This HCl is produced within the system. Furthermore, all inert gases used for reaction rate control, energy release control, flow control, and inactivation of process equipment and heating / cooling are also discharged together with the gas stream in different amounts depending on the process stage.

[0050] This idea enables the improvement of CDC production technology. It should be noted that not all advantages need to be present simultaneously or with the same intensity. The advantages include, but are not limited to, the following. - Gas-solid separation with an efficiency of over 90% operating within the heating zone of the reactor - A gas-solid separation method operable under process conditions above 600 °C and in the presence of halogens - A significant reduction in the solids content in the gas stream flowing out of the reaction zone / reactor - Maintain a uniform application of process conditions such as the temperature of the solid (partially or fully converted CDC) and eliminate fluctuations in the parameters of the solid. - Reduce the contact between the solid (partially or fully converted CDC) and surface / structural materials that may introduce contaminants and act as a graphitization catalyst for CDC. - Reduce any effects of surface wear by the solid. - Provide the option to increase the feed gas flow rate of the halogen gas, thereby shortening the overall batch cycle. - Reduce the maintenance and cleaning operations of the downflow equipment / units due to the reduction in solids entrained in the gas stream flowing out of the reactor. - Reduce the corrosion rate caused by solids contacting the downflow equipment / unit.

[0051] One idea of this invention is to improve the purity of both the solid and the gas stream by reducing the possibility of contact between the solid exiting the heating zone or reactor and other materials. Another idea is to reduce the solids discharged with the gas stream; otherwise, the solids would contaminate the gas stream (partially or fully reacted CDC). Ideally, a separation efficiency of over 90% is achieved. With a higher separation efficiency and different approaches to gas-solid separation, a higher overall gas flow rate can be realized, and the time required for the conversion from carbide to CDC can be shortened overall.

[0052] The total number of filter elements can be selected between 2 and 10, and usually 6 filter elements are used. It should be noted that even with 1 filter element, an improvement can be seen compared to the conventional configuration. The arrangement of the filter elements can be vertical, horizontal, and / or other possible arrangements and / or combinations. The filter elements can be used in any form of batch, semi-batch, or continuous. The ideas disclosed herein eliminate the need for a filter cleaning system such as a pulse system. The filter elements are composed of materials that conform to the process requirements and do not contaminate the final product or by-products during the process. Examples of such materials include carbon ceramic materials manufactured from different carbon particle size fractions, where the carbon particles are integrally bonded by carbon bridges.

Brief Description of the Drawings

[0053] The present invention will be described with reference to the accompanying schematic drawings.

Figure 1

Figure 2

[0054] Referring to FIG. 1, the reactor 10 is preferably configured as a fluidized bed reactor. The reactor 10 includes a reaction chamber 12, a gas distribution plate 14, and a plenum 16. The reactor 10 further includes a filter device 18 supported in the reaction chamber 12 at the upper part of the reaction chamber 20. The filter device 18 includes a plurality of filter elements 22 extending from the upper part of the reaction chamber 20 towards the gas distribution plate 14.

[0055] During operation, a carbide particulate material such as SiC is filled into the reaction chamber 12. A suitable halogen gas, such as Cl2, is supplied from the inlet 24 to the plenum 16 and distributed into the reaction chamber 12 by the gas distribution plate 14. The carbide particles collide with the halogen gas to form a fluidized bed 26.

[0056] Due to the exothermic nature of the reaction and external heating, a non-reactive zone 28 and a reaction zone 30 separated by the temperature T = 600 °C are formed in the reaction chamber 12 by the solid material and the gas. The temperature of the reaction zone 30 is at least 600 °C, while the temperature of the non-reactive zone 28 is less than 600 °C.

[0057] The filter element 22 extends into the reaction zone 30 to separate the gas from the solid. Each filter element 22 is substantially hollow cylindrical and closed at the bottom. Inside the filter element 22, there is a gas channel 32 with an open upper part and a closed bottom. The gas flows into the hollow filter element 22 and is filtered. Then, the gas is further discharged through the gas channel 32 and supplied to further downstream processes such as a cyclone or a washer (both not shown). The gas flows from two filter elements 22 are preferably combined into a single exhaust stream and then supplied downstream.

[0058] As a result, the solid particles carried with the gas flow exiting the fluidized bed 26 are removed by in-situ high-temperature filtration within the reaction zone 30.

[0059] In-situ high-temperature filtration for gas-solid separation, unlike most gas-solid separation units, can handle a wide range of particle size distributions from 2.5 μm and above, as well as the degree of solid conversion from carbide to carbon (in combination with the change in density and weight of the entire particle).

[0060] In the modification depicted in FIG. 2, the filtration element 22 extends not only into the reaction zone 30 but also into the fluidized bed 26.

Description of Reference Numerals

[0061] 10: Reactor 12: Reaction chamber 14: Gas distribution plate 16: Plenum 18: Filter device 20: Upper part of the reaction chamber 22: Filtration element 24: Inlet 26: Fluidized bed 28: Non-reaction zone 30: Reaction zone 32: Gas channel

Claims

1. A reaction apparatus (10) for producing carbon derived from carbides by reacting a halogen gas with a metal carbide material, Reaction chamber (12), A filter device (18) having at least one filter element (22) configured to discharge gas and perform gas-solid separation, Equipped with, During operation, the reaction chamber (12) has a reaction zone (30) having a temperature exceeding 600°C, and the filtration element (22) is configured to enable gas-solid separation within the reaction zone (30), in the reaction apparatus (10).

2. The reactor (10) is configured as a fluidized bed reactor and comprises a plenum (16) and a gas distribution plate (14) separating the plenum (16) from the reaction chamber (12), wherein, during operation, the reaction zone (30) is formed adjacent to the gas distribution plate (14), as described in claim 1.

3. The reaction chamber (12) has an upper part (20), and during operation, a non-reaction zone (28) with a temperature of less than 600°C is formed adjacent to the reaction zone (30). The reaction apparatus (10) according to claim 2, wherein the filtration element (22) extends from the upper part (20) of the reaction chamber through the non-reaction zone (28) toward the reaction zone (30).

4. The reaction apparatus (10) according to claim 1, wherein the filtration element (22) extends into the reaction zone (30).

5. The reaction apparatus (10) according to claim 2, wherein the filtration element (22) extends into the fluidizing material during operation.

6. The filtration element (22) has a filtration wall that defines a gas channel (32), The reaction apparatus (10) according to claim 1, wherein the gas channel (32) is separated from the reaction chamber (12) by the filter wall.

7. The reaction apparatus (10) according to claim 1, wherein the filtration element (22) is made of a macroporous material, preferably a macroporous ceramic carbon material, and has a pore size configured to reduce the amount of partially or completely converted carbon from carbides leaking out of the reaction chamber (12).

8. The reaction apparatus (10) according to claim 1, wherein the filter device (18) comprises a first filter element (22) and a second filter element (22), and the first filter element (22) and the second filter element (22) are fluidly connected to combine the gas flows from the first filter element (22) and the second filter element (22) into a single exhaust flow.

9. A reaction apparatus (10) having a reaction chamber (12), preferably a reaction apparatus (10) according to any one of the preceding claims having a reaction chamber (12), is used to react a halogen gas with a metal carbide material. A method for producing carbon derived from carbides, wherein gas-solid separation is performed by a filtration element (22) of a filter device (18) in the reaction zone (30) of the reaction chamber (12) during the reaction of a halogen gas with the carbide material, and the reaction zone (30) has a temperature of over 600°C.

10. The method according to claim 9, wherein the reaction apparatus (10) is configured as a fluidized bed reaction apparatus and comprises a plenum (16) and a gas distribution plate (14) that separates the reaction chamber (12) from the plenum (16), and during operation, the reaction zone (30) is formed adjacent to the gas distribution plate (14).

11. The reaction chamber (12) has an upper part (20) of the reaction chamber, and during operation, a non-reaction zone (28) with a temperature of less than 600°C is formed adjacent to the reaction zone (30). The method according to claim 10, wherein the filtration element (22) performs gas-solid separation within the non-reacting zone (28) and the reacting zone (30).

12. The method according to claim 10, wherein during operation, the filtration element (22) comes into contact with a material fluidized by the gas flowing from the plenum (16) to the reaction chamber (12).

13. The method according to claim 9, wherein the filtration element (22) performs gas-solid separation at the filtration wall and discharges the filtered gas through the gas channel (32).

14. The method according to claim 9, wherein the filter device (18) includes a plurality of filtration elements (22), and the filter device (18) combines the gas flow from each of the filtration elements (22) into a single exhaust flow.

15. The use of the filtration element (22), which is made of a porous material, is brought into contact with a reaction zone (30) at a temperature of at least 600°C, and optionally into contact with a corrosive environment such as a halogen gas, in order to perform gas-solid separation.

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