In-situ thermal filtration for gas-solid separation in carbide-derived carbon production

Abstract

In order to increase the efficiency of a CDC production process, the invention proposes a reactor (10) for producing carbide-derived carbon by reacting halogen gas with metal carbide material, the reactor (10) comprising a reaction chamber (12) and a filter device (18) configured for discharging gas and having at least one filter element (22), and the filtering element is configured to be used for gas-solid separation. The reactor (10) is characterized in that, during operation of the reactor (10), the reaction chamber (12) has a reaction zone (30) at a temperature above 600 DEG C, and the filter element (22) is configured to allow gas-solid separation within the reaction zone (30).

Description

Technical Field

[0001] The present invention relates to an advanced production process for microporous carbon. The apparatus and method described herein relate to in-situ hot filtration for gas-solid separation in a heated zone of a reactor, and are related to the production of porous carbon and metal halides from metal carbides. More specifically, the apparatus and method described herein relate to a process and apparatus for performing a batch, semi-batch or continuous gas-solid separation process in a heated zone of a reactor, which is achieved by direct filtration to form porous carbon and metal halides from the halogenation of metal carbides. Background Art

[0002] Porous carbon materials are finding use in applications ranging from energy storage to filtration and adsorption processes. In particular, the high specific surface area of ​​such materials is of interest in energy storage as well as filtration applications. Carbide derived carbons (CDCs) represent a class of high surface area microporous carbons with narrow pore size distribution and high surface to volume ratio. Typically, CDCs are made by chemically stripping metal carbides or metalloid carbides from metal or metalloid contents by halogenation at high temperatures (e.g., in the range of 200° C. to 1200° C. as the reaction zone temperature), leaving metal chlorides or metalloid chlorides and microporous carbon as products.

[0003] CDCs can be synthesized from many different precursors, referred to as carbides in the following: binary carbides (e.g. TiC, SiC, Al4C3, MO2C, SiC, B4C, ZrC, NbC, etc.), or with oxygen (e.g. carbon oxides, MC x O y ) or nitrogen (e.g. carbonitrides, MC x N y ) or tertiary carbides (such as M1 x M2 y C), or a mixture of these compounds. Typically, the precursor is in the form of a powder with a variable particle size distribution, but agglomerates or particles or films of carbides can also be used. The precursor carbide can be a monolithic crystal or a polycrystalline or porous biomorphic carbide or any other form from the perspective of structural order.

[0004] There are several methods to extract non-carbon atoms from carbides. The most common method is chemical extraction using halogen gas (X2) at high temperature (Formula (1)):

[0005] MC x +y / 2X2→MX y +xC(1).

[0006] Gas-solid reactors, such as fixed beds, rotary kilns or fluidized bed reactors, can be used for the reaction of raw materials (reactants), carbides and halogen gases. In the heated reaction zone, a mixture of reactants and products is found. In principle, the solids (solid bed, fluidized bed) remain in the reaction zone (or in the reactor), while the gas stream (halogen) enters as reactant and leaves as a mixture of metal halide and halogen.

[0007] US 2012 / 219488 A1 discloses a typical fixed bed reactor apparatus for continuously producing porous carbon materials by halogenation of carbides.

[0008] A typical reaction type uses chlorine (Cl2). Based on the mass balance of the chlorination reaction (see equation (1)), the theoretical yield of carbide-derived carbon (CDC) from different carbides can range from about 6 wt% for molybdenum carbide to almost 30 wt% for silicon carbide. In fact, the main products of the carbide chlorination reaction are chlorides of various carbide-forming metals or metalloids (MCl y ), as shown in Table 1. Therefore, the reactor for efficient production of porous carbon by halogenation of metal carbides at high temperature must be designed in such a way as to provide maximum separation of the two products, CDC and metal chloride, while maintaining consistent temperature conditions in the heated reaction zone.

[0009] Table 1. Products obtained by chlorination of different carbides (CDC and MCl y )'s relative weight distribution.

[0010]

[0011] The CDC recovery rate is related to the overall yield of the process, and it is necessary to remove all solid components (in this case, CDC and / or partially reacted carbides and / or pure carbides) from the gas stream of metal halides and halogens leaving the reactor, any solids in the gas stream will lead to complications in downstream units (such as condensers, filters, pumps, etc.), as well as complications in the further processing of metal halides and halogens. It is also relevant to maintain consistent conditions for the solids, which means that changes and / or fluctuations in the temperature of the solids will generally lead to inconsistent characteristics of the produced CDC, which should be avoided. In addition, the solids (partially or completely converted CDC) should be prevented from contacting with any surface / material that may be a source of contaminants and / or provide possible catalytic capacity for the graphitization of the CDC.

[0012] Gas-solid reactors usually include a gas / solid separation unit, such as a cyclone separator and / or a filter. The limitation of cyclone separators as gas / solid separators is that the efficiency decreases with particle size above 20 μm. The United States Environmental Protection Agency (USEPA) reports the following efficiencies in document (EPA-452 / F-03-005):

[0013] Table 2. Cyclone type vs. PM removal efficiency (%)

[0014]

[0015] Therefore, particles within the range of 10 μm or less are unlikely to be separated.

[0016] US 6673133 B2 shows the difficulty of separating particles smaller than 50 μm in an FCC unit, which results in FCC catalyst concentrations of 200-1000 mg / Nm 3 .

[0017] Note that even if the PSD (particle size distribution) of the raw material, metal carbide or metalloid carbide used for CDC production can be measured, this does not mean that the resulting CDC will have exactly the same PSD as the particles subjected to attrition. This is caused by mechanical stresses on the particles due to particle-particle collisions and / or collisions of the solid bed with the walls, which in turn leads to a gradual degradation of the particles (abrasion).

[0018] The exothermic nature of the reaction produced by CDC is also a contributing factor and increases thermal stresses which may be localized at discrete times and lead to structural fractures (fragmentation).

[0019] The use of gas-solid separation methods, such as cyclones and / or filters, at different stages of CDC production requires changes in flow properties (e.g., temperature), is inefficient, and exposes the material to different conditions, which affects the characteristics and, ultimately, the performance of the CDC. Exiting the material from the reaction zone or reactor itself and coming into contact with other unit operations or other structural materials also exposes the fully or partially reacted CDC to contaminants, which in turn affects the performance of the material when it is returned to the reactor and recovered as a product. Low gas-solid separation efficiency also introduces the risk of accumulation, formation of sludge with condensed metal halides, and plugging of unit operations, equipment, and pipelines, which can have serious safety implications.

[0020] The gas stream associated with CDC production consists of metal halides (eg, metal chlorides) and halogen gases (eg, chlorine) or their hydrogen derivatives (eg, hydrogen chloride).

[0021] Due to the CDC production reaction conditions, the gas stream leaves the reactor at high temperatures in excess of 600°C. It is well known that metal chlorides can cause high corrosion rates in metal alloys, necessitating the use of specialty materials for the condenser’s construction materials. The corrosion of the metal alloys introduces undesirable contaminants into the gas stream. Even specialty materials can introduce contaminants at high temperatures. This also means that any partially or fully reacted CDC that comes into contact with different construction materials at locations other than the reactor itself will return to the reactor or heating zone, where contaminants may form due to the high temperatures and the corrosive nature of the metal halides and halogens. These contaminants, in turn, can affect the purity and / or characteristics of the CDC produced, ultimately affecting performance.

[0022] According to (Special Metals Corporation) publication (SMC-026), the recommended upper limit for dry chlorine contact operation for 316L stainless steel, a typical material of construction that can be used for cyclone separators, is 343°C. Summary of the invention

[0023] The object of the present invention is to improve the efficiency of the CDC production process.

[0024] This object is achieved by the subject matter of the independent claims. Preferred embodiments are the subject matter of the dependent claims.

[0025] The present invention provides a reactor for producing carbide-derived carbon by reacting a halogen gas with a metal carbide material, the reactor comprising a reaction chamber and a filter device, the filter device being configured to discharge gas and having at least one filter element, the filter element being configured to perform gas-solid separation, wherein, during operation, the reaction chamber has a reaction zone with a temperature greater than 600° C., and the filter element is configured to allow gas-solid separation to be performed within the reaction zone.

[0026] Preferably, the reactor is configured as a fluidized bed reactor and comprises a plenum and a gas distribution plate separating the reaction chamber from the plenum, wherein, in operation, a reaction zone is formed adjacent the gas distribution plate.

[0027] Preferably, the reaction chamber has a chamber top, and in operation, a non-reaction zone having a temperature below 600° C. is formed near the reaction zone, and the filter element extends from the chamber top through the non-reaction zone toward the reaction zone.

[0028] Preferably, the filter element extends into the reaction zone.

[0029] Preferably, the filter element extends such that, in operation, the filter element extends into the fluidised material.

[0030] Preferably, the filter element has a filter wall defining the gas channel, and the filter wall separates the gas channel from the reaction chamber.

[0031] Preferably, the filter element is made of a macroporous material, preferably a macroporous ceramic carbon material, wherein the pore size is configured to reduce the amount of partially or fully converted carbide derived carbon escaping from the reaction chamber.

[0032] Preferably, the filter device comprises a first filter element and a second filter element, the first filter element and the second filter element being fluidly connected so as to combine the airflow from each of the first filter element and the second filter element into a single exhaust flow.

[0033] The present invention provides a method for producing carbide-derived carbon by reacting a halogen gas with a metal carbide material in a reactor, preferably a reactor according to any one of the preceding claims, the reactor having a reaction chamber, wherein during the reaction of the halogen gas with the carbide material, gas-solid separation is performed by a filter element of a filter device in a reaction zone of the reaction chamber, and the temperature of the reaction zone is higher than 600°C.

[0034] Preferably, the reactor is configured as a fluidized bed reactor and comprises a plenum and a gas distribution plate, the gas distribution plate separating the reaction chamber from the plenum, wherein during operation a reaction zone is formed adjacent the gas distribution plate.

[0035] Preferably, the reaction chamber has a chamber top, and during operation, a non-reaction zone having a temperature below 600° C. is formed near the reaction zone, and the filter element performs gas-solid separation in the non-reaction zone and the reaction zone.

[0036] Preferably, during operation, the filter element engages material fluidized by gas flowing from the plenum to the reaction chamber.

[0037] Preferably, the filter element utilizes a filter wall to perform gas-solid separation and discharges the filtered gas through a gas channel.

[0038] Preferably, the filter arrangement comprises a plurality of filter elements and the filter arrangement combines the airflow from each filter element into a single exhaust gas flow.

[0039] The present invention provides gas-solid separation using a filter element made of a porous material in contact with a reaction zone having a temperature of at least 600° C. and optionally in contact with a corrosive environment (eg, halogen gas).

[0040] The present invention provides an in-situ hot filtration method for gas-solid separation in the heating zone of a fluidized bed reactor when producing carbon from metal carbides or metalloid carbides or mixtures of these carbides by reacting the carbides with a halogen-containing gas at high temperature to extract non-carbon atoms from the metal carbides or metalloid carbides.

[0041] The method described in this document involves performing in-situ gas-solid separation in the heated zone of the reactor while maintaining the gas stream leaving the reactor free of any solid particles, reducing exposure to any parameter fluctuations of the partially fully converted CDC and exposure to any parameter fluctuations of the structure surfaces / materials that could introduce impurities into the solid bed.

[0042] This makes it possible to achieve higher gas flow rates, which helps reduce the overall time requirements for ongoing batches. This is possible because of the different separation methods used for gas-solid separation compared to other methods such as cyclones.

[0043] Thermal shock, material compatibility, and filtration capabilities, such as low pressure drop requirements and the formation and support of a permeable filter cake, are considered. Any and all materials in contact with the solids (partially or fully converted CDC) are made of materials that do not introduce contaminants or act as catalysts for graphitization when in contact with the solids. Materials of construction are also selected based on their ability to withstand process conditions without or with minimal degradation.

[0044] Preferably, the method for producing carbide-derived carbon by reacting a metal carbide or metalloid carbide with a halogen gas comprises a reaction chamber equipped with an inlet for a reagent gas stream, a filter device located in a hot zone and an outlet for the exiting gas stream. Preferably, an efficient gas-solid separation is integrated in the reaction chamber at a high temperature of more than 600° C. and in a corrosive environment.

[0045] Preferably, the halogen gas is chlorine gas, and the temperature of the reaction unit is in the range of 600-1200°C.

[0046] Preferably, the gas-solid separation reduces or minimizes the loss of partially or fully converted carbide-derived carbon in the reactor, which increases the overall yield of CDC.

[0047] Preferably, contact between partially and / or fully converted CDCs and contaminated surfaces is reduced or eliminated.

[0048] Preferably, a consistent parameter profile (eg, temperature) exposure is maintained for partial and / or full conversion of the CDC.

[0049] Preferably, the solid content of the exiting gas stream is reduced or eliminated.

[0050] Preferably, the gas-solid separation allows the overall batch cycle and / or conversion time to be reduced by increasing the halogen flow rate into the reactor.

[0051] Preferably, the fluidized bed reactor comprises a reaction chamber, a gas inlet for reactive gas and / or inert gas. Preferably, at least two filter elements are arranged in the reactor zone with a temperature above 600° C. Preferably, the filter element comprises a filtered gas flow outlet, at which the filtered gas flow from the first filter element is combined with the filtered gas flow from the second filter element, which filtered gas flow is further forwarded to the downstream unit.

[0052] Preferably, the filter element is at least partially located anywhere within the heating zone and / or at any height within the heating zone, even immersed in the solid bed.

[0053] In one embodiment, silicon carbide SiC is used for the synthesis of CDC according to the general reaction shown in Table 1, and the reaction is carried out at about 900-1200°C, depending on the requirements, the heating curve of the reactor and the length of the heating zone. In the case of SiC chlorination, the composition of the gas stream is mainly silicon tetrachloride (SiCl4, STC) and unreacted chlorine (Cl2). In addition to these main components, it should be noted that due to some moisture in the chlorine gas stream (99.8% purity), the gas stream may contain an unknown amount of hydrochloric acid (HCl), which is then converted into HCl in the system. In addition, depending on the process stage, any inert gas used for reaction kinetics control, energy release control, fluidization control and inertization and / or heating / cooling of process equipment also leaves with the gas stream in different amounts.

[0054] The concept of the present invention can improve CDC production technology. It should be noted that not all advantages must exist at the same time or with the same intensity. Advantages include but are not limited to:

[0055] - Operates in the heated zone of the reactor with a high gas / solid separation efficiency of over 90%;

[0056] - Capability to operate the gas / solid separation process at process conditions exceeding 600°C and in the presence of halogens;

[0057] - Significant reduction of solids in the gas stream leaving the reaction zone / reactor;

[0058] - Maintaining consistent exposure of the solids (partially or fully converted CDC) to process conditions (e.g., temperature), eliminating parameter fluctuations in the solids;

[0059] - Reduce the contact between solids (partially or fully converted CDC) and structural surfaces / materials that may introduce contaminants or act as graphitization catalysts for CDC;

[0060] - Reduce any abrasive impact of solid objects on the surface;

[0061] -Introduction of the option to increase the feed gas flow rate for halogens, thereby reducing the overall batch cycle time;

[0062] - Reduced maintenance and cleaning of downstream equipment / units due to reduced solids entrainment in the gas stream out of the reactor;

[0063] - Lower corrosion rates due to solids contact with downstream equipment / units.

[0064] One concept of the present invention is to improve the purity of the solid and gas streams by reducing the chance of any solids leaving the heating zone or reactor coming into contact with other materials. Another concept includes reducing the solids that leave with the gas stream, which would otherwise contaminate the gas stream (partially or fully reacted CDC). Ideally, separation efficiencies of more than 90% are achieved. Due to the higher separation efficiency and different gas / solid separation methods, higher total gas flow rates can be achieved, thereby reducing the total time requirement for carbide to CDC conversion.

[0065] The total number of filter elements can be selected between two and ten filter elements, wherein six filter elements are generally used. It should be noted that even one filter element also shows some improvements to the traditional configuration. The arrangement of the filter element can be vertical, horizontal and / or any other possible arrangement and / or combination. The filter element can be used in batches and / or semi-batch and / or continuous forms. Utilizing the concept disclosed herein, filter cleaning systems such as pulse systems can be avoided. The filter element is composed of materials that meet the process requirements and will not introduce pollutants in the process, the final product or the by-product. An example of this material is a carbon ceramic material, which is made of different carbon particle size portions, and the carbon particles are integrally connected by carbon bridges. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The present invention is described with reference to the accompanying drawings, in which:

[0067] Figure 1 depicts an embodiment of a reactor during operation; and

[0068] Figure 2 Depicted Figure 1 Variations of the reactor. DETAILED DESCRIPTION

[0069] refer to Figure 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 pressure ventilation system 16. The reactor 10 also includes a filter device 18 supported by the reaction chamber 12 at its chamber top 20. The filter device 18 includes a plurality of filter elements 22 extending from the chamber top 20 to the gas distribution plate 14.

[0070] During operation, particulate carbide material, such as SiC, is filled into the reaction chamber 12. A suitable halogen gas, such as Cl2, is supplied to the pressure ventilation system 16 through the inlet 24 and distributed into the reaction chamber 12 through the gas distribution plate 14. The particulate carbide material is impacted by the halogen gas and forms a fluidized bed 26.

[0071] Due to the exothermic nature of the reaction and external heating, the solid material and gas cause the reaction chamber 12 to form a non-reactive zone 28 and a reactive zone 30, which are separated by a temperature T = 600. The temperature of the reactive zone 30 is at least 600°C, while the temperature of the non-reactive zone 28 is less than 600°C.

[0072] Filter element 22 extends in reaction zone 30, and separates gas from solid.Each filter element 22 has roughly hollow cylindrical shape, and is closed to the bottom.In filter element 22 inside, there is gas channel 32, and gas channel 32 is open at the top, closed at the bottom.Gas escapes in hollow filter element 22 and is filtered.Then, gas further escapes by gas channel 32, and is supplied to downstream (for example cyclone separator and scrubber (all not shown)) further processing.Airflow from two filter elements 22 preferably merges into single exhaust flow before supplying exhaust flow to downstream.

[0073] As a result, solid particles carried by the gas stream leaving the fluidized bed 26 are filtered out by in-situ hot filtration within the reaction zone 30 .

[0074] Unlike most gas-solid separation units, the in-situ hot filtration used in the gas-solid separation unit is able to handle a wide range of particle size distributions from 2.5 μm and above, as well as the degree of conversion of solids from carbides to carbon (combined with the overall density and weight change of the particles).

[0075] exist Figure 2 In the variant shown, the filter element 22 extends not only into the reaction zone 30 but also into the fluidized bed 26 .

[0076] List of reference numerals:

[0077] 10 Reactor

[0078] 12. Reaction Chamber

[0079] 14 Gas distribution plate

[0080] 16 Pressure ventilation system

[0081] 18 Filter device

[0082] 20 Room Top

[0083] 22 Filter element

[0084] 24 Entrance

[0085] 26 Fluidized Bed

[0086] 28 Non-reactive zone

[0087] 30 Reaction Zone

[0088] 32 Gas channel

Claims

1. A reactor (10) for producing carbide-derived carbon by reacting a halogen gas with a metal carbide material, the reactor (10) comprising a reaction chamber (12) and a filter device (18), the filter device (18) being configured to discharge gas and having at least one filter element (22), the filter element (22) being configured to perform gas-solid separation, wherein: In operation, the reaction chamber (12) has a reaction zone (30) with a temperature above 600° C., and the filter element (22) is configured to allow gas-solid separation within the reaction zone (30).

2. The reactor (10) according to claim 1, wherein the reactor (10) is configured as a fluidized bed reactor and comprises a pressure ventilation system (16) and a gas distribution plate (14), wherein the gas distribution plate (14) separates the reaction chamber (12) from the pressure ventilation system (16), wherein In operation, the reaction zone (30) is formed adjacent the gas distribution plate (14).

3. The reactor (10) according to claim 2, wherein the reaction chamber (12) has a chamber top (20), and during operation, a non-reaction zone (28) with a temperature below 600° C. is formed near the reaction zone (30), and the filter element (22) extends from the chamber top (20) through the non-reaction zone (28) to the reaction zone (30).

4. The reactor (10) according to any one of the preceding claims, wherein the filter element (22) extends into the reaction zone (30).

5. The reactor (10) according to any one of claims 2 to 4, wherein the filter element (22) extends such that, in operation, the filter element (22) extends into the fluidized material.

6. The reactor (10) according to any of the preceding claims, wherein the filter element (22) has a filter wall defining a gas channel (32), and the filter wall separates the gas channel (32) from the reaction chamber (12).

7. A reactor (10) according to any of the preceding claims, wherein the filter element (22) is made of a macroporous material, preferably a macroporous ceramic carbon material, wherein the pore size is configured to reduce the amount of partially or fully converted carbide-derived carbon escaping from the reaction chamber (12).

8. A reactor (10) according to any one of the preceding claims, wherein the filter device (18) comprises a first filter element (22) and a second filter element (22), wherein the first filter element (22) and the second filter element (22) are fluidically connected so as to combine the airflow from each of the first filter element (22) and the second filter element (22) into a single exhaust flow.

9. A method for producing carbide-derived carbon by reacting a halogen gas with a metal carbide material in a reactor (10), preferably a reactor (10) according to any one of the preceding claims, the reactor (10) having a reaction chamber (12), wherein: During the reaction of the halogen gas with the carbide material, gas-solid separation is performed by the filter element (22) of the filter device (18) in the reaction zone (30) of the reaction chamber (12), and the temperature of the reaction zone (30) is higher than 600°C.

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

11. The method according to claim 10, wherein the reaction chamber (12) has a chamber top (20), and during operation, a non-reaction zone (28) with a temperature below 600° C. is formed near the reaction zone (30), and the filter element (22) performs gas-solid separation in the non-reaction zone (28) and the reaction zone (30).

12. The method according to claim 10 or 11, wherein: During operation, the filter element (22) engages material fluidized by gas flowing from the plenum (16) to the reaction chamber (12).

13. The method according to any one of claims 9 to 12, wherein the filter element (22) performs gas-solid separation by using a filter wall, and discharges the filtered gas through a gas channel (32).

14. A method according to any one of claims 9 to 13, wherein the filter device (18) comprises a plurality of filter elements (22), and the filter device (18) combines the gas flow from each filter element (22) into a single exhaust gas flow.

15. Gas-solid separation using a filter element (22) made of a porous material, the filter element (22) being in contact with a reaction zone (30) having a temperature of at least 600° C. and optionally in contact with a corrosive environment, such as a halogen gas.

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