Method for regenerating molecular sieving carbon

Abstract

One aspect of the present invention relates to a method for regenerating molecular sieving carbon in which pores are controlled, the method including performing heat treatment using a heating gas that is substantially free of oxygen and carbon dioxide.

Description

Method for regenerating molecular sieve carbon

[0001] The present invention relates to a method for regenerating controlled pore molecular sieve carbon.

[0002] Gas separation methods include the pressure swing abatement method (hereinafter referred to as the PSA method), membrane separation method, and liquid absorption method. These gas separation methods are not limited to the production of high-purity nitrogen by separating nitrogen gas and oxygen gas, but also to the extraction of methane (CH4) from biogas and digester gas. ４ It has also been applied to the separation of HCl (Patent Documents 1, 2 and 3).

[0003] Among these methods, the PSA method uses a molecular sieve carbon as an adsorbent. While the molecular sieve carbon is useful as an adsorbent due to its excellent heat resistance and chemical resistance, it is not easy to control its pore distribution. Many studies have been conducted on controlling the pore distribution of the molecular sieve carbon (for example, Non-Patent Document 1).

[0004] As an example of a method for controlling pores, spherical carbon particles obtained by firing and carbonizing phenolic resin particles in an inert gas atmosphere have been reported (Patent Document 4). More specifically, the spherical carbon particles described in this document are carbon particles for fixing carbon dioxide gas that selectively adsorb carbon dioxide gas, and it is reported that they are obtained by firing and carbonizing phenolic resin particles that have an average particle size of 100 μm or less after carbonization at 800 to 1200° C. in an inert gas atmosphere.

[0005] Furthermore, as a method for modifying and improving the gas separation properties of molecular sieving carbon, a method has been reported in which pore adjustment is performed by chemical vapor deposition of pyrolytic hydrocarbons on the surface of coconut shell charcoal at 600 to 770°C, thereby improving oxygen / nitrogen separation performance (Patent Document 5). Furthermore, a method has also been reported in which the gas separation properties of a carbon molecular sieve are modified by mixing the carbon molecular sieve with a diluent gas consisting of helium under pyrolysis conditions and bringing it into contact with gaseous volatile carbon-containing organic compounds (Patent Document 6).

[0006] As mentioned above, molecular sieves are useful as adsorbents in PSA processes and the like, and methods for controlling their pore size distribution and improving their separation properties have been reported. However, the degradation of the separation properties of molecular sieves with controlled pore size due to airborne contaminants is an unavoidable problem. However, it is expected to be quite difficult to regenerate such molecular sieves without affecting the pore size or surface treatment (coating), and specific regeneration methods have not yet been discussed.

[0007] Vacuum, Vol. 35 (1992), No. 12, pp. 965-971

[0008] JP 2003-320221, JP 6-173119, JP 8-67513, JP 11-79722, International Publication No. 2003 / 018189, JP 5-49920

[0009] Therefore, a main object of the present invention is to provide a method for regenerating molecular sieve carbon whose gas separation performance has deteriorated.

[0010] As a result of intensive research to solve the above problems, the present inventors have found that the above problems can be solved by a method having the following configuration, and have completed the present invention through further research based on this finding.

[0011] That is, a method for regenerating molecular sieve carbon according to one aspect of the present invention is a method for regenerating molecular sieve carbon with controlled pores, characterized in that it comprises heat treatment using a heated gas that is substantially free of oxygen and carbon dioxide.

[0012] FIG. 1 is a schematic diagram showing the configuration of the PSA apparatus used in the examples.

[0013] Hereinafter, embodiments of the present invention will be specifically described, but the present invention is not limited to these.

[0014] The regeneration method of the present embodiment is a method for regenerating a molecular sieve carbon having controlled pores, and includes heat treatment using a heated gas that is substantially free of oxygen and carbon dioxide. With this configuration, the deteriorated molecular sieve carbon can be regenerated and its gas separation performance can be restored.

[0015] First, the carbon molecular sieve used in this embodiment will be described.

[0016] The molecular sieve carbon used in the regeneration method of this embodiment is a molecular sieve carbon with controlled pores, obtained by carbonizing and / or activating a raw material having a large number of pores at high temperatures. The raw material is not particularly limited, and examples include coal, coconut shells, rice husks, grain husks, beer lees, shochu lees, lignin, cellulose, and other plant-derived materials, as well as synthetic resins such as phenolic resins. Carbonization of the raw material is typically performed in the absence of oxygen or air at temperatures of, for example, 400 to 800°C, preferably 450 to 800°C, and more preferably 480 to 750°C. The activation method can be either gas activation or chemical activation, or a combination of gas activation and chemical activation. The molecular sieve carbon obtained by carbonization and / or activation as described above has a large number of pores, the pores of which are controlled to the desired pore diameter.

[0017] There is no particular limitation on the method for controlling the pores in the carbon molecular sieve. For example, as a surface treatment, hydrocarbon gases such as methane, ethylene, and toluene are pyrolyzed, and the pyrolyzed product (pyrolytic carbon) is allowed to adhere to the pore walls to adjust the pore size, thereby controlling the pore distribution.

[0018] In this embodiment, the term "pores" is not particularly limited, but refers to pores having a pore diameter of about 0.1 to 5 nm. The molecular sieve carbon having pores in this embodiment has a specific surface area of, for example, 500 m ２ / g or less, and ２ / g or less, and even 300m ２ / g or less is more preferable.

[0019] The molecular sieving carbon has excellent gas separation performance for mixed gases and is suitably used as an adsorbent in a PSA process for separating mixed gases, etc. The regeneration method of the present embodiment can regenerate molecular sieving carbon that has been used for separating mixed gases and whose separation performance has deteriorated.

[0020] The mixed gas is not particularly limited, and the method of this embodiment can regenerate molecular sieve charcoal used to separate various mixed gases. Examples of the mixed gas include a mixed gas containing nitrogen and oxygen, a mixed gas containing methane and carbon dioxide, a mixed gas containing nitrogen and carbon dioxide, and a mixed gas containing nitrogen and methane. In particular, the molecular sieve charcoal regenerated in this embodiment is preferably a molecular sieve charcoal used to separate at least one mixed gas selected from a mixed gas containing nitrogen and oxygen and a mixed gas containing methane and carbon dioxide.

[0021] In this embodiment, a degraded molecular sieve carbon that has been used as an adsorbent in a PSA apparatus or the like for a certain period of time is regenerated. Specifically, for example, a mixed gas is separated in a PSA apparatus or the like, and after a predetermined time has passed, the molecular sieve carbon that was installed in the adsorption tower of the PSA apparatus is removed and the regeneration method of this embodiment can be carried out. The degree of degradation of the used molecular sieve carbon to be regenerated is not particularly limited, but it is preferable to perform regeneration when, for example, the separation performance has decreased by about 10 to 50% compared to before use.

[0022] The regeneration method of this embodiment involves heat-treating the molecular sieve carbon used in separating the mixed gas using a heated gas that is substantially free of oxygen and carbon dioxide. The heat-treatment method is not particularly limited, and can be performed by heating the molecular sieve carbon with heated gas, by heat conduction from the outer wall of a heat treatment furnace, or by generating heat by carbon vibration such as with microwaves. In consideration of equipment load, reusability, etc., a method of heating with heated gas is preferred. Such heat treatment can be performed, for example, by directly charging the molecular sieve carbon into a reactor and heating it with heated gas.

[0023] The heating gas used in this embodiment is a gas that is substantially free of oxygen and carbon dioxide. Here, "substantially free of oxygen and carbon dioxide" means that the heating gas does not contain either oxygen or carbon dioxide to an extent that would be strongly involved in combustion or oxidation. Specifically, the heating gas has an oxygen and carbon dioxide content of 3% by volume or less, preferably 2% by volume or less, and more preferably 1% by volume or less.

[0024] Heat treatment can decompose and remove foreign matter such as oil that adheres to the surface of the molecular sieve when it is used for gas separation, restoring the gas separation performance of the molecular sieve. If the heated gas contains oxygen and carbon dioxide to a level that strongly contributes to combustion and oxidation, activation and other processes can occur during heating, causing changes in the structure of the pores of the molecular sieve, which can lead to a decrease in performance. Weight loss due to combustion and other factors can also occur. Therefore, by heating with a gas that is substantially free of oxygen and carbon dioxide, adsorption inhibitors can be removed without changing the physical properties of the molecular sieve, thereby preventing performance degradation and weight loss of the molecular sieve.

[0025] Examples of such heating gases include inert gases such as helium, nitrogen, and argon, and superheated steam. These may be used alone or in combination. From the viewpoint of thermal conductivity, the heating gas of this embodiment preferably contains superheated steam. Steam has high thermal conductivity and a low activation temperature. Therefore, by including superheated steam in the heating gas, only foreign matter such as oil that adheres to the surface of used molecular sieve charcoal during gas separation can be decomposed and removed without damaging the surface treatment (such as a coating) that was applied to the surface. As a result, the molecular sieve charcoal can be regenerated without reducing the gas separation performance originally possessed by the molecular sieve charcoal.

[0026] The heating gas may be a mixture of superheated steam and nitrogen gas. Since the thermal conductivity of superheated steam alone may be too high, mixing nitrogen gas, which has a relatively low thermal conductivity, makes it easier to control the increase in the heat treatment temperature.

[0027] The proportion of superheated steam or a mixed gas containing superheated steam and nitrogen gas in the heating gas is preferably 10% by volume or more, and more preferably 100% by volume.

[0028] When the heating gas is a mixed gas containing superheated steam and nitrogen gas, the ratio (molar ratio) of superheated steam to nitrogen gas in the mixed gas (steam:nitrogen gas) may be in the range of 1:100 to 100:1, and more preferably, in consideration of thermal conductivity, in the range of 10:90 to 100:1, and even more preferably in the range of 50:50 to 100:1. Note that the mixed gas may contain gases other than superheated steam and nitrogen gas in amounts that do not impair the effects of the present invention.

[0029] The flow rate of the heating gas in the heat treatment of this embodiment is not particularly limited, since it depends on the amount of the carbon molecular sieve charged into the reactor. Preferably, the flow rate is adjusted to a range of 0.01 L / min to 10,000 L / min, more preferably 0.1 L / min to 8,000 L / min, and even more preferably 0.4 L / min to 4,000 L / min, in order to facilitate heat conduction to the carbon molecular sieve and to facilitate removal of foreign matter adhering to the carbon molecular sieve.

[0030] The heat treatment temperature in this embodiment may be any temperature at which substances adhering to the surface of the carbon molecular sieve and blocking the pores (foreign matter adhering as a result of gas separation) are decomposed and removed. Furthermore, in the case of a carbon molecular sieve whose pores have been adjusted by surface treatment (pyrolytic carbon deposits or coatings), the temperature range is not particularly limited as long as it does not decompose the pyrolytic carbon deposits used for pore adjustment. The heat treatment in this embodiment is typically carried out in the temperature range of 300°C to 700°C. Heat treatment temperatures that are too high are undesirable because they may clog the pores of the carbon molecular sieve. From the viewpoint of heat conduction time and / or avoiding damage to the carbon molecular sieve, the heat treatment temperature is more preferably 400°C to 650°C, and even more preferably 450°C to 600°C.

[0031] The heating time (heat treatment time) for the molecular sieve carbon is not particularly limited as long as it can restore the gas separation performance of the molecular sieve carbon, and can be appropriately determined based on the size and amount of the molecular sieve carbon, the amount of adsorbed substance, etc. Typically, the heating is performed for a residence time in the range of 1 minute to 600 minutes. If the heating time is too short, there is a risk that the decomposition and removal of surface deposits will not be sufficient. On the other hand, if the heating time is too long, there is a risk that the pores of the restored molecular sieve carbon will be blocked by heat, resulting in a decrease in performance, which is not preferred. The heat treatment is more preferably performed in the range of 5 minutes to 500 minutes, and even more preferably in the range of 10 minutes to 480 minutes.

[0032] In this embodiment, the heat treatment method is not particularly limited, and can be carried out in either a batch system or a continuous system. From the viewpoint of regeneration efficiency, it is preferable to carry out the heat treatment in a continuous system.

[0033] When carried out in a batchwise manner, the molecular sieve carbon to be regenerated is placed in an atmosphere-controllable device such as a box furnace, and heated after or while removing oxygen from the furnace, adjusting the temperature so that the furnace is substantially oxygen-free when a predetermined temperature is reached, and the treatment can be carried out at a predetermined temperature for a predetermined time.

[0034] On the other hand, in the case of a continuous method, the molecular sieve carbon to be regenerated and heated gas can be continuously introduced into a tubular furnace such as a rotary kiln when the furnace reaches a substantially oxygen-free state and a predetermined temperature. Alternatively, the molecular sieve carbon can be continuously introduced into a tunnel furnace such as a belt furnace or a pusher furnace, and passed through a zone of heated gas that is continuously blown onto the carbon so as to maintain a substantially oxygen-free environment.

[0035] In this embodiment, the heat treatment decomposes and volatilizes organic substances such as oil that have adhered to the molecular sieve carbon due to its use in gas separation. During the decomposition by the heat treatment, some of the organic substances are oxidatively decomposed to carbon dioxide, but the volatiles may contain some harmful substances. Since such substances cannot be released directly into the atmosphere, they are detoxified as needed by absorbing acidic substances using an alkali scrubber, decomposing by flame combustion, decomposing by catalytic combustion, or the like.

[0036] After the heat treatment, the carbon molecular sieve can be cooled and then removed from the reactor. The temperature at which it is removed is preferably a temperature at which it is not oxidized by oxygen in the air. Therefore, it is preferable to cool the carbon molecular sieve in the reactor to 300°C or less, more preferably 200°C or less, and then expose it to the atmosphere.

[0037] In this embodiment, the molecular sieve carbon regenerated by the heat treatment can be recovered as it is and reused again for separating mixed gases, for example as an adsorbent in a PSA device.

[0038] The molecular sieving carbon regenerated by the regeneration method of this embodiment has its gas separation performance restored and regenerated.

[0039] As described above, this specification discloses various aspects of the technology, but the main technologies among them are summarized below.

[0040] The method for regenerating molecular sieve carbon according to a first aspect of the present invention is a method for regenerating molecular sieve carbon with controlled pores, and is characterized by comprising heat treatment using a heated gas that is substantially free of oxygen and carbon dioxide.

[0041] With this configuration, it is possible to regenerate deteriorated molecular sieve carbon and restore its gas separation performance.

[0042] The method for regenerating molecular sieving carbon according to the second aspect of the present invention is the same as the method for regenerating molecular sieving carbon according to the first aspect, except that the heating gas contains superheated steam. This is thought to enable the molecular sieving carbon to be regenerated without reducing the gas separation performance originally possessed by the molecular sieving carbon.

[0043] A method for regenerating a carbon molecular sieve according to a third aspect of the present invention is the method for regenerating a carbon molecular sieve according to the first or second aspect, wherein the temperature of the heat treatment is 300 to 700° C. By performing the heat treatment in such a temperature range, it is thought that blocking of the pores of the carbon molecular sieve due to high temperatures can be suppressed.

[0044] The regeneration method for a molecular sieve carbon according to a fourth aspect of the present invention is the regeneration method according to any one of the first to third aspects, in which the molecular sieve carbon is a molecular sieve carbon used for separating a mixed gas. It is believed that this can further enhance the effects described above.

[0045] The regeneration method for carbon molecular sieves according to the fourth aspect of the present invention is the regeneration method according to any one of the first to fourth aspects, wherein the mixed gas is at least one selected from the group consisting of a mixed gas containing nitrogen and oxygen, and a mixed gas containing methane and carbon dioxide. This is believed to make it possible to more effectively achieve the effects described above.

[0046] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0047] <Production of charcoal molecular sieve> (Reference Production Example 1) Charcoal molecular sieve A 100 parts by weight of finely pulverized coconut shell charcoal were mixed with 40 parts by weight of coal tar and 8 parts by weight of water, and the mixture was pressurized with a hydraulic press and extruded through a 0.8 mm nozzle to form a cylindrical pellet. The obtained cylindrical pelletized charcoal was heat-treated at 600°C for 30 minutes in a fluidized dry distillation furnace and cooled in nitrogen.

[0048] Next, the coal was thoroughly immersed in 0.6N (normal) hydrochloric acid at 80°C while stirring, and then the hydrochloric acid was separated by filtration. This hydrochloric acid washing was repeated three times, followed by water washing and drying to obtain purified coal. The obtained purified coal was placed in an externally heated electric furnace, heat-treated at 900°C, and cooled in nitrogen gas. Thereafter, 3 parts by weight of a 140-260°C fraction of creosote oil was added, and the coal was heated from room temperature to 400°C in 20 minutes in a rotary kiln with a small amount of nitrogen gas flowing through it, thereby thoroughly impregnating the coal with the creosote oil. The coal was further heat-treated by heating to 700°C in 20 minutes, and then cooled to room temperature in nitrogen to obtain molecular sieve carbon A. The specific surface area of ​​the obtained molecular sieve carbon A was 270 m ２ / g.

[0049] (Reference Production Example 2) Carbon Molecular Sieve B The carbon distillate obtained by granulating phenolic resin and carbonizing it at 450 to 750°C was weakly activated by heat treatment for 3 hours at 800°C in a mixed gas atmosphere of 20% carbon dioxide and 80% nitrogen. Next, the resulting treated product was heat treated in nitrogen gas at a treatment temperature of 1000°C for 1 hour. Further, it was exposed to nitrogen gas containing 10% ethylene at 750°C for 1 hour. Thereafter, it was cooled to room temperature in nitrogen gas to obtain carbon molecular sieve B. The specific surface area of ​​the resulting carbon molecular sieve B was 227 m ２ / g.

[0050] <Use of carbon molecular sieve> (Examples 1 to 4) Using the carbon molecular sieves A and B obtained above, nitrogen / oxygen gas adsorption separation was carried out by the PSA method. The PSA apparatus shown in Figure 1 was used for gas separation in this test. The symbols in the figure represent the following: 1 raw gas supply line, 2 compressor, 3 cooler, 4 and 5 adsorption towers, 6 product tank, 7 to 16 valves, 17 product gas withdrawal line, 18 exhaust gas line, 19 vacuum pump, 20 waste gas line, 21 check valve.

[0051] First, 3.0 L of carbon molecular sieve A or B was packed into the adsorption columns 4 and 5 of the PSA apparatus shown in FIG.

[0052] Then, adsorption separation of nitrogen / oxygen gas was carried out using a PSA apparatus under the conditions shown in Table 1. After the operation time shown in Table 1 had elapsed, the amount of nitrogen gas generated and the air consumption unit of the molecular sieve carbon used in each use example were calculated by operating the apparatus at a predetermined pressure to an oxygen concentration of 100 ppm (nitrogen purity 99.99%) and measuring the amount of nitrogen generated and the amount of air consumed.

[0053] In the table, "NL" stands for normal liter, which represents the amount of nitrogen gas under standard conditions.

[0054]

[0055] From Table 1, it can be seen that by comparing Usage Examples 1 and 3 with Usage Examples 2 and 4, the gas separation performance of molecular sieve carbon A in Usage Example 2 and molecular sieve carbon B in Usage Example 4, which were subjected to adsorption for 7,200 hours, has deteriorated.

[0056] <Regeneration of carbon molecular sieve> (Example 1) 200 g of carbon molecular sieve A used in Use Example 2 and whose performance had deteriorated was placed in a box furnace connected to a superheated steam generator "UPSS W-20H" (manufactured by Tokuden Co., Ltd.). Then, in a superheated steam atmosphere (steam amount 2 kg / Hr, oxygen content 5 ppm (0.0005%)), the temperature was set to 500°C and the treatment time (30 minutes) was set, and heat treatment was performed to regenerate the carbon molecular sieve. After 30 minutes, the temperature was cooled to 200°C, and the treated product (regenerated carbon molecular sieve) was taken out.

[0057] The resulting regenerated molecular sieve carbon was loaded into the PSA apparatus shown in Figure 1, operated at a predetermined pressure to an oxygen concentration of 100 ppm (nitrogen purity 99.99%), and the nitrogen gas generation rate and air consumption rate were measured for the first hour of operation to calculate the nitrogen gas generation rate and air consumption rate. The results are shown in Table 2.

[0058] (Example 2) The regeneration of molecular sieving carbon was carried out in the same manner as in Example 1, except that the heat treatment temperature was changed to 600°C. The nitrogen gas generation amount and air consumption rate of the obtained regenerated molecular sieving carbon were measured in the same manner as in Example 1. The results are shown in Table 2.

[0059] (Example 3) The molecular sieve carbon was regenerated in the same manner as in Example 1, except that the deteriorated molecular sieve carbon B obtained in Use Example 4 was used as the regeneration target instead of the molecular sieve carbon A obtained in Use Example 2. The nitrogen gas generation amount and air consumption rate of the obtained regenerated molecular sieve carbon were measured in the same manner as in Example 1. The results are shown in Table 2.

[0060] (Example 4) The molecular sieve carbon was regenerated in the same manner as in Example 1, except that the heat treatment temperature was changed to 300°C. The nitrogen gas generation amount and air consumption rate of the obtained regenerated molecular sieve carbon were measured in the same manner as in Example 1. The results are shown in Table 2.

[0061] (Example 5) The molecular sieve carbon was regenerated in the same manner as in Example 1, except that the heat treatment conditions were changed to introduce heated nitrogen at 500°C without introducing superheated steam and the treatment time was changed to 1.5 hours. The nitrogen gas generation amount and air consumption unit of the obtained regenerated molecular sieve carbon were measured in the same manner as in Example 1. The results are shown in Table 2.

[0062] (Comparative Example 1) The molecular sieve carbon was regenerated in the same manner as in Example 1, except that air was introduced into the atmosphere in the box furnace at 250 L / Hr simultaneously with superheated steam. The nitrogen gas generation amount and air consumption unit of the obtained regenerated molecular sieve carbon were measured in the same manner as in Example 1. The results are shown in Table 2.

[0063] Comparative Example 2: 200 g of the used, performance-degraded molecular sieve carbon B obtained in Use Example 4 was placed in a box furnace and heat-treated at 800°C for 180 minutes in a mixed gas atmosphere of 20% carbon dioxide (carbon dioxide) gas and 80% nitrogen, thereby regenerating the molecular sieve carbon. After 30 minutes, the temperature was cooled to 200°C, and the treated product (regenerated molecular sieve carbon) was removed. The nitrogen gas generation rate and air consumption rate of the obtained regenerated molecular sieve carbon were measured in the same manner as in Example 1. The results are shown in Table 2.

[0064]

[0065] In Table 2, "pressure" refers to the pressure applied during PSA separation, "operation time" refers to the operation time during which PSA was carried out, and "oxygen concentration" refers to the oxygen concentration in the discharged nitrogen (purified nitrogen) during PSA.

[0066] (Discussion) As is clear from the results in Table 2, the molecular sieve carbon regenerated by the methods of Examples 1 to 3 has recovered gas separation performance to the same extent as that of Usage Examples 1 and 3, compared to the state after 7,200 hours of use (before heat treatment).

[0067] In contrast, in Comparative Example 1, in which heat treatment was performed using not only superheated steam but also air containing oxygen and carbon dioxide, the gas separation performance of the molecular sieve charcoal was not restored.Furthermore, in the regeneration method of Comparative Example 2, in which heat treatment was performed using combustion gas containing carbon dioxide, the gas separation performance of the molecular sieve charcoal was not restored.

[0068] This application is based on Japanese Patent Application No. 2023-103384 filed on June 23, 2023, the contents of which are incorporated herein by reference.

[0069] In order to express the present invention, the present invention has been properly and sufficiently described above through embodiments with reference to specific examples, etc. However, it should be recognized that those skilled in the art can easily change and / or improve the above-described embodiments. Therefore, unless changes or improvements made by those skilled in the art deviate from the scope of the claims set forth in the claims, such changes or improvements are construed as being encompassed within the scope of the claims.

[0070] The present invention has wide industrial applicability in technical fields related to activated carbon, a method for regenerating the same, and water purification using activated carbon.

Claims

1. A method for regenerating a controlled pore molecular sieve carbon, comprising heat treating the carbon with a heated gas substantially free of oxygen and carbon dioxide.

2. The regeneration method of claim 1, wherein the heating gas comprises superheated steam.

3. The regeneration method according to claim 1, wherein the temperature of the heat treatment is 300 to 700°C.

4. The regeneration method according to claim 1, wherein the molecular sieve carbon is a molecular sieve carbon that has been used for separating a mixed gas.

5. The regeneration method according to claim 4, wherein the mixed gas is at least one selected from a mixed gas containing nitrogen and oxygen, and a mixed gas containing methane and carbon dioxide.