A core-shell type CO adsorbent and preparation method thereof

Abstract

This invention discloses a method for preparing a core-shell activated carbon-based CO adsorbent. This method introduces a novel core-shell carbon monoxide adsorbent. By spraying porous, high-strength, and inexpensive sodium carboxymethyl cellulose-sodium alginate porous cross-linked fibers onto the surface of preformed Cu(I)-loaded activated carbon, the adsorbent effectively mitigates surface powdering and catalyst shedding without significantly impacting gas mass transfer and adsorption.

Description

Technical Field

[0001] The present invention belongs to the field of adsorbent synthesis, and in particular relates to a CO activated carbon adsorbent and a preparation method thereof. Background Art

[0002] Carbon monoxide is an important chemical raw material and is widely used in chemical synthesis. At the same time, with the vigorous development of hydrogen fuel cells, the demand for hydrogen for fuel cells has gradually increased, and the development of hydrogen purification related technologies has entered a rising period. Currently, most of the raw gas for hydrogen purification comes from refinery by-product hydrogen. The carbon monoxide content is difficult to meet the standard and needs to be removed with the help of a special carbon monoxide adsorbent. Traditional carbon monoxide adsorbents can be divided into activated carbon-based and molecular sieve-based. Cu (I) is introduced into the adsorbent structure, pores or surface through ion exchange, thermal dispersion or impregnation. The adsorption performance of the adsorbent for carbon monoxide is increased by π complex adsorption between Cu (I) and carbon monoxide. The present invention is an activated carbon-based adsorbent, so the molecular sieve-based is not used for comparison. There are many ways to introduce Cu (I) into traditional activated carbon-based carbon monoxide adsorbents: (1) directly using CuCl as raw material, mixing with activated carbon raw powder by thermal dispersion, and the whole process is carried out in a dry inert protective gas environment. (2) impregnation with a solution containing Cu (II) and heating reduction under a reducing atmosphere. (3) Using a soluble salt containing Cu(II) as a precursor, Cu(II)-loaded activated carbon is prepared by thermal dispersion and then heated and reduced in a reducing atmosphere.

[0003] The preparation process of traditional activated carbon-based carbon monoxide adsorbents requires high temperature heating and activation for several hours. If Cu (II) solution is used, there will be Cu 2+ and Cl - The problem of ion pollution to the environment. At the same time, powder will fall off on the surface after molding. In fact, it is because the surface copper salt has insufficient adhesion and falls off. During the packaging, transportation and filling of the adsorbent, the surface material falls off, thereby reducing the adsorption performance. At the same time, it increases the particulate matter content of the product gas of the purification device and reduces the quality of the product gas.

[0004] Therefore, it is crucial to adopt an energy-saving, low-pollution and efficient method for preparing carbon monoxide adsorbents that introduces Cu(I) into the pores and surface of activated carbon while effectively reducing surface powder loss. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention provides a method for preparing a core-shell CO adsorbent. This method incorporates a porous, cross-linked fiber, sodium carboxymethyl cellulose-sodium alginate, used in food chemistry and medical biochemistry. This porous, high-strength, and inexpensive coating, sprayed onto the surface of preformed activated carbon, effectively mitigates surface powder loss and shedding of the loaded copper salt without significantly impacting gas mass transfer and adsorption.

[0006] A method for preparing a core-shell type CO adsorbent of the present invention comprises the following steps:

[0007] (1) 70-80 parts by weight of activated carbon powder and 20-30 parts by weight of CuCl are mixed evenly and reduced in a dry inert atmosphere to obtain activated carbon with internal pores loaded with Cu(I);

[0008] (2) 75-85 parts by weight of the Cu(I)-loaded activated carbon obtained in step (1) is mixed with 5-10 parts by weight of a binder and 10-15 parts by weight of water, kneaded, and then formed. The mixture is then activated in an inert atmosphere at a certain temperature for a certain period of time, and the finished product is stored under dry conditions for future use;

[0009] (3) Sodium alginate and sodium carboxymethyl cellulose powders are added to water in proportion and mixed evenly to prepare a mixed dispersion;

[0010] (4) The mixed dispersion obtained in step (3) is mixed with a calcium salt solution to obtain a spraying liquid; the spraying liquid is sprayed on the surface of the activated carbon obtained in step (2), and a cross-linking reaction occurs on the surface of the activated carbon, and then freeze-dried to obtain a Cu(I)-loaded CO activated carbon-based adsorbent having a porous cross-linked fiber shell.

[0011] Furthermore, the reduction temperature in step (1) is in the range of 250-400°C, preferably 170-320°C, and the reduction time is 1-1.5 hours; the inert atmosphere used is at least one of nitrogen, argon, and helium.

[0012] Furthermore, the mixing process in step (1) is performed using a stirrer, and the stirring speed of the stirrer is generally 200-400 rpm, and the stirring time is 40-60 seconds. It should be noted that if a high speed of greater than 300 rpm is used for dispersion, friction between the activated carbon raw powder particles will generate excessive heat, which may easily cause some CuCl to be oxidized at high temperature. In this case, the stirring and mixing process can be divided into 2-3 stages, with an interval of 5-10 seconds between each stage.

[0013] Furthermore, the hydraulic forming conditions in step (2) are 7-10 MPa, maintained for 15-25 minutes, and the temperature is maintained at 100-150°C.

[0014] Furthermore, the activation temperature in step (2) is 250-300° C., the activation time is 2-3 hours, and the gas atmosphere used is at least one of nitrogen or carbon monoxide.

[0015] Furthermore, the ratio of the mixed dispersion in step (3) is: sodium carboxymethyl cellulose: sodium alginate: water = 1: (2-4): 2.

[0016] Furthermore, in step (4), the weight ratio of sodium alginate to sodium carboxymethyl cellulose is generally 2-4, preferably 2.5-3. Specifically, the weight ratio of sodium alginate to sodium carboxymethyl cellulose can be 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, and any value in the range formed by any two of these values.

[0017] Through research, the inventors of this application have discovered that the ratio of sodium alginate to sodium carboxymethylcellulose affects the gas mass transfer and strength of the coating. Generally, coatings formed with a high sodium carboxymethylcellulose ratio have a richer pore distribution and better gas mass transfer performance, while coatings formed with a high sodium alginate ratio have higher fiberization and better strength, but lower gas permeability. The ratio of sodium alginate to sodium carboxymethylcellulose specified in the present invention results in a porous, cross-linked fiber shell layer with both good mechanical strength and excellent air permeability.

[0018] Furthermore, after the two solutions in step (4) are mixed, the Ca 2+ The cross-linking reaction occurs in the environment. The activated carbon surface coating process is carried out simultaneously during the cross-linking reaction. The mixed colloidal solution after adding calcium chloride is coated on the activated carbon surface. During the spraying process, the cross-linking reaction temperature must be maintained at 20-35°C, preferably 25-30°C. The cross-linking time is 30-70 minutes depending on the material ratio. The coating process must be carried out within this time period and temperature range.

[0019] Furthermore, the coating process in step (4) can be carried out using a common low-flow rate spray gun, which is evenly sprayed on the surface of the activated carbon formed in step (2) at a flow rate of 0.5-1 mL / min, so that a cross-linked fiber coating is formed on the surface of the activated carbon, and the thickness is controlled to be 5-10 microns.

[0020] Furthermore, the volume ratio of the calcium salt solution added in step (4) to the mixed solution prepared in step (3) is (1-1.2):1, wherein the calcium salt is at least one of calcium chloride and calcium nitrate, preferably calcium chloride, and the mass ratio of the calcium salt solute and the two substances in step (3) is: sodium alginate: sodium carboxymethyl cellulose: calcium salt = (2-4):1: (0.3-0.8).

[0021] Furthermore, the freeze-drying conditions in step (4) are freezing at -30 to -50°C for 3 to 5 hours, followed by drying under vacuum conditions for 12 to 24 hours. Finally, an activated carbon-based carbon monoxide adsorbent loaded with Cu(I) and coated with a sodium carboxymethyl cellulose-sodium alginate cross-linked fiber layer is obtained.

[0022] The second aspect of the present invention further provides a core-shell activated carbon-based CO adsorbent, which is prepared by the method described above.

[0023] Furthermore, the core layer of the core-shell activated carbon-based CO adsorbent has a length of 3-10 mm, a diameter of 0.5-2 mm, and a thickness of 5-10 microns of the porous cross-linked fiber shell layer.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention innovatively introduces a porous cross-linked fiber: sodium carboxymethyl cellulose-sodium alginate. By spraying it on the surface of the formed activated carbon to form a cross-linked fiber shell, it can effectively alleviate the surface powder loss and shedding of the loaded copper salt of the traditional Cu (I)-loaded activated carbon-based carbon monoxide adsorbent without basically affecting the gas mass transfer adsorption, thereby increasing the stability of the adsorbent.

[0026] 2. The present invention adjusts the ratio of sodium alginate, carboxymethyl cellulose and calcium salt, which is different from traditional medical gels and medical fibers, so that the porosity and strength of the sprayed cross-linked fiber layer are optimally balanced under the corresponding preparation process. DETAILED DESCRIPTION

[0027] The technical content and effects of the present invention are further illustrated below with reference to the embodiments, but the present invention is not limited to the scope of the embodiments.

[0028] Examples 1-6

[0029] Examples 1-6 provide different proportions of sodium alginate, carboxymethyl cellulose, calcium chloride and water, respectively. Water 1 is the amount of water used to prepare the sodium alginate-carboxymethyl cellulose dispersion, and water 2 is the amount of water used to prepare the calcium chloride solution, as shown in Table 1 below.

[0030] Table 1 Addition amount of components in different proportions in Examples 1-6 (parts by mass)

[0031]

[0032] The preparation method of the Cu(I)-loaded activated carbon-based CO adsorbent coated with sodium alginate-carboxymethyl cellulose cross-linked fibers in Examples 1-6 is as follows:

[0033] Take 80 parts by weight of raw activated carbon powder and 20 parts by weight of CuCl powder and heat disperse them in a tube furnace at 300°C in a nitrogen atmosphere for 1 hour. Take 80 parts by weight of the activated carbon powder after heat dispersion and 10 parts by weight of sodium carboxymethyl cellulose, mix them thoroughly, add 10 parts by weight of water to the mixed powder, stir evenly, and pour into a hydraulic press to form a molded unactivated activated carbon. Take the molded activated carbon and place it in a tube furnace, heat and disperse it in a carbon monoxide atmosphere at 270°C for 3 hours to obtain the finished activated carbon without the cross-linked fibers wrapped. Store it in a dry environment for later use.

[0034] Sodium carboxymethyl cellulose, sodium alginate, and water were stirred together, and calcium chloride solution was added and mixed thoroughly. The mixture was then sprayed evenly onto the surface of the finished activated carbon using a spray gun at room temperature, with a flow rate of 0.5 mL / min. The fully sprayed activated carbon was frozen at -40°C for 3 hours and then dried under vacuum for 24 hours to obtain the final activated carbon-based carbon monoxide adsorbent loaded with Cu(I) and coated with sodium carboxymethyl cellulose-sodium alginate cross-linked fibers.

[0035] Comparative Examples 1-3

[0036] The adsorbent was prepared in the same manner as in Examples 1-6, except that: in Comparative Example 1, no cross-linked fiber coating was sprayed on the surface; in Comparative Example 2, the cross-linked fiber coating had a very low carboxymethyl cellulose content; and in Comparative Example 3, the cross-linked fiber coating had a very low sodium alginate content. The amounts of sodium alginate, carboxymethyl cellulose, calcium chloride, and water added in varying proportions are shown in Table 2 below.

[0037] Table 2 Addition amount of components in different proportions in Comparative Examples 1-3 (parts by mass)

[0038]

[0039] Adsorbent Performance Testing: The evaluation methods used in Examples 1-6 and Comparative Examples 1-3 were the same. Adsorption performance was tested using a Micromatics HPVA high-pressure adsorption instrument. Pretreatment conditions were 150°C for 4 hours at 5 bar in a CO atmosphere, followed by evacuation and cooling to room temperature. Adsorption isotherms were obtained, and the adsorption capacity at 1 bar is listed in Table 3. Strength testing was conducted in accordance with the national standard GB / T 12496.6-1999.

[0040] The properties of the activated carbon-based CO adsorbents obtained in Examples 1-6 and Comparative Examples 1-2 are listed in Table 3.

[0041] Table 3 Properties of CO adsorbents

[0042]

[0043] It can be seen from Table 3 that the different proportions of cross-linked fiber raw material ratios in Examples 1-6 all improve the strength of the adsorbent to varying degrees, confirming that the coating formed by a high proportion of sodium carboxymethyl cellulose has a richer pore distribution and good gas mass transfer performance, while the coating formed by a high proportion of sodium alginate has higher fiberization and good strength but its gas permeability is not as good as the former.

[0044] From Comparative Example 1, it can be seen that the strength of the activated carbon after surface coating is improved, but the cross-linked fiber layer still affects the gas mass transfer on the adsorbent surface, which is reflected in a slight decrease in the adsorption amount.

[0045] From Comparative Examples 2-3, it can be seen that fiber material ratios that are not within a reasonable range will affect the performance of the fiber. Although the strength of the adsorbent is partially improved, the lack of certain raw materials makes it impossible to form a fiber structure, which greatly affects the gas mass transfer on the adsorbent surface, which is reflected in a significant decrease in the adsorption amount.

Claims

1. A method for preparing a core-shell CO adsorbent, comprising the following steps: (1) 70-80 parts by weight of activated carbon powder and 20-30 parts by weight of CuCl are mixed evenly and reduced in a dry inert atmosphere to obtain activated carbon with internal pores loaded with Cu(I); (2) 75-85 parts by weight of the Cu(I)-loaded activated carbon obtained in step (1) is mixed with 5-10 parts by weight of sodium carboxymethyl cellulose and 10-15 parts by weight of water, kneaded, and then formed. The mixture is then activated in nitrogen or carbon monoxide at a certain temperature for a certain period of time, and the finished product is stored under dry conditions for future use; (3) Sodium alginate and sodium carboxymethyl cellulose powders are added to water in proportion and mixed evenly to prepare a mixed dispersion; (4) mixing the mixed dispersion obtained in step (3) with a calcium salt solution to obtain a spraying liquid; spraying the spraying liquid on the surface of the activated carbon obtained in step (2), causing a cross-linking reaction on the surface of the activated carbon, and then freeze-drying to obtain a Cu(I)-loaded CO activated carbon-based adsorbent having a porous cross-linked fiber shell; in, The reduction temperature in step (1) is 250-400°C, and the reduction time is 1-1.5 hours; The activation temperature in step (2) is 250-300°C and the activation time is 2-3 hours; The ratio of the mixed dispersion in step (3) is: sodium carboxymethyl cellulose: sodium alginate: water = 1: (2-4):

2.

2. The preparation method according to claim 1, characterized in that The inert atmosphere is at least one of nitrogen, argon and helium.

3. The preparation method according to claim 1, characterized in that The mixing process in step (1) uses a stirrer, the stirring speed of the mixing stirrer is 200-400 rpm, and the stirring time is 40-60 seconds.

4. The preparation method according to claim 3, characterized in that The mixing stirrer rotates at a speed of 300-400 rpm, and the mixing process is divided into 2-3 stages, with an interval of 5-10 seconds between each stage.

5. The preparation method according to claim 1, characterized in that The molding conditions in step (2) are: pressure 7-10 MPa, maintaining for 15-25 minutes, and maintaining the temperature at 100-150°C.

6. The preparation method according to claim 1, characterized in that The cross-linking reaction temperature in step (4) is 20-35° C., and the cross-linking time is 30-70 minutes.

7. The preparation method according to claim 6, characterized in that The cross-linking reaction temperature in step (4) is 25-30°C.

8. The preparation method according to claim 1, characterized in that The spraying in step (4) uses a common low-flow rate spray gun with a flow rate controlled at 0.5-1 mL / min, so that a cross-linked fiber coating is formed on the surface of the activated carbon with a thickness controlled at 5-10 microns.

9. The preparation method according to claim 1, characterized in that The volume ratio of the calcium salt solution to the mixed dispersion in step (4) is (1-1.2):

1.

10. The preparation method according to claim 1, characterized in that The calcium salt is at least one of calcium chloride and calcium nitrate, and the mass ratio of the calcium salt solute and the two substances in step (3) is: sodium alginate: sodium carboxymethyl cellulose: calcium salt = (2-4): 1: (0.3-0.8).

11. The preparation method according to claim 1, characterized in that The freeze-drying conditions in step (4) are: freezing at -30 to -50°C for 3 to 5 hours, and then drying under vacuum conditions for 12 to 24 hours.

12. A core-shell activated carbon-based CO adsorbent obtained by the preparation method according to any one of claims 1 to 11.

13. The CO adsorbent according to claim 12, characterized in that The core layer of the core-shell activated carbon-based CO adsorbent has a length of 3-10 mm and a diameter of 0.5-2 mm, and the thickness of the porous cross-linked fiber shell layer is 5-10 microns.

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