阅读说明：本技术 一种载体改性的银基乙烯脱除剂及其制备方法和应用 (Carrier modified silver-based ethylene remover and preparation method and application thereof ) 是由 张楚馨 陈建东 吴军良 叶代启 于 2021-05-12 设计创作，主要内容包括：本发明公开了一种载体改性的银基乙烯脱除剂及其制备方法和应用,该脱除剂的制备包括以下步骤：(1)载体预处理：将分子筛载体过筛、干燥、活化后冷却备用；(2)载体改性：将步骤(1)所述预处理后的分子筛载体加入到酸溶液中,冷凝回流处理,再经过离心、抽滤、洗涤至中性为止,最后干燥得到改性分子筛载体；(3)活性组分担载：将改性后分子筛载体加入到银的前驱物溶液中,分散后放入真空条件下老化、干燥,并在的O-2/惰性气体气氛中焙烧后得到。本发明的乙烯脱除剂在常温条件下对乙烯具有高效的脱除性能和稳定性,具有可重复利用性；制备过程简便易行,制备成本较低。(The invention discloses a carrier modified silver-based ethylene remover and a preparation method and application thereof, wherein the preparation of the remover comprises the following steps: (1) pretreatment of a carrier: sieving, drying and activating the molecular sieve carrier, and cooling for later use; (2) modification of a carrier: adding the pretreated molecular sieve carrier in the step (1) into an acid solution, performing condensation reflux treatment,centrifuging, filtering, washing until the solution is neutral, and finally drying to obtain the modified molecular sieve carrier; (3) active component loading: adding the modified molecular sieve carrier into precursor solution of silver, dispersing, aging under vacuum condition, drying, and adding into O 2 And/or roasting in inert gas atmosphere. The ethylene remover has high-efficiency removal performance and stability on ethylene at normal temperature, and has reusability; the preparation process is simple and easy to implement, and the preparation cost is low.)

1. A preparation method of a carrier modified silver-based ethylene remover is characterized by comprising the following steps:

(1) pretreatment of a carrier: sieving, drying and activating the molecular sieve carrier, and cooling for later use;

(2) modification of a carrier: adding the pretreated molecular sieve carrier in the step (1) into an acid solution, performing condensation reflux treatment, centrifuging, performing suction filtration and washing until the molecular sieve carrier is neutral, and finally drying to obtain a modified molecular sieve carrier;

(3) active component loading: adding the modified molecular sieve carrier in the step (2) into a precursor solution of silver, dispersing, aging and drying under a vacuum condition, and adding O₂And/or roasting in inert gas atmosphere to obtain the silver-based ethylene remover.

2. The preparation method of claim 1, wherein the molecular sieve support in step (1) is HZSM-5; in the step (1), the sieving is 40-60 mesh sieving, the activation temperature is 400-600 ℃, the activation time is 1-5h, and the temperature rise rate of the activation is 3-10 ℃/min.

3. The method of claim 2, wherein the HZSM-5 has a silica/alumina ratio of 25 to 80.

4. The method according to claim 1, wherein the acid in step (2) is one or two of nitric acid, oxalic acid, citric acid and acetic acid, and the concentration of the acid solution is 0.1-0.8M.

5. The preparation method according to claim 1, wherein the mass ratio of the molecular sieve support to the acid solution in the step (2) is 1:10 to 1: 20; the temperature of the condensation reflux treatment is 60-120 ℃, and the time of the condensation reflux treatment is 5-24 h.

6. The method according to claim 1, wherein the precursor solution of silver of step (3) is a silver nitrate solution; the vacuum degree under the vacuum condition is 0.5-1 Mpa; the aging time is 2-24 h; the drying temperature is 50-100 ℃.

7. The process according to claim 1, whereinCharacterized in that, step (3) is O₂O in an inert gas atmosphere₂Is 10-30% by volume, and the inert gas is N₂(ii) a The roasting temperature is 450-750 ℃, and the roasting time is 1-6 h.

8. The carrier-modified silver-based ethylene removal agent prepared by the preparation method according to any one of claims 1 to 7, wherein the silver-based ethylene removal agent contains 3 to 8% by mass of silver.

9. Use of the support-modified silver-based ethylene removal agent of claim 8 for removing ethylene.

10. Use according to claim 9, wherein the temperature for removing ethylene is 0-40 ℃.

Technical Field

The invention belongs to the technical field of ethylene removal, and particularly relates to a carrier-modified silver-based ethylene removal agent, and a preparation method and application thereof.

Background

Ethylene is used as a plant growth hormone, and the mature rot degree of fruits and vegetables can be accelerated by the existence of a large amount of ethylene in the storage process of the fruits and vegetables, so that the storage time of the fruits and vegetables is short, and huge economic loss is brought by excessive rotten fruits and vegetables. It is of great practical significance to develop a material capable of efficiently removing ethylene from the atmosphere and in a closed storage space.

Ethylene is a neutral gas, has the characteristic of being difficult to dissolve in water, and is difficult to degrade or adsorb. The main methods currently used for removing ethylene are physical adsorption, direct oxidation, photocatalysis and thermocatalysis. The physical adsorption method adopts porous adsorbents such as activated carbon, resin, molecular sieve and the like, utilizes rich pore channel structures to enable ethylene molecules to generate strong interaction with pore walls, and generates adsorption effect so as to achieve the purpose of removing ethylene in air; but have limited adsorption capacity and no selectivity to adsorbates in air, limited by temperature and humidity. The direct oxidation method usually adopts potassium permanganate as a strong oxidant to oxidize ethylene into glycol or acetic acid, and when the potassium permanganate is excessive, the ethylene can be oxidized into carbon dioxide and water; but it is unstable, susceptible to humidity, and cannot be recycled, and the disposal of by-products is inconvenient. The photocatalytic method is a method for degrading ethylene by utilizing sunlight through photocatalysis, and has the characteristics of environmental protection, but has great limitation in use due to the influence of daytime and climate. However, in the storage space of fruits and vegetables, the temperature and the humidity are often lowWet, dull and green environmental protection is required; these harsh conditions make none of the above methods suitable. Although the thermal removal method for degrading ethylene is a popular high-efficiency method at present, the thermal removal method generally needs to be carried out at a certain temperature, and metal oxides (Co) are mostly adopted at home and abroad₃O₄Etc.), silica/alumina or carbon-based material support metals catalytically degrade ethylene at temperatures of 200 ℃ or even higher. Although there are some catalytic materials at room temperature, the service life is limited and the reusability is low due to the problem of service life or humidity. HonglingYang used Ag as Active component to be supported on molecular sieve to prepare Ethylene catalyst at Room Temperature, the time of reaching 100% Catalytic effect under 100ppm, 7500 mL/(g.h) test condition is about 6h, the problem of long time needing to be replaced in practical application still exists, and whether the reusability of the modified material exists is not researched (Hong L Y, Ma C Y, Zhang X, et al]ACS Catalysis,2018,8(2): 1248-1258.). For more practical applications, it is desirable that the material be free of ethylene for a longer period of time and be capable of repeated regeneration for use, which is of practical interest for cost control. On the basis of the above documents, the invention modifies the carrier and then carries Ag to prepare the ethylene removal material, and tests and explores the reusability of the ethylene removal material.

Disclosure of Invention

The invention provides a preparation method of a carrier modified lifting silver-based ethylene remover, which is used for decomposing ethylene gas at normal pressure and low temperature by taking a modified molecular sieve as a carrier to carry silver to prepare the ethylene remover. The silver-based ethylene remover prepared by the method has highly dispersed active centers, low preparation cost, excellent reusability, and high-efficiency catalytic performance and stability for ethylene gas at room temperature.

The invention realizes the aim through the following technical scheme:

a preparation method of a carrier modified silver-based ethylene remover comprises the following steps:

(1) pretreatment of a carrier: sieving, drying and activating the molecular sieve carrier, and cooling for later use;

(2) modification of a carrier: adding the pretreated molecular sieve carrier in the step (1) into an acid solution, performing condensation reflux treatment, centrifuging, performing suction filtration and washing until the molecular sieve carrier is neutral, and finally drying to obtain a modified molecular sieve carrier;

(3) active component loading: adding the modified molecular sieve carrier in the step (2) into a precursor solution of silver, dispersing, aging and drying under a vacuum condition, and adding O₂And/or roasting in inert gas atmosphere to obtain the silver-based ethylene remover.

Preferably, the molecular sieve carrier in the step (1) is HZSM-5; further preferably, the HZSM-5 in the step (1) has a silica-alumina ratio of 25-80. The HZSM-5 molecular sieve with low silica-alumina ratio has adjustable acidity and high stability, is favorable for modifying the carrier to treat amorphous aluminum in an elution pore channel so as to improve the specific surface, reduce the acid content to form structural defects and further improve the dispersion of active components.

Preferably, the sieving in the step (1) is 40-60 mesh sieving;

preferably, the activation temperature in the step (1) is 400-600 ℃, the activation time is 1-5h, and the temperature rise rate of the activation is 3-10 ℃/min.

Preferably, the step (1) is carried out by sieving, washing with water and drying.

Preferably, the acid in the step (2) is one or two of nitric acid, oxalic acid, citric acid and acetic acid;

preferably, the concentration of the acid solution in the step (2) is 0.1-0.8M. Further preferably, the concentration of the acid solution is 0.2 to 0.4M.

Preferably, in the step (2), the solvent of the acid solution is water.

Preferably, the mass ratio of the molecular sieve carrier in the step (2) to the acid solution is 1:10-1: 20;

preferably, the temperature of the condensation reflux treatment in the step (2) is 60-120 ℃, and the time of the condensation reflux treatment is 5-24 h. Further preferably, the temperature of the condensation reflux treatment is 80-100 ℃, and the time of the condensation reflux treatment is 12-18 h.

Preferably, the silver precursor solution in the step (3) is a silver nitrate solution;

preferably, the vacuum degree of the vacuum condition in the step (3) is 0.5-1 Mpa; further preferably, the vacuum degree under the vacuum condition is 0.6-0.9 Mpa;

preferably, the aging time of the step (3) is 2-24 h;

preferably, the drying temperature in the step (3) is 50-100 ℃, and the drying time is 2-6 h. Further preferably, the drying temperature in the step (3) is 50-90 ℃, and the drying time is 3-5 h.

Preferably, O is used in step (3)₂O in an inert gas atmosphere₂The volume fraction of (A) is 10-30%; further preferably, O is used in the step (3)₂O in an inert gas atmosphere₂Is 21% by volume;

preferably, the inert gas in the step (3) is N₂；

Preferably, the roasting temperature in the step (3) is 450-. More preferably, the roasting temperature is 550-650 ℃, and the roasting time is 2-4 h.

Preferably, the dispersion in step (3) is ultrasonic or stirring;

the carrier-modified silver-based ethylene remover prepared by the preparation method has the mass percentage content of silver in the silver-based ethylene remover of 3-8%.

Preferably, the mass percent of silver in the silver-based ethylene remover is 3-5%.

The carrier modified silver-based ethylene remover is applied to removing ethylene.

Preferably, the temperature for removing ethylene is 0 to 40 ℃.

According to the invention, the specific surface area and pore volume of the modified molecular sieve carrier are improved, and then silver is loaded to promote the silver species of the active component to form particles (known from the characterization result of a transmission electron microscope product) with uniform size and high dispersion on the surface of the carrier, so that the contact probability of ethylene and an active center is increased, and the inlet and outlet of reactants in a remover pore channel are improved.

Compared with the prior art, the invention has the following beneficial effects:

1. the prepared catalytic material has high-efficiency catalytic performance and stability on ethylene under the normal temperature condition;

2. the preparation process is simple and easy to implement, and the preparation cost is low;

3. the prepared catalytic material can be used for storing and preserving fruits and vegetables;

4. the prepared catalytic material has reusability.

Drawings

FIGS. 1a and 1b are graphs showing the stability of the stripping agent samples prepared in examples 1 to 6 of the present invention in removing ethylene at room temperature, specifically, graphs showing the change of the ethylene removal rate with the reaction time.

FIG. 2a is a TEM image of a sample of the stripping agent prepared in example 1 of the present invention.

FIG. 2b is a graph showing the particle size distribution of a sample of the stripping agent prepared in example 1 of the present invention (calculated from 50 points in FIG. 2 a).

Fig. 3 is a graph showing the performance of the removal agent prepared in example 1 of the present invention in removing ethylene after the removal agent is repeatedly used for 4 times, specifically, a graph showing the change of the removal rate of ethylene with the reaction time.

Detailed Description

For the convenience of understanding of those skilled in the art, the present invention will be further described with reference to the accompanying drawings and examples, but the embodiments and the scope of the present invention are not limited thereto.

HZSM-5 used in the examples was sieved through a 50 mesh sieve, washed with water, and dried.

Example 1

A preparation method of a carrier modified lifting ethylene remover comprises the following steps:

1) pretreatment of the support

Weighing 3g of HZSM-5 (silica-alumina ratio: 36) molecular sieve, placing the molecular sieve in a closed environment, controlling the heating rate at 5 ℃/min, heating to 500 ℃ from the room temperature, keeping the temperature for 3h, and then naturally cooling to the room temperature.

2) Modification of supports

Weighing citric acid, and dissolving the citric acid in 200mL of deionized water to prepare a 0.4M citric acid solution; and then adding the pretreated molecular sieve into the solution, wherein the solid-liquid mass ratio is 1:20, condensing and refluxing the solution at 90 ℃ for 16 hours, centrifuging, filtering, washing until the solution is neutral, and finally drying to obtain the modified molecular sieve carrier.

3) Preparation of remover precursor

Weighing 0.2548g of silver nitrate to be dispersed in 10mL of deionized water under the condition of keeping out of the sun, and stirring to ensure that the silver nitrate is uniformly dispersed to be recorded as solution 1; and adding the modified molecular sieve into the solution 1, uniformly dispersing, then soaking and aging in a vacuum environment for one night, and then performing vacuum drying at 70 ℃ for 4h to obtain the precursor of the modified molecular sieve supported silver catalytic material.

4) Forming by removing agent

Placing the precursor of the remover in 21 percent of O₂/N₂In the atmosphere, controlling the heating rate to be 5 ℃/min, raising the temperature from room temperature to 600 ℃ and keeping for 2h, promoting silver species to form uniformly-sized and uniformly-dispersed particles on the surface of the molecular sieve carrier, and simultaneously reducing partial silver ions into silver simple substances, which is beneficial to the reaction; and after high-temperature roasting, naturally cooling to room temperature to obtain the silver-based ethylene removal material.

FIG. 2a is a TEM image of a sample of the stripping agent prepared in example 1 of the present invention.

FIG. 2b is a graph showing the particle size distribution of a sample of the stripping agent prepared in example 1 of the present invention (calculated from 50 points in FIG. 2 a).

From the TEM results of fig. 2a, it can be seen that the Ag particles are uniformly distributed over the material, and as a dominant species, high dispersion is beneficial for ethylene to contact with it. As can be seen from FIG. 2b, the silver-based ethylene removal material prepared in this example has a uniform pore size with an average pore size of 2.05; meanwhile, according to the BET result shown in Table 1, the highly dispersed Ag particles cannot block the pore structure of the molecular sieve, so that the ethylene molecules can enter deeper pores, and the ethylene can be removed from the gas.

Table 1 BET test results of the silver-based ethylene removal materials prepared in examples 1 and 6 and HZSM-5(36)

Test for regeneration of scavenger by activation

The remover is placed at room temperature to react with the ethylene oxide until the remover loses efficacy, and then placed under the atmosphere of 21% O2/N2 for heating regeneration, and the regenerated remover can still be reused, and the effect of the remover is compared with that of the remover used for the first time as shown in figure 3.

Fig. 3 is a graph showing the performance of the removal agent prepared in example 1 of the present invention in removing ethylene after the removal agent is repeatedly used for 4 times, specifically, a graph showing the change of the removal rate of ethylene with the reaction time. From the results in the figure, after 4 times of cyclic regeneration, the removing agent still maintains more than 80% of ethylene removing effect (calculated by the removing efficiency being more than or equal to 98% of the using time) in the fourth time of use, and the ethylene is removed from the surface of the material and is partially oxidized into carbon dioxide by heating treatment for a period of time, so that the Ag species playing a role in removing are recovered to a state of being reused, thereby showing that the removing agent has reusability.

Example 2

A preparation method of a carrier modified lifting ethylene remover comprises the following steps:

1) pretreatment of the support

Weighing 3g of nano HZSM-5(25) molecular sieve, placing in a closed environment, controlling the heating rate at 5 ℃/min, heating to 550 ℃ from room temperature, keeping for 6h, and naturally cooling to room temperature.

2) Modification of supports

Weighing nitric acid, dissolving in 200mL of deionized water, and preparing into a 0.1M nitric acid solution; and adding the pretreated molecular sieve into the mixture, wherein the solid-to-liquid ratio is 1: 12.5, condensing and refluxing for 20h at 60 ℃, centrifuging, filtering, washing until the solution is neutral, and finally drying to obtain the modified molecular sieve carrier.

3) Preparation of remover precursor

Weighing 0.2548g of silver nitrate to be dispersed in 10mL of deionized water under the condition of keeping out of the sun, and stirring to ensure that the silver nitrate is uniformly dispersed to be recorded as solution 1; and adding the modified molecular sieve into the solution 1, uniformly dispersing, then soaking and aging in a vacuum environment for one night, and then performing vacuum drying at 70 ℃ for 6 hours to obtain the ethylene removal material.

4) Forming by removing agent

Placing the precursor of the remover in 21 percent of O₂/N₂In the atmosphere, controlling the heating rate to be 5 ℃/min, heating to 500 ℃ from the room temperature, keeping for 4h, and then naturally cooling to the room temperature to obtain the silver-based ethylene removal material.

Example 3

A preparation method of a carrier modified lifting ethylene remover comprises the following steps:

1) pretreatment of the support

Weighing 3g of HZSM-5(36) molecular sieve, placing in a closed environment, controlling the heating rate at 5 ℃/min, heating to 500 ℃ from room temperature, keeping for 3h, and naturally cooling to room temperature.

2) Modification of supports

Weighing oxalic acid, dissolving in 200mL of deionized water, and preparing into 0.2M oxalic acid solution; and adding the pretreated molecular sieve into the mixture, wherein the solid-to-liquid ratio is 1:20, condensing and refluxing for 16h at 90 ℃, centrifuging, filtering, washing until the solution is neutral, and finally drying to obtain the modified molecular sieve carrier.

3) Preparation of remover precursor

Weighing 0.2548g of silver nitrate to be dispersed in 10mL of deionized water under the condition of keeping out of the sun, and stirring to ensure that the silver nitrate is uniformly dispersed to be recorded as solution 1; and adding the modified molecular sieve carrier into the solution 1, uniformly dispersing, then soaking and aging in a vacuum environment for one night, and drying at 100 ℃ for 2 hours to obtain the precursor of the modified molecular sieve silver-loaded ethylene removal material.

4) Forming by removing agent

Placing the precursor of the remover in 21 percent of O₂/N₂In the atmosphere, controlling the heating rate to be 5 ℃/min, raising the temperature from room temperature to 600 ℃ and keeping for 2h, and then naturally cooling to room temperature to obtain the silver-based ethylene removal material.

Example 4

A preparation method of a carrier modified lifting ethylene remover comprises the following steps:

1) pretreatment of the support

Weighing 3g of nano HZSM-5(25) molecular sieve, placing in a closed environment, controlling the heating rate at 5 ℃/min, heating to 550 ℃ from room temperature, keeping for 6h, and naturally cooling to room temperature.

2) Modification of supports

Weighing citric acid, and dissolving the citric acid in 200mL of deionized water to prepare a 0.1M citric acid solution; and then adding the pretreated molecular sieve into the solution, wherein the solid-to-liquid ratio is 1:10, condensing and refluxing for 5 hours at 120 ℃, centrifuging, filtering, washing until the solution is neutral, and finally drying to obtain the modified molecular sieve carrier.

3) Preparation of remover precursor

Under the condition of keeping out of the sun, 0.1529g of silver nitrate is weighed and dispersed in 10mL of deionized water, and the mixture is uniformly dispersed by stirring and is recorded as solution 1; and adding the modified molecular sieve into the solution 1, uniformly dispersing, then soaking and aging in a vacuum environment for one night, and then performing vacuum drying at 70 ℃ for 4h to obtain the precursor of the modified molecular sieve supported silver catalytic material.

4) Forming by removing agent

Placing the precursor of the remover in 21 percent of O₂/N₂In the atmosphere, controlling the heating rate to be 5 ℃/min, heating to 700 ℃ from the room temperature, keeping for 1h, and then naturally cooling to the room temperature to obtain the silver-based ethylene removal material.

Example 5

A preparation method of a carrier modified lifting ethylene remover comprises the following steps:

1) pretreatment of the support

Weighing 3g of HZSM-5(36) molecular sieve, placing in a closed environment, controlling the heating rate at 5 ℃/min, heating to 500 ℃ from room temperature, keeping for 3h, and naturally cooling to room temperature.

2) Modification of supports

Weighing citric acid, and dissolving the citric acid in 200mL of deionized water to prepare a 0.2M citric acid solution; and then adding the pretreated molecular sieve into the solution, wherein the solid-to-liquid ratio is 1:20, condensing and refluxing the solution at 90 ℃ for 16 hours, centrifuging, filtering, washing the solution until the solution is neutral, and finally drying the solution to obtain the modified molecular sieve carrier.

3) Preparation of remover precursor

Under the condition of keeping out of the sun, 0.4077g of silver nitrate is weighed and dispersed in 10mL of deionized water, and the mixture is uniformly dispersed by stirring and is recorded as solution 1; and adding the modified molecular sieve into the solution 1, uniformly dispersing, then soaking and aging in a vacuum environment for one night, and drying at 100 ℃ for 2 hours to obtain the precursor of the modified molecular sieve supported silver catalytic material.

4) Forming by removing agent

Placing the precursor of the remover in 21 percent of O₂/N₂In the atmosphere, controlling the heating rate to be 5 ℃/min, heating to 550 ℃ from the room temperature, keeping for 3h, and then naturally cooling to the room temperature to obtain the silver-based ethylene removal material.

Example 6

A preparation method of a carrier unmodified ethylene remover comprises the following steps:

1) pretreatment of the support

Weighing 3g of HZSM-5 (silica-alumina ratio: 36) molecular sieve, placing the molecular sieve in a closed environment, controlling the heating rate at 5 ℃/min, heating to 500 ℃ from the room temperature, keeping the temperature for 3h, and then naturally cooling to the room temperature.

2) Preparation of remover precursor

Weighing 0.2548g of silver nitrate to be dispersed in 10mL of deionized water under the condition of keeping out of the sun, and stirring to ensure that the silver nitrate is uniformly dispersed to be recorded as solution 1; and adding the modified molecular sieve into the solution 1, uniformly dispersing, then soaking and aging in a vacuum environment for one night, and then performing vacuum drying at 70 ℃ for 4 hours to obtain an ethylene removal material precursor.

3) Forming by removing agent

Placing the precursor of the remover in 21 percent of O₂/N₂In the atmosphere, controlling the heating rate to be 5 ℃/min, raising the temperature from room temperature to 600 ℃ and keeping the temperature for 2h, and then naturally cooling to room temperature to obtain the silver-based ethylene removal material with unmodified carrier.

Testing of remover Performance

The removal performance of the removal agent materials prepared in examples 1-6, respectively, for the degradation of ethylene gas in a fluidized bed was tested. The specific process is as follows:

respectively weighing 0.1g of a 40-60-mesh sample, placing the sample into a quartz tube with the inner diameter of 6mm, reacting at 25 ℃ under the condition that the reaction gas is air containing 50ppm of ethylene gas (wherein the oxygen content is 21 percent, and nitrogen is balanced), and sampling at the gas flow rate of 50mL/min (namely 30000 mL/(g.h)), and detecting the concentration change of the ethylene gas in an instrument by adopting a gas chromatograph at intervals of 3 min.

FIG. 1 is a graph showing the stability of the removal of ethylene at room temperature for the samples of the removing agent prepared in examples 1 to 6 of the present invention, specifically, a graph showing the change of the removal rate of ethylene with the reaction time. As can be seen from the figure, the time for the removal agent prepared in example 1 to maintain efficient removal (the removal efficiency is more than or equal to 98%) is longer, and is 1.6 times that of the carrier which is not modified and supports Ag (namely, example 6), and is 1.2 times that of examples 2-5. This is because the kind and concentration of the acid used for modifying the carrier, the amount of the loaded Ag, and the control of the temperature and time during the preparation process have important influences on the pore structure, Ag dispersion, acid sites and the like of the removing agent, and the main action mechanism of the removing agent material of the invention depends on the Ag species and the pore structure of the material, wherein the acid sites are used for adjusting the dispersion condition of Ag on the surface of the carrier, so the above factors are the starting point of the invention for removing ethylene from the gas flow. Since the strong acidity negatively affects the effect of the removing agent in terms of the acidity strength (including species and concentration), an appropriate acidity strength is necessary, and the use of a relatively mild acid-modified carrier has a better removing effect.

The above examples are only some embodiments of the present invention, and the description thereof is specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present invention is subject to the appended claims.