阅读说明：本技术 一种tempo-4-氯化铵的制备方法 (Preparation method of TEMPO-4-ammonium chloride ) 是由 蔡红云 袁鑫鑫 项瞻波 姚忠 于 2021-09-15 设计创作，主要内容包括：本发明涉及领域,具体提供了一种TEMPO-4-氯化铵的制备方法,包括如下步骤：S1将三丙酮胺与二甲胺加入水中,然后加入加氢催化剂进行加氢还原反应,得到N,N,2,2,6,6-六甲基哌啶基-4-胺；S2在催化剂作用下,N,N,2,2,6,6-六甲基哌啶基-4-胺与双氧水在溶剂中进行氧化反应,得到N,N,2,2,6,6-六甲基哌啶基氧基-4-胺；S3将N,N,2,2,6,6-六甲基哌啶基氧基-4-胺加入非质子溶剂中,然后通入氯甲烷,反应得到目标产物TEMPO-4-氯化铵,本发明的原料转化率高,溶剂绿色环保,且可直接进入下一步进行氧化反应操作；反应整体工序简单易操作,提纯步骤少、产物纯度高,成本低廉,原子经济,符合绿色生产的理念。(The invention relates to the field of preparation, and particularly provides a preparation method of TEMPO-4-ammonium chloride, which comprises the following steps: s1 adding triacetonamine and dimethylamine into water, and then adding a hydrogenation catalyst to carry out hydrogenation reduction reaction to obtain N, N,2,2,6, 6-hexamethyl piperidyl-4-amine; s2, under the action of a catalyst, carrying out oxidation reaction on N, N,2,2,6, 6-hexamethyl piperidyl-4-amine and hydrogen peroxide in a solvent to obtain N, N,2,2,6, 6-hexamethyl piperidyl oxy-4-amine; s3, adding N, N,2,2,6, 6-hexamethyl piperidyl oxy-4-amine into an aprotic solvent, then introducing methyl chloride, and reacting to obtain a target product TEMPO-4-ammonium chloride; the whole reaction process is simple and easy to operate, the purification steps are few, the product purity is high, the cost is low, the atom economy is realized, and the concept of green production is met.)

1. TEMPO-4-ammonium chloride, wherein the TEMPO-4-ammonium chloride has the formula (I):

（Ⅰ）；

the molecular formula of the TEMPO-4-ammonium chloride is C₂₁H₂₆ON₂Cl, the preparation method of which comprises the following steps:

s1: adding triacetonamine and dimethylamine into water, and then adding a hydrogenation catalyst to perform hydrogenation reduction reaction to obtain an N, N,2,2,6, 6-hexamethyl piperidyl-4-amine aqueous solution;

；

s2: under the action of a catalyst, carrying out oxidation reaction on an aqueous solution of N, N,2,2,6, 6-hexamethyl piperidyl-4-amine and hydrogen peroxide in a solvent to obtain N, N,2,2,6, 6-hexamethyl piperidyl oxy-4-amine;

；

s3: adding N, N,2,2,6, 6-hexamethyl piperidyl oxy-4-amine into an aprotic solvent, then introducing methane chloride, and reacting to obtain a target product TEMPO-4-ammonium chloride;

。

2. the method according to claim 1, wherein the mass ratio of triacetonamine to dimethylamine, to hydrogenation catalyst, to water in step S1 is 1: 0.4-1.5: 0.001-0.2: 1-10.

3. The method of claim 1, wherein the hydrogenation catalyst in step S1 is Pd/C, Pd/Al in an amount of 0.1-10 wt%₂O₃One or two of them.

4. The method of claim 1, wherein the temperature of the hydrogenation reduction reaction in step S1 is 0-160 ℃, the pressure of the hydrogenation reduction reaction is 1-60bar, and the time of the hydrogenation reduction reaction is 0.5-8 h.

5. The method for preparing TEMPO-4-ammonium chloride according to claim 1, wherein the mass ratio of the aqueous solution of N, N,2,2,6, 6-hexamethylpiperidinyl-4-amine to the hydrogen peroxide to the catalyst to the solvent in step S2 is 1: 0.5-10: 0.01-0.5: 0.01-10.

6. The method of claim 1, wherein the catalyst for the oxidation reaction in step S2 is one or more of magnesium sulfate, magnesium hydroxide, sodium tungstate, sodium carbonate, and sodium bicarbonate; the solvent for the oxidation reaction is water.

7. The method for preparing TEMPO-4-ammonium chloride according to claim 1, wherein the temperature of the oxidation reaction in step S2 is 20-100 ℃; the time of the oxidation reaction is 2-24 h.

8. The method according to claim 1, wherein the molar ratio of N,2,2,6, 6-hexamethylpiperidinyloxy-4-amine to monochloromethane in step S3 is 1: 1-10; the mass ratio of the N, N,2,2,6, 6-hexamethyl piperidyloxy-4-amine to the aprotic solvent is 1: 0.5-10.

9. The method of claim 1, wherein the aprotic solvent in step S3 is one or more of acetone, acetonitrile, tetrahydrofuran, benzene, and toluene.

10. The method of claim 1, wherein the temperature of the reaction in step S3 is 30-90 ℃, the pressure of the reaction is 1-20bar, and the reaction time is 0.5-16 h.

Technical Field

The invention belongs to the technical field of redox active materials of flow batteries, and particularly relates to a preparation method of TEMPO-4-ammonium chloride.

Background

Energy is an important material basis for social and economic development, and as the second major economic entity and the largest developing countries in the world, China is still in the middle and later stages of industrialized and urbanized development stages at present, the demand for energy is in a rapidly and continuously increasing state, and the current energy situation of 'rich coal, lean oil and less gas' forms a plurality of challenges such as resource shortage, environmental pollution, climate change and the like.

In order to solve the energy crisis and environmental pollution, the search and development of renewable clean energy has become a common consensus in the international society. Wind power and solar power have received much attention as clean, environmentally friendly, green energy sources, and have gained staged efforts and applications in recent years.

However, wind power and solar power can generate unstable, intermittent and other unstable power output in the power generation process due to factors such as wind speed, solar radiation intensity and time, and particularly when the wind power and solar power are used in large-scale grid connection, impact is easily generated on a power grid, huge hidden dangers are brought to the quality and safe operation of electric energy provided by the power grid, and the problems of power grid access and consumption are faced. After the electric energy generated by wind energy and solar energy can be stored by adopting a large-scale energy storage system, stable output of electric power is realized through manual intervention, the quality of the electric energy is improved, the requirement of a power grid on power generation of renewable clean energy is met, and the safety of the power grid is ensured. Therefore, the energy storage technology corresponding to the large-scale energy storage system has become the key point for solving the energy problem.

At present, the scale energy storage technology suitable for renewable energy power generation mainly comprises a pumped storage technology, a compressed air energy storage technology, an electrochemical energy storage technology and the like. The pumped storage technology and the compressed air energy storage technology are the most mature and widely applied scale energy storage technologies at present, and have the remarkable advantages of good economical efficiency, large energy storage capacity and the like. The two technologies have higher requirements on geographic positions and geological conditions, and have the problems of longer construction period, high early-stage investment cost and the like, so that the further development of the technologies is limited.

In terms of the current technical development level, the electrochemical energy storage technology is not constrained by factors such as geographical positions and the like, has the advantages of flexible design, easy scale expansion, adjustable and controllable properties, relatively high energy conversion efficiency and the like, and is an ideal energy storage method. In the electrochemical energy storage technology, the flow battery adopts aqueous solution as electrolyte, so that the safety is high, the power unit and the capacity unit are relatively independent, the flow battery has the remarkable advantages of flexible design, large energy storage scale, long cycle life and the like, can meet the requirement of large-scale energy storage, can realize the functions of peak regulation, frequency regulation and the like of a power grid, and is the most suitable energy storage technology in the electrochemical energy storage technology.

Among them, the redox flow battery is an energy storage system with high cycle efficiency, adjustable properties and wide prospect. Compared with an inorganic flow battery system, the organic flow battery using TEMPO and derivatives thereof as redox active materials has the advantages of low cost, high voltage, good reversibility, adjustable structure and the like. This is because 2,2,6, 6-tetramethylpiperidine-nitrogen-oxide (2,2,6,6-tetramethylpiperidine-1-oxyl, TEMPO) is a stable heterocyclic nitrogen oxide radical whose structure is sterically hindered by the four ortho methyl groups to avoid dimer formation. The free radical can undergo a reversible one-electron oxidation process as follows:

prior to application to flow batteries, TEMPO has been extensively studied in organic chemistry as an intermediate in oxidation reactions, and derivatives that attach TEMPO's basic structure to polymers have also been extensively studied as electrode materials for reversible lithium batteries.

Based on the special performance, many synthetic reports about TEMPO-based related redox active materials are published at home and abroad. Patent CN109803955A discloses in 2017 that triacetonamine and dimethylamine are subjected to hydrogenation reduction in an organic solvent, after solvent removal, the intermediate obtained by reduction and chloromethane generate ammonium salt in a mixed solvent of acetonitrile and toluene, and finally oxidation is performed to obtain TEMPO-4-ammonium chloride. In patent CN108140864A, triacetonamine is sequentially oxidized by hydrogen peroxide, reduced by equivalent reducing agent, reacted with methyl iodide to form salt and subjected to anion exchange to obtain TEMPO-4-ammonium chloride. U.S. Pat. No. 4, 20180072669, 1 discloses the use of 2,2,6, 6-tetramethylpiperidin-4-amine with formaldehyde in the presence of formic acid to form N, N,2,2,6, 6-hexamethylpiperidin-4-amine.

Compared with the prior art, the method has the advantages that triacetonamine and dimethylamine are adopted for hydrogenation reduction in water, the raw material conversion rate is high, the catalyst can be recycled, the solvent is green and environment-friendly, and the next step of oxidation reaction operation can be directly carried out. The whole reaction process is simple and easy to operate, low in cost and atom-economical, and accords with the concept of green production.

Disclosure of Invention

In order to solve the problems, the invention discloses a preparation method of TEMPO-4-ammonium chloride, which has the advantages of low cost, simple process, less purification steps and high product purity and adopts a green and environment-friendly hydrosolvent.

In order to achieve the purpose, the invention provides the following specific technical scheme:

the invention provides TEMPO-4-ammonium chloride, which has a structural formula shown as a formula (I):

（Ⅰ）；

the molecular formula of the TEMPO-4-ammonium chloride is C₂₁H₂₆ON₂Cl。

A preparation method of TEMPO-4-ammonium chloride comprises the following steps:

s1: adding triacetonamine and dimethylamine into water, and then adding a hydrogenation catalyst to perform hydrogenation reduction reaction to obtain an N, N,2,2,6, 6-hexamethyl piperidyl-4-amine aqueous solution;

；

s2: under the action of a catalyst, carrying out oxidation reaction on an aqueous solution of N, N,2,2,6, 6-hexamethyl piperidyl-4-amine and hydrogen peroxide in a solvent to obtain N, N,2,2,6, 6-hexamethyl piperidyl oxy-4-amine;

；

s3: adding N, N,2,2,6, 6-hexamethyl piperidyl oxy-4-amine into an aprotic solvent, then introducing methane chloride, and reacting to obtain a target product TEMPO-4-ammonium chloride;

。

further, in the step S1, the mass ratio of triacetonamine to dimethylamine to hydrogenation catalyst to water is 1: 0.4-1.5: 0.001-0.2: 1-10.

Preferably, the molar ratio of triacetonamine to dimethylamine in step S1 is 1: 1.8-3; the adding mass of the hydrogenation catalyst is 0.5-5% of the mass of triacetonamine.

Further, the hydrogenation catalyst in the step S1 is Pd/C, Pd/Al with the mass content of 0.1-10%₂O₃One or two of them.

Preferably, the hydrogenation catalyst in the step S1 is Pd/Al with the mass content of 0.5-5%₂O₃。

Further, the temperature of the hydrogenation reduction reaction in the step S1 is 0-160 ℃, the pressure of the hydrogenation reduction reaction is 1-60bar, and the time of the hydrogenation reduction reaction is 0.5-8 h.

Preferably, the temperature of the hydrogenation reduction reaction in the step S1 is 0-10 ℃, 40-60 ℃, 80-90 ℃, 105-110 ℃, 140-145 ℃; the pressure of the hydrogenation reduction reaction is 5-40 bar; the time of the hydrogenation reduction reaction is 2-6 h.

Further, in the step S2, the mass ratio of the aqueous solution of N,2,2,6, 6-hexamethylpiperidinyl-4-amine to the hydrogen peroxide to the catalyst to the solvent is 1: 0.5-10: 0.01-0.5: 0.01-10.

Further, the catalyst for the oxidation reaction in step S2 is one or more of magnesium sulfate, magnesium hydroxide, sodium tungstate, sodium carbonate and sodium bicarbonate; the solvent for the oxidation reaction is water.

Preferably, the catalyst for the oxidation reaction in step S2 is one or both of magnesium hydroxide and sodium bicarbonate.

Further, the temperature of the oxidation reaction in the step S2 is 20-100 ℃; the time of the oxidation reaction is 2-24 h.

Preferably, the temperature of the oxidation reaction in the step S2 is 60-100 ℃; the time of the oxidation reaction is 4-16 h.

Further, in the step S3, the molar ratio of N,2,2,6, 6-hexamethylpiperidinyloxy-4-amine to methyl chloride is 1: 1-10; the mass ratio of the N, N,2,2,6, 6-hexamethyl piperidyloxy-4-amine to the aprotic solvent is 1: 0.5-10.

Further, the aprotic solvent in step S3 is one or more of acetone, acetonitrile, tetrahydrofuran, benzene, and toluene.

Preferably, the aprotic solvent in step S3 is one or more of acetonitrile, tetrahydrofuran and toluene.

Further, the reaction temperature in the step S3 is 30-90 ℃, the reaction pressure is 1-20bar, and the reaction time is 0.5-16 h.

Preferably, the reaction temperature in the step S3 is 60-90 ℃, the reaction pressure is 1-10bar, and the reaction time is 0.5-8 h.

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

1. this patent adopts triacetonamine and dimethylamine to carry out hydrogenation reduction in aqueous, and the solvent green accords with the theory of green production.

2. The raw materials used by the invention have wide sources and low cost, so that the invention has higher economic value.

3. The invention has high conversion rate of raw materials, and is economic and environment-friendly.

4. The whole reaction process is simple and easy to operate, and the reaction is safe and reliable.

Drawings

FIG. 1 is an infrared spectrum of a target product prepared in step S1 of example 1 of the present invention;

FIG. 2 is a HNMR map of the target product prepared in step S1 of example 1 of the present invention;

FIG. 3 is an infrared spectrum of a target product prepared in step S2 of example 1 of the present invention;

FIG. 4 is a HNMR map of the target product prepared in step S2 of example 1 of the present invention;

FIG. 5 is an infrared spectrum of a target product prepared in step S3 of example 1 of the present invention;

fig. 6 is a HNMR map of the target product prepared in step S3 of example 1 of the present invention.

Detailed Description

The present invention is described in detail below with reference to the drawings and examples, but the present invention is not limited thereto.

Example 1

S1: 155g of triacetonamine, 250g of dimethylamine aqueous solution (40 wt.%), 200g of water and 2g of 2 wt.% Pd/C are put into a high-pressure kettle, nitrogen and hydrogen are sequentially replaced, stirring is carried out under normal pressure, the temperature is reduced to 5-10 ℃ for reaction for 1h, the temperature is increased to 55-60 ℃ and the pressure is increased to 10bar for reaction for 2h, finally, the temperature is increased to 105 ℃ and 110 ℃ and the pressure is kept at 20bar for reaction for 4h, the temperature is reduced and the nitrogen is replaced, the reaction solution is subjected to suction filtration and reduced pressure distillation to remove residual dimethylamine and 150g of water, and the N, N,2,2,6, 6-hexamethylpiperidyl-4-amine aqueous solution with the GC content of 97% is obtained.

¹H NMR (400MHz, D₂O) 2.71 (t, 1H), 2.19 (s, 6H), 1.75 (dd, 2H), 1.12 (d, 12H), 1.02 (t, 2H). The HNMR map is shown in FIG. 2.

S2: putting 140g of the N, N,2,2,6, 6-hexamethyl piperidyl-4-amine aqueous solution, 8g of sodium bicarbonate and 10g of water into a four-neck round-bottom flask, stirring, heating to 92 ℃, dropwise adding 330g of hydrogen peroxide aqueous solution (30 wt.%), carrying out heat preservation reaction for 12h, detecting that the content of N, N,2,2,6, 6-hexamethyl piperidyl oxy-4-amine is 95% by HPLC (high performance liquid chromatography), adjusting the pH value to 5-6, carrying out heat preservation stirring for 1h, carrying out reduced pressure distillation to remove water, dissolving with 200mL of methanol, carrying out suction filtration to remove salt, and carrying out reduced pressure distillation to remove methanol to obtain 190g of orange red N, N,2,2,6, 6-hexamethyl piperidyl oxy-4-amine, wherein the content of GC is 97%.

¹H NMR (400MHz, D₂O) 3.51 (t, 1H), 3.09 (s, 6H), 2.16 (d, 2H), 1.65 (t, 2H), 1.19 (s, 6H), 1.15 (s, 6H). The HNMR map is shown in FIG. 4.

S3: 188g of the N, N,2,2,6, 6-hexamethylpiperidinyloxy-4-amine, 200g of acetonitrile and 200g of toluene obtained in the previous step are added into an autoclave, nitrogen and methyl chloride are sequentially replaced, stirring is started, the temperature is raised to 80 ℃, 192g of methyl chloride is introduced, after 4 hours of reaction, the pressure is observed to be constant, and then the temperature is reduced, the filtration and the drying are carried out, so that 242g of orange-red solid TEMPO-4-ammonium chloride with the HPLC content of 94% is obtained.

¹H NMR (400MHz, D₂O) 3.76 (t, 1H), 3.14 (s, 9H), 2.22 (d, 2H), 1.77 (t, 2H), 1.27 (s, 6H), 1.24 (2, 6H). The HNMR map is shown in FIG. 6.

Detecting N, N,2,2,6, 6-hexamethylpiperidyl-4-amine, N,2,2,6, 6-hexamethylpiperidyloxy-4-amine and TEMPO-4-ammonium chloride with infrared spectrum shown in FIG. 1, FIG. 3 and FIG. 5.

The IR spectrum shown in FIG. 1 shows absorption peaks at 1470cm-1, 1460cm-1, 1375cm-1 and 1210cm-1, indicating the presence of vCH₃、vCH₂The stretching and bending vibration vC-H; a characteristic absorption peak at 1020-1360cm-1, indicating the presence of saturated vC-N; a characteristic absorption peak at 1300-; the characteristic absorption peak at 1510-1570cm-1 is the absorption peak due to coupling between δ NH and vC-N; characteristic absorption peaks of saturated CH and benzene ring CH are at 2800-3000cm < -1 >; there was an vNH peak for absorption of stretching vibration at 3300 cm-1.

The infrared spectrum shown in FIG. 3 shows absorption peaks at 1470cm-1, 1453cm-1, 1375cm-1 and 1210cm-1, indicating the presence of vCH₃、vCH₂The stretching and bending vibration vC-H; a characteristic absorption peak at 1100cm-1, indicating the presence of v-NO, and a characteristic absorption peak at 1020-1360cm-1, indicating the presence of saturated vC-N; the characteristic absorption peak at 1550cm-1, being the vC-N absorption peak; characteristic absorption peaks of saturated CH and benzene ring CH are at 2800-3000 cm-1.

The IR spectrum shown in FIG. 5 can see absorption peaks at 1477cm-1, 1460cm-1, 1375cm-1 and 1231cm-1, indicating the presence of vCH₃、vCH₂The stretching and bending vibration vC-H; a characteristic absorption peak at 1106cm-1 indicating the presence of v-NO, and a characteristic absorption peak at 1020-1360cm-1 indicating the presence of saturated vC-N; the characteristic absorption peak at 1570cm-1 is a vC-N absorption peak, and the intensity of the absorption peak is higher than that of the absorption peak NN,2,2,6, 6-hexamethylpiperidinyloxy-4-amine became significantly higher; characteristic absorption peaks of saturated CH and benzene ring CH are at 2800-3000 cm-1.

Example 2

S1: 1000g of triacetonamine, 1800g of dimethylamine aqueous solution (40 wt.%), 1500g of water and 10g of Pd/C are put into a high-pressure kettle, nitrogen and hydrogen are sequentially replaced, stirring is carried out under normal pressure, the temperature is reduced to 5-10 ℃ for reaction for 1h, the temperature is increased to 55-60 ℃ and the pressure is increased to 10bar for reaction for 2h, finally the temperature is increased to 105 ℃ and 110 ℃ and the pressure is kept at 20bar for reaction for 4h, the temperature is reduced and the nitrogen is replaced, the reaction solution is subjected to suction filtration and reduced pressure distillation to remove residual dimethylamine and part of water, and 2800g of N, N,2,2,6, 6-hexamethylpiperidyl-4-amine aqueous solution with the GC content of 98% is obtained.

S2: 2800g of N, N,2,2,6, 6-hexamethylpiperidyl-4-amine aqueous solution, 37g of magnesium hydroxide and 50g of water are put into a four-neck round-bottom flask, stirred and heated to 95 ℃, 5400g of hydrogen peroxide aqueous solution (30 wt.%) is dropwise added into the flask, the flask is kept warm for 14 hours to react, the content of N, N,2,2,6, 6-hexamethylpiperidyl-oxy-4-amine is 96% by HPLC (high performance liquid chromatography), the flask is cooled and filtered, the pH value is adjusted to 5-6, the flask is stirred at 90 ℃ for 1 hour, the flask is distilled under reduced pressure to remove water, 200mL of methanol is used for dissolving, filtering and desalting, and the flask is distilled under reduced pressure to remove methanol, 1230g of orange red N, N,2,2,6, 6-hexamethylpiperidyl-oxy-4-amine is obtained, and the GC content is 98%.

S3: 1230g of the N, N,2,2,6, 6-hexamethylpiperidinyloxy-4-amine, 1500g of acetonitrile and 1500g of toluene obtained above are added into an autoclave, nitrogen and methyl chloride are sequentially replaced, stirring is started, the temperature is raised to 80 ℃, 1250g of methyl chloride is introduced, reaction is carried out for 6 hours, after the pressure is observed to be constant, the temperature is reduced, suction filtration is carried out, cold acetonitrile is repeatedly washed, suction filtration is carried out, and then drying is carried out, thus obtaining 1620g of orange red solid TEMPO-4-ammonium chloride with the HPLC content of 92%.

Example 3

S1: 310g of triacetonamine, 500g of dimethylamine aqueous solution (40 wt.%), 400g of water and 3g of Pd/C are put into a high-pressure kettle, nitrogen and hydrogen are sequentially replaced, stirring is carried out under normal pressure, the temperature is reduced to 5-10 ℃ for reaction for 1h, the temperature is increased to 55-60 ℃ and the pressure is increased to 10bar for reaction for 2h, finally the temperature is increased to 105 ℃ and 110 ℃ and the pressure is kept at 20bar for reaction for 4h, the temperature is reduced and the nitrogen is replaced, the reaction solution is filtered, and the residual dimethylamine and part of water are removed by reduced pressure distillation, so 650g of N, N,2,2,6, 6-hexamethylpiperidyl-4-amine aqueous solution with the GC content of 97% is obtained.

S2: putting 650g of the N, N,2,2,6, 6-hexamethylpiperidyl-4-amine aqueous solution, 10.2g of magnesium hydroxide and 50g of water into a four-neck round-bottom flask, stirring and heating to 60-65 ℃, then dropwise adding 820g of hydrogen peroxide aqueous solution (50 wt.%), carrying out heat preservation reaction for 14h, detecting that the content of N, N,2,2,6, 6-hexamethylpiperidyl-oxy-4-amine is 95% by HPLC (high performance liquid chromatography), carrying out cooling suction filtration, stirring at 90 ℃ for 1.5h, carrying out reduced pressure distillation to remove water, dissolving and carrying out suction filtration to remove salt by using 200mL of methanol, and carrying out reduced pressure distillation to remove methanol to obtain 415g of orange N, N,2,2,6, 6-hexamethylpiperidyl-oxy-4-amine with the content of HPLC of 93%.

S3: 415g of the obtained N, N,2,2,6, 6-hexamethylpiperidinyloxy-4-amine and 500g of acetonitrile are added into an autoclave, nitrogen and methyl chloride are sequentially replaced, stirring is started, the temperature is raised to 80 ℃, 425g of methyl chloride is introduced, after reaction for 4 hours, the pressure is observed to be constant, then cooling and suction filtration are carried out, and after repeated washing and suction filtration of cold acetonitrile, drying is carried out, 501g of orange solid TEMPO-4-ammonium chloride is obtained, wherein the HPLC content is 90%.

The technical means disclosed in the invention scheme are not limited to the technical means disclosed in the above embodiments, but also include the technical scheme formed by any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and such improvements and modifications are also considered to be within the scope of the present invention.