Use of nicotine and its salts in the preparation of rust-preventive liquids and rust-preventive liquids

Abstract

The application discloses a use of nicotine and its salt in preparing a rust-proof liquid and the rust-proof liquid. The application first proposes to use nicotine and its salt as an active component of the rust-proof liquid, and uses the nicotine and its salt as a rust-proof agent. The application also provides components and compositions of the rust-proof liquid, which include, in percentage by mass, 20-60 parts of rust-proof agents, 10-20 parts of rust-proof additives, 3-5 parts of film forming agents, and 50-70 parts of water, wherein the rust-proof agents are one or more of nicotine or nicotine salts. The rust-proof agents are natural alkaloids nicotine extracted from plants such as tobacco and nicotine salts prepared by reacting the nicotine with organic acids. By adding appropriate amounts of rust-proof additives and film forming agents, a water-based rust-proof liquid which is green, environment-friendly, non-toxic and does not need to add an antibacterial agent can be obtained. The rust-proof liquid can be applied to metal processing and storage processes and has a good rust-proof effect on metal products.

Description

Technical Field

[0001] This invention belongs to the field of rust inhibitor technology, and particularly relates to the use of nicotine and its salts in the preparation of rust inhibitors and the rust inhibitors themselves. Background Technology

[0002] Corrosion of metals and alloys is a significant economic and industrial problem. During processing and storage, metals and metal components may be exposed to corrosive media, resulting in changes in appearance and properties through physical or chemical processes. According to incomplete statistics, the economic losses caused by corrosion each year exceed the combined losses from natural disasters and various accidents. Therefore, selecting appropriate corrosion control measures is crucial. Rust inhibitors are widely used in metal processing and storage, and can be used as additives in cutting fluids or rust-preventive liquids for rust prevention treatment of metal surfaces. Rust inhibitors can be divided into water-based and oil-based types. While rust-preventive oils offer excellent protection, the subsequent treatment and cleaning processes are relatively cumbersome, making water-based rust inhibitors more popular. Many existing rust inhibitors may have problems such as cumbersome preparation and toxicity. For example, nitrites, although possessing excellent rust-preventive properties, are currently banned due to their carcinogenicity. Furthermore, some rust inhibitors may accumulate in soil and aquatic organisms, causing environmental harm. Therefore, finding a green, non-toxic, biodegradable rust inhibitor with excellent rust-preventive performance has become an urgent market demand.

[0003] As is well known, many products now use non-toxic natural compounds as alternatives to synthetic chemicals. Utilizing nature's abundant sustainable resources to protect the environment is extremely important, as it will have an increasingly significant impact on the well-being of society and people. It has been reported that the main components of plant extracts are various organic compounds, including polyphenols, terpenes, carboxylic acids, and alkaloids. These compounds mostly contain multiple atoms such as P, N, S, and O in their structures, allowing them to adsorb onto the surface of metal materials. Some of these compounds also have the ability to inhibit microbial growth, making them potential as rust inhibitors. Nicotine is a natural chemical extracted from plants. This invention discovers that nicotine and nicotine salts have good water solubility and excellent rust-preventing properties against ferrous metals. Addressing the potential environmental and human health hazards of existing products, this invention proposes for the first time the application of nicotine and its salts in rust-preventive liquids, particularly in the preparation of rust-preventive liquids, and further provides a method for preparing a green, environmentally friendly, and highly effective water-based rust-preventive liquid. Summary of the Invention

[0004] To address the problems of complex post-treatment processes and potential harm to human health and the environment associated with current commercially available rust-preventive oils, this invention utilizes the reaction of nicotine extracted from plants such as tobacco with organic acids. After adding unsuitable solvents, nicotine salts are obtained, which are then compounded with nicotine to serve as a rust inhibitor. This solution is further mixed with rust-preventive additives, film-forming agents, and deionized water to prepare a water-based rust-preventive liquid with excellent rust-preventive effects. This invention is the first to propose the application of nicotine and its salts in rust-preventive liquids. The resulting water-based rust-preventive liquid is environmentally friendly, non-toxic, biodegradable, and requires no additional antibacterial agents. The preparation method is simple, the process is scientific and environmentally friendly, and it has significant application value.

[0005] It should be further noted that the nicotine and nicotine salts of the present invention are not limited to natural extraction, but also include those obtained by other synthetic methods.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The first aspect of this invention proposes the use of nicotine and its salts in the preparation of rust-preventive liquids, wherein nicotine or nicotine salts are the active components in the rust-preventive liquids.

[0008] Furthermore, the rust inhibitor is a water-based rust inhibitor or a vapor-phase rust inhibitor.

[0009] A second aspect of the present invention provides a water-based rust inhibitor containing nicotine and its salts, wherein the water-based rust inhibitor comprises, by mass percentage, 20-60 parts of rust inhibitor, 10-20 parts of rust inhibitory additive, 3-5 parts of film-forming agent, and 50-70 parts of water, wherein the rust inhibitor is one or more of nicotine or nicotine salts.

[0010] Nicotine or nicotine salts, as rust inhibitors, are the core components of water-based rust inhibitors. Nicotine and nicotine salts alter the environment surrounding the metal, quickly adsorbing onto the metal surface to form a protective film, effectively isolating the metal from corrosive media and thus achieving rust prevention. Simultaneously, nicotine inhibits the growth and reproduction of microorganisms in the rust inhibitor, preventing microbial contamination from affecting the performance of the rust inhibitor and maintaining its stability and effectiveness. Furthermore, nicotine derivatives and their salts can also play an equivalent role.

[0011] The addition of rust inhibitors further enhances rust prevention performance while reducing the amount of rust inhibitor used, thus saving costs. The use of film-forming agents facilitates the adhesion of rust inhibitors and rust inhibitors to the metal surface, enhancing the rust prevention effect.

[0012] Furthermore, the aforementioned nicotine salt is one or more of the following: nicotine caprylate, nicotine decanoate, nicotine laurate, nicotine cinnamate, nicotine leucine salt, and nicotine lysine salt.

[0013] Furthermore, the aforementioned rust-inhibiting additive is one or more of monoethanolamine, diethanolamine, and triethanolamine.

[0014] Furthermore, the film-forming agent mentioned above is one or more of polyvinyl alcohol, glyceryl stearate, dodecyl thiourea, and sodium dodecyl sulfate.

[0015] The present invention also provides a method for preparing the above-mentioned nicotine salt, comprising:

[0016] Step 1. Mix nicotine and organic acid and react at 30-50℃ for 5-24 hours to obtain solution A;

[0017] Step 2. Add a poor solvent to solution A, and after filtration, washing, and distillation, obtain nicotine salt;

[0018] The organic acid mentioned is one or more of the following: octanoic acid, capric acid, lauric acid, cinnamic acid, leucine, and lysine.

[0019] Furthermore, the molar ratio of nicotine to organic acid is 1.1-1.5.

[0020] Furthermore, the aforementioned unsuitable solvents are one or more of diethyl ether, acetone, and n-hexane.

[0021] A third aspect of the present invention also provides a method for preparing a water-based rust inhibitor containing nicotine and its salts, comprising the following steps:

[0022] S1. Rust inhibitor and rust inhibitor additive are added to a container containing a certain volume of deionized water in sequence according to the mass percentage, and stirred at room temperature to fully mix and dissolve to obtain rust inhibitor solution A;

[0023] S2. Slowly add the film-forming agent to the rust inhibitor A and continue stirring until completely dissolved to obtain the water-based rust inhibitor.

[0024] Furthermore, in step S1, the stirring speed is 400-2000 rpm and the time is 10-60 min. In step S2, the stirring speed is 600-2500 rpm and the time is 5-30 min.

[0025] A fourth aspect of this invention discloses the application of a water-based rust inhibitor containing nicotine and its salts in the field of rust prevention. Adding the water-based rust inhibitor provided by this invention to cutting fluids or spraying it onto metal surfaces can prevent rusting.

[0026] The beneficial effects of this invention are:

[0027] This invention selects water-soluble, green, environmentally friendly, and biodegradable nicotine and nicotine salts as rust inhibitors for use in water-based rust inhibitors. On the one hand, nicotine can quickly adsorb onto the metal surface to form a protective film, preventing ferrous metal products from rusting. Nicotine also has a bactericidal effect, so there is no need to add additional antibacterial agents to the formula. On the other hand, the rust inhibitor can be used in many fields by adding it to cutting fluids or by direct spraying. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below.

[0029] Figure 1 The images show the appearance of the iron sheets in the experimental and control groups after soaking in the water-based rust inhibitor prepared in Example 1 of this invention for 12 hours. Detailed Implementation

[0030] Those skilled in the art can refer to the content of this document and appropriately improve the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The product of this invention has been described through preferred embodiments, and those skilled in the art can obviously make modifications or appropriate alterations and combinations to the product described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention. The invention is further illustrated below through specific embodiments; it should be noted that the following embodiments should not be construed as limiting the invention.

[0031] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0032] The phrase "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for conventional impurities associated with them. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0033] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including the ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0034] In some instances, approximate terms may correspond to the precision of the instrument used to measure the value. In this specification and claims, scope definitions may be combined and / or interchanged, unless otherwise stated, these scopes include all sub-scopes contained therein.

[0035] The indefinite articles “a” and “an” preceding an element or component of this invention do not impose any limitation on the quantity (i.e., number of times) of the element or component. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers only to the singular form.

[0036] The terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., used in this invention refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms are not necessarily directed at the same embodiment or example. Furthermore, the technical features involved in the various embodiments of the invention can be combined with each other as long as they do not conflict with each other.

[0037] Unless otherwise specified, the raw materials and equipment used in this invention can be purchased from the market or are commonly used in the field. Unless otherwise specified, the methods in the embodiments are conventional methods in the field.

[0038] The following will describe the specific solutions and implementation methods in detail:

[0039] In some embodiments, nicotine and its salts are used as active components in the preparation of rust inhibitors for the first time.

[0040] In some embodiments, a water-based rust inhibitor containing nicotine and its salts comprises, by mass percentage, 20-60 parts of rust inhibitor, 10-20 parts of rust inhibitory additive, 3-5 parts of film-forming agent, and 50-70 parts of water, wherein the rust inhibitor is one or more of nicotine or nicotine salts. Preferably, the rust inhibitor may be 20, 25, 30, 35, 40, 45, 50, 55, or 60 parts; the rust inhibitory additive may be 10, 12, 14, 16, 18, or 20 parts; the film-forming agent may be 3, 3.5, 4.0, 4.5, or 5 parts; and the water may be 50, 55, 60, 65, or 70 parts.

[0041] In some embodiments, the nicotine salt is one or more selected from nicotine caprylate, nicotine decanoate, nicotine laurate, nicotine cinnamate, nicotine leucine salt, and nicotine lysine salt. For example, a rust inhibitor is a mixture of nicotine, nicotine caprylate, nicotine laurate, and nicotine leucine salt. Nicotine derivatives and their salts can also perform equivalent functions.

[0042] In some embodiments, the rust inhibitor is one or more of monoethanolamine, diethanolamine, and triethanolamine.

[0043] In some embodiments, the film-forming agent is one or more of polyvinyl alcohol, glyceryl stearate, dodecyl thiourea, and sodium dodecyl sulfate.

[0044] In some embodiments, the present invention further discloses a method for preparing the above-mentioned nicotine salt, comprising:

[0045] Step 1. Mix nicotine and organic acid and react at 30-50℃ for 5-24 hours to obtain solution A;

[0046] Step 2. Add a poor solvent to solution A, and after filtration, washing, and distillation, obtain nicotine salt;

[0047] The organic acid mentioned is one or more of the following: octanoic acid, capric acid, lauric acid, cinnamic acid, leucine, and lysine.

[0048] In some embodiments, the molar ratio of nicotine to organic acid is 1.1-1.5, preferably 1.1, 1.2, 1.3, 1.4 or 1.5.

[0049] In some embodiments, the aforementioned undesirable solvent is one or more of diethyl ether, acetone, and n-hexane.

[0050] In some embodiments, the present invention also provides a method for preparing a water-based rust inhibitor containing nicotine and its salts, comprising the following steps:

[0051] S1. Rust inhibitor and rust inhibitor additive are added to a container containing a certain volume of deionized water in sequence according to the mass percentage, and stirred at room temperature to fully mix and dissolve to obtain rust inhibitor solution A;

[0052] S2. Slowly add the film-forming agent to the rust inhibitor A and continue stirring until completely dissolved to obtain the water-based rust inhibitor.

[0053] Furthermore, in step S1, the stirring speed is 400-2000 rpm and the time is 10-60 min. In step S2, the stirring speed is 600-2500 rpm and the time is 5-30 min.

[0054] A third aspect of this invention also provides the application of the water-based rust inhibitor containing nicotine and its salts, as described above, in the field of rust prevention. Adding the water-based rust inhibitor provided by this invention to cutting fluids or spraying it onto metal surfaces can prevent rusting.

[0055] The present invention will be described below with reference to specific embodiments, as follows:

[0056] Example 1

[0057] A water-based rust inhibitor with metal rust-preventing effect is prepared as follows:

[0058] Mix 25 parts nicotine with 70 parts deionized water and stir thoroughly to obtain a rust inhibitor; add 5 parts polyvinyl alcohol to the rust inhibitor and stir at 1500 rpm for 60 minutes until completely dissolved to obtain a water-based rust inhibitor.

[0059] Figure 1 The images show the appearance of iron sheets from the experimental and control groups after immersion in the water-based rust inhibitor prepared in Example 1 of this invention for 12 hours, with and without the rust inhibitor. It can be seen that after 12 hours of testing, the control group showed significant rusting, while the iron sheets with the added water-based rust inhibitor had a smooth, rust-free surface.

[0060] Example 2

[0061] A water-based rust inhibitor with metal rust-preventing effect is prepared as follows:

[0062] Add 25 parts of nicotine octanoate to 70 parts of deionized water and stir thoroughly to obtain a rust inhibitor; add 5 parts of polyvinyl alcohol to the rust inhibitor and stir at 1500 rpm for 60 minutes until completely dissolved to obtain a water-based rust inhibitor.

[0063] Example 3

[0064] A water-based rust inhibitor with metal rust-preventing effect is prepared as follows:

[0065] Add 10 parts nicotine, 4 parts nicotine octanoate, 5 parts nicotine decanoate, 3 parts nicotine leucine salt, and 10 parts monoethanolamine to a beaker in the specified proportions. Add 65 parts deionized water and stir thoroughly to obtain a rust-preventive solution. Add 3 parts polyvinyl alcohol to the rust-preventive solution and stir at 1500 rpm for 60 minutes until completely dissolved to obtain a water-based rust-preventive solution.

[0066] Example 4

[0067] A water-based rust inhibitor with metal rust-preventing effect is prepared as follows:

[0068] Add 7 parts nicotine, 6 parts nicotine octanoate, 4 parts nicotine laurate, 5 parts nicotine lysine salt, and 14 parts diethanolamine to a beaker in the specified proportions. Add 60 parts deionized water and stir thoroughly to obtain a rust-preventive solution. Add 4 parts polyvinyl alcohol to the rust-preventive solution and stir at 1500 rpm for 60 minutes until completely dissolved to obtain a water-based rust-preventive solution.

[0069] Example 5

[0070] A water-based rust inhibitor with metal rust-preventing effect is prepared as follows:

[0071] Add 10 parts nicotine, 10 parts nicotine decanoate, 5 parts nicotine cinnamate, 5 parts nicotine lysine, and 10 parts diethanolamine to a beaker in the specified proportions. Add 55 parts deionized water and stir thoroughly to obtain a rust-preventive solution. Add 5 parts sodium dodecyl sulfate to the rust-preventive solution and stir at 1500 rpm for 60 minutes until completely dissolved to obtain a water-based rust-preventive solution.

[0072] Example 6

[0073] A water-based rust inhibitor with metal rust-preventing effect is prepared as follows:

[0074] Add 15 parts nicotine, 5 parts nicotine octanoate, 5 parts nicotine decanoate, 5 parts nicotine laurate, 5 parts nicotine cinnamate, 5 parts nicotine leucine salt, and 15 parts triethanolamine to a beaker in the specified proportions. Add 55 parts deionized water and stir thoroughly to obtain a rust-inhibiting solution. Add 5 parts dodecyl thiourea to the rust-inhibiting solution and stir at 1500 rpm for 60 minutes until completely dissolved to obtain a water-based rust-inhibiting solution.

[0075] Comparative Example 1

[0076] Add 10 parts triethanolamine, 10 parts diethanolamine, 15 parts monoethanolamine, and 5 parts antibacterial agent to a beaker in the specified proportions, add 55 parts deionized water and stir thoroughly to obtain a rust-preventive solution; add 5 parts polyvinyl alcohol to the rust-preventive solution and stir at 1500 rpm for 60 minutes until completely dissolved to obtain a water-based rust-preventive solution.

[0077] Comparative Example 2

[0078] Add 5 parts of triethanolamine borate, 10 parts of benzotriazole, 5 parts of triethanolamine, 10 parts of monoethanolamine, and 5 parts of antibacterial agent to a beaker in the specified proportions. Add 60 parts of deionized water and stir thoroughly to obtain a rust-preventive solution. Add 5 parts of polyvinyl alcohol to the rust-preventive solution and stir at 2000 rpm for 60 minutes until completely dissolved to obtain a water-based rust-preventive solution.

[0079] The rust-preventive properties of the water-based rust inhibitors prepared in Examples 1, 2, 3, 4, 5, 6 and Comparative Examples 1, 2 were tested for iron. The experimental methods are as follows:

[0080] (1) Exposure experiment: The iron metal test piece was suspended on a rubber stopper with a hook, and then the test piece was immersed in the rust-preventive liquid (the blank group was immersed in deionized water). After 10 seconds, it was taken out and placed in a test tube containing 30 mL of deionized water. The device was placed in a 50℃ oven for 1 day.

[0081] (2) Immersion test: The iron metal test piece was immersed in a neutral corrosive solution with 1 wt% water-based rust inhibitor added for 3 days. No rust inhibitor was added in the blank group. After the experiment, the test piece was washed with an acidic solution to remove the surface rust and then weighed.

[0082] After the exposure experiment, the surface corrosion was observed. For the immersion experiment, the corrosion rate and corrosion inhibition efficiency were calculated based on the mass changes before and after the experiment. The formulas for calculating the corrosion rate and corrosion inhibition efficiency are as follows:

[0083] Corrosion rate = (WL) 0 -WL) / (A×t)×100

[0084] Corrosion inhibition efficiency = (Corrosion rate of blank group - Corrosion rate of experimental group) / Corrosion rate of blank group WL 0 W and L represent the mass (g) of the metal sample before and after the experiment, respectively, and A represents the surface area (m²) of the sample. 2 ), where t is the soaking time (d). The experimental results are shown in the table below:

[0085]

[0086] Examples 1 and 2 are water-based rust inhibitors formulated with pure nicotine and nicotine salts. Examples 3, 4, 5, and 6 are water-based rust inhibitors containing different proportions of nicotine and its salts. The rust-preventive effect decreases when the nicotine and its salt content is low. However, exposure experiments simulating the storage of the rust inhibitor on a metal surface under high temperature and humidity conditions demonstrate that the water-based rust inhibitor of this invention can provide excellent protection for metals. Immersion experiments show that adding the water-based rust inhibitor of this invention significantly inhibits the corrosion rate of metals in neutral corrosive media, achieving a corrosion inhibition efficiency of over 80%. Furthermore, the comparative experimental results in the table show that the rust-preventive effect of this water-based rust inhibitor on ferrous metals is superior to that of Comparative Examples 1 and 2 (without nicotine and nicotine salts) with the same rust inhibitor ratio, giving it a certain degree of market competitiveness.

[0087] In summary, this invention uses nicotine and nicotine salts as rust inhibitors, which not only have excellent rust-preventive effects but are also green and biodegradable. A highly efficient, environmentally friendly, water-based rust inhibitor that requires no additional antibacterial agents has been prepared, which can be applied to various fields such as metal processing and storage, meeting market demands.

[0088] It should be noted that the descriptions of the above embodiments each have their own emphasis. Where the descriptions in some embodiments are not exhaustive, please refer to the descriptions in other embodiments.

[0089] The embodiments described above are merely illustrative of implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. The use of nicotine and its salts in the preparation of rust inhibitors, characterized in that, The active component in the rust inhibitor is nicotine or nicotine salt.

2. The use of nicotine and its salts in the preparation of rust-preventive liquid according to claim 1, characterized in that, The rust inhibitor is a water-based rust inhibitor or a vapor-phase rust inhibitor.

3. The water-based rust inhibitor according to claim 2, characterized in that, The water-based rust inhibitor comprises, by weight, 20-60 parts of rust inhibitor, 10-20 parts of rust inhibitory additive, 3-5 parts of film-forming agent, and 50-70 parts of water, wherein the rust inhibitor is one or more of nicotine or nicotine salt.

4. The water-based rust inhibitor according to claim 3, characterized in that, The nicotine salt is one or more of the following: nicotine caprylate, nicotine decanoate, nicotine laurate, nicotine cinnamate, nicotine leucine salt, and nicotine lysine salt.

5. The water-based rust inhibitor according to any one of claims 3-4, characterized in that, The rust inhibitor is one or more of monoethanolamine, diethanolamine, and triethanolamine; the film-forming agent is one or more of polyvinyl alcohol, glyceryl stearate, dodecyl thiourea, and sodium dodecyl sulfate.

6. The water-based rust inhibitor according to any one of claims 3-4, characterized in that, The method for preparing the nicotine salt includes: Step 1. Mix nicotine and organic acid and react at 30-50℃ for 5-24 hours to obtain solution A; Step 2. Add a poor solvent to solution A, and after filtration, washing, and distillation, obtain nicotine salt; The organic acid mentioned is one or more of the following: octanoic acid, capric acid, lauric acid, cinnamic acid, leucine, and lysine.

7. The water-based rust inhibitor according to claim 6, characterized in that, The molar ratio of nicotine to organic acid is 1.1-1.

5.

8. The water-based rust inhibitor according to claim 6, characterized in that, The unsuitable solvent is one or more of diethyl ether, acetone, and n-hexane.

9. The method for preparing the water-based rust inhibitor according to any one of claims 3-8, characterized in that, The preparation method includes the following steps: S1. Rust inhibitor and rust inhibitor additive are added to a container containing a certain volume of deionized water in sequence according to the mass percentage, and stirred at room temperature to fully mix and dissolve to obtain rust inhibitor solution A; S2. Slowly add the film-forming agent to the rust inhibitor A and continue stirring until completely dissolved to obtain the water-based rust inhibitor.

10. The preparation method according to claim 9, characterized in that, In step S1, the stirring speed is 400-2000 rpm and the time is 10-60 min; in step S2, the stirring speed is 600-2500 rpm and the time is 5-30 min.

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