Preparation method of aluminate coupling agent and application thereof in surface modification of calcium carbonate

Abstract

The application belongs to the technical field of coupling agent and calcium carbonate surface modification, and particularly relates to a preparation method of aluminate coupling agent and application of the aluminate coupling agent in calcium carbonate surface modification. The application takes metal aluminum and isopropyl alcohol as starting raw materials, and generates isopropyl aluminum intermediate product under the action of isopropyl aluminum-iodine catalyst. The product is directly reacted with a composite fatty acid composed of oleic acid, palmitic acid and stearic acid to generate the aluminate coupling agent without separation. Compared with the traditional process, the synthesis route is greatly shortened, and the production cost of the product is effectively reduced. The calcium carbonate modified by the aluminate coupling agent prepared by the application has excellent dispersion performance, and the oil absorption value is significantly reduced, so the calcium carbonate has a wide application prospect in related industrial fields.

Description

Technical Field

[0001] This invention belongs to the field of coupling agents and calcium carbonate surface modification technology, specifically relating to a method for preparing an aluminate coupling agent and its application in calcium carbonate surface modification. Background Technology

[0002] Aluminate coupling agents are a new type of coupling agent developed after silane coupling agents and titanate coupling agents. They have advantages such as simple synthesis, low cost, and excellent performance, and are widely used in the fields of inorganic powder surface treatment and polymer composites. However, the existing preparation technology of aluminate coupling agents still has technical bottlenecks in terms of raw material selection, catalyst system, and synthesis process, which restricts their industrial production and application.

[0003] In terms of raw material selection, the preparation of traditional aluminate coupling agents often uses aluminum isopropoxide as the direct starting material. Aluminum isopropoxide is chemically reactive and highly hygroscopic, readily undergoing hydrolysis in water to produce aluminum hydroxide and isopropanol, leading to decreased product purity and reduced reactivity. Therefore, aluminum isopropoxide is not only difficult to store and transport for long periods, but also imposes stringent requirements on the warehousing conditions of manufacturing enterprises, significantly increasing logistics costs and safety management risks. Furthermore, the relatively high market price of aluminum isopropoxide directly raises the overall production cost of aluminate coupling agents.

[0004] Regarding catalyst systems, the production of aluminate coupling agents mostly uses chlorides, toxic heavy metals, and sulfides as catalysts. While these catalysts can promote the reaction to some extent, they can sublimate or decompose during the vacuum distillation purification of crude aluminum isopropoxide, and these catalysts can be mixed into the refined aluminum isopropoxide during the purification process, severely affecting the purity, reactivity, and appearance of the product. More seriously, these toxic and harmful substances can remain in the final aluminate coupling agent product, causing toxic side effects during production and application. Simultaneously, the presence of chlorides and heavy metals can significantly reduce the aging resistance of rubber and plastic products, failing to meet the requirements of modern green and environmentally friendly chemical development.

[0005] In terms of synthesis process, stearic acid is currently widely used in industry as a starting material to react with aluminum isopropoxide. Although stearic acid has advantages such as low cost, good chemical stability and sufficient source, its molecular structure has inherent defects. Stearic acid is a fully saturated straight-chain fatty acid with a linear rigid structure and does not contain any unsaturated bonds (C=C double bonds). This structural defect causes the synthesized aluminate coupling agent to have the following problems in practical application: (1) In rubber vulcanization or plastic crosslinking system, it cannot participate in the chemical crosslinking reaction of polymer, and can only rely on physical entanglement to combine with the matrix. The interfacial bonding force is weak, which limits its reinforcing performance; (2) The melting point of stearic acid is as high as 69℃-70℃, which causes the viscosity of the synthesized aluminate coupling agent to increase significantly at lower temperatures. The low-temperature fluidity is poor, which affects the dispersion and coating effect on the calcium carbonate surface; (3) The rigid straight-chain structure makes the molecules lack flexibility and spatial adaptability when coating the surface of inorganic powder, making it difficult to form a dense and effective surface coating layer.

[0006] In summary, there is an urgent need to develop new, efficient production processes for aluminate coupling agents, focusing on aspects such as raw material selection, catalyst systems, and synthesis techniques, in order to break through the bottlenecks of existing synthesis technologies. Summary of the Invention

[0007] To address the current technical bottlenecks in the synthesis of aluminate coupling agents, this invention uses aluminum sheets and isopropanol as starting materials, and aluminum isopropoxide and iodine as a composite catalyst to synthesize the intermediate product aluminum isopropoxide. Then, oleic acid, palmitic acid, and stearic acid are added in the same reactor to react the complex fatty acids with the intermediate aluminum isopropoxide, ultimately generating the aluminate coupling agent. This invention optimizes the production process of aluminate coupling agents, resulting in a new process for the high-efficiency production of aluminate coupling agents.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a method for preparing an aluminate coupling agent, the method comprising the following steps: S1. Using aluminum and isopropanol as starting materials, and aluminum isopropoxide and iodine as composite catalysts, aluminum, a portion of isopropanol and the composite catalyst are mixed and heated to the boiling point of isopropanol (82.4℃). After the reaction starts and stabilizes for a period of time, the remaining isopropanol is added and the temperature is controlled to continue the reaction to generate aluminum isopropoxide intermediate. S2. A complex fatty acid composed of oleic acid, palmitic acid and stearic acid is added to the aluminum isopropoxide intermediate reaction system of S1. After heating, the reaction is carried out under vacuum to obtain the aluminate coupling agent.

[0009] Preferably, in S1, the metallic aluminum refers to aluminum sheets with a purity of 97% or higher, the isopropanol refers to isopropanol with a purity of 99% or higher, and the iodine refers to elemental iodine with a purity of 99%.

[0010] Preferably, in S1, the amount of composite catalyst used accounts for 10-15% of the mass of metallic aluminum, and the composite catalyst contains 85-95 wt% aluminum isopropoxide and 5-15 wt% iodine.

[0011] Preferably, in S1, the mass ratio of the metallic aluminum to isopropanol is 1:10-15.

[0012] Preferably, in S1, 1 / 3 to 1 / 2 of the isopropanol is first mixed with metallic aluminum and the composite catalyst, and the remaining isopropanol is added after the reaction is started.

[0013] Preferably, in S1, the remaining isopropanol is added after the reaction has started and stabilized for 20-40 minutes.

[0014] Preferably, in S1, the reaction temperature is controlled at 85-105℃ and the reaction time is controlled at 5-8h.

[0015] Preferably, in S2, by mass ratio, the complex fatty acid contains 5-10 wt% oleic acid, 10-30 wt% palmitic acid, and 60-85 wt% stearic acid; the mass ratio of the metallic aluminum to the complex fatty acid is 1:23-30.

[0016] Preferably, in S2, the temperature is raised to 110-140℃ and then reacted under a vacuum of 0.090-0.101 MPa for 1-3 hours.

[0017] The second aspect of the present invention also provides an aluminate coupling agent prepared by the preparation method described in the first aspect.

[0018] The third aspect of the present invention also provides the application of the aluminate coupling agent described in the second aspect in the surface modification of calcium carbonate.

[0019] Preferably, the calcium carbonate includes heavy calcium carbonate, light calcium carbonate, nano calcium carbonate, and mineral powder mainly composed of calcium carbonate.

[0020] Preferably, the specific modification method is as follows: add 1-3% by weight of aluminate coupling agent to calcium carbonate, stir at 55-70℃ for 20-50 minutes, and collect the sample after cooling.

[0021] Compared with the prior art, the beneficial effects of the present invention are: Aluminate coupling agents are important surface modifiers, widely used in the surface modification of calcium carbonate. However, traditional aluminate coupling agent preparation processes mostly use aluminum isopropoxide as a starting material, which is not only chemically reactive but also relatively expensive. Therefore, developing a new process to directly synthesize aluminate coupling agents using readily available and inexpensive isopropanol and metallic aluminum as raw materials has significant practical and application value. To this end, this invention provides an efficient method for preparing aluminate coupling agents. This method uses metallic aluminum and isopropanol as starting materials. Under the action of an aluminum isopropoxide-iodine catalyst, an aluminum isopropoxide intermediate is generated. This intermediate is then reacted directly with a complex fatty acid composed of oleic acid, palmitic acid, and stearic acid to generate the aluminate coupling agent without separation. Compared with traditional processes, the synthesis route of aluminate coupling agents prepared using this invention is significantly shortened, effectively reducing the production cost of the product. Calcium carbonate modified with the aluminate coupling agent prepared by this invention exhibits excellent dispersibility and a significantly reduced oil absorption value, showing broad application prospects in related industrial fields. Detailed Implementation

[0022] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0024] This invention provides a method for preparing an aluminate coupling agent. The method involves selecting a suitable catalyst to initiate the first step reaction, synthesizing aluminum isopropoxide intermediate, and then carrying out the second step reaction with a complex fatty acid in the same reactor to generate the aluminate coupling agent.

[0025] Because traditional catalysts used in the production of aluminate coupling agents have toxic side effects, some producers have begun to switch to using aluminum isopropoxide or iodine as catalysts. However, the following drawbacks still exist: using aluminum isopropoxide alone for autocatalysis results in a slow reaction rate and incomplete reaction; using iodine alone as a catalyst, although it has good catalytic performance, requires a large amount (usually 2%-4% of the aluminum mass), leading to high costs, and the reaction solution is yellow, affecting the product color. Considering environmental protection and cost issues, this invention innovatively uses an aluminum isopropoxide-iodine composite catalytic system, utilizing the synergistic effect of the two to rapidly initiate the reaction. First, aluminum isopropoxide acts as an initiator, providing active species in advance, reducing the activation energy of the reaction, and shortening the induction period; second, iodine acts as a co-catalyst, continuously destroying the oxide film on the aluminum surface, maintaining reaction activity. Thus, the autocatalytic effect of aluminum isopropoxide and the oxide film destruction effect of iodine mutually promote each other, reducing the amount of iodine used to 0.5%-1% (1 / 2-1 / 3 of the traditional amount), while maintaining a high reaction rate and product yield.

[0026] Meanwhile, due to the structural defects of stearic acid, this invention introduces oleic acid and palmitic acid, which together with stearic acid are used as a complex fatty acid in the second step of the reaction. The aluminate coupling agent synthesized using oleic acid has the following advantages: (1) The mechanical properties of active calcium carbonate are significantly improved: In rubber systems such as EPDM, the unsaturated bonds of oleic acid can participate in vulcanization crosslinking, so that calcium carbonate is transformed from a simple filler into an active filler with reinforcing properties; (2) The aluminate coupling agent has excellent low-temperature performance: Oleic acid has a low melting point (13℃-14℃) and is liquid at room temperature, so the aluminate coupling agent can still maintain good fluidity at lower temperatures, which is beneficial for processing; (3) The dispersibility of active calcium carbonate is better: The presence of double bonds makes the oleic acid molecular chain have a certain curved configuration, unlike the straight-chain rigid structure of stearic acid. This structure makes the aluminate coupling agent molecules have better flexibility and spatial adaptability when coated on the surface of calcium carbonate, and can more effectively cover the surface of calcium carbonate particles, so that the modified calcium carbonate has better dispersibility in organic media. However, oleic acid is generally more expensive than stearic acid, making it unsuitable for large-scale production. Palmitic acid, on the other hand, acts as a balancing agent between oleic and stearic acids. As a medium-chain saturated fatty acid, its melting point falls between that of oleic and stearic acids. This not only maintains good low-temperature fluidity in the product but also avoids the problem of the product becoming too soft due to excessive oleic acid content. Furthermore, its shorter carbon chain can fill the gaps between stearic acid molecules. Therefore, aluminate coupling agents synthesized from these three fatty acids can form a denser surface coating layer on the surface of calcium carbonate. Moreover, palmitic acid is moderately priced, helping to balance raw material costs, and as a saturated acid, it can reduce product discoloration and spoilage caused by the oxidation of oleic acid double bonds, thus improving the product's storage stability.

[0027] Finally, aluminum isopropoxide is chemically reactive and highly hygroscopic, readily undergoing hydrolysis upon contact with water, making its storage difficult. This invention effectively addresses this technical challenge: the aluminum isopropoxide generated in the first step does not require separation and purification; it can directly react with the complex fatty acids in the same reactor, thus preventing degradation due to contact with air or moisture. This results in a final aluminate coupling agent with both high purity and high yield.

[0028] To fully and clearly present the technical solution and significant advantages of the present invention, the present invention will be described in detail below with reference to specific embodiments.

[0029] Example 1: A method for preparing an aluminate coupling agent and its application in the surface modification of calcium carbonate. 1. Synthetic aluminate coupling agents (1) Polish the aluminum sheet with 150-mesh sandpaper, and put the treated aluminum sheet (purity above 97%) into the reaction flask. First, add 10% aluminum isopropoxide and 1 / 3 isopropanol (purity above 99%), which account for 10% of the mass of the aluminum sheet. Then, add 1% iodine (purity 99%) as a co-catalyst. Then, heat to the boiling point of isopropanol (82.4℃) to achieve reflux. After the reaction starts for 30 minutes, slowly add the remaining 2 / 3 isopropanol (mass ratio of aluminum sheet to isopropanol is 1:15). React at a constant temperature of 85℃ for 5 hours to obtain aluminum isopropoxide.

[0030] (2) Prepare each organic acid according to the ratio of 5wt% oleic acid, 25wt% palmitic acid and 70wt% stearic acid (the mass ratio of aluminum sheet to complex fatty acid is 1:23), mix them thoroughly, and put them into the reaction flask of step (1). Then heat to 130℃ and react at a constant temperature for 1h under a vacuum of 0.098MPa. After the reaction is completed, cool the system and collect the target product, aluminate coupling agent.

[0031] 2. Modification of calcium carbonate Heavy calcium carbonate with a mesh size of 325 and a purity of 99% was selected as the modification raw material. 2% (by mass) of the self-made aluminate coupling agent was added, and the mixture was stirred at 60°C for 30 minutes to ensure thorough mixing, thus completing the modification process. After modification, a small sample was taken for analysis and testing. The sample showed an activation rate of 97.19%, a contact angle of 128.3°, and an oil absorption value of 21.44 gDOP / 100g CaCO3.

[0032] The activation test method is as follows: 5g of modified calcium carbonate is weighed using an electronic balance, 50g of distilled water is added, and the mixture is ultrasonically vibrated for 15 minutes and then allowed to stand. The floating portion of the sample is removed, dried, weighed using an analytical balance, and the value is recorded. The activation rate is H = weight of the floating portion of the sample / total weight of the sample. The contact angle test method is as follows: Modified calcium carbonate powder is compressed into tablets (compression conditions: pressure 20MPa, holding time 4min). The contact angle of the liquid on the surface of the modified calcium carbonate tablet is measured at room temperature using an OCA40 video contact angle meter. The oil absorption value test method is as follows: 5g of modified calcium carbonate is weighed using an electronic balance and placed on a petri dish. Dioctyl phthalate (DOP) is added dropwise using a dropper containing a known mass of DOP, while continuously mixing and stirring with a spatula or glass rod. Initially, the sample is dispersed, then gradually agglomerates until it is completely wetted by DOP and forms a clump (similar to a sphere). Then, weigh the dropper bottle. The oil absorption value M = mass of DOP consumed / total sample mass.

[0033] Example 2: A method for preparing an aluminate coupling agent and its application in the surface modification of calcium carbonate. 1. Synthetic aluminate coupling agents (1) Polish the aluminum sheet with 150-mesh sandpaper, and put the treated aluminum sheet (purity above 97%) into the reaction flask. First, add 10% aluminum isopropoxide and 1 / 3 isopropanol (purity above 99%), which account for 10% of the mass of the aluminum sheet. Then, add 1% iodine (purity 99%) as a co-catalyst. Then, heat to the boiling point of isopropanol (82.4℃) to achieve reflux. After the reaction starts for 30 minutes, slowly add the remaining 2 / 3 isopropanol (mass ratio of aluminum sheet to isopropanol is 1:15). React at a constant temperature of 85℃ for 5 hours to obtain aluminum isopropoxide.

[0034] (2) Prepare each organic acid according to the ratio of 10wt% oleic acid, 20wt% palmitic acid and 70wt% stearic acid (the mass ratio of aluminum sheet to complex fatty acid is 1:23), mix them thoroughly, and put them into the reaction flask of step (1). Then heat to 130℃ and react at a constant temperature for 1h under a vacuum of 0.098MPa. After the reaction is completed, cool the system and collect the target product, aluminate coupling agent.

[0035] 2. Modification of calcium carbonate Heavy calcium carbonate with a mesh size of 325 and a purity of 99% was selected as the modification raw material. 2% (by mass) of the self-made aluminate coupling agent was added, and the mixture was stirred at 60°C for 30 minutes to ensure thorough mixing, thus completing the modification process. After modification, a small sample was taken for analysis and testing. The sample showed an activation rate of 99.18%, a contact angle of 136.8°, and an oil absorption value of 17.92 gDOP / 100g CaCO3.

[0036] Example 3: A method for preparing an aluminate coupling agent and its application in the surface modification of calcium carbonate. 1. Synthetic aluminate coupling agents (1) Polish the aluminum sheet with 150-mesh sandpaper, and put the treated aluminum sheet (purity above 97%) into the reaction flask. First, add 10% aluminum isopropoxide and 1 / 3 isopropanol (purity above 99%), which account for 10% of the mass of the aluminum sheet. Then, add 1% iodine (purity 99%) as a co-catalyst. Then, heat to the boiling point of isopropanol (82.4℃) to achieve reflux. After the reaction starts for 30 minutes, slowly add the remaining 2 / 3 isopropanol (mass ratio of aluminum sheet to isopropanol is 1:15). React at a constant temperature of 85℃ for 5 hours to obtain aluminum isopropoxide.

[0037] (2) Prepare each organic acid according to the ratio of 7wt% oleic acid, 15wt% palmitic acid and 78wt% stearic acid (the mass ratio of aluminum sheet to complex fatty acid is 1:23). After thorough mixing, put it into the reaction flask of step (1). Then heat it to 130℃ and react it at a constant temperature for 1h under a vacuum of 0.098MPa. After the reaction is completed, cool the system and collect the target product, aluminate coupling agent.

[0038] 2. Modification of calcium carbonate Heavy calcium carbonate with a mesh size of 325 and a purity of 99% was selected as the modification raw material. 2% (by mass) of the self-made aluminate coupling agent was added, and the mixture was stirred at 60°C for 30 minutes to ensure thorough mixing, thus completing the modification process. After modification, a small sample was taken for analysis and testing. The sample showed an activation rate of 97.64%, a contact angle of 133.5°, and an oil absorption value of 20.72 gDOP / 100g CaCO3.

[0039] Comparative Example 1: 1. Synthetic aluminate coupling agents (1) Polish the aluminum sheet with 150-mesh sandpaper. Put the treated aluminum sheet (purity above 97%) into the reaction flask. First, add 10% aluminum isopropoxide and 1 / 3 isopropanol (purity above 99%), which accounts for 10% of the mass of the aluminum sheet. Then, add 1% iodine (purity 99%) as a co-catalyst. Then, heat to the boiling point of isopropanol (82.4℃) to achieve reflux. After the reaction starts for 30 min, slowly add the remaining 2 / 3 isopropanol (mass ratio of aluminum sheet to isopropanol is 1:15). React at a constant temperature of 85℃ for 5 h to obtain aluminum isopropoxide.

[0040] (2) Prepare each organic acid (the mass ratio of aluminum sheet to complex fatty acid is 1:23) according to the ratio of 25wt% oleic acid and 75wt% stearic acid. After thorough mixing, put it into the reaction flask of step (1). Then raise the temperature to 130℃ and react at a constant temperature for 1h under a vacuum of 0.098MPa. After the reaction is completed, cool the system and collect the target product, aluminate coupling agent.

[0041] 2. Modification of calcium carbonate Heavy calcium carbonate with a mesh size of 325 and a purity of 99% was selected as the modification raw material. 2% (by mass) of the self-made aluminate coupling agent was added, and the mixture was stirred at 60°C for 30 minutes to ensure thorough mixing, thus completing the modification process. After modification, a small sample was taken for analysis and testing. The sample showed an activation rate of 90.06%, a contact angle of 123.4°, and an oil absorption value of 24.14 g DOP / 100 g CaCO3.

[0042] Comparative Example 2: 1. Synthetic aluminate coupling agents (1) Polish the aluminum sheet with 150-mesh sandpaper, and put the treated aluminum sheet (purity above 97%) into the reaction flask. First, add 10% aluminum isopropoxide and 1 / 3 isopropanol (purity above 99%), which account for 10% of the mass of the aluminum sheet. Then, add 1% iodine (purity 99%) as a co-catalyst. Then, heat to the boiling point of isopropanol (82.4℃) to achieve reflux. After the reaction starts for 30 minutes, slowly add the remaining 2 / 3 isopropanol (mass ratio of aluminum sheet to isopropanol is 1:15). React at a constant temperature of 85℃ for 5 hours to obtain aluminum isopropoxide.

[0043] (2) Prepare each organic acid (the mass ratio of aluminum sheet to complex fatty acid is 1:23) according to the ratio of palmitic acid 25wt% and stearic acid 75wt%, mix them thoroughly, and put them into the reaction flask of step (1). Then heat to 130℃ and react at a constant temperature for 1h under a vacuum of 0.098MPa. After the reaction is completed, cool the system and collect the target product, aluminate coupling agent.

[0044] 2. Modification of calcium carbonate Heavy calcium carbonate with a mesh size of 325 and a purity of 99% was selected as the modification raw material. 2% (by mass) of the self-made aluminate coupling agent was added, and the mixture was stirred at 60°C for 30 minutes to ensure thorough mixing, thus completing the modification process. After modification, a small sample was taken for analysis and testing. The sample showed an activation rate of 88.54%, a contact angle of 118.7°, and an oil absorption value of 26.28 g DOP / 100 g CaCO3.

[0045] Comparative Example 3: Heavy calcium carbonate with a mesh size of 325 and a purity of 99% was selected as the modifying raw material. A modifier (commercially available DL-411 aluminate coupling agent, synthesized in one step using aluminum isopropoxide and stearic acid) at 2% of the mass of the heavy calcium carbonate was added, and the mixture was thoroughly mixed to complete the modification treatment. After modification, a small sample was taken for analysis and testing. The sample showed an activation rate of 84.67%, a contact angle of 113.6°, and an oil absorption value of 28.05 g DOP / 100 g CaCO3.

[0046] Comparative Example 4: 1. Synthetic aluminate coupling agents (1) Polish the aluminum sheet with 150-mesh sandpaper. Put the treated aluminum sheet (purity above 97%) into a reaction flask. First, add 10% aluminum isopropoxide and 1 / 3 isopropanol (purity above 99%), which accounts for 10% of the mass of the aluminum sheet. Then, add 1% iodine (purity 99%) as a co-catalyst. Then, heat to the boiling point of isopropanol (82.4℃). After the reaction starts for 30 min, slowly add the remaining 2 / 3 isopropanol (mass ratio of aluminum sheet to isopropanol is 1:15). React at 85℃ for 5 h to produce aluminum isopropoxide. The produced aluminum isopropoxide is then vacuum distilled to obtain high-quality aluminum isopropoxide.

[0047] The distillation process involves adding crude aluminum isopropoxide to a distillation vessel, evacuating the system to below 133 Pa, and slowly heating it to 120-140°C. Under these conditions, the aluminum isopropoxide vaporizes, and the fraction is collected via a condenser. The fore-fraction (low-boiling impurities) is removed first, and the main fraction, which is the refined aluminum isopropoxide, is collected after the temperature stabilizes.

[0048] (2) Take each organic acid according to the ratio of 10wt% oleic acid, 20wt% palmitic acid and 70wt% stearic acid, mix them thoroughly, and react them with the refined aluminum isopropoxide separated and purified in step (1) (the mass ratio of refined aluminum isopropoxide to complex fatty acid is 1:2.2-3). Heat to 130℃ and react at a constant temperature for 1h under a vacuum of 0.098MPa. After the reaction is completed, cool the system and the target product aluminum ester coupling agent can be collected.

[0049] 2. Modification of calcium carbonate Heavy calcium carbonate with a mesh size of 325 and a purity of 99% was selected as the modification raw material. 2% (by mass) of the self-made aluminate coupling agent was added, and the mixture was stirred at 60°C for 30 minutes to ensure thorough mixing, thus completing the modification process. After modification, a small sample was taken for analysis and testing. The sample showed an activation rate of 95.62%, a contact angle of 131.3°, and an oil absorption value of 20.48 g DOP / 100 g CaCO3.

[0050] Based on Examples 1-3 and Comparative Examples 1-4, it can be seen that Examples 1-3 used aluminum sheets and isopropanol as starting materials, and aluminum isopropoxide and iodine as composite catalysts to synthesize the intermediate product aluminum isopropoxide. This intermediate product was then directly reacted with a complex fatty acid without separation. By adjusting the ratio of oleic acid, palmitic acid, and stearic acid in the ternary compound, the resulting aluminate coupling agent significantly improved the activation rate and hydrophobicity of calcium carbonate, and reduced the oil absorption value, demonstrating advantages such as cost reduction, efficiency improvement, and excellent modification effect. Example 2 showed the best modification effect. In contrast, Comparative Examples 1-2, which used a combination of dicarboxylic acids, performed far worse than the combination of ternary fatty acids, confirming the necessity of the synergistic effect of ternary fatty acids. Comparative Example 3, which used a commercially available coupling agent, had the worst performance across all indicators, demonstrating that the method of this invention for preparing aluminate coupling agents has achieved significant progress. Comparative Example 4, which added an aluminum isopropoxide purification step, experienced a decline in performance and an increase in cost, indicating that the method of this invention generates an aluminum isopropoxide intermediate that does not require separation and can directly react with fatty acids to generate aluminate coupling agents. Furthermore, the aluminate coupling agent prepared has better calcium carbonate dispersibility and a significantly lower oil absorption value.

[0051] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for preparing an aluminate coupling agent, characterized in that, Includes the following steps: S1. Using aluminum and isopropanol as starting materials, aluminum isopropoxide and iodine as composite catalysts, aluminum, a portion of isopropanol and the composite catalyst are mixed and heated to reflux. After the reaction starts and stabilizes for a period of time, the remaining isopropanol is added and the temperature is controlled to continue the reaction to generate aluminum isopropoxide intermediate. S2. A complex fatty acid composed of oleic acid, palmitic acid and stearic acid is added to the aluminum isopropoxide intermediate reaction system of S1. After heating, the reaction is carried out under vacuum to obtain the aluminate coupling agent.

2. The method for preparing an aluminate coupling agent according to claim 1, characterized in that, In S1, the metallic aluminum refers to aluminum sheets with a purity of 97% or higher, the isopropanol refers to isopropanol with a purity of 99% or higher, and the iodine refers to elemental iodine with a purity of 99%.

3. The method for preparing an aluminate coupling agent according to claim 1, characterized in that, In S1, the amount of composite catalyst used accounts for 10-15% of the mass of metallic aluminum. In the composite catalyst, the content of aluminum isopropoxide is 85-95 wt%, and the content of iodine is 5-15 wt%. The mass ratio of metallic aluminum to isopropanol is 1:10-15.

4. The method for preparing an aluminate coupling agent according to claim 1, characterized in that, In S1, 1 / 3 to 1 / 2 of the isopropanol is first mixed with metallic aluminum and the composite catalyst, and the remaining isopropanol is added after the reaction is started.

5. The method for preparing an aluminate coupling agent according to claim 1, characterized in that, In S1, after the reaction has started and stabilized for 20-40 minutes, the remaining isopropanol is added; the reaction temperature is then controlled at 85-105℃ for 5-8 hours.

6. The method for preparing an aluminate coupling agent according to claim 1, characterized in that, In S2, by mass ratio, oleic acid accounts for 5-10 wt%, palmitic acid accounts for 10-30 wt%, and stearic acid accounts for 60-85 wt% of the complex fatty acids; the mass ratio of the metallic aluminum to the complex fatty acids is 1:23-30.

7. The method for preparing an aluminate coupling agent according to claim 1, characterized in that, In S2, the temperature is raised to 110-140℃ and then reacted under a vacuum of 0.090-0.101MPa for 1-3 hours.

8. An aluminate coupling agent prepared by the preparation method according to any one of claims 1-7.

9. The application of the aluminate coupling agent according to claim 8 in the surface modification of calcium carbonate.

10. The application according to claim 9, characterized in that, The calcium carbonate includes heavy calcium carbonate, light calcium carbonate, nano calcium carbonate, and mineral powder mainly composed of calcium carbonate.