A method for synthesizing calcium hexahydrophthalate

Abstract

The present application relates to the field of organic carboxylic acid salt synthesis and preparation, in particular to a synthesis method of calcium hexahydrophthalate. The present application strengthens the water absorption capacity by adding inert anhydrous water absorption aid during dissolution; the calcium hydroxide is made into alcohol phase suspension liquid before neutralization and is added dropwise at a constant speed; the gradient alcohol washing process and two-stage drying are used in post-processing. The purity of the target product is improved to more than 99.5%, the yield is improved to more than 98%, the residual alcohol content is less than or equal to 0.05%, there is no deliquescence and caking for more than 12 months of storage, and the method is simple, no new complex equipment is needed, the water absorption aid and alcohol solvent can be recycled and regenerated, and the cost is effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of organic carboxylate synthesis and preparation, specifically to a method for synthesizing calcium hexahydrophthalate. Background Technology

[0002] Calcium hexahydrophthalate, as an important organic carboxylate, is widely used in plastic heat stabilizers, coating curing accelerators, and rubber additives. Its purity and moisture content directly determine the performance of downstream products. Calcium hexahydrophthalate is commonly prepared by acid-base neutralization of hexahydrophthalic acid and calcium hydroxide in an alcohol solvent. The core step in its preparation is to dissolve hexahydrophthalic acid in methanol, ethanol, or other alcohol solvents to form a homogeneous solution. The alcohol solvent acts as both a reaction medium and a water absorbent. Calcium hydroxide is slowly added under stirring to carry out the neutralization reaction, generating calcium hexahydrophthalate precipitate. After filtration and separation, the precipitate is washed with alcohol and dried to obtain the product. However, existing synthesis methods have many problems that affect the performance of the target product. For example, alcohol solvents have limited water absorption capacity, and the water generated in the later stages of the reaction cannot be completely adsorbed, resulting in the formation of calcium hexahydrophthalate hydrate, which is difficult to detect with conventional methods. However, this hydrate will lead to a decrease in the heat resistance of downstream materials. Calcium hydroxide has poor wettability in alcohols, and it is easy to agglomerate during the feeding process, leading to local excess alkali and the formation of calcium hydrogen phthalate byproduct, which is difficult to separate from the target product, making it difficult to achieve a purity of 99.0%. During alcohol washing, calcium hexahydrophthalate dissolves in trace amounts, resulting in a decrease in product yield. Conventional atmospheric pressure drying cannot eliminate the alcohol-water azeotropic effect, leaving trace amounts of alcohol solvent in the product. Long-term storage makes it prone to moisture absorption and clumping, resulting in poor stability.

[0003] Therefore, it is very promising to invent a method for synthesizing calcium hexahydrophthalate that can simultaneously improve the purity, yield and stability of the product. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention aims to develop a method for synthesizing calcium hexahydrophthalate. This method enhances water absorption capacity by adding an inert anhydrous desiccant during dissolution; calcium hydroxide is prepared as an alcohol suspension and added dropwise at a uniform rate before neutralization; post-treatment employs a gradient alcohol washing process and two-stage drying. This method improves the purity of the target product to over 99.5%, the yield to over 98%, and the residual alcohol content to ≤0.05%. The product exhibits no deliquescence or clumping after storage for over 12 months. Furthermore, this method is simple, requires no additional complex equipment, and the desiccant and alcohol solvent are recyclable, effectively reducing costs.

[0005] This invention discloses a method for synthesizing calcium hexahydrophthalate, comprising the following steps:

[0006] Preparation of target product S1: Hexahydrophthalic acid was added to a solvent and stirred until completely dissolved to form a homogeneous solution. Then, an inert anhydrous desiccant was added. Calcium hydroxide was added to the solvent and stirred to prepare a homogeneous calcium hydroxide suspension. The above homogeneous solution was then heated, and the suspension was added dropwise to the heated homogeneous solution, with the dropping rate controlled. After the addition was completed, the mixture was kept at the temperature and stirred to allow a neutralization reaction to occur, yielding a reaction solution. S2 Post-processing purification: The reaction solution obtained in step S1 is filtered while hot, and the filtrate and filter cake are collected separately. Then the filter cake is washed in a gradient. After washing, it is dried in stages to obtain the target product calcium hexahydrophthalate.

[0007] Preferably, in step S1, the solvent is methanol or ethanol.

[0008] Preferably, in step S1, the homogeneous solution is heated to 40~50°C.

[0009] Preferably, in step S1, the drop acceleration rate is 2~5 mL / min.

[0010] Preferably, in step S1, the temperature is heated to 40-50°C and the reaction is carried out for 4-5 hours.

[0011] Preferably, in step S1, the molar ratio of hexahydrophthalic acid to calcium hydroxide is 1:(1.0~1.3).

[0012] Preferably, in step S1, the inert anhydrous water-absorbing aid is anhydrous magnesium sulfate, and the mass ratio of the inert anhydrous water-absorbing aid to hexahydrophthalic acid is (0.05~0.1):1.

[0013] Preferably, in step S2, the gradient washing is divided into two stages. The first stage involves washing with a mixed solution of alcohol and water, and the washing is performed three times. The mass ratio of the mixed solution to the filter cake is (2~3):1. The second stage involves washing with anhydrous alcohol twice, and the mass ratio of the anhydrous alcohol to the filter cake is (0.5~1):1.

[0014] Preferably, the volume ratio of alcohol to water in the mixed solution is (5~10):1.

[0015] Preferably, in step S2, the segmented drying is divided into two stages: the first stage is low-temperature drying at normal pressure, and the second stage is high-temperature drying under vacuum.

[0016] Preferably, the drying temperature for atmospheric pressure low-temperature drying is 50~60℃ and the time is 3~5h; the drying temperature for vacuum decompression high-temperature drying is 90~100℃ and the time is 2~3h, with a vacuum degree of -0.05~-0.1MPa.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a method for synthesizing calcium hexahydrophthalate, which has the following characteristics: (1) By adding an inert water-absorbing agent, the water absorption capacity of the system is enhanced and the formation of crystal hydrates is avoided; the calcium hydroxide pre-dispersion process alleviates the problem of local alkali excess, and there are basically no calcium hydrogen phthalate by-products, and the product purity is stable at ≥99.5%.

[0018] (2) The gradient alcohol washing process not only ensures the complete removal of impurities, but also significantly reduces the dissolution loss of the target product, increasing the product yield to over 98%.

[0019] (3) Two-stage drying effectively solves the alcohol-water azeotropic effect, so that the residual alcohol content of the product is ≤0.05% and the moisture content is ≤0.1%. It does not deliquesce or clump after more than 12 months of storage, and has good long-term storage stability.

[0020] (4) The method provided by the present invention does not require the addition of complex equipment, and the absorbent can be recycled and regenerated, and the alcohol solvent can be reused, thereby reducing production costs and being suitable for large-scale continuous production. Detailed Implementation

[0021] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0022] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0023] Example 1: A method for synthesizing calcium hexahydrophthalate, comprising the following steps: Preparation of target product S1: Hexahydrophthalic acid was added to methanol and stirred until completely dissolved to form a homogeneous solution. Then, an inert anhydrous magnesium sulfate was added as a desiccant, wherein the mass ratio of anhydrous magnesium sulfate to hexahydrophthalic acid was 0.05:1. Calcium hydroxide was added to methanol and stirred to prepare a homogeneous calcium hydroxide suspension. The homogeneous solution was then heated to 40°C, and the suspension was added dropwise to the heated homogeneous solution at a rate of 2 mL / min. After the addition was complete, the mixture was kept at 40°C and stirred for 3 hours to allow a neutralization reaction to occur, resulting in a reaction solution with a molar ratio of hexahydrophthalic acid to calcium hydroxide of 1:1.0.

[0024] Post-processing purification (S2): The reaction solution obtained in step S1 was filtered while hot, and the filtrate and filter cake were collected separately. The filter cake was then subjected to gradient washing in two stages. The first stage involved washing with a mixed solution of methanol and water at a volume ratio of 5:1, for a total of 3 washes. The mass ratio of the mixed solution to the filter cake was 2:1. The second stage involved washing twice with anhydrous methanol at a mass ratio of 0.5:1. After washing, a segmented drying process was performed in two stages. The first stage was low-temperature drying under normal pressure at 50°C for 3 hours. The second stage was high-temperature drying under vacuum at 90°C for 2 hours, with a vacuum level of -0.05 MPa. After drying, the target product, calcium hexahydrophthalate, was obtained.

[0025] Example 2: A method for synthesizing calcium hexahydrophthalate, comprising the following steps: Preparation of target product S1: Hexahydrophthalic acid was added to methanol and stirred until completely dissolved to form a homogeneous solution. Then, an inert anhydrous magnesium sulfate was added as a desiccant, wherein the mass ratio of anhydrous magnesium sulfate to hexahydrophthalic acid was 0.06:1. Calcium hydroxide was added to methanol and stirred to prepare a homogeneous calcium hydroxide suspension. The homogeneous solution was then heated to 42°C, and the suspension was added dropwise to the heated homogeneous solution at a rate of 2.5 mL / min. After the addition was complete, the mixture was kept at 42°C and stirred for 3 hours to allow a neutralization reaction to occur, resulting in a reaction solution with a molar ratio of hexahydrophthalic acid to calcium hydroxide of 1:1.05.

[0026] Post-processing purification (S2): The reaction solution obtained in step S1 was filtered while hot, and the filtrate and filter cake were collected separately. The filter cake was then subjected to gradient washing in two stages. The first stage involved washing with a mixed solution of methanol and water at a volume ratio of 6:1, for a total of 3 washes. The mass ratio of the mixed solution to the filter cake was 2.2:1. The second stage involved washing twice with anhydrous methanol at a mass ratio of 0.6:1. After washing, a segmented drying process was performed in two stages. The first stage was low-temperature drying under normal pressure at 52°C for 3.5 hours. The second stage was high-temperature drying under reduced vacuum at 92°C for 2.2 hours, with a vacuum degree of -0.06 MPa. After drying, the target product, calcium hexahydrophthalate, was obtained.

[0027] Example 3: A method for synthesizing calcium hexahydrophthalate, comprising the following steps: Preparation of target product S1: Hexahydrophthalic acid was added to methanol and stirred until completely dissolved to form a homogeneous solution. Then, an inert anhydrous magnesium sulfate was added as a desiccant, wherein the mass ratio of anhydrous magnesium sulfate to hexahydrophthalic acid was 0.07:1. Calcium hydroxide was added to methanol and stirred to prepare a homogeneous calcium hydroxide suspension. The homogeneous solution was then heated to 44°C, and the suspension was added dropwise to the heated homogeneous solution at a rate of 3 mL / min. After the addition was complete, the mixture was kept at 44°C and stirred for 3 hours to allow a neutralization reaction to occur, resulting in a reaction solution with a molar ratio of hexahydrophthalic acid to calcium hydroxide of 1:1.1.

[0028] Post-processing purification (S2): The reaction solution obtained in step S1 was filtered while hot, and the filtrate and filter cake were collected separately. The filter cake was then subjected to gradient washing in two stages. The first stage involved washing with a mixed solution of methanol and water at a volume ratio of 7:1, for a total of 3 washes. The mass ratio of the mixed solution to the filter cake was 2.4:1. The second stage involved washing twice with anhydrous methanol at a mass ratio of 0.7:1. After washing, a segmented drying process was performed in two stages. The first stage was low-temperature drying under normal pressure at 54°C for 4 hours. The second stage was high-temperature drying under reduced vacuum at 94°C for 2.4 hours, with a vacuum degree of -0.07 MPa. After drying, the target product, calcium hexahydrophthalate, was obtained.

[0029] Example 4: A method for synthesizing calcium hexahydrophthalate, comprising the following steps: Preparation of target product S1: Hexahydrophthalic acid was added to methanol and stirred until completely dissolved to form a homogeneous solution. Then, an inert anhydrous magnesium sulfate was added as a desiccant, wherein the mass ratio of anhydrous magnesium sulfate to hexahydrophthalic acid was 0.08:1. Calcium hydroxide was added to methanol and stirred to prepare a homogeneous calcium hydroxide suspension. The homogeneous solution was then heated to 46°C, and the suspension was added dropwise to the heated homogeneous solution at a rate of 3.5 mL / min. After the addition was complete, the mixture was kept at 46°C and stirred for 3 hours to allow a neutralization reaction to occur, resulting in a reaction solution with a molar ratio of hexahydrophthalic acid to calcium hydroxide of 1:1.1.5.

[0030] Post-processing purification (S2): The reaction solution obtained in step S1 was filtered while hot, and the filtrate and filter cake were collected separately. The filter cake was then subjected to gradient washing in two stages. The first stage involved washing with a mixed solution of methanol and water at a volume ratio of 8:1, for a total of 3 washes. The mass ratio of the mixed solution to the filter cake was 2.6:1. The second stage involved washing twice with anhydrous methanol at a mass ratio of 0.8:1. After washing, a segmented drying process was performed in two stages. The first stage was low-temperature drying under normal pressure at 56°C for 4.3 hours. The second stage was high-temperature drying under reduced vacuum at 96°C for 2.6 hours, with a vacuum degree of -0.08 MPa. After drying, the target product, calcium hexahydrophthalate, was obtained.

[0031] Example 5: A method for synthesizing calcium hexahydrophthalate, comprising the following steps: Preparation of target product S1: Hexahydrophthalic acid was added to methanol and stirred until completely dissolved to form a homogeneous solution. Then, an inert anhydrous magnesium sulfate was added as a desiccant, wherein the mass ratio of anhydrous magnesium sulfate to hexahydrophthalic acid was 0.09:1. Calcium hydroxide was added to methanol and stirred to prepare a homogeneous calcium hydroxide suspension. The homogeneous solution was then heated to 48°C, and the suspension was added dropwise to the heated homogeneous solution at a rate of 4 mL / min. After the addition was complete, the mixture was kept at 48°C and stirred for 3 hours to allow a neutralization reaction to occur, resulting in a reaction solution with a molar ratio of hexahydrophthalic acid to calcium hydroxide of 1:1.2.

[0032] Post-processing purification (S2): The reaction solution obtained in step S1 was filtered while hot, and the filtrate and filter cake were collected separately. The filter cake was then subjected to gradient washing in two stages. The first stage involved washing with a mixed solution of methanol and water at a volume ratio of 9:1, for a total of 3 washes. The mass ratio of the mixed solution to the filter cake was 2.8:1. The second stage involved washing twice with anhydrous methanol at a mass ratio of 0.9:1. After washing, a segmented drying process was performed in two stages. The first stage was low-temperature drying under normal pressure at 58°C for 4.7 hours. The second stage was high-temperature drying under reduced vacuum at 98°C for 2.8 hours, with a vacuum level of -0.09 MPa. After drying, the target product, calcium hexahydrophthalate, was obtained.

[0033] Example 6: A method for synthesizing calcium hexahydrophthalate, comprising the following steps: Preparation of target product S1: Hexahydrophthalic acid was added to methanol and stirred until completely dissolved to form a homogeneous solution. Then, an inert anhydrous magnesium sulfate was added as a desiccant, wherein the mass ratio of anhydrous magnesium sulfate to hexahydrophthalic acid was 0.1:1. Calcium hydroxide was added to methanol and stirred to prepare a homogeneous calcium hydroxide suspension. The homogeneous solution was then heated to 50°C, and the suspension was added dropwise to the heated homogeneous solution at a rate of 5 mL / min. After the addition was complete, the mixture was kept at 50°C and stirred for 3 hours to allow a neutralization reaction to occur, resulting in a reaction solution with a molar ratio of hexahydrophthalic acid to calcium hydroxide of 1:1.3.

[0034] Post-processing purification (S2): The reaction solution obtained in step S1 was filtered while hot, and the filtrate and filter cake were collected separately. The filter cake was then subjected to gradient washing in two stages. The first stage involved washing with a mixed solution of methanol and water at a volume ratio of 10:1, for a total of 3 washes. The mass ratio of the mixed solution to the filter cake was 3:1. The second stage involved washing twice with anhydrous methanol at a mass ratio of 1:1. After washing, a segmented drying process was performed in two stages. The first stage was low-temperature drying under normal pressure at 60°C for 5 hours. The second stage was high-temperature drying under reduced vacuum at 100°C for 3 hours, with a vacuum level of -0.1 MPa. After drying, the target product, calcium hexahydrophthalate, was obtained.

[0035] Example 7: A method for synthesizing calcium hexahydrophthalate, comprising the following steps: Preparation of target product S1: Hexahydrophthalic acid was added to ethanol and stirred until completely dissolved to form a homogeneous solution. Then, an inert anhydrous magnesium sulfate was added as a desiccant, wherein the mass ratio of anhydrous magnesium sulfate to hexahydrophthalic acid was 0.08:1. Calcium hydroxide was added to ethanol and stirred to prepare a homogeneous calcium hydroxide suspension. The homogeneous solution was then heated to 46°C, and the suspension was added dropwise to the heated homogeneous solution at a rate of 3.5 mL / min. After the addition was complete, the mixture was kept at 46°C and stirred for 3 hours to allow a neutralization reaction to occur, resulting in a reaction solution with a molar ratio of hexahydrophthalic acid to calcium hydroxide of 1:1.1.5.

[0036] Post-processing purification (S2): The reaction solution obtained in step S1 was filtered while hot, and the filtrate and filter cake were collected separately. The filter cake was then subjected to gradient washing in two stages. The first stage involved washing with a mixed solution of ethanol and water at a volume ratio of 8:1, for a total of three washes. The mass ratio of the mixed solution to the filter cake was 2.6:1. The second stage involved washing twice with anhydrous ethanol at a mass ratio of 0.8:1. After washing, a segmented drying process was performed in two stages. The first stage was low-temperature drying under normal pressure at 56°C for 4.3 hours. The second stage was high-temperature drying under reduced vacuum at 96°C for 2.6 hours, with a vacuum level of -0.08 MPa. After drying, the target product, calcium hexahydrophthalate, was obtained.

[0037] Example 8: A method for synthesizing calcium hexahydrophthalate, comprising the following steps: Preparation of target product S1: Hexahydrophthalic acid was added to a mixed solvent of methanol and ethanol in a volume ratio of 1:1 and stirred until completely dissolved to form a homogeneous solution. Then, an inert anhydrous magnesium sulfate was added, wherein the mass ratio of anhydrous magnesium sulfate to hexahydrophthalic acid was 0.08:1. Calcium hydroxide was added to the mixed solvent and stirred to prepare a homogeneous calcium hydroxide suspension. The homogeneous solution was then heated to 46°C, and the suspension was added dropwise to the heated homogeneous solution at a rate of 3.5 mL / min. After the addition was complete, the mixture was kept at 46°C and stirred for 3 hours to allow a neutralization reaction to occur, resulting in a reaction solution with a molar ratio of hexahydrophthalic acid to calcium hydroxide of 1:1.1.5.

[0038] Post-processing purification (S2): The reaction solution obtained in step S1 was filtered while hot, and the filtrate and filter cake were collected separately. The filter cake was then subjected to gradient washing in two stages. The first stage involved washing with a mixed solution of ethanol and water at a volume ratio of 8:1, for a total of three washes. The mass ratio of the mixed solution to the filter cake was 2.6:1. The second stage involved washing twice with anhydrous ethanol at a mass ratio of 0.8:1. After washing, a segmented drying process was performed in two stages. The first stage was low-temperature drying under normal pressure at 56°C for 4.3 hours. The second stage was high-temperature drying under reduced vacuum at 96°C for 2.6 hours, with a vacuum level of -0.08 MPa. After drying, the target product, calcium hexahydrophthalate, was obtained.

[0039] Example 9: Using existing conventional synthesis methods, the specific steps are as follows: S1 Dissolution: Add hexahydrophthalic acid to ethanol and stir until completely dissolved; S2 acid-base neutralization: Under constant temperature stirring at 30℃, slowly add calcium hydroxide, and after the addition is complete, keep warm and stir for 2.5 hours; S3 post-treatment: After filtration, wash three times with anhydrous ethanol, dry at 85°C under normal pressure for 4 hours, and cool to obtain the target product calcium hexahydrophthalate.

[0040] Example 10: In step S1, no inert anhydrous magnesium sulfate was added, and the remaining steps and conditions were the same as in Example 4.

[0041] Example 11: The gradient washing in step S2 was replaced with direct washing with anhydrous alcohol 5 times, while the remaining steps and conditions were the same as in Example 4.

[0042] Example 12: The segmented drying in step S2 was replaced with direct vacuum decompression high-temperature drying, while the remaining steps and conditions were the same as in Example 4.

[0043] The performance of the calcium hexahydrophthalate prepared in Examples 1-12 was tested, and the test results are shown in the table below:

[0044] The data in the table above shows that the target products obtained in Examples 1-8 have a stable purity ≥99.5%, a yield ≥98%, a residual alcohol content ≤0.05%, and a moisture content ≤0.1%, and show no deliquescence or clumping after storage for more than 12 months. This is because the inert anhydrous magnesium sulfate desiccant can quickly adsorb and neutralize the water molecules generated in the reaction, reducing the formation of crystalline hydrates from the combination of calcium hexahydrophthalate and water, thus avoiding the introduction of hidden impurities; the pre-dispersed calcium hydroxide and its dropwise addition after slurrying solve the problem of poor wettability and easy agglomeration of calcium hydroxide in alcohol solvents, avoiding the formation of calcium hydrogen phthalate byproducts due to excessive local alkali, further ensuring the purity of the target product; in the gradient alcohol washing process, the high proportion of alcohol-water mixture ensures that the unreacted raw materials are free hexahydrophthalic acid. The solubility of calcium hydroxide in the alcohol phase is reduced, and the trace solubility of calcium hexahydrophthalate in alcohol is also reduced due to the presence of a small amount of water, which greatly reduces washing losses; the two-stage drying first removes most of the solvent at low temperature and normal pressure, and then vacuum drying breaks the alcohol-water azeotropic effect, avoiding solvent residue caused by conventional drying, ensuring that the residual alcohol is ≤0.05% and the moisture is ≤0.1%; the low residual amount can maintain the lattice stability of calcium hexahydrophthalate, and there is no free alcohol water as a moisture-absorbing medium, so there is no deliquescence or clumping after 12 months of storage at room temperature.

[0045] The target product obtained in Example 4 has the best properties because the mass ratio of anhydrous magnesium sulfate to hexahydrophthalic acid is 0.08:1, which can completely adsorb and neutralize the water generated in the reaction without causing excessive desiccant residue, thus balancing the dehydration effect and separation efficiency. The volume ratio of methanol to water is 8:1, at which point the solubility of free impurities and the anti-loss effect of the target product are balanced. If the alcohol-water ratio is too low, the impurity removal efficiency will decrease slightly; if it is too high, the loss of the target product will increase slightly. 8:1 is the critical optimal value. The reaction temperature of 46℃, the drying at atmospheric pressure of 56℃, and the vacuum drying at 96℃ avoid the product decomposition caused by high temperature and can efficiently remove the solvent. The vacuum degree of -0.08MPa is between -0.05 and -0.1MPa, which achieves the best energy consumption and removal efficiency, and the lowest residual alcohol and water content.

[0046] Ethanol was used as the solvent in Example 7. The solubility of hexahydrophthalic acid in ethanol is lower than that in methanol, resulting in slightly poorer homogeneity of the reaction system and slightly weaker neutralization reaction, leading to a slightly lower purity than in Example 4. Ethanol has a higher boiling point than methanol, and the removal rate during vacuum drying is slower, resulting in a higher residual alcohol content than in Example 4, which in turn leads to a slightly higher water content and a slightly worse overall performance than in Example 4.

[0047] Example 9 was prepared using a conventional method. The absence of a desiccant led to the formation of water of crystallization, resulting in a moisture content of 0.56% and a purity of only 98.25%. Direct addition of calcium hydroxide resulted in localized alkali excess and numerous byproducts. Washing with anhydrous alcohol resulted in significant losses, with a yield of only 93.1%. Drying under normal pressure failed to break the azeotropic reaction, leaving 0.28% residual alcohol. After 12 months of storage, the product exhibited severe deliquescence.

[0048] In Example 10, anhydrous magnesium sulfate was missing, so the water generated by the neutralization reaction could not be completely adsorbed, resulting in trace amounts of crystalline hydrates. The water content increased to 0.32%, and some deliquescence occurred.

[0049] In Example 11, without gradient washing, the calcium hexahydrophthalate was washed directly with anhydrous methanol. The trace amount of calcium hexahydrophthalate dissolved and was lost in anhydrous methanol, resulting in a decrease in yield to 97.2%.

[0050] Example 12: Direct vacuum drying without first removing most of the solvent at ambient pressure and low temperature resulted in the alcohol-water azeotropic effect not being completely eliminated during the vacuum stage, with the residual alcohol content rising to 0.065%, and slight deliquescence appearing after 12 months of storage.

[0051] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for synthesizing calcium hexahydrophthalate, characterized in that, Includes the following steps: Preparation of target product S1: Hexahydrophthalic acid was added to a solvent and stirred until completely dissolved to form a homogeneous solution. Then, an inert anhydrous desiccant was added. Calcium hydroxide was added to the solvent and stirred to prepare a homogeneous calcium hydroxide suspension. The above homogeneous solution was then heated, and the suspension was added dropwise to the heated homogeneous solution, with the dropping rate controlled. After the addition was completed, the mixture was kept at the temperature and stirred to allow a neutralization reaction to occur, resulting in a reaction solution. S2 Post-processing purification: The reaction solution obtained in step S1 is filtered while hot, and the filtrate and filter cake are collected separately. Then the filter cake is washed in a gradient. After washing, it is dried in stages to obtain the target product calcium hexahydrophthalate.

2. The method for synthesizing calcium hexahydrophthalate according to claim 1, characterized in that, In step S1, the solvent is methanol or ethanol.

3. The method for synthesizing calcium hexahydrophthalate according to claim 1, characterized in that, In step S1, the homogeneous solution is heated to 40~50℃.

4. The method for synthesizing calcium hexahydrophthalate according to claim 1, characterized in that, In step S1, the drop acceleration rate is 2~5 mL / min.

5. The method for synthesizing calcium hexahydrophthalate according to claim 1, characterized in that, In step S1, the molar ratio of hexahydrophthalic acid to calcium hydroxide is 1:(1.0~1.3).

6. The method for synthesizing calcium hexahydrophthalate according to claim 1, characterized in that, In step S1, the inert anhydrous water-absorbing agent is anhydrous magnesium sulfate, and the mass ratio of the inert anhydrous water-absorbing agent to hexahydrophthalic acid is (0.05~0.1):

1.

7. The method for synthesizing calcium hexahydrophthalate according to claim 1, characterized in that, In step S2, the gradient washing is divided into two stages. The first stage uses a mixed solution of alcohol and water for washing three times, with the mass ratio of the mixed solution to the filter cake being (2~3):

1. The second stage uses anhydrous alcohol for washing twice, with the mass ratio of the anhydrous alcohol to the filter cake being (0.5~1):

1.

8. The method for synthesizing calcium hexahydrophthalate according to claim 7, characterized in that, The volume ratio of alcohol to water in the mixed solution is (5~10):

1.

9. The method for synthesizing calcium hexahydrophthalate according to claim 1, characterized in that, In step S2, the segmented drying is divided into two stages: the first stage is low-temperature drying at normal pressure, and the second stage is high-temperature drying under vacuum.

10. The method for synthesizing calcium hexahydrophthalate according to claim 9, characterized in that, The atmospheric pressure low-temperature drying process involves a drying temperature of 50~60℃ and a drying time of 3~5h; the vacuum pressure high-temperature drying process involves a drying temperature of 90~100℃ and a drying time of 2~3h, with a vacuum degree of -0.05~-0.1MPa.

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