Preparation method of high-purity calcium citrate

Abstract

The invention belongs to the field of calcium citrate production, and particularly relates to a preparation method of high-purity calcium citrate, which comprises the following steps: reacting calcium carbonate slurry with a citric acid solution until the solution is in an unstable solution state without producing precipitates, then quickly and precisely filtering the solution, and reacting the filtered solution with food-grade calcium hydroxide to generate calcium citrate. And centrifugally separating and drying to obtain the high-purity calcium citrate. Compared with a traditional method for producing calcium citrate, the method has the characteristics that most impurities in the reaction process are removed, impurities such as black spots and acid-insoluble substances in the product are few, and heavy metal ions are less than 20ppb; the obtained calcium citrate does not generate carbon dioxide bubbles in an acidic solution or colloid, so that the product quality is ensured.

Description

Technical Field

[0001] The invention belongs to the field of calcium citrate production, and particularly relates to a method for preparing high-purity calcium citrate. Background Art

[0002] Calcium citrate is the full name of tricalcium citrate tetrahydrate. It is a white, tasteless crystalline powder or fine powder, slightly soluble in water and easily soluble in dilute hydrochloric acid. Calcium citrate is an organic calcium that can effectively supplement the calcium needed by the body. It has a good effect on alleviating problems such as osteoporosis caused by calcium deficiency or knee pain. It is relatively easy to absorb and will not irritate the stomach and intestines. It can be used in dairy products, baby food and beverages, fruit processing, and clinical nutrition.

[0003] Generally, the traditional method for preparing calcium citrate is to react calcium carbonate with citric acid to generate calcium citrate. In this method, impurities in the raw material calcium carbonate will be introduced into the calcium citrate product, and during the reaction, calcium carbonate will be embedded with calcium citrate as it is generated, which affects the quality of the calcium citrate product. The product has more black spots and acid insolubles, and contains insoluble silicon salts, heavy metal ions and mechanical impurities.

[0004] As mentioned above, calcium carbonate is embedded in the calcium citrate prepared by the traditional preparation method. When encountering an acidic solution or colloid, the carbonate reacts with the hydrogen ions to form carbon dioxide bubbles, which may cause gas expansion in the product during packaging or use. This gas expansion may affect the appearance and stability of the product, especially in the case of sealed packaging, which may cause the packaging to swell or rupture.

[0005] Therefore, how to obtain higher purity calcium citrate becomes one of the problems to be solved urgently by those skilled in the art. Summary of the invention

[0006] In order to overcome the problems that when calcium citrate is prepared in the prior art, the product has black spots, acid insolubles, more impurities resulting in lower purity, and the product generates carbon dioxide bubbles in an acidic solution or colloid, the present invention provides a method for preparing high-purity calcium citrate, using calcium carbonate slurry to react with citric acid solution to an unstable solution state without producing precipitation, and then quickly fine filtering the solution, the filtered solution reacts with food-grade calcium hydroxide to generate calcium citrate, centrifugation, and drying to obtain high-purity calcium citrate. Compared with the traditional process for producing calcium citrate, the present invention removes most of the impurities in the reaction process, the product has less impurities such as black spots and acid insolubles, less heavy metal ions than 20ppb, and significantly improved light transmittance; the obtained calcium citrate will not generate carbon dioxide bubbles in an acidic solution or colloid, thereby ensuring product quality.

[0007] The present invention continuously injects calcium carbonate slurry into a citric acid solution to react until a solution state in which solids are about to be generated but not yet generated, at which time the calcium carbonate is completely dissolved and no calcium carbonate solid exists in the solution system. Subsequently, calcium hydroxide is used as a raw material to continue the reaction. During the entire reaction process, no undissolved calcium carbonate solid exists, and therefore no calcium carbonate embedding phenomenon occurs.

[0008] The present invention uses a precision filtration method to filter out most impurities during the preparation process of calcium citrate, and there is no calcium carbonate embedding. The product has a small amount of impurities such as black spots and acid-insoluble substances, and the heavy metal ions are less than 20 ppb, and has high purity. In particular, the calcium citrate produced by the process will not generate carbon dioxide bubbles in an acidic solution or colloid, and can be widely used in medicines, infant formula milk powder, health products, dairy products, ice cream, milkshakes, soft candies, chewing gum and other products.

[0009] The method for preparing high-purity calcium citrate provided by the present invention comprises the following steps: (1) Dissolving the finished food-grade citric acid product in pure water to obtain a citric acid solution; (2) slurrying food-grade calcium carbonate with pure water to obtain calcium carbonate slurry; (3) At a certain reaction temperature, the calcium carbonate slurry is continuously added to the citric acid solution, stirred, and the reaction is stopped when the pH value reaches 2.6-2.8, at which point a solid and solution state is about to be produced; (4) finely filtering the solution obtained in step (3); (5) slurrying food-grade calcium hydroxide with pure water to obtain calcium hydroxide slurry; (6) adding calcium hydroxide slurry to the solution filtered in step (4) at 60-80° C., stirring, and reacting until the pH value reaches 4.4-4.8 to reach the reaction endpoint, thereby generating calcium citrate; If the end point pH value is too high, excessive calcium hydroxide raw materials will be consumed, increasing costs; if the pH value is too low, the generated calcium citrate will have a large dissolution loss, reducing the yield and increasing costs.

[0010] (7) After the reaction, centrifugal drying is performed to obtain high-purity calcium citrate.

[0011] Preferably, the content of the citric acid after dissolution in step (1) is 10-30 g / 100 ml. If the citric acid content is too high, the dissolution time will be long and the energy consumption will be high. If the citric acid content is too low, a large amount of pure water will be required, and the water consumption will increase.

[0012] Preferably, the mass fraction of the calcium carbonate after slurry adjustment in step (2) is 30%-50%. The mass fraction after slurry adjustment affects the normal production of calcium citrate. Too high a mass fraction will deteriorate the fluidity, while too low a mass fraction will increase water consumption and the cost of subsequent treatment.

[0013] Preferably, the reaction temperature in step (3) is 20-40° C. In the reaction temperature range, the higher the temperature, the lower the solubility of calcium citrate, and the easier it is to produce calcium citrate precipitation; when the temperature is low, the solubility of calcium citrate is high, which is more conducive to the reaction.

[0014] Preferably, the precision filtration method described in step (4) adopts membrane filtration; more preferably, the filtration accuracy of the membrane filtration is 0.8 μm.

[0015] Preferably, the mass fraction of the calcium hydroxide after slurry adjustment in step (5) is 50-60%. A mass fraction that is too low is not conducive to the reaction, while a mass fraction that is too high causes a rapid reaction and is not conducive to controlling the pH value at the reaction endpoint.

[0016] The calcium citrate prepared by the above method has high purity, less impurities such as black spots and acid-insoluble matter, and a heavy metal ion content of less than 20 ppb. It is not easy to generate carbon dioxide bubbles in acidic solutions or colloids, and can be widely used in medicines, infant formula milk powder, health products, dairy products, ice cream, milkshakes, soft candies, chewing gum and other products.

[0017] The preparation method of calcium citrate according to the present invention achieves the following technical effects: 1) In this scheme, the citric acid solution is first reacted with the calcium carbonate slurry until the pH is 2.6-2.8, when the solution is in a critical state where solid calcium citrate is about to be generated but is not generated. Then, the solution is finely filtered to remove impurities such as black spots, acid insoluble matter, and heavy metals. The solution is then reacted with the calcium hydroxide slurry to significantly reduce the impurity level in the product and improve the purity of the calcium citrate product. 2) The calcium citrate prepared by the method does not generate carbon dioxide bubbles in an acidic solution or colloid, and can be widely used in medicines, infant formula milk powder, health products, dairy products, ice cream, milkshakes, soft candies, chewing gums and other products, which is beneficial to their appearance, shelf life and storage stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the state of calcium citrate prepared in Example 3 in a test tube; Figure 2 This is a schematic diagram of the state of calcium citrate prepared in Example 3 in a beaker; Figure 3 This is a schematic diagram of the state of calcium citrate prepared in Comparative Example 2 in a test tube; Figure 4 This is a schematic diagram of the state of calcium citrate prepared in Comparative Example 2 in a beaker. DETAILED DESCRIPTION

[0019] The following is a further detailed description of the above contents of the present invention through specific implementation methods in the form of embodiments, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples. All technologies implemented based on the above contents of the present invention belong to the scope of the present invention, and unless otherwise specified, the following embodiments are all completed using conventional existing technologies.

[0020] Example 1 A method for preparing high-purity calcium citrate comprises the following steps: (1) Dissolve the finished food-grade citric acid product in pure water to a concentration of 10 g / 100 ml to obtain a citric acid solution; (2) slurrying food-grade calcium carbonate with pure water to a mass fraction of 30%; (3) At 20°C, add the calcium carbonate slurry to the citric acid solution continuously, stir, and react until the pH value reaches 2.6 and stop the reaction; (4) filtering the solution obtained in step (3) using a 0.8 μm membrane; (5) slurrying food-grade calcium hydroxide with pure water to a mass fraction of 50%; (6) adding calcium hydroxide slurry to the solution filtered in step (4) at 60° C., stirring, and reacting until the pH value reaches 4.4 to reach the reaction endpoint, thereby generating calcium citrate; (7) After the reaction, the mixture is centrifuged and dehydrated, and then dried at 90-110° C. for 1-2 hours to obtain high-purity calcium citrate.

[0021] Example 2 A method for preparing high-purity calcium citrate comprises the following steps: (1) Dissolve the finished food-grade citric acid product in pure water to a concentration of 20 g / 100 ml to obtain a citric acid solution; (2) slurrying food-grade calcium carbonate with pure water to a mass fraction of 40%; (3) At 30°C, add the calcium carbonate slurry to the citric acid solution continuously, stir, and react until the pH value reaches 2.7 to stop the reaction; (4) filtering the solution obtained in step (3) using a 0.8 μm membrane; (5) slurrying food-grade calcium hydroxide with pure water to a mass fraction of 50%; (6) adding calcium hydroxide slurry to the solution filtered in step (4) at 70° C., stirring, and reacting until the pH value reaches 4.6 to reach the reaction endpoint, thereby generating calcium citrate; (7) After the reaction, the mixture is centrifuged and dehydrated, and then dried at 90-110° C. for 1-2 hours to obtain high-purity calcium citrate.

[0022] Example 3 A method for preparing high-purity calcium citrate comprises the following steps: (1) Dissolve the finished food-grade citric acid product in pure water to a concentration of 30 g / 100 ml to obtain a citric acid solution; (2) slurrying food-grade calcium carbonate with pure water to a mass fraction of 50%; (3) At 40°C, add the calcium carbonate slurry to the citric acid solution continuously, stir, and react until the pH value reaches 2.8 to stop the reaction; (4) filtering the solution obtained in step (3) using a 0.8 μm membrane; (5) slurrying food-grade calcium hydroxide with pure water to a mass fraction of 60%; (6) adding calcium hydroxide slurry to the solution filtered in step (4) at 80° C., stirring, and reacting until the pH value reaches 4.8 to reach the reaction endpoint, thereby generating calcium citrate; (7) After the reaction, the mixture is centrifuged and dehydrated, and then dried at 90-110° C. for 1-2 hours to obtain high-purity calcium citrate.

[0023] Comparative Example 1 A method for preparing calcium citrate using a conventional process, comprising the following steps: (1) adding calcium carbonate slurry (calcium carbonate content of 50% by weight) to citric acid solution (citric acid monohydrate, citric acid content of 15g / 100ml); the contact temperature of calcium carbonate slurry and citric acid solution is 75°C, adding calcium carbonate slurry under continuous stirring until the final pH of the mixture is 4.8, indicating that the reaction is complete and calcium citrate solid is generated, and controlling the amount of calcium carbonate slurry added so that the final pH of the solid-liquid mixture is 4.8 to stop the reaction; (2) The solid-liquid mixture in step (1) is centrifuged and dehydrated, and then dried at 90-110° C. for 1-2 hours to obtain high-purity calcium citrate.

[0024] Comparative Example 2 A method for preparing calcium citrate, comprising the following steps: (1) Dissolve the finished food-grade citric acid product in pure water to a concentration of 10 g / 100 ml to obtain a citric acid solution; (2) slurrying food-grade calcium carbonate with pure water to a mass fraction of 30%; (3) At 75°C, continuously add the calcium carbonate slurry into the citric acid solution and stir until the pH value reaches 4.8; (4) slurrying food-grade calcium hydroxide with pure water to a mass fraction of 50%; (5) at 75° C., continuously adding calcium hydroxide slurry to step (3) to react until the pH value reaches 9.0, thereby generating calcium citrate; (6) After the reaction, the mixture is centrifuged and dehydrated, and then dried at 90-110° C. for 1-2 hours to obtain high-purity calcium citrate.

[0025] Index detection The products of Example 3 and the comparative example were tested according to the national standard for calcium citrate (GB 1903.14-2016) and the EU standard, wherein the calcium citrate content, drying loss, fluoride, lead and arsenic were tested according to the national standard (GB 1903.14-2016), and other indicators were tested according to the EU standard. By comparison, it can be seen that the indicators of the calcium citrate prepared by the present invention meet the requirements of the national standard and are significantly better than the calcium citrate product prepared by the traditional process. The results are shown in Table 1 below: Table 1 Performance indexes of calcium citrate prepared in Examples and Comparative Examples .

[0026] Experimental example At room temperature and pressure, weigh 1 g of the calcium citrate prepared in Example 3, dissolve it in 10 ml of 2 mol / L hydrochloric acid solution, and put it into a test tube and a beaker. Figure 1 and Figure 2 shown.

[0027] At room temperature and pressure, weigh 1 g of calcium citrate prepared in Comparative Example 2, dissolve it in 10 ml of 2 mol / L hydrochloric acid solution, and put it into a test tube and a beaker. Figure 3 and Figure 4 shown.

[0028] from Figures 1 to 4 It can be observed that when the calcium citrate product prepared by the method of Example 3 is dissolved in an acidic solution, the bubbles generated are significantly reduced compared with the calcium citrate obtained in Comparative Example 2, and no bubbles are observed when the calcium citrate prepared in Example 3 is dissolved in an acidic solution.

[0029] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any equivalent substitutions, modifications, etc. made by technicians in this field without any creative work within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing high-purity calcium citrate, characterized in that: The following steps are involved: (1) Dissolving the finished food-grade citric acid product in pure water to obtain a citric acid solution; (2) slurrying food-grade calcium carbonate with pure water to obtain calcium carbonate slurry; (3) At a certain reaction temperature, the calcium carbonate slurry is continuously added to the citric acid solution, stirred, and the reaction is stopped when the pH value reaches 2.6-2.8; (4) finely filtering the solution obtained in step (3); (5) slurrying food-grade calcium hydroxide with pure water to obtain calcium hydroxide slurry; (6) adding calcium hydroxide slurry to the solution filtered in step (4) at 60-80° C., stirring, and reacting until the pH value reaches 4.4-4.8 to reach the reaction endpoint, thereby generating calcium citrate; (7) After the reaction, centrifugal drying is performed to obtain high-purity calcium citrate.

2. The method for preparing high-purity calcium citrate according to claim 1, wherein The content of the citric acid after dissolution in step (1) is 10-30 g / 100 ml.

3. The method for preparing high-purity calcium citrate according to claim 1, characterized in that: The mass fraction of the calcium carbonate after slurry adjustment in step (2) is 30%-50%.

4. The method for preparing high-purity calcium citrate according to claim 1, characterized in that: The reaction temperature in step (3) is 20-40°C.

5. The method for preparing high-purity calcium citrate according to claim 1, characterized in that: The precision filtration method described in step (4) is membrane filtration.

6. The method for preparing high-purity calcium citrate according to claim 5, characterized in that: The filtration accuracy of the membrane filtration is 0.8 μm.

7. The method for preparing high-purity calcium citrate according to claim 1, characterized in that: The mass fraction of the calcium hydroxide after slurry adjustment in step (5) is 50-60%.

8. High-purity calcium citrate prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The heavy metal ion content is less than 20ppb.

Images