A green and environmentally friendly method for extracting citric acid

Abstract

The invention belongs to the field of citric acid production, and specifically relates to a green and environmentally friendly citric acid extraction method, wherein the main method is to add calcium carbonate to citric acid fermentation liquid, react citric acid with calcium carbonate to generate calcium citrate, react calcium citrate with citric acid fermentation clear liquid to generate calcium hydrogen citrate, react calcium hydrogen citrate with sulfuric acid to generate citric acid and calcium sulfate, add ammonium carbonate or ammonium bicarbonate to calcium sulfate to generate ammonium sulfate and calcium carbonate, wherein ammonium sulfate can be used as fertilizer, and calcium carbonate can be recycled. The invention solves the problem of difficult treatment of calcium sulfate solid waste in the citric acid production process, realizes the recycling of calcium carbonate, and reduces production costs.

Description

Technical Field

[0001] The invention belongs to the field of citric acid production, and particularly relates to a green and environmentally friendly citric acid extraction method. Background Art

[0002] Citric acid, also known as citric acid, is a colorless translucent crystal or white granule or white crystalline powder at room temperature. It is odorless, extremely sour, and slightly deliquescent in humid air. In the organic acid market, citric acid has a market share of more than 70%. Citric acid has a mild and refreshing sour taste and is widely used in the manufacture of various beverages, sodas, wines, candies, snacks, biscuits, canned juices, dairy products and other foods. It can be used as a flavoring agent and an antioxidant for edible oils. It also improves the sensory properties of food, enhances appetite and promotes the digestion and absorption of calcium and phosphorus substances in the body.

[0003] Traditional citric acid extraction processes mainly use calcium salt method, ion exchange method, chromatography method, extraction method, etc. The disadvantage of the calcium salt method is that it consumes a large amount of calcium carbonate and discharges a large amount of solid waste such as calcium sulfate, which imposes a great burden on the environment; the ion exchange method produces sulfate as a byproduct during the process, which requires further treatment; the chromatography method has the disadvantages of low citric acid extract concentration, high carbonization multiple, and high energy consumption; the extraction method has emulsification during the extraction process, which is not conducive to reuse.

[0004] Therefore, how to solve the problem of difficult solid waste treatment of calcium sulfate in the citric acid production process is a technical problem that needs to be solved urgently in this field. Summary of the invention

[0005] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a green and environmentally friendly citric acid extraction method, wherein calcium carbonate is added to citric acid fermentation supernatant, citric acid and calcium carbonate react to generate calcium citrate, calcium citrate reacts with citric acid fermentation supernatant to generate calcium hydrogen citrate, calcium hydrogen citrate reacts with sulfuric acid to generate citric acid and calcium sulfate, and calcium sulfate is added to ammonium carbonate or ammonium bicarbonate to generate ammonium sulfate and calcium carbonate, wherein the ammonium sulfate can be used as a fertilizer, and the calcium carbonate can be recycled.

[0006] The technical solution adopted by the present invention is specifically as follows: A green and environmentally friendly citric acid extraction method specifically comprises the following steps: (1) filtering the citric acid fermentation broth to obtain a citric acid fermentation clear liquid; (2) Add water to calcium carbonate to prepare slurry; (3) At a certain reaction temperature, the calcium carbonate slurry is continuously added to the citric acid clear solution, and the reaction is stirred until the pH of the system reaches 4-6; (4) performing solid-liquid separation on the system after the reaction in step (3) to obtain a calcium citrate precipitate and a filtrate; (5) washing the calcium citrate precipitate obtained in step (4) to remove impurities; (6) The washed calcium citrate is mixed with the citric acid fermentation supernatant again to carry out a secondary neutralization reaction until the pH of the system reaches 3-3.5 to complete the reaction and obtain calcium hydrogen citrate; (7) adding concentrated sulfuric acid stream to calcium hydrogen citrate to carry out acid hydrolysis reaction to obtain citric acid solution and calcium sulfate; the citric acid solution is subjected to decolorization, desorption, evaporation and crystallization, centrifugal drying and screening to obtain citric acid product; (8) Add water to ammonium carbonate or ammonium bicarbonate to prepare a slurry; (9) adding ammonium carbonate or ammonium bicarbonate slurry to the calcium sulfate obtained in step (7) to react and generate calcium carbonate and ammonium sulfate.

[0007] In the step (2), the mass fraction of calcium carbonate after slurry adjustment is 30-50%.

[0008] In the step (3), the reaction temperature is 30-50°C and the reaction time is 1-3h.

[0009] In the step (4), the solid-liquid separation method is centrifugal separation.

[0010] In the step (6), the reaction temperature is controlled at 60-80°C and the reaction time is 1-2h.

[0011] In the step (7), the acid hydrolysis temperature is controlled at 60-80°C, the pH value is controlled at 1-1.5, the reaction time is 1-3h, and the citric acid solution and calcium sulfate can be separated by a vacuum belt filter.

[0012] In the step (8), the mass fraction of ammonium carbonate or ammonium bicarbonate after slurry adjustment is 20-50%.

[0013] In the step (9), the reaction temperature is 25-40° C., the mass ratio of calcium sulfate to ammonium carbonate or ammonium bicarbonate is 1:1.5-3, and the reaction time is 1-2 h.

[0014] In the step (9), the ammonium sulfate obtained after the reaction can be used as a fertilizer, and the calcium carbonate is further recycled to the step (2).

[0015] Compared with the prior art, the citric acid extraction method provided by the present invention avoids the generation of calcium sulfate solid waste in the reaction process, solves the problem of difficult treatment of calcium sulfate solid waste in the citric acid production process, and realizes the effective recycling of calcium carbonate. Since the calcium carbonate generated by the reaction of calcium sulfate with ammonium carbonate or ammonium bicarbonate has a small particle size, the calcium carbonate particle size can reach 800 mesh, and the impurity content is reduced, when it is reused in the previous citric acid neutralization reaction process, the calcium carbonate embedded in calcium citrate is reduced, the reaction time is shortened, and the impurities are reduced, and the quality of the obtained citric acid product is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0017] The present invention will be further described below in conjunction with specific embodiments, so that those skilled in the art can understand the present invention more comprehensively, but the present invention is not limited in any way. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention. Unless otherwise specified, the relevant processes in the following embodiments all adopt conventional processes and parameters in the art, and the inventor will not repeat them.

[0018] Example 1 A green and environmentally friendly method for extracting citric acid, the specific steps are: (1) filtering the citric acid fermentation broth to obtain a citric acid fermentation clear liquid; (2) Adding water to calcium carbonate to prepare a slurry to obtain a calcium carbonate solution with a mass fraction of 30%; (3) At 40°C, the calcium carbonate slurry was continuously added to the citric acid fermentation supernatant, stirred, and reacted until the pH value was 5.5. The reaction time was 1.5 h; (4) centrifuging the solid-liquid mixture after the reaction to obtain a calcium citrate precipitate and a filtrate; (5) washing the obtained calcium citrate precipitate to remove impurities; (6) The washed calcium citrate is mixed with the citric acid fermentation supernatant again to carry out a secondary neutralization reaction, the reaction temperature is controlled at 60°C, the reaction is carried out until the pH value of the system is 3.5, and the reaction time is 2 hours; (7) Adding concentrated sulfuric acid stream to calcium hydrogen citrate to carry out acid hydrolysis reaction for 2 hours to obtain citric acid solution and calcium sulfate, which are separated by vacuum belt filter. The citric acid solution is subjected to decolorization, desorption, evaporation and crystallization, centrifugal drying and screening to obtain citric acid product; (8) Add water to ammonium carbonate to make a slurry of 30%; (9) adding the ammonium carbonate slurry to the calcium sulfate to carry out a reaction, controlling the mass ratio of calcium sulfate to ammonium carbonate to be 1:1.5 and the reaction temperature to be 25°C; After the reaction, the conversion rate of calcium sulfate was 96.15%, and the obtained calcium carbonate was recycled to the corresponding process step of producing citric acid. The reaction time was 2 hours, the yield of citric acid was 92.21%, and the quality of citric acid product met the national standards.

[0019] Example 2 A green and environmentally friendly method for extracting citric acid, the specific steps are: (1) filtering the citric acid fermentation broth to obtain a citric acid fermentation clear liquid; (2) Adding water to calcium carbonate to prepare a slurry to obtain a calcium carbonate solution with a mass fraction of 50%; (3) At 30°C, the calcium carbonate slurry was continuously added to the citric acid fermentation supernatant, stirred, and reacted until the pH value was 4.5. The reaction time was 3 hours; (4) centrifuging the solid-liquid mixture after the reaction to obtain a calcium citrate precipitate and a filtrate; (5) washing the obtained calcium citrate precipitate to remove impurities; (6) The washed calcium citrate is mixed with the citric acid fermentation supernatant again to carry out a secondary neutralization reaction, the reaction temperature is controlled at 80°C, the reaction is carried out until the pH value of the system is 3, and the reaction time is 1.5 hours; (7) Adding concentrated sulfuric acid stream to calcium hydrogen citrate to carry out acid hydrolysis reaction for 2.5 hours to obtain citric acid solution and calcium sulfate, which are separated by vacuum belt filter. The citric acid solution is subjected to decolorization, desorption, evaporation and crystallization, centrifugal drying and screening to obtain citric acid product; (8) Add water to ammonium bicarbonate to make a slurry of 40%; (9) adding the ammonium bicarbonate slurry to the calcium sulfate to carry out a reaction, controlling the mass ratio of calcium sulfate to ammonium bicarbonate to be 1:3 and the reaction temperature to be 40°C; After the reaction, the conversion rate of calcium sulfate was 98.15%, and the obtained calcium carbonate was recycled to the corresponding process step of producing citric acid. The reaction time was 1 hour, the yield of citric acid was 93.23%, and the quality of the citric acid product met the national standards.

[0020] Example 3 A green and environmentally friendly method for extracting citric acid, the specific steps are: (1) filtering the citric acid fermentation broth to obtain a citric acid fermentation clear liquid; (2) Adding water to calcium carbonate to prepare a slurry to obtain a calcium carbonate solution with a mass fraction of 40%; (3) At 50°C, the calcium carbonate slurry was continuously added to the citric acid fermentation supernatant, stirred, and reacted until the pH value was 4. The reaction time was 2 hours; (4) centrifuging the solid-liquid mixture after the reaction to obtain a calcium citrate precipitate and a filtrate; (5) washing the obtained calcium citrate precipitate to remove impurities; (6) The washed calcium citrate was mixed with the citric acid fermentation supernatant again to carry out a secondary neutralization reaction, the reaction temperature was controlled at 70°C, the reaction was carried out until the pH of the system reached 3, and the reaction time was 1.5 h; (7) Adding concentrated sulfuric acid stream to calcium hydrogen citrate to carry out acid hydrolysis reaction for 1.5 hours to obtain citric acid solution and calcium sulfate, which are separated by vacuum belt filter. The citric acid solution is subjected to decolorization, desorption, evaporation and crystallization, centrifugal drying, and sieving to obtain citric acid product; (8) Add water to ammonium carbonate to adjust the slurry to 25%; (9) adding the ammonium carbonate slurry to the calcium sulfate to carry out a reaction, controlling the mass ratio of calcium sulfate to ammonium carbonate to be 1:2 and the reaction temperature to be 35°C; After the reaction, the conversion rate of calcium sulfate was 97.68%, and the obtained calcium carbonate was recycled to the corresponding process step of producing citric acid. The reaction time was 1.5h, the citric acid yield was 92.36%, and the quality of the citric acid product met the national standards.

[0021] Taking the calcium carbonate prepared in Example 2 as an example, a quality analysis comparison was carried out with the purchased calcium carbonate, as shown in Table 1. It can be seen that the calcium carbonate prepared by the present invention has a lower impurity content and a smaller particle size, and can better meet the production requirements.

[0022] Table 1 Quality comparison of purchased calcium carbonate and recycled calcium carbonate (Example 2) .

[0023] Comparative Example A citric acid production process, the specific steps are: (1) filtering the citric acid fermentation broth to obtain a citric acid fermentation clear liquid; (2) Add water to the purchased calcium carbonate to prepare a slurry to obtain a calcium carbonate solution with a mass fraction of 50%; (3) adding calcium carbonate slurry to the citric acid fermentation supernatant at 50°C, stirring, and reacting until the pH value reaches 5; (4) performing solid-liquid separation on the solution after the reaction to obtain calcium citrate precipitate and filtrate; (5) washing the obtained calcium citrate precipitate to remove impurities; (6) The washed calcium citrate is mixed with the citric acid fermentation supernatant again to carry out a secondary neutralization reaction, the reaction temperature is controlled at 60°C, and the reaction is carried out until the pH of the system reaches 3.5; (7) adding concentrated sulfuric acid stream to calcium hydrogen citrate to carry out acid hydrolysis reaction to obtain citric acid solution and calcium sulfate; the citric acid solution is subjected to decolorization, separation, evaporation crystallization, centrifugal drying and screening to obtain citric acid product; the reaction time of calcium carbonate and citric acid fermentation clear liquid is 2.5 hours, and the quality of citric acid product meets national standards; Table 2 shows the reaction time, product yield and product quality comparison results of extracting citric acid by using purchased calcium carbonate in the comparative example and extracting citric acid by recycling calcium carbonate in Example 2 of the present invention. Table 2 Comparison of the quality of citric acid produced by purchasing calcium carbonate and recycling calcium carbonate (Example 2) It can be seen that the calcium carbonate prepared by the method provided by the present invention has a small particle size and a low impurity content. In the process of recycling to generate citric acid, the amount of calcium citrate embedded in calcium carbonate is reduced, the reaction time is shortened, the citric acid yield and product quality are improved, the problem of difficult solid waste treatment of calcium sulfate in the citric acid production process is solved, and the effective recycling of calcium carbonate is achieved.

[0024] 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 green and environmentally friendly citric acid extraction method, characterized in that: The specific steps include: (1) filtering the citric acid fermentation broth to obtain a citric acid clear solution; (2) Add water to calcium carbonate to prepare slurry; (3) At a certain reaction temperature, the calcium carbonate slurry is continuously added to the citric acid clear solution, and the reaction is stirred until the pH of the system reaches 4-6; (4) performing solid-liquid separation on the system after the reaction in step (3) to obtain a calcium citrate precipitate and a filtrate; (5) washing the calcium citrate precipitate obtained in step (4) to remove impurities; (6) The washed calcium citrate is mixed with the citric acid clear solution again to carry out a secondary neutralization reaction until the pH of the system reaches 3-3.5 to complete the reaction and obtain calcium hydrogen citrate; (7) adding concentrated sulfuric acid to the above-mentioned calcium hydrogen citrate to carry out acid hydrolysis reaction to obtain citric acid solution and calcium sulfate. The citric acid solution is subjected to decolorization, desorption, evaporation and crystallization, centrifugal drying and screening to obtain a citric acid product; (8) Add water to ammonium carbonate or ammonium bicarbonate to prepare a slurry; (9) adding ammonium carbonate or ammonium bicarbonate slurry to the calcium sulfate obtained in step (7) to react and generate calcium carbonate and ammonium sulfate.

2. The method according to claim 1, characterized in that The mass fraction of calcium carbonate after slurry adjustment in step (2) is 30-50%.

3. The method according to claim 1, characterized in that The reaction temperature in step (3) is 30-50°C, the reaction time is 1-3h, and the pH at the end of the reaction is 4-6.

4. The method according to claim 1, characterized in that: The reaction temperature in step (6) is 60-80°C, the pH value is controlled at 3-3.5, and the reaction time is 1-2h.

5. The method according to claim 1, characterized in that: The acid hydrolysis temperature in step (7) is controlled at 60-80°C, the reaction time is 1-3h, and the pH value is controlled at 1-1.

5.

6. The method according to claim 1, characterized in that The mass fraction of the ammonium carbonate or ammonium bicarbonate after slurry adjustment in step (8) is 20-50%.

7. The method according to claim 1, characterized in that The reaction temperature in step (9) is 25-40° C., the mass ratio of calcium sulfate to ammonium carbonate or ammonium bicarbonate is 1:1.5-3, and the reaction time is 1-2 h.

8. The method according to claim 1 or 7, characterized in that: After the reaction in step (9), the ammonium sulfate obtained is used as a fertilizer, and the calcium carbonate is recycled to step (2).

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