A method for citric acid production using carbon column regeneration treatment

Abstract

The present application belongs to the field of biological separation technology, and particularly relates to a method for regenerating a carbon column for citric acid production. The method mainly adds sodium carbonate or potassium carbonate or other possible carbonates (hereinafter referred to as soluble carbonates) for soaking in the regeneration process, so that the soluble carbonates react with slightly soluble calcium sulfate crystals to generate more insoluble calcium carbonate and soluble sulfates. After washing with softened water, the soluble sulfates are removed, and then hydrochloric acid solution is added to decompose the insoluble calcium carbonate to generate soluble calcium ions, water and carbon dioxide. The calcium ions are then washed and removed with softened water to achieve the removal of calcium sulfate. The method can easily solve the problem of calcium sulfate hardening and increase the service life of activated carbon.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of biological separation technology, and particularly relates to a method for regenerating a carbon column for production of citric acid. BACKGROUND

[0002] Citric acid (CA), also known as citrate, has a molecular formula of C6H8O7, is an important organic acid, is a colorless crystal, has no odor, has a strong sour taste, and is easily soluble in water, is an acidity regulator and food additive. It is mainly used in the food industry, the pharmaceutical industry, the chemical industry, and has a very broad application in the electronic, textile, petroleum, leather, building, photography, plastic, casting and ceramic industries.

[0003] In the production process of citric acid, the calcium salt method is mainly used to extract citric acid. This method has the advantages of simple operation, easy to master, safe product, and low cost. The production steps of this method mainly include filtration, primary neutralization, secondary neutralization, acidolysis, and then active carbon decolorization. The acidolysis solution after decolorization still contains a large amount of sulfate ions and calcium ions. The content of sulfate ions is about 800-1500 ppm, and the content of sulfate ions is about 500-1000 ppm. When the acidolysis solution enters the carbon column, due to changes in temperature and active carbon adsorption, a large amount of calcium sulfate crystals is produced, which is attached to the upper layer of the carbon column and the voids of the active carbon, is intercepted or adsorbed, and after a long time of accumulation, a thick layer of calcium sulfate plate or active carbon voids is filled with calcium sulfate, or the active carbon is wrapped with calcium sulfate. Calcium sulfate cannot be effectively removed by traditional liquid alkali soaking and hydrochloric acid soaking. Long-term accumulation causes poor regeneration effect and obvious degradation of active carbon, which seriously affects the service life and processing capacity of the carbon column. In addition, macromolecular substances are adsorbed into the voids of the active carbon by the active carbon, and the substances in the voids of the active carbon cannot be washed out by the traditional regeneration method, which will fill the voids of the active carbon and make the active carbon lose the adsorption performance.

[0004] Usually, a large amount of purified water is used to backflush the caked active carbon. If the water pressure is too small, the caked active carbon cannot be loosened, and if the water pressure is too large, the active carbon is easily washed out, causing the active carbon to run off, and a large amount of water is wasted, which brings certain pressure to environmental protection. Compressed air is used for scrubbing, and if the pressure of the compressed air is too small, it cannot loosen the active carbon, and if the pressure is too large, it easily causes the active carbon to run off or damages the structure of the bottom active carbon, increasing the breakage rate. The above methods have poor treatment effect on the caked active carbon, cannot achieve complete regeneration, and the impurities in the voids of the active carbon are not easy to be washed out.

[0005] Therefore, this invention uses a soluble hydrochloric acid solution to soak the activated carbon, replacing it with a more easily precipitated calcium carbonate and soluble sulfate solution. Then, softened water is used to rinse out the soluble sulfate solution. Hydrochloric acid is then added to react with calcium carbonate in a double decomposition reaction, generating carbon dioxide and water. The softened water then rinses out the soluble calcium ions. Furthermore, the addition of soluble carbonate reacts with citric acid or hydrochloric acid to generate carbon dioxide gas. This gas further cleanses and loosens the activated carbon, increasing the dissolution of calcium sulfate and preventing calcium sulfate caking. Simultaneously, the carbon dioxide in the pores of the activated carbon flushes out large molecules, facilitating activated carbon regeneration and reducing wastewater discharge, thus alleviating environmental pressure. Following these steps easily solves the problem of calcium sulfate caking, increases the service life of activated carbon, increases the carbon column's processing capacity, achieves complete and effective regeneration, extends the service life, and reduces production costs. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for regenerating citric acid using carbon columns. This method primarily involves soaking the activated carbon with sodium carbonate or potassium carbonate (hereinafter referred to as soluble carbonates) during the regeneration process. The soluble carbonates react with slightly soluble calcium sulfate crystals to form even more insoluble calcium carbonate and soluble sulfates. After rinsing with softened water to remove the soluble sulfates, hydrochloric acid solution is added to decompose the insoluble calcium carbonate, generating soluble calcium ions, water, and carbon dioxide. The calcium ions are then removed by rinsing with softened water, thus removing the calcium sulfate. This method easily solves the problem of calcium sulfate caking and increases the service life of activated carbon.

[0007] The technical solution of this invention is as follows:

[0008] A method for regenerating carbon columns in citric acid production involves regenerating the carbon column when the transmittance of the decolorizing solution falls below 90%. The specific steps include:

[0009] 1) Use softened water to inject into the carbon column at a flow rate of 1-4 times the column volume / hour to pump out the failed liquid. The water should be injected from top to bottom until the citric acid mass percentage concentration in the effluent is not higher than 1%.

[0010] 2) Add soluble carbonate solution to the carbon column at a flow rate of 1-5 column volumes / hour, with the flow direction being bottom in and top out. This will generate a large number of bubbles. Continue this process until the pH of the effluent is between 10 and 14, and soak for 1-15 days. Afterward, flush out the soluble carbonate solution with softened water at a flow rate of 1-4 column volumes / hour, with the flow direction being top in and bottom out, until the concentration of the soluble carbonate solution decreases to a pH of 8-14.

[0011] 3) Add sodium hydroxide solution, inject into the carbon column at a flow rate of 0.5-4 times the column volume per hour, the addition direction is from top to bottom, until the effluent pH is 10-14, soak for 1-20 days; then use softened water to flush out the sodium hydroxide solution at a flow rate of 0.5-4 times the column volume per hour, the addition direction is from top to bottom, until the sodium hydroxide solution concentration is reduced to pH 8-14.

[0012] 4) Finally, add the prepared 1-10% hydrochloric acid solution, inject into the carbon column at a flow rate of 1-3 times the column volume per hour, the addition direction is from bottom to top, the feeding process will produce a large amount of bubbles, the feeding speed needs to be controlled, soak for 1-10 days; then use softened water to flush out the hydrochloric acid in the carbon column at a flow rate of 1-4 times the column volume per hour, the addition direction is from top to bottom, until the eluent pH is 4-7.

[0013] Wherein, step 2) and step 3) can be reversed in order, and the addition direction of the soluble carbonate solution in step 3) is from top to bottom after reversing the order.

[0014] Preferably, after step 1) is completed, the following steps can be performed before step 2) is performed:

[0015] After recovering the citric acid, use softened water to perform backflush, the water inlet mode is from bottom to top, inject into the carbon column at a flow rate of 5-10 times the column volume per hour to perform flushing, flush for 2 times the column volume.

[0016] Preferably, in step 2), the soluble carbonate is selected from common soluble carbonates such as sodium carbonate, potassium carbonate, etc.; the mass concentration of the soluble carbonate solution is preferably 1-20%, more preferably 5-15%. The soluble carbonate needs to be of a certain concentration, and sufficient soaking time and sufficient concentration are required to facilitate the generation of bubbles during the addition of hydrochloric acid reaction, which can allow the soluble carbonate to invade the pores of the activated carbon, and is more conducive to the regeneration treatment of activated carbon.

[0017] Preferably, in step 3), the mass concentration of the sodium hydroxide solution is 1-10%.

[0018] Preferably, the softened water used is deionized water to prevent impurities from being brought in due to poor water quality.

[0019] Preferably, the soluble carbonate used is an analytical pure reagent with high purity.

[0020] Preferably, in step 2), the soaking time of the soluble carbonate solution is 5-15 days to allow the calcium sulfate to fully react with the soluble carbonate solution.

[0021] Preferably, in step 2), the temperature for adding the soluble carbonate is 0-90°C, more preferably 40-80°C.

[0022] The hydrochloric acid is preferably added from bottom to top to avoid the problem of excessive column pressure caused by carbon dioxide;

[0023] The hydrochloric acid is preferably added at a flow rate of 2 times the column volume per hour.

[0024] In the method for producing citric acid using the carbon column regeneration treatment of the present application:

[0025] First, the soluble carbonate solution is used to soak the activated carbon, and a carbonate that is easier to precipitate and a soluble sulfate solution are produced by the reaction, the sulfate is in ionic state, and the sulfate solution is washed out using softened water, and then hydrochloric acid is added to react with the calcium carbonate solution to generate calcium chloride, water and carbon dioxide, thereby achieving the removal of calcium sulfate. Second, the soluble carbonate enters the activated carbon interstices during the soaking process, and when it reacts with citric acid or hydrochloric acid, a large amount of carbon dioxide gas is generated, which will bubble out of the activated carbon interstices, loosen the impurities in the interstices and carry them out, which is beneficial to the regeneration of activated carbon. Third, the reaction of soluble carbonate with citric acid or hydrochloric acid produces a large amount of carbon dioxide gas, which can scrub and loosen the activated carbon, reducing the caking of activated carbon.

[0026] The soluble carbonate is fully soaked into the activated carbon interstices and reacts with the calcium sulfate crystals in the interstices, and at the same time, the soluble carbonate reacts with hydrochloric acid to generate a large amount of fine bubbles, which slowly discharge from the interstices, carrying away a large amount of insoluble impurities in the interstices, further cleaning the impurities in the activated carbon interstices. This bubble discharge is relatively mild and easy to control, reducing damage to the activated carbon. The carbon dioxide gas overflowing from the activated carbon interstices collects into larger bubbles, which are used to fully loosen the activated carbon to achieve the purpose of loosening all the activated carbon, facilitating full regeneration. Reducing the amount of backwash water, reducing the problem of excessive backwash water column pressure caused by caking of activated carbon, which can easily damage the motor and other effects. Reducing sewage discharge, reducing the pressure of environmental sewage treatment. Avoid the risk of resin running caused by excessive air pressure when using compressed air to scrub the activated carbon, and avoid the problem of excessive impact force on the bottom activated carbon caused by the large pressure of compressed air, which can damage the structure of the activated carbon, causing the activated carbon to break, increasing the production cost of the enterprise, or the pressure being too small to effectively loosen the activated carbon, affecting normal regeneration.

[0027] In summary, the present application adopts adding soluble carbonate solution for soaking, and fully reacts with calcium sulfate crystal, then uses softened water to flush out soluble sulfate, and then adds hydrochloric acid solution, uses generated carbon dioxide gas to fully loosen activated carbon, realizes full regeneration, and generates soluble calcium chloride, then uses softened water to flush out calcium chloride, so as to realize dissolving and removing of the hardened calcium sulfate layer, effectively saves the use of softened water, and further realizes energy saving and emission reduction. The method fully meets the activated carbon regeneration effect, protects the service life of the activated carbon, increases the activated carbon treatment capacity, reduces the consumption of hydrochloric acid, liquid alkali and the like in the regenerant, reduces the treatment column frequency, further realizes energy saving and emission reduction, reduces the discharge of low-concentration citric acid solution, reduces the environmental protection pressure, realizes high quality, low energy consumption, low cost and high stability production standard. Embodiment

[0028] The above content of the present application is further described in detail through the specific embodiments in the form of examples, but this should not be understood as the scope of the above subject matter of the present application being limited to the following examples. Any technology realized based on the above content of the present application belongs to the scope of the present application, and the following examples are completed by using conventional prior art unless otherwise specified. Example 1

[0029] A method for regenerating and treating a carbon column used in citric acid production:

[0030] When the carbon column decolorizing solution transmittance is lower than 90%, the carbon column is subjected to regeneration treatment, and the specific steps are as follows:

[0031] 1) The softened water is injected into the carbon column at a flow rate of 2 times the column volume per hour to press out the invalid liquid, the water inlet direction is from top to bottom, and the process is continued until the mass percentage concentration of the outflowing liquid citric acid is not higher than 1%.

[0032] 2) After recovering the citric acid, the softened water is used for back flushing, the water inlet direction is from bottom to top, the softened water is injected into the carbon column at a flow rate of 8 times the column volume per hour for flushing, and the column volume for flushing is 2 times.

[0033] 3) Then, the prepared 5% sodium hydroxide solution is injected into the carbon column at a flow rate of 2 times the column volume per hour, the adding direction is from top to bottom, the process is continued until the pH value of the outflowing liquid is 10-14, and the soaking time is 10 days; then, the softened water is used to flush out the sodium hydroxide solution at a flow rate of 2 times the column volume per hour, the adding direction is from top to bottom, and the process is continued until the concentration of the sodium hydroxide solution is reduced to pH 8-14.

[0034] 4) Then add the prepared 10% sodium carbonate solution, the temperature of sodium carbonate solution is 40℃, inject into the carbon column at a flow rate of 2 times column volume per hour, the adding direction is from top to bottom, until the effluent pH value is 10-14, soak for 10 days; then use softened water to flush out the sodium carbonate solution at a flow rate of 2 times column volume per hour, the adding direction is from top to bottom, until the concentration of sodium carbonate solution is reduced to pH 10-14;

[0035] 5) Finally, add the prepared 5% hydrochloric acid solution, inject into the carbon column at a flow rate of 2 times column volume per hour, the adding direction is from bottom to top, a large amount of bubbles will be generated during the feeding process, which needs to be controlled, the generated bubbles will further scrub the activated carbon and loosen the caked activated carbon, soak for 5 days; then use softened water to flush out the hydrochloric acid in the carbon column at a flow rate of 2 times column volume per hour, the adding direction is from top to bottom, until the eluent pH value is 4-7. Example 2

[0036] A method for regenerating a carbon column used in citric acid production:

[0037] When the carbon column decolorizing solution transmittance is lower than 90%, the carbon column is regenerated, the specific steps are as follows:

[0038] 1) Use softened water to inject into the carbon column at a flow rate of 2 times column volume per hour to press out the invalid liquid, the water inlet direction is from top to bottom, until the effluent citric acid mass percentage concentration is not higher than 1%.

[0039] 2) After recovering citric acid, use softened water to backflush, the water inlet direction is from bottom to top, inject into the carbon column at a flow rate of 8 times column volume per hour for flushing, flush for 2 times column volume.

[0040] 3) Then add the prepared 5% sodium hydroxide solution, inject into the carbon column at a flow rate of 2 times column volume per hour, the adding direction is from top to bottom, until the effluent pH value is 10-14, soak for 10 days; then use softened water to flush out the sodium hydroxide solution at a flow rate of 2 times column volume per hour, the adding direction is from top to bottom, until the concentration of sodium hydroxide solution is reduced to pH 8-10.

[0041] 4) Then add the prepared 15% sodium carbonate solution, the temperature of sodium carbonate solution is 40℃, inject into the carbon column at a flow rate of 2 times column volume per hour, the adding direction is from top to bottom, until the effluent pH value is 10, soak for 10 days; then use softened water to flush out the sodium carbonate solution at a flow rate of 2 times column volume per hour, the adding direction is from top to bottom, until the concentration of sodium carbonate solution is reduced to pH 10-14.

[0042] 5) Finally, add the prepared 5% hydrochloric acid solution, inject it into the carbon column at a flow rate of 2 times the column volume per hour, and the addition direction is from bottom to top. A large amount of bubbles will be generated during the feeding process, and the feeding speed needs to be controlled. The generated bubbles will further scrub the activated carbon and loosen the caked activated carbon. Soak for 5 days. Then use softened water to flush out the hydrochloric acid in the carbon column at a flow rate of 2 times the column volume per hour, and the addition direction is from top to bottom. Continue until the pH value of the eluent is 4-7. Example 3

[0043] A method for regenerating a carbon column used in citric acid production:

[0044] When the carbon column decolorizing solution transmittance is lower than 90%, the carbon column needs to be regenerated. The specific steps are as follows:

[0045] 1) Use softened water to inject it into the carbon column at a flow rate of 2 times the column volume per hour to press out the invalid liquid. The water inlet direction is from top to bottom. Continue until the mass percentage concentration of citric acid in the effluent is not higher than 1%.

[0046] 2) After recovering the citric acid, add the prepared 10% sodium carbonate solution, and the temperature of the sodium carbonate solution is 40℃. Inject it into the carbon column at a flow rate of 2 times the column volume per hour, and the addition direction is from bottom to top. A large amount of bubbles will be generated during this process, which is used to scrub the activated carbon. Control the speed of adding sodium carbonate to prevent a large amount of bubbles from flushing out the activated carbon. Continue until the pH value of the effluent is 10-14, and soak for 15 days. Then use softened water to flush out the sodium carbonate solution at a flow rate of 2 times the column volume per hour. The softened water addition direction is from top to bottom. Continue until the concentration of the sodium carbonate solution is reduced to a pH of 8-14.

[0047] 3) Then add the prepared 5% sodium hydroxide solution, inject it into the carbon column at a flow rate of 2 times the column volume per hour, and the addition direction is from top to bottom. Continue until the pH value of the effluent is 10-14, and soak for 10 days. Then use softened water to flush out the sodium hydroxide solution at a flow rate of 2 times the column volume per hour. The addition direction is from top to bottom. Continue until the concentration of the sodium hydroxide solution is reduced to a pH of 8-14.

[0048] 4) Finally, add the prepared 5% hydrochloric acid solution, and the addition direction is from bottom to top. This process will generate a large amount of carbon dioxide gas. Control the feeding flow rate and inject it into the carbon column at a flow rate of 2 times the column volume per hour. Continue until the pH value of the effluent is 1-4, and soak for 5 days. Then use softened water to flush out the hydrochloric acid in the carbon column at a flow rate of 2 times the column volume per hour. The addition direction is from top to bottom. Continue until the pH value of the eluent is 4-7. Example 4

[0049] A method for regenerating a carbon column used in citric acid production:

[0050] When the transmittance of the decoloring solution of the carbon column is lower than 90%, the carbon column is regenerated by the following steps:

[0051] 1) The carbon column is injected with softened water at a flow rate of 2 times the column volume per hour to pressurize the column, and the water is injected from top to bottom and discharged from bottom to top until the mass percentage concentration of citric acid in the effluent is not higher than 1%.

[0052] 2) After the citric acid is recovered, the carbon column is back-flushed with softened water, the water is injected from bottom to top and discharged from top to bottom, and the column is flushed at a flow rate of 8 times the column volume per hour, and the column is flushed for 2 times the column volume.

[0053] 3) A prepared 15% sodium carbonate solution is added, the temperature of the sodium carbonate solution is 40°C, the sodium carbonate solution is injected into the carbon column at a flow rate of 2 times the column volume per hour, the sodium carbonate solution is added from bottom to top, a large amount of bubbles is generated in the process, the speed of adding the sodium carbonate solution is controlled to prevent the active carbon from being washed out by the large amount of bubbles, and the process is continued until the pH value of the effluent is 10-14, and the sodium carbonate solution is soaked for 10 days. The sodium carbonate solution is flushed out with softened water at a flow rate of 2 times the column volume per hour, the softened water is added from top to bottom, and the concentration of the sodium carbonate solution is reduced to a pH value of 10-14.

[0054] 4) Then, a prepared 5% sodium hydroxide solution is added, the sodium hydroxide solution is injected into the carbon column at a flow rate of 2 times the column volume per hour, the sodium hydroxide solution is added from top to bottom, and the process is continued until the pH value of the effluent is 10-14, and the sodium hydroxide solution is soaked for 10 days. Then, the sodium hydroxide solution is flushed out with softened water at a flow rate of 2 times the column volume per hour, the softened water is added from top to bottom, and the concentration of the sodium hydroxide solution is reduced to a pH value of 8-14.

[0055] 5) Finally, a prepared 5% hydrochloric acid solution is added, the hydrochloric acid solution is added from bottom to top, a large amount of carbon dioxide gas is generated in the process, the flow rate of the hydrochloric acid solution is controlled to be 2 times the column volume per hour, and the process is continued until the pH value of the effluent is 1-4, and the hydrochloric acid solution is soaked for 5 days. Then, the hydrochloric acid solution is flushed out with softened water at a flow rate of 2 times the column volume per hour, the softened water is added from top to bottom, and the pH value of the effluent is 4-7.

[0056] The regenerated carbon column obtained by the method of the embodiment of the present application can be fully regenerated, the hardened calcium sulfate layer can be dissolved and removed, the use of softened water can be effectively saved, energy saving and emission reduction can be further achieved. The method fully meets the regeneration effect of the active carbon, the service life of the active carbon is protected, the treatment capacity of the active carbon is increased, the consumption of hydrochloric acid, liquid alkali and other regeneration agents is reduced, the frequency of processing the column is reduced, energy saving and emission reduction are further achieved, the discharge of low-concentration citric acid solution is reduced, the environmental protection pressure is reduced, and the production standards of high quality, low energy consumption, low cost and high stability are realized.

Claims

1. A method for producing citric acid using a carbon column regeneration process, characterized by, When the carbon column decolorizing liquid transmittance is lower than 90%, the carbon column enters the regeneration process, the specific steps include: 1) using softened water to inject into the carbon column at a flow rate of 1-4 times the column volume / hour to press out the invalid liquid, the water inlet direction is from top to bottom, until the effluent citric acid mass percentage concentration is not higher than 1%; 2) adding soluble carbonate solution, injecting into the carbon column at a flow rate of 1-5 times the column volume / hour, the adding direction is from bottom to top, a large amount of bubbles will be generated, until the effluent pH value is 10-14, soaking for 1-15 days; then using softened water to flush out the soluble carbonate solution at a flow rate of 1-4 times the column volume / hour, the softened water adding direction is from top to bottom, until the soluble carbonate solution concentration is reduced to pH 8-14; 3) adding sodium hydroxide solution, injecting into the carbon column at a flow rate of 0.5-4 times the column volume / hour, the adding direction is from top to bottom, until the effluent pH value is 10-14, soaking for 1-20 days; then using softened water to flush out the sodium hydroxide solution at a flow rate of 0.5-4 times the column volume / hour, the adding direction is from top to bottom, until the sodium hydroxide solution concentration is reduced to pH 8-14; 4) finally adding prepared 1-10% hydrochloric acid solution, injecting into the carbon column at a flow rate of 1-3 times the column volume / hour, the adding direction is from bottom to top, a large amount of bubbles will be generated during the feeding process, the feeding speed needs to be controlled, soaking for 1-10 days; then using softened water to flush out the hydrochloric acid in the carbon column at a flow rate of 1-4 times the column volume / hour, the adding direction is from top to bottom, until the eluent pH value is 4-7; Wherein, steps 2) and 3) can be reversed in order, after reversing the order, the adding direction of the soluble carbonate solution in step 3) is from top to bottom.

2. The method for producing citric acid using a carbon column regeneration process according to claim 1, characterized by, After completing step 1), the following steps are performed before step 2) is performed: After recovering citric acid, use softened water to backflush, the water inlet mode is from bottom to top, inject into the carbon column at a flow rate of 5-10 times the column volume / hour for flushing, flush for 2 times the column volume.

3. The method for producing citric acid using a carbon column regeneration process according to claim 1, characterized by, The soluble carbonate in step 2) is selected from sodium carbonate, potassium carbonate.

4. The method for producing citric acid using a carbon column regeneration process according to claim 1, characterized by, The mass concentration of the soluble carbonate solution in step 2) is 1-20%.

5. The method of claim 4, wherein the carbon column is regenerated by using a citric acid production process. The mass concentration of the soluble carbonate solution in step 2) is 5-15%.

6. The method for producing citric acid using a carbon column regeneration process according to claim 1, characterized by, The mass concentration of the sodium hydroxide solution in step 3) is 1-10%.

7. The method for producing citric acid using a carbon column regeneration process according to claim 1, characterized by, The softened water is deionized water.

8. The method for citric acid production using carbon column regeneration treatment according to claim 1, characterized by, The soaking time of the soluble carbonate solution in step 2) is 5-15 days.

9. The method for regenerating the carbon column treatment for citric acid production according to claim 1, characterized by, The temperature for adding the soluble carbonate in step 2) is 0-90°C.

10. The method of claim 9, wherein the carbon column is regenerated by using a citric acid production process. The temperature for adding the soluble carbonate in step 2) is 40-80°C.