Process for treating phosphate waste liquor in immobilized enzyme production

Abstract

The present application relates to the technical field of immobilized enzyme production, and particularly relates to a phosphate waste liquid treatment process in immobilized enzyme production, which comprises the following steps: (1) the phosphate waste liquid enters a cation resin column and an anion resin column in sequence, and a second effluent is collected; (2) a potassium hydroxide solution elutes the anion resin column, and the collected desorption liquid is subjected to concentration, cooling, filtration and washing, and dipotassium hydrogen phosphate crystals and a first mother liquor are collected respectively; (3) a phosphoric acid solution elutes the cation resin column, and the collected desorption liquid is subjected to concentration and other operations, and dipotassium hydrogen phosphate crystals and a second mother liquor are collected respectively; (4) the first and second mother liquors are combined, and filtration, pH adjustment and other operations are performed to obtain a potassium dihydrogen phosphate product; and (5) the dipotassium hydrogen phosphate crystals are combined, water and a decoloring agent are added, and stirring and other operations are performed to obtain a dipotassium hydrogen phosphate product. The above treatment process can effectively treat the phosphate waste liquid in the immobilized enzyme production, and two products, the potassium dihydrogen phosphate and the dipotassium hydrogen phosphate, are obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of immobilized enzyme production, and particularly relates to a phosphate waste liquid treatment process in immobilized enzyme production. BACKGROUND

[0002] Dipotassium hydrogen phosphate, alias dipotassium hydrogen phosphate trihydrate, molecular formula K2HPO4·3H2O, appearance is white crystal or amorphous white powder, easily soluble in water, aqueous solution is slightly alkaline, slightly soluble in alcohol, hygroscopic, self-dissolved at high temperature. Relative density is 2.338, 204℃ when the internal dehydration of the molecule is converted into potassium pyrophosphate. The pH value of 1% aqueous solution is 8.9. Mainly used for medicine, fermentation, bacterial culture and preparation of potassium pyrophosphate, etc., also can be used as corrosion inhibitor of antifreeze, nutrient agent of antibiotic culture medium, phosphorus and potassium regulator of fermentation industry, feed additive, water treatment agent and microbial culture agent, etc.

[0003] Immobilized enzyme has the advantages of good stability, easy separation from the reaction system, easy control and repeated use, and is therefore widely promoted in enzymatic reaction. However, in the preparation process of immobilized penicillin acylase, immobilized glycanase and other immobilized enzymes, phosphate buffer (PBS) is used to maintain the pH of the system, in addition, phosphate buffer solution is used to activate the carrier resin, and finally phosphate buffer solution is used to wash the final immobilized enzyme; these operations will inevitably produce a large amount of phosphate waste liquid. If the waste liquid enters the sewage treatment system, it not only increases the environmental protection pressure and the sewage treatment cost, but also causes resource waste and reduces economic benefits. Therefore, in view of the above problems, it is necessary to establish a phosphate waste liquid treatment process in immobilized enzyme production. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a phosphate waste liquid treatment process in immobilized enzyme production in view of the deficiencies of the prior art, which can effectively treat the phosphate waste liquid and obtain dipotassium hydrogen phosphate product, thereby increasing the economic benefits of enterprises.

[0005] To solve the above technical problems, the technical scheme of the present application is as follows:

[0006] A phosphate waste liquid treatment process in immobilized enzyme production, the treatment process comprises the following steps:

[0007] (1) The phosphate waste liquid first enters the cation resin column, the first effluent collected enters the anion resin column, and the second effluent collected is reserved;

[0008] (2) Eluting the anion resin column with potassium hydroxide solution, and collecting the desorption solution to concentrate, cool, filter and wash to collect potassium phosphate dibasic crystals and a first mother liquor, respectively;

[0009] (3) Eluting the cation resin column with phosphoric acid solution, and collecting the desorption solution to concentrate, adjust pH, warm, cool after white solid precipitates, filter, wash, and dry to obtain potassium phosphate dibasic product;

[0010] (4) Combining the first mother liquor in step (2) and the second mother liquor in step (3), adjusting the pH of the collected filtrate to be acidic, concentrating to precipitate crystals, cooling, filtering, washing, and drying to obtain potassium phosphate dibasic product;

[0011] (5) Combining the potassium phosphate dibasic crystals in step (2) and the potassium phosphate dibasic crystals in step (3), dissolving in water, adding a decolorizing agent, stirring, filtering, cooling, filtering, and drying to obtain potassium phosphate dibasic product.

[0012] As an improved technical solution, the phosphate salt waste liquid in step (1) enters the cation resin column at a flow rate of 0.5-1.5 BV / h, and the first effluent enters the anion resin column at a flow rate of 1-3 BV / h.

[0013] As an improved technical solution, the filler in the cation resin column and the anion resin column in step (1) is macroporous adsorption resin.

[0014] As an improved technical solution, the concentration of the potassium hydroxide solution in step (2) is 10-30 wt%, and the potassium hydroxide solution enters the anion resin column at a flow rate of 1-3 BV / h.

[0015] As an improved technical solution, the desorption solution in step (2) is concentrated to a solid content of 70-90 wt% and cooled to 20-30℃.

[0016] As an improved technical solution, the concentration of the phosphoric acid solution in step (3) is 80-85 wt%, and the phosphoric acid solution enters the cation resin column at a flow rate of 0.5-1.5 BV / h.

[0017] As an improved technical solution, the effluent in step (3) is concentrated to 20-30 poise, potassium hydroxide is added to adjust the pH to 8.5-9.5, and then warmed to 60-80℃ for 1-3 h, and then cooled to 20-30℃ after white crystals precipitate.

[0018] As an improved technical solution, the filtrate after the first mother liquor and the second mother liquor are combined and filtered in step (4) is adjusted to pH 4.0-4.5 by phosphoric acid; and then concentrated to precipitate crystals, and then cooled to 20-30 DEG C.

[0019] After the above technical solution is adopted, the application has the following beneficial effects:

[0020] In the application, the phosphate waste liquid in the immobilized enzyme production is collected first into a cation resin column, so that metal cations in the phosphate waste liquid can be adsorbed, and then the phosphate waste liquid is introduced into an anion resin column, so that phosphate ions can be adsorbed. Then, the anion resin column is eluted by sodium hydroxide solution, and the desorption liquid collected is concentrated, cooled, filtered, and dried to obtain dipotassium hydrogen phosphate crystals and a first mother liquor. Then, the cation resin column is eluted by phosphoric acid, and the effluent collected is concentrated, adjusted to a certain pH, heated, cooled, filtered, washed, and dried to obtain potassium dihydrogen phosphate product. The first mother liquor and the second mother liquor are combined, filtered, adjusted to a certain pH, concentrated to precipitate crystals, cooled, filtered, washed, and dried to obtain potassium dihydrogen phosphate product. The above treatment process can effectively recover potassium ions and phosphate ions in the phosphate waste liquid in the immobilized enzyme production, and obtain two products, i.e., potassium dihydrogen phosphate and dipotassium hydrogen phosphate, thereby avoiding resource waste, increasing economic benefits of enterprises, and reducing environmental pollution. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a picture of potassium dihydrogen phosphate in Example 3 under 10 times optical microscope.

[0022] Figure 2 It is a picture of dipotassium hydrogen phosphate in Example 3 under 10 times optical microscope. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the application more clear and understandable, the application is further described in detail below in combination with examples. It should be understood that the specific examples described herein are only used to explain the application, and are not used to limit the application.

[0024] Example 1

[0025] A phosphate waste liquid treatment process in immobilized enzyme production includes the following steps:

[0026] (1) 60L phosphate waste liquid (phosphate content of 13.5g / L) is first introduced into a 15L cation resin column (macroporous adsorption resin C150) at a flow rate of 0.5BV / h, and the first effluent of 70L is introduced into a 15L anion resin column (macroporous adsorption resin D201) at a flow rate of 1BV / h, and the second effluent is collected for standby;

[0027] (2) 30L, 10wt% potassium hydroxide solution is used to elute the anion resin column at a flow rate of 1BV / h, and 20L of the desorption liquid is concentrated under the conditions of 50°C and vacuum degree of -0.092Mpa to obtain 4.0L of concentrated liquid with a solid content of 70wt%, which is then cooled to 20°C, filtered and washed (after stirring and removing impurities by suction filtration), and 300g of dipotassium hydrogen phosphate crystals and 2.0L of first mother liquor are collected respectively;

[0028] (3) 30L, 80wt% phosphoric acid solution is used to elute the cation resin column at a flow rate of 0.5BV / h, and 28L of the desorption liquid is concentrated to 20Poise, and then pH is adjusted to 8.5 by potassium hydroxide, and then the temperature is raised to 60°C and kept for 1h until white solid precipitates, and then the temperature is lowered to 20°C, and the filtrate is filtered and washed (after stirring and removing impurities by suction filtration), and 200g of dipotassium hydrogen phosphate crystals and 1.5L of second mother liquor are collected respectively;

[0029] (4) The first mother liquor of 2.0L in step (2) and the second mother liquor of 1.5L in step (3) are combined, and 2.8L of the filtrate is collected, and then pH is adjusted to 4.0 by phosphoric acid, and then the temperature is lowered to 20°C after the crystal precipitates, and then the filtrate is filtered and washed (after stirring and removing impurities by suction filtration), and then dried (temperature is 95°C) to obtain potassium dihydrogen phosphate product;

[0030] (5) 300g of dipotassium hydrogen phosphate crystals in step (2) and 200g of dipotassium hydrogen phosphate crystals in step (3) are combined, and then 0.5L of water is added for dissolution, and then decolorizing agent (the amount of activated carbon is 1% of the combined mass of potassium phosphate crystals) is added, and then stirred and suction filtered, and then 0.51L of the decolorized liquid is collected, and then suction filtered and dried (temperature is 80°C) to obtain dipotassium hydrogen phosphate product.

[0031] Example 2

[0032] A phosphate waste liquid treatment process in the production of immobilized enzyme, comprising the following steps:

[0033] (1) 60L phosphate waste liquid (phosphate content of 13.5g / L) is first introduced into a 15L cation resin column (macroporous adsorption resin C150) at a flow rate of 0.8BV / h, and the first effluent of 70L is introduced into a 15L anion resin column (macroporous adsorption resin D201) at a flow rate of 1.5BV / h, and the second effluent is collected for standby;

[0034] (2) 30L, 15wt% potassium hydroxide solution was used to elute the anion resin column at a flow rate of 1.5BV / h, and 28L of desorption solution was collected. Under the conditions of 55°C and vacuum degree of -0.094Mpa, the desorption solution was concentrated to obtain 3.65L of concentrated solution with solid content of 75wt%. Then the concentrated solution was cooled to 23°C, filtered, and washed (after stirring to remove impurities by adding ethanol, suction filtration). Potassium phosphate dibasic crystals 220g and the first mother liquor 1.2L were collected respectively;

[0035] (3) 1.8L, 82wt% phosphoric acid solution was used to elute the cation resin column at a flow rate of 0.8BV / h, and 28L of desorption solution was collected. The desorption solution was concentrated to 23Poise, and the pH was adjusted to 8.8 by potassium hydroxide. Then the solution was heated to 65°C and kept for 1.5h until white solids precipitated. After that, the solution was cooled to 23°C, filtered, and washed (after stirring to remove impurities by adding ethanol, suction filtration). Potassium phosphate dibasic crystals 220g and the second mother liquor 1.2L were collected respectively;

[0036] (4) The first mother liquor 1.8L in step (2) and the second mother liquor 1.2L in step (3) were combined, and the filtrate 2.8L was collected. The pH was adjusted to 4.2 by phosphoric acid, and the solution was concentrated until crystals precipitated. After that, the solution was cooled to 23°C, filtered, and washed (after stirring to remove impurities by adding ethanol, suction filtration), and dried (temperature was 95°C) to obtain potassium phosphate monobasic product;

[0037] (5) The potassium phosphate dibasic crystals 310g in step (2) and the potassium phosphate dibasic crystals 220g in step (3) were combined, and 0.53L of water was added to dissolve the crystals. Then decolorizing agent (the amount of activated carbon was 1.5% of the combined mass of potassium phosphate crystals) was added, and the solution was stirred and suction filtered. 0.55L of decolorized solution was collected, and then cooled to 25°C, suction filtered, and dried (temperature was 80°C) to obtain potassium phosphate dibasic product.

[0038] Example 3

[0039] A process for treating phosphate waste liquid in immobilized enzyme production, comprising the following steps:

[0040] (1) 60L of phosphate waste liquid (phosphate content was 13.5g / L) was first introduced into a 15L cation resin column (macroporous adsorption resin C150) at a flow rate of 1BV / h. The first effluent 70L was collected and then introduced into a 15L anion resin column (macroporous adsorption resin D201) at a flow rate of 2BV / h. The second effluent was collected for later use;

[0041] (2) 30L, 20wt% potassium hydroxide solution was used to elute the anion resin column at a flow rate of 2BV / h, and 20L of the desorption solution was collected. The solution was concentrated at 60°C under a vacuum of -0.094Mpa to obtain 3.5L of concentrated solution with a solid content of 80wt%. The concentrated solution was cooled to 25°C, filtered, and washed (ethanol was added to stir and remove impurities, and then suction filtration). Potassium phosphate dibasic crystals 330g and the first mother liquor 1.4L were collected, respectively;

[0042] (3) 30L, 83wt% phosphoric acid solution was used to elute the cation resin column at a flow rate of 1BV / h, and 20L of the desorption solution was collected. The solution was concentrated to 25Poise, and the pH was adjusted to 9 using potassium hydroxide. The solution was heated to 70°C and kept for 2h until white solids precipitated. The solution was cooled to 25°C, suction filtered, and washed (ethanol was added to stir and remove impurities, and then suction filtration). Potassium phosphate dibasic crystals 230g and the second mother liquor 1.0L were collected, respectively;

[0043] (4) The first mother liquor 1.4L in step (2) and the second mother liquor 1.0L in step (3) were combined, and 23L of filtrate was collected. The pH was adjusted to 4.3 using phosphoric acid, and the solution was concentrated until crystals precipitated. The solution was cooled to 25°C, suction filtered, washed (ethanol was added to stir and remove impurities, and then suction filtration), and dried (temperature was 95°C) to obtain potassium dihydrogen phosphate product;

[0044] (5) The potassium phosphate dibasic crystals 330g in step (2) and the potassium phosphate dibasic crystals 230g in step (3) were combined, and 0.56L of water was added to dissolve the crystals. Decolorizing agent (the amount of activated carbon was 2% of the combined mass of potassium phosphate crystals) was added, and the solution was stirred and suction filtered. 0.58L of decolorized solution was collected, cooled to 25°C, suction filtered, and dried (temperature was 80°C) to obtain potassium phosphate dibasic product.

[0045] Example 4

[0046] A process for treating phosphate waste liquid in immobilized enzyme production, comprising the following steps:

[0047] (1) 60L of phosphate waste liquid (phosphate content was 13.5g / L) was first introduced into a 15L cation resin column (macroporous adsorption resin C150) at a flow rate of 1.2BV / h. The first effluent 70L was collected and then introduced into a 15L anion resin column (macroporous adsorption resin D201) at a flow rate of 2.5BV / h. The second effluent was collected for later use;

[0048] (2) The anion exchange resin column was eluted with 30L of 25wt% potassium hydroxide solution at a flow rate of 2.5BV / h. 20L of the desorption solution was collected and concentrated at 65℃ and vacuum degree -0.094Mpa to obtain 3.3L of concentrate with a solid content of 85wt%. The concentrate was then cooled to 28℃, filtered, and washed (ethanol was added and stirred to remove impurities before vacuum filtration). 305g of dipotassium hydrogen phosphate crystals and 1.35L of the first mother liquor were collected respectively.

[0049] (3) The cation exchange resin column was eluted with 30L of 84wt% phosphoric acid solution at a flow rate of 1.2BV / h. 28L of the desorption solution was collected and concentrated to 28 Pomer. The pH was adjusted to 9.2 with potassium hydroxide, and then the temperature was raised to 75℃ and kept at this temperature for 2.5h until a white solid precipitated. The temperature was then lowered to 28℃, filtered, and washed (ethanol was added and stirred to remove impurities before filtration). 215g of dipotassium hydrogen phosphate crystals and 0.95L of the second mother liquor were collected respectively.

[0050] (4) Combine the 1.35L first mother liquor from step (2) and the 0.95L second mother liquor from step (3), filter and collect 2.2L of filtrate, adjust the pH to 4.3 with phosphoric acid, concentrate until crystals precipitate, then cool to 28℃, filter, wash (add ethanol, stir to remove impurities, then filter), and dry (at 95℃) to obtain potassium dihydrogen phosphate product;

[0051] (5) Combine the 315g of dipotassium hydrogen phosphate crystals from step (2) and the 215g of dipotassium hydrogen phosphate crystals from step (3), dissolve them in 0.53L of water, add a decolorizing agent (the amount of activated carbon is 2.5% of the mass of the combined potassium phosphate crystals), stir, filter, collect 0.54L of the decolorizing liquid, cool it to 25℃, filter, and dry it (at 80℃) to obtain the dipotassium hydrogen phosphate product.

[0052] Example 5

[0053] A process for treating phosphate waste liquid in immobilized enzyme production includes the following steps:

[0054] (1) 60L of phosphate waste liquid (phosphate content is 13.5g / L) is first fed into a 15L cation exchange resin column (macroporous adsorption resin C150) at a flow rate of 1.5BV / h. The collected first effluent of 70L is then fed into a 15L anion exchange resin column (macroporous adsorption resin D201) at a flow rate of 3BV / h. The collected second effluent is reserved for later use.

[0055] (2) 30L, 30wt% potassium hydroxide solution was used to elute the anion resin column at a flow rate of 3BV / h, and 20L of the desorption solution was collected. The desorption solution was concentrated at 70°C under a vacuum of -0.094Mpa to obtain 3.1L of concentrated solution with a solid content of 90wt%. The concentrated solution was cooled to 30°C, filtered, and washed (after stirring to remove impurities by adding ethanol, suction filtration). Dipotassium hydrogen phosphate crystals 310g and the first mother liquor 1.20L were collected, respectively;

[0056] (3) 30L, 84wt% phosphoric acid solution was used to elute the cation resin column at a flow rate of 1.5BV / h, and 28L of the desorption solution was collected. The desorption solution was concentrated to 30Poise, and the pH was adjusted to 9.5 by potassium hydroxide. The solution was heated to 80°C and kept for 3h until white solids precipitated. The solution was cooled to 30°C, filtered, and washed (after stirring to remove impurities by adding ethanol, suction filtration). Dipotassium hydrogen phosphate crystals 200g and the second mother liquor 0.90L were collected, respectively;

[0057] (4) The first mother liquor 1.2L in step (2) and the second mother liquor 0.90L in step (3) were combined, and the 2.0L filtrate was collected. The pH was adjusted to 4.5 by phosphoric acid, and the solution was concentrated until crystals precipitated. The solution was cooled to 30°C, filtered, and washed (after stirring to remove impurities by adding ethanol, suction filtration), and dried (at a temperature of 95°C) to obtain potassium dihydrogen phosphate product;

[0058] (5) The dipotassium hydrogen phosphate crystals 310g in step (2) and the dipotassium hydrogen phosphate crystals 200g in step (3) were combined, and 0.51L of water was added to dissolve the crystals. Then, a decolorizing agent (the amount of activated carbon was 3% of the combined mass of the potassium phosphate crystals) was added, and the solution was stirred, filtered, and collected. The 0.53L decolorized solution was cooled to 25°C, filtered, and dried (at a temperature of 80°C) to obtain dipotassium hydrogen phosphate product.

[0059] To better prove that the treatment process of the present application can effectively treat the phosphate waste liquid and simultaneously obtain high-content, high-purity, and high-yield potassium dihydrogen phosphate and dipotassium hydrogen phosphate products, eight comparative examples were given with reference to Example 3. The yield, yield, and purity of potassium dihydrogen phosphate and dipotassium hydrogen phosphate in Examples 1-5 and Comparative Examples 1-8 are shown in Table 1.

[0060] Comparative Example 1

[0061] Different from Example 3, the phosphate waste liquid in step (1) entered the cation resin column at a flow rate of 2BV / h, and the first effluent entered the anion resin column at a flow rate of 3BV / h. The remaining operations were the same.

[0062] Comparative Example 2

[0063] Different from example 3, the filler in the cation resin column in step (1) is strong acid cation exchange resin D67; the filler in the anion resin column is weak base anion exchange resin D301.

[0064] Comparative example 3

[0065] Different from example 3, in step (2), the potassium hydroxide solution elutes the anion resin column at a flow rate of 4 BV / h, and the rest of the operations are the same.

[0066] Comparative example 4

[0067] Different from example 3, in step (3), the phosphoric acid solution elutes the cation resin column at a flow rate of 2 BV / h, and the rest of the operations are the same.

[0068] Comparative example 5

[0069] Different from example 3, in step (3), potassium hydroxide is used to adjust the pH to 7.5, and the rest of the operations are the same.

[0070] Comparative example 6

[0071] Different from example 3, in step (4), phosphoric acid is used to adjust the pH to 5, and the rest of the operations are the same.

[0072] Comparative example 7

[0073] Different from example 3, in step (4), phosphoric acid is used to adjust the pH to 3.5, and the rest of the operations are the same.

[0074] Comparative example 8

[0075] Different from example 3, in step (3), the desorption solution is concentrated to 40 poise, and the rest of the operations are the same.

[0076] Table 1

[0077]

[0078] From the data in Table 1, it can be found that the yield, recovery rate and purity of dipotassium hydrogen phosphate and potassium dihydrogen phosphate obtained by the treatment process of examples 1-5 of the present application are better than those of comparative examples 1-8.

[0079] The above description is only the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A process for treatment of phosphate waste liquor in immobilized enzyme production, characterized by, The treatment process comprises the following steps: (1) The phosphate waste liquid first enters a cation resin column, the first effluent collected is then introduced into an anion resin column, and the second effluent collected is reserved; the phosphate waste liquid is introduced into the cation resin column at a flow rate of 0.5-1.5 BV / h, and the first effluent is introduced into the anion resin column at a flow rate of 1-3 BV / h; the filler in the cation resin column is macroporous adsorption resin-C150; and the filler in the anion resin column is macroporous adsorption resin-D201; (2) The anion resin column is eluted with a potassium hydroxide solution, the desorption liquid collected is concentrated, cooled, filtered and washed, and the potassium hydrogen phosphate crystals and the first mother liquor are collected respectively; the potassium hydroxide solution is introduced into the anion resin column at a flow rate of 1-3 BV / h; (3) The cation resin column is eluted with a phosphoric acid solution, the desorption liquid collected is concentrated, potassium hydroxide is added to adjust the pH to 8.5-9.5, the temperature is increased, and after the white solid is precipitated, the temperature is decreased, and the potassium hydrogen phosphate crystals and the second mother liquor are collected respectively; the phosphoric acid solution is introduced into the cation resin column at a flow rate of 0.5-1.5 BV / h; (4) The first mother liquor in step (2) and the second mother liquor in step (3) are combined, the filtrate collected is adjusted to a pH of 4.0-4.5 with phosphoric acid, concentrated until the crystals are precipitated, cooled, filtered, washed and dried to obtain the potassium dihydrogen phosphate product; (5) The potassium hydrogen phosphate crystals in step (2) and the potassium hydrogen phosphate crystals in step (3) are combined, dissolved in water, and then a decolorizing agent is added, stirred, filtered, and the decolorized liquid is cooled, filtered and dried to obtain the potassium hydrogen phosphate product.

2. The process for treatment of phosphate waste liquor in immobilized enzyme production according to claim 1, characterized in that, The concentration of the potassium hydroxide solution in step (2) is 10-30 wt%.

3. The process for treatment of phosphate waste liquor in immobilized enzyme production according to claim 1, characterized in that, The desorption liquid in step (2) is concentrated to a solid content of 70-90 wt% and then cooled to 20-30°C.

4. The process as claimed in claim 1, wherein the process is characterized by, The concentration of the phosphoric acid solution in step (3) is 80-85 wt%.

5. The process as claimed in claim 1, wherein the process is characterized by, In step (3), the effluent is concentrated to 20-30 poise, then the temperature is increased to 60-80°C, and after the white crystals are precipitated, the temperature is decreased to 20-30°C.

6. The process as claimed in claim 1, wherein the process is characterized by, In step (4), the filtrate collected after the first mother liquor and the second mother liquor are combined and filtered is concentrated until the crystals are precipitated, and then cooled to 20-30°C.

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