Method for recycling calcium salt slag in calcium pantothenate synthesis process

Abstract

The invention provides a method for recycling calcium salt slag in a calcium pantothenate synthesis process, which comprises the following steps: 1) carrying out solvent removal on the calcium salt slag by using a horizontal double-shaft dryer to obtain dealcoholized calcium salt slag powder; 2) pulping and mixing the calcium salt slag powder and water to obtain calcium salt slag water slurry; 3) reacting the calcium salt slag aqueous solution with sulfuric acid to obtain a neutralization solution; 4) carrying out solid-liquid separation on the neutralized liquid to obtain calcium sulfate residues and a beta-aminopropionic acid aqueous solution; 5) carrying out continuous decompression dehydration concentration on the beta-aminopropionic acid aqueous solution to obtain a concentrated solution and water; returning the water to the step 2) for mechanical application; (6) cooling and crystallizing the concentrated solution, and centrifugally separating to obtain a beta-aminopropionic acid wet product and a mother solution; and returning the mother liquor to the step (5) for mechanical application. According to the method, residual calcium propionate and methanol in the calcium salt slag can be recycled, the material utilization rate is increased, and the production cost is reduced; and after residual organic matters in the calcium salt slag are completely recovered, the total amount of dangerous solid wastes is greatly reduced, so that the solid waste treatment cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of calcium salt slag treatment, and in particular relates to a method for recovering and reusing calcium salt slag in a process of synthesizing calcium pantothenate. Background Art

[0002] Calcium pantothenate is mainly used in medicine, food and feed additives. It participates in the metabolism of carbohydrates, fats and proteins. It is an indispensable trace substance for humans and animals to maintain normal physiological functions. More than 70% of it is used as a feed additive. In recent years, my country's feed industry has developed rapidly, and the demand for calcium pantothenate has also increased accordingly. The feed industry alone has an annual demand of no less than 50,000 tons. Therefore, the development prospects are very broad, with good domestic and foreign market prospects and extremely high economic benefits.

[0003] During the synthesis of calcium pantothenate, the main reaction is the condensation reaction of calcium β-aminopropionate and left ester to produce calcium pantothenate. Calcium β-aminopropionate, one of the main raw materials for synthesis, is produced by the reaction of β-aminopropionic acid and calcium oxide in a methanol system to produce calcium β-aminopropionate. After solid-liquid separation, a methanol solution of calcium β-aminopropionate is obtained. The calcium β-aminopropionate solution is then used in the next step to undergo an acylation reaction with the left ester to produce calcium pantothenate. The remaining insoluble calcium salt slag is collected and discharged as hazardous waste. In addition to excess calcium hydroxide and calcium oxide, the calcium salt slag also contains some calcium β-aminopropionate residues from the separation, as well as a large amount of methanol, which results in material waste and certain pollution to the environment. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a method for recovering and reusing calcium salt residue in the process of synthesizing calcium pantothenate, which can recover calcium β-alanine and methanol, improve material utilization and reduce production costs.

[0005] The present invention provides a method for recovering and reusing calcium salt residue in a process of synthesizing calcium pantothenate, comprising the following steps:

[0006] 1) removing the solvent from the calcium salt slag by a horizontal double-shaft dryer to obtain dealcoholized calcium salt slag powder;

[0007] 2) mixing the calcium salt slag powder and water to obtain calcium salt slag water slurry;

[0008] 3) reacting the calcium salt slag aqueous solution with sulfuric acid to obtain a neutralized solution;

[0009] 4) separating the neutralized liquid from the solid to obtain calcium sulfate slag and β-alanine aqueous solution;

[0010] 5) continuously decompressing and dehydrating the β-alanine aqueous solution to obtain a concentrate and water; the water is returned to step 2) for reuse;

[0011] 6) Cooling the concentrated solution for crystallization and centrifuging to obtain a wet product of β-alanine and a mother liquor; the mother liquor is returned to step 5) for application.

[0012] Preferably, the calcium salt slag comprises 30-50% methanol, 5-20% calcium β-alanine and 25-45% alkaline substances;

[0013] The alkaline substance includes calcium oxide and calcium hydroxide.

[0014] Preferably, the temperature for the reaction of the calcium salt slag aqueous solution and sulfuric acid is 40-100° C., and the pH value at the end point of the reaction is 6-8.

[0015] Preferably, the temperature for solvent removal is 60-130°C.

[0016] Preferably, the continuous reduced pressure dehydration concentration is carried out in a falling film evaporator; the heating residence time is less than 10 seconds, the concentration is 55-63%, the vacuum degree is -0.070MPa to -0.095MPa, and the temperature is 70-95°C.

[0017] Preferably, the terminal temperature of crystallization is 20-30° C., and the crystallization time is 3-5 h.

[0018] Preferably, in step 2), the mass ratio of water to calcium salt slag powder is 1 to 2:1.

[0019] Preferably, the methanol obtained by solvent removal is directly transported to the methanol raw material system in the synthesis of calcium β-alanine for application.

[0020] Preferably, the wet β-alanine is dried at 80-90° C. for 55-65 min to obtain β-alanine.

[0021] The present invention provides a method for recycling calcium salt slag in the process of synthesizing calcium pantothenate, comprising the following steps: 1) removing the solvent from the calcium salt slag by a horizontal double-shaft dryer to obtain a calcium salt slag powder after dealcoholization; 2) mixing the calcium salt slag powder with water by beating and mixing to obtain a calcium salt slag water slurry; 3) reacting the calcium salt slag aqueous solution with sulfuric acid to obtain a neutralized solution; 4) separating the neutralized solution from solid to liquid to obtain calcium sulfate slag and a β-alanine aqueous solution; 5) continuously decompressing and dehydrating the β-alanine aqueous solution to obtain a concentrated solution and water; the water is returned to step 2) for application; 6) cooling and crystallizing the concentrated solution, centrifuging to obtain a β-alanine wet product and a mother liquor; the mother liquor is returned to step 5) for application. The above method can recover the calcium propionate and methanol remaining in the calcium salt slag, improve material utilization, and reduce production costs; after the organic matter remaining in the calcium salt slag is completely recovered, the total amount of hazardous solid waste is greatly reduced, thereby reducing the cost of solid waste treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of the process of recycling calcium salt slag in the process of synthesizing calcium pantothenate provided by the present invention;

[0023] Figure 2 This is a liquid chromatogram of β-alanine recovered in Example 1 of the present invention. DETAILED DESCRIPTION

[0024] The present invention provides a method for recovering and reusing calcium salt residue in a process of synthesizing calcium pantothenate, comprising the following steps:

[0025] 1) removing the solvent from the calcium salt slag by a horizontal double-shaft dryer to obtain dealcoholized calcium salt slag powder;

[0026] 2) mixing the calcium salt slag powder and water to obtain calcium salt slag water slurry;

[0027] 3) reacting the calcium salt slag aqueous solution with sulfuric acid to obtain a neutralized solution;

[0028] 4) separating the neutralized liquid from the solid to obtain calcium sulfate slag and β-alanine aqueous solution;

[0029] 5) continuously decompressing and dehydrating the β-alanine aqueous solution to obtain a concentrate and water; the water is returned to step 2) for reuse;

[0030] 6) Cooling the concentrated solution for crystallization and centrifuging to obtain a wet product of β-alanine and a mother liquor; the mother liquor is returned to step 5) for application.

[0031] The method provided by the present invention recovers the calcium propionate and methanol remaining in the calcium salt slag, thereby improving material utilization and reducing production costs; after the residual organic matter in the calcium salt slag is completely recovered, the total amount of hazardous solid waste is greatly reduced, thereby reducing the cost of solid waste treatment.

[0032] The present invention uses a horizontal double-axis dryer to remove the solvent from the calcium salt slag to obtain a dealcoholized calcium salt slag powder. The calcium salt slag in the present invention includes 30-50wt% methanol, 5-20wt% calcium β-alanine and 25-45wt% alkaline substances; the alkaline substances include calcium oxide and calcium hydroxide. The present invention uses a double-axis dryer to remove the solvent, that is, methanol removal; the temperature for solvent removal is 60-130°C, preferably 60-110°C, and more preferably 85-95°C. In a specific embodiment, the temperature for solvent removal is 60°C, 85°C or 110°C. The double-axis dryer used in the present invention is low in cost and does not involve secondary separation.

[0033] The present invention recovers evaporated gaseous methanol through a condenser, and the recovered methanol is directly transported to a methanol raw material system in the synthesis of calcium beta-alanine for application.

[0034] After obtaining the calcium salt slag powder, the present invention mixes the calcium salt slag powder and water by beating to obtain calcium salt slag water slurry. The present invention directly discharges the dealcoholized calcium salt slag powder into a calcium salt slag mixing kettle filled with water, and mixes it by beating with water; the mass ratio of water to calcium salt slag powder is 1 to 2:1, preferably 1.2 to 1.8:1, and more preferably 1.5:1.

[0035] In the present invention, the calcium salt slag aqueous solution is reacted with sulfuric acid to obtain a neutralized solution. The reaction temperature is 40 to 100°C, preferably 50 to 80°C; the pH value at the reaction end point is 6 to 8, preferably 6.5 to 7.5; and the mass concentration of sulfuric acid used is 98%. In a specific embodiment, the reaction temperature is 50°C, and the pH value at the reaction end point is 7.2.

[0036] The present invention separates the neutralized liquid into solid and liquid to obtain calcium sulfate slag and a β-alanine aqueous solution. The present invention preferably uses a scraper centrifuge for solid-liquid separation; the scraper centrifuge is a vertical scraper centrifuge or a horizontal scraper centrifuge. The present invention detects by chromatography (the detection instrument is HPLC1260, the detection wavelength Wavelength = 200nm) that the β-alanine chromatographic content in the β-alanine aqueous solution is greater than 98%.

[0037] The present invention continuously decompresses and dehydrates the β-alanine aqueous solution to obtain a concentrate and water; the water is returned to step 2) for application. The continuous decompression and dehydration concentration is carried out in a falling film evaporator; the heating residence time is less than 10 seconds, and the concentration is 58-63%, the vacuum degree is -0.070MPa to -0.095MPa, and the temperature is 70-95°C. In a specific embodiment, the vacuum degree is -0.09MPa and the temperature is 90°C. The present invention uses a falling film evaporator to carry out decompression and dehydration continuously.

[0038] The present invention obtains concentrated liquid at the outlet of the falling film evaporator; the concentrated liquid is cooled and crystallized, and centrifuged to obtain a wet product of β-alanine and a mother liquor; the mother liquor is returned to step 5) for application. The present invention performs cooling crystallization in a crystallization kettle; the terminal temperature of the crystallization is 20 to 30° C., and the crystallization time is 3 to 5 hours.

[0039] The crystallized material is separated by centrifugation to obtain a wet product of β-alanine, which is preferably dried in a fluidized bed dryer to obtain β-alanine; the drying time is preferably 55 to 65 minutes, and the drying temperature is preferably 80° C. to 90° C. The β-alanine composition is detected by chromatography (the detection instrument is HPLC1260, and the detection wavelength Wavelength=200 nm), and the chromatographic content of β-alanine is greater than 99%.

[0040] The mother liquor can be returned to step 5) for application, and the content of β-alanine in the mother liquor is detected to be greater than 90%. The chromatographic content of β-alanine is greater than 99% by using a chromatographic instrument (HPLC1260, wavelength = 200 nm) to detect the composition of β-alanine.

[0041] In order to further illustrate the present invention, a method for recovering and applying calcium salt residue in a process of synthesizing calcium pantothenate provided by the present invention is described in detail below in conjunction with embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0042] Example 1

[0043] 1) a certain amount of calcium salt residue filtered in the synthesis process of calcium β-alanine is continuously pumped into a horizontal double-shaft dryer by a screw feed pump for heating and evaporation to recover methanol;

[0044] 2) Control the heating temperature of the heat medium in the horizontal double-shaft dryer and control the internal temperature of the heated material at 85°C;

[0045] 3) The methanol evaporated from the vapor phase is cooled and collected by the condensation system to obtain a methanol condensate with a methanol content greater than 99%, a methanol water content less than 0.5%, and a methanol recovery rate of 98%. The quality of the methanol meets the requirements of the raw material methanol and can be returned to the synthesis process of calcium β-alanine for application;

[0046] 4) After dealcoholization, the calcium salt slag powder is continuously discharged into a mixing kettle containing dilution water through a gear pump at the tail end of the horizontal double-shaft dryer;

[0047] 5) The amount of mixing water is 1.5 times the mass of the calcium salt slag after dealcoholization, and the liquid phase temperature of the mixing kettle is controlled at 40°C;

[0048] 6) Add 98% concentrated sulfuric acid for neutralization, the neutralization temperature is controlled at 40°C-50°C, and the end point pH is 7.2;

[0049] 7) The calcium sulfate precipitated during the neutralization process is separated into solid and liquid by a horizontal scraper centrifuge to obtain an aqueous solution containing β-alanine, and the β-alanine composition is detected by chromatography (the detection instrument is HPLC1260, and the detection wavelength Wavelength = 200 nm), and the chromatographic content of β-alanine is 99.5%;

[0050] 8) The aqueous solution of β-alanine is continuously concentrated and dehydrated by a falling film evaporator at a vacuum degree of -0.095 MPa, and the heating residence time is less than 10 seconds. The concentrated material is collected in a crystallization kettle, and the liquid phase temperature at the concentrated outlet is controlled at 85° C. The β-alanine content in the outlet material is about 55%;

[0051] 9) The cooling time of a single batch of crystallization materials is controlled within 5 hours, and the terminal crystallization temperature is 20°C;

[0052] 10) separating the crystallized material into solid and liquid by a horizontal scraper centrifuge to obtain a wet β-alanine and a β-alanine mother liquor;

[0053] 11) The wet β-alanine was dried in a fluidized bed dryer at 85°C for 1 hour to obtain the finished β-alanine. The mass content of β-alanine was detected to be 95%. The composition of β-alanine was detected by chromatography (the detection instrument was HPLC1260, the detection wavelength was Wavelength = 200nm). The detection result showed that the chromatographic content of β-alanine was greater than 99% (see Figure 2 ), the single β-alanine recovery rate was 55%;

[0054] 12) The β-alanine mother liquor separated in step 10) is returned to step 8) for recycling, and the total recovery rate of β-alanine after multiple recycling is 96%.

[0055] Example 2

[0056] The difference from Example 1 is that the temperature of the heated material in the horizontal double-axis dryer is controlled at 110°C, the recovered methanol content is greater than 99%, the methanol moisture is less than 0.5%, and the methanol recovery rate is 99%; the amount of mixed water before sulfuric acid neutralization is 1.5 times the mass of the calcium salt slag, the neutralization endpoint pH value is 6.5, the obtained β-aminopropionic acid aqueous solution has a chromatographic content of 95.5%, and after concentration, dehydration and crystallization, the β-aminopropionic acid mass content is 94% after drying, the β-aminopropionic acid chromatographic content is 99%, the single β-aminopropionic acid recovery rate is 50%, and the total recovery rate of β-aminopropionic acid after the crystallization mother liquor is applied is 91%.

[0057] Example 3

[0058] The difference from Example 1 is that the temperature of the heated material in the horizontal twin-shaft dryer is controlled at 60°C, the recovered methanol content is greater than 99%, the methanol moisture is less than 0.5%, the methanol recovery rate is 80%, the neutralization endpoint pH value is 7, the obtained β-aminopropionic acid aqueous solution has a chromatographic content of 99.4%, the concentration and dehydration outlet temperature is controlled at 70°C, the β-aminopropionic acid content is detected after crystallization and drying, and the single β-aminopropionic acid recovery rate is 45%, and the total recovery rate of β-aminopropionic acid after the crystallization mother liquor is applied is 95%.

[0059] Comparative Example 1

[0060] The difference from Example 1 is that a horizontal twin-shaft dryer is not used, and methanol is directly distilled and recovered in a kettle after dilution with 2 times the volume of water. The terminal temperature of the heated material for recovering methanol from the calcium salt slag aqueous solution is controlled at 100°C, the moisture content of the recovered methanol is 0.5%, the methanol recovery rate is 90%, the process flow is increased, and the steam energy consumption is greatly increased.

[0061] Comparative Example 2

[0062] The difference from Example 1 is that the β-alanine is concentrated and dehydrated by a vacuum autoclave, the terminal temperature of the concentrated material is 85°C, the β-alanine content is detected after crystallization and drying, and the β-alanine content is 93.6%, the β-alanine chromatographic content is 97.5%, and the total recovery rate of β-alanine is 88% after application.

[0063] As can be seen from the above embodiments, the present invention provides a method for recycling calcium salt slag in the process of synthesizing calcium pantothenate, comprising the following steps: 1) removing the solvent from the calcium salt slag using a horizontal double-axis dryer to obtain a calcium salt slag powder after dealcoholization; 2) mixing the calcium salt slag powder with water to obtain a calcium salt slag water slurry; 3) reacting the calcium salt slag aqueous solution with sulfuric acid to obtain a neutralized solution; 4) separating the neutralized solution from solid to liquid to obtain calcium sulfate slag and a β-aminopropionic acid aqueous solution; 5) continuously decompressing and dehydrating the β-aminopropionic acid aqueous solution to obtain a concentrated solution and water; the water is returned to step 2) for application; 6) cooling and crystallizing the concentrated solution, centrifuging to obtain a β-aminopropionic acid wet product and a mother liquor; the mother liquor is returned to step 5) for application. The above method can recover the calcium propionate and methanol remaining in the calcium salt slag, improve material utilization, and reduce production costs; after the organic matter remaining in the calcium salt slag is completely recovered, the total amount of hazardous solid waste is greatly reduced, thereby reducing the cost of solid waste treatment.

[0064] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for recovering and reusing calcium salt residue in a process of synthesizing calcium pantothenate, comprising the following steps: 1) removing the solvent from the calcium salt slag by a horizontal double-shaft dryer to obtain dealcoholized calcium salt slag powder; 2) mixing the calcium salt slag powder and water to obtain calcium salt slag water slurry; 3) reacting the calcium salt slag aqueous solution with sulfuric acid to obtain a neutralized solution; 4) separating the neutralized liquid from the solid to obtain calcium sulfate slag and β-alanine aqueous solution; 5) continuously decompressing and dehydrating the β-alanine aqueous solution to obtain a concentrate and water; the water is returned to step 2) for reuse; 6) Cooling the concentrated solution for crystallization and centrifuging to obtain a wet product of β-alanine and a mother liquor; the mother liquor is returned to step 5) for application.

2. The method according to claim 1, characterized in that: The calcium salt slag comprises 30-50% methanol, 5-20% calcium β-alanine and 25-45% alkaline substances; The alkaline substance includes calcium oxide and calcium hydroxide.

3. The method according to claim 1, characterized in that The temperature of the reaction of the calcium salt slag aqueous solution and sulfuric acid is 40-100° C., and the pH value at the end point of the reaction is 6-8.

4. The method according to claim 1, characterized in that The temperature for solvent removal is 60-130°C.

5. The method according to claim 1, characterized in that The continuous reduced pressure dehydration concentration is carried out in a falling film evaporator; the heating residence time is less than 10 seconds, the concentration is 55-63%, the vacuum degree is -0.070MPa--0.095MPa, and the temperature is 70-95°C.

6. The method according to claim 1, characterized in that The terminal temperature of crystallization is 20-30°C, and the crystallization time is 3-5h.

7. The method according to claim 1, characterized in that In step 2), the mass ratio of water to calcium salt slag powder is 1 to 2:

1.

8. The method according to claim 1, characterized in that The methanol obtained by solvent removal is directly transported to the methanol raw material system in the synthesis of calcium β-alanine for application.

9. The method according to claim 1, characterized in that: The wet β-alanine product is dried at 80-90° C. for 55-65 min to obtain β-alanine.

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