A method for resource recovery of disodium tetraborate decahydrate from waste salt

Abstract

This invention provides a method for recovering disodium tetraborate decahydrate from waste salt. The waste salt contains borates, chlorides, and organic matter. The method includes the following steps: S1, dissolving the waste salt in water at 60-85°C to form a waste salt solution; then hot-filtering the waste salt solution to obtain a clear hot solution; S2, removing the organic matter from the clear hot solution using an adsorbent and performing precision filtration to obtain a filtrate; S3, freezing and crystallizing the filtrate at a cooling rate of 0.5-5°C / h, and separating the resulting wet crystals; S4, post-processing the wet crystals to obtain the borate product. This method has a reasonable process flow, high separation efficiency, and high product yield; furthermore, the recovered product has high purity.

Description

Technical Field

[0001] This invention belongs to the field of industrial solid waste resource utilization and green chemistry technology, and specifically relates to a method for resource utilization of disodium tetraborate decahydrate from waste salt. Background Technology

[0002] In the production of high-end active pharmaceutical ingredients (APIs) such as anti-AIDS and anti-malarial drugs, sodium borohydride is often used as a reducing agent in key synthetic steps (e.g., reducing the intermediate CME). After the reaction is completed, the main product is separated through acidification, neutralization, and extraction. Simultaneously, a large amount of solid waste salt with specific components is generated. This waste salt mainly originates from sodium ions, unreacted borate ions (existing as hydrolysis products of sodium borohydride), and chloride ions in the reaction system; sodium and chloride ions are introduced during pH adjustment by adding acids and bases (such as hydrochloric acid and sodium hydroxide). The typical composition of this waste salt is approximately 60%-80% disodium tetraborate decahydrate, 15%-35% sodium chloride, and approximately 5% or less organic matter and other impurities. The organic matter is complex and may include API synthesis intermediates, byproducts, and residual solvents such as ethanol used in the process.

[0003] Such waste salts are typically classified as hazardous waste because they contain active pharmaceutical ingredients or similar organic compounds. Incineration or landfill disposal is not only costly and environmentally burdensome, but also represents a significant waste of valuable boron and sodium resources. Disodium tetraborate decahydrate is an important basic chemical product; high-purity recovery from waste salts could transform waste into a valuable resource.

[0004] Existing processes for extracting borates from natural boron ore or salt lake brine are primarily designed for inorganic impurities (such as calcium, magnesium, and sulfate), with limited ability to remove complex organic matter. Conventional industrial waste salt resource recovery technologies (such as simple recrystallization and high-temperature calcination) face significant challenges when applied to this specific waste salt: 1) Simple recrystallization struggles to effectively separate sodium chloride, which has a similar solubility to disodium tetraborate decahydrate, and cannot deeply remove specific organic matter that affects product color and safety; 2) High-temperature treatment may lead to carbonization of organic matter or the generation of toxic gases, and may cause disodium tetraborate decahydrate to lose water, making it impossible to obtain the target product.

[0005] Therefore, there is an urgent need to develop a specialized method that can effectively and economically produce sodium tetraborate decahydrate that meets national standards from such pharmaceutical waste salts, thereby addressing the challenges of sodium chloride separation and deep removal of specific pharmaceutical organic compounds. This method has pressing practical significance and significant environmental and economic value. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies in recovering borates from specific pharmaceutical waste salts, this invention provides a method for recovering disodium tetraborate decahydrate from waste salts. This method has a reasonable process flow, high separation efficiency, and high product yield. Furthermore, the recovered product has high purity.

[0007] The present invention achieves the above objectives through the following technical solutions:

[0008] This invention provides a method for resource recovery of disodium tetraborate decahydrate from waste salt, wherein the waste salt comprises borates, chlorides, and organic matter; the method includes the following steps:

[0009] S1. Dissolve the waste salt in water at 60-85℃ to form a waste salt solution; then perform hot filtration on the waste salt solution to obtain a clear hot solution;

[0010] S2. Remove organic matter from the clarified hot solution using an adsorbent and perform precision filtration to obtain filtrate;

[0011] S3. The filtrate is subjected to freeze crystallization at a cooling rate of 0.5-5℃ / h, and wet crystals are obtained after separation; the final temperature of the freeze crystallization is 0-40℃.

[0012] S4. Post-process the wet crystals to obtain disodium tetraborate decahydrate product.

[0013] In this invention, the waste salt may optionally originate from the production process of raw materials for anti-AIDS drugs or anti-malarial drugs. The waste salt contains a recyclable borate, specifically disodium tetraborate decahydrate (Na₂B₄O₇·10H₂O, or disodium tetraborate decahydrate). Alternatively, the method of this invention can also recycle disodium tetraborate pentahydrate (Na₂B₄O₇·5H₂O, or disodium tetraborate pentahydrate) or anhydrous disodium tetraborate (Na₂B₄O₇) from the waste salt.

[0014] In some embodiments, the waste salt includes waste salt generated during the preparation of the active pharmaceutical ingredient using the sodium borohydride reduction method. Generally, the waste salt is generated as follows: anhydrous ethanol is added to the raw material CME for dissolution, followed by the addition of boric acid and sodium borohydride for a reduction reaction, then hydrochloric acid and sodium hydroxide are added to adjust the pH value, and finally the waste salt is separated by centrifugation.

[0015] In a specific embodiment, the content of borate in the waste salt is 60%-80%, the content of chloride is 15%-35%, and the content of organic matter is 3%-7%; wherein, % is the mass percentage of each component to the waste salt.

[0016] In one embodiment, the waste salt contains 60%-80% disodium tetraborate decahydrate, 15%-35% sodium chloride, and 3%-7% organic matter; where % represents the mass percentage of each component to the waste salt.

[0017] In step S1 of this invention, hot water selective dissolution and primary filtration are used to initially separate the target substance from insoluble impurities. During this process, the temperature of the water used to dissolve the waste salt needs to be controlled, and hot filtration is required to avoid incomplete dissolution of the waste salt, which would reduce the product yield.

[0018] In some implementations, step S1 satisfies the following condition:

[0019] i. Dissolve the waste salt in water at 70-80℃;

[0020] ii. The temperature of the heat filtration is 70-80℃;

[0021] iii. In the waste salt solution, the mass ratio of the waste salt to the water is 1:(3-5); wherein the mass ratio of the waste salt to the water is at least 1:3, so that the waste salt is completely dissolved in the water; at the same time, the amount of water used is controlled to reduce the time and energy consumption of subsequent processes.

[0022] In some embodiments, in step S2, the adsorbent includes powdered activated carbon; activated carbon can efficiently and deeply remove characteristic drug organic matter, and has better impurity removal efficiency.

[0023] In a specific embodiment, the specific surface area of ​​the powdered activated carbon is ≥600 m². 2 / g.

[0024] In a specific embodiment, the specific pore volume of the powdered activated carbon is ≥0.4 cm³. 3 / g.

[0025] In a specific embodiment, the volume percentage of the powdered activated carbon with a pore size of 2-50 nm is ≥50%.

[0026] In a specific embodiment, the particle size of the powdered activated carbon is ≥200 mesh.

[0027] In a specific embodiment, the chloride content in the powdered activated carbon is ≤0.5%.

[0028] In step S2 of the present invention, in order to fully remove organic matter, preferably, a gradient adsorption method is used to remove organic matter from the clarified hot solution using the adsorbent.

[0029] In some embodiments, step S2, the process of removing organic matter from the clarified hot solution using the adsorbent, includes: first cooling the clarified hot solution from step S1 to 50-65°C, adding the adsorbent for a first adsorption; then heating it to 70-80°C, adding the adsorbent for a second adsorption.

[0030] The primary adsorption targets pharmaceutical intermediates and byproducts with large molecular weight and strong polarity; the secondary adsorption targets small molecules, volatile or non-polar organic compounds (such as solvents such as ethanol that may remain); the combination of primary and secondary adsorption achieves the effect of deep impurity removal.

[0031] In a specific embodiment, during the first adsorption, the mass ratio of the added adsorbent to the clarified hot solution is 0.5%-1.5%; the stirring time for the first adsorption is 20-40 min; during the second adsorption, the mass ratio of the added adsorbent to the clarified hot solution is 0.2%-0.5%; the stirring time for the second adsorption is 10-20 min.

[0032] In step S2 of the present invention, after removing organic matter with an adsorbent, the filtrate is subjected to precision filtration while hot. That is, the precision filtration is carried out under the temperature conditions of secondary adsorption to completely remove the adsorbent and the adsorbed organic matter, and obtain a colorless or nearly colorless clear solution.

[0033] In step S3 of this invention, the characteristic that the solubility of borate (disodium tetraborate decahydrate) decreases sharply at low temperatures is utilized to cause it to precipitate out preferentially in large quantities, while the solubility of chloride changes little and it mainly remains in the mother liquor, thus avoiding chloride precipitation and thereby ensuring high purity of borate. At the same time, by controlling the cooling rate and the final cooling temperature, the borate in the filtrate can be crystalline.

[0034] In some embodiments, the endpoint temperature of the freeze crystallization in step S3 is 20-30°C.

[0035] In some embodiments, in step S3, the aging time for the frozen crystals is 1-2 hours.

[0036] In some embodiments, in step S3, the cooling rate is 1-4°C / h; under this cooling rate, and in conjunction with a thorough stirring process, the target substance in the filtrate can be fully cryogenically crystallized.

[0037] In some implementations, step S3 includes centrifugal separation as the separation method.

[0038] In some embodiments, in step S4, the post-processing sequentially includes a washing process and a drying process; the washing process includes spray washing with pure water; the drying process includes vacuum drying or fluidized bed drying at 30-40°C.

[0039] Preferably, a small amount of ice water or a low-temperature aqueous solution of ethanol (volume concentration 10%-20%) is used as a detergent to spray and wash the wet crystals, so as to replace and remove the small amount of mother liquor containing sodium chloride that coats the crystal surface.

[0040] The drying process is carried out at low temperature to prevent the crystals from melting or losing water.

[0041] In step S4 of the present invention, a borate product is obtained after post-processing. The quality of the borate product meets the superior grade standard of GB / T 537-2009, and the chloride content in the borate product is less than 0.05%.

[0042] In some embodiments, the method of the present invention can recover and refine high-purity disodium tetraborate decahydrate product that meets the national standard GB 537-2009 from boron-containing waste salt; the boron-containing waste salt is produced by sodium borohydride reduction reaction during the production of raw materials for anti-AIDS drugs and anti-malarial drugs.

[0043] The present invention also provides disodium tetraborate decahydrate, which is recovered by the method described above.

[0044] In this invention, the disodium tetraborate decahydrate has a chloride (calculated as Cl) content ≤0.03%, water-insoluble matter ≤0.04%, and extremely low impurity content, meeting the requirements for superior grade products in GB / T 537-2009.

[0045] Compared with the prior art, the present invention has the following significant advantages:

[0046] 1. The method of the present invention can be used to treat waste salt generated during the preparation of specific active pharmaceutical ingredients by sodium borohydride reduction. The specificity of this process method is far superior to general waste salt treatment technologies.

[0047] 2. The method of the present invention is based on the combination of "hot dissolution-freeze crystallization" in the solubility theory, which realizes the efficient separation of borates and chlorides. The process is simple and the energy consumption is relatively low.

[0048] 3. The method of the present invention has a high boron recovery rate and the recovered product has high value. The purity of the final product can reach the national standard of superior grade, realizing the high-value resource recovery of hazardous waste, with significant economic and environmental benefits.

[0049] 4. The entire process of the method of this invention is mainly based on physical methods, without introducing new pollutants that are difficult to treat, which is in line with the principles of green chemistry. Detailed Implementation

[0050] The present invention will be further described in detail below through preferred embodiments, but the scope of protection of the present invention is not limited thereto.

[0051] Example 1

[0052] This embodiment discloses a method for resource recovery of disodium tetraborate decahydrate from waste salt.

[0053] The method includes the following steps:

[0054] S0. Take 1000 grams of waste salt generated during the production process of antimalarial drug raw materials (using sodium borohydride reduction process); the composition of the waste salt is: 80.5% disodium tetraborate decahydrate, 15.2% sodium chloride, 4.3% organic matter and other components, where % is the mass percentage of each component in the waste salt.

[0055] S1. Add the above waste salt to 3800g of deionized water at 72℃ and stir for 40 minutes to fully dissolve it to form a waste salt solution; then use a heat-insulated Buchner funnel to perform vacuum filtration to remove insoluble matter and obtain a clear hot solution.

[0056] S2. Cool the clarified hot solution to 58℃, add 25g of powdered activated carbon, and stir for 35 minutes to remove organic matter and other impurities from the filtrate. Then heat to 78℃, add 15g of granular activated carbon, and stir for 15 minutes. The powdered activated carbon must have a specific surface area ≥600 m². 2 / g, pore volume ≥0.4 cm³ 3 / g, volume fraction of pores with a diameter of 2-50nm ≥50%, particle size ≥200 mesh, chloride content ≤0.5%;

[0057] The solution is then filtered through a precision filtration device to obtain a clear and transparent filtrate.

[0058] S3. Slowly cool the filtrate to 30°C at a rate of 4°C per hour and age it for 1.5 hours. The purpose of slow cooling is to increase the particle size of the crystals, which helps in subsequent separation operations and improves product purity. Then, centrifuge to obtain wet disodium tetraborate decahydrate.

[0059] S4. Spray the crystals with 100 ml of pre-cooled pure water to 5°C to wash them; finally, place the wet crystals in a vacuum drying oven at 38°C and dry them to constant weight to obtain 768 g of white disodium tetraborate decahydrate product.

[0060] Using a sieve, the crystal particle size of the disodium tetraborate decahydrate product is greater than 100 mesh, and the crystal morphology is good.

[0061] The product's main content (Na2B4O7·10H2O) is ≥99.5%, chloride (calculated as Cl) content is ≤0.03%, water-insoluble matter is ≤0.04%, and the solution is clear and transparent. All indicators meet the requirements for superior grade products in GB / T 537-2009.

[0062] Calculations show that the yield of disodium tetraborate decahydrate is 768 / (1000*80.5%)*100%=95.4%, and the boron yield is 768*(44 / 381) / (1000*80.5%*(44 / 381))*100%=95.4%; thus, both the product yield and the boron yield are above 95%.

[0063] Example 2

[0064] This embodiment discloses a method for resource recovery of disodium tetraborate decahydrate from waste salt.

[0065] The steps in this embodiment are largely the same as in embodiment 1, with the only difference being:

[0066] Step S2: Cool the clarified hot solution directly to 58°C, add 40g of powdered activated carbon, and keep it warm while stirring for 50 minutes; gradient adsorption was not used in this step.

[0067] After cooling, crystallization, and washing, the wet crystals were dried in a vacuum drying oven at 38°C until constant weight was obtained, yielding 668 grams of white disodium tetraborate decahydrate product.

[0068] Using a sieve, the crystal particle size of the disodium tetraborate decahydrate product is greater than 100 mesh, indicating good crystal morphology.

[0069] The product's main content (Na2B4O7·10H2O) is ≥99.5%, chloride (calculated as Cl) content is ≤0.03%, water-insoluble matter is ≤0.04%, and the solution is clear and transparent. All indicators meet the requirements for superior grade products in GB / T 537-2009.

[0070] Calculations show that the yield of disodium tetraborate decahydrate is 668 / (1000*80.5%)*100%=83.0%, and the boron yield is 668*(44 / 381) / (1000*80.5%*(44 / 381))*100%=83.0%; it can be seen that both the product yield and the boron yield are above 80%.

[0071] Example 3

[0072] This embodiment discloses a method for resource recovery of disodium tetraborate decahydrate from waste salt.

[0073] The steps in this embodiment are largely the same as those in embodiment 1, with the following differences:

[0074] S3. Slowly cool the filtrate to 40°C at a rate of 4°C per hour.

[0075] The wet crystals were dried in a vacuum drying oven at 38°C until constant weight was obtained, yielding 713 grams of white disodium tetraborate decahydrate product.

[0076] Using a sieve, the crystal particle size of the disodium tetraborate decahydrate product is greater than 100 mesh, the crystal shape is poor, and the quantity is small.

[0077] The product's main content (Na2B4O7·10H2O) is ≥99.5%, chloride (calculated as Cl) content is ≤0.03%, water-insoluble matter is ≤0.04%, and the solution is clear and transparent. All indicators meet the requirements for superior grade products in GB / T 537-2009.

[0078] Calculations show that the yield of disodium tetraborate decahydrate is 713 / (1000*80.5%)*100%=88.6%, and the boron yield is 713*(44 / 381) / (1000*80.5%*(44 / 381))*100%=88.6%; thus, both the product yield and the boron yield are above 88%.

[0079] Comparative Example 1

[0080] This comparative example discloses a method for resource recovery of borate from waste salt.

[0081] The steps for this comparative example are largely the same as those in Example 1, with the following differences:

[0082] S3. Slowly cool the filtrate to 30°C at a rate of 10°C per hour.

[0083] After cooling, crystallization, and washing, the wet crystals were dried in a vacuum drying oven at 38°C until constant weight was obtained, yielding 461 grams of white disodium tetraborate decahydrate product.

[0084] Using a sieve, the crystal particle size of the sodium tetraborate decahydrate product is greater than 180 mesh, the crystal shape is poor, and the quantity is small.

[0085] The product was tested and found to have a main content (Na2B4O7·10H2O) ≥95%, chloride (calculated as Cl) content ≤0.05%, water-insoluble matter ≤0.04%, and the solution was clear and transparent. All indicators met the requirements for qualified products in GB / T 537-2009.

[0086] The yield of disodium tetraborate decahydrate was calculated to be 461 / (1000*80.5%)*100%=57.3%, and the boron yield was 461*(44 / 381) / (1000*80.5%*(44 / 381))*100%=57.3%.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the principles of the present invention should be included within the protection scope of the present invention.

[0088] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for resource recovery of disodium tetraborate decahydrate from waste salt, characterized in that, The waste salt contains borates, chlorides, and organic matter; in the waste salt, the content of borates is 60%-80%, the content of chlorides is 15%-35%, and the content of organic matter is 3%-7%; where % represents the mass percentage of each component to the waste salt; The method includes the following steps: S1. Dissolve the waste salt in water at 60-85℃ to form a waste salt solution; then perform hot filtration on the waste salt solution to obtain a clear hot solution; S2. Remove organic matter from the clarified hot solution using an adsorbent and perform precision filtration to obtain filtrate; the process of removing organic matter from the clarified hot solution using the adsorbent includes: first, cooling the clarified hot solution from step S1 to 50-65℃, adding the adsorbent for primary adsorption; then heating it to 70-80℃, adding the adsorbent for secondary adsorption. S3. The filtrate is subjected to freeze crystallization at a cooling rate of 0.5-5℃ / h, and wet crystals are obtained after separation; the final temperature of the freeze crystallization is 0-40℃. S4. The wet crystals are post-processed to obtain disodium tetraborate decahydrate product.

2. The method as described in claim 1, characterized in that, The waste salt includes waste salt generated during the preparation of active pharmaceutical ingredients using the sodium borohydride reduction method.

3. The method as described in claim 1, characterized in that, Step S1 satisfies the following conditions: i. Dissolve the waste salt in water at 70-80℃; ii. The temperature of the heat filtration is 70-80℃; iii. In the waste salt solution, the mass ratio of waste salt to water is 1:(3-5).

4. The method as described in claim 1, characterized in that, In step S2, the adsorbent comprises powdered activated carbon; the powdered activated carbon satisfies at least one of the following conditions: i. the specific surface area of the powdered activated carbon is > 600 m 2 / g; ii. the specific pore volume of the powdered activated carbon is > 0.4 cm 3 / g; iii. In the powdered activated carbon, the volume percentage of pores with a diameter of 2-50 nm is ≥50%; iv. The particle size of the powdered activated carbon is ≥200 mesh; v. The chloride content in the powdered activated carbon is ≤0.5%.

5. The method as described in claim 1, characterized in that, During the first adsorption, the mass ratio of the adsorbent added to the clarified hot solution is 0.5%-1.5%; the stirring time for the first adsorption is 20-40 min. During the secondary adsorption, the mass ratio of the added adsorbent to the clarified hot solution is 0.2%-0.5%; the stirring time for the secondary adsorption is 10-20 min.

6. The method as described in claim 1, characterized in that, Step S3 satisfies at least one of the following conditions: i. The endpoint temperature for the freeze-crystallization is 20-30℃; ii. The aging time for the frozen crystallization is 1-2 hours; iii. The cooling rate is 1-4℃ / h; iv. The separation method includes centrifugal separation.

7. The method as described in claim 1, characterized in that, In step S4, the post-processing sequentially includes a washing process and a drying process; The washing process includes spray washing with pure water; The drying process includes vacuum drying or fluidized bed drying at 30-40°C.