A method for refining and purifying long-chain dibasic acids

Abstract

The application provides a refining and purifying method of long-chain dibasic acid, which comprises the following steps: S1, dissolving long-chain dibasic acid crude product prepared by a biological fermentation method in an organic solvent, decolorizing through activated carbon, filtering, reducing temperature and crystallizing, and separating solid and liquid to obtain long-chain dibasic acid fine product and a refined mother liquor; S2, adding an inorganic impurity removing agent to the refined mother liquor, removing impurities by temperature gradient control, removing precipitates by filtering, and obtaining a refined recovery mother liquor; and S3, recycling and applying the refined recovery mother liquor as the organic solvent in step S1. The application utilizes the characteristics of long-chain dibasic acid crude product in the organic solvent, i.e. dissolving at high temperature and precipitating at low temperature. After the refined mother liquor is treated by the inorganic impurity removing agent, other organic impurities in the refined mother liquor are removed, the treated refined mother liquor can be directly applied to the refining of long-chain dibasic acid again, high-purity products are obtained, the overall yield of dibasic acid is effectively improved, and the energy consumption of rectification and recovery of the organic solvent is avoided.

Description

Technical Field

[0001] This invention belongs to the field of biochemical technology, specifically relating to a method for refining and purifying long-chain dicarboxylic acids. Background Technology

[0002] DC12 (lauric acid), with a carbon density of 12, is one of the earliest industrially applied long-chain dicarboxylic acids. Its applications and development are more extensive than other long-chain dicarboxylic acids, making it one of the long-chain dicarboxylic acids (DC10-18) with the largest market demand. Currently, the global market for lauric acid is segmented by application, primarily including materials, industrial and chemical products, fragrances, and other high-value-added products. High-performance polyamides and nylon are the largest downstream markets for lauric acid and are the core drivers of market demand.

[0003] Currently, the industrial production of lauryl ic acid mainly relies on bio-fermentation. This method has advantages such as a wide range of raw material sources, mild reaction conditions, and environmental friendliness, and has gradually replaced traditional chemical synthesis methods as the mainstream production method. After fermentation, the extraction and purification of lauryl ic acid is a crucial step that determines product quality and production costs. Current mainstream extraction processes are mainly divided into two categories: solvent extraction and aqueous extraction. Aqueous extraction often fails to meet the extraction efficiency and product purity requirements of high-end applications. Solvent extraction, due to the high solubility of lauryl ic acid in organic solvents, can significantly improve extraction efficiency and product purity, making it the most widely used extraction method in industrial production. However, in the refining and extraction of lauryl ic acid using traditional solvent extraction methods, long-chain dicarboxylic acids such as tetradecanoic acid and hexadecanoic acid from the fermentation broth continuously accumulate in the solvent. These impurities have similar physicochemical properties to lauryl ic acid and are difficult to remove using conventional separation methods. To avoid the accumulation of impurities affecting product quality, a complex solvent recovery process must be implemented, separating solvents from impurities through distillation, rectification, and other methods. This not only increases equipment investment but also consumes a large amount of energy, leading to a significant increase in production costs. Furthermore, the solvent recovery process may generate secondary pollution, which is inconsistent with the concept of green production. Summary of the Invention

[0004] The purpose of this invention is to provide a method for refining and purifying long-chain dicarboxylic acids, which can at least solve some of the defects existing in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for purifying long-chain dicarboxylic acids includes the following steps:

[0007] S1. The crude long-chain dicarboxylic acid prepared by bio-fermentation is dissolved in an organic solvent, decolorized by activated carbon, filtered, cooled and crystallized, and the solid-liquid separation is performed to obtain the refined long-chain dicarboxylic acid and the refined mother liquor.

[0008] S2. An inorganic impurity remover is added to the refined mother liquor, and the impurity is removed by temperature gradient control. The precipitate is removed by filtration to obtain a refined and recovered mother liquor. The inorganic impurity remover can form a precipitate insoluble in organic solvents with long-chain dicarboxylic acids with a carbon chain length greater than 12 in the refined mother liquor.

[0009] S3. The refined and recovered mother liquor is recycled as the organic solvent in step S1.

[0010] Furthermore, the inorganic impurity remover is one or more of the inorganic salts or oxides of calcium, barium, magnesium, zinc, and manganese, and the amount of the inorganic impurity remover added is 0.25wt% to 10wt% of the mass of the purified mother liquor.

[0011] Furthermore, the inorganic impurity remover is calcium oxide, barium acetate, or magnesium carbonate.

[0012] Furthermore, the inorganic impurity remover is added in the form of a solid, suspension, or clear solution.

[0013] Furthermore, in S2, the temperature gradient control process is as follows:

[0014] First stage: Add inorganic impurity remover and heat to 70-90℃, and maintain at 70-90℃ for 15-60 minutes;

[0015] Second stage: Cool down to 35-65℃ at a rate of 0.5-1℃ / min, and maintain at 35-65℃ for 15-60min;

[0016] The third stage: cool down to 15-30℃ and filter out insoluble substances from the solution.

[0017] Furthermore, the temperature in the first stage is 75–80°C, and the duration is 30–40 minutes; the temperature in the second stage is 45–55°C, and the duration is 30–40 minutes.

[0018] Furthermore, in S1, the refining process of the crude long-chain dicarboxylic acid involves feeding it into a decolorization tank, adding an organic solvent (the amount of which is 2 to 6 times the mass of the crude long-chain dicarboxylic acid), heating it to 50 to 90°C, and after the material is completely dissolved, adding activated carbon for decolorization (the amount of which is 0.2 wt% to 5 wt% of the mass of the crude long-chain dicarboxylic acid), decolorizing for 20 to 100 minutes, filtering it through a filter to obtain a clear liquid, transferring the clear liquid to a crystallization tank, heating it to 50 to 80°C, maintaining the temperature for 20 to 70 minutes with stirring, and then slowly cooling it to 5 to 30°C: first cooling it to 50 to 55°C within 1 hour, and then cooling it down by 10 to 20°C per hour until it reaches the process temperature; separating the refined long-chain dicarboxylic acid and the refined mother liquor.

[0019] Furthermore, in S1, the organic solvent is one or more of the following: C3-C14 n-alkanes, C1-C8 n-alcohols, C1-C8 n-carboxylic acids, ethyl acetate, butyl acetate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, and isooctane.

[0020] Furthermore, in S1, the long-chain dicarboxylic acid concentrate is washed in a centrifuge using one or both of the following methods: hot water rinsing and pulp washing.

[0021] Furthermore, the water temperature for the hot water rinsing is 50–95°C, and the rinsing time is 1–15 min; the mass ratio of the solvent for the slurry washing to the long-chain dicarboxylic acid concentrate is 2–6:1.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) Simple process: Utilizing the characteristics of crude long-chain dicarboxylic acid in organic solvents to "dissolve at high temperature and precipitate at low temperature", combined with the treatment of the mother liquor impurity removal agent, the process is simple and easy to operate, without complicated procedures, and is suitable for industrial production needs.

[0024] (2) Low cost and energy consumption: effectively reduces energy consumption in organic solvent distillation recovery and reduces energy loss; the refined mother liquor can be directly reused after impurity removal without additional recovery treatment, which greatly saves solvent consumption and related equipment investment costs.

[0025] (3) Product stability: Through fermentation, crude extraction, refining and purification and mother liquor purification and recycling, high-purity lauryl acid products can be obtained stably, ensuring product quality.

[0026] (4) Good practicality: The overall process is simple and efficient, avoiding the pain points of impurity enrichment and high recycling cost of traditional solvent methods, taking into account both practicality and economy, and is easy to promote on a large scale. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] This invention provides a method for purifying long-chain dicarboxylic acids, comprising the following steps:

[0029] S1. The crude long-chain dicarboxylic acid prepared by bio-fermentation is dissolved in an organic solvent, decolorized by activated carbon, filtered, cooled and crystallized, and the solid and liquid are separated to obtain the refined long-chain dicarboxylic acid and the refined mother liquor.

[0030] Specifically, the refining process of crude long-chain dicarboxylic acid is as follows: The product is fed into a decolorization tank, and an organic solvent is added. The amount of organic solvent added is 2 to 6 times the mass of the crude long-chain dicarboxylic acid. The temperature is raised to 50 to 90°C. After the material is completely dissolved, activated carbon is added for decolorization. The amount of activated carbon added is 0.2 wt% to 5 wt% of the mass of the crude long-chain dicarboxylic acid. Decolorization takes 20 to 100 minutes. The product is filtered to obtain a clear liquid. The clear liquid is transferred to a crystallization tank, heated to 50 to 80°C, and kept at this temperature for 20 to 70 minutes with stirring. Then, the temperature is slowly lowered to 5 to 30°C. The temperature is first lowered to 50 to 55°C within 1 hour, and then lowered by 10 to 20°C per hour until the process temperature is reached. The refined long-chain dicarboxylic acid and the refining mother liquor are then separated.

[0031] The organic solvent may be selected from one or more of the following: C3-C14 n-alkanes, C1-C8 n-alcohols, C1-C8 n-carboxylic acids, ethyl acetate, butyl acetate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, and isooctane.

[0032] Optionally, for the post-processing of the long-chain dicarboxylic acid product, it can be washed in a centrifuge using one or both of the following methods: hot water rinsing and pulp washing. After washing, it is dried in a dryer at a controlled temperature of 55–100°C to obtain the product. Specifically, the hot water rinsing temperature is 50–95°C, preferably 80–95°C, and the rinsing time is 1–15 min, preferably 10–15 min; the mass ratio of the solvent to the long-chain dicarboxylic acid product in the pulp washing is 2–6:1.

[0033] S2. An inorganic impurity remover is added to the refined mother liquor, and the impurity is removed by temperature gradient control. The precipitate is removed by filtration to obtain a refined and recovered mother liquor. The inorganic impurity remover can form a precipitate insoluble in organic solvents with long-chain dicarboxylic acids with a carbon chain length greater than 12 in the refined mother liquor.

[0034] Specifically, the inorganic impurity remover can be one or more of inorganic salts such as calcium salts, barium salts, magnesium salts, zinc salts, and manganese salts, as well as oxides of calcium, barium, magnesium, zinc, and manganese; the amount of the inorganic impurity remover added is 0.25wt% to 10wt% of the mass of the purified mother liquor, preferably 1wt%, 2wt%, 3wt%, or 4wt%. Meanwhile, the inorganic impurity remover is added in the form of a solid, suspension, or clear solution.

[0035] After adding an inorganic impurity remover to the refined mother liquor, temperature gradient control is employed. The specific temperature gradient control process is as follows:

[0036] First stage: Add inorganic impurity remover and heat to 70–90°C, maintaining this temperature for 15–60 minutes; preferably, control the temperature at 75–80°C and the time for 30–40 minutes. During this stage, under high temperature conditions, all long-chain dicarboxylic acids and their carboxylates with metal ions in the system completely dissolve, achieving a homogeneous state and ensuring sufficient contact between the inorganic impurity remover and each component to complete the salt formation reaction.

[0037] The second stage involves cooling to 35–65°C at a rate of 0.5–1°C / min and maintaining this temperature for 15–60 min; preferably, the temperature is controlled to drop to 45–55°C and maintained for 30–40 min. During this stage, as the temperature slowly decreases, the solubility of long-chain dicarboxylic acids with a carbon chain length greater than 12 first reaches supersaturation, preferentially precipitating as tiny crystal nuclei. The solubility curve of C12 long-chain dicarboxylic acids remains below the actual concentration line of the mother liquor within this temperature range, indicating that they have not yet reached supersaturation and therefore do not precipitate. Simultaneously, the slow cooling rate (0.5–1°C / min) helps control the crystal growth rate, resulting in larger precipitate particles that are easier to filter.

[0038] The third stage involves cooling the solution to 15–30°C and filtering to remove insoluble substances. During this stage, the temperature decreases further, leading to a further reduction in the solubility of long-chain dicarboxylic acids with a carbon chain length greater than 12, which promotes the complete precipitate removal. Simultaneously, the low temperature reduces the system viscosity, facilitating subsequent filtration.

[0039] S3. The refined and recovered mother liquor is recycled as the organic solvent in step S1.

[0040] In this invention, the long-chain dicarboxylic acid molecule structure consists of two polar carboxyl groups (–COOH) and a hydrophobic methylene chain in the middle (…). The composition is as follows: as the carbon chain length increases, the proportion of polar groups in the molecule gradually decreases, and the hydrophobicity increases significantly. When an inorganic impurity remover is added to the purified mother liquor, the carboxyl groups in the long-chain dicarboxylic acid molecule undergo a deprotonation reaction, forming dicarboxylate salts with metal ions. The resulting dicarboxylate salts are organometallic acid salts, and their solubility in organic solvents is significantly affected by the carbon chain length. The higher the proportion of nonpolar carbon chains, the worse the solubility of the metal carboxylate salt in nonpolar / weakly polar organic solvents. Even if the carbon chain length increases from 12 to 14, the difference is only two methylene groups (…). This is sufficient to cause a step change in the solubility of metal carboxylate salts, thereby enabling the inorganic impurity remover in this invention to selectively remove long-chain dicarboxylic acids (mainly tetradecanoic acid, hexadecanoic acid, etc.) with a carbon chain length greater than 12 from the purified mother liquor, while having virtually no effect on the target product lauryl dicitate (dodecanoic acid).

[0041] Meanwhile, by utilizing the differences in the solubility-temperature curves of metal carboxylates with different carbon chain lengths, and through precise temperature control, C14+ impurities are selectively precipitated while the C12 target product remains in a dissolved state. If only inorganic impurity removers are added without the temperature control strategy of this invention (such as high-temperature filtration throughout the process or rapid cooling), selective separation cannot be achieved. For example, high-temperature filtration throughout the process may result in impurity salts not precipitating due to excessively high temperatures, or the impurity crystallization temperature may not be maintained for a sufficient period, leading to a metastable supersaturated state where effective precipitation is impossible. Rapid cooling or excessively low temperatures can cause crystal "bursting," which can also lead to C12 salt co-precipitation. All of these situations can result in impurity removal failure or loss of the target product.

[0042] The purification process and effects of the long-chain dicarboxylic acid of the present invention are illustrated below through specific embodiments and comparative examples.

[0043] Preparation of crude long-chain dicarboxylic acids: Adjust the pH of the fermentation broth to 9–14 with 10–50% alkali solution, heat to 50–90℃, and maintain the temperature for 20–180 min while stirring; stop stirring and let stand for 12–64 h. After the material has completely separated into layers, discharge the material to obtain the lower and middle layers. Use a ceramic membrane for solid-liquid separation and sterilization, selecting a ceramic membrane with a pore size of 5–100 nm for filtration to obtain a clear liquid; concentrate the material 3–10 times and then add water for replacement, with the replacement water volume being 3–20 times the minimum circulation volume of the ceramic membrane. The pH of the clarified liquid was adjusted by adding acid, and the material was heated to 60–70°C. The acid was added dropwise over a period of 0.5–3 hours, and the final pH was controlled to be 2–4. The temperature was then raised to above 95°C and maintained at this temperature for 1–3 hours with stirring. The temperature was then slowly lowered to 70–80°C over 2–4 hours, and then further lowered by 5–20°C per hour until the final temperature reached 20–60°C. The wet crude product was obtained by plate and frame separation. The wet crude product was then rinsed or slurryed with 3–30 times its weight of water at a temperature of 20–80°C. The wet crude product was then dried using a dryer to obtain the crude long-chain dicarboxylic acid. This crude long-chain dicarboxylic acid was used in all subsequent experiments.

[0044] Example 1:

[0045] Refining of crude long-chain dicarboxylic acid: 99 kg of crude long-chain dicarboxylic acid (96.1% purity) was taken and added to fresh acetic acid at a mass ratio of 1:3.5. The mixture was heated to 77°C and stirred until the crude product was completely dissolved. 2.3 kg of activated carbon was added, and the mixture was kept at 77°C for 36 min to decolorize. The mixture was filtered to remove the activated carbon, and the liquid was transferred to a crystallization vessel. The vessel was kept at 77°C for 52 min, and then slowly cooled. The temperature was lowered from 77°C to 52°C over 60 min, and from 51°C to 19°C over 140 min. Solid-liquid separation yielded refined long-chain dicarboxylic acid and 305 L of refining mother liquor. The refined long-chain dicarboxylic acid was washed with hot water at 80°C for 4 min and dried to obtain 87.0 kg of product with a purity of 99.22% and a yield of 91.45%.

[0046] Refined mother liquor treatment: Add 3.5wt% calcium oxide to the refined mother liquor, heat to 75℃ until the insoluble substances are completely dissolved, keep warm for 30 minutes, slowly cool down to 50℃, keep warm for 30 minutes, and then continue to cool down to 30℃. Filter to obtain 280L of refined recovered mother liquor.

[0047] One-cycle reuse: 100 kg of crude long-chain dicarboxylic acid from the same batch was taken and added to 280 L of purified and recovered mother liquor. Fresh acetic acid was added to make the mass ratio of crude long-chain dicarboxylic acid to solvent (purified and recovered mother liquor + fresh acetic acid) 1:3.5. The temperature was raised to 77℃ and stirred until the crude product was completely dissolved. 2.4 kg of activated carbon was added and the temperature was maintained at 77℃ for 38 min for decolorization. The mixture was filtered to remove the activated carbon and transferred to a crystallization vessel. The solution was kept at 77℃ for 48 min and then slowly cooled. The temperature was lowered from 77℃ to 52℃ for 60 min and from 52℃ to 19℃ for 135 min. Solid-liquid separation was performed to obtain the refined long-chain dicarboxylic acid and the purified mother liquor. The refined long-chain dicarboxylic acid obtained from the first-cycle reuse was also washed with hot water at 80℃ for 4 min and dried to obtain 94.1 kg of product with a purity of 99.15% and a yield of 97.92%.

[0048] Secondary recycling: Repeat the above steps to process and reuse the refined mother liquor obtained from the first recycling. Take 100 kg of crude long-chain dicarboxylic acid from the same batch, and follow the same procedure as the first recycling to obtain 93.8 kg of product with a purity of 99.18% and a yield of 97.61%.

[0049] Three cycles of reuse: Repeat the above steps of refining mother liquor treatment and reuse, take 100 kg of crude long-chain dicarboxylic acid from the same batch, and follow the same procedure as the first cycle of reuse to obtain 93.2 kg of product with a purity of 99.14% and a yield of 96.98%.

[0050] Four cycles of reuse: Repeat the above steps of refining mother liquor treatment and reuse, take 101 kg of crude long-chain dicarboxylic acid from the same batch, and follow the same procedure as the first cycle of reuse to obtain 94.2 kg of product with a purity of 99.25% and a yield of 97.05%.

[0051] Five cycles of reuse: Repeat the above steps of refining mother liquor treatment and reuse, take 99 kg of crude long-chain dicarboxylic acid from the same batch, and follow the same procedure as one cycle of reuse to obtain 93.1 kg of product with a purity of 99.25% and a yield of 97.86%.

[0052] After five cycles, the product purity stabilized at around 99.05%, and the average yield of the refined mother liquor reached over 97%, indicating a stable process.

[0053] Example 2:

[0054] Refining of crude long-chain dicarboxylic acid: Take 99 kg of crude long-chain dicarboxylic acid with a purity of 96.2%, add fresh acetic acid at a mass ratio of 1:4.5, heat to 73℃, stir until the crude product is completely dissolved, add 2.4 kg of activated carbon, maintain 73℃, decolorize for 43 min, filter, remove activated carbon, transfer liquid to crystallization vessel, keep at 73℃ for 50 min, slowly cool, from 73℃ to 52℃ for 60 min, and from 52℃ to 20℃ for 140 min, solid-liquid separation to obtain refined long-chain dicarboxylic acid and 425 L of refining mother liquor. The refined long-chain dicarboxylic acid was washed with 80℃ hot water for 4 min, dried to obtain 86.4 kg of product with a purity of 99.35% and a yield of 90.72%.

[0055] Refined mother liquor treatment: Add 4.0 wt% barium acetate to the refined mother liquor, heat to 76°C until the insoluble substances are completely dissolved and keep warm for 35 min, slowly cool to 52°C, keep warm for 40 min, cool to 15°C, and filter to obtain 420 L of refined recovered mother liquor.

[0056] One cycle of reuse: 101 kg of crude long-chain dicarboxylic acid from the same batch was added to 420 L of purified and recovered mother liquor, along with fresh acetic acid, until the mass ratio of crude long-chain dicarboxylic acid to solvent (purified and recovered mother liquor + fresh acetic acid) was 1:4.5. The temperature was raised to 77°C, and the mixture was stirred until the crude product was completely dissolved. 2.4 kg of activated carbon was added, and the temperature was maintained at 77°C for 42 min for decolorization. The mixture was filtered to remove the activated carbon, and the liquid was transferred to a crystallization vessel. The vessel was kept at 77°C for 51 min, and then slowly cooled. The temperature was lowered from 77°C to 50°C over 60 min, and from 50°C to 19°C over 135 min. Solid-liquid separation yielded refined long-chain dicarboxylic acid and purified mother liquor. The refined long-chain dicarboxylic acid obtained from the first cycle was also washed with hot water at 80°C for 5 min and dried to obtain 94.8 kg of product with a purity of 99.26% and a yield of 97.57%.

[0057] Secondary recycling: Repeat the above steps of refining mother liquor treatment and mother liquor recycling, take 100kg of crude long-chain dicarboxylic acid from the same batch, and operate in the same manner as the first recycling to obtain 93.9kg of product with a purity of 99.29% and a yield of 97.61%.

[0058] Three cycles of reuse: Repeat the above steps of refining mother liquor treatment and reuse, take 100 kg of crude long-chain dicarboxylic acid from the same batch, and follow the same procedure as the first cycle of reuse to obtain 94.1 kg of product with a purity of 99.23% and a yield of 97.82%.

[0059] Four cycles of reuse: Repeat the above steps of refining mother liquor treatment and reuse, take 101 kg of crude long-chain dicarboxylic acid from the same batch, and follow the same procedure as the first cycle of reuse to obtain 92.2 kg of product with a purity of 99.24% and a yield of 96.89%.

[0060] Five cycles of reuse: Repeat the above steps of refining mother liquor treatment and reuse, take 99 kg of crude long-chain dicarboxylic acid from the same batch, and follow the same procedure as one cycle of reuse to obtain 94.8 kg of product with a purity of 99.23% and a yield of 99.54%.

[0061] After five cycles, the product purity stabilized at over 99.13%, with an average yield of over 97%, indicating a stable process.

[0062] Example 3:

[0063] Refining of crude long-chain dicarboxylic acid: Take 100 kg of crude long-chain dicarboxylic acid with a purity of 96.1%, add fresh acetic acid at a mass ratio of 1:5.5, heat to 68℃, stir until the crude product is completely dissolved, add 2.4 kg of activated carbon, maintain 68℃, decolorize for 39 min, filter, remove activated carbon, transfer liquid to crystallization vessel, keep at 69℃ for 40 min, slowly cool, from 69℃ to 52℃ for 60 min, and from 52℃ to 20℃ for 138 min, solid-liquid separation to obtain refined long-chain dicarboxylic acid and 525 L of refining mother liquor. The refined long-chain dicarboxylic acid was washed with 80℃ hot water for 4 min, dried to obtain 84.4 kg of product with a purity of 99.39% and a yield of 87.82%.

[0064] Refined mother liquor treatment: Add 5.0 wt% magnesium carbonate to the refined mother liquor, heat to 79°C until the insoluble substances are completely dissolved, keep warm for 35 min, slowly cool down to 48°C, keep warm for 40 min, then cool down to 15°C, and filter to obtain 520 L of refined recovered mother liquor.

[0065] One-cycle reuse: Take 100 kg of crude long-chain dicarboxylic acid from the same batch, add 520 L of treated refining mother liquor, and add fresh acetic acid until the mass ratio of crude long-chain dicarboxylic acid to solvent (refining mother liquor + fresh acetic acid) is 1:5.5. Heat to 75℃ and stir until the crude product is completely dissolved. Add 2.4 kg of activated carbon, maintain 75℃, decolorize for 32 min, filter, remove activated carbon, transfer to crystallization vessel, keep at 75℃ for 52 min, slowly cool down, from 75℃ to 50℃ for 60 min, and from 50℃ to 19℃ for 135 min. Solid-liquid separation yields refined long-chain dicarboxylic acid and refining mother liquor. The refined long-chain dicarboxylic acid obtained from the one-cycle reuse is also washed with 80℃ hot water for 5 min and dried to obtain 94.1 kg of product with a purity of 99.30% and a yield of 97.92%.

[0066] Secondary recycling: Repeat the above steps of refining mother liquor treatment and mother liquor recycling, take 100kg of crude long-chain dicarboxylic acid from the same batch, and operate in the same manner as the first recycling to obtain 93.9kg of product with a purity of 99.33% and a yield of 97.71%.

[0067] Three cycles of reuse: Repeat the above steps of refining mother liquor treatment and reuse, take 100 kg of crude long-chain dicarboxylic acid from the same batch, and follow the same procedure as the first cycle of reuse to obtain 94.0 kg of product with a purity of 99.33% and a yield of 97.81%.

[0068] Four cycles of reuse: Repeat the above steps of refining mother liquor treatment and reuse, take 101 kg of crude long-chain dicarboxylic acid from the same batch, and follow the same procedure as the first cycle of reuse to obtain 94.3 kg of product with a purity of 99.40% and a yield of 97.15%.

[0069] Five cycles of reuse: Repeat the above steps of refining mother liquor treatment and reuse, take 100 kg of crude long-chain dicarboxylic acid from the same batch, and follow the same procedure as one cycle of reuse to obtain 94.1 kg of product with a purity of 99.35% and a yield of 97.92%.

[0070] After five cycles, the product purity stabilized at over 98.99%, with an average yield of over 96%, indicating a stable process.

[0071] Comparative Example 1:

[0072] Refining of crude long-chain dicarboxylic acid: Take 100 kg of crude long-chain dicarboxylic acid with a purity of 95.8%, add fresh acetic acid at a mass ratio of 1:3.6, heat to 75℃, stir until the crude product is completely dissolved, add 2.3 kg of activated carbon, maintain 75℃, decolorize for 46 min, filter, remove activated carbon, transfer liquid to crystallization vessel, keep at 75℃ for 32 min, slowly cool down, from 75℃ to 51℃ for 60 min, and from 51℃ to 17℃ for 120 min, solid-liquid separation to obtain refined long-chain dicarboxylic acid and 310 L of refining mother liquor. The refined long-chain dicarboxylic acid was washed with 80℃ hot water for 5 min, dried to obtain 88.1 kg of product with a purity of 99.20% and a yield of 91.96%.

[0073] The mother liquor was directly recycled: 100 kg of crude long-chain dicarboxylic acid from the same batch was added to 310 L of mother liquor obtained during the crude product refining process. Fresh acetic acid was added until the mass ratio of crude long-chain dicarboxylic acid to solvent (mother liquor + fresh acetic acid) was 1:3.6. The temperature was raised to 75°C, and the mixture was stirred until the crude product was completely dissolved. 2.3 kg of activated carbon was added, and the temperature was maintained at 75°C for 41 min for decolorization. The mixture was filtered to remove the activated carbon, and the liquid was transferred to a crystallization vessel. The vessel was kept at 75°C for 43 min, and then slowly cooled. The temperature was lowered from 75°C to 50°C over 60 min, and from 50°C to 18°C ​​over 133 min. Solid-liquid separation yielded the refined long-chain dicarboxylic acid. The refined long-chain dicarboxylic acid was washed with hot water at 80°C for 4 min and dried to obtain 96.0 kg of product with a purity of 97.83% and a yield of 100.21%. Because the product purity was lower than the industry standard of 98.5%, subsequent recycling was discontinued.

[0074] Comparative Example 2:

[0075] Refining of crude long-chain dicarboxylic acid: Take 102 kg of crude long-chain dicarboxylic acid with a purity of 95.5%, add fresh acetic acid at a mass ratio of 1:5, heat to 65℃, stir until the crude product is completely dissolved, add 2.5 kg of activated carbon, maintain at 69℃, decolorize for 45 min, filter, remove activated carbon, transfer to crystallization vessel, keep at 70℃ for 30 min, slowly cool, from 65℃ to 55℃ for 60 min, and from 55℃ to 20℃ for 120 min, solid-liquid separation to obtain refined long-chain dicarboxylic acid and 440 L of refining mother liquor. The refined long-chain dicarboxylic acid was washed with 80℃ hot water for 5 min, dried to obtain 85.8 kg of product with a purity of 99.44% and a yield of 88.08%.

[0076] The mother liquor was directly recycled: 101 kg of crude long-chain dicarboxylic acid from the same batch was added to 440 L of the mother liquor obtained during the crude product refining process. Fresh acetic acid was added until the mass ratio of crude long-chain dicarboxylic acid to solvent (mother liquor + fresh acetic acid) was 1:5. The temperature was raised to 69°C, and the mixture was stirred until the crude product was completely dissolved. 2.6 kg of activated carbon was added, and the temperature was maintained at 69°C for 44 min for decolorization. The mixture was filtered to remove the activated carbon, and the liquid was transferred to a crystallization vessel. The vessel was kept at 70°C for 40 min, and then slowly cooled. The temperature was lowered from 70°C to 53°C over 60 min, and from 55°C to 20°C over 130 min. Solid-liquid separation yielded the refined long-chain dicarboxylic acid. The refined long-chain dicarboxylic acid was washed with hot water at 80°C for 5 min and dried to obtain 95.9 kg of product with a purity of 98.04% and a yield of 99.42%. Because the product purity was lower than the industry standard of 98.5%, further recycling was discontinued.

[0077] Comparative Example 3:

[0078] Refining of crude long-chain dicarboxylic acid: 101 kg of crude long-chain dicarboxylic acid (95.4% purity) was taken and added to fresh acetic acid at a mass ratio of 1:4.5. The mixture was heated to 72°C and stirred until the crude product was completely dissolved. 2.5 kg of activated carbon was added, and the mixture was kept at 72°C for 40 min to decolorize. The mixture was filtered to remove the activated carbon, and the liquid was transferred to a crystallization vessel. The vessel was kept at 72°C for 30 min, and then slowly cooled. The temperature was lowered from 65°C to 55°C over 65 min, and from 55°C to 20°C over 120 min. Solid-liquid separation yielded refined long-chain dicarboxylic acid and 420 L of refining mother liquor. The refined long-chain dicarboxylic acid was washed with hot water at 80°C for 5 min and dried to obtain 86.9 kg of product with a purity of 99.48% and a yield of 90.19%.

[0079] Refined mother liquor treatment: Add 3.0wt% barium acetate to the refined mother liquor, heat to 76℃ until the insoluble substances are completely dissolved and keep warm for 35 minutes, then quickly cool to 15℃ and filter to obtain 410L of refined recovered mother liquor.

[0080] One cycle of reuse: 101 kg of the same batch of crude long-chain dicarboxylic acid was added to 420 L of treated purified mother liquor, and fresh acetic acid was added until the mass ratio of crude long-chain dicarboxylic acid to solvent (purified mother liquor + fresh acetic acid) was 1:4.5. The temperature was raised to 78℃, and the mixture was stirred until the crude product was completely dissolved. 2.4 kg of activated carbon was added, and the temperature was maintained at 78℃ for 40 min for decolorization. The mixture was filtered to remove the activated carbon, and the liquid was transferred to a crystallization vessel. The vessel was kept at 78℃ for 45 min, and then slowly cooled. The temperature was lowered from 78℃ to 50℃ over 60 min, and from 50℃ to 20℃ over 130 min. Solid-liquid separation was performed to obtain the purified long-chain dicarboxylic acid and the purified mother liquor. The purified long-chain dicarboxylic acid obtained from the first cycle of reuse was also washed with hot water at 80℃ for 4 min and dried to obtain 94.9 kg of product with a purity of 99.01% and a yield of 98.49%.

[0081] Secondary recycling: Repeat the previous steps of refining mother liquor treatment and mother liquor recycling, take 100 kg of crude long-chain dicarboxylic acid from the same batch, and follow the same procedure as the first recycling to obtain 93.0 kg of product with a purity of 98.42% and a yield of 97.48%. Since the product purity is lower than the industry standard of 98.5%, subsequent recycling is stopped.

[0082] Table 1: Summary of Results

[0083] As can be seen from the above examples and comparative examples, if the refined mother liquor is used directly without treatment with an inorganic impurity remover, or if an inorganic impurity remover is added but no temperature control strategy is adopted, the mother liquor can only be recycled once or twice before the product purity is lower than the industry standard, and the number of recycling times is limited. However, the present invention adds an inorganic impurity remover to the refined mother liquor and combines it with precise temperature control, so that impurities in the refined mother liquor selectively precipitate out. After multiple recycling, high-purity lauryl ic acid products can be stably obtained, ensuring product quality.

[0084] This invention utilizes the difference in solubility between inorganic impurity removers and the purified mother liquor to effectively remove other long-chain dicarboxylic acids with carbon chains greater than 12 from the purified mother liquor. When other long-chain dicarboxylic acids with carbon chains greater than 12 form precipitates in the purified mother liquor, they can be removed by filtration, greatly reducing the enrichment of non-target long-chain dicarboxylic acids in the mother liquor.

[0085] It should be noted that, for manufacturing enterprises, the purity of products from different companies in the market varies. As long as the product meets the qualification standard, it can be sold. Therefore, the yield calculation in the embodiments and comparative examples of this invention refers to the percentage value of the total amount of the target product in the crude product that is actually separated and obtained.

[0086] The above examples are merely illustrative of the present invention and do not constitute a limitation on the scope of protection of the present invention. All designs that are the same as or similar to the present invention are within the scope of protection of the present invention.

Claims

1. A method for purifying and refining long-chain dicarboxylic acids, characterized in that, Includes the following steps: S1. The crude long-chain dicarboxylic acid prepared by bio-fermentation is dissolved in an organic solvent, decolorized by activated carbon, filtered, cooled and crystallized, and the solid and liquid are separated to obtain the refined long-chain dicarboxylic acid and the refined mother liquor; wherein, the organic solvent is one or more of C3-C14 n-alkanes, C1-C8 n-alcohols, C1-C8 n-carboxylic acids, ethyl acetate, butyl acetate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, and isooctane; S2. An inorganic impurity remover is added to the refined mother liquor, and impurity removal is performed using temperature gradient control. The precipitate is removed by filtration to obtain a refined recovered mother liquor. The inorganic impurity remover is capable of forming a precipitate insoluble in organic solvents with long-chain dicarboxylic acids with a carbon chain length greater than 12 in the refined mother liquor. The inorganic impurity remover is one or more of the inorganic salts of calcium, barium, magnesium, zinc, and manganese or their oxides. S3. The refined and recovered mother liquor is recycled as the organic solvent in step S1.

2. The method for purifying and refining long-chain dicarboxylic acids as described in claim 1, characterized in that, The amount of inorganic impurity remover added is 0.25wt% to 10wt% of the mass of the purified mother liquor.

3. The method for purifying and refining long-chain dicarboxylic acids as described in claim 1, characterized in that, The inorganic impurity remover is calcium oxide, barium acetate, or magnesium carbonate.

4. The method for purifying and refining long-chain dicarboxylic acids as described in claim 1, characterized in that, The inorganic impurity remover is added in the form of a solid, suspension, or clear solution.

5. The method for purifying and refining long-chain dicarboxylic acids as described in claim 1, characterized in that, In S2, the temperature gradient control process is as follows: First stage: Add inorganic impurity remover and heat to 70-90℃, and maintain at 70-90℃ for 15-60 minutes; Second stage: Cool down to 35-65℃ at a rate of 0.5-1℃ / min, and maintain at 35-65℃ for 15-60min; The third stage: cool down to 15-30℃ and filter out insoluble substances from the solution.

6. The method for purifying and refining long-chain dicarboxylic acids as described in claim 5, characterized in that, The temperature in the first stage is 75-80℃, and the duration is 30-40 minutes; the temperature in the second stage is 45-55℃, and the duration is 30-40 minutes.

7. The method for purifying and refining long-chain dicarboxylic acids as described in claim 1, characterized in that, In step S1, the refining process of the crude long-chain dicarboxylic acid involves feeding it into a decolorization tank, adding an organic solvent (2-6 times the mass of the crude long-chain dicarboxylic acid), heating it to 50-90°C, and after the material is completely dissolved, adding activated carbon for decolorization (0.2wt%-5wt% of the crude long-chain dicarboxylic acid mass), decolorizing for 20-100 minutes, filtering it to obtain a clear liquid, transferring the clear liquid to a crystallization tank, heating it to 50-80°C, maintaining the temperature for 20-70 minutes with stirring, and then slowly cooling it to 5-30°C: first cooling it to 50-55°C within 1 hour, then cooling it down by 10-20°C per hour until it reaches the process temperature; separating the refined long-chain dicarboxylic acid and the refining mother liquor.

8. The method for purifying and refining long-chain dicarboxylic acids as described in claim 1, characterized in that, In S1, the long-chain dicarboxylic acid concentrate is washed in a centrifuge using one or both of the following methods: hot water rinsing and pulp washing.

9. The method for purifying and refining long-chain dicarboxylic acids as described in claim 8, characterized in that, The hot water rinsing temperature is 50-95℃, and the rinsing time is 1-15 minutes; the mass ratio of the solvent used for slurry washing to the long-chain dicarboxylic acid concentrate is 2-6:1.

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