A method for extracting and purifying long-chain dibasic acids from a fermentation broth

Abstract

The application provides a method for extracting and purifying long-chain dibasic acid from fermentation liquor, which comprises the following steps: 1) a solid-liquid separation step: performing first solid-liquid separation on long-chain dibasic acid fermentation liquor to obtain insoluble matter 1 and filtrate 1; 2) a slurry conditioning and water removal step: performing slurry conditioning on the insoluble matter 1 by using short-chain organic acid, and performing second solid-liquid separation to replace water in the insoluble matter 1, thereby obtaining insoluble matter 2 and filtrate 2; 3) a high-temperature dissolution step: dissolving the insoluble matter 2 at 80-85 DEG C by using short-chain organic acid to obtain a dissolution liquid; 4) a ceramic membrane filtration step: performing ceramic membrane filtration on the dissolution liquid at 80-85 DEG C to collect a permeate; and 5) a purification step: purifying the permeate to obtain long-chain dibasic acid products. The method has the advantages that protein removal is complete, the product purity can reach more than 98.5%, the total nitrogen content is low, the color is white, and the method fully meets the requirements of polymerization-grade products.

Description

Technical Field

[0001] This invention belongs to the field of purification technology and relates to a method for extracting and purifying long-chain dicarboxylic acids from fermentation broth, specifically a method for extracting and purifying long-chain dicarboxylic acid fermentation broth based on an acid-resistant ceramic membrane. Background Technology

[0002] Long-chain dicarboxylic acids (LCDA) are organic dicarboxylic acids containing more than 10 carbon atoms in their carbon chain, with a carboxyl group at both the α and ω positions. Their general structural formula is HOOC(CH2). n COOH (n≥8) includes both saturated and unsaturated dicarboxylic acids. These compounds are key monomers for the synthesis of high-performance nylon, fragrances, hot melt adhesives, and other important materials. Currently, the mainstream production method for long-chain dicarboxylic acids is bio-fermentation. However, the fermentation broth is complex, containing not only the target product but also a large number of impurities such as bacteria, proteins, pigments, and inorganic salts, making extraction and purification difficult.

[0003] Currently, the "alkali-dissolving membrane" process is commonly used in industry (as cited in reference 1). This involves adjusting the pH of the fermentation broth to alkaline conditions to dissolve long-chain dicarboxylic acids, followed by the removal of bacterial cells and insoluble proteins using ultrafiltration or ceramic membranes. However, this process has inherent drawbacks: 1) Proteins exhibit increased solubility or colloidal stability under alkaline conditions, resulting in limited protein removal efficiency by membrane filtration, leading to a higher total nitrogen content and poorer color in the final product; 2) Subsequent use of large amounts of acid is required to adjust the pH and precipitate the product, resulting in high acid and alkali consumption and the generation of high-salt wastewater, posing significant environmental pressure.

[0004] To reduce the amount of acid and alkali used, reference 2 provides a method for demulsifying and purifying long-chain dicarboxylic acid fermentation broth. This method adjusts the fermentation broth to a pH below 4, causing the long-chain dicarboxylic acid and bacterial cells to co-precipitate before separation. However, this method has certain drawbacks: the co-precipitate is viscous and gelatinous when the water content is high, making plate and frame filtration or centrifugation extremely difficult and slow; the co-precipitate needs to be pre-dried to a moisture content below 5%, a process that is energy-intensive; and impurities such as bacterial cells, proteins, and pigments in the co-precipitate are difficult to completely remove using conventional activated carbon decolorization and plate and frame filtration, resulting in a final product with high impurity content and a yellowish color, making it difficult to meet polymerization-grade standards.

[0005] Reference 3 provides a method for purifying long-chain dicarboxylic acid fermentation broth using a ceramic nanofiltration membrane. This method involves acidification and crystallization to co-precipitate the long-chain dicarboxylic acid with bacterial cells, followed by dissolution with an aqueous solution of a lower alcohol. The bacterial cells are then removed via plate and frame filtration, and a ceramic nanofiltration membrane is used to further remove small amounts of bacterial cells, proteins, and pigments. However, this method also carries significant risks: during subsequent high-temperature processing or storage, the lower alcohol readily undergoes esterification with the long-chain dicarboxylic acid, generating dicarboxylic acid esters, which remain as impurities in the final product. These ester impurities may lead to chain termination or uneven molecular weight distribution during downstream polymerization, severely affecting the quality of the polymer product.

[0006] Therefore, developing a long-chain dicarboxylic acid extraction method that can efficiently remove proteins, avoid esterification risks, and is environmentally friendly and energy-saving has become a pressing technical challenge in this field.

[0007] References:

[0008] Reference 1: CN110272924A;

[0009] Reference 2: CN104693018A;

[0010] Reference 3: CN118239833A. Summary of the Invention

[0011] The problem the invention aims to solve

[0012] The present invention aims to overcome the above-mentioned defects of the prior art and provide a method for the extraction and purification of long-chain dicarboxylic acids that has good protein removal effect, no risk of esterification side reaction, low inorganic acid and base consumption and low energy consumption.

[0013] Solution for solving the problem

[0014] [1]. This invention provides a method for extracting and purifying long-chain dicarboxylic acids from fermentation broth, comprising the following steps:

[0015] 1) Solid-liquid separation step: The long-chain dicarboxylic acid fermentation broth is subjected to a first solid-liquid separation to obtain insoluble matter 1 and filtrate 1, wherein the water content of insoluble matter 1 is 30-40 wt%;

[0016] 2) Slurry preparation and dewatering steps: The insoluble matter 1 is prepared by using short-chain organic acids and a second solid-liquid separation is performed to displace the water in the insoluble matter 1, resulting in insoluble matter 2 and filtrate 2. The water content of the insoluble matter 2 is less than 10 wt%.

[0017] 3) High-temperature dissolution step: Dissolve the insoluble substance 2 at 80-85℃ using a short-chain organic acid to obtain a solution;

[0018] 4) Steps for ceramic membrane filtration: The solution is filtered through a ceramic membrane at 80-85°C, and the permeate is collected;

[0019] 5) Purification step: The permeate is purified to obtain a long-chain dicarboxylic acid product;

[0020] The long-chain dicarboxylic acid fermentation broth has a pH value below 6.0; the long-chain dicarboxylic acid is a dicarboxylic acid with 10-21 carbon atoms.

[0021] [2]. According to the method described in [1], the pH value of the long-chain dicarboxylic acid fermentation broth is 5.8-6.0; the long-chain dicarboxylic acid is a dicarboxylic acid with 10-18 carbon atoms.

[0022] [3]. According to the method described in [1] or [2], wherein,

[0023] The solid-liquid separation is carried out using a plate and frame filter press or a centrifuge.

[0024] The solid-liquid separation temperature is below 30°C.

[0025] [4]. The method according to any one of [1]-[3], wherein the short-chain organic acid includes one or more of formic acid, acetic acid and propionic acid, and the water content of the short-chain organic acid is less than 10%.

[0026] [5]. According to any one of [1]-[4], in the step of preparing the slurry and removing water,

[0027] The amount of the short-chain organic acid is 1-3 times the mass of the insoluble substance 1;

[0028] The temperature of the slurry preparation is below 30℃.

[0029] [6]. According to any one of [1]-[5], wherein, in the high-temperature dissolution step,

[0030] The amount of the short-chain organic acid is 2-5 times the dry weight of the long-chain dicarboxylic acid in the insoluble substance 2.

[0031] [7]. The method according to any one of [1]-[6], wherein, in the step of ceramic membrane filtration,

[0032] The ceramic membrane is made of at least one of alumina, zirconium oxide, and titanium oxide;

[0033] The ceramic membrane has an average pore size of 20-200 nm.

[0034] [8]. The method according to any one of [1]-[7], wherein the purification step is selected from one or more of decolorization, crystallization, washing and drying.

[0035] [9]. The method according to any one of [1]-[8], wherein the purification step includes at least decolorization and crystallization, wherein the decolorization includes treating the permeate with activated carbon; wherein the crystallization is achieved by concentrating the decolorized solution to a solid content of 25-30 wt% and then slowly cooling it to 10-30 °C.

[0036]

[10] . The method according to any one of [1]-[9], wherein the long-chain dicarboxylic acid includes any one of undecanoic acid, dodecanoic acid and tridecanoic acid.

[0037] The effects of the invention

[0038] 1) High product purity and good quality: protein is thoroughly removed (removal rate of over 99%), product purity can reach over 98.5%, total nitrogen content is low (less than 20ppm), white color, fully meeting the requirements of polymerization grade products.

[0039] 2) Outstanding environmental benefits: The entire process requires almost no strong acids or alkalis for pH adjustment, the consumption of inorganic acids and alkalis is zero, and the salt content and COD load of wastewater are significantly reduced.

[0040] 3) Simplified process and low energy consumption: There is no need to pre-dry the coprecipitate. After solvent replacement, it can be directly dissolved in a wet state with short-chain organic acids, which simplifies the steps, saves a lot of heat energy required for drying, and has a fast filtration speed and high production efficiency.

[0041] 4) No side reaction risk: Using short-chain organic acids as solvents completely eliminates the risk of esterification side reactions that occur during the purification process of long-chain dicarboxylic acids, ensuring the chemical stability of the product and excellent performance in downstream applications. Detailed Implementation

[0042] Various exemplary embodiments, features, and aspects of the present invention will be described in detail below. The term "exemplary" as used herein means "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as superior to or better than other embodiments.

[0043] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art should understand that the present invention can be practiced without certain specific details. In other instances, methods, means, apparatus, and steps well known to those skilled in the art have not been described in detail in order to highlight the spirit of the present invention.

[0044] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors that are unavoidable in industrial production.

[0045] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0046] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "implementation," etc., refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to that embodiment, which are included in at least one of the embodiments described herein and may or may not be present in other embodiments. Furthermore, it should be understood that these elements may be combined in any suitable manner in various embodiments.

[0047] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0048] In this specification, unless otherwise expressly stated, it should be understood that all ranges, quantities, values, and percentages used in this invention are modified with the word "about". Here, "about" generally means that the actual value is within ±5%, ±3%, ±1%, or ±0.5% of a specific value or range.

[0049] All unit names used in this manual are international standard unit names, and unless otherwise stated, the "%" indicates weight or mass percentage.

[0050] In this manual, the term "quantity" refers to "mass" unless otherwise specified.

[0051] In this instruction manual, "dry weight" refers to the weight of the dry matter obtained after removing the water from the substance.

[0052] Unless otherwise specified, “room temperature” or “room temperature” as used in this instruction manual usually refers to a temperature of 23±2℃.

[0053] The primary objective of this invention is to provide a method for extracting and purifying long-chain dicarboxylic acids from fermentation broth. Specifically, it is a method for extracting and purifying long-chain dicarboxylic acids from fermentation broth based on an acid-resistant ceramic membrane. This invention is mainly based on the following insights:

[0054] In traditional processes, the fermentation broth is first adjusted to neutral or alkaline by adding alkali, allowing the long-chain dicarboxylic acids to exist in the form of soluble disodium or ammonium salts ("alkali dissolution"). Subsequently, a large amount of inorganic acid (such as sulfuric acid) is added to convert them into insoluble dicarboxylic acids, which then precipitate out ("acid precipitation"). This "alkali dissolution-acid precipitation" route not only consumes large amounts of inorganic acids and alkalis but also generates high-salt wastewater, posing a significant environmental burden.

[0055] This invention reveals that when a long-chain dicarboxylic acid fermentation broth with a pH value below 6.0 is obtained (for example, through conventional fermentation followed by acidification, or preferably directly using a low-pH fermentation process), the long-chain dicarboxylic acid mainly exists in the form of free acid precipitate, accounting for more than 95%. Therefore, there is no need to add additional inorganic acid for acid precipitation, eliminating this step at the source and significantly reducing acid and alkali consumption and salt emissions.

[0056] Furthermore, the small amount (less than 5%) of long-chain dicarboxylic acid monosodium salt present in the precipitate can displace sodium ions from the monosodium salt during subsequent slurry conditioning and dewatering with short-chain organic acids. This is because the short-chain organic acids are stronger (lower pKa) than the long-chain dicarboxylic acids, converting them into free long-chain dicarboxylic acids. Simultaneously, the corresponding short-chain organic acid sodium salt is generated (which is soluble in the aqueous phase and thus removed). This conversion mechanism improves the yield of the target product while preventing sodium ions from contaminating the final product.

[0057] Subsequently, the long-chain dicarboxylic acid precipitate was dissolved using short-chain organic acids at high temperatures. Short-chain organic acids (such as acetic acid) have excellent dissolving power, and long-chain dicarboxylic acids remain stable in their molecular state under acidic conditions, making them less prone to degradation or side reactions. Based on this, a ceramic membrane was used for filtration in a continuously acidic environment—the acid-resistant ceramic membrane maintains a stable surface charge state under low pH conditions, effectively retaining residual bacterial fragments, denatured proteins, and other insoluble particles, while the target product permeates through the membrane pores in a dissolved state. Subsequent purification processes, including decolorization, crystallization, washing, and drying, yielded a high-purity long-chain dicarboxylic acid product that meets polymerization-grade requirements.

[0058] Specifically:

[0059] 1) This invention creatively constructs a continuous acidic environment operation path of "solid-liquid separation of fermentation broth → slurry preparation with short-chain organic acids → high-temperature dissolution of short-chain organic acids → acidic high-temperature ceramic membrane filtration". This path is completely different from the traditional "alkali dissolution-acidification" process, avoiding the use of inorganic acids and alkalis from the source, and significantly reducing acid and alkali consumption and high-salt wastewater discharge.

[0060] 2) This invention uses short-chain organic acids as excellent solvents for long-chain dicarboxylic acids, which have high solubility. They are acidic themselves, which can convert a small amount of long-chain dicarboxylic acid sodium salt in fermentation precipitate into free long-chain dicarboxylic acid without the need to add inorganic acid. At the same time, the dissolution and filtration process is always kept in an acidic environment, which is conducive to protein denaturation and precipitation and effective retention by ceramic membrane. No esterification reaction occurs between short-chain organic acids and long-chain dicarboxylic acids, which fundamentally eliminates the quality risk of ester impurities to the downstream polymerization process.

[0061] 3) In this invention, after solid-liquid separation of the fermentation broth at a lower temperature, the slurry is adjusted with short-chain organic acids with low water content, and the water in the filter cake is effectively replaced by secondary separation; the short-chain organic acids are used to dissolve long-chain dicarboxylic acids at high temperature and simultaneously perform high-temperature membrane filtration, which not only improves the solubility of the target product, but also significantly reduces the viscosity of the solution, thereby greatly increasing the membrane filtration flux. It can directly process the wet filter cake after water replacement and avoid the high-energy-consuming drying step in the traditional process.

[0062] 4) This invention organically combines an acid-resistant ceramic membrane with a short-chain organic acid system. The acid-resistant ceramic membrane ensures long-term operational stability under high-temperature and acidic conditions; the short-chain organic acid system improves the solubility of the target analyte, reduces the viscosity of the feed solution, and effectively alters the morphology of impurities (such as sodium salts of long-chain dicarboxylic acids and proteins). The synergistic effect of these two systems, complementing the precision sieving function of the ceramic membrane, achieves highly efficient separation of high-quality long-chain dicarboxylic acid solutions from large molecular impurities such as bacterial cells and denatured proteins.

[0063] The technical solution of the present invention will be further described in detail below:

[0064] This invention provides a method for extracting and purifying long-chain dicarboxylic acids from fermentation broth, comprising the following steps:

[0065] 1) Solid-liquid separation steps: The long-chain dicarboxylic acid fermentation broth is subjected to the first solid-liquid separation to obtain insoluble matter 1 and filtrate 1;

[0066] 2) Slurry preparation and dewatering steps: The insoluble matter 1 is prepared by using short-chain organic acids, and a second solid-liquid separation is performed to displace the water in the insoluble matter 1, resulting in insoluble matter 2 and filtrate 2.

[0067] 3) High-temperature dissolution step: Dissolve the insoluble substance 2 at 80-85℃ using a short-chain organic acid to obtain a solution;

[0068] 4) Steps for ceramic membrane filtration: The solution is filtered through a ceramic membrane at 80-85°C, and the permeate is collected;

[0069] 5) Purification step: Purify the permeate to obtain a long-chain dicarboxylic acid product.

[0070] (Steps for solid-liquid separation)

[0071] In the solid-liquid separation step of this invention, the main step is to perform a first solid-liquid separation on the long-chain dicarboxylic acid fermentation broth to obtain insoluble matter 1 and filtrate 1.

[0072] In some specific implementations, the pH value of the long-chain dicarboxylic acid fermentation broth is below 6.0, preferably 5.8-6.0.

[0073] In some preferred embodiments, the long-chain dicarboxylic acid fermentation broth is obtained through a low-pH fermentation process.

[0074] In this invention, fermentation is a technology that uses the metabolic functions of microorganisms to convert raw materials into target products under controlled conditions. Specifically, the prepared seed culture is inoculated into a fermentation tank containing alkane substrates and nutrients. Microorganisms grow and metabolize within the tank, ultimately oxidizing the alkane into the target product. The entire process is carried out at ambient temperature and pressure, using n-alkane as the raw material. Relying on the unique oxidizing ability of microorganisms (mainly including *Candida tropicalis*, *Candida sake*, and *Candida viswanathii*), the methyl groups at both ends of the n-alkane molecule are oxidized to carboxyl groups, thereby converting it into a dicarboxylic acid (i.e., a long-chain dicarboxylic acid) of the corresponding carbon chain length.

[0075] In some specific embodiments, the long-chain dicarboxylic acid fermentation broth contains water, residual fermentation substrate, long-chain dicarboxylic acid salt, bacterial cells, and other impurities. In some specific embodiments, the long-chain dicarboxylic acid is a dicarboxylic acid with 10-21 carbon atoms, preferably a dicarboxylic acid with 10-18 carbon atoms.

[0076] In some specific implementations, the solid-liquid separation is carried out using a plate and frame filter press or a centrifuge, with a centrifuge being preferred.

[0077] In some specific implementations, the solid-liquid separation temperature is below 30°C, preferably 15-20°C, for example, it can be 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, etc.

[0078] In the solid-liquid separation step of this invention, within the above-mentioned pH and temperature range, the solubility of the long-chain dicarboxylic acid and its sodium salt in the fermentation broth is extremely low, and most of the target product exists in solid form. Therefore, solid-liquid separation can directly obtain insoluble matter rich in long-chain dicarboxylic acid, while most soluble impurities (such as inorganic salts, pigments, etc.) are removed by entering the filtrate.

[0079] In some specific implementations, the water content of the insoluble substance 1 is 30-40 wt%, for example, it can be 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, 40 wt%, etc.

[0080] (Steps for preparing slurry and removing water)

[0081] In the slurry preparation and dewatering step of this invention, short-chain organic acids are mainly used to prepare the insoluble material 1, and a second solid-liquid separation is performed to displace the water in the insoluble material 1, thereby obtaining insoluble material 2 and filtrate 2.

[0082] In some specific embodiments, the short-chain organic acid includes one or more of formic acid, acetic acid, and propionic acid, preferably acetic acid.

[0083] In some specific embodiments, the water content of the short-chain organic acid is less than 10%, preferably less than 5%. Using short-chain organic acids with low water content for slurry preparation can displace water between and inside insoluble particles through concentration gradient diffusion between the liquid and solid phases, while simultaneously converting the monosodium salt into a free dicarboxylic acid.

[0084] In some specific implementations, the amount of the short-chain organic acid is 1-3 times the mass of the insoluble substance 1, preferably 1.2-1.5 times, for example, it can be 1 times, 1.2 times, 1.5 times, 1.8 times, 2 times, 2.2 times, 2.5 times, 2.8 times, 3 times, etc.

[0085] In some specific implementations, the temperature of the slurry preparation is below 30°C, preferably 15-20°C, such as 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, etc.

[0086] In some specific implementations, the solid-liquid separation is carried out using a plate and frame filter press or a centrifuge, with a centrifuge being preferred.

[0087] In some specific implementations, the solid-liquid separation temperature is below 30°C, preferably 15-20°C, for example, it can be 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, etc.

[0088] In some specific implementations, in step 2), the water content of the insoluble substance 2 is less than 10 wt%, for example, it can be 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 8.7 wt%, 9 wt%, 9.5 wt%, 10 wt%, etc.

[0089] After the slurry conditioning and dewatering steps of this invention, the water content of the insoluble material 2 can be reduced to below 10 wt%, thereby avoiding side reactions caused by water during subsequent high-temperature dissolution (such as the reverse shift of the equilibrium of dicarboxylic acid hydrolysis or esterification), and also providing a purer dissolution environment for subsequent ceramic membrane filtration.

[0090] (The step of high-temperature dissolution)

[0091] In the high-temperature dissolution step of this invention, the insoluble substance 2 is mainly dissolved at 80-85°C using a short-chain organic acid to obtain a solution.

[0092] In some specific implementations, in step 3), the amount of the short-chain organic acid is 2-5 times the dry weight of the long-chain dicarboxylic acid in the insoluble substance 2, preferably 2.5-3 times, for example, it can be 2 times, 2.2 times, 2.5 times, 2.8 times, 3 times, 3.2 times, 3.5 times, 3.8 times, 4 times, 4.2 times, 4.5 times, 4.8 times, 5 times, etc.

[0093] In some specific embodiments, the short-chain organic acid includes one or more of formic acid, acetic acid, and propionic acid, preferably acetic acid.

[0094] In some specific implementations, the water content of the short-chain organic acid is less than 10%, preferably less than 5%.

[0095] In this invention, long-chain dicarboxylic acids are almost insoluble in water or dilute acids at room temperature, but their solubility in short-chain organic acids (especially acetic acid) is significantly increased at high temperatures (80-85°C). Short-chain organic acids, as polar solvents, can form hydrogen bonds with the carboxyl groups of long-chain dicarboxylic acids, promoting their molecular dispersion. Simultaneously, high temperatures accelerate dissolution kinetics and help release some of the dicarboxylic acids bound to proteins or bacterial cells.

[0096] (Steps of ceramic membrane filtration)

[0097] In the ceramic membrane filtration process of this invention, the main step is to filter the solution using a ceramic membrane at 80-85°C and collect the permeate.

[0098] In some specific embodiments, the ceramic membrane is made of acid-resistant ceramic membrane, preferably at least one of alumina, zirconium oxide, and titanium oxide.

[0099] In some specific implementations, the average pore size of the ceramic membrane is 20-200 nm, preferably 20-50 nm, and can be, for example, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, etc.

[0100] Under acidic and high-temperature conditions, the solution may still contain tiny bacterial fragments, denatured protein aggregates, and some pigment particles. Ordinary organic membranes are prone to swelling or degradation under these conditions, while acid-resistant ceramic membranes exhibit excellent chemical and thermal stability. Their filtration mechanism primarily relies on sieving, combined with the charge effect on the membrane surface—at acidic pH, most proteins and bacterial fragments are positively charged or uncharged, while the ceramic membrane surface is typically negatively charged or neutral. Through electrostatic repulsion and adsorption, these impurities can be efficiently retained. Since the target product, a long-chain dicarboxylic acid, dissolves in the short-chain organic acid in molecular form, its molecular weight is much smaller than the membrane's molecular weight cutoff, allowing for smooth permeation. Continuous acidic filtration also prevents the precipitation of dicarboxylic acid salts, ensuring high throughput and long-term stable operation.

[0101] (Purification steps)

[0102] The purification step of this invention mainly involves purifying the permeate to obtain a long-chain dicarboxylic acid product.

[0103] In some specific implementations, the purification step is selected from one or more of decolorization, crystallization, washing, and drying processes.

[0104] In some preferred embodiments, the purification step includes at least decolorization and crystallization.

[0105] In some specific embodiments, the decolorization includes treating the permeate with activated carbon; wherein the amount of activated carbon added is 2-5% of the dry weight of the long-chain dicarboxylic acid in the permeate, preferably 2-3%, for example, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, etc. The activated carbon removes residual pigments and trace organic impurities through physical adsorption.

[0106] In some specific implementations, the decolorization temperature is 80-85℃, and the decolorization time is 40-60 minutes.

[0107] In some specific embodiments, the crystallization involves concentrating the decolorized solution to a solid content of 25-30 wt%, followed by slow cooling to 10-30°C, causing the long-chain dicarboxylic acid to precipitate as high-purity crystals. Slow cooling facilitates the formation of regular crystals and reduces impurity inclusions.

[0108] In some specific implementations, the crystallized product is washed with a small amount of short-chain organic acid or water to further remove surface-adhered impurities, and finally dried under vacuum or airflow to obtain a polymer-grade long-chain dicarboxylic acid product.

[0109] In some specific implementations, the long-chain dicarboxylic acid includes any one of undecanoic acid, dodecanoic acid, and tridecanoic acid.

[0110] By implementing the above method, the purity of the obtained long-chain dicarboxylic acid product can reach 98.5% or more, preferably 99.0% or more, more preferably 99.5% or more; the total nitrogen content is less than 40 ppm, preferably less than 30 ppm, more preferably less than 20 ppm, and even more preferably less than 15 ppm; the ash content is less than 50 ppm, preferably less than 40 ppm; and the light transmittance (430 nm) is as high as 99.5% or more, preferably 99.8% or more.

[0111] Example

[0112] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0113] In this invention, loss on drying refers to the weight reduction of a sample after drying it to constant weight under specified conditions. It is usually expressed as a percentage and is mainly used to reflect the content of moisture and volatile substances in the sample. The calculation formula is: (Wet sample mass - Dry sample mass) / Wet sample mass × 100%. The detection method refers to GB / T 5009.236-2016.

[0114] The term "monodicarboxylic acid" below refers to a non-condensed monodicarboxylic acid.

[0115] Example 1:

[0116] 1) Solid-liquid separation: The tridecanoic acid fermentation broth was placed in a tank, and centrifuged at pH 5.8 and 30°C to obtain insoluble matter, which contained long-chain dicarboxylic acid, sodium salt of long-chain dicarboxylic acid and bacterial cells, with a water content of 38%.

[0117] 2) Slurry preparation and dehydration: The insoluble matter is prepared with acetic acid with a water content of 4%, and the temperature is controlled at 20℃. The amount of acetic acid is 1.5 times the weight of the insoluble matter. The insoluble matter is separated twice to replace the water in the insoluble matter. The insoluble matter contains long-chain dicarboxylic acids and bacterial cells. The drying loss is 35%, and the water content is 8.7%.

[0118] 3) High-temperature dissolution: Dissolve the insoluble substance in acetic acid with 3 times the mass of the long-chain dicarboxylic acid at a dissolution temperature of 85°C to obtain a solution;

[0119] 4) Ceramic membrane filtration: 50nm ceramic membrane filtration is used, with an operating temperature of 85℃ and an operating pressure of 0.2MPa. The protein retention rate of the permeate is over 99.5%.

[0120] 5) Decolorization and crystallization: Add 3% of the dry weight of long-chain dicarboxylic acid to the permeate and decolorize at 85°C for 1 hour. Filter to separate the clear liquid and concentrate the clear liquid under reduced pressure to a solid content of 28%. Slowly cool to 30°C to crystallize. Centrifuge, wash and dry to obtain tridecanoic acid product.

[0121] The test results showed that the crystal content was 99.38%, the total acid content was 99.99%, the proportion of mono- and dicarboxylic acids was 99.52%, the nitrogen content was 10 ppm, the ash content was 39 ppm, the melting point was 113.8-114.1℃, the transmittance of 5% sodium salt aqueous solution at 430nm was 99.5%, and the moisture content was 0.2%.

[0122] Example 2:

[0123] 1) Solid-liquid separation: The tridecanoic acid fermentation broth was placed in a tank, centrifuged at pH 6.0 and 25°C to obtain insoluble matter, which contained long-chain dicarboxylic acid, sodium salt of long-chain dicarboxylic acid and bacterial cells, with a water content of 35%;

[0124] 2) Slurry preparation and dehydration: The insoluble matter is prepared with propionic acid containing 5% water at a temperature controlled at 15℃. The amount of propionic acid used is 1.2 times the mass of the insoluble matter. The insoluble matter is separated twice to replace the water in the insoluble matter. The insoluble matter contains long-chain dicarboxylic acids and bacterial cells. The drying loss is 38%, and the moisture content is 9.5%.

[0125] 3) High-temperature dissolution: Dissolve the insoluble substance in 2.5 times the mass of propionic acid, a long-chain dicarboxylic acid, at a dissolution temperature of 80℃ to obtain a solution;

[0126] 4) Ceramic membrane filtration: 20nm ceramic membrane filtration is used, with an operating temperature of 80℃ and an operating pressure of 0.2MPa. The protein retention rate of the permeate is over 99%.

[0127] 5) Decolorization and crystallization: Add 3% of the dry weight of long-chain dicarboxylic acid to the permeate and decolorize at 80°C for 1 hour. Filter to separate the clear liquid and concentrate the clear liquid under reduced pressure to a solid content of 30%. Slowly cool to 10°C to crystallize. Centrifuge, wash and dry to obtain tridecanoic acid product.

[0128] The test results showed that the crystal content was 99.19%, the total acid content was 99.90%, the proportion of mono- and dicarboxylic acids was 99.32%, the nitrogen content was 16 ppm, the ash content was 33 ppm, the melting point was 114.1-114.4℃, the transmittance of 5% sodium salt aqueous solution at 430nm was 99.8%, and the moisture content was 0.3%.

[0129] Example 3:

[0130] Similar to Example 1, except that in steps 2) and 3), formic acid with a water content of 3% is used for slurry preparation and dissolution.

[0131] Comparative Example 1:

[0132] According to the method disclosed in patent document CN104693018A, 98% sulfuric acid was directly added to the tridecanoic acid fermentation broth to acidify the pH to 2.0, followed by plate and frame filtration and drying to a moisture content of 3.0%. Acetic acid (2% water content) of 2.5 times its mass in solid form was added, heated to 95°C to dissolve, filtered to remove impurities, and slowly cooled to 20°C to obtain a long-chain dicarboxylic acid crystal solution. This solution was centrifuged, washed, and dried to obtain the tridecanoic acid product.

[0133] The test results showed that the crystal content was 97.11%, the total acid content was 98.16%, the proportion of mono- and dicarboxylic acids was 97.38%, the nitrogen content was 604 ppm, the ash content was 485 ppm, the melting point was 113.1-115.7℃, the transmittance of 5% sodium salt aqueous solution at 430nm was 83.2%, and the moisture content was 0.4%.

[0134] Comparative Example 2:

[0135] Similar to Example 1, except that step 2 is omitted, i.e., the insoluble matter in step 1) is directly dissolved in step 3).

[0136] Comparative Example 3:

[0137] Similar to Example 1, except that in step 2), an aqueous solution of acetic acid with a water content of 15% was used for slurry preparation.

[0138] The test results of the products obtained in each embodiment and comparative example are shown in Table 1.

[0139] Table 1:

[0140]

[0141] The "single dicarboxylic acid %" in Table 1 refers to the proportion of the target product, tridecanoic acid, in the total acid content. This content is determined using the gas chromatography area normalization method, and is automatically calculated by the chromatography workstation according to the area normalization method. Relevant testing can be referenced in the following standards (described as "single acid" in the standards): Group Standard T / CIEP-0034-2023, Enterprise Standard Q / KSWS 005-2022, and Q / 370682LHL.

[0142] It should be noted that although the technical solution of the present invention has been described with specific examples, those skilled in the art will understand that the present invention should not be limited thereto.

[0143] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for extracting and purifying long-chain dicarboxylic acids from fermentation broth, comprising the following steps: 1) Solid-liquid separation step: The long-chain dicarboxylic acid fermentation broth is subjected to a first solid-liquid separation to obtain insoluble matter 1 and filtrate 1, wherein the water content of insoluble matter 1 is 30-40 wt%; 2) Slurry preparation and dewatering steps: The insoluble material 1 is prepared by using short-chain organic acids and a second solid-liquid separation is performed to displace the water in the insoluble material 1, resulting in insoluble material 2 and filtrate 2. The water content of the insoluble material 2 is less than 10 wt%, thereby avoiding the side reactions caused by water during the following high-temperature dissolution. 3) High-temperature dissolution step: Dissolve the insoluble substance 2 at 80-85℃ using a short-chain organic acid to obtain a solution; 4) Steps for ceramic membrane filtration: The solution is filtered through a ceramic membrane at 80-85°C, and the permeate is collected; the average pore size of the ceramic membrane is 20-200 nm. 5) Purification step: The permeate is purified to obtain a long-chain dicarboxylic acid product; The long-chain dicarboxylic acid fermentation broth has a pH value below 6.0; the long-chain dicarboxylic acid is a dicarboxylic acid with 10-21 carbon atoms. The short-chain organic acid has a water content of less than 10%.

2. The method according to claim 1, characterized in that, The pH value of the long-chain dicarboxylic acid fermentation broth is 5.8-6.0; the long-chain dicarboxylic acid is a dicarboxylic acid with 10-18 carbon atoms.

3. The method according to claim 1, characterized in that, The solid-liquid separation is carried out using a plate and frame filter press or a centrifuge. The solid-liquid separation temperature is below 30°C.

4. The method according to any one of claims 1-3, characterized in that, The short-chain organic acids include one or more of formic acid, acetic acid, and propionic acid.

5. The method according to any one of claims 1-3, characterized in that, In the step of preparing the slurry and removing water... The mass of the short-chain organic acid is 1-3 times the mass of the insoluble substance 1; The temperature of the slurry preparation is below 30℃.

6. The method according to any one of claims 1-3, characterized in that, In the high-temperature dissolution step The amount of the short-chain organic acid used is 2-5 times the dry weight of the long-chain dicarboxylic acid in the insoluble substance 2.

7. The method according to any one of claims 1-3, characterized in that, In the ceramic membrane filtration step The ceramic membrane is made of at least one of alumina, zirconium oxide, and titanium oxide.

8. The method according to any one of claims 1-3, characterized in that, The purification steps are selected from one or more of the following: decolorization, crystallization, washing, and drying.

9. The method according to any one of claims 1-3, characterized in that, The purification steps include at least decolorization and crystallization. The decolorization includes treating the permeate with activated carbon. The crystallization is achieved by concentrating the decolorized solution to a solid content of 25-30 wt% and then slowly cooling it to 10-30°C.

10. The method according to any one of claims 1-3, characterized in that, The long-chain dicarboxylic acid includes any one of undecanoic acid, dodecanoic acid, and tridecanoic acid.

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