Method for removing protein from dicarboxylic acid fermentation broth

Abstract

The application provides a method for removing protein in a dicarboxylic acid fermentation liquor. The dicarboxylic acid salt filtrate after inactivation and filtration treatment is introduced into an electrodialyzer for electrodialysis. The dicarboxylic acid salt filtrate is introduced into a dilute chamber, and alkali liquor is continuously added into the dilute chamber during the electrodialysis process, so that the pH of the dilute chamber is maintained at 8-12, preferably 9-10. The purified dicarboxylic acid salt is obtained in a concentrated chamber. The application finds that, by maintaining the pH of the aqueous dicarboxylic acid salt solution in the dilute chamber to be alkaline, the dicarboxylic acid salt is in a double salt state, which is the key to improving the efficiency of the electrodialysis treatment. This technical means increases the current density in the electrodialyzer and accelerates the migration rate of the salt. By maintaining the pH of the dilute chamber to be alkaline, the ionization rate of the dicarboxylic acid salt is increased, the concentration of the dicarboxylic acid monosalt is effectively reduced, the precipitation of the monosalt to block the electrodialyzer is avoided, and the stable and long-period operation of the electrodialyzer for treating the dicarboxylic acid salt fermentation liquor is realized.

Description

Technical Field

[0001] This invention relates to a method for removing proteins from dicarboxylic acids, particularly a method for removing proteins from long-chain dicarboxylic acid products obtained from C10-C18 n-alkane fermentation broth, belonging to the field of dicarboxylic acid refining technology. Background Technology

[0002] The composition of dicarboxylic acid fermentation broth is quite complex, mainly consisting of 80%-85% water, 12%-18% dicarboxylate, 0.5%-1% bacterial cells, and 0.1%-0.5% water-soluble protein, unused culture medium, and microbial secretions. The high protein content significantly complicates the extraction and purification of dicarboxylic acids, severely impacting product purity and applications.

[0003] Currently, the market has stringent requirements for the protein content of dicarboxylic acid products, with total nitrogen <30µg / g (in this product category, total nitrogen is used to characterize the protein content). The largest application of dicarboxylic acids is in the production of nylon engineering plastics. Nylon polymerization occurs at high temperatures, approximately 230–280°C. To achieve specific mechanical properties, nylon needs to reach a very high molecular weight, which places high demands on the quality of dicarboxylic acid products. Unlike other chemically synthesized polymer-grade dicarboxylic acids, fermented dicarboxylic acids contain residual protein. At polymerization temperatures, this protein denatures and degrades, reducing catalyst activity, causing discoloration that affects the polymer's appearance and applications, and most importantly, producing monofunctional substances that act as polymerization inhibitors, resulting in a lower-than-expected polymer molecular weight and consequently affecting the polymer's mechanical properties.

[0004] Therefore, total nitrogen is a key indicator in polymer-grade dicarboxylic acids and a decisive factor in their polymerization applications.

[0005] Currently, the common processes used in the dicarboxylic acid industry to obtain polymerization-grade products include:

[0006] 1) Extraction process of crude dicarboxylic acid

[0007] The fermentation broth is heated to inactivate it, and then passed through a microfiltration or ultrafiltration device to remove water-insoluble solids such as bacterial cells, resulting in a clear filtrate containing dissolved dicarboxylic acid salts. Sulfuric acid is added to acidify the filtrate to a pH of 2.0–4.0 to obtain an aqueous solution of dicarboxylic acid crystals. After filtration, washing, and drying, crude dicarboxylic acid is obtained.

[0008] 2) Solvent purification process of dicarboxylic acids

[0009] The process involves extracting crude dicarboxylic acid as raw material, mixing it with a solvent, heating to dissolve it, adding activated carbon to adsorb impurities such as pigments, filtering while hot, cooling the filtrate to crystallize, separating the solid and liquid phases to obtain crude dicarboxylic acid crystals, and then further drying to obtain the product. The solvents used in this process mainly include acetic acid, alcohols, ketones, esters, and aromatic hydrocarbons.

[0010] Generally, after the above two processes, the total nitrogen of the dicarboxylic acid product can meet the requirements for use as a polymerization raw material.

[0011] As is well known, in the extraction of crude dicarboxylic acid, insoluble solids such as proteins are removed from the fermentation broth through microfiltration or ultrafiltration, while water-soluble proteins and other impurities remain dissolved in the filtrate and are not removed by filtration. During further acidification with sulfuric acid, soluble proteins precipitate or denature under acidic conditions, and dicarboxylic acid salts also crystallize out during acidification. This results in the precipitated soluble proteins mixing with the crude dicarboxylic acid, leading to a total nitrogen content in the crude dicarboxylic acid exceeding 30 µg / g. The high protein content in the crude dicarboxylic acid filter cake results in a yellow, viscous, and easily agglomerated crude product. This not only increases the energy consumption for drying and dehydrating the crude dicarboxylic acid but also increases the load on subsequent solvent refining, leading to a longer refining process, lower product yield, and higher equipment investment. Ultimately, this increases production costs and reduces production efficiency.

[0012] There are generally three main methods for protein removal: one is to use physical or chemical methods to denature and precipitate the protein, which is then removed by filtration; the second is to use adsorption methods, such as adsorption resins; and the third is to use salting-out methods, which involve adding a large amount of inorganic salt to the solution to change the solubility of the protein in water, causing the protein to precipitate, which is then removed by filtration.

[0013] Physical methods for protein denaturation include heating, pressurization, stirring, shaking, ultraviolet irradiation, X-rays, and ultrasound; chemical methods include strong acids, strong bases, heavy metal salts, inorganic salts (sodium sulfate, sodium chloride, and ammonium sulfate, etc.), trichloroacetic acid, and organic solvents.

[0014] However, among the protein removal methods mentioned above, protein denaturation can only remove part of the protein. Denaturation methods such as ultraviolet irradiation, X-rays, and ultrasound are only suitable for small-scale laboratory-scale protein removal processes, and the related equipment is expensive, making it unsuitable for industrial-scale protein removal of crude dicarboxylic acid products.

[0015] Chemical denaturation using strong acids is clearly unsuitable for crude dicarboxylic acid systems. Under acidic conditions, the precipitated crude dicarboxylic acid encapsulates most of the protein, resulting in poor protein removal. Other chemical denaturation methods, such as heavy metal salts and trichloroacetic acid, are expensive and only suitable for laboratory-scale protein removal processes. Furthermore, the precipitation reaction between heavy metal salts and crude dicarboxylic acid means that while the protein is precipitated, the heavy metal salt in the crude dicarboxylic acid also precipitates, failing to achieve the desired protein removal effect and leading to the loss of crude dicarboxylic acid.

[0016] CN201310045908.X discloses a method for removing organic amine nitrogen impurities from crude dicarboxylic acids produced by microbial methods, which includes the following steps: a) using a long-chain dicarboxylic acid as a primary product, dissolving the primary product in acetone or butanone liquid condensed after distillation at room temperature and pressure; b) filtering the solution formed after dissolving the primary product in step a) with filter media with a filtration precision of 0.1-50 μm, retaining the filtrate, and the filter residue is the removed product; c) concentrating the filtered filtrate in a heated evaporator by distillation, and recycling the condensed acetone or butanone vapor; d) in the heated evaporator, dicarboxylic acid crystals will precipitate from the concentrated mother liquor, the solid phase will be collected by filtration, and after being purged with clean air, the refined long-chain dicarboxylic acid product is obtained. Although the nitrogen content in the long-chain dicarboxylic acid product obtained by its patented process is less than 12 ppm, the use of low-boiling-point solvents such as acetone or butanone (acetone 56.1℃, butanone 79.6℃) places higher demands on the sealing performance of the equipment during the processing. In particular, the patented process involves purging the crystalline dicarboxylic acid containing solvent with air, which is a relatively dangerous process that can easily form an explosive gas mixture. Moreover, the ketone solvent in this mixture is difficult to recover, inevitably causing environmental pollution. Furthermore, acetone is unstable in the presence of acid and easily forms isopropylidene acetone, affecting the purity and application of the final product.

[0017] The article "Study on Protein Removal Methods in the Extraction of Water-Soluble Arabicaxylan from Wheat Flour" published in the March 2012 issue of the *Journal of Henan University of Technology (Natural Science Edition)* uses diatomaceous earth to adsorb proteins. The study suggests that the protein removal rate in the extract gradually increases with the increase of diatomaceous earth addition. However, the maximum removal rate does not exceed 55%. Diatomaceous earth, while adsorbing proteins, also adsorbs the target product, resulting in a loss rate of nearly 20% of the target product.

[0018] The article "Simultaneous Removal of Pigments and Proteins from Cordyceps Sinensis Crude Polysaccharides by Resin Method" published in the July 2012 issue of *Food Industry Technology* evaluated the deproteinization effects of eight resins on Cordyceps sinensis crude polysaccharides. D113 resin showed ideal deproteinization, achieving a deproteinization rate of 82.2% ± 1.7%. However, this method struggles to reduce the protein content in crude dicarboxylic acids to the ppm level. Not only is the target product lost through adsorption at a rate as high as 20% ± 2.2%, but the resin also requires regeneration with a 50% ethanol-hydrochloric acid solution.

[0019] As can be seen from the two articles above, when using adsorption methods to remove proteins from dicarboxylic acid fermentation broth, regardless of whether adsorption resin, diatomaceous earth, activated carbon, or other types of adsorbents are used, dicarboxylic acid is also adsorbed along with the protein, leading to dicarboxylic acid loss, and the protein adsorption is incomplete. Furthermore, resin regeneration or adsorbent deactivation generates large amounts of high-salinity wastewater and solid waste, placing significant pressure on environmental protection.

[0020] Salting out is a process where a concentrated inorganic salt (such as (NH4)2SO4 or Na2SO4) solution is added to a protein solution, altering the protein's solubility in water. This causes the protein to aggregate and precipitate from the solution. While adding salt to a protein solution causes precipitation, the protein remains soluble in water, and its original properties are not affected. Therefore, salting out is a reversible process.

[0021] The method for refining dicarboxylic acids disclosed in patent CN97121846.3 employs an inorganic salt salting-out method, which includes the following steps: adding alkali to the terminated fermentation broth to separate oil, filtering and sterilizing, then acidifying and filtering to obtain crude acid, adding alkali and water to the crude acid to make a salt solution, then adding a salting-out agent (sodium sulfate, sodium chloride and ammonium sulfate, preferably sodium chloride) to salt out and filter the dicarboxylic acid salt, adding water to dissolve the dicarboxylic acid salt, filtering to remove impurities, and finally, the filtrate undergoes acidification, crystallization, filtration and drying steps to obtain the dicarboxylic acid product. In the implementation of this patent, solids such as bacterial protein are removed by filtration, while soluble protein remains in the filtrate. Subsequent salting causes dicarboxylic acid disalt to precipitate out. The solubility of soluble protein also decreases under the action of high concentrations of inorganic salts, and it precipitates out together with the dicarboxylic acid disalt. In this process, the protein only precipitates and does not denature. After the dicarboxylic acid disalt is dissolved in water in this patent, the co-precipitated protein will also dissolve in the water. Therefore, this process is still difficult to remove the protein, resulting in the total nitrogen content not meeting the requirements.

[0022] Patent CN201910128959.6 discloses a decolorization method for mixed long-chain dicarboxylic acids, which employs electrodialysis to treat the mixed long-chain dicarboxylic acid salt solution. Electrodialysis is a standard procedure for treating conventional salt solutions, but it is difficult to implement using conventional methods to treat dicarboxylic acid fermentation broths. This is due to the properties and characteristics of dicarboxylic acids and their fermentation material system, which preclude the use of conventional electrodialysis. However, the patent does not recognize or address the fundamental problem affecting the efficiency of electrodialysis in treating dicarboxylic acid solutions, nor does it provide corresponding solutions. This is highly detrimental to the practical application and operation of electrodialysis in the field of dicarboxylic acids. Summary of the Invention

[0023] To address the above shortcomings, this invention provides a method for removing proteins from dicarboxylic acids that is mild in processing conditions, does not require the addition of any organic solvents or other compounds, is simple and safe in operation, can be run for a long time, is easy to produce on an industrial scale, and is low-cost and efficient.

[0024] To achieve the above technical objectives, the technical solution of the present invention is as follows:

[0025] This invention provides a method for removing proteins from dicarboxylic acid fermentation broth. The method involves introducing a dicarboxylic acid filtrate, after inactivation and filtration, into an electrodialysis unit for electrodialysis. The electrodialysis unit is composed of alternating anion exchange membranes and cation exchange membranes. Each pair of anion exchange membranes and cation exchange membranes constitutes a membrane pair unit. Within each membrane pair unit, the space between the anion exchange membranes and cation exchange membranes is a dilute chamber, the space between adjacent membrane pairs is a concentrate chamber, and the two sides are polar chambers. The dicarboxylic acid filtrate is introduced into the dilute chamber, and during electrodialysis, an alkali solution is added to the dilute chamber to maintain the pH of the dilute chamber at 8-12, preferably 9-10. The purified dicarboxylic acid is obtained in the concentrate chamber.

[0026] The general formula of the dicarboxylic acid molecule referred to in this invention is C2. n H 2n-2 O4, where n is 10-18, is a metabolic product obtained by microorganisms through fermentation using raw materials such as C10-C18 alkanes. The dicarboxylic acid fermentation broth contains a single dicarboxylic acid or a mixture of dicarboxylic acids.

[0027] Furthermore, the alkaline solution is selected from one or more aqueous solutions of sodium bicarbonate, sodium carbonate, sodium hydroxide, potassium bicarbonate, potassium carbonate, and potassium hydroxide, with a solute mass concentration of 10.0% to 40.0%; preferably, it is an aqueous solution of sodium hydroxide.

[0028] Furthermore, the voltage of each membrane pair unit in the electrodialysis unit is 0.6V~2V.

[0029] Furthermore, in the dilute chamber of the electrodialysis device, the concentration of dicarboxylate is 40~150g / L, preferably 50g / L~100g / L.

[0030] Furthermore, in the concentration chamber of the electrodialysis unit, the concentration of dicarboxylate is maintained at 10 g / L to 100 g / L, preferably 20 g / L to 70 g / L, and the dicarboxylate is removed from the electrodialysis unit in a timely manner.

[0031] Furthermore, the pH of the dicarboxylate introduced into the dilute chamber of the electrodialysis unit is 8-10.

[0032] Furthermore, the electrodialysis is performed at a temperature of 20~35℃.

[0033] Furthermore, the pore size of the anion exchange membrane and the cation exchange membrane is 1 nm to 30 nm, preferably 2 nm to 10 nm.

[0034] Those skilled in the art should understand that the electrodialysis device described is a conventional electrodialysis device in the prior art. The dicarboxylate filtrate enters the dilute chamber, and under the influence of an electric field, ions pass through the ion exchange membrane into the concentrate chamber, while macromolecules and electrically neutral substances remain in the dilute chamber. Through the electrodialysis condition control of this invention, proteins, pigments, and other impurities that cannot permeate the ion exchange membrane are efficiently separated from the dicarboxylate, and the device can operate stably for a long period.

[0035] Furthermore, as a more specific implementation, the removal method includes the following:

[0036] I. Inactivate the dicarboxylic acid fermentation broth by heating after fermentation has been terminated;

[0037] II. Remove bacterial cells and other solids to obtain dicarboxylate filtrate;

[0038] III. The dicarboxylate filtrate is introduced into the dilute chamber of the electrodialysis apparatus, and the pH of the dilute chamber is maintained at 8-12, preferably 9-10. Under the action of the electric field, the dicarboxylate migrates to the concentrated chamber, and a dialysis solution rich in dicarboxylate is obtained.

[0039] IV. Selectively add an adsorbent to the dicarboxylate solution obtained in step III, and filter to remove solids;

[0040] V. Acidify the filtrate obtained in step IV to obtain a dicarboxylic acid crystal solution;

[0041] VI. Separate the dicarboxylic acid crystallization liquid, filter and dry to obtain the dicarboxylic acid product.

[0042] In the method of this invention, the heating inactivation temperature in step I is 75℃~100℃.

[0043] In the method of the present invention, step II uses filtration to remove bacteria and other impurities. The filtration uses conventional single devices or combinations of multiple sterilization methods and equipment such as microfiltration, ultrafiltration or centrifugation.

[0044] In the method of the present invention, the dicarboxylate obtained in step II includes a monovalent cation, specifically sodium, potassium or ammonium.

[0045] The method of this invention also includes a step of further electrodialysis treatment of the dicarboxylate dialysis solution collected in the concentrate chamber. This second electrodialysis not only recovers most of the alkali solution, significantly reducing the amount of inorganic or organic acid used for subsequent acidification of the dicarboxylate, but also allows the recovered alkali solution to be recycled to adjust the pH of the dilute chamber of the electrodialysis unit.

[0046] The method of the present invention also includes a step of recovering and reusing the decarboxylate solution containing proteins and the like obtained in the dilute chamber of step III, which can be used for re-fermentation to reduce the pressure on wastewater treatment.

[0047] In the method of the present invention, the adsorbent in step IV is activated carbon and / or activated clay, preferably activated carbon, and the amount added is 0.01wt% to 5.0wt% of the dry weight of the organic acid, preferably 0.5wt% to 2.0wt%, and the adsorption time is 30min to 60min.

[0048] In the method of this invention, the acidification in step V is carried out using conventional methods. The pH value of the acidification is 2.0~4.0. The acid used for acidification can be any concentration of inorganic acids such as H2SO4, HNO3, HCl, and H3PO4, or organic acids such as acetic acid.

[0049] Electrodialysis is a standard procedure for treating conventional salt solutions. However, during their research, the inventors discovered that the efficiency of electrodialysis in treating fermented dicarboxylate solutions decreased over time, and membrane pores became clogged, making long-term, large-scale operation difficult. To address these technical problems, the inventors optimized the electrodialysis treatment conditions and identified key factors affecting treatment efficiency and cycle time: during electrodialysis of dicarboxylate solutions, the pH in the dilute chamber gradually decreased, and the current density also decreased accordingly, slowing the migration of dicarboxylate to the concentrate chamber. Through research and analysis, the inventors concluded that these changes prevented the dicarboxylate in the dilute chamber from ionizing in a timely manner and achieving effective separation. Through experimental research, the inventors discovered that maintaining the pH in the dilute chamber at 8-12, preferably 9-10, allows the dicarboxylate in the dilute chamber to exist in a dual-salt state. This means that the higher the total number of dicarboxylate anions in the dilute chamber solution, the higher the ionic strength, and the faster the ions permeate through the ion exchange membrane to the concentrate chamber (the storage chamber after the dicarboxylate has passed through the ion exchange membrane). This results in a higher current reading on the electrodialysis ammeter and higher efficiency in treating the dicarboxylate, and vice versa. Therefore, the treatment efficiency of the electrodialysis unit is highly correlated with the pH in the dilute chamber. The fundamental reason is that dicarboxylate dissolved in water exists in a dynamic dissociation equilibrium. Taking sodium dicarboxylate as an example, the ionization equilibrium equation for sodium dicarboxylate in water is as follows:

[0050] NaOOC-(CH2) n -COONa + H₂O → NaOOC-(CH₂) n -COOH+NaOH

[0051] As can be seen from the dissociation equilibrium equation, the dicarboxylic acid disalt in aqueous solution hydrolyzes into dicarboxylic acid monosalt and sodium hydroxide, exhibiting a dynamic ionization equilibrium. Since dicarboxylic acid is a weak electrolyte and sodium hydroxide is a strong electrolyte, during electrodialysis operation, the strong base migrates to the concentrate chamber more rapidly. This results in an increasingly higher concentration of dicarboxylic acid monosalt in the dilute chamber, a rapid decrease in pH, and a rapid decrease in ionic strength and current density, significantly impacting the efficiency of electrodialysis. This invention addresses this by supplementing the dilute chamber with alkali to maintain its pH, thus shifting the equilibrium towards the dicarboxylic acid disalt. This significantly increases the total charge in the dilute chamber, and the current in the electrodialyzer increases accordingly, significantly accelerating the migration rate of carboxylic acid from the dilute to the concentrate chamber.

[0052] The inventors' research also revealed that conventional electrodialysis not only reduces treatment efficiency but also causes crystals to precipitate in the dilute chamber, clogging the membrane pores and affecting long-term operation. The inventors' analysis suggests that because dicarboxylic acid monosalts have low solubility in water, the pH in the dilute chamber continuously decreases as the reaction proceeds, slowing the ionization of the dicarboxylic acid. This leads to an increase in the concentration of dicarboxylic acid monosalt in the dilute chamber, resulting in monosalt precipitation that clogs the ion migration channels of the ion exchange membrane, reducing electrodialysis efficiency, and in severe cases, causing failure. Therefore, to improve electrodialysis efficiency and prevent monosalt precipitation and clogging of the electrodialyzer, it is essential to add alkali to the dilute chamber to maintain a constant pH, ensuring the carboxylic acid in the dilute chamber remains in a dual-salt state. Otherwise, the electrodialyzer cannot achieve stable industrial-scale operation when treating dicarboxylic acid fermentation broth.

[0053] Based on their research, the inventors have proposed a new scheme for the efficient and stable operation of electrodialysis equipment for the purification of dicarboxylic acids. Compared with existing technologies, this invention has the following advantages:

[0054] (1) Research has found that maintaining the pH of the dicarboxylate aqueous solution in the dilute chamber to be alkaline, so that the dicarboxylate is in a double salt state, is the key to improving the efficiency of electrodialysis treatment. This technique increases the current density in the electrodialyzer and accelerates the rate of salt migration.

[0055] (2) Research has shown that maintaining the pH of the dilute chamber at an alkaline level increases the ionization rate of dicarboxylate, effectively reduces the concentration of dicarboxylate monosalt, avoids monosalt precipitation and blockage of the electrodialyzer, and enables the electrodialyzer to operate stably for a long period of time to process dicarboxylate fermentation broth.

[0056] (3) The optimal process conditions for electrodialysis treatment were comprehensively optimized, including pH control in the dilute chamber, unit voltage of the membrane pair, dicarboxylate concentration in the concentrated salt chamber, operating temperature and pore size of the ion exchange membrane, in order to ensure the treatment efficiency of the device and achieve long-term operation of the device.

[0057] The method of this invention can purify and obtain dicarboxylic acid products that meet low nitrogen requirements from an aqueous phase. Impurities such as pigments, proteins, and sugars in the fermentation broth are retained by electrodialysis, while dicarboxylic acid salts are selectively permeated through electrodialysis, thereby being purified. Further treatment through acidification and other steps ensures that the total nitrogen content in the product meets the requirements for polymerization grade.

[0058] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0059] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0060] In the method of this invention, the dicarboxylic acid fermentation broth contains liquid wax, bacterial cells, unused culture medium, metabolites, and microbial secretions, especially containing a large amount of impurities such as proteins and pigments. The dicarboxylic acid filtrate can be obtained using methods commonly employed in the art, such as at least one of the following methods:

[0061] Heat the terminated fermentation broth to 85℃~100℃, adjust the pH value to 8~10, let it stand for about 2 hours, then separate the upper layer of residual liquid wax, and cool the lower layer of dicarboxylate solution containing bacteria to 30℃~90℃. Filter through microfiltration or ultrafiltration equipment to remove bacteria and other impurities to obtain dicarboxylate solution.

[0062] Alternatively, the fermentation broth can be heated to 75℃~90℃ and then passed through a microfiltration or ultrafiltration device to remove bacterial cells and liquid wax, etc., to obtain a dicarboxylate filtrate.

[0063] Example 1

[0064] I. Take 2000 mL of C obtained from the fermentation of Candida tropicalis. 12 H 22 O4 fermentation broth was heated to 95°C to inactivate it.

[0065] II. Adjust the pH to 10, let stand for about 2 hours, separate the upper layer of liquid wax, and the lower layer containing bacteria (C) 12 H 22 The O4 salt solution was filtered through a membrane to obtain a dodecanoic acid dicarboxylate filtrate.

[0066] III. The electrodialysis unit has 5 membrane pairs, each consisting of an anion exchange membrane and a cation exchange membrane. The membrane size is 100mm × 300mm, and the pore size is 5nm. The above-mentioned dodecanoic acid dicarboxylate filtrate is added to each dilute chamber to maintain the concentration of dicarboxylate in the dilute chamber at 80~90g / L. Electrodialysis is performed at 26℃ and a total voltage of 5.0V. At the same time, sodium hydroxide solution is added to the dilute chamber to maintain the pH value of the feed chamber at 9.6. The dialysis solution containing 70g / L of dodecanoic acid dicarboxylate in the concentrate chamber is collected.

[0067] IV. Add activated carbon to the dialysis solution, decolorize for 30 minutes, and then filter.

[0068] V. Adjust the pH of the dodecanoic acid dicarboxylic acid dialysis solution to 3.0 using H2SO4, and heat to 80℃ to obtain C. 12 H 22 O4 crystallization aqueous solution;

[0069] VI. Filter to obtain a wet filter cake, which is then washed, filtered, and dried to obtain the dodecanoic acid product.

[0070] Product quality is shown in Table 1.

[0071] Example 2

[0072] I. Take 2000 mL of C obtained from the fermentation of Candida tropicalis. 13 H 24 O4 fermentation broth was heated to 80°C to inactivate it.

[0073] II. Adjust the pH to 9, filter through a ceramic microfiltration membrane to remove bacteria and residual liquid wax to obtain the filtrate;

[0074] III. The electrodialysis unit has 5 membrane pairs, each consisting of an anion exchange membrane and a cation exchange membrane. The membrane size is 100mm × 300mm, and the pore size is 5nm. The above-mentioned tridecanoic acid dicarboxylate filtrate is added to each dilute chamber to maintain the concentration of dicarboxylate in the dilute chamber at 70~80g / L. Electrodialysis is performed at 29℃ and a total voltage of 6.0V. At the same time, sodium hydroxide solution is added to the dilute chamber to maintain the pH value of the feed chamber at 9.2. The dialysis solution containing 60g / L of tridecanoic acid dicarboxylate in the concentrate chamber is collected.

[0075] IV. Add activated carbon to the dialysis solution, decolorize for 30 minutes, and then filter.

[0076] V. Adjust the pH of the tridecanoic acid dicarboxylate dialysis solution to 3.5 using H2SO4, and heat to 80℃ to obtain C. 13 H 22 O4 crystallization aqueous solution;

[0077] VI. Filter to obtain a wet filter cake, which is then washed, filtered, and dried to obtain the tridecanoic acid dicarboxylic acid product.

[0078] Product quality is shown in Table 1.

[0079] Example 3

[0080] I. Take 2000 mL of C obtained from the fermentation of Candida tropicalis. 14 H 24 O4 fermentation broth was heated to 70°C to inactivate it.

[0081] II. Adjust the pH to 8.5, filter through a ceramic microfiltration membrane to remove bacterial cells and residual liquid wax to obtain the filtrate;

[0082] III. The electrodialysis unit has 5 membrane pairs, each consisting of an anion exchange membrane and a cation exchange membrane. The membrane size is 100mm × 300mm, and the membrane pore size is 5nm. The above-mentioned tetradecanoic acid dicarboxylate filtrate is added to each dilute chamber to maintain the dicarboxylate concentration in the dilute chamber at 60~70g / L. Electrodialysis is performed at 30℃ and a total voltage of 5.5V. At the same time, sodium hydroxide solution is added to the dilute chamber to maintain the pH value of the feed chamber at 9.1. The dialysis solution containing 50g / L tetradecanoic acid dicarboxylate in the concentrate chamber is collected.

[0083] IV. Add activated carbon to the dialysis solution, decolorize for 30 minutes, and then filter.

[0084] V. Adjust the pH of the tetradecyl dicarboxylate dialysis solution to 3.0 using H2SO4, and heat to 80℃ to obtain C. 14 H 22 O4 crystallization aqueous solution;

[0085] VI. Filter to obtain a wet filter cake, which is then washed, filtered, and dried to obtain the tetradecanoic acid product.

[0086] Product quality is shown in Table 1.

[0087] Example 4

[0088] I. Take 2000 mL of the mixed long-chain dicarboxylic acid fermentation broth obtained by fermentation of Candida tropicalis, adjust the pH to 8, and heat to 70℃;

[0089] II. The filtrate is obtained by filtering through a ceramic microfiltration membrane to remove bacteria and residual liquid wax.

[0090] III. The electrodialysis unit has 5 membrane pairs, each consisting of an anion exchange membrane and a cation exchange membrane. The membrane size is 100mm × 300mm, and the membrane pore size is 10nm. The above-mentioned mixed long-chain dicarboxylic acid salt filtrate is added to each dilute chamber to maintain the dicarboxylic acid salt concentration in the dilute chamber at 70~80g / L. Electrodialysis is performed at 27℃ and a total voltage of 5.0V. At the same time, sodium hydroxide solution is added to the dilute chamber to maintain the pH value of the feed chamber at 9.3. The dialysis solution containing 60g / L of mixed long-chain dicarboxylic acid salts in the concentrate chamber is collected.

[0091] IV. Add activated carbon to the dialysis solution, decolorize for 30 minutes, and then filter.

[0092] V. Adjust the pH of the mixed long-chain dicarboxylate dialysis solution to 3.0 using 50% H2SO4, and heat to 60℃ to obtain C. 14 H 22 O4 crystallization aqueous solution;

[0093] VI. Filter to obtain a wet filter cake, which is then washed, filtered, and dried to obtain a mixed long-chain dicarboxylic acid product.

[0094] Comparative Example 1

[0095] Take 2000 mL of C obtained by fermentation with Candida tropicalis 12 H 22 The O4 fermentation broth, with a concentration of 160 g / L, was filtered through a microfiltration membrane to obtain a dodecanoic acid dicarboxylate filtrate. The pH of the dodecanoic acid dicarboxylate filtrate was adjusted to 3.0 with H2SO4, and then heated to 95°C to obtain C. 12 H 22 O4 crystallization aqueous solution. (The solution is prepared at 95℃ using C...) 12 H 22 The O4 crystallization aqueous solution was slowly cooled to 30°C and filtered to obtain a wet filter cake. After washing, filtering, and drying, the dodecanoic acid product was obtained. The quality is shown in Table 1.

[0096] Comparative Example 2

[0097] I. Take 2000 mL of C obtained from the fermentation of Candida tropicalis. 12 H 22 O4 fermentation broth was heated to 95°C to inactivate it.

[0098] II. Adjust the pH to 10, let stand for about 2 hours, separate the upper layer of liquid wax, and the lower layer containing bacteria (C) 12 H 22 The O4 salt solution was filtered through a membrane to obtain a dodecanoic acid dicarboxylate filtrate.

[0099] III. The electrodialysis unit has five membrane pairs, each consisting of one anion exchange membrane and one cation exchange membrane. The membrane size is 100mm × 300mm, and the pore size is 5nm. The aforementioned dodecanoic acid dicarboxylate filtrate was added to each dilute chamber to maintain a dicarboxylate concentration of 80-90 g / L. Electrodialysis was performed at 26°C and a total voltage of 5.0V. During the same time period as in Example 1, a significant decrease in the electrodialysis rate was observed, and only 30 g / L of dodecanoic acid dicarboxylate-containing dialysis solution was collected in the concentrate chamber. Simultaneously, significant turbidity was observed in the dilute chamber, and dodecanoic acid monosalt precipitates were found adhering to the membrane surface, rendering the device inoperable.

[0100] IV. Add activated carbon to the dialysis solution, decolorize for 30 minutes, and then filter.

[0101] V. Adjust the pH of the dodecanoic acid dicarboxylic acid dialysis solution to 3.0 using H2SO4, and heat to 80℃ to obtain C. 12 H 22 O4 crystallization aqueous solution;

[0102] VI. Filter to obtain a wet filter cake, which is then washed, filtered, and dried to obtain the dodecanoic acid product.

[0103] Table 1.

[0104]

Claims

1. A method for removing proteins from dicarboxylic acid fermentation broth, characterized in that, The dicarboxylate filtrate, after inactivation and filtration, is introduced into an electrodialysis unit for electrodialysis. The electrodialysis unit is composed of alternating anion exchange membranes and cation exchange membranes. Each pair of anion exchange membranes and cation exchange membranes constitutes a membrane pair unit. The space between the anion exchange membranes and cation exchange membranes in each membrane pair unit is a dilute chamber, the space between adjacent membrane pair units is a concentrated chamber, and the two sides are polar chambers. The dicarboxylate filtrate is introduced into the dilute chamber, and alkali solution is added into the dilute chamber during electrodialysis to maintain the pH of the dilute chamber at 8-12. The purified dicarboxylate is obtained in the concentrated chamber.

2. The removal method according to claim 1, characterized in that, During electrodialysis, alkali solution is added to the dilute chamber to maintain the pH of the dilute chamber at 9-10.

3. The removal method according to claim 1, characterized in that, The alkaline solution is selected from one or more aqueous solutions of sodium bicarbonate, sodium carbonate, sodium hydroxide, potassium bicarbonate, potassium carbonate, and potassium hydroxide, with a solute mass concentration of 10.0% to 40.0%.

4. The removal method according to claim 1, characterized in that, The voltage of each membrane pair unit in the electrodialysis unit is 0.6V~2V.

5. The removal method according to claim 1, characterized in that, In the dilute chamber of the electrodialysis unit, the concentration of dicarboxylate is 40~150 g / L.

6. The removal method according to claim 5, characterized in that, In the dilute chamber of the electrodialysis apparatus, the concentration of dicarboxylate is 50 g / L to 100 g / L.

7. The removal method according to claim 1, characterized in that, In the concentration chamber of the electrodialysis apparatus, the concentration of dicarboxylate is maintained at 10 g / L to 100 g / L.

8. The removal method according to claim 1, characterized in that, The pH of the dicarboxylate introduced into the dilute chamber of the electrodialysis unit is 8-10.

9. The removal method according to claim 1, characterized in that, The electrodialysis is performed at a temperature of 20~35℃.

10. The removal method according to claim 1, characterized in that, The anion exchange membrane and cation exchange membrane are monovalent membranes with a pore size of 1 nm to 30 nm.

11. The removal method according to claim 1, characterized in that, The removal method includes the following: I. Inactivate the dicarboxylic acid fermentation broth by heating after fermentation has been terminated; II. Remove bacterial cells and other solids to obtain dicarboxylate filtrate; III. The dicarboxylate filtrate is introduced into the dilute chamber of the electrodialysis unit, and the pH of the dilute chamber is maintained at 8-12. Under the action of the electric field, the dicarboxylate migrates to the concentrated chamber, resulting in a dialysis solution rich in dicarboxylate. IV. Selectively add an adsorbent to the dicarboxylate solution obtained in step III, and filter to remove solids; V. Acidify the filtrate obtained in step IV to obtain a dicarboxylic acid crystal solution; VI. Separate the dicarboxylic acid crystallization liquid, filter and dry to obtain the dicarboxylic acid product.

12. The removal method according to claim 11, characterized in that, In step III, maintain the pH of the dilute chamber at 9-10.

13. The removal method according to claim 11, characterized in that, The dicarboxylate obtained in step II includes a monovalent cation, specifically sodium, potassium, or ammonium.

14. The removal method according to claim 11, characterized in that, It also includes a step of further electrodialysis treatment of the dicarboxylate dialysis solution collected in the concentration chamber.

15. The removal method according to claim 11, characterized in that, The adsorbent mentioned in step IV is activated carbon and / or activated clay, and the amount added is 0.01wt%~5.0wt% of the dry weight of the organic acid, and the adsorption time is 30min~60min.

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