Purification of aliphatic dicarboxylic acids produced by biotechnological processes

Abstract

Describes a method for purifying a saturated straight-chain aliphatic dicarboxylic acid or a mixture thereof obtained by a biotechnological method.

Description

Technical Field

[0001] The present invention relates to a method for purifying saturated linear aliphatic dicarboxylic acids obtained by biotechnological processes. Background Art

[0002] Saturated linear aliphatic dicarboxylic acids are extremely important compounds in industry. Due to their bifunctionality, they are widely used as monomers for the production of polymers (such as polyamides, polyesters, and polyurethanes).

[0003] The production of polyamides is perhaps the application that requires the most attention to the purity of the starting monomers: impurities (such as mono- or polyfunctional compounds, chromophores, or heat-sensitive compounds), even at trace levels, can hinder polymerization, cause polymer chain branching, or more generally limit the downstream applications of polyamides. When polyamides are used in the textile industry, the purity requirements for the monomers are particularly high (products that meet the purity requirements in the textile field are defined as "fiber grade").

[0004] Saturated linear aliphatic dicarboxylic acids are usually produced from petroleum derivatives using traditional techniques, usually resulting in relatively simple mixtures of compounds, where the desired acid is the main compound so far. These mixtures are then subjected to purification processes that have been developed and optimized to be effective for purifying these simple mixtures.

[0005] However, in recent years, the chemical industry has been looking for alternatives to petroleum products, reducing dependence on this non-renewable energy source, and providing processes and products that are more sustainable from an environmental and safety perspective.

[0006] The development of biotechnology allows the production of these compounds, including linear aliphatic dicarboxylic acids, from alternative sources such as renewable sources like sugars, fatty acids, vegetable oils, animal fats, etc., or non-renewable sources such as alkanes of different chain lengths. However, the chemical quality of the monomers obtained in this way is not high enough to be widely used in polyamides, especially in the production of nylon for textile applications, thus limiting their use to the production of polymers for articles almost exclusively dedicated to the plastics materials industry. The main problems are related to the nature of the raw materials used and / or the biological nature of the fermentation processes employed, resulting in the accumulation of chromophoric and volatile substances in the final product, which tend to produce a yellowish to brown color and an unpleasant odor.

[0007] The obtaining of the downstream products of the fermentation process is carried out through two macro-stages: the first stage, usually called extraction, aims to recover the product of interest from the fermentation broth, while the second stage, generally called purification, consists of a series of individual operations through which the crude product reaches the purity required by the market.

[0008] In the first stage, typical operations involve the disruption and removal of cell debris (flocculation, pasteurization, centrifugation, filtration, etc.), and the recovery of the product in crude form (acidification, precipitation, liquid extraction, etc.). As for the second stage, typical operations involve product purification (crystallization, distillation, resin and activated carbon passage, chromatography, liquid-liquid extraction, etc.) and processing (crystallization to obtain the desired crystal structure, drying, freeze-drying, sterilization, etc.). The operations in this stage are usually the most complex and the most important part of the process to obtain the compound of interest downstream of fermentation.

[0009] The first of these two macroscopic stages (crude product recovery) is described in several patent publications.

[0010] US Patent 5,034,105 describes a method for recovering deprotonated succinic acid from fermentation broth by electrodialysis after cell and debris separation. Using electrical energy and an ion-selective membrane, sodium succinate is converted back to its acid form while simultaneously recovering the sodium hydroxide used for pH control during fermentation. This method has the advantage of not requiring neutralization with strong mineral acids and producing no waste salts. However, the use of electricity results in significant energy consumption, increasing process costs. Furthermore, the membranes, particularly when operating under conditions of high organic concentrations, are susceptible to fouling, significantly reducing their efficiency and requiring continuous cleaning or replacement of the same membrane.

[0011] US Patent No. 6,288,275B1 describes a method for obtaining long-chain dicarboxylic acids (>C 12 ) technology. According to this method, the pH of the fermentation broth is reduced to below 2 by adding a strong mineral acid, and then maintained at a temperature of 60 to 105°C for 2 hours. Three immiscible phases are formed by decantation: an upper organic phase containing the compound of interest, an aqueous phase in the middle, and a solid phase composed of cell debris at the bottom of the container. The addition of a water-immiscible organic solvent favors the formation of an organic phase in which the dicarboxylic acid is dissolved; once separated from the fermentation broth, this phase is sent for final purification. The method described in this document involves exposing the fermentation broth to high temperatures for a long time, which may cause it to turn yellow significantly and inevitably reduce the quality of the recovered acid.

[0012] The second macro-stage (purification and processing of the product) is in turn described in various patent publications.

[0013] International Patent Application WO 2011 / 082378 A2 describes a method involving a first step of purifying succinic acid through an ion-exchange resin. According to this method, after removing upstream cells and cell debris, the ammonium succinate obtained from fermentation can be restored to its acid form while passing it through a cation-exchange resin to separate it from inorganic salts. Alternatively, an anion-exchange resin can be used to retain succinate, followed by acid regeneration for recovery. The acid thus obtained is then sent for further purification to achieve the desired final purity. However, the extensive use of ion-exchange resins results in a large consumption of eluent during the bed regeneration step, generating a large amount of waste that needs to be treated through special processes. In addition, over time, the resin exchange capacity gradually decreases, leading to the need for more frequent regeneration (increasing the amount of waste generated) or the need for complete replacement (increasing the variable cost of the method).

[0014] US Patent Application 2015 / 0344397 A1 describes a method for purifying succinic acid from a fermentation broth that has been previously microfiltered / ultrafiltered and acidified with concentrated H2SO4 using simulated moving bed chromatography (SMBC). However, further purification (such as through nanofiltration, using activated carbon or adsorption resins, etc.) is still required to obtain the final product with the desired purity. Since the chemico-physical operating principles of this technology are similar to those described above, it is affected by the same problems.

[0015] US Patent 8,729,298 B2 also describes a method based on simulated moving bed chromatography (SMBC) for the purification and separation of medium- and long-chain (C9-C 18 ) dicarboxylic acids.

[0016] US Patent 9,517,996 B2 describes a method for purifying fermentation-produced dicarboxylic acids with a chain length >C8, which basically involves reducing the pH of the fermentation broth to precipitate the long-chain dicarboxylic acids, filtering the suspension, removing the aqueous phase that does not contain the desired solids and cell residues, and then subjecting the dicarboxylic acid mixture to one or more crystallizations in an organic solvent (preferably acetic acid). However, using a monocarboxylic acid (such as acetic acid) as a solvent causes problems in that traces of this compound remain as impurities in the final product, acting as a chain terminator in the polymerization process using the dicarboxylic acid.

[0017] Patent Application WO 2018 / 01057 A1 describes a method similar to previous literature, in which an acid is added to the fermentation broth to reduce its pH to less than 6, resulting in demulsification of the system; the obtained biphasic system is centrifuged; and finally, the dicarboxylic acid is separated from the phase containing the dicarboxylic acid (e.g., by filtration).

[0018] Finally, patent application CN 105712871 A describes a method for purifying long-chain dicarboxylic acids, comprising the following steps: subjecting the fermentation broth to acid pretreatment, adding concentrated sulfuric acid to the system, adding activated carbon to remove impurities, cooling the system to precipitate long-chain dicarboxylic acid crystals, and finally separating the crystals by filtration, washing, and drying.

[0019] Therefore, all methods known in the art for recovering dicarboxylic acids from fermentation broths are based on a series of physical separation methods (separation by filtration membranes, crystallization, adsorption resins, etc.) and / or ion exchange methods, which, although effective, do not achieve the purpose of obtaining a product suitable for the most critical applications at the fiber grade.

[0020] The object of the present invention is to provide a method for purifying saturated straight-chain aliphatic dicarboxylic acids obtained by biotechnological methods, which method does not have the drawbacks present in the prior art methods and is particularly conveniently applicable on an industrial scale. Summary of the Invention

[0021] These objects are achieved by a method for purifying saturated straight-chain aliphatic dicarboxylic acids having from 4 to 18 carbon atoms or mixtures thereof obtained from fermentation broths, said method comprising the following steps:

[0022] a) removing cells and / or cell residues from the fermentation broth;

[0023] b) lowering the pH of the fermentation broth, precipitating the saturated straight-chain aliphatic dicarboxylic acid, and separating it from said fermentation broth;

[0024] c) dissolving the crude mixture obtained in step b), containing one or more saturated straight-chain aliphatic dicarboxylic acids and impurities, in a nitric acid oxidation solution at a temperature of 60 to 100 °C and a concentration of 45 to 68% by weight for 0.1 to 4 hours;

[0025] d) recovering the saturated straight-chain aliphatic dicarboxylic acid from the oxidation solution of step c);

[0026] e) redissolving the saturated straight-chain aliphatic dicarboxylic acid in an aqueous mixture containing activated carbon;

[0027] f) recovering the saturated straight-chain aliphatic dicarboxylic acid from the aqueous mixture. Detailed Description of the Invention

[0028] The present invention can be used to separate and subsequently purify saturated straight-chain aliphatic dicarboxylic acids or mixtures of saturated straight-chain aliphatic dicarboxylic acids having 4 to 18 carbon atoms, in particular 6 to 12 carbon atoms, from a fermentation broth. Since the acids are straight-chain, the carboxyl functional groups are necessarily located at the α and ω positions (i.e., the two terminal positions) of the carbon atom chain. Thus, the dicarboxylic acids of interest in the present invention are succinic acid (C4), glutaric acid (C5), adipic acid (C6), pimelic acid (C7), suberic acid (C8), azelaic acid (C9), sebacic acid (C10), undecanedioic acid (C11), dodecanedioic acid (C12), tridecanedioic acid (C13), tetradecanedioic acid (C14), pentadecanedioic acid (C15), hexadecanedioic acid (C16), heptadecanedioic acid (C17) and octadecanedioic acid (C18). Among them, the acids of particular interest in the present invention are adipic acid, dodecanedioic acid or a mixture of adipic acid and suberic acid.

[0029] The above-mentioned dicarboxylic acids or mixtures of dicarboxylic acids are produced by a biotechnological method in a fermenter, in which a raw material of fossil origin or renewable origin can be supplied.

[0030] Different from the prior art methods that are almost entirely based on physical separation and purification methods, the method of the present invention includes a treatment for chemically degrading cell residues and impurities, which would make the final product yellow and odorous and are also produced together with the saturated straight-chain aliphatic dicarboxylic acids during the fermentation process.

[0031] For the sake of brevity, saturated straight-chain aliphatic dicarboxylic acids will be abbreviated as dicarboxylic acids in the rest of the specification.

[0032] The term "cell residues" as used herein refers to cell debris and biomolecules such as proteins, nucleic acids, amino acids, carbohydrates, nucleotides, peptides, etc.

[0033] In the specification and claims, unless otherwise indicated, the contents of the components in solutions and mixtures and the concentrations of solutions are given in weight percentages.

[0034] For the sake of simplicity, in the following description, unless otherwise indicated, a dicarboxylic acid is referred to, but all indications of process steps are equally valid for the case of a mixture of dicarboxylic acids.

[0035] The method of the present invention includes steps a) to f).

[0036] The dicarboxylic acid is initially present in the fermentation broth, which is produced in the fermentation broth by microorganisms such as yeast, bacteria, molds, algae, especially genetically modified yeast, which are capable of converting the supplied raw materials into the desired product. At the end of the fermentation process, in addition to these microorganisms, the fermentation broth may also contain: cell residues, sugars, vegetable oil residues, animal fats or fatty acids with a variable length of C12 to C20, as well as unsaturated dicarboxylic acids or dicarboxylic acids with any other functional group.

[0037] The dicarboxylic acid exists in the fermentation broth in the form of a mono-salt or a di-salt, where the counterion can be any metal cation or ammonium ion, provided that it does not cause the compound to precipitate in the fermentation broth. Usually, the cation combined with the dicarboxylic acid is the ammonium ion. The existence of the mono-salt or di-salt form of the dicarboxylic acid depends on the pH at which the fermentation is carried out. By taking advantage of the high solubility of these salt forms, the solid part composed of cells and cell debris can be removed from the fermentation broth.

[0038] In step a), any cell residues and / or cells that may remain in the fermentation broth are completely or at least partially removed using known centrifugation and membrane filtration processes or a combination thereof. The fermentation broth can optionally be subjected to flocculation or pasteurization operations to reduce the viscosity of the suspension. After removing the cells, a membrane with a narrower cut-off value (such as ultrafiltration membranes and nanofiltration membranes or a combination thereof) can be used to further filter the fermentation broth to remove other smaller cell residues, such as proteins, carbohydrates, nucleic acids, divalent salts, etc.

[0039] Thus, a fermentation broth is obtained that is free of cell residues and / or cells, or contains a very small amount of cell residues and / or cells, and contains the mono-salt or di-salt form of the dicarboxylic acid in solution, with a pH value between 4 and 8, depending on the nature of the biotechnological fermentation process employed.

[0040] In the following step b), the pH of the fermentation broth is lowered to a range of 1.5 to 3, preferably 1.5 to 2, by passing it through a strong cationic resin or by adding a strong inorganic acid, such as hydrochloric acid, nitric acid, or sulfuric acid, preferably nitric acid or sulfuric acid. This addition can be performed at a temperature of 20 to 60°C, preferably 30 to 40°C, and under constant stirring. This acidification converts all dicarboxylic acids present in the mixture into their free diacid forms. Lowering the pH results in almost complete precipitation of long-chain and medium-chain dicarboxylic acids (from C8 to C18), which have low solubility in aqueous media, and partial precipitation of partially soluble medium-chain dicarboxylic acids (C6 and C7) and short-chain acids with even numbers of carbon atoms (C4), while short-chain acids with odd numbers of carbon atoms (C5) remain in solution due to their very high solubility. In particular, dicarboxylic acids with a solubility of less than 5 g / L at 25°C are almost completely precipitated, allowing direct filtration to remove the fermentation broth, which is almost completely free of the product of interest. On the other hand, dicarboxylic acids with a solubility > 5 g / L at 25°C are only partially precipitated, and therefore, the fermentation broth needs to be concentrated 2 to 10 times using a multiple-effect evaporator system or a reverse osmosis system, or preferably a combination of both systems, depending on the solubility of the acid and the amount of water used in the filtration process.

[0041] The precipitated solids are separated and removed from the residual fermentation broth, retaining most of the ammonium salts produced by neutralization, chromophores, and cellular residues such as proteins, sugars, and nucleic acids. The resulting solids are brown in color, enriched in all of the aforementioned substances, as well as any solid cell debris not removed during the cell filtration stage, and can be subjected to the subsequent steps of the process of the present invention.

[0042] In step c), the crude dicarboxylic acid, typically in solid form, is dissolved in an aqueous nitric acid solution having a concentration of 45 to 68% by weight, preferably 50 to 65% by weight. At these concentrations, nitric acid is a strong oxidizing agent. Nitric acid concentrations below those indicated only reduce the oxidizing effect, while higher concentrations are difficult to manage under safe conditions.

[0043] The crude dicarboxylic acid is added to the nitric acid solution in an amount of 1-40%, preferably 10-30%, depending on its solubility in the oxidation mixture.

[0044] The reaction temperature is between 60 and 100°C, preferably between 70 and 90°C: temperatures below 60°C result in low impurity decomposition efficiency, while temperatures above 100°C significantly accelerate corrosion of the reactor steel and lead to decomposition of nitric acid, thereby increasing operating costs.

[0045] The reaction time may be between 0.1 and 4 hours, preferably between 0.5 and 3 hours.

[0046] The oxidizing agent, nitric acid, attacks all molecules that absorb visible and low-UV radiation (chromogenic impurities), typically organic molecules with one or more carbon-carbon double bonds, often conjugated double bond systems. This reagent also hydrolyzes / oxidizes any cellular residues remaining from the fermentation process, such as proteins, nucleic acids, and other biomacromolecules. However, the oxidizing agent leaves the dicarboxylic acids in the mixture unchanged, because the chain-terminal carbons are already in the most oxidized state of the organic compound, while the carbons in the center of the chain (without double bonds and other functional groups) are not oxidized under the process conditions.

[0047] The oxidation treatment can be carried out discontinuously or continuously. In the case of continuous treatment, the reactor used can be a continuous flow stirred tank reactor (referred to in the art as a CSTR) or a plug flow reactor (or PFR), provided that the contact time is guaranteed; preferably, the reactor is continuously or intermittently mixed. The process gas is removed in an absorption tower using known techniques (e.g., supplying cooling water or an alkaline solution, such as an aqueous solution of NaOH, KOH, Ba(OH)2, etc.) in countercurrent to the gas flow.

[0048] In step d) of the process, the dicarboxylic acid of interest is recovered from the oxidation solution.

[0049] The technique used can be crystallization, preferably by cooling crystallization. Depending on the solubility of the dicarboxylic acid, the oxidation mixture containing the dicarboxylic acid is gradually cooled until its temperature reaches 10 to 40°C, preferably 20 to 30°C. To maintain a constant supersaturation, the cooling must be slow in the first part and fast in the last part. The resulting crystals are separated from the crystallization mother liquor using well-known chemical engineering techniques, such as centrifuges, drum filters, filter presses, etc. The solid is preferably recovered by centrifugation.

[0050] The solid dicarboxylic acid is then washed with demineralized water to remove any oxidant remaining between the crystals. The mother liquor can be purified and replenished with fresh oxidant for reuse in the oxidation reactor.

[0051] The next step e) of the process is to remove traces of mother liquor and impurities from the oxidation treatment from the dicarboxylic acid crystals. Since these impurities generally lead to (unwanted) coloration of the dicarboxylic acid and the polymers produced, this treatment is also known as "bleaching".

[0052] In this step, the dicarboxylic acid obtained in step d) is redissolved in water or an aqueous mixture containing suspended activated carbon. The term "aqueous mixture" is used to denote any solution consisting of at least 50% water.

[0053] The wet crystals are dissolved in an aqueous mixture to form a solution containing 1-40%, preferably 10-30%, of the dicarboxylic acid. If an aqueous mixture is used, it preferably consists of water and an organic solvent. The amount of organic solvent should be carefully selected so that it is soluble in water at all process temperatures (20 to 100°C). Among these organic solvents, primary, secondary, and tertiary alcohols such as ethanol, propanol, isopropanol, butanol, tert-butanol, and 2-butanol; ketones such as acetone, methyl ethyl ketone, and diethyl ketone; or esters such as ethyl acetate can be used. The type and weight percentage of the solvent should be carefully selected to minimize the solvent's potential reactivity toward the dicarboxylic acid at the process temperature and under the conditions of the activated carbon. The solvent should have a sufficiently high boiling point to ensure that the dicarboxylic acid has a low solubility at temperatures between 20 and 40°C, with the solubility of the dicarboxylic acid increasing as this parameter increases.

[0054] For dicarboxylic acids having 7 or fewer carbon atoms, the use of water alone at elevated temperature is sufficient to render the dicarboxylic acid in solution, suitable for treatment with activated carbon. For dicarboxylic acids having 8 or more carbon atoms, the use of 0 to 50% by weight of solvent is necessary to render the dicarboxylic acid in solution and enable bleaching treatment.

[0055] The treatment is carried out at a temperature of 60 to 100° C., preferably 70 to 90° C. The treatment is carried out using activated carbon, preferably in powdered form, by forming a stirred suspension. If powdered activated carbon is used, the amount used is 0.5 to 50 g, preferably 1 to 25 g, per kg of dicarboxylic acid to be treated. The solution / carbon contact time ranges from 0.25 to 2 hours, preferably 0.5 to 1.5 hours. At the end of the process, the powdered activated carbon is filtered according to methods and equipment known in chemical plant engineering, and the purified solution is sent to the final product recovery step.

[0056] Finally, in step f) of the process, the decolorized dicarboxylic acid is recovered from the bleaching treatment solution using known techniques, such as, preferably, crystallization.

[0057] Depending on the nature of the mixture, the desired particle size, and the solubility of the dicarboxylic acid in the bleaching solution, crystallization is carried out by cooling, evaporation, or vacuum adiabatic evaporation. The solid obtained from the crystallization is filtered continuously or discontinuously or preferably centrifuged and then washed with cold demineralized water to effectively remove the mother liquor remaining between the crystals. If a dry product is required, the obtained solid can be sent to a drying stage to remove residual moisture. If an organic solvent is used, drying in an inert atmosphere is particularly recommended. The dicarboxylic acids obtained by the process according to the invention have optical properties comparable to similar compounds synthesized from fossil sources and are therefore suitable for all fields of application, even those with the most stringent quality requirements, such as the synthesis of textile polyamides (nylons).

[0058] The method of the present invention ensures the acquisition of a high-purity dicarboxylic acid, characterized by an APHA color value <15 as defined by ASTM D1209 and an absorbance value <300 (x1000) at 275 nm, as better specified in the examples.

[0059] The present invention will be further illustrated by the following examples.

[0060] Methods, Instruments, and Materials

[0061] The composition of the fermentation broth and the final purity of the dicarboxylic acid treated in the examples were determined using an Agilent 1260 Infinity II series HPLC instrument equipped with a G7115A diode array detector and a G7162A refractive index detector. The optical properties of the product were determined using an Agilent Cary60 UV-Vis spectrophotometer.

[0062] Example 1

[0063] By using the second-generation genetically modified yeast Candida viswanathii to ferment fatty acids, a fermentation broth containing a mixture of dicarboxylic acids was prepared. In particular, HPLC analysis measured 80 g / L of adipic acid (in the form of ammonium adipate) and 4.5 g / L of suberic acid (in the form of ammonium suberate). Cells and other solids were removed by ultrafiltration / diafiltration (using an Alfa-Laval RC70PP ultrafiltration membrane made of spiral-wound regenerated cellulose, with an 80-mil spacer equivalent to 2 mm and a 10-kDa cut-off value), resulting in a clear fermentation broth free of any cell debris, with HPLC analysis determining concentrations of 35.8 g / L of adipic acid and 1.96 g / L of suberic acid, both in their monosalt forms. 1700 g of the fermentation broth was acidified with 65 wt% HNO3 (Radici Chimica SpA) until the pH reached 1.8. The acidification converted ammonium adipate and ammonium suberate to the acid forms, i.e., adipic acid and suberic acid. Since the main product adipic acid is partially soluble in water, the fermentation broth was concentrated 7-fold by evaporation to a concentration of 25.1 wt% of this compound. After cooling to room temperature (20 °C), most of the acid precipitated, and the crystals were filtered and washed with softened water. Subsequently, they were dissolved in 55% concentrated nitric acid (Radici Chimica SpA), placed at 80 °C, and kept under stirring for 2 hours. The concentration of the wet solid in the nitric acid solution was equal to 30 wt%. At the end of the oxidation, the mixture was cooled to 25 °C to allow crystallization, and then filtered on a porous septum. The obtained crystals were washed twice with softened water, with the amount of softened water being 1:1 (by weight) relative to the wet crystals. Subsequently, the obtained wet product was redissolved in water and heated to 85 °C, thus forming a dicarboxylic acid solution at 30 wt% relative to the wet product. Powdered activated carbon (Ceca, 65 mass%, with a particle size <40 μm) was added to the solution at a dosage equal to 3.33 g of carbon / kg of dicarboxylic acid mixture, and then the solution was kept under constant stirring for 60 minutes. At the end of the treatment, the carbon was hot-filtered on a Büchner funnel, and the solid-free solution was cooled to 20 °C to allow crystallization. The crystals were separated from the mother liquor through a porous septum, washed with softened water, and dried in an oven at 70 °C for 24 hours. The recovery rate in terms of total solids (the sum of the two acids) relative to the starting material was 68.9%, and the obtained crystals were composed of 96.4 wt% adipic acid and 3.3 wt% suberic acid as measured by HPLC (the remaining part being residual moisture). The dried crystals were analyzed by a spectrophotometer to determine the optical properties. 7.66 g of the powder was dissolved in 60 g of a 5 wt% ammonia solution, carefully filtered through a syringe filter, and analyzed using an Agilent Cary 60 spectrophotometer equipped with a quartz cuvette with a 50-mm optical path length. The absorbance x1000 obtained at 275 nm was equal to 117, and the APHA colority obtained at 390 nm was equal to 7.4.

[0064] Example 2

[0065] 1900 g of the same ultrafiltered fermentation broth described in Example 1 were purified using the same method. However, the nitric acid treatment lasted for 30 minutes instead of 2 hours. The recovery of both acids was 69.2% and the crystals obtained were composed of 97.14% adipic acid and the remainder suberic acid as measured by HPLC. The dried crystals were analyzed spectrophotometrically to determine the optical properties. 7.66 g of the powder were dissolved in 60 g of a 5% by weight ammonia solution, carefully filtered using a syringe filter and analyzed using an Agilent Cary 60 spectrophotometer equipped with a quartz cuvette with a 50 mm pathlength. The absorbance obtained at 275 nm x 1000 was equal to 107 and the APHA color obtained at 390 nm was equal to 6.9.

[0066] Example 3

[0067] 1600 g of the same ultrafiltered fermentation broth described in Example 1 were purified using the same method. The nitric acid treatment was performed using a 65% by weight nitric acid solution instead of a 55% by weight nitric acid solution. The recovery of both acids was 64% and the crystals obtained were composed of 98.3% adipic acid and the remainder suberic acid as measured by HPLC. The dried crystals were analyzed spectrophotometrically to determine the optical properties. 7.66 g of the powder were dissolved in 60 g of a 5% by weight ammonia solution, carefully filtered using a syringe filter and analyzed using an Agilent Cary 60 spectrophotometer equipped with a quartz cuvette with a 50 mm pathlength. The absorbance obtained at 275 nm x 1000 was equal to 86 and the APHA color obtained at 390 nm was equal to 5.2.

[0068] Example 4

[0069] The fermentation broth sample described in Example 1 was subjected to ultrafiltration / diafiltration to remove cells, followed by nanofiltration / diafiltration (SUEZ GE DL, polyamide TFC, spiral wound; cut-off value 150 - 300 Da) to remove biopolymers such as proteins and sugars, divalent salts and most colored impurities. By HPLC measurement, the concentration of adipic acid in the nanofiltrate was 31.57 g / L, while the concentration of suberic acid was 1.95 g / L. 1900 g of this fermentation broth was purified using the same method described in Example 1. The recovery of the two acids was 61.7%, and the obtained crystals were analyzed by HPLC and consisted of 96.4% adipic acid and 3.36% suberic acid (the other component was moisture). The dried crystals were analyzed using a spectrophotometer to determine the optical properties. 7.66 g of the powder was dissolved in 60 g of 5 wt% ammonia solution, carefully filtered using a syringe filter, and analyzed using an Agilent Cary 60 spectrophotometer equipped with a quartz cuvette with a 50 mm path length. The absorbance obtained at 275 nm x1000 was equal to 134, and the APHA color value obtained at 390 nm was equal to 5.4.

[0070] Example 5

[0071] A fermentation broth containing 50 g / L adipic acid (in the form of monoammonium salt) as measured by HPLC analysis was prepared by fermenting fatty acids using the second-generation transgenic yeast Candida viswanathii. At the end of fermentation, 1800 grams of the fermentation broth was centrifuged to remove most of the cells and solid residues. The fermentation broth still containing a small amount of cell solids was purified using the same method reported in Example 1. The recovery of the product was 71.7%, and the obtained crystals were analyzed by HPLC and consisted of 99.7% adipic acid (the rest was moisture). The dried crystals were analyzed using a spectrophotometer to determine the optical properties. 7.66 g of the powder was dissolved in 60 g of 5 wt% ammonia solution, carefully filtered using a syringe filter, and analyzed using an Agilent Cary 60 spectrophotometer equipped with a quartz cuvette with a 50 mm path length. The absorbance obtained at 275 nm x1000 was equal to 84, and the APHA color value obtained at 390 nm was equal to 5.1.

[0072] The following presents a summary table of the results obtained from the conducted tests.

[0073]

[0074]

Claims

1. A method for purifying a saturated straight-chain aliphatic dicarboxylic acid having 4 to 18 carbon atoms or a mixture thereof obtained from a fermentation broth, comprising the following steps: a) Removing cells and / or cell residues from the fermentation broth; b) Lowering the pH of the fermentation broth, precipitating the saturated straight-chain aliphatic dicarboxylic acid, and separating it from the fermentation broth to obtain a crude mixture containing one or more saturated straight-chain aliphatic dicarboxylic acids and impurities; c) Dissolving the crude mixture containing one or more saturated straight-chain aliphatic dicarboxylic acids and impurities obtained in step b) in a nitric acid oxidation solution at a temperature of 60 to 100 °C and a concentration of 45 to 68 wt% for 0.1 to 4 hours; d) Recovering the saturated straight-chain aliphatic dicarboxylic acid from the oxidation solution of step c); e) Redissolving the saturated straight-chain aliphatic dicarboxylic acid in an aqueous mixture containing activated carbon at a temperature of 60 to 100 °C; f) Recovering the saturated straight-chain aliphatic dicarboxylic acid from the aqueous mixture.

2. The method according to claim 1, wherein the saturated straight-chain aliphatic dicarboxylic acid has 6 to 12 carbon atoms.

3. The method according to claim 2, wherein the acid is selected from adipic acid, dodecanedioic acid, and a mixture of adipic acid and suberic acid.

4. The method according to any one of the preceding claims, wherein step a) is carried out by centrifugation and / or membrane filtration.

5. The method according to claim 1, wherein in step b), the operation is carried out at a temperature of 20 to 60 °C, and the pH value is adjusted to 1.5 to 3 using a strong inorganic acid.

6. The method according to claim 1, wherein step b) uses a multi-effect evaporator system and / or a reverse osmosis system to concentrate the fermentation broth 2 to 10 times.

7. The method according to claim 1, wherein the concentration of the aqueous nitric acid solution used in step c) is 50 to 65 wt%.

8. The method according to claim 1, wherein in step c), the crude mixture containing one or more saturated straight-chain aliphatic dicarboxylic acids and impurities obtained in step b) is added to the nitric acid solution, and the addition amount of the dicarboxylic acid is such that its concentration in the resulting solution is 1 to 40 wt%.

9. The method according to claim 1, wherein step c) is carried out at a temperature of 70 to 90 °C for 0.5 to 3 hours.

10. The method according to claim 1, wherein step d) is carried out by crystallizing the dicarboxylic acid present in the oxidation mixture and then separating the crystals from the mixture by centrifugation or filtration.

11. The method according to claim 1, wherein step e) is carried out at a temperature of 70 to 90 °C, and the dicarboxylic acid crystals recovered in step d) are dissolved in water or an aqueous mixture containing suspended powdered activated carbon in an amount of 0.5 to 50 g of activated carbon per kg of the dicarboxylic acid to be treated, and the aqueous mixture contains at least one second component selected from primary alcohols, secondary alcohols, or tertiary alcohols, ketones, and esters.

12. The method according to claim 1, wherein step f) is carried out by crystallization.

Images