A method for two-step extraction of 1,3-propanediol and organic acids from fermentation broth using a boronic acid-based deep eutectic solvent

Abstract

This invention relates to the field of bioseparation technology, specifically disclosing a method for two-step extraction of 1,3-propanediol and organic acids from fermentation broth using a boric acid-based eutectic solvent. The method includes: using boric acid as a hydrogen bond donor, selecting suitable hydrogen bond acceptors based on the COSMO-RS model and extraction efficiency indicators such as extraction rate and selectivity, and synthesizing an eutectic solvent system; proposing a two-step extraction method to separate 1,3-propanediol, glycerol, and organic acids from the fermentation broth. The extraction and separation of the 1,3-propanediol system is carried out in two steps. In the first step, a boric acid / proline eutectic solvent system is used as the extractant, with yields of butyric acid and acetic acid of 94.56% and 75.60%, respectively. In the second step, a boric acid / thymol eutectic solvent system is used as the extractant, performing a four-stage extraction, ultimately achieving yields of 86.04% for 1,3-propanediol and 81.11% for glycerol. The eutectic solvent is recycled through back-extraction. This method is simple to operate, has a high extraction yield, and the eutectic solvent is easy to prepare, low in toxicity, environmentally friendly, and easy to scale up industrially.

Description

Technical Field

[0001] This invention relates to the field of bioseparation technology, and specifically discloses a two-step extraction method for 1,3-propanediol and organic acids from fermentation broth using a borate-based eutectic solvent. Background Technology

[0002] 1,3-Propanediol (PDO) is an important chemical raw material, particularly as a monomer for the production of high-performance polyester materials such as propylene glycol terephthalate (PTT) and polyurethane. The industrial production routes for 1,3-propanediol are mainly divided into two categories: chemical methods and biological methods. Due to the problems involved in the chemical production of 1,3-propanediol, including high temperature and pressure, intermediate toxicity, and the difficulty in separating byproducts with similar properties, it has gradually withdrawn from the industrial market. Microbial fermentation has gradually become the mainstream direction for the industrial production of 1,3-propanediol. The domestic 1,3-propanediol industry started relatively late. Due to the complex composition of the fermentation broth and the inherent characteristics of 1,3-propanediol, such as its strong hydrophilicity and high boiling point, downstream separation and purification face many difficulties. Downstream separation costs account for more than 50% of the total cost of 1,3-propanediol production via microbial fermentation, becoming a bottleneck problem that urgently needs to be solved for its industrial production.

[0003] To more effectively separate 1,3-propanediol from fermentation broth, scientists both domestically and internationally have made unremitting efforts and proposed many processes, such as salting-out extraction, mixed solvent extraction, reactive extraction, electrodialysis, and ion exchange. However, these separation processes all have shortcomings. Salting-out extraction suffers from the flammability and explosiveness of organic solvents and the difficulty in recovering organic salts; mixed solvent extraction suffers from low extraction efficiency and poor selectivity; reactive extraction is often accompanied by side reactions and easily leads to catalyst deactivation, and the use of acetaldehyde in the reaction process also poses toxicity and safety hazards; electrodialysis has a high product loss rate, and the membrane is prone to fouling and has high costs; ion exchange requires frequent resin elution and regeneration, consuming large amounts of acidic and alkaline solutions, generating large amounts of wastewater, and incurring high environmental treatment costs. Therefore, there is an urgent need to develop low-cost, efficient, and environmentally friendly separation processes.

[0004] Deep eutectic solvents (DES) are considered a new generation of green solvents due to their many excellent properties, such as stable solvent structure and unique solubility. Using DES as an organic extractant to separate 1,3-propanediol from fermentation broth holds promise for achieving a green separation process. Summary of the Invention

[0005] In order to overcome the problems of toxicity, flammability and explosiveness, high environmental treatment costs, low separation efficiency and high separation cost in the existing process of separating 1,3-propanediol, this invention provides a two-step extraction method for 1,3-propanediol and organic acids from fermentation broth using a borate-based eutectic solvent.

[0006] The technical solution adopted by the present invention to achieve the above-mentioned objective is: a method for two-step extraction of 1,3-propanediol and organic acids from fermentation broth using a boric acid-based eutectic solvent, comprising the following steps:

[0007] S1: Theoretical screening of hydrogen bond acceptors: Based on the COSMO-RS model, using boric acid as the hydrogen bond donor, hydrogen bond acceptor A with high extraction ability of organic acids and hydrogen bond acceptor B with high extraction ability of 1,3-propanediol were screened according to the extraction efficiency indicators of partition coefficient, extractant loss, solvent solubility and extraction selectivity.

[0008] S2: Preparation of eutectic solvent: Boric acid is heated and mixed with equimolar amounts of hydrogen bond acceptor A and hydrogen bond acceptor B selected in step S1 to form a homogeneous, transparent and stable mixed system, thus obtaining boric acid-A eutectic solvent and boric acid-B eutectic solvent.

[0009] S3: Preparation of 1,3-propanediol concentrate: Evaporate and dehydrate the 1,3-propanediol fermentation broth to 15-30% of its original volume to obtain 1,3-propanediol concentrate;

[0010] S4: First step extraction: Take the 1,3-propanediol concentrate and adjust the pH to neutral or acidic. Mix the boric acid-A eutectic solvent mentioned in step S1 with the 1,3-propanediol concentrate. After stirring at a constant temperature, separate the phases to obtain the extract phase and the raffinate phase. The extract phase is the boric acid-A eutectic solvent phase rich in organic acids, and the raffinate phase is the aqueous phase rich in 1,3-propanediol and glycerol.

[0011] S5: First step back-extraction: Add Na2CO3 solution to the boric acid-A eutectic solvent phase described in step S4, stir and separate the phases to perform organic acid back-extraction, and obtain organic acid or organic acid salt solution and boric acid-A eutectic solvent.

[0012] S6: Second step extraction: Take the aqueous phase rich in 1,3-propanediol and glycerol from step S4 and adjust its pH to neutral or alkaline. Mix the boric acid-B eutectic solvent from step S1 with the aqueous phase rich in 1,3-propanediol and glycerol. After stirring at a constant temperature, separate the phases to obtain the extract phase and raffinate phase of the first-stage extraction. Take the raffinate phase of the first-stage extraction and add boric acid-B eutectic solvent for second-stage extraction. The operating conditions are the same as the first stage. Repeat the extraction 2-6 times. Mix the extract phases obtained from each stage extraction to obtain the boric acid-B eutectic solvent phase rich in 1,3-propanediol and glycerol.

[0013] S7: Second step back-extraction: Water is added to the boric acid-B eutectic solvent phase rich in 1,3-propanediol and glycerol described in step S6, and the mixture is stirred to back-extract 1,3-propanediol and glycerol to obtain an aqueous solution of 1,3-propanediol and glycerol and the boric acid-B eutectic solvent.

[0014] Furthermore, the organic acid is butyric acid and acetic acid.

[0015] Preferably, the hydrogen bond acceptor A in step S2 is any one of proline, n-heptanol, n-octanol, n-decanol, n-hexanoic acid, n-octanoic acid, or lauric acid, and the hydrogen bond acceptor B is any one of thymol, tetramethylammonium bromide, tetramethylphosphorus chloride, or tetraethylammonium chloride.

[0016] Furthermore, in step S2, the hydrogen bond acceptor A is proline, and the hydrogen bond acceptor B is thymol.

[0017] Preferably, in step S2, the boric acid and equimolar proline are heated to 130°C and stirred for 30 minutes; the boric acid and equimolar thymol are heated to 160°C and stirred for 30 minutes.

[0018] Preferably, in step S4, the pH is 4-7, the volume ratio of the boric acid-A eutectic solvent to the 1,3-propanediol concentrate is 1:1, the temperature is 60-80℃, the stirring speed is 250 r / min, and the stirring time is 2-18 min; in step S5, the volume ratio of the boric acid-A eutectic solvent phase to the Na2CO3 solution is 4:1-1:1, and the concentration of the Na2CO3 solution is 0-0.8 mol / L; in step S6, the pH is 7-13, the volume ratio of the boric acid-B eutectic solvent to the aqueous phase rich in 1,3-propanediol and glycerol is 1:1, the temperature is 60-80℃, the stirring speed is 250 r / min, and the stirring time is 2-18 min; in step S7, the volume ratio of the boric acid-B eutectic solvent phase rich in 1,3-propanediol and glycerol to water is 1:1-3:1.

[0019] Preferably, in step S4, the pH is 4, the volume ratio of the boric acid-A eutectic solvent to the 1,3-propanediol concentrate is 1:1, the temperature is 70°C, the stirring speed is 250 r / min, and the stirring time is 8 min; in step S5, the volume ratio of the boric acid-A eutectic solvent phase to the Na2CO3 solution is 1:1, and the concentration of the Na2CO3 solution is 0.8 mol / L; in step S6, the pH is 7, the volume ratio of the boric acid-B eutectic solvent to the aqueous phase rich in 1,3-propanediol and glycerol is 1:1, the temperature is 75°C, the stirring speed is 250 r / min, and the stirring time is 10 min; in step S7, the volume ratio of the boric acid-B eutectic solvent phase rich in 1,3-propanediol and glycerol to water is 1:1.

[0020] Compared with existing technologies, the advantages of this invention lie in its use of a eutectic solvent as the extractant. Due to its stable solvent structure and unique solubility properties, it enables a green separation process. The eutectic solvent is simple to prepare, and the extraction system is easily scaled up. Compared to solvent extraction, this invention exhibits significantly better extraction results, facilitates back-extraction after extraction, and allows for the recycling of the eutectic solvent, thereby reducing costs. A combination of quantum chemical calculations and experiments is used to screen boric acid-based eutectic solvent extraction systems with high extraction capabilities, greatly improving the efficiency of the screening process. A two-step method is employed to improve separation efficiency while simultaneously recovering organic acids, enhancing added value. Attached Figure Description

[0021] Figure 1 Schematic diagram of a two-step extraction process for separating 1,3-propanediol and organic acids using a borate-based eutectic solvent.

[0022] Figure 2 Scatter plot of the partition coefficient calculation results for fifteen eutectic solvents;

[0023] Figure 3 Scatter plot of solvent solubility calculation results;

[0024] Figure 4 Scatter plot of loss calculation results for fifteen eutectic solvents;

[0025] Figure 5 The effect of the first-step extraction temperature on the extraction recovery rates of butyric acid and acetic acid;

[0026] Figure 6 The effect of the first-step extraction mixing and stirring time on the butyric acid extraction recovery rate;

[0027] Figure 7 The effect of the first-step extraction mixing and stirring time on the acetic acid extraction recovery rate;

[0028] Figure 8The effect of the first-step back-extraction on the recovery rates of butyric acid and acetic acid;

[0029] Figure 9 The effect of sodium carbonate solution concentration in the first step of back-extraction on the recovery rates of butyric acid and acetic acid;

[0030] Figure 10 The effect of the second extraction stage on the recovery of 1,3-propanediol and glycerol;

[0031] Figure 11 The effect of the second-step extraction stirring and mixing time on the recovery rates of 1,3-propanediol and glycerol;

[0032] Figure 12 The effect of extraction temperature in the second step on the recovery rates of 1,3-propanediol and glycerol;

[0033] Figure 13 The effect of the second-step back-extraction on the recovery of 1,3-propanediol and glycerol. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, the experimental methods used are conventional methods, and the reagents or instruments used are all commercially available conventional products.

[0035] The 1,3-propanediol fermentation broth processed in this embodiment was obtained by fermentation with *Clostridium butyricum* using glycerol as a substrate. The concentrated 1,3-propanediol used was obtained by evaporation and dehydration of the fermentation broth, wherein the concentrations of 1,3-propanediol (1,3-PDO), glycerol, acetic acid (HAc), and butyric acid (HBu) were 372.73, 46.49, 36.63, and 68.77 g / L, respectively. A schematic diagram of the two-step extraction process for separating 1,3-propanediol and organic acids from the concentrated 1,3-propanediol is shown below. Figure 1 .

[0036] The concentrations of 1,3-propanediol, glycerol, acetic acid, and butyric acid were determined by high-performance liquid chromatography (HPLC). The detection conditions were: Aminex HPX-87H column; differential detector, detection wavelength 410 nm; injection volume 20 μL; mobile phase 5 mM sulfuric acid; flow rate 0.6 mL / min; detection time 27 min.

[0037] Theoretical screening of hydrogen bond acceptors: Based on the COSMO-RS thermodynamic model, the corresponding shielding charge density distribution function was obtained, and the corresponding infinite dilution activity coefficient was calculated using COSMO thermX software. The specific steps are as follows:

[0038] First, construct the component structures (components not included in the database). Use TurboMole software to construct 3D molecular or ionic structures, selecting the BP86 functional from density functional theory (DFT) for structure and energy optimization. Perform preliminary conformation optimization to reduce the time required for subsequent quantization calculations. After quantization, the surface shielding charge density distribution of the molecules or ions can be obtained. For components already included in the database, the .cosmo files containing the BP86-TZVP parameters for each substance required for calculation can be directly obtained from the database.

[0039] Eutectic solvents are composed of hydrogen bond acceptors (HBA) and donors (HBD) in a specific molar ratio. Their mixing process is widely regarded as a neutral mixture. The shielding charge density distribution function of eutectic solvents is established by the two-component method, and the total σ-profile of eutectic solvents can be obtained by calculation using the following formula.

[0040] p DES (σ)=f HBA (σ)p HBA (σ)+f HBD (σ)p HBD (σ)

[0041] In the formula p HBA (σ) is the shielding charge density distribution of the hydrogen bond acceptor, p HBD (σ) is the shielding charge density distribution of the hydrogen bond donor, f HBA and f HBD These are the corresponding proportionality coefficients.

[0042] Further calculations were performed on the infinite dilution activity coefficient of the eutectic solvent at a specific temperature. The partition coefficient (D), extractant loss in the solvent (SL), solute solubility in the solvent (SP), and extraction selectivity coefficient (S), reflecting extraction performance, were also calculated and used as screening criteria. Specifically, D reflects the partitioning behavior of the solute between the two phases; a higher value indicates a greater content of solute molecules in the extraction phase, resulting in a more significant extraction effect. SL represents the solubility of the extractant (eutectic solvent) in the solvent, reflecting extractant loss; a higher value indicates greater loss in the solvent. Therefore, lower extractant loss is better while meeting separation requirements. SP reflects the solubility of the substance to be extracted in the extractant; its value reflects the extraction capacity. S, or extraction selectivity, reflects the extractant's ability to separate substances from the original solution. The corresponding calculation formulas are shown below.

[0043]

[0044] In the formula, This represents the activity coefficient of solute A at infinite dilution in solvent B; This represents the dilution-limiting activity coefficient of solute A in extractant S; D represents the activity coefficient of extractant S at infinite dilution in solvent B. A D represents the partition coefficient of solute A. A ˊ represents the partition coefficient of solute Aˊ.

[0045] Example 1

[0046] Using 1,3-propanediol as the solute and water molecules as the solvent, a corresponding molecular structure was constructed. DES molecules were used as the extractant, with a hydrogen bond acceptor to hydrogen bond donor molar ratio of 1:1. The partition system (D), extractant loss (SL), solvent solubility (SP), and selectivity coefficient (S) for the 15 eutectic solvents listed in Table 1 were calculated.

[0047] Table 1. Molecular structure information of hydrogen bond acceptors and hydrogen bond donors.

[0048]

[0049]

[0050] Example 2

[0051] It is largely the same as Example 1, except that glycerol is used as the solute.

[0052] Example 3

[0053] It is largely the same as Example 1, except that acetic acid is used as the solute.

[0054] Example 4

[0055] It is largely the same as Example 1, except that butyric acid is used as the solute.

[0056] Due to the complex composition of the fermentation broth, the target product (1,3-PDO) and coexisting substances (glycerol, acetic acid, and butyric acid) were used as solutes, water molecules as solvent molecules, and corresponding molecular structures were constructed. DES molecules were used as the extractant, with a hydrogen bond acceptor-to-hydrogen bond donor molar ratio of 1:1. Based on four parameters—partition system (D), extractant loss (SL), solvent solubility (SP), and selectivity coefficient (S)—as indicators for selecting the extractant, the indicator parameters corresponding to Examples 1-4 and the 15 eutectic solvents in Table 1 were calculated, and the results are shown in [Table 1]. Figure 2-4 And Table 2.

[0057] like Figure 2As shown, based on the partition coefficients of the 15 DESs, DES generally exhibits better extraction capabilities for butyric acid and acetic acid than for 1,3-PDO and glycerol. This is because polyhydroxy alcohols are highly hydrophilic and relatively difficult to extract. When thymol is used as the hydrogen bond acceptor, the BA (boronic acid) / Thymol system shows better extraction performance for 1,3-PDO and glycerol. The solubility (SP) of 1,3-PDO and glycerol in this system is high, with a partition coefficient of 4.23 for 1,3-PDO and 2.46 for glycerol. For acetic acid and butyric acid, DES systems represented by BA / Heptanol, BA / Octanol, BA / Decanol, and BA / Proline show good extraction performance for butyric acid, with an average partition coefficient (D) approaching 33. However, choline-based and organic amine salt-based DES systems show poor extraction performance for organic acids, especially butyric acid. Figure 3 It is known that butyric acid has very low solubility in this type of DES system, resulting in poor extraction efficiency.

[0058] DES loss is also a key factor to consider during the extraction process, such as... Figure 4 As shown, the DES systems of betaine, choline, and organic ammonium salts exhibit poor hydrophobicity because betaine, choline, and organic ammonium salts themselves have a certain degree of hydrophilicity. Other DES systems, including the BA / Proline and BA / Thymol systems, show good hydrophobicity.

[0059] Table 2 Extraction Selectivity of DES System

[0060]

[0061] As shown in Table 2, the BA / Proline system exhibited better extraction efficiency and the highest selectivity for butyric acid and acetic acid. The selectivity coefficients for butyric acid to 1,3-PDO and glycerol were 137.48 and 71.94, respectively, while those for acetic acid were 24.19 and 12.66, respectively. Based on the different extraction characteristics, the following suggestions are made... Figure 1 The novel two-step extraction process for 1,3-PDO and organic acids from 1,3-propanediol fermentation concentrate is shown. First, butyric acid and acetic acid are separated from the fermentation concentrate using a BA / Proline eutectic solvent system. Then, the target product 1,3-PDO and residual glycerol are extracted using a BA / Thymol eutectic solvent system.

[0062] Examples 5-40

[0063] A method for two-step extraction of 1,3-propanediol and organic acids from fermentation broth using a borate-based eutectic solvent, comprising the following steps:

[0064] Preparation of eutectic solvents: Eutectic solvents were prepared by heating Proline and Thymol with equimolar amounts of boric acid. Specifically, Proline and BA were heated in an oil bath at 130°C for 30 min with magnetic stirring; Thymol and BA were heated in an oil bath at 160°C for 30 min with magnetic stirring. This process ensured complete dissolution of the crystals, forming homogeneous, transparent, and stable mixed systems, thus yielding BA-Proline and BA-Thymol eutectic solvents.

[0065] Step 1 Extraction: Take 5 mL of BA-Proline eutectic solvent into a 20 mL stoppered test tube, add 5 mL of 1,3-propanediol concentrate (adjust the pH of the concentrate to acidic or neutral with concentrated sulfuric acid), mix thoroughly at a specific mixing temperature and a rotation speed of 250 rpm, centrifuge to obtain the extract phase and raffinate phase. The extract phase is a BA-Proline eutectic solvent phase rich in organic acids, mainly acetic acid and butyric acid; the raffinate phase is an aqueous phase rich in 1,3-propanediol and glycerol.

[0066] Step 1 back-extraction: Take the BA-Proline eutectic solvent phase rich in organic acids obtained from the first step extraction, and add Na2CO3 solution at 60℃ and 250 r / min to back-extract butyric acid and acetic acid, to obtain an organic acid / organoacid salt solution and BA-Proline eutectic solvent. The BA-Proline eutectic solvent can be recycled.

[0067] Second-stage extraction: Take 5 mL of BA-Thymol eutectic solvent into a 20 mL stoppered test tube, add 5 mL of the aqueous phase rich in 1,3-propanediol and glycerol from the first-stage extraction (adjust the pH to 7 with alkali solution first), mix and shake well at a specific mixing temperature and a rotation speed of 250 r / min, then centrifuge to obtain the extract phase and raffinate phase from the first-stage extraction. Take the raffinate phase from the first-stage extraction, add BA-Thymol eutectic solvent for a second-stage extraction, and repeat the extraction under the same conditions as the first stage. Combine the extract phases obtained from each stage to obtain the BA-Thymol eutectic solvent phase rich in 1,3-propanediol and glycerol.

[0068] Second step back-extraction: Water is added to the BA-Thymol eutectic solvent phase rich in 1,3-propanediol and glycerol obtained in the second step extraction process, and the mixture is stirred to back-extract 1,3-propanediol and glycerol to obtain an aqueous solution of 1,3-propanediol and glycerol and BA-Thymol eutectic solvent. The BA-Thymol eutectic solvent can be recycled.

[0069] The process parameters for Examples 5-40 are shown in Table 3.

[0070] Table 3 Process Parameters of the Embodiments

[0071]

[0072]

[0073] The extract phase and raffinate from the first extraction step were analyzed to calculate the partition coefficient, phase ratio, and yield of the organic acid. The formulas for calculating the partition coefficient (K), phase ratio (R), and yield (Y) are as follows:

[0074]

[0075] In the formula, C t -Concentration of substances in the extract phase, g / L; C b -Concentration of substances in the raffinate phase, g / L; V t - Extraction phase volume, mL, V b - Residual phase volume, mL.

[0076] During back-extraction, the ratio refers to the volume ratio of the extractant phase rich in eutectic solvent to the back-extractant (sodium carbonate solution or water), while the yield of the target product refers to the percentage of product in the back-extractant phase.

[0077] Examples 5-8 investigated the effect of different pH values ​​in the first extraction step on the partitioning behavior of organic acids in DES. The pH of the concentrate was adjusted so that the organic acid salts in the concentrate existed in the form of organic acids, facilitating the extraction of acetic acid and butyric acid. The partitioning behavior of acetic acid, butyric acid, 1,3-propanediol, and glycerol in the BA / Proline eutectic solvent extraction systems of Examples 5-8 is shown in Table 4.

[0078] Table 4. Partition behavior of acetic acid, butyric acid, 1,3-propanediol, and glycerol under different pH conditions.

[0079]

[0080] As shown in Table 4, the extraction capabilities of the BA / Proline eutectic solvent system for each substance in the fermentation broth are in the following order: butyric acid > acetic acid > glycerol ≈ 1,3-propanediol. 1,3-propanediol and glycerol exhibit poor extraction efficiency due to their strong hydrophilicity, which is consistent with the theoretical screening results for extractants. With decreasing pH, the partition coefficients and yields of acetic acid and butyric acid significantly increase. When the pH of the fermentation broth is adjusted to 4, the recovery rates of butyric acid and acetic acid in the DES extraction system are 94.56% and 81.03%, respectively, indicating that most of the organic acids are recovered, and high extraction selectivity is observed for 1,3-propanediol and glycerol.

[0081] Examples 8-12 investigated the effect of different extraction temperatures in the first step of extraction on the recovery rate of organic acid extraction, and the results are as follows: Figure 5 As shown, increasing the temperature can improve the extraction yield of organic acids, but when the extraction temperature is increased to above 70℃, the increase in temperature has no significant effect on the recovery rate. Therefore, the extraction temperature was chosen to be 70℃.

[0082] Examples 8 and 13-17 investigated the effects of different stirring times in the first step of extraction on the recovery rate of organic acid extraction, and the results are as follows: Figure 6 , Figure 7 As shown, the extraction recovery rate of butyric acid approaches its maximum when the mixing and stirring time reaches 6 minutes; while the extraction recovery rate of acetic acid approaches its maximum when the mixing and stirring time reaches 8 minutes. Therefore, the suitable stirring time is 8 minutes, at which point both butyric acid and acetic acid can achieve maximum recovery.

[0083] Examples 8 and 18-20 investigated the effect of the volume ratio of the organic acid-rich BA-Proline eutectic solvent phase to the Na2CO3 solution on the recovery rates of butyric acid and acetic acid in the first-step back-extraction. The results are as follows: Figure 8 As shown, the yields of acetic acid and butyric acid increase with the increase of the back-extraction ratio. Therefore, the appropriate back-extraction ratio is 1:1, at which point acetic acid and butyric acid can be recovered to the maximum extent.

[0084] Examples 8 and 21-24 investigated the effects of sodium carbonate concentration on the recovery rates of butyric acid and acetic acid during the first-step back-extraction, and the results are as follows: Figure 9 As shown, the recoveries of both butyric acid and acetic acid increased with increasing sodium carbonate solution concentration. When the concentration was 0.8 mol / L, the recoveries of butyric acid and acetic acid were 85.32% and 91.37%, respectively.

[0085] Examples 8 and 25-27 investigated the effect of the second extraction stage on the recovery rates of 1,3-propanediol and glycerol, respectively, and the results are as follows: Figure 10 As shown, after four stages of extraction, the yields of 1,3-propanediol and glycerol reached 80.17% and 73.64%, respectively. Multi-stage extraction increases the extraction recovery rate, but increasing the number of extraction stages requires a larger amount of DES, which is equivalent to continuously diluting the concentrate and increasing the volume of the extract phase, thus increasing the throughput for subsequent back-extraction. Therefore, optimization of the extraction process was considered, with the optimal number of extraction stages being four. In industrial production, continuous countercurrent extraction is commonly used, which reduces the amount of extractant and increases the extraction yield.

[0086] Examples 8 and 28-32 investigated the effect of stirring time during the second extraction step on the recovery rates of 1,3-propanediol and glycerol, respectively. The results are as follows: Figure 11As shown, extending the stirring time can improve the recovery rate of 1,3-propanediol and glycerol. When the stirring time is 10 min, the yields of 1,3-propanediol and glycerol tend to stabilize, with the yields increasing by 3.53% and 4.11%, respectively.

[0087] Examples 8 and 33-36 investigated the effects of different extraction temperatures on the recovery rates of 1,3-propanediol and glycerol in the second extraction step, respectively. The results are as follows: Figure 12 As shown, increasing the extraction temperature improves the recovery rates of 1,3-propanediol and glycerol. When the temperature increases from 60℃ to 75℃, the recovery rates of both tend to stabilize, with the yields of 1,3-propanediol and glycerol increasing by 5.99% and 6.01%, respectively. Therefore, the optimal extraction temperature for the second extraction step is 75℃.

[0088] Examples 8 and 37-40 investigated the effect of the ratio on the recovery of 1,3-propanediol and glycerol in the second-step back-extraction. Figure 13 The results showed that as the back-extraction ratio increased, i.e., the volume of water used for back-extraction decreased, the yields of 1,3-propanediol and glycerol also decreased. For example, the yield of 1,3-propanediol was 95.64% when the back-extraction ratio was 1:1, but it dropped to 82.18% when the back-extraction ratio was 3:1; correspondingly, the yield of glycerol also decreased from 94.15% to 80.26%, and the optimal back-extraction ratio was 1:1.

[0089] The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A method for two-step extraction of 1,3-propanediol and organic acids from fermentation broth using a borate-based eutectic solvent, characterized in that, Includes the following steps: S1: Theoretical screening of hydrogen bond acceptors: Based on the COSMO-RS model, using boric acid as the hydrogen bond donor, hydrogen bond acceptor A with high extraction ability for organic acids and hydrogen bond acceptor B with high extraction ability for 1,3-propanediol were screened according to the extraction efficiency indicators of partition coefficient, extractant loss, solvent solubility and extraction selectivity. Hydrogen bond acceptor A is selected from any one of proline, n-heptanol, n-octanol, n-decanol, n-hexanoic acid, n-octanoic acid or lauric acid, and hydrogen bond acceptor B is selected from any one of thymol, tetramethylammonium bromide, tetramethylphosphorus chloride or tetraethylammonium chloride. S2: Preparation of eutectic solvent: Boric acid is heated and mixed with equimolar amounts of hydrogen bond acceptor A and hydrogen bond acceptor B selected in step S1 to form a homogeneous, transparent and stable mixed system, thus obtaining boric acid-A eutectic solvent and boric acid-B eutectic solvent. S3: Preparation of 1,3-propanediol concentrate: Evaporate and dehydrate the 1,3-propanediol fermentation broth to 15-30% of its original volume to obtain 1,3-propanediol concentrate; S4: First step extraction: Take the 1,3-propanediol concentrate and adjust the pH to neutral or acidic. Mix the boric acid-A eutectic solvent mentioned in step S1 with the 1,3-propanediol concentrate. After stirring at a constant temperature, separate the phases to obtain the extract phase and the raffinate phase. The extract phase is the boric acid-A eutectic solvent phase rich in organic acids, and the raffinate phase is the aqueous phase rich in 1,3-propanediol and glycerol. S5: First step back-extraction: Add Na2CO3 solution to the boric acid-A eutectic solvent phase described in step S4, stir and separate the phases to perform organic acid back-extraction, and obtain organic acid or organic acid salt solution and boric acid-A eutectic solvent. S6: Second step extraction: Take the aqueous phase rich in 1,3-propanediol and glycerol from step S4 and adjust its pH to neutral or alkaline. Mix the boric acid-B eutectic solvent from step S1 with the aqueous phase rich in 1,3-propanediol and glycerol. After stirring at a constant temperature, separate the phases to obtain the extract phase and raffinate phase of the first-stage extraction. Take the raffinate phase of the first-stage extraction and add boric acid-B eutectic solvent for second-stage extraction. The operating conditions are the same as the first stage. Repeat the extraction 2-6 times. Mix the extract phases obtained from each stage extraction to obtain the boric acid-B eutectic solvent phase rich in 1,3-propanediol and glycerol. S7: Second step back-extraction: Water is added to the boric acid-B eutectic solvent phase rich in 1,3-propanediol and glycerol described in step S6, and the mixture is stirred to back-extract 1,3-propanediol and glycerol to obtain an aqueous solution of 1,3-propanediol and glycerol and the boric acid-B eutectic solvent.

2. The method for two-step extraction of 1,3-propanediol and organic acids from fermentation broth using a borate-based eutectic solvent according to claim 1, characterized in that, The organic acids mentioned are butyric acid and acetic acid.

3. The method for two-step extraction of 1,3-propanediol and organic acids from fermentation broth using a borate-based eutectic solvent according to claim 1, characterized in that, In step S2, hydrogen bond acceptor A is proline, and hydrogen bond acceptor B is thymol.

4. The method for two-step extraction of 1,3-propanediol and organic acids from fermentation broth using a borate-based eutectic solvent according to claim 3, characterized in that, In step S2, the boric acid and equimolar proline are heated to 130°C and stirred for 30 minutes; the boric acid and equimolar thymol are heated to 160°C and stirred for 30 minutes.

5. The method for two-step extraction of 1,3-propanediol and organic acids from fermentation broth using a borate-based eutectic solvent according to claim 1, characterized in that, In step S4, the pH is 4-7, the volume ratio of boric acid-A eutectic solvent to 1,3-propanediol concentrate is 1:1, the temperature is 60-80℃, the stirring speed is 250 r / min, and the stirring time is 2-18 min; in step S5, the volume ratio of boric acid-A eutectic solvent phase to Na2CO3 solution is 4:1-1:1, and the concentration of Na2CO3 solution is 0-0.8 mol / L; in step S6, the pH is 7-13, the volume ratio of boric acid-B eutectic solvent to the aqueous phase rich in 1,3-propanediol and glycerol is 1:1, the temperature is 60-80℃, the stirring speed is 250 r / min, and the stirring time is 2-18 min; in step S7, the volume ratio of boric acid-B eutectic solvent phase rich in 1,3-propanediol and glycerol to water is 1:1-3:

1.

6. The method for two-step extraction of 1,3-propanediol and organic acids from fermentation broth using a borate-based eutectic solvent according to claim 1, characterized in that, In step S4, the pH is 4, the volume ratio of boric acid-A eutectic solvent to 1,3-propanediol concentrate is 1:1, the temperature is 70℃, the stirring speed is 250 r / min, and the stirring time is 8 min; in step S5, the volume ratio of boric acid-A eutectic solvent phase to Na2CO3 solution is 1:1, and the concentration of Na2CO3 solution is 0.8 mol / L; in step S6, the pH is 7, the volume ratio of boric acid-B eutectic solvent to the aqueous phase rich in 1,3-propanediol and glycerol is 1:1, the temperature is 75℃, the stirring speed is 250 r / min, and the stirring time is 10 min; in step S7, the volume ratio of boric acid-B eutectic solvent phase rich in 1,3-propanediol and glycerol to water is 1:1.

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