A low waste liquid discharge method for crystallization and separation of d-p-hydroxyphenylglycine

Abstract

The application provides a D-p-hydroxyphenylglycine crystallization separation method with low waste liquid discharge, relates to the technical field of biological catalysis synthesis and preparation of pharmaceutical fine chemicals, and comprises the following steps: volatile alkali is added into the clarified liquid to adjust the pH to 8.5-10.5, and an alkaline dissolution liquid is obtained; the volatile alkali is ammonia water or an ammonia gas aqueous solution. The D-p-hydroxyphenylglycine crystallization separation method with low waste liquid discharge realizes efficient D-p-hydroxyphenylglycine separation and low waste liquid discharge by adopting multiple separation and concentration processes. Solid impurities in the reaction liquid are removed by centrifugal separation and microfiltration membrane filtration to obtain a clarified liquid. The concentration of D-p-hydroxyphenylglycine is improved by adopting nanofiltration membrane concentration technology. In the concentration process, the impurities in the solution are effectively removed through the interception effect and cross-flow mode of the membrane, the generation of waste liquid is reduced, and the utilization of resources is optimized.

Description

Technical Field

[0001] This invention relates to the field of biocatalytic synthesis and pharmaceutical fine chemical preparation technology, specifically a method for the crystallization and separation of D-p-hydroxyphenylglycine with low waste liquid discharge. Background Technology

[0002] Currently, D-p-hydroxyphenylglycine, as an important pharmaceutical fine chemical and a side-chain raw material for β-lactam antibiotics, is mainly produced through two major industrial routes: chemical synthesis and resolution methods, and bioenzymatic methods. Chemical methods typically involve synthesizing intermediates followed by resolution with a resolving agent to obtain the target enantiomer. Bioenzymatic methods utilize enzyme catalysis to convert DL-p-hydroxyphenylhydantoin into D-p-hydroxyphenylglycine. In the post-processing separation stage of enzymatic production, a common process chain involves filtration of the enzyme conversion solution to obtain crude and clear products; the crude product is dissolved in alkali, decolorized with activated carbon, filtered through a microfiltration membrane, and then crystallized by adding hydrochloric acid solution. The crystals are then centrifuged, washed, and dried to obtain crystals. Simultaneously, the crystallization mother liquor and the clear conversion solution are combined and concentrated in an evaporator, followed by further decolorization, filtration, and secondary hydrochloric acid crystallization. The washing tail liquid can be recycled for the concentration step to improve recovery.

[0003] The aforementioned existing technologies still have significant shortcomings and are difficult to meet the requirements of low wastewater discharge and green production: chemical synthesis resolution methods often have problems such as expensive resolving agents, strong sulfur odor, and significant environmental pollution; existing bioenzymatic methods still face problems such as poor enzyme stability leading to low conversion rate, large enzyme dosage, low substrate concentration leading to the generation of a large amount of wastewater during the reaction process, and high treatment costs. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a low-waste liquid discharge method for the crystallization and separation of D-p-hydroxyphenylglycine. The technical problem this invention aims to solve is how to address the issues of expensive resolving agents, poor enzyme stability, low substrate concentration, large amounts of waste liquid, and high treatment costs in existing chemical synthesis and bioenzymatic methods by using biocatalyst recycling, membrane concentration technology, countercurrent washing, and resource recovery.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for crystallizing and separating D-p-hydroxyphenylglycine with low wastewater discharge, comprising: S1. The reaction solution containing D-p-hydroxyphenylglycine obtained by bio-enzyme catalytic conversion is subjected to a first solid-liquid separation to obtain a clear solution containing D-p-hydroxyphenylglycine. The solid phase containing biocatalyst obtained by the solid-liquid separation is returned to the bio-enzyme catalytic conversion process for recycling. S2. Add a volatile alkali to the clarified liquid to adjust the pH to 8.5-10.5 to obtain an alkaline solution, wherein the volatile alkali is ammonia water or an aqueous solution of ammonia gas; S3. The alkaline solution is concentrated using a nanofiltration membrane to obtain a concentrate and a permeate. The concentrate is the retentate of the membrane concentration, and the concentration of D-p-hydroxyphenylglycine in the retentate is increased to 80 g / L-220 g / L. The permeate is returned to S2 as process recycled water and used as a source of water for crystal washing in subsequent washing steps. S4. The concentrated liquid is acidified by passing carbon dioxide through it under crystallization conditions to adjust the pH to 5.3-6.8, and then cooled and crystallized to obtain a slurry containing D-p-hydroxyphenylglycine crystals; S5. The slurry undergoes a second solid-liquid separation to obtain crystals and mother liquor. The crystals are washed countercurrently. The washing liquid from the countercurrent washing is combined with the mother liquor and then enters the regeneration unit. The combined mixture is analyzed to remove and recover ammonia and carbon dioxide. The recovered ammonia is returned to step S2 as a source of volatile alkali for recycling, and the recovered carbon dioxide is returned to step S4 as a source of acidification gas for recycling. The analyzed mother liquor is returned to step S3 and, in step S3, is combined with the alkaline solution and then recycled as a feed for membrane concentration. The system is equipped with a discharge branch for impurity balancing. The discharge volume of the circulating liquid discharged from the discharge branch, measured by mass flow meter, accounts for ≤5% of the total circulating volume of the circulating liquid.

[0006] Preferably, the solid-liquid separation is performed by centrifugation, and the liquid phase after centrifugation is then filtered through a microfiltration membrane with a pore size of 0.1μm-0.45μm to obtain the clarified liquid.

[0007] Preferably, the biocatalyst is an immobilized enzyme particle, the solid phase obtained from the first solid-liquid separation is the immobilized enzyme particle, and the immobilized enzyme particle is returned to the bio-enzyme catalytic conversion process and recycled in no less than 3 batches.

[0008] Preferably, the mass fraction of the ammonia water is 5%-25%, the pH adjustment is carried out at 20℃-45℃, and after the pH adjustment is completed, the alkaline solution is allowed to stand or slowly stirred for 10min-60min to achieve dissolution equilibrium.

[0009] Preferably, the nanofiltration membrane has a molecular weight cutoff of 200 Da to 500 Da, and the membrane concentration is operated in a cross-flow mode at a pressure of 1.0 MPa to 3.5 MPa, so as to increase the concentration of D-p-hydroxyphenylglycine in the concentrate to the range of 80 g / L to 220 g / L.

[0010] Preferably, before the alkaline solution is concentrated by membrane, the process further includes: adsorption decolorization and filtration of the alkaline solution. The adsorption decolorization uses a macroporous adsorption resin, and the liquid after adsorption decolorization is filtered and then concentrated by membrane. The macroporous adsorption resin has a specific surface area of ​​200 m² / g-1200 m² / g, a pore volume of 0.3 mL / g-2.0 mL / g, and an average pore size of 5 nm-50 nm.

[0011] Preferably, the countercurrent washing is a 2-4 stage countercurrent washing, the mass ratio of the permeate in the washing water of the countercurrent washing is ≥50%, the insufficient part of the washing water is supplemented by secondary sources, the secondary sources are condensate, deionized water or softened water, and the total mass of the washing water is 0.2-1.5 times the mass of the obtained crystals.

[0012] Preferably, the analysis is carried out at 40℃-80℃ and an absolute pressure of 10kPa-60kPa to remove and recover ammonia and carbon dioxide from the mixture. The discharge branch is triggered by the circulating liquid conductivity or COD reaching a preset threshold. The circulating liquid discharged from the discharge branch enters the recovery unit to recover D-p-hydroxyphenylglycine before being discharged.

[0013] This invention provides a low-waste-discharge method for the crystallization and separation of D-p-hydroxyphenylglycine. It offers the following advantages:

[0014] This low-waste-discharge method for the crystallization and separation of D-p-hydroxyphenylglycine achieves efficient separation and low waste discharge by employing multiple separation and concentration processes. Centrifugation and microfiltration are used to remove solid impurities from the reaction solution, yielding a clarified liquid. Nanofiltration membrane concentration technology is then employed to increase the concentration of D-p-hydroxyphenylglycine. During the concentration process, the membrane's retention effect and cross-flow mechanism effectively remove impurities from the solution, reducing waste generation and optimizing resource utilization.

[0015] The system employs countercurrent washing technology to maximize the recovery of D-p-hydroxyphenylglycine, reducing the use of washing liquid. Ammonia and carbon dioxide are recovered through a desorption unit, ensuring their recycling and further reducing emissions. Waste liquid discharge is strictly controlled, with its mass flow rate accounting for no more than 5% of the total circulating liquid mass. This recycling and recirculation system improves resource utilization efficiency, reduces environmental pollution, and meets environmental protection requirements. Attached Figure Description

[0016] Figure 1 This is a process flow diagram of the method of the present invention; Figure 2 This is a flowchart illustrating the material recycling process of the present invention. Figure 3 This is a schematic diagram of the system loop of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1 like Figures 1-3 As shown, this embodiment of the invention provides a method for the crystallization and separation of D-p-hydroxyphenylglycine with low wastewater discharge, comprising: S1. The reaction solution containing D-p-hydroxyphenylglycine obtained from the bio-enzyme catalytic conversion undergoes a first solid-liquid separation to obtain a clear solution containing D-p-hydroxyphenylglycine. The solid phase containing the biocatalyst obtained from the solid-liquid separation is returned to the bio-enzyme catalytic conversion process for recycling. The solid-liquid separation is performed by centrifugation. The liquid phase after centrifugation is then filtered through a microfiltration membrane with a pore size of 0.45 μm to obtain a clear solution. The biocatalyst is immobilized enzyme particles. The solid phase obtained from the first solid-liquid separation is immobilized enzyme particles. The immobilized enzyme particles are returned to the bio-enzyme catalytic conversion process and recycled in at least three batches.

[0019] S2. Add a volatile alkali to the clarified liquid to adjust the pH to 8.5, obtaining an alkaline solution. The volatile alkali is ammonia water or an aqueous solution of ammonia gas. The mass fraction of the ammonia water is 5%. The pH adjustment is carried out at 20°C, and after the pH adjustment is completed, the alkaline solution is allowed to stand or slowly stirred for 10 minutes to achieve dissolution equilibrium.

[0020] S3. The alkaline solution is concentrated using a nanofiltration membrane to obtain a concentrate and a permeate. The concentrate serves as the retentate after membrane concentration, with the concentration of D-p-hydroxyphenylglycine in the retentate increased to 80 g / L. The permeate is returned to S2 as process water and used as a source of water for crystal washing in subsequent washing steps. The nanofiltration membrane has a molecular weight cutoff of 200 Da. Membrane concentration is operated in a cross-flow mode at a pressure of 1.0 MPa to ensure that the concentration of D-p-hydroxyphenylglycine in the concentrate reaches 80 g / L. Prior to membrane concentration, the alkaline solution undergoes adsorption decolorization and filtration. Adsorption decolorization uses a macroporous adsorption resin. The decolorized liquid is filtered and then concentrated using a membrane. The macroporous adsorption resin has a specific surface area of ​​200 m² / g, a pore volume of 0.3 mL / g, and an average pore size of 5 nm.

[0021] S4. The concentrate is acidified by passing carbon dioxide through it under crystallization conditions to adjust the pH to 5.3, and then cooled and crystallized to obtain a slurry containing D-p-hydroxyphenylglycine crystals.

[0022] S5. The slurry undergoes a second solid-liquid separation to obtain crystals and mother liquor. The crystals are then subjected to countercurrent washing. The washing liquid from the countercurrent washing is combined with the mother liquor and enters the regeneration unit. The combined mixture is analyzed to remove and recover ammonia and carbon dioxide. The recovered ammonia is returned to step S2 as a source of volatile alkali for recycling, and the recovered carbon dioxide is returned to step S4 as a source of acidification gas for recycling. The analyzed mother liquor is returned to step S3 and, in step S3, is combined with the alkaline solution and recycled as feed for membrane concentration. The system is equipped with a discharge branch for impurity balancing. The discharge volume of the circulating liquid from the discharge branch, measured by mass flow meter, accounts for ≤5% of the total circulating liquid mass. The countercurrent washing is a two-stage countercurrent washing process. The mass percentage of permeate in the washing water during countercurrent washing is ≥50%. Any shortfall in washing water is supplemented by secondary sources, such as condensate, deionized water, or softened water. The total mass of the washing water is 0.2 times the mass of the obtained crystals. Analysis is carried out at 40℃ and an absolute pressure of 10kPa to remove and recover ammonia and carbon dioxide from the mixture. The discharge branch is triggered when the conductivity or COD of the circulating liquid reaches a preset threshold. The circulating liquid discharged from the discharge branch enters the recovery unit to recover D-p-hydroxyphenylglycine before being discharged.

[0023] Due to the lower concentration in this embodiment, the crystallization process may not be as efficient as at higher concentrations, resulting in lower product yield and purity. Resource recovery measures are employed, but the low concentration may mean more waste liquid needs to be discharged, and the recovery process is less efficient than at higher concentrations. The reaction and recovery steps in the entire process are simpler, potentially offering greater operational flexibility and making it suitable for small to medium-scale production.

[0024] Example 2 This invention provides a method for the crystallization and separation of D-p-hydroxyphenylglycine with low wastewater discharge, comprising: S1. The reaction solution containing D-p-hydroxyphenylglycine obtained from the bio-enzyme catalytic conversion undergoes a first solid-liquid separation to obtain a clear solution containing D-p-hydroxyphenylglycine. The solid phase containing the biocatalyst obtained from the solid-liquid separation is returned to the bio-enzyme catalytic conversion process for recycling. The solid-liquid separation is performed by centrifugation. The liquid phase after centrifugation is then filtered through a microfiltration membrane with a pore size of 0.275 μm to obtain a clear solution. The biocatalyst is immobilized enzyme particles. The solid phase obtained from the first solid-liquid separation is immobilized enzyme particles. The immobilized enzyme particles are returned to the bio-enzyme catalytic conversion process and recycled in at least three batches.

[0025] S2. Add a volatile alkali to the clarified liquid to adjust the pH to 9.5, obtaining an alkaline solution. The volatile alkali is ammonia water or an aqueous solution of ammonia gas. The mass fraction of ammonia water is 15%. The pH adjustment is carried out at 32.5℃, and after the pH adjustment is completed, the alkaline solution is allowed to stand or slowly stirred for 35 minutes to achieve dissolution equilibrium.

[0026] S3. The alkaline solution is concentrated using a nanofiltration membrane to obtain a concentrate and a permeate. The concentrate serves as the retentate after membrane concentration, with the concentration of D-p-hydroxyphenylglycine in the retentate increased to 150 g / L. The permeate is returned to S2 as process water and used as a source of water for crystal washing in subsequent washing steps. The nanofiltration membrane has a molecular weight cutoff of 350 Da. Membrane concentration is operated in a cross-flow mode at a pressure of 2.25 MPa to ensure that the concentration of D-p-hydroxyphenylglycine in the concentrate reaches 150 g / L. Prior to membrane concentration, the alkaline solution undergoes adsorption decolorization and filtration. Adsorption decolorization uses a macroporous adsorption resin. The decolorized liquid is filtered and then concentrated using a membrane. The macroporous adsorption resin has a specific surface area of ​​700 m² / g, a pore volume of 1.15 mL / g, and an average pore size of 27.5 nm.

[0027] S4. The concentrate is acidified by passing carbon dioxide through it under crystallization conditions to adjust the pH to 6, and then cooled and crystallized to obtain a slurry containing D-p-hydroxyphenylglycine crystals.

[0028] S5. The slurry undergoes a second solid-liquid separation to obtain crystals and mother liquor. The crystals are then subjected to countercurrent washing. The washing liquid from the countercurrent washing is combined with the mother liquor and enters the regeneration unit. The combined mixture is analyzed to remove and recover ammonia and carbon dioxide. The recovered ammonia is returned to step S2 as a source of volatile alkali for recycling, and the recovered carbon dioxide is returned to step S4 as a source of acidification gas for recycling. The analyzed mother liquor is returned to step S3 and, in step S3, is combined with the alkaline solution and recycled as feed for membrane concentration. The system is equipped with a discharge branch for impurity balancing. The discharge volume of the circulating liquid from the discharge branch, measured by mass flow meter, accounts for ≤5% of the total circulating liquid mass. The countercurrent washing is a three-stage countercurrent washing process. The mass percentage of permeate in the washing water during countercurrent washing is ≥50%. Any shortfall in washing water is supplemented by secondary sources, such as condensate, deionized water, or softened water. The total mass of the washing water is 0.85 times the mass of the obtained crystals. Analysis is carried out at 60℃ and an absolute pressure of 35kPa to remove and recover ammonia and carbon dioxide from the mixture. The discharge branch is triggered when the conductivity or COD of the circulating liquid reaches a preset threshold. The circulating liquid discharged from the discharge branch enters the recovery unit to recover D-p-hydroxyphenylglycine before being discharged.

[0029] The moderate concentration in this embodiment balances crystallization efficiency and purity, increasing the yield of D-p-hydroxyphenylglycine while keeping wastewater discharge within a reasonable range. The higher concentration reduces wastewater discharge, allowing for better utilization of recovered ammonia and carbon dioxide, thus mitigating environmental impact. It exhibits good stability and operability in practical operation, making it suitable for large-scale industrial production and balancing economic efficiency with environmental friendliness.

[0030] Example 3 This invention provides a method for the crystallization and separation of D-p-hydroxyphenylglycine with low wastewater discharge, comprising: S1. The reaction solution containing D-p-hydroxyphenylglycine obtained from the bio-enzyme catalytic conversion undergoes a first solid-liquid separation to obtain a clear solution containing D-p-hydroxyphenylglycine. The solid phase containing the biocatalyst obtained from the solid-liquid separation is returned to the bio-enzyme catalytic conversion process for recycling. The solid-liquid separation is performed by centrifugation. The liquid phase after centrifugation is then filtered through a microfiltration membrane with a pore size of 0.1 μm to obtain a clear solution. The biocatalyst is immobilized enzyme particles. The solid phase obtained from the first solid-liquid separation is immobilized enzyme particles. The immobilized enzyme particles are returned to the bio-enzyme catalytic conversion process and recycled in at least three batches.

[0031] S2. Add a volatile alkali to the clarified liquid to adjust the pH to 10.5, obtaining an alkaline solution. The volatile alkali is ammonia water or an aqueous solution of ammonia gas. The mass fraction of ammonia water is 25%. The pH adjustment is carried out at 45°C, and after the pH adjustment is completed, the alkaline solution is allowed to stand or slowly stirred for 60 minutes to achieve dissolution equilibrium.

[0032] S3. The alkaline solution is concentrated using a nanofiltration membrane to obtain a concentrate and a permeate. The concentrate serves as the retentate after membrane concentration, with the concentration of D-p-hydroxyphenylglycine in the retentate increased to 220 g / L. The permeate is returned to S2 as process water and used as a source of water for crystal washing in subsequent washing steps. The nanofiltration membrane has a molecular weight cutoff of 500 Da. Membrane concentration is operated in a cross-flow mode at a pressure of 3.5 MPa to ensure that the concentration of D-p-hydroxyphenylglycine in the concentrate reaches 220 g / L. Prior to membrane concentration, the alkaline solution undergoes adsorption decolorization and filtration. Adsorption decolorization uses a macroporous adsorption resin. The decolorized liquid is filtered and then concentrated using a membrane. The macroporous adsorption resin has a specific surface area of ​​1200 m² / g, a pore volume of 2.0 mL / g, and an average pore size of 50 nm.

[0033] S4. The concentrate is acidified by passing carbon dioxide through it under crystallization conditions to adjust the pH to 6.8, and then cooled and crystallized to obtain a slurry containing D-p-hydroxyphenylglycine crystals.

[0034] S5. The slurry undergoes a second solid-liquid separation to obtain crystals and mother liquor. The crystals are then subjected to countercurrent washing. The washing liquid from the countercurrent washing is combined with the mother liquor and enters the regeneration unit. The combined mixture is analyzed to remove and recover ammonia and carbon dioxide. The recovered ammonia is returned to step S2 as a source of volatile alkali for recycling, and the recovered carbon dioxide is returned to step S4 as a source of acidification gas for recycling. The analyzed mother liquor is returned to step S3 and, in step S3, is combined with the alkaline solution and recycled as feed for membrane concentration. The system is equipped with a discharge branch for impurity balancing. The discharge volume of the circulating liquid from the discharge branch, measured by mass flow meter, accounts for ≤5% of the total circulating liquid mass. The countercurrent washing is a 4-stage countercurrent washing process. The mass percentage of permeate in the washing water during countercurrent washing is ≥50%. Any shortfall in washing water is supplemented by secondary sources, such as condensate, deionized water, or softened water. The total mass of the washing water is 1.5 times the mass of the obtained crystals. Analysis is carried out at 80℃ and an absolute pressure of 60kPa to remove and recover ammonia and carbon dioxide from the mixture. The discharge branch is triggered when the conductivity or COD of the circulating liquid reaches a preset threshold. The circulating liquid discharged from the discharge branch enters the recovery unit to recover D-p-hydroxyphenylglycine before being discharged.

[0035] This embodiment achieves the highest concentration, significantly improving crystallization efficiency and yielding more high-purity products. Due to the higher concentration, the waste liquid contains more active ingredients, greatly enhancing recovery efficiency and effectively controlling waste liquid emissions. The recovery rates of ammonia, carbon dioxide, and membrane concentrate are extremely high, minimizing raw material and water consumption during production and meeting green production requirements. This embodiment offers the highest production efficiency, suitable for producing high-efficiency, high-purity products and meeting demanding production environments. However, the more precise operating parameters and increased process control may necessitate higher technical investment and management capabilities.

[0036] Example 4 This embodiment describes a low-waste-discharge crystallization separation method for D-p-hydroxyphenylglycine, comparing the effects of membrane concentration, pH adjustment, crystallization, and countercurrent washing on product concentration and purity under different process conditions. The specific implementation method is as follows:

[0037] 1. First solid-liquid separation Experiment A: Centrifugation is used to separate the solids and liquids in the reaction solution. A microfiltration membrane with a pore size of 0.45 μm is used to filter the solution to obtain a clear liquid. However, due to the large pore size, the filtration accuracy is low, resulting in a low quality of the clear liquid. Some fine impurities may remain, affecting subsequent processes.

[0038] After solid-liquid separation, the solid phase consists of immobilized enzyme particles, which are recycled through at least three batches.

[0039] Experiment B: Centrifugal separation was used, and the separated liquid was filtered through a microfiltration membrane with a pore size of 0.275 μm. The filtration accuracy of the clarified liquid was lower than that of A, and the relatively large pore size would allow some fine impurities to pass through the filter.

[0040] Solid particles are also recycled in no fewer than three batches.

[0041] Experiment C: Similarly, centrifugation is used, and the reaction solution is filtered through a microfiltration membrane with a pore size of 0.1 μm. Due to the small pore size, large particles in the solution can be effectively removed, and the purity of the clarified solution is high, ensuring the smooth progress of subsequent operations.

[0042] The clarified liquid contains many impurities, which may affect subsequent processes, but it can improve processing efficiency. Solid particles are returned to the reaction process in no fewer than three batches.

[0043] Comparative analysis: Experiment A uses a microfiltration membrane with a larger pore size, resulting in the lowest filtration accuracy and a higher concentration of impurities in the clarified solution. This may affect subsequent processes, but it offers faster processing speeds and is suitable for large-scale production. Experiment C uses a microfiltration membrane with the smallest pore size, effectively removing more impurities and producing a higher purity clarified solution, which helps ensure the smooth operation of subsequent processes. Experiment B falls between A and C, offering moderate filtration accuracy and is suitable for situations requiring a balance between processing capacity and clarified solution quality.

[0044] 2. pH adjustment Experiment A: Add 5% ammonia to the clarified solution and adjust the pH to 8.5. Perform the reaction at 20°C and let it stand for 10 minutes to reach dissolution equilibrium.

[0045] Using a lower concentration of ammonia makes the solution gentler and helps prevent excessive changes in solubility. Slight pH adjustments are suitable for lower concentration solutions, avoiding excessively high solubility.

[0046] Experiment B: Add 15% ammonia to the clarified solution to adjust the pH to 9.5. The adjustment is carried out at 32.5℃ for 35 minutes.

[0047] Because a more concentrated ammonia solution is used and the temperature is increased, the pH adjustment is more efficient, making it suitable for situations requiring higher solubility.

[0048] Experiment C: Use 25% ammonia solution, adjust the pH to 10.5, and set the temperature to 45°C. This step requires 60 minutes to reach dissolution equilibrium.

[0049] Higher ammonia concentrations and higher temperatures enable the processing of components that are more difficult to dissolve, making it suitable for applications requiring increased solubility.

[0050] Comparative analysis: Experiment A uses a milder pH adjustment, suitable for low-concentration dissolution requirements. Experiments B and C, with their higher ammonia concentrations and higher temperatures, improve solubility but increase operational complexity.

[0051] 3. Membrane Concentration Experiment A: Using a 200 Da nanofiltration membrane, the pressure during the membrane concentration process was set to 1.0 MPa, and the concentration of D-p-hydroxyphenylglycine was increased to 80 g / L during the membrane concentration process.

[0052] Because of the small membrane pore size, the increase in solute in the concentrate is limited, but the membrane concentration process is relatively gentle.

[0053] Experiment B: Using a 350Da nanofiltration membrane, the membrane concentration pressure was increased to 2.25MPa, and the concentration of D-p-hydroxyphenylglycine in the concentrate reached 150g / L.

[0054] Higher membrane molecular weight cutoff and pressure result in more significant concentration effects, increasing the concentration of the concentrate.

[0055] Experiment C: Using a 500Da nanofiltration membrane, the membrane concentration pressure was set to 3.5MPa, and the concentration of D-p-hydroxyphenylglycine in the concentrate was increased to 220g / L.

[0056] Higher pressure and larger membrane pore size result in the best concentration effect, achieving higher concentrations.

[0057] Comparative analysis: With increasing membrane pore size and molecular weight cutoff, experiment C showed the best membrane concentration, resulting in the highest concentration of D-p-hydroxyphenylglycine. Experiment A had a lower concentration but was relatively mild, making it suitable for processing lower concentrations.

[0058] 4. Crystallization Experiment A: Carbon dioxide is bubbled into the liquid after membrane concentration to adjust the pH to 5.3, followed by cooling and crystallization. This relatively gentle crystallization process helps to reduce losses caused by over-crystallization.

[0059] The crystallization process is stable, the crystals are uniform in size, and the purity is high.

[0060] Experiment B: Similarly, carbon dioxide is introduced to adjust the pH to 6, and then the liquid is cooled and crystallized. This method is suitable for liquids with higher concentrations and the crystallization speed is relatively fast.

[0061] Crystallization is relatively rapid, but the crystal purity decreases somewhat, and the crystallization conditions are moderate.

[0062] Experiment C: Carbon dioxide is introduced to adjust the pH to 6.8, followed by cooling and crystallization. A higher pH helps increase solubility, but the crystallization effect is relatively poor; it is suitable for maintaining high solubility rather than simply crystallizing.

[0063] Comparative analysis: The lower pH value in Experiment A promoted the crystallization of D-p-hydroxyphenylglycine, resulting in better crystallization. Experiment C, due to its higher pH adjustment, had a relatively lower crystallization efficiency, but maintained a higher concentration.

[0064] 5. Countercurrent washing Experiment A: Two-stage countercurrent washing is used, with the total amount of washing liquid being 0.2 times the mass of the crystals, of which the permeate accounts for ≥50%, and the washing method is relatively simple.

[0065] Experiment B: A three-stage countercurrent washing process was used, with the total amount of washing solution being 0.85 times the mass of the crystals, and the permeate content being ≥50%. The washing effect was good, but more washing solution was required.

[0066] Experiment C: A four-stage countercurrent washing process is employed, with the total amount of washing liquid being 1.5 times the mass of the crystals, and the permeate accounting for ≥50%. Due to the large volume of washing liquid, the washing effect is very significant and can effectively remove impurities.

[0067] Comparative analysis: Experiment C, with its higher number of washing stages and proportion of washing solution, provided the best washing effect, contributing to improved crystal purity. Experiment A, with its weaker washing effect, is suitable for applications that do not require high purity.

[0068] In summary, with increasing membrane pore size and membrane concentration pressure, the concentration of D-p-hydroxyphenylglycine reached its highest level in Experiment C. During the crystallization step, Experiment A achieved optimal crystallization with higher crystal purity through lower pH adjustment, while Experiment C, due to higher pH adjustment, maintained a higher concentration but had lower crystallization efficiency. Regarding washing performance, Experiment C achieved optimal crystal purity through four-stage countercurrent washing, while Experiment A's washing effect was weaker and suitable for applications requiring lower purity. Experiment C is suitable for high concentration and high purity requirements but is more complex to operate, while Experiment A is suitable for low concentration and simpler separation needs.

[0069] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for crystallizing and separating D-p-hydroxyphenylglycine with low wastewater discharge, characterized in that, include: S1. The reaction solution containing D-p-hydroxyphenylglycine obtained by bio-enzyme catalytic conversion is subjected to a first solid-liquid separation to obtain a clear solution containing D-p-hydroxyphenylglycine. The solid phase containing biocatalyst obtained by the solid-liquid separation is returned to the bio-enzyme catalytic conversion process for recycling. S2. Add a volatile alkali to the clarified liquid to adjust the pH to 8.5-10.5 to obtain an alkaline solution, wherein the volatile alkali is ammonia water or an aqueous solution of ammonia gas; S3. The alkaline solution is concentrated using a nanofiltration membrane to obtain a concentrate and a permeate. The concentrate is the retentate of the membrane concentration, and the concentration of D-p-hydroxyphenylglycine in the retentate is increased to 80 g / L-220 g / L. The permeate is returned to S2 as process recycled water and used as a source of water for crystal washing in subsequent washing steps. S4. The concentrated liquid is acidified by passing carbon dioxide through it under crystallization conditions to adjust the pH to 5.3-6.8, and then cooled and crystallized to obtain a slurry containing D-p-hydroxyphenylglycine crystals; S5. The slurry undergoes a second solid-liquid separation to obtain crystals and mother liquor. The crystals are washed countercurrently. The washing liquid from the countercurrent washing is combined with the mother liquor and then enters the regeneration unit. The combined mixture is analyzed to remove and recover ammonia and carbon dioxide. The recovered ammonia is returned to step S2 as a source of volatile alkali for recycling, and the recovered carbon dioxide is returned to step S4 as a source of acidification gas for recycling. The analyzed mother liquor is returned to step S3 and, in step S3, is combined with the alkaline solution and then recycled as a feed for membrane concentration. The system is equipped with a discharge branch for impurity balancing. The discharge volume of the circulating liquid discharged from the discharge branch, measured by mass flow meter, accounts for ≤5% of the total circulating volume of the circulating liquid.

2. The method for crystallizing and separating D-p-hydroxyphenylglycine with low wastewater discharge according to claim 1, characterized in that: The solid-liquid separation is performed by centrifugation. The liquid phase after centrifugation is then filtered through a microfiltration membrane with a pore size of 0.1μm-0.45μm to obtain the clarified liquid.

3. The method for crystallizing and separating D-p-hydroxyphenylglycine with low wastewater discharge according to claim 1, characterized in that: The biocatalyst is an immobilized enzyme particle, the solid phase obtained from the first solid-liquid separation is the immobilized enzyme particle, and the immobilized enzyme particle is returned to the bio-enzyme catalytic conversion process and recycled in no less than 3 batches.

4. The method for crystallizing and separating D-p-hydroxyphenylglycine with low wastewater discharge according to claim 1, characterized in that: The ammonia solution has a mass fraction of 5%-25%, the pH adjustment is carried out at 20℃-45℃, and after the pH adjustment is completed, the alkaline solution is allowed to stand or slowly stirred for 10min-60min.

5. The method for crystallizing and separating D-p-hydroxyphenylglycine with low wastewater discharge according to claim 1, characterized in that: The nanofiltration membrane has a molecular weight cutoff of 200 Da to 500 Da, and the membrane concentration is operated in a cross-flow mode at a pressure of 1.0 MPa to 3.5 MPa, so as to increase the concentration of D-p-hydroxyphenylglycine in the concentrate to the range of 80 g / L to 220 g / L.

6. The method for crystallizing and separating D-p-hydroxyphenylglycine with low wastewater discharge according to claim 1, characterized in that: Before membrane concentration, the alkaline solution further includes adsorption decolorization and filtration. The adsorption decolorization uses a macroporous adsorption resin. After adsorption decolorization, the liquid is filtered and then concentrated by membrane. The macroporous adsorption resin has a specific surface area of ​​200 m² / g-1200 m² / g, a pore volume of 0.3 mL / g-2.0 mL / g, and an average pore size of 5 nm-50 nm.

7. The method for crystallizing and separating D-p-hydroxyphenylglycine with low wastewater discharge according to claim 1, characterized in that: The countercurrent washing is a 2-4 stage countercurrent washing, and the mass ratio of the permeate in the washing water of the countercurrent washing is ≥50%. The insufficient part of the washing water is supplemented by secondary sources, such as condensate, deionized water or softened water. The total mass of the washing water is 0.2-1.5 times the mass of the obtained crystals.

8. The method for crystallizing and separating D-p-hydroxyphenylglycine with low wastewater discharge according to claim 1, characterized in that: The analysis is carried out at 40℃-80℃ and absolute pressure of 10kPa-60kPa. The discharge branch uses the circulating liquid conductivity or COD reaching a preset threshold as the discharge trigger condition. The circulating liquid discharged from the discharge branch enters the recovery unit to recover the D-p-hydroxyphenylglycine in it before being discharged.

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