Desalting process for producing compound amino acid by acidolysis method

Abstract

The invention relates to the technical field of biochemical engineering, and discloses a desalting process for producing compound amino acid by using an acidolysis method, which comprises the steps of pretreatment of compound amino acid acidolysis solution, continuous fluidized bed adsorption, adsorbent desorption regeneration and electrodialysis refining and cyclic utilization. Wherein inorganic cations are selectively adsorbed by utilizing a pH response type intelligent adsorption material in a fluidized bed. The process can reduce chemical consumption and environmental load, realizes continuous production, and ensures product quality and high-efficiency cyclic utilization of resources.

Description

Technical Field

[0001] This invention belongs to the field of biochemical technology and relates to a desalting process for producing composite amino acids using acid hydrolysis. Background Technology

[0002] Amino acids are the fundamental building blocks of life and play an irreplaceable role in key fields such as medicine, food, and agriculture. Currently, the acid hydrolysis of proteins is commonly used in industry to prepare complex amino acids. This method is economical and efficient, hydrolyzing natural proteins into peptides and free amino acids to provide raw materials for subsequent processing. However, it generates a large amount of inorganic salts. If these residual salts are not removed, they will seriously affect the purity, stability, and bioactivity of amino acid products, and also hinder their application in high-end products such as biological agents and nutritional fortifiers. Therefore, efficient desalination of the acid hydrolysate is a key challenge in amino acid production. Ion exchange technology is widely used for the desalination of complex amino acid solutions due to its simple operation and high desalination efficiency. Its principle is based on the reversible exchange of ions in the solution between the active groups of ion exchange resins—cation exchange resins remove inorganic cations, while anion exchange resins remove inorganic anions. By using the two types of resins in series or in combination, most salts can be effectively removed. This technology has provided a reliable guarantee for the industrial production of amino acids and promoted the large-scale development of the industry. However, with technological advancements and increasing market demands for higher purity, production costs, and environmental friendliness in amino acid products, the inherent problems of traditional ion exchange technology are becoming increasingly apparent, making it difficult to balance desalination efficiency, cost, environmental protection, and product quality. Acid-hydrolyzed amino acid stock solutions have high salt content, causing the resin exchange capacity to quickly saturate during treatment, necessitating frequent regeneration. The regeneration process not only consumes large amounts of strong acids and bases, increasing material costs, but also generates high-salt wastewater that is difficult to treat even after neutralization, exacerbating the environmental burden. Furthermore, regeneration is an intermittent operation, requiring production to be suspended for backwashing, regeneration, and rinsing, reducing production continuity and efficiency. Moreover, amino acids are pH-sensitive; strong acids and bases during regeneration can cause drastic pH fluctuations, easily triggering irreversible degradation of amino acids such as racemization, hydrolysis, decarboxylation, and deamination, resulting in loss of effective components, reduced yield, and the introduction of impurities, affecting product purity and increasing the difficulty of subsequent purification. Summary of the Invention

[0003] To achieve the aforementioned objectives, this invention provides a desalination process for producing composite amino acids using acid hydrolysis. This process aims to address the technical challenges of existing ion exchange methods for treating acid-hydrolyzed composite amino acid solutions, including frequent regeneration, high chemical consumption, large wastewater discharge, discontinuous production processes, and easy degradation of amino acids. This invention introduces pH-responsive intelligent adsorption materials and combines them with continuous fluidized bed adsorption, continuous adsorbent desorption and regeneration, and electrodialysis purification units to construct a highly efficient, environmentally friendly, continuous desalination production system with minimal impact on amino acid quality.

[0004] The present invention discloses a desalting process for producing composite amino acids by acid hydrolysis, comprising the following steps: The first step involves separating the complex amino acid hydrolysate obtained through protein acid hydrolysis into solid and liquid components, for example, by microfiltration or ultrafiltration, to remove protein residues and large molecular impurities, resulting in a clear complex amino acid filtrate. The pH of the complex amino acid filtrate is typically below 3.5.

[0005] The second step involves continuously pumping the clarified composite amino acid filtrate into a series- or parallel continuous fluidized bed adsorption unit. The adsorption unit is filled with a pH-responsive smart adsorbent. Within the fluidized bed adsorption unit, the pH-responsive smart adsorbent comes into full contact with the composite amino acid filtrate. Under the acidic environment of the filtrate, the pH-responsive smart adsorbent selectively adsorbs inorganic cations in the solution, such as sodium, potassium, calcium, and magnesium ions. Due to the specific zwitterionic properties of the composite amino acid molecules and the surface design of the adsorbent, the affinity between the composite amino acid molecules and the smart adsorbent is extremely low under adsorption conditions, thus ensuring minimal adsorption loss of amino acids. After adsorption, the desalted composite amino acid solution continuously flows out from the outlet of the adsorption unit and enters the subsequent purification stage.

[0006] Thirdly, when the pH-responsive smart adsorbent material in the fluidized bed adsorption unit reaches the preset adsorption saturation, or according to the preset adsorption cycle time, the saturated adsorbent material is continuously transferred in slurry form to the continuous desorption and regeneration unit via a continuous transfer device. The desorption and regeneration unit is filled with a weakly alkaline desorption solution, such as dilute ammonia solution or dilute sodium bicarbonate solution, and the pH value of the desorption solution is maintained above 7.5. In a weakly alkaline environment, the ionization state of the surface functional groups of the pH-responsive smart adsorbent material changes, resulting in a decrease in its affinity for inorganic cations, and the adsorbed inorganic cations are rapidly and efficiently released into the desorption solution.

[0007] In a more preferred embodiment of the present invention, the desorbed adsorbent material is subjected to solid-liquid separation with the salt-containing desorption solution. If the smart adsorbent material is magnetic, a continuous high-gradient magnetic separation device is used for separation and recovery; if it is non-magnetic, a continuous cross-flow filtration or centrifugal separation device is used for separation and recovery. The recovered adsorbent material is washed and its pH is adjusted as needed, and then it is continuously returned to the fluidized bed adsorption unit for recycling.

[0008] The fourth step involves continuously pumping the salt-containing desorption solution, a dilute alkaline solution rich in inorganic salts, produced by the desorption regeneration unit into the electrodialysis purification unit. Driven by a DC electric field, the electrodialysis purification unit utilizes the selective permeability of the cation and anion exchange membranes to migrate inorganic salt ions from the desalination chamber into the concentrate chamber, thereby achieving further concentration and desalination of the salt solution. The desalination product from the electrodialysis unit is demineralized water, which can be recycled back to the desorption regeneration unit as water for preparing the desorption solution or as washing water for the adsorbent materials. The concentrate product from the electrodialysis unit is a high-concentration salt solution.

[0009] The pH-responsive smart adsorbent material provided by this invention comprises superparamagnetic nanoparticles and a functionalized shell grafted with a pH-responsive polymer. The superparamagnetic nanoparticles are composed of iron(III) oxide or γ-iron oxide, with an average particle size ranging from 5 nm to 50 nm, providing magnetic responsiveness to facilitate rapid separation and recovery of the adsorbent material. The surface of the nanoparticles is modified with a silane coupling agent to form a stable protective oxide layer and provides abundant surface hydroxyl or amino functional groups as active sites for subsequent polymer grafting.

[0010] Functionalized shells are created by covalently grafting pH-responsive polymer chains onto the surface of modified nanoparticles via atom transfer radical polymerization or free radical polymerization. The polymer chains have molecular weights ranging from 5,000 to 100,000 Da, with grafting densities controlled between 0.1 mmol / g and 2.0 mmol / g. The pH-responsive polymer chains contain ionizable functional groups such as carboxyl groups, phosphate groups, or specific amine groups.

[0011] The pH-responsive smart adsorbent material used in this invention has an average particle size of 1 μm to 10 μm and a particle size distribution D50 between 3 μm and 5 μm, ensuring good dispersibility and fluidization performance in fluids, while providing a sufficiently high specific surface area to achieve efficient adsorption.

[0012] The isoelectric point of smart adsorbent materials is precisely designed so that, under acidic conditions, specific functional groups (such as protonated amine groups or carboxyl groups with specific conformations) can selectively bind inorganic cations in solution through ionic bonds, complexation, or chelation. The conformation and charge distribution of these functional groups are optimized for low pH environments, thereby enhancing the capture capacity of metal cations. For example, under low pH conditions, specific sites on the polymer chain form polydentate ligand structures, exhibiting high affinity for divalent and multivalent metal ions while also effectively adsorbing monovalent cations.

[0013] On the other hand, when the ambient pH rises to weakly alkaline conditions, the deprotonation or conformational rearrangement of functional groups leads to a sharp decrease in their binding affinity for inorganic cations, thereby achieving rapid desorption of the adsorbed cations. The adsorption capacity of the smart adsorbent material for complex amino acid molecules remains below 5% of the total adsorption capacity throughout the entire pH operating range, ensuring product yield and quality. After 200 consecutive cycles, the adsorption capacity decay rate of the adsorbent material is less than 10%, demonstrating excellent stability and reusability.

[0014] Furthermore, the continuous fluidized bed adsorption unit of the present invention is specifically configured as follows: the adsorption unit is a vertical cylindrical reactor with a height-to-diameter ratio between 5:1 and 15:1. A conical section is provided at the bottom of the reactor, and a gas distributor and a liquid distributor are configured to ensure uniform fluid entry and good fluidization of the adsorbent material. The effective volume to throughput ratio of the adsorption unit is designed with a residence time of 0.5 hours to 2 hours to ensure sufficient adsorption contact. Multiple spaced sieves or overflow weirs are provided inside the reactor to stabilize the fluidized bed, prevent adsorbent material agglomeration, and optimize axial mixing.

[0015] In a preferred embodiment of the present invention, the composite amino acid filtrate is continuously pumped into the bottom of the fluidized bed adsorption unit using an acid-resistant peristaltic pump or a diaphragm pump. The flow rate is precisely controlled according to the particle size, density, and required fluidization ratio of the adsorbent material to maintain a uniform fluidization state, thereby maximizing liquid-solid contact efficiency. The pH value of the filtrate before entering the adsorption unit is monitored in real time by an online pH sensor, and precisely adjusted by automatically adding trace amounts of dilute hydrochloric acid or citric acid solution using a precision metering pump to ensure it is maintained within a preset range of pH < 3.5.

[0016] In a preferred embodiment of the present invention, the adsorption unit is equipped with an online conductivity sensor, a pH sensor, and a temperature sensor for real-time monitoring of changes in solution composition, pH value, and temperature during the adsorption process. The temperature is maintained between 20°C and 50°C to optimize adsorption kinetics. An outlet is provided at the top of the adsorption unit for continuously discharging the desalted composite amino acid solution. An adsorbent slurry outlet is provided on the side or bottom of the adsorption unit for continuously or quasi-continuously transferring partially saturated adsorbent slurry to the desorption and regeneration unit after a preset time or saturation point is reached. The axial dispersion coefficient of the adsorbent in the fluidized bed is optimized to ensure near-piston flow characteristics, thereby improving adsorption efficiency.

[0017] In a preferred embodiment of the present invention, the continuous adsorbent desorption and regeneration unit is specifically configured as follows: the desorption and regeneration unit is a vertical stirred tank or another continuous fluidized bed reactor, with an effective volume to adsorbent throughput ratio designed for a residence time of 0.2 hours to 1 hour. The unit is equipped with a mechanical stirrer or gas distributor to ensure thorough mixing of the adsorbent and the desorption solution. The desorption solution is a 0.1 mol / L to 0.5 mol / L dilute ammonia solution or a 0.5 mol / L to 1.0 mol / L dilute sodium bicarbonate solution, which is continuously or intermittently pumped into the desorption and regeneration unit using a precision metering pump. The pH value within the unit is precisely controlled and maintained between 8.0 and 9.5 using an online pH sensor and a PID control system. The desorption temperature is maintained between 25°C and 55°C to accelerate ion release kinetics.

[0018] The saturated adsorbent slurry is continuously pumped from the adsorption unit into the desorption and regeneration unit. After desorption, the solid-liquid separation of the salt-containing desorption solution and the regenerated adsorbent is performed using a continuous magnetic separation device. This device includes a permanent magnet or electromagnetic separator. As the slurry passes through the magnetic separator, the magnetic adsorbent is captured, while the salt-containing desorption solution flows out. The magnetic adsorbent is then desorbed from the magnetic separator and recovered by mechanical scraping or periodic rinsing.

[0019] The recovered adsorbent slurry is pumped to a washing tank and washed with 0.5 to 2 times its volume of deionized or purified water to remove residual desorption solution and impurities. The washed slurry is then pumped back to the continuous fluidized bed adsorption unit, achieving a closed-loop circulation. The magnetic separation unit achieves an adsorbent recovery rate of over 99.8%, ensuring low-loss operation of the adsorbent.

[0020] In a more preferred embodiment of the present invention, the electrodialysis purification and recycling unit of the present invention is specifically configured as follows: the electrodialysis unit consists of multiple electrodialysis membrane stacks, each membrane stack comprising alternately arranged cation exchange membranes and anion exchange membranes, and flow channel partitions for forming desalination compartments and concentrate compartments. The effective area of ​​the membranes ranges from 0.1 m². 2 Up to 1.0m 2 Each pair of membranes.

[0021] As a more preferred embodiment of the present invention, the cation exchange membrane is, for example, a sulfonic acid-based polystyrene-divinylbenzene copolymer membrane with a selective permeability greater than 98%; the anion exchange membrane is, for example, a quaternary ammonium-based polystyrene-divinylbenzene copolymer membrane with a selective permeability greater than 96%.

[0022] The electrode materials of the electrodialysis membrane stack are platinum-iridium alloy coated titanium plates or graphite plates. A salt-containing desorption solution is used as the feed liquid and is continuously pumped into the desalination compartment of the electrodialysis membrane stack. The DC voltage applied to the electrodialysis unit is 1V to 5V per membrane pair, and the current density is maintained at 5mA / cm². 2 Up to 20mA / cm 2 The flow rates of the feed solution, desalinated product, and concentrated product are independently controlled using precision flow meters. The electrodialysis unit is equipped with online conductivity sensors to monitor the conductivity of the desalinated and concentrated effluents, and automatically adjusts the voltage or flow rate through a feedback control system to ensure that the desalination rate and concentration ratio reach the preset targets.

[0023] The freshwater byproduct, i.e., purified water, is piped to the desorption and regeneration unit as a diluent for the desorption solution or as washing water, forming an internal cycle. High-concentration saline concentrate is continuously discharged from the electrodialysis unit and collected in a storage tank, where it can be further utilized through crystallization, evaporation, or other chemical transformation methods. The electrodialysis unit consumes only 0.5 kW·h / m³ to 2.0 kW·h / m³ of freshwater byproduct, demonstrating its high efficiency and energy saving.

[0024] This invention also relates to the coordinated control and integrated operation of the entire desalination process. The process is centrally monitored and automated through a distributed control system or programmable logic controller (PLC) system. The control system integrates all online sensors (pH, conductivity, temperature, flow rate, pressure, liquid level) and actuators (pumps, valves, magnetic field controllers). The DCS / PLC system uses preset control strategies and algorithms.

[0025] In a preferred embodiment of the present invention, precise control of each unit is achieved through PID control, fuzzy logic control, or model predictive control. In the fluidized bed adsorption unit, the DCS system adjusts the pump speed and acid addition amount in real time based on the feed pH, the liquid level and flow rate of the adsorbent material in the fluidized bed to maintain a stable fluidization state and optimal adsorption efficiency. In the desorption and regeneration unit, the DCS system automatically starts or adjusts the transfer rate of the saturated adsorbent material based on the saturation data of the adsorbent material, and precisely controls the pH and temperature of the desorption solution to ensure efficient desorption. In the electrodialysis unit, the DCS system dynamically adjusts the voltage or flow rate of the electrodialysis membrane stack based on the conductivity settings of the desalination and concentrate water to optimize desalination efficiency and energy consumption. Furthermore, the control system also has fault diagnosis, alarm prompts, and historical data recording functions to support process optimization and maintenance. The material and information flows between all units are coordinated through the central control system to ensure the continuous, stable, and efficient operation of the entire process chain, and to minimize energy consumption and material loss by optimizing process parameters.

[0026] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention employs pH-responsive intelligent adsorption materials for ion adsorption and desorption, avoiding the problem of consuming large amounts of strong acids and bases during the regeneration of traditional ion exchange resins. The desorption process requires only a mild, weakly alkaline solution, reducing the amount of chemicals used and lowering production costs. Simultaneously, the resulting wastewater is no longer a high-salinity, high-pH, strong acid / base waste liquid, but rather a relatively easy-to-treat weakly alkaline saline solution. Salt concentration and freshwater reuse can be achieved through an electrodialysis unit, fundamentally eliminating the high-salinity wastewater discharge problem caused by traditional methods and reducing environmental pollution.

[0027] 2. The continuous fluidized bed adsorption unit, continuous adsorbent desorption and regeneration unit, and continuous magnetic separation technology employed in this invention together constitute a highly automated continuous production process. The continuous recycling of adsorbent materials replaces the intermittent regeneration mode of traditional ion exchange resins, effectively avoiding production interruptions and significantly improving the continuity, stability, and overall operating efficiency of production, which is beneficial for large-scale industrial production.

[0028] 3. The entire desalination process of this invention is carried out under mild pH conditions. During the adsorption stage, the pH value of the composite amino acid filtrate is maintained in a low acidic range, ensuring the stable conformation of the amino acids. During the desorption and regeneration stage, a weakly alkaline solution is used for desorption, avoiding degradation reactions such as racemization, hydrolysis, decarboxylation, or deamination of amino acids that may occur during traditional strong acid and strong alkali regeneration processes. This ensures the yield of the effective components of the composite amino acids, maintains the purity, optical activity, and biological efficacy of the product, thereby improving the market competitiveness of the final product.

[0029] 4. The electrodialysis purification unit can effectively concentrate the inorganic salts in the desorption solution, and the generated fresh water can be directly reused for washing the adsorption material and preparing the desorption solution, realizing the internal recycling of water resources and reducing the consumption of fresh water.

[0030] 5. The pH-responsive smart adsorbent material used in this invention has a high specific surface area, high adsorption selectivity, and good physicochemical stability. It exhibits strong selective adsorption capacity for inorganic cations and demonstrates excellent stability during continuous cyclic use, with a low adsorption capacity decay rate, thereby extending the service life of the adsorbent material and reducing operating costs. Detailed Implementation

[0031] This invention provides a desalination process for producing composite amino acids using acid hydrolysis, aiming to address a series of technical challenges faced by existing technologies in treating acid-hydrolyzed composite amino acid solutions. These challenges include frequent regeneration via ion exchange, high chemical consumption, large wastewater discharge, intermittent production processes, and susceptibility to damage to amino acid quality. This process introduces pH-responsive intelligent adsorption materials and combines them with continuous fluidized bed adsorption, continuous adsorbent desorption and regeneration, and electrodialysis purification units to construct a highly efficient, environmentally friendly, continuously operating desalination production system with minimal impact on the quality of the composite amino acids.

[0032] Example 1: Pretreatment of composite amino acid hydrolysate: Solid-liquid separation was performed using a polyvinylidene fluoride microfiltration membrane to remove protein residues and macromolecular impurities, resulting in a clear composite amino acid filtrate with a pH of 2.0; membrane filtration was carried out under a constant transmembrane pressure difference.

[0033] Continuous fluidized bed adsorption: The clarified filtrate is continuously pumped into a vertical cylindrical fluidized bed adsorption unit (height-to-diameter ratio 8:1, effective volume to throughput ratio corresponding to a residence time of 1.0 hour) via an acid-resistant diaphragm pump; the adsorption unit is filled with pH-responsive smart adsorption material (using 20nm iron(III) oxide as superparamagnetic nanoparticles, with polyacrylate polymer chains grafted onto the surface after modification with a silane coupling agent, molecular weight 50000 Da, grafting density 1.0 mmol / g, average particle size 4μm, D50 4μm); during adsorption, the pH of the filtrate is monitored and adjusted to maintain 2.0 via an online pH sensor, and the temperature is controlled at 30℃, with conductivity, pH, and temperature sensors providing real-time monitoring; the desalted composite amino acid solution continuously flows out from the top outlet of the adsorption unit.

[0034] Adsorbent desorption and regeneration: When the adsorbent material reaches the preset saturation, it is transferred to the vertical stirred tank desorption and regeneration unit through a continuous transfer device (the ratio of effective volume to adsorbent material throughput corresponds to a residence time of 0.5 hours); the desorption solution is a 0.3 mol / L dilute ammonia solution, and the pH in the unit is controlled at 8.5 and the temperature is maintained at 40℃ through a PID control system; after desorption, a continuous permanent magnet separation device is used for solid-liquid separation, and the recovered adsorbent material is washed with purified water (the amount of which is 1 times the volume of the adsorbent material) and returned to the fluidized bed adsorption unit for recycling without additional pH adjustment.

[0035] Electrodialysis purification and recycling: The salt-containing desorption solution is pumped into the electrodialysis purification unit (the membrane stack consists of alternating sulfonated polystyrene-divinylbenzene copolymer cation exchange membranes and quaternary ammonium polystyrene-divinylbenzene copolymer anion exchange membranes, with an effective membrane area of ​​0.5 m² / pair); a DC voltage of 3V / pair and a current density of 12 mA / cm² are applied; the generated deionized water is recycled for the preparation of desorption solutions and the washing of adsorption materials, and the high-concentration salt-containing concentrate is collected for further resource utilization.

[0036] Example 2: Pretreatment of composite amino acid hydrolysate: Solid-liquid separation was performed using a polyethersulfone ultrafiltration membrane to obtain a clear composite amino acid filtrate with a pH of 1.8; membrane filtration was carried out under a constant transmembrane pressure difference.

[0037] Continuous fluidized bed adsorption: The clarified filtrate is continuously pumped into a vertical cylindrical fluidized bed adsorption unit (height-to-diameter ratio 10:1, effective volume to throughput ratio corresponding to a residence time of 1.2 hours) via an acid-resistant peristaltic pump; the adsorption unit is filled with pH-responsive smart adsorption material (using 10nm γ-iron oxide as superparamagnetic nanoparticles, with the surface modified by a silane coupling agent and grafted with polyethyleneimine derivative polymer chains, molecular weight 80000Da, grafting density 1.5mmol / g, average particle size 3μm, D50 3μm); during adsorption, the pH is maintained at 1.8, the temperature is controlled at 35℃, and multiple sensors are used for real-time monitoring; the desalted composite amino acid solution continuously flows out from the top outlet.

[0038] Adsorbent desorption and regeneration: Saturated adsorbent material is transferred to a vertical stirred tank desorption and regeneration unit (the ratio of effective volume to adsorbent material throughput corresponds to a residence time of 0.6 hours); the desorption solution is a 0.4 mol / L dilute ammonia solution, with the pH adjusted to 9.0 and the temperature maintained at 45℃; solid-liquid separation is performed using a continuous electromagnetic separation device, and the recovered adsorbent material is washed with purified water (1.5 times the volume of adsorbent material) and returned to the fluidized bed.

[0039] Electrodialysis purification and recycling: The effective area of ​​the electrodialysis unit membrane is 0.8 m² / pair, the applied DC voltage is 4V / pair, and the current density is 15 mA / cm²; the demineralized water is recycled and reused, and the high-concentration saline concentrate is collected.

[0040] Example 3: Pretreatment of composite amino acid hydrolysate: Solid-liquid separation was performed using a polyvinylidene fluoride microfiltration membrane to obtain a clear composite amino acid filtrate with a pH of 2.5; membrane filtration was carried out under a constant transmembrane pressure difference.

[0041] Continuous fluidized bed adsorption: The clarified filtrate is continuously pumped into a vertical cylindrical fluidized bed adsorption unit (height-to-diameter ratio 5:1, effective volume to throughput ratio corresponding to a residence time of 0.8 hours) via an acid-resistant diaphragm pump; the adsorption unit is filled with pH-responsive smart adsorption material (using 30nm iron oxide as superparamagnetic nanoparticles, with polyacrylate-polyethyleneimine copolymer chains grafted onto the surface after modification with a silane coupling agent, molecular weight 60000Da, grafting density 0.8mmol / g, average particle size 5μm, D50 5μm); during adsorption, the pH is maintained at 2.5, the temperature is controlled at 25℃, and multiple sensors are used for real-time monitoring; the desalted composite amino acid solution continuously flows out from the top outlet.

[0042] Adsorbent desorption and regeneration: Saturated adsorbent material is transferred to a continuous fluidized bed desorption and regeneration unit (the ratio of effective volume to adsorbent throughput corresponds to a residence time of 0.4 hours); the desorption solution uses a 0.8 mol / L dilute sodium bicarbonate solution, with the pH adjusted to 8.8 and the temperature maintained at 35℃; solid-liquid separation is performed using a continuous permanent magnet separation device, and the recovered adsorbent material is washed with purified water (0.8 times the volume of adsorbent material) and returned to the fluidized bed.

[0043] Electrodialysis purification and recycling: The effective area of ​​the electrodialysis unit membrane is 0.3 m² / pair, the applied DC voltage is 2V / pair, and the current density is 8 mA / cm²; the demineralized water is recycled and reused, and the high-concentration saline concentrate is collected.

[0044] Example 4: Pretreatment of composite amino acid hydrolysate: Solid-liquid separation was performed using a polyethersulfone ultrafiltration membrane to obtain a clear composite amino acid filtrate with a pH of 2.2; membrane filtration was carried out under a constant transmembrane pressure difference.

[0045] Continuous fluidized bed adsorption: The clarified filtrate is continuously pumped into a vertical cylindrical fluidized bed adsorption unit (height-to-diameter ratio 12:1, effective volume to throughput ratio corresponding to a residence time of 1.5 hours) via an acid-resistant peristaltic pump; the adsorption unit is filled with pH-responsive smart adsorption material (using 40nm γ-iron oxide as superparamagnetic nanoparticles, with polyacrylate polymer chains grafted onto the surface after modification with a silane coupling agent, molecular weight 30000Da, grafting density 1.2mmol / g, average particle size 3.5μm, D50 3.5μm); during adsorption, the pH is maintained at 2.2, the temperature is controlled at 40℃, and multiple sensors are used for real-time monitoring; the desalted composite amino acid solution continuously flows out from the top outlet.

[0046] Adsorbent desorption and regeneration: Saturated adsorbent material is transferred to a vertical stirred tank desorption and regeneration unit (the ratio of effective volume to adsorbent material throughput corresponds to a residence time of 0.7 hours); the desorption solution is a 0.2 mol / L dilute ammonia solution, the pH is adjusted to 8.2, and the temperature is maintained at 50℃; solid-liquid separation is performed using a continuous electromagnetic separation device, and the recovered adsorbent material is washed with purified water (1.2 times the volume of adsorbent material) and returned to the fluidized bed.

[0047] Electrodialysis purification and recycling: The effective area of ​​the electrodialysis unit membrane is 0.6 m² / pair, the applied DC voltage is 3.5 V / pair, and the current density is 18 mA / cm²; the demineralized water is recycled and reused, and the high-concentration saline concentrate is collected.

[0048] Example 5: Pretreatment of composite amino acid hydrolysate: Solid-liquid separation was performed using a polyvinylidene fluoride microfiltration membrane to obtain a clear composite amino acid filtrate with a pH of 1.5; membrane filtration was carried out under a constant transmembrane pressure difference.

[0049] Continuous fluidized bed adsorption: The clarified filtrate is continuously pumped into a vertical cylindrical fluidized bed adsorption unit (height-to-diameter ratio 15:1, effective volume to throughput ratio corresponding to a residence time of 2.0 hours) via an acid-resistant diaphragm pump; the adsorption unit is filled with pH-responsive smart adsorption material (50nm iron(III) oxide superparamagnetic nanoparticles, with silane coupling agent modified surface and grafted with polyethyleneimine derivative polymer chains, molecular weight 100,000 Da, grafting density 0.5 mmol / g, average particle size 4.5 μm, D50 4.5 μm); during adsorption, the pH is maintained at 1.5, the temperature is controlled at 20℃, and multiple sensors are used for real-time monitoring; the desalted composite amino acid solution continuously flows out from the top outlet.

[0050] Adsorbent desorption and regeneration: Saturated adsorbent material is transferred to a continuous fluidized bed desorption and regeneration unit (the ratio of effective volume to adsorbent material throughput corresponds to a residence time of 1.0 hour); the desorption solution uses a 1.0 mol / L dilute sodium bicarbonate solution, with the pH adjusted to 9.5 and the temperature maintained at 55℃; solid-liquid separation is performed using a continuous permanent magnet separation device, and the recovered adsorbent material is washed with purified water (the amount of which is 2.0 times the volume of the adsorbent material) and then returned to the fluidized bed.

[0051] Electrodialysis purification and recycling: The effective area of ​​the electrodialysis unit membrane is 1.0 m² / pair, the applied DC voltage is 5V / pair, and the current density is 20 mA / cm²; the demineralized water is recycled and reused, and the high-concentration saline concentrate is collected.

[0052] Comparative Example 1, Traditional cationic-anionic resin series desalination process: Pretreatment of composite amino acid hydrolysate: Solid-liquid separation was performed using the same polyvinylidene fluoride microfiltration membrane as in Example 1 to obtain a clear composite amino acid filtrate with a pH of 2.0.

[0053] Ion exchange adsorption: The clarified filtrate is pumped into a fixed-bed adsorption column filled with 001×7 strong acid cation exchange resin, and then into a fixed-bed adsorption column filled with 201×7 strong base anion exchange resin; the adsorption process is intermittent, and the feed is stopped when the resin reaches saturation.

[0054] Resin regeneration: Cation exchange resin is regenerated using 5% hydrochloric acid solution and anion exchange resin is regenerated using 8% sodium hydroxide solution; production needs to be suspended for 1 hour during the regeneration process, and the high-salt wastewater generated after regeneration is directly discharged without recycling.

[0055] Subsequent processing: After regeneration, the material is re-fed, eliminating the need for electrodialysis purification and water recycling.

[0056] Comparative Example 2, Traditional Mixed Bed Resin Desalination Process: Pretreatment of Composite Amino Acid Hydrolysate: Solid-liquid separation was performed using the same polyethersulfone ultrafiltration membrane as in Example 2, resulting in a clear composite amino acid filtrate with a pH of 1.8.

[0057] Ion exchange adsorption: The clarified filtrate is pumped into a mixed bed adsorption column filled with 001×7 strong acid cation exchange resin and 201×7 strong base anion exchange resin; the adsorption process is intermittent, and the feed is stopped after the resin is saturated.

[0058] Resin regeneration: The mixed bed resin is regenerated in steps using a 5% hydrochloric acid solution and an 8% sodium hydroxide solution; the regeneration process requires a 0.8-hour production halt, and the regeneration wastewater is discharged directly.

[0059] Subsequent processing: After regeneration, the material is re-fed, eliminating the need for electrodialysis purification and water recycling.

[0060] Data comparison table:

[0061] The desalination rates of all five embodiments were between 96.5% and 98.2%, and the yield of composite amino acids reached 98.1% to 99.0%, which is higher than that of Comparative Example 1 (desalination rate 91.5%, yield 90.2%) and Comparative Example 2 (desalination rate 89.3%, yield 88.5%). The core reason is that the pH-responsive smart adsorption material used in this invention has stronger selectivity for inorganic cations, and operates in a low-acid adsorption environment of 1.5-3.0 and a weakly alkaline desorption environment of 8.0-9.5 throughout the process. This avoids the amino acid degradation caused by strong acids and alkalis during regeneration in traditional ion exchange methods. At the same time, continuous fluidized bed adsorption ensures sufficient liquid-solid contact, further improving the desalination and production preservation effects.

[0062] In the examples, the capacity decay rate of the adsorbent material after 200 cycles was only 7.5%-9.5%, far lower than that of Comparative Example 1 (16.8%) and Comparative Example 2 (18.2%), indicating that the smart adsorbent material has better physicochemical stability and a longer service life. Furthermore, the chemical consumption per unit processing capacity in the examples was only 0.18-0.3 kg / t, only 1 / 12-1 / 19 of that in the comparative examples, significantly reducing raw material costs. In addition, the water resource reuse rate in the examples reached 82%-88%, further reducing fresh water consumption and improving process economy.

[0063] The example demonstrates a high-salinity wastewater discharge of only 0.08-0.12 t / t, which is only 1 / 25-1 / 44 of that in the comparative example, reducing pollutant emissions at the source. Furthermore, the entire process is continuous, eliminating the regeneration shutdown required in traditional processes, thus improving production efficiency. In contrast, the comparative example, due to intermittent regeneration, requires a 0.8-1 hour shutdown every 8 hours, resulting in significant long-term capacity loss, and the direct discharge of high-salinity wastewater places a heavy environmental burden.

[0064] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A desalting process for producing composite amino acids using acid hydrolysis, characterized in that, Includes the following steps: The first step is to perform solid-liquid separation on the complex amino acid hydrolysate obtained by protein acid hydrolysis to remove protein residues and macromolecular impurities, and obtain a clear complex amino acid filtrate. The second step is to continuously pump the clarified composite amino acid filtrate into a continuous fluidized bed adsorption unit, which is filled with pH-responsive smart adsorption material. In the acidic environment of the filtrate, the pH-responsive smart adsorbent material selectively adsorbs inorganic cations in the solution to obtain a desalted composite amino acid solution. Third step: When the pH-responsive smart adsorption material reaches the preset adsorption saturation, the saturated adsorption material is continuously transferred to the continuous desorption and regeneration unit through a continuous transfer device; in the weakly alkaline desorption solution environment inside the desorption and regeneration unit, the pH-responsive smart adsorption material releases the adsorbed inorganic cations to obtain a salt-containing desorption solution and the regenerated adsorption material. The regenerated adsorbent material, after solid-liquid separation, washing, and pH adjustment, is continuously returned to the fluidized bed adsorption unit for recycling. Step 4: The salt-containing desorption solution generated by the desorption and regeneration unit is continuously pumped into the electrodialysis purification unit. The electrodialysis purification unit is driven by a DC electric field and utilizes the selective permeability of the anion and cation exchange membranes to migrate inorganic salt ions from the fresh water compartment to obtain desalinated water product and high-concentration salt-containing concentrated water product. The desalinated water product is recycled back to the desorption and regeneration unit as water for preparing the desorption solution or for washing the adsorbent material.

2. The desalination process according to claim 1, characterized in that, The pH-responsive smart adsorption material includes superparamagnetic nanoparticles and a functionalized shell grafted with pH-responsive polymers. The superparamagnetic nanoparticles are composed of iron(II) oxide or γ-iron oxide, with an average particle size ranging from 5 nm to 50 nm. The surface of the nanoparticles is modified with a silane coupling agent to form a stable silica protective layer and provide surface hydroxyl or amino functional groups. The functionalized shell is formed by covalently grafting polymer chains with pH-responsive properties onto the surface of the modified nanoparticles through atom transfer radical polymerization or free radical polymerization.

3. The desalination process according to claim 2, characterized in that, The pH-responsive polymer chain is a polyacrylate, a polyethyleneimine derivative, or a copolymer thereof; the molecular weight of the polymer chain ranges from 5,000 to 100,000 Da, and the grafting density is controlled between 0.1 mmol / g and 2.0 mmol / g; the pH-responsive polymer chain contains ionizable carboxyl, phosphate, or amino functional groups. The average particle size of the smart adsorption material is 1 μm to 10 μm, and its particle size distribution D50 is between 3 μm and 5 μm.

4. The desalination process according to claim 1, characterized in that, The pretreatment of the first step of the compound amino acid hydrolysate includes: Solid-liquid separation is performed by microfiltration or ultrafiltration to remove protein residues and macromolecular impurities, resulting in a clear composite amino acid filtrate; the pH value of the composite amino acid filtrate is below 3.5 and between 1.5 and 3.

0. Membrane filtration is performed under a constant transmembrane pressure differential, and the membrane material includes polyvinylidene fluoride or polyethersulfone.

5. The desalination process according to claim 1, characterized in that, The second step of the continuous fluidized bed adsorption unit is configured as follows: The fluidized bed adsorption unit is a vertical cylindrical reactor with a height-to-diameter ratio between 5:1 and 15:

1. The reactor has a conical section at the bottom and is equipped with a gas distributor and a liquid distributor; The ratio of the effective volume to the throughput of the adsorption unit is designed to be a residence time of 0.5 hours to 2 hours. The reactor is equipped with multiple spaced sieves or overflow weirs to stabilize the fluidized bed and optimize axial mixing. The composite amino acid filtrate is continuously pumped into the bottom of the fluidized bed adsorption unit via an acid-resistant peristaltic pump or a diaphragm pump.

6. The desalination process according to claim 5, characterized in that, The second step, the continuous fluidized bed adsorption step, includes: The pH value of the composite amino acid filtrate before entering the adsorption unit is monitored in real time by an online pH sensor, and adjusted by automatically adding a trace amount of dilute hydrochloric acid or citric acid solution through a precision metering pump. The adsorption unit is equipped with an online conductivity sensor, pH sensor and temperature sensor to monitor the changes in solution composition, pH value and temperature in real time during the adsorption process. The adsorption unit is provided with an outlet at the top for continuously exporting the desalted composite amino acid solution; the adsorption unit is provided with an adsorption material slurry outlet at the side or bottom for continuously or quasi-continuously transferring a portion of the saturated adsorption material slurry to the desorption and regeneration unit after a preset time or saturation is reached.

7. The desalination process according to claim 1, characterized in that, The third-step continuous adsorbent desorption and regeneration unit is configured as follows: The adsorbent desorption and regeneration unit is a vertical stirred tank or another continuous fluidized bed reactor, and its effective volume to adsorbent throughput ratio is designed to be a residence time of 0.2 hours to 1 hour. The desorption solution is a dilute ammonia solution of 0.1 mol / L to 0.5 mol / L or a dilute sodium bicarbonate solution of 0.5 mol / L to 1.0 mol / L, which is continuously or intermittently pumped into the desorption and regeneration unit by a metering pump, and the pH value in the adsorbent desorption and regeneration unit is controlled between 8.0 and 9.5 by an online pH sensor and a PID control system. The temperature for the desorption operation is maintained between 25°C and 55°C.

8. The desalination process according to claim 7, characterized in that, The third step, continuous adsorbent desorption and regeneration, also includes: The solid-liquid separation of the salt-containing desorption solution and the regenerated adsorbent material is performed using a continuous magnetic separation device. The continuous magnetic separation device includes a permanent magnet or electromagnetic separator; The magnetic adsorption material is desorbed and recovered from the magnetic separator by mechanical scraping or periodic rinsing. The recovered adsorbent material is washed in a washing tank with deionized water or purified water at a volume of 0.5 to 2 times that of the adsorbent material.

9. The desalination process according to claim 1, characterized in that, The fourth step, electrodialysis purification and recycling unit, is configured as follows: The electrodialysis purification and recycling unit consists of multiple electrodialysis membrane stacks, each stack containing alternating cation exchange membranes and anion exchange membranes, as well as flow channel partitions for forming desalination and concentrate compartments; the effective area of ​​the membranes ranges from 0.1 m². 2 Up to 1.0m 2 Each pair of membranes; The electrodialysis purification and recycling unit applies a DC voltage of 1V to 5V per membrane pair, with a current density of 5mA / cm². 2 Up to 20mA / cm 2 .

10. The desalination process according to claim 9, characterized in that, The cation exchange membrane is a sulfonic acid-based polystyrene-divinylbenzene copolymer membrane; The anion exchange membrane is a quaternary ammonium polystyrene-divinylbenzene copolymer membrane; The electrode material of the electrodialysis membrane stack is a platinum-iridium alloy coated titanium plate or a graphite plate.

Images