Method for continuously preparing acrylamide aqueous solution from immobilized enzyme with core-shell structure

Abstract

The invention provides a method for continuously preparing an acrylamide aqueous solution by using a core-shell structure immobilized enzyme, and relates to the field of chemical engineering, the preparation method comprises the following steps: simultaneously introducing an acrylonitrile stock solution and water into a catalytic reaction unit for hydration reaction; the reaction temperature of the catalytic reaction unit is 10-20 DEG C; enabling reaction effluent to enter a primary purification unit, a deep purification unit and a terminal purification unit to obtain an acrylamide aqueous solution; wherein the catalytic reaction unit is a fixed reactor filled with a core-shell structure enzyme catalyst. The method has the advantages of few product impurities, low energy consumption and high safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemical industry, in particular to a method for continuously preparing acrylamide aqueous solution by using core-shell structure immobilized enzyme. BACKGROUND

[0002] Acrylamide is an important chemical monomer, and its polymer, polyacrylamide, is widely used in oil exploration, water treatment, papermaking and other fields.

[0003] The continuous production method of acrylamide includes skeleton copper catalytic hydration method, the core principle of which is to make acrylonitrile and water undergo hydration reaction under the action of skeleton copper catalyst at high temperature and high pressure. It can be designed in the form of multiple fixed bed reactors in series to realize continuous feeding and discharging. The disadvantage is that the reaction conditions are harsh (high temperature and high pressure), the energy consumption is high, the safety risk is large. The conversion rate is low (only 50-70%), there are many by-products, the product purity is poor, and complex rectification purification is needed. The catalyst is easy to deactivate, and the environment is polluted.

[0004] And the current mainstream continuous production of microorganism / enzyme method, the core is to use the continuous, stable and efficient synthesis of acrylamide by biological catalyst (microbial cells or enzymes). The production of acrylamide by microbial enzyme method (nitrile hydratase catalysis) has become the mainstream process because of its mild conditions and high selectivity. However, this process has the problems of poor stability and short service life of immobilized enzyme catalyst. The enzyme will be irreversibly inactivated due to heat, substrate / product inhibition, impurity poisoning and other reasons during the reaction, resulting in frequent replacement of the catalyst, increasing the production cost and operation complexity. On the other hand, the traditional immobilized enzyme catalyst will continuously release enzyme protein fragments, carrier debris and other particulate and macromolecular organic impurities during use and regeneration. These impurities are chain transfer agents in the subsequent polymerization process, which can seriously limit the molecular weight of the polymer. The residual metal ions and unreacted acrylonitrile in the reaction solution can affect the conductivity and color of acrylamide, and pose a risk of toxicity.

[0005] CN120060391A discloses a resin-MOFs-enzyme composite system to improve the stability of the heated enzyme, but the preparation process is complex, the cost is high, and it is difficult to regenerate after deactivation. CN115161357A uses sodium alginate immobilization, but the mechanical strength is poor and the enzyme is easy to leak. CN104059948B uses a membrane reactor to strengthen mass transfer, but there are problems of membrane pollution and complex operation.

[0006] Therefore, it is urgent to provide a continuous production method of acrylamide with low catalytic cost and low product impurities to solve the above problems. SUMMARY

[0007] The present application aims to provide a method for continuously preparing acrylamide aqueous solution by using core-shell structure immobilized enzyme, which adopts core-shell structure catalyst, has low catalytic cost, less impurities, low energy consumption and high safety.

[0008] The present application solves the technical problems by adopting the following technical solutions.

[0009] In one aspect, the present application provides a method for continuously preparing acrylamide aqueous solution by using core-shell structure immobilized enzyme, which comprises the following steps: The acrylonitrile stock solution and water are simultaneously introduced into the catalytic reaction unit for hydration reaction, and the reaction temperature of the catalytic reaction unit is 10-20 DEG C; The reaction effluent enters the primary purification unit to remove solid particles and macromolecular impurities; The solution treated by the primary purification unit enters the deep purification unit for deionization treatment; The solution treated by the deionization treatment enters the terminal purification unit to remove residual acrylonitrile and volatile impurities, thereby obtaining the acrylamide aqueous solution; The catalytic reaction unit is a fixed reactor filled with core-shell structure enzyme catalyst.

[0010] In some embodiments of the present application, the catalyst is prepared by the following steps: The freeze-dried powder of nitrile hydratase is dispersed in a sodium alginate aqueous solution, and stirred uniformly to obtain an enzyme-sodium alginate mixed solution; the mixed solution is added dropwise into a calcium chloride solution under stirring, and after the dropwise addition is completed, solidification is continued for 1-1.2 h to obtain sodium alginate microspheres embedded with nitrile hydratase; The free nitrile hydratase and the sodium alginate microspheres are added to a gelatin solution at 35-40 DEG C, and stirred uniformly to obtain a core mixed solution; the core mixed solution is then added dropwise into vegetable oil at 10-15 DEG C, and is allowed to stand for 1-1.2 h; the vegetable oil is removed, and the wet microspheres are washed to obtain wet microspheres; The mesoporous silica precursor sol is mixed with the wet microspheres, and is oscillated at room temperature and 60-80 rpm for 16-24 h, filtered, aged, dried to obtain core-shell particles; the core-shell particles are mixed with anhydrous ethanol solution of concentrated hydrochloric acid as an extraction solvent, and are continuously refluxed for 32-48 h, washed, and dried to obtain the catalyst.

[0011] The catalyst prepared by the method has a double-fixed and synergistically protected core-shell structure, forming a sodium alginate microsphere, a gelatin double-layer fixed inner layer and a mesoporous silica outer layer. Sodium alginate and gelatin are both biocompatible materials, which provide a hydrophilic and mild microenvironment for the enzyme, and can maximize the maintenance of the natural conformation and activity of the enzyme. The mesoporous silica shell has high mechanical strength, which can effectively resist the shear force of the reaction liquid flow, prevent enzyme leakage and physical wear, and block the attack of external harmful macromolecules (such as protease).

[0012] The core biological enzyme includes free working enzyme and standby enzyme embedded in the sodium alginate microsphere. When the external working enzyme is inactivated, the internal standby enzyme can be released by heating to trigger gelatin melting to replace it, realizing in-situ regeneration of the catalyst activity and extending the service life by orders of magnitude. The standby enzyme is embedded in the microsphere, and the release during regeneration is more controllable, which can effectively supplement the site vacated by the melting of gelatin, and the regeneration efficiency is high. The pore size of the silica shell is controlled by the template and pore expander, and the pore size of the mesoporous silica shell is large enough to allow the substrate (acrylonitrile) and the product (acrylamide) to diffuse quickly and unhindered, and to react with the internal enzyme. Although there is a shell, the mass transfer resistance is very small, which ensures a high reaction rate.

[0013] Moreover, when the enzyme in the catalyst is completely inactivated, the mesoporous silica can be reused by calcining at high temperature to remove organic matter in the mesoporous silica.

[0014] In some embodiments of the present application, the pore size of the mesoporous silica in the catalyst is 10-20 nm.

[0015] In some embodiments of the present application, the sum of the mass of the nitrile hydratase freeze-dried powder and the mass of the enzyme protein in the free nitrile hydratase accounts for 2-5% of the total mass of the catalyst; the mass ratio of the nitrile hydratase freeze-dried powder to the mass of the enzyme protein in the free nitrile hydratase is 1:2-2:1.

[0016] In some embodiments of the present application, the ratio of tetraethyl orthosilicate to wet microspheres in the mesoporous silica precursor sol is 1:2-1:5.

[0017] In some embodiments of the present application, the free nitrile hydratase is a concentrated enzyme solution obtained by centrifugation, ultrafiltration and concentration after fermentation of Rhodococcus or Pseudomonas.

[0018] In some embodiments of the present application, the filter assembly of the primary purification unit is a hollow fiber ultrafiltration membrane with a molecular weight cut-off of 10000-50000 Da, and the material of the hollow fiber is one of polysulfone, polyether sulfone and polyvinylidene fluoride.

[0019] In some embodiments of the present application, the deep purification unit is a mixed bed ion exchanger or a combination of anion and cation exchange columns in series.

[0020] In some embodiments of the present application, the terminal purification unit is a spray vacuum devolatilizer.

[0021] Compared with the prior art, the embodiments of the present application have at least the following advantages or benefits: The continuous preparation method provided by the present application passes acrylonitrile stock solution and water into the catalytic reaction unit for hydration reaction, and under the action of the catalyst, acrylamide is generated, and then the impurities in the product are removed through the primary purification unit, the deep purification unit and the terminal purification unit, so as to obtain acrylamide water with low impurity content. The production method has high efficiency and low energy consumption.

[0022] In the catalytic reaction unit, the reactants and the catalyst react at a low temperature of 10-20℃, which maximizes the activity and stability of the nitrile hydratase, and avoids enzyme inactivation caused by high temperature. The fixed bed reactor is used as the catalytic unit, the catalyst and the product are easy to separate, the bed temperature distribution is uniform, and the industrialization amplification is easy.

[0023] In the preparation method provided by the present application, the enzyme catalyst with core-shell structure is used, which has self-repairing ability and can realize long-period continuous operation. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme of the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0025] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to specific embodiments.

[0026] Embodiment 1 The catalyst was prepared according to the following steps: 1000 mg of high-activity nitrile hydratase freeze-dried powder was weighed and dispersed in 100 mL of 1.5% (w / v) sodium alginate (molecular weight about 80000-120000) aqueous solution, and then magnetically stirred at 4℃ for 30 minutes to fully mix, to obtain an enzyme-sodium alginate mixed solution.

[0027] The mixture was dropped into 1000 mL of 1.0 M calcium chloride (CaCl2) solution at a rate of 100 drops per minute using a microfluidic device. During the dropping process, the CaCl2 solution was kept at 4 °C and stirred gently (200 rpm). After the dropping was completed, the solution was kept at 4 °C for another 60 minutes to solidify the sodium alginate microspheres. The microspheres were collected by filtration and washed with 4 °C ultrapure water for 3 times to remove the residual CaCl2 on the surface of the microspheres. The sodium alginate microspheres were obtained and stored in a 4 °C refrigerator for later use.

[0028] A 10% (w / v) high-strength gelatin (Bloom strength 250-260) solution was prepared by weighing 50 g of gelatin powder into 500 mL of phosphate buffer (50 mM, pH 7.0) at 40 °C and stirring until completely dissolved. The gelatin solution was kept in a 37 °C water bath to prevent solidification.

[0029] The sodium alginate microspheres (20 g) and free hydratase enzyme (500 mg of enzyme protein) were added to the above gelatin solution at 37 °C and stirred gently to mix well without generating air bubbles to obtain a core mixture.

[0030] The core mixture was dropped into a container containing soybean oil pre-cooled to 10 °C using another set of microfluidic devices. After the dropping was completed, the solution was left to stand for 1 h. The flow rate ratio of the oil phase to the water phase was controlled at 5:1, and uniform droplets were formed by surface tension. The oil phase containing the droplets was collected and placed in an ice-water bath (0-4 °C) for 60 minutes to gel the gelatin droplets completely to form solid microspheres. The upper oil phase was discarded, and the microspheres were repeatedly washed with 0.5% (w / v) Tween-80 aqueous solution and a large amount of 4 °C ultrapure water until completely clean. Wet microspheres were obtained.

[0031] A sol-gel reaction solution was prepared by sequentially adding 900 mL of anhydrous ethanol, 100 mL of ultrapure water, and 20 mL of 0.1 M hydrochloric acid into a 2500 mL container. While stirring vigorously, 50 mL of tetraethyl orthosilicate (TEOS) was slowly added to the above solution. Then, 10 g of the template agent dodecyltrimethylammonium bromide and 3 g of mesitylene were added. The stirring was continued for 2 hours until the solution became clear or translucent to obtain a mesoporous silica precursor sol.

[0032] The wet microspheres were carefully transferred to a 5000 mL reaction flask. The prepared precursor sol was poured into the reaction flask to ensure that the microspheres were completely immersed. The reaction flask was placed in a shaking bed under mild conditions of room temperature (25 °C) and 60 rpm for 24 hours. During this process, the silica network gradually deposited and condensed on the surface of the core microspheres to form a preliminary shell. After the reaction was completed, the core-shell particles coated with silica gel were collected by filtration using a 200-mesh nylon filter.​

[0033] The obtained core-shell particles were aged at room temperature for 12 hours under the condition of 50% humidity to strengthen the silica network structure. Subsequently, the particles were dried in a vacuum drying oven at 40°C under the condition of -0.1 MPa vacuum for 24 hours to obtain dried core-shell particles.

[0034] The dried core-shell particles were placed in a Soxhlet extractor. Anhydrous ethanol solution containing 1% (v / v) concentrated hydrochloric acid was used as the extraction solvent, and continuous reflux extraction was carried out for 48 hours to completely remove the template CTAB and complete the final activation of the silica channels. After the extraction was completed, the particles were washed with anhydrous ethanol 3 times. The catalyst particles were again vacuum dried at 40°C for 6 hours to obtain the catalyst.

[0035] Example 2 The difference from Example 1 is that the amount of added nitrile hydratase freeze-dried powder is adjusted to 500 mg, and the mass of enzyme protein in the added free nitrile hydratase is 1000 mg, and the rest of the steps and raw material amounts are the same as those of Example 1.

[0036] Example 3 The difference from Example 1 is that the amount of added nitrile hydratase freeze-dried powder is adjusted to 1000 mg, and the mass of enzyme protein in the added free nitrile hydratase is 1000 mg, and the rest of the steps and raw material amounts are the same as those of Example 1.

[0037] Example 4 The acrylamide aqueous solution was prepared as follows: Based on the continuous production system, the system mainly consists of a catalytic reaction unit, a primary purification unit, a deep purification unit and a terminal purification unit. The catalytic reaction unit is a fixed reactor filled with core-shell structured enzyme catalyst; the filtration assembly of the primary purification unit is a hollow fiber ultrafiltration membrane with a molecular weight cutoff of 10000-50000 Da, and the material of the hollow fiber is polysulfone; the deep purification unit is a mixed bed ion exchanger; the terminal purification unit is a spray type vacuum devolatilizer.

[0038] Based on the catalysts of Examples 1-3 above, acrylamide was prepared as follows.

[0039] Catalytic reaction unit: acrylonitrile stock solution (content above 99.5%) and ultrapure water were simultaneously introduced into a multi-tube fixed bed reactor, and the reaction temperature was strictly controlled at 15±0.5°C. The acrylonitrile stock solution was continuously introduced into the top of the reactor at a liquid hourly space velocity (LHSV) of 1 h -1 -1, and the flow rate of ultrapure water was controlled according to the concentration of acrylamide AM in the effluent.

[0040] Primary purification unit: The liquid from the fixed reactor is directly fed into a hollow fiber (hydrophilic polyether sulfone, molecular weight cut-off 30000 Da) ultrafiltration membrane system. The whole flow is filtered, the transmembrane pressure (TMP) is 0.5-1.5 bar, and the temperature is 15-25°C. The nanometer silicon dioxide particles and the trace amount of enzyme protein that may be leaked due to catalyst abrasion are continuously intercepted and concentrated. The concentrated liquid is partially returned to the reactor.

[0041] Deep purification unit: The permeate liquid generated by the ultrafiltration membrane of the primary purification unit is directly fed into a system composed of multiple groups of mixed bed ion exchange columns. The space velocity (SV) is 5 h -1 .

[0042] Terminal purification unit: The acrylamide solution after deionization is fed into a spray type vacuum devolatilizer, the operating pressure is 5-10 kPa (about -0.095 MPa), the temperature is 25-30°C, and the residence time is 3 minutes. The acrylonitrile condensed and recovered from the top of the devolatilizer can be returned to the raw material pretreatment unit. The high-purity acrylamide aqueous solution is obtained from the bottom of the devolatilizer.

[0043] Example 5 Based on the acrylamide preparation system and method of Example 4, when it is detected that the acrylamide concentration at the reactor outlet monitored by the online analyzer is continuously lower than the set threshold value (corresponding to a conversion rate ≤ 90%) for 15 minutes, a catalyst regeneration program can be performed.

[0044] Specific composition of the regeneration system: Regeneration medium storage tank, with a capacity of 2 times the bed volume of the fixed bed reactor. It is filled with sterile, pyrogen-free, and dissolved oxygen-removed ultrapure water. It is equipped with a sterile breather (0.22 μm hydrophobic air filter) and an online temperature control unit (which can be heated / cooled).

[0045] Regeneration waste liquid collection tank: The capacity is equivalent to that of the regeneration medium storage tank. It is made of corrosion-resistant stainless steel or plastic and is used to collect and temporarily store the regeneration waste liquid.

[0046] Regeneration circulation loop: regeneration pump; regeneration heater, which raises the circulating liquid from the reaction temperature to the trigger temperature in a short time; and regeneration cooler, which is connected with a chilled water system and is used for rapid cooling after the regeneration is completed.

[0047] Regeneration pipeline, valve and instrument: a pipeline system that is independent and physically separated from the main process pipeline, connecting the reactor, the storage tank and the collection tank.

[0048] Liquid seal forming unit: located on the permeate side of the primary purification unit (ultrafiltration membrane). Sterile ultrapure water is injected in reverse and a pressure slightly higher than that of the main process line is maintained to form a one-way flow water seal on the permeate side of the ultrafiltration membrane.

[0049] When the online analyzer monitors that the acrylamide concentration at the reactor outlet is continuously below the set threshold (corresponding to a conversion of < 90%) for 15 minutes, the system automatically prompts regeneration. The catalyst regeneration is carried out in the following steps: The main feed is shut off, the remaining reaction solution in the reactor and pre-pipeline is pushed into the primary purification unit, the fixed bed reactor is disconnected from the main production line and connected to the closed regeneration circulation loop. The liquid seal protection is started, 25°C ultrapure water is injected into the permeation side of the ultrafiltration membrane at a flow rate of 1.0 L / min in the reverse direction. The regeneration pump is started, 25°C ultrapure water is pumped from the regeneration medium tank into the reactor from the bottom to the top (reverse flushing) at a flow rate of 2 times the reactor bed volume per hour. The flushing liquid is directly discharged into the regeneration waste liquid collection tank for 10-15 minutes. Circulation warming: the valve to the waste liquid tank is closed and the regeneration circulation loop is opened. The online instantaneous heater is started and the temperature of the circulating liquid is uniformly raised from room temperature to, for example, 35°C within 5-10 minutes. At this temperature, the circulation is maintained for 30 minutes. The temperature-sensitive hydrogel of the catalyst core melts, the reserve enzyme in the inner layer is released, and the inactivated enzyme in the outer layer is replaced and diffused into the circulating liquid. The circulation flow rate is maintained at 1 times the bed volume per hour.

[0050] The valve is switched again to connect the circulation loop to the regeneration waste liquid collection tank. The reactor is flushed with 35°C ultrapure water at a flow rate of 2 times the bed volume per hour for 15-20 minutes to ensure that all inactivated enzyme fragments are thoroughly washed out and collected into the waste liquid tank. The heater is turned off and the online cooler is turned on to quickly reduce the temperature of the circulating liquid to 15°C within 15 minutes. The temperature-sensitive hydrogel of the catalyst core is re-solidified, the new high-activity enzyme is firmly fixed, and the reconstruction of the core is completed.

[0051] The injection of ultrapure water into the permeation side of the ultrafiltration membrane is stopped. The liquid in the regeneration loop is completely discharged into the waste liquid collection tank. Valve switching: the valve group is automatically switched to reconnect the fixed bed reactor to the main production line. The reactor is flushed with reaction buffer at a low flow rate until the outlet conductivity and pH meet the standards. The acrylonitrile feed is restored and a new round of production is started.

[0052] Comparative Example 1 The difference from Example 1 is that, in the preparation of the catalyst, the wet-state microspheres are not prepared, but a high-activity nitrile hydratase freeze-dried powder is directly used instead, and the subsequent steps are the same as those of Example 1.

[0053] Based on this catalyst, acrylamide is prepared by the method of Example 4.

[0054] Comparative Example 2 The difference from Example 1 is that, in the preparation of the catalyst, the wet-state microspheres are not prepared, but a free nitrile hydratase is directly used instead, and the subsequent steps are the same as those of Example 1.

[0055] Based on the catalyst, using the method of example 4, acrylamide was prepared.

[0056] Experimental example Based on example 4 and example 5, the service life, acrylamide yield, purity, etc. of the catalysts of examples 1-3 were statistically analyzed, and the results are shown in table 1.

[0057] Among them, the catalytic life: defined as the total time from the beginning of the use of the single loading catalyst to the first time when the conversion rate of catalyzing acrylonitrile hydration is reduced to below 90%.

[0058] Acrylamide yield: during the catalyst life test, periodic sampling analysis was carried out, and the total amount of acrylamide produced per unit mass of catalyst was calculated to comprehensively measure the activity and stability of the catalyst.

[0059] Yield after regeneration: the total amount of acrylamide produced per unit mass of catalyst in the second life cycle of the catalyst after completing the first regeneration process. Used to evaluate the regeneration effect.

[0060] Table 2

[0061] The catalysts of examples 1-3 have super long catalytic life (650-750 hours) and high total yield. Because of the strong protection of the mesoporous silica shell, it effectively prevents the leakage, deactivation and physical wear of the enzyme in long-term operation.

[0062] The catalysts of comparative examples 1 and 2 have short life and total yield less than 25% of example 1 due to the lack of double-layer core structure, and the enzyme is quickly deactivated in the reaction.

[0063] The regeneration effect of examples 1 and 3 is good, and the recovery degree of yield after regeneration is more than 94%. This shows that the internal sodium alginate gel coated standby enzyme can fully replace the external deactivated enzyme during the regeneration process, so that the catalyst performance can be restored to the level before deactivation. The recovery degree of example 2 is slightly lower, which shows that its standby enzyme capacity is relatively insufficient, but it still maintains a high level of more than 90%.

[0064] The catalysts of comparative examples 1 and 2 have no regeneration ability at all, and once deactivated, the whole must be replaced, which is worse than the present invention in terms of economy and operation.

[0065] In summary, the present application has super long initial life and in-situ regeneration ability through the synergistic design of core-shell structure and double-layer enzyme. The example data fully prove that the catalyst and its supporting continuous production process far exceed the traditional immobilized enzyme catalyst in key performance indicators, and provide reliable technical support for realizing low impurity, high efficiency and low cost green production of acrylamide.

[0066] The embodiments described above are only part of the embodiments of the present application, rather than all the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but only to represent selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

Claims

1. A method for the continuous production of acrylamide aqueous solution by core-shell structure immobilized enzyme, characterized in that, The method comprises the following steps: The acrylonitrile stock solution and water are simultaneously introduced into a catalytic reaction unit for hydration reaction, and the reaction temperature of the catalytic reaction unit is 10-20℃; The reaction effluent is introduced into a primary purification unit to remove solid particles and macromolecular impurities; The solution treated by the primary purification unit is introduced into a deep purification unit for deionization treatment; The solution treated by the deionization treatment is introduced into a terminal purification unit to remove residual acrylonitrile and volatile impurities, thereby obtaining the acrylamide aqueous solution. The catalytic reaction unit is a fixed reactor filled with an enzyme catalyst with a core-shell structure.

2. The process for the continuous production of acrylamide aqueous solution by core-shell structure immobilized enzyme according to claim 1, characterized in that, The catalyst is prepared by the following steps: The freeze-dried powder of nitrile hydratase is dispersed in a sodium alginate aqueous solution to obtain an enzyme-sodium alginate mixture, and the mixture is added dropwise into a calcium chloride solution under stirring, and then solidified for 1-1.2 h after the dropwise addition is completed, thereby obtaining sodium alginate microspheres embedded with nitrile hydratase; The free nitrile hydratase and the sodium alginate microspheres are added into a gelatin solution at 35-40℃ and stirred to obtain a core mixture, and then the core mixture is added dropwise into vegetable oil at 10-15℃ and left to stand for 1-1.2 h; The vegetable oil is removed and the wet microspheres are obtained by washing; The mesoporous silica precursor sol is mixed with the wet microspheres, and the mixture is oscillated at room temperature and at 60-80 rpm for 16-24 h, filtered, aged, dried, and then mixed with concentrated hydrochloric acid in anhydrous ethanol as an extraction solvent, and continuously refluxed for 32-48 h, washed, and dried, thereby obtaining the catalyst.

3. The process for the continuous production of acrylamide aqueous solution by core-shell structure immobilized enzyme according to claim 2, characterized in that, The pore size of the mesoporous silica in the catalyst is 10-20 nm.

4. The process for continuous preparation of acrylamide aqueous solution by core-shell structure immobilized enzyme according to claim 2, characterized in that, The total mass of the freeze-dried powder of nitrile hydratase and the enzyme protein in the free nitrile hydratase accounts for 2-5% of the total mass of the catalyst, and the mass ratio of the freeze-dried powder of nitrile hydratase to the enzyme protein in the free nitrile hydratase is 1:2-2:

1.

5. The process for continuous production of acrylamide aqueous solution by core-shell structure immobilized enzyme according to claim 2, characterized in that, The mass ratio of tetraethyl orthosilicate in the mesoporous silica precursor sol to the wet microspheres is 1:2-1:

5.

6. The process for continuous production of acrylamide aqueous solution by core-shell structure immobilized enzyme according to claim 2, wherein, The free nitrile hydratase is a concentrated enzyme solution obtained by centrifugation, ultrafiltration, and concentration after fermentation of Rhodococcus or Pseudomonas.

7. The process for continuous production of acrylamide aqueous solution by core-shell structure immobilized enzyme according to claim 1, characterized in that, The filter assembly of the primary purification unit is a hollow fiber ultrafiltration membrane with a molecular weight cut-off of 10000-50000 Da, and the material of the hollow fiber is one of polysulfone, polyethersulfone, and polyvinylidene fluoride.

8. The process for continuous production of acrylamide aqueous solution by core-shell structure immobilized enzyme according to claim 1, characterized in that, The deep purification unit is a mixed bed ion exchanger or a combination of anion and cation exchange columns in series.

9. The process for continuous production of acrylamide aqueous solution by core-shell structure immobilized enzyme according to claim 1, characterized in that, The terminal purification unit is a spray-type vacuum devolatilizer.

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