Method for circularly treating and recycling alkali liquor for preparing chitosan

Abstract

The invention relates to the technical field of resource recycling of industrial waste liquid, in particular to a cyclic treatment and reutilization method of alkali liquor for chitosan preparation, which comprises the following steps: step 1, on-line monitoring and shunting of the state of the alkali liquor; step 2, multi-stage separation and impurity removal; 3, dynamic regulation and control of ion components: adjusting the flow rate based on the change rate of the conductivity value at the inlet of the ion exchange resin column, and triggering resin regeneration when the pH value at the outlet reaches a regeneration critical point; 4, alkali activity compensation: dynamically supplementing alkali according to the effective alkali concentration of regenerated alkali liquor and the demand of a target recycling process section; and 5, sequential control recycling: injecting fresh alkali liquor when the initial-stage deacetylation reaction is started, and proportionally pumping regenerated alkali liquor when the middle-stage reaction reaches a temperature peak value. According to the method, the quality and the reaction efficiency of the alkali liquor are effectively controlled, various parameters in the production process are optimized through accurate dynamic regulation and control, the recycling rate of the alkali liquor is increased, the production cost is reduced, and the dual effects of environmental protection and energy conservation are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of resource recycling of industrial waste liquid, and particularly relates to a method for recycling and reusing alkali liquor for chitosan preparation. BACKGROUND

[0002] In the process of preparing chitosan by deacetylation of chitin, a high-concentration sodium hydroxide solution (usually 40-50 wt%) is a key reaction medium. In order to reduce production costs, the alkali liquor is generally recycled in industry. However, the existing recycling technology has the following inherent defects: During the deacetylation reaction process, proteins, lipids and colloidal substances in chitin are continuously dissolved. The traditional recycling technology only relies on plate and frame filtration or centrifugal separation, and cannot remove soluble proteins (molecular weight 5-100 kDa) and colloidal particles (particle size <10 μm).

[0003] Experiments show that the viscosity of the alkali liquor increases by more than 300% (from 15 cP to 60 cP) after 5 cycles, resulting in a 40%-50% decrease in the mass transfer coefficient of the reaction system.

[0004] High-viscosity alkali liquor hinders the diffusion of sodium hydroxide to the chitin microcrystalline region, significantly prolonging the time required for complete deacetylation (from 8 hours to 12 hours), and increasing energy consumption by more than 30%.

[0005] In addition, deacetylation consumes free alkali (NaOH→CH3COONa+H2O), and the traditional alkali supplementing method only simply supplements sodium hydroxide without simultaneously removing the byproduct sodium acetate.

[0006] After 10 cycles, the concentration of sodium acetate in the alkali liquor can reach 12 wt%, accounting for 35% of the total sodium ion molar ratio, resulting in a virtual high concentration of effective alkali (the measured pH is 13.5, but the deacetylation activity is only equivalent to 65% of that of fresh alkali liquor).

[0007] Mechanism analysis: The ionization of sodium acetate inhibits the OH - ion activity, and changes the ionic strength of the reaction system, so that the deacetylation reaction activation energy increases from 42 kJ / mol to 58 kJ / mol.

[0008] Therefore, there is an urgent need for a method for recycling and reusing alkali liquor for chitosan preparation to solve the above problems. SUMMARY

[0009] Based on the above purpose, the present application provides a method for recycling and reusing alkali liquor for chitosan preparation, comprising the following steps: Step 1: On-line monitoring and shunting of alkali liquor state: Real-time collection of the dynamic viscosity value, conductivity value and turbidity value of the alkali solution after deacetylation reaction, and according to the preset viscosity-turbidity correlation threshold, the alkali solution is divided into primary or deep treatment channel; Step 2: multi-stage separation and impurity removal: The alkali solution flows through the solid residue interception device, the colloid adsorption device and the nano protein capture device in turn, and the alkali solution in the deep treatment channel is additionally subjected to soluble organic matter separation; Step 3: dynamic regulation of ion components: The flow rate is adjusted based on the change rate of the conductivity value at the inlet of the ion exchange resin column, and the resin regeneration is triggered when the outlet pH value reaches the critical point of regeneration; Step 4: alkali activity compensation: According to the effective alkali concentration of the regenerated alkali solution and the demand of the target reuse process section, the alkali is dynamically compensated; Step 5: time sequence control reuse: When the primary deacetylation reaction is started, fresh alkali solution is injected, and when the middle stage reaction reaches the temperature peak, the regenerated alkali solution is pumped in proportion.

[0010] Preferably, the determination process of the viscosity-turbidity correlation threshold in step 1 comprises: A negative correlation model of the viscosity of the alkali solution and the mass transfer efficiency of the deacetylation reaction is established by orthogonal test, and the viscosity threshold is the viscosity value when the mass transfer efficiency decreases to a set percentage; The linear relationship between the colloid concentration and the turbidity in the historical circulating alkali solution is analyzed, and the turbidity threshold is the turbidity value corresponding to the viscosity sudden change critical value when the colloid concentration reaches the viscosity sudden change critical value; The viscosity threshold and the turbidity threshold are correlated to form a two-dimensional decision matrix, and when the real-time data point is located in the high-risk area of the matrix, the deep treatment channel is started.

[0011] Preferably, the operation of the soluble organic matter separation in step 2 comprises: The alkali solution flows through the tubular ceramic membrane device, and the molecular weight fractionation interception is realized by driving through the transmembrane pressure; The setting method of the transmembrane pressure is: within the pressure limit range of the membrane, the minimum pressure value is selected to make the target organic matter interception rate reach a set percentage; When the membrane flux attenuation reaches a set proportion of the initial value, reverse pulse cleaning is started, and the pulse frequency is dynamically adjusted according to the flux attenuation rate.

[0012] Preferably, the method of adjusting the flow rate based on the change rate of the conductivity value at the inlet of the ion exchange resin column in step 3 comprises: A mapping relationship between the conductivity decline rate and the resin adsorption efficiency is established: when the rate exceeds a first set rate, it indicates that the resin is not saturated, and the flow rate is increased to avoid equipment overload; when the rate is lower than a second set rate, it indicates that the resin is nearly saturated, and the flow rate is reduced to prolong the contact time; The determination method of the set rate is as follows: through a resin column breakthrough experiment, a critical conductivity rate value at which the adsorption efficiency suddenly drops is obtained.

[0013] Preferably, the determination of the regeneration critical point in step 3 comprises: Real-time calculation of the unit time drop of the pH value at the outlet of the resin column, and when the drop in three consecutive sampling periods exceeds the set drop, it is determined as the critical point; The determination method of the set drop is as follows: the adsorption capacity decay curve of the resin is determined by titration method, and the pH change rate when the adsorption capacity drops to a set percentage is taken as the benchmark.

[0014] Preferably, the acquisition of the effective alkali concentration in step 4 comprises: The density-conductivity combined detection method is used: the density value of the alkali solution is obtained by an online density meter, combined with the data of the conductivity sensor, and input into a pre-established sodium hydroxide concentration calculation model; The construction method of the calculation model is as follows: simulate alkali solution samples with different impurity contents, and determine the corresponding relationship between their density, conductivity and true sodium hydroxide concentration, and establish a compensation equation through multiple regression analysis.

[0015] Preferably, in the dynamic alkali supplementing according to the effective alkali concentration of the regeneration alkali solution and the target reuse process section requirement in step 4, it comprises alkali concentration control, specifically: The alkali supplement target concentration setting method for the initial stage deacetylation: based on the chitin swelling kinetics experiment, the minimum alkali concentration required to make the swelling rate reach a set range is determined; The alkali supplement target concentration setting method for the middle stage deacetylation: according to the deacetylation reaction activation energy model, the alkali concentration compensation value required to maintain a constant reaction rate is calculated.

[0016] Preferably, the identification of the temperature peak in step 5 comprises: Real-time monitoring of the temperature change curve of the reaction kettle, and when the following conditions are met at the same time, the peak value is determined: (a) The temperature rise rate drops below a set rate threshold; (b) The temperature fluctuation range is less than a set tolerance value; The rate threshold is determined by inflection point analysis of the reaction heat release curve.

[0017] Preferably, the determination of the reuse ratio of the regeneration alkali solution in step 5 comprises: The free radical concentration of the regeneration alkali solution is monitored by a redox potential sensor, and a inverse relationship model of the potential value and the activity coefficient of the alkali solution is established; According to the ratio of the real-time activity coefficient to the fresh alkali solution, the maximum reusable ratio is dynamically calculated; When the temperature of the reaction system exceeds the set temperature, the recycling ratio upper limit is raised by the proportional coefficient.

[0018] Preferably, the start-up conditions of the depth treatment channel further comprise: Forced start-up of the depth treatment when the number of lye circulation reaches a set number threshold. The determination method of the number threshold is: counting the average number of cycles before viscosity mutation in multiple batches of production, and rounding off after deducting the safety margin.

[0019] The beneficial effects of the present application are: 1. The present application can effectively remove dissolved organic matter, colloids and nanoscale proteins through the multi-stage separation device, including solid residue interception device, colloid adsorption device and nanoscale protein capture device. This step not only improves the quality of lye, but also maintains the mass transfer efficiency of the reaction system, thereby reducing the negative impact of viscosity increase and significantly improving the reaction efficiency.

[0020] 2. The present application can make the lye enter different treatment channels according to the actual situation by real-time monitoring of the viscosity, conductivity and turbidity of the lye, and combining the viscosity-turbidity correlation threshold. Especially in the depth treatment channel, the tubular ceramic membrane separation device is used for the separation of dissolved organic matter, which can effectively reduce the viscosity of the lye, ensure the diffusion efficiency of sodium hydroxide in the reaction system, significantly shorten the deacetylation reaction time, and reduce the energy consumption.

[0021] 3. The present application can dynamically supplement sodium hydroxide by combining the effective alkali concentration of regenerated lye and the demand of target recycling process section, while accurately calculating the concentration of sodium hydroxide by density-conductivity combined detection method to avoid excessive accumulation of sodium acetate. In addition, through the regeneration control of ion exchange resin column, when the adsorption capacity of the resin approaches saturation, the system automatically adjusts the flow rate and regeneration conditions to ensure the stability of the effective alkali concentration in the lye and avoid the influence of sodium acetate on the concentration of the lye.

[0022] 4. The present application can dynamically regulate the ion components, especially when using ion exchange resin column, the flow rate is adjusted by the conductivity change rate to realize accurate control of resin regeneration. When the concentration of sodium acetate rises to a certain extent, the system can reduce the inhibitory effect of sodium acetate by regenerating the resin column and compensating the effective alkali concentration to restore the activity of the reaction system and ensure the smooth progress of the deacetylation reaction.

[0023] 5. The present invention achieves precise management of the alkali solution by real-time monitoring of multiple parameters such as viscosity, conductivity, turbidity, and pH value of the alkali solution, combined with timing control and dynamic adjustment mechanisms. When parameters such as the temperature and viscosity of the alkali solution change during the reaction, the system can automatically adjust the inflow ratio of the alkali solution and the amount of alkali replenishment, thereby ensuring the stable progress of the deacetylation reaction and avoiding manual operation errors and unnecessary waste of resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0025] Fig. 1 is a flow chart of the steps of the method of the present invention; Fig. 2 Flow chart of the process of determining the viscosity-turbidity correlation threshold value in step 1 of the method of the present invention; Fig. 3 This is a flow chart of the steps for controlling the alkali concentration in the target reuse process section in step 4 of the method of the present invention. DETAILED DESCRIPTION

[0026] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. It is also noted that, to provide a more detailed description, the following embodiments are best and preferred embodiments, and those skilled in the art may employ alternative methods for implementing certain known technologies. Furthermore, the accompanying drawings are intended only to provide a more detailed description of the embodiments and are not intended to limit the present invention.

[0027] See Figs. 1-3 The embodiment of the present invention provides a method for recycling and reusing alkali solution for chitosan preparation. By precisely controlling the state of the alkali solution, removing harmful impurities, dynamically regulating the ion concentration, and compensating for the alkali activity, the efficient recovery and reuse of the alkali solution is achieved, the production cost is reduced, and the efficiency of the deacetylation reaction is improved.

[0028] In step 1, the current state of the alkali liquor after the deacetylation reaction is first determined by real-time monitoring of key parameters such as its dynamic viscosity, conductivity, and turbidity. By setting thresholds for the correlation between viscosity and turbidity, the purity of the alkali liquor can be determined promptly. When the viscosity and turbidity of the alkali liquor exceed the preset range, the alkali liquor is diverted to primary or advanced treatment channels. Primary treatment is suitable for lighter pollution, while advanced treatment is suitable for treating dissolved organic matter and fine impurities, ensuring that the recovered alkali liquor has higher purity and reducing the increase in viscosity and the decrease in reaction efficiency.

[0029] In step 2, after entering the deep treatment channel, the lye will pass through the solid residue interception device, the colloid adsorption device, and the nano-protein capture device in turn. This multi-stage separation process can effectively remove proteins, lipids, colloidal particles, and other organic matter dissolved in the lye. In particular, the nano-protein capture device can effectively remove these impurities, prevent their accumulation in the lye, reduce the increase in viscosity, and ensure good mass transfer conditions in the reaction system, targeting proteins with a molecular weight of 5-100 kDa.

[0030] In step 3, by monitoring the conductivity change rate at the inlet of the ion exchange resin column in the lye, the flow rate is adjusted to optimize the adsorption performance of the resin. The conductivity change rate reflects the concentration change of soluble salt substances, and by adjusting the flow rate, the optimal working state of the ion exchange resin can be maintained. When the pH value of the lye reaches the preset critical value, the regeneration process of the resin is triggered. This process can effectively remove accumulated impurities, improve the adsorption capacity of the resin, prolong its service life, and ensure the stability of the lye in the reaction.

[0031] In step 4, during the regeneration of the lye, the system dynamically supplements sodium hydroxide according to the effective alkali concentration of the lye and the requirements of the target reuse process section. In this way, the concentration of sodium hydroxide during the reaction can be ensured to be appropriate, avoiding incomplete deacetylation or slowing down the reaction rate due to too low lye concentration.

[0032] In step 5, in the initial stage of the deacetylation reaction, the system will inject fresh lye to ensure the start of the reaction. As the reaction progresses, if the reaction temperature reaches the peak value, the regenerated lye will be pumped in proportion. This time sequence control method can flexibly adjust the amount of lye input according to the different needs of the reaction stage, ensuring the stability and efficiency of the reaction process.

[0033] Through multi-level lye treatment and precise time sequence control, not only the impurities in the lye are effectively removed, the increase in viscosity is reduced, and the mass transfer efficiency of the reaction system is maintained, but also the composition and flow rate of the lye are dynamically regulated, the reaction conditions are optimized, the reaction time is shortened, and the energy consumption is reduced. At the same time, precise alkali supplementation and resin regeneration mechanism effectively avoid the inhibition of sodium acetate on the reaction, improve the reuse efficiency of the lye, and reduce production costs. Ultimately, this method makes it possible to recycle the lye in the chitosan preparation process, which not only meets economic benefits but also meets environmental protection requirements.

[0034] In one possible implementation, first, a negative correlation model between viscosity and mass transfer efficiency is established by using orthogonal test method in combination with different concentrations of lye and mass transfer efficiency of deacetylation reaction under different conditions. Specifically, in the test process, by adjusting the concentration, temperature, time and other variables of the lye, the mass transfer efficiency and the corresponding viscosity value under different conditions are recorded. When the mass transfer efficiency decreases to a set percentage, the viscosity value can be used as the viscosity threshold.

[0035] It can be understood that the viscosity threshold is used as a basis for determining whether the lye enters the deep processing channel. If the viscosity exceeds this value, it indicates that the lye has exceeded the ideal reaction range and may affect the reaction rate or effect, and therefore needs to be further processed.

[0036] By analyzing the turbidity and colloidal concentration data of the historical circulating lye, a linear relationship between them is established. The turbidity value is an indicator reflecting the concentration of suspended particles in the lye, while the colloidal concentration directly affects the sedimentation and reaction efficiency of the lye. Through experimental analysis, when the colloidal concentration reaches a certain critical value, the turbidity of the lye will change significantly. This critical turbidity value is used as the turbidity threshold to determine whether there is an excess of colloids or impurities in the lye.

[0037] By combining the above viscosity threshold and turbidity threshold, a two-dimensional decision matrix is formed. Each region in the matrix corresponds to a different lye state, including normal, warning and high-risk regions. Specifically, when the real-time monitoring data (viscosity value and turbidity value) are located in the high-risk region of the matrix, it indicates that the lye has exceeded the preset safety threshold and may affect the efficiency and stability of the subsequent reaction. At this time, the system will automatically start the deep processing channel for further impurity removal and lye purification to ensure the stability of the reaction conditions.

[0038] By combining the dual control indicators of viscosity and turbidity, the treatment of lye is more accurate and effective. By establishing a negative correlation model and a linear relationship, the quality change trend of the lye can be more scientifically judged, avoiding the errors of traditional single parameter judgment and improving the processing efficiency. The application of the two-dimensional decision matrix provides a clear reference basis for real-time decision-making, reduces the errors of human operation, ensures that the lye can be processed in time when its quality is abnormal, and prevents the reaction efficiency from being reduced or the equipment from being damaged. At the same time, the optimized lye recycling mechanism not only ensures efficient production, but also improves the resource recovery rate and economic benefits, meeting the needs of sustainable development.

[0039] In one possible implementation, the preliminarily treated alkaline liquor first flows into a tubular ceramic membrane device. The ceramic membrane has high mechanical strength and chemical stability, and is suitable for treating the dissolved organic matter in the alkaline liquor. The membrane device is internally set with a certain transmembrane pressure to push the alkaline liquor to flow through the membrane surface. The pore size and properties of the membrane can grade the organic matter according to the molecular weight. Through the difference in transmembrane pressure, the macromolecular organic matter is retained on one side of the membrane, and the small molecular substances can pass through the membrane pores to the other side, so as to realize the separation of the organic matter.

[0040] When setting the transmembrane pressure, it is necessary to ensure that the membrane device works within the pressure limit range, and to select a minimum pressure value that can make the retention rate of the target organic matter reach a certain percentage. Although high pressure can improve the separation efficiency, it can also aggravate the pollution and loss of the membrane. Low pressure may lead to unsatisfactory separation effect. Therefore, in the setting process, the transmembrane pressure is optimized according to the molecular weight of different types of organic matter, the flux characteristics of the membrane and the required retention efficiency, so as to ensure that the target organic matter can be effectively retained and the service life of the membrane can be prolonged.

[0041] With the increase of the use time, some retained organic matter and other impurities will accumulate on the membrane surface, causing the flux of the membrane to gradually decay. When the flux of the membrane decays to a certain percentage of the initial value, the reverse pulse cleaning process is triggered. In the cleaning process, the pulse frequency is dynamically optimized according to the rate of flux decay. The pulse cleaning removes the organic matter and impurities attached to the membrane surface by changing the direction of the fluid and using high-pressure water flow to impact the membrane surface for a short time, so as to restore the flux of the membrane. The dynamic adjustment of the pulse cleaning frequency can finely control the degree of membrane pollution, prevent excessive cleaning from damaging the membrane, and improve the cleaning efficiency.

[0042] Firstly, the ceramic membrane separation can accurately remove the macromolecular organic matter in the alkaline liquor, effectively reduce the pollutants in the alkaline liquor, and ensure the stability of the subsequent process. Secondly, the accurate setting of the transmembrane pressure can minimize the damage to the membrane and energy waste while ensuring the separation effect, thereby prolonging the service life of the membrane. In addition, the dynamic adjustment function of the reverse pulse cleaning makes the membrane cleaning process more efficient, and can be adjusted according to the actual degree of pollution, avoiding the influence of excessive cleaning on the performance of the membrane, and improving the adaptability of the cleaning frequency and reducing the production interruption caused by membrane pollution. This technology not only improves the recycling efficiency of the alkaline liquor, but also effectively reduces the production cost and meets the requirements of sustainable development.

[0043] In one possible implementation, first, the conductivity at the inlet of the resin column is monitored, and its change over time is analyzed. Conductivity is an indicator of ion concentration in the solution, and the resin adsorption efficiency is closely related to the change in conductivity. When the resin adsorbs ions in the solution, the conductivity of the solution gradually decreases. Therefore, the rate of change of conductivity (i.e., the amount of change in conductivity per unit time) can reflect the efficiency of resin adsorption.

[0044] When the conductivity decrease rate is too fast, it indicates that the resin has not reached saturation, and the ion exchange process is still efficient. At this time, the flow rate should be appropriately increased to avoid overuse of the resin and prevent equipment overload. When the conductivity decrease rate is slow, it indicates that the resin is close to saturation, and the adsorption efficiency gradually decreases. At this time, the flow rate should be reduced to prolong the contact time of the fluid with the resin, ensuring that the adsorption process continues and achieves optimal results.

[0045] The determination of the set rate is accomplished through a breakthrough experiment of the resin column. The purpose of the breakthrough experiment is to simulate the adsorption behavior of the resin column in actual use, by adjusting the flow rate and the change in conductivity, and observing the adsorption performance of the resin. Through experimental data, the rate of change of conductivity (i.e., the critical conductivity change rate) at which the resin adsorption efficiency drops sharply can be determined.

[0046] This critical rate value serves as a reference for setting two rate thresholds: the first set rate and the second set rate. When the conductivity decrease rate is higher than the first set rate, the flow rate can be increased; when the conductivity decrease rate is lower than the second set rate, the flow rate should be reduced. This setting method optimizes the working state of the resin, ensuring that the resin is fully utilized when it is not saturated, and avoiding waste when it is close to saturation, maximizing the adsorption effect of the resin.

[0047] By monitoring the change in conductivity in real time and adjusting the flow rate, the adsorption efficiency of the resin can be accurately controlled, avoiding the impact of too fast or too slow flow rates on the treatment effect. Increasing the flow rate helps to avoid inefficient operation when the resin is not saturated, while reducing the flow rate when the resin is close to saturation prolongs the contact time with the resin, ensuring the full performance of the ion exchange process.

[0048] By determining the critical conductivity change rate value through a breakthrough experiment, the flow rate adjustment is more scientific and reasonable, avoiding the previous single mode of relying on a fixed flow rate. Finally, this adjustment method can improve the service life and adsorption efficiency of the resin, reducing resource waste and improving the economic efficiency and sustainability of the entire caustic solution recycling process.

[0049] In one possible implementation, first, the pH value at the outlet of the resin column is monitored, and its change is recorded. The change in the pH value directly reflects the adsorption of ions in the solution by the resin. When the resin adsorbs ions in the solution, the pH value of the solution changes, usually showing a gradual decrease in the pH value. Therefore, real-time calculation of the decrease in the pH value in a unit of time can effectively reflect the change in the adsorption capacity of the resin. By continuously tracking the change in the pH value, the attenuation of the performance of the resin can be captured in a timely manner.

[0050] To accurately determine the regeneration critical point of the resin, data of three consecutive sampling periods are used for determination. When the decrease in the pH value exceeds the preset set decrease in the three consecutive sampling periods, it is determined that this is the regeneration critical point of the resin. The set decrease is a value determined through actual operation experience and experiments, which is closely related to the adsorption capacity and running state of the resin. Once the pH value changes in the three consecutive periods reach this set value, it indicates that the adsorption capacity of the resin has significantly decreased and is close to the saturation state, and needs to be regenerated.

[0051] The determination method of the set decrease is to determine the adsorption capacity attenuation curve of the resin by titration. The titration method can determine the ability of the resin to adsorb ions in the solution during the treatment process, and draw a curve of the attenuation of the adsorption capacity with time. When the adsorption capacity of the resin decreases to a set percentage, the change rate of the pH value will change significantly. This change rate is used as a reference standard for setting the decrease, to ensure that the critical point can be accurately and timely determined when the adsorption capacity of the resin is close to saturation.

[0052] By monitoring the change in the pH value at the outlet of the resin column in real time, the adsorption performance of the resin can be dynamically tracked, and whether the adsorption capacity of the resin has attenuated to the critical point can be found in a timely manner. Compared with the traditional static detection method, this real-time calculation method is more accurate, can realize continuous monitoring of the performance of the resin, and avoids the performance degradation due to the failure of timely regeneration of the resin.

[0053] By setting the critical point to be determined when the decrease exceeds the set decrease in three consecutive sampling periods, misjudgment can be effectively avoided, and the regeneration operation can be performed when the adsorption capacity of the resin significantly attenuates, thereby improving the regeneration efficiency. Finally, the determination method of the set decrease scientifically analyzes the attenuation of the adsorption capacity of the resin by titration, so that the determination standard is more accurate, the regeneration operation is avoided to be performed too early or too late, the regeneration period is optimized, the utilization efficiency of the resin is improved, and the operation cost is reduced.

[0054] In one possible implementation, first, the density value of the lye is obtained by an online densimeter. The density value reflects the concentration of solutes in the lye, but using the density value alone may not accurately reflect the sodium hydroxide concentration, especially when the lye contains other impurities. To solve this problem, the data of the conductivity sensor are combined, which can further improve the accuracy of the measurement. Conductivity reflects the concentration of ions in the solution, and the conductivity of a sodium hydroxide solution is generally proportional to its concentration. Therefore, by monitoring both density and conductivity, more comprehensive and accurate data on the concentration of sodium hydroxide can be obtained.

[0055] To achieve accurate calculation of the concentration of sodium hydroxide, first, simulated lye samples with different impurity contents need to be prepared through experiments. In the experiment, the density, conductivity, and actual sodium hydroxide concentration of each sample are determined. Through these data, a relationship between density, conductivity, and actual sodium hydroxide concentration is established. This process requires the use of multiple lye samples containing impurities to ensure the universality and accuracy of the model. Then, using multivariate regression analysis, the data are fitted to establish a compensation equation, thereby eliminating the influence of impurities on the measurement results.

[0056] The compensation equation effectively adjusts the calculation results of the concentration of sodium hydroxide by considering the influence of impurities, ensuring its accuracy. By inputting the real-time acquired density and conductivity data, the pre-established calculation model can be used to calculate the concentration of sodium hydroxide in the lye in real time and accurately.

[0057] Through the combined detection of density and conductivity, both physical properties can be used to monitor the concentration of sodium hydroxide, which has higher accuracy and reliability compared to traditional single methods. Especially when the lye contains different types of impurities, a single density or conductivity may not accurately reflect the true concentration of sodium hydroxide, but by establishing a multivariate regression analysis model and using a compensation equation, the error caused by impurities can be effectively eliminated, ensuring the accuracy of the concentration calculation.

[0058] This method is suitable for various complex component lyes and can be used for real-time monitoring in actual production processes, reducing human intervention and errors and improving the automation and control accuracy of the production process. In addition, real-time acquisition of sodium hydroxide concentration data can provide a basis for the recycling of lye, optimize the use efficiency of lye, reduce resource waste, and improve the economic efficiency and environmental sustainability of production.

[0059] In one possible implementation, during the initial deacetylation process, the swelling of chitosan is a critical step, and the rate of swelling can affect the efficiency of acetyl group removal. To ensure that the swelling rate is within the set range, it is necessary to determine the appropriate alkali concentration through chitin swelling kinetics experiments. The swelling kinetics experiment can find a minimum alkali concentration value by observing the swelling rate of chitosan in alkali solution under different alkali concentrations, so that chitosan can be fully swollen, and the swelling rate can be maintained within the predetermined range at this concentration. This minimum alkali concentration will be used as the target concentration of alkali supplementation for the initial deacetylation, thereby ensuring the smooth progress of the reaction.

[0060] The speed of the middle-stage deacetylation reaction is affected by the reaction activation energy, and maintaining a constant reaction rate is the key to improving yield and product quality. According to the activation energy model of deacetylation reaction, the alkali concentration compensation value required to maintain a stable reaction rate under different reaction conditions is calculated. The core of this method is to understand the energy change of the deacetylation reaction, and calculate how to adjust the alkali concentration when the external conditions change during the middle-stage process, to ensure that the reaction rate is maintained at a constant level, thereby avoiding the loss of efficiency caused by too fast or too slow reaction.

[0061] The initial deacetylation process can ensure the full swelling of chitosan by setting the alkali concentration based on chitin swelling kinetics, which helps to improve the removal efficiency of acetyl groups and thus improve the effectiveness of subsequent reactions. Secondly, the middle-stage deacetylation process can effectively maintain a constant reaction rate by considering the reaction activation energy model for alkali concentration compensation, avoiding fluctuations in the reaction process, ensuring the stability and controllability of the entire reaction process, and thus improving the quality and consistency of the final product. Through such fine control, the efficiency of alkali use is improved, and the waste of resources and abnormal reactions caused by excessive or insufficient use of alkali are avoided, thereby optimizing the production process, improving economic efficiency and environmental friendliness.

[0062] In one possible implementation, the temperature in the reaction kettle needs to be monitored in real time throughout the reaction process. The temperature sensor continuously acquires temperature data inside the reaction kettle and draws a temperature change curve. Through continuous temperature monitoring, the temperature rise, fluctuations and eventual stabilization process can be clearly seen. Real-time data helps to identify possible temperature peaks in the reaction process in a timely manner, providing accurate basis for subsequent operations.

[0063] During the temperature change process, when the temperature rise rate gradually slows down and falls below the set rate threshold, it can be considered that the reaction process has approached the peak of thermal reaction. The setting of the rate threshold is determined by analyzing the exothermic curve of the reaction. The exothermic curve can reveal the change of heat release in the reaction, and usually at the inflection point of the reaction, the rate of heat release will change significantly, which is also a sign of the slowing down of the temperature rise rate. Therefore, by setting the rate threshold at the inflection point of the exothermic curve, it helps to accurately capture the key nodes of temperature change.

[0064] When the temperature rise rate falls below the set threshold, further confirmation of the stability of temperature fluctuation is also needed. By setting a tolerance value of temperature fluctuation range, if the temperature fluctuation is small within the tolerance range, it means that the temperature has stabilized and the reaction is close to completion, at which time the appearance of the temperature peak can be judged.

[0065] This method can accurately identify the temperature peak and further infer the progress state of the reaction. By monitoring the temperature change in real time and combining the set temperature rise rate threshold and fluctuation tolerance value, the key temperature change nodes in the reaction can be accurately captured, avoiding reaction control errors caused by human factors or monitoring delays. The way of setting the temperature rise rate threshold and the temperature fluctuation tolerance value helps to ensure that the temperature control in the reaction process is within a reasonable range, preventing adverse effects on reaction rate and product quality due to excessively high or low temperature.

[0066] At the same time, the determination of the rate threshold through the inflection point analysis of the exothermic curve makes this method more scientific and accurate. This method helps to improve the controllability of the entire reaction process, reduces production fluctuations or substandard products caused by unstable temperature, ultimately improves production efficiency, product quality, and effectively saves energy and raw materials, reduces production cost.

[0067] In one possible implementation, during the reaction process, a redox potential sensor is used to monitor the concentration of free radicals in the regenerated lye in real time. The concentration of free radicals is a key indicator of active substances in the reaction, which directly affects the reaction rate and efficiency. By monitoring the concentration changes of these free radicals in real time, the activity information of the lye can be obtained. There is a certain relationship between the redox potential and the concentration of free radicals, which helps to judge the activity level of the lye.

[0068] According to the relationship between the redox potential and the concentration of free radicals, a reverse relationship model is further established to describe the changes between the potential value and the activity coefficient of the lye. This model provides a basis for dynamically calculating the activity coefficient of the lye, and through the monitoring of the potential value, the activity of the lye can be evaluated in real time, and then the proportion suitable for reuse is determined.

[0069] In each reaction cycle, the maximum recyclable proportion is calculated based on the ratio of the monitored lye activity coefficient to the activity coefficient of fresh lye. This proportion is dynamically adjusted, taking into account the activity changes of the lye during the reaction process, thereby ensuring that the recycled lye can maximize the use of fresh lye and improve resource utilization efficiency under the premise of meeting the reaction requirements.

[0070] When the reaction system temperature exceeds the set temperature, the reaction rate will accelerate, and the activity of the lye may also increase. At this time, the upper limit of the recycling proportion can be appropriately increased according to the preset proportion coefficient to ensure that the recycled lye can maintain sufficient activity when the temperature rises, thereby ensuring the stable progress of the reaction process.

[0071] Through real-time monitoring and dynamic adjustment, the recycling proportion of regenerated lye can be accurately controlled, thereby maximizing resource utilization. By monitoring the free radical concentration through a redox potential sensor and evaluating the activity of the lye based on the inverse relationship between the potential value and the lye activity coefficient, the determination of the recycling proportion becomes more scientific and accurate. This dynamic adjustment can effectively avoid the negative impact of insufficient lye activity on the reaction effect, while reducing the consumption of fresh lye and lowering production costs.

[0072] In addition, by timely increasing the upper limit of the recycling proportion under high-temperature reaction conditions, the method can better adapt to changes in reaction conditions, ensuring the stability and efficiency of the reaction process when the temperature rises, and further improving the economic and environmental performance of the overall production process. Therefore, this method not only improves the efficiency and stability of the reaction, but also plays a positive role in reducing resource consumption and environmental burden.

[0073] In one possible implementation, during the production process of multiple batches, the viscosity change of the lye after each cycle needs to be recorded. Specifically, the viscosity change after each cycle is monitored, and when a significant mutation occurs, the point is recorded as the "mutation point". The average value of the cycle number before the viscosity mutation is calculated. This step is based on a large amount of production data to ensure that the selected cycle number accurately reflects the use of lye in the reaction process.

[0074] To ensure the stability of the production process, a safety margin is set. The safety margin is a reserved value set considering the possible fluctuations in the production process, and its purpose is to avoid premature or late activation of deep processing due to accidental factors. Therefore, the safety margin is deducted from the average cycle number obtained by statistics to ensure that deep processing will not be prematurely or late activated due to external interference.

[0075] A reasonable cycle threshold is determined by the above method, when the cycle number of lye reaches the threshold, the system will automatically trigger the deep treatment operation. The setting of this condition not only considers the viscosity change in actual production, but also ensures the stability of the treatment through the setting of safety margin. By accurately setting the threshold of the cycle number of lye, the reduction of reaction efficiency caused by the decline of lye quality is effectively avoided. By counting the average cycle number before viscosity mutation in multiple batches of production, it can ensure that the starting time of deep treatment is just right, thereby maximizing the service life of lye. The method of deducting safety margin can ensure that unexpected factors are dealt with during production, ensure that deep treatment will not start early or late due to external factors, and thus ensure the stability of production.

[0076] In addition, setting the cycle threshold based on actual data makes the method highly practical and adaptable. It can be flexibly adjusted according to the production conditions of different batches, avoiding excessive or insufficient deep treatment, thereby maximizing resource utilization, reducing production cost, and improving the efficiency and product quality of chitosan preparation.

[0077] The present application encompasses any alternative, modification, equivalent method and scheme made on the essence and scope of the present application. In order to make the public have a thorough understanding of the present application, specific details are described in the following preferred embodiments of the present application, and the present application can also be fully understood without the description of these details to those skilled in the art. In addition, in order to avoid unnecessary confusion to the essence of the present application, well-known methods, processes, procedures, elements and circuits, etc. are not described in detail.

[0078] The above is only the preferred embodiment of the present application, it should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can also be made, these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for recycling alkali solution for chitosan preparation, characterized in that: The following steps are involved: Step 1: Online monitoring and diversion of alkali solution status: The dynamic viscosity, conductivity and turbidity values ​​of the alkali liquor after the deacetylation reaction are collected in real time, and the alkali liquor is diverted to the primary or deep treatment channel according to the preset viscosity-turbidity correlation threshold; Step 2: Multi-stage separation and impurity removal: The alkali liquor is passed through the solid residue interception device, the colloid adsorption device and the nano-protein capture device in sequence, and the alkali liquor in the deep treatment channel is additionally separated from the dissolved organic matter; Step 3: Dynamic regulation of ion composition: The flow rate is adjusted based on the rate of change of the conductivity value at the inlet of the ion exchange resin column, and the resin regeneration is triggered when the outlet pH value reaches the regeneration critical point; Step 4: Alkali activity compensation: Dynamic alkali replenishment based on the effective alkali concentration of the regenerated alkali solution and the target reuse process section demand; Step 5: Timing control reuse: Fresh alkali solution is injected when the initial deacetylation reaction starts, and regenerated alkali solution is pumped in proportion when the middle reaction reaches the temperature peak.

2. The method for recycling alkali solution for preparing chitosan according to claim 1, wherein: The process of determining the viscosity-turbidity correlation threshold in step 1 includes: A negative correlation model between alkali solution viscosity and mass transfer efficiency of deacetylation reaction was established through orthogonal test, and the viscosity value when the mass transfer efficiency dropped to a set percentage was used as the viscosity threshold. The linear relationship between colloid concentration and turbidity in historical circulating alkali solution was analyzed, and the turbidity value corresponding to the critical value of viscosity sudden change of colloid concentration was taken as the turbidity threshold; The viscosity threshold and the turbidity threshold are associated to form a two-dimensional decision matrix, and the deep processing channel is initiated when the real-time data point is located in the high-risk area of ​​the matrix.

3. The method for recycling alkali solution for chitosan preparation according to claim 1, wherein: The operation of separating the dissolved organic matter in step 2 includes: The alkali solution is passed through a tubular ceramic membrane device and molecular weight fractionation is achieved by driving the transmembrane pressure; The method for setting the transmembrane pressure is: within the membrane pressure limit, select the minimum pressure value that makes the target organic matter rejection rate reach the set percentage; When the membrane flux decays to a set ratio of the initial value, reverse pulse cleaning is started, and the pulse frequency is dynamically adjusted according to the flux decay rate.

4. The method for recycling alkali solution for preparing chitosan according to claim 1, wherein: The method of adjusting the flow rate based on the rate of change of the conductivity value at the inlet of the ion exchange resin column in step 3 includes: Establish a mapping relationship between the conductivity decrease rate and the resin adsorption efficiency: when the rate exceeds the first set rate, it indicates that the resin is not saturated, and the flow rate is increased to avoid equipment overload; when the rate is lower than the second set rate, it indicates that the resin is nearly saturated, and the flow rate is reduced to extend the contact time; The method for determining the set rate is: obtaining the critical conductivity change rate value when the adsorption efficiency suddenly drops through a resin column penetration experiment.

5. The method for recycling alkali solution for preparing chitosan according to claim 1, wherein: The determination of the regeneration critical point in step 3 includes: The pH value drop per unit time at the resin column outlet is calculated in real time. When the drop in three consecutive sampling cycles exceeds the set drop, it is determined to be a critical point. The method for determining the set drop amount is: measuring the resin adsorption capacity decay curve by titration, and taking the pH change rate when the adsorption capacity drops to the set percentage as a benchmark.

6. The method for recycling and reusing alkali solution for preparing chitosan according to claim 1, characterized in that: The acquisition of the effective alkali concentration in step 4 includes: The density-conductivity combined detection method is used: the alkali solution density value is obtained by an online density meter, combined with the conductivity sensor data, and input into the pre-established sodium hydroxide concentration calculation model; The calculation model is constructed by preparing simulated alkali solution samples with different impurity contents, measuring the corresponding relationship between the density and conductivity of the simulated alkali solution samples and the actual sodium hydroxide concentration, and establishing a compensation equation through multiple regression analysis.

7. The method for recycling and reusing alkali solution for preparing chitosan according to claim 1, characterized in that: The dynamic alkali replenishment according to the effective alkali concentration of the regenerated alkali solution and the target reuse process section demand in step 4 includes alkali concentration control, specifically: Method for setting the target concentration of alkali supplementation for the initial deacetylation: Based on chitin swelling kinetics experiments, determine the minimum alkali concentration required to make the swelling rate reach the set range; Method for setting target concentration of alkali supplement for mid-stage deacetylation: Based on the activation energy model of the deacetylation reaction, calculate the alkali concentration compensation value required to maintain a constant reaction rate.

8. The method for recycling alkali solution for chitosan preparation according to claim 1, wherein: The identification of the temperature peak in step 5 includes: Monitor the temperature change curve of the reactor in real time and determine the peak value when the following conditions are met at the same time: (a) The temperature rise rate drops below the set rate threshold; (b) The temperature fluctuation range is less than the set tolerance value; The rate threshold is determined by inflection point analysis of the reaction exotherm curve.

9. The method for recycling and reusing alkali solution for preparing chitosan according to claim 1, characterized in that: The determination of the reuse ratio of the regenerated alkali solution in step 5 includes: The free radical concentration of the regenerated alkali solution was monitored by an oxidation-reduction potential sensor, and an inverse relationship model between the potential value and the activity coefficient of the alkali solution was established. The maximum reusable ratio is dynamically calculated based on the ratio of real-time activity coefficient to fresh alkali solution; When the temperature of the reaction system exceeds the set temperature, the upper limit of the reuse ratio is increased according to the proportional coefficient.

10. The method for recycling and reusing alkali solution for preparing chitosan according to claim 2, characterized in that: The starting conditions of the deep processing channel also include: When the number of alkali solution cycles reaches the set threshold, deep treatment is forced to start; The method for determining the number threshold is: counting the average number of cycles before the viscosity mutation in multiple batches of production, and rounding it up after deducting the safety margin.

Images