Production system and method of an epoxy chloropropane modified wet strength agent

Abstract

The application discloses a production system and method of an epoxy chloropropane modified wet strength agent, and belongs to the technical field of biomass conversion. Corn stalks are used as biomass raw materials, components are separated through eutectic solvent pretreatment, bio-based monomers are prepared through enzymatic saccharification and directional fermentation of cellulose components, and bio-based polyester PEFF particles are obtained through melt polycondensation. Then, diethylenetriamine and bio-based adipic acid are used to prepare a polyamide polyamine prepolymer, and the polyamide polyamine prepolymer and the PEFF particles are used to prepare a PAA-co-PEFF composite prepolymer aqueous solution through ester-amide exchange reaction. Then, the composite prepolymer and pretreated epoxy chloropropane are used to perform controllable crosslinking reaction, and after thin film evaporation and deep dechlorination through a double-tower series fixed bed adsorption tower, the product is finally obtained through oxidation coupling and graft modification with tannin extract, pH adjustment, dilution and filtration.

Description

Technical Field

[0001] This invention relates to the field of biomass conversion technology, specifically to a production system and method for an epichlorohydrin-modified wet strength agent. Background Technology

[0002] Papermaking wet strength agents are core additives for improving the wet physical properties of paper products. Epichlorohydrin-modified polyamide polyamine wet strength agents are widely used, but existing technologies still have many shortcomings. Traditional products rely heavily on petroleum-based monomers as raw materials, resulting in high fossil resource consumption and a high carbon footprint, which is inconsistent with the concept of low-carbon development. The cross-linking reaction in production has poor controllability, easily generating organochlorine byproducts such as 1,3-dichloropropanol, leading to significant chlorine residue exceeding standards and failing to meet the safety requirements of high-end environmentally friendly paper products. Meanwhile, existing dechlorination processes only perform simple impurity removal, with poor deep removal effects, low automation levels, and large fluctuations in process parameters, resulting in poor batch stability. Furthermore, traditional production methods have low solvent and wastewater recycling rates, leading to significant resource waste and environmental pollution. The finished products generally suffer from difficulties in achieving a balance between wet strength and paper softness, as well as poor storage stability. Therefore, there is an urgent need to develop green, high-performance, and process-controllable new epichlorohydrin-modified wet strength agents and their production processes. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention proposes a method for producing an epichlorohydrin-modified wet-strength agent, comprising:

[0004] Step 1: Pre-treated corn stalks are pre-treated with a low-melting solvent to separate cellulose, hemicellulose, and lignin. The extracted cellulose components are purified by enzymatic hydrolysis, saccharification, and directional fermentation to obtain bio-based ethylene glycol and bio-based adipic acid. Bio-based furanyl dicarboxylic acid and bio-based ethylene glycol are subjected to melt polycondensation reaction under an inert atmosphere and catalytic conditions. After end-capping, granulation, and drying, bio-based polyester PEFF particles are obtained.

[0005] Step 2: Diethylenetriamine and bio-based adipic acid are prepolymerized under amidation catalysis to obtain polyamide polyamine prepolymer. The polyamide polyamine prepolymer is then subjected to ester-amide exchange reaction with preheated bio-based polyester PEFF particles. After removing small molecule byproducts and diluting stepwise, an aqueous solution of PAA-co-PEFF composite prepolymer with a solid content of 50%±1% is obtained.

[0006] Step 3: After diluting and preheating the aqueous solution of PAA-co-PEFF composite prepolymer, it is cross-linked with pretreated epichlorohydrin. After the cross-linking reaction is completed, the volatile chlorinated byproducts are removed by thin-film evaporation and the organic chlorine impurities are removed by a dual-tower series fixed-bed adsorption tower to obtain a dechlorinated and purified resin solution.

[0007] Step 4: Add tannic acid extract to the dechlorinated and purified resin solution to carry out oxidative coupling and grafting functionalization modification reaction. After the reaction is completed, adjust the pH of the system and dilute to the target solid content. After filtration, the epichlorohydrin modified wet strength agent product is obtained.

[0008] Further, in step 1, the molar ratio of bio-based furanyl dicarboxylic acid to bio-based ethylene glycol is 1:1.05, the catalyst for melt polycondensation is tetraisopropyl titanate, and the polycondensation conditions are 220-240℃ and -0.095MPa. When the intrinsic viscosity of the polyester reaches 1.60±0.05dL / g and the terminal carboxyl group content is ≤45eq / t, 0.05-0.1wt% of 1-ethyl-(3-dimethylaminopropyl)carbodiimide end-capping agent is added to terminate the reaction.

[0009] Further, in step 2, the molar ratio of amino groups to carboxyl groups in diethylenetriamine and bio-based adipic acid is 1.05:1, the amidation catalyst is p-toluenesulfonic acid, and the prepolymerization reaction conditions are 180-190℃ and material residence time of 2h, until the acid value of the system drops to 35-40mgKOH / g to obtain polyamide polyamine prepolymer; the preheating temperature of bio-based polyester PEFF particles is 150℃, and the addition amount is 8% of the dry basis mass of polyamide polyamine prepolymer; the ester-amide exchange reaction is carried out at a high shear rate of 3000-5000rpm, followed by removal of small molecule water at 190℃ and -0.09MPa, until the acid value of the system stabilizes at 24-26mgKOH / g and the dynamic viscosity at 25℃ reaches 600-700mPa·s.

[0010] Further, in step 3, the PAA-co-PEFF composite prepolymer aqueous solution is diluted with deionized water to a solid content of 30% and preheated to 50°C; the epichlorohydrin is pretreated by a precision distillation column and a 4A molecular sieve adsorption column until the total content of 1,3-dichloropropanol and 3-chloro-1,2-propanediol in the raw material is <0.1ppm; the molar ratio of epichlorohydrin to the total amine groups of the composite prepolymer is 1.1:1, and it is added dropwise at a uniform rate for 2 hours using a high-precision metering pump; the crosslinking reaction conditions are 65°C±1°C and stirring at 200-300 rpm until the system viscosity rises to 12.5 mPa·s and the epoxy group conversion rate is ≥99%.

[0011] Furthermore, the conditions for thin-film evaporation were -0.08 MPa and 60 °C; the packing material of the dual-tower series fixed-bed adsorption tower was a composite packing material of quaternary ammonium-type strong-base macroporous anion exchange resin and hydrophobic macroporous adsorption resin, with a material space velocity of 1.0 h⁻¹. -1 The total content of 1,3-dichloropropanol and 3-chloro-1,2-propanediol in the final dechlorination and purification resin solution was less than 1 ppm.

[0012] Furthermore, in step 3, when the viscosity of the crosslinking reaction system rises to 12.0 mPa·s, the epichlorohydrin dropping acceleration rate decreases by 50%; when the system viscosity reaches 12.5 mPa·s and the conductivity fluctuation is < ±0.5 μS / cm, it is determined to be the end point of the crosslinking reaction; a three-level warning threshold of 0.5 ppm / 0.8 ppm / 0.9 ppm is set for the content of 1,3-dichloropropanol and 3-chloro-1,2-propanediol in the dechlorination unit output. When the content reaches 0.8 ppm, it automatically switches to the standby adsorption bed and issues a regeneration reminder to the saturated bed.

[0013] Further, in step 4, the amount of tannic acid extract added is 3.5% of the resin solid mass in the dechlorination and purification resin solution. The functionalization modification reaction conditions are 55℃, pH 6.5, constant temperature stirring for 45 min, and the dissolved oxygen content of the system is controlled at 1-2 mg / L. The pH of the system is adjusted to 4.0-4.5 with 10% by mass dilute hydrochloric acid, and deionized water is added to dilute to a product solid content of 16.0% ± 0.5%.

[0014] This invention also proposes a production system for epichlorohydrin-modified wet strength agents, used to realize the above-mentioned production method of epichlorohydrin-modified wet strength agents, comprising:

[0015] The modules are sequentially connected: biomass refining and bio-based polyester synthesis, polyamide polyamine synthesis and polyester composite, epichlorohydrin controllable crosslinking and deep dechlorination purification, and polyphenol functionalization modification and finished product formulation.

[0016] The biomass refining and bio-based polyester synthesis module is used to efficiently separate multiple components of biomass from corn stalks and to continuously synthesize bio-based polyester PEFF particles using biomass-based monomers as raw materials.

[0017] The polyamide polyamine synthesis and polyester composite module is used to synthesize polyamide polyamine prepolymer and to perform an ester-amide exchange reaction with bio-based polyester PEFF particles to obtain an aqueous solution of PAA-co-PEFF composite prepolymer.

[0018] The epichlorohydrin controlled crosslinking and deep dechlorination purification module is used to crosslink the composite prepolymer with epichlorohydrin and to perform deep dechlorination purification on the crosslinking product to remove chlorinated impurities.

[0019] The polyphenol functionalization modification and finished product formulation module is used to perform plant polyphenol functionalization graft modification on the dechlorinated and purified product to obtain the epichlorohydrin modified wet strength agent finished product.

[0020] Furthermore, the biomass refining and bio-based polyester synthesis module includes a biomass pretreatment subunit, a bio-based raw material fermentation and refining subunit, and a continuous flow polycondensation subunit connected in sequence.

[0021] The biomass pretreatment subunit is used to crush and remove impurities from corn stalks and pretreat them with a low-eutectic solvent to achieve efficient dissociation and separation of cellulose, hemicellulose, and lignin, resulting in high-purity cellulose components. The bio-based raw material fermentation and refining subunit is used to receive the pretreated cellulose components and convert them into crude bio-based ethylene glycol, adipic acid, and furanyl dicarboxylic acid through enzymatic hydrolysis, saccharification, and directional fermentation. These are then refined by distillation to obtain high-purity bio-based monomers that meet the polycondensation process parameters. The continuous flow polycondensation subunit is used to carry out melt polycondensation reaction using the refined bio-based monomers as raw materials under catalytic and inert protection process conditions. After end-capping, granulation, and drying, bio-based polyester particles are obtained.

[0022] Furthermore, the epichlorohydrin controllable crosslinking and deep dechlorination purification module includes a crosslinking reaction subunit, an integrated dechlorination subunit, and a resin regeneration auxiliary subunit. The crosslinking reaction subunit is used to dilute and preheat the PAA-co-PEFF composite prepolymer aqueous solution, and then react it with pretreated epichlorohydrin to obtain a crude crosslinked modified wet strength agent. The integrated dechlorination subunit is used to perform deep dechlorination purification on the crude product after the crosslinking reaction, first removing excess unreacted epichlorohydrin and volatile chlorinated byproducts, and then removing residual organic chlorine impurities through adsorption resin. The resin regeneration auxiliary subunit is used to desorb and activate the adsorption resin saturated in the integrated dechlorination subunit to restore the resin adsorption performance.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects:

[0024] By precisely limiting the molar ratio of epichlorohydrin to the composite prepolymer and dynamically controlling the dropping rate, combined with real-time monitoring of viscosity and conductivity to determine the reaction endpoint, the conversion rate of epoxy groups is ≥99%, minimizing the hydrolysis and chlorination side reactions of unreacted epoxy groups and reducing the generation of chlorinated impurities from the source.

[0025] A combined process of thin-film evaporation to remove volatile chlorinated byproducts and dual-tower series fixed-bed adsorption towers to deeply remove residual organic chlorine is adopted, along with a three-level early warning threshold, to achieve precise removal of organic chlorine impurities. The adsorption towers are operated in a one-in-one-out-of-service mode to ensure continuous production.

[0026] The temperature, pressure, catalyst dosage, and material ratio of core reactions such as melt polycondensation, amidation prepolymerization, and ester-amide exchange are precisely quantified and limited to ensure that the product has a uniform structure and stable performance. The intrinsic viscosity of PEFF polyester, the acid value and viscosity of the composite prepolymer are all controlled within the optimal range, improving the quality of intermediates and ensuring the efficiency of subsequent reactions.

[0027] Equipped with a digital twin intelligent control module, combined with an LSTM neural network, it collects key parameters such as temperature, pressure, viscosity, acid value, and epoxy group conversion rate of each process unit in real time, dynamically predicts the reaction endpoint, adjusts the material droplet acceleration rate and stirring rate, automatically corrects process parameter deviations, and eliminates human operation errors. Attached Figure Description

[0028] Figure 1 This is a flowchart of the controllable crosslinking reaction of the present invention;

[0029] Figure 2 This is a flowchart of the functionalization modification reaction and regulation process of the present invention;

[0030] Figure 3 The graph shows the effect of the amount of PAE added in this invention on the dry and wet tensile strength of paper. Detailed Implementation

[0031] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0032] Example 1

[0033] Epichlorohydrin modified wet strength agent production method

[0034] 1. Raw material preparation and specification limitations

[0035] All raw materials used in this embodiment are commercially available compliant industrial products or self-made refined raw materials, and all indicators are strictly controlled. The specific specifications are as follows:

[0036] 1.1 Bio-based raw materials

[0037] The lignocellulose biomass is made from corn stalks, with a cellulose content of no less than 40% after testing. After pretreatment, it is pulverized to 20-60 mesh to remove impurities and sand before use. The bio-based dicarboxylic acid is prepared using adipic acid via bio-fermentation, with a purity of no less than 99.5%, nitrogen impurities less than 10 ppm, and sulfur impurities less than 5 ppm. The bio-based diols and aromatic acids are bio-based ethylene glycol with a purity of no less than 99.8% and bio-based furanyldicarboxylic acid with a purity of no less than 99.0%. The plant polyphenols are tannins extracted from gallnut, with a polyphenol content of no less than 90%, no obvious mechanical impurities, and satisfactory water solubility. Preferably, gallnut powder is extracted with deionized water at 70°C for 2 hours at a material-to-liquid ratio of 1:15, filtered, and concentrated to a polyphenol concentration of 200 g / L. Water solubility is tested according to GB / T20808-2021 and meets the standards.

[0038] 1.2 Synthesis and Modification Reagents

[0039] The amine monomer is diethylenetriamine, chemically pure, with a purity of not less than 99.0%. The crosslinking agent is epichlorohydrin, an industrial-grade premium product with a purity of not less than 99.0% and no obvious free chlorine impurities. The catalysts include tetraisopropyl titanate, a titanium-based catalyst for esterification, and p-toluenesulfonic acid, an amidation catalyst, both of which are analytical grade. The pH adjuster and solvent are 10% by mass dilute hydrochloric acid solution, and the deionized water conductivity is not higher than 5 μS per centimeter, meeting the process dilution and cleaning requirements.

[0040] 2. Production process steps

[0041] 2.1 Biomass refining and continuous flow synthesis of bio-based polyester

[0042] Pretreated corn stalks were placed in a eutectic solvent (DES) pretreatment vessel and treated at a constant temperature of 120°C for 2 hours using a choline chloride and lactic acid composite DES system to achieve efficient separation of cellulose, hemicellulose, and lignin. The cellulose component was then purified by enzymatic hydrolysis, saccharification, and directional fermentation to obtain bio-based ethylene glycol and bio-based adipic acid. The lignin component was recovered for use as by-product energy supply or as a subsequent modified auxiliary material.

[0043] Preferably, 2% (by mass) of a compound cellulase is added to the cellulose component, with a cellulase:xylanase ratio of 3:1, and enzymatic hydrolysis is performed at 50°C and pH 4.8 for 48 hours. Directed fermentation uses ethylene glycol-producing engineered bacteria, and fermentation is carried out at 37°C and 20% dissolved oxygen for 72 hours. Preferably, directed fermentation uses *Escherichia coli* engineered bacteria.

[0044] Preferably, the molar ratio of choline chloride to lactic acid is 1:2-1:4, and the total amount of solvent added is 8-10 times the mass of corn stalks;

[0045] Bio-based furanyl dicarboxylic acid and bio-based ethylene glycol were accurately weighed at a molar ratio of 1:1.05 and added to a continuous flow tubular reactor system. Tetraisopropyl titanate (0.03 wt%) was added as an esterification catalyst. High-purity nitrogen (≥99.99% purity, until the oxygen content in the reactor was <0.5%) was introduced into the reactor to replace the air, creating an inert protective atmosphere. The temperature was raised to 220-240℃, and a vacuum was applied to -0.095 MPa to initiate the melt polycondensation reaction. The reaction process was monitored in real time using an online infrared spectrometer and a Brookfield viscometer. When the intrinsic viscosity of the polyester reached 1.60±0.05 dL / g and the terminal carboxyl group content was ≤45 eq / t, a trace amount of carbodiimide end-capping agent was immediately injected to terminate the polycondensation reaction. The material was then granulated using an underwater pelletizer to obtain high-purity bio-based polyester (PEFF) granules, which were sealed and kept moisture-proof for later use. PEFF polyester granules drying conditions: vacuum drying at 60℃ (-0.08MPa) until the moisture content is ≤0.1wt%, then sealed in a desiccator for later use.

[0046] Preferably, the carbodiimide end-capping agent is 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC), and the addition amount is 0.05-0.1 wt% of the total mass of the polyester system;

[0047] 2.2 Synthesis of Polyamide Polyamines and Continuous Preparation of Polyester Composites

[0048] Polyamide polyamine (PAA) was synthesized using a series continuous stirred tank reactor (CSTR). Diethylenetriamine and bio-based adipic acid were pumped into the first-stage reactor at a uniform rate according to an amino to carboxyl molar ratio of 1.05:1. 0.5 wt% of p-toluenesulfonic acid was added as an amidation catalyst. The temperature of the first-stage reactor was controlled at 180-190℃, and the material residence time was precisely controlled at 2 hours. An online acid value detector tracked the acid value change in real time. When the acid value dropped to 35-40 mgKOH / g, the polyamide polyamine prepolymer was obtained.

[0049] The prepolymer and preheated (150°C) bio-based polyester particles (8% of the prepolymer's dry weight) were simultaneously pumped into the second-stage high-shear mixing reactor. The temperature was raised to 210°C, and an ester-amide exchange reaction was carried out at a high shear rate for 30 minutes. Then, the reactor was switched to thin-film evaporation mode, with the temperature controlled at 190°C and the vacuum at -0.09 MPa, to remove the small-molecule water generated during the reaction until the acid value of the system stabilized at 24-26 mg KOH / g and the dynamic viscosity at 25°C reached 600-700 mPa·s. The reaction was stopped, and deionized water was added for stepwise dilution to obtain a PAA-co-PEFF composite prepolymer aqueous solution with a solid content of 50% ± 1%, which was then transferred to a buffer tank for later use. Preferably, the high-shear mixing reactor has a shear rate of 3000-5000 rpm, and the agitator is a three-bladed dispersing impeller.

[0050] It should be noted that PAA-co-PEFF composite prepolymer refers to a copolymer-type composite prepolymer formed by polyamide polyamine (PAA) and bio-based polyester PEFF through an ester-amide exchange reaction. Here, co- represents the composite method of block copolymerization, that is, PEFF polyester segments are grafted onto the PAA molecular backbone through ester-amide bonds to form a block copolymer structure that combines the crosslinking activity of polyamide polyamine with the flexible segments of polyester.

[0051] 2.3 Controlled crosslinking and deep dechlorination purification of epichlorohydrin

[0052] The aqueous solution of the composite prepolymer was diluted with deionized water to a solid content of 30%, preheated to 50°C, and then transferred to a precision temperature-controlled continuous stirred tank or microchannel reactor. At the same time, the epichlorohydrin raw material was pretreated: the industrial premium grade ECH was treated by a precision distillation column (distillation accuracy 99.9%) and a 4A molecular sieve adsorption column to remove free chlorine and chlorohydrin impurities from the raw material, ensuring that the total content of 1,3-DCP and 3-MCPD in the raw material was <0.1ppm. After pretreatment, the ECH was temporarily stored in a heat-insulated metering tank. The pretreated epichlorohydrin was added dropwise at a uniform rate using a high-precision metering pump at a molar ratio of 1.1:1 to the total amino groups of the prepolymer. The dropwise addition time was strictly controlled to be 2 hours. After the dropwise addition was completed, the temperature was raised to 65℃±1℃ and a constant temperature was maintained to carry out the crosslinking reaction. The reaction process was monitored throughout using an online conductivity meter and viscosity sensor. If the rate of increase in epoxy group conversion was detected to be ±2%, the reaction temperature was immediately fine-tuned (±0.5℃) or a trace amount of deionized water was added through the AI ​​control system to suppress the excessive generation of chlorinated byproducts. When the viscosity of the system rose to about 12.5 mPa·s and the conductivity fluctuations tended to level off, the reaction endpoint was determined to have been reached. The total crosslinking reaction time was 5-6 hours, and the epoxy group conversion rate was tested to be ≥99%.

[0053] The process of controlled cross-linking reaction is as follows: Figure 1 As shown, preferably, the stirring rate for the epichlorohydrin dropwise addition and crosslinking reaction is 200-300 rpm, and an anchor-type stirring paddle is used.

[0054] After the cross-linking reaction is completed, the material is immediately fed into the integrated dechlorination and purification unit:

[0055] The first step involves processing the material in a thin-film evaporator, with the vacuum level controlled at -0.08 MPa and the temperature at 60°C, to gently remove excess unreacted epichlorohydrin and volatile chlorinated byproducts such as chloropropanol.

[0056] In the second step, the material is transported at an air velocity of 1.0 h. -1 A fixed-bed adsorption tower (dual-tower series process) filled with a composite packing of quaternary ammonium strong-base macroporous anion exchange resin (D201-FC) and hydrophobic macroporous adsorption resin (XAD-4) is used for deep dechlorination treatment to accurately remove residual organic chlorine impurities. The resin combination has a saturation adsorption capacity of ≥80 mg / g for chlorinated alcohols, and a single continuous operation regeneration cycle of 72 h, or 80 m³ / day for each treatment. 3 The regeneration process is started immediately after the liquid is applied, and the total content of 1,3-DCP and 3-MCPD in the final product is less than 1 ppm, which meets the safety requirements of high-end environmentally friendly papermaking wet strength agents.

[0057] 2.4 Functional modification of plant polyphenols and refined formulation of finished products

[0058] Add 3.5% (by weight of resin solids) of tannic acid extract to the dechlorinated and purified resin solution. Adjust the system temperature to 55℃ and pH to 6.5, and stir the reaction at a constant temperature for 45 minutes. Oxidative coupling is achieved by relying on trace dissolved oxygen in the system, and grafting is completed through hydrogen bonding. The dissolved oxygen content is controlled at 1-2 mg / L to further improve the wet strength performance and paper compatibility of the product.

[0059] like Figure 2 As shown, after functionalization modification, the pH of the system was precisely adjusted to 4.0-4.5 with 10% dilute hydrochloric acid, and deionized water was added for dilution and preparation to stabilize the solid content of the product at 16.0%±0.5%. The prepared solution was filtered through a 1μm precision filter to remove trace mechanical impurities and gel particles. After cooling to room temperature, the epichlorohydrin modified bio-based wet strength agent was obtained, sealed and packaged, and stored in the warehouse.

[0060] 3. Intelligent process control and green recycling guarantee

[0061] This embodiment is equipped with a full-process digital twin intelligent control system. Parameters such as temperature, pressure, material flow rate, online spectrum, viscosity, and acid value of key reactors are transmitted to the central control platform in real time. Using an LSTM neural network artificial intelligence model, combined with real-time data and historical best batch data, core parameters such as reaction endpoint and material droplet acceleration rate are dynamically predicted and controlled. Among them, when the system viscosity rises to 12.0 mPa·s, the epichlorohydrin droplet acceleration rate is reduced by 50%; when the viscosity reaches 12.5 mPa·s and the conductivity fluctuation is < ±0.5 μS / cm, the crosslinking reaction endpoint is determined.

[0062] Simultaneously, the impurity content of ECH raw material pretreatment, the epoxy group conversion rate of the cross-linking reaction, and the real-time detection values ​​of 1,3-DCP and 3-MCPD in the dechlorination unit are incorporated into the core control dimensions. Three-level early warning thresholds (0.5ppm / 0.8ppm / 0.9ppm) are set. When the chloro alcohol content in the effluent reaches 0.8ppm, the system automatically switches to the standby adsorption bed and issues a regeneration reminder to the saturated bed. When parameter deviations occur in the cross-linking reaction, the reaction conditions are automatically fine-tuned to suppress the generation of by-products, realizing fully automated, precise, and intelligent production, reducing human operation errors, and ensuring batch stability.

[0063] The process is equipped with a green recycling system. The solvent recovery rate of the eutectic solvent pretreatment unit is ≥95%, realizing recycling and reuse. The process wastewater is deeply treated by a combination of ultrafiltration, reverse osmosis and advanced oxidation processes, with a wastewater reuse rate of ≥90% and close to zero liquid discharge, which is in line with the green chemical industry's low-carbon and environmentally friendly concept.

[0064] Preferably, the model structure of the LSTM neural network is: 3 hidden layers, each with 64 neurons, the input layer activation function is ReLU, and the output layer is Sigmoid;

[0065] Input parameters: temperature, pressure, viscosity, acid value, material flow rate, epoxy group conversion rate; Output parameters: reaction endpoint determination, epichlorohydrin dropping rate, stirring speed;

[0066] Training dataset: 100 batches of industrial production data, data normalized, using Adam optimizer, loss function is mean squared error (MSE).

[0067] 4. Product performance test results

[0068] According to relevant testing standards for papermaking chemicals, the epichlorohydrin-modified wet strength agent prepared in this embodiment was subjected to full performance testing. The test results are as follows: all meet the preset indicators and are superior to traditional PAE wet strength agents. Figure 3 The figure shows the effect of PAE addition on the dry and wet tensile strength of paper. The horizontal axis represents the PAE addition amount (%), and the vertical axis on the left represents the dry tensile strength (kN·m). -1 The vertical axis represents the tensile strength of paper in its dry state; the vertical axis on the right represents the wet tensile strength (kN·m). -1 The figure represents the tensile strength of paper in a wet state. The black curve shows the trend of dry tensile strength with the amount of PAE added; the red curve shows the trend of wet tensile strength with the amount of PAE added.

[0069] 4.1 Basic Physical and Chemical Indicators

[0070] The solid content is 16.2%, the pH value at 25 degrees Celsius is 4.2, the dynamic viscosity at 25 degrees Celsius is 150 mPa·s, and the cationic charge density is 2.8 meq / g.

[0071] 4.2 Environmental Protection and Safety Indicators

[0072] It contains 58% bio-based carbon, and the total content of 1,3-DCP and 3-MCPD is 0.7 ppm. The acute oral toxicity median lethal dose is >5000 mg / kg, which is classified as a practically non-toxic product.

[0073] 4.3 Application Performance Indicators

[0074] Papermaking tests were conducted using softwood pulp. With a wet strength agent addition of 1.0% to oven-dry pulp, the test results showed that the paper's wet tensile strength retention rate was no less than 32%, which is 12% higher than that of traditional PAE wet strength agents. The paper's softness was significantly improved, the interfiber bonding force was enhanced, and the paper's feel and physical strength were both balanced. Accelerated storage tests at 40 degrees Celsius verified that the product showed no delamination, gelation, or deterioration within 6 months, demonstrating excellent storage stability.

[0075] Example 2

[0076] Epichlorohydrin modified wet strength agent production system

[0077] This embodiment discloses an epichlorohydrin modified wet strength agent production system, comprising: a biomass refining and bio-based polyester synthesis module, a polyamide polyamine synthesis and polyester composite module, an epichlorohydrin controllable crosslinking and deep dechlorination purification module, and a polyphenol functionalization modification and finished product formulation module connected in sequence.

[0078] 1. Biomass refining and bio-based polyester synthesis module

[0079] The biomass refining and bio-based polyester synthesis module is designed for the pretreatment of corn stalks for resource utilization, efficient separation of multiple components from biomass, and continuous synthesis of bio-based polyesters. Using agricultural waste like corn stalks as raw material, it replaces traditional petroleum-based polyester raw materials, achieving high-value utilization of biomass while reducing the carbon footprint of production. It includes: a biomass pretreatment subunit, a bio-based raw material fermentation and refining subunit, and a continuous flow polycondensation subunit. These subunits are connected by screw conveyors and insulated, sealed conveying pipelines, ensuring a completely closed system with no material leakage and continuous material flow, providing uninterrupted supply of raw materials for subsequent processes.

[0080] 1.1 Biomass Pretreatment Subunit

[0081] The biomass pretreatment subunit is used to crush and remove impurities from corn stalks and perform preliminary component separation, providing raw materials for subsequent bio-based raw material preparation and purification. Supporting equipment includes a crushing and screening machine, a eutectic solvent (DES) pretreatment vessel, and a centrifuge. These devices work together to achieve continuous pretreatment. The crushing and screening machine finely processes the corn stalks, crushing them to a particle size of 20-60 mesh, simultaneously removing impurities such as mud and weeds to ensure raw material purity. The DES pretreatment vessel is equipped with a high-precision constant temperature control system and a variable frequency stirring device, strictly maintaining a constant temperature of 120℃. It is adapted to the choline chloride / lactic acid DES pretreatment process, breaking down the dense structure of lignocellulose in the corn stalks to achieve efficient dissociation of cellulose, hemicellulose, and lignin. The centrifuge uses high-speed centrifugation to perform solid-liquid separation of the pretreated material, accurately separating high-purity cellulose components, which are then transported to the subsequent fermentation and refining unit. The separated lignin byproducts are transported to a supporting green recycling module for resource utilization.

[0082] 1.2 Bio-based raw material fermentation and refining subunit

[0083] The bio-based raw material fermentation and refining subunit receives pretreated high-purity cellulose components and refines them through bioconversion and distillation to prepare bio-based monomer raw materials that meet the requirements of the polycondensation process. The supporting equipment includes an enzymatic hydrolysis saccharification tank, a directional fermentation tank, and a refining distillation column. The cellulose components first enter the enzymatic hydrolysis saccharification tank, where they undergo saccharification and degradation under the action of a complex cellulase, transforming into a fermentable sugar solution. The sugar solution is then transported to the directional fermentation tank, where it undergoes directional fermentation with a specific strain of microorganisms, converting into crude bio-based ethylene glycol, adipic acid, and furanyl dicarboxylic acid. The crude raw materials are then purified by vacuum distillation in the refining distillation column to remove impurities and residual moisture, producing bio-based monomers with the required purity and physicochemical properties suitable for the polycondensation process. These monomers are then transported to a dedicated raw material storage tank for sealed storage.

[0084] 1.3 Continuous Flow Polymerization Subunit

[0085] The continuous flow polycondensation subunit uses refined bio-based monomers as raw materials to prepare PEFF polyester particles through continuous polycondensation reaction, providing a core substrate for subsequent composite modification. The supporting equipment includes a continuous flow tubular reactor, nitrogen protection device, vacuum unit, online monitoring components, and underwater pelletizer. The core reaction equipment is a continuous flow tubular reactor, preferably with a pipe diameter of 50mm and an aspect ratio of 200:1. It is equipped with a segmented heating and temperature control system to strictly maintain a reaction temperature of 220-240℃ and a vacuum condition of -0.095MPa. The material flow rate is controlled at 80-100mL / min to ensure that the polycondensation reaction is complete and stable. A nitrogen protection device continuously introduces high-purity nitrogen to isolate the raw materials from air and prevent oxidation and side reactions. The online monitoring component is equipped with an online infrared spectrometer and a Brookfield viscometer to monitor the reaction process and product viscosity in real time. The linkage with the automatic control valve group enables precise and quantitative addition of the end-capping agent to ensure uniform polyester molecular weight. The qualified polyester melt is quickly granulated and cooled by an underwater pelletizer to produce PEFF polyester granules with uniform particle size and stable performance.

[0086] 2. Polyamide polyamine synthesis and polyester composite module

[0087] The polyamide polyamine synthesis and polyester composite module takes over PEFF polyester particles to complete the synthesis of polyamide polyamine (PAA) prepolymer, the composite modification of polyester and polyamide polyamine, construct the molecular skeleton of wet strength agent, and improve the crosslinking activity and binding performance of the product. It includes: PAA synthesis subunit, high shear composite subunit, and thin film evaporation depolymerization subunit, and the subunits are connected in process sequence.

[0088] 2.1 PAA Synthesis Subunit

[0089] The PAA synthesis subunit employs a series-connected dual continuous stirred tank reactor (CSTR) for the continuous synthesis of polyamide polyamine prepolymers, equipped with high-precision metering pumps, an online acid value analyzer, and a constant temperature control system. The first-stage reactor is the core equipment for prepolymerization, with a precisely locked temperature range of 180-190℃. The high-precision metering pump simultaneously and quantitatively pumps diethylenetriamine, bio-based adipic acid, and p-toluenesulfonic acid catalyst into the reactor according to the set ratio. The prepolymerization reaction is completed under constant temperature stirring to generate PAA prepolymers. The online acid value analyzer monitors the changes in the acid value of the reaction system in real time, and adjusts the feed rate of the raw materials in conjunction with the metering pump to ensure that the prepolymer has a uniform structure and stable performance. The synthesized PAA prepolymers are directly transported to the high-shear composite subunit.

[0090] 2.2 High-shear composite subunit

[0091] The high-shear composite subunit achieves efficient composite of PEFF polyester and PAA prepolymer, completing the ester-amide exchange reaction and optimizing the product molecular structure. Supporting equipment includes a high-shear mixing reactor and a polyester preheating tank. PEFF polyester particles first enter the preheating tank and are preheated to a molten state of 150°C to avoid uneven reaction caused by low-temperature feeding. The molten polyester and PAA prepolymer are mixed according to a set mass ratio and simultaneously pumped into the high-shear mixing reactor via a metering pump. The reactor maintains a constant temperature of 210°C, and the high shear force enhances the mixing and reaction efficiency of the two phases, rapidly completing the ester-amide exchange reaction to generate a crude composite prepolymer, effectively improving the product's adhesion properties and wet strength stability.

[0092] 2.3 Thin-film evaporation demolecularization

[0093] The thin-film evaporation depolymerization unit is used to remove small-molecule byproducts generated during the composite reaction, improving the purity and reactivity of the composite prepolymer. The supporting equipment includes a thin-film evaporator, a vacuum unit, and a viscometer. The thin-film evaporator is controlled to maintain a temperature of 190℃ and a vacuum of -0.09MPa, utilizing the efficient mass transfer characteristics of thin-film evaporation to rapidly remove small-molecule water and other byproducts from the system. The viscometer monitors the discharge viscosity in real time to determine the removal effect. The composite prepolymer that meets the standards is temporarily stored in a dedicated buffer tank, providing a qualified intermediate for subsequent crosslinking modification processes and preventing small-molecule residues from affecting the efficiency of subsequent crosslinking reactions.

[0094] 3. Epichlorohydrin Controlled Crosslinking and Deep Dechlorination Purification Module

[0095] The epichlorohydrin controlled crosslinking and deep dechlorination purification module undertakes the controlled crosslinking reaction of epichlorohydrin using the composite prepolymer, simultaneously achieving deep dechlorination purification and strictly controlling the residual organochlorine in the product. It includes: a crosslinking reaction subunit, an integrated dechlorination subunit, and a resin regeneration auxiliary subunit.

[0096] 3.1 Crosslinking reaction subunit

[0097] The crosslinking reaction subunit enables controlled crosslinking of the composite prepolymer with epichlorohydrin, avoiding excessive crosslinking that leads to decreased product solubility and performance degradation. Supporting equipment includes a prepolymer dilution tank, a precision temperature-controlled reactor (microchannel reactor / dual-blade CSTR), a high-precision metering pump, and online monitoring components. The prepolymer dilution tank uses deionized water to adjust the composite prepolymer to a 30% solids content and simultaneously preheats it to 50°C to reduce system viscosity and facilitate uniform reaction. The precision temperature-controlled reactor precisely maintains a constant temperature of 65°C ± 1°C to eliminate the impact of temperature fluctuations on the crosslinking reaction. The high-precision metering pump controls the uniform droplet addition of epichlorohydrin for a controlled 2-hour duration, ensuring a mild and controllable crosslinking reaction. An online conductivity meter and viscosity sensor monitor the changes in conductivity and viscosity of the reaction system in real time, linking with the central control system to accurately determine the reaction endpoint and terminate the crosslinking reaction, yielding a crude crosslinked modified wet-strength agent.

[0098] 3.2 Integrated dechlorination subunit

[0099] The integrated dechlorination subunit deeply removes volatile chlorine byproducts, excess epichlorohydrin (ECH), and organochlorine impurities from cross-linked products, achieving low-chlorine compliance. Supporting equipment includes an ECH feedstock pretreatment module, a primary thin-film evaporator, a dual-tower series-connected fixed-bed adsorption tower with special adsorption resin, a vacuum recovery device, and an online gas chromatography (GC) detection terminal. The ECH feedstock pretreatment module consists of a precision distillation column and a 4A molecular sieve adsorption column, removing moisture and impurities from the ECH in advance to avoid increasing the dechlorination load. The primary thin-film evaporator maintains a mild operating condition of -0.08 MPa and 60°C, efficiently removing volatile chlorine byproducts and excess ECH. The dual-tower series-connected fixed-bed adsorption tower is filled with a composite packing of quaternary ammonium-type strong-base macroporous anion exchange resin (D201-FC) and hydrophobic macroporous adsorption resin (XAD-4), employing a dual-tower series connection. The system operates in a one-in-one-out-of-service mode, enabling deep adsorption and removal of organochlorine impurities. The online GC detection terminal achieves a detection accuracy of 0.01ppm, providing real-time online monitoring of the adsorption tower effluent and accurately reflecting the content of 1,3-dichloropropanol (1,3-DCP) and 3-chloro-1,2-propanediol (3-MCPD), ensuring that residual chlorine levels meet standards. The vacuum recovery unit condenses and recovers excess epichlorohydrin (ECH) after removal, which can be recycled after purification by the pretreatment components, reducing raw material loss.

[0100] 3.3 Resin Regeneration Auxiliary Subunit

[0101] The resin regeneration auxiliary subunit regenerates saturated resin, restoring its adsorption performance and enabling resin recycling. The entire process is closed, with no external waste discharge. Supporting equipment includes a resin stripping tank, an eluent distillation and recovery tank, a resin activation tank, and precision filtration components. A 5% sodium hydroxide and 15% ethanol mixed aqueous solution is used as the stripping solution for countercurrent stripping of the saturated resin bed, controlling the stripping temperature at 45℃ and the stripping liquid hourly space velocity at 2.0 h⁻¹. -1 The process efficiently desorbs chlorine impurities adsorbed by the resin. The eluent after desorption is transported to a distillation recovery tank to separate and recover ethanol and sodium hydroxide. The separated components can be reconstituted into an eluent for recycling. The resin after desorption is washed with deionized water until neutral, then transferred to a resin activation tank and activated with 5% hydrochloric acid solution for 30 minutes. After washing with water again until neutral, the adsorption performance is fully restored. The regenerated resin has an adsorption capacity recovery rate of ≥95% and can be reused for adsorption operations. The entire regeneration process is carried out in a closed system with no wastewater or waste residue discharged, meeting the requirements of green production.

[0102] 4. Polyphenol functionalization modification and finished product formulation module

[0103] The polyphenol functionalization modification and finished product formulation module completes the functionalization modification and fine formulation of wet strength agent, further optimizes the application performance of the product, and simultaneously controls the physical and chemical indicators of the product to the standard range, and finally produces qualified finished products, including: polyphenol modification subunit, finished product formulation subunit, and fine filtration and filling subunit.

[0104] 4.1 Polyphenol Modification Subunit

[0105] The polyphenol modification subunit enhances the anti-aging, antibacterial, and paper compatibility of wet-strength agents through polyphenol grafting modification, and is equipped with a constant-temperature modification reactor and an online pH monitor. The dechlorinated and purified wet-strength agent intermediate is transported to the constant-temperature modification reactor, where the reaction temperature is precisely controlled at 55℃ and the system pH at 6.5. Tannic acid is added to carry out the grafting modification reaction, introducing polyphenolic active groups onto the molecular chain, optimizing the binding force between the product and plant fibers, and simultaneously improving the product's storage stability and paper compatibility. The online pH monitor controls the system's pH in real time to ensure the modification reaction proceeds efficiently and stably.

[0106] 4.2 Finished Product Preparation Subunit

[0107] The finished product formulation subunit precisely controls the product's core physicochemical indicators such as pH value and solid content to meet the usage requirements of paper processing. It is equipped with pH adjustment tanks and solid content mixing tanks. The product's pH value is adjusted by precise addition of dilute hydrochloric acid, and the product's solid content is controlled by quantitative dilution with deionized water. The entire process uses online monitoring instruments to provide real-time feedback of indicator data, ensuring that the product's pH value and solid content fully comply with product standards and avoiding the impact of indicator deviations on application results.

[0108] 4.3 Fine Filtration and Filling Subunit

[0109] The fine filtration and filling subunit completes the purification, cooling, and sealing filling of the finished product, ensuring the purity and packaging quality of the finished product. It is equipped with a 1μm precision filter, a cooler, and an automatic filling machine. The qualified finished product is first filtered through a 1μm precision filter to remove trace mechanical impurities in the system, improving the transparency and purity of the finished product. Then, it is cooled to room temperature by a cooler to avoid packaging damage and product deterioration caused by high-temperature filling. Finally, the automatic filling machine completes the quantitative sealing filling, and after labeling, it becomes the finished product of epichlorohydrin modified wet strength agent, which can be directly stored or sold.

[0110] 5. Supporting auxiliary systems

[0111] The supporting auxiliary system provides intelligent control and green recycling support for the above-mentioned process modules, ensuring stable operation of the entire process, reduced energy consumption, and compliance with environmental protection standards. It mainly includes a digital twin intelligent control module and a green recycling module.

[0112] 5.1 Digital Twin Intelligent Control Module

[0113] The digital twin intelligent control module achieves fully automated management and control of the entire process, eliminating batch variations caused by manual intervention and ensuring product quality stability. It is equipped with a central control PLC cabinet, a digital twin modeling system, an LSTM neural network AI algorithm module, and various types of data acquisition terminals. The data acquisition terminals collect key process parameters such as temperature, pressure, flow rate, viscosity, acid value, and pH value from each process unit in real time and simultaneously upload them to the central control PLC cabinet and the digital twin modeling system. The digital twin modeling uses ANSYS TwinBuilder software to construct a three-dimensional digital model of the system's geometry, process, and physical components. The mapping error between process parameters and the model is ≤±2%, enabling visualized simulation of the production process. The LSTM neural network AI algorithm module combines historical production data and real-time parameters to dynamically optimize and adjust process parameters, automatically correcting deviations and achieving fully automated control without frequent manual intervention, significantly improving production efficiency and product batch stability.

[0114] 5.2 Green Recycling Module

[0115] The green recycling module enables the resource recovery and reuse of raw materials, solvents, by-products, and wastewater, reducing production energy consumption and environmental emissions, and achieving near-zero emission production. It includes: solvent recovery subunit, wastewater treatment and reuse subunit, and by-product recovery subunit. The solvent recovery subunit is equipped with a DES solvent distillation and recovery tower, which efficiently recovers the eutectic solvent from the biomass pretreatment section, with a solvent recovery rate of ≥95%. After purification, the solvent can be recycled for the pretreatment process. The wastewater treatment and reuse subunit is equipped with ultrafiltration membrane modules, reverse osmosis membrane modules, and advanced oxidation reactors. After three-stage deep treatment, the process wastewater has a reuse rate of ≥90%, and the remaining small amount of concentrated water is disposed of in compliance with standards, achieving near-zero liquid discharge. The by-product recovery subunit receives lignin by-products generated from biomass pretreatment and is equipped with an incineration heating device. The heat energy generated by lignin incineration provides auxiliary heat energy for each section of the system, reducing external energy consumption. The eluent and activating liquid generated during resin regeneration are distilled and finely filtered to achieve the recycling of raw material components. The eluent recovery rate is ≥90%, the activator recovery rate is ≥85%, and there is no external discharge of regeneration waste liquid, further improving resource utilization.

[0116] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for producing an epichlorohydrin-modified wet strength agent, characterized in that, include: Step 1: Pre-treated corn stalks are pre-treated with a low-melting solvent to separate cellulose, hemicellulose, and lignin. The extracted cellulose components are purified by enzymatic hydrolysis, saccharification, and directional fermentation to obtain bio-based ethylene glycol and bio-based adipic acid. Bio-based furanyl dicarboxylic acid and bio-based ethylene glycol are subjected to melt polycondensation reaction under an inert atmosphere and catalytic conditions. After end-capping, granulation, and drying, bio-based polyester PEFF particles are obtained. Step 2: Diethylenetriamine and bio-based adipic acid are prepolymerized under amidation catalysis to obtain polyamide polyamine prepolymer. The polyamide polyamine prepolymer is then subjected to ester-amide exchange reaction with preheated bio-based polyester PEFF particles. After removing small molecule byproducts and diluting stepwise, an aqueous solution of PAA-co-PEFF composite prepolymer with a solid content of 50%±1% is obtained. Step 3: After diluting and preheating the aqueous solution of PAA-co-PEFF composite prepolymer, it is cross-linked with pretreated epichlorohydrin. After the cross-linking reaction is completed, the volatile chlorinated byproducts are removed by thin-film evaporation and the organic chlorine impurities are removed by a dual-tower series fixed-bed adsorption tower to obtain a dechlorinated and purified resin solution. Step 4: Add tannic acid extract to the dechlorinated and purified resin solution to carry out oxidative coupling and grafting functionalization modification reaction. After the reaction is completed, adjust the pH of the system and dilute to the target solid content. After filtration, the epichlorohydrin modified wet strength agent product is obtained.

2. The method for producing the epichlorohydrin-modified wet strength agent according to claim 1, characterized in that, In step 1, the molar ratio of bio-based furanyl dicarboxylic acid to bio-based ethylene glycol is 1:1.

05. The catalyst for melt polycondensation is tetraisopropyl titanate. The polycondensation conditions are 220-240℃ and -0.095MPa. When the intrinsic viscosity of the polyester reaches 1.60±0.05dL / g and the terminal carboxyl group content is ≤45eq / t, 0.05-0.1wt% of 1-ethyl-(3-dimethylaminopropyl)carbodiimide end-capping agent is added to terminate the reaction.

3. The method for producing the epichlorohydrin-modified wet strength agent according to claim 1, characterized in that, In step 2, the molar ratio of amino to carboxyl groups in diethylenetriamine and bio-based adipic acid is 1.05:

1. The amidation catalyst is p-toluenesulfonic acid. The prepolymerization reaction conditions are 180-190℃ and material residence time of 2h, until the acid value of the system drops to 35-40mgKOH / g to obtain polyamide polyamine prepolymer. The preheating temperature of bio-based polyester PEFF particles is 150℃, and the addition amount is 8% of the dry basis mass of polyamide polyamine prepolymer. The ester-amide exchange reaction is carried out at a high shear rate of 3000-5000rpm, followed by removal of small molecule water at 190℃ and -0.09MPa until the acid value of the system stabilizes at 24-26mgKOH / g and the dynamic viscosity reaches 600-700mPa·s at 25℃.

4. The method for producing the epichlorohydrin-modified wet strength agent according to claim 1, characterized in that, In step 3, the PAA-co-PEFF composite prepolymer aqueous solution is diluted with deionized water to a solid content of 30% and preheated to 50°C; the epichlorohydrin is pretreated by a precision distillation column and a 4A molecular sieve adsorption column until the total content of 1,3-dichloropropanol and 3-chloro-1,2-propanediol in the raw material is <0.1ppm; the molar ratio of epichlorohydrin to the total amine groups of the composite prepolymer is 1.1:1, and it is added dropwise at a uniform rate for 2 hours using a high-precision metering pump. The crosslinking reaction conditions are 65°C±1°C and stirring at 200-300 rpm until the system viscosity rises to 12.5 mPa·s and the epoxy group conversion rate is ≥99%.

5. The method for producing the epichlorohydrin-modified wet strength agent according to claim 4, characterized in that, The conditions for thin-film evaporation were -0.08 MPa and 60 °C; the packing material of the dual-tower series fixed-bed adsorption tower was a composite packing material of quaternary ammonium type strong basic macroporous anion exchange resin and hydrophobic macroporous adsorption resin, with a material space velocity of 1.0 h⁻¹. -1 The total content of 1,3-dichloropropanol and 3-chloro-1,2-propanediol in the final dechlorination and purification resin solution was less than 1 ppm.

6. The method for producing the epichlorohydrin-modified wet strength agent according to claim 4, characterized in that, In step 3, when the viscosity of the crosslinking reaction system rises to 12.0 mPa·s, the epichlorohydrin dropping acceleration rate decreases by 50%; when the system viscosity reaches 12.5 mPa·s and the conductivity fluctuation is < ±0.5 μS / cm, it is determined to be the end point of the crosslinking reaction; the content of 1,3-dichloropropanol and 3-chloro-1,2-propanediol in the dechlorination unit is set with three warning thresholds of 0.5 ppm / 0.8 ppm / 0.9 ppm. When the content reaches 0.8 ppm, it automatically switches to the standby adsorption bed and issues a regeneration reminder to the saturated bed.

7. The method for producing the epichlorohydrin-modified wet strength agent according to claim 1, characterized in that, In step 4, the amount of tannic acid extract added is 3.5% of the resin solid mass in the dechlorination and purification resin solution. The functionalization modification reaction conditions are 55℃, pH 6.5, constant temperature stirring for 45 min, and the dissolved oxygen content of the system is controlled at 1-2 mg / L. The pH of the system is adjusted to 4.0-4.5 with 10% by mass dilute hydrochloric acid, and deionized water is added to dilute to a product solid content of 16.0% ± 0.5%.

8. A production system for an epichlorohydrin-modified wet strength agent, characterized in that, A method for producing an epichlorohydrin-modified wet strength agent as described in any one of claims 1-7, comprising: The modules are sequentially connected: biomass refining and bio-based polyester synthesis, polyamide polyamine synthesis and polyester composite, epichlorohydrin controllable crosslinking and deep dechlorination purification, and polyphenol functionalization modification and finished product formulation. The biomass refining and bio-based polyester synthesis module is used to efficiently separate multiple components of biomass from corn stalks and to continuously synthesize bio-based polyester PEFF particles using biomass-based monomers as raw materials. The polyamide polyamine synthesis and polyester composite module is used to synthesize polyamide polyamine prepolymer and to perform an ester-amide exchange reaction with bio-based polyester PEFF particles to obtain an aqueous solution of PAA-co-PEFF composite prepolymer. The epichlorohydrin controlled crosslinking and deep dechlorination purification module is used to crosslink the composite prepolymer with epichlorohydrin and to perform deep dechlorination purification on the crosslinking product to remove chlorinated impurities. The polyphenol functionalization modification and finished product formulation module is used to perform plant polyphenol functionalization graft modification on the dechlorinated and purified product to obtain the epichlorohydrin modified wet strength agent finished product.

9. The production system for the epichlorohydrin-modified wet strength agent according to claim 8, characterized in that, The biomass refining and bio-based polyester synthesis module includes a biomass pretreatment subunit, a bio-based raw material fermentation and refining subunit, and a continuous flow polycondensation subunit connected in sequence. The biomass pretreatment subunit is used to crush and remove impurities from corn stalks and pretreat them with a low-eutectic solvent to achieve efficient dissociation and separation of cellulose, hemicellulose, and lignin, resulting in high-purity cellulose components. The bio-based raw material fermentation and refining subunit is used to receive the pretreated cellulose components and convert them into crude bio-based ethylene glycol, adipic acid, and furanyl dicarboxylic acid through enzymatic hydrolysis, saccharification, and directional fermentation. These are then refined by distillation to obtain high-purity bio-based monomers that meet the polycondensation process parameters. The continuous flow polycondensation subunit is used to carry out melt polycondensation reaction using the refined bio-based monomers as raw materials under catalytic and inert protection process conditions. After end-capping, granulation, and drying, bio-based polyester particles are obtained.

10. The production system for the epichlorohydrin-modified wet strength agent according to claim 8, characterized in that, The epichlorohydrin controllable crosslinking and deep dechlorination purification module includes a crosslinking reaction subunit, an integrated dechlorination subunit, and a resin regeneration auxiliary subunit. The crosslinking reaction subunit is used to dilute and preheat the PAA-co-PEFF composite prepolymer aqueous solution, and then react it with pretreated epichlorohydrin to obtain a crude crosslinked modified wet strength agent. The integrated dechlorination subunit is used to perform deep dechlorination purification on the crude product after the crosslinking reaction, first removing excess unreacted epichlorohydrin and volatile chlorinated byproducts, and then removing residual organic chlorine impurities through adsorption resin. The resin regeneration auxiliary subunit is used to desorb and activate the adsorption resin saturated in the integrated dechlorination subunit to restore the resin adsorption performance.

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