Pyridine base synthesis quench liquid ammonia recovery method and device based on nanometer pore composite membrane

Abstract

The application discloses a pyridine base synthesis quenching liquid ammonia recovery method and device based on nanopore composite film, and steps are as follows: PTFE fine powder, zinc salt micro powder and hydrocarbon lubricant are uniformly mixed, aging, extrusion molding, calendering, heat treatment, longitudinal stretching and shaping are carried out, and PTFE / ZnO nanopore composite film is prepared; the assembled tubular membrane module is sequentially washed and activated; the obtained pretreatment liquid is sent into an ultrafiltration membrane module to form a permeate; the obtained permeate is preheated and sent into a multi-stage series membrane distillation module; mixed steam on the permeate side of the membrane distillation is introduced into a gas-liquid separation tank for gas-liquid separation; and the obtained ammonia-lean concentrated liquid is sent into an extraction section to recover pyridine base products. The ultrafiltration permeate is sent into the membrane distillation module adopting the PTFE / ZnO nanopore composite film to carry out selective ammonia separation, so that ammonia recovery rate, ammonia gas purity and tar removal rate are greatly improved, pyridine base loss rate is reduced, the operation cycle of the membrane module is prolonged, and equipment investment and operation cost are reduced.

Description

Technical Field

[0001] This invention relates to the field of chemical separation and resource recovery technology, and in particular to a method and apparatus for quenching liquid ammonia recovery from pyridine base synthesis based on nanoporous composite membranes. Background Technology

[0002] Pyridine bases are important chemical raw materials and pharmaceutical intermediates, mainly prepared industrially through the condensation reaction of formaldehyde, acetaldehyde, and ammonia in the presence of a catalyst. The reaction equation is as follows:

[0003] CH2O + 2CH3CHO + NH3 → C5H5N + 3H2O + H2 (pyridine)

[0004] 2CH2O + 2CH3CHO + NH3 → C6H7N + 4H2O (methylpyridine)

[0005] This reaction is typically carried out in a fixed-bed reactor at a temperature of 350-550℃, with a molar ratio of ammonia to aldehydes usually between 1.5 and 3:1. Due to the large excess of ammonia, the gas after the reaction contains a significant amount of unreacted ammonia, typically accounting for 30-50% of the feed ammonia.

[0006] In industry, the high-temperature gas produced after the pyridine base synthesis reaction needs to be quenched to form a quench liquid containing pyridine base, unreacted ammonia, water, and tar. Due to the extremely high solubility of ammonia in water, the concentration of ammonia in the quench liquid can typically reach 10-25 wt%. How to efficiently and with low energy consumption recover high-value ammonia from this quench liquid, while avoiding impacting the subsequent recovery of pyridine base, is a key technical challenge in the industry.

[0007] Traditional ammonia recovery methods primarily employ steam stripping. For example, patent application CN102020603A discloses a method for recovering ammonia using benzene as an extractant combined with steam stripping. While this method can achieve ammonia recovery, it has several significant drawbacks in practical applications: First, using benzene as an extractant not only increases the cost of solvent recovery and loss but also poses serious safety and environmental risks due to its carcinogenicity; second, the stripping operation requires high temperatures of 120-160℃, resulting in enormous steam consumption and persistently high energy consumption; third, the quench liquid contains 1-5 wt% of tar, a viscous byproduct of the reaction. This substance easily accumulates and forms scale on the stripping tower trays, reboilers, and heat exchangers, causing equipment blockage and forcing frequent shutdowns for cleaning, severely impacting the continuity and stability of production. Patent CN215440288U discloses a three-stage cyclone wastewater treatment device for pyridine. The process involves separating and condensing the pyridine synthesis reaction gas via a cyclone separator, then introducing it into a quench tower for further condensation. The quench liquid discharged from the bottom of the quench tower is sent to a stripping tower to recover ammonia. While this method achieves the recovery and reuse of ammonia from the quench liquid, the tar and catalyst powder entrained in the quench liquid, after entering the stripping tower, will adhere and accumulate on the surfaces of the trays and reboiler, forming scale. This leads to increased tower pressure, increased tower resistance, and decreased feed throughput, requiring frequent shutdowns for cleaning. Simultaneously, the packing material inside the quench tower is easily clogged by the combined action of tar and catalyst powder, resulting in uneven liquid distribution, poor ammonia absorption, and affecting the stability of the stripping feed and the continuous operation of production.

[0008] To address the problem of tar blockage, patent CN206069394U proposes a heat exchanger anti-blockage cleaning system. However, this solution only alleviates the blockage symptoms through online cleaning, failing to address the root cause of tar accumulation in the system or improve the ammonia recovery process itself. Furthermore, the cleaning process may introduce impurities, affecting product purity. Patent CN205773481U discloses a cleaning system for an ammonia stripping unit, using a mixture of wash oil and crude benzene to dissolve blockages in the ammonia stripping tower trays, pipes, and wastewater heat exchangers. While this method ensures the treatment effect of the ammonia stripping tower, it requires frequent shutdowns for cleaning, resulting in significant waste of manpower and resources, and exacerbating corrosion of equipment and pipes.

[0009] In recent years, some studies have attempted to apply membrane technology to such systems. For example, patent application CN121041830A mentions a treatment method combining low-temperature stripping and pervaporation membranes. However, this method has a complex technical route, the cost of pervaporation membranes is high, and membrane fouling remains a prominent problem when treating tar-containing systems. Its industrial application maturity and economic viability require further verification. Patent application CN115583685A discloses a recovery device and method for treating wastewater containing high concentrations of ammonia and methylpyridine. When obtaining the finished liquid (liquid pyridine sulfate) or flake pyridine sulfate, the total recovery rate of useful substances is 95%. However, this patent can only achieve simultaneous separation of ammonia and methylpyridine, and cannot achieve selective recovery of ammonia, making it unsuitable for ammonia recovery from quench liquids. Patent CN103112871A discloses a method for separating and purifying low-concentration ammonia water to prepare high-concentration ammonia, which has the characteristics of high product purity and good operation stability. However, this method is only suitable for ammonia water concentration and purification, and the purity of the final product ammonia is only 97%, and it is not suitable for the recovery of pyridine base quenching liquid.

[0010] In summary, existing technologies for processing pyridine base synthesis quench liquids generally suffer from problems such as tar clogging leading to short operating cycles and the need to improve ammonia recovery efficiency. Summary of the Invention

[0011] The purpose of this invention is to provide a method and apparatus for recovering quenched liquid ammonia from pyridine base synthesis based on a nanoporous composite membrane. This method solves the problems of tar blockage and pyridine base loss. The ultrafiltration permeate is fed into a membrane distillation module using a PTFE / ZnO nanoporous composite membrane for selective ammonia separation. This invention can significantly improve the ammonia recovery rate, ammonia purity, and tar removal rate, reduce the pyridine base loss rate, extend the membrane module's operating cycle, and reduce equipment investment and operating costs, thereby solving the problems mentioned in the background art.

[0012] To achieve the above objectives, the present invention provides the following technical solution:

[0013] A method for quenching liquid ammonia recovery during pyridine base synthesis based on nanoporous composite membranes includes the following steps:

[0014] S1: PTFE fine powder, zinc salt micro powder and hydrocarbon lubricant are mixed evenly and aged in a sealed container to form a paste. The paste is extruded into a strip preform and calendered to obtain a membrane material. The membrane material is then heat-treated, stretched longitudinally, and sintered to obtain a PTFE / ZnO nanoporous composite membrane.

[0015] S2: Cut the prepared PTFE / ZnO nanoporous composite membrane, encapsulate it with polypropylene or stainless steel end caps and silicone rubber O-rings, assemble it into a tubular membrane module, and sequentially rinse the assembled tubular membrane module with deionized water circulation, anhydrous ethanol, and deionized water until neutral to complete the activation.

[0016] S3: The quench liquid from the pyridine base synthesis quench tower is passed through a pretreatment filter to remove solid particles and suspended matter, and the pretreatment liquid is sent into the ultrafiltration membrane module. Tar and macromolecular impurities are intercepted and discharged, while ammonia, water and pyridine base permeate through the membrane to form the permeate.

[0017] S4: The obtained permeate is preheated and then fed into a multi-stage tandem membrane distillation unit. Membrane distillation separation is carried out under vacuum conditions on the permeate side. Volatile components vaporize and permeate through the membrane pores, while non-volatile components are retained to form a lean ammonia concentrate.

[0018] S5: The mixed steam from the permeate side of the membrane distillation is introduced into the gas-liquid separator for gas-liquid separation to obtain a gas phase rich in ammonia and a liquid phase containing water and pyridine base. The gas phase ammonia is sent to the synthesis reactor as raw material, and the liquid phase is recycled back to the membrane distillation feed inlet. The lean ammonia concentrate obtained in S4 is sent to the extraction section to recover the pyridine base product.

[0019] Furthermore, for S1, the zinc salt micro powder is one of zinc chloride, zinc sulfate, and zinc acetate, and the addition amount is 5%-20% of the mass of PTFE fine powder. The hydrocarbon lubricant is naphtha, and the amount used is 50%-80% of the mass of PTFE fine powder. The aging temperature is 20℃-50℃, and the aging time is 24 hours.

[0020] Furthermore, the heat treatment of the membrane material in S1 includes two stages. In the first stage, the temperature is raised to 100-150℃ and held for 30-60 minutes to volatilize and remove hydrocarbon lubricants. In the second stage, the temperature is raised to 200-260℃ and held for 60-120 minutes to decompose the zinc salt micropowder in situ and form a nanoporous ring structure in the PTFE matrix.

[0021] Furthermore, in S1, the film thickness is 100-300μm, the longitudinal stretching temperature is 300-350℃, the stretching ratio is 2-5 times, the sintering and shaping temperature is 350-400℃, and the sintering time is 5-15 minutes.

[0022] Further, in S2, the activation step is as follows: rinse with deionized water at a temperature of 30-50℃ for 30 minutes to remove impurities from the membrane surface and pores, then rinse with anhydrous ethanol for 10 minutes to wet the membrane pores, and finally rinse with deionized water until neutral.

[0023] Furthermore, in S3, the membrane material of the ultrafiltration membrane module is polyethersulfone or polyvinylidene fluoride, with a molecular weight cutoff of 1000-5000 Da, an ultrafiltration operating pressure of 0.2-0.6 MPa, an operating temperature of 30-50℃, and a membrane flux of 50-150 L / (m²·h).

[0024] Furthermore, in S4, the preheating temperature is 40-60℃, the multi-stage series membrane distillation assembly consists of 3-7 stages in series, the operating temperature of each stage is 40-80℃, and the permeate side pressure is 70-120kPa.

[0025] Furthermore, in S5, the operating temperature of the gas-liquid separator is 10-60℃.

[0026] See Figure 1 A device for recovering liquid ammonia from pyridine base synthesis using a nanoporous composite membrane, characterized by comprising:

[0027] Coolant storage tank, used for temporary storage of cooled coolant;

[0028] A pretreatment filter connected to the quench liquid storage tank is used to remove solid particles and suspended matter from the quench liquid;

[0029] The ultrafiltration membrane module is equipped with a feed inlet, a permeate outlet, and a retentate outlet. The feed inlet is connected to the pretreatment filter, the permeate outlet is connected to the membrane distillation module, and the retentate outlet is connected to the tar treatment device.

[0030] A multi-stage membrane distillation unit connected in series is provided with a feed inlet, a concentrate outlet, and a permeate steam outlet;

[0031] The gas-liquid separator has its inlet connected to the permeate vapor outlet of the membrane distillation unit. The gas-liquid separator has a gas phase outlet and a liquid phase outlet. The gas phase outlet of the gas-liquid separator is connected to a vacuum system.

[0032] Furthermore, the quench liquid in the quench liquid storage tank is pumped to the pretreatment filter, and the liquid phase from the liquid phase outlet of the gas-liquid separator is pumped back to the membrane distillation unit.

[0033] This composite membrane forms a nanoporous ring structure within a PTFE matrix through in-situ decomposition of zinc salts. The selective coordination of ZnO with ammonia enhances the transmembrane selectivity of ammonia while maintaining excellent hydrophobicity and antifouling capabilities. Based on this, the invention first separates tar from the quench liquid using an ultrafiltration membrane before it enters the membrane distillation system, removing tar at the source and preventing it from entering the subsequent membrane distillation system, fundamentally solving the problems of tar clogging and pyridine base loss. Then, the ultrafiltration permeate is fed into a membrane distillation module using a PTFE / ZnO nanoporous composite membrane for selective ammonia separation. This invention achieves an ammonia recovery rate of over 99%, ammonia purity exceeding 99%, a pyridine base loss rate of less than 1%, a tar removal rate of over 93%, and extends the membrane module's operating cycle to over 720 hours, reducing equipment investment and operating costs.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1. This invention employs an ultrafiltration pretreatment coupled with PTFE / ZnO nanoporous membrane distillation process to achieve efficient and selective recovery of ammonia. The PTFE / ZnO nanoporous membrane utilizes the strong Lewis acid-base adsorption of ammonia by ZnO and the dual mass transfer channels of nanoporous rings formed by in-situ decomposition to improve the transmembrane selectivity and mass transfer efficiency of ammonia.

[0036] 2. The present invention sets up an ultrafiltration pretreatment unit before membrane distillation, and uses the sieving and retention effect of ultrafiltration membrane to remove tar-like substances at the source, thereby avoiding membrane pore blockage and pollution problems caused by tar entering the membrane distillation system.

[0037] 3. This invention utilizes the selective permeability of ultrafiltration membranes to allow pyridine base to enter the membrane distillation unit along with the permeate. Combined with the selective ammonia transport promotion effect of PTFE / ZnO nanoporous composite membrane and the effective retention of pyridine base, low-loss recovery of pyridine base is achieved. While ensuring high ammonia recovery rate and high tar retention rate, it also achieves effective retention of high value-added components. Attached Figure Description

[0038] Figure 1 This is a structural diagram of the device of the present invention.

[0039] In the diagram: 1. Quenching liquid storage tank; 2. Pretreatment filter; 3. Ultrafiltration membrane module; 4. Membrane distillation module; 5. Gas-liquid separator. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1: Preparation of PTFE / ZnO nanoporous composite membrane: PTFE fine powder, zinc acetate micro powder and naphtha were mixed evenly at a mass ratio of 10:1:6 and aged at 40℃ to form a paste. The paste was extruded and calendered to obtain a membrane material with a thickness of 200μm. The membrane material was heated at 130℃ and 250℃ for 60min and 120min respectively. The heat-treated membrane material was longitudinally stretched at 330℃ to 3 times its original size. Then it was sintered at 380℃ for 10 minutes to fix the shape, thus obtaining the PTFE / ZnO nanoporous composite membrane.

[0042] Membrane module preparation and activation: The prepared PTFE / ZnO nanoporous composite membrane was cut and encapsulated with stainless steel end caps and silicone rubber O-rings to assemble into a tubular membrane module; the assembled tubular membrane module was sequentially rinsed with deionized water for 30 minutes, anhydrous ethanol for 10 minutes, and deionized water until neutral at 40°C to wet the membrane pores, thus completing the activation and naming it PTFE / ZnO-1. The PTFE / ZnO-1 membrane was then installed in a membrane distillation apparatus.

[0043] Pyridine base separation and ammonia recovery: The pyridine base synthesis quench liquid (stored in quench liquid storage tank 1) is passed through a pretreatment filter 2 to remove solid particles and suspended matter. The pretreated quench liquid then enters a polyvinylidene fluoride ultrafiltration membrane module (molecular weight cutoff 3000 Da, operating pressure 0.4 MPa, operating temperature 40℃, membrane flux 85 L / (m²·h)). Tar is retained in the concentrate and discharged. The permeate is preheated (preheating temperature 50℃) and then enters a membrane distillation module 4. The membrane distillation module adopts a 5-stage series structure with an absolute pressure of 85 kPa on the permeate side. Each stage provides mass transfer driving force through a temperature gradient. The operating conditions are: stage 1 temperature 50℃, stage 2 temperature 52℃, stage 3 temperature 55℃, stage 4 temperature 58℃, and stage 5 temperature 60℃. The steam permeate from the membrane distillation enters the gas-liquid separator 5 (operating temperature 20℃). The water vapor and pyridine base condense into liquid phase and return to the membrane distillation feed inlet for recycling. The uncondensed ammonia gas enters the dry screw vacuum pump through the upper outlet of the gas-liquid separator. After passing through the pump body, the ammonia gas is discharged at the pump outlet under a slight positive pressure and directly sent into the reactor circulation pipeline for reuse. The experiment showed that the ammonia recovery rate was 99.2%, the pyridine base loss rate was 0.80%, and the ammonia purity was 99.2%.

[0044] Example 2: Preparation of PTFE / ZnO nanoporous composite membrane: PTFE fine powder, zinc chloride micro powder and naphtha were mixed evenly at a mass ratio of 10:1:6 and aged at 40°C to form a paste. The paste was extruded and calendered to obtain a membrane material with a thickness of 200 μm. The membrane material was heated at 130°C and 250°C for 60 min and 120 min, respectively. The heat-treated membrane material was longitudinally stretched at 330°C to 3 times its original size. Subsequently, it was sintered at 380°C for 10 minutes to fix the shape, thus obtaining the PTFE / ZnO nanoporous composite membrane.

[0045] Membrane module preparation and activation: The prepared PTFE / ZnO nanoporous composite membrane was cut and encapsulated with stainless steel end caps and silicone rubber O-rings to assemble into a tubular membrane module. The assembled tubular membrane module was sequentially rinsed at 40°C with deionized water for 30 minutes, anhydrous ethanol for 10 minutes, and deionized water until neutral to wet the membrane pores, thus completing the activation. It was named PTFE / ZnO-2 and installed in a membrane distillation device.

[0046] Pyridine base separation and ammonia recovery: The pyridine base synthesis quench liquid is passed through a pretreatment filter to remove solid particles and suspended matter. The pretreated quench liquid then enters a polyvinylidene fluoride ultrafiltration membrane module (molecular weight cutoff 3000 Da, operating pressure 0.4 MPa, operating temperature 40℃, membrane flux 85 L / (m²·h)). Tar is retained in the concentrate and discharged. The permeate is preheated (preheating temperature 50℃) and then enters a membrane distillation module. The membrane distillation module adopts a 5-stage series structure with an absolute pressure of 85 kPa on the permeate side. Each stage provides mass transfer driving force through a temperature gradient. The operating conditions are: stage 1 temperature 50℃, stage 2 temperature 52℃, stage 3 temperature 55℃, stage 4 temperature 58℃, and stage 5 temperature 60℃. The steam permeate from the membrane distillation enters the gas-liquid separator (operating temperature 20℃), where the water vapor and pyridine base condense into a liquid phase and return to the membrane distillation feed inlet for recycling. Uncondensed ammonia gas enters a dry screw vacuum pump through the upper outlet of the gas-liquid separator. After passing through the pump body, the ammonia gas is discharged at the pump outlet under slight positive pressure and directly fed into the reactor's circulation pipeline for reuse. Experiments showed an ammonia recovery rate of 97.1%, a pyridine base loss rate of 0.88%, and an ammonia purity of 98.3%.

[0047] Example 3: Preparation of PTFE / ZnO nanoporous composite membrane: PTFE fine powder, zinc sulfate micro powder and naphtha were mixed evenly at a mass ratio of 10:1:6 and aged at 40℃ to form a paste. The paste was extruded and calendered to obtain a membrane material with a thickness of 200μm. The membrane material was heated at 130℃ and 250℃ for 60min and 120min respectively. The heat-treated membrane material was longitudinally stretched at 330℃ to 3 times its original size. Then it was sintered at 380℃ for 10 minutes to fix the shape, thus obtaining the PTFE / ZnO nanoporous composite membrane.

[0048] Membrane module preparation and activation: The prepared PTFE / ZnO nanoporous composite membrane was cut and encapsulated with stainless steel end caps and silicone rubber O-rings to assemble into a tubular membrane module. The assembled tubular membrane module was sequentially rinsed with deionized water for 30 minutes, anhydrous ethanol for 10 minutes, and deionized water until neutral at 40°C to wet the membrane pores and complete the activation. It was named PTFE / ZnO-3 and installed in a membrane distillation device.

[0049] Pyridine base separation and ammonia recovery: The pyridine base synthesis quench liquid is passed through a pretreatment filter to remove solid particles and suspended matter. The pretreated quench liquid then enters a polyvinylidene fluoride ultrafiltration membrane module (molecular weight cutoff 3000 Da, operating pressure 0.4 MPa, operating temperature 40℃, membrane flux 85 L / (m²·h)). Tar is retained in the concentrate and discharged. The permeate is preheated (preheating temperature 50℃) and then enters a membrane distillation module. The membrane distillation module adopts a 5-stage series structure with an absolute pressure of 85 kPa on the permeate side. Each stage provides mass transfer driving force through a temperature gradient. The operating conditions are: stage 1 temperature 50℃, stage 2 temperature 52℃, stage 3 temperature 55℃, stage 4 temperature 58℃, and stage 5 temperature 60℃. The steam permeate from the membrane distillation enters the gas-liquid separator (operating temperature 20℃), where the water vapor and pyridine base condense into a liquid phase and return to the membrane distillation feed inlet for recycling. Uncondensed ammonia gas enters a dry screw vacuum pump through the upper outlet of the gas-liquid separator. After passing through the pump body, the ammonia gas is discharged at the pump outlet under slight positive pressure and directly fed into the reactor's circulation pipeline for reuse. Experiments showed an ammonia recovery rate of 94.6%, a pyridine base loss rate of 1.25%, and an ammonia purity of 96.0%.

[0050] The experimental results of Examples 1-3 are shown in Table 1 below.

[0051] Table 1. Experimental results of different types of zinc salts

[0052] Example Zinc salt micro powder Ammonia recovery rate (%) Pyridine base loss rate (%) Ammonia purity (%) Example 1 Zinc acetate micro powder 99.2 0.80 99.2 Example 2 Zinc chloride micro powder 97.1 0.88 98.3 Example 3 Zinc sulfate powder 94.6 1.25 96.0

[0053] As shown in Table 1, when zinc acetate micro powder is used as zinc salt micro powder, the ammonia recovery rate is 99.2%, the pyridine base loss rate is 0.80%, and the ammonia purity is 99.2%. The ammonia recovery rate and purity are the best. Zinc acetate decomposes in situ and forms a uniformly dispersed ZnO nanoporous ring structure after the decomposition temperature is precisely matched with the 250℃ heat treatment window, resulting in the best mass transfer efficiency and selectivity.

[0054] Example 4: Preparation of PTFE / ZnO nanoporous composite membrane: PTFE fine powder, zinc acetate micro powder and naphtha were mixed evenly at a mass ratio of 10:1:6 and aged at 40℃ to form a paste. The paste was extruded and calendered to obtain a membrane material with a thickness of 200μm. The membrane material was heated at 130℃ and 250℃ for 60min and 120min respectively. The heat-treated membrane material was longitudinally stretched at 330℃ to 3 times its original size. Then it was sintered at 380℃ for 10 minutes to fix the shape, thus obtaining the PTFE / ZnO nanoporous composite membrane.

[0055] Membrane module preparation and activation: The prepared PTFE / ZnO nanoporous composite membrane was cut and encapsulated with stainless steel end caps and silicone rubber O-rings to assemble into a tubular membrane module. The assembled tubular membrane module was sequentially rinsed at 40°C with deionized water for 30 minutes, anhydrous ethanol for 10 minutes, and deionized water until neutral to wet the membrane pores, thus completing the activation. It was named PTFE / ZnO-4 and installed in a membrane distillation device.

[0056] Pyridine base separation and ammonia recovery: The pyridine base synthesis quench liquid is passed through a pretreatment filter to remove solid particles and suspended matter. The pretreated quench liquid then enters a polyvinylidene fluoride ultrafiltration membrane module (molecular weight cutoff 1000 Da, operating pressure 0.4 MPa, operating temperature 40℃, membrane flux 85 L / (m²·h)). Tar is retained in the concentrate and discharged. The permeate is preheated (preheating temperature 50℃) and then enters a membrane distillation module. The membrane distillation module adopts a 5-stage series structure with an absolute pressure of 85 kPa on the permeate side. Each stage provides mass transfer driving force through a temperature gradient. The operating conditions are: stage 1 temperature 50℃, stage 2 temperature 52℃, stage 3 temperature 55℃, stage 4 temperature 58℃, and stage 5 temperature 60℃. The steam permeate from the membrane distillation enters the gas-liquid separator (operating temperature 20℃). The water vapor and pyridine base condense into a liquid phase and return to the membrane distillation feed inlet for recirculation. Uncondensed ammonia gas enters a dry screw vacuum pump through the upper outlet of the gas-liquid separator. After passing through the pump body, the ammonia gas is discharged at the pump outlet under slight positive pressure and directly fed into the reactor's circulation pipeline for reuse. Experiments showed an ammonia recovery rate of 99.1%, a pyridine base loss rate of 1.8%, a tar removal rate of 95.7%, and an ammonia purity of 99.1%.

[0057] Example 5: Preparation of PTFE / ZnO nanoporous composite membrane: PTFE fine powder, zinc acetate micro powder and naphtha were mixed evenly at a mass ratio of 10:1:6 and aged at 40°C to form a paste. The paste was extruded and calendered to obtain a membrane material with a thickness of 200 μm. The membrane material was heated at 130°C and 250°C for 60 min and 120 min, respectively. The heat-treated membrane material was longitudinally stretched at 330°C to 3 times its original size. Subsequently, it was sintered at 380°C for 10 minutes to fix the shape, thus obtaining the PTFE / ZnO nanoporous composite membrane.

[0058] Membrane module preparation and activation: The prepared PTFE / ZnO nanoporous composite membrane was cut and encapsulated with stainless steel end caps and silicone rubber O-rings to assemble into a tubular membrane module. The assembled tubular membrane module was sequentially rinsed at 40°C with deionized water for 30 minutes, anhydrous ethanol for 10 minutes, and deionized water until neutral to wet the membrane pores, thus completing the activation. It was named PTFE / ZnO-5 and installed in a membrane distillation device.

[0059] Pyridine base separation and ammonia recovery: The pyridine base synthesis quench liquid is passed through a pretreatment filter to remove solid particles and suspended matter. The pretreated quench liquid then enters a polyvinylidene fluoride ultrafiltration membrane module (molecular weight cutoff 5000 Da, operating pressure 0.4 MPa, operating temperature 40℃, membrane flux 85 L / (m²·h)). Tar is retained in the concentrate and discharged. The permeate is preheated (preheating temperature 50℃) and then enters a membrane distillation module. The membrane distillation module adopts a 5-stage series structure with an absolute pressure of 85 kPa on the permeate side. Each stage provides mass transfer driving force through a temperature gradient. The operating conditions are: stage 1 temperature 50℃, stage 2 temperature 52℃, stage 3 temperature 55℃, stage 4 temperature 58℃, and stage 5 temperature 60℃. The steam permeate from the membrane distillation enters the gas-liquid separator (operating temperature 20℃). The water vapor and pyridine base condense into a liquid phase and return to the membrane distillation feed inlet for recirculation. Uncondensed ammonia gas enters a dry screw vacuum pump through the upper outlet of the gas-liquid separator. After passing through the pump body, the ammonia gas is discharged at the pump outlet under slight positive pressure and directly fed into the reactor's circulation pipeline for reuse. Experiments showed an ammonia recovery rate of 99.1%, a pyridine base loss rate of 0.5%, a tar removal rate of 89.9%, and an ammonia purity of 99.2%.

[0060] The experimental results of Examples 1, 4, and 5 are shown in Table 2 below.

[0061] Table 2 Experimental results for different molecular weight cutoffs in ultrafiltration

[0062] Example Molecular weight cutoff (Da) Ammonia recovery rate (%) Pyridine base loss rate (%) Tar removal rate (%) Ammonia purity (%) Example 1 3000 99.2 0.8 93.5 99.2 Example 4 1000 99.1 1.8 95.7 99.1 Example 5 5000 99.1 0.5 89.9 99.2

[0063] Table 2 shows that with a molecular weight cutoff of 3000 Da, the ammonia recovery rate is 99.2%, the pyridine base loss rate is 0.8%, and the tar removal rate is 93.5%, exhibiting the best overall performance. A molecular weight cutoff of 1000 Da results in the highest tar removal rate but a relatively high pyridine base loss rate, while a molecular weight cutoff of 5000 Da results in the lowest pyridine base loss rate but a relatively low tar removal rate. This indicates that a molecular weight cutoff of 3000 Da is the optimal choice for ultrafiltration membranes.

[0064] Example 6: Preparation of PTFE / ZnO nanoporous composite membrane: PTFE fine powder, zinc acetate micro powder and naphtha were mixed evenly at a mass ratio of 10:1:6 and aged at 40°C to form a paste. The paste was extruded and calendered to obtain a membrane material with a thickness of 200 μm. The membrane material was heated at 130°C and 250°C for 60 min and 120 min, respectively. The heat-treated membrane material was longitudinally stretched at 330°C to 3 times its original size. Subsequently, it was sintered at 380°C for 10 minutes to fix the shape, thus obtaining the PTFE / ZnO nanoporous composite membrane.

[0065] Membrane module preparation and activation: The prepared PTFE / ZnO nanoporous composite membrane was cut and encapsulated with stainless steel end caps and silicone rubber O-rings to assemble into a tubular membrane module. The assembled tubular membrane module was sequentially rinsed with deionized water for 30 minutes, anhydrous ethanol for 10 minutes, and deionized water until neutral at 40°C to wet the membrane pores and complete the activation. It was named PTFE / ZnO-6 and installed in a membrane distillation device.

[0066] Pyridine base separation and ammonia recovery: The pyridine base synthesis quench liquid is passed through a pretreatment filter to remove solid particles and suspended matter. The pretreated quench liquid then enters a polyvinylidene fluoride ultrafiltration membrane module (molecular weight cutoff 3000 Da, operating pressure 0.4 MPa, operating temperature 40℃, membrane flux 85 L / (m²·h)). Tar is retained in the concentrate and discharged. The permeate is preheated (preheating temperature 50℃) and then enters a membrane distillation module. The membrane distillation module adopts a 5-stage series structure with an absolute pressure of 85 kPa on the permeate side. Each stage provides mass transfer driving force through a temperature gradient. The operating conditions are: stage 1 temperature 40℃, stage 2 temperature 42℃, stage 3 temperature 45℃, stage 4 temperature 48℃, and stage 5 temperature 50℃. The steam permeate from the membrane distillation enters the gas-liquid separator (operating temperature 20℃). The water vapor and pyridine base condense into a liquid phase and return to the membrane distillation feed inlet for recirculation. Uncondensed ammonia gas enters a dry screw vacuum pump through the upper outlet of the gas-liquid separator. After passing through the pump body, the ammonia gas is discharged at the pump outlet under slight positive pressure and directly fed into the reactor's circulation pipeline for reuse. Experiments showed an ammonia recovery rate of 96.5%, a pyridine base loss rate of 0.70%, and an ammonia purity of 99.3%.

[0067] Example 7: Preparation of PTFE / ZnO nanoporous composite membrane: PTFE fine powder, zinc acetate micro powder and naphtha were mixed evenly at a mass ratio of 10:1:6 and aged at 40°C to form a paste. The paste was extruded and calendered to obtain a membrane material with a thickness of 200 μm. The membrane material was heated at 130°C and 250°C for 60 min and 120 min, respectively. The heat-treated membrane material was longitudinally stretched at 330°C to 3 times its original size. Then it was sintered at 380°C for 10 minutes to fix the shape, thus obtaining the PTFE / ZnO nanoporous composite membrane.

[0068] Membrane module preparation and activation: The prepared PTFE / ZnO nanoporous composite membrane was cut and encapsulated with stainless steel end caps and silicone rubber O-rings to assemble into a tubular membrane module. The assembled tubular membrane module was sequentially rinsed with deionized water for 30 minutes, anhydrous ethanol for 10 minutes, and deionized water until neutral at 40°C to wet the membrane pores and complete the activation. It was named PTFE / ZnO-7 and installed in a membrane distillation device.

[0069] Pyridine base separation and ammonia recovery: The pyridine base synthesis quench liquid is passed through a pretreatment filter to remove solid particles and suspended matter. The pretreated quench liquid then enters a polyvinylidene fluoride ultrafiltration membrane module (molecular weight cutoff 3000 Da, operating pressure 0.4 MPa, operating temperature 40℃, membrane flux 85 L / (m²·h)). Tar is retained in the concentrate and discharged. The permeate is preheated (preheating temperature 50℃) and then enters a membrane distillation module. The membrane distillation module adopts a 5-stage series structure with an absolute pressure of 85 kPa on the permeate side. Each stage provides mass transfer driving force through a temperature gradient. The operating conditions are: stage 1 temperature 60℃, stage 2 temperature 62℃, stage 3 temperature 65℃, stage 4 temperature 68℃, and stage 5 temperature 70℃. The steam permeate from the membrane distillation enters the gas-liquid separator (operating temperature 20℃), where the water vapor and pyridine base condense into a liquid phase and return to the membrane distillation feed inlet for recycling. Uncondensed ammonia gas enters a dry screw vacuum pump through the upper outlet of the gas-liquid separator. After passing through the pump body, the ammonia gas is discharged at the pump outlet under slight positive pressure and directly fed into the reactor's circulation pipeline for reuse. Experiments showed an ammonia recovery rate of 99.5%, a pyridine base loss rate of 1.7%, and an ammonia purity of 98.2%.

[0070] Example 8: Preparation of PTFE / ZnO nanoporous composite membrane: PTFE fine powder, zinc acetate micro powder and naphtha were mixed evenly at a mass ratio of 10:1:6 and aged at 40°C to form a paste. The paste was extruded and calendered to obtain a membrane material with a thickness of 200 μm. The membrane material was heated at 130°C and 250°C for 60 min and 120 min, respectively. The heat-treated membrane material was longitudinally stretched at 330°C to 3 times its original size. Then it was sintered at 380°C for 10 minutes to fix the shape, thus obtaining the PTFE / ZnO nanoporous composite membrane.

[0071] Membrane module preparation and activation: The prepared PTFE / ZnO nanoporous composite membrane was cut and encapsulated with stainless steel end caps and silicone rubber O-rings to assemble into a tubular membrane module. The assembled tubular membrane module was sequentially rinsed with deionized water for 30 minutes, anhydrous ethanol for 10 minutes, and deionized water until neutral at 40°C to wet the membrane pores and complete the activation. It was named PTFE / ZnO-8 and installed in a membrane distillation device.

[0072] Pyridine base separation and ammonia recovery: The pyridine base synthesis quench liquid is passed through a pretreatment filter to remove solid particles and suspended matter. The pretreated quench liquid then enters a polyvinylidene fluoride ultrafiltration membrane module (molecular weight cutoff 3000 Da, operating pressure 0.4 MPa, operating temperature 40℃, membrane flux 85 L / (m²·h)). Tar is retained in the concentrate and discharged. The permeate is preheated (preheating temperature 50℃) and then enters a membrane distillation module. The membrane distillation module adopts a 5-stage series structure with an absolute pressure of 85 kPa on the permeate side. Each stage provides mass transfer driving force through a temperature gradient. The operating conditions are: stage 1 temperature 70℃, stage 2 temperature 72℃, stage 3 temperature 75℃, stage 4 temperature 78℃, and stage 5 temperature 80℃. The steam permeate from the membrane distillation enters the gas-liquid separator (operating temperature 20℃), where the water vapor and pyridine base condense into a liquid phase and return to the membrane distillation feed inlet for recycling. Uncondensed ammonia gas enters a dry screw vacuum pump through the upper outlet of the gas-liquid separator. After passing through the pump body, the ammonia gas is discharged at the pump outlet under slight positive pressure and directly fed into the reactor's circulation pipeline for reuse. Experiments showed an ammonia recovery rate of 99.7%, a pyridine base loss rate of 2.9%, and an ammonia purity of 96.8%.

[0073] The experimental results of Examples 1 and 6-8 are shown in Table 3 below.

[0074] Table 3 Experimental results at different membrane distillation temperatures

[0075] Example Temperature range (°C) Ammonia recovery rate (%) Pyridine base loss rate (%) Ammonia purity (%) Example 1 50-60 99.2 0.8 99.2 Example 6 40-50 96.5 0.7 99.3 Example 7 60-70 99.5 1.7 98.2 Example 8 70-80 99.7 2.9 96.8

[0076] Table 3 shows that at a membrane distillation temperature of 40-50℃, the ammonia recovery rate was only 96.5%, indicating that excessively low temperatures are not conducive to the complete separation of ammonia. At a membrane distillation temperature of 70-80℃, the ammonia recovery rate reached 99.7%, but the pyridine base loss rate was as high as 2.9%, indicating that excessively high temperatures lead to the loss of pyridine base through the membrane. Simultaneously, excessively high temperatures cause a large amount of water and pyridine to permeate through the membrane, significantly reducing the purity of the ammonia separated in the gas-liquid separator and affecting the subsequent reactor reaction process. At a membrane distillation temperature of 50-60℃, the ammonia recovery rate was 99.2%, and the pyridine base loss rate was 0.8%, showing the best overall effect. This indicates that a membrane distillation temperature of 50-60℃ is the most suitable operating condition.

[0077] Example 9: Preparation of PTFE / ZnO nanoporous composite membrane: PTFE fine powder, zinc acetate micro powder and naphtha were mixed evenly at a mass ratio of 10:1:6 and aged at 40°C to form a paste. The paste was extruded and calendered to obtain a membrane material with a thickness of 200 μm. The membrane material was heated at 130°C and 250°C for 60 min and 120 min, respectively. The heat-treated membrane material was longitudinally stretched at 330°C to 3 times its original size. Subsequently, it was sintered at 380°C for 10 minutes to fix the shape, thus obtaining the PTFE / ZnO nanoporous composite membrane.

[0078] Membrane module preparation and activation: The prepared PTFE / ZnO nanoporous composite membrane was cut and encapsulated with stainless steel end caps and silicone rubber O-rings to assemble into a tubular membrane module; the assembled tubular membrane module was sequentially rinsed at 40°C with deionized water for 30 minutes, anhydrous ethanol for 10 minutes, and deionized water until neutral to wet the membrane pores, completing the activation and naming it PTFE / ZnO-9, and the PTFE / ZnO-9 membrane was installed in a membrane distillation device.

[0079] Pyridine base separation and ammonia recovery: The pyridine base synthesis quench liquid is passed through a pretreatment filter to remove solid particles and suspended matter. The pretreated quench liquid then enters a polyvinylidene fluoride ultrafiltration membrane module (molecular weight cutoff 3000 Da, operating pressure 0.4 MPa, operating temperature 40℃, membrane flux 85 L / (m²·h)). Tar is retained in the concentrate and discharged. The permeate is preheated (preheating temperature 50℃) and then enters a membrane distillation module. The membrane distillation module adopts a 5-stage series structure with an absolute pressure of 85 kPa on the permeate side. Each stage provides mass transfer driving force through a temperature gradient. The operating conditions are: stage 1 temperature 50℃, stage 2 temperature 52℃, stage 3 temperature 55℃, stage 4 temperature 58℃, and stage 5 temperature 60℃. Membrane distillation permeate steam enters a gas-liquid separator (operating temperature 20℃). Water vapor and pyridine base condense into a liquid phase and return to the membrane distillation feed inlet for recirculation. Uncondensed ammonia gas enters a dry screw vacuum pump through the upper outlet of the gas-liquid separator. After passing through the pump body, the ammonia gas is discharged at the pump outlet under slight positive pressure and directly fed into the reactor's circulation pipeline for reuse. After 120 hours of continuous operation, the membrane distillation flux decreased from the initial 4.8 kg / (m²·h) to 4.6 kg / (m²·h) (96% of the initial value). Experiments showed an ammonia recovery rate of 99.1%, a pyridine base loss rate of 0.9%, a tar removal rate of 94.5%, and an ammonia purity of 99.2%. Inspection of the membrane module revealed almost no tar deposition on the membrane surface.

[0080] Example 10: Long-term continuous operation verification was conducted under the same operating conditions as in Example 9. After 720 hours of continuous operation, the membrane distillation flux decreased from the initial 4.8 kg / (m²·h) to 3.9 kg / (m²·h) (82% of the initial value). Throughout the operation, the ammonia recovery rate remained stable above 98.5%, and the pyridine base loss rate remained below 1%. The experimental results indicate that after ultrafiltration pretreatment, the membrane module operates stably, and the operating cycle can exceed 720 hours. Upon inspection of the membrane module, slight tar deposition was observed on the membrane surface.

[0081] Comparative Example 1: Preparation of PTFE nanoporous composite membrane: PTFE fine powder and naphtha were mixed evenly at a mass ratio of 10:6 and aged at 40℃ to form a paste. The paste was extruded and calendered to obtain a membrane material with a thickness of 200μm. The membrane material was heated at 130℃ and 250℃ for 60min and 120min, respectively. The heat-treated membrane material was longitudinally stretched at 330℃ to 3 times its original size. Subsequently, it was sintered at 380℃ for 10 minutes to fix the shape, thus obtaining the PTFE nanoporous composite membrane.

[0082] Membrane module preparation and activation: The prepared PTFE nanoporous composite membrane was cut and encapsulated with stainless steel end caps and silicone rubber O-rings to assemble into a tubular membrane module; the assembled tubular membrane module was sequentially rinsed with deionized water for 30 minutes, anhydrous ethanol for 10 minutes, and deionized water until neutral at 40°C to wet the membrane pores, thus completing the activation and naming it PTFE-1. The membrane was then installed in a membrane distillation device.

[0083] Pyridine base separation and ammonia recovery: The pyridine base synthesis quench solution is passed through a pretreatment filter to remove solid particles and suspended matter. The pretreated quench solution then enters a PVDF ultrafiltration membrane module (molecular weight cutoff 3000 Da, operating pressure 0.4 MPa, operating temperature 40℃, membrane flux 85 L / (m²·h)). Tar is retained in the concentrate and discharged. The permeate is preheated (preheating temperature 50℃) and then enters a membrane distillation module. The membrane distillation module adopts a 5-stage series structure with an absolute pressure of 85 kPa on the permeate side. Each stage provides mass transfer driving force through a temperature gradient. The operating conditions are: stage 1 temperature 50℃, stage 2 temperature 52℃, stage 3 temperature 55℃, stage 4 temperature 58℃, and stage 5 temperature 60℃. The steam permeate from the membrane distillation enters the gas-liquid separator (operating temperature 20℃). The water vapor and pyridine base condense into a liquid phase and return to the membrane distillation feed inlet for recirculation. Uncondensed ammonia gas enters a dry screw vacuum pump through the upper outlet of the gas-liquid separator. After passing through the pump body, the ammonia gas is discharged at the pump outlet under slight positive pressure and directly fed into the reactor's circulation pipeline for reuse. Experiments showed an ammonia recovery rate of 86.3%, a pyridine base loss rate of 0.81%, and an ammonia purity of 91.0%.

[0084] Comparative Example 2: Preparation of PTFE / FeO nanoporous composite membrane: PTFE fine powder, ferric acetate micro powder and naphtha were mixed evenly at a mass ratio of 10:1:6 and aged at 40℃ to form a paste. The paste was extruded and calendered to obtain a membrane material with a thickness of 200μm. The membrane material was heated at 130℃ and 250℃ for 60min and 120min respectively. The heat-treated membrane material was longitudinally stretched at 330℃ to 3 times its original size. Then it was sintered at 380℃ for 10 minutes to fix the shape, thus obtaining the PTFE / FeO nanoporous composite membrane.

[0085] Membrane module preparation and activation: The prepared PTFE / FeO nanoporous composite membrane was cut and encapsulated with stainless steel end caps and silicone rubber O-rings to assemble into a tubular membrane module. The assembled tubular membrane module was sequentially rinsed with deionized water for 30 minutes, anhydrous ethanol for 10 minutes, and deionized water until neutral at 40°C to wet the membrane pores and complete the activation. It was named PTFE / FeO-1 and installed in a membrane distillation device.

[0086] Pyridine base separation and ammonia recovery: The pyridine base synthesis quench solution is passed through a pretreatment filter to remove solid particles and suspended matter. The pretreated quench solution then enters a PVDF ultrafiltration membrane module (molecular weight cutoff 3000 Da, operating pressure 0.4 MPa, operating temperature 40℃, membrane flux 85 L / (m²·h)). Tar is retained in the concentrate and discharged. The permeate is preheated (preheating temperature 50℃) and then enters a membrane distillation module. The membrane distillation module adopts a 5-stage series structure with an absolute pressure of 85 kPa on the permeate side. Each stage provides mass transfer driving force through a temperature gradient. The operating conditions are: stage 1 temperature 50℃, stage 2 temperature 52℃, stage 3 temperature 55℃, stage 4 temperature 58℃, and stage 5 temperature 60℃. The steam permeate from the membrane distillation enters the gas-liquid separator (operating temperature 20℃), where the water vapor and pyridine base condense into a liquid phase and return to the membrane distillation feed inlet for recycling. Uncondensed ammonia gas enters a dry screw vacuum pump through the upper outlet of the gas-liquid separator. After passing through the pump body, the ammonia gas is discharged at the pump outlet under slight positive pressure and directly fed into the reactor's circulation pipeline for reuse. Experiments showed an ammonia recovery rate of 93.7%, a pyridine base loss rate of 0.80%, and an ammonia purity of 95.3%.

[0087] Comparative Example 3: Preparation of PTFE / CuO nanoporous composite membrane: PTFE fine powder, copper acetate micro powder and naphtha were mixed evenly at a mass ratio of 10:1:6 and aged at 40℃ to form a paste. The paste was extruded and calendered to obtain a membrane material with a thickness of 200μm. The membrane material was heated at 130℃ and 250℃ for 60min and 120min respectively. The heat-treated membrane material was longitudinally stretched at 330℃ to 3 times its original size. Then it was sintered at 380℃ for 10 minutes to fix the shape, thus obtaining the PTFE / CuO nanoporous composite membrane.

[0088] Membrane module preparation and activation: The prepared PTFE / CuO nanoporous composite membrane was cut and encapsulated with stainless steel end caps and silicone rubber O-rings to assemble into a tubular membrane module; the assembled tubular membrane module was sequentially rinsed with deionized water for 30 minutes, anhydrous ethanol for 10 minutes, and deionized water until neutral at 40°C to wet the membrane pores, thus completing the activation and naming it PTFE / CuO-1. The PTFE / CuO-1 membrane was then installed in a membrane distillation apparatus.

[0089] Pyridine base separation and ammonia recovery: The pyridine base synthesis quench liquid is passed through a pretreatment filter to remove solid particles and suspended matter. The pretreated quench liquid then enters a polyvinylidene fluoride ultrafiltration membrane module (molecular weight cutoff 3000 Da, operating pressure 0.4 MPa, operating temperature 40℃, membrane flux 85 L / (m²·h)). Tar is retained in the concentrate and discharged. The permeate is preheated (preheating temperature 50℃) and then enters a membrane distillation module. The membrane distillation module adopts a 5-stage series structure with an absolute pressure of 85 kPa on the permeate side. Each stage provides mass transfer driving force through a temperature gradient. The operating conditions are: stage 1 temperature 50℃, stage 2 temperature 52℃, stage 3 temperature 55℃, stage 4 temperature 58℃, and stage 5 temperature 60℃. The steam permeate from the membrane distillation enters the gas-liquid separator (operating temperature 20℃), where the water vapor and pyridine base condense into a liquid phase and return to the membrane distillation feed inlet for recycling. Uncondensed ammonia gas enters a dry screw vacuum pump through the upper outlet of the gas-liquid separator. After passing through the pump body, the ammonia gas is discharged at the pump outlet under slight positive pressure and directly fed into the reactor's circulation pipeline for reuse. Experiments showed an ammonia recovery rate of 90.2%, a pyridine base loss rate of 0.82%, and an ammonia purity of 94.4%.

[0090] The results of Example 1 and Comparative Examples 1-3 are shown in Table 4 below:

[0091] Table 4. Effects of different metal salts on ammonia recovery

[0092] Example Metal salts Ammonia recovery rate (%) Pyridine base loss rate (%) Ammonia purity (%) Example 1 Zinc acetate 99.2 0.80 99.2 Comparative Example 1 No metal salts added 86.3 0.81 91.0 Comparative Example 2 Ferric acetate 93.7 0.80 95.3 Comparative Example 3 Copper acetate 90.2 0.82 94.4

[0093] As shown in Table 4, under the same process conditions, the ammonia recovery rate and ammonia purity of Example 1 (with zinc acetate) were significantly higher than those of the comparative examples: the ammonia recovery rate reached 99.2%, which was far superior to the schemes without metal salt (86.3%), with the addition of ferric acetate (93.7%) and copper acetate (90.2%); the ammonia purity was 99.2%, which was also significantly higher than that without metal salt (91.0%) and with ferric and copper salts (95.3% and 94.4%, respectively).

[0094] More importantly, zinc metal exhibits a highly selective binding capacity for ammonia—efficiently capturing and allowing ammonia molecules to pass through, thereby significantly improving recovery rate and product purity. Simultaneously, the pyridine base loss rate (0.80%) did not increase with the improved ammonia recovery efficiency, remaining on par with the optimal comparative example 2 and slightly lower than comparative example 3 (0.82%). This indicates that zinc ions, in the process of preferentially binding with ammonia, can effectively suppress the accompanying permeation of pyridine base, achieving the dual advantages of high ammonia selective recovery and low pyridine entrainment. Zinc acetate, as a metal salt additive, utilizes the strong selective coordination between zinc and ammonia to significantly improve ammonia recovery efficiency and purity without increasing the pyridine base loss rate. Its overall performance is significantly superior to schemes without metal salts or with the addition of ferric acetate or copper acetate.

[0095] Comparative Example 4: Preparation of PTFE / ZnO nanoporous composite membrane: PTFE fine powder, zinc acetate micro powder and naphtha were mixed evenly at a mass ratio of 10:1:6 and aged at 40℃ to form a paste. The paste was extruded and calendered to obtain a membrane material with a thickness of 200μm. The membrane material was heated at 130℃ and 250℃ for 60min and 120min respectively. The heat-treated membrane material was longitudinally stretched at 330℃ to 3 times its original length. Then it was sintered at 380℃ for 10 minutes to fix the shape, thus obtaining the PTFE / ZnO nanoporous composite membrane.

[0096] Membrane module preparation and activation: The prepared PTFE / ZnO nanoporous composite membrane was cut and encapsulated with stainless steel end caps and silicone rubber O-rings to assemble into a tubular membrane module; the assembled tubular membrane module was sequentially rinsed with deionized water for 30 minutes, anhydrous ethanol for 10 minutes, and deionized water until neutral at 40°C to wet the membrane pores, thus completing the activation and naming it PTFE / ZnO-1. The PTFE / ZnO-1 membrane was then installed in a membrane distillation apparatus.

[0097] The pyridine base synthesis quench solution was directly fed into the membrane distillation module without any tar pretreatment. Tar was collected from the final side stream of the membrane distillation system, and the remaining operating conditions were the same as in Example 9 for continuous operation. The initial membrane distillation flux was 4.8 kg / (m²·h), and after 120 hours of operation, the flux decreased to 2.1 kg / (m²·h) (44% of the initial value). The experimental results showed an ammonia recovery rate of 92.5%, a pyridine base loss rate of 5.8%, a tar removal rate of 35.2%, and an ammonia purity of 88.5%. Upon inspection of the membrane module, significant tar deposition was found on the membrane surface, and the membrane pores were partially blocked.

[0098] Comparative Example 5: Preparation of PTFE / ZnO nanoporous composite membrane: PTFE fine powder, zinc acetate micro powder and naphtha were mixed evenly at a mass ratio of 10:1:6 and aged at 40℃ to form a paste. The paste was extruded and calendered to obtain a membrane material with a thickness of 200μm. The membrane material was heated at 130℃ and 250℃ for 60min and 120min respectively. The heat-treated membrane material was longitudinally stretched at 330℃ to 3 times its original length. Then it was sintered at 380℃ for 10 minutes to fix the shape, thus obtaining the PTFE / ZnO nanoporous composite membrane.

[0099] Membrane module preparation and activation: The prepared PTFE / ZnO nanoporous composite membrane was cut and encapsulated with stainless steel end caps and silicone rubber O-rings to assemble into a tubular membrane module; the assembled tubular membrane module was sequentially rinsed with deionized water for 30 minutes, anhydrous ethanol for 10 minutes, and deionized water until neutral at 40°C to wet the membrane pores, thus completing the activation and naming it PTFE / ZnO-1. The PTFE / ZnO-1 membrane was then installed in a membrane distillation apparatus.

[0100] Pyridine base separation and ammonia recovery: The pyridine base synthesis quench liquid was pretreated through a bag filter (filtration accuracy 10 μm) before entering the membrane distillation module. All other operating conditions were the same as in Example 9, with continuous operation. The initial membrane distillation flux was 4.8 kg / (m²·h). After 120 hours of operation, the membrane distillation flux decreased to 2.8 kg / (m²·h) (58% of the initial value). The experimental results showed an ammonia recovery rate of 93.5%, a pyridine base loss rate of 4.2%, a tar removal rate of 42.5% (approximately 15% removed by pretreatment and approximately 27.5% collected from the final stage side stream of membrane distillation), and an ammonia purity of 90.2%. Upon inspection of the membrane module, tar deposits were still found on the membrane surface.

[0101] Comparative Example 6: Preparation of PTFE / ZnO nanoporous composite membrane: PTFE fine powder, zinc acetate micro powder and naphtha were mixed evenly at a mass ratio of 10:1:6 and aged at 40℃ to form a paste. The paste was extruded and calendered to obtain a membrane material with a thickness of 200μm. The membrane material was heated at 130℃ and 250℃ for 60min and 120min respectively. The heat-treated membrane material was longitudinally stretched at 330℃ to 3 times its original length. Then it was sintered at 380℃ for 10 minutes to fix the shape, thus obtaining the PTFE / ZnO nanoporous composite membrane.

[0102] Membrane module preparation and activation: The prepared PTFE / ZnO nanoporous composite membrane was cut and encapsulated with stainless steel end caps and silicone rubber O-rings to assemble into a tubular membrane module; the assembled membrane module was sequentially rinsed with deionized water for 30 minutes, anhydrous ethanol for 10 minutes, and deionized water until neutral at 40°C to wet the membrane pores, thus completing the activation and naming it PTFE / ZnO-1. The PTFE / ZnO-1 membrane was then installed in a membrane distillation apparatus.

[0103] Pyridine base separation and ammonia recovery: After the pyridine base synthesis quench liquid was allowed to settle for 2 hours, the supernatant was fed into the membrane distillation unit. The remaining operating conditions were the same as in Example 9, with continuous operation. The initial membrane distillation flux was 4.8 kg / (m²·h). After 120 hours of operation, the membrane distillation flux decreased to 3.2 kg / (m²·h) (67% of the initial value). The experimental results showed an ammonia recovery rate of 94.2%, a pyridine base loss rate of 3.5%, a tar removal rate of 48.5% (approximately 25% removed by sedimentation and approximately 23.5% collected from the final stage side stream of membrane distillation), and an ammonia purity of 91.8%. Upon inspection of the membrane unit, slight tar deposition was observed on the membrane surface.

[0104] The results of Example 9 and Comparative Examples 4-6 are shown in Table 5 below:

[0105] Table 5. Effects of different pretreatments on ammonia recovery

[0106] Preprocessing conditions Example 9 Comparative Example 4 Comparative Example 5 Comparative Example 6 Tar pretreatment methods Ultrafiltration membrane No pretreatment ordinary filtration settlement Running time (h) 120 120 120 120 Initial membrane distillation flux (kg / m²·h) 4.8 4.8 4.8 4.8 Membrane distillation flux after operation (kg / m²·h) 4.6 2.1 2.8 3.2 Flux retention rate (%) 96 44 58 67 Ammonia recovery rate (%) 99.1 92.5 93.5 94.2 pyridine base loss rate 0.9 5.8 4.2 3.5 Tar removal rate (%) 94.5 35.2 42.5 48.5

[0107] As shown in Table 5, after ultrafiltration membrane pretreatment in Example 9, the membrane distillation flux retention rate reached 96% during 120 hours of operation, while the retention rates of Comparative Example 4 (no pretreatment), Comparative Example 5 (ordinary filtration), and Comparative Example 6 (sedimentation) were only 44%–67%. Ultrafiltration membranes effectively delayed membrane fouling. Simultaneously, Example 9 achieved an ammonia recovery rate of 99.1%, which was 4.9–6.6 percentage points higher than the comparative examples; the pyridine base loss rate was only 0.9%, far lower than the 3.5%–5.8% of the comparative examples; and the tar removal rate reached 94.5%, more than twice the removal rate of Comparative Examples 4–6 (35.2%–48.5%). Example 10 demonstrates that the device maintained stability even after 720 hours of continuous operation, with ammonia recovery rate remaining at a high level and membrane distillation flux remaining highly efficient for an extended period, facilitating long-term stable operation. Therefore, ultrafiltration membrane pretreatment can deeply remove tar, ensure high-flux operation of membrane distillation, and reduce pyridine base loss while improving ammonia recovery efficiency.

[0108] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for quenching liquid ammonia recovery during pyridine base synthesis based on nanoporous composite membranes, characterized in that, Includes the following steps: S1: PTFE fine powder, zinc salt micro powder and hydrocarbon lubricant are mixed evenly and aged in a sealed container to form a paste. The paste is extruded into a strip preform and calendered to obtain a membrane material. The membrane material is then heat-treated, stretched longitudinally, and sintered to obtain a PTFE / ZnO nanoporous composite membrane. S2: Cut the prepared PTFE / ZnO nanoporous composite membrane, encapsulate it with polypropylene or stainless steel end caps and silicone rubber O-rings, assemble it into a tubular membrane module, and sequentially rinse the assembled tubular membrane module with deionized water circulation, anhydrous ethanol, and deionized water until neutral to complete the activation. S3: The quench liquid from the pyridine base synthesis quench tower is passed through a pretreatment filter to remove solid particles and suspended matter, and the pretreatment liquid is sent into the ultrafiltration membrane module. Tar and macromolecular impurities are intercepted and discharged, while ammonia, water and pyridine base permeate through the membrane to form the permeate. S4: The obtained permeate is preheated and then fed into a multi-stage tandem membrane distillation unit. Membrane distillation separation is carried out under vacuum conditions on the permeate side. Volatile components vaporize and permeate through the membrane pores, while non-volatile components are retained to form a lean ammonia concentrate. S5: The mixed steam from the permeate side of the membrane distillation is introduced into the gas-liquid separator for gas-liquid separation to obtain a gas phase rich in ammonia and a liquid phase containing water and pyridine base. The gas phase ammonia is sent to the synthesis reactor as raw material, and the liquid phase is recycled back to the membrane distillation feed inlet. The lean ammonia concentrate obtained in S4 is sent to the extraction section to recover the pyridine base product.

2. The method for quenching liquid ammonia recovery from pyridine base synthesis based on nanoporous composite membranes according to claim 1, characterized in that, For S1, the zinc salt micro powder is one of zinc chloride, zinc sulfate, and zinc acetate, and the addition amount is 5%-20% of the mass of PTFE fine powder. The hydrocarbon lubricant is naphtha, and the amount used is 50%-80% of the mass of PTFE fine powder. The aging temperature is 20℃-50℃, and the aging time is 24 hours.

3. The method for quenching liquid ammonia recovery from pyridine base synthesis based on nanoporous composite membranes according to claim 2, characterized in that, The heat treatment of the membrane material in S1 includes two stages. In the first stage, the temperature is raised to 100-150℃ and held for 30-60 minutes to volatilize and remove hydrocarbon lubricants. In the second stage, the temperature is raised to 200-260℃ and held for 60-120 minutes to decompose the zinc salt micropowder in situ and form a nanoporous ring structure in the PTFE matrix.

4. The method for quenching liquid ammonia recovery from pyridine base synthesis based on nanoporous composite membranes according to claim 1, characterized in that, In S1, the film thickness is 100-300μm, the longitudinal stretching temperature is 300-350℃, the stretching ratio is 2-5 times, the sintering and shaping temperature is 350-400℃, and the sintering time is 5-15 minutes.

5. The method for quenching liquid ammonia recovery from pyridine base synthesis based on nanoporous composite membranes according to claim 1, characterized in that, In S2, the activation steps are as follows: rinse with deionized water at a temperature of 30-50℃ for 30 minutes, then rinse with anhydrous ethanol for 10 minutes, and finally rinse with deionized water until neutral.

6. The method for quenching liquid ammonia recovery from pyridine base synthesis based on nanoporous composite membranes according to claim 1, characterized in that, In S3, the membrane material of the ultrafiltration membrane module is polyethersulfone or polyvinylidene fluoride, with a molecular weight cutoff of 1000-5000 Da, an ultrafiltration operating pressure of 0.2-0.6 MPa, an operating temperature of 30-50℃, and a membrane flux of 50-150 L / (m²·h).

7. The method for quenching liquid ammonia recovery from pyridine base synthesis based on nanoporous composite membranes according to claim 1, characterized in that, In S4, the preheating temperature is 40-60℃, the multi-stage series membrane distillation assembly consists of 3-7 stages in series, the operating temperature of each stage is 40-80℃, and the permeate side pressure is 70-120kPa.

8. The method for quenching liquid ammonia recovery from pyridine base synthesis based on nanoporous composite membranes according to claim 1, characterized in that, In S5, the operating temperature of the gas-liquid separator is 10-60℃.

9. A device for recovering liquid ammonia from pyridine base synthesis based on a nanoporous composite membrane, used to implement the method for recovering liquid ammonia from pyridine base synthesis as described in claim 1, characterized in that, include, Coolant storage tank (1), used for temporary storage of cooled coolant; A pretreatment filter (2) connected to the quench liquid storage tank (1) is used to remove solid particles and suspended matter from the quench liquid; The ultrafiltration membrane module (3) is provided with a feed inlet, a permeate outlet and a retentate outlet. The feed inlet is connected to the pretreatment filter (2), the permeate outlet is connected to the membrane distillation module (4), and the retentate outlet is connected to the tar treatment device. The multi-stage membrane distillation unit (4) is equipped with a feed inlet, a concentrate outlet and a permeate steam outlet; The gas-liquid separator (5) has its inlet connected to the permeate vapor outlet of the membrane distillation unit (4). The gas-liquid separator (5) is provided with a gas phase outlet and a liquid phase outlet. The gas phase outlet of the gas-liquid separator is connected to the vacuum system.

10. The pyridine base synthesis quenching liquid ammonia recovery device based on a nanoporous composite membrane according to claim 1, characterized in that, The quench liquid in the quench liquid storage tank (1) is pumped to the pretreatment filter (2), and the liquid phase from the liquid phase outlet of the gas-liquid separator (5) is circulated back to the membrane distillation unit (4) by the pump.

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