A method for purifying and distilling hydrochloric acid

Abstract

This invention discloses a method for purifying and distilling hydrochloric acid, belonging to the field of compound purification technology. This method involves sequentially processing industrial-grade hydrochloric acid through high-level temporary storage, atmospheric pressure distillation, condensation and collection, quality testing, and filtration to achieve the graded removal of volatile and non-volatile impurities. The filtration step employs a filtration device composed of two long-lasting microporous membranes. These microporous membranes are polytetrafluoroethylene (PTFE) long-lasting microporous membranes prepared using a specific lubricant system, possessing a stable microporous structure and excellent resistance to strong acids. Simultaneously, the hydrochloric acid waste gas generated during distillation and packaging is treated with water absorption, achieving waste gas treatment and resource recovery. Compared with existing technologies, this invention features a simple process flow, strong applicability, high filtration stability and operational reliability, effectively improving the quality of hydrochloric acid purification and reducing overall system operational risks, making it suitable for industrial-scale application.

Description

Technical Field

[0001] This invention relates to the field of compound purification technology, and in particular to a method for purifying and distilling hydrochloric acid. Background Technology

[0002] Hydrochloric acid, as an important basic chemical raw material, is widely used in chemical synthesis, metallurgy, electronics, pharmaceuticals, and fine chemicals. The hydrochloric acid obtained in industrial production processes is usually from complex sources, often accompanied by metal ions, organic byproducts, non-volatile impurities, or trace particulate matter, making it difficult to directly meet high purity or specific application requirements. Therefore, various hydrochloric acid purification and recovery methods have been proposed in existing technologies to address different sources and impurity characteristics, mainly including adsorption methods, oxidation, combined adsorption methods, distillation methods, and their combinations.

[0003] Patent CN104058370A discloses a purification method for hydrochloric acid, a byproduct of dimethyldichlorosilane hydrolysis. This method employs a silane-modified macroporous polyvinylidene chloride (PVDC) adsorption resin to selectively adsorb and remove siloxane impurities from the hydrochloric acid. While this method shows good specificity in certain byproduct hydrochloric acid systems, it relies on a specially modified resin, limiting its applicability. Furthermore, its ability to remove non-siloxane impurities or metal ions is limited, and resin regeneration and long-term stability remain somewhat constrained.

[0004] Patent CN104891440A discloses a purification and recovery system and method for iron-containing waste hydrochloric acid. It employs a process combining hydrogen peroxide oxidation and resin adsorption, effectively removing iron ions and achieving acid recovery. While this system has certain advantages in metal ion removal, it involves numerous process units, resulting in a relatively complex system structure. It also requires high precision in reagent dosing and operational control, and is primarily designed for iron-containing waste acid systems, lacking adaptability to hydrochloric acid from other sources or situations where multiple impurities coexist.

[0005] In summary, existing hydrochloric acid purification technologies are mostly optimized for specific impurities or hydrochloric acid from specific sources. They generally suffer from limited applicability, complex processes, strong dependence on consumables or chemicals, and insufficient long-term operational stability. In particular, while achieving high-purity, continuous, and low-cost purification, a technology that simultaneously ensures filtration stability under strong acid conditions and facilitates waste gas resource recovery remains lacking. Therefore, a highly integrated, reliable, and industrially viable technical solution is urgently needed for improvement and refinement. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to provide a method for purifying and distilling hydrochloric acid.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A method for purifying and distilling hydrochloric acid is as follows:

[0009] Step 1: Industrial-grade hydrochloric acid is temporarily stored in an elevated tank equipped with a level gauge and a pneumatic regulating valve for quantitative feed control during the subsequent distillation process.

[0010] Step 2: The industrial-grade hydrochloric acid in the high-level tank flows by gravity into the quartz glass distillation unit. Before feeding, the cooling circulating water system is turned on, and then the electric heating device is turned on to heat and distill the hydrochloric acid in the distillation kettle. The hydrochloric acid vapor is condensed by the condenser to form distillate liquid and flows into the finished product collection tank. The distillation residue is discharged from the bottom of the kettle as industrial-grade hydrochloric acid recovery.

[0011] Step 3: Take a sample of the distilled hydrochloric acid from the finished product collection tank and send it to the testing laboratory for quality testing. If it meets the requirements, it is qualified; otherwise, return it to the distillation process.

[0012] Step 4: Filter the qualified hydrochloric acid through a filtration device. The filter material of the filtration device is composed of two layers of long-lasting microporous membrane. After filtration, package the product.

[0013] Step 5: The hydrochloric acid waste gas generated during the distillation and packaging process is introduced into a mobile waste gas absorption device through a pipeline. Clean water is used as the absorption medium to absorb and treat the waste gas. After the absorption is completed, the dilute hydrochloric acid absorption liquid obtained is recycled as industrial-grade dilute hydrochloric acid.

[0014] The long-lasting microporous membrane is made by mixing and maturing polytetrafluoroethylene dispersion resin and lubricant, followed by pre-pressing, paste extrusion, calendering into a base tape, longitudinal stretching, high-temperature activation and annealing, transverse stretching and heat setting, cooling and winding.

[0015] The lubricant is composed of isohexadecane and decahydronaphthalene in a mass ratio of 0.5-2:0.5-2.

[0016] The industrial-grade hydrochloric acid has a mass fraction of 36-38%.

[0017] In step 1, the pump's working pressure is controlled at 0.3-0.5 MPa and the feed temperature is controlled at 20-30℃ during the conveying process.

[0018] In step 2, the cooling water inlet temperature is set to 15-25℃, and the flow rate is set to 1.5-2m³ / h. 3 / h.

[0019] In step 2, the hydrochloric acid is heated and distilled to stabilize its boiling point at 48-50°C. The distillation process is carried out under normal pressure, and the feed flow rate is controlled at 8-12 L / h. The liquid level in the distillation vessel is kept stable by adjusting the feed rate.

[0020] In step 3, the quality testing is to determine that the hydrochloric acid mass fraction is 36.4-36.6%, the appearance is colorless, transparent and clear with no visible suspended matter, Fe≤1.0 mg / L, heavy metals (as Pb)≤1.0 mg / L, and non-volatile matter≤10 mg / L.

[0021] The mass fraction of the dilute hydrochloric acid absorption solution obtained after absorption in step 5 is 8-12%.

[0022] The method for preparing the long-lasting microporous membrane is as follows:

[0023] S1. Mix polytetrafluoroethylene dispersion resin and lubricant at a mass ratio of 4-6:0.5-2 and then cure. Set the curing conditions to 50-60℃ for 10-48h to ensure that the lubricant is fully impregnated and to obtain cured material. Pre-press the cured material into a preform at room temperature with a pre-pressing pressure of 4-6MPa and a holding pressure of 1-5min to form a preform. Then push the preform into an extruder and keep it in a feed gun at 35-45℃ for 5-15min before extruding the paste. Set the extrusion compression ratio to 160-200:1 to obtain strip preforms. Then roll the strips with a thickness of 160-200μm to obtain PTFE base tape.

[0024] S2. The PTFE base tape is directly fed into the longitudinal stretching unit. The temperature of the longitudinal stretching unit is set in a gradient manner as 190-210℃, 220-240℃, and 240-260℃, the longitudinal stretching ratio is set to 5-7 times, and the stretching speed is set to 1.2-2.5m / min. Then it enters the high-temperature activation zone and is held at 280-320℃ for 20-60s. Finally, it enters the annealing and winding zone and is held at 170-190℃ for 30-90s to obtain the longitudinally stretched film.

[0025] S3. The longitudinally stretched film obtained in step S2 is stretched laterally to form a stable microporous structure. The lateral stretching temperature is set to 310-330℃, the lateral stretching ratio is set to 8-12 times, and the stretching speed is set to 8-15m / min. After the lateral stretching is completed, the film is held in a clamped state and heat-set at 340-380℃ for 20-60s. Then it is cooled and wound up to obtain a long-lasting microporous film.

[0026] The lubricant is at least one of n-dodecane, n-tetradecane, isohexadecane, triacontane, isoeicosaecontane, and decahydronaphthalene.

[0027] In the method for preparing the long-lasting microporous membrane, step S2 can also be:

[0028] The PTFE base tape is directly fed into the longitudinal stretching unit. The longitudinal stretching unit is set with a temperature gradient of 190-210℃, 220-240℃, and 240-260℃, with segment ratios of 1.8-2.2 times, 1.2-1.8 times, and 1.8-2.2 times, respectively. The total longitudinal stretching ratio is 5-7 times, and the stretching speed is set to 1.2-2.5 m / min. Then, it enters the high-temperature activation zone and is held at 280-320℃ for 20-60 seconds. Finally, it enters the annealing and winding zone and is held at 170-190℃ for 30-90 seconds to obtain the longitudinally stretched film.

[0029] In the method for preparing the long-lasting microporous membrane, step S3 can also be:

[0030] The longitudinally stretched film obtained in step S2 is laterally stretched to form a stable microporous structure. The lateral stretching temperature is maintained at 310-330℃ for two-stage stretching, with the first stage having a lateral stretching ratio of 3-5 times and the second stage having a lateral stretching ratio of 2-3 times. The stretching speed is set to 8-15m / min. After the lateral stretching is completed, the film is held in a clamped state and heat-set at 340-380℃ for 20-60s. Then it is cooled and wound up to obtain a long-lasting microporous film.

[0031] This invention addresses the problem that industrial-grade hydrochloric acid may still carry trace amounts of non-volatile impurities, metal ions, and particles after distillation, and that the strong corrosiveness of hydrochloric acid leads to short lifespan and poor filtration stability of conventional filter media. It adopts an integrated approach that uses atmospheric pressure distillation for main purification, long-term microporous membranes for end-of-pipe purification, and waste gas absorption for closed-loop recovery. The key material for the filtration process is designed as a long-term microporous membrane of PTFE with stable pore size distribution, resistance to strong acids, and no premature degradation over long term, thus balancing purification effect, operational stability, and resource recovery.

[0032] At the level of membrane material mechanism, based on the difficult processing of PTFE and the characteristics of lamellar slip fiber formation, a lubricant system that can fully wet and disperse resin particles is selected. The lubricant reduces the activation energy of lamellar slip and fibril formation by diffusion between crystal domains. Furthermore, a synergistic compound lubricant system of isohexadecane and decahydronaphthalene is introduced to make the curing swelling, oil-containing molding and subsequent stretching pore formation process more matched, thereby improving the continuity of fiber formation and longitudinal fiber strength from the source, reducing the risk of transverse tensile fracture and improving the uniformity of pore structure.

[0033] Secondly, in terms of structural construction mechanism, the microporous network is controllably generated through a series of processes including paste extrusion, calendering into a substrate, longitudinal stretching, high-temperature activation, annealing, transverse stretching, and heat setting. The longitudinal stretching stage promotes the full sliding of the lamellar crystals and the formation of continuous fibrils and node skeletons. At the same time, the activation and annealing processes enhance the connection strength between lamellar crystals and promote the regular arrangement of molecular chains, thereby improving the interfacial strength of nodes. Subsequently, the transverse stretching drives the nodes and fibrils to further expand into pores. Combined with heat setting to solidify the micropore morphology, a long-lasting microporous membrane with stable pore size distribution and long-term filtration performance is obtained.

[0034] Compared with the prior art, the present invention has the following beneficial technical effects:

[0035] 1) This invention achieves the graded removal of volatile and non-volatile impurities in hydrochloric acid through a synergistic process of atmospheric pressure distillation and long-term microporous membrane filtration. The purification process is stable and continuous, and suitable for industrial operation.

[0036] 2) This invention employs a specific lubricant synergistic compounding and combined with a biaxial stretching membrane forming process to obtain a long-lasting microporous membrane with stable pore structure and resistance to strong acid corrosion, which significantly improves the long-term reliability of the filtration process.

[0037] 3) This invention integrates waste gas absorption and product recycling into a single design, achieving effective treatment and resource utilization of hydrochloric acid waste gas, reducing system operation risks and minimizing secondary pollution. Detailed Implementation

[0038] Polytetrafluoroethylene dispersion resin with a number average molecular weight of 10 million, crystallinity ≥97%, and volatile matter ≤0.10%.

[0039] IsoparV, brand: ExxonMobil.

[0040] In the embodiments and comparative examples of this invention, all raw materials are commercially available products.

[0041] Example 1

[0042] A method for purifying and distilling hydrochloric acid is as follows:

[0043] Step 1: 37% industrial-grade hydrochloric acid is temporarily stored in an elevated tank using an acid-resistant pneumatic diaphragm pump. During the transport process, the pump's working pressure is controlled at 0.4 MPa and the feed temperature is controlled at 25°C. The elevated tank is equipped with a level gauge and a pneumatic regulating valve for quantitative feed control in the subsequent distillation process.

[0044] Step 2: The industrial-grade hydrochloric acid in the high-level tank is automatically metered via a pneumatic regulating valve and then flows by gravity into the quartz glass distillation unit. Before feeding, the cooling water circulation system is turned on, with the cooling water inlet temperature set to 20℃ and the flow rate set to 1.8m³ / h. 3 / h, then turn on the electric heating device to heat the hydrochloric acid in the distillation kettle to make it boil stably at 49℃. The distillation process is carried out under normal pressure conditions, and the feed flow rate is controlled at 10L / h. By adjusting the feed rate, the liquid level in the distillation kettle is kept stable. The hydrochloric acid vapor is condensed by the condenser to form distillate liquid and flows into the finished product collection tank. The distillation residue is discharged from the bottom of the kettle as industrial-grade hydrochloric acid recovery.

[0045] Step 3: Take a sample of the distilled hydrochloric acid from the finished product collection tank and send it to the testing laboratory for quality testing. The hydrochloric acid mass fraction is 36.5%, the appearance is colorless, transparent and clear with no visible suspended matter, Fe≤1.0 mg / L, heavy metals (as Pb)≤1.0 mg / L, and non-volatile matter≤10 mg / L. If the above indicators are met, it is qualified; otherwise, it is returned to distillation.

[0046] Step 4: Filter the qualified hydrochloric acid through a filtration device. The filter material of the filtration device is composed of two layers of long-lasting microporous membrane. After filtration, the hydrochloric acid is directly put into acid-resistant ton containers for sealing and packaging. During the packaging process, the ambient temperature is maintained at 25°C.

[0047] Step 5: The hydrochloric acid waste gas generated during the distillation and packaging process is introduced into a mobile waste gas absorption device through a pipeline. Water is used as the absorption medium to absorb and treat the waste gas. After absorption, a dilute hydrochloric acid absorption liquid with a mass fraction of 10% is obtained. The absorption liquid is recycled as industrial-grade dilute hydrochloric acid.

[0048] The method for preparing the long-lasting microporous membrane is as follows:

[0049] S1. Polytetrafluoroethylene dispersion resin and lubricant are mixed evenly at a mass ratio of 5:1 and then cured. The curing conditions are set at 55℃ for 24 hours to ensure that the lubricant is fully impregnated and to obtain cured material. The cured material is pre-pressed at room temperature with a pre-pressing pressure of 5MPa and a holding pressure of 3min to form a preform. The preform is then pushed into an extruder and kept at 40℃ in a feed gun for 10min before paste extrusion. The extrusion compression ratio is set at 180:1 to obtain strip-shaped preforms, which are then rolled by two rollers to obtain PTFE base tape with a thickness of 180μm.

[0050] S2. The PTFE base tape is directly fed into the longitudinal stretching unit. The temperature of the longitudinal stretching unit is set in a gradient of 200℃, 230℃ and 250℃, the longitudinal stretching ratio is set to 6 times and the stretching speed is set to 2m / min. Then it enters the high temperature activation zone and is kept at 300℃ for 40s. Finally, it enters the annealing and winding zone and is kept at 180℃ for 60s to obtain the longitudinally stretched film.

[0051] S3. The longitudinally stretched film obtained in step S2 is stretched laterally to form a stable microporous structure. The lateral stretching temperature is set to 320℃, the lateral stretching ratio is set to 10 times, and the stretching speed is set to 12m / min. After the lateral stretching is completed, the film is held in a clamped state and heat-set at 360℃ for 45s. Then it is cooled and wound up to obtain a long-lasting microporous film.

[0052] The lubricant is n-dodecane.

[0053] Example 2

[0054] A method for purifying and distilling hydrochloric acid is basically the same as that in Example 1, except that the lubricant used in the preparation method of the long-lasting microporous membrane is n-tetradecane.

[0055] Example 3

[0056] A method for purifying and distilling hydrochloric acid is basically the same as that in Example 1, except that the lubricant used in the preparation method of the long-lasting microporous membrane is isocetane.

[0057] Example 4

[0058] A method for purifying and distilling hydrochloric acid is basically the same as that in Example 1, except that the lubricant used in the preparation method of the long-lasting microporous membrane is triacontane.

[0059] Example 5

[0060] A method for purifying and distilling hydrochloric acid is basically the same as that in Example 1, except that the lubricant used in the preparation method of the long-lasting microporous membrane is isoeicosane.

[0061] Example 6

[0062] A method for purifying and distilling hydrochloric acid is basically the same as that in Example 1, except that the lubricant used in the preparation method of the long-lasting microporous membrane is decahydronaphthalene.

[0063] Example 7

[0064] A method for purifying and distilling hydrochloric acid is basically the same as that in Example 1, except that the lubricant used in the preparation method of the long-lasting microporous membrane is composed of isohexadecane and decahydronaphthalene in a mass ratio of 1:1.

[0065] Example 8

[0066] A method for purifying and distilling hydrochloric acid is basically the same as that in Example 1, except that the lubricant used in the preparation method of the long-lasting microporous membrane is composed of n-dodecane and n-tetradecane in a mass ratio of 1:1.

[0067] Example 9

[0068] A method for purifying and distilling hydrochloric acid is basically the same as that in Example 7, except that the preparation method of the long-lasting microporous membrane is different.

[0069] The method for preparing the long-lasting microporous membrane is as follows:

[0070] S1. Polytetrafluoroethylene dispersion resin and lubricant are mixed evenly at a mass ratio of 5:1 and then cured. The curing conditions are set at 55℃ for 24 hours to ensure that the lubricant is fully impregnated and to obtain cured material. The cured material is pre-pressed at room temperature with a pre-pressing pressure of 5MPa and a holding pressure of 3min to form a preform. The preform is then pushed into an extruder and kept at 40℃ in a feed gun for 10min before paste extrusion. The extrusion compression ratio is set at 180:1 to obtain strip-shaped preforms, which are then rolled by two rollers to obtain PTFE base tape with a thickness of 180μm.

[0071] S2. The PTFE base tape is directly fed into the longitudinal stretching unit. The longitudinal stretching unit uses a gradient temperature setting with three temperature zones of 200℃, 230℃, and 250℃ for gradual stretching. The segment ratios are 2.0 times, 1.5 times, and 2.0 times respectively, with a total longitudinal stretching ratio of 6 times and a stretching linear speed of 1.5 m / min. Then, it enters the high-temperature activation zone and is held at 300℃ for 40 seconds. Finally, it enters the annealing and winding zone and is held at 180℃ for 60 seconds to obtain the longitudinally stretched film.

[0072] S3. The longitudinally stretched film obtained in step S2 is stretched laterally to form a stable microporous structure. The lateral stretching temperature is set to 320℃, the lateral stretching ratio is set to 10 times, and the stretching speed is set to 12m / min. After the lateral stretching is completed, the film is held in a clamped state and heat-set at 360℃ for 45s. Then it is cooled and wound up to obtain a long-lasting microporous film.

[0073] The lubricant is composed of isohexadecane and decahydronaphthalene in a mass ratio of 1:1.

[0074] Example 10

[0075] A method for purifying and distilling hydrochloric acid is basically the same as that in Example 9, except that the preparation method of the long-lasting microporous membrane is different.

[0076] The method for preparing the long-lasting microporous membrane is as follows:

[0077] S1. Polytetrafluoroethylene dispersion resin and lubricant are mixed evenly at a mass ratio of 5:1 and then cured. The curing conditions are set at 55℃ for 24 hours to ensure that the lubricant is fully impregnated and to obtain cured material. The cured material is pre-pressed at room temperature with a pre-pressing pressure of 5MPa and a holding pressure of 3min to form a preform. The preform is then pushed into an extruder and kept at 40℃ in a feed gun for 10min before paste extrusion. The extrusion compression ratio is set at 180:1 to obtain strip-shaped preforms, which are then rolled by two rollers to obtain PTFE base tape with a thickness of 180μm.

[0078] S2. The PTFE base tape is directly fed into the longitudinal stretching unit. The longitudinal stretching unit uses a gradient temperature setting with three temperature zones of 200℃, 230℃, and 250℃ for gradual stretching. The segment ratios are 2.0 times, 1.5 times, and 2.0 times respectively, with a total longitudinal stretching ratio of 6 times and a stretching linear speed of 1.5 m / min. Then, it enters the high-temperature activation zone and is held at 300℃ for 40 seconds. Finally, it enters the annealing and winding zone and is held at 180℃ for 60 seconds to obtain the longitudinally stretched film.

[0079] S3. The longitudinally stretched film obtained in step S2 is stretched laterally to form a stable microporous structure. The lateral stretching temperature is maintained at 320℃ for two-stage stretching. The first stage of lateral stretching is 4 times, and the second stage of lateral stretching is 2.5 times. The stretching speed is 12m / min. After the lateral stretching is completed, the film is held in a clamped state and heat-set at 360℃ for 45s. Then it is cooled and wound up to obtain a long-lasting microporous film.

[0080] The lubricant is composed of isohexadecane and decahydronaphthalene in a mass ratio of 1:1.

[0081] Comparative Example 1

[0082] A method for purifying and distilling hydrochloric acid is basically the same as that in Example 1, except that the lubricant used in the preparation method of the long-lasting microporous membrane is kerosene.

[0083] Comparative Example 2

[0084] A method for purifying and distilling hydrochloric acid is basically the same as that in Example 1, except that the lubricant used in the preparation method of the long-lasting microporous membrane is paraffin oil.

[0085] Test Example 1

[0086] Pore ​​size distribution and uniformity test:

[0087] Three locations (A, B, and C) were uniformly taken from the transverse direction of the long-lasting microporous membranes of Examples 1-10 and Comparative Examples 1-2; three more points (1, 2, and 3) were taken from each location (a total of 9 samples). The samples were cut into circles as required by the instrument, ensuring that the interior of the sample was not cut. The samples were immersed in the surfactant required by the PMI equipment for 30 minutes to ensure full wetting. The samples were then placed into the test chamber of the PMI (Gas Permeation Pore Size Analyzer) and sealed. The program was run to obtain the average pore size.

[0088] Uniformity is evaluated by calculating the standard deviation SD based on the sample pore size;

[0089] The test results are shown in Table 1.

[0090] Table 1

[0091] Experimental protocol Average pore size (μm) Standard deviation SD Example 1 0.25 0.010 Example 2 0.26 0.009 Example 3 0.25 0.008 Example 4 0.28 0.014 Example 5 0.27 0.011 Example 6 0.25 0.009 Example 7 0.25 0.006 Example 8 0.26 0.009 Example 9 0.25 0.005 Example 10 0.25 0.004 Comparative Example 1 0.30 0.020 Comparative Example 2 0.29 0.018

[0092] Test Example 2

[0093] Mechanical performance retention test before and after long-term hydrochloric acid filtration:

[0094] The long-lasting microporous membranes prepared in Examples 1-10 and Comparative Examples 1-2 were assembled into two-layer composite filter media in the same manner. Filtering was performed continuously for 72 hours at 25°C using 36.5% hydrochloric acid as the filter medium and a constant pressure of 0.20 MPa. After filtration, the membranes were removed and rinsed sequentially with hydrochloric acid and deionized water of the same concentration, then dried at room temperature to constant weight. Long strip samples were cut longitudinally from both the unfiltered and filtered membranes, and tensile tests were conducted using a universal testing machine at 25°C with a tensile speed of 50 mm / min to determine the longitudinal tensile strength.

[0095] Let σ0 be the longitudinal tensile strength of the membrane before filtration, and σ be the longitudinal tensile strength of the membrane after filtration for 72 hours. 72 Calculate the tensile strength retention rate (σ) 72 The percentage (σ0×100%) was used as the evaluation index. By comparing the test results of all examples with those of the comparative examples, the resistance of microporous membranes to mechanical property degradation during long-term hydrochloric acid filtration under different lubricant systems and membrane-making processes was evaluated.

[0096] Each group was measured in parallel three times, and the average value was taken. The relevant test data are summarized in Table 2.

[0097] Table 2

[0098] Experimental protocol Tensile strength retention rate (%) Example 1 92.3 Example 2 93.2 Example 3 94.6 Example 4 90.1 Example 5 91.5 Example 6 93.0 Example 7 96.1 Example 8 92.4 Example 9 97.2 Example 10 98.0 Comparative Example 1 82.3 Comparative Example 2 84.1

[0099] During the curing stage, the lubricant fully impregnates the PTFE dispersion resin, reducing interparticle friction and achieving more uniform stress during paste extrusion, thus minimizing extrusion and calendering defects. In the subsequent stretching process, the lubricant promotes the continuity of lamellar slippage and fibril formation, reducing microcracks and localized overstretching, resulting in a more stable junction and fibril microporous framework. The uniform pore structure and fewer defects make the membrane less prone to strength degradation and tearing during long-term hydrochloric acid filtration.

[0100] Example 3 uses isohexadecane as a lubricant, whose kinematic viscosity, volatility, and flow characteristics are better matched to the PTFE paste extrusion and subsequent biaxial stretching process: it is easier to wet and evenly disperse between resin particles during curing, and there is less friction and shear and fewer defects during extrusion and calendering; during stretching, the lamellar slippage is more complete, the fibrils are more continuous, and microcracks and local overstretching are reduced, so the pore size is more uniform (lower SD), and the strength retention rate after long-term hydrochloric acid filtration is higher than that of the other single lubricants in Examples 1-6.

[0101] In Example 7, isohexadecane readily diffuses and wets, reducing initial shear and friction; decahydronaphthalene provides stronger lubrication and is more beneficial to structural stability. The combination of the two ensures both easy wetting and stable lubrication, resulting in more balanced stress transmission during extrusion and stretching, more consistent fibril length and knot distribution, and suppression of macropore and pore size fluctuations. Therefore, the pore size SD is smaller, and the mechanical retention rate is higher after long-term hydrochloric acid filtration.

[0102] Example 9 employs a three-stage temperature zone gradual stretching with segmented scaling ratios in the longitudinal direction. This disperses the total deformation across multiple stages, reducing stress concentration and microcracks caused by a single stretching operation. The lower linear velocity extends the heating and relaxation time, allowing residual lubricant to diffuse and evaporate more evenly. This results in more complete lamellar slippage, gradual fiber growth, and stable connection, thereby improving longitudinal fiber strength and pore skeleton consistency. This more stable longitudinal skeleton provides a foundation for subsequent transverse pore formation, reducing strength degradation after long-term filtration.

[0103] Example 10 uses a two-stage transverse stretching method instead of a single-stage high-ratio stretching method, allowing pore formation to be completed in stages from channel establishment to uniform refinement. This avoids local overstretching, fiber breakage, and an increase in large pore tails caused by sudden large deformation. The second stage further unifies the channels on the existing skeleton, making the pore size distribution more concentrated. Combined with a heat-setting locking structure, it can effectively suppress pore enlargement and mechanical failure caused by long-term hydrochloric acid filtration, thus achieving optimal uniformity and retention.

Claims

1. A method for purifying and distilling hydrochloric acid, characterized in that, The method is as follows: Step 1: Industrial-grade hydrochloric acid is temporarily stored in an elevated tank equipped with a level gauge and a pneumatic regulating valve for quantitative feed control during the subsequent distillation process. Step 2: The industrial-grade hydrochloric acid in the high-level tank flows by gravity into the quartz glass distillation unit. Before feeding, the cooling circulating water system is turned on, and then the electric heating device is turned on to heat and distill the hydrochloric acid in the distillation kettle. The hydrochloric acid vapor is condensed by the condenser to form distillate liquid and flows into the finished product collection tank. The distillation residue is discharged from the bottom of the kettle as industrial-grade hydrochloric acid recovery. Step 3: Take a sample of the distilled hydrochloric acid from the finished product collection tank and send it to the testing laboratory for quality testing. If it meets the requirements, it is qualified; otherwise, return it to the distillation process. Step 4: Filter the qualified hydrochloric acid through a filtration device. The filter material of the filtration device is composed of two layers of long-lasting microporous membrane. After filtration, package the product. Step 5: The hydrochloric acid waste gas generated during the distillation and packaging process is introduced into a mobile waste gas absorption device through a pipeline. Clean water is used as the absorption medium to absorb and treat the waste gas. The dilute hydrochloric acid absorption liquid obtained after absorption is recycled as industrial-grade dilute hydrochloric acid. The long-lasting microporous membrane is made by mixing and maturing polytetrafluoroethylene dispersion resin and lubricant, followed by pre-pressing, paste extrusion, calendering into a base tape, longitudinal stretching, high-temperature activation and annealing, transverse stretching and heat setting, cooling and winding. The lubricant is composed of isohexadecane and decahydronaphthalene in a mass ratio of 0.5-2:0.5-2.

2. The hydrochloric acid purification and distillation method as described in claim 1, characterized in that, The industrial-grade hydrochloric acid has a mass fraction of 36-38%.

3. The hydrochloric acid purification and distillation method as described in claim 1, characterized in that, In step 1, the pump's working pressure is controlled at 0.3-0.5 MPa and the feed temperature is controlled at 20-30℃ during the conveying process.

4. The hydrochloric acid purification and distillation method as described in claim 1, characterized in that, In step 2, the cooling water inlet temperature is set to 15-25℃, and the flow rate is set to 1.5-2m³ / h. 3 / h.

5. The hydrochloric acid purification and distillation method as described in claim 1, characterized in that, In step 2, the hydrochloric acid is heated and distilled to stabilize its boiling point at 48-50°C. The distillation process is carried out under normal pressure, and the feed flow rate is controlled at 8-12 L / h. The liquid level in the distillation vessel is kept stable by adjusting the feed rate.

6. The hydrochloric acid purification and distillation method as described in claim 1, characterized in that, In step 3, the quality testing is to determine that the hydrochloric acid mass fraction is 36.4-36.6%, the appearance is colorless, transparent and clear with no visible suspended matter, Fe≤1.0 mg / L, heavy metals (calculated as Pb)≤1.0 mg / L, and non-volatile matter≤10 mg / L.

7. The hydrochloric acid purification and distillation method as described in claim 1, characterized in that, The mass fraction of the dilute hydrochloric acid absorption solution obtained after absorption in step 5 is 8-12%.

8. The method for purifying and distilling hydrochloric acid as described in claim 1, characterized in that, The method for preparing the long-lasting microporous membrane is as follows: S1. Mix polytetrafluoroethylene dispersion resin and lubricant at a mass ratio of 4-6:0.5-2 and then cure. Set the curing conditions to 50-60℃ for 10-48h to ensure that the lubricant is fully impregnated and to obtain cured material. Pre-press the cured material into a preform at room temperature with a pre-pressing pressure of 4-6MPa and a holding pressure of 1-5min to form a preform. Then push the preform into an extruder and keep it in a feed gun at 35-45℃ for 5-15min before paste extrusion. Set the extrusion compression ratio to 160-200:1 to obtain strip preforms. Then roll the strips with a thickness of 160-200μm to obtain PTFE base tape. S2. The PTFE base tape is directly fed into the longitudinal stretching unit. The temperature of the longitudinal stretching unit is set in a gradient manner as 190-210℃, 220-240℃, and 240-260℃, the longitudinal stretching ratio is set to 5-7 times, and the stretching speed is set to 1.2-2.5m / min. Then it enters the high-temperature activation zone and is held at 280-320℃ for 20-60s. Finally, it enters the annealing and winding zone and is held at 170-190℃ for 30-90s to obtain the longitudinally stretched film. S3. The longitudinally stretched film obtained in step S2 is stretched laterally to form a stable microporous structure. The lateral stretching temperature is set to 310-330℃, the lateral stretching ratio is set to 8-12 times, and the stretching speed is set to 8-15m / min. After the lateral stretching is completed, the film is held in a clamped state and heat-set at 340-380℃ for 20-60s. Then it is cooled and wound up to obtain a long-lasting microporous film.

9. The method for purifying and distilling hydrochloric acid as described in claim 8, characterized in that, In the method for preparing the long-lasting microporous membrane, step S2 can also be: The PTFE base tape is directly fed into the longitudinal stretching unit. The longitudinal stretching unit is set with a temperature gradient of 190-210℃, 220-240℃, and 240-260℃, with segment ratios of 1.8-2.2 times, 1.2-1.8 times, and 1.8-2.2 times, respectively. The total longitudinal stretching ratio is 5-7 times, and the stretching speed is set to 1.2-2.5 m / min. Then, it enters the high-temperature activation zone and is held at 280-320℃ for 20-60 seconds. Finally, it enters the annealing and winding zone and is held at 170-190℃ for 30-90 seconds to obtain the longitudinally stretched film.

10. The method for purifying and distilling hydrochloric acid as described in claim 1 or 8, characterized in that, In the method for preparing the long-lasting microporous membrane, step S3 can also be: The longitudinally stretched film obtained in step S2 is laterally stretched to form a stable microporous structure. The lateral stretching temperature is maintained at 310-330℃ for two-stage stretching, with the first stage having a lateral stretching ratio of 3-5 times and the second stage having a lateral stretching ratio of 2-3 times. The stretching speed is set to 8-15m / min. After the lateral stretching is completed, the film is held in a clamped state and heat-set at 340-380℃ for 20-60s. Then it is cooled and wound up to obtain a long-lasting microporous film.