Preparation method of hollow fiber deammoniation membrane fibers

Abstract

This invention discloses a method for preparing hollow fiber deammoniation membrane filaments, belonging to the field of polymer membrane technology. The method includes the following steps: S101: Mixing 15-25 parts by weight of polypropylene, 3-8 parts by weight of polyethylene, 3-8 parts by weight of plasticizer, 50-60 parts by weight of filler powder, 0.5-2 parts by weight of coupling agent, 2-5 parts by weight of lubricant, and 0.5-3 parts by weight of ammonia adsorbent at high speed at 5-25°C to prepare a mixed powder; S102: Extruding the mixed powder in an extruder at 120-160°C to form granules, while simultaneously injecting 12-17 parts by weight of plasticizer through the oil filling hole of the extruder; S103: Melting the granules obtained in step S102 at 130-165°C and extruding to obtain hollow fiber filaments; S104: Stretching the hollow fiber filaments obtained in step S103, followed by enzymatic hydrolysis or acid washing, and finally washing and drying to obtain deammoniation hollow fiber membrane filaments.

Description

Technical Field

[0001] This invention belongs to the field of polymer membrane technology, and specifically relates to a method for preparing membrane fibers of a hollow fiber deammoniation membrane. Background Technology

[0002] High ammonia nitrogen wastewater typically produces foul odors, causing deterioration of natural water environments such as rivers, and requires effective treatment before discharge. Currently, methods for treating ammonia nitrogen include biological methods, adsorption methods, breakpoint chlorination, chemical precipitation, and air stripping. Biological methods are generally suitable for domestic sewage and low-concentration industrial wastewater with low ammonia nitrogen levels and sufficient carbon sources; adsorption methods are generally used in situations with very low ammonia nitrogen content; breakpoint chlorination and chemical precipitation are generally used in special water bodies and have limited removal efficiency; air stripping is used for wastewater with relatively high ammonia nitrogen levels, but it requires heating or large amounts of air for stripping, and carbon dioxide in the air reacts with calcium and magnesium ions to form precipitates, resulting in high operating costs, low removal efficiency, and the treatment efficiency is greatly affected by temperature; at low temperatures, the treatment effect is difficult to meet requirements, and ammonia gas is prone to leakage during the treatment process, causing secondary pollution.

[0003] With advancements in membrane technology, its advantages in environmental applications are becoming increasingly apparent, and membrane ammonia removal technology for ammonia nitrogen wastewater is a hot topic in research and application. Membrane ammonia removal systems based on the membrane contact reaction principle are receiving increasing attention and use.

[0004] Compared to air stripping, membrane ammonia removal offers advantages such as lower energy consumption and higher ammonia removal efficiency. Commonly used membrane ammonia removal technologies include vacuum membrane ammonia removal, membrane absorption ammonia removal, and membrane bioreactor ammonia removal. Among these, membrane bioreactors, a branch of biological ammonia removal, have limited application in the removal of ammonia from high-concentration, recalcitrant industrial wastewater. Both vacuum membrane ammonia removal and membrane absorption ammonia removal utilize microporous membranes to separate liquid-gas or liquid-liquid phases. The membrane pores provide the interface for mass transfer between the two phases, driven by the ammonia partial pressure difference across the membrane interface. Vacuum membrane ammonia removal utilizes vacuum technology to rapidly remove ammonia molecules across the membrane interface, creating an interfacial ammonia partial pressure difference. Membrane absorption ammonia removal uses an acidic solution as an absorbent; its rapid chemical reaction significantly increases the interfacial ammonia partial pressure difference, resulting in high ammonia removal efficiency. Membrane ammonia removal technology provides a larger contact area, representing a novel and more effective contact mass transfer method. Membrane deammoniation has the advantages of low investment, low energy consumption, high efficiency, convenient use and simple operation. It also has the advantages of large mass transfer area and no phenomena such as mist entrainment, flooding, channeling and bubbling. Its technical advantages are very obvious.

[0005] Currently, selective deammoniation membranes have not been researched or applied in production. Membrane-based deammoniation utilizes a hydrophobic membrane as an interface, employing acid absorption to increase the ammonia partial pressure difference and achieve deammoniation. Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or polypropylene (PP) are commonly used hydrophobic membrane materials. PTFE is an expensive and difficult-to-process material, while PVDF-based hydrophobic membranes have poor hydrophobic properties and are prone to fouling. Furthermore, the polymethylacetamide solvent used in the production of hydrophobic membranes is not easily biochemically reacted, causing significant environmental pollution. Polypropylene is a highly crystalline, non-polar polymer with good chemical stability, acid and alkali resistance, heat stability, and low cost, and has been extensively researched both domestically and internationally. However, polypropylene, after being stretched into membranes, especially hollow fiber membranes, has extremely poor transverse strength, resulting in insufficient membrane elasticity and making it prone to flattening during membrane module fabrication and practical applications. Therefore, improving the transverse strength of polypropylene membranes is necessary. Currently, most polypropylene fiber membranes produced use solvents such as white oil, dioctyl ester, or soybean oil. During the membrane manufacturing process, the organic solvents are extracted by soaking the membrane in alcohol or No. 7 gasoline, and then the alcohol or gasoline is recycled, which greatly increases production investment costs and raw material consumption. In addition, alcohol and No. 7 gasoline are flammable and explosive, posing certain risks during the production process.

[0006] In addition, although using hydrophobic membranes as a membrane-based method for ammonia removal is an effective means, hydrophobic membranes do not have selective permeability, so the ammonia removal rate is relatively low, only between 83-86% under the same conditions. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for preparing hollow fiber deammoniation membrane fibers. Using polypropylene, polyethylene, filler powder, coupling agent, plasticizer, lubricant, and ammonia adsorbent as raw materials, the process involves granulation using a high-mixing twin-screw extruder, followed by spinning using a conical twin-screw extruder. The membrane fibers are then stretched, enzymatically hydrolyzed or acid-washed, washed with water, and dried to produce the hollow fiber deammoniation membrane. The membrane fibers produced by this method have advantages such as simple production process, low cost, environmental friendliness, adjustable membrane pore size, and high deammoniation rate. The technical solution is as follows:

[0008] This invention provides a method for preparing hollow fiber deammoniation membrane fibers, comprising the following steps:

[0009] S101: 15-25 parts by weight of polypropylene, 3-8 parts by weight of polyethylene, 3-8 parts by weight of plasticizer, 50-60 parts by weight of filler powder, 0.5-2 parts by weight of coupling agent, 2-5 parts by weight of lubricant, and 0.5-3 parts by weight of ammonia adsorbent are mixed at high speed at 5-25℃ to prepare a mixed powder. In this step, the material temperature will rise during high-speed mixing, and due to the relatively large amount of plasticizer added; if the temperature is too high, the material will become sticky, making it difficult to feed during extrusion granulation.

[0010] In addition, in this patent, adding a certain proportion of polyethylene to polypropylene can significantly improve the rigidity and lateral tensile strength of the membrane fibers.

[0011] S102: The mixed powder is extruded into granules in an extruder at 120-160℃, while 12-17 parts by weight of plasticizer is injected into the extruder through the oil filling hole.

[0012] In this patent, the plasticizer is added in steps S101 and S102 respectively. The reason is that polypropylene has a very low oil absorption value; adding all the plasticizer would create a very sticky dough during high-temperature mixing, making it impossible to feed during extrusion granulation. Therefore, an oil injection hole needs to be opened in the second heating section of the twin-screw extruder, and a peristaltic pump is used to inject the plasticizer into the extruder for mixing and granulation. Adding more plasticizer results in higher porosity, thereby improving the deammoniation rate of the membrane fibers.

[0013] S103: The particles obtained in step S102 are melted at 130-165℃ and extruded to obtain hollow fiber filaments.

[0014] S104: The hollow fiber filaments obtained in step S103 are stretched, then enzymatically hydrolyzed or acid-washed, and finally washed with water and dried to obtain deaminated hollow fiber membrane filaments.

[0015] The plasticizer is selected from triethyl citrate or glycerol, etc.

[0016] The filler powder is selected from corn starch, water-soluble starch, maltodextrin, or nano-calcium carbonate, etc.

[0017] The lubricant is selected from No. 20 white oil, triethyl citrate, dioctyl phthalate, or dewaxing agents, etc.; No. 20 white oil is preferred, as it serves both internal and external lubrication functions, and its effect is particularly pronounced when corn starch is used as the filler powder.

[0018] The coupling agent is selected from titanate coupling agents or aluminate coupling agents, preferably liquid titanate coupling agents, which can modify the filler powder at low temperature.

[0019] The ammonia adsorbent is selected from sulfonyl-modified silica aerosol or fluorosilane-modified silica aerosol, etc.

[0020] Triethyl citrate is a plasticizer for polypropylene and polyethylene, and it can also act as a lubricant for starch.

[0021] When the filler powder is selected from corn starch, water-soluble starch, or maltodextrin, the plasticizer is glycerol, and the post-stretching treatment in step S104 is enzymatic hydrolysis. Because polypropylene and polyethylene have very low oil absorption values, while corn starch has a very high oil absorption value, more soluble glycerol can be added to the film-forming system, resulting in a higher porosity for the hollow fiber membrane. The membrane pore size can be controlled by adjusting the ratio of glycerol to starch. Furthermore, when using corn starch, water-soluble starch, or maltodextrin as filler powder, if glycerol is chosen as the plasticizer, it reacts with corn starch, water-soluble starch, or maltodextrin at high temperatures to produce thermoplastic starch. Thermoplastic starch has good compatibility with polypropylene and can be used to make high-strength membrane fibers; simultaneously, the larger specific surface area of ​​starch can significantly improve the porosity of the deaminated membrane.

[0022] When the filler powder is nano-calcium carbonate, the plasticizer is triethyl citrate. In step S104, the post-stretching treatment is pickling. Triethyl citrate is a biodegradable and slightly water-soluble organic compound. During pickling and washing, it can be extracted from the membrane fibers without the need for extraction with alcohol or No. 7 gasoline, greatly reducing investment costs and the risk of flammability and explosion during production.

[0023] In step S101, polypropylene, polyethylene, filler powder, ammonia adsorbent and lubricant are put into a high-speed mixer and mixed at high speed for 1-2 minutes (specifically 2 minutes) according to the formula. Then, coupling agent is added and mixing continues for 4-6 minutes (specifically 5 minutes). Finally, plasticizer is added and mixed at low speed for 8-12 minutes (specifically 10 minutes).

[0024] Specifically, in step S102, the plasticizer is added from the oil injection hole of the second heating section of the extruder.

[0025] Preferably, in step S102, granulation is performed using a twin-screw extruder, specifically a φ45 twin-screw extruder with an aspect ratio of 44. In step S103, the material is melted in a conical twin-screw extruder and then extruded through a dual-hole annular spinneret to produce hollow fiber membrane filaments. The conical twin-screw extruder has a higher feed ratio, which can improve the density and rigidity of the membrane filaments, making it easier to form a uniform mesh structure when stretching the filaments and increasing the porosity of the membrane filaments. Adjusting the spinning speed and the diameter of the spinneret can produce products of different specifications. Specifically, in step S103, hollow fiber filaments with an inner / outer diameter of 1.0 / 1.3 mm are produced; in step S104, deaminated hollow fiber membrane filaments with an inner / outer diameter of 0.7 / 1.0 mm are produced. In this patent, the membrane pore size is mainly controlled by the particle size of the filler powder, the draw ratio, and the ratio between the lubricant and the plasticizer.

[0026] Specifically, in step S104, the enzyme treatment process involves processing with a solution containing low-temperature amylase and saccharifying enzyme. Specifically, the low-temperature amylase hydrolyzes corn starch, water-soluble starch, or maltodextrin into short-chain starch, while the saccharifying enzyme hydrolyzes the short-chain starch into glucose, facilitating the washing of starch from the membrane fibers. Specifically, hydrochloric acid can be used for the acidic process.

[0027] Specifically, in step S104, the stretching process is as follows: stretching is performed using four five-roller traction machines rotating in the same direction, with a stretching ratio of 3.0-5.5; the hollow fiber membrane filaments are drawn out from the first traction machine, heated in the first heating channel, and then introduced into the second heating channel at a speed higher than the first traction machine. They are then introduced into the third heating channel by a third traction machine at the same speed as the second traction machine, and drawn out from the fourth traction machine at 85-90% of the speed of the third traction machine for winding; wherein, the length of the first heating channel is 5-7 meters (specifically 6 meters), and the temperature is 60-80℃; the length of the second and third heating channels is 8-12 meters (specifically 10 meters), and the temperature is 100-110℃. Conventional heat setting of polypropylene deammonium-free membrane involves stretching the membrane filaments and then allowing them to stand at a certain temperature for 24 hours. This invention allows for continuous heat setting, greatly improving production efficiency.

[0028] In this embodiment of the invention, the particle size of the nano-calcium carbonate is 100-200 nanometers.

[0029] Preferably, in the embodiments of the present invention, when the filler powder is selected from corn starch, water-soluble starch or maltodextrin, the lubricant is 20% white oil.

[0030] Preferably, the polyethylene in the embodiments of the present invention is high-density polyethylene of the fiber grade or hollow grade. This grade of polyethylene is easier to mold and less prone to fiber breakage.

[0031] In this patent, the polyethylene and polypropylene used are more than ten times cheaper than polyvinylidene fluoride and polytetrafluoroethylene. The calcium carbonate, starch and other filler powders used to replace organic solvents for pore making are also relatively inexpensive. The large amount of triethyl citrate, glycerin and other lubricants added in this method are biodegradable and can be directly discharged into sewage treatment plants for biochemical treatment. There is no need to use alcohol or No. 7 gasoline for recycling, so there is no need to build explosion-proof workshops and distillation towers. Therefore, the membrane fibers prepared by this invention are inexpensive and environmentally friendly. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in further detail below.

[0033] The film-forming system is prepared according to the following steps:

[0034] (1) Put the polypropylene, polyethylene, filler powder, ammonia adsorbent and lubricant into a high-speed mixer and mix at high speed for 2 minutes. Then inject it into a coupling machine and continue mixing for 5 minutes. Finally, inject some plasticizer and mix at low speed for 10 minutes.

[0035] (2) The mixture obtained in step (1) is melt-granulated at 140-160°C using a φ45 twin-screw extruder with an aspect ratio of 44. At the same time, the remaining plasticizer is injected proportionally from the second heating section of the extruder.

[0036] (3) The obtained particles are added to a conical twin screw for hollow fiber spinning. The water temperature of the spinning cooling water tank should be controlled below 25℃ and the water inlet distance should be controlled at about 3cm so that the newly spun membrane fibers have a rapid cooling process to obtain high-strength membrane fibers with high opening rate.

[0037] Stretching and heat setting process:

[0038] The hollow fiber membrane filaments are stretched using four five-roller traction machines rotating in the same direction, with a stretch ratio of 3.0-5.5. The filaments are drawn out from the first traction machine, heated in the first heating channel, and then introduced into the second heating channel at a speed higher than the first traction machine. They are then introduced into the third heating channel by the third traction machine at the same speed as the second traction machine, and drawn out from the fourth traction machine at 85-90% of the speed of the third traction machine for winding. The first heating channel is 6 meters long and has a temperature of 60-80℃, while the second and third heating channels are both 10 meters long and have a temperature of 100-110℃.

[0039] Enzymatic hydrolysis or acid washing process:

[0040] The stretched membrane fibers are bundled together and immersed in hydrochloric acid solution or a solution containing amylase and saccharifying enzyme for 4 hours, repeated 3 times to extract the filler powder. Then, they are soaked in water once and washed repeatedly 6 times. The washed membrane fibers are then dried to obtain the hollow fiber deammoniation membrane.

[0041] Example 1

[0042] Example 1 provides a method for preparing hollow fiber deammoniation membrane filaments, comprising the following steps: granulating and melt-spinning 2.5 kg of polypropylene, 0.50 kg of high-density polyethylene, 0.1 kg of titanate coupling agent, 4.6 kg of corn starch, 0.5 kg of white oil, 0.2 kg of sulfonated modified silica, and 1.6 kg of glycerol; removing corn starch from the hollow fiber membrane by soaking with amylase and saccharifying enzyme to obtain hollow fiber membrane filaments. The hollow fiber membrane filaments have an outer diameter of 1.0 mm, an inner diameter of 0.7 mm, a pore size of 0.2 μm, a porosity of 65%, and a deammoniation rate of 92%.

[0043] Example 2

[0044] Example 2 provides a method for preparing hollow fiber deammoniation membrane filaments, comprising the following steps: 2.4 kg of polypropylene, 0.4 kg of high-density polyethylene, 0.1 kg of titanate coupling agent, 4.6 kg of corn starch, 0.7 kg of triethyl citrate, 0.2 kg of sulfonated modified silica, and 1.6 kg of glycerol are blended and granulated, melt-spun, and the corn starch in the hollow fiber membrane is removed by soaking with amylase and saccharifying enzyme. The membrane is then washed with water to remove triethyl citrate, yielding hollow fiber membrane filaments. The hollow fiber membrane filaments have an outer diameter of 1.0 mm, an inner diameter of 0.7 mm, a pore size of 0.2 μm, a porosity of 65%, and a deammoniation rate of 95%.

[0045] Example 3

[0046] Example 3 provides a method for preparing hollow fiber deammoniation membrane filaments, comprising the following steps: 2.5 kg of polypropylene, 0.6 kg of high-density polyethylene, 0.1 kg of titanate coupling agent, 4.6 kg of water-soluble starch, 0.4 kg of dewaxing agent, 0.2 kg of sulfonated modified silica, and 1.6 kg of glycerol are blended and granulated, melt-spun, and the water-soluble starch in the hollow fiber membrane is removed by soaking with amylase and saccharifying enzyme. The membrane filaments are then washed with water to obtain the hollow fiber membrane filaments. The hollow fiber membrane filaments have an outer diameter of 1.0 mm, an inner diameter of 0.7 mm, a pore size of 0.2 μm, a porosity of 60%, and a deammoniation rate of 93%.

[0047] Example 4

[0048] Example 4 provides a method for preparing hollow fiber deammoniation membrane filaments, comprising the following steps: 2.4 kg of polypropylene, 0.4 kg of high-density polyethylene, 0.1 kg of titanate coupling agent, 4.6 kg of corn starch, 0.7 kg of triethyl citrate, 0.1 kg of sulfonated modified silica, 0.1 kg of fluorosilane-modified silica, and 1.6 kg of glycerol are blended and granulated, melt-spun, and the corn starch in the hollow fiber membrane is removed by soaking with amylase and saccharifying enzyme. The hollow fiber membrane filaments are then washed with water to remove triethyl citrate, resulting in hollow fiber membrane filaments. The hollow fiber membrane filaments have an outer diameter of 1.0 mm, an inner diameter of 0.7 mm, a pore size of 0.2 μm, a porosity of 68%, and a deammoniation rate of 98%.

[0049] Example 5

[0050] Example 5 provides a method for preparing hollow fiber deammoniation membrane filaments, comprising the following steps: 2.1 kg of polypropylene, 0.3 kg of high-density polyethylene, 0.1 kg of titanate coupling agent, 5.3 kg of nano-calcium carbonate, 0.5 kg of dioctyl phthalate, 0.2 kg of sulfonated modified silica, and 1.5 kg of triethyl citrate are blended and granulated, melt-spun, and the nano-calcium carbonate in the hollow fiber membrane is removed by immersion in hydrochloric acid. The triethyl citrate is then removed by washing with water to obtain hollow fiber membrane filaments. The hollow fiber membrane filaments have an outer diameter of 1.0 mm, an inner diameter of 0.7 mm, a pore size of 0.5 μm, a porosity of 63%, and a deammoniation rate of 95%.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing membrane fibers of a hollow fiber deammoniation membrane, characterized in that, Includes the following steps: S101: A mixed powder is prepared by high-speed mixing of 15-25 parts by weight of polypropylene, 3-8 parts by weight of polyethylene, 3-8 parts by weight of plasticizer, 50-60 parts by weight of filler powder, 0.5-2 parts by weight of coupling agent, 2-5 parts by weight of lubricant and 0.5-3 parts by weight of ammonia adsorbent at 5-25℃. S102: The mixed powder is extruded into granules in an extruder at 120-160℃, while 12-17 parts by weight of plasticizer is injected into the extruder through the oil filling hole of the extruder. S103: The granules obtained in step S102 are melted at 130-165℃ and extruded to obtain hollow fiber filaments; S104: The hollow fiber filaments obtained in step S103 are stretched, then enzymatically hydrolyzed, and finally washed and dried to obtain deaminated hollow fiber membrane filaments. The plasticizer is selected from glycerin; The filler powder is selected from corn starch, water-soluble starch, or maltodextrin; The lubricant is selected from No. 20 white oil, triethyl citrate, dioctyl phthalate, or dewaxing agent; The coupling agent is selected from titanate coupling agents or aluminate coupling agents; The ammonia adsorbent is selected from sulfonyl modified silica aerosol or fluorosilane modified silica aerosol. The enzyme treatment process involves processing the enzyme with a solution containing low-temperature amylase and saccharifying enzyme.

2. The method for preparing the membrane fibers of the hollow fiber deammoniation membrane according to claim 1, characterized in that, In step S101, polypropylene, polyethylene, filler powder, ammonia adsorbent and lubricant are put into a high-speed mixer and mixed at high speed for 1-2 minutes according to the formula. Then, coupling agent is added and mixing continues for 4-6 minutes. Finally, plasticizer is added and mixed at low speed for 8-12 minutes.

3. The method for preparing the membrane fibers of the hollow fiber deammoniation membrane according to claim 1, characterized in that, In step S102, the plasticizer is added from the oil injection port of the second heating section of the extruder.

4. The method for preparing the membrane fibers of the hollow fiber deammoniation membrane according to claim 1, characterized in that, In step S102, granulation is performed using a twin-screw extruder; in step S103, the material is melted in a conical twin-screw extruder and then extruded through a double-hole annular spinneret to form hollow fiber membrane filaments.

5. The method for preparing the membrane fibers of the hollow fiber deammoniation membrane according to claim 1, characterized in that, In step S104, the stretching process is as follows: stretching is performed by four five-roller traction machines rotating in the same direction, with a stretching ratio of 3.0-5.5; hollow fiber membrane filaments are drawn out from the first traction machine, heated in the first heating channel, and then introduced into the second heating channel at a speed higher than that of the first traction machine in the second traction machine. They are then introduced into the third heating channel by the third traction machine at the same speed as the second traction machine, and drawn out from the fourth traction machine at 85-90% of the speed of the third traction machine for winding; wherein, the length of the first heating channel is 5-7 meters and the temperature is 60-80℃, and the length of the second and third heating channels is 8-12 meters and the temperature is 100-110℃.

6. The method for preparing the membrane fibers of the hollow fiber deammoniation membrane according to claim 1, characterized in that, The lubricant is 20% white oil.

7. The method for preparing the membrane fibers of the hollow fiber deammoniation membrane according to claim 1, characterized in that, The polyethylene is high-density polyethylene of fiber grade or hollow grade.