WO2024012121A1 - Membrane à fibres creuses en polyoléfine pour dégazage asymétrique, son procédé de préparation et son utilisation - Google Patents

Membrane à fibres creuses en polyoléfine pour dégazage asymétrique, son procédé de préparation et son utilisation Download PDF

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WO2024012121A1
WO2024012121A1 PCT/CN2023/099640 CN2023099640W WO2024012121A1 WO 2024012121 A1 WO2024012121 A1 WO 2024012121A1 CN 2023099640 W CN2023099640 W CN 2023099640W WO 2024012121 A1 WO2024012121 A1 WO 2024012121A1
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hollow fiber
fiber membrane
temperature
microfibers
polyolefin
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PCT/CN2023/099640
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English (en)
Chinese (zh)
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贾建东
陈梦泽
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杭州科百特过滤器材有限公司
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Publication of WO2024012121A1 publication Critical patent/WO2024012121A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/08—Hollow fibre membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D19/00—Degasification of liquids
    • B01D19/0073—Degasification of liquids by a method not covered by groups B01D19/0005 - B01D19/0042
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0002—Organic membrane manufacture
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/24—Mechanical properties, e.g. strength

Definitions

  • the present invention relates to the technical field of membrane materials, and more specifically to a polyolefin hollow fiber membrane for asymmetric degassing and its preparation method and use.
  • the existing degassing membranes are generally polyolefin hollow fiber membranes, and common polyolefins are PP, PE, PMP and other substances;
  • the main methods for preparing polyolefin hollow fiber membranes currently include melt stretching method and thermally induced phase separation method;
  • the basic principle of the thermally induced phase separation method is that a mixture of polymer and high boiling point, low molecular weight diluent forms a homogeneous solution at high temperature, which is then extruded through a hollow die, and the molded product undergoes liquid-liquid or liquid-to-liquid or The solid-liquid phase separates, and the sites occupied by the diluent form micropores after removal.
  • the basic principle of the melt stretching method is to use pure polymer melt for melt extrusion.
  • the formation of micropores is mainly related to the hard elasticity of the polymer material.
  • the hard elastic material is perpendicular to and parallel to the extrusion direction.
  • the arranged lamellar structure is pulled apart to form micropores, and then the pore structure is fixed through a heat setting process.
  • Its preparation process mainly includes melt spinning, drafting, heat treatment, stretching, heat setting and other steps. This method is introduced in detail in patents such as US3558764, US4055696 and US4664681.
  • the hollow fiber membrane produced by this method does not contain diluent, so it is particularly suitable for the degassing of ultrapure water, ensuring that no new impurities (such as diluents) are introduced during the degassing process;
  • the hollow fiber membrane produced by the stretching method also has a major disadvantage, that is, the porosity is too low, which generally can only reach a maximum of about 30%. This greatly restricts the exchange efficiency between gas and liquid, resulting in deoxidation efficiency/deoxygenation. The carbon (carbon dioxide) efficiency is too low.
  • the existence of the above problems has greatly restricted the development of degassing membranes.
  • the object of the present invention is to provide a polyolefin hollow fiber membrane for asymmetric degassing and its preparation method and use.
  • the hollow fiber membrane is prepared by a melt stretching method and has a high porosity. , the deoxidation efficiency/decarbonization (carbon dioxide) efficiency is high, and it has high mechanical properties and long service life. It is especially suitable for the degassing of ultrapure water.
  • a polyolefin hollow fiber membrane for asymmetric degassing including a main body, one side of the main body is an inner surface facing the inner cavity, and the other side is an outer surface, There is a non-directional tortuous passage in the main body, and there are several microfibers on the inner surface for forming a porous structure.
  • the average length of the microfibers is 100-400nm and the average width is 15-60nm;
  • the length direction of the microfibers is consistent with the length direction of the hollow fiber membrane, and the width direction of the microfibers is consistent with the circumferential direction of the hollow fiber membrane;
  • the surface energy of the outer surface is 15-40mN/m, and the outer surface is a dense surface.
  • the hollow fiber membrane of the present invention is mainly used to remove various gas components in liquids, such as removing oxygen and carbon dioxide from ultrapure water, these liquids to be treated will interact with the hollow fiber membranes.
  • the outer surface of the fiber membrane is in direct contact. The dense outer surface ensures the service life of the hollow fiber membrane. There is no risk of leakage (that is, the liquid will not penetrate the membrane fiber wall thickness and enter the inner cavity of the membrane), thereby ensuring that the hollow fiber membrane has Good degassing efficiency;
  • the surface energy of water at 20°C is 72.8mN/m. If the surface energy of the membrane is lower than 72.8mN/m, it means that the outer surface of the membrane has certain hydrophobic properties. The greater the hydrophobicity of the membrane, the hollow The surface energy of the outer surface of the fiber membrane at 20°C is 15-40mN/m, indicating that the outer surface of the membrane has strong hydrophobic properties and is not easily wetted by hydrophilic liquids such as water, further improving the performance of the hollow fiber of the present invention.
  • the degassing membrane has a long service life and can perform degassing for a long time; but if there are many holes on the outer surface of the degassing membrane and it is not dense enough, then even if the outer surface of the membrane has strong hydrophobicity, then During the degassing process, the membrane filaments are also easily hydrophilic, that is, they are wetted by the liquid in a short period of time.
  • the service life of the membrane filaments with such a structure will be very short; in addition, the dense outer surface is conducive to improving the mechanical strength of the membrane filaments. strength;
  • microfibers fiber structures of a certain length and thickness
  • These microfibers are evenly distributed on the inner surface of the membrane, and corresponding holes are formed between the microfibers, resulting in a certain number of holes with a certain pore size appearing on the inner surface of the membrane.
  • the existence of these holes ensures that the hollow fiber membrane has a relatively high performance.
  • High porosity facilitates the rapid penetration of oxygen and other gases; and the size of the pores on the inner surface is related to the length of the microfibers.
  • the greater the length of the microfibers the larger the pore diameter of the membrane pores (that is, the microfibers).
  • the degassing efficiency (the degassing efficiency in the present invention mainly refers to the deoxygenation efficiency and the carbon dioxide removal efficiency, other gases are not considered in the present invention) cannot meet the needs of practical applications; and the length of the microfibers is too long.
  • the hole diameter on the inner surface is too large, the mechanical strength of the membrane will be too low to meet practical needs; on the other hand, during the long-term degassing process, the microfibers that are too long will easily break, thus making the degassing membrane weak.
  • the service life is greatly reduced; and the average length of the microfibers in the present invention is 100-400nm (the length direction of the microfibers is consistent with the length direction of the hollow fiber membrane), so that there are holes with suitable pore sizes on the inner surface, thereby ensuring the detachment.
  • the air film has a high degassing rate and degassing efficiency, while ensuring that the degassing film has high mechanical strength and a long service life;
  • the length of the microfibers reflects the size of the holes on the inner surface; and the width (thickness) of the microfibers reflects the number of holes on the inner surface to a certain extent, because in the circumferential direction of the membrane, the width of the microfibers
  • the size is the distance between adjacent holes. The greater the width of the microfiber, the greater the distance between adjacent holes, and the fewer the number of holes. If the number of holes on the inner surface is too small, it will affect the performance of the degassing membrane.
  • the width of the microfibers cannot be too large; if the width of the microfibers is too small, it means that the microfibers are very thin, then these very thin microfibers are easy to break and create holes during the degassing process. It is also easy to collapse, causing the degassing membrane to be unable to continue to have a degassing effect and the service life is too short; the average width is 15-60nm (the width direction of the microfibers is consistent with the circumferential direction of the hollow fiber membrane), ensuring that the inner surface has a suitable The number of holes further ensures that the degassing membrane has a high degassing rate and degassing efficiency. At the same time, it ensures that the degassing membrane has high mechanical strength and long service life;
  • the surface energy test method of the outer surface of the hollow fiber membrane is to use a dyne pen to test the hollow fiber membrane.
  • the surface energy of the ink tested is the surface energy of the outer surface of the film; the microfibers on the film surface can be measured by using a scanning electron microscope to measure the film.
  • the membrane surface can be characterized first with an electron microscope to obtain the corresponding SEM image, and since the microfibers on the membrane surface are roughly uniform , so you can select a certain area, such as 1 ⁇ m 2 (1 ⁇ m times 1 ⁇ m) or 25 ⁇ m 2 (5 ⁇ m times 5 ⁇ m).
  • the specific area size depends on the actual situation, and then use the corresponding computer software or manually measure all the microns on the area.
  • the length and width of the fibers are then calculated to obtain the average length and average width of the microfibers on the surface; of course, those skilled in the art can also obtain the above parameters through other measurement methods, and the above measurement methods are for reference only.
  • the average spacing between adjacent microfibers, the hole area ratio of the inner surface, the average width of the platelet area and the average length of the breathable area can all be measured by the above method;
  • the difference between the maximum length and the minimum length of the microfiber does not exceed 350nm; the difference between the maximum width and the minimum width of the microfiber does not exceed 70nm;
  • the average length of the microfibers is 4-10 times the average width of the microfibers
  • the average spacing between adjacent microfibers is 20-80nm.
  • the length of the microfibers cannot Too small; and the difference between the maximum length and the minimum length of the microfibers in the present invention does not exceed 350nm, which can indicate that the pore sizes on the outer surface are relatively uniform, and there are neither holes (defect holes) with particularly large pore diameters nor The holes (false holes) with extremely small pore diameters not only ensure the overall mechanical strength of the membrane, but also have high degassing efficiency;
  • the width (i.e., thickness) of the microfibers reflects the number of holes on the inner surface to a certain extent.
  • the width of the microfibers is too large, the number of holes in a certain area of the inner surface will be too few, resulting in excessive Few holes will inevitably affect the degassing efficiency, and at the same time, the resistance to gas penetration will be greatly increased, and the pressure loss during the degassing process will be greatly increased.
  • the width of the microfibers is too small, more holes will appear in a certain area on the inner surface. If there are holes (that is, in this area, the hole area ratio is too high, and the solid area ratio is too low), then this must be a big flaw.
  • the difference between the maximum width and the minimum width of the microfibers does not exceed 70nm, which means that the thickness of the microfibers is relatively uniform (there are no particularly thick microfibers). fibers, and there are no particularly fine microfibers), which also shows that the distribution of holes in a certain area on the inner surface is relatively uniform (the distribution of holes will not be too dense or too sparse), further ensuring that the membrane filaments have High degassing performance and mechanical properties.
  • the main function of the microfibers in the present invention is to maintain the stability of the holes and ensure that during the degassing process, the holes on the inner surface are not prone to collapse and other restrictions, thereby making the entire membrane have high mechanical strength and excellent performance over a long period of time. degassing performance; so what kind of microfibers can better control the stability of the holes?
  • the length and width of the microfibers need to have a suitable ratio, because the larger the pore diameter, the larger the hole.
  • the holes will easily There is a risk of collapse and the service life is greatly reduced; and when the ratio is too small, it means that the length of the microfibers is too small (in fact, it also means that the hole diameter is too small) or the width of the microfibers is too large (it is very thick, so that the number of holes (too few), at this time, although the microfibers can improve the stability of the holes, the diameter of the holes on the inner surface is too small and the number is too small, making the degassing efficiency too low and unable to meet the needs of practical applications; the microfibers in the present invention
  • the average length of the fibers is 4-10 times the average width of the microfibers.
  • the microfibers can efficiently maintain the stability of the holes for a long time, ensuring that the hollow membrane filaments have a long service life and mechanical strength.
  • the inner surface has a suitable pore size and a suitable number of holes, so that the membrane fiber has a greater degassing efficiency and meets the needs of practical applications;
  • elliptical holes are formed between adjacent microfibers on the inner surface of the membrane; that is, in the circumferential direction of the hollow fiber membrane, the holes between adjacent microfibers
  • the spacing reflects the width of the hole.
  • the greater the spacing between microfibers the greater the width of the hole (that is, there is a positive correlation between the circumferential spacing between microfibers and the width of the hole); when the microfibers are When the circumferential spacing between the microfibers is too large, the width of the holes will be too large, and the microfibers cannot effectively maintain the stability of the holes, and the membrane fibers cannot be guaranteed to degas for a long time.
  • the width of the hole will be too small. Even if the length of the hole on the inner surface is very long, the width of the hole will The area is still very small (that is, the hole area ratio on the inner surface of the membrane is too low), then the degassing rate of the membrane fiber is too low at this time and cannot meet the needs of time application; the average circumferential spacing between adjacent microfibers in the present invention It is 20-80nm, so that the holes have a suitable width, which further ensures that the hollow fiber membrane has excellent degassing rate, high mechanical properties and service life.
  • the average length of the microfibers is 2-8 times the average spacing between adjacent microfibers in the film circumferential direction; the average width of the microfibers is 2-8 times the average distance between adjacent microfibers.
  • the average spacing between fibers in the circumferential direction of the film is 50%-95%; the hole area ratio of the inner surface is 10-35%.
  • elliptical-shaped holes are formed between adjacent microfibers, in which the length of the microfibers is positively correlated with the major diameter (length) of the holes, and the circumferential spacing between the microfibers is directly related to the short diameter of the holes.
  • the diameter (width) There is a positive correlation with the diameter (width); and we all hope that the ratio between the long diameter and the short diameter of the hole will not be too large or too small (when the ratio is too low or too high, the overall degassing rate of the membrane and the degassing rate will be affected.
  • the gas efficiency is not high); and in the present invention, the average length of the microfibers and the circumferential spacing between the microfibers are controlled to ensure that holes with ideal long and short diameters appear on the inner surface of the membrane.
  • microfibers The main function of microfibers is to maintain the stability of holes. Generally speaking, the greater the average width of microfibers, the stronger the support effect on holes; and in addition to the length of microfibers, which will affect the support effect of microfibers on holes, The circumferential spacing between microfibers will also affect the supporting effect of microfibers on holes; generally speaking, the greater the circumferential spacing between microfibers, the stronger the supporting effect of microfibers on holes is required (that is, when The larger the circumferential spacing between the microfibers, the thicker the microfibers are required); and the larger the circumferential spacing between the microfibers, it means that the pore diameter on the inner surface is also larger, which is more conducive to improving detachment.
  • microfibers are regularly arranged to form an air-permeable area for air permeability; the air-permeable area is in a strip shape; the average length of the air-permeable area is 400-1100nm , the average length of the breathable area is greater than the average width of the breathable area;
  • the length direction of the air permeable area is consistent with the circumferential direction of the hollow fiber membrane; the width direction of the air permeable area is consistent with the length direction of the hollow fiber membrane.
  • the microfibers were relatively evenly distributed on the inner surface (this should be related to the film formation through melt stretching method), and in the circumferential direction of the membrane, several microfibers Regularly arranged, a long strip-shaped area is finally formed. In this area, there are a large number of holes and a high hole area ratio. Gases (such as oxygen, carbon dioxide, etc.) mainly enter the inner cavity of the membrane through this area, so This area is called the breathable area; further observation found that the width direction of the breathable area is basically the same as the length direction of the hollow fiber membrane, and the width of the breathable area is basically the same as the length of the microfiber.
  • the influencing factor is the length of the breathable membrane.
  • the larger the length of the breathable area the larger the area of the breathable area.
  • the larger the area of the breathable area the easier it is for gas to pass through, thereby increasing the gas transmission rate and further improving the gas permeability rate.
  • Improve the degassing efficiency of membrane filaments however, an excessively large breathable area will cause the local hole area ratio on the inner surface of the hollow fiber membrane to be too large, which may lead to the possibility of structural damage due to stress concentration, resulting in a greatly reduced service life of the membrane filaments.
  • the average length of the breathable zone in the present invention is 400-1100nm, which not only ensures the degassing rate, but also makes the membrane fiber have high mechanical strength and service life.
  • a solid structure of lamellae areas is formed between adjacent breathable areas; the average width of the lamellae areas is 80-280nm; the average width of the lamellae areas is The width is 0.3-1.5 times the average width of the breathable area; the width direction of the platelet area is consistent with the length direction of the hollow fiber membrane.
  • lamellar areas On the inner surface of the hollow fiber membrane, in addition to the breathable areas with several holes, there are also corresponding solid areas. These solid areas are called lamellar areas.
  • the lamellar areas are located between adjacent breathable areas (can also be considered It is the stretching effect between the lamellar area and the lamellar area that forms a breathable area containing several holes inside); generally we think that microfibers are used to maintain the stability of the holes, so the existence of the lamellar area is used to maintain The stability of the breathable area; therefore, if the width of the lamellar area is too small, the stability of the breathable area cannot be maintained, which not only affects the mechanical strength of the membrane filament, but also affects the degassing efficiency of the membrane filament; and if the width of the lamellar area If it is too large, although the mechanical strength of the entire membrane is ensured, the area of the breathable area will be too small, and the gas will not be able to quickly penetrate the membrane thickness and enter the inner cavity of
  • the average length of the breathable area is 2-5 times the average width of the breathable area; the hole area ratio in the breathable area is 30-70%, and the hole area ratio of the breathable area The overall hole area ratio is 20-50% higher than that of the inner surface.
  • the ratio of the length to the width of the breathable area can reflect the sufficient degree of stretching during the preparation process of the hollow fiber membrane.
  • the ratio of the length to the width of the breathable area is too small, it means that the hollow fiber membrane has been stretched excessively, and excessive stretching is likely. It leads to the breakage of the microfiber tie structure of the hollow fiber membrane, the collapse of the micropores and the increase in the porosity of the surface, resulting in a decrease in both the degassing effect and mechanical properties; and when the ratio of the length to the width of the breathable zone is too large, it means that Insufficient stretching of the hollow fiber membrane or improper heat setting process causes the breathable area to shrink.
  • the breathable area is the main area for gas transmission on the inner surface, the hole area ratio in the breathable area must be higher, so that the membrane fiber has a higher degassing effect.
  • the air rate however, the hole area rate in the breathable area cannot be too high, otherwise there will still be a risk of hole collapse and the service life is too short; in the present invention, the hole area rate in the breathable area is 30-70%, and the breathable area
  • the hole area ratio of the zone is 20-50% higher than the overall hole area ratio of the inner surface. Such a hole area ratio further ensures that the hollow fiber membrane has both a high degassing rate and strong dimensional stability.
  • the main body includes a skin layer and a support layer.
  • One side of the support layer is the inner surface, and one side of the skin layer is the outer surface.
  • the thickness of the skin layer is 0.5-4 ⁇ m. The thickness accounts for 1-8% of the overall thickness of the film; the porosity of the skin layer is not higher than 10%.
  • the main body of the membrane mainly includes two areas. In the area close to the outer surface, the number of holes is small and relatively dense, and the thickness of this area is very small. In the present invention This area is called the cortex; and on the side area close to the inner surface, the pore diameter is relatively large and the number of holes is relatively large, which is called the support layer in the present invention; in this application, the cortex and The support layers are all made of the same material. The two layers are combined into an overall structure and are formed directly during the membrane preparation process.
  • the membranes prepared by the application are asymmetric membranes; in contrast, for example, composite membranes have a multilayer structure in which a dense layer as a separation layer is applied in a separate process step to a porous, often microscopic On the support layer or support membrane of the hole, the materials constituting the support layer and the skin layer in the composite membrane are often different;
  • the penetration rate of gas in the skin layer must be lower than the diffusion rate of gas in the microporous structure. Therefore, it can be expected that the degassing effect of an asymmetric hollow fiber membrane with a dense skin layer must be significantly lower than Degassing effect of hollow fiber membrane with internal and external microporous structure.
  • the inventors of this application unexpectedly discovered that on the basis that the microporous structure of the hollow fiber membrane body is relatively good, it is only necessary to compare the thickness of the skin layer of the hollow fiber membrane and the ratio of the thickness of the hollow fiber membrane to the wall thickness of the hollow fiber membrane. Controlling within a certain range (the thickness of the skin layer is 0.5-4 ⁇ m, and the thickness of the skin layer accounts for 1-8% of the overall thickness of the membrane), the asymmetric hollow fiber membrane with a dense skin layer can be compared with the one with an internal and external microporous structure.
  • the degassing effect of the hollow fiber membrane is only slightly reduced; however, the existence of the dense skin layer will greatly extend the service life of the membrane filament, enabling efficient degassing for a long time and high economic benefits; in addition, during the degassing process of ultrapure water
  • people also control an additional indicator - the water vapor transmission rate, that is, they hope that the water vapor transmission rate (the amount of water vapor transmission per unit time) can be reduced as soon as possible, but under normal circumstances, oxygen penetration
  • the passing rate the higher the water vapor transmission rate
  • the present invention surprisingly found that through the existence of a certain thickness of dense cortex, although the oxygen transmission rate also decreased slightly, the water vapor transmission rate was significantly improved. Descending, only a small amount of water vapor will penetrate through the wall thickness and enter the inner cavity.
  • the thickness of the support layer is 38-58 ⁇ m, and the support layer is at least 35 ⁇ m larger than the thickness of the cortex; the porosity of the support layer is 40-70%; the average pore diameter in the support layer It gradually decreases from the area closer to the inner surface to the area closer to the cortex.
  • the thickness of the support layer in the present invention is 38-58 ⁇ m.
  • the support layer is at least 35 ⁇ m thicker than the cortex, that is, the thickness of the support layer is much greater than the thickness of the cortex, and the porosity in the support layer is 40%-70%.
  • Such a support layer structure makes the polyolefin hollow fiber membrane not only have a relatively high High mechanical properties and high porosity ensure the overall degassing efficiency of the membrane.
  • the average pore size gradient of the support layer is 1.5-4 nm/ ⁇ m; the support layer has porous fibers for forming a porous structure, and the average diameter of the porous fibers is 60-300 nm.
  • the speed of the change of the pore diameter in the support layer with the thickness is reflected by the size of the average pore diameter change gradient.
  • the larger the value the faster the pore diameter changes.
  • the smaller the value the smaller the pore diameter change.
  • the value can be passed (closer to The average pore diameter of the inner surface - the average pore diameter near the cortex)/thickness is obtained, so the unit is nm (representing the average pore diameter)/1 ⁇ m (representing the thickness), the average pore diameter change gradient in the support layer of the present invention is 1.5-4nm/ ⁇ m; the pore size change gradient value is very small, which shows that the membrane in the support layer of the present invention The pore diameter changes with a small gradient with the thickness.
  • the pore diameter in the support layer is very small and changes too quickly, and there are no overly large holes, so that the overall membrane has good mechanical strength, and at the same time it has high porosity, degassing rate and degassing.
  • the efficiency is relatively high; in addition, the support layer structure with small gradient changes in the pores and the appropriate microfiber structure on the inner surface further ensure that the degassing efficiency is minimized and the water vapor permeability is further reduced; at the same time, , the support layer also has a number of porous fibers used to form a porous structure.
  • porous fibers ensures the stability of the holes in the support layer; the average diameter (thickness) of the porous fibers is related to the pore size and pore size in the support layer
  • the average diameter of the porous fibers in the present invention is 60-300nm.
  • Such thick and thin porous fibers are conducive to ensuring that the overall membrane has high mechanical strength and can perform efficient degassing for a long time, so it is suitable for use as a degassing membrane. , especially suitable for degassing ultrapure water.
  • the thickness of the hollow fiber membrane is 40-60 ⁇ m, the porosity is 30-50%, and the inner diameter is 175-225 ⁇ m; the overall crystallinity of the hollow fiber membrane is 30-55%;
  • the film-forming material of the hollow fiber membrane is at least one of PP, PE and PMP.
  • the thickness of the hollow fiber membrane in the present invention is 40-60 ⁇ m, which is relatively thin and is particularly suitable for use as a degassing membrane on the basis of ensuring the mechanical strength of the membrane filaments.
  • the inner cavity diameter of the hollow fiber membrane of the present invention is 175-225 ⁇ m, which not only ensures that the membrane as a whole has high pressure-resistant strength, but also allows more gas to be absorbed per unit time.
  • the porosity of the membrane is 30-50%, so that the membrane not only has good tensile strength, It also has a large degassing rate and degassing efficiency, and has high economic benefits;
  • the hollow fiber membrane of the present invention is made of polyolefins and contains only two elements: carbon and hydrogen, and no other elements; further, it can be any one of PP, PE and PMP, and the raw materials are widely sourced and easy to obtain.
  • the thickness and inner diameter of the hollow fiber membrane of the present invention can be obtained by using a scanning electron microscope to characterize the morphology of the membrane structure, and then using computer software (such as Matlab, NIS-Elements, etc.) or manual measurement; the volume porosity of the membrane can be obtained It is produced according to the mercury porosimetry method using a mercury porosimeter.
  • the invention also provides a method for preparing a polyolefin hollow fiber membrane for asymmetric degassing, which includes the following steps:
  • pre-crystallization place the molded product in the air section for pre-crystallization;
  • the melting point of the polyolefin material is Tm
  • the outer surface temperature of the molded product after pre-crystallization is Tm-(Tm+15)°C.
  • the temperature of the inner surface is greater than the temperature of the outer surface, and the average temperature change gradient of the molded product after pre-crystallization is 0.01-0.2°C/1um;
  • Air-cooling crystallization The molded product obtained in step S2 is air-cooled and crystallized by blowing air cooling. Air-cooled crystallization includes a rapid cooling zone and a slow cooling zone. The molded product passes through the rapid cooling zone and the slow cooling zone in sequence and then is rolled up to obtain virgin fibers; wherein, after passing through the rapid cooling zone, the outer surface temperature of the molded product drops to (Tg+80)-(Tg+120)°C; and in the rapid cooling zone, the cooling rate of the outer surface of the molded product is not less than 80°C/mm@(100-200)m/min, and the molded product The cooling rate of the inner surface is 20-60°C/m@(100-200)m/min;
  • the virgin fiber is heat-set for the first time to obtain the heat-set semi-finished product
  • the melt index of the polyolefin in S1 is 1-7g/min@(Tm+20°C, 5kg); the crystallinity of the polyolefin is 40-70%;
  • the die aspect ratio in S1 is 2-5; the die temperature is (Tm+10)-(Tm+40)°C.
  • the length of the air section in S2 is 30-1000mm; the temperature of the air section is 40-70°C; the speed of the cooling airflow during blow cooling in S3 is 30-60m/min, and the temperature of the cooling airflow The temperature is 30-70°C, and the path length of the slow cooling zone is 4-8m.
  • the cold drawing temperature mentioned in S5 is (Tg+30)-(Tg+80)°C, the cold drawing elongation is 20-40%, and the cold drawing rate is (10-30)%/ min;
  • the hot drawing temperature mentioned in S6 is (Tm-60)-(Tm-30)°C, the hot drawing elongation is 2-6 times the cold drawing elongation, and the hot drawing rate is not higher than 15% of the cold drawing rate. .
  • the first heat setting temperature in S4 is (Tm-60)-(Tm-20)°C, and the setting time is 20-40 minutes; the second heat setting temperature in S7 is higher than the first heat setting temperature.
  • the temperature is 10-30°C higher and the setting time is 0.5-3min.
  • the present invention prepares polyolefin hollow fiber membranes through a melt stretching method, that is, no additional steps are required during the preparation process.
  • the corresponding diluent is added externally, and the raw material used is only the film-forming material polyolefin, such as any one of PP, PE and PMP; thus the obtained film is very pure, and when the corresponding liquid is degassed, no Impurities such as diluents will be dissolved, ensuring the purity of the liquid; that is, the polyolefin hollow fiber membrane produced by the present invention is suitable for degassing various liquids, and is particularly suitable for degassing ultrapure water.
  • the first step is to melt the polyolefin at a suitable temperature and then extrude it to form a molded product with an inner surface and an outer surface; during the process of extruding the molded product, the cavity-forming fluid is simultaneously introduced , common cavity-forming fluids are inert gases, such as nitrogen, argon and other gases.
  • cavity-forming fluids can effectively avoid concave deformation of molded products and ensure that the film has a relatively uniform wall thickness; as we all know, the relationship between raw materials Performance is the basis for the surface properties of membrane fibers and related microporous morphological structures; after research, parameters such as the crystallinity and melt index of the raw materials have a great impact on the performance of the film; the crystallinity of the polyolefin raw materials in this application is 40-70 % (measured by DSC method).
  • the crystallinity of the raw material polyolefin is too small, the porosity of the film will be too low, which will in turn cause the gas transmission rate to be too low and the degassing efficiency to be too low; therefore, choose polyolefins with high crystallinity
  • the raw materials are conducive to ensuring that the film has high porosity and excellent mechanical properties
  • the melt index is a value that indicates the fluidity of the material during processing; the larger the melt index value, the better the processing fluidity of the material, and vice versa; when the melt index is too small, the obstacles to molecular chain arrangement increase. , molecular chain diffusion, the activation energy required for the crystal phase structure increases, resulting in a decrease in the ability of the molecular chains to be arranged regularly, thereby reducing the crystallinity.
  • the polyolefin melt index in this application is 1-7g/min@(Tm+20°C, 5kg), where Tm is the melting point of the polyolefin raw material , that is, the melt index of the polyolefin of the present invention is measured at 20°C above the melting point of the corresponding raw material polyolefin; by selecting the raw material with such a melt index, it shows that the raw material has good processing fluidity, makes the film thickness more uniform, and improves the processing efficiency of the raw material , reduce energy consumption and production costs; at the same time, it is also beneficial to profitability
  • the membrane acquires higher mechanical properties;
  • the die extrusion temperature of this application is (Tm+10)-(Tm+40)°C, that is, the temperature at which the polyolefin is extruded through the die is 10-40°C above the melting point of the polyolefin, preferably 15-15°C above the melting point of the polyolefin.
  • the flow viscosity of the polymer melt is significantly affected by temperature. Generally, the viscosity decreases as the temperature increases. When the temperature of the die extrusion is too low, the viscosity of the polyolefin increases, which increases the size of the extrusion die.
  • the resistance of the die head increases the energy consumption of the extrusion process, and at the same time increases the thickness of the prepared film, which prevents better expansion and stretching, thereby affecting the tensile strength of the film; when the extrusion temperature of the die head is too high, Not only is it easy to cause thermal degradation of polyolefin, causing the main chain of the polyolefin to break from the weak bond in the middle, thereby reducing its molecular weight and significantly reducing its mechanical properties, thereby reducing the mechanical properties of the film; it can also easily cause the chain segment mobility of the polymer molecules.
  • the aspect ratio of the die is the ratio of the effective length of the screw to the diameter of the screw.
  • the aspect ratio of the die in this application is 2-5.
  • a suitable die aspect ratio not only has a suitable crystallinity, but also has a uniform film thickness, so that the prepared film has a more uniform hole structure and greater tensile strength;
  • the second step is to naturally cool the molded product extruded from the die through the air section for preliminary shaping, so that the molded product has a certain strength; in the air section, the overall temperature of the molded product will be reduced to a certain extent.
  • the cooling rate of the outer surface is relatively faster, while the cooling rate of the inner surface is relatively slower; after research, The study found that controlling the temperature of the inner and outer surfaces of the molded product after natural cooling can affect the number of overall lamellae to a certain extent, allowing the support layer in the hollow fiber membrane to form a larger number of microporous structures, while the skin layer forms a relatively dense membrane pore structure.
  • the outer surface temperature of the molded product after natural cooling is Tm-(Tm+15)°C (Tm is the melting point of the polyolefin raw material), and the inner surface temperature The temperature is greater than the temperature of the outer surface, and the average temperature gradient of the molded product after pre-crystallization is 0.01-0.2°C/1um; under such an outer surface temperature and the temperature gradient of the molded product, combined with the subsequent Blowing crystallization and the corresponding cold and hot drawing processes are conducive to obtaining the ideal film structure, changing the situation that the existing stretching method cannot obtain higher porosity, and truly making the film have higher porosity, and then high degassing rate and degassing efficiency; further research found that the temperature of the outer surface of the molded product after natural cooling cannot be too high or too low, because if the temperature of the outer surface is too high at this time, then when entering the subsequent air-cooled crystallization, the overall molded product will All
  • the length of the air section is 30-1000mm.
  • the temperature is 40-70°C, and the gas in the air section can be air, preferably an inert gas (such as nitrogen), so that the molded product has an ideal temperature gradient after natural cooling.
  • the cooling behavior of the molded product during natural cooling is very To a large extent, it will affect the size and uniformity of the tensile stress experienced by subsequent film filaments, and tensile stress is an important factor affecting the growth and orientation of lamellae; if the natural cooling rate is too slow, the polyolefin material will remain relatively stable for a long time.
  • the drawing stress is reduced, and the crystallization power of the polyolefin material is insufficient, resulting in the crystallinity of the inner layer of the molded product (i.e., the porous layer of the product) and The degree of crystallization orientation is low; if the natural cooling rate is too fast, although the drawing stress of the fiber becomes larger, the drawing stress is too concentrated, the uniformity of the drawing stress becomes poor, and the crystallinity and crystal orientation of the molded product are also relatively low.
  • both the inner surface temperature and the outer surface temperature of the molded product of the present invention can be measured by a depth thermal imager, and of course can also be measured by other methods;
  • the average temperature change gradient of the molded product in the present invention is measured by (inner surface temperature - Outer surface temperature)/molded product thickness obtained;
  • the molded product is then subjected to air-cooling crystallization.
  • the air-cooled crystallization is divided into two stages with different cooling speeds. That is, the pre-crystallized molded product will first pass through the rapid cooling zone for rapid cooling, and then quickly enter the slow cooling zone for slow cooling. Cooling, the cooling rate of the molded product when it is rapidly cooled is not less than 80°C/mm@(100-200)m/min, and the temperature of the outer surface of the molded product after rapid cooling is (Tg+80)-(Tg+120 )°C, where Tg is the glass transition temperature of the polyolefin raw material.
  • the outer surface The smaller the number of crystal nuclei, the smaller the number of holes that will appear on the outer surface after the step of cold drawing to form holes; and because the number of crystal nuclei on the outer surface is smaller in the present invention, then after the step of cold drawing to form holes, the number of holes on the outer surface will be smaller. After this step, the number of holes on the outer surface will be very small, resulting in a dense outer surface. If the cooling rate of the outer surface of the molded product is too slow, the macromolecular segments in the outer surface will have enough time to move and adjust.
  • the crystallinity of the outer surface increases, and under the action of drawing stress, its crystal orientation will also increase; then, during the stretching pore-forming step, a porous structure will appear on the outer surface and in the area near the outer surface, becoming It is no longer dense; therefore, it is necessary to control the cooling rate of the outer surface of the molded product in the rapid cooling zone to not be lower than 80°C/mm@(100-200)m/min;
  • the cooling rate in this application is not less than 80°C/mm@(100-200)m/min, which means that the molded product has a linear speed of 100-200m/min in a 1mm cooling path.
  • the temperature reduction value is not less than 80°C, so the length of the rapid cooling zone is very short, generally at the millimeter level;
  • the speed of the cooling airflow when cooling by blowing in the present invention is 30-60m/min, and the temperature of the cooling airflow The temperature is 30-70°C, so that the molded products can be cooled quickly in the rapid cooling zone;
  • the cooling rate of the inner surface is much lower.
  • the cooling rate on the outer surface is generally 20-60°C/m@(100-200)m/min.
  • This cooling rate ensures that more crystal nuclei can appear on the inner surface, and further the remaining areas inside the molded product ( Subsequently forming the support layer), more crystal nuclei appear; when the molded product passes through the rapid cooling zone, it will enter a slow cooling zone (rapid cooling and slow cooling are mainly for cooling the outer surface of the molded product, while the inner surface The difference in cooling rate between the two areas is not that big).
  • the outer surface and its nearby area are basically solidified and the temperature difference with the external environment becomes smaller, so they cool down slowly.
  • the outer surface is basically no longer conducive to the generation of crystal nuclei.
  • the outer surface of the final film fiber is still dense and the skin thickness accounts for a low proportion of the film wall thickness (an overly thick skin layer will not be formed); and in the slow cooling zone, the remaining areas of the molded product will still undergo Continuous cooling, by setting the path length of the slow cooling zone to 4-8 meters, allows the remaining areas of the molded product to generate as many crystal nuclei as possible, thereby ultimately obtaining a support layer with high porosity; in the present invention, the specific two-stage wind Cold crystallization can form a sudden change in temperature in the wall thickness direction of the molded product, instead of the conventionally recognized gradual temperature gradient.
  • the temperature of the area near the inner surface of the molded product is low, while the temperature of the remaining areas (the area where the support layer is subsequently formed) is higher and the temperature gradient in the wall thickness direction is small; that is, the molded product is divided into two temperature distributions: inside and outside.
  • the temperature distribution in each area is relatively uniform, the temperature difference between the two areas is large; therefore, the remaining areas of the molded product (the area where the support layer is subsequently formed) have strong mobility of macromolecular segments.
  • the fourth step is to perform the first heat setting treatment on the air-cooled crystallized and rolled nascent fibers.
  • the first heat setting temperature is (Tm-60)-(Tm-20)°C, and the setting time is 20-40min; once
  • the shaping process determines the crystallinity, crystal form, orientation and lamellar size of the fiber before stretching into holes, and one-time shaping can eliminate structural defects in the primary fiber (similar to annealing treatment) and improve the structural integrity of the fiber. Reduce the possibility of excessive concentration of tensile stress during the subsequent stretching and hole forming process;
  • This application specifically adopts a cold drawing process of less drawing and fast drawing combined with a hot drawing process of multiple drawing and slow drawing, so that the support layer has higher porosity and better pore structure.
  • the main function of drawing is to pull apart the lamellae and form the initial microfiber lace structure and pore structure; the main function of hot drawing is to further pull apart the lamellae that have not been pulled apart during the cold drawing stage, and to separate the lamellae produced during the cold drawing stage.
  • the micropores expand; therefore, cold drawing and hot drawing are interrelated and mutually influencing processes, and there is a high degree of correlation between the process parameters of the two, rather than being two isolated steps.
  • the hot drawing rate must match the cold drawing rate. This is because different cold drawing rates produce different pore structures and internal residual stress conditions. Different, the degree of separation of the lamellae and the structure of the microfiber lace are also different, and these conditions will affect the hot drawing rate. Therefore, the cold drawing rate or the hot drawing rate cannot be adjusted in isolation.
  • the hot stretching elongation and the cold stretching elongation must also be matched.
  • the degree of lamellae separation of the inner fiber layer, the length and thickness of the microfiber tie, etc. are different under different cold stretching elongations.
  • the hot drawing elongation also needs to be adjusted based on the fiber structure caused by different cold drawing elongation. When the ratio of hot drawing elongation to cold drawing elongation is too small, it means excessive cold drawing and/or insufficient hot drawing; when the ratio of hot drawing elongation to cold drawing elongation is too large, it means insufficient cold drawing and/or insufficient hot drawing.
  • the invention also provides the use of a polyolefin hollow fiber membrane for asymmetric degassing.
  • the polyolefin hollow fiber membrane is used to remove oxygen and carbon dioxide from ultrapure water; the O2 permeation of the polyolefin hollow fiber membrane is The rate is 15-30L/(min ⁇ bar ⁇ m 2 ), and the CO 2 penetration rate is 20-35L/(min ⁇ bar ⁇ m 2 );
  • the deoxygenation efficiency of the polyolefin hollow fiber membrane is not less than 80%, and the carbon dioxide removal efficiency is not less than 70%; the tensile strength of the polyolefin hollow fiber membrane is not less than 150CN, and the elongation at break is 30-150%. .
  • the membrane fiber produced by the present invention can degas various liquids, is particularly suitable for degassing high-purity water, and can achieve long-term and efficient degassing.
  • the polyolefin hollow fiber membrane provided by the present invention has a dense outer surface, and the surface energy of the outer surface is 15-40mN/m, so that the hollow fiber membrane has a longer service life and is not easily damaged. Moistened by aqueous liquid; there are several microfibers on the inner surface used to form a porous structure. The average length of the microfibers is 100-400nm and the average width is 15-60nm; the length direction of the microfibers is consistent with the length direction of the hollow fiber membrane.
  • the width direction of the microfibers is consistent with the circumferential direction of the hollow fiber membrane; the inner surface of such a structure ensures that the hollow fiber membrane has high porosity, thereby having a greater degassing (oxygen and carbon dioxide) rate and degassing efficiency , at the same time, the membrane as a whole has great mechanical properties and is suitable for use as a degassing membrane; in addition, the present invention also provides a melt stretching method to prepare the hollow fiber membrane without diluent, thereby further making the hollow fiber membrane suitable Used for degassing ultrapure water; this preparation method is fast, effective, simple to operate, and suitable for large-scale promotion.
  • Figure 1 is a scanning electron microscope (SEM) image of the inner surface of the hollow fiber membrane prepared in Example 1, where the magnification is 10000 ⁇ ;
  • Figure 2 is a further enlarged scanning electron microscope (SEM) image of the inner surface of the hollow fiber membrane prepared in Example 1, where the magnification is 20000 ⁇ ;
  • Figure 3 is a scanning electron microscope (SEM) image of the outer surface of the hollow fiber membrane prepared in Example 1, where the magnification is 10000 ⁇ ;
  • Figure 4 is a further magnified scanning electron microscope (SEM) image of the outer surface of the hollow fiber membrane prepared in Example 1, where the magnification is 20000 ⁇ ;
  • Figure 5 is a schematic diagram of the device for testing the degassing efficiency of the present invention.
  • Example 1 A method for preparing a polyolefin hollow fiber membrane for asymmetric degassing:
  • Polyolefin is melted and extruded in the die to form a molded product with an inner surface and an outer surface.
  • the aspect ratio of the die is 3; the extrusion temperature of the die is 190°C; the polyolefin is PP.
  • the PP is homopolymerized isotactic PP, the crystallinity of the PP is 55% (measured by DSC method), the isotactic degree is 99.9%, and the melt index is 4g/min @ (190°C, 5kg); the melting point of the PP Tm is 170°C, glass transition temperature Tg is -10°C;
  • pre-crystallization place the molded product in the air section (under nitrogen atmosphere) for pre-crystallization; the length of the air section is 400mm; the temperature of the air section is 55°C; after pre-crystallization, the outer surface temperature of the molded product is 175°C , and the average temperature gradient of the molded product after pre-crystallization is 0.062°C/1um; the inner surface temperature is higher than the outer surface temperature (the inner surface temperature is 183°C);
  • the molded product is air-cooled and crystallized by blowing cooling.
  • the air-cooled crystallization includes a rapid cooling zone and a slow cooling zone.
  • the molded product passes through the rapid cooling zone and the slow cooling zone in sequence and then is rolled up to obtain virgin fibers. ;
  • the outer surface temperature of the molded product drops to 90°C after passing through the rapid cooling zone; and in the rapid cooling zone
  • the speed of the cooling airflow is 50m/min, and the temperature of the cooling airflow is 45°C, so that the cooling speed of the outer surface of the molded product is not less than 80°C/mm@150m/min, and at the same time, the temperature of the inner surface of the molded product is controlled.
  • the cooling rate is 40°C/m@150m/min; and the path length of the slow cooling zone is 6m;
  • the virgin fiber is heat-set for the first time to obtain a heat-set semi-finished product;
  • the first heat-setting temperature is 130°C, and the setting time is 30 minutes;
  • the heat-set semi-finished product is cold-drawn to obtain a cold-drawn semi-finished product;
  • the cold-drawing temperature is 40°C, the cold-drawing elongation is 30%, and the cold-drawing rate is 20%/min;
  • Hot drawing and hole expansion The cold drawn semi-finished product is hot drawn and hole expanded to obtain the hot drawn semi-finished product; the hot drawing temperature is 125°C, the hot drawing elongation is 100%, and the hot drawing rate is 2%/min;
  • Secondary setting perform a second heat setting treatment on the hot-drawn semi-finished product to obtain a hollow fiber membrane; the second heat setting temperature is 155°C and the setting time is 2 minutes.
  • Example 2 A method for preparing a polyolefin hollow fiber membrane for asymmetric degassing:
  • the polyolefin is melted and extruded in the die to form a molded product with an inner surface and an outer surface.
  • the aspect ratio of the die is 5; the extrusion temperature of the die is 205°C; the polyolefin is PP.
  • the PP is homopolymerized isotactic PP, the crystallinity of the PP is 65% (measured by DSC method), the isotactic degree is 99.9%, the melt index is 2g/min @ (190°C, 5kg); the melting point of the PP Tm is 170°C, glass transition temperature Tg is -10°C;
  • pre-crystallization place the molded product in the air section (under nitrogen atmosphere) for pre-crystallization; the length of the air section is 600mm; the temperature of the air section is 65°C; after pre-crystallization, the outer surface temperature of the molded product is 185°C , and the average temperature gradient of the molded product after pre-crystallization is 0.067°C/1um; the inner surface temperature is higher than the outer surface temperature (the inner surface temperature is 198°C);
  • the molded product is air-cooled and crystallized by blowing cooling.
  • the air-cooled crystallization includes a rapid cooling zone and a slow cooling zone.
  • the molded product passes through the rapid cooling zone and the slow cooling zone in sequence and then is rolled up to obtain virgin fibers. ;
  • the outer surface temperature of the molded product drops to 100°C after passing through the rapid cooling zone; and in the rapid cooling zone
  • the speed of the cooling airflow is 30m/min
  • the temperature of the cooling airflow is 70°C, so that the cooling speed of the outer surface of the molded product is not less than 80°C/mm@120m/min, and at the same time, the temperature of the inner surface of the molded product is controlled.
  • the cooling rate is 25°C/m@120m/min; and the path length of the slow cooling zone is 8m;
  • the virgin fiber is heat-set for the first time to obtain a heat-set semi-finished product;
  • the first heat-setting temperature is 140°C, and the setting time is 25 minutes;
  • the heat-set semi-finished product is cold-drawn to obtain a cold-drawn semi-finished product;
  • the cold-drawing temperature is 50°C, the cold-drawing elongation is 35%, and the cold-drawing rate is 18%/min;
  • Hot-drawing hole expansion The cold-drawn semi-finished product is hot-drawn and hole-expanded to obtain a hot-drawn semi-finished product; the hot-drawing temperature is 135°C, the hot-drawing elongation is 140%, and the hot-drawing rate is 1.8%/min;
  • Example 3 A method for preparing a polyolefin hollow fiber membrane for asymmetric degassing:
  • the aspect ratio of the die is 4; the extrusion temperature of the die is 200°C; the polyolefin is PP , the PP is homopolymerized isotactic PP, the crystallinity of the PP is 60% (measured by DSC method), the isotactic degree is 99.9%, and the melt index is 3g/min @ (190°C, 5kg); the melting point of the PP Tm is 170°C, glass transition temperature Tg is -10°C;
  • pre-crystallization place the molded product in the air section (under nitrogen atmosphere) for pre-crystallization; the length of the air section is 500mm; the temperature of the air section is 60°C; after pre-crystallization, the outer surface temperature of the molded product is 180°C , and the average temperature gradient of the molded product after pre-crystallization is 0.070°C/1um; the inner surface temperature is higher than the outer surface temperature (the inner surface temperature is 192°C);
  • the molded product is air-cooled and crystallized by blowing cooling.
  • the air-cooled crystallization includes a rapid cooling zone and a slow cooling zone.
  • the molded product passes through the rapid cooling zone and the slow cooling zone in sequence and then is rolled up to obtain virgin fibers. ;
  • the outer surface temperature of the molded product dropped to 95°C after passing through the rapid cooling zone; and in the rapid cooling zone
  • the speed of the cooling airflow is 35m/min
  • the temperature of the cooling airflow is 65°C, so that the cooling speed of the outer surface of the molded product is not less than 80°C/mm@130m/min, and at the same time, the temperature of the inner surface of the molded product is controlled.
  • the cooling rate is 30°C/m@130m/min; and the path length of the slow cooling zone is 7m;
  • the virgin fiber is heat-set for the first time to obtain a heat-set semi-finished product;
  • the first heat-setting temperature is 145°C, and the setting time is 20 minutes;
  • the heat-set semi-finished product is cold-drawn to obtain a cold-drawn semi-finished product;
  • the cold-drawing temperature is 60°C, the cold-drawing elongation is 40%, and the cold-drawing rate is 14%/min;
  • Hot-drawing hole expansion The cold-drawn semi-finished product is hot-drawn and hole-expanded to obtain a hot-drawn semi-finished product; the hot-drawing temperature is 140°C, the hot-drawing elongation is 120%, and the hot-drawing rate is 1.2%/min;
  • the polyolefin is melted and extruded in the die to form a molded product with an inner surface and an outer surface.
  • the aspect ratio of the die is 3; the extrusion temperature of the die is 195°C; the polyolefin is PP , the PP is homopolymerized isotactic PP, the crystallinity of the PP is 50% (measured by DSC method), the isotacticity is 99.9%, the melt index is 5g/min @ (190°C, 5kg); the melting point of the PP Tm is 170°C, glass transition temperature Tg is -10°C;
  • pre-crystallization place the molded product in the air section (under nitrogen atmosphere) for pre-crystallization; the length of the air section is 300mm; the temperature of the air section is 50°C; after pre-crystallization, the outer surface temperature of the molded product is 178°C , and the average temperature gradient of the molded product after pre-crystallization is 0.068°C/1um; the inner surface temperature is higher than the outer surface temperature (the inner surface temperature is 188°C);
  • the molded product is air-cooled and crystallized by blowing cooling.
  • the air-cooled crystallization includes a rapid cooling zone and a slow cooling zone.
  • the molded product passes through the rapid cooling zone and the slow cooling zone in sequence and then is rolled up to obtain virgin fibers. ;
  • the outer surface temperature of the molded product dropped to 85°C after passing through the rapid cooling zone; and in the rapid cooling zone
  • the speed of the cooling airflow is 40m/min
  • the temperature of the cooling airflow is 60°C, so that the cooling speed of the outer surface of the molded product is not less than 80°C/mm@140m/min, and at the same time, the temperature of the inner surface of the molded product is controlled.
  • the cooling rate is 35°C/m@140m/min; and the path length of the slow cooling zone is 6.5m;
  • the virgin fiber is heat-set for the first time to obtain a heat-set semi-finished product;
  • the first heat-setting temperature is 125°C, and the setting time is 35 minutes;
  • the heat-set semi-finished product is cold-drawn to obtain a cold-drawn semi-finished product;
  • the cold-drawing temperature is 25°C, the cold-drawing elongation is 28%, and the cold-drawing rate is 22%/min;
  • Hot drawing hole expansion perform hot drawing hole expansion on the cold drawn semi-finished product to obtain the hot drawing semi-finished product; the hot drawing temperature is 130°C, the hot drawing elongation is 120%, and the hot drawing rate is 2.2%/min;
  • Secondary setting perform a second heat setting treatment on the hot-drawn semi-finished product to obtain a hollow fiber membrane; the second heat setting temperature is 145°C and the setting time is 2.5 minutes.
  • the aspect ratio of the die is 2; the extrusion temperature of the die is 185°C; the polyolefin is PP. , the PP is homopolymerized isotactic PP, the crystallinity of the PP is 48% (measured by DSC method), the isotacticity is 99.9%, and the melt index is 6g/min @ (190°C, 5kg); the melting point of the PP Tm is 170°C, glass transition temperature Tg is -10°C;
  • pre-crystallization place the molded product in the air section (under nitrogen atmosphere) for pre-crystallization; the length of the air section is 200mm; the temperature of the air section is 48°C; after pre-crystallization, the outer surface temperature of the molded product is 174°C , and the average temperature gradient of the molded product after pre-crystallization is 0.054°C/1um; the inner surface temperature is higher than the outer surface temperature (the inner surface temperature is 182°C);
  • the molded product is air-cooled and crystallized by blowing cooling.
  • the air-cooled crystallization includes a rapid cooling zone and a slow cooling zone.
  • the molded product passes through the rapid cooling zone and the slow cooling zone in sequence and then is rolled up to obtain virgin fibers. ;
  • the outer surface temperature of the molded product drops to 80°C after passing through the rapid cooling zone; and in the rapid cooling zone
  • the speed of the cooling airflow is 52m/min
  • the temperature of the cooling airflow is 43°C, so that the cooling speed of the outer surface of the molded product is not less than 80°C/mm@160m/min, and at the same time, the temperature of the inner surface of the molded product is controlled.
  • the cooling rate is 45°C/m@160m/min; while the path length of the slow cooling zone is 5.5m;
  • the virgin fiber is heat-set for the first time to obtain a heat-set semi-finished product;
  • the first heat-setting temperature is 120°C, and the setting time is 40 minutes;
  • the heat-set semi-finished product is cold-drawn to obtain a cold-drawn semi-finished product;
  • the cold-drawing temperature is 30°C, the cold-drawing elongation is 24%, and the cold-drawing rate is 24%/min;
  • Hot-drawing hole expansion The cold-drawn semi-finished product is hot-drawn and hole-expanded to obtain a hot-drawn semi-finished product; the hot-drawing temperature is 120°C, the hot-drawing elongation is 150%, and the hot-drawing rate is 2%/min;
  • Polyolefin is melted and extruded in a die to form a molded product with an inner surface and an outer surface.
  • the aspect ratio of the die is 2; the extrusion temperature of the die is 180°C; the polyolefin is PP.
  • the PP is homopolymerized isotactic PP, the crystallinity of the PP is 44% (measured by DSC method), the isotactic degree is 99.9%, the melt index is 7g/min @ (190°C, 5kg); the melting point of the PP Tm is 170°C, glass transition temperature Tg is -10°C;
  • pre-crystallization place the molded product in the air section (under nitrogen atmosphere) for pre-crystallization; the length of the air section is 80mm; the temperature of the air section is 45°C; after pre-crystallization, the outer surface temperature of the molded product is 172°C , and the average temperature gradient of the molded product after pre-crystallization is 0.050°C/1um; the inner surface temperature is higher than the outer surface temperature (the inner surface temperature is 177°C);
  • the molded product is air-cooled and crystallized by blowing cooling.
  • the air-cooled crystallization includes a rapid cooling zone and a slow cooling zone.
  • the molded product passes through the rapid cooling zone and the slow cooling zone in sequence and then is rolled up to obtain virgin fibers. ;
  • the outer surface temperature of the molded product dropped to 75°C after passing through the rapid cooling zone;
  • the speed of the cooling airflow is 55m/min, and the temperature of the cooling airflow is 40°C, so that the cooling speed of the outer surface of the molded product is not less than 80°C/mm@180m/min, and at the same time, the temperature of the inner surface of the molded product is controlled.
  • the cooling rate is 50°C/m@180m/min; and the path length of the slow cooling zone is Sm;
  • the virgin fiber is heat-set for the first time to obtain a heat-set semi-finished product;
  • the first heat-setting temperature is 135°C, and the setting time is 32 minutes;
  • the heat-set semi-finished product is cold-drawn to obtain a cold-drawn semi-finished product;
  • the cold-drawing temperature is 35°C, the cold-drawing elongation is 20%, and the cold-drawing rate is 28%/min;
  • Hot-drawing hole expansion The cold-drawn semi-finished product is hot-drawn and hole-expanded to obtain a hot-drawn semi-finished product; the hot-drawing temperature is 115°C, the hot-drawing elongation is 100%, and the hot-drawing rate is 2%/min;
  • Secondary setting perform a second heat setting treatment on the hot-drawn semi-finished product to obtain a hollow fiber membrane; the second heat setting temperature is 150°C and the setting time is 2 minutes.
  • the polyolefin is melted and extruded in the die to form a molded product with an inner surface and an outer surface.
  • the aspect ratio of the die is 3; the extrusion temperature of the die is 140°C; the polyolefin material is PE.
  • mLLDPE metalocene linear low-density polyethylene
  • the crystallinity of the mLLDPE is 50% (measured by DSC method), and the melt index is 4g/min @ (140°C, 5kg); in addition , the melting point Tm of the mLLDPE is about 120°C, and the glass transition temperature Tg is about -40°C;
  • pre-crystallization place the molded product in the air section (under nitrogen atmosphere) for pre-crystallization; the length of the air section is 350mm; the temperature of the air section is 50°C; after pre-crystallization, the outer surface temperature of the molded product is 125°C , and the average temperature gradient of the molded product after pre-crystallization is 0.069°C/1um; the inner surface temperature is higher than the outer surface temperature (the inner surface temperature is 134°C);
  • the molded product is air-cooled and crystallized by blowing air cooling.
  • the air-cooled crystallization includes a rapid cooling zone and a slow cooling zone.
  • the molded product passes through the rapid cooling zone and the slow cooling zone in sequence before being rolled up.
  • Virgin fibers are obtained; among them, the outer surface temperature of the molded product drops to 45°C after passing through the rapid cooling zone; and in the rapid cooling zone, the speed of the cooling airflow is 45m/min, and the temperature of the cooling airflow is 55°C, so that the outer surface of the molded product
  • the cooling rate of the surface is not less than 80°C/mm@150m/min, and the cooling rate of the inner surface of the molded product is controlled to be 30°C/m@150m/min; and the path length of the slow cooling zone is 6m;
  • the virgin fiber is heat-set for the first time to obtain a heat-set semi-finished product;
  • the first heat-setting temperature is 80°C, and the setting time is 35 minutes;
  • the heat-set semi-finished product is cold-drawn to obtain a cold-drawn semi-finished product;
  • the cold-drawing temperature is 20°C, the cold-drawing elongation is 30%, and the cold-drawing rate is 20%/min;
  • Hot-drawing hole expansion The cold-drawn semi-finished product is hot-drawn and hole-expanded to obtain a hot-drawn semi-finished product; the hot-drawing temperature is 75°C, the hot-drawing elongation is 100%, and the hot-drawing rate is 2%/min;
  • Secondary setting perform a second heat setting treatment on the hot-drawn semi-finished product to obtain a hollow fiber membrane; the second heat setting temperature is 100°C and the setting time is 2 minutes.
  • the polyolefin is melted and extruded in the die to form a molded product with an inner surface and an outer surface.
  • the aspect ratio of the die is 4; the extrusion temperature of the die is 265°C; in this example, PMP is selected as the polyolefin material.
  • the crystallinity of the PMP is 55% (measured by DSC method) and the melting index is 3g/min@(260°C, 5kg).
  • the melting point Tm of the PMP is about 240°C and the glass transition temperature Tg About 30°C;
  • Pre-crystallization place the molded product in the air section (under nitrogen atmosphere) for pre-crystallization; the length of the air section is 450mm, and the temperature of the air section is 60°C; after pre-crystallization, the outer surface temperature of the molded product is 245°C, and The average temperature gradient of the molded product after pre-crystallization is 0.085°C/1um; the inner surface temperature is higher than the outer surface temperature (the inner surface temperature is 256°C);
  • the molded product is air-cooled and crystallized by blowing air cooling.
  • the air-cooled crystallization includes a rapid cooling zone and a slow cooling zone.
  • the molded product passes through the rapid cooling zone and the slow cooling zone in sequence before being rolled up.
  • Virgin fibers were obtained; among them, the outer surface temperature of the molded product dropped to 155°C after passing through the rapid cooling zone; and in the rapid cooling zone, the speed of the cooling airflow was 50m/min, and the temperature of the cooling airflow was 40°C, so that the outer surface of the molded product
  • the cooling rate of the surface is not less than 80°C/mm@150m/min, and the cooling rate of the inner surface of the molded product is controlled to 46°C/m@150m/min; and the path length of the slow cooling zone is 6m;
  • the virgin fiber is heat-set for the first time to obtain a heat-set semi-finished product;
  • the first heat-setting temperature is 200°C, and the setting time is 25 minutes;
  • the heat-set semi-finished product is cold drawn to obtain a cold-drawn semi-finished product;
  • the cold drawing temperature is 80°C, the cold drawing elongation is 30%, and the cold drawing rate is 20%/min;
  • Hot drawing hole expansion perform hot drawing hole expansion on the cold drawn semi-finished product to obtain the hot drawing semi-finished product; the hot drawing temperature is 200°C, the hot drawing elongation is 100%, and the hot drawing rate is 1.5%/min;
  • Secondary setting perform a second heat setting treatment on the hot-drawn semi-finished product to obtain a hollow fiber membrane; the second heat setting temperature is 220°C and the setting time is 2.5 minutes.
  • Comparative Example 1 The main difference between Comparative Example 1 and Example 1 is that in step S3, the molded product is rapidly cooled down by liquid cooling; that is, step S3 of Comparative Example 1 includes the following process steps:
  • the cooling medium is deionized water.
  • the temperature of the deionized water is 40°C, and the cooling path length is 1m.
  • the fiber is dried in an oven at 70°C, and the virgin fiber is obtained after winding up. It should be noted that since it needs to be used for degassing of deionized water, in order to prevent solvent residues from affecting the quality of ultrapure water , only deionized water or ultrapure water can be used as the cooling medium.
  • step S3 of Comparative Example 2 includes the following process steps: further cooling the molded product by air blow cooling, so that the molded product undergoes cooling crystallization behavior.
  • the speed of the cooling air flow is 10m/min
  • the temperature of the cooling air flow is 90°C.
  • Comparative Example 3 The main difference between Comparative Example 3 and Example 3 is that in step S3, the fibers were not cooled by blowing cooling, but continued to be cooled by air cooling;
  • step S3 of Comparative Example 3 includes the following process steps: further cooling the fiber by natural cooling, controlling the path length of natural cooling to 6m, and controlling the temperature of the surrounding atmosphere to 55°C,
  • the hollow fibers prepared in Examples 1-8 have an ideal membrane structure, a thin and dense cortex, and a thick and porous support layer, thereby ensuring that the membrane filaments can be degassed efficiently for a long time; while for 1, due to the The cooling rate during the crystallization process is too fast, resulting in excessive thickness of the skin layer; while for pairs 2 and 3, the cooling rate during the crystallization process is too slow, so there is no skin layer, and the entire structure is porous.
  • Examples 1-8 all have ideal breathable areas and lamellar areas; while the breathable area of Comparative Example 1 is too small, resulting in inability to degas efficiently; the breathable areas of Comparative Examples 2 and 3 are too large, resulting in poor mechanical properties of the membrane filaments. .
  • Tensile strength and elongation at break test Use a tensile machine to stretch each sample at a constant speed at room temperature (stretching speed is 50mm/min, the distance between the upper and lower clamps is 30mm) until it breaks, and then measure the tensile strength. and elongation at break, repeat 3 times, and take the average value; the average value is the final tensile strength value and elongation at break value of the film;
  • the tensile strength of the hollow fiber membranes prepared in Examples 1-8 is not less than 150CN, and the elongation at break is 30-150%, that is, they all have large tensile strength and elongation at break, and can meet the requirements of industrialization needs;
  • the detection method is as follows: under the conditions of a temperature of 25°C, a pressure of 0.1bar, and a membrane sample area of 0.1 square meters. , subject one side of the membrane sample to the gas to be measured (oxygen, carbon dioxide); supply the gas to be measured into the inner cavity of the hollow fiber membrane; use a flow meter (Japanese KOFLOC/4800) to measure the volumetric flow rate of the gas passing through the sample membrane wall; Test three times from the inside of the membrane to the outside of the membrane, and three times from the outside of the membrane to the inside of the membrane, and then take the average value. The average value is the gas permeation rate of the membrane.
  • Gas permeation rate unit L/min
  • 2.3 Deoxygenation efficiency use the hollow fiber membranes prepared in each example or comparative example as raw materials, assemble a module with a membrane area of 0.65m2 , and connect the dissolved oxygen meter, water channel and module for testing.
  • the waterway is used to transport the degassed liquid, the components are used to degas the degassed liquid, and the dissolved oxygen meter is used to detect the oxygen content of the degassed liquid after the degassing treatment.
  • the degassing liquid flows out of the outside of the membrane.
  • the degassing liquid is deionized water.
  • the temperature of the degassing liquid is 25°C.
  • the inside of the membrane is vacuum swept. (As shown in Figure 5)
  • Step 1 Detect the initial oxygen content of the degassing liquid, pump the degassing liquid into the waterway, turn off the vacuum equipment at this time, so that the inside of the membrane is at normal pressure, and the degassing liquid passes through the component (without degassing) and then passes through the dissolved oxygen instrument, protect Keep the flow rate of degassing liquid into the dissolved oxygen meter at about 1.8GLH. Observe the changes in the dissolved oxygen display on the dissolved oxygen meter in real time. After the dissolved oxygen meter display stabilizes (when the change in the dissolved oxygen meter display is less than 1% within 5 minutes), read the dissolved oxygen display on the dissolved oxygen meter. O begins .
  • Step 2 Detect the final oxygen content of the degassed liquid after degassing.
  • step 1 On the basis of step 1, turn on the vacuum equipment to vacuum sweep the inner layer of the membrane to degas the degassed liquid. Maintain the vacuum during vacuum sweep.
  • the degree indication is -0.094MPa (50torr).
  • the deoxidation efficiency is calculated by the following formula:
  • test method 2.3 On the basis of test method 2.3, after starting degassing, run the system for 5 hours, and record the mass m2 of ultrapure water entering within 5 hours. After the operation is completed, collect the condensed water in the vacuum equipment, and measure the mass m1 of the condensed water. According to The following formula calculates the water vapor transmission rate:
  • the water vapor transmission rate of the hollow fiber membranes prepared in Examples 1-8 does not exceed 5 ⁇ , that is, when 1kg of pure water is removed, the condensed water generated in the vacuum measurement does not exceed 5g.
  • test method 2.3 replace the degassing liquid with a hydrochloric acid solution with a concentration of 5 mol/L. Observe the module condition every 4 hours. When leakage occurs on the inside of the membrane, it is considered that the module has been broken through and the degassing ability has been lost. Record the module. Time to be breached.
  • test method 2.3 replace the degassing liquid with a sodium hydroxide solution with a concentration of 5 mol/L. Observe the component condition every 4 hours. When leakage occurs on the inside of the membrane, it is considered that the component has been broken through and has lost its degassing ability. Record the time when the component was breached.
  • the hollow fiber membranes prepared in Examples 1-8 of the present invention all have degassing rate and degassing efficiency, and have a longer service life, while the degassing efficiency and degassing rate of Comparative Example 1 are both higher. Low, the service life of Comparative Example 2 and Comparative Example 3 is shorter.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

L'invention concerne une membrane à fibres creuses en polyoléfine pour le dégazage asymétrique, son procédé de préparation et son utilisation dans l'élimination de l'oxygène et du dioxyde de carbone de l'eau ultrapure. La membrane à fibres creuses en polyoléfine comprend un corps principal ; un côté du corps principal est une surface interne faisant face à la cavité interne, et l'autre côté du corps principal est une surface externe ; un trajet sinueux non directionnel est disposé dans le corps principal ; une pluralité de microfibres pour former une structure poreuse sont disposées sur la surface interne du corps principal, et les microfibres présentent une longueur moyenne de 100 à 400 nm et une largeur moyenne de 15 à 60 nm ; la direction de la longueur des microfibres est cohérente avec celle de la membrane à fibres creuses, et la direction de la largeur des microfibres est cohérente avec la direction circonférentielle de la membrane à fibres creuses ; l'énergie de surface de la surface externe est de 15 à 40 mN/m, et la surface externe est une surface dense. Le procédé de préparation comprend les étapes suivantes : S1, le filage ; S2, la pré-cristallisation ; S3, la réalisation d'une cristallisation refroidie par air ; S4, la réalisation d'un réglage primaire ; S5, la réalisation d'un étirage à froid pour former des pores ; S6, la réalisation d'un étirage à chaud pour agrandir les pores ; et S7, la réalisation d'un réglage secondaire.
PCT/CN2023/099640 2022-07-11 2023-06-12 Membrane à fibres creuses en polyoléfine pour dégazage asymétrique, son procédé de préparation et son utilisation WO2024012121A1 (fr)

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