CN112076633A - Reverse osmosis membrane and preparation method thereof - Google Patents

Reverse osmosis membrane and preparation method thereof Download PDF

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Publication number
CN112076633A
CN112076633A CN202011040113.6A CN202011040113A CN112076633A CN 112076633 A CN112076633 A CN 112076633A CN 202011040113 A CN202011040113 A CN 202011040113A CN 112076633 A CN112076633 A CN 112076633A
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diaphragm
reverse osmosis
osmosis membrane
polyolefin
pore diameter
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蒋涛
刘涛涛
翁星星
陈朝晖
贡晶晶
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Jiangsu Housheng New Energy Technology Co Ltd
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Jiangsu Housheng New Energy Technology Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/26—Polyalkenes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/025—Reverse osmosis; Hyperfiltration
    • 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
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/441—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2323/00—Details relating to membrane preparation
    • B01D2323/08—Specific temperatures applied
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2323/00—Details relating to membrane preparation
    • B01D2323/50—Control of the membrane preparation process
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/02—Details relating to pores or porosity of the membranes
    • B01D2325/022—Asymmetric membranes
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/08—Seawater, e.g. for desalination
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A20/00—Water conservation; Efficient water supply; Efficient water use
    • Y02A20/124—Water desalination
    • Y02A20/131—Reverse-osmosis

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Water Supply & Treatment (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Environmental & Geological Engineering (AREA)
  • Organic Chemistry (AREA)
  • Nanotechnology (AREA)
  • Manufacturing & Machinery (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

The invention discloses a reverse osmosis membrane and a preparation method thereof, wherein the reverse osmosis membrane comprises a polyamide microporous layer and a polyolefin membrane; the polyolefin diaphragm is compounded with a polyamide microporous layer; the pore diameters of the upper surface and the lower surface of the polyolefin diaphragm are not equal; the pore diameter of the upper surface of the polyolefin diaphragm is D1, the pore diameter of the lower surface of the polyolefin diaphragm is D2, and D2/D1 is more than or equal to 3 and less than or equal to 10; the pore diameter D1 on the upper surface of the polyolefin diaphragm is 10-15 nm; the pore diameter D2 of the lower surface of the polyolefin diaphragm is 50-100 nm. According to the invention, polysulfone and non-woven fabrics are replaced by the multi-level olefin diaphragm with asymmetric apertures on two sides, the thickness of the reverse osmosis membrane is reduced to be below 30nm, the water flux is greatly improved, and the operation process is simple and energy-saving; three methods are provided in the heat treatment process stage, and the cost and the operation efficiency are optimized; besides being applied to the field of seawater desalination, the reverse osmosis membrane prepared by the invention can also be applied to the fields of sewage treatment, non-aqueous liquid filtration and the like.

Description

Reverse osmosis membrane and preparation method thereof
Technical Field
The invention relates to the technical field of reverse osmosis membranes, in particular to a reverse osmosis membrane and a preparation method thereof.
Background
The total amount of fresh water resources in China is 28000 billions of cubic meters, and the world is the fourth famous, but the per capita water volume only accounts for one fourth of the world level. However, China is the country with the most water consumption in the world, and only in 2002, the national fresh water consumption reaches 5497 billions of cubic meters, which accounts for about 13% of the world year consumption. However, the seawater resources in China are very abundant, so how to apply the seawater desalination method which is more efficient, more practical and low in cost is an urgent problem to be solved.
The currently used methods for desalinating seawater include a seawater thawing method, an electrodialysis method, a distillation method and a reverse osmosis method, and the reverse osmosis method using the reverse osmosis membrane has the advantages of simple equipment, easy maintenance and modular equipment, and is the most widely applied method for desalinating seawater. In the materials of the reverse osmosis membrane, polysulfone gradually replaces early cellulose materials due to the characteristics of stable chemical structure, higher heat resistance, good mechanical strength, easy processing and the like, and becomes a research subject in recent years; the composite membrane with high water flux can be prepared by adopting the porous layer, the thickness of the composite membrane is up to 150nm, the running cost is high, simultaneously, in the heat setting process of the membrane, the two surfaces of the membrane are treated by adopting the same temperature, the pore diameters of the upper surface and the lower surface are consistent, the effect is poor in the aspects of cost control, running efficiency and the like, and a reverse osmosis membrane device capable of effectively reducing the cost is urgently needed to be applied to the field of liquid treatment.
Disclosure of Invention
The present invention is directed to a reverse osmosis membrane and a method for preparing the same, which solves the above problems of the prior art.
In order to solve the technical problems, the invention provides the following technical scheme:
a reverse osmosis membrane comprising a polyamide microporous layer, the reverse osmosis membrane comprising a polyolefin membrane; the polyolefin diaphragm is compounded with a polyamide microporous layer; the pore diameters of the upper surface and the lower surface of the polyolefin diaphragm are not equal.
In an optimized scheme, the pore diameter of the upper surface of the polyolefin diaphragm is D1, the pore diameter of the lower surface of the polyolefin diaphragm is D2, and the ratio of D2/D1 is not more than 3.
In an optimized scheme, the pore diameter D1 on the upper surface of the polyolefin diaphragm is 10-15 nm; the pore diameter D2 of the lower surface of the polyolefin diaphragm is 50-100 nm.
In a more optimized scheme, the thickness of the polyolefin separator is 7-30 mu m.
In a more optimized scheme, the polyolefin diaphragm comprises ultra-high molecular weight polyethylene resin PE1 and high density polyethylene resin PE 2; the mass ratio of the PE1 to the PE2 is 5: 5-95; the average molecular weight of the ultra-high molecular weight polyethylene resin PE1 is 1 × 106-4×106(ii) a The average molecular weight of the high-density polyethylene resin PE2 is 5 multiplied by 105-8×105。
According to an optimized scheme, the preparation method of the reverse osmosis membrane comprises the following steps:
1) passing the ultra-high molecular weight polyethylene resin PE1, the high density polyethylene resin PE2 and paraffin through a double-screw co-rotating extruder to obtain a melt;
2) casting and stretching the melt obtained in the step 1) to obtain a stretched film;
3) removing paraffin by using an extracting agent through an extraction tank on the stretched film obtained in the step 2), drying to remove the extracting agent, and performing heat setting processing on the stretched film to obtain polyolefin diaphragms with unequal upper and lower surface apertures;
4) and (3) winding and cutting the polyolefin membrane obtained in the step (3) to obtain the reverse osmosis membrane.
In an optimized scheme, in the step 3), the heat setting method is one of heat oven treatment, physical pretreatment and hot roller treatment.
In an optimized scheme, the thermal oven treatment is to pass the diaphragm through the thermal oven, wherein the processing temperature of the upper surface of the diaphragm is set to be 130-150 ℃, and preferably 135-140 ℃; the lower surface processing temperature is set to 100-130 ℃, preferably 120-125 ℃.
In an optimized scheme, the physical pretreatment is to perform brush friction treatment on the upper surface of the diaphragm and then perform a heat setting process; wherein the heat setting temperature is 120-135 ℃ (the same temperature for upper and lower surface treatment).
According to an optimized scheme, the heat roller treatment is to pass the diaphragm dried by the heat drying oven through a group of traction rollers distributed in an S shape, and the temperature of the heat roller passing through the upper surface of the diaphragm is 130-150 ℃, preferably 135-140 ℃; the temperature of the hot roller passing through the lower surface of the diaphragm is 30-90 ℃, preferably 40-70 ℃; wherein, the temperature of the hot oven is set to be 120 ℃ to 130 ℃, the diameter of the roller is 500mm to 800mm, and the number of the group is 4-8.
In an optimized scheme, in the step 1), the paraffin is 60-90% and the PE1+ PE2 is 10-40% by mass; the temperature of the double-screw co-extrusion machine is 150-250 ℃.
The application of the reverse osmosis membrane is characterized in that the reverse osmosis membrane is utilized, seawater is applied with certain pressure through a high-pressure water pump, firstly passes through a polyamide microporous layer in a composite membrane and then passes through the upper surface of a diaphragm to block impurities, bacteria and salt substances in the water, and drinkable fresh water is obtained on the lower surface; the pressure is 6-9kg/cm2。
Compared with the prior art, the invention has the following beneficial effects:
1) the invention ensures the inconsistency of the microporous structures on the two sides of the diaphragm through the process treatment, obtains the diaphragm with compact small pore diameter distributed on one side and large pore diameter distributed on the other side, and can achieve the purpose of filtering impurities, bacteria and macromolecular salt substances with the diameter more than 10nm in the seawater in use, thereby desalinating the seawater and obtaining drinkable fresh water. The invention replaces polysulfone and non-woven fabrics in the prior art with the multi-level olefin diaphragm with asymmetric aperture on both sides, reduces the thickness of the reverse osmosis membrane to be less than 30nm, greatly improves water flux and effectively reduces the cost of seawater desalination.
2) The pore diameter D1 of the upper surface of the polyolefin diaphragm adopted by the invention is 10-15nm, the pore diameter D2 of the lower surface is 50-100nm, wherein D2/D1 is more than or equal to 3. When the ratio is less than 3, the difference between the pore diameters of the two surfaces is too small, the pressure drop before and after the filtering membrane is large, the filtering membrane is easy to damage, and the service life is too short.
3) The invention provides three methods in the heat setting working section, namely heat oven treatment, physical pretreatment and hot roller treatment, and compared with the diaphragm prepared by the conventional heat setting method, the diaphragm prepared by the three methods has more uniform micropore structure and less large branch crystal lines, thereby effectively improving the use efficiency and prolonging the use period; before the thermal oven treatment, the membrane is pretreated by the hairbrush, namely micropores on the upper surface of the membrane are sealed in a hairbrush friction treatment mode, and the micropores become blind holes, so that the same processing temperature can be adopted for the upper surface and the lower surface during the subsequent thermal oven treatment, the energy consumption is reduced, the cost is saved, the pore diameter difference of the upper surface and the lower surface can be ensured, and the double-sided pore diameter asymmetry is realized; the diaphragm processed by the hot roller has lower high-temperature heat shrinkage rate and better shrinkage performance, can be applied to the field of water treatment, and can also show excellent effect in the field of battery diaphragms.
4) The reverse osmosis membrane obtained in the invention has a plurality of winding layers, the expected water throughput is 8-12 times of that of the prior art, and the reverse osmosis membrane has the advantages of good high liquid permeability, high desalination rate, low pressure drop and the like, effectively reduces the operation cost and improves the treatment efficiency. The preparation process is simple, energy-saving, safe and environment-friendly in raw materials, optimized in cost and operation efficiency, and more suitable for large-scale processing production; besides being applied to the field of seawater desalination, the reverse osmosis membrane prepared by the invention can also be applied to the fields of sewage treatment, non-aqueous liquid filtration and the like.
Detailed Description
Example 1
A reverse osmosis membrane comprising a polyolefin membrane; the polyolefin diaphragm is compounded with a polyamide microporous layer; the pore diameters of the upper surface and the lower surface of the polyolefin diaphragm are not equal.
A reverse osmosis membrane and a preparation method thereof, wherein the process comprises the following steps:
1) mixing PE1 ultrahigh molecular weight polyethylene resin and PE2 high density polyethylene resin in a mass ratio of 5: 95; mixing 40% PE1 and PE2 with 60% paraffin oil by massPassing through a double-screw co-rotating extruder, wherein the temperature of the extruder is 160 ℃, and performing melt extrusion to obtain a melt at 190 ℃; the average molecular weight of the PE1 is 1 x 106PE2 average molecular weight 5X 105；
2) Casting the melt obtained in the step 1) at 20 ℃, longitudinally stretching the melt by 6.5 times at 100 ℃, and transversely stretching the melt by 8.5 times at 105 ℃;
3) cleaning the stretched film obtained in the step 2) with graphite through an extraction tank, and drying to remove an extractant; wherein the extractant is dichloromethane; the drying temperature is 35 ℃;
4) processing the extracted stretched film obtained in the step 3) by an oven heat treatment process, wherein the processing temperature of the upper surface of the diaphragm is 130 ℃, and the processing temperature of the lower surface of the diaphragm is 100 ℃; the average pore diameters of the obtained diaphragms are respectively 10nm and 50nm, and the heat setting stretching ratio is 1.2;
5) winding the diaphragm obtained in the step 4) at the speed of 30 m/min by a winding machine, and slitting the diaphragm by a slitting machine at the speed of 100 m/min to obtain products with different width specifications.
Example 2
A reverse osmosis membrane comprising a polyolefin membrane; the polyolefin diaphragm is compounded with a polyamide microporous layer; the pore diameters of the upper surface and the lower surface of the polyolefin diaphragm are not equal.
A reverse osmosis membrane and a preparation method thereof, wherein the process comprises the following steps:
1) mixing PE1 high molecular weight polyethylene resin and PE2 high density polyethylene resin in a mass ratio of 5: 50; according to the mass percentage, 25% of PE1 and PE2 mixture and 75% of paraffin oil are extruded by a double-screw co-rotating extruder, the temperature of the extruder is 180 ℃, and melt extrusion is carried out to obtain 250 ℃ melt; the average molecular weight of the PE1 is 2 x 106PE2 average molecular weight 6X 105；
2) Casting the melt obtained in the step 1) at 45 ℃, longitudinally stretching 8.5 times at 115 ℃ and transversely stretching 11 times at 118 ℃;
3) cleaning the stretched film obtained in the step 2) with graphite through an extraction tank, and drying to remove an extractant; wherein the extractant is dichloromethane; the drying temperature is 50 ℃;
4) processing the extracted stretched film obtained in the step 3) by an oven heat treatment process, wherein the processing temperature of the upper surface of the diaphragm is 137 ℃, and the processing temperature of the lower surface of the diaphragm is 120 ℃; the average pore diameters of the obtained diaphragms are respectively 12.5nm and 75nm, and the heat setting stretch ratio is 1.3;
5) winding the diaphragm obtained in the step 4) at the speed of 60 m/min by a winding machine, and slitting the diaphragm by a slitting machine at the speed of 150 m/min to obtain products with different width specifications.
Example 3
A reverse osmosis membrane comprising a polyolefin membrane; the polyolefin diaphragm is compounded with a polyamide microporous layer; the pore diameters of the upper surface and the lower surface of the polyolefin diaphragm are not equal.
A reverse osmosis membrane and a preparation method thereof, wherein the process comprises the following steps:
1) mixing PE1 high molecular weight polyethylene resin and PE2 high density polyethylene resin in a mass ratio of 5: 5; according to the mass percentage, 40 percent of PE1 and PE2 mixture and 60 percent of paraffin oil are extruded by a double-screw co-rotating extruder, the temperature of the extruder is 160 ℃, and melt extrusion is carried out to obtain melt of 190 ℃ and 250 ℃; the average molecular weight of the PE1 is 3 x 106PE2 average molecular weight 7X 105；
2) Casting the melt obtained in the step 1) at 20 ℃, longitudinally stretching the melt by 6.5 times at 100 ℃, and transversely stretching the melt by 8.5 times at 105 ℃;
3) cleaning the stretched film obtained in the step 2) with graphite through an extraction tank, and drying to remove an extractant; wherein the extractant is dichloromethane; the drying temperature is 35 ℃;
4) processing the extracted stretched film obtained in the step 3) by an oven heat treatment process, wherein the processing temperature of the upper surface of the diaphragm is 140 ℃, and the processing temperature of the lower surface of the diaphragm is 130 ℃; the average pore diameters of the obtained diaphragms are 15nm and 100nm respectively;
5) winding the diaphragm obtained in the step 4) at the speed of 90 m/min by a winding machine, and slitting the diaphragm by a slitting machine at the speed of 200 m/min to obtain products with different width specifications.
Example 4
A reverse osmosis membrane comprising a polyolefin membrane; the polyolefin diaphragm is compounded with a polyamide microporous layer; the pore diameters of the upper surface and the lower surface of the polyolefin diaphragm are not equal.
A reverse osmosis membrane and a preparation method thereof, wherein the process comprises the following steps:
1) mixing PE1 high molecular weight polyethylene resin and PE2 high density polyethylene resin in a mass ratio of 5: 50; according to the mass percentage, 25% of PE1 and PE2 mixture and 75% of paraffin oil are extruded by a double-screw co-rotating extruder, the temperature of the extruder is 180 ℃, and melt extrusion is carried out to obtain 250 ℃ melt; the average molecular weight of the PE1 is 4 x 106PE2 average molecular weight 8X 105；
2) Casting the melt obtained in the step 1) at 45 ℃, longitudinally stretching 8.5 times at 115 ℃ and transversely stretching 11 times at 118 ℃;
3) cleaning the stretched film obtained in the step 2) with graphite through an extraction tank, and drying to remove an extractant; wherein the extractant is dichloromethane; the drying temperature is 50 ℃;
4) carrying out heat setting on the stretched film obtained after extraction in the step 3), wherein the upper surface of the diaphragm is subjected to physical pretreatment, a set of hairbrush is added before the heat setting process, and hairbrush friction treatment is carried out on the upper surface of the diaphragm; then, passing the upper surface and the lower surface through a hot oven, wherein the temperature is set to be 120 ℃; the apertures of the upper surface and the lower surface of the obtained diaphragm are respectively 12nm and 90 nm;
5) winding the diaphragm obtained in the step 4) at the speed of 60 m/min by a winding machine, and slitting the diaphragm by a slitting machine at the speed of 150 m/min to obtain products with different width specifications.
Example 5
A reverse osmosis membrane comprising a polyolefin membrane; the polyolefin diaphragm is compounded with a polyamide microporous layer; the pore diameters of the upper surface and the lower surface of the polyolefin diaphragm are not equal.
A reverse osmosis membrane and a preparation method thereof, wherein the process comprises the following steps:
1) mixing PE1 high molecular weight polyethylene resin and PE2 high density polyethylene resin in a mass ratio of 5: 50; according to the mass percentage, 25% of PE1 and PE2 mixture and 75% of paraffin oil are extruded by a double-screw co-rotating extruder, the temperature of the extruder is 180 ℃, and melt extrusion is carried out to obtain 250 ℃ melt; the average molecular weight of the PE1 is 4 x 106PE2 average molecular weight 8X 105；
2) Casting the melt obtained in the step 1) at 45 ℃, longitudinally stretching 8.5 times at 115 ℃ and transversely stretching 11 times at 118 ℃;
3) cleaning the stretched film obtained in the step 2) with graphite through an extraction tank, and drying to remove an extractant; wherein the extractant is dichloromethane; the drying temperature is 50 ℃;
4) drying the extracted stretched film obtained in the step 3) by a hot oven, and then carrying out hot roller treatment, wherein the temperature of the hot oven is set to be 120 ℃, the temperature of a hot roller passing through the upper surface of the diaphragm is 135 ℃, and the temperature of a hot roller passing through the lower surface of the diaphragm is 40 ℃; wherein the hot roller is a group of traction rollers distributed in S shape, the diameter of the roller is 500mm, and the number of the group of rollers is 4; the average pore diameters of the obtained diaphragms are 15nm and 100nm respectively;
5) winding the diaphragm obtained in the step 4) at the speed of 60 m/min by a winding machine, and slitting the diaphragm by a slitting machine at the speed of 150 m/min to obtain products with different width specifications.
Comparative example 1
The same procedure as described in example 3 was followed to give comparative example 1. Wherein the processing temperature of the oven heat treatment process to the upper surface and the lower surface of the diaphragm is consistent and is 120 ℃.
Comparative example 2
The same procedure as described in example 1 was followed to give comparative example 2. The average pore diameter of the obtained upper surface was 20nm, and D2/D1 was 2.5.
Comparative example 3
The same procedure as described in example 1 was followed to give comparative example 2. The average pore diameter on the upper surface obtained was 35nm, and D2/D1 was 1.67.
Comparative example 4
The same procedure as described in example 1 was followed to give comparative example 2. Wherein the resulting average pore size of the upper surface was 5 nm.
Comparative example 5
The same procedure as described in example 1 was followed to give comparative example 2. Wherein the average pore size of the obtained lower surface was 45 nm.
Comparative example 6
The same procedure as described in example 1 was followed to give comparative example 2. Wherein the average pore size of the obtained lower surface was 120 nm.
The salt rejection, recovery rate, operating pressure difference at two sides of the membrane, water flux and microporous structure of the membrane products obtained in examples 1-5 and comparative examples 1-6 of the invention were tested, and the obtained membrane performance was as follows:
Figure BDA0002706362720000071
Figure BDA0002706362720000081
remarking:
1. salt rejection: removing the percentage of soluble impurity concentration from the inlet water of the system through a reverse osmosis membrane, wherein the desalination rate is (1-water production salinity/inlet water salinity) multiplied by 100%;
2. and (3) recovery rate: the percent of feed water in the membrane system converted into product water or permeate is expressed, and the recovery rate is (product water flow/inlet water flow) multiplied by 100 percent;
3. water flux: in a typical 4040 unit (40 inches long and 4 inches in diameter) the maximum flux of feed water converted to product water or permeate.
4. Microporous structure: and (3) scanning the diaphragm by using an electron microscope to observe the micropore structure and the texture of the large dendrite (the texture of the dendrite is that the texture similar to that of the large root appears near the micropore structure of the diaphragm along the stretching direction, and the diameter of the large dendrite is 200-5000 nm).
And (4) conclusion:
examples 1-5 were prepared according to the inventive protocol, and examples 1-5 were compared to comparative examples 1-6.
As can be seen from the above table, the reverse osmosis membranes prepared in examples 1 to 5 are superior to those of comparative examples 1 to 6 in salt rejection, recovery rate, operating pressure difference across the membrane, and water flux of 4040 apparatus.
As can be seen from comparison between example 3 and comparative example 1, when the upper and lower surfaces of the membrane were processed at the same temperature, the pore diameters of the micropores on the upper and lower surfaces of the membrane were the same, but the expected reverse osmosis membrane effect was not achieved due to the same pore diameters on both surfaces, and the salt rejection rate and recovery rate were significantly reduced.
As can be seen from the comparison between example 1 and comparative examples 2 to 3, when D2/D1 is less than 3, the difference in pore sizes between both sides is too small, the operating pressure difference between both sides of the membrane is too large, and the membrane is easily damaged, so that the salt rejection rate and the recovery rate are reduced, and the salt rejection rate and the recovery rate are positively correlated with the pore size ratio.
As can be seen from the comparison between example 1 and comparative example 4, when the pore diameter of the upper surface is too small, the water flux is directly reduced significantly, and the liquid is accumulated on one side of the upper surface, so that the operating pressure difference between both sides of the membrane is too large, the membrane may be damaged, and the desalting and recycling effects are not satisfactory.
As can be seen from comparison between example 1 and comparative example 5, when the pore diameter of the lower surface is decreased, that is, the pore ratio between the upper surface and the lower surface is decreased, and the pressure drop before and after the filtration membrane is large, the recovery rate and the water flux are significantly decreased, and the operating pressure difference between both sides of the membrane is too large.
As can be seen from comparison between example 1 and comparative example 5, when the pore diameter of the lower surface is too large, the operating pressure difference between both sides of the membrane is too large, and the filtration membrane is easily damaged, so that the service life of the filtration membrane is too short.
The invention discloses a reverse osmosis membrane and a preparation method thereof, wherein polysulfone and non-woven fabrics are replaced by a multi-level olefin diaphragm with asymmetric aperture on two sides, the thickness of the reverse osmosis membrane is reduced to be below 30nm, the water flux is greatly improved, and the seawater desalination cost is effectively reduced; and three methods are provided in the heat treatment process stage, so that the method is optimized in cost and operation efficiency and is more suitable for large-scale processing production.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are therefore intended to be embraced therein.

Claims (10)

1. A reverse osmosis membrane comprising a polyamide microporous layer characterized by: the reverse osmosis membrane comprises a polyolefin membrane; the polyolefin diaphragm is compounded with a polyamide microporous layer; the pore diameters of the upper surface and the lower surface of the polyolefin diaphragm are not equal.
2. A reverse osmosis membrane according to claim 1, wherein: the pore diameter of the upper surface of the polyolefin diaphragm is D1, the pore diameter of the lower surface of the polyolefin diaphragm is D2, and D2/D1 is not more than 3 and not more than 10.
3. A reverse osmosis membrane according to claim 2, wherein: the pore diameter D1 on the upper surface of the polyolefin diaphragm is 10-15 nm; the pore diameter D2 of the lower surface of the polyolefin diaphragm is 50-100 nm.
4. A reverse osmosis membrane according to claim 1, wherein: the thickness of the polyolefin separator is 7-30 μm.
5. A reverse osmosis membrane according to claim 1, wherein: the polyolefin diaphragm comprises an ultra-high molecular weight polyethylene resin PE1 and a high density polyethylene resin PE 2; the mass ratio of the PE1 to the PE2 is 5: 5-95; the average molecular weight of the ultra-high molecular weight polyethylene resin PE1 is 1 × 106-4×106(ii) a The average molecular weight of the high-density polyethylene resin PE2 is 5 multiplied by 105-8×105。
6. A preparation method of a reverse osmosis membrane is characterized by comprising the following steps: the preparation method comprises the following steps:
1) passing the ultra-high molecular weight polyethylene resin PE1, the high density polyethylene resin PE2 and paraffin through a double-screw co-rotating extruder to obtain a melt;
2) casting and stretching the melt obtained in the step 1) to obtain a stretched film;
3) passing the stretched film obtained in 2) through an extraction tank, removing paraffin by using an extractant, drying to remove the extractant,
carrying out heat setting processing on the stretched film to obtain polyolefin diaphragms with unequal upper and lower surface apertures;
4) and (3) winding and cutting the polyolefin membrane obtained in the step (3) to obtain the reverse osmosis membrane.
7. The method of preparing a reverse osmosis membrane according to claim 6, wherein: in the step 3), the heat setting method is one of heat oven treatment, physical pretreatment and hot roller treatment.
8. A method of preparing a reverse osmosis membrane according to claim 7, wherein: the thermal oven treatment is to pass the diaphragm through the thermal oven, wherein the processing temperature of the upper surface is set to be 130-150 ℃, and the processing temperature of the lower surface is set to be 100-130 ℃.
9. A method of preparing a reverse osmosis membrane according to claim 7, wherein: the physical pretreatment is to perform brush friction treatment on the upper surface of the diaphragm and then perform heat setting treatment by a heat oven; wherein the thermal oven temperature was set at 120-135 ℃.
10. A method of preparing a reverse osmosis membrane according to claim 7, wherein: the hot roller treatment is that the diaphragm dried by the hot oven passes through a group of traction rollers distributed in an S shape, the temperature of the hot roller passing through the upper surface of the diaphragm is 130-150 ℃, and the temperature of the hot roller passing through the lower surface of the diaphragm is 30-90 ℃; wherein the diameter of the roller is 500-800mm, and the number of the group is 4-8.
CN202011040113.6A 2020-09-28 2020-09-28 Reverse osmosis membrane and preparation method thereof Withdrawn CN112076633A (en)

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CN110838566A (en) * 2019-11-06 2020-02-25 江苏厚生新能源科技有限公司 Preparation method of multilayer polyethylene diaphragm
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