KR20230148044A - A stretchable superhydrophobic membrane, a manufacturing method thereof, and a membrane distillation using same - Google Patents

Abstract

The present invention relates to a superhydrophobic separation membrane that can increase a permeation flux by including elastic materials, capable of maintaining superhydrophobicity when forming a pore size to prevent the separation membrane from getting wet, and allowing the pore size to be adjusted. The present invention provides the superhydrophobic separation membrane, the manufacturing method thereof, and a membrane distillation method using the same. The superhydrophobic separation membrane includes a fibrous membrane layer containing elastic material; and a coating layer in which the fibrous membrane is coated with hydrophobic microspheres.

Description

Stretchable superhydrophobic membrane, manufacturing method thereof, and membrane distillation method using the same

The present invention relates to a superhydrophobic separation membrane capable of controlling pore size using a stretchable material and a membrane distillation system using the same.

Desalination technology is currently used to solve the problem of freshwater shortage by obtaining freshwater from various salty or polluted sources, including seawater, groundwater, and wastewater.

Among desalination technologies, reverse osmosis (RO) has the highest energy efficiency and currently accounts for more than 60% of global desalination capacity. However, the reverse osmosis method had the disadvantage of being difficult to apply to the treatment of high-salt water whose osmotic pressure greatly exceeds the tolerance of the reverse osmosis membrane.

Direct contact membrane distillation (DM) is one of the promising desalination technologies that moves only vapor molecules from the warm saline supply channel to the cold permeation channel through a hydrophobic microporous membrane. The driving force of the desalination technology is the separation between the supply channel and the permeation channel. It is a vapor pressure gradient created by temperature differences.

Unlike pressure-driven membrane processes such as reverse osmosis, membrane distillation is a type of heat-driven separation technology that has the advantage of low operating pressure and high solute removal rate. However, due to the inevitable phase change from liquid to vapor, energy efficiency is low and the permeation flow rate is lower than that of reverse osmosis. However, the disadvantage to energy efficiency is that membrane distillation can operate using low-grade heat energy below the boiling point. It won't be a big problem.

Therefore, the problem to be solved in the current membrane distillation method is to improve the permeation flow rate of water without wetting the membrane.

In recent years, significant progress has been made in the fabrication technology of new separators with special surface wettability, such as superhydrophobicity, omniphobicity, or dual hydrophilic-hydrophobicity, which can reduce or prevent membrane wetting. For example, Korean Patent Publication No. 10-2015-0076508 discloses a hydrophilic-hydrophobic double layer separator for membrane distillation in which a hydrophilic oxide film layer is deposited on a porous separator using an atomic layer deposition method and then a hydrophobic thin film layer is additionally formed.

On the other hand, in order to increase the permeation flux, the pore size of the porous membrane must be increased. As the pore size of the porous membrane increases, the possibility of membrane wetting increases, so an optimized membrane that can satisfy both conditions of preventing membrane wetting and increasing the permeate flux is needed. There is a need for a method to control pore size.

Korean Patent Publication No. 10-2015-0076508

The present invention is intended to solve the above problems, and maintains superhydrophobicity when forming the pore size to prevent the separator from getting wet, and includes a flexible material capable of adjusting the pore size to increase the permeation flow rate. It's about the separation membrane.

A superhydrophobic separator according to an embodiment of the present invention includes a fibrous membrane layer containing a stretchable material; The fibrous membrane layer includes a coating layer coated with hydrophobic microspheres, and the superhydrophobic separator provides a superhydrophobic separator whose pore diameter is changed by mechanical deformation.

A method of manufacturing a superhydrophobic separator according to another embodiment of the present invention includes manufacturing a fibrous membrane by electrospinning a solution containing a stretchable material; and coating the fibrous membrane by electrospraying a solution containing hydrophobic microspheres. It includes a superhydrophobic separator and provides a method of manufacturing a superhydrophobic separator whose pore diameter is changed by mechanical deformation.

Another embodiment of the present invention provides a membrane distillation method using the superhydrophobic separation membrane.

The superhydrophobic separator of the present invention can significantly reduce the increase in liquid entry pressure and separator wettability due to superhydrophobicity, and at the same time, the pore size can be adjusted by modifying the superhydrophobic separator, making it possible to control the permeate flow rate. In particular, the permeation flow rate of water can be increased by enlarging the pore size through deformation.

The superhydrophobic separation membrane of the present invention can improve the problem of low freshwater separation efficiency when the salt concentration of salt water increases to a high concentration following freshwater separation.

Another effect of the present invention is that fresh water can be produced using industrial wastewater or saline water at a relatively low temperature (about 60°C), which can be reached in a simple manner using solar power, thereby minimizing energy consumption.

With the introduction of the superhydrophobic membrane of the present invention, the pore size of the membrane can be specifically controlled, and the field of application can be expanded to seawater desalination, wastewater and water supply treatment, ultrapure water and drinking water production, etc., leading to the future commercialization of membrane distillation membranes. and can contribute to commercialization.

Figure 1 shows the vapor movement pattern according to the modification of the superhydrophobic membrane of the present invention.
Figure 2a is a schematic diagram of the superhydrophobic separator manufacturing process of the present invention.
Figure 2b is (i) a conceptual diagram of (ii) adjusting the pore size and increasing the permeate flow rate of the superhydrophobic separator by applying mechanical strain to the superhydrophobic separator of the present invention, and (iii) an SEM image of the cross section of the superhydrophobic separator of the present invention. .
Figure 2c shows a photograph of the surface structure of the polyurethane fiber membrane layer through electrospinning of the present invention.
Figure 2d shows a photograph of the surface structure of the coating layer (b) and a photograph of the surface structure of the elastic and inelastic bilayers (c) after coating PDMS microspheres through electrospraying.
Figure 3 shows SEM images of the surface of the superhydrophobic separator of the present invention under mechanical strain ranging from 0% to 150% of the examples and comparative examples.
Figure 4 is a photograph taken to determine whether superhydrophobicity is maintained when mechanical deformation is applied to the superhydrophobic separator, and the water droplets are dyed red.
Figure 5 shows how water does not permeate when water jetting is performed on the superhydrophobic separator of the present invention.
Figure 6a is a graph showing the contact angle of water according to the strain rate of the superhydrophobic separator of the present invention.
Figure 6b is a graph showing the sliding angle of water according to the strain rate of the superhydrophobic separator of the present invention.
Figure 7 is a graph showing the average pore size and maximum pore size according to strain rate of the superhydrophobic separator of the present invention.
Figure 8 is a graph showing the pore size distribution according to strain rate of the superhydrophobic separator of the present invention.
Figure 9 is a graph showing the measured value (LEPm) and calculated value (LEPc) of liquid entry pressure according to the strain rate of the superhydrophobic separator of the present invention.
Figure 10 is a graph showing the permeation flux according to the strain rate of the superhydrophobic separator of the present invention.
Figure 11 shows the conductivity of fluid at different strain rates in the permeation channel of the superhydrophobic membrane of the present invention.
Figure 12 shows modeling of the supply channel, permeation channel, and superhydrophobic membrane inside the membrane distillation membrane module for computer simulation of the membrane distillation process.
Figure 13 shows the temperature gradient and permeate flow rate gradient simulation results for 0.0 to 0.5 seconds.
Figure 14 is a comparative graph between the experimental and calculated membrane distillation permeate flux values of the superhydrophobic membrane according to the pore diameter controlled by applying mechanical strain.

The invention will be described in detail below. The embodiment is not limited to the content disclosed below and may be modified into various forms as long as the gist of the invention is not changed.

In this specification, when a part “includes” a certain component, this means that it may further include other components rather than excluding other components, unless specifically stated to the contrary.

In addition, all numerical ranges representing physical property values, dimensions, etc. of components described in this specification should be understood as being modified by the term “about” in all cases unless otherwise specified.

Superhydrophobic membrane

The superhydrophobic separator of one embodiment of the present invention includes a fibrous membrane layer containing a stretchable material; and a coating layer in which the fibrous membrane layer is coated with hydrophobic microspheres, wherein the pore diameter of the superhydrophobic separator is changed by mechanical deformation.

Elastic materials include polyurethane, polyester (PE), polydimethylsiloxane (PDMS), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), sulfonated polyarylenethioether sulfone (SPTES), silicone rubber, It may be one or more selected from the group consisting of acrylic rubber, SBS rubber, polyisoprene, polyisobutylene (PIB), and polychloroprene, and is preferably polyurethane. When the elastic material is polyurethane, it exhibits excellent elasticity and has excellent mechanical properties such as tensile strength and elongation, making it suitable for mechanical deformation.

The fiber diameter of the fibrous membrane may be 0.1 ㎛ to 3.0 ㎛. Specifically, the fiber diameter of the fibrous membrane may be 0.5 ㎛ to 2.0 ㎛, 1.0 ㎛ to 1.8 ㎛, 1.1 ㎛ to 1.5 ㎛, or 1.2 ㎛ to 1.4 ㎛, but is not limited thereto.

Hydrophobic microspheres include polydimethylsiloxane (PDMS), poly(vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), poly(lactic acid-co-glycolic acid) (PLGA), polycaprolactone (PCL), It may include one or more selected from the group consisting of polystyrene (PS), polytetrafluoroethylene (PTFE), and high-density polyethylene (HDPE).

Hydrophobic microspheres may include PDMS and PVDF-HFP. PDMS serves to provide very high superhydrophobicity to the surface of the separator, and PVDF-HFP serves to improve the adhesion between polyurethane and microspheres.

The weight ratio of PDMS and PVDF-HFP included in the hydrophobic microspheres may be 1:0.8 to 1.2. Specifically, the weight ratio of PDMS and PVDF-HFP included in the hydrophobic microspheres may be 1:0.9 to 1.1. If the weight ratio of PDMS and PVDF-HFP is outside the above range, it may be spun in the form of fibers rather than beads during electrospraying.

PDMS may be PDMS that does not contain a curing agent, or may be PDMS that has been cured by including a curing agent.

The curing agent may be included in an amount of 0.1% to 3% by weight based on the total solution. Specifically, the curing agent may be included in an amount of 0.2% to 1.5% by weight based on the total solution.

The weight average molecular weight of PVDF-HFP may be 200 kDa to 1,000 kDa. Specifically, the weight average molecular weight of PVDF-HFP may be 300 kDa to 700 kDa or 400 kDa to 600 kDa.

The average diameter of the hydrophobic microspheres may be 2.0 ㎛ or less, 1.8 ㎛ or less, 1.7 ㎛ or less, 1.6 ㎛ or less, or 1.5 ㎛ or less. When the average diameter of the hydrophobic microspheres satisfies the above range, the diameter of the hydrophobic microspheres becomes smaller, and it is advantageous to maintain a constant distribution of microspheres even when the separator is mechanically deformed, showing high superhydrophobicity.

The superhydrophobic separator may include a polyurethane fiber membrane layer and a PDMS microsphere coating layer.

The overall average thickness of the superhydrophobic separator may be 50 ㎛ to 200 ㎛, 70 ㎛ to 150 ㎛, 80 ㎛ to 120 ㎛, or 90 ㎛ to 100 ㎛. Superhydrophobic membranes require mechanical rigidity to withstand the pressure of the supply channel or permeation channel. At this time, the thinner the thickness of the superhydrophobic separator, the smoother the transport of vapor, and the thicker the superhydrophobic separator, the higher the temperature difference between each channel can be maintained, increasing efficiency. For example, when the overall average thickness of the superhydrophobic membrane is 70㎛ or more, energy loss is small due to small heat exchange between the warm salt water supply channel and the permeation channel, and when it is 150㎛ or less, vapor transport is smooth. Therefore, the overall average thickness of the superhydrophobic separator needs to be set to the minimum thickness that can withstand the pressure of each channel and allows smooth water vapor movement, so it is desirable to adjust the overall average thickness of the superhydrophobic separator within the above range.

The average thickness of the polyurethane fiber membrane layer may be 50 μm to 120 μm, 70 μm to 100 μm, or 75 μm to 90 μm. When the average thickness of the polyurethane fiber membrane layer satisfies the above range, a strain rate of 100% or more can be stably achieved.

The average thickness of the PDMS microsphere coating layer may be 5 μm to 40 μm, 10 μm to 30 μm, or 10 μm to 20 μm.

The pore size of a superhydrophobic separator can be controlled by mechanical deformation, and Figure 1 shows controlling the pore size of the separator through mechanical deformation to improve vapor transport.

The strain rate of the superhydrophobic separator due to mechanical deformation may be 0% or more and 150% or less based on the length, and specifically, may be 20% or more, 30% or more, or 50% or more, 120% or less, 110% or less, 105 It may be % or less or 100% or less, but is not limited thereto. If the strain rate is too small, the permeate flow rate is not sufficient and the operating efficiency of the membrane distillation method is reduced, and if the strain rate is too large, the superhydrophobicity of the separator may be damaged and the separation function between the supply channel and the permeation channel may be impaired. Here, when the strain rate is 100%, it means that the superhydrophobic separator is stretched to twice the length of the superhydrophobic separator when the strain rate is 0%.

As the mechanical strain rate increases, the fibrous membrane layer is stretched, and dense microscale pores are formed between the superhydrophobic microsphere layers. When the superhydrophobic separator is stretched, the uniformly distributed PDMS microsphere layer is divided into clusters of fine PDMS microspheres.

At this time, in order for the superhydrophobic separator to maintain superhydrophobicity even under mechanical deformation, the pores formed in the superhydrophobic microsphere layer should not be too wide, and the pore clusters should form a dense and repetitive hierarchical structure. When the PDMS microspheres are distributed uniformly throughout the modified separator, the superhydrophobicity of the entire separator is not damaged due to pores between clusters.

When the strain rate of the superhydrophobic separator due to mechanical deformation is 20% to 120%, the average pore diameter of the superhydrophobic separator due to mechanical deformation may be 2.343 ㎛ to 4.493 ㎛, specifically, 2.35 ㎛ to 4.49 ㎛, 2.5 ㎛ to 4.4 μm, 3.0 μm to 4.3 μm, or 3.5 μm to 4.3 μm. When the average pore diameter is within the above range, the pore size increases, the vapor transport flow is improved, and the superhydrophobicity of the separator surface can be maintained.

When the strain rate of the superhydrophobic separator due to mechanical deformation is 20% to 120%, the maximum pore diameter of the superhydrophobic separator due to mechanical deformation may be 5.416 ㎛ to 8.274 ㎛ or less, specifically, 5.5 ㎛ to 8.1 ㎛ or 6.0 ㎛. It may be from 7.0 ㎛, but is not limited thereto.

Membrane wetting can cause damage to the separation process when brine from the supply channel flows into the permeation channel through the pores of the membrane, so it is necessary to prevent membrane wetting during membrane distillation.

Liquid entry pressure (LEP) is a numerical indicator of wettability. The higher the superhydrophobicity of the separator and the smaller the pore size of the porous membrane, the higher the liquid entry pressure, and the higher the liquid entry pressure, the water pressure the separator can withstand. As the temperature rises, the separator does not get wet well. Therefore, at water pressure below the liquid entry pressure value, membrane distillation occurs normally and the membrane does not get wet.

For example, the hydraulic pressure caused by water in a salt water supply channel is 8.2 kPa, considering the flow rate (250 ml/min), density (998.2 kg/m ³ ), and kinematic viscosity of water passing through the channel.

When the strain rate of the superhydrophobic separator due to mechanical deformation is 20% to 120%, the liquid entry pressure may be 10 kPa to 18 kPa. When the liquid entry pressure is within the above range, the superhydrophobicity of the separator is maintained even when considering the hydraulic pressure caused by water, thereby preventing wetting of the separator. Specifically, the liquid entry pressure may be 12 kPa to 15 kPa.

The wettability of a superhydrophobic separator can be expressed as a contact angle (CA) or a sliding angle (SA). If the contact angle decreases or the sliding angle increases, the superhydrophobic properties of the separator may deteriorate, which causes Due to mechanical deformation, large pores are formed in the PDMS microspheres, allowing moisture to contact the polyurethane fiber membrane.

When the strain rate of the superhydrophobic separator due to mechanical deformation is 20% to 120%, the contact angle (CA) of the superhydrophobic separator may be 160 ° or more, 163 ° or more, or 165 ° or more. When the contact angle satisfies the above range, the superhydrophobicity of the separator can be maintained at the initial level despite mechanical deformation.

Additionally, when the strain rate of the superhydrophobic separator due to mechanical deformation is 20% to 120%, the change rate of the contact angle may be 1.3% or less. Preferably, it may be 1.0% or less. As the contact angle change rate satisfies the above range, superhydrophobicity can be maintained at the initial level.

When the strain rate of the superhydrophobic separator due to mechanical deformation is 20% or more and 120% or less, the sliding angle (SA) of the superhydrophobic separator may be 5° to 10° or less. When the sliding angle satisfies the above range, the superhydrophobicity of the separator can be maintained at the initial level despite mechanical deformation.

Method for manufacturing superhydrophobic membrane

In one embodiment of the present invention, a method for manufacturing a superhydrophobic separator includes manufacturing a fibrous membrane by electrospinning a solution containing a stretchable material; and coating the fibrous membrane by electrospraying a solution containing hydrophobic microspheres; It includes, and the pore diameter of the superhydrophobic separator manufactured by the method of manufacturing a superhydrophobic separator is changed by mechanical deformation.

Since the elastic materials and hydrophobic microspheres have been described above, redundant information will be omitted.

In the solution containing the elastic material or the solution containing the hydrophobic microspheres, the solvent is tetrahydrofuran (THF), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), chloroform, It may be one or more selected from the group consisting of CHCl ₃ ), ethanol, and dimethylacetamide (DMAc), and specifically, it may be THF and/or DMF.

When THF and DMF are used as solvents, the solvent may be a mixed solvent in which the weight ratio of THF and DMF is 40:60 to 60:40.

The solvent may be 80% to 90% by weight based on the total solution weight. When the solvent content satisfies the above range, a polyurethane fiber membrane layer can be manufactured with an appropriate average thickness. Specifically, the solvent may be 85% by weight to 88% by weight based on the total solution weight.

In the step of manufacturing or coating a fibrous membrane, a solution containing an elastic material or a solution containing hydrophobic microspheres is used at 0.1 mL/h to 5.0 mL/h, 0.3 mL/h to 3.5 mL/h, or 0.5 mL/h. Voltage of 1 kV to 30 kV, 2 kV to 25 kV or 5 kV to 15 kV over a distance of 1 cm to 50 cm, 5 cm to 40 cm or 10 cm to 20 cm between nozzle and collector, at an injection rate of from h to 2.0 mL/h. Electrospinning or electrospraying can be performed by applying.

At this time, both electrospinning and electrospraying can be performed using the same device consisting of a high voltage supply, a syringe pump, and an aluminum plate collector, or can be performed using other devices.

Specifically, electrospinning may be performed by applying a voltage of 5 kV to 10 kV between the nozzle and the collector over a distance of 10 cm to 20 cm at an injection rate of 1.0 mL/h to 2.0 mL/h, but is not limited thereto.

Specifically, electrospraying can be performed by applying a voltage of 10 kV to 15 kV over 10 cm to 20 cm at an injection rate of 0.5 mL/h to 1.5 mL/h, but is not limited thereto.

membrane distillation

In one embodiment of the present invention, the membrane distillation method of the present invention uses the superhydrophobic separation membrane.

Membrane distillation is based on the principle of moving only vapor molecules from a warm brine supply channel to a cold permeation channel through a superhydrophobic membrane.

In the membrane distillation method, the feed water of the supply channel may be seawater, wastewater, or contaminated water, and the salt concentration of the brine may be 3.0 to 4.5% by weight based on the weight of the total brine solution.

In the membrane distillation method, the permeate water of the permeation channel can be fresh water, such as groundwater, deionized water, or distilled water.

The temperature of the salt water in the supply channel may be 40 to 80 °C, and the temperature of the fresh water in the permeation channel may be 10 to 30 °C.

The temperature difference between the supply channel and the transmission channel may be 10 to 70°C, 20 to 60°C, or 30 to 50°C. When the temperature difference between the supply channel and the permeation channel is in the above range, vapor permeation occurs due to a vapor pressure gradient generated by the temperature difference between the supply channel and the permeation channel.

The circulation rate of the feed channel or the permeation channel may be 150 to 300 mL/min or 200 to 250 mL/min.

The permeation flow rate of vapor is continuously monitored by timely recording the weight increase in the permeation channel tank using a digital scale. The permeation flow rate of the superhydrophobic separator may be 20 to 40.3 L/m ² h, 20 to 40 L/m ² h, or 25 to 37 L/m ² h.

The inflow rate into the separation membrane module may be 200 ml/h to 600 ml/h. When the inlet flow rate is too small

The process efficiency of the membrane distillation method decreases, and if the inlet flow rate is too high, the superhydrophobicity of the membrane may be damaged and wetting may occur due to an increase in hydraulic pressure caused by water. Specifically, the inflow rate into the separation membrane module may be 200ml/h to 400ml/h.

The conductivity of the transmission channel is continuously monitored during the measurement using a conductivity meter. The conductivity of the transmission channel may be 0 to 150 μS/cm, 0 to 120 μS/cm, 0 to 110 μS/cm, 0 to 100 μS/cm, 0 to 90 μS/cm, or 0 to 50 μS/cm.

By determining the salt concentration of the permeate water from the conductivity of the permeate channel and calculating the amount of salt removed from the feed channel to the permeate channel. Determine the salt removal rate.

The salt removal rate of the superhydrophobic separator may be 99.9% or more, specifically, 99.95% or more or 99.99% or more.

If the salt removal rate is less than 99.9%, the salt concentration requirements of the permeate intended to be produced through membrane distillation cannot be satisfied.

The superhydrophobic separation membrane according to an embodiment of the present invention can maintain superhydrophobicity and at the same time optimize the pore size for membrane distillation performance, resulting in excellent permeate flow rate and salt removal rate.

[Example]

Manufacturing example: Fabrication of superhydrophobic separator

(Preparation of electrospinning solution)

10% by weight of thermoplastic polyurethane elastomer (Pellethane® 2363-80AE, Lubrizol) was dissolved in a solvent mixture of tetrahydrofuran (THF, Samchun Chemical) and dimethylformamide (DMF, Samchun Chemical) mixed at a volume ratio of 0:40. Then, the solution was stirred at room temperature overnight to completely dissolve the thermoplastic polyurethane elastomer pellets, thereby preparing a polyurethane solution.

(Preparation of electrospray solution)

Poly(vinylidene fluoride-co-hexafluoropropylene; PVDF-HFP. Sigma-Aldrich, MW: 455 kDa) and cured polydimethylsiloxane (PDMS, Sylgard® 184, Dow Corning) ) solution (precursor and curing agent 10% by weight: 1% by weight) and PVDF-HFP were dissolved in a solvent mixture of THF and DMF mixed at a weight ratio of 50:50. Final weight ratio of PDMS, PVDF-HFP and THF/DMF solvent. was 2.5: 2.5: 95. The PDMS polymer microsphere solution was prepared by stirring the solution overnight on a hot plate set at 60°C.

(Production of superhydrophobic membrane)

The fibrous membrane of the superhydrophobic separator was manufactured by electrospinning a polyurethane solution, and a voltage of 7kV was applied between the nozzle and the collector over 15cm at an injection rate of 1.5mL/h.

The resulting polyurethane fiber membrane was coated with PDMS polymer microspheres by electrospraying the PDMS polymer microsphere solution. Next, a voltage of 13 kV was applied to the PDMS solution over 17 cm between the nozzle and the collector at an injection rate of 1.0 mL/h.

At this time, both the electrospinning and the electrospraying were performed using the same device consisting of a high voltage supply, a syringe pump, and an aluminum plate collector.

The manufacturing method of the superhydrophobic separator in the manufacturing example is shown in Figure 2a.

The total thickness of the separator in the manufacturing example is 95㎛ and is composed of a polyurethane fiber membrane layer and a PDMS microsphere layer with a thickness of 80 and 15㎛, respectively.

Examples 1 and 2, Comparative Examples 1 and 2

The separator of the manufacturing example was subjected to mechanical strain ranging from 0% to 150% in the longitudinal direction to produce Example 1 (strain rate 50%), Example 2 (strain rate 100%), Comparative Example 1 (strain rate 0%), and Comparative Example 2. A superhydrophobic separator (strain rate of 150%) was manufactured.

Comparative Example 3: Commercial PVDF separator

A commercial PVDF membrane (Durapore® Membrane Filters, Merck Millipore Ltd.) with a pore size of 0.22 ㎛ was used.

[Experimental example]

Experimental Example 1: Measurement of contact angle (CA) and sliding angle (SA) of separator

The surface wettability of the separators of Examples and Comparative Examples was measured by measuring the water contact angle and sliding angle using the sessile drop method and the tilting method, respectively. The contact angle and sliding angle of the distilled water droplet on the separator surface were measured using the EasyDROP CA measurement system (Femto Science).

Experimental Example 2: Pore size distribution and porosity measurement

The pore size distribution and average pore size of the separation membranes of Examples and Comparative Examples were measured using a capillary porometer (PoroLuxTM 1000, POROMETER) based on the gas-liquid displacement porosity measurement method.

Experimental Example 3: Liquid Entry Pressure (LEP) Measurement

The liquid entry pressure of the separators of Examples and Comparative Examples was measured using a laboratory setting. A microfluidic pressure regulator was used to apply pressure to the inlet of a water-filled vessel. The other end of the container was equipped with the separator of Examples and Comparative Examples, and the separator of Examples and Comparative Examples was installed in a container filled with water by applying a mechanical strain ranging from 0% to 150%.

Stainless steel mesh was used as mechanical reinforcement beneath the separator. Due to the elasticity of the separator, if there is no mechanical reinforcement, mechanical deformation may occur due to pressure and the pore size of the separator may change, so reinforcement is used to prevent this. The pressure applied to the membrane was gradually increased to determine the minimum pressure required to allow water to penetrate the pores of the membrane. As more pressure was applied to the vessel, water eventually penetrated the membrane.

Experimental Example 4: Membrane distillation method performance experiment

The membrane distillation performance of the membranes of Examples and Comparative Examples was evaluated using a laboratory-scale direct contact membrane distillation experimental setup with an effective membrane area of 8 cm ² .

The experimental setup consisted of two gear pumps, a digital scale, a hot plate, a cooler, a heat exchanger, a conductivity meter, two tanks, and a separation membrane module.

To simulate seawater, 3.5 wt% NaCl in deionized water was used as a supply channel, and pure deionized water (conductivity was about 4 μS) was used as a permeation channel.

The supply channel was heated to 60°C using a hot plate and the permeate channel was maintained at 20°C using a cooler and heat exchanger. The feed and permeate channels were circulated using gear pumps at rates of 250 and 200 mL/min, respectively.

The permeate flow rate was continuously monitored by timely recording the weight increase in the permeate channel tank using a digital scale.

The conductivity of the transmission channel was continuously monitored during the measurements using a conductivity meter.

The conductivity of the permeate channel tank was monitored during membrane distillation operation to obtain the salt rejection rate. The concentration of the permeate tank was determined and compared with the concentration of the feed water (3.5% by weight). The salt rejection rate was determined by calculating the amount of salt removed from the feed channel to the permeate channel. At this time, the conductivity of seawater with a salt concentration of 3.5% by weight is 53 mS/cm.

All monitored data was transferred to the computer in real time.

Experimental Example 5: Membrane distillation simulation

After constructing the supply channel, the separation membrane and permeation channel of Examples and Comparative Examples, the direct contact membrane distillation process was performed by considering three transport phenomena: energy convection and conduction, moment transport for the supply and permeation channel, and mass transport for the superhydrophobic separator. Modeled.

COMSOL Multiphysics® software was used to numerically solve the equations using boundary and initial conditions to calculate the temperature distribution and permeate flux across the membrane.

Experiment Result 1: Surface shape of superhydrophobic membrane according to mechanical deformation

Figures 2b to 3 below show images of the cross-section or surface of the superhydrophobic separator measured using a scanning electron microscope (SEM).

Figure 2b shows a conceptual diagram of (i) applying mechanical strain to the superhydrophobic membrane of the present invention and (ii) controlling the pore size of the superhydrophobic membrane and increasing the permeate flux.

Figure 2b (iii) shows an SEM image of a cross section of the superhydrophobic separator of the present invention, showing the layered structure of the fiber membrane layer and the coating layer. Shows an image of the separation membrane of the manufacturing example observed with a scanning electron microscope (SEM),

Figure 2c shows an SEM image of an electrospun polyurethane fiber membrane with an average fiber diameter of 1.3 ㎛, and Figure 2d shows the surface of the separator of the preparation example completed after deposition of PDMS microspheres (average diameter 1.5 ㎛) by electrospray.

As shown in Figure 3, the surface of the superhydrophobic separator subjected to mechanical strain ranging from 0% to 150% was observed using SEM. As the mechanical strain rate increased, the pores between PDMS microsphere clusters widened, and pores in the form of parallel valleys perpendicular to the strain direction were created.

The structure of the superhydrophobic microsphere layer of the prepared separator was found to be advantageous in maintaining the superhydrophobicity of the separator by inducing the formation of dense microscale pores between microspheres, and the planar superhydrophobic layer was found to be advantageous when mechanical deformation was applied. When some membranes were broken at random locations, it was observed that large voids were formed. Therefore, it is expected that the superhydrophobicity of the separator will be damaged when the superhydrophobic separator undergoes excessive mechanical deformation.

Experiment Result 2: Analysis of wettability of superhydrophobic membrane according to mechanical deformation

The visual observation results of the superhydrophobicity of the separator are shown in Figures 4 and 5.

Figure 4 shows that the separators of Examples and Comparative Examples maintain superhydrophobicity when mechanical strain ranging from 0% to 150% is applied.

Figure 5 shows that even when water jetting is performed on the superhydrophobic separator of the present invention, water is not transmitted but is repelled.

To further investigate the wetting properties of the separator, the contact angle (CA) and sliding angle (SA) according to mechanical strain state were measured and shown in Table 1 and Figures 6a and 6b below.

division Comparative Example 1 Example 1 Example 2 Comparative Example 2 strain rate 0% 50% 100% 150% Contact angle (°) 165.12 165.0 166.1 164.7 Sliding angle (°) 5.4 7.6 8 8.6

In Figure 6a, the contact angle of the separators of Examples and Comparative Examples is maintained at 160° or more at a strain rate of 0 to 150%, and Figure 6b shows that the sliding angle is maintained at 10° or less at a strain rate of up to 150%. This indicates that the superhydrophobicity of the separator was well preserved under large mechanical deformation of more than 100%.

However, when the mechanical strain rate reached 150%, the sliding angle tended to increase, indicating that the hydrophobic properties of the separator were deteriorated. The deterioration is expected to be due to the formation of large pores in the PDMS microspheres due to extreme mechanical deformation, allowing water droplets to contact the polyurethane fiber membrane.

Experimental result 3: Pore analysis of superhydrophobic membrane under mechanical deformation

Figures 7, 8, and Table 2 show the average pore diameter, maximum pore diameter, and pore distribution of the superhydrophobic membrane experimentally measured under various mechanical strains (ranging from 0% to 150%).

The average pore diameter and maximum pore diameter of the separation membranes of Examples and Comparative Examples according to the mechanical modification are shown in Table 2 below.

division Comparative Example 1 Example 1 Example 2 Comparative Example 2 strain rate 0% 50% 100% 150% Average pore diameter (㎛) 2.343 3.644 4.240 4.493 Maximum pore diameter (㎛) 5.416 6.340 6.856 8.274

As the mechanical strain rate increased, the average and maximum pore diameters of the membrane increased correspondingly.

The average pore diameter increases proportionally to the square root of the mechanical strain, which is correlated with the relationship between area and length dimensions when mechanical strain is applied, and the maximum pore diameter also showed a similar trend to the average pore diameter up to a strain rate of 100%.

However, for mechanical deformation of more than 150%, the maximum pore diameter shows a rapid increase of up to 8㎛ or more. This is expected to be due to tearing of the polyurethane fibers in localized areas of the separator of Comparative Example 2 when larger pores were created.

Figure 8 shows that the average pore diameter tends to increase as the mechanical strain rate increases, and this is because the pore diameter distribution curve moves to a larger diameter due to mechanical strain. The pore diameter distribution curve shows a tendency to narrow when strain rates of up to 100% are applied.

Experiment Result 4: Liquid Entry Pressure (LEP) Analysis of Superaqueous Membrane under Mechanical Deformation

Liquid entry pressure is a measurement of the pressure applied at the exact moment when the separator is penetrated by water. Water was considered to have penetrated through the largest pores on the membrane surface. This is because the lowest pressure is required to pass through this hole.

The LEP of the separator of Examples and Comparative Examples can be calculated by Equation 1 below.

[Equation 1]

In Equation 1 above, B is the geometric porosity coefficient,

γ _l is the liquid surface tension (water: 72 dyne/cm),

r _max is the maximum pore radius,

θ is CA.

The measured values of liquid entry pressure (LEPm) and calculated values of liquid entry pressure (LEPc) of the separators of Examples and Comparative Examples according to mechanical strain ranging from 0% to 150% are listed in Table 3 below, and each value in FIG. 9 Compare.

division Comparative Example 1 Example 1 Example 2 Comparative Example 2 strain rate 0% 50% 100% 150% LEPm (kPa) 19.6 14.7 12.2 6.2 LEPc (kPa) 17.086 14.155 13.132 10.777

Both LEPm and LEPc values are inversely proportional to the increase in strain applied to the separator.

For the separator of Comparative Example 2 to which 150% mechanical strain was applied, LEPm showed a significant decrease. This was attributed to tearing of the polyurethane fibers in localized areas of the separator of Comparative Example 2 and when creating larger pores.

Both LEPm and LEPc show similar trends, but LEPm decreases more rapidly than LEPc depending on the mechanical strain rate. This is thought to be an error range arising from the limitations of the LEPm measurement method in the laboratory.

To measure LEPm, the separators of Examples and Comparative Examples were wrapped around one end of a cylindrical container and tightly fixed with a rubber band. This mounting process may cause the strain rate to be unevenly distributed across the separators of the Examples and Comparative Examples, creating greater strain in the portion of the separator pressed against the edge of the container inlet than in the portion floating in the air at the center of the container inlet. This will result in a broad pore size distribution curve and a larger maximum pore size than expected. The formation of an unexpected maximum pore size causes LEPm to eventually decrease below LEPc when the mechanical strain becomes larger.

Additionally, the pressure acting on the internal membrane located inside the membrane module was measured, and when measured with parameters such as volumetric flow rate, the hydraulic pressure applied to the channel wall during membrane distillation operation was estimated to be 8.2 kPa.

On the other hand, when 150% mechanical strain was applied, the LEPm value of the separator of Comparative Example 2 was about 6.2 kPa, which was lower than the expected pressure acting on the internal separator, indicating that water had penetrated through the permeation channel of the separator.

Experiment Result 5: Membrane distillation performance of superhydrophobic membrane

A laboratory-scale direct contact membrane distillation setup was used to evaluate the membrane distillation performance (membrane distillation permeate flux values and salt removal rates) of the Example and Comparative membranes at various strain rates.

division Comparative Example 1 Example 1 Example 2 Comparative Example 2 strain rate 0% 50% 100% 150% Flow rate (L/m ² h) 10.13 25.01 36.59 40.32 Salt removal rate (%) 99.99 99.99 99.96 99.34

In order to verify the reliability of the membrane distillation method settings, a commercial PVDF separation membrane was used as Comparative Example 3, and the permeate flow rate for the membrane of Comparative Example 3 was about 20 L/m ² h.

Figure 10 shows the permeation flow rate of the membrane distillation method of the separation membrane of Examples and Comparative Examples. It shows that the permeation flux of the separation membrane of the Examples and Comparative Examples to which a larger strain rate was applied increases.

The superhydrophobic separator of Comparative Example 1 without modification recorded a permeation flux of 10.13 L/m ² h, which is lower than that of Comparative Example 3. On the other hand, the separator of Example 1 with a 50% strain rate had a permeation flux of 25.01 L/m ² h, which was higher than that of Comparative Example 3, and as the strain rate increased, the permeation flux also increased.

The separator of Comparative Example 2 with a 150% strain rate recorded the highest permeation flux value of 40.32 L/m ² h, but showed unstable permeation flux values throughout operation.

As can be seen in Figure 11, the separation membranes of Examples 1 and 2 and Comparative Example 1 to which mechanical strain rates ranging from 0% to 100% were applied all showed stable conductivity throughout the membrane distillation operation. However, the separator of Comparative Example 2, to which 150% mechanical strain was applied, showed an immediate increase in conductivity at the start of membrane distillation operation, indicating that the separator was partially wet and the supplied water penetrated into the permeation channel of the separator.

Considering that the conductivity of seawater is 53 mS/cm, the membrane of Comparative Example 2 to which 150% mechanical strain was applied also showed a high salt removal rate of 99.34%, but the membrane to which 100% or less of mechanical strain was applied showed a salt removal rate of more than 99.9%. .

Experimental Result 6: Comparison of experimental and theoretical membrane distillation permeation fluxes

The membrane distillation permeate flux was further investigated through computer simulation to verify the relationship between pore size and membrane distillation permeate flux.

Figure 12 shows modeling of the inlet channel, permeation channel, and separation membrane of Examples and Comparative Examples within the membrane distillation membrane module.

Membrane distillation operating parameters were set to reflect a realistic laboratory-scale direct contact membrane distillation setup. Transport of dilute species in porous media was considered the dominant mass transfer principle across the membrane domain. The governing equation is as follows:

[Equation 2]

In Equation 2 above, the diffusion coefficient Dm is determined by the Knudsen number, which is defined as the ratio of the pore diameter of the membrane and the mean free path of vapor. The pore size range of the separation membranes of Examples and Comparative Examples to which various modifications were applied belongs to the transition region between Knudsen diffusion and molecular diffusion. The diffusion coefficients for Knudsen diffusion and molecular diffusion are given in Equations 3 and 4 below.

[Equation 3]

[Equation 4]

[Equation 5]

The membrane distillation permeation flux was calculated using computer simulation using Dm as shown in Equation 5. A transient simulation of the temperature gradient, transmitted flux gradient and resulting flux graph for 0.0-0.5 seconds is shown in Figure 13.

Using these simulation results, the permeation flux values of the membrane distillation method of the superhydrophobic membrane according to the pore diameter adjusted by applying the mechanical strain rate were compared with the experimental values and the calculated values are shown in FIG. 14.

The experimental and calculated membrane distillation permeate flux values showed significant similarity, and when estimated in the form of an involution of the pore diameter, both permeate flux values were expressed along the second power of the pore diameter. Since the coefficient of molecular diffusion is the square of the pore diameter, it can be seen that the main diffusion mode of the separators of the Examples and Comparative Examples is molecular diffusion.

Claims (13)

A fibrous membrane layer containing elastic material; and
A superhydrophobic separator wherein the fibrous membrane layer includes a coating layer coated with hydrophobic microspheres,
The superhydrophobic separator is a superhydrophobic separator whose pore diameter is changed by mechanical deformation.
According to claim 1,
The elastic materials include polyurethane, polyester (PE), polydimethylsiloxane (PDMS), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), sulfonated polyarylenethioether sulfone (SPTES), and silicone rubber. At least one selected from the group consisting of acrylic rubber, SBS rubber, polyisoprene, polyisobutylene (PIB), and polychloroprene,
A superhydrophobic separator wherein the fiber membrane has a fiber diameter of 0.1 to 3.0 ㎛.
According to claim 1,
The hydrophobic microspheres include polydimethylsiloxane (PDMS), poly(vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), poly(lactic acid-co-glycolic acid) (PLGA), and polycaprolactone (PCL). , may include one or more selected from the group consisting of polystyrene (PS), polytetrafluoroethylene (PTFE), and high-density polyethylene (HDPE),
A superhydrophobic separator wherein the hydrophobic microspheres have a diameter of 2.0 ㎛ or less.
According to claim 3,
The hydrophobic microspheres include the PDMS and the PVDF-HFP,
A superhydrophobic separator wherein the weight ratio of the PDMS and the PVDF-HFP is 1:0.8 to 1.2.
According to claim 1,
A superhydrophobic separator wherein the strain rate of the superhydrophobic separator due to the mechanical deformation is 20% or more and 120% or less based on the length.
According to claim 5,
A superhydrophobic separator having an average pore diameter of 2.343 ㎛ or more and 4.493 ㎛ or less when the strain rate is 20% or more and 120% or less.
According to claim 5,
A superhydrophobic separator having a maximum pore diameter of 5.416 ㎛ or more and 8.274 ㎛ or less when the strain rate is 20% or more and 120% or less.
Manufacturing a fibrous membrane by electrospinning a solution containing an elastic material;
Coating the fibrous membrane by electrospraying a solution containing hydrophobic microspheres; A method for manufacturing a superhydrophobic separator comprising:
A method of manufacturing a superhydrophobic separator, wherein the pore diameter of the superhydrophobic separator is changed by mechanical deformation.
According to claim 8,
In a solution containing the elastic material or a solution containing the hydrophobic microspheres,
The solvent is a mixed solvent of tetrahydrofuran (THF) and dimethylformamide (DMF) at a weight ratio of 40:60 to 60:40, and the mixed solvent is 90 to 95% by weight based on the total solution weight, a superhydrophobic separator Manufacturing method.
According to claim 8,
In the step of manufacturing or coating the fiber membrane,
Applying a voltage of 1 to 30 kV over a distance of 1 to 50 cm between the nozzle and the collector to the solution containing the elastic material or the solution containing the hydrophobic microspheres at an injection rate of 0.1 to 5.0 mL/h, Method for manufacturing superhydrophobic membrane.
Membrane distillation method using the superhydrophobic membrane of claims 1 to 7.
According to claim 11,
A membrane distillation method in which the permeation flow rate of the superhydrophobic membrane is 20 to 40.3 L/m ² h.
According to claim 11,
The salt removal rate of the superhydrophobic separator is 99.9% or more. Membrane distillation.