KR20030003833A - Maintenance of membranes by prefiltration at high pressure and by cleaning their microstructures with supercritical fluids - Google Patents

Abstract

PURPOSE: A maintenance of membranes by prefiltration at high pressure and by cleaning their microstructures with supercritical fluids is provided, in which contamination of main separation membrane is minimized by cleaning the pre-treatment filtration media, with the cleaning being conducted by stabilizing and forcibly adsorbing the hydrophilic or hydrophobic contaminants at high pressure of 2 to 20 atm higher than the saturation pressure of bubble. And the regeneration of main separation membrane is conducted within a shortened time by washing the surface and pore inside of the separation membrane by using supercritical fluids without any restrictions of sort, figure, process concerning with the separation membrane. CONSTITUTION: The method comprises two steps of minimizing contamination of the pre-treatment separation membrane and regeneration performance of the main separation membrane. The minimization method comprises stabilizing the subject material to separate at a state of 2 to 20 atm higher than the saturation pressure of bubble at the pre-treatment filter media consisting of the same separation membrane or similar material from the hydrophilic or hydrophobic point of view followed by forcible adsorption. The regeneration method of performance of the separation membrane comprises washing the surface and pore inside of the separation membrane by using supercritical fluid of supercritical carbon dioxide or reformed supercritical fluid reformed by methanol, ethanol, and isopropanol followed by drying.

Description

Maintenance of membranes by prefiltration at high pressure and by cleaning their microstructures with supercritical fluids}

The present invention relates to a method for maintaining and restoring membrane performance by high pressure pretreatment and supercritical fluid cleaning, and more particularly, in order to solve the problems of fouling and performance degradation of the membrane generated in the membrane separation process, pretreatment filtration under high pressure. The present invention relates to a method for removing contaminants in advance and a method for regenerating a contaminated separator using a cleaning agent having special physical properties. In the pretreatment filtration method, by pressurizing at a predetermined pressure in a pretreatment filtration device composed of the same material as the main separation membrane or a material similar in hydrophilicity and hydrophobicity, the possibility of contamination of the main separation membrane can be minimized by actively adsorbing contaminants. In addition, the contaminated membrane is washed in a short time using a supercritical fluid or a modified supercritical fluid within a short time, thereby minimizing the structural morphological deformation of the membrane, and thus the selective separation efficiency and treatment capacity of the membrane can be restored. It can be applied not only to the membrane that has been decontaminated and contaminated, but also to the membrane module unit where the membrane is installed. Therefore, the present invention can maintain the efficiency of the membrane separation process as long as the initial state, and to maintain the membrane performance of a new concept that can extend the replacement cycle of the membrane to improve the economics and practicality of the membrane separation process And a restoration method.

Membranes are widely used alone or in hybrid form in water purification, wastewater treatment, seawater desalination, separation and purification processes in chemical processes, and concentrated food processing processes, and the size of molecules or associations of substances to be separated and their physical interaction with the membrane. Separation takes place by exploiting differences in physical and chemical properties such as action, chemical interaction with the membrane, and vapor pressure. Recently, the membrane tends to be complicated by structural morphology, such as complex, multi-layered structure, or endowed with heterogeneous characteristics. Also, the membrane process is gradually diversified in terms of application field, and in size. have. Although membranes utilizing various separation mechanisms have emerged and are being applied, basically, membranes can be classified in terms of pore structure characteristics of the membrane and the physicochemical characteristics of the hydrophobicity or hydrophilicity of the membrane material. The pores of the membrane vary from less than 1 μm to several tens of μm, and the pores are connected in an open structure bidirectionally in the form of micropores, such as hydrophobic membranes for membrane distillation, and membranes for pervaporation. It can be divided into the case where the micropores are opened only to the primary side (raw material supply side) that developed the surface area in the form of wrinkles as follows. The membrane material is also made of polyvinyl alcohol (PVA), cellulose acetate, and sodium alginate from hydrophobic materials such as polytetrafluoroethylene (PTFE), polypropylene (PP), and polyvinylidene difluoride (PVdF). crosslinked products such as alginate) and chitosan, and hydrophilic materials such as ion exchange resin membranes.

Membrane separation process using these membranes is very strict operation conditions, the specification of the mixture to be supplied to the membrane within a certain range must be controlled. As a result, many additional pretreatment unit processes are required, and the membrane module itself is designed to assist in securing a means to cope with the degradation of the membrane. In general, a separation system is constructed and utilized in a form in which pretreatment methods such as prefilter and back-flushing methods are mixed. Nevertheless, there are problems such as contamination of the membrane, deterioration of separation efficiency, reduction of treatment capacity, and the like, thereby limiting the application area of the membrane and preventing expansion thereof, and improving the service life of the membrane. And the practicality is generally determined. In a real membrane separation system, membrane module replacement cycles are determined based on the performance curve provided by the membrane module supplier. For example, when 70% of the initial flux is reached, Replace or perform a regeneration procedure such as backwash. On the other hand, it is very difficult to completely return to the initial performance only by simple backwashing operation, and thus gradually lose the function of the separator and ultimately discard the used membrane and replace it with a new membrane. It is known that the use cycle of these membranes is short for several months to long for two to three years.

The regeneration process of the separation membrane used is mostly limited to physical backwashing, although a chemical substitution operation may be performed in the case of a special purpose membrane such as an ion exchange membrane. This method of recovering the efficiency of the membrane is actually made directly through the change of the flow path and flow direction without disassembly of the membrane module, and the separated contaminants remain on the primary side without being removed from the separator. Therefore, there is a high possibility of re-adsorption of contaminants that hinder the separation efficiency of the separation membrane, and the same separation efficiency degradation phenomenon will recur. In addition, certain components in the mixture to be separated affect the morphological properties of the membrane, causing irreversible changes that cannot be recovered by physical methods such as backwashing. In the case of the polymer membrane, the amorphous domain and the crystalline domain are properly mixed, and selective penetration or diffusion of the separation target material occurs through the elastic amorphous region. Separation will occur. However, as in the example of pervaporation, when the solute is deposited on the membrane substrate and the plasticization process proceeds, the flexible amorphous region is hardly deformed like the crystalline region, so that the glass transition temperature is increased. Morphological modification processes, such as rising, can proceed. In this case, conventional regeneration methods such as backwashing cannot be applied and the separator must be replaced. In the case of hydrophobic membranes used for membrane distillation, an air layer must exist as an inert separation medium in the micropores having a pore range of 2 to 5 μm, and a meniscus must be formed in the micropores. Separation is achieved by evaporation and condensation induced by the difference. If the pressure balance at both ends of the membrane is broken and the liquid having low vapor pressure condenses in the micropores or is contaminated with non-volatile hydrophobic material and the micropores are blocked, the separation ability is lost. Separators having a range of micropores in the above range is very difficult to apply backwashing, and in particular, since the backwashing cannot be performed without breaking the pressure balance, the micropores cannot be restored to their original state by conventional backwashing means. In addition, the degree of hydrophobic interaction varies depending on the contaminants present in the membrane surface and the micropores, and in the case where such interaction is very large, it may be difficult to remove even after long-term washing using a liquid washing medium. In the case of microfiltration membranes, the backwashing method may be effective, but when the composition of the mixture to be separated is changed in a wide range, contamination of the membrane may be serious and its service life may be shortened. Recently, a chain type microfiltration technology capable of self-assembling and disassembling the microfiltration membrane according to the direction of fluid flow has also been developed, but has a disadvantage in that the selective separation characteristics of the membrane are weak. Is very limited. Conventional backwashing methods, which have been applied in various forms as described above, have a long membrane penetration due to the poor material transfer characteristics of the washing medium and low solubility or partition coefficient of the washing medium. The separation operation time is shortened, and as a result, the processing capacity is reduced compared to the design capacity.

In general, the surface of the separator is functionalized with a hydrophobic or hydrophilic material, and many wrinkles and fine pore structures are well developed in the pores of the separator. The separator may be made in the form of a laminated structure by different materials for a special separation purpose, or may be manufactured in the form of a composite membrane. The pore inlet and the pore interior of the membrane surface are functionally functionalized to allow selective interactions in which separation occurs, and in order to maintain separation selectivity, the surface state or interfacial interface state must be kept clean, The irreversible physicochemical change of s should be minimized to avoid damaging the membrane's function. In most membrane separation processes, these changes are caused by the appearance of a dispersed phase, such as an emulsion, or by the incorporation of a mist-like entraintment during the oil-separation or vapor phase condensation prior to the membrane separation process. There is always the possibility of incorporation of substances that can be produced. Therefore, it is essential to predict possible types of contaminants, mixing characteristics, contamination loads, and major contaminant positions for the function maintenance of the membrane, and identify the major contaminated sites by understanding the structural characteristics and the physicochemical characteristics of the substrate. It is necessary to do The mechanical properties of the membrane are determined by the distribution of microstructures in the crystalline and amorphous regions of the membrane substrate, including the membrane support, and these morphological properties change with the maintenance and cleaning of the membrane. Should be minimized. At this time, the membrane may be regenerated without dismantling the membrane module according to the characteristics of the membrane separation process and the degree of contamination load, or may be reassembled after regenerating by using a separate membrane regeneration facility for only the membrane separated and dismantled completely Can be installed and used.

In general, the membrane module can be classified into a flat membrane module, hollow fiber membrane module, spiral wound membrane module, etc., the module type is selected according to the degree of flux in the membrane, the degree of polarization phenomenon, the membrane separation mechanism. Most spiral wound or hollow fiber membrane modules are designed to operate at low or vacuum conditions of around 10 atm. In contrast, the flat membrane module can be easily adjusted locally and variably in a wide range of temperature and pressure, and unlike the spiral wound or hollow fiber membrane module, the module can be designed to be cleaned and regenerated in an assembled module unit. In the case of membrane distillation, the temperature difference for evaporation and condensation, which is the driving force of the separation, must be applied to both sides of the membrane, and there is a significant difference in the vapor pressure through the membrane pores that offsets the contribution by osmotic distillation. It should be done. In order to achieve this goal easily, heat transfer through the membrane should be minimized and local sophisticated temperature control should be possible. In addition, proper mixing means are required to maintain uniform temperature between the raw material supply side, which is the primary side, and the rear end side, which is the secondary side. Flow obstructions may be provided in close proximity to the membrane support surface. In the case of membrane distillation, in order to maintain the dry state in the membrane pore, the differential pressure must be negligibly small so that there is no penetration of the liquid mixture, and when the interlayer differential pressure above the allowable differential pressure is applied, This results in loss of separation. Therefore, in the process of regenerating the membrane for distillation of the membrane, it is necessary to maintain the pressure balance of both sides of the membrane, and be able to efficiently remove condensable residues in the micropores. In this process, the cleaning regeneration process must be completed within a shorter contact time than the characteristic time at which structural deformation occurs, so that morphological deformation such as mechanical damage and swelling of the membrane substrate is minimized, and the cleaning medium has its solvent and physicochemical characteristics. This should be tuned broadly. In order to restore the micropore internal structure to a dry state, a means for efficiently removing and drying the liquid moistened inside the micropore is required.

In the present invention, to extend the service life of the membrane through the operation to maintain the separation performance of the membrane used in the membrane separation process, the study to improve the economics and efficiency of the membrane separation process. To this end, we propose a prefiltration method that can minimize membrane contamination. In addition, it has good material transfer characteristics, quickly penetrates micropores using a cleaning medium that can easily increase solubility against a wide range of contaminants, and has excellent cleaning ability with a single operation in a short time. I would like to propose a technical means to recover. In particular, when the pore characteristics in the membrane must be maintained very strictly and dry pore state, such as membrane distillation membrane, and the function such as flux due to clogging of pore inlet by adsorption of hydrophobic organic contaminants on the membrane surface It is intended to provide rapid and reliable membrane cleaning regeneration and drying techniques for severe cases.

The present invention in the pre-treatment filtration of the membrane separation process,

In the pretreatment filtration medium made of the same material as the separator or similar in hydrophilicity and hydrophobicity, the material to be separated is stabilized at a high pressure, and forced adsorption treatment is performed to minimize contamination of the separator.

In addition, the present invention is a method for cleaning the separation membrane to restore the separation function,

Another feature is a method of restoring separator performance by cleaning and drying the surfaces of contaminated separators and the interior of pores using a supercritical fluid or a modified supercritical fluid.

The present invention will be described in more detail as follows.

First, the high pressure pretreatment filtration method according to the present invention will be described. This method is a principle of forcibly adsorbing a substance to be separated to a filtration medium by putting a substance to be separated into a filtration apparatus and applying a high pressure. In this case, the filter medium that can be used is the same material as the separator, or a similar material in terms of hydrophilicity and hydrophobicity is preferable. That is, if the separator is hydrophilic, the material of the medium used for pretreatment filtration is preferably hydrophilic. Similarly, if the separator is hydrophobic, it is preferable to use a hydrophobic material. The pressure is preferably adjusted to a pressure range of 2-20 atm higher than the bubble saturation pressure in the phase diagram of the pressure-composition (P-x) of the mixture. If the pressure is not higher than the saturation pressure, the phase stability of the fluid mixture is poor, bubbles are generated, and the contact with the preliminary filtration medium is poor and can easily pass through without being collected, and the forced adsorption removal effect by pressurization Falls. However, increasing the pressure too much more than necessary is obviously undesirable in terms of manufacturing and operating costs of the separation system, and the effect of stabilization and forced adsorption removal of the fluidized bed by the pressurization is that the pressure of the system is higher than that of saturated vapor pressure. A high 20 atm should suffice in most cases.

It is preferable that most of the contaminants incorporated into the primary side of the membrane module are first removed in a prefilter. The potential sources of contamination for the membranes vary greatly in type and nature, but the case of irreversible adsorption and morphological structural modifications to the membrane should be considered most seriously. Therefore, it is most efficient to utilize a pretreatment filtration medium containing the same material as that of the separator. However, in consideration of its service life and replacement cost, it is practical not to demand the pore and surface properties of the filtration medium. In the present invention, by selecting a material very similar to the material of the separator in terms of hydrophilicity or hydrophobicity to configure the pretreatment filtration apparatus, and artificially harshly controlling the operating conditions, it is possible to increase the collection efficiency of contaminants.

In the membrane separation process associated with the reactor to which the vapor phase condensate of the reactor is to be separated, contaminants may be incorporated from the entrained liquid in the condensate supplied to the primary side. Conversely, in the case of using a partial condenser, fluctuations in the process conditions of the pretreatment filter and in the filtration media are approaching the gas-liquid saturation of the bubble point of the condensed liquid. Due to the complex flow behavior, contaminants to be collected are often vaporized and easily passed through, thus reducing the treatment effect. In this case, the pretreatment filtration process can stabilize the liquid phase under pressure and promote reversible or irreversible adsorption, thereby improving treatment efficiency and reliability.

In addition, the supercritical fluid cleaning method according to the present invention will be described. This method uses a supercritical fluid having excellent material transfer properties and the like to quickly clean the surface of the contaminated membrane and the inside of the pores.

The supercritical fluid state of a substance refers to the thermodynamically stable state of the material at its critical temperature, at critical temperatures and above its pressure. Supercritical fluids are compressible fluids, whose density can vary significantly with changes in conditions of temperature and pressure, and the properties of the supercritical fluid medium can be characterized by the manipulation of macroscopic process variables, It is possible to induce and control the change in physical properties continuously in a wide range so as to obtain the same effect as changing the medium. Supercritical fluids can be used as process solvents such as supercritical fluid extraction of natural compounds due to their good permeability to porous media with micropores, and are also used to produce nanoparticles using controllable solubility. It is used as a cleaning medium for semiconductor materials, electronic parts, and precision machine parts based on its excellent penetration and dissolving power. Organic synthesis reactions can occur in supercritical fluids to take advantage of kinetic gains and reaction yields.For example, in supercritical water oxidation technology, materials that do not mix with each other, such as oxidants and organic contaminants, are added to the supercritical fluid medium. Solubilization can also quickly and completely oxidize the waste or wastewater. When a phase change occurs between a gas and a liquid, a phase transition generally occurs through a discontinuous coexistence curve where an interface exists, between the gas state and the liquid state via the supercritical fluid region. Inducing the phase change of can lead to continuous and gradual phase transitions in both directions without the appearance of discontinuous interfaces. In the present invention, this feature of the supercritical fluid is used to overcome the capillary force caused by the condensed phase in the pore during the washing of the porous medium having very low mechanical strength, thereby preventing the collapse and deformation of the structure. It is possible to remove the target substance present in the micropores without causing.

As the supercritical fluid, supercritical carbon dioxide, supercritical ammonia, supercritical propane, supercritical chlorofluorocarbons, supercritical ethylene, supercritical propylene, supercritical water, and the like may be used, more preferably supercritical water. Use critical carbon dioxide. The supercritical water may be used in a limited case where there is little thermal deformation, such as in the case of an inorganic separator. Among the supercritical fluids, the most widely used medium for cleaning and extraction purposes is supercritical carbon dioxide, which has a strong penetration into the pore structure and exhibits strong interactions with hydrophobic groups including materials containing fluorine atoms. Because. Carbon dioxide has a relatively low critical temperature (31.1 ° C.) and critical pressure (72.8 atm), and is present in supercritical fluid at about 40 ° C. and 75 atm. Deformation of the membrane substrate by supercritical carbon dioxide can be prevented by minimizing exposure time or by using modifiers that alter the nonpolar nature of the supercritical carbon dioxide. The use of such modifiers can be applied to all of the above supercritical fluids in addition to supercritical carbon dioxide, i.e., the supercritical fluid can be used directly or in a properly modified state. Modifiers are dissolved in supercritical fluids. Modifiers include alcohols such as methanol, ethanol and isopropanol, amines such as primary amines, secondary amines and tertiary amines, carbon monoxide, normal paraffins, and olefins. Oleffins and aromatic compounds may be used, and more preferably alcohols and amines are used. The modifier applied to the supercritical fluid is selected in consideration of the properties of the contaminants and the characteristics of the membrane substrate, and one or more modifiers may be applied to remove the contaminants quickly without damaging the separator.

When the separator is a hydrophilic pervaporation separator, it is preferable to use supercritical carbon dioxide as the supercritical fluid. In addition, when the separator is a hydrophobic membrane distillation membrane, it is preferable to use supercritical carbon dioxide or supercritical propane as the supercritical fluid. In the case of the hydrophobic membrane distillation membrane, the mixture to be separated may include, for example, a solution containing water and acetic acid, and the membrane is used to selectively separate water.

If the inside of the separator is to be kept dry, the condensed phase should not be formed in the pores, and any contaminated condensed phase should be removed. To this end, macroscopic parameters are set to bypass the gas-liquid coexistence curve to extract and remove the condensation condensate phase using a supercritical fluid as a cleaning medium, and to ensure that the residual condensable gas and supercritical fluid do not condense in the micropores. By adjusting, the gas state is reached as the final target state. The cleaning medium and the pore gas in the cleaning system are preferably replaced with inert, non-condensable gases such as nitrogen, helium and argon. In this way, residual condensable material in the micropores can be removed to keep the micropores dry.

The supercritical fluid may be applied not only to individual membranes but also to the membrane module unit, that is, the supercritical fluid may be introduced into the assembled membrane module without disassembling the membrane module. In addition, a regeneration process may be added in the middle of the separation process, such as a backwashing process of the membrane module. In general, since the separation membrane is very thin (1 mm or less), it can be seen that the penetration distance required for the micropore washing can be sufficiently effected by washing for several seconds in consideration of the diffusion coefficient in the supercritical fluid state. As described above, the present invention removes contaminant droplets or adsorbates using a supercritical fluid, thereby restoring and regenerating the membrane pore structure to maintain the function of the separator for a long time.

Hereinafter, the present invention will be described in more detail based on the following comparative examples and examples, but the technical contents and scope of the present invention are not limited to the examples.

Comparative Example 1

Reaction of synthesizing triacetin using acetic acid and glycerine was performed. Analysis of the condensate recovered from the partial condenser at the top of the esterification reactor showed 73.2% acetic acid, 3400 ppm triacetin, 2900 ppm glycerin and the remainder as moisture. The mixture was skipped by pretreatment filtration using an effective diameter 45 mm polytetrapuloethylene (PTFE) separation membrane having 0.22 μm fine pores, and water was selectively removed to concentrate acetic acid. When direct contact membrane distillation was carried out while maintaining the temperature on the primary side at 35 ° C. and the temperature on the secondary side at 15 ° C., the flux of water was maintained at 5.83 mole / (m 2 · hr). At this time, the concentration of acetic acid on the secondary side was reduced to 47.2% to confirm that the water was selectively separated. After 72 hours of continuous operation, the flux was measured at 92% of the initial value and the secondary side acetic acid concentration was analyzed to be 48.8% similar to the initial concentration.

Example 1

The primary side mixture of Comparative Example 1 was passed through a prefilter consisting of a polypropylene (PP) membrane having a micropore diameter in the range of about 20 to 40 μm and a glass filter under pressure of 10 to 15 atm. Thereafter, membrane distillation was performed as in Comparative Example 1. After 72 hours of continuous operation, the water flux decreased to 97% of the initial flux, and the change in secondary side acetic acid concentration was 47.6%.

Example 2

The PTFE separator of Comparative Example 1 was immersed in the primary mixture of Comparative Example 1 for 30 days at room temperature at about 20 ° C. and stirred to artificially contaminate the surface and pores of the membrane. Membrane distillation experiments were carried out using the contaminated membrane as in Comparative Example 1, and the water flux was reduced to 78% of the initial value. However, the concentration of the secondary side acetic acid was 47.9%, indicating that the membrane remained almost at its initial separation selectivity despite contamination. The membrane was disassembled from the membrane module, and the supercritical carbon dioxide at 45 ° C. and 80 atm was passed through an isopropanol layer and washed with a supercritical fluid saturated for 1 minute, and replaced with nitrogen gas for 10 minutes. It was regenerated under reduced pressure for 30 minutes and dried. Membrane distillation experiment using the regenerated membrane showed that the water flux was recovered to 98% or more of the initial value, and the separation selectivity was also recovered within the range of 1%.

Example 3

An aqueous solution of polyvinyl alcohol (PVA) having an average molecular weight of about 1500 was crosslinked and dried using glutaaldehyde (glutaldehyde) corresponding to about 5% by volume to prepare a hydrophilic pervaporation separator. When the primary side temperature of the water-acetic acid mixture system is 40 ° C and the secondary side pressure is reduced to about 10 torr, the total flux is about 150 g / (m 2 · hr), and the separation coefficient for water at this time factor) was calculated to be about 120. The membrane was immersed in the mixture of Comparative Example 1 at room temperature for 30 days while being forced to contaminate. As a result, the total flux was reduced to 92% of the initial value, and the separation coefficient for water was reduced by about 27%.

The contaminated membrane was washed for 3 minutes using supercritical carbon dioxide at 50 ° C. and 150 atm, and decompressed over 30 minutes without substitution of nitrogen gas. The total flux recovered more than 98% of the initial flux, and the separation coefficient for water also recovered to 95% or more of the initial value.

Example 4

The porosity was measured after contaminating the cellulose nitrate membrane with a micropore size of 3.0 μm and the porosity of 12% by treating it with octyl nitrate for 30 days to contaminate it. Decreased to 83%. This was washed for 3 minutes using supercritical ammonia at 135 ° C. and 120 atm, and slowly depressurized over 20 minutes. After performing the above two cleaning operations, the measured porosity of the separator was restored to about 96% of the initial porosity.

Example 5

After disassembling the membrane distillation module equipped with the contaminated separator as in Example 2, the primary side and the secondary side were opened to achieve pressure balance, and then saturated methanol in supercritical carbon dioxide at 50 ° C. and 100 atm simultaneously in both directions. It was fed and treated for 2 minutes. The carbon dioxide was replaced with nitrogen gas and slowly depressurized to regenerate the membrane module. Moisture flux recovered more than 98% of the initial value, it was confirmed that the selectivity for moisture is maintained within 2% by weight fraction.

As described above, according to the present invention, hydrophobic and hydrophilic contaminants that cause degradation of the membrane and shorten its lifespan are stabilized in a pressurized condition by using a pretreatment filtration medium having a substrate similar to that of the membrane, thereby forcibly adsorbing the primary membrane. Contamination can be minimized. In addition, by using a supercritical fluid or a modified supercritical fluid to clean and remove contaminants present in the main separator within a very short process time, the pore structure of the separator may be restored to restore the function of the separator. Such membrane cleaning and regeneration techniques are not limited to the type and form of the membrane, the specific mechanism of the membrane separation process, and the like, and may be cleaned, dried, and regenerated in a membrane module unit or a separate membrane unit. The basic medium for supercritical fluid cleaning is the use of a small amount of modifier in the supercritical fluid or by adjusting macro variables such as temperature and pressure to prevent mechanical and morphological damage of the membrane substrate. You can control the density of the indicator medium. The technique proposed in the present invention can improve the lifespan and replacement cost of the membrane material, which is considered as the dominant factor that determines the economics of the membrane process, thereby increasing the lifetime of the membrane and ensuring economic feasibility and practicality of the membrane separation process. It has an effect.

Claims (9)

In pretreatment filtration of the membrane separation process, A method for minimizing contamination of a separator, characterized by stabilizing a material to be separated at a high pressure in a pretreatment filtration medium made of the same material as that of the separator or having a similar hydrophilicity and hydrophobicity. The method of claim 1, wherein the pressure is in the range of 2 to 20 atm higher than the bubble saturation pressure. In the method of washing the separation membrane to restore the separation function, A method of restoring membrane performance, characterized in that the surface of the contaminated membrane and the inside of the pores are cleaned and dried using a supercritical fluid or a modified supercritical fluid. The method of claim 3, wherein the supercritical fluid is selected from supercritical carbon dioxide, supercritical ammonia, supercritical propane, supercritical chlorofluorocarbons, supercritical ethylene, supercritical propylene, and supercritical water. To restore the membrane performance. 5. The method of claim 4 wherein the supercritical fluid is supercritical carbon dioxide. The method of claim 3, 4 or 5, wherein the modifying agent for modifying the supercritical fluid is selected from alcohols including methanol, ethanol and isopropanol, and amines including primary amine, secondary amine and tertiary amine. Method for restoring the performance of the separator, characterized in that. 4. The method of claim 3, wherein when the contaminated membrane is a hydrophilic pervaporation separator, supercritical carbon dioxide is used as the supercritical fluid. 4. The method of claim 3, wherein when the contaminated membrane is a hydrophobic membrane distillation membrane, supercritical fluid is used as supercritical carbon dioxide or supercritical propane. 4. The method of claim 3, wherein the contaminated membrane introduces supercritical fluid into the assembled membrane module without disassembling the membrane module.