JP2001162142A - Membrane separation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane separation method which is high in a ratio of obstructing the particles and ions tending to permeate permeable membranes and is large in permeation flow flux. SOLUTION: Membrane separation is carried out while the permeable membranes in a membrane module 3 arranged with the permeable membranes is vibrated when liquid to be treated is subjected to the membrane separation by supplying the liquid to be treated to one side of the membrane module 3, permeating permeation components to the other side, taking a permeate out of the other side and taking a non-permeable liquid does not permeate the permeable membranes out of the one side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a latex concentrate,
Colloidal silica concentration, valuables recovery, waste liquid treatment, metal classification, tap water filtration, activated sludge treatment, tap water sludge treatment, food waste liquid treatment, ion removal, COD removal, BOD removal, diafiltration of slurry and colloid components, etc. The present invention relates to an improvement of a membrane separation method that is useful for a method.

[0002]

2. Description of the Related Art Conventionally, as a method for separating a liquid to be treated into a membrane, a cross-flow type membrane separation apparatus having a permeable membrane having micropores is used to separate a permeated liquid and a non-permeated liquid. Methods for separating are known. The cross-flow type membrane separation device separates the liquid to be treated into a permeate component and a non-permeate component by a permeable membrane, and supplies the non-permeate component again to the apparatus inlet side, and the permeate component and the non-permeate component are also transmitted by the permeable membrane This is a method in which the concentration of the non-permeate is increased by repeating the same operation thereafter to perform membrane separation. In this case, in order to avoid clogging of the membrane due to the suspended matter in the non-permeate and prevent the permeation efficiency from decreasing, the flow rate of the liquid to be treated is increased to increase the shear force on the membrane surface. There is a method of removing foreign matter from the material. That is,
The most important thing in membrane separation is to keep the membrane surface from being contaminated with foreign matters so that a uniform flow of the processing solution is formed on the membrane surface.

[0003] In general, a permeable membrane in which the size of the micropores of the membrane is reduced (the rejection of the membrane is high) in order to prevent the permeation of particles and ions in the non-permeate liquid is reduced. The flow rate of the liquid permeating per unit area per unit time) is small, and conversely, a membrane having a low rejection rate has a large permeation flux. That is, the rejection rate of the membrane and the permeation flux are in an opposite relationship, and a conventional membrane separation method cannot obtain a large permeation flux with a membrane having a high rejection rate.

[0004] The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide a high ratio of blocking particles and ions which try to pass through a permeable membrane, and An object of the present invention is to provide a membrane separation method having a large permeation flux.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for applying a large shear rate to a fluid on a membrane surface by vibrating a permeable membrane. Suppresses clogging and suppresses concentration polarization on the film surface (the occurrence of an abnormally high concentration near the film surface), lowering the concentration on the film surface, resulting in a large permeation flux. And the rejection of the film can be improved.

[0006]

That is, the gist of the present invention is that a liquid to be treated is supplied to one side of a membrane separation apparatus having a permeable membrane, a permeated component is transmitted to the other side, and the permeated liquid is supplied from the other side. In the method of separating the liquid to be treated by taking out the non-permeate liquid which does not pass through the permeable membrane from one side, improving the rejection rate of the membrane by performing the membrane separation while vibrating the permeable membrane. A membrane separation method.

According to the present invention configured as described above,
If membrane separation is performed while vibrating the permeable membrane, the high-concentration components near the membrane surface are discharged from the non-permeate side outlet without adhering to the membrane surface due to the shear force generated by the vibration of the permeable membrane, and the permeable components Permeates through the permeable membrane with a high flux. In addition, since a high shear field is formed on the film surface due to the vibration, the film surface is kept clean and clogging of the film is prevented. Even if the liquid to be treated with a higher viscosity flows, a shear field is generated on the membrane surface due to vibration, so that the water trapped between the particles becomes free water and the fluidity is improved. Since the apparent viscosity coefficient is reduced, it is possible to process a high-concentration liquid to be processed, and it is possible to reduce the average flow rate of the non-permeate liquid.

[0008] Most of the energy for moving the membrane surface is converted into a fluid near the membrane surface as a shear force, and the liquid to be treated can be separated with high efficiency.

Thus, the liquid to be treated supplied to one side of the permeable membrane is taken out as a permeated liquid from the other side and taken out as a non-permeated liquid from one side, and the permeation processing is performed while vibrating the permeable membrane. As a result, the rejection of particles and ions that are likely to penetrate the permeable membrane (referred to herein as the "rejection of the membrane") remains high and at a given concentration under a large permeation flux. The liquid to be treated can be smoothly concentrated.

As described above, according to the present invention, the rejection rate and the permeation flux of the membrane can be controlled by adjusting the oscillation conditions of the permeable membrane. The oscillation conditions are described later. Thus, the amplitude of the permeable membrane and the average shear rate generated on the membrane surface have a large effect on the rejection rate and the permeation flux of the membrane, and by increasing the amplitude and the average shear rate, the rejection rate of the membrane is increased. A large permeation flux can be ensured.

Further, according to the present invention, the concentration of the membrane surface is reduced by the shear force generated by vibrating the permeable membrane, and the deposition of particles and ions in the liquid to be treated on the membrane surface is suppressed. Is also possible.

The condition of the amplitude and the vibration frequency when the permeable membrane is vibrated is that the permeable membrane is made to have an amplitude of 0.5 cm or more in a circumferential direction in a horizontal plane and a vibration frequency of 40 to 60 Hz.
Is preferable.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a vibration type membrane separation apparatus suitable for applying the membrane separation method of the present invention.
Referring to FIG. 1, 1 is a supply tank of a liquid to be treated, 2 is a pump for pumping the liquid to be treated, 3 is a membrane module in which many flat membrane type permeable membranes are laminated, and 4 is a membrane module in the membrane module 3. The permeable membrane has an amplitude of 0.5 to 2.5 in the circumferential direction in the horizontal plane.
A torsion bar for transmitting a reciprocating motion of a small amplitude of 4 cm and a vibration frequency of 40 to 60 Hz, a storage tank 5 for a non-permeated liquid (concentrated liquid) and a storage tank 6 for a permeated liquid. Reference numeral 7 denotes a flow control valve for controlling the discharge amount of the non-permeate discharged from the membrane module 3 via the pipe line 8.

As shown in FIG. 2, a metal plate 11 is provided inside the membrane module 3 between two upper and lower permeable membranes 9 and 9 'via two to fifteen nonwoven fabric drain cloths 10 and 10'. The stacked components are arranged in a horizontal direction, and are arranged in multiple stages with a predetermined gap provided in a vertical direction. In the figure, the upper side of the upper permeable film 9 is one side (supply side), and the drain cross 10 side is the other side (transmission side). When the liquid to be treated is supplied to this supply side, the internal pressure on the supply side is set to a higher pressure (about 0.20 to 3.92 MPa) than that on the permeation side. As shown, particles (permeation components) smaller than the micropores of the permeable membrane 9 pass through the membrane pores 12 and reach the other side. The non-permeate liquid after the permeation component has passed is supplied to the supply side of the permeable membrane 9 in the next stage in FIG. 2, and the permeation component permeates through the membrane pores.

During the permeation process, the permeable membrane in the membrane module 3 shown in FIG. 1 continues to reciprocate with a small amplitude in the circumferential direction in the horizontal plane due to the action of the torsion bar 4.
In the liquid to be treated in the vicinity of the film surface, concentration polarization (the generation of an abnormally high concentration portion in the vicinity of the film surface) is suppressed by the shearing effect due to vibration, and clogging of the film is prevented. Further, the flow path in the membrane module is less likely to be blocked. Thus, by applying an appropriate pressure to the liquid to be treated by the pump 2,
The liquid to be treated can be efficiently separated into a permeate and a non-permeate under a high permeation flux and a high membrane rejection. The permeation process is sequentially performed in this manner, and the obtained permeated liquid is sent to the storage tank 6 via the pipe 13, and the non-permeated liquid in the pipe 8 is sent to the storage tank 5. Thus, the liquid to be treated in the tank 1 can be supplied to the membrane module 3 via the conduit 14, and can be efficiently separated into a permeated liquid and a non-permeated liquid by the above-mentioned vibration type membrane separation device.

As the permeable membrane of the vibration type membrane separation device, a reverse osmosis membrane, a microfiltration membrane, a nanofilter, an ultrafiltration membrane or the like can be suitably used.

FIG. 4A is a view showing the flow of the liquid to be treated in the membrane module. The liquid to be treated flows into the membrane module from the path 15, and the permeated liquid that has passed through the permeable membrane passes through the path 16.
And the non-permeated liquid is discharged from the passage 17. 1
Reference numeral 8 denotes a non-permeate liquid flow path (a gap between the permeable film 9 'immediately above and the permeable film 9 immediately below is a non-permeate liquid flow path; see an enlarged view of FIG. 2). FIG. 4B is an enlarged plan view of the permeable membrane.
Reference numeral 19 denotes a flow path for the permeated liquid, and reference numeral 20 denotes a flow path for the liquid to be treated.

The effect of vibration conditions on the rejection and permeation flux of the membrane was investigated using the vibrating membrane separation apparatus constructed as described above, and will be described below. (1) Test conditions a. Liquid to be treated An aqueous solution of NaCl was used. b. The permeable membrane has a relatively low NaCl rejection rate so that a clear difference appears in the test results depending on the presence or absence of vibration of the permeable membrane because the NaCl aqueous solution that can easily evaluate the rejection rate of the membrane is used. A nanofilter was used. c. Common test conditions Vibration type membrane separation device = outer diameter of about 30 cm and inner diameter of about 10 cm
A vibration-type membrane separation apparatus having a configuration shown in FIG. 1 and having a circular flat membrane nanofilter having a membrane area of 0.045 m ² was used.

Vibration frequency = about 58 Hz Temperature = 20 ° C. Flow rate = 3.5 liter / min. (2) Test results Effect of amplitude on NaCl rejection of membrane and permeation flux Difference in transmembrane pressure (difference in pressure between supply side and permeation side of liquid to be treated with respect to permeable membrane) using NaCl at a concentration of 0.2%
FIG. 5 shows a change in the NaCl rejection of the permeable membrane when the amplitude is gradually increased while the permeable membrane is vibrated under the condition of 1.03 MPa. The horizontal axis in FIG. 5 is the amplitude (inch) of the permeable membrane, the vertical axis on the left shows the NaCl rejection (%), and the vertical axis on the right is the permeation flux (liter / m ² / hr). Is shown. In FIG. 5, ● represents the rejection of NaCl, and Δ represents the permeation flux. Since the concentration of NaCl that is proportional to the electrical conductivity, rejection of NaCl measuring the electrical conductivity (C ₀₎ and the permeate electric conductivity (C ₁₎ of the stock solution, the following equation
Calculated from (1).

NaCl rejection (%) = (1−C ₁ / C ₀ ) × 100 (1) As shown in FIG. 5, as the amplitude increases, the NaCl rejection increases, while transmission increases. Flux is increasing slightly but with amplitude. B. Effect of shear rate on NaCl rejection of membrane The shear rate generated on the membrane surface is represented by the following equation (2).

Shear rate = (representative velocity) / (representative length) [sec ⁻¹ ] (2) Assuming that the representative velocity of the fluid on the membrane surface coincides with the vibration velocity, the representative velocity is expressed by the following equation (3). expressed. Where ω:
Angular velocity, P: amplitude, f: vibration frequency Representative velocity = 2ωP = 4πfP [m / sec] (3) The representative length is given as the thickness of the velocity boundary layer, and the following equation (4)
It is represented by Where μ: viscosity coefficient, ρ: density, representative length = (μ / ρf) ^0.5 [m] (4) By dividing equation (3) by equation (4), an arbitrary point in the radial direction of the film surface can be obtained. Is given by the following equation (5).

Shear rate = (4πf ^1.5 ρ ^0.5 ) P / μ ^0.5 [sec ⁻¹ ] (5) From equation (5), it can be seen that the shear rate on the film surface is proportional to the amplitude P, but the amplitude is The shear rate differs at any point in the radial direction on the film surface because the shear rate decreases from the outer peripheral portion toward the central portion. Therefore, it is necessary to evaluate the shear rate of the membrane surface by an average value obtained by integrating the shear rate of the entire membrane surface in the radial direction and dividing by the membrane area, and this average shear rate is obtained by the following equation (6). Where A: membrane area, r: radius of the permeable membrane, r ₁ : radius of the inner periphery of the permeable membrane, r ₂ : radius of the outer periphery of the permeable membrane, P ₂ : amplitude average at radius r ₂ shear rate ^{= {(4πf 1.5 ρ 0.5)} / μ 0.5} ∫P · 2πrdr / A = ^{[8π 2 f 1.5 ρ 0.5) /} μ 0.5 ] × [P ₂ / r _2] × [(r ₂ ³ -r ₁ ³ ) / 3A] (6) FIG. 6 shows the relationship between the average shear rate obtained by equation (6) and
NaC of membrane when NaCl concentration is fixed at 0.2%
It is a figure which shows the change of 1 rejection. Each symbol in FIG. 6 (●,
Δ, Δ, Δ) indicate the transmembrane pressure difference. As shown in FIG.
The Cl rejection increases with an increase in the average shear rate, and when the transmembrane pressure increases, the NaCl rejection of the membrane tends to increase. That is, irrespective of the value of the transmembrane pressure, increasing the average shear rate increases the NaCL rejection of the membrane.

FIG. 7 is a diagram showing a change in the NaCl rejection of the membrane when the transmembrane pressure is constant at 1.03 MPa with respect to the average shear rate obtained by the equation (6). Each symbol (●, △, ■, ◇, ▼) in FIG. 7 indicates the concentration of NaCl. As shown in FIG. 7, even if the concentration of NaCl is changed, when the average shear rate is increased, the NaCl rejection of the film increases. C. Effect of vibration on permeation flux As a liquid to be treated, a solution in which calcium sulfate is dissolved in pure water to a saturated concentration is used, and NaC is used as a permeable membrane.
1 Using a nanofilter having a rejection of 85%, a transmembrane pressure difference of 1.
The change in the permeation flux when the saturated solution of calcium sulfate was concentrated was examined for the case where the permeable membrane was vibrated at 03 MPa and the amplitude of 1 inch and the case where the permeable membrane was not vibrated. As a result, as shown in FIG. 8, when the membrane was not vibrated, the permeation flux decreased sharply from the initial stage of the concentration, but when the membrane was vibrated, the permeate flux almost decreased until the membrane was concentrated to about three times. It can be seen that the bundle has not decreased. This is because the vibration of the membrane reduced the calcium sulfate concentration on the membrane surface and suppressed the precipitation of calcium sulfate on the membrane surface, thereby suppressing the decrease in the permeation flux.

[0024]

Since the present invention is configured as described above, the following effects can be obtained.

According to the first aspect of the present invention, it is possible to provide a membrane separation method which has a high ratio of blocking particles and ions which are going to permeate the permeable membrane and has a large permeation flux. That is, by employing the vibrating membrane separation method, a large permeation flux was maintained even when a membrane having a high permeation flux and a low ability to block particles and ions that would pass through the permeable membrane was used. Since the rejection of the membrane can be improved as it is, when the same amount of the liquid to be treated is subjected to membrane separation, according to the present invention, as compared with the conventional cross-flow membrane separation method,
A film having a small film area can be used, and the processing cost can be significantly reduced.

That is, as in the second aspect of the present invention,
By adjusting the vibration conditions of the permeable membrane, the rejection and permeation flux of the membrane can be controlled. Specifically, by increasing the amplitude of the permeable membrane, the rejection of the membrane can be increased while maintaining a large permeation flux. Claim 4
As in the described invention, the rejection of the film can be increased by increasing the average shear rate generated on the film surface.

According to the fifth aspect of the present invention, the concentration of the surface of the membrane is reduced by the shear force generated by vibrating the permeable membrane, and the particles and ions in the liquid to be treated are deposited on the surface of the membrane. Can be suppressed.

According to the sixth aspect of the present invention, it is possible to provide suitable amplitude and vibration frequency conditions for vibrating the permeable membrane.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a vibration type membrane separation apparatus suitable for applying a membrane separation method of the present invention.

FIG. 2 is a sectional view showing a part of a membrane module used in the vibration type membrane separation device of FIG.

FIG. 3 is a diagram showing a concept of a permeation process by a vibration type membrane separation device.

FIG. 4 (a) is a diagram showing a flow of a liquid to be treated in a membrane module by a vibrating membrane separation device, and FIG. 4 (b) is an enlarged plan view of a permeable membrane.

FIG. 5 shows the effect of amplitude on NaCl rejection and permeation flux of the membrane.

FIG. 6 is a diagram showing a change in NaCl rejection of a film when a NaCl concentration is constant with respect to an average shear rate.

FIG. 7 is a diagram showing a change in NaCl rejection of a membrane when a transmembrane pressure is constant with respect to an average shear rate.

FIG. 8 is a diagram showing a change in permeation flux when a saturated solution of calcium sulfate is concentrated.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Supply tank 3 ... Membrane module 5 ... Non-permeate liquid storage tank 6 ... Permeate liquid storage tank 7 ... Flow control valve 9, 9 '... Permeable membrane 18 ... Non-permeate liquid flow path 19 ... Permeate liquid flow path 20 ... Flow path of liquid to be treated

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[Procedure amendment]

[Submission date] July 4, 2000 (200.7.4)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction contents]

That is, as in the second aspect of the present invention,
By adjusting the vibration conditions of the permeable membrane, the rejection and permeation flux of the membrane can be controlled. Specifically, the amplitude of the permeable membrane is increased as in the invention of claim 3, or the vibration frequency is adjusted as in the invention of claim 4, thereby maintaining a large permeation flux. The rejection of the film can be increased. Claim 5
As in the described invention, the rejection of the film can be increased by increasing the average shear rate generated on the film surface.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0027

[Correction method] Change

[Correction contents]

Further, according to the invention of claim 6, the concentration of the surface of the membrane is reduced by the shear force generated by vibrating the permeable membrane, and the particles and ions in the liquid to be treated are deposited on the surface of the membrane. Can be suppressed.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction contents]

According to the seventh aspect of the present invention, it is possible to provide suitable amplitude and vibration frequency conditions for vibrating the permeable membrane.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D006 GA03 GA06 GA07 HA41 JA03C KA41 KE04Q MA03 PA01 PB06 PB08 PB23 PC11 PC62 PC64 4D028 BC17 BD00 BD17 4D059 AA03 BE42 BK30

Claims (6)

[Claims] 1. A liquid to be treated is supplied to one side of a membrane separation apparatus provided with a permeable membrane, a permeated component is permeated to the other side, and a permeated liquid is taken out from the other side. A method of separating a liquid to be treated by membrane by extracting a non-permeate liquid that does not pass through, wherein the membrane separation method is performed by vibrating a permeable membrane to improve the rejection of the membrane. 2. The method according to claim 1, wherein the rejection rate and the permeation flux of the membrane are controlled by adjusting the vibration conditions of the permeable membrane. 3. The method according to claim 2, wherein the vibration condition is an amplitude. 4. The membrane separation method according to claim 2, wherein the vibration condition is an average shear rate generated on the membrane surface. 5. The method according to claim 1, wherein a concentration of the surface of the membrane is reduced by a shear force generated by vibrating the permeable membrane, thereby suppressing precipitation of particles and ions in the liquid to be treated on the surface of the membrane. 2. The membrane separation method according to 1. 6. The permeable membrane is vibrated in a circumferential direction in a horizontal plane with an amplitude of 0.5 cm or more and a vibration frequency of 40 to 60 Hz. The membrane separation method according to the above.