JP2002028459A - Method for controlling inter-membrane differential pressure inside membrane module and membrane module for control - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that fouling easily occurs since a pressure loss inside a membrane module is great and it is difficult to easily keep the inter- membrane differential pressure of the entire module constant in solute separation and solid-liquid separation by means of the membrane module. SOLUTION: By providing an inter-membrane differential pressure equalizing member on the permeated liquid side of the separating membrane of the membrane module, the inter-membrane differential pressure is controlled. As an inter-membrane differential pressure equalizing member, there are a spacer 2 interposed between separating membranes 1, a supporting layer for the active layer of the separating membrane and a reinforcing member for reinforcing the active layer and the supporting layer of the separating film or the like. Besides, by changing the thickness of the active layer of the separating membrane, the inter-membrane differential pressure can be controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a transmembrane pressure difference of a separation membrane generated during filtration in a separation operation using a membrane module, and a control membrane module.

[0002]

2. Description of the Related Art Conventionally, in a separation operation using a separation membrane, generally a membrane separation operation performed by a cross flow filtration (cross flow filtration) method, a membrane module has a large pressure loss in the module, and the It is difficult to keep the transmembrane pressure constant throughout the module. In other words, since the transmembrane pressure increases due to the high pressure at the module inlet and the permeation flux increases at the beginning of filtration, solutes are more likely to be present at the inlet compared to the vicinity of the outlet where the transmembrane pressure is low. And suspended solids
(Hereinafter referred to as solutes) easily cause fouling.

[0003] Such fouling causes nanofiltration (NF), ultrafiltration (UF) and microfiltration (MF).
In this case, the rejection rate changes, so that the accuracy of separation of solutes and the like by the separation membrane decreases. Therefore, if the transmembrane pressure across the membrane module is kept constant,
The permeation flux is kept constant throughout the membrane module, and the original separation performance of the membrane can be maintained without causing fouling.

Therefore, in order to keep the transmembrane pressure constant, a method of circulating the solution to the permeated liquid side is performed so as to generate the same pressure loss as the pressure loss generated in the retained liquid side. In addition, methods such as rotating the membrane in the liquid to be treated and exerting the same shearing force on the membrane surface as cross-flow filtration, giving fluidity to the solution near the membrane in the immersion membrane module, and vibrating the separation membrane, etc. Has been done.

[0005]

However, these methods require the cost of equipment and power for circulating the solution on the permeate side, the cost of equipment for rotating the separation membrane, and the immersion membrane. In this case, there are various problems such as difficulty in sufficiently providing the flow of the solution, and inability to provide sufficient vibration to the separation membrane to set a sufficiently high permeation flux.

[0006]

Therefore, as a result of intensive studies and studies to solve the above-mentioned problems, for example, in a flat membrane module performing cross flow filtration, in a flow in which a permeate flows out of the module, The shape of the permeate-side spacer was designed to increase the pressure loss near the inlet from the retentate inlet to the outlet, and to reduce the pressure loss continuously or stepwise gradually toward the outlet. By developing a membrane module in which a spacer is provided in a separation membrane, it has been found that the problem relating to the fall control can be solved at a stretch, and the present invention has been completed.

In the above-mentioned membrane module, the structure of the support layer for supporting the active layer of the separation membrane is such that the pressure loss of the permeate is large near the inlet from the inlet side of the retentate to the outlet side, and the structure is toward the outlet. The above problem can also be solved in a membrane module provided with a support layer designed to reduce the pressure loss of the permeated liquid.

Further, in the above membrane module, a reinforcing material for reinforcing the separation membrane consisting of the active layer and the support layer is provided such that the pressure loss of the permeated liquid is large near the inlet from the inlet side of the retentate to the outlet side, and the outlet is toward the outlet. Accordingly, the above problem can be solved even with a membrane module provided with a reinforcing material designed to reduce the pressure loss of the permeated liquid.

Furthermore, by changing the thickness of the active layer of the separation membrane, the pressure loss accompanying permeation increases near the inlet from the inlet side of the retentate to the outlet side, and the pressure loss accompanying permeation increases toward the outlet. The above-mentioned problem can be solved even with a membrane module provided with a separation membrane designed to reduce the number.

As described above, the method for controlling a transmembrane pressure according to the present invention provides a transmembrane pressure that can also cause a pressure loss on the permeate side and cancel the pressure loss on the retentate side in the membrane separation operation. This is achieved by using a member having a pressure equalizing function and / or a separation membrane having an adjusted active layer thickness to cause a pressure loss on the permeate side. This method is an epoch-making method that can exhibit the original performance of the membrane with a slight improvement of a membrane module that performs ordinary cross-flow filtration and the like, and has a low production cost and high practicability.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the present invention provides various members having a function of equalizing the transmembrane pressure on the permeate side of the separation membrane 1 of the membrane module, This is a method for controlling the transmembrane pressure by changing the thickness or appropriately combining them, and is a novel membrane module having a function of making the transmembrane pressure uniform.

The member having a function of equalizing the pressure difference between the membranes used in the present invention includes a pressure loss in the permeated liquid while the permeated liquid permeates the membrane and is discharged out of the module. Any material may be used as long as it is designed to cancel the generated pressure loss and thereby average the transmembrane pressure. Specifically, the structure of the member is designed to be dense on the inlet side of the membrane module and gradually roughened toward the outlet side, so as to generate a pressure loss when the permeated liquid permeates. The pressure loss caused by the above is cancelled, and the structure is such that the transmembrane pressure can be made uniform.

The spacer 2, which is one of the members having the function of equalizing the transmembrane pressure difference used in the present invention, has a mesh structure or a porous structure made of a material such as a plastic, a stainless steel sheet, a ceramic sheet, or the like. Should be fine. Then, the structure of the spacer is designed to be a dense structure 4 near the entrance 3 or a structure that enhances the adhesion between the spacer and the film. The structure is designed to reduce the adhesiveness between the membrane and the membrane, so that a pressure loss occurs in the flow of the permeate (FIG. 1).

The support layer 12 for supporting the active layer 11 of the separation membrane 1, which is one of the members having a function of equalizing the pressure difference between the membranes used in the present invention, is an ultrafiltration membrane or a microfiltration membrane. It is possible to use ones having different pore diameters or different opening ratios.
In the flow where the permeate flows out of the membrane module from the retentate inlet to the outlet side, the pressure loss is increased near the inlet by using the densely structured support layer 13, and the structure gradually becomes rougher toward the outlet. The support layers 14 and 15 are designed to reduce the pressure loss (FIG. 2).

Further, the active layer 11 and the support layer 12, which are one of the members having a function of equalizing the transmembrane pressure difference used in the present invention.
In many cases, a non-woven fabric is used as the reinforcing material 21 for reinforcing the separation membrane containing, but the pores of the permeate flow path are changed from the module inlet to the module outlet by changing the denseness or fiber diameter of the fiber used. A material that is gradually designed to have a rough structure so that the pressure loss can be controlled can be used. In the flow in which the permeate flows out of the module from the retentate inlet to the outlet, a dense structure near the inlet 2
2, the pressure loss is large, and the rough structures 23 and 24 gradually reduce the pressure loss toward the outlet (FIG. 3).

Further, the separation membrane 1 having the function of equalizing the transmembrane pressure difference used in the present invention has a structure in which the thickness of the active layer 11 is changed so that the permeation near the inlet from the retentate inlet to the outlet is achieved. The pressure loss accompanying the permeation can be reduced as the pressure loss is increased toward the outlet (FIG. 4).

In general, in a separation operation using a membrane module, if the flow path of the supply processing liquid is constant, the pressure loss on the retentate side is determined by the viscosity of the processing liquid and the supply flow rate.
The pressure loss on the permeate side is determined by the viscosity and flow rate of the permeate. Also, in general, the permeate has a viscosity close to that of water,
By designing the structure on the permeate side or adjusting the thickness of the active layer in accordance with the pressure loss and permeate flux of the target processing solution, the transmembrane pressure difference can be kept almost uniform. The present invention has been made for the first time based on the above-described permeation theory, and has a structure of a member having a function of equalizing the transmembrane pressure difference on the permeate side and separation membranes having different active layer thicknesses in accordance with the properties of the treatment liquid. By preparing various types and using them properly, the original performance of the film can be expressed in the entire module.

[0018]

(Embodiment 1) This embodiment is controlled by a spacer 30. As shown in a sectional view of a flat membrane module in FIG. 5, a permeated liquid is supplied to three places from a supply liquid inlet side 33 of a membrane module 32. It was designed so that it could be divided and taken out of the system, and subjected to 34, 35 and 36 tests. That is, as shown in the module mounting portion of FIG. 5, the permeated liquid can be taken out in three parts, namely, a support part 37, a support part 38 and a support part 39.

The spacer 30 is made of 20 micron thick poly.
Stack 3 ethylene films, 1cm ²30 holes per
Was opened with a needle to form a porous film. On the side where the needle was stabbed
Were spacers A, B, and C. Spacer A is supported
Except for the part covering the body part 37, the support body part 38 and the same three parts
The portion covering 39 is cut off (the portion 40 covering the frame).
Was left). Spacer B consists of 1 part 37 of the support and 2 parts 3 of the same
8 and leave the part covering the support 3
(The portion 41 covering the frame was left). Spacer
-C was used without being cut off. Where the frame
The O-rings 42 and 43 leave the covering parts 40 and 41.
Keep the height constant for sealing with
This is to prevent liquid leakage.

The spacer 30 is attached to the module 32 as shown in FIG.
By slightly shifting the positions of the holes, the diameter of communicating pores formed when three spacers were stacked was changed, and the resistance as a spacer was changed. That is,
The pressure loss on the permeate side was controlled by adjusting the pore diameter.

(Test) An ultrafiltration membrane 31 was placed on the above three spacers, and filtration was performed. The flat membrane module used was 20 cm long and had a pressure drop of 30 kPa at a flow rate of 1.3 m / sec. The membrane used for the separation was an ultrafiltration membrane having a molecular weight cutoff of 50,000. The sample used was a three-fold dilution of tomato puree.

(Results) The permeation flux (L /
Table 2 shows the results of measuring the pressure loss for m ² h).

[0023]

[Table 1]

As shown in Table 1, 1 part, 2 parts and 3 parts of the support maintained an average permeation flux of 13.5 to 14.2 (L / m ² h). Further, it was visually confirmed that no fouling occurred on the film surface.

When filtration is performed under the same conditions as above without performing the adjustment using the spacers, the permeation flux is further reduced.
Violent fouling was observed near the module entrance.

(Embodiment 2) FIG. 2 shows an active layer 1 of a separation membrane.
1, a high-density support layer 13, a medium-density support layer 14, and a low-density support layer 15 are sequentially used for a support layer 12 supporting
A module 1 having a membrane having a very thin active layer 11 on the upper surface of these support layers 12 is shown. In this embodiment,
An ultrafiltration membrane having a molecular weight cut-off of 50,000 on the dense support layer 13, a microfiltration membrane with a pore size of 0.1 μm on the medium support layer 14,
For 5, a 1 μm microfiltration membrane was used. Then, an extremely thin cellulose acetate film 11 was formed on the upper surface of these support layers 12, and the same sample as in Example 1 was filtered. Test results,
The permeation flux was 10 to 12 (L / m ² h) in each part, and no fouling on the surface of the separation membrane was observed.

(Embodiment 3) FIG. 3 shows a module in which a reinforcing member 21 for reinforcing a separation membrane including an active layer 11 and a support layer 12 is provided as a pressure loss adjusting material in a module. As this reinforcing material, filter papers 22, 23 and 24 of 7 μm, 10 μm and 15 μm were sequentially used. Then, a cellulose acetate film was formed on the reinforcing material, and the same sample as in Example 1 was filtered. As a result of the test, the permeation flux was 10 to 13 (L / m ² h) in each part, and no fouling on the surface of the separation membrane was observed in this example.

Example 4 As shown in FIG. 4, the active layer 11 having a changed thickness is formed by providing a cellulose acetate film on a glass plate and blowing air from the surface along the film surface. Was. When the air is blown, the amount of air flowing on the film surface is adjusted so that the portion where the active layer 11 is formed thickly is applied with a large amount of air, and the portion where the active layer 11 is formed thinly is prevented from being exposed to excessive wind. The thickness of the active layer was controlled by controlling the evaporation of the mixed acetone. After appropriately adjusting the evaporation of acetone in this manner, the cellulose acetate membrane was immersed in cold water and gelled, and subjected to an experiment. The same sample as in Example 1 was filtered. As a result of the test, the permeation flux was 10 to 13.5 (L / m ² h) in each part, and no fouling on the surface of the separation membrane was observed. Without adjusting the thickness of the active layer, in a uniform cellulose acetate film, it was observed that fouling occurred violently near the entrance.

[0029]

According to the present invention, as described above, in the solute separation, solid-liquid separation and other separation operations, the generation of fouling is effectively controlled to prevent the membrane function from deteriorating, and the concentration of solutes and the like is reduced. This is a fall control method effective for optimizing the treatment of a high solution, and the separation operation can be performed more effectively. In addition, such a control membrane module can be economically provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a part of a membrane module according to an embodiment of the present invention in a developed manner.

FIG. 2 is an explanatory view showing a part of a membrane module according to another embodiment.

FIG. 3 is an explanatory view showing a part of a membrane module according to still another embodiment.

FIG. 4 is an explanatory view showing a part of a membrane module of another example.

FIG. 5 is an exploded end view of the flat-plate membrane module.

FIG. 6 is a bottom view of the flat film module of FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Separation membrane 2, 30 Spacer 3 Inlet 4 High density structure part of spacer 5 Exit 6 Medium density structure part of spacer 7 Low density structure part of spacer 11 Active layer 12 Support layer 13 High density support layer 14 Medium density support layer 15 Low density support layer 21 Reinforcement material 32 Membrane module

Claims (7)

[Claims] When performing a separation operation using a membrane module, a member having a function of equalizing the transmembrane pressure difference is provided on the permeate side of the separation membrane of the membrane module, and / or A method for controlling a transmembrane pressure, comprising adjusting the thickness of an active layer. 2. The method for controlling a transmembrane pressure according to claim 1, wherein the member having the function of equalizing the transmembrane pressure is a spacer provided on the permeated liquid side between the separation membranes. 3. The method for controlling a transmembrane pressure according to claim 1, wherein the member having the function of equalizing the transmembrane pressure is a support layer of an active layer of a separation membrane. 4. The method for controlling a transmembrane pressure according to claim 1, wherein the member having the function of equalizing the transmembrane pressure is a reinforcing material for reinforcing a membrane including an active layer and a support layer of the separation membrane. 5. The method of controlling a transmembrane pressure difference comprising a plurality of spacers of a member having a function of equalizing a transmembrane pressure, a support layer of an active layer, a reinforcing material of a separation membrane, or a plurality of active layers having a controlled thickness of the separation membrane. The method for controlling a transmembrane pressure according to claim 1, which is performed by a combination. 6. Control of the transmembrane pressure with a member having a function of equalizing the transmembrane pressure on the permeated liquid side of the separation membrane of the membrane module and / or with an active layer of the separation membrane whose thickness is adjusted. Membrane module for 7. A spacer of a member having a function of equalizing the transmembrane pressure difference on the permeated liquid side of the separation membrane to control the transmembrane pressure difference of the separation membrane, a support layer of the active layer, a reinforcing material of the separation membrane or separation. A membrane module for controlling a transmembrane pressure, comprising a combination of a plurality of active layers each having a controlled thickness.