JPH0639247A - Method for maintaining separation performance of separation membrane - Google Patents

Abstract

PURPOSE:To maintain the separation performance over the long term of a high molecular separation membrane used in a vapor percolation method by sealing a starting liquid mixture with inert gas and feeding the starting liquid mixture to a membrane module. CONSTITUTION:A liquid mixture to be treated is stored in a raw material tank 1 and inert gas, such as nitrogen, helium and methane is fed from an inert gas feed line 12 to the raw material tank 1 which is sealed to shut out air. The raw material sealed in by the inert gas is fed to the primary side of a membrane module 5 internally provided with a high molecular separation membrane 6 by a raw material feed pump 2 through a heat exchanger 3 and a heater 4 where the temperature of the raw material is adjusted to a specified one, e.g. ordinary temperatures to 140 deg.C. The secondary side of the membrane module is connected to a vacuum pump 11 though a condenser 9. Thus, the separation performance of the membrane is maintained over a long term.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for maintaining the separation performance of a polymer separation membrane used when separating a liquid mixture by a pervaporation method.

[0002]

2. Description of the Related Art The pervaporation method is a method for separating a liquid mixture using a polymer separation membrane, which supplies the liquid to be treated to the high pressure side (primary side) of the polymer separation membrane and permeates it. This is a separation method in which a substance that easily does is selectively permeated to the low pressure side (secondary side) as vapor. This method separates and concentrates a liquid mixture that could not be separated by a simple method, such as an azeotropic mixture such as ethanol / water or a mixture such as benzene / cyclohexane having a close boiling point and a specific volatility close to 1. It is attracting attention as a way to do it. Regarding the polymer separation membrane used in this pervaporation method, many studies on the polymer separation membrane have been made and reported for each target liquid mixture.

Pervapor using these polymer separation membranes
Figure 2 shows an example of the general process flow of the ration method.
You As shown in the figure, the liquid to be processed from the raw material tank 1
The mixture is heated by the raw material supply pump 2 to the heat exchanger 3 and the heater 4.
Are sequentially sent to the membrane and heated, and the membrane module consisting of the polymer separation membrane 6 is
It is supplied to the module 5. Polymer in membrane module 5 Reference number = A0042
(2) A substance that easily permeates the separation membrane 6 is reduced to a low pressure by the vacuum pump 11.
Is separated into steam on the secondary side, and is intended on the primary side.
The substance is concentrated. In this way, the easily permeable substance is vapor.
Therefore, the latent heat of vaporization is removed and the temperature of the primary side liquid
The primary side liquid is reheated if necessary.
It is heated at 4 and supplied to the next membrane module 5. Finally
After concentrating to the target concentration, cool it with the heat exchanger 3 and the cooler 7.
It is rejected and stored in the product tank 8. Separated as steam
The permeated components collected are cooled, liquefied and collected by the condenser 9.
Collected in the permeate tank 10 and collected from the line 13.
To be done.

The separation performance of a polymer separation membrane used in a membrane module in the pervaporation method is usually represented by a unit membrane area and a permeation amount of a permeation substance per unit time and a separation coefficient. The separation coefficient, for example, the separation coefficient (α _A ^B ) in the AB binary system is expressed by the following equation. α _A ^B = (y _B / y _A ) / (x _B / x _A ) In the formula, x _A and x _B respectively represent the concentrations of the A component and B component on the primary side, and y _A and y _B are Secondary A component, B respectively
Indicates the concentration of a component.

As is clear from the above equation, a polymer separation membrane having a large amount of permeation and a large separation coefficient can be said to be a good separation membrane. The permeation amount has a large influence on the treatment capacity, and the separation coefficient is a factor related to the separation efficiency. In order to stably operate the separation process by the pervaporation method,
It is necessary to stably maintain the separation performance of the polymer separation membrane, that is, the permeation amount and the separation coefficient. Since the pervaporation method is used by heating the liquid mixture during the separation operation due to the characteristics of the separation operation, other liquid treatment membrane separation processes such as reverse osmosis or ultrafiltration used at room temperature are used. As compared with the method, the heat load is applied to that extent, and as a result, the polymer separation membrane is deteriorated, so that more difficulty is involved in maintaining the separation performance of the polymer separation membrane. Reference number = A0042
(3)

The method for maintaining the separation performance in the reverse osmosis method or the ultrafiltration method is to remove the contaminants adhering to the membrane surface by a physical washing method or a chemical injection treatment to improve the separation performance. The method of recovery is adopted. However, since the pervaporation method is technically new and a lot of research is being focused on the development of a new polymer separation membrane, a method of maintaining the separation performance is to filter the treatment liquid by filtration with a filter. Removal of suspended solids and operating temperature,
At present, the operation is carried out under the condition where the operating pressure is as mild as possible, and a method for chemically maintaining stable separation performance for a long period of time has not yet been developed. Therefore, in the pervaporation method, the polymer separation membrane whose separation performance has deteriorated had to be replaced with a new polymer separation membrane with much labor and cost.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and makes it possible to maintain the separation performance of a polymer separation membrane used in the pervaporation method for a long period of time. The purpose is to provide a method.

[0008]

DISCLOSURE OF THE INVENTION The inventors of the present invention have earnestly studied, when separating a liquid mixture by a pervaporation method, a method for maintaining long-term separation performance of a polymer separation membrane used in the pervaporation method. As a result, it was found that the separation performance of the polymer separation membrane for pervaporation can be maintained extremely effectively by sealing the raw material liquid mixture with an inert gas and supplying the raw material liquid mixture to the membrane module. Reached

Next, a method for maintaining the separation performance of the polymer separation membrane of the present invention will be described with reference to the drawings. FIG. 1 is a flow chart showing an example of the present invention. Reference number = A0042
(4) In the figure, 1 is a raw material tank, 2 is a raw material supply pump, 3 is a heat exchanger, 4 is a heater, 5 is a membrane module, 6 is a polymer separation membrane, 7 is a cooler, 8 is a product tank, 9 is a condenser,
10 is a permeate tank, 11 is a vacuum pump, and 12 is an inert gas supply line.

As the raw material liquid mixture to be treated, for example, a liquid mixture of two or more components such as an organic liquid / water mixture or an organic liquid / organic liquid mixture is used. Examples of the organic liquid / water mixture include ethanol, normal propanol, isopropanol, normal butanol,
Forms an azeotropic mixture of water with a mixture of alcohols such as isobutanol and water, a mixture of water with ketones such as methyl ethyl ketone and methyl isobutyl ketone, or a mixture of water with ethers such as dioxane and methyl tertiary butyl ether. A mixture of Organic liquid / organic liquid mixtures include, for example, benzene / cyclohexane mixtures, xylene isomer mixtures or ethanol / isopropanol mixtures with close boiling points.
Mixtures that do not form an azeotrope or mixtures that do not have close boiling points, such as acetone / water, methanol / water, ethylene glycol / water mixtures, etc., can of course be used as the processing liquid of the present invention.

The raw material tank 1 is filled with the liquid mixture to be treated.
Storage, inert gas from the inert gas supply line 12, eg
Supply nitrogen, helium, methane, etc. to the raw material tank 1
Seal and block air. Other separation processes, eg
Pervaporation continuously from the distillation or extraction process
Do not use the raw material tank when separating by the
It's good. For example, in the case of the atmospheric distillation method, via a condenser
Directly from the reflux drum, which is open to the atmosphere.
When supplying the liquid mixture to the vaporization device,
Install an inert gas supply line on the reflux drum and seal it.
Of course, this method is also included in the present invention. Inert moth
The gas supply line blows directly into the liquid mixture in the raw material tank.
It may be fed into the tank, or it may be connected to the top of the raw material tank.
Inert gas will be supplied to the tank. Reference number = A0042
(5) You may ask.

The raw material sealed with an inert gas is heated by the raw material supply pump 2 to a predetermined temperature in the heat exchanger 3 and the heater 4, for example, but not limited to room temperature to 14
It is adjusted to 0 ° C. and supplied to the primary side of the membrane module 5 in which the polymer separation membrane 6 is installed. The type of the membrane module is a plate-and-frame type or spiral type membrane module when the polymer separation membrane is a flat membrane, and a hollow fiber type or a spiral fiber type when the polymer separation membrane is a hollow fiber or a tube. It is a tubular membrane module. In the method of the present invention, the type of the membrane module is not particularly limited. The secondary side of the membrane module is connected to the vacuum pump 11 via the condenser 9. The degree of pressure reduction on the secondary side is not particularly limited, but by keeping the pressure reduction degree of usually 300 mmHg or less, preferably 30 mmHg or less, the component that easily permeates the polymer separation membrane in the raw material treatment liquid is Corresponding to the separation performance of the membrane, it is separated as steam on the secondary side. When the component that easily permeates is separated as vapor, the latent heat of vaporization is taken away, and the temperature of the treated liquid on the primary side decreases by an amount commensurate with the latent heat of vaporization. Supply to the membrane module 5. As the heating method, in addition to the method of using an external heater as shown in FIG. 1, a method of heating the entire membrane module with a heating medium jacket or a partition wall provided in the membrane module to directly heat the heating medium in the membrane module. A method of supplying and heating may be mentioned, but the heating method is not particularly limited. The numbers of the membrane module 5 and the heater 4 may be appropriately selected according to the treatment amount of the treatment liquid and the target concentration, and may be used in combination. The treatment liquid concentrated to the target concentration flowing out from the primary side of the membrane module is cooled by the heat exchanger 3 and the cooler 7 and stored in the product tank 8.

Permeation as vapor to the secondary side of the membrane module
The condensed components are cooled below the dew point in the condenser 9 and condensed.
Stored in the permeate tank 10 and collected from the line 13.
To be done. Materials for polymer separation membranes used in membrane modules
Depends on the type of liquid to be treated.
Molecule, polyethylene, polyvinyl, polyamide, poly Reference number = A0042
(6) Stell, polysulfone, polycarbonate, polyimi
Do not use commonly used materials such as
In addition to considering the affinity for the separation target component.
In consideration, various functional groups such as alcohol group and
Rubonic acid group, ether group, amino group, imide group, ester
Polymers containing polymer groups, nitrile groups, etc. introduced into the polymer separation membrane
It is also possible to use a separation membrane or so-called ion exchange membrane.
It The present invention is not limited to these polymer separation membrane materials.
Yes.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to the drawings. Example A raw material tank 1 having an internal capacity of 5 liters was charged with 3.5 liters of an aqueous 93.5 wt% ethanol solution, and a commercially available polyvinyl alcohol-based water selective permeation separation membrane 6 was attached to the membrane separation cell (membrane module) 5 (Effective film area: 12.19c
m), using the raw material supply pump 2, the ethanol aqueous solution is passed through the heat exchanger 3 and the heater 4 at a temperature of 115 ° C.,
The pressure was 4 kg / cm ² G and the flow rate was 30 l / h. The aqueous ethanol solution flowing out from the primary side of the membrane separation cell 5 was cooled by the heat exchanger 3 and the cooler 7 to normal pressure, and then circulated to the raw material tank 1 through the line 14. A sampler with a septum (not shown) attached to the raw material tank 1 was used for sampling to analyze the liquid composition on the primary side. The pressure on the secondary side of the membrane separation cell was adjusted to 10 mmHg by a vacuum pump 11 and a vacuum control valve (not shown). The vapor mainly consisting of water that has permeated through the separation membrane in the membrane separation cell was collected as a liquid in the permeated liquid tank 10 by using the condenser 9 adjusted to 0 ° C. In the long-term membrane separation performance test, in order to maintain the concentration of the raw material ethanol at a constant concentration of 93.5% by weight, the same amount of water lost as steam on the secondary side in the membrane separation cell was lost. Water was constantly added to the raw material tank 1 from a water tank (not shown) using a water pump (not shown). Since the permeation amount of ethanol was small, addition or replacement was performed once every three months.

Permeate collected by permeation in the permeate tank 10.
Analyze body weight and composition, and perform membrane separation Reference number = A0042
(7) Separation performance of the separation membrane 6 attached to the module (membrane module) 5
Permeation amount (g / m²・ H) and separation factor are displayed, and the change over time is displayed.
It was measured. The results are shown in Fig. 3. In the figure, ○ is the transmission amount, △ is the minute
Indicates the separation coefficient. As is clear from the figure, the above-mentioned pervapor
18 days after the start of the experiment under stable conditions
Permeation rate of 3125g / m²・ H, the separation factor is 500
It was After that, the amount of permeation gradually increased, 282 after the start of the experiment.
3978 g / m at the time of day²・ It was h. During this time
The separation factor of was stable between 484 and 668, but 2
After 80 days, the amount of permeation increased rapidly and the separation factor decreased.
Started to do. After 300 days, raw material tank 1 and
Nitrogen was used as an inert gas in the water tank (not shown).
And sealed, and the experiment was continued. As a result,
The increase will be gradual, and the separation factor will increase slightly
It became stable at around 500, which is the same as the separation factor. Inert gas
If not measured, as shown in the comparative example,
Deterioration of the membrane separation performance in the form of
Although it is recognized, due to the inert gas seal, the membrane separation performance,
Especially, the separation factor was stably maintained.

Comparative Example Using the same apparatus as in Example, a water permeation separation membrane similar to that in Example was attached to a membrane separation cell, and the temperature was 100 ° C. for the first 176 days, and 110 ° C. thereafter. Other conditions were the same as in the example. However, the raw material tank and the water tank were not sealed with an inert gas throughout the entire period. The results are shown in Fig. 4. In the figure, ◯ represents the amount of transmission, and Δ represents the separation coefficient. As is clear from the figure, the permeation amount at the time when the temperature was 110 ° C. (191 days later) was 1993 g / m ² · h, and the separation coefficient was 767. 400 days after the start of the experiment (temperature 11
The permeation amount increased sharply and the separation coefficient drastically decreased after about 224 days from 0 ° C. 61 after the start of the experiment
The permeation amount after 3 days (temperature of 110 ° C for 437 days) is 3486 g / m ² · h, which is 1.75 times that of the temperature of 110 ° C, and the separation factor is 244 and 11
It fell to 31.8% when it was set to 0 ° C.

Reference number = A0042
(8)

[Effect] The life of the polymer separation membrane used in the pervaporation method is said to be several months for a short one and several years for a long one, although it depends on the condition of use. In the past, membranes with poor separation performance were replaced with new membranes by replacing the membrane or replacing the membrane module, but this replacement operation stopped the device, took out the membrane module, and replaced the membrane. Or, it has to be replaced with a membrane module incorporating a new membrane, which requires a great deal of labor and cost. According to the present invention, the membrane separation performance can be maintained for a long period of time by a very simple operation of sealing a tank or a drum containing a liquid mixture with an inert gas. The time for refilling, replacement of the membrane module, etc. can be extended accordingly, and as a result, a labor-saving, energy-saving, and less expensive liquid mixture separation system is realized. According to the present invention, the reason why the membrane separation performance is maintained for a long period of time by sealing the treatment liquid with an inert gas has not yet been theoretically sufficiently clarified, but it is probably dissolved in the treatment liquid. It is considered that oxygen acts on the polymer membrane, the polymer chains and polymer arrangements are subtly changed, and part of the polymer is oxidized by oxygen, so that the membrane separation performance is deteriorated. According to the above, it is considered that such deterioration is prevented.

[0018]

[Brief description of drawings]

FIG. 1 is a flow chart showing an embodiment of the present invention.

FIG. 2 is a flow chart showing a conventional method.

FIG. 3 is a graph in which the amount of permeation and the separation coefficient are measured according to the elapsed days using the method of the present invention.

[Figure 4] Reference number = A0042
(9) A graph in which the amount of permeation and the separation coefficient are measured according to the number of days elapsed using a conventional method.

[Explanation of symbols]

1 Raw Material Tank 2 Raw Material Supply Pump 3 Heat Exchanger 4 Heater 5 Membrane Module 6 Polymer Separation Membrane 7 Cooler 8 Product Tank 9 Condenser 10 Permeate Tank 11 Vacuum Pump 12 Inert Gas Supply Line 13 Line 14 Line

Claims (1)

[Claims] 1. A polymer separation membrane for pervaporation, characterized in that, when a liquid mixture is separated by a pervaporation method, a raw material liquid mixture is sealed with an inert gas and the liquid mixture is supplied to a membrane module. Separation performance maintenance method.