JP3336150B2 - How to recover the performance of a permselective pervaporation membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for restoring the performance of a permselective pervaporation membrane having reduced separation performance, and more particularly, to a method for recovering water having a higher water content than a water-containing organic liquid to be dehydrated. The present invention relates to a method for restoring the performance of a water-permselective pervaporation membrane by contacting a contained organic liquid with a water-permselective pervaporation membrane.

[0002]

2. Description of the Related Art When a solvent is used in a chemical process, an extremely high purity is often required, and strict restrictions are imposed particularly on mixing of water. In recent years, as a method for dehydrating water-containing organic liquids, a dehydration method using a separation technique using a pervaporation membrane has attracted attention. The separation method by pervaporation is a pervaporation membrane and a substance separation method performed through two partitions separated by this membrane.If one component to be separated is water, the separation method results. Become. Specifically, by using a water selective permeation pervaporation membrane (hereinafter, simply referred to as a PV membrane) as the pervaporation membrane, a water-containing organic liquid such as water When an ethanol mixed solution is supplied and the second partition, that is, the secondary side is set to a negative pressure, only water molecules in the water / ethanol mixed solution are selectively transmitted from the primary side to the secondary side via the PV membrane. As a result, the water / ethanol mixed solution can be dehydrated.

[0003]

The performance of dewatering by pervaporation depends on the separation performance of the PV membrane. However, long-term use of the PV membrane may decrease the separation performance, and once the separation performance is reduced, it often remains lowered. In addition, a decrease in the resolution is observed not only in the long-term operation but also in the following cases. For example, when a water / ethanol mixed solution is taken as an example of the water-containing organic liquid, a decrease in separation ability is observed when the PV membrane is stored by immersion in high-concentration ethanol. Also, when the water-containing organic liquid is kept accumulated when the operation of the separation device is stopped, a decrease in membrane performance may be observed at the next start-up. Further, even if the separation coefficient is not reduced during the use of the PV membrane, the separation performance may be reduced when the vacuum is stopped. Such a decrease in the separation performance of the PV membrane is not essentially a decrease in the membrane performance due to the deterioration of the PV membrane itself, and the membrane performance may be able to be recovered by a certain operation. However, since the history of dehydration by pervaporation is relatively young, details of the mechanism for reducing the separation ability of the PV membrane and the method for solving the problem are often not clarified. Regarding the method of recovering the performance of the organic substance selectively permeable PV membrane (Japanese Patent Laid-Open No. 5-103957), the performance recovery method of contacting the organic substance selectively permeable PV membrane with an organic solvent having an affinity, followed by drying to remove the organic solvent. Only the method is disclosed.

On the other hand, according to the dehydration method using a PV membrane, it is possible to separate a mixture which has conventionally been difficult to separate and has been separated by an azeotropic method. In particular, in the azeotropic method, it is necessary to distill and remove benzene, cyclohexane, and the like used for azeotropy with water. Therefore, another separation equipment is required. However, such a separation equipment is unnecessary in the PV method, and the cost is low. Energy saving and equipment saving are achieved. In addition, the multi-component mixture is easy to dewater, there is no risk of product contamination or pollution,
There are advantages such as being able to purify to high purity and easy automation. As described above, the use field of the PV membrane is expected to expand in the future, and the size of the membrane module is expected to increase in order to cope with the increase in the throughput. Therefore, simply replacing the membrane module using a PV membrane when the performance of the separation membrane is reduced increases the cost and requires disposal of the unnecessary membrane module. There is a keen need to develop methods for restoring the performance of PV membranes.

[0005]

The inventor of the present invention has studied in detail the state of performance degradation of the PV membrane and the like. As a result, by bringing the PV membrane into contact with a water-containing organic liquid having a high water content, the problem is solved. Can be solved, and the present invention has been completed.

That is, the present invention relates to a water-containing organic liquid (A)
And contacting the water-selective permeation vaporized membrane having a reduced separation performance with a water-containing organic liquid (B) having a water content of 3 to 40% by weight higher than the water-containing organic liquid (A). The present invention provides a method for restoring the performance of a permselective pervaporation membrane. Further, the water-containing organic liquid (A) is 90 to 9%.
9.9% by weight of water-containing alcohol, and wherein the water-containing organic liquid (B) is 60 to 95% by weight of water-containing alcohol. It is. Further, the present invention provides a method for restoring the performance of the water-permselective pervaporation membrane, wherein the contact is to pervaporate the water-containing organic liquid (B). Hereinafter, the present invention will be described in detail.

[0007] The present invention provides a method for selectively permeating and vaporizing a water-containing organic liquid (A) using a PV membrane, wherein the separation coefficient is reduced. The water-containing organic liquid (B) whose content is higher by 3 to 40% by weight is PV
The separation performance of the PV membrane is restored by being brought into contact with the membrane. The water-containing organic liquid (A) and the water-containing organic liquid (B) only need to have a different water content, and the contained organic liquid does not need to be different between (A) and (B). Further, the water content of the water-containing organic liquid (A) varies depending on the characteristics of the PV film used. This is because if the water content is too high, the PV film may swell significantly, and the water-containing organic liquid (A) in a range that does not significantly swell is used. The water content of the water-containing organic liquid (B) of the present invention is 3% by weight higher than that of the water-containing organic liquid (A), and the water content of the PV membrane generally usable is 40% by weight or less. Should be fine. Preferably, the difference in water content between the water-containing organic liquid (A) and the water-containing organic liquid (B) is in the range of 5 to 20% by weight. When the water-containing organic liquid (A) is an aqueous alcohol solution, the water-containing organic liquid (B) is 90 to 99.9% by weight of a water-containing alcohol, and the water-containing organic liquid (B) is 60 to 9% by weight.
Preferably, it is 5% by weight of hydrous alcohol. In addition, the contact means that the water-containing organic liquid (A)
Instead, it is achieved by immersion in the water-containing organic liquid (B) or by pervaporation of the water-containing organic liquid (B). When immersing, besides simply immersing, set the temperature to 2
When the temperature is set to 0 to 80C, particularly preferably 40 to 70C, the performance recovery time can be shortened. In the case of pervaporation, the performance recovery time is reduced by setting the degree of pressure reduction to 0.1 to 100 torr, particularly preferably 1 to 50 torr, and the temperature to 40 to 80 ° C, particularly preferably 60 to 80 ° C. be able to. The time for pervaporation is
Preferably, it is 5 to 200 hours, particularly preferably 10 hours.
~ 100 hours.

The water-containing organic liquid (A) that can be used in the performance recovery method of the present invention includes ethanol, propanol,
Alcohols such as butanol and methanol, acetone,
Organic solvents such as diethyl ether, pyridine, and ethyl acetate; organic acids such as acetic acid; sugar solutions such as fructose; polar aprotic solvents such as dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, and N-methyl-2-pyrrolidone; and water. Any organic liquid containing and intended for dehydration may be used, and particularly preferably an aqueous solution containing ethanol. The case where the water-containing organic liquid (A) is treated and the separation performance of the PV membrane is reduced includes, for example, the case where the PV membrane is stored in a high-concentration organic liquid in addition to the deterioration of the separation performance due to long-term use of the PV membrane. When the operation is stopped, the PV membrane may be left with the water-containing organic liquid (A) stored therein.

As the PV membrane which can be used in the present invention, any membrane may be used as long as it has water-permeability and is not soluble in a water-containing organic solvent for the purpose of separation. For example, preferred materials include polyon complex, cellulose ester, chitosan, polyamide, polyimide, polysulfone, polyacrylonitrile-based polymer and the like, and in particular, polyon complex, polyacrylonitrile-based copolymer, chitosan and the like. preferable. As the acrylonitrile-based polymer, a copolymer having an acrylonitrile content in the range of 90 to 97 mol% is preferable, and other monomers constituting the copolymer include vinyl acetate, methacrylic acid, acrylic acid, Examples include methacrylic esters, acrylic esters, acrylamide, vinylsulfonic acid, styrenesulfonic acid, vinylpyrrolidone, vinylpyridine, diethylaminoethyl methacrylate, maleic anhydride, 2-acrylamido-2-methyl-1-propanesulfonic acid, and the like. Preferred molecular weight of the copolymer,
It is 20,000 to 500,000.

[0010] In addition, PV which can be used in the present invention.
The membrane may be a membrane module, and the membrane used may be of any shape. For example, a hollow fiber type membrane, a flat membrane, a spiral type membrane, a pleated type membrane, a tubular type membrane and the like can be mentioned.

[0011] The PV membrane that can be used in the present invention is:
90 to 99.9% by weight of an aqueous ethanol solution
The separation coefficient when used at a temperature of 1 ° C. and a secondary pressure of 1 to 50 torr is about 1000, and it is preferable to apply when the separation coefficient becomes 500 or less. Here, the separation coefficient (α) is (Cw / Ce) secondary side / (C
w / Ce) expressed on the primary side. Here, Cw indicates the concentration of water, and Ce indicates the concentration of ethanol. Further, according to the performance recovery method of the present invention, the membrane performance with a separation coefficient of 500 or less is 2
It is possible to recover the separation coefficient to 800 or more by processing within 0 days.

[0012]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

(Example 1) A module of a polyionic complex (PIC) hollow fiber membrane (inner diameter 0.5 mm, outer diameter 0.8 mm) produced by hydrolyzing a polyacrylonitrile-based hollow fiber membrane and then immersing in a polycation. A pervaporation experiment was performed using a membrane area of 300 cm ² ).
In the experiment, first, a 99.0% by weight aqueous ethanol solution was supplied to the inner surface side of the hollow fiber membrane at a supply inlet temperature to the membrane module of 75 ° C., and the outer surface side of the hollow fiber membrane was decompressed to 10 mmHg for evaluation. went. At this time, the separation factor of the membrane is 5,0.
00, and the permeation rate was 130 g / m ² · hr. Next, the reduced pressure on the permeation side of the membrane was released to the atmosphere, and the supply liquid was kept at room temperature for 12 hours while keeping the supply liquid in contact with the inside of the hollow fiber membrane in the module. Thereafter, the evaluation was performed again under the same conditions as above, and as a result, the separation coefficient of the membrane was reduced to 300. Therefore, an 80.5% by weight aqueous solution of ethanol (concentration of 75% under normal pressure) was placed on the interior side of the hollow fiber membrane.
° C) and allowed to stand for 17 days, after which the separation factor of the membrane was measured and recovered to 1,500.

Example 2 A 94.0% by weight aqueous ethanol solution (temperature: 75 ° C.) was placed on the inner surface side of the membrane whose separation coefficient was reduced from 3,000 to 540 by the same operation as in Example 1.
Was supplied and pervaporation was performed at a reduced pressure of 1.5 mmHg, and the separation coefficient of the membrane recovered to 2,000 5 days after the start of pervaporation.

Comparative Example 1 A 98.6% by weight aqueous solution of ethanol (temperature 75 ° C.) was placed on the inner surface side of the membrane whose separation coefficient was reduced from 3,000 to 420 by the same operation as in Example 1.
And pervaporation at a reduced pressure of 10.0 mmHg,
Six days after the start of pervaporation, the separation coefficient of the membrane increased to 460. However, the separation performance is a practical lower limit of 800.
It was below and did not lead to performance recovery.

[0016]

According to the present invention, there is no need to remove the module, the recovery process can be performed with the module attached, and there is no contamination of the device by a special recovery agent. Therefore, unlike post-treatment with a recovery agent, no post-treatment such as drying, washing and removal of chemicals is required, and no special waste is produced. Further, it is sufficient to use only a very simple operation of increasing the water content of the liquid to be separated, and the process can be easily shifted from the recovery process to the normal operation simply by changing the composition of the feed solution. Furthermore, an organic liquid having a higher water content than that of the organic liquid to be treated can be recovered by a simple process of merely enclosing the module in the primary side of the module and allowing it to stand. If performed, the separation performance can be recovered in a very short time.

Continuation of front page (56) References JP-A-5-103957 (JP, A) JP-A-62-250907 (JP, A) JP-A-6-218254 (JP, A) JP-A-8-229365 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 65/06 B01D 61/36 B01D 69/02

Claims (3)

(57) [Claims] 1. A method of treating a water-containing organic liquid (A) by treating a water-selective permeation vaporized membrane having a reduced separation performance with a water content of 3 to 40% by weight higher than that of the water-containing organic liquid (A). A method for restoring the performance of a permselective pervaporation membrane characterized by contacting with an organic liquid (B). 2. The water-containing organic liquid (A) is 90 to 99.9.
Water-containing alcohol (B)
The method for recovering the performance of a permselective water vapor permeation membrane according to claim 1, wherein is a water-containing alcohol of 60 to 95% by weight. 3. The method for recovering performance of a permselective pervaporation membrane according to claim 1, wherein the contacting is to pervaporate the water-containing organic liquid (B).