JPH0456653B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating organic matter from an aqueous solution of organic matter. Conventionally, a distillation method has generally been adopted as a method for separating organic substances from an aqueous solution of organic substances. For azeotropic aqueous solutions of organic substances that can be separated by distillation methods and aqueous solutions of near-boiling organic substances that are energy inefficient, azeotropic distillation methods, extractive distillation methods, etc. are used.

In recent years, membrane separation technology has developed, and reverse osmosis has been put into practical use for concentrating some low-temperature aqueous solutions of organic substances. However, since reverse osmosis requires applying a pressure higher than the osmotic pressure of the separated liquid to the separated liquid, it cannot be applied to highly concentrated aqueous solutions with high osmotic pressure, or there are limits to its concentration. .

Recently, the pervaparation method has attracted attention as a new separation method for separating aqueous solutions of organic substances. The perveparation method involves supplying a separated liquid to the primary side (feed liquid side) of the membrane, and reducing the pressure on the secondary side (permeation side) of the membrane, or passing inert gas as a carrier gas. Therefore, in a method in which the substance to be separated is passed through a membrane in a gaseous state, the membrane permeate is usually collected by cooling and condensing the permeated vapor. This perveparation method is not affected by osmotic pressure;
It has advantages such as being able to perform separation regardless of the concentration of the separated liquid, and there have been many reports of its application to azeotropic mixtures that are difficult to separate using conventional distillation methods. However, conventionally reported membranes have not been put into practical use because of their low membrane permeation rate (m ³ /m ² ·day) or small separation coefficient (α ^A _B ). Here, the separation coefficient (α ^A _B ) is expressed by the following formula.

α ^A _B = (weight% of component A in permeate/weight% of component B in permeate)/(weight% of component A in feed solution/weight% of component B in feed solution) A non-porous uniform membrane with a thickness of 3 μm or less or a separation membrane having a non-porous skin layer (dense layer) having a separation function for an organic aqueous solution was used, and the organic aqueous solution was vaporized on one side of the membrane. Selective permeation of water vapor by supplying a gas mixture and keeping the other permeate side under vacuum or in contact with an inert carrier gas has been evaluated in conventional perveparation methods for the separation of aqueous organic solutions. It was discovered that the separation coefficient could be improved compared to the permeation rate in the case where the permeation rate was previously reported without causing a significant decrease in the permeation rate, and a patent application was filed (patent application dated November 2, 1981). . That is, this method is a method in which a gas mixture of the separated liquid is supplied to the primary side of the membrane instead of supplying the separated liquid to the primary side of the membrane in the perveparation method.
The present inventors further studied the above-mentioned gas permeation separation method as a method for separating an aqueous solution of organic matter, and as a result, they arrived at the present invention.

That is, in the present invention, an organic aqueous solution is supplied to one side of the membrane through a separation membrane, and the other permeate side is kept under reduced pressure or an inert carrier gas is brought into contact between the separation membrane and the organic aqueous solution. This invention relates to a method for membrane separation of an aqueous solution of an organic substance, which is characterized by interposing an inert hydrophobic porous membrane and allowing water vapor to selectively permeate through the porous membrane and the separation membrane.

In the method of the present invention, as in the perveparation method, an organic aqueous solution is supplied to the primary side of the separation membrane,
The secondary side of the separation membrane is reduced in pressure or an inert gas is passed through it, but by overlaying an inert hydrophobic porous membrane on the primary side of the separation membrane, the separation between the separated liquid and the separation membrane is prevented. A void is created in between by the porous membrane, and gas is generated in the void on the primary side of this membrane. It has been found that this method can improve the separation coefficient without significantly reducing the permeation rate compared to the perveparation method using the same separation membrane. Here, an inert hydrophobic porous membrane is defined as a liquid state within the porous membrane under the separation conditions, that is, the composition of the separation solution, the temperature of the separation liquid, and the total pressure of the gas mixture within the inert hydrophobic porous membrane. A membrane that does not permeate. Therefore, within this inert hydrophobic porous membrane, there exists a gas mixture produced by vapor-liquid equilibrium with the separated liquid that is in contact with the primary side (separated liquid supply side) of this porous membrane. In the method of the present invention, a separation membrane is layered on the secondary side of an inert hydrophobic porous membrane, and this separation membrane contains a gas mixture generated by vapor-liquid equilibrium of a separated liquid such as upper air. are in contact. Therefore, although the method of the present invention is apparently a perveparation method, the permeation mechanism of the water/organic substance mixture passing through the separation membrane is vapor permeation, and it is thought that this improves the separation coefficient. It will be done. Note that in carrying out the present invention, the inert hydrophobic porous membrane and the separation membrane may be in close contact with each other, but other porous membranes, porous partitions, etc. may be inserted between the two membranes. They may be separated from each other.

As membrane materials for the inert hydrophobic porous membrane used in the present invention, homopolymers and copolymers made of fluorine-containing monomers such as tetrafluoroethylene and hexafluoropropylene, which have a large contact angle with water, are preferred. , other hydrophobic polymers such as polyolefin polymers such as polyethylene and polypropylene, and vinyl polymers such as acrylic polymers may also be used. The pore diameter of the hydrophobic porous membrane made from these membrane materials is 0.05 μm to 100 μm, preferably 1 μm.
~50 μm, and the porosity is 30-90%, preferably 60
~80%. The film thickness is suitably 50 μm to 3 mm, preferably 70 μm to 1 mm. The permeability of hydrophobic porous membrane is 1 to 200/min・cm ² for air, 70cmHg
It is.

As the separation membrane, the membrane described in the specification of the patent application dated November 2, 1982, filed by the present applicant is preferred. For example, in addition to cellulose membranes (regenerated cellulose membranes and cellulose membranes), polyvinyl alcohol membranes, membranes of condensed synthetic polymers such as cellulose acetate, polyamide, polybenzimidazole, and polybenzimidazolone, which are conventionally used as reverse osmosis membranes, A membrane made of a crosslinked polymer having a crosslinked structure, such as polyether, polyamine, polyamide, polyvinyl alcohol, etc., and having a thickness of 3 μm or less is suitable. Here, the reverse osmosis membrane is, for example,
Temperature 25℃, pressure for NaCl 0.35% by weight aqueous solution
Reverse osmosis performance evaluation at 40Kg/ ^cm2 indicates water permeation rate.
The membrane has a performance of 0.3Kg/cm ² or more and a NaCl rejection rate of 70% or more. The separation membrane made of such a non-porous uniform membrane with a thickness of 3 μm or less can be used as an asymmetric structure membrane consisting of a skin layer and a porous support layer below the skin layer, or the above separation membrane can be used as a porous membrane or a porous partition wall. Laminate or
Laminated membranes or composite membranes in which a skin layer is formed on these porous membranes or porous partition walls are preferred. As such porous membranes and porous partition walls, those having low gas permeation resistance and mechanical strength that allow practical handling can be used. The material is natural polymer,
Synthetic polymers, rigid metals, nonmetallic inorganic compounds, etc. are used. These can be produced by known methods, but commercially available microfilters, ultrafiltration membranes, sintered metals, ceramics, etc. can also be used. The higher the liquid temperature is, the better, as long as it is below the boiling point of the separated liquid. Further, the pressure applied to the separated liquid is usually atmospheric pressure, but it is possible to apply such a pressure that the separated liquid does not permeate the inert hydrophobic porous membrane. When reducing the pressure on the secondary side of the separation membrane, the pressure should be 100 torr or less, preferably
It is less than 10torr.

In carrying out the present invention, even if the solution does not permeate through the inert hydrophobic porous membrane, the solution can be permeated through the inert hydrophobic porous membrane by applying pressure to the solution or reducing pressure on the permeate side. It becomes like that. In the present invention, the pressure or degree of vacuum at which the solution begins to permeate the inert hydrophobic porous membrane is referred to as critical fluid osmotic pressure or critical fluid osmotic pressure degree. In the separation of organic matter/organic matter or organic matter/water mixture using the laminated or composite membrane of the present invention of an inert hydrophobic porous membrane and a separation membrane, when reducing the pressure on the permeate side, the inert hydrophobic membrane separated by the separation membrane Either adjust the degree of vacuum on the permeate side so that the inside of the porous membrane does not reach the critical fluid permeation vacuum, or adjust the temperature of the feed liquid to increase the vapor pressure of organic matter or water within the inert hydrophobic porous membrane. It is necessary to increase and implement this.

In the present invention, instead of laminating an inert hydrophobic porous membrane and a separation membrane, it is also possible to form a composite membrane in which a separation membrane is directly formed on one side of an inert hydrophobic porous membrane. In this case, the separation membrane material (polymer)
is dissolved in a water-insoluble solvent such as benzene or chloroform, and then cast onto the water surface, followed by overlaying an inert hydrophobic porous membrane on top of the cast membrane. Transfer onto a membrane to create a composite membrane. When the polymer solvent is water-soluble, instead of being cast onto the water surface, it can also be cast onto a smooth casting plate placed on the water surface. A laminated membrane is a membrane in which a dry thin film is laminated on a porous membrane, and a composite membrane is a membrane in which a solvent-containing thin membrane or a cast thin membrane and a porous membrane are laminated, and after the solvent is removed, they are integrated. Further, the shape of the laminated membrane or composite membrane of the inert hydrophobic porous membrane and the separation membrane may be any of flat plate type, tube type, hollow fiber type, etc.

Examples of organic substances in the organic aqueous solution that can be separated by the method of the present invention include methanol, ethanol, n-propanol, i-propanol, n-
Examples include aliphatic alcohols such as butanol, sec-butanol, ter-butanol, and ethylene glycol; aliphatic carboxylic acids such as formic acid, acetic acid, propionic acid, and butyric acid; and ketones such as acetone, methyl ethyl ketone, and cyclohexanone.

Although the method of the present invention has been described above with respect to a method for separating water and organic matter in an aqueous organic matter solution, that is, a liquid mixture of water/organic matter, the method of the present invention can also be applied to the separation of a liquid mixture of organic matter/organic matter. That is, organic substances that do not permeate a hydrophobic porous membrane include glycerin, formamide, etc., and the present invention can also be applied to the separation of mixtures of these or mixtures of these and other organic substances as described above. As mentioned above, as a measure of membrane performance, there are permeation rate (hereinafter abbreviated as Q) and separation coefficient (hereinafter abbreviated as α), and the superiority or inferiority of membrane performance must be evaluated based on the combination of Q and α. .
In addition, since α indicates that no separation function is exhibited at all when α is 1, Q×(α−1) will be used in the following example as a comprehensive evaluation scale of membrane performance.

Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Example 1 Polyflon paper as an inert hydrophobic porous membrane
5L (manufactured by Daikin Corporation, registered trademark, film thickness 550 μm, porosity 75 vol%, maximum pore diameter 45 μm, made of polytetrafluoroethylene) was used, and cellophane (film thickness
(22 μm) were overlapped, and a 10% by weight aqueous ethanol solution was separated using a magnetic stirring type pervaporation device. The ethanol aqueous solution at 60°C was brought into contact with the 5L side of Polyflon paper, and the pressure on the cellophane side (membrane permeation side) was reduced to 266 pa. The resulting permeation rate
Q0.74Kg・m ^-2・hr ^-1 , separation coefficient α water ethanol

Claims (1)

[Claims] 1. An organic aqueous solution is supplied to one side of the membrane through a separation membrane, and the other permeate side is maintained at a reduced pressure or brought into contact with an inert carrier gas, and the separation membrane and the organic aqueous solution are connected to each other. an inert hydrophobic porous membrane through which the organic substance aqueous solution does not permeate in liquid form under separation conditions, and selectively allows water vapor to permeate through the porous membrane and the separation membrane. Separation method. 2. The membrane separation method according to claim 1, wherein the separation membrane is a non-porous uniform membrane with a thickness of 3 μm or less or a membrane having a non-porous skin layer.