JPS6099314A - Concentration of aqueous solution of organic substance - Google Patents

Abstract

PURPOSE:To permeate steam selectively by pervaporation process by using a separating membrane having a nonporous uniform film or nonporous skin layer of <=3mum film thickness. CONSTITUTION:Permeation rate is remarkably improved in pervaporation process if the film thickness is regulated to <=3mum for a kind of membrane material without causing severe decrease of separation coefft. A separation membrane comprising a nonporous uniform film having <=3mum film thickness is laminated on another porous film or porous diaphragm, or a laminated film or composite film formed on these porous film or porous diaphragm is used. Suitable material for the nonporous uniform film is water permselective hydrophilic polymer, such as polymers modified with cellulose, polyvinyl alcohol, or polyvinyl pyrrolidone or blended polymer thereof. As reinforcement of the uniform film, porous film or porous diaphragm of natural or synthetic polymer, rigid metal or nonmetal or other inorg. compds, are used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating organic matter from an aqueous solution of organic matter. More specifically, the present invention relates to a method for concentrating an aqueous solution of organic matter by a gas permeation method using a separation membrane.

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 cannot be separated by distillation methods and aqueous solutions of near-boiling organic substances that are energy inefficient, azeotropic distillation methods, extraction/distillation methods, etc. are used. In recent years, with the development of membrane separation technology, reverse osmosis has been put into practical use for concentrating some low-concentration organic substance aqueous solutions. However, since the reverse osmosis method requires applying a pressure higher than the osmotic pressure of the separated liquid to the separated liquid, it is not applicable to highly concentrated aqueous solutions with high osmotic pressure, or there are limits to its concentration.

On the other hand, pervenolysis (which is not affected by osmotic pressure)
The pervaporatlon method is attracting attention as a new separation method, and many research examples have been reported. For example, regarding the separation of ethanol aqueous solutions, JP-A-54-55278 and JP-A-57-1677
No. 02, UEIP No. 2955502 Br1tisch
Chemical Finineering9(8)
, 52 in 1964).

J,ApplePol,y,Sci,, 14, 23
41 (1970), J, hppl, POny.

Sai, 18j51 (1974), etc. The perpetuation method is a process in which a separated liquid is supplied to the primary side of the membrane, and the secondary side (permeation side) of the membrane is subjected to reduced pressure, or the separated substance is passed through the membrane in a gaseous state by passing a carrier gas through the membrane. In order to collect the membrane permeate using the permeation method, the vapor on the permeate side is usually cooled and condensed.

However, the reason why the pervaporation method has not reached the level of a practical alternative technology to other separation methods for the separation of aqueous solutions of organic substances such as azeotropic mixtures and near-boiling point mixtures is that membrane permeation This may be due to a low speed or a low water/organic separation coefficient. In membrane separation methods other than the pervaporation method, the objective of improving the permeation rate can be achieved to some extent by reducing the thickness of the separation membrane. However, in the pervaporation method, the influence of film thickness is relatively small, and even if the film thickness is made thinner, the permeation rate cannot be increased in proportion to this. Therefore, methods of changing the chemical structure of separation membranes have been used to increase the permeation rate. For example, JP-A-54-58278 and JP-A-57-167702.
When the purpose is to increase the selective permeability of water, as in the method described in
, -NH-, and -1-hydrophilic groups have been adopted. As a result of extensive research into membrane separation of organic aqueous solutions, the inventors of the present invention have found that, without changing the chemical structure of the membrane,
We discovered a method to significantly improve the separation performance of the membrane (permeation rate 9 separation coefficient) and arrived at the present invention. Here, permeation rate is the amount of liquid that permeates per unit time and unit membrane area expressed in weight. In this specification, y, tyr2.
It is displayed in units of "hr-".

The separation coefficient is expressed by the following formula: ○ Separation coefficient - (weight percentage of water in the permeate mixture V weight percentage of organic matter in the permeate mixture) / (weight percentage of water in the separated liquid v ' weight percentage of the water in the separated liquid) (% by weight of organic matter) That is, the present invention uses a non-porous uniform membrane with a thickness of 3 μm or less or a separation membrane having a non-porous skin layer to supply a gas mixture obtained by vaporizing an organic matter aqueous solution at one side of the layer, The method for separating an aqueous organic solution of the present invention relates to a method for concentrating an aqueous solution of organic matter, characterized in that the other permeation side is maintained at reduced pressure or brought into contact with an inert carrier gas to selectively permeate water vapor. I will explain in detail. In the pervaporation method, as described above, one separated liquid is supplied to the membrane in a liquid state, but in the membrane separation method according to the present invention, the separated liquid is vaporized and supplied to the membrane in a gaseous state.

The water selectively permeable membrane used in the pervelation method in the gas permeation method of the present invention has a membrane thickness of 10 μm to
Compared to the barbeparation method using a uniform membrane of 100 μm, the separation coefficient is improved in the range of 2 times or more and 1000 times or less, but the permeation rate is significantly lowered. However, in the pervaporation method, even if the film thickness is reduced as described above, there is no significant increase in the permeation rate;
In the separation method adopted in the present invention, it has been found that even with the same membrane material, by reducing the membrane thickness to 3 μm or less, the permeation rate can be significantly improved without causing a significant decrease in the separation coefficient. However, a film having a thickness of 3 μm or less usually has low mechanical strength when used alone, and it is difficult to withstand practical film performance evaluation. Therefore, in the present invention, 3 μm
A separation membrane such as a non-porous uniform membrane having the following membrane thickness:
A laminated membrane or a composite membrane which is laminated on another porous membrane or porous partition wall or formed on these porous membranes or porous partition walls is used. Or, by using the separation membrane material to produce an asymmetrically structured membrane having a dense layer (non-porous skin layer) of 3 μm or less and a porous support layer below it, it can withstand practical membrane performance evaluation. A separation membrane with strength can be obtained.

Materials for forming the separation membrane, which is a non-porous uniform membrane with a thickness of 6 μm or less, include cellulose having water selective permeability, hydrophilic polymers such as polyvinyl alcohol, polyvinylpyrrolidone modified or blended polymers, and Cellulose acetate such as cellulose diacetate, condensation synthetic polymers such as polyamide, polybenzimidazole, and polybenzimidazole, which are used as reverse osmosis membrane materials, as well as polyamides, polyamines, acrylonitrile polymers, and polyamides with crosslinked structures. For example, reverse osmosis membranes include ether-based synthetic polymers, etc.
O salt removal permeate concentration rate which is a membrane having performance of water permeation rate of o, snfAt-8 or more and salt rejection rate of 70% or more at a pressure of 40/J and a temperature of 25C for a 55% Na0j aqueous solution. is the feed concentration expressed as (1-) x 100%. Porous membranes and porous partition walls for reinforcing the non-porous uniform membrane used in the present invention include:

It is possible to use materials that have low gas permeation resistance and mechanical strength that allows practical handling. The materials used include natural polymers, synthetic polymers, and rigid metal/nonmetallic inorganic compounds. These materials can be prepared by known methods, but commercially available microphone filters, ultrap
It is also possible to use membranes, sintered metals, ceramics, etc. The shapes of these separation membranes include flat membrane types, tube types, and hollow fiber discs.

Since the membrane used in the present invention is a separation membrane that selectively permeates water from an aqueous organic solution, a relatively hydrophilic polymer is used as the membrane material.

In addition, since the separation membrane is a thin film with a thickness of 3t. Even if a porous membrane or a porous partition wall is used as a support for the separation membrane and the separation membrane is laminated thereon, or the separation membrane is formed on the porous membrane or the porous partition wall. Since the mechanical strength of the separation membrane decreases, it becomes difficult to handle it mechanically in practical use, or the separation coefficient decreases significantly.75 Therefore, according to the present invention, the separation membrane Since the gas permeation method is adopted in which the organic substance/water mixture is vaporized and brought into contact with the first fl!l as a gas mixture, even a separation membrane formed from a hydrophilic polymer can be used in a dry state. The strength of the separation membrane is that it is not swollen by an aqueous organic solution as in the case of the ration method, and there is little decrease in mechanical strength, so even a thin film of 3 μm or less can be used. - In the ventilation method, even if there is no blind crab or an extremely small separation film, the method according to the present invention provides excellent separation ability (expected 0) Separation and separation of aqueous organic matter solutions using multi-gas permeation method
As a membrane suitable for carrying out concentration, the perpeparation method has almost no separation property R, but the gas permeation method has excellent separation performance. Examples include membranes laminated or composited on the sexual septum. For example, a separation membrane in which a cellulose thin film or a silicone thin film with a thickness of 5 μm or less is laminated on a polyethersulfone ultrafiltration membrane has shown excellent performance in separating and concentrating ethanol aqueous solutions, acetic acid aqueous solutions, etc. by the gas permeation method. In addition, reverse osmosis membranes with an asymmetric structure of cellulose acetate (non-porous skin layer thickness of 3 μm or less), reverse osmosis membranes that do not exhibit separation performance using the pervaporation method, and reverse osmosis membranes plasma-treated with nitrogen-containing monomers or polymers ( A composite membrane made of polyacrylonitrile plasma polymer is available from Sumitomo Chemical under the trade name Solrox.

See Japanese Patent Application Laid-open No. 137405/1983. ), a reverse osmosis membrane formed by in 5 in situ polymerization of a thin polyamide film on a porous support (as a polyamide/polysulfone composite membrane?
Product name of i1m-Tech, Corp. FT-! So
There is. Separation membranes such as those disclosed in JP-A-55-147106 have shown excellent separation performance in the gas permeation method of the present invention, as shown in Examples below.

In the perpetuation method, since the separation liquid is supplied to the t-liquid liquid separation membrane, the temperature of the separation liquid is below the boiling point of the separation liquid, preferably at least 5C lower than the boiling point. However, in the present invention, since the separated liquid is supplied as a gas mixture to the primary side of the membrane, the temperature of the separated gas mixture can be raised up to the allowable temperature limit of the membrane. The higher the concentration (or partial pressure) of the separated gas mixture supplied to the separation membrane, the higher the water (water vapor) permeation rate, so increase the temperature of the separated liquid to increase the partial pressure of the separated gas mixture. It's good. Therefore, it is preferable to keep the liquid temperature at the boiling point. The total pressure of the gas supplied to the separation membrane is preferably atmospheric pressure, but it is also possible to pressurize the gas mixture to an extent that does not condense. The difference in vapor pressure between the separated mixed gas at K (side) and K is preferably 0.3 kg·crn-2 or more, more preferably 0.05 to 9·crn-2 or more. According to the present invention, water ( The membrane permeation rate for water vapor) is
The separation coefficient can be improved to a degree comparable to that of the barbeparation method, and the separation coefficient can also be significantly higher than that of the barbeparation method. In carrying out the present invention, the pressure on the membrane permeation side is maintained at reduced pressure, and the higher the degree of reduced pressure, the higher the membrane permeation rate. The degree of vacuum required is at least such that the permeate gas mixture does not condense. Normally 13000Pa (100Pa H7
) or less, preferably 130 OPa (10 degrees He) or less.

It is also possible to vent inert gas instead of reducing the pressure on the permeate side, but it is necessary that the separated gas mixture does not condense on the surface of the separation membrane. For this reason, it is necessary to maintain the separation membrane at a temperature higher than the temperature of the gas mixture in vapor-liquid equilibrium with the separation liquid. Therefore, it is preferable to maintain the temperature of the separation membrane at least 2C higher than that of the gas mixture.

Examples of organic compounds that can be applied to the method for separating an organic aqueous solution according to the present invention include methanol-ethanol, n-butanol, 1-propanol, 1n-butanol, 5ec
- Aliphatic alcohols such as butanol, tert-butanol, ethylene glycol, alicyclic alcohols such as cyclohenasanol, aromatic alcohols such as phenol,
Organic carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid,
These include ketones such as acetone and methyl ethyl ketone, cyclic ethers such as tetrahydrofuran and dioxane, and organic amines such as dibutylamine and aniline.In recent years, attempts have been made to produce ethanol from biomass; The concentration is 1
Therefore, in order to produce pure ethanol from this, conventionally, it was first concentrated to 95.6% by weight of the azeotropic composition by distillation, and then an entrainer such as benzene or ethyl acetate was added to this. and azeotropic distillation is performed in the second distillation column to produce pure ethanol. However, there is a drawback that a large amount of energy is required to remove a small amount of water from the azeotropic composition due to the reflux of the entrainer in the 20th azeotropic distillation tower. The method for separating aqueous organic matter solutions according to the present invention is promising as an alternative technology to these azeotropic distillations.

Of course, the pervaporation method is also considered as an alternative technique to this azeotropic distillation, but in the case of the pervaporation method, the distillate from the first distillation column is condensed and vaporized again by the membrane, which is a hassle. In this case, for example, in order to prevent the ethanol/water mixed vapor distilled from the first distillation column from decondensing, it is necessary to cool the Ir to 145C or less;
The cooled distillate is then subjected to membrane separation. However, when the gas permeation method according to the present invention is used, it is possible to membrane-separate the distillate gas mixture from the first distillation column as it is, so it is an advantageous method in terms of energy such as condensation, temperature increase, and vaporization. .

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

As mentioned above, the permeation rate (hereinafter abbreviated as Q) and the separation coefficient (hereinafter abbreviated as α) are used as a measure of membrane performance, and the superiority or inferiority of membrane performance must be evaluated based on the total of Q and α. No. In addition, when α is 1, it indicates that no separation function is exhibited at all, so Q and X(α-1) will be used in the following Examples and Comparative Examples as a comprehensive evaluation scale of membrane performance.

Example 1 A 5 weight aqueous acetic acid solution was refluxed under atmospheric pressure, and a gaseous mixture of acetic acid/water, which was in vapor-liquid equilibrium with the acetic acid aqueous solution at its boiling point (100 G), was heated to 105C.
-30 membrane CF' 11 m.

Tech, 0orp-jJJ (USA) Composite membrane for reverse osmosis; 0.2-thick polyamide with crosslinked structure
5μ formed on a porous polysulfone membrane]. The polyamide side of the FT-30 membrane was set to the reduced pressure side and maintained at 213 Pa (1,6 rHrrHy). The permeated vapor was condensed and collected in a liquid nitrogen cooling trap.

The concentration of acetic acid aqueous solution was determined by alkaline titration. Permeation rate 1.7 kg-m-2, hr-1, separation factor 6.
It was 0.

Comparative Example 1 (Perpevalation) In Example 1, a 5% by weight acetic acid aqueous solution (a5C) was supplied under atmospheric pressure instead of the acetic acid/water gas mixture in the separation membrane. Permeate side pressure reduction degree Fi226PFL (1°7 myn H
f). When the transmission velocity is 0.81 to 9 m-2
·hr-'' and separation coefficient of 1.5, both of which were smaller than those of Example 1.

Example 2 (1) Preparation of 2 μm cellulose laminated side Liethersulfone porous membrane: Cellulose Otsu 5 parts by weight, N,N-dimethylacetamide 184.5 parts by weight, Li0t8.5x
A cellulose solution prepared in bulk was cast onto a glass plate to a thickness of 5 ml (75 tc++), and immediately immersed in water to prepare a cellulose thin film. This membrane was manufactured by Daicel Chemical Industries, Ltd.
The dried cellulose was laminated on top of the membrane and left at room temperature for 24 hours to produce a dried cellulose l1ltffiholj ethersulfone membrane. The thickness of the dry cellulose membrane part is 2
It was the other side.

(2) 7% by weight ethanol water, the solution was refluxed under atmospheric pressure, and the gaseous mixture of ethanol/water generated at this time was heated to 99C. The gas mixture at this time was introduced into the cooling pipe, and the ethanol temperature of the condensate was measured.
It was 6% by weight. 186cm (1,4cm) on the other side of the membrane
The pressure was reduced to f). The transmission rate is 2.2 kf・z>+,
-hr s separation factor was 181.

Comparative Example 2 (Pervaporation) Example 2 (In Section 23, a 56% by weight ethanol aqueous solution of 45C was supplied to the membrane in place of the 56% by weight ethanol/water vapor mixture. Permeation rate 8.0k
g・tyt−2・hr−”, but the separation coefficient was 0.9
Ethanol selectively permeated through water.

Example S, 4.5 In Example 2, the membrane and evaluation conditions described in Table 1 were used as substitutes for the membrane described in Example 2-(0) and the evaluation conditions described in Example 2-(2J). Other than that.

I did exactly the same thing. Although the permeation rate was somewhat low, the separation coefficient was high and the membrane was practical. It was fabricated by immersing it in 1 ml, 1-10 panol, and 1 clj hexane for 30 minutes, and then air drying.

Comparative example 5. 4. 5 (Pervaporation) Example 3
, 4.5, the same weight % ethanol aqueous solution was used as a substitute for the ethanol/water gas temperature mixture, and the evaluation conditions listed in Table 1 were used instead of the membrane performance evaluation conditions described in Comparative Example 1. I did exactly the same thing. The separation coefficient was low and did not reach practical separation performance.

Example 6 (Gas Permeation) Instead of using the FT-50 membrane in Example 1, DUB-
0Y5 manufactured by Tone Silicone Co., Ltd. on the 40 membrane (polyethersulfone ultrafiltration membrane manufactured by Daicel Chemical Industries, Ltd.)
2-205 A composite membrane (dimethyl silicone layer thickness: 2 μm) prepared by applying a mixture of 10 parts of dimethyl silicone and 1 part by weight of catalyst and then heat-treating at 120C for 30 minutes was used under the conditions shown in Table 1. The material was tested using a gas permeation method, and the results shown in Table 1 were obtained.

Comparative Example 6 (Barbeparation) The results shown in Table 1 were obtained in the same manner as in Example 6 except that the pervelation method was used under the conditions shown in Table 1.

Claims (1)

[Claims] 1. A separation membrane having a non-porous homogeneous membrane or a non-porous skin layer with a thickness of 3 μm or less is used, and a gas mixture obtained by vaporizing an organic aqueous solution is supplied to one side of the layer. A method for concentrating an aqueous solution of an organic substance, characterized in that the other permeation side is maintained at a reduced pressure or brought into contact with an inert carrier gas to selectively permeate water vapor. 2. The concentration method according to claim 1, wherein the separation membrane is a membrane formed by laminating a non-porous uniform membrane with a thickness of 3 μm or less on a porous membrane or a porous partition wall. 3. The concentration method according to claim 1, wherein the separation membrane is a porous membrane or a composite membrane in which a non-porous skin layer is provided on a support made of a porous partition wall. 4. The concentration method according to claim 1, wherein the separation membrane is an asymmetric structure membrane formed from a non-porous skin layer and a porous structure of the same material supporting the non-porous skin layer. 5 The concentration method according to claim 2, wherein the non-porous uniform membrane is a cell 0-2 thin film. 6 The concentration method according to claim 2, wherein the non-porous uniform membrane is a silicone thin film. 7 6. A method of concentration according to claim 5, wherein the non-porous skin layer is polyamide. 8 The separation membrane is a polyamide thin film on a porous support for 1 ns.
The concentration method according to claim 7, which is a reverse osmosis membrane formed by ITU mixing. 9 The concentration method according to claim 3, wherein the separation membrane is a reverse osmosis membrane in which a nitrogen-containing monomer or polymer is plasma-treated. concentration method. 10 The concentration method according to claim 4, wherein the separation membrane is an asymmetric structure membrane of cellulose acetate having a non-porous skin layer with a thickness of 3 μm or less. 0, B ky layer or more Concentration method according to any one of claims 1 to 10 012 The separation membrane is 0.35 weight by weight - Na C3 aqueous solution is used as the feed liquid, and the pressure is 40 kg. //l, #, temperature 25
The water permeation rate when evaluating reverse osmosis performance in C is 0.5
n? 2. The concentration method according to claim 1, wherein the reverse osmosis membrane is a reverse osmosis membrane having a NaCjt rejection rate of 70% or more.