JPS6144523B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for membrane-separating a water-organic liquid mixture by pervaporation. Distillation has long been known as a method for separating organic liquid mixtures and is generally widely used.
However, in the distillation method, it is extremely difficult to separate azeotropic mixtures, near-boiling point mixtures, heat-denatured mixtures, and the like. For example, in order to separate a water-ethanol azeotrope by distillation, it is necessary to add a third component (eg benzene) and carry out azeotropic distillation at a high reflux ratio. Therefore, the amount of energy consumed is large, and it is difficult to avoid the third component from being mixed into the final product. In order to solve these difficulties, methods for separating liquid mixtures in a gas-liquid system using polymer membranes have been studied for a long time.
It has been proposed in No. 2953502, etc. This separation method is called pervaporation, in which the liquid to be treated is supplied to the primary side (high pressure side) of the polymer membrane, and substances that are easily permeable are preferentially converted into vapor on the secondary side (low pressure side). This is a method that allows the information to pass through. The polymer membrane material used in this pervaporation method is
Membranes that have an affinity for the components to be permeated in the liquid to be separated are selected, and conventional membranes made from polyethylene, polypropylene, cellulose acetate, cellulose, polyester, polyamide, polyethane, polyacrylonitrile, polytetrafluoroethylene, etc. Are known. However, since these are homogeneous membranes (films) with a thickness of 10 to 100 μm, the liquid permeation rate is extremely low, and the separation performance is also unsatisfactory. The permeation rate can be improved by reducing the film thickness, but if the film thickness is less than 5 μm, the mechanical strength becomes insufficient and it is difficult to put it into practical use. The present inventors have conducted intensive studies to solve the above drawbacks, and have found that by forming an ultra-thin film layer with a specific structure on a microporous support membrane, it has mechanical strength and extremely high separation properties. It was discovered that a membrane could be obtained, and the present invention was achieved. That is, when separating a water-organic liquid mixture by pervaporation, the present invention crosslinks polyethyleneimine with a bifunctional aromatic crosslinking agent for acid halide groups and/or isocyanate groups on a microporous support membrane. This is a method for separating a water-organic liquid mixture, which is characterized by using a composite membrane obtained by reaction. The composite membrane used in the present invention is produced by a manufacturing method known in the field of reverse osmosis membranes, which perform liquid-liquid separation (for example,
-103945)).
In other words, polyethyleneimine (hereinafter abbreviated as PEI)
A solution of the above is applied onto a microporous support membrane, followed by contact with a solution of the bifunctional crosslinking agent, followed by dry heat treatment to form a crosslinked ultra-thin film layer insoluble in water and organic liquids on the support membrane. The desired composite film can be obtained by forming the desired composite film. The manufacturing method will be described in more detail below. The polyethyleneimine used in the present invention is obtained by polymerizing ethyleneimine, and is highly branched with a ratio of primary, secondary, and tertiary nitrogen atoms of approximately 1:2:1. Any molecular weight between 300 and 100,000 can be used, and these commercially available products can be used as they are without purification. The solvent for preparing the PEI solution may include water, methanol, ethanol, etc., but water is most preferred for the purposes of the present invention. The PEI concentration in the solution is 0.05-10.0% by weight, preferably 0.1-10.0% by weight
It is 5.0% by weight. As a method for applying the PEI solution onto the microporous support membrane, conventionally known methods such as a dipping method, a casting method, a spray method, etc. can be employed. After removing excess solution, the support membrane coated with the PEI solution is dried to remove the solvent at room temperature or under heat, and then brought into contact with the crosslinking agent solution. Acid halide group and/or used in the present invention
Or as a bifunctional crosslinking agent containing an isocyanate group, dicarboxylic acid dihalides such as aliphatic, alicyclic and disulfonic acid dihalides having 1 to 20 carbon atoms, and aromatic dihalides having 5 to 20 carbon atoms, disulfonic acid dihalides diisocyanates, Alternatively, stabilized diisocyanates and the like may be mentioned. Examples of these are adipic chloride, sebacyl chloride, fumaric chloride,
Succinic acid chloride, isophthalic acid chloride, terephthalic acid chloride, 4,4-benzophenonedicarboxylic acid chloride, 1,4-naphthalenedicarboxylic acid chloride, 1,4-cyclohexanedicarboxylic acid chloride, etc., 1,3-benzenedisulfonic acid chloride, Examples include 1,4-benzenedisulfonic acid chloride, 1,4-naphthalenedisulfonic acid chloride, ethylene diisocyanate, propylene diisocyanate, tolylene diisocyanate, naphthalene diisocyanate, methylene bis(4-phenyl isocyanate), and the like.
Among these, aromatic crosslinking agents are particularly preferred. Also included in the bifunctional crosslinking agent are those which form a diacid halide by themselves. Examples of this include oxalyl chloride, phosgene, thionyl chloride, and the like. Each bifunctional crosslinking agent may be used alone,
Also, a mixture of two or more types may be used. The reaction between PEI and the crosslinking agent is usually carried out by immersion in a solution of the crosslinking agent. The solvent for the crosslinking agent solution is selected from those that do not dissolve PEI and the support film, and n-hexane, heptane, octane, cyclohexane, etc. can be suitably used. The purpose can be effectively achieved by setting the concentration of the crosslinking agent in the solution to 0.05 to 10.0% by weight, preferably 0.1 to 5.0% by weight. The thickness of the thin film layer obtained in this way ranges from several hundred Å to 1
It is about μ. When applying acid halides as crosslinking agents,
Hydrogen halide is produced as a by-product by reaction with amine. This is accepted by PEI itself and the reaction proceeds, but caustic alkali, sodium phosphate, sodium acetate, pyridine, triethylamine, etc. can also be used as a promoter. These reaction accelerators (hydrogen halide acceptors) can be added directly to the PEI aqueous solution before the crosslinking reaction, or can be added in a separate step after the crosslinking reaction. Although the crosslinking reaction proceeds even at low temperatures, it is desirable to carry out a dry heat treatment in order to obtain a suitable crosslinking density. The dry heat treatment temperature is in the range of 60 to 150°C, preferably 90 to 130°C, and the dry heat treatment time is in the range of 1 to 60 minutes, preferably 5 to 30 minutes. The PEI crosslinked composite membrane that has been subjected to the dry heat treatment may be coated with a protective coating such as polyvinyl alcohol or polyvinylpyrrolidone at an appropriate stage before it is made into a module, if desired. The microporous support film referred to in the present invention is coated with
Although there is no particular limitation as long as it does not dissolve or swell in the PEI solvent or the crosslinking agent solvent, it is desirable that an asymmetric microporous membrane structure can be easily created and that it has excellent chemical resistance and PH resistance. Suitable examples of such a microporous support membrane include, but are not limited to, polysulfone and polyvinyl chloride.
In particular, polysulfone has excellent performance as a material for the microporous support membrane of the present invention. The polysulfone microporous support membrane can be manufactured by a known method, for example, the method described in U.S. Department of the Interior, Bureau of Salt Water, Research and Development Report, No. 359. It is preferable that such a membrane material has a surface pore size of generally between about 100 and 1000 Å, but is not limited to this, and the surface pore size may vary depending on the final use of the membrane. It can vary between ~5000 Å. These substrates can be used in asymmetrical or symmetrical configurations. A preferable supporting membrane constant is 1 to 10 ^-4 g/cm ² .
sec・atm, particularly preferably 10 ⁻¹ to 10 ⁻³ g/cm ²・se
c・a
tm range. Note that the membrane constant here is a value representing the amount of pure water permeated under a pressure of 2 Kg/cm ² . The supporting membrane may have any shape such as hollow fiber, flat plate, or tubular shape. In the case of a flat or tubular shape, it is preferable to use it with the back side reinforced with woven or non-woven fabric. Such woven fabrics and non-woven fabrics include:
polyethylene terephthalate, polypropylene,
Preferred examples include those made of nylon or vinyl chloride. Since the composite membrane thus obtained has a high affinity for water, it becomes possible to selectively permeate water from the water-organic liquid mixture and increase the concentration of organic matter in the mixture to be separated. In the present invention, the active layer agent (PEI crosslinked thin film layer side) of the membrane is brought into contact with the feed liquid (primary side), and the substance that has permeated through the membrane is taken out in a gaseous state from the secondary side. Therefore, it is necessary to reduce the pressure on the secondary side or to flow an inert gas such as air to keep the chemical potential lower than that on the primary side. The pressure on the primary side can be applied within the range of 1 to 100Kg/cm ² , but preferably from atmospheric pressure to 10Kg/cm ²
It is. When reducing the pressure on the secondary side, below atmospheric pressure,
Preferably 400mmHg or less, more preferably 100mm
It is best to maintain a vacuum below Hg. The applicable temperature in the separation method of the present invention is 0 to 100
℃, preferably 0 to 90℃. It has been known that in pervaporation using a membrane, the higher the operating temperature, the higher the permeation rate, but the lower the separation coefficient. However, it has been found that the membrane used in the present invention has a large permeation rate and separation coefficient depending on the type of liquid to be separated. Therefore, in such cases, separation at high temperatures is considered advantageous. Water-organic liquid mixtures that can be separated in the present invention include water/isopropyl alcohol, water/ethyl alcohol, water/n-propyl alcohol, water/allyl alcohol, water/2,3-dichloro-1-propanol, water/ 2-methoxyethanol, water/
Isobutyl alcohol, water/1-butanol,
Water such as water/2-butanol, water/furfuryl alcohol, water/1-pentanol, water/2-pentanol, water/4-methyl-1-butanol, etc.
Alcohol mixtures; examples include water-organic solvent systems such as water/tetrahydrofuran, water/dioxane, and water/methyl ethyl ketone. Among these, the present invention can be particularly advantageously used for separating an azeotropic mixture of water and alcohols. The composite membrane used in the present invention can be used in the form of a hollow module, spiral module, plate/frame module, or tubular module depending on the form of the microporous support membrane.
Among them, hollow modules can be used particularly advantageously because they can provide a large membrane area within a certain volume. Hereinafter, the present invention will be explained in more detail with reference to Examples. Pervaporation experimental method The supply side of the water/organic liquid mixture was conducted under atmospheric pressure, and the collection side was conducted under reduced pressure of 0.3 mmHg. The active layer surface (ultra-thin film surface) of the membrane was directed toward the supply side, and the feed liquid kept at a constant temperature was circulated over the membrane surface. The effective area of the membrane is
It is ^11.0cm2 . The water and effective liquid that permeated the membrane were condensed and collected, and the amount of permeation (Flux) was determined in units of Kg/m ² ·hr. In addition, the composition ratio of the collected liquid was determined by TCD-gas chromatography, and the separation coefficient (α) of the membrane was determined. Note that the separation coefficient α is defined as follows. αA/B=yA/yB/xA/xB However, in the above equation, xA and xB are the weight percent of components A and B in the feed liquid, and yA and yB are the weight percent of components A and B in the collected liquid (permeate liquid). It is expressed in weight %, and component A indicates a component that selectively permeates. Since the membrane used in the present invention selectively permeates water from any water-organic liquid mixture, the A component is water.

[Table] Example 2 Using the composite membrane obtained in Example 1, the separation characteristics for each composition of a water-ethanol mixture were measured at an operating temperature of 30°C.
The results were as shown in Table 2.

[Table] Example 3 Using the composite membrane obtained in Example 1, the separation characteristics of an azeotropic mixture system of water/isopropanol = 12/88 (wt%) were measured and showed excellent values as shown in Table 3. Ta.

[Table] Example 4 Using the composite membrane obtained in Example 1, the separation characteristics of each composition of a water-isopropanol mixture were measured at an operating temperature of 30°C, and the results were as shown in Table 4.

[Table] Example 5 In Example 1, toluene-
A composite membrane was formed in exactly the same manner except that isophthalic acid chloride was used instead of 2,4-diisocyanate, and water/ethanol = 4.5/95.5 (wt%).
When the separation characteristics of the azeotropic mixture system were measured at various temperatures, as shown in Table 5, the higher the temperature, the more
The same phenomenon as in Example 1 was observed in that both Flux and α increased.

[Table] Example 6 Using the composite membrane obtained in Example 5, the separation characteristics for each composition of water-ethanol mixture were measured at an operating temperature of 30°C.
The results were as shown in Table 6.

[Table] Example 7 Using the composite membrane obtained in Example 5, the separation characteristics of an azeotropic mixture system of water/isopropanol = 12/88 (wt%) were measured, and the results were as shown in Table 7.

[Table] Example 8 Using the composite membrane obtained in Example 5, the separation characteristics for each composition of a water-isopanol mixture were measured at an operating temperature of 30°C.
When measured at °C, the results were as shown in Table 8.

【table】

Claims (1)

[Claims] 1 When a water-organic liquid mixture is separated by pervaporation, polyethyleneimine is crosslinked with a bifunctional aromatic crosslinking agent for acid halide groups and/or isocyanate groups on a microporous support membrane. A method for separating a water-organic liquid mixture, the method comprising using a composite membrane comprising: