JPH0453571B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for selectively separating water-soluble organic compounds from a mixed liquid of water/water-soluble organic compounds by pervaporation using a synthetic polymer membrane. Distillation has long been known as a method for obtaining a water-soluble organic compound from a water/water-soluble organic compound mixed liquid, and is generally widely used. However, there is a drawback that a large amount of energy is consumed when obtaining an organic compound from a low concentration aqueous solution of an organic compound or when obtaining an organic compound from a mixed liquid of an organic compound/water having an azeotropic composition. As a way to overcome this difficulty, pervaporation methods using synthetic polymer membranes have been studied for some time.
This separation method is a method in which a liquid to be treated is supplied to the primary side of a polymer membrane, and substances that are easily permeable are allowed to permeate to the secondary side as vapor. The material of the polymer membrane used in this pervaporation method is selected from one that has an affinity for the component to be permeated. As an example of this method, Membrane, 8(3), 177 (1983) and J.Mem.Scl, 10, 253 (1982) use silicone rubber to
It has been reported that ethanol and isopropanol can be separated from a water mixture. However, these methods have the disadvantage that the separation coefficient of alcohol to water is low. JP-A-57-159501 describes a method of adding salt to the mixed liquid in order to improve the above-mentioned method and improve the separation efficiency. In this method, by adding inorganic salts such as lithium chloride, magnesium chloride, aluminum chloride, and sodium iodide, and fatty acid salts such as sodium acetate and potassium lactate to the mixed liquid, it is possible to improve the separation efficiency and the amount of permeation. It is written that it became. However, there is no mention at all of the difference between metal salt types, that is, the effect of the anion that is the ligand of the metal salt, and there is no mention of salts in which the anion is phosphoric acid. The present inventors conducted extensive studies on the effects of adding various metal salt compounds to the aqueous solution system in pervaporative separation of organic compound aqueous solutions using polymer membranes, and found that anions, which are ligands of metal salts, are separated. They discovered that this has an effect on efficiency and permeation performance, leading to the following invention. That is, in a pervaporation method that separates an organic component from a mixed solution consisting of water and a water-soluble organic component, this is a method for separating a water-soluble organic compound in which a metal salt of phosphoric acid is present in the mixed solution. The metal salt as used in the present invention is a metal salt in which the metal is selected from alkali metals such as lithium, sodium, potassium, rubidium, and cesium, and the ligand is phosphoric acid. Specific examples include phosphates such as sodium (di)hydrogen phosphate, sodium (di)hydrogen phosphate, sodium phosphate, potassium (di)hydrogen phosphate, potassium (di)hydrogen phosphate, and potassium phosphate. . Among these, potassium (di)hydrogen phosphate and potassium (di)hydrogen phosphate are particularly preferred. It is also possible to make a polymer compound having these compounds in its side chain exist in the mixed solution and in both the mixed solution and the polymer membrane. There are no particular restrictions on the method of adding the salt, but when adding an inorganic metal salt to the mixed solution, it is preferable to dissolve the metal salt in the mixed solution in advance. The salt concentration at this time is not particularly limited, but a high salt concentration is not preferred in practice. If the salt concentration is low, the effect of salt addition decreases, so a range of 0.1 to 20 wt% is preferable.
When using a polymeric metal salt as an additive, this range is not limited. The membrane used for separation is preferably a membrane that has excellent affinity with organic compounds, such as polyester, polyamide, polyurethane, polyimide, polyolefin in polyvinyl alcohol, cured epoxy resin, cellulose polymer compound, polysulfone, silicone polymer compound, polyvinyl alcohol, polyacrylonitrile, polymethacrylic acid ester,
Membranes obtained from homopolymers such as and copolymers thereof can be used, and can be appropriately selected depending on the components of the mixed liquid. The thickness of the separation membrane is not particularly determined, but is preferably 0.1 to 160μ. If the membrane has sufficient strength, it is practically preferable to make it as thin as possible, as this increases the amount of permeation. The shape of the membrane may be a flat membrane, for example, a cylindrical shape or a hollow fiber shape to increase the surface area of the membrane. The water/water-soluble organic compound mixed liquid in the present invention is a liquid in which an organic compound is uniformly dissolved in water, and examples include the following. Examples of organic compounds include alcohols (methanol, ethanol, propanol, isopropanol, etc.), organic acids (formic acid, acetic acid, propionic acid, butyric acid, etc.), organic acid esters (methyl acetate, ethyl acetate, etc.), and ketones (acetone, methyl ethyl ketone, etc.). ) cyclic ethers (dioxane, tetrahydrofuran, etc.)
Examples include compounds. It is also possible for the mixed liquid to contain two or more of the above compounds. Separation of the water-soluble organic compound from the water/water-soluble organic compound mixed liquid of the present invention is performed by a normal pervaporation method, and the pressure on the opposite side of the separation membrane that does not come into contact with the mixed liquid is the side that is in contact with the mixed liquid. The pressure must be lower than that of the The larger the pressure difference, the more effective it is, but preferably 0.01 to 100 mmHg. Both separation efficiency and permeation rate are improved by evaporating the substance that has passed through the membrane on the low-pressure side and taking it out in gaseous form. Therefore, it is preferable to maintain the low pressure side at a pressure lower than the vapor pressure of the substance passing through. There are two ways to keep the pressure low: by pulling a vacuum to reduce the pressure, or by flowing an inert gas to keep the vapor pressure low. The applicable temperature range for the separation method of the present invention may be within a range that does not cause thermal decomposition of the mixed liquid or denaturation of the membrane, but is preferably 0 to 100°C. The qualitative and quantitative effects obtained by the present invention will be described below based on Examples and Comparative Examples.
The present invention is not limited by these. Experiments Pervaporation Experimental Method The following experiment was conducted under atmospheric pressure on the supply side of the water/water-soluble organic compound mixture and under reduced pressure of 0.33 mmHg on the permeate side. With the active layer side of the membrane facing the supply side, the supply liquid was added onto the membrane surface and stirred at a constant temperature. The effective area of the membrane at this time is 15.2 cm ² . The water and organic compounds that permeated the membrane were condensed with liquid nitrogen and collected.
N-propanol was added to the permeate as an internal standard, and the permeation amount and separation coefficient were determined by TCD-gas chromatography. The separation coefficient a of ethanol with respect to water, a ^EtoH _H2O , is defined as follows. aEtOH/H ₂ O=YEtOH/YH _{2 O/XEtOH/XH 2 O} However, in the above formula, _XEtOH ,
represents the weight percent of ethanol and water in the permeate. Example 1 Polydimethylsiloxane resin (Shin-Etsu Chemical, EK
-45-TS) was coated on a Teflon plate to a thickness of 64 μm, and after being left at room temperature for 2 days, a polydimethylsiloxane film was obtained. The membrane thus obtained was set in a pervaporation device cell (effective area 15.2 cm ² ), and 100 ml of a 20 Vol% ethanol aqueous solution was added to the cell.
Add a solution containing 0.2 mol of sodium dihydrogen phosphate. After leaving the mixture in a constant temperature bath for about 30 minutes, while stirring the mixed liquid, the other side of the mixed liquid was sucked to about 0.35 mmHg using a vacuum pump to perform separation. The permeation rate at that time (unit: Kg・m/m ²・day),
and the separation coefficient a of ethanol to water, a ^EtoH _H2 O, were as shown in Table 1. Example 2 The same procedure as in Example 1 was carried out except that the metal salt was K ₂ HPO ₄ and the amount added was 0.1 mol. The permeation rate and separation coefficient were as shown in Table 1. Comparative Example 1 A polydimethylsiloxane membrane was synthesized by the same method as in Example 1, and the resulting membrane was set in a pervaporation device cell (effective area: 15.2 cm ² ), and 20 Vol% was contained in the cell.
Add 100ml of ethanol aqueous solution and place in a constant temperature bath at 40℃.
Leave for 30 minutes. Next, the other side of the mixed liquid was suctioned to approximately 0.3 mmHg using a vacuum pump to perform separation.
The results obtained are shown in Table 1. Comparative Examples 2 to 7 The same procedure as in Example 1 was conducted using sodium and potassium halides, and the results are shown in Table 1. Comparative Examples 8 and 9 The same procedure as in Example 1 was conducted using sodium and potassium acetates, and the results are shown in Table 1.

[Table] Example 3 2 gram equivalent metals each of sodium chloride, sodium bromide, sodium iodide, potassium chloride, potassium bromide, potassium iodide, potassium (di)hydrogen phosphate, and sodium (di)hydrogen phosphate/ 1-20Vol%
A liquid mixture of an aqueous ethanol solution was prepared. The water and ethanol activities {A(H ₂ O), A(EtoH)} in each mixed liquid were measured using headspace gas chromatography (manufactured by PerkinElmer). Its activity ratio {A(EtoH)/A(H ₂ O)} (this indicates the degree of ease of movement of ethanol with respect to water) and the separation coefficient in Examples 1 and 2 and Comparative Examples 1 to 7
a The relationship between ^EtoH and _H2O is shown in Figure 1. For sodium and potassium halides, there is a linear relationship between the activity ratio and the separation coefficient, but potassium(di)hydrogenphosphate and sodium(di)hydrogenphosphate deviate from this relationship. This means that phosphates in the ethanol aqueous solution have a different ethanol selective permeability effect than halides.

[Brief explanation of the drawing]

FIG. 1 shows the relationship between the activity ratio of water and ethanol and the separation coefficient.

Claims (1)

[Claims] 1. From a mixed liquid consisting of water and a water-soluble organic component,
A method for separating water-soluble organic compounds, characterized in that in the pervaporation method for separating the organic components, a metal salt of phosphoric acid is made to exist in the mixed liquid. 2. The separation method according to claim 1, wherein the metal is selected from the group consisting of lithium, sodium, potassium, rubidium, and cesium.