JPH0712420B2 - Separation membrane for dehydration - Google Patents

Description

Detailed Description of the Invention

The present invention relates to a separation membrane for dehydration for separating and concentrating an organic liquid aqueous solution, or for removing water contained in an organic solvent, particularly a water-soluble alcohol solution such as methanol, ethanol, or propanol. In particular, the present invention relates to a separation membrane for dehydration, which is characterized by exhibiting highly efficient separation performance for dehydration of a highly water-containing aqueous methanol or ethanol solution.

[0001]

[Industrial application] The membrane separation technology of the pervaporation method is a renewable technology which has been taken up as one of the solutions for separating and concentrating technology, especially energy saving in the dehydration process of organic solvents and solving future energy problems. Attention has been paid from two viewpoints of efficient concentration of alcohol in effective utilization of biomass energy. Therefore, in the former case, the target of separation is often a general organic liquid, and in the latter case, the separation of a water-alcohol mixed system, especially an ethanol aqueous solution, is often the goal of research and development. Separation membranes for separating the water-containing organic liquid containing the water-alcohol mixed system are roughly classified into two types, a water selective permeation type (for dehydration) and an alcohol selective permeation type.

[0002]

2. Description of the Related Art Regarding water selective separation membranes, which have been widely studied as dehydration membranes and partially put into practical use, there is an interaction in which the membrane material has a high affinity for water. However, electrostatic interaction and hydrogen bonding interaction are typical examples.

As water selective permeation type separation membranes focusing on electrostatic interaction, there are ion exchange membranes of cation exchange membranes and anion exchange membranes having ion exchange type charged groups in the membranes. As the cation exchange membrane, sulfonated polyethylene was used (J.Polym.Sci., Polym.Lett.Ed. 23 , 577, 1985) and Nafion hollow fiber was used (J.Memb.Sci.,
24 , 101, 1985), which similarly reported that the membrane performance was affected by counterions. Among the alkali metal ions, the smaller the hydration number, the more the water selectivity tended to improve. It is thought that this is due to complex effects such as the hydration number of the counterion, hydrogen bonding interaction, and the structure of the formed cluster. Furthermore, in this case, it is inferred that water permeates the ion cluster region formed by the charged groups present in the membrane, while alcohol permeates the membrane while dissolving and diffusing the amorphous portion in the membrane. .

As an example of separation of a water-ethanol mixed solution by an anion exchange membrane, a study example by a quaternized poly (4-vinylpyridine-co-acrylonitrile) membrane (J.Appl.Polym.Sci.,
33 , 2369, 1987). This membrane had a separation performance sufficient for practical use, except for the low permeation flow rate and durability.

Membrane materials having functional groups such as imide groups and carboxyl groups have been studied as separation membranes utilizing hydrogen bonding interaction. For example, a copolymer membrane having both imide groups and ester groups (Macromolecules, 19 , 47, 1986) gave a separation coefficient of 2000 or more, but its permeation rate is too low from the viewpoint of practical use. It was

[0006]

As described above, the typical interactions between the membrane and the permeate, which have a high affinity for water, include electrostatic interactions and hydrogen bonding interactions. Permeation type separation membrane has been developed, but other than this, strong interaction is not
There is a chemical affinity for a kind of hydrophilic polymer having a nonionic hydrophilic group.

However, conventional dehydration membranes utilizing these interactions are applied only to low-water-content organic solvents as separation targets, and generally, extremely low permeation flow rates are obtained in this low-concentration region. This is because these dehydrated membranes have a strong affinity for water in a high water content concentration region, so that not only the separation performance is deteriorated but also the membranes are destroyed. Therefore, there has been a strong demand for a dehydration membrane that can be applied to the concentration in the high water content region and has a high permeation flow rate.

[0008]

In order to overcome the above drawbacks, the present invention has variously studied other synthetic polymer materials,
As a result of repeated studies, a hydrophilic-hydrophobic monomer co-polymer which is composed of a homopolymer monomer component having a strong affinity for water-ethanol, that is, having a high solubility, but is insoluble in a water-ethanol mixed solution is used. Focusing on the polymer film, the present invention has been completed.

[0009] Electrostatic interaction and hydrogen-bonding interaction are considered to be necessary conditions for the preferential permeation of water and maintaining a high separation coefficient according to the studies so far. As can be seen in the examples of dehydration membranes up to
Separability is high and cannot be maintained for a highly water-containing mixture. Therefore, even if it is not a nonionic hydrophilic group, it needs a membrane material that has a chemical structure that weakens electrostatic or hydrogen interactions to some extent and that has a strong affinity for a water-alcohol mixed solution in order to increase the permeation flow rate. I knew it was.

The copolymer film of the present invention is a binary copolymer of methyl methacrylate, which is a hydrophobic monomer, and acrylic acid, which is a hydrophilic monomer, and is formed by a solvent evaporation method. In the dehydrated film of the present invention, only the copolymerization of methyl methacrylate and acrylic acid and the composition are examined, and an example in which a crosslinking agent is added has not been examined, but a crosslinked structure is formed by a crosslinking agent such as diepoxide or diamine. By doing so, it is considered that the separation performance and durability are improved.

[0011]

From a different point of view, the copolymer treated in the present invention is such that polymethylmethacrylate, which is a homopolymer of methylmethacrylate as a component, is dissolved in a water-ethanol mixed solution and The homopolymer polyacrylic acid is also partially dissolved in the water-ethanol mixed solution, if not completely dissolved, such that the homopolymer component of the copolymer is easily dissolved in the feed solution. I have it. In other words, the homopolymers of both components have a very high affinity for the water-ethanol mixed liquid to be separated even if they are classified into hydrophilic and hydrophobic. In the present invention, as described above, a hydrophilic monomer and a hydrophobic monomer respectively corresponding to the separation active domain which has been hydrophilized to impart the water-selective separation property and the structural support domain for suppressing the swelling caused by the separation active domain. It is considered that even the copolymer membrane made of (1) has a high affinity for the liquid to be separated, that is, a high-performance liquid separation behavior because it is a polymer film made of a soluble monomer.

[0012]

EXAMPLES Next, the present invention will be described more specifically by way of examples. In general, methyl methacrylate and acrylic acid monomers contain a polymerization inhibitor, so remove the polymerization inhibitor with an aqueous solution of sodium hydrogen sulfite or an aqueous solution of sodium hydroxide, filter once and perform vacuum distillation, and immediately after purification. used.

Copolymerization of methyl methacrylate and acrylic acid is carried out by using 0.05 mol% of the total amount of monomers, α, α'-azobisisobutyronitrile (AIBN) as an initiator, and conducting the sealed tube polymerization at 55 ° C. for 3 hours. And synthesized. When performing bulk polymerization, after adding methyl methacrylate and acrylic acid monomers into the polymerization ampoule tube, freeze-melt degassing was repeated using a vacuum line to remove dissolved air in the monomers, and then the monomer The polymerization tube containing was sealed and bulk polymerization was carried out. After the lapse of the polymerization time, it was dissolved in special grade tetrahydrofuran (THF) and reprecipitated for purification.

The solubility of several solvents known as solvents for methyl methacrylate and acrylic acid was investigated, and THF was selected as the solvent for forming the film of the copolymer of the present invention.
For film formation, methyl methacrylate-acrylic acid was completely dissolved in special grade THF to a concentration of about 2 wt% and cast on a leveled glass plate. After drying, the entire glass plate was immersed in deionized water to peel off the film. The stripped film was stored in deionized water until used in the next experiment.

For the purpose of increasing the water content of the copolymer film and increasing the permeability, a modification reaction was carried out to convert the carboxyl groups of acrylic acid in the copolymer film into Na type (-COONa). 1N
After immersing the membrane in the aqueous sodium hydroxide solution described above and leaving it at room temperature for 24 hours, the membrane was taken out and washed with deionized water.

In the examples, the permeation rate and the separation coefficient were measured by using an ordinary measuring device for pervaporation. Measuring device shown in Fig. 1 (effective area 15.9 cm ² )
Attach a separation membrane to the, supply a mixture of water-methanol, water-ethanol, water-2-propanol, etc. to the supply under atmospheric pressure, and keep the exhaust side at 0.1 mmHg or less with a vacuum pump. did. The weight composition of the feed liquid and the permeate was measured by a gas chromatograph, and the separation coefficient was calculated by the following formula (1).

[A] ₁ and [B] ₁ : Weight fraction of A (water) and B (alcohol) before permeation through the membrane [A] ₂ and [B]
₂ : Weight fraction of A (water) and B (alcohol) after permeation through the membrane The permeation rate was calculated by the following formula (2).

[Chemical 2]

Example 1 The charging ratio (mol%) of methyl methacrylate and acrylic acid was 8
Polymerization was performed at 9:11 to obtain a copolymer. A tetrahydrofuran solution of this copolymer was cast on a glass plate and the solvent was gradually evaporated at room temperature to obtain a separation membrane for dehydration having a thickness of 23 μm. The separation membrane 12 was attached to the liquid permeation cell 6 of the measuring device shown in FIG. 1 and a dehydration separation experiment of a methanol aqueous solution was conducted. The results of the dehydration experiment are shown in Table 1.

Example 2 A dehydration separation experiment was conducted in exactly the same manner as in Example 1 except that a dehydration separation membrane having a film thickness of 21 μm was used and an ethanol aqueous solution was supplied as an alcohol aqueous solution to be separated. The results of the dehydration experiment are shown in Table 2.

Example 3 A dehydration separation experiment was conducted in exactly the same manner as in Example 1 except that a dehydration separation membrane having a film thickness of 20 μm was used and an aqueous alcohol solution to be separated was supplied with a 2-propanol aqueous solution. . The results of the dehydration experiment are shown in Table 3.

Example 4 The charging ratio (mol%) of methyl methacrylate and acrylic acid was 8
Polymerization was performed at 0:20 to obtain a copolymer. A tetrahydrofuran solution of this copolymer was cast on a glass plate and the solvent was gradually evaporated at room temperature to obtain a dehydration separation membrane having a thickness of 13 μm. The separation membrane 12 was attached to the liquid permeation cell 6 of the measuring device shown in FIG. 1 and a dehydration separation experiment of a methanol aqueous solution was conducted. The results of the dehydration experiment are shown in Table 4.

Example 5 A dehydration separation experiment was conducted in exactly the same manner as in Example 4 except that a dehydration separation membrane having a film thickness of 16 μm was used and an ethanol aqueous solution was supplied as the alcohol aqueous solution to be separated. The results of the dehydration experiment are shown in Table 5.

Example 6 A dehydration separation experiment was carried out in exactly the same manner as in Example 4 except that a dehydration separation membrane having a film thickness of 16 μm was used and an aqueous 2-propanol solution was supplied as the alcohol aqueous solution to be separated. . The results of the dehydration experiment are shown in Table 6.

Example 7 The charging ratio (mol%) of methyl methacrylate and acrylic acid was 9
Polymerization was performed at 5: 5 to obtain a copolymer. A tetrahydrofuran solution of this copolymer was cast on a glass plate and the solvent was gradually evaporated at room temperature to obtain a separation membrane for dehydration having a film thickness of 14 μm. The separation membrane 1 is provided in the liquid permeation cell 6 of the measuring device shown in FIG.
2 was attached and the dehydration separation experiment of the methanol aqueous solution was performed. The results of the dehydration experiment are shown in Table 7.

Example 8 A dehydration separation experiment was conducted in exactly the same manner as in Example 7 except that a dehydration separation membrane having a thickness of 12 μm was used and an ethanol aqueous solution was supplied as the alcohol aqueous solution to be separated. The results of the dehydration experiment are shown in Table 8.

Example 9 A dehydration separation experiment was conducted in exactly the same manner as in Example 7, except that a dehydration separation membrane having a film thickness of 15 μm was used and an aqueous alcohol solution to be separated was supplied with a 2-propanol aqueous solution. . The results of the dehydration experiment are shown in Table 9.

Example 10 The charging ratio (mol%) of methyl methacrylate and acrylic acid was 8
Polymerization was performed at 5:15 to obtain a copolymer. A tetrahydrofuran solution of this copolymer was cast on a glass plate and the solvent was gradually evaporated at room temperature to obtain a dehydration separation membrane having a thickness of 16 μm. The separation membrane 12 was attached to the liquid permeation cell 6 of the measuring device shown in FIG. 1 and a dehydration separation experiment of a methanol aqueous solution was conducted. The results of the dehydration experiment are shown in Table 10.

Example 11 A dehydration separation experiment was conducted in exactly the same manner as in Example 10 except that a dehydration separation membrane having a film thickness of 12 μm was used and an ethanol aqueous solution was supplied as an alcohol aqueous solution to be separated. The results of the dehydration experiment are shown in Table 11.

Example 12 A dehydration separation experiment was carried out in the same manner as in Example 10 except that a dehydration separation membrane having a film thickness of 16 μm was used and an aqueous alcohol solution to be separated was supplied with a 2-propanol aqueous solution. . The results of the dehydration experiment are shown in Table 12.

[0020]

As shown in Examples 1 and 2, a very high value of a separation factor of water of 5000 or more was obtained for each aqueous solution of methanol and ethanol. In addition, the separation coefficient was 5000 even with the aqueous ethanol solution of Example 5.
The above is shown. These high separation performances were achieved with an aqueous alcohol solution having a water content of 80% in a high water content concentration range, and the dehydration membrane of the present invention was excellent in dehydration of a high water content alcohol, generally a high water content organic solvent. It has advantages. At the ethanol concentration of 22% in Example 5, the permeation flow rate is about 0.7 kg / m ² Kg, which is not a small value. As described above, it is a great advantage that the dehydration membrane of the present invention exhibits highly efficient separation performance against the dehydration operation of the highly water-containing organic solvent, which has been the long-awaited demand for the dehydration separation membrane.

[Brief description of drawings]

FIG. 1 is a measuring device used for measuring the permeation separation characteristics of a dehydration separation membrane of the present invention.

[Explanation of symbols]

 1 ... Vacuum pump 2 ... Cold trap 3 ... Glass cock 4 ... Rotating macleod 5 ... Cold trap for collecting permeated vapor 6 ... Liquid permeation cell 7 ... Stirring motor 8 ... Stirrer 9 ... Immersion heater 10 ... Electronic relay 11 ... Constant temperature water tank 12 ... Separation membrane 13 ... Alcohol aqueous solution 14 ... Permeation side chamber

Claims (1)

[Claims] 1. From methyl methacrylate and acrylic acid
Separation membrane for dehydration obtained by forming a binary copolymer of