JPH0454484B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION The present invention relates to a method for membrane separation of specific component substances from a liquid mixture. More specifically, the target component to be separated in a liquid mixture is concentrated inside large particles formed using a liquid containing a compound that reversibly forms a complex with the target component, and the large particles are separated under an electrostatic field. The present invention relates to a method for transporting and separating substances using a porous polymer membrane. BACKGROUND ART Various techniques for separating only specific component substances from a homogeneous liquid mixture have been studied in the past, and one of the techniques most widely put into practical use at present is the distillation method.
However, near-boiling point mixtures and azeotropic mixtures require repeated distillation several times or azeotropic distillation in order to separate them at high concentrations, which requires a large amount of energy. Further, vacuum distillation and steam distillation are used to separate components that are easily decomposed at high temperatures near the boiling point, but in this case, more energy is required than normal pressure distillation. Therefore, there is a need to develop a technology for separating liquid mixtures to replace the distillation method, and membrane separation methods are currently attracting attention. Problems to be Solved by the Invention However, in the current membrane separation technology, both separation and permeability are considered to be different, such that if the separation is high, the permeability is low, or if the permeability is high, the separation is low. Membrane separation technology that can increase the size of both has not yet been obtained. Therefore, in order to put it into practical use, it is necessary to reduce the membrane thickness to increase liquid permeability, or to compensate for poor selectivity by multi-stage membrane permeation, and for the former, the membrane strength is insufficient. In the latter method, there were problems such as the device becoming complicated. Under such circumstances, the present inventors investigated the relationship between the separation performance of substances and the average pore diameter of polymer membranes in order to realize membrane separation technology for substances that increases both separation performance and permeability at the same time. , we have achieved this technology. In other words, as a result of intensive studies focusing on the fact that the diffusion rate of molecules in liquids is 10 to ¹⁰³ times higher than that in solids and that the permeation rate of liquids through porous polymer membranes is high, we have found that the above objectives can be achieved satisfactorily. The present invention has been achieved to achieve this goal. Means for Solving the Problem The present invention provides a method for separating a liquid mixture by removing a compound that reversibly forms a complex with a component to be separated by 0.001.
Large particles are formed in the liquid mixture to be separated using a liquid that is contained at a concentration of mol/1 or more and is not mutually soluble in the liquid mixture to be separated, and the component to be separated is concentrated inside the large particles, and an electrostatic field is applied. This membrane separation method is characterized in that the large particles are separated by the porous polymer membrane while the large particles are transported to the surface of the porous polymer membrane at the bottom. First, the liquid mixture in the present invention refers to a liquid mixture of two or more components that is in a uniform one-phase liquid state under separation operation conditions, and is a liquid with a large latent heat of vaporization that consumes a large amount of energy in separation by distillation. The present invention is particularly useful for separating liquid mixtures or near-boiling liquid mixtures containing . Examples of such liquid mixtures include aqueous solutions of alcohols such as methanol, ethanol, n-propanol, isopropanol, t-butanol, aqueous solutions of acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, pyridine, acetic acid, etc., and methylcyclohexane/toluene, cyclohexane. /toluene and the like can be mentioned. Furthermore, the present invention can also be applied to the separation of gas dissolved in a liquid. From such a liquid mixture, the target component to be separated is concentrated inside large particles formed using a liquid containing a carrier, and the surface charge of the large particles is used to cause particle transport under an electrostatic field. While transporting the large particles to the surface of the porous polymer membrane, the particles are separated by the porous polymer membrane. Surface charging of large particles occurs due to the dielectric constant difference between the particle liquid and the liquid mixture or the localization of ion concentration near the interface, but a small amount of polar molecules may be added for the purpose of positively charging the particles. . The average diameter of large particles at this time is 0.1 μm to 10 μm.
It is preferably within the range of m. Particle size is 0.1μm
If the diameter is less than 10 μm, particle transport will not be achieved efficiently due to the Brownian motion of the particles, and if the particle diameter exceeds 10 μm, the surface area per unit volume of the particles will become small.
The amount of mass transfer at the particle interface per unit volume of particles decreases, resulting in a decrease in separation performance. Next, when concentrating the target component to be separated from the liquid mixture into large particles, the liquid containing the carrier is used to form large particles in the liquid mixture to be separated. Here, the carrier is a substance that is inert to substances other than the target component in the liquid mixture, selectively forms a complex only with the target component, and has such properties that this complex formation reaction occurs reversibly. Refers to a substance. If the target component is recovered from the complex formed by the carrier and the target component, the carrier remains and can be reused as it is. Examples of carriers exhibiting such properties include 1,1,6,6-tetraphenyl-2,4-hexadiyn-1,6-diol or ,1,4,4-tetraphenyl-
When the liquid mixture is an aqueous alcohol solution such as methanol, ethanol, isopropanol, or t-butanol, an acetylene diol compound such as 2-butyne-1,4-diol can be added to 9-fluoren-9-ol, 9-(1 Fluorenol compounds such as -propynyl) can be used. In addition, a liquid containing a carrier means a liquid that dissolves 0.001 mol/or more of a carrier and does not dissolve itself mutually with a liquid mixture,
The carrier is selected to retain selective reversible complexing ability. According to the membrane separation method of the present invention using a liquid containing such a carrier, it is possible to obtain a separation coefficient exceeding the value achieved under thermodynamic equilibrium conditions. This is thought to be because the carrier is localized at the particle interface, increasing the rate of incorporation of the target component into the particle, and the particles are separated by the porous polymer membrane before thermodynamic equilibrium is reached.
The carrier concentration in the liquid containing the carrier is
When the amount is less than 0.001 mol/mol, the above effect is small and the amount of the target component incorporated into the particles is small, resulting in a decrease in separation efficiency. Therefore, the carrier concentration is
0.001 mol/or more is preferable. In addition, in order to prevent the liquid containing the carrier from dissolving mutually with the liquid mixture to be separated, for example, if the liquid mixture is an aqueous solution, it is necessary to
The solubility in water at ℃ and 1 atm is 0.1 (g/100
g) The following is preferable. Solubility in water
If it exceeds 0.1, the liquid containing the carrier and the aqueous solution that is the liquid mixture will partially dissolve in each other, making it impossible to form particles, resulting in a decrease in the recovery rate of particles when they are separated using a porous polymer membrane. Additionally, by stirring the liquid mixture to which the carrier-containing liquid is added, large particles can be formed that concentrate the components to be separated. As a stirring method, not only mechanical stirring but also ultrasonic vibration and the like can be used. Also,
By adding a surfactant and stirring, more stable large particles can be formed. The diameter of large particles can be set by controlling the amount of surfactant added and the stirring time, and large particles with a diameter of 0.01 μm to 10 μm can be formed. Inside the particles formed in this way, particles/
Due to mass transfer at the interface of the liquid mixture (matrix), the target component is concentrated inside the large particles,
By utilizing the surface charge of the particles and creating a potential difference between the membrane surface and the liquid mixture, the particles are transported to the surface of the porous polymer membrane while reducing the pressure difference on both sides of the membrane and the interfacial tension difference between the particles and the matrix. Using
Particles are separated by a porous polymer membrane. Here, the potential difference is the driving force that generates an electric force due to the surface charge of the particles and efficiently transports the particles to the membrane surface.When the particles are positively charged, the membrane through which the particles pass becomes negatively charged, and the particles If the particles are negatively charged, a potential difference is provided so that the membrane through which the particles pass becomes positive. By creating a potential difference between the membrane surface and the liquid mixture, the amount of particles passing through the porous membrane can be increased. In order to increase the surface charge of particles, it is effective to use an ionic surfactant during particle formation. Among these, anionic surfactants are preferred as the surfactant from the viewpoint of particle transport efficiency under an electrostatic field utilizing surface charge of particles. The reason for this is not clear, but particle movement occurs together with secondary ions that have the same charge as the particles. When the surfactant is anionic, the secondary ions are hydroxide ions, and when the surfactant is cationic, the secondary ions are hydrogen ions. It is thought that particle transport efficiency is better when using an anionic surfactant than a cationic surfactant due to the difference in mobility between the surfactant and the hydroxyl ion. Furthermore, when the liquid mixture is an aqueous solution and particles are formed using an ionic surfactant with an HLB value of 8 or more, separation of the surfactant can be achieved simultaneously with particle separation using a porous polymer membrane. In addition, the surfactant
HLB titer ( Hydrophilic Lipophilic Balance )
Griffin, WC (J.Soc.Cosmetic Chemists, 1
(1949)) for nonionic surfactants, and later Davies (2nd Inter.Congress of
Surface Activity, 1 (1957)), it came to be applied to all surfactants. The HLB value in the present invention is determined by the Davies method. Ionic surfactants with an HLB value of 8 or higher form stable O/W emulsion-like particles, but when these particles are passed through a hydrophobic polymer porous membrane, only the particle phase passes through the membrane, and most The surfactant can be blocked by the hydrophobic polymer porous membrane and left in the matrix phase. Furthermore, when passing through a hydrophilic polymer porous membrane, only the matrix phase (liquid mixture) containing most of the surfactant passes through the membrane.
Particles formed using an ionic surfactant with an HLB value of less than 8 can also be separated using a porous polymer membrane, but separation of the surfactant and the particle phase is not always possible. Particles transported in this way can be separated into a particle phase and a matrix phase by a porous polymer membrane by utilizing the interfacial tension with the matrix phase that has phase-separated into an emulsion and the pressure difference on both sides of the membrane. . The porous polymer membrane in the present invention preferably has an average pore diameter of 0.02 μm or more and a gravimetric porosity of 40% or more, and includes polyethylene, polypropylene, polyvinylidene fluoride, polytetraroethylene, polysulfone, PVC,
Porous polymer membranes made of polymers or copolymers such as polyvinyl alcohol, polyamide, cellulose, etc. are suitable. If the average pore diameter is less than 0.02 μm, the permeability of the membrane will be low, and if it is 50 times or more the particle diameter, the particle phase and matrix phase will not be sufficiently separated. Furthermore, if the porosity is less than 40%, sufficient permeability cannot be obtained.
Such a porous polymer membrane can also be produced by a known method, for example, the method described in JP-A-54-16382. Furthermore, the porous polymer membrane may be in any form such as a flat membrane, a tube, or a hollow fiber. The film thickness of these porous polymer membranes is
The thickness is 10 μm to 1 mm, preferably 10 to 200 μm. Depending on whether the liquid mixture system of large particles phase-separated into an emulsion and a matrix and the porous polymer membrane used are hydrophilic or hydrophobic, the large particles may pass through the membrane or the matrix may pass through the membrane. It is decided whether to do so. The present invention can be used in either case, and by using a hydrophilic and hydrophobic porous polymer membrane in combination, large particles can be rapidly separated. When the particle phase is an aqueous liquid and the matrix phase is a non-aqueous liquid, if a hydrophilic porous polymer membrane pre-wetted with water is used, the particle phase will pass through the membrane, whereas if a hydrophobic polymer porous membrane is used, the particle phase will pass through the membrane. The matrix phase permeates the membrane. Furthermore, if a hydrophilic membrane and a hydrophobic membrane, which are pre-wetted with water, are used in combination, the particle phase permeates the hydrophilic membrane and the matrix phase permeates the hydrophobic membrane, resulting in more efficient particle separation. When the particle phase is a non-aqueous liquid and the matrix phase is an aqueous liquid, the particle phase passes through a hydrophobic membrane and the matrix phase passes through a hydrophilic membrane, respectively. The hydrophilic porous polymer membrane referred to here is one in which the contact angle between the membrane and the water droplet is 0 to 5 degrees when a water droplet with a diameter of 2 mm or less is dropped on the membrane surface at 25°C and 1 atm. On the other hand, a hydrophobic polymer porous membrane is one whose contact angle with water exceeds 10 degrees. In this way, the target component is recovered from the large particle phase separated by the porous polymer membrane, but the recovery at this time no longer consumes a lot of energy and a distillation method can be used. According to the method for separating a liquid mixture of the present invention, separation of a liquid mixture, which requires a large amount of energy in a distillation method, can be converted into separation of a liquid mixture that can be easily separated by a distillation method. Incidentally, the large particle diameter, porosity of the porous polymer membrane, and average pore diameter referred to in the present invention are measured by the following methods. (Method for measuring particle size) Optical quasi-elastic scattering method was used. That is, when a solution containing particles that undergo Brownian motion is irradiated with light, the frequency of light scattered from the particles exhibits the Doppler effect.
Therefore, by analyzing the temporal intensity changes of this light scattering electric field, the diffusion coefficient (D) of particles can be determined (for example, DEKoppel.J.Chem.Phys. 57 , 4814
(1972)). Then, using the Einstein-Stokes equation: D=kt/3πηr from this diffusion coefficient,
The average particle diameter was calculated. Here, k, T, η, and r represent the Boltzmann constant, the absolute temperature of the emulsion, the viscosity coefficient, and the particle diameter, respectively. (Average pore diameter of porous polymer membrane) If the number of pores with a pore radius of r to r + dr per 1 cm ² of a porous membrane is expressed as N(r)dr (N(r) is the pore size distribution function), then The average hole radius i is given by equation (1). i＝∫ ^∞ / ₀ r ⁱ N(r)dr／∫ ^∞ / ₀ r ^i-1 N(r)
dr(1) Take an electron micrograph of the surface of the porous polymer membrane using a scanning electron microscope. The pore size distribution function N(r) is calculated from the photograph by a known method and substituted into equation (1). That is, a scanning electron micrograph is enlarged to an appropriate size (for example, 20 cm x 20 cm) and printed, and 20 test lines (straight lines) are drawn at equal intervals on the resulting photograph. Each test line traverses multiple holes. The length of the test line existing in the hole when it crosses the hole is measured, and its frequency distribution function is determined. Using this frequency distribution function, for example, stereology (for example, "Quantitative Morphology" by Norio Suwa)
Determine N(r) using the method of Iwanami Shoten). Note that the average pore diameter is 2 ₃ (i.e., i=3 in equation (1)). (Porosity) From the measured value of the apparent density (ρa) of the porous membrane,
The porosity (Pr) is calculated using the following formula. Pr=(1-ρa/ρp)×100 (2) Here, ρp is the density of the porous membrane material, and ρp is the measured value of the weight W of the porous membrane and the volume V including the pores, so ρa=W/V It is calculated by Note that Pr is expressed as a percentage. Examples Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited in any way by the Examples below. Examples 1 to 3 1,1,6,6-tetraphenyl-2,4-hexadiyne-1,6-diol was added as a carrier-containing liquid to 100 ml of a 10% by weight acetone aqueous solution.
Added 100ml of trioctyl phosphate containing 0.01 molar concentration and 0.1g of sodium lauryl sulfate, 28KHz
By changing the application time of ultrasonic vibration,
A trioctyl phosphate phase having a specific particle size formed particles and an emulsion was obtained in which the particles were dispersed in an aqueous acetone solution. This emulsion was coated with a polytetrafluoroethylene porous membrane (Fluoropore manufactured by Sumitomo Electric Industries, Ltd., nominal average pore diameter).
10 μm) under a pressure of 0.01 Kg/cm ² and a potential gradient of 35 V/cm. The results are summarized in Table 1. By passing through a polytetrafluoroethylene porous membrane, only the trioctyl phosphate phase dispersed in particulate form permeated through the membrane, forming a continuous phase in the permeate. In addition, analysis of the composition of the membrane permeate obtained in Example 1 revealed that trioctyl phosphate was 87%, acetone
10% and 3% water. Comparative Example 1 The same procedure as in Example 1 was carried out except that the concentration of 1,1,6,6-tetraphenyl-2,4-hexadiyne-1,6-diol was set to 0. The results at this time are shown in Table 1. From Table 1, it can be seen that the use of a carrier increases the separation factor. Comparative Example 2 The same procedure as in Example 1 was carried out except that the potential gradient was set to 0. The results at this time are also shown in Table 1. It can be seen from Table 1 that by providing a potential gradient, the membrane permeation rate of particles, that is, the liquid flow rate increases significantly. Example 4 In Example 1, trioctyl phosphate containing 0.1 molar concentration of 1,1,4,4-tetraphenyl-1,3-butyne-1,4-diol and 2,6,10 , 14-tetramethylpentadecane (2:1 weight ratio) was used, and the potential gradient was 8 V/cm. The results at this time are shown in Table 1. The composition of the obtained membrane permeate was 86% trioctyl phosphate, 9.3% acetone, and 4.7% water. Comparative Example 3 According to Example 1, an emulsion in which particles having an average particle diameter of 0.15 μm were dispersed was obtained. This emulsion was passed through a Teflon porous membrane with an average pore diameter (10 μm) exceeding 50 times the average particle diameter under a pressure of 0.01 Kg/cm ² and a potential gradient of 10 V/cm, but no liquid was obtained. pressure
A liquid was obtained when the concentration was 0.055 Kg/cm ² , but in this liquid trioctyl phosphate remained dispersed in the form of particles.

[Table] Acetone/water molar ratio in liquid mixture
Effects of the Invention As described above, according to the present invention, a specific component can be selectively concentrated and easily separated from a liquid mixture that requires a large amount of energy for separation or a liquid mixture that is difficult to separate.

Claims (1)

[Claims] 1. In the separation of a liquid mixture, a compound that reversibly forms a complex with the component to be separated is added at a rate of 0.001 mol/1.
In the liquid mixture to be separated, use a liquid that is contained in the liquid mixture to be separated at a concentration of
Forming large particles with a diameter of 0.1 to 10 μm, concentrating the target component to be separated inside the large particles, and transporting the large particles to the surface of the porous polymer membrane under an electrostatic field, 50 times the average diameter of the large particles. A membrane separation method characterized by separation using a porous polymer membrane having the following average pore diameter. 2. The membrane separation method according to claim 1, wherein the liquid mixture is an acetone aqueous solution, and the compound that reversibly forms a complex with acetone is acetylene diol. 2. The membrane separation method according to item 1 or 2 above, characterized in that an ionic surfactant is used when forming the large particles that concentrate the target component.