JPS61274710A - Membrane separation of liquid mixture - Google Patents

Abstract

PURPOSE:To simultaneously enhance separability and permeability, by growing an objective component to be separated into large particles which are, in turn, separated by a polymer porous membrane under an electrostatic field. CONSTITUTION:For example, a liquid-liquid phase separation agent such as potassium carbonate or a liquid-liquid extractant such as trioctylphosphate is added to a liquid mixture such as an aqueous alcohol solution of ethanol under stirring to form large particles with a particle size of 0.1-10mum containing a component to be separated at high concn. Said large particles are filtered under an electrostatic field by using a polytetrafluoroethylene porous membrane with an average pore size 50 times or less the particle size of said large particles and the large particle phase is separated from a matrix phase, which generated phase separation in an emulsion form, by utilizing the surface charge of the large particles. As the porous membrane, both hydrophilic and hydrophobic ones can be utilized and both of them may be used together.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for separating liquid mixtures. More specifically, it relates to a method in which a target component to be separated in a liquid mixture is made into large particles, and then the large particles are separated using a porous polymer membrane under an electrostatic field.

[Conventional technology]

BACKGROUND ART Various techniques for separating only specific liquid components from a homogeneous liquid mixture have been studied in the past, and one of the techniques that is currently in widespread practical use 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. Also,
Vacuum distillation or steam distillation is used to separate components that are easily decomposed at high temperatures near the boiling point, but in this case, more energy is required than atmospheric 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.

[Problem that the invention seeks to solve]

However, with the current membrane separation technology, if the separation is high, the permeability is low, or if the permeability is high, the separation is low. is not obtained. Therefore, in order to put it into practical use, it is necessary to make the membrane thinner to increase liquid permeability, or to compensate for poor selectivity by multi-stage membrane permeation. However, in the latter method, there were problems such as the complexity of the device.

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 a membrane separation technology for liquid mixtures that increases both separation performance and permeability at the same time. However, this technology has been developed. That is, the diffusion rate of a molecule in a liquid is 1O~103 in a solid.
As a result of intensive study, paying attention to the fact that it is more than twice l- and that the liquid permeation rate of the porous polymer membrane is high, we have arrived at the present invention which can fully achieve the above objectives.

[Means for solving problems]

The present invention is a method for separating a liquid mixture, which is characterized in that the target components to be separated are made into large particles, and then the large particles are separated using a porous polymer membrane under an electrostatic field. .

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, but has 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-containing or near-boiling mixtures. Examples of such liquid mixtures include methanol, ethanol, n-
Propatool, isopropatool, t-butanol, etc. →
Examples include aqueous solutions of alcohols such as acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, pyridine, acetic acid, and mixtures of methylcyclohexane/toluene, cyclohexane/toluene, and the like.

From such a liquid mixture, the target component to be separated is made into large particles, the surface charge of the large particles is used to cause particle transport under an electrostatic field, and the particle phase is separated using a porous polymer membrane. , the average diameter of the large particles at this time is 0.1 μm-10
Preferably, it is in the μm range. Particle size is 0.1μ
If the particle diameter is less than 10 m, 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 of the particles will become small, the amount of mass transfer at the particle interface will become small, and the separation performance will deteriorate.

Next, as a method of making large particles of the target component to be separated from the liquid mixture of the present invention, there is a method of adding a liquid-liquid phase separating agent or a liquid-liquid extracting agent to the liquid mixture and stirring them. Here, the liquid-liquid phase separation agent refers to a substance that causes phase separation of a liquid mixture into a concentrated phase and a dilute phase of the target component under separation operation conditions. Such a liquid-liquid phase separation agent is selected as appropriate depending on the liquid mixture system, but for example, potassium carbonate is used for ethanol/water systems, water is used for methylcyclohexane/toluene systems, ethanol is used for cyclohexane/toluene systems, and acetic acid/ Toluene or the like can be used for water systems.

Furthermore, the liquid-liquid extractant refers to a liquid that does not dissolve in the liquid mixture itself, but has the property of dissolving a target component in the liquid mixture in a larger amount than other components. The liquid-liquid extractant is preferably one that can be easily separated from the component to be separated, which is the extract. For example, when the liquid mixture is an aqueous alcohol solution, the solubility in water at 30°C and 1 atm is 0. 1 or less, and a liquid having a polar group in its chemical structure or a mixed liquid of a liquid having a polar group and a liquid having no polar group can be used. Liquid-liquid extractant 3
If the solubility in water at 0° C. and 1 atm exceeds 0.1, the liquid-liquid extractant and the alcohol aqueous solution that is the liquid mixture will dissolve in each other, making it impossible to form particles.

In addition, in order to facilitate the separation of the liquid-liquid extractant and alcohol, the vapor pressure of the liquid-liquid extractant must be 30 mm at 200°C.
It is preferably as low as Hg or less. Furthermore, the liquid-liquid extractant has a chemical structure in which -COO-1-〇-1>C=0. >N
A pure liquid or a mixed liquid containing one or more polar groups selected from the group consisting of H, P, -0H8-N1 (Co-) is preferred. It is particularly useful for separating alcohol from an aqueous alcohol solution by the method of the present invention. Specific examples of liquid-liquid extractants include trioctyl phosphate or trioctyl phosphate and
．． A mixed solution of 6,10,14-tetramethylpentadecane and the like can be mentioned.

Further, by stirring a liquid mixture to which a liquid-liquid phase separation agent or a liquid-liquid extractant is added, particles containing a concentrated component to be separated can be formed. As for the stirring method,
In addition to mechanical stirring, ultrasonic vibration and the like can be used. In addition, it is possible to make large particles by adding a surfactant and applying ultrasonic vibration, and the diameter of the large particles can be set by controlling the amount of surfactant added and the ultrasonic application time. O1μm
Large particles of ~10m can be formed.

In this way, large particles richly containing the components to be separated are produced.
Utilizing the interfacial tension with the matrix liquid phase-separated into an emulsion, it can be separated into a particle phase and a 7-trisox phase using a porous polymer membrane.

The porous polymer membrane in the present invention preferably has an average pore diameter of 0.02 ftm or more, a gravimetric porosity of 40% or more, and polyethylene 1. Porous membranes made of polymers or copolymers such as Ng propylene, polyvinylidene fluoride, polytetrafluoroethylene, polysulfone, polyamide, and cellulose are used. Depending on the component system of the large particles phase-separated in an emulsion and the matrix and whether the porous polymer membrane used is hydrophilic or hydrophobic, either the large particles pass through the wire membrane or the matrix passes through the wire membrane. is determined. 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. In order for the porous polymer membrane to efficiently separate the particle phases, the average pore diameter of the linear membrane must be 50 times or less than the large particle diameter. Membranes with an average pore diameter of more than 50 times do not provide sufficient separation between the particle phase and the matrix phase. The sharper the pore size distribution of the membrane, the better. The term "hydrophilic porous polymer membrane" as used herein means one in which the contact angle of the membrane with water is 0 degrees when a water droplet with a diameter of 2 dragons or less is dropped onto the membrane surface at 25°C and normal pressure. ,
On the other hand, a linear aqueous porous polymer membrane refers to one whose contact angle with water exceeds 0 degrees.

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 linear aqueous porous membrane is used, the particle phase will pass through the membrane. Matri and Tass phases permeate through the membrane. Furthermore, if a hydrophilic membrane and a hydrophobic membrane wetted with pre-wet water are used in combination, the particle phase permeates the hydrophilic membrane and the matrix phase permeates the hydrophobic membrane, making particle separation more efficient.

When the particle phase is a non-aqueous liquid and the matrix phase is an aqueous liquid, the particle phase permeates through the hydrophobic membrane, respectively.
The matrix phase permeates the hydrophilic membrane.

Furthermore, by applying an electrostatic field and creating a potential difference between the membrane surface and the liquid mixture by utilizing the pressure difference on the membrane surface side and/or the charge of the large particles, large particles can be rapidly separated by the porous polymer membrane. It can be carried out quickly and continuously.

Here, the potential difference causes an electric force due to the charge on the particles,
This is the driving force that allows particles to efficiently contact the membrane surface. When particles are positively charged, the membrane through which they pass becomes negatively charged.
If the particles are negatively charged, a potential difference is provided (]O) 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.

The target component is recovered from the large-grain prephase separated in this way, but since the recovery at this time no longer consumes a lot of energy, 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 performed.
It can be converted to separation of a mixed liquid that can be easily separated by distillation.

The porosity, particle diameter, and average pore diameter of the porous polymer membrane referred to in this specification were measured by the following methods.

<Average pore size of porous polymer membrane> If the number of pores with a pore radius of r to r10dr per cJ of porous membrane is expressed as N (rldr (N tr+ is the pore size distribution function), then the i-th order average pore is The radius 〒i is given by equation (1).

r i -m=----ill An electron micrograph of the surface of the porous polymer membrane is taken using a scanning electron microscope. A pore size distribution function N (r) is calculated from the photograph using a known method, and this is substituted into formula +11.

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 obtained photograph. Each test line traverses multiple holes. Measure the length of the test line existing in the hole when crossing the hole,
Find this frequency distribution function. Using this frequency distribution function, N if) is determined, for example, by the method of stereology (for example, "Quantitative Morphology °' Iwanami Shoten," by Norio Suwa).
The average pore size is 2〒3.

<Porosity> From the measured value of the apparent density (/pa) of the porous membrane, the porosity (Pr) is calculated by the following formula.

Pr=(1-fa/f'p) xloo
t2+ Here, ζp is the density of the porous membrane material, and Pa is fa− from the measured value of the weight W of the porous membrane and the volume ■ including the pores.
Calculated as W/V. Note that Pr is expressed as a percentage.

Measurement method of particle size> The lead-vehicle 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 change of this light scattering electric field, the diffusion coefficient (D) of the particle can be determined (for example, D, [!, Koppel, J, Chem, Phys.
, 57.4814 (1972)). From this diffusion coefficient, the Einstein-Stokes equation: D=k
The average particle diameter was calculated using T/3πηr.

Here, k, T, η, and r represent the Portzmann constant, the absolute temperature of the emulsion, the viscosity coefficient, and the particle diameter, respectively.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the Examples below.

Examples 1 to 3 100 ml of trioctyl phosphate and 0.1 g of sodium lauryl sulfate were added to 100 mA of a 20% by volume ethanol aqueous solution, and trioctyl phosphate of a specific particle size was prepared by changing the application time of 21 (kHz ultrasonic vibration). formed particles and obtained an emulsion dispersed in an aqueous ethanol solution.This emulsion was transferred to a polytetrafluoroethylene porous membrane (
Fluorobore manufactured by Judenenko, nominal average pore diameter 10μm), pressure 0.01kg/cn! , potential gradient 4.5 V
/cm below. The results are summarized in Table 1.

By filtering through a polytetrafluoroethylene porous membrane, only the trioctyl phosphate phase dispersed in particulate form permeated the membrane, and the permeate formed a continuous phase.

In addition, we analyzed the composition of the membrane permeate obtained in Example 214) and found that trioctyl phosphate was 90% and ethanol was 7.2%.
%, water 2.8%.

Comparative example 1 The same procedure as in Example 2 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 the flow rate increases significantly by providing a potential gradient.

Table 1 Example 1 0.3 9B, 0 14.7 Example 2 2.5 97.1 14.2 Example 3 5.0 94.5 14.3 Comparative Example 2 Average according to Examples 1 to 3 An emulsion in which particles having a particle size of 0.1 μm were dispersed was obtained. This emulsion was passed through a Teflon porous membrane with an average pore size 100 times the particle size under a pressure of 0.01 kg.
/cJ, but no filtrate was obtained. A filtrate was obtained when the pressure was increased to 0.05 kg/cI11 or higher, but trioctyl phosphate remained dispersed in the form of particles in this filtrate.

Example 4 The emulsion obtained according to Example 2 was coated with a regenerated cellulose porous membrane (manufactured by Toyo Roshi ■, nominal average pore size 3 μm) on one side, and a polytetrafluoroethylene porous membrane (average pore size 3 μm) on the other side. 4.5 V so that the polytetrafluoroethylene membrane side is positive using a filter equipped with
Filtration was carried out under a pressure of 0.01 kg/cJ at a potential gradient of /cm. The flow rate of membrane permeation at this time was 97 kg/r+(・hr for the Teflon membrane and 70 kg/m・hr for the regenerated cellulose membrane. Also, the flow rate of ethanol from the matrix phase to the particle phase was 97 kg/m・hr). The coefficient was 14.

As described above, by using a hydrophilic porous polymer membrane and a hydrophobic polymer porous membrane in combination, the separation rate between the dispersed droplets of the emulsion and the dispersion medium can be increased.Example 5 20% ethanol by volume Aqueous solution 100rr+7! A mixed solution of trioctyl phosphate and 2.6,10.14-tetramethylpentadecane (2:1 weight ratio) 100rr
1 and 0.2 g of sodium lauryl sulfate,
Ultrasonic vibrations of 8 kHz were applied for 2 minutes. As a result, an emulsion was obtained in which the trioctyl phosphate/2,6.10.14-tetramethylpentadecane mixture formed particles with an average particle diameter of 0.3 μm and was dispersed in an aqueous ethanol solution. This emulsion was heated at a pressure of 0.01 kg/cJ and a potential gradient of 4, 5
When filtered through a polytetrafluoroethylene porous membrane with a nominal average pore size of 2.0 μm under V/cm, trioctyl phosphate/2.6.10°14- was dispersed in particulate form.
Only the tetramethylpentadecane phase permeated the membrane at a flow rate of 48 kg/i·hr, and the permeate formed a continuous phase.

As a result of analyzing the composition of the permeate, it was found that trioctyl phosphate 60
%, 2,6.10.14-tetramethylpentadecane 3
0%, ethanol 8.5%, and water 1.5%.

When this permeate was subjected to simple distillation at 105°C, an 85% ethanol aqueous solution was obtained.

〔Effect 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 separating a liquid mixture, the target component is 0.1 to 1
A method for separating a liquid mixture, which comprises converting the particles into large particles to a diameter of 0 μm, and then separating the large particles under an electrostatic field using a porous polymer membrane having an average pore size of 50 times or less the diameter of the large particles. 2. The separation method according to claim 1, characterized in that a liquid-liquid phase separating agent is used when forming large particles. 3. The separation method according to claim 1, characterized in that a liquid-liquid extractant is used when forming large particles. 4. The separation method according to any one of claims 1 to 3, characterized in that a hydrophilic porous polymer membrane and/or a hydrophobic porous polymer membrane is used as the porous polymer membrane. 5. The liquid mixture is an alcohol aqueous solution, and the liquid used for forming large particles has a solubility in water of 0.1 or less at 30°C and 1 atm, and has a polar group in its chemical structure, or Claim 1, characterized in that the liquid is a mixture of a liquid having a polar group and a liquid having no polar group.
Separation method described in section. 6. The liquid mixture is an alcohol aqueous solution, and when making large particles, trioctyl phosphate or trioctyl phosphate/2
, 6,10,14-tetramethylpentadecane mixture is used.