JP2015006646A - Separation method of metal nanoparticle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for separating metal nanoparticles from liquid containing the metal nanoparticles, while maintaining a high permeation flow rate.SOLUTION: Liquid containing metal nanoparticles in a raw liquid tank 1 is supplied to an ultrafiltration membrane module 2, and filtered at a filtration pressure of 50 kPa or less by a cross-flow method, and then refined liquid containing the metal nanoparticles is returned into the raw liquid tank 1, and permeated liquid is drained. Back-pressure washing is performed periodically by using water having an electric conductance of 300 μS/cm or less as back-pressure washing water, and washing waste water is returned into the raw liquid tank 1.

Description

  The present invention relates to a method for separating metal nanoparticles from a liquid containing metal nanoparticles using a separation membrane.

A technique for separating metal nanoparticles and impurities from a liquid containing useful metal nanoparticles and unnecessary impurities is known.
Patent Document 1 discloses a method for removing impurities such as salts and ions produced as a by-product in a synthesis process after hydrolyzing an aqueous titanium compound solution or neutralizing an aqueous titanium compound solution by adding an alkali. It is manufactured through a step of filtering titanium oxide fine particles (paragraph number 0008 of Patent Document 1). The average particle diameter of the obtained titanium oxide fine particles is described as 1 to 30 nm. Moreover, as a filtration means, the ion exchange method and the ultrafiltration method other than the normal filtration method are illustrated.

  Patent Document 2 describes a separation method in which a solution containing inorganic nanoparticles is cross-flow filtered using an ultrafiltration membrane, and inorganic nanoparticles having different particle diameters are separated and filtered. In the examples, a polysulfone polymer membrane is used as the ultrafiltration membrane.

In Patent Document 3, in the method for fractionating a dispersion of oxide nanoparticles, at least one method step is a membrane-type cross-flow filtration step, and overflow of the membrane by the dispersion is driven and rotated. The method produced by the member is described.
Paragraph No. 0028 describes that permeate 2 (clear permeate, not permeate 1 containing fines) can be returned to the filtration step.

  In US Pat. No. 6,057,033, a suspension solid is concentrated using a cross-flow separation method, a backwash method or a backwash is used to quickly release retained solids, and separation and release are performed. A method for the concentration of a solid in a suspension, consisting of repeated for a long time, is described. For backwashing, a clarified liquid and a gas are used (Example 1).

  In Patent Document 5, in a precision or ultrafiltration module having a filtration membrane having a supply liquid side and an osmotic solution side, a part of the filtered osmotic solution is recirculated to the osmotic solution side of the filtration module to obtain a filtration membrane. While maintaining parallel flow on the supply liquid side and the permeate side, the contaminants attached to the filter membrane are expelled and washed away by an operation that makes the pressure difference between the supply liquid side and the permeate side zero or reverse. Filtration methods and systems that reduce or eliminate membrane fouling are described.

Japanese Patent Laid-Open No. 10-158015 JP 2010-46621 A JP 2009-119461 A Japanese Examined Patent Publication No. 6-67459 Special table 2010-538823

In the prior art described above, the permeation flow rate is greatly reduced when the filtration operation is continued, and there is room for improvement.
An object of the present invention is to provide a separation method capable of separating metal nanoparticles from a liquid containing metal nanoparticles while maintaining a high permeation flow rate.

As a means for solving the problems, the present invention
A method of separating metal nanoparticles from a liquid containing metal nanoparticles,
The metal nanoparticles are those having an average particle diameter of 1 to 300 nm made of a metal and a metal compound,
The separation method includes a filtration step and a washing step,
When the filtration step supplies and filters the liquid containing metal nanoparticles in the stock solution tank to the ultrafiltration membrane module, it is filtered at a filtration pressure of 50 kPa or less by a cross flow method, and the purified liquid containing metal nanoparticles is Return to the stock solution tank and drain the permeate,
The washing step is a reverse pressure washing step that is periodically performed by interrupting the filtration step, using water having an electric conductivity of 300 μS / cm or less as the back pressure washing water, and returning the washing wastewater to the stock solution tank. Process,
Provided is a method for separating metal nanoparticles, wherein a combination of the filtration step and the washing step is set as one cycle and this is repeated a plurality of cycles.

  According to the method for separating metal nanoparticles of the present invention, impurities can be removed from a liquid containing metal nanoparticles while maintaining a high permeation flow rate, and the purity of the metal nanoparticles can be increased.

The flowchart for implementing the separation method of the metal nanoparticle of this invention.

In the separation method of the present invention, the metal nanoparticles are separated from the liquid containing the metal nanoparticles and impurities (impurities such as salts and ions generated as a by-product in the synthesis step) (that is, the impurities are separated), This is a separation method for increasing the purity of metal nanoparticles in a liquid.
Hereinafter, the separation method of the present invention will be described with reference to the flowchart of the separation method of FIG.

The stock solution tank 1 contains a liquid containing metal nanoparticles as a stock solution supplied from the stock solution line 10. The stock solution tank 1 can be provided with a stirring device.
The stock solution in the stock solution tank 1 can be diluted to maintain the permeate flow rate at a high level and facilitate removal of impurities.
The dilution water used at this time is preferably pure water having an electric conductivity of 10 μS / cm or less, more preferably 1 μS / cm or less.
The dilution is preferably adjusted so that the concentration of metal nanoparticles in the stock solution is 0.1 to 1.0% by mass, and is adjusted so that the concentration of metal nanoparticles is 0.2 to 0.4% by mass. It is more preferable.

The metal nanoparticles to be separated by the separation method of the present invention have an average particle diameter of 1 to 300 nm made of a metal and a metal compound.
The metal and metal compound constituting the metal nanoparticle are not particularly limited, and examples thereof include titanium, gold, silver, copper, or oxides, nitrides, and carbides thereof. In many cases, the metal nanoparticles contain impurities such as salts by-produced in the synthesis process and coexisting ions, and these salts and ions are removed and purified. Filter and separate the nanoparticles.
The average particle diameter is preferably 5 to 200 nm, more preferably 10 to 100 nm. The average particle size is measured by the method described in the examples.

The stock solution (liquid containing metal nanoparticles) in the stock solution tank 1 is supplied to the ultrafiltration membrane module 2 from the stock solution water supply line 11 and separated by filtration. A pump 21 is installed in the line 11.
Filtration is performed by a cross flow method at a filtration pressure of 50 kPa or less (transmembrane pressure difference). The filtration pressure is preferably 30 kPa or less.
After filtration, the purified liquid containing the metal nanoparticles is returned from the purified liquid line 12 to the stock solution tank 1, and the permeate not containing the metal nanoparticles is sent from the permeate liquid lines 13 and 14 to the permeate tank 3 and then drained. An opening / closing valve (such as an electromagnetic valve) can be provided at a branch portion between the permeate line 13 and the permeate line 14.
The filtration step is preferably performed at intervals of 30 to 60 minutes.

  The filtration membrane (separation membrane) used in the ultrafiltration membrane module 2 can be made of a known material, and examples thereof include polysulfone, polyethersulfone, and polyacrylonitrile.

As the separation membrane, a flat membrane, a hollow fiber membrane, or a tube membrane can be used.
Among these, a hollow fiber membrane is preferable because the filtration operation and back pressure washing of the present invention are easy. As the hollow fiber membrane, either an internal pressure type or an external pressure type can be used, but an internal pressure type is more preferable from the viewpoint of securing an appropriate film surface linear velocity and ease of backwashing.
The inner diameter of the hollow fiber membrane is preferably 0.5 to 2 mm, more preferably 0.7 to 1.5 mm.
The outer diameter of the hollow fiber membrane is preferably 0.8 to 3 mm, more preferably 1.1 to 2.2 mm.
The film thickness is preferably 150 to 500 μm.
The ultrafiltration membrane preferably has a molecular weight cut off of about 1 to 500,000.

The ultrafiltration membrane module can be used as a spiral module, a flat membrane module, a hollow fiber membrane module, or a tubular module using them.
Among these, the hollow fiber membrane module is preferable because the filtration operation of the present invention is easy.

After carrying out the filtration step for a predetermined time, the filtration step is interrupted and back pressure washing is carried out as a washing step.
In the reverse pressure cleaning, the pump 22 is driven, and the water in the reverse pressure cleaning water tank 4 is supplied to the ultrafiltration membrane module 2 from the back pressure cleaning line (a part is shared with the permeate line) 13. carry out.
Backwashing is performed for 1-2 minutes.
The pressure at the time of back pressure washing is higher than the filtration pressure (50 kPa at the maximum) and is preferably 200 kPa or less. More preferably, it is 180-200 kPa.
The water in the back pressure wash water tank 4 (back pressure wash water) is water having an electrical conductivity of 300 μS / cm or less, preferably 10 μS / cm or less, supplied from a wash water (pure water) supply line 15. More preferably, the water is 1 μS / cm or less.
Waste water after back pressure washing (back pressure washing waste water) contains a small amount of metal nanoparticles adhering to the membrane surface of the ultrafiltration membrane module 2, and a part of the stock solution water line 11 and back pressure washing. Return to the stock solution tank 1 from the drainage line 15. An opening / closing valve (such as an electromagnetic valve) can be provided at a branch portion between the stock solution water supply line 11 and the counter pressure washing / drainage line 15.

In the separation method of the present invention, the combination of the filtration step and the washing step is set as one cycle, and this is repeated a plurality of cycles.
The number of cycles to be repeated is preferably 2 to 5 cycles, and more preferably 2 to 4 cycles.

In the separation method of the present invention, the purified liquid (liquid containing metal nanoparticles) obtained by the filtration step is returned to the stock solution tank 1 and the permeated liquid containing impurities is drained.
In the separation method of the present invention, water having an electric conductivity of 300 μS / cm or less is used as the back pressure washing water in the washing step, and the back pressure washing waste water (containing a small amount of metal nanoparticles) is used as a stock solution tank. Return to 1.
For this reason, the concentration of impurities is reduced from the stock solution in the stock solution tank 1, but the reverse pressure washing waste water that does not substantially contain impurities is periodically supplied, so that the permeate flow rate in the ultrafiltration membrane module 2 Is maintained at a high level.
Moreover, it becomes easy to maintain the permeate flow rate at a high level by adding a step of diluting the stock solution with water having low electrical conductivity.
And the liquid containing a metal nanoparticle with high purity is obtained by repeating the combination of a filtration process and a washing process in multiple cycles.
The separation method of the present invention is suitable as a method for separating metal nanoparticles, a method for purifying metal nanoparticles, or a method for recovering metal nanoparticles.

<Measurement of average particle diameter of metal nanoparticles>
Observation with a transmission electron microscope and image analysis were performed to obtain an average value of the particle diameters of 50 particles.

Example 1
<Filtering process>
Zinc oxide particles (manufactured by Wako Pure Chemical Industries, Ltd.) having an average particle diameter of 20 nm were used as metal nanoparticles, and diluted with pure water (electric conductivity 1 μS / cm) so that the metal nanoparticle concentration was 0.2 mass%.
Furthermore, magnesium sulfate (reagent special grade, Wako Pure Chemical Industries) was added to and dissolved in the metal nanoparticle-containing solution so as to be 1000 ppm (mass basis) as an impurity to obtain an unpurified stock solution (stock solution).
This unpurified stock solution is diluted 2-fold with pure water (electric conductivity 1 μS / cm), and then an ultrafiltration hollow fiber membrane module (FB03-VC-FUS15C1) made of polyethersulfone and having a molecular weight cut-off of 150,000; Cross flow filtration was performed at a filtration pressure of 30 kPa using Daisen Membrane Systems Co., Ltd. At this time, the stock solution in the stock solution tank was stirred.
By this cross flow filtration, sodium sulfate was transferred to the permeate side, and metal nanoparticles were transferred to the purified liquid side.
The purified solution was returned to the stock solution tank, and the permeate was sent to the permeate tank.

<Washing process>
The filtration operation was continued for 60 minutes (permeation flow rate 120 L / m ² · h), and then the filtration operation was stopped and back pressure washing was performed for 1 minute.
The back pressure washing water used for back pressure washing had an electrical conductivity of 1 μS / cm, and the amount of back pressure washing water used was the same as the amount of permeate for 60 minutes.
After the entire amount of the backwash water was returned to the stock tank, the stock solution was further diluted 2-fold with pure water (electric conductivity 1 μS / cm).

The combination of the above filtration step and washing step was taken as one cycle, and a total of 3 cycles were carried out.
As described above, the permeate amount in the first filtration step is 120 L / m ² · h, the permeate amount in the second filtration step is 140 L / m ² · h, and the permeate amount in the third filtration step is 150 L. / m ² · h.
The electrical conductivity of the unpurified stock solution was 1500 μS / cm, and the electrical conductivity of the purified solution containing metal nanoparticles after 3 cycles was 840 μS / cm.
From this result, it was confirmed that impurities (magnesium sulfate) were removed and the purity of the metal nanoparticles was increased while maintaining a high permeation flow rate.

Comparative Example 1
This was carried out in the same manner as in Example 1 except that pure water (electric conductivity 1 μS / cm) having the same amount as the permeate flow rate was added to the stock solution tank once every 60 minutes without filtration under back pressure.
Permeate volume during the first filtration step is 120L / m ² · h, the permeate volume at the permeate volume is 110L / m ² · h, 3 round of filtration step in the second filtration step 115L / m ²・ It was h.
The electrical conductivity of the unpurified stock solution was 1500 μS / cm, and the electrical conductivity of the purified solution after 3 cycles was 850 μS / cm.

DESCRIPTION OF SYMBOLS 1 Stock solution tank 2 Ultrafiltration membrane module 3 Permeate tank 4 Back pressure washing water tank 10 Stock solution line 11 Stock solution feed line 12 Purified solution line 13 Permeate line 15 Back pressure washing drainage line

Claims (4)

A separation method for separating metal nanoparticles from a liquid containing metal nanoparticles,
The metal nanoparticles are those having an average particle diameter of 1 to 300 nm made of a metal and a metal compound,
The separation method includes a filtration step and a washing step,
When the filtration step supplies and filters the liquid containing metal nanoparticles in the stock solution tank to the ultrafiltration membrane module, it is filtered at a filtration pressure of 50 kPa or less by a cross flow method, and the purified liquid containing metal nanoparticles is Return to the stock solution tank and drain the permeate,
The washing step is a reverse pressure washing step that is periodically performed by interrupting the filtration step, using water having an electric conductivity of 300 μS / cm or less as the back pressure washing water, and returning the washing wastewater to the stock solution tank. Process,
A method for separating metal nanoparticles, wherein a combination of the filtration step and the washing step is set as one cycle and this is repeated a plurality of cycles.   The concentration of the metal nanoparticles is adjusted to 0.2 to 0.4% by mass by diluting water having an electric conductivity of 1 μS / cm or less into the liquid containing the metal nanoparticles in the stock solution tank. The method for separating metal nanoparticles according to claim 1, comprising the step of:   The method for separating metal nanoparticles according to claim 1 or 2, wherein the filtration step is a step of performing a filtration operation for 30 to 60 minutes, and the washing step is a step of performing reverse pressure washing for 1 to 2 minutes.   The method for separating metal nanoparticles according to any one of claims 1 to 3, wherein the ultrafiltration membrane module uses a hollow fiber membrane made of polyethersulfone as the ultrafiltration membrane.

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