JP2001096140A - Regeneration method of ultrafiltration membrane module for zirconia powder production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a regeneration method of an ultrafiltration membrane module to be used for producing a zirconia powder with excellent dispersibility, formability, and sintering property. SOLUTION: An ultrafiltration membrane module for production of a zirconia powder is employed for producing a zirconia powder by filtering, washing, and concentrating a zirconia sol obtained by heating and hydrolyzing an aqueous zirconium chloride solution by the ultrafiltration membrane module and then drying and previously firing the resultant sol either after adding a sintering aid of such as Y, Ca, Mg, Ce and the like to the resultant zirconia sol or using the sol as it is a concentrated solution. A method for regenerating the ultrafiltration membrane module for production of a zirconia powder is carried out using an aqueous hydrofluoric acid solution. The method for regenerating the ultrafiltration membrane module for production of a zirconia powder is carried out using an aqueous hydrofluoric acid solution in a concentration of 0.01-10% by either immersing the ultrafiltration membrane module in the aqueous hydrofluoric solution for 2-100 hours or circulating the solution through the module.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to solid electrolytes for fuel cells, functional ceramics such as oxygen sensors, NOx sensors, and thermal barrier coating materials, and structural members such as pulverizer members, precision machine parts, and optical connector parts. The present invention relates to a method for regenerating an ultrafiltration membrane used in a method for producing zirconia fine powder used as a raw material for ceramics.

[0002]

2. Description of the Related Art Conventionally, as a method for producing zirconia fine powder, an aqueous solution of a zirconium salt or an aqueous solution in which a stabilizer is dissolved in an aqueous solution of a zirconium salt is heated and hydrolyzed.
A method for obtaining a fine zirconia powder by drying and calcining the obtained hydrated zirconia sol is widely known.
However, in this method, strong sintering between particles occurs at the stage of drying and sintering, so that a fine powder having good dispersibility used as a zirconia ceramic material cannot be obtained.

[0003] In recent years, as a method for obtaining zirconia fine powder having good dispersibility and excellent sinterability, which is used as such a zirconia-based ceramic raw material, zirconia sol is washed and concentrated by an ultrafiltration membrane to obtain zirconia sol. A method for obtaining a powder has been proposed. For example, Tokuho 3-55
In 413, a zirconia sol obtained by hydrolyzing an aqueous solution of a zirconium salt is mixed with an average pore size of 10 to 500.
A method of washing using a filtration membrane having a permeation hole in the range of 0 ° is disclosed. In Japanese Patent Publication No. 3-55414, the zirconia sol is washed with pure water using an ultrafiltration membrane, and then washed with sodium hydroxide. A method for washing with a basic substance is disclosed. Further, JP-A-63-185821 and JP-A-Hei.
No. 83521 discloses a method of adding a stabilizer after filtration and washing by ultrafiltration. The zirconia powder produced by these methods has very good dispersibility and also has a feature of being excellent in sinterability, and a method for obtaining zirconia fine powder using an ultrafiltration membrane is: It is a very effective method for producing ceramic raw materials. In addition, by concentrating the sol after filtration and washing, it has a feature that a sol having a low viscosity and a very good dispersibility can be obtained at a high concentration and a high purity, and the productivity in the post-process, especially in drying, is improved. Improve dramatically.

Here, when an ultrafiltration membrane is used industrially, it is necessary to increase the filtration area.
Bundling multiple ultrafiltration membranes such as tube type and capillary type,
Alternatively, a spiral shape is generally used in units called “membrane modules”. In order to further increase the filtration area, several to several tens of these membrane modules are arranged in parallel and / or in series,
Used as "ultrafiltration device". However, this membrane module is very expensive and needs to be used repeatedly to make it an industrially viable process.
Therefore, filtration characteristics, especially stability of filtration speed, when used repeatedly, are very important.

[0005]

However, when the zirconia sol obtained by hydrolyzing an aqueous solution of a zirconium salt is washed and concentrated by ultrafiltration, its filtration characteristics are not stable, that is, it is used repeatedly. As a result, a stable production could not be performed due to a decrease in the filtration rate. Replacing the membrane module after several uses has been very disadvantageous economically because the membrane module is very expensive and uses many. For these reasons, the current situation is that the production process of zirconia powder using this ultrafiltration membrane has not been industrially satisfactory.

According to the present invention, the zirconia sol obtained by hydrolyzing an aqueous solution of a zirconium salt is filtered, washed and concentrated using an ultrafiltration membrane module, so that the zirconia sol has good dispersibility, excellent moldability, and excellent sinterability. In a method for regenerating an ultrafiltration membrane module for producing zirconia powder used in a method for producing zirconia powder having excellent binding properties, industrially satisfactory, that is, an ultrafiltration method capable of being used repeatedly A method for regenerating a filtration membrane module is provided.

[0007]

Means for Solving the Problems The present inventors have found that a zirconia sol obtained by hydrolyzing an aqueous solution of a zirconium salt is filtered, washed and concentrated with an ultrafiltration membrane module to obtain a good dispersibility and a good moldability. Study on the relationship between the treatment method of the ultrafiltration membrane module used in the method for producing zirconia powder having excellent sinterability and the ultrafiltration characteristics, especially the filtration characteristics when used repeatedly. As a result, by using a hydrofluoric acid aqueous solution as a treatment chemical, the ultrafiltration membrane module is efficiently regenerated,
The present inventors have found that it can be used repeatedly, leading to the present invention.

That is, the present invention provides a method for regenerating an ultrafiltration membrane module for producing zirconia powder, which comprises treating the ultrafiltration membrane module used in the method for producing zirconia powder with a hydrofluoric acid aqueous solution. is there.

[0009] In this specification, the term "filtration rate (liter / Hr)" refers to the total amount of filtrate (liter) discharged during filtration using an ultrafiltration membrane module.
Is divided by the time required for processing (Hr). Further, “water permeability” refers to “filtration speed” when pure water is passed through the ultrafiltration membrane module under a certain condition, and “water permeability” refers to a state in which actual liquid is not flowing. Indicates the ratio of "water permeability" when the water permeability of the unused ultrafiltration membrane module is 100%.

Hereinafter, the present invention will be described in detail.

Conventionally, when washing and concentration are repeatedly performed using an ultrafiltration membrane module, the filtration characteristics, especially the filtration speed, decrease remarkably with the number of repetitions, and the process is not industrially satisfactory. . The amount of water permeation was measured by passing pure water through the ultrafiltration membrane module whose filtration rate was reduced, and the permeation rate was reduced to 40%. Furthermore, when the same filtration operation was repeated and tested, it was found that the water permeability further decreased. Although the cause of the decrease in water permeability is not clear, certain zirconia components present in the hydrated zirconia sol obtained by hydrolysis adversely affect the ultrafiltration membrane, reduce the water permeability, and further reduce the filtration rate. It was presumed that the speed was also reduced.

The inventors of the present invention have attempted to regenerate the ultrafiltration membrane having reduced water permeability with various chemicals, and have found that the hydrofluoric acid aqueous solution is extremely effective. That is, the ultrafiltration membrane module having a water permeability of 20% repeatedly used in the washing / concentrating operation was immersed in a hydrofluoric acid aqueous solution for 12 hours. As a result, the water permeability was recovered to 70% or more. Washing and cleaning with this regenerated ultrafiltration membrane module
When the concentration operation was performed, no decrease in the filtration rate was observed,
It was found that the repetition characteristics were excellent.

Here, the hydrofluoric acid aqueous solution used preferably has a hydrofluoric acid concentration of 0.01 to 10% by weight.
If it is less than 0.01%, it cannot be sufficiently regenerated, and if it is used repeatedly, the filtration characteristics will be poor. Further, hydrofluoric acid is toxic, and it is preferable to treat it at 10% or less in consideration of safety. The regeneration method using a hydrofluoric acid aqueous solution requires that the portion of the ultrafiltration membrane module that substantially performs filtration is in contact with the hydrofluoric acid aqueous solution, and the ultrafiltration membrane module is immersed in a hydrofluoric acid aqueous solution. A method of circulating and washing the acid aqueous solution can be mentioned, but any method can provide a sufficient effect.

The frequency of regeneration may be performed every time a series of ultrafiltration operations are completed. However, it is more efficient to perform regeneration processing when the water permeability has decreased to some extent after completion of several batches. It is preferable in terms of properties. In this case, the water permeability is 10
%, It is preferable to carry out the regeneration processing at a point in time when it does not become lower. This is because if it is lower than 10%, it becomes extremely difficult to reproduce. The time of regeneration treatment is related to the amount of water permeation of the ultrafiltration membrane module.
-100 hours, preferably 5-50 hours. The reason is that if the length is shorter than this range, a sufficient reproduction effect cannot be obtained, and if the time is longer than this range, the productivity is significantly reduced. In addition, the higher the processing temperature, the shorter the time and the lower the concentration of the ultrafiltration membrane module can be regenerated.
It is preferable to perform the following. By the method as described above, the once-permeated water permeability can be easily regenerated to, for example, 70% or more.

The zirconia sol used in the present invention is:
As long as it is obtained by hydrolysis of an aqueous zirconium salt solution, it may be obtained under any reaction conditions. For example, a method of adjusting and hydrolyzing an aqueous solution of zirconium salt, a method of adding an alkali or an acid to the aqueous solution of zirconium salt and then performing hydrolysis, and adding a predetermined amount of hydrated zirconia sol to the aqueous solution of zirconium salt and hydrolyzing the aqueous solution. Methods and the like can be mentioned. In particular, part of the solution containing the zirconia sol obtained by hydrolysis of the aqueous solution of the zirconium salt is continuously and / or intermittently discharged from the reaction tank in terms of productivity and operability, and contains the zirconia sol. So that the volume of the solution is kept constant
The same amount of zirconium salt aqueous solution as the discharge amount is continuously and / or
Alternatively, a method of obtaining a zirconia sol by intermittently supplying the reaction tank is preferable. Here, "continuous" means that the zirconia sol is withdrawn from the reaction tank at a constant discharge rate, and simultaneously, a zirconium salt aqueous solution adjusted to a predetermined concentration at the same supply rate as the discharge rate is supplied into the reaction tank. ,
The term “intermittent” refers to a fixed amount (hereinafter, this amount is represented by the ratio of the amount of liquid supplied to the amount of liquid in the reaction tank, and the “supply ratio (vol.
%) ". After the zirconia sol of (1) is extracted from the reaction tank, an aqueous solution of zirconium salt in the same amount as the discharged amount is immediately added to the reaction tank, and the mixture is hydrolyzed for a predetermined time (hereinafter, referred to as “intermittent time”). Means to repeat. Thus, by performing the thermal hydrolysis, a hydrated zirconia sol having excellent productivity and high conversion can be easily obtained.

The zirconium salt used in the production of the zirconia sol used in the present invention includes zirconium oxychloride, zirconium nitrate, zirconium chloride, zirconium sulfate and the like. In addition, zirconium hydroxide and acid May be used.

Next, in the present invention, the zirconia sol obtained by the above method is filtered, washed and concentrated by ultrafiltration, and the ultrafiltration membrane has a cut-off molecular weight of 500 to 3,
Preferably, it is 0,000,000. Molecular weight cut off 5
If it is less than 00, the filtration speed is remarkably reduced and the filtration efficiency is reduced. On the other hand, if the molecular weight cut-off exceeds 3,000,000, the sol particles are poorly captured and the yield decreases, and the strength as an ultrafiltration membrane also decreases. As the type of the ultrafiltration membrane module used, any of a flat membrane module, a tubular membrane module, a spiral type module, and a capillary type membrane module can be used.
A capillary type membrane module is desirable because of its large filtration area and good filtration efficiency. As the ultrafiltration method,
A circulation system in which the zirconia sol is filtered by circulating through a membrane module by a pump and the filtrate is discharged is preferable.

At this time, impurities in the zirconia sol can be efficiently removed by adding pure water. In addition, a basic solution such as sodium hydroxide or ammonia can be added at the time of filtration and washing. By performing only filtration without adding pure water, it is possible to concentrate to a desired concentration.

When performing filtration and washing, the conductivity of the discharged filtrate is 10 mS / cm or less, more preferably 5 mS / c.
m or less. 10ms /
If it is higher than cm, a sufficient cleaning effect cannot be obtained, and a desired zirconia powder cannot be obtained. Further, the amount of the filtrate is preferably not more than 50 times as represented by the ratio Q / V ₀ of the amount V ₀ of the zirconia sol solution to be treated and the total amount Q of the filtrate. If the amount is more than 50 times, the accompanying drainage equipment will be large-scale. In order to perform the filtration and washing more efficiently, it is desirable to first perform the concentration and concentration of the zirconia sol to reduce the amount of the treatment liquid and perform the filtration and washing. By performing the washing in this manner, the dispersibility of the concentrated liquid is improved, and as the final concentrated liquid, a zirconia concentrated sol having a high zirconia concentration of 20 to 50% by weight and a high zirconia concentration is further obtained. Obtainable.

When obtaining a zirconia powder in which a stabilizer is dissolved in solid form, a salt, hydroxide or oxide of Y, Ca, Mg, Ce or the like is added to the obtained zirconia concentrated sol as a solid. , Hydrated zirconia powder in which the stabilizer is uniformly dispersed can be obtained by using the mixed solution and drying.

The method for drying the concentrated zirconia sol is not particularly limited, and examples thereof include spray drying and a method of adding an organic solvent to dry.

Next, in the present invention, the dried zirconia powder is calcined. The calcining temperature at this time is 30
The range of 0 to 1300 ° C is preferred. Calcination temperature is 300 ℃
When the temperature is lower than the above, it is difficult to obtain a zirconia powder sufficiently dissolved in the stabilizer, and when the temperature is higher than 1300 ° C., strong agglomeration due to sintering between particles occurs. It is difficult to obtain. More preferably, it is 400 to 1200 ° C. The holding time of calcination is
0.5 to 10 hours is good, and the heating rate is 0.5 to 10 ° C /
Minutes are preferred. If the holding time during calcination is less than 0.5 hour, it is difficult to uniformly calcine, and if it is more than 10 hours, the productivity is reduced, which is not preferable. On the other hand, if the heating rate is lower than 0.5 ° C./min, the time required to reach the set temperature is prolonged. If the heating rate is higher than 10 ° C./min, the powder scatters violently during calcination, resulting in poor operability. Productivity decreases.

Since the calcined powder obtained as described above hardly undergoes strong coagulation between particles, it becomes a zirconia fine powder having good dispersibility only by easy pulverization.
In addition, as a sintering aid as required at the time of grinding, for example,
Alumina or the like may be added.

[0024]

As described above, according to the present invention,
The filtration characteristics when filtering and washing and concentrating the zirconia sol obtained by hydrolysis by ultrafiltration, especially the stability of the filtration characteristics when used repeatedly, are dramatically improved.
It is possible to stably produce zirconia powder having good dispersibility, excellent moldability, and excellent sinterability.

[0025]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 A 0.4 mol / liter aqueous solution of ZrOCl ₂ was boiled under reflux, and a hydrolysis reaction was carried out for 200 hours. Continued
To 50 liters of the obtained hydrolysis solution, 90 liters of a 2 mol / L aqueous solution of ZrOCl ₂ and 360 liters of pure water were added to make the whole 500 liters, and then the mixture was boiled under reflux for 100 hours. Decomposed.

Subsequently, 100 liters of this zirconia sol was used for washing and concentration with a filtration device in which an ultrafiltration membrane module (molecular weight cut off: 6,000, total filtration area: 0.1 m ³ , capillary type membrane module) was set. Was done. In the filtration method, first, the zirconia sol was filtered by circulating through a membrane module by a pump, and concentrated to 20 liters. Next, the filtrate was washed while adding pure water so that the liquid level of the concentrated sol became constant, thereby washing the filtrate until the conductivity of the filtrate became 1.5 mS / cm. At this time, the total filtrate volume was 420 liters and the required time was 71.2 hours. Therefore, the filtration rate was 5.9 liter / Hr. The measured water permeability at this time was 40%.

In the same manner, the filtration test of the zirconia sol was further repeated twice. FIG. 1 shows the result of repeating the filtration rate, and FIG. 2 shows the result of repeating the water permeability. Twice and three
It was found that it decreased with the number of repetitions.

The ultrafiltration membrane module with reduced water permeability is immersed in a 0.5% hydrofluoric acid aqueous solution for 12 hours, and then thoroughly washed with water. When the actual liquid is not circulated, the water permeability reaches 75%. Has recovered.

Using the recovered ultrafiltration membrane module, a similar washing and concentration operation was performed as a fourth repetition operation. As a result, as shown in FIG. 1, the filtration rate returned to 5.5 L / Hr, a state before dropping, and as shown in FIG. 2, the water permeability also returned to the original 40%.

Yttrium chloride was added to the concentrated and desalted zirconia sol (3 mol% in terms of Y ₂ O ₃ ) and spray-dried to obtain a dry powder. The dried powder was calcined at 1050 ° C. for 2 hours, washed with water and pulverized. The obtained zirconia fine powder was molded by a mold press at a molding pressure of 700 kgf / cm ² , and the density of the molded body was 2.60 g / cm ³ . When the obtained molded body was sintered at 1500 ° C. for 2 hours, the sintered body density was 6.06 g / cm ³ and the bending strength was 135 kgf / mm ^2.
Met.

Examples 2 to 4 With respect to the regeneration treatment method using a hydrofluoric acid aqueous solution, the degree of recovery of the water permeability of the membrane module was tested by changing the conditions. Table 1 shows the obtained results.

Comparative Examples 1 to 5 The degree of recovery of water permeability was tested by changing the conditions of the regeneration method. Table 1 shows the obtained results.

[0034]

[Table 1]

Comparative Example 6 ZrOCl_TwoReturn an aqueous solution with a concentration of 0.4 mol / liter
The hydrolysis was carried out at the boiling temperature under flowing water for 100 hours. This
Yttrium chloride is added to the luconia sol (Y_TwoO_ThreeExchange
(Calculated, 3 mol%) and spray dried to obtain a dry powder.
The dried powder is calcined at 1050 ° C. for 2 hours and then washed with water.
And crushed. The obtained zirconia fine powder is the same as in the example.
When molded and sintered under the conditions, the compact density was 2.55
g / cm ^ThreeAnd the sintered body density is 5.95 g / cm^Three, Song
The spinning strength is 77kgf / mm^TwoMet.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in filtration rate according to the number of repetitions of a washing and concentration operation in Example 1.

FIG. 2 is a diagram showing a change in water permeability according to the number of repetitions of a washing and concentration operation in Example 1.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D006 GA06 HA01 HA93 KA62 KA72 KB30 KC02 KC16 KD13 KE02P KE03P KE08P KE11R KE16R KE19R KE28R MA01 MB05 PA03 PB12 PB15 PB70 PC01 PC80 4G031 AA03 AA08A07A08A08 AC04 AD02 AE01 AE06

Claims (3)

[Claims] 1. A zirconia sol obtained by heating and hydrolyzing an aqueous solution of a zirconium salt is filtered, washed and concentrated by an ultrafiltration membrane module, and then Y, Ca, Mg, Ce.
After the addition of a sintering aid or the like, or by drying and calcining the concentrated liquid, the ultrafiltration membrane module used in the method for producing zirconia powder is regenerated with a hydrofluoric acid aqueous solution. A method for regenerating an ultrafiltration membrane module for producing zirconia powder. 2. The method for regenerating an ultrafiltration membrane module for producing zirconia powder according to claim 1, wherein the concentration of the hydrofluoric acid aqueous solution used for regenerating the ultrafiltration membrane module is 0.01 to 10%. 2 to 100% in the hydrofluoric acid solution
A method for regenerating an ultrafiltration membrane module for producing zirconia powder, comprising immersing for a time or circulating through the ultrafiltration membrane module. 3. The method for regenerating an ultrafiltration membrane module for producing zirconia powder according to claim 1 or 2,
A method for regenerating an ultrafiltration membrane module for producing zirconia powder, wherein the ultrafiltration membrane module is a capillary type membrane module.